Acetonitrile Recovery Method

Abstract

The present disclosure relates to improved methods for recovering acetonitrile from aqueous and organic waste streams, particularly those produced during oligonucleotide manufacturing processes.

Description

[Technical field]

[0001] The present disclosure relates to the recovery and / or purification of acetonitrile from waste solvent streams, particularly those produced during oligonucleotide manufacturing processes. The acetonitrile produced by the methods of the present disclosure is particularly suitable for use in the manufacture of oligonucleotides, e.g., chemically modified oligonucleotides, such as those used therapeutically. [Background technology]

[0002] The relative proportions of the components of the waste solvent acetonitrile can vary over a wide range depending on a variety of conditions. Many chemical processes use acetonitrile as a solvent or wash, resulting in the production of low-grade acetonitrile waste streams. When these processes are carried out on a manufacturing scale, the volumes of low-grade acetonitrile waste streams produced can be significant.

[0003] Twelve oligonucleotide drugs have entered the market to date, with hundreds more in clinical trials and preclinical development, but traditional techniques for oligonucleotide production impose waste and cost burdens on manufacturers. Older techniques utilize large amounts of hazardous reagents and solvents, as well as energy-intensive processes in synthesis, purification, and isolation. In 2016, the American Chemical Society (ACS) Green Chemistry Institute Pharmaceutical Roundtable (GCIPR) identified the development of more environmentally friendly processes for oligonucleotide active pharmaceutical ingredients (APIs) as a critical unmet need. As a result, the Roundtable formed a focus team charged with identifying green chemistry and engineering improvements that could make oligonucleotide manufacturing more sustainable (Andrews et al. J. Org. Chem. 2021, 86, 49-61). For example, a typical solid-phase oligonucleotide synthesis process requires 3000 kg of acetonitrile to produce 1 kg of oligonucleotide-based active pharmaceutical ingredient (API), thus resulting in the formation of large amounts of contaminated acetonitrile waste.Therefore, there are strong economic, environmental and supply reasons to regenerate the contaminated acetonitrile for reuse in the process.

[0004] Typically, waste solvent from oligonucleotide production acetonitrile contains up to 90% acetonitrile and various amounts of acrylonitrile, toluene and ethanol, among others, which are difficult to separate from acetonitrile, especially at manufacturing scale. Severe constraints are imposed on the quality of the fresh acetonitrile used in the process. It must have an assay purity of more than 99.90% and preferably contain less than 30 ppm water, so that the quality of the product oligonucleotide and oligonucleotide production method is maintained.

[0005] There are prior methods for purifying acetonitrile from acetonitrile waste solvent. However, none of the prior art methods anticipates the separation problems associated with the impurities from oligonucleotide manufacturing processes, taking into account the unique oligonucleotide feedstock streams containing ethanol, toluene and N-containing impurities, and / or both organic and aqueous waste streams. Furthermore, the prior art methods are not suitable for recovering acetonitrile from acetonitrile waste solvent from organic synthesis and aqueous purification steps during oligonucleotide synthesis with acetonitrile purity of more than 99.90% and high yield. Thus, there is a need for an improved method for effectively separating and / or recovering acetonitrile from organic process waste streams, especially from both organic and aqueous production process waste streams.

[0006] The present disclosure thus relates to methods by which an organic waste solvent acetonitrile stream, particularly with respect to oligonucleotide production, may be purified to obtain acetonitrile, which may be recovered and reused, particularly in oligonucleotide production.

[0007] The present disclosure also relates to a method in which aqueous and organic waste solvent acetonitrile streams can be purified in the same system to obtain purified acetonitrile, which is recovered and reused, particularly in oligonucleotide production. The novel method disclosed herein is easy and simple to implement and can be performed batchwise or continuously. Furthermore, the method disclosed herein does not rely on expensive stationary phases, but instead relies on energy. Surprisingly, the method disclosed herein relies on the use of water as a separation agent. Water has a destructive effect during oligonucleotide synthesis reactions. However, by incorporating water as a separation agent during the regeneration process, contrary to common sense, there are several benefits in terms of design, purification efficiency, process integration and investment. Thus, by using a water feed step in which water is added to the acetonitrile distillate, the desired purified acetonitrile can be obtained.

[0008] While existing prior art focuses on purifying either the water-rich stream or the organic stream, the disclosed process configuration allows for either or both to be processed in the same system, which is also capable of processing high concentrations of impurities without the need for costly regeneration steps. Summary of the Invention

[0009] The present disclosure is based on the finding that acetonitrile can be recovered, purified and reused during oligonucleotide production according to the method disclosed herein.The present disclosure is also based on the discovery that high purity acetonitrile can be recovered by a continuous distillation procedure carried out in at least three zones.

[0010] A key aspect of the method is the use of water as a separation agent. Water has a destructive effect during oligonucleotide synthesis. However, the use of water as a separation agent in the regeneration process, which is largely counter to common sense, has been surprisingly found to have several benefits in terms of design, purification efficiency, process integration and investment according to the present disclosure.

[0011] Specifically, the addition of water to the organic side of the process facilitates the separation of otherwise difficult-to-treat impurities by forming binary and ternary azeotropes that have lower boiling points compared to acetonitrile. This eliminates the need for multiple columns to separate impurities with a range of boiling points (above and below that of acetonitrile). The binary and ternary azeotropes formed all have lower boiling points than acetonitrile, making the separation operation much easier. The overall boiling point difference compared to acetonitrile is also increased. From a design perspective, this requires fewer stages of separation and therefore less capital cost.

[0012] The use of water as a separating agent also allows both aqueous and organic streams to be processed in a common piece of equipment. At first glance, both streams would be processed separately to produce two separate qualities for the synthesis (water-free) and purification (water-rich) parts of the process. Instead, a single physical process can be used to produce a single quality that can be used in either part of the process while utilizing a single common purification structure. There is further synergy with this approach, where the water inherent to the purification part of the process can be used as an entrainer. The process can be run independently, e.g., continuously, with either feed stream or with both combined.

[0013] Such use of water also reduces the loss of acetonitrile from the process as the azeotrope is mostly an impurity and rich in water at lower acetonitrile content. As an entrainer, this property is desirable.

[0014] Two main acetonitrile waste streams are generated from the oligonucleotide production process. A water-poor organic waste stream is generated from the oligonucleotide synthesis section of the process, and a water-rich aqueous waste stream is generated from the subsequent purification steps. The organic waste stream contains about 90% acetonitrile by weight, and the aqueous acetonitrile waste stream contains about 11% acetonitrile by weight. Both of these streams are sent to a process where the acetonitrile is regenerated until it is of a suitable quality for recycling directly back into the oligonucleotide synthesis process. The amount of acetonitrile that can be regenerated in this way represents 70-90% of the total acetonitrile consumed in the oligonucleotide synthesis process. An additional waste stream is generated from the process of the present disclosure, which is very low in acetonitrile content and is sent directly to waste. This will be apparent from the description of the method described herein.

[0015] The organic waste streams (105, 205, 301) contain high levels of 2,6-lutidine, acetic anhydride, dichloroacetic acid, pyridine, toluene, 1-methylimidazole, 5-ethylthio-1H-tetrazole and lesser amounts of diethylamine, diisopropylamine, acetic acid, N,N-dimethylformamide, organic iodine and sulfur compounds, as well as residual oligonucleotide building blocks and traces of water. It has also been found that acetonitrile-containing waste streams may contain additional impurities, such as acrylonitrile, dichloroacetic acid. It has also been found that acrylonitrile and / or dichloroacetic acid may be present as additional by-products of conventional oligonucleotide production processes, creating significant problems during acetonitrile separation and / or purification. Conventional methods of acetonitrile separation and / or purification provide little or no guidance for effective acrylonitrile separation and separation of the above impurities. As a result, acrylonitrile may remain present in the recovered acetonitrile product of these conventional methods, which may result in insufficient final purity levels and low yields of oligonucleotide products.

[0016] The aqueous waste stream (101, 201, 302) contains mainly inorganic salts, ethanol and impure oligonucleotide chains as impurities, with the remainder being acetonitrile (e.g., 6-13 wt%, e.g., 6-11 wt%, e.g., 9.5 wt%, 11 wt%) and water.

[0017] Therefore, there is a need to develop a method that can effectively recover acetonitrile from oligonucleotide synthesis waste streams, and the acetonitrile can be recovered with a purity of 99.90% (area%) or more, as measured, for example, by gas chromatography analysis.Preferably, the recovered acetonitrile contains less than 30 parts per million (ppm) water.The technical problem is solved by the method of the present disclosure.

[0018] Thus, in a first aspect, there is provided a method for recovering and / or purifying acetonitrile from waste acetonitrile (105, 205, 301) generated during oligonucleotide synthesis, comprising: A * ) introducing an organic waste feedstock (105, 205) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a distillation column (106, 206) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the distillation column and condensed to produce a distillate (107, 207) and the second set of organic impurities is produced as a second distillation column bottoms (108, 208); B * ) introducing the distillate (107, 207) into a water feed section (109, 209) to produce a water-enriched acetonitrile stream (111, 210, 210a); C * ) introducing the water-enriched acetonitrile stream (111, 210, 210a) into a second distillation column (112, 212) and separating the first set of organic impurities from the acetonitrile, which is produced as second distillation column bottoms (113, 213); Includes; A method is thereby provided whereby recovered and / or purified acetonitrile is obtained.

[0019] In a second embodiment, a method for recovering and / or purifying acetonitrile from waste acetonitrile (101, 105) generated during oligonucleotide synthesis is provided, comprising the steps of: A1) introducing an aqueous waste feedstock (101) containing acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile into a first distillation column (102) and separating the acetonitrile and the first set of impurities from the second set of impurities, wherein the acetonitrile and the first set of impurities are withdrawn as vapor from the first distillation column and condensed to produce a first distillate (103) and the second set of impurities is produced as first distillation column bottoms (104); B1) introducing an organic waste feedstock (105) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a second distillation column (106) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the second distillation column and condensed to produce a second distillate (107), and the second set of organic impurities are produced as second distillation column bottoms (108); C1) introducing the second distillate (107) into a water supply section (109) and enriching it with water to produce a water-enriched acetonitrile stream (111); D1) introducing the water-enriched acetonitrile stream (111) into a third distillation column (112) and separating the first set of organic impurities from the acetonitrile, the acetonitrile being produced as third distillation column bottoms (113); E1) feeding the first distillate (103) of step A1 and the third distillation column bottoms (113) of step D1 to a mixing zone (116) and combining therein; Includes; A method is thereby provided whereby recovered and / or purified acetonitrile is obtained.

[0020] In a third embodiment, a method for recovering acetonitrile from waste acetonitrile (201, 205) generated during oligonucleotide synthesis is provided, comprising: A) introducing an aqueous waste feedstock (201) containing acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile into a first distillation column (202) and separating the acetonitrile and the first set of impurities from the second set of impurities, wherein the acetonitrile and the first set of impurities are withdrawn as a vapor from the first distillation column and condensed to produce a first distillate (203) and the second set of impurities is produced as first distillation column bottoms (204); B) introducing an organic waste feedstock (205) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a second distillation column (206) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the second distillation column and condensed to produce a second distillate (207), and the second set of organic impurities are produced as second distillation column bottoms (208); C) feeding the first distillate (203) of step A and the second distillate (207) of step B to a water supply area (209); C1) combining therein to produce a water-enriched acetonitrile stream (210a); or C2) combining therein and enriching with water to produce a water-enriched acetonitrile stream (210); D) introducing the water-enriched acetonitrile stream (210, 210a) into a third distillation column (212) and separating the first set of impurities from the acetonitrile, which is produced as third distillation column bottoms (213); Includes; A method is thereby provided whereby recovered and / or purified acetonitrile is obtained.

[0021] In a fourth embodiment, there is provided a method for recovering and / or purifying acetonitrile from waste acetonitrile (301, 302) generated during oligonucleotide synthesis, comprising: A') introducing into a first mixing zone (303) and combining therein an organic waste feedstock (301) comprising acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile, and an aqueous waste feedstock (302) comprising acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile, to form an acetonitrile waste feedstock comprising said impurities; or introducing an organic waste feedstock (301) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a first mixing zone (303) and enriching with water to produce a water-enriched acetonitrile stream containing said impurities; B') introducing the acetonitrile waste feedstock or the water-enriched acetonitrile stream into a first distillation column (304) to separate acetonitrile and a first set of impurities having a boiling point lower than acetonitrile from a second set of impurities having a boiling point higher than acetonitrile, wherein acetonitrile and the first set of impurities are withdrawn as vapor from the first distillation column and condensed to produce a first distillate (306) and the second set of impurities is produced as first distillation column bottoms (305); C') optionally introducing the first distillate (306) containing acetonitrile and low boiling impurities into a water feed section (307) and enriching it with water to produce a water-enriched acetonitrile stream (307a); D') introducing the water-enriched acetonitrile stream (306, 307a) into a second distillation column (308) and separating the acetonitrile from low-boiling impurities, wherein acetonitrile is produced as second distillation column bottoms (309); Includes; A method is thereby provided whereby recovered and / or purified acetonitrile is obtained.

[0022] It has been demonstrated that the acetonitrile thus regenerated can be used to synthesize oligonucleotides with the same efficiency as using fresh acetonitrile.The oligonucleotide produced by using the recovered acetonitrile according to the method of the present disclosure is preferably a therapeutic oligonucleotide.In particular, the oligonucleotide is a single-stranded oligonucleotide having at least one modified nucleotide residue, wherein the modification is selected from the group consisting of the modification at the 2' position of the sugar moiety, the modification of the nucleobase, and the modification of the backbone.

[0023] In a further aspect, there is provided a use of acetonitrile for oligonucleotide production, the acetonitrile having a purity of at least 99.90% as measured by gas chromatography, the acetonitrile being recovered from oligonucleotide synthesis waste, in particular according to the methods disclosed herein.

[0024] In a further aspect, a method for synthesizing an oligonucleotide is provided, comprising recovering and / or purifying acetonitrile from waste acetonitrile according to the methods disclosed herein, and using at least a portion of the recovered acetonitrile in a process for synthesizing an oligonucleotide and / or for washing an oligonucleotide or a support-bound oligonucleotide.

[0025] In a further embodiment, a system for purifying and / or recovering acetonitrile from waste acetonitrile (105, 205, 301) generated during an oligonucleotide manufacturing process is provided, comprising: a first distillation column (106, 206, 304) configured to receive the acetonitrile organic waste stream (105, 205, 301) and produce a first distillate (107, 207, 306) comprising acetonitrile and a first set of impurities, the first distillation column (106, 206, 304) having a condenser coupled to an upper portion of the first distillation column; and a second distillation column (112, 212, 308) configured to receive the first distillate (107, 207, 306), separate the first set of organic impurities from the acetonitrile, and produce purified acetonitrile as a second distillation column bottoms; The system, the first distillate (107, 207, 306) is first enriched with water before reaching the second distillation column (112, 212, 308) so as to obtain purified and / or recovered acetonitrile; or The system is provided further comprising a water feed zone (109, 209, 303, 307) arranged such that waste acetonitrile (301) is enriched with water before reaching the first distillation column (304) so ​​as to obtain purified and / or recovered acetonitrile.

[0026] In a further embodiment, a system (100) for purifying and / or recovering acetonitrile from waste acetonitrile (101, 105) generated during an oligonucleotide manufacturing process is provided, comprising: a first distillation column (102) configured to receive the aqueous acetonitrile waste stream (101) and produce a first distillate (103) comprising acetonitrile and a first set of impurities, the first distillation column (102) having a condenser coupled to an upper portion of the first distillation column (102); a second distillation column (106) configured to receive the acetonitrile organic waste stream (105) and produce a second distillate (107) comprising acetonitrile and the first set of impurities, the second distillation column (106) having a condenser coupled to an upper portion of the second distillation column (106); and a third distillation column (112) configured to receive the second distillate (107) and separate the first set of organic impurities from the acetonitrile and produce purified acetonitrile as a third distillation column bottoms; A system (100) is provided, the system further comprising: a water feed section (109) arranged such that the second distillate (107) is first enriched with water before reaching the third distillation column (112); and a mixing section (116) configured to mix the first distillate (103) from the first distillation column (102) and the third distillation column bottoms (113) from the third distillation column (112) so as to obtain purified and / or recovered acetonitrile.

[0027] In a further embodiment, a system (200) for purifying and / or recovering acetonitrile from waste acetonitrile (201, 205) generated during an oligonucleotide manufacturing process is provided, comprising: a first distillation column (202) configured to receive the aqueous acetonitrile waste stream (201) and produce a first distillate (203) comprising acetonitrile and a first set of impurities, the first distillation column (202) having a condenser coupled to an upper portion of the first distillation column (202); a second distillation column (206) configured to receive the acetonitrile organic waste stream (205) and produce a second distillate (207) comprising acetonitrile and the first set of impurities, the second distillation column (206) having a condenser coupled to an upper portion of the second distillation column (206); and a third distillation column (212) configured to receive the first and second distillates (203, 207), separate the first set of impurities from the first and second distillates, and produce purified acetonitrile as a third distillation column bottoms (213); A system (200) is provided, the system further comprising a water feed section (209) arranged such that the first and second distillates (203, 207) are first mixed and enriched with water before reaching the third distillation column (212) so as to obtain purified and / or recovered acetonitrile.

[0028] In a further embodiment, a system (300) for purifying and / or recovering acetonitrile from waste acetonitrile (301, 302) generated during an oligonucleotide manufacturing process is provided, comprising: a first distillation column (304) configured to receive the mixed acetonitrile aqueous and organic waste stream and produce a first acetonitrile distillate (306) comprising acetonitrile and a first set of impurities, the first distillation column (304) having a condenser coupled to an upper portion of the first distillation column (304), e.g., coupled to an overhead stream; a second distillation column (308) configured to receive the first acetonitrile distillate (306) and produce a second acetonitrile distillate (309) comprising an acetonitrile / water azeotrope, the second distillation column (308) having a condenser coupled to an upper portion of the second distillation column (308), e.g., coupled to an overhead stream; and a third distillation column (311) configured to receive the second acetonitrile distillate (309) and separate the acetonitrile from the acetonitrile / water azeotrope to produce acetonitrile as a third distillation column bottoms (312); The system is configured such that the first acetonitrile distillate (306) is first enriched with water (307) before reaching the second distillation column (308); and / or A system (300) is provided which further comprises a water feed zone (303, 307) arranged such that the organic waste acetonitrile (301) is first enriched with water by mixing the aqueous acetonitrile and organic waste streams (303) before reaching the first distillation column (304) to obtain purified and / or recovered acetonitrile.

[0029] In yet another aspect, there is provided acetonitrile obtained by the methods disclosed herein.

[0030] The above aspects and embodiments herein may be combined. Other objects, features, advantages and aspects of the present disclosure will become apparent to those skilled in the art from the following description and the appended claims. However, it should be understood that the following description, the appended claims, and specific examples showing preferred embodiments of the present application are given by way of illustration only. Various modifications and changes within the spirit and scope of the present disclosure will become readily apparent to those skilled in the art from reading the following. [Brief description of the drawings]

[0031] [Figure 1] 2 is an exemplary flow diagram of an implementation of the method according to the first aspect of the present disclosure. [Diagram 2] 4 is an exemplary flow diagram of an implementation of the method according to the second aspect of the present disclosure. [Diagram 3] 4 is an exemplary flow diagram of an implementation of a method according to a third aspect of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] definition The term "and / or" means either "and" or "or" unless otherwise indicated.

[0033] As used herein, the term "bottoms" means the fraction that remains in and / or is removed from the lower portion of a distillation column.

[0034] As used herein, the term "drying section" refers to a process step in which the water content of an acetonitrile stream is reduced to recover acetonitrile having a water content of less than 30 ppm water, e.g., less than 29 ppm water, less than 28 ppm water, less than 27 ppm water, less than 26 ppm water, less than 25 ppm water, less than 24 ppm water, less than 23 ppm water, less than 22 ppm water, less than 21 ppm water, less than 20 ppm water, less than 19 ppm water, less than 18 ppm water, less than 17 ppm water, less than 16 ppm water, less than 15 ppm water, less than 14 ppm water, less than 13 ppm water, less than 12 ppm water, less than 11 ppm water, less than 10 ppm water, less than 9 ppm water, less than 8 ppm water, less than 7 ppm water, less than 6 ppm water, less than 5 ppm water, less than 4 ppm water, less than 3 ppm water, less than 2 ppm water, less than 1 ppm water, as measured by gas chromatography. Preferably, the water content is reduced by the use of pressure swing distillation. The water content can be determined according to standard methods in the art, such as Karl Fischer titration, gas chromatography.

[0035] As used herein, gram scale is defined as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 grams or more, for example, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 grams.

[0036] As used herein, kilogram scale is defined as 1 kg or more, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 kg or more.

[0037] High boiling impurities or higher boiling impurities are defined as impurities having a boiling point higher than acetonitrile (81.6° C. at atmospheric pressure). Examples of high boiling impurities include, but are not limited to, diisopropylamine (boiling point: 84° C. at atmospheric pressure), water (boiling point: 100° C. at atmospheric pressure), toluene (boiling point: 110.6° C. at atmospheric pressure), pyridine (boiling point: 115° C. at atmospheric pressure), acetic acid (boiling point: 118.1° C. at atmospheric pressure), 2,6-lutidine (boiling point: 144° C. at atmospheric pressure), N,N-dimethylformamide (boiling point: 153° C. at atmospheric pressure), dichloroacetic acid (boiling point: 194° C. at atmospheric pressure), and 1-methylimidazole (boiling point: 198° C. at atmospheric pressure).

[0038] Low boiling impurities or lower boiling impurities are defined as impurities that have a boiling point lower than acetonitrile (e.g., 81.6° C. at atmospheric pressure) or form azeotropes with a boiling point lower than acetonitrile, e.g., acetonitrile / water azeotrope (boiling point: 76° C. at atmospheric pressure). Examples of low boiling impurities are, but are not limited to, toluene / acetonitrile azeotrope (boiling point: 81.4° C. at atmospheric pressure), diethylamine (boiling point: 55.5° C. at atmospheric pressure), acetone (boiling point: 56.2° C. at atmospheric pressure), methanol (boiling point: 64.5° C. at atmospheric pressure), ethanol / water / acetonitrile azeotrope (boiling point: 72.9° C. at atmospheric pressure), acrylonitrile (boiling point: 77° C. at atmospheric pressure), ethanol (boiling point: 78.37° C. at atmospheric pressure).

[0039] As used herein, "industrial scale" means at a scale other than laboratory scale. Thus, waste acetonitrile can be more than 5 liters, 10 liters, 100 liters, 1000 liters, 2000 liters, 3000 liters, 4000 liters, or even more than 5000 liters. Alternatively, waste acetonitrile can be more than 10 kg, 100 kg, 1000 kg, 2000 kg, 3000 kg, 4000 kg, 5000 kg, 10,000 kg, 20,000 kg, or even more than 30,000 kg.

[0040] As used herein, the term "modified oligonucleotide" refers to a nucleotide residue or oligonucleotide that contains at least one aspect of its chemical structure that differs from a natural nucleotide residue or oligonucleotide. Such modifications can be present in any portion of the nucleotide residue, e.g., the sugar, base, or phosphate. Examples of modifications of nucleotides are disclosed herein. In some embodiments, the modifications are selected from: (a) optionally a modified backbone selected from phosphorothioate (e.g., chiral phosphorothioate) or methylphosphonate internucleotide linkages; (b) optionally a 2'-O-methyl (2'-OMe), 2'-fluoro (2'-F), 2'-deoxy, 2'-deoxy-2'-fluoro, 2'-O-methoxyethyl (2'-O-MOE), 2'-O-aminopropyl (2'-O-AP), 2'-O-dimethylaminoethyl (2'-O-DMAOE), 2'-O-dimethylaminopropyl (2'-O-DMAP), 2'-O-dimethylaminoethyloxyethyl (2'-O- modified nucleotides selected from: 2'-O-DMAEOE), 2'-ON-methylacetamide (2'-O-NMA), locked nucleic acid (LNA), glycol nucleic acid (GNA), phosphoramidates (e.g., mesyl phosphoramidate), 2',3'-seconucleotide mimics, 2'-F-arabinonucleotides, abasic nucleotides, 2'-amino modified nucleotides, 2'-alkyl-modified nucleotides, morpholino nucleotides, vinyl phosphonates (e.g., 5' vinyl phosphonate), and cyclopropyl phosphonate deoxyribonucleotides; and / or (c) conjugation to a ligand, e.g., a GalNAc ligand.

[0041] As used herein, the term "mixing zone" refers to a process step where one or more components, e.g., a process stream, are mixed with another composition, e.g., another process stream, of a system. A mixing zone can include a vessel capable of mixing one or more components, e.g., a process stream, of a process.

[0042] As used herein, the term "oligonucleotide" refers to a polymer of nucleotide residues, either deoxyribonucleotides (the resulting oligonucleotide is DNA), ribonucleotides (the resulting oligonucleotide is RNA), or a mixture thereof. An oligonucleotide may be composed entirely of nucleotide residues found in nature, or may contain at least one nucleotide or at least one bond between nucleotides that is modified. An oligonucleotide may be single-stranded or double-stranded. In one embodiment, an oligonucleotide is 10-200 nucleotides long, optionally 20-30 nucleotides long, optionally 20-25 nucleotides long. An oligonucleotide of the present disclosure may be conjugated to another molecule, such as N-acetylgalactosamine (GaINAc) or a plurality thereof (GaINAc cluster). Thus, the term oligonucleotide encompasses any type of oligonucleotide of any particular length, including modified oligonucleotides, and therapeutic oligonucleotides.

[0043] As used herein, the term "overhead stream" means the stream or fraction removed from the upper portion of a distillation column.

[0044] As used herein, the terms "purified," "pure," or "substantially pure" refer to an assay purity of acetonitrile of at least 95% (area %) on a water-free basis as measured by gas chromatography. In particular, "purified," "pure," or "substantially pure" refers to a purity of acetonitrile that is at least 96% (area%), at least 97% (area%), at least 98% (area%), at least 99% (area%), at least 99.10% (area%), at least 99.20% (area%), at least 99.30% (area%), at least 99.40% (area%), at least 99.50% (area%), at least 99.60% (area%), at least 99.70% (area%), at least 99.80% (area%), at least 99.90% (area%), 99.91% (area%), 99.92% (area%), 99.93% (area%), 99.94% (area%), 99.95% (area%), 99.96% (area%), 99.97% (area%), 99.98% (area%), or 99.99% (area%) on a water-free basis as measured by gas chromatography. "Water free" basis indicates that the composition refers to a composition based solely on the organic components in the sample. The water fraction is excluded from this measurement.

[0045] As used herein, the term "highly purified" or "high purity" refers to a purity of acetonitrile of at least 99.9% (area %) and having less than 30 ppm water as measured by gas chromatography. In particular, "highly purified" or "high purity" refers to at least 96% (area%), at least 97% (area%), at least 98% (area%), at least 99% (area%), at least 99.10% (area%), at least 99.20% (area%), at least 99.30% (area%), at least 99.40% (area%), at least 99.50% (area%), at least 99.60% (area%), at least 99.70% (area%), at least 99.80% (area%), at least 99.90% (area%), 99.91% (area%), 99.92% (area%), 99.93% (area%), 99.94% (area%), 99.95% (area%), 99.96% (area%), 99.97% (area%), 99.98% (area%), 99.9 ... % (area %), 99.99% (area %), and refers to the purity of acetonitrile having less than 30 ppm water, for example, less than 29 ppm water, less than 28 ppm water, less than 27 ppm water, less than 26 ppm water, less than 25 ppm water, less than 24 ppm water, less than 23 ppm water, less than 22 ppm water, less than 21 ppm water, less than 20 ppm water, less than 19 ppm water, less than 18 ppm water, less than 17 ppm water, less than 16 ppm water, less than 15 ppm water, less than 14 ppm water, less than 13 ppm water, less than 12 ppm water, less than 11 ppm water, less than 10 ppm water, less than 9 ppm water, less than 8 ppm water, less than 7 ppm water, less than 6 ppm water, less than 5 ppm water, less than 4 ppm water, less than 3 ppm water, less than 2 ppm water, less than 1 ppm water. In one embodiment, the method and system of the present disclosure results in high purity acetonitrile. Purity can be measured according to standard methods in the art, e.g., titration, NMR, chromatography, e.g., HPLC, GC, GC / MS.

[0046] As used herein, the term "recovered acetonitrile" refers to acetonitrile that has been purified and / or regenerated from waste acetonitrile generated during a manufacturing process, for example, during a solid phase oligonucleotide manufacturing process.

[0047] As used herein, the term "support-bound oligonucleotide" refers to an oligonucleotide that is conjugated or attached to a support material.

[0048] The support material may be a soluble support material. The soluble support material may be selected from the group consisting of polyethylene glycol, soluble organic polymers, DNA, proteins, dendrimers, polysaccharides, oligosaccharides, and carbohydrates. The support material may be an insoluble support material. The support material may be a solid support material. The solid support material may be selected from the group consisting of glass beads, polymer beads, fibrous supports, membranes, streptavidin-coated beads, and cellulose.

[0049] A solid support may also refer to a porous or non-porous solvent-insoluble material. As used herein, "porous" means that the material contains pores with a substantially uniform diameter (e.g., in the nm range). Porous materials include paper, synthetic filters, and the like. In such porous materials, reactions can occur within the pores. The support may have any one of many shapes, such as pins, chips, plates, disks, rods, cylindrical structures, particles (including beads), and the like. The supports may be hydrophilic or capable of being made hydrophilic, used by themselves or with other materials; inorganic powders such as silica, magnesium sulfate, and alumina; natural polymeric materials, particularly cellulosic and cellulose-derived materials such as fiber-containing papers, e.g., filter paper, chromatography paper; synthetic or modified natural polymers, e.g., nitrocellulose, cellulose acetate, poly(vinyl chloride), polyacrylamide, cross-linked dextran, agarose, polyacrylates, polyethylene, polypropylene, poly(4-methylbutene), polystyrene, polymethacrylates, poly(ethylene terephthalate), nylon, poly(vinyl butyrate), polyvinylidene difluoride (PVDF) membranes, glass, controlled pore glass, magnetically controlled pore glass, ceramics, metals, and the like.

[0050] As used herein, the term "therapeutic oligonucleotide" refers to an oligonucleotide that has therapeutic use. Such oligonucleotides typically contain one or more modified nucleotide residues or linkages. Therapeutic oligonucleotides function through one of several different mechanisms, including, but not limited to, antisense, splice switching or exon skipping, immune stimulation, and RNA interference (RNAi) via, for example, microRNA (miRNA) and small interfering RNA (siRNA). Therapeutic oligonucleotides can be aptamers. Therapeutic oligonucleotides usually, but not necessarily, have a defined sequence. Exemplary oligonucleotides include, but are not limited to, antisense oligonucleotides (ASOs), siRNAs, miRNAs, miRNA mimics, shRNAs, aptamers, anti-microRNAs, guide molecules for CRISPR systems, DNA decoys, and DNAzymes.

[0051] As used herein, the term "feedwater section" refers to a process step in which one or more process streams are mixed with water. The feedwater section may include one or more components of the process, such as a vessel capable of mixing the process stream with water. Water may be added directly and / or may be added as a component of another process stream, for example, present in the acetonitrile distillate (103, 203) or waste stream (301) from the aqueous purification process. Water may be added to the feedwater section via any conventional means known in the art, for example, injected into the process stream, added to the vessel via an inlet or by incorporating a static mixer.

[0052] As used herein, the term "waste acetonitrile" or "oligonucleotide synthesis waste" refers to an acetonitrile composition that includes aqueous inorganic and organic impurities, such as water, toluene, ethanol, diisopropylamine, diethylamine, acrylonitrile, imidazole, 2,6-lutidine, acetic acid, dimethylformamide, ETT, PADS, pyridine, and non-volatile salts, for example, as an aqueous mixture, from the synthesis and washing steps. Aqueous acetonitrile waste or "aqueous impurities" originates from the purification step of the oligonucleotide process, while organic waste or "organic impurities" originates from the oligonucleotide synthesis section. For example, the relative proportions of the components of waste acetonitrile in the organic and aqueous waste streams can vary over a wide range depending on various conditions, which can vary from process to process depending on the oligonucleotide being synthesized.

[0053] Methods of the Disclosure In one embodiment, a method for recovering and / or purifying acetonitrile from waste acetonitrile (105, 205) generated during oligonucleotide synthesis, comprising: A * ) introducing an organic waste feedstock (105, 205) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a distillation column (106, 206) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the distillation column and condensed to produce a distillate (107, 207) and the second set of organic impurities is produced as a second distillation column bottoms (108, 208); B * ) introducing the distillate (107, 207) into a water feed section (109, 209) to produce a water-enriched acetonitrile stream (111, 210, 210a); C *) introducing the water-enriched acetonitrile stream (111, 210, 210a) into a second distillation column (112, 212) and separating the first set of organic impurities from the acetonitrile, which is produced as second distillation column bottoms (113, 213); Includes; A method is thereby provided whereby recovered and / or purified acetonitrile is obtained.

[0054] Advantageously, process step A above * ~C * provides an improved acetonitrile recovery and / or purification process. Such a process can successfully remove high boiling hydrophobic organic impurities from acetonitrile waste streams, such as those produced during oligonucleotide synthesis. * ~C * The acetonitrile produced according to the method is 99.90% (area%) pure by gas chromatography analysis. Such recovered acetonitrile can be conveniently reused directly in the oligonucleotide synthesis process.

[0055] In one embodiment, a method for recovering acetonitrile from waste acetonitrile (101, 105) generated during oligonucleotide synthesis, comprising: A1) introducing an aqueous waste feedstock (101) containing acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile into a first distillation column (102) and separating the acetonitrile and the first set of impurities from the second set of impurities, wherein the acetonitrile and the first set of impurities are withdrawn as vapor from the first distillation column and condensed to produce a first distillate (103) and the second set of impurities is produced as first distillation column bottoms (104); B1) introducing an organic waste feedstock (105) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a second distillation column (106) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the second distillation column and condensed to produce a second distillate (107), and the second set of organic impurities are produced as second distillation column bottoms (108); C1) introducing the second distillate (107) into a water supply section (109) and enriching it with water to produce a water-enriched acetonitrile stream (111); D1) introducing the water-enriched acetonitrile stream (111) into a third distillation column (112) and separating the first set of organic impurities from the acetonitrile, the acetonitrile being produced as third distillation column bottoms (113); E1) feeding the first distillate (103) of step A1 and the third distillation column bottoms (113) of step D1 to a mixing zone (116) and combining therein; Includes; A method is thereby provided whereby recovered and / or purified acetonitrile is obtained.

[0056] The distillations of steps A1 and B1 can be carried out independently, e.g., one after the other in any order or in proportions ranging from 0 to 100%, or in parallel, e.g., simultaneously. Since the waste streams are generated in the same proportions from the main synthesis / purification section of the process, the steps can be started simultaneously, but this is not required.

[0057] Process step A1 is carried out in the so-called second distillation section (Figure 1, section 2), also called the inorganic aqueous purification section. The aqueous acetonitrile waste (101) entering this section is separated into a stream (103) enriched in acetonitrile and containing some water and ethanol. The heavy boiling portion (104) contains non-volatile salts and organic residues from the main process purification as aqueous solutions. This section is operated to maximize the yield of acetonitrile in the form of an azeotrope while removing as much excess water as possible from the process.

[0058] In step A1, an acetonitrile fraction is withdrawn from an upper portion of a distillation column (102), for example, overhead. The acetonitrile fraction exits as a vapor and is passed through a condenser to produce a condensate (103). A portion of the condensate is then returned to the column as a reflux stream, and the remainder is withdrawn as product. The acetonitrile fraction (103) comprises acetonitrile and light-boiling impurities, for example, an acetonitrile / water azeotrope. The acetonitrile fraction may further comprise ethanol. For example, heavy aqueous impurities having a boiling point higher than acetonitrile are withdrawn as distillation column bottoms (104). The heavy-boiling aqueous impurities (104) comprise non-volatile salts and organic residues and are withdrawn as a bottoms product. The bottoms product (104) is considered waste and is discarded. The bottoms product (104), or at least a portion thereof, is then fed to a separate mixing zone (125), for example in the third distillation zone (FIG. 1, zone 3), whereby it is mixed with the aqueous bottoms product from further processing, for example from the low pressure distillation (119) in the third distillation zone, before being discarded.

[0059] Process steps B1, C1 and D1 are carried out in the so-called first distillation section (Figure 1, section 1), also called the organic purification section. The organic waste stream (105) fed to this section contains a mixture of acetonitrile and organic impurities such as 2,6-lutidine, toluene, acrylonitrile and smaller amounts of pyridine, imidazole, 1-methylimidazole, diethylamine, diisopropylamine, acetic acid, 5-ethylthio-1H-tetrazole, N,N-dimethylformamide, organic iodine and sulfur compounds, and residual oligonucleotide building blocks, as well as traces of water. Many of these compounds are difficult to separate from acetonitrile because they have a very similar volatility to acetonitrile within certain concentration ranges or because they form azeotropes with acetonitrile.

[0060] The distillation step B1 includes introducing an organic waste feedstock (105) containing acetonitrile and the above-mentioned organic impurities into a first distillation column (106), distilling the organic waste containing acetonitrile to remove the organic impurities therefrom and producing a first acetonitrile distillate (107) containing acetonitrile and a first set of impurities including azeotrope formers and low boiling impurities, and a second set of impurities including heavy organics, e.g., having a higher boiling point than acetonitrile. The acetonitrile distillate together with the first set of impurities (107) is withdrawn from an upper portion of the distillation column (106), e.g., overhead. The second set of impurities is produced as a distillation column bottom product (108). The first set of impurities generally have a lower boiling point compared to water (100° C. at atmospheric pressure), and in particular compared to acetonitrile (82° C. at atmospheric pressure). The azeotrope former includes at least one of toluene, ethanol, and acrylonitrile, or mixtures thereof. The low boiling impurities include at least one of diethylamine, diisopropylamine, and acrylonitrile, or a mixture thereof.

[0061] The second set of impurities comprising heavy organics (108) comprises at least one of toluene, acetic acid, and N-containing compounds, or mixtures thereof. In one embodiment, the N-containing compounds are at least one of 1-methylimidazole, 2,6-lutidine, dimethylformamide, pyridine, acrylonitrile, diisopropylamine, diethylamine, phenylacetyl (disulfide), and 5-(ethylthio)-1H-tetrazole, 5-(ethylthio)tetrazole, or mixtures thereof.

[0062] Step C1 comprises introducing the distillate (107) from step B1 into a water feed section (109) and enriching said distillate (107) with water to produce a water-enriched acetonitrile stream (111). To separate azeotrope-forming agents with acetonitrile, such as toluene, acrylonitrile or ethanol, an entrainer (e.g., water) can be added to the feed, which forms azeotropes with these compounds with lower boiling points compared to acetonitrile, making them easier to separate from acetonitrile. To the inventors' surprise, water unexpectedly reduces the loss of acetonitrile from the process, since the azeotrope is mainly impurities, rich in water, and has a lower acetonitrile content. The amount of water added compared to acetonitrile can be more than 0.24 w / w, but can range from 0.05 to 0.40 w / w or more, based on the amount of acetonitrile present in the stream. Amounts greater than 0.24 w / w ensure optimal separation of toluene and acrylonitrile from acetonitrile. The amount of water added is related to the amount of acetonitrile that ensures stable column operation.

[0063] The lower boiling azeotrope of the water-enriched acetonitrile stream (111) of step C1 comprises at least one of acetonitrile, water, toluene, ethanol, diethylamine, diisopropylamine, and acrylonitrile, or mixtures thereof. Preferably, the lower boiling azeotrope of step C1 comprises at least one of acetonitrile / water, acrylonitrile / water, acetonitrile / toluene, acetonitrile / diethylamine, acetonitrile / diisopropylamine, toluene / water, ethanol / water, toluene / water / acrylonitrile, toluene / water / acetonitrile, diisopropylamine / water / acetonitrile, diethylamine / toluene / water, or mixtures thereof.

[0064] The water-rich acetonitrile stream (111) is fed to a distillation column (112). The water-rich acetonitrile feedstock (111) is distilled and separated into an acetonitrile bottoms product (113) containing a lower boiling azeotrope and an overhead fraction (114), the acetonitrile bottoms product (113) having a higher acetonitrile concentration than the water-rich acetonitrile stream (111) from step C1. The lower boiling azeotrope of the water-rich acetonitrile stream (111) is withdrawn from the upper part of the distillation column (112), e.g., overhead. Such a lower boiling azeotrope fraction (114) can be directed to organic waste. In one embodiment, at least a portion of the lower boiling azeotrope fraction (114) is first mixed with other organic impurities, e.g., from the previous distillation step (108), e.g., in a separate mixing section (115), before being directed to organic waste.

[0065] Advantageously, the above process steps A1-D1 provide an improved acetonitrile recovery and / or purification process. Such a process can successfully remove high boiling hydrophobic organic and inorganic aqueous impurities from acetonitrile waste streams, such as those produced during oligonucleotide synthesis. The amount of acetonitrile that can be regenerated in the process using steps A1-D1 corresponds to 70-90% of the total acetonitrile consumed in the oligonucleotide synthesis process. The acetonitrile produced according to steps A1-D1 is 99.90% (area%) pure by gas chromatography analysis. Such recovered acetonitrile can be conveniently reused directly in the oligonucleotide synthesis process.

[0066] In one embodiment of the present disclosure, the reflux ratio of the distillation column (102) in step A1 is 0.25 to 2, for example, 1. In one embodiment of the present disclosure, the reflux ratio of the distillation column (106) in step B1 is 2 to 8, for example, 5. In one embodiment of the present disclosure, the reflux ratio of the distillation column (112) in step D1 is 5 to 40, for example, 30.

[0067] The acetonitrile stream produced in step D1 can be subjected to further processing steps. Thus, in step E1, the acetonitrile bottoms product (113) from step D1 and the acetonitrile distillate (103) from step A1 can then be fed to a mixing zone (116) where they are combined to produce an acetonitrile-rich stream (110). The resulting acetonitrile-rich stream contains purified acetonitrile having a purity of at least 99.90% (area %) as measured by gas chromatography (GC), among other things.

[0068] The acetonitrile-rich stream can then be fed to a dehydration zone, also referred to as the third distillation zone (FIG. 1, zone 3), where the water content of the incoming acetonitrile stream is reduced by use of pressure swing distillation to recover acetonitrile having a water content of less than 30 ppm.

[0069] The acetonitrile recovered from the pressure swing distillation process is, for example, more than 99.90% pure, as measured by gas chromatography.Preferably, the recovered acetonitrile has a purity of at least 99.90% (area %) and a water content of 30 ppm or less.Such recovered acetonitrile can be conveniently directly reused in the oligonucleotide synthesis process.

[0070] In one embodiment, the method of the present disclosure comprises: F1) introducing the acetonitrile-rich stream (110) into a fourth distillation column (117) and distilling it at less than atmospheric pressure to remove water therefrom, wherein acetonitrile is withdrawn as a vapor from said fourth distillation column and condensed to produce a fourth distillate (118) and water is produced as fourth distillation column bottoms (119); F2) introducing the fourth distillate (118) into a fifth distillation column (120) and carrying out a second distillation at a pressure above atmospheric pressure, for example 5 bar, to produce a lower boiling fraction (122) which is withdrawn via the upper part of the fifth distillation column (120) and acetonitrile which is produced as the fifth distillation column bottoms (121).

[0071] The acetonitrile withdrawn from the column in step F2 is greater than 99.90% pure, based on the total content of the acetonitrile stream (121), as measured by GC.

[0072] The lower boiling fraction withdrawn in step F1 via the upper portion, e.g., from the top of the distillation column, comprises an acetonitrile composition approaching the azeotropic composition. The lower boiling impurities in step F2 comprise at least one of ethanol, water, an ethanol / water azeotrope, and an acetonitrile / water azeotrope, or mixtures thereof.

[0073] Thereby, it is ensured that the acetonitrile stream (118) arriving at the fifth distillation column (120), in which the distillation of step F2 takes place, has a reduced water content and is as rich as possible in acetonitrile. During the distillation step F2, which is carried out at a pressure higher than that of the distillation step F1, the water content increases and reaches at least 23% by weight excluding the azeotropic composition, producing a composition approaching the azeotropic composition at the working pressure of the column. The remaining water can thus be distilled off in the form of an acetonitrile / water azeotrope. This azeotrope (122) can be recycled, for example via the water supply section (109) of step C1, into the acetonitrile feedstock for the distillation of step D1.

[0074] In one embodiment of the present disclosure, the reflux ratio of the distillation column (117) in step F1 is 0.05 to 1, for example, 0.1. In one embodiment of the present disclosure, the reflux ratio of the distillation column (120) in step F2 is 0.05 to 1, for example, 0.25.

[0075] In a preferred embodiment, at least a portion of the acetonitrile / water azeotrope (122) is recycled to the distillation of step D1, and a higher proportion is returned to the mixing step (116).

[0076] Thus, in one embodiment, any impurities present in the dehydration zone, e.g., from a pressure swing distillation step, e.g., in step F2, that may form a light azeotrope with water and acetonitrile, are withdrawn from the upper part of the column (120), e.g., overhead, and recycled back to the first distillation zone with the remaining acetonitrile and water. In one embodiment, the azeotropic fraction (122) from the dehydration zone, e.g., step F2, is fed back to step D1. In a further embodiment, said light azeotropic fraction (122) is fed or recycled back to the first distillation zone, step D1, via the feed water zone (109) of step C1, where the feed is enriched with water to produce a lower boiling azeotrope compared to acetonitrile (111), and then introduced into the third distillation column (112) where the distillation of step D1 takes place.

[0077] Alternatively, the lower boiling azeotropic fraction (122) is recycled directly to the mixing step (116). In one embodiment, the lower boiling azeotropic fraction (122) is recycled via mixing section (116) back to the dehydration section, e.g., pressure swing distillation steps, e.g., steps F1 and F2, where the acetonitrile feed from steps A1 and D1 is combined. In a preferred embodiment, at least a portion of the light azeotropic fraction (122) is recycled back to the distillation of step D1, with a higher proportion being returned to the mixing step (116), where the acetonitrile feed from steps A1 and D1 is combined.

[0078] Alternatively, the lower boiling azeotropic fraction (122) from the dehydration section, for example from step F2, is purged (123) and sent to organic waste (115).

[0079] If the water content in the acetonitrile product stream from step F2 is not low enough, a further stage of separation (124) can be added which can remove the residual water as an azeotrope, or it can be removed by adsorption onto a stationary phase, for example molecular sieves.

[0080] Thus, in a further embodiment of the present disclosure, the process further comprises feeding the acetonitrile bottoms product (121) from step F2 to a water adsorption zone (124) and contacting the acetonitrile bottoms product (121) with a water reducing adsorbent to produce acetonitrile with less than 30 ppm water exiting the adsorption zone (124). Further details and embodiments of the adsorbent are described in WO2015126713A1, paragraphs

[0033] to

[0038] .

[0081] The water reducing adsorbent can be a molecular sieve. In one embodiment, the molecular sieve has a pore size of less than 20 angstroms, for example, 3, 4 or 5 angstroms. In a preferred embodiment, the molecular sieve has a pore size of 3 angstroms. A pore size of 3 angstroms is very efficient for separation because water has a smaller size and acetonitrile has a larger size. The acetonitrile leaving the adsorption zone has a purity of at least 99.90% (area %) and a water content of less than 30 ppm, as measured, for example, by gas chromatography.

[0082] In another embodiment, a method for recovering acetonitrile from waste acetonitrile (201, 205) generated during oligonucleotide synthesis, comprising: A) introducing an aqueous waste feedstock (201) containing acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile into a first distillation column (202) and separating the acetonitrile and the first set of impurities from the second set of impurities, wherein the acetonitrile and the first set of impurities are withdrawn as a vapor from the first distillation column and condensed to produce a first distillate (203) and the second set of impurities is produced as first distillation column bottoms (204); B) introducing an organic waste feedstock (205) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a second distillation column (206) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the second distillation column and condensed to produce a second distillate (207), and the second set of organic impurities are produced as second distillation column bottoms (208); C) feeding the first distillate (203) of step A and the second distillate (207) of step B to a water supply area (209); C1) combining therein to produce a water-enriched acetonitrile stream (210a); or C2) combining therein and enriching with water to produce a water-enriched acetonitrile stream (210); D) introducing the water-enriched acetonitrile stream (210, 201a) into a third distillation column (212) and separating the first set of impurities from the acetonitrile, wherein acetonitrile is produced as third distillation column bottoms (213); Includes; A method is thereby provided whereby recovered and / or purified acetonitrile is obtained.

[0083] The distillations of steps A and B may be carried out independently, e.g., one after the other in any order or in proportions ranging from 0 to 100%, or in parallel, e.g., simultaneously. The steps may be started simultaneously, but this is not required, since the waste streams are generated in the same proportions from the main synthesis / purification section of the process. The process steps A and B are carried out in the first distillation zone (Figure 2, zone 1) of the second embodiment of the present disclosure.

[0084] In process steps A and B, inorganic aqueous and organic purification steps are performed. The goal is to separate as many of the heavy boilers as possible from the acetonitrile and any other light boilers in the feed stream. Aqueous acetonitrile waste comes from the purification area of ​​the oligonucleotide process, while organic waste comes from the oligonucleotide synthesis section. The bottoms products from each distillation are sent to waste. The overhead products are combined to produce the aqueous feed to the light boilers column (212) in the second distillation zone (Figure 2, Zone 2).

[0085] Aqueous acetonitrile waste (201) entering this zone is enriched in acetonitrile and separated into a stream (203) containing water and ethanol. The heavy boiling portion (204) contains non-volatile salts and organic residues from the main process purification as aqueous solutions. This zone is operated to maximize the yield of acetonitrile in the form of an azeotrope while removing as much excess water as possible from the process.

[0086] The organic waste stream (205) fed to this section contains a mixture of acetonitrile and organic impurities such as 2,6-lutidine, toluene, acrylonitrile and lesser amounts of pyridine, imidazole, 1-methylimidazole, diethylamine, diisopropylamine, acetic acid, 5-ethylthio-1H-tetrazole, N,N-dimethylformamide, organic iodine and sulfur compounds, and residual oligonucleotide building blocks, as well as traces of water. Many of these compounds are difficult to separate from acetonitrile because they have very similar volatility to acetonitrile within certain concentration ranges, or because they form azeotropes with acetonitrile.

[0087] In step A, an acetonitrile fraction is withdrawn from an upper portion of a distillation column (202), e.g., overhead. The acetonitrile fraction exits as a vapor and passes through a condenser to produce a condensate (203). A portion of the condensate is then returned to the column (202) as a reflux stream, and the remainder is removed as a distillate. The acetonitrile fraction (203) comprises acetonitrile and light-boiling impurities, e.g., an acetonitrile / water azeotrope. The acetonitrile fraction (203) may further comprise ethanol. For example, heavy aqueous impurities having a boiling point higher than acetonitrile are withdrawn as distillation column bottoms (204). The heavy-boiling aqueous impurities, which comprise non-volatile salts and organic residues, are withdrawn as a bottoms product (204). The bottoms product (204) is considered waste and is discarded. The bottoms product (204), or at least a portion thereof, can be fed, for example, to a separate mixing section (224) in the third distillation section (FIG. 2, section 3) whereby it is mixed with the aqueous bottoms product from the low pressure distillation (218) in the third distillation section before being discarded.

[0088] The distillation of step B includes introducing an organic waste feedstock (205) containing acetonitrile and the organic impurities described above into a distillation column (206) and distilling the organic waste containing acetonitrile to remove the organic impurities therefrom to produce a first acetonitrile distillate (207) containing acetonitrile and a first set of impurities including azeotrope formers and lower boiling point impurities, and a second set of impurities including heavy organics having a higher boiling point than acetonitrile, for example. The acetonitrile distillate (207) is withdrawn from an upper portion of the distillation column (206), for example, overhead, along with the first set of impurities. The second set of impurities is produced as a distillation column bottom product (208). The first set of impurities generally have a lower boiling point compared to water (100° C. at atmospheric pressure), and in particular compared to acetonitrile (82° C. at atmospheric pressure). The azeotrope former includes at least one of toluene, ethanol, and acrylonitrile, or mixtures thereof. The low boiling impurities include at least one of diethylamine, diisopropylamine, and acrylonitrile, or a mixture thereof.

[0089] The second set of impurities comprising heavy organics (208) includes at least one of toluene, acetic acid, and N-containing compounds, or mixtures thereof. In one embodiment, the N-containing compounds include at least one of 1-methylimidazole, 2,6-lutidine, dimethylformamide, pyridine, acrylonitrile, diisopropylamine, diethylamine, phenylacetyl (disulfide), and 5-(ethylthio)-1H-tetrazole, 5-(ethylthio)tetrazole, or mixtures thereof.

[0090] Process steps C and D are carried out in the so-called second distillation section (Figure 2).

[0091] Step C comprises feeding the acetonitrile distillate (203) from step A and the acetonitrile distillate (207) from step B to a water supply area (209); combining therein to produce a water-enriched acetonitrile stream (210a); or and combining therein and enriching with water to produce a water-enriched acetonitrile stream (210).

[0092] In one embodiment of step C, step C may include the further step of feeding a recycled acetonitrile stream (221) into the feed water section, the recycled acetonitrile stream (221) being, for example, a by-product of a further processing step from pressure swing distillation, for example, steps F1 and F2. The recycled acetonitrile stream (221) comprises a composition that is at or near the acetonitrile / water azeotropic composition at the operating conditions of column (219) of step F2. Stream (221) may further comprise ethanol, which accumulates in the system. The amount of ethanol present will vary depending on the feed concentration and flow rate of this stream compared to the feed stream (213) entering the pressure swing distillation steps, for example, steps F1 and F2. The recycled acetonitrile stream (221) may contain acetonitrile in the range of 70-76 wt%, e.g., 75 wt%, acetonitrile in the range of 0-3 wt%, e.g., 1.3 wt%, ethanol, and water in the range of 24-30 wt%, e.g., 24 wt%, based on the total content of the stream. Recycling 10-30% of this stream allows ethanol to be purged from the process in the form of an ethanol / water azeotrope. Recycling the step ensures optimal removal of ethanol from the process.

[0093] The water-enriched acetonitrile stream (210, 201a) is then fed to a distillation column (212). The water-enriched acetonitrile feed (210, 210a) is distilled and separated into an acetonitrile bottoms product (213) and a lower boiling fraction (214) containing a lower boiling azeotrope. Any impurities in the feed are separated from the upper portion of the column, e.g., overhead, as a binary or ternary azeotrope. The lower boiling azeotrope of fraction (214) is withdrawn from the upper portion of the distillation column (212), e.g., overhead. Such lower boiling azeotrope fraction (214) may be directed to organic waste. In one embodiment, at least a portion of the lower boiling azeotropic fraction (214) is first mixed, e.g., with other organic impurities from a previous distillation step, e.g., the distillation column bottoms product (208) of step B, e.g., in a separate mixing section (223), and then directed to the organic waste.

[0094] Advantageously, the above process steps A-D provide an improved acetonitrile recovery and / or purification process in terms of efficiency. The process also ensures that any light boiling material entering through the aqueous waste stream (201) is purged from the process in the third distillation column (212) of step D, either in the form of a single component or in the form of an azeotrope. Such a process can successfully remove high boiling hydrophobic organic and inorganic aqueous impurities from acetonitrile waste streams, such as those produced during oligonucleotide synthesis. The amount of acetonitrile that can be regenerated in the process using steps A-D corresponds to 70-90% of the total acetonitrile consumed in the oligonucleotide synthesis process. The acetonitrile produced according to steps A-D is 99.90% (area%) pure according to gas chromatography analysis. Such recovered acetonitrile can be conveniently reused directly in any oligonucleotide synthesis process.

[0095] In one embodiment of the present disclosure, the reflux ratio of the distillation column (202) in step A is 0.25 to 2, for example, 1. In one embodiment of the present disclosure, the reflux ratio of the distillation column (206) in step B is 2 to 8, for example, 5. In one embodiment of the present disclosure, the reflux ratio of the distillation column (212) in step D is 5 to 40, for example, 30.

[0096] The acetonitrile stream produced in step D may be subjected to further processing steps.

[0097] The acetonitrile-rich stream (e.g., 110, 216) can then be fed to a dehydration section (also referred to as a third distillation section (FIG. 2)) where the water content of the incoming acetonitrile stream (e.g., 110, 216) is reduced by use of pressure swing distillation to recover acetonitrile having a water content of less than 30 ppm.

[0098] The acetonitrile recovered from the pressure swing distillation process is 99.90% (area%) ultrapure, for example, as measured by gas chromatography.Preferably, the recovered acetonitrile has a purity of at least 99.90% (area%), for example, as measured by gas chromatography, and a water content of less than 30 ppm.Such recovered acetonitrile can be conveniently directly reused in any oligonucleotide synthesis process, for example, solid-phase oligonucleotide synthesis process.

[0099] In one embodiment, the method of the second aspect of the disclosure comprises: F1) introducing the acetonitrile bottoms product (213) from the third distillation of step D into a fourth distillation column (216) and distilling it at less than atmospheric pressure to remove water therefrom, wherein acetonitrile is withdrawn from said fourth distillation column as a vapor and condensed to produce a fourth distillate (217) and water is produced as fourth distillation column bottoms (218); F2) introducing the fourth distillate (217) into a fifth distillation column (219) and carrying out a second distillation at a pressure above atmospheric pressure, for example 5 bar, to produce a lower boiling fraction (221) which is withdrawn via the upper part of the fifth distillation column (219) and acetonitrile which is produced as the fifth distillation column bottoms (220).

[0100] The acetonitrile withdrawn from the column in step F2 is 99.90% (area %) ultra-pure, based on the total content of the acetonitrile stream (220), as measured by GC.

[0101] The acetonitrile fraction withdrawn through the upper portion, for example from the top of the distillation column in step F1, comprises an acetonitrile composition approaching the azeotropic composition. The lower boiling impurities in step F2 comprise at least one of ethanol, water, an ethanol / water azeotrope and an acetonitrile / water azeotrope, or mixtures thereof.

[0102] Thereby, it is ensured that the acetonitrile stream (217) arriving at the fifth distillation column (219), in which the distillation of step F2 takes place, has a reduced water content and is as rich as possible in acetonitrile. During the distillation step F2, which is carried out at a higher pressure than the distillation step F1, the water content increases and reaches at least 23% by weight excluding the azeotropic composition, producing a composition approaching the azeotropic composition at the working pressure of the column. Thus, the remaining water can be distilled off in the form of an acetonitrile / water azeotrope.

[0103] In one embodiment of the present disclosure, the reflux ratio of the distillation column (216) in step F1 is 0.05 to 1, for example, 0.1. In one embodiment of the present disclosure, the reflux ratio of the distillation column (219) in step F2 is 0.05 to 1, for example, 0.25.

[0104] The azeotropic acetonitrile composition (221) can be recycled, for example, via the water supply section (209) of step C to the acetonitrile feedstock for the distillation of step D.

[0105] Thus, in one embodiment, step C may comprise the further step of feeding a recycled acetonitrile stream (221) into the feed water section, which is a by-product of further processing steps, e.g. pressure swing distillation, e.g. from steps F1 and F2, e.g. from the dehydration section (third distillation section, FIG. 2), and comprises water, acetonitrile and ethanol, which accumulates in the system. The recycled acetonitrile stream (221) comprises an acetonitrile / water azeotrope and ethanol. Recycling 10-30% of this stream allows ethanol to be purged from the process in the form of an ethanol / water azeotrope. The recycle step ensures optimal removal of ethanol from the process.

[0106] In one embodiment, at least a portion of the acetonitrile / water azeotrope (221) is recycled back to step C and at least a portion is returned to the further mixing zone (215) (step E).

[0107] In one embodiment, the method of the second aspect of the disclosure further comprises mixing the acetonitrile bottoms product (213) from the third distillation of step D with a portion of the recycled azeotropic acetonitrile composition (221) from a further processing step, e.g., pressure swing distillation, e.g., step F2, before subjecting to steps F1 and F2 (step E). Mixing the acetonitrile bottoms product (213) from the third distillation of step D with the recycled azeotropic acetonitrile composition (221) can be carried out in a further mixing zone (215). This embodiment can also comprise a prior step of feeding the recycled acetonitrile stream (221) disclosed above into the feed water zone (209).

[0108] Thus, in one embodiment, any impurities present in the dehydration zone, e.g., in step F2, that may form a light azeotrope with water and acetonitrile are withdrawn from an upper portion of column (221), e.g., overhead, and recycled, along with the remaining acetonitrile and water, back to the second distillation zone, e.g., steps C, D, and E.

[0109] Alternatively, the lower boiling azeotropic fraction (221) from the dehydration section, for example from step F2, can be purged (222) and sent to organic waste.

[0110] If the water content in the acetonitrile product stream (220) from step F2 is not low enough, a further stage of separation (225) can be added which can remove the residual water as an azeotrope, or it can be removed by adsorption onto a stationary phase, for example molecular sieves.

[0111] Thus, in a further embodiment of the present disclosure, the method further comprises feeding the acetonitrile bottom product (220) from step F2 to a water adsorption zone (225) and contacting the acetonitrile bottom product (220) with a water reducing adsorbent to produce acetonitrile with less than 30 ppm water exiting the adsorption zone (225). The water reducing adsorbent can be a molecular sieve. Further details and embodiments of the adsorbent are described in WO2015126713 A1, paragraphs

[0033] to

[0038] . However, in a preferred embodiment, a molecular sieve is used. In one embodiment, the molecular sieve has a pore size of less than 20 angstroms, for example 3, 4 or 5 angstroms. In a preferred embodiment, the molecular sieve has a pore size of 3 angstroms. A pore size of 3 angstroms is very efficient for separation because water has a smaller size and acetonitrile has a larger size. The acetonitrile exiting the adsorption zone has a purity of at least 99.90% (area %), as measured, for example, by gas chromatography, and a water content of less than 30 ppm.

[0112] In yet another embodiment, a method for recovering and / or purifying acetonitrile from waste acetonitrile (301, 302) generated during oligonucleotide synthesis, comprising: A') introducing into a first mixing zone (303) and combining therein an organic waste feedstock (301) comprising acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile, and an aqueous waste feedstock (302) comprising acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile, to form an acetonitrile waste feedstock comprising said impurities; or introducing an organic waste feedstock (301) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a first mixing zone (303) and enriching with water to produce a water-enriched acetonitrile stream containing said impurities; B') introducing the acetonitrile waste feedstock or the water-enriched acetonitrile stream into a first distillation column (304) to separate acetonitrile and a first set of impurities having a boiling point lower than acetonitrile from a second set of impurities having a boiling point higher than acetonitrile, wherein acetonitrile and the first set of impurities are withdrawn as vapor from the first distillation column and condensed to produce a first distillate (306) and the second set of impurities is produced as first distillation column bottoms (305); C') optionally introducing the first distillate (306) containing acetonitrile and low boiling impurities into a water feed section (307) and enriching it with water to produce a water-enriched acetonitrile stream (307a); D') introducing the water-enriched acetonitrile stream (306, 307a) into a second distillation column (308) and separating the acetonitrile from low-boiling impurities, wherein acetonitrile is produced as second distillation column bottoms (309); Includes; A method is thereby provided whereby recovered and / or purified acetonitrile is obtained.

[0113] The second distillation column bottoms (309) produced as a result of the second distillation step D' comprises an acetonitrile / water azeotrope.

[0114] In order to reduce the water content of the acetonitrile product to less than 30 ppm, a further step E') can be further employed by introducing the second distillation column bottoms product (309) of step D' into a third distillation column (311) to separate acetonitrile from the acetonitrile / water azeotrope, wherein acetonitrile is produced as third distillation column bottoms (312).

[0115] Further details and embodiments of the fourth aspect of the present disclosure are disclosed below.

[0116] The following details and embodiments of the first, second, and third distillation zones are applicable to and may be combined with all aspects of the present disclosure, including the processes of the first, second, third and fourth aspects of the present disclosure.

[0117] First Aspect of the Disclosure According to a first aspect, there is provided a method for recovering and / or purifying acetonitrile from waste acetonitrile (105, 205) generated during oligonucleotide synthesis, comprising the steps of: A * ) introducing an organic waste feedstock (105, 205) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a distillation column (106, 206) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the distillation column and condensed to produce a distillate (107, 207) and the second set of organic impurities is produced as a second distillation column bottoms (108, 208); B *) introducing the distillate (107, 207) into a water feed section (109, 209) to produce a water-enriched acetonitrile stream (111, 210, 210a); C * ) introducing the water-enriched acetonitrile stream (111, 210, 210a) into a second distillation column (112, 212) and separating the first set of organic impurities from the acetonitrile, which is produced as second distillation column bottoms (113, 213); Includes; Methods are provided herein whereby recovered and / or purified acetonitrile is obtained.

[0118] The acetonitrile produced as the second distillation column bottoms can be collected and recycled or can be further processed by using steps A1 and E1 or steps A and C according to the second or third aspects of the present disclosure. By using these further steps, the yield of recovered acetonitrile can be improved. Thus, separation of acetonitrile from an aqueous waste process stream is not required to produce recovered and / or purified acetonitrile from an organic waste stream in accordance with the present disclosure.

[0119] The light acetonitrile stream (107, 207) fed to the feed water section (109, 209) contains light impurities (107, 207) and is enriched with water to produce a water-enriched acetonitrile stream (111, 210, 210a). Some compounds in the feed to the feed water section are made lighter boiling, either in the form of binary or ternary azeotropes, for example toluene / water / acetonitrile, acetonitrile / water / diisopropylamine, acetonitrile / water / ethanol, acetonitrile / water / ethyl acetate, etc.

[0120] Water can be added directly to the first acetonitrile distillate (107, 207) or can be added to the first acetonitrile distillate (107, 207) as a component of a further acetonitrile process stream, e.g., present in the acetonitrile distillate from an aqueous purification step. Addition of water via the acetonitrile process stream advantageously eliminates the need for further enrichment with water.

[0121] By incorporating a water feed section, separation of the inherently complex mixture of light-boiling impurities and azeotrope formers, such as toluene, acrylonitrile, ethanol, ethyl acetate, and low-boiling amines, among others, can be achieved. * ~C * The acetonitrile produced according to the process has a purity of at least 99.90%. All of the impurities in the feed (111, 210, 210a) are separated from the upper portion of the column (112, 212), e.g., overhead, as a binary or ternary azeotrope, and acetonitrile is produced as the second distillation column bottoms (113, 213). Thus, by using water as an entrainer, successful separation and sorting of organic waste from the acetonitrile process stream can be achieved.

[0122] Process A * Further details and embodiments of the first aspect of the present disclosure for the distillation of are equivalent to those disclosed according to step B1 or step B according to the second or third aspect of the present disclosure and are given below.

[0123] Process C * Further details and embodiments of the first aspect of the present disclosure for the distillation of are equivalent to those disclosed according to step D1 or step D according to the second or third aspect of the present disclosure and are given below.

[0124] Second Aspect of the Disclosure First Distillation Zone The first distillation section may be referred to as the organic purification section and includes at least two distillation columns (106, 112). The organic waste stream fed to this section contains a combination of acetonitrile, 2,6-lutidine, acetic anhydride, dichloroacetic acid, pyridine, toluene, 1-methylimidazole, and lesser amounts of diethylamine, diisopropylamine, acetic acid, 5-ethylthio-1H-tetrazole, N,N-dimethylformamide, organic iodine and sulfur compounds, as well as residual oligonucleotide building blocks and trace amounts of water. The heavy organics produced as bottoms product (108) in step B1 are considered waste. The concentration of compounds in solution may be present in concentrations ranging from negligible to up to 10% by weight. Many of these compounds are difficult to separate from acetonitrile because they have very similar volatility to acetonitrile within certain concentration ranges or because they form azeotropes with acetonitrile. Several purification steps in this section may be used to separate acetonitrile from other compounds present. A stage may be used to first separate the heavy fraction of compounds from acetonitrile, light boilers and azeotrope formers. This stage may be designed to take advantage of the minimal difference in relative volatility of the compounds being separated to increase the purity of the acetonitrile stream. The light fraction from this stage (107), containing most of the acetonitrile, may then be fractionated in a further stage, for example in a second distillation column (112), to produce a substantially pure acetonitrile product stream (113) and a more volatile light boiler waste stream (114). To separate azeotrope formers with acetonitrile, for example toluene, acrylonitrile or ethanol, an entrainer such as water may be added to the feed (109), which forms azeotropes with these compounds that have a lower boiling point compared to acetonitrile, making them easier to separate from acetonitrile (111).

[0125] The organic waste stream (105) of the present disclosure entering the first distillation zone comprises acetonitrile. In some embodiments, the organic waste stream (105) comprises a relatively high content of acetonitrile. In one embodiment, the organic waste stream (105) comprises acetonitrile in an amount ranging from 70% to 95% by weight, e.g., 75% to 95% by weight, 80% to 94% by weight, 85% to 93% by weight, or 87% to 92% by weight, e.g., 90% by weight, based on the total weight of the feedstock stream (105). On the upper end, the feedstock stream may comprise less than 95% by weight acetonitrile, e.g., less than 94% by weight, less than 93% by weight, less than 92% by weight, or less than 91% by weight. In terms of the lower limit, the feed stream may contain greater than 70 wt% acetonitrile, e.g., greater than 75 wt%, greater than 80 wt%, greater than 85 wt%, greater than 86 wt%, greater than 87 wt%, greater than 88 wt%, or greater than 89 wt% acetonitrile.

[0126] In some embodiments, the distillation column (106) of step B1 operates at a pressure in the range of 50 to 980 mbar, preferably 100 to 300 mbar. In terms of the lower limit, the distillation column (106) may operate at a pressure greater than 50 mbar, e.g., greater than 100, greater than 200, greater than 300 mbar, greater than 400 mbar, greater than 500 mbar, greater than 600 mbar, greater than 700 mbar, or greater than 800 mbar. In terms of the upper limit, the first distillation column may operate at a pressure less than 900 mbar, e.g., less than 800 mbar, less than 700 mbar, less than 600 mbar, less than 500 mbar, less than 400 mbar, less than 300 mbar, or less than 200 mbar.

[0127] Generally, the distillation column (106) contains structured packing or physical trays or plates whose purpose is to provide sufficient surface area to promote intimate contact between the liquid and vapor phases moving in a countercurrent direction inside the column. The height of the packing within the column, along with the hydraulic properties of the gas and liquid, determines the number of separation stages contained within the column. The number of stages required for a particular separation is determined by the complexity of the separation required. In general, it can be said that the closer the boiling points between the compound of interest and other accompanying compounds, the more stages will be required to achieve the desired separation. The column can be operated to improve the purity of the desired compound and increase the separation of impure compounds by changing the operating pressure, feed position, and reflux ratio.

[0128] In one embodiment of the present disclosure, the reflux ratio of the distillation column (106) in step B1 is 2 to 8, for example, 5.

[0129] The light fraction (107) produced in step B1 comprises about 90% to 99.5% by weight of acetonitrile. In some embodiments, the light fraction (107) comprises an amount of acetonitrile in the range of 96% to 99.5% by weight of acetonitrile, e.g., 96.5% to 99.5% by weight, 97% to 99.5% by weight, 97.5% to 99.5% by weight, or 98% to 99.5% by weight of acetonitrile, based on the total weight of the distillate (107). In terms of upper limits, the light fraction (107) may comprise less than 99.5% by weight of acetonitrile, e.g., less than 99%, less than 98.5%, less than 98%, less than 97.5%, less than 97%, less than 96.5%, less than 96%, less than 95.5%, or less than 95% by weight of acetonitrile. In terms of the lower limit, the light boiling fraction (107) can contain greater than 90% acetonitrile by weight, e.g., greater than 91%, greater than 92%, greater than 93%, greater than 94%, greater than 95%, greater than 95.5%, greater than 96%, greater than 96.5%, greater than 97%, greater than 97.5%, greater than 98%, greater than 98.5%, or greater than 99% by weight.

[0130] Impurities having a boiling point between the acetonitrile azeotrope boiling point and the acetonitrile boiling point will be withdrawn together with the low-boiling impurities, the acetonitrile azeotrope and acetonitrile. The light-boiling fraction is withdrawn from the upper part from the column, for example from the top of the column. Azeotrope formers include toluene, ethanol, water and acrylonitrile. This fraction further contains high-boiling hydrophobic impurities such as toluene. This occurs because such high-boiling hydrophobic impurities can form hydrophobic-hydrophobic interactions with acetonitrile, thereby being dragged to the top during distillation. Thus, the fraction withdrawn from the top of the column contains acetonitrile as well as light-boiling impurities, for example binary and ternary azeotropes such as acetonitrile / diethylamine, acetonitrile / diisopropylamine, toluene / water / acrylonitrile, toluene / water / acetonitrile, diisopropylamine / water / acetonitrile, acetonitrile / water, acetonitrile / toluene, toluene / water or ethanol / water, or mixtures thereof. The low boiling impurities may further include at least one N-containing compound, such as diethylamine, diisopropylamine, and acrylonitrile, or mixtures thereof.

[0131] The light fraction (107) produced in step B1 may also contain ethanol as an impurity. In some embodiments, the light fraction (107) contains a relatively low content of ethanol. In one embodiment, the light fraction (107) contains an amount of ethanol in the range of 0.5% to 3% ethanol by weight, e.g., 0.6% to 3%, 0.7% to 3%, 0.8% to 3% ethanol by weight, based on the total weight of the fraction (107). In terms of upper limits, the light fraction (107) may contain less than 3% ethanol by weight, e.g., less than 2.8%, less than 2.6%, less than 2.4%, less than 2.2%, less than 2%, less than 1.5% ethanol by weight. In terms of the lower limit, the light boiling fraction (107) may contain more than 0.5% by weight ethanol, e.g., more than 0.6% by weight, more than 0.7% by weight, more than 0.8% by weight, more than 0.9% by weight, more than 1% by weight, more than 1.2% by weight, more than 1.5% by weight, more than 1.7% by weight, more than 2% by weight, or more than 2.5% by weight ethanol.

[0132] In some embodiments, the light fraction (107) comprises toluene in an amount ranging from 0.2 wt% to 5 wt% toluene, e.g., 0.5 wt% to 5 wt%, 1 wt% to 5 wt%, 1.5 wt% to 5 wt%, 2 wt% to 5 wt%, 2.5 wt% to 5 wt%, 3 wt% to 5 wt%, 3.5 wt% to 5 wt% toluene. In terms of upper limits, the light fraction (107) may comprise less than 5 wt% toluene, e.g., less than 4.5 wt%, less than 4 wt%, less than 3.5 wt% toluene, less than 3 wt%, less than 2.5 wt%, less than 2 wt%, less than 1.5 wt%, less than 1 wt%, or less than 0.5 wt% toluene. In terms of the lower limit, the light boiling fraction (107) can contain more than 0.2 wt.% toluene, e.g., more than 0.5 wt.%, more than 0.8 wt.%, more than 1 wt.%, more than 1.2 wt.%, more than 1.5 wt.%, more than 1.8 wt.%, more than 2 wt.%, more than 2.2 wt.%, more than 2.5 wt.%, more than 2.8 wt.%, more than 3 wt.%, more than 3.2 wt.%, more than 3.5 wt.%, more than 3.8 wt.%, more than 4 wt.%, or more than 4.5 wt.% toluene.

[0133] In some embodiments, the light fraction (107) contains an amount of acrylonitrile in the range of 1 to 200 ppm, e.g., 5 to 180 ppm, 50 to 150 ppm acrylonitrile. In terms of upper limits, the light fraction (107) may contain less than 200 ppm acrylonitrile, e.g., less than 180 ppm, less than 150 ppm, less than 120 ppm, less than 100 ppm, less than 75 ppm, less than 50 ppm, or less than 20 ppm acrylonitrile. In terms of the lower limit, the light boiling fraction (107) can contain more than 1 ppm acrylonitrile, e.g., more than 5 ppm, more than 10 ppm, more than 20 ppm, more than 30 ppm, more than 40 ppm, more than 50 ppm, more than 60 ppm, more than 70 ppm, more than 80 ppm, more than 90 ppm, more than 100 ppm, more than 120 ppm, or more than 150 ppm acrylonitrile.

[0134] In some embodiments, the light fraction (107) contains an amount of diethylamine in the range of 5 to 300 ppm, e.g., 10 to 300 ppm, 20 to 280 ppm, 50 to 250 ppm diethylamine. In terms of upper limits, the light fraction (107) may contain less than 300 ppm diethylamine, e.g., less than 280 ppm, less than 250 ppm, less than 230 ppm, less than 210 ppm, less than 200 ppm, less than 180 ppm, less than 150 ppm, less than 130 ppm, less than 100 ppm, or less than 50 ppm diethylamine. In terms of the lower limit, the light boiling fraction (107) may contain more than 5 ppm diethylamine, e.g., more than 20 ppm, more than 50 ppm, more than 75 ppm, more than 100 ppm, more than 120 ppm, more than 150 ppm, more than 175 ppm, more than 200 ppm, more than 250 ppm diethylamine.

[0135] In some embodiments, the light fraction (107) contains diisopropylamine in an amount ranging from 10 to 600 ppm, e.g., from 50 to 550 ppm, from 75 to 500 ppm, from 100 to 400 ppm diisopropylamine. In terms of upper limits, the light fraction (107) may contain less than 600 ppm diisopropylamine, e.g., less than 550 ppm, less than 500 ppm, less than 450 ppm, less than 400 ppm, less than 350 ppm, less than 300 ppm, less than 250 ppm, less than 200 ppm, or less than 150 ppm diisopropylamine. In terms of the lower limit, the light boiling fraction (107) may contain more than 10 ppm diisopropylamine, e.g., more than 50 ppm, more than 75 ppm, more than 100 ppm, more than 150 ppm, more than 175 ppm, more than 200 ppm, more than 250 ppm, more than 300 ppm, more than 350 ppm, more than 400 ppm, more than 550 ppm, or more than 500 ppm diisopropylamine.

[0136] The light fraction (107) exits as a vapor and is passed through a condenser to produce a condensate, a portion of which is then returned to the column as a reflux stream and the remainder is removed as product.

[0137] The heavy boiling organic impurities withdrawn from the distillation column (106) as the bottoms product (108) are considered waste and are discarded. In some embodiments, the heavy boiling organic impurities include at least one of 1-methylimidazole, 2,6-lutidine, acetic acid, dimethylformamide, ETT, PADS, pyridine, and toluene, or mixtures thereof.

[0138] To purify acetonitrile from light-boiling organic impurities present in the light fraction (107) from the distillation of step B1, the resulting acetonitrile stream (107) is then fed to a water feed section (109), where water can be added to the feed, which forms an azeotrope with these impurity compounds of lower boiling point compared to acetonitrile, which are easier to separate from acetonitrile (111). The amount of water added can range from 0.05 to 0.40 w / w based on the amount of acetonitrile present in the stream. Preferably, the lower boiling azeotrope present in the acetonitrile stream (111) comprises at least one of acetonitrile / water, acrylonitrile / water, acetonitrile / toluene, acetonitrile / diethylamine, acetonitrile / diisopropylamine, toluene / water, ethanol / water, toluene / water / acrylonitrile, toluene / water / acetonitrile, diisopropylamine / water / acetonitrile, and diethylamine / toluene / water, or mixtures thereof.

[0139] The water-enriched acetonitrile stream (111) is then fed to a distillation column (112) and comprises about 5% to 40% acetonitrile by weight, based on the total weight of the water-enriched acetonitrile stream (111). In some embodiments, the water-enriched acetonitrile stream (111) comprises an amount of acetonitrile ranging from 10% to 40% by weight, e.g., 15% to 35% by weight of acetonitrile. In terms of the upper limit, the water-enriched acetonitrile stream (111) may comprise less than 40% by weight of acetonitrile, e.g., less than 35% by weight, less than 30% by weight, or less than 20% by weight of acetonitrile. In terms of the lower limit, the water-enriched acetonitrile stream (111) may comprise more than 5% by weight of acetonitrile, e.g., more than 10% by weight, more than 20% by weight, or more than 30% by weight of acetonitrile.

[0140] In some embodiments, the distillation of step D1 operates in the range of 100 to 980 mbar, preferably 900 to 980 mbar. In terms of the lower limit, the distillation column (112) may operate at a pressure greater than 100 bar, e.g., greater than 200 mbar, greater than 300 mbar, greater than 400 mbar, greater than 500 mbar, greater than 600 mbar, greater than 700 mbar, or greater than 800 mbar. In terms of the upper limit, the distillation column (112) may operate at a pressure less than 980 mbar, e.g., less than 950 mbar, less than 900 mbar, or less than 800 mbar.

[0141] Generally, the distillation column (112) contains structured packing or physical trays or plates whose purpose is to provide sufficient surface area to promote intimate contact between the liquid and vapor phases moving in a countercurrent direction inside the column. The height of the packing within the column, along with the hydraulic properties of the gas and liquid, determines the number of separation stages contained within the column. The number of stages required for a particular separation is determined by the complexity of the separation required. In general, it can be said that the closer the boiling points between the compound of interest and other accompanying compounds, the more stages will be required to achieve the desired separation. The column can be operated to increase the purity of the desired compound and increase the separation of impure compounds by changing the operating pressure, feed position, and reflux ratio.

[0142] In one embodiment of the present disclosure, the reflux ratio of the distillation column (112) in step D1 is 5 to 40, for example, 30.

[0143] In step D1, the water-enriched acetonitrile stream (111) is introduced into a distillation column (112) and separated into a lower boiling azeotropic fraction (114) and an acetonitrile distillation column bottoms product (113). The lower boiling azeotropic fraction (114) comprises at least one of acetonitrile / water, acrylonitrile / water, acetonitrile / toluene, acetonitrile / diethylamine, acetonitrile / diisopropylamine, toluene / water, ethanol / water, toluene / water / acrylonitrile, toluene / water / acetonitrile, diisopropylamine / water / acetonitrile, and diethylamine / toluene / water, or mixtures thereof.

[0144] The lower boiling azeotropic fraction (114) exits as a vapor and is passed through a condenser to produce a condensate. The lower boiling azeotropic fraction (114) is withdrawn as a vapor from an upper portion of column (112), e.g., overhead.

[0145] The acetonitrile withdrawn from the distillation column (112) as bottoms product (113) comprises about 60-90% acetonitrile by weight. In one embodiment, the acetonitrile bottoms product (113) comprises an amount of acetonitrile ranging from 65% to 90% acetonitrile by weight, e.g., 65% to 85% acetonitrile by weight, based on the total weight of the recovered acetonitrile bottoms product (113). On the upper end, the acetonitrile bottoms product (113) can comprise less than 90% acetonitrile by weight, e.g., less than 85%, less than 80%, less than 75%, or less than 70% acetonitrile by weight. On the lower end, the acetonitrile bottoms product (113) can comprise more than 65% acetonitrile by weight, e.g., more than 70%, more than 75%, more than 80%, or more than 85% acetonitrile by weight.

[0146] The lower boiling acetonitrile azeotrope (114) that is withdrawn from the upper portion of the distillation column (112), for example overhead, is considered waste and is discarded.

[0147] Thereby, it is ensured that the acetonitrile stream (113) arriving at the distillation column (117, 120) in the third distillation zone has a reduced water and impurity content and is as rich in acetonitrile as possible. In one embodiment, the acetonitrile (113) recovered according to steps A1-D1 according to the first aspect of the present disclosure is at least 99.90% (area %) pure as measured by gas chromatography (GC) analysis.

[0148] The acetonitrile stream produced in step D1 can be subjected to further processing steps. Thus, in one embodiment, the acetonitrile bottoms product (113) from step D1 and the acetonitrile distillate (103) from step A1 can then be fed to a mixing zone (116) where they are combined to obtain an acetonitrile-rich stream (110) (step E1).

[0149] The acetonitrile-rich stream (110) comprises about 60-90% acetonitrile by weight. In one embodiment, the acetonitrile-rich stream (110) comprises an amount of acetonitrile in the range of 65%-90% acetonitrile by weight, e.g., 65%-85% acetonitrile by weight, based on the total weight of each stream. On the upper end, stream (110) may comprise less than 90% acetonitrile by weight, e.g., less than 85%, less than 80%, less than 75%, or less than 70% acetonitrile by weight. On the lower end, stream (110) may comprise more than 65% acetonitrile by weight, e.g., more than 70%, more than 75%, more than 80%, or more than 85% acetonitrile by weight.

[0150] In one embodiment, the acetonitrile-rich stream (110) comprises at most 1 wt.% ethanol. In a further embodiment, the acetonitrile-rich stream (110) comprises at most 20 ppm pyridine. In a further embodiment, the acetonitrile-rich stream (110) comprises at most 50 ppm toluene.

[0151] Second Distillation Zone The second distillation section may be called the inorganic aqueous purification section. The acetonitrile waste (101) entering this section is separated into a lighter stream (103) enriched in acetonitrile and containing some water and ethanol. The heavier fraction (104) contains non-volatile salts and organic residues from the main process purification as aqueous solutions. This section is operated to maximize the yield of acetonitrile in the form of an azeotrope while removing as much excess water as possible from the process.

[0152] The aqueous waste stream (101) entering the inorganic purification section (also referred to herein as the second distillation section) of the first aspect of the present disclosure comprises acetonitrile. In some embodiments, the aqueous waste stream (101) comprises a relatively low content of acetonitrile. In one embodiment, the aqueous waste stream (101) comprises an amount of acetonitrile ranging from 5% to 13% by weight, e.g., 6% to 13% by weight, e.g., 9.5% by weight, based on the total weight of the aqueous waste stream (101). In terms of the upper limit, the aqueous waste stream (101) may comprise less than 15% by weight of acetonitrile, e.g., less than 14% by weight, less than 13% by weight, less than 12% by weight, less than 11% by weight, or less than 10% by weight of acetonitrile. In terms of the lower limit, the aqueous waste stream (101) may comprise more than 5% by weight of acetonitrile, e.g., more than 6% by weight of acetonitrile, more than 7% by weight of acetonitrile, more than 8% by weight, or more than 9% by weight of acetonitrile.

[0153] Generally, as used herein, weight percentages are based on the total weight of each stream. With respect to the aqueous waste stream (101), the weight percentages include all components of the feedstock, including most of the water. In some embodiments, for example, the aqueous waste stream (101) comprises at least 87% water by weight, e.g., at least 88% by weight, at least 89% by weight, or at least 90% by weight water.

[0154] The aqueous waste stream (101) of the present disclosure further comprises ethanol. In some embodiments, the aqueous waste stream (101) comprises a relatively small amount of ethanol. In one embodiment, the aqueous waste stream (101) comprises an amount of ethanol in the range of 0.05% to 0.8% by weight, e.g., 0.08% to 0.6% by weight, 0.1% to 0.5% by weight, e.g., 0.2% by weight, based on the total weight of the aqueous waste stream (101). In terms of upper limits, the aqueous waste stream (101) may comprise less than 0.8% by weight of ethanol, e.g., less than 0.7% by weight, less than 0.6% by weight, or less than 0.5% by weight of ethanol. In terms of lower limits, the aqueous waste stream (101) may comprise more than 0.08% by weight of ethanol, e.g., more than 0.1% by weight, more than 0.15% by weight, more than 0.18% by weight, more than 0.2% by weight, or more than 0.5% by weight of ethanol.

[0155] An aqueous waste stream (101) is fed into a distillation column (102) whereby a light fraction (103) comprising acetonitrile, water and ethanol is withdrawn from an upper portion of the column (102), e.g., overhead. The light fraction (103) exits as a vapor and is passed through a condenser to produce a condensate.

[0156] The light acetonitrile fraction (103) withdrawn from the top of column (102) contains about 70% acetonitrile by weight. In some embodiments, the light acetonitrile fraction (103) contains an amount of acetonitrile in the range of 60% to 80% acetonitrile by weight, based on the total weight of the recovered light acetonitrile fraction (103). On the upper end, the light acetonitrile fraction (103) may contain less than 80% acetonitrile by weight, e.g., less than 78%, less than 75%, less than 73%, or less than 70% acetonitrile by weight. On the lower end, the light acetonitrile fraction (103) may contain more than 60% acetonitrile by weight, e.g., more than 65%, more than 68%, or more than 70% acetonitrile by weight.

[0157] In some embodiments, the light fraction (103) contains an amount of water ranging from 20% to 40% by weight water, for example, 22% to 38% by weight water, based on the total weight of the recovered light fraction (103). On the upper end, the light fraction (103) may contain less than 40% by weight water, for example, less than 38% by weight, less than 35% by weight, less than 33% by weight, or less than 30% by weight water. On the lower end, the light fraction (103) may contain more than 20% by weight water, for example, more than 22% by weight, more than 25% by weight, more than 28% by weight, more than 30% by weight, or more than 35% by weight water. The weight percent of water present includes water present in azeotropic and non-azeotropic forms.

[0158] In some embodiments, the light fraction (103) comprises an amount of ethanol ranging from 0% to 2% ethanol by weight, e.g., 0.05% to 2%, 0.1% to 2%, 0.5% to 2% ethanol by weight, based on the total weight of the recovered light fraction (103). On the upper end, the light fraction (103) may comprise less than 2% ethanol by weight, e.g., less than 1.8%, less than 1.5%, or less than 1% ethanol by weight. On the lower end, the light fraction (103) may comprise more than 0.05% ethanol by weight, e.g., more than 0.1%, more than 0.5%, more than 1%, more than 1.5%, or more than 1.75% ethanol by weight.

[0159] In some embodiments, the distillation of step A1 operates at a pressure in the range of 200 to 980 mbar, preferably 400 to 500 mbar. In terms of the lower limit, the distillation column (102) may operate at a pressure greater than 200 mbar, e.g., greater than 300 mbar, greater than 400 mbar, greater than 500 mbar, greater than 600 mbar, greater than 700 mbar, or greater than 800 mbar. In terms of the upper limit, the distillation column (102) may operate at a pressure less than 980 mbar, e.g., less than 900, less than 800, less than 700 bar, less than 600 mbar, or less than 500 mbar.

[0160] Generally, the distillation column (102) contains structured packing or physical trays or plates whose purpose is to provide sufficient surface area to promote intimate contact between the liquid and vapor phases moving in a countercurrent direction inside the column. The height of the packing within the column, along with the hydraulic properties of the gas and liquid, determines the number of separation stages contained within the column. The number of stages required for a particular separation is determined by the complexity of the separation required. In general, it can be said that the closer the boiling points between the compound of interest and other accompanying compounds, the more stages will be required to achieve the desired separation. The column can be operated to increase the purity of the desired compound and increase the separation of impure compounds by changing the operating pressure, feed position, and reflux ratio.

[0161] In one embodiment of the present disclosure, the reflux ratio of the distillation column (102) in step A1 is 0.25 to 2, for example, 1.

[0162] The light boiling fraction (103) is then fed to a mixing section (116) where it is mixed with the substantially pure acetonitrile bottoms product (113) from step D1 (step E1). The resulting acetonitrile-rich stream (110) comprises about 76% acetonitrile by weight. In some embodiments, the mixture (110) comprises an amount of acetonitrile ranging from 60% to 85% acetonitrile by weight, based on the total weight of the acetonitrile-rich stream (110). In terms of the upper limit, the acetonitrile-rich stream (110) may comprise less than 85% acetonitrile by weight, e.g., less than 80%, less than 75%, or less than 70% acetonitrile by weight. In terms of the lower limit, the acetonitrile-rich stream (110) may comprise more than 60% acetonitrile by weight, e.g., more than 65%, more than 70%, more than 75%, or more than 80% acetonitrile by weight.

[0163] The higher boiling aqueous bottom product (104) of step A1, which contains non-volatile salts and organic residues, is withdrawn as a bottom product. The bottom product (104) is considered waste and is discarded. The aqueous bottom product (104) can, for example, be fed to a second mixing section (125) in the third distillation section, whereby it is mixed, for example, with further aqueous waste (119) from a dehydration step, for example, pressure swing distillation, for example, from steps F1 and F2, before being discarded.

[0164] Third Aspect of the Disclosure First Distillation Zone The first distillation section of the third embodiment of the present disclosure may be called the dual aqueous and organic purification section and includes at least two distillation columns (202, 206). Process steps A and B are carried out in the so-called first distillation section (Figure 2), where the organic and inorganic aqueous purification steps are carried out. The goal is to separate as many heavy boilers as possible from acetonitrile and any other light boilers in the feed stream. Aqueous acetonitrile waste (201) comes from the purification area of ​​the oligonucleotide process, while organic waste (205) comes from the oligonucleotide synthesis section. The bottom products (204, 208) from each section are sent to waste. The overhead products (203, 207) are combined and enriched with water to produce the aqueous feed (210) to the light boilers column (212) in the second distillation section (Figure 2).

[0165] Aqueous acetonitrile waste (201) entering this zone is separated into a lighter stream (203) enriched in acetonitrile and containing some water and ethanol. The heavier portion (204) contains non-volatile salts and organic residues from the primary process purification as aqueous solutions. This zone is operated to maximize the yield of acetonitrile in the form of an azeotrope while removing as much excess water as possible from the process.

[0166] The aqueous acetonitrile waste stream (201) entering the first distillation zone of the second aspect of the present disclosure comprises acetonitrile. In some embodiments, the aqueous waste stream (201) comprises a relatively low content of acetonitrile. In one embodiment, the aqueous waste stream (201) comprises an amount of acetonitrile ranging from 5% to 13% by weight, e.g., 6% to 13% by weight, e.g., 9.5% by weight, based on the total weight of the feedstock stream (201). On the upper end, the aqueous waste feedstock stream (201) may comprise less than 15% by weight acetonitrile, e.g., less than 14% by weight, less than 13% by weight, less than 12% by weight, less than 11% by weight, or less than 10% by weight acetonitrile. On the lower end, the aqueous waste feedstock stream (201) may comprise more than 5% by weight acetonitrile, e.g., more than 6% by weight acetonitrile, more than 7% by weight acetonitrile, more than 7% by weight, or more than 9% by weight acetonitrile.

[0167] Generally, as used herein, weight percentages are based on the total weight of each stream. With respect to the aqueous waste stream (201), the weight percentages include all components of the feedstock, including most of the water. In some embodiments, for example, the aqueous waste stream (201) comprises at least 87% water by weight, e.g., at least 88% by weight, at least 89% by weight, or at least 90% by weight water.

[0168] The aqueous waste stream (201) of the present disclosure further comprises ethanol. In some embodiments, the aqueous waste stream (201) comprises a relatively small amount of ethanol. In one embodiment, the aqueous waste stream (201) comprises an amount of ethanol in the range of 0.05 wt.% to 0.8 wt.%, e.g., 0.08 wt.% to 0.6 wt.%, 0.1 wt.% to 0.5 wt.%, e.g., 0.2 wt.%, based on the total weight of the feedstock stream (201). On the upper limit, the aqueous waste feedstock stream (201) may comprise less than 0.8 wt.% ethanol, e.g., less than 0.7 wt.%, less than 0.6 wt.%, or less than 0.5 wt.% ethanol. On the lower limit, the feedstock stream may comprise more than 0.08 wt.% ethanol, e.g., more than 0.1 wt.%, more than 0.15 wt.%, more than 0.18 wt.%, or more than 0.2 wt.% ethanol.

[0169] An aqueous waste stream (201) is fed into a distillation column (202) whereby a light fraction (203) comprising acetonitrile, water, and ethanol is withdrawn from an upper portion of the column (202), e.g., overhead. The light fraction (203) exits as a vapor and is passed through a condenser to produce a condensate.

[0170] The light acetonitrile fraction (203) withdrawn from the top of the column (202) contains about 70% acetonitrile by weight. In some embodiments, the light acetonitrile fraction (203) contains an amount of acetonitrile in the range of 60% to 80% acetonitrile by weight, based on the total weight of the recovered light acetonitrile fraction (203). On the upper end, the light acetonitrile fraction (203) may contain less than 80% acetonitrile by weight, for example, less than 78%, less than 75%, less than 73%, or less than 70% acetonitrile by weight. On the lower end, the light acetonitrile fraction (203) may contain more than 60% acetonitrile by weight, for example, more than 65%, more than 68%, or more than 70% acetonitrile by weight.

[0171] In some embodiments, the light acetonitrile fraction (203) contains an amount of water ranging from 20 wt.% to 40 wt.% water, e.g., 22 wt.% to 38 wt.% water, based on the total weight of the recovered light fraction (203). On the upper end, the feed stream may contain less than 40 wt.% water, e.g., less than 38 wt.%, less than 35 wt.%, less than 33 wt.%, or less than 30 wt.% water. On the lower end, the feed stream may contain more than 20 wt.% water, e.g., more than 22 wt.%, more than 25 wt.%, more than 28 wt.%, more than 30 wt.%, or more than 35 wt.% water. The weight percent of water present includes water present in azeotropic and non-azeotropic forms.

[0172] In some embodiments, the light acetonitrile fraction (203) contains an amount of ethanol ranging from 0% to 2% ethanol by weight, e.g., 0.05% to 2%, 0.1% to 2%, 0.5% to 2% ethanol by weight, based on the total weight of the recovered light fraction (203). On the upper end, the light fraction (203) may contain less than 2% ethanol by weight, e.g., less than 1.8%, less than 1.5%, or less than 1% ethanol by weight. On the lower end, the light fraction (203) may contain more than 0.05% ethanol by weight, e.g., more than 0.1%, more than 0.5%, more than 1%, more than 1.5%, or more than 1.75% ethanol by weight.

[0173] In some embodiments, the distillation of step A operates at a pressure in the range of 200 to 980 mbar, preferably 400 to 500 mbar. In terms of the lower limit, the distillation column (201) may operate at a pressure greater than 200 mbar, e.g., greater than 300 mbar, greater than 400 mbar, greater than 500 mbar, greater than 600 mbar, greater than 700 mbar, or greater than 800 mbar. In terms of the upper limit, the distillation column (201) may operate at a pressure less than 980 mbar, e.g., less than 900, less than 800, less than 700 bar, less than 600 mbar, or less than 500 mbar.

[0174] Generally, the distillation column (202) contains structured packing or physical trays or plates whose purpose is to provide sufficient surface area to promote intimate contact between the liquid and vapor phases moving in a countercurrent direction inside the column. The height of the packing within the column, along with the hydraulic properties of the gas and liquid, determines the number of separation stages contained within the column. The number of stages required for a particular separation is determined by the complexity of the separation required. In general, it can be said that the closer the boiling points between the compound of interest and other accompanying compounds, the more stages will be required to achieve the desired separation. The column can be operated to increase the purity of the desired compound and increase the separation of impure compounds by changing the operating pressure, feed position, and reflux ratio.

[0175] In one embodiment of the present disclosure, the reflux ratio of the distillation column (202) in step A is 0.25 to 2, for example, 1.

[0176] The higher boiling aqueous mixture containing non-volatile salts and organic residues is withdrawn as bottoms product (204). Bottoms product (204) is considered waste and is discarded. The aqueous bottoms product (204) may be fed, for example, to a second mixing section (224) in the third distillation section, whereby it is mixed with other aqueous waste products from the third distillation section, for example, aqueous bottoms product (218), before being discarded.

[0177] The organic waste stream (205) fed to this section contains a combination of acetonitrile, 2,6-lutidine, acetic anhydride, dichloroacetic acid, pyridine, toluene, 1-methylimidazole, and lesser amounts of diethylamine, diisopropylamine, acetic acid, 5-ethylthio-1H-tetrazole, N,N-dimethylformamide, organic iodine and sulfur compounds, as well as residual oligonucleotide building blocks and trace amounts of water. The heavy organics produced as bottoms product (208) in the first distillation section of step B are considered waste. The concentration of the compounds in solution may be present in concentrations ranging from negligible to up to 10% by weight. Many of these compounds are difficult to separate from acetonitrile because they have very similar volatility to acetonitrile within certain concentration ranges or because they form azeotropes with acetonitrile. Several purification stages in this section may be used to separate acetonitrile from other compounds present. One stage may be used to first separate the heavy fraction of compounds from acetonitrile, the light boilers and the azeotrope formers. This stage may be designed to take advantage of minimal differences in the relative volatility of the compounds being separated to increase the purity of the acetonitrile stream. The light fraction (207) from this stage, containing most of the acetonitrile, may then be fractionated in further stages, for example in a second distillation section (212), to produce a purified acetonitrile product stream (213) and a more volatile light waste stream (214).

[0178] The organic waste stream (205) of the present disclosure entering the first distillation zone comprises acetonitrile. In some embodiments, the organic waste stream comprises a relatively high content of acetonitrile. In one embodiment, the organic waste stream comprises an amount of acetonitrile ranging from 70% to 95% acetonitrile by weight, e.g., 80% to 94%, 85% to 93%, or 87% to 92% acetonitrile by weight, e.g., 90% by weight, based on the total weight of the feedstock stream. On the upper end, the feedstock stream may comprise less than 95% acetonitrile by weight, e.g., less than 94%, less than 93%, less than 92%, or less than 91% acetonitrile by weight. On the lower end, the feedstock stream may comprise more than 70% acetonitrile by weight, e.g., more than 75%, more than 80%, more than 85%, more than 86%, more than 87%, more than 88%, more than 89% acetonitrile by weight, or more than 90% acetonitrile by weight.

[0179] In some embodiments, the distillation column (206) operates in the range of 50 to 980 mbar, preferably 100 to 300 mbar. In terms of the lower limit, the first distillation column can operate at a pressure greater than 50 mbar, e.g., greater than 100, greater than 200, greater than 300 mbar, greater than 400 mbar, greater than 500 mbar, greater than 600 mbar, greater than 700 mbar, or greater than 800 mbar. In terms of the upper limit, the first distillation column can operate at a pressure less than 900 mbar, e.g., less than 800 mbar, less than 700 mbar, less than 600 mbar, less than 500 mbar, less than 400 mbar, less than 300 mbar, or less than 200 mbar.

[0180] Generally, the distillation column (206) contains structured packing or physical trays or plates whose purpose is to provide sufficient surface area to promote intimate contact between the liquid and vapor phases moving in a countercurrent direction inside the column. The height of the packing within the column, along with the hydraulic properties of the gas and liquid, determines the number of separation stages contained within the column. The number of stages required for a particular separation is determined by the complexity of the separation required. In general, it may be said that the closer the boiling points between the compound of interest and other accompanying compounds, the more stages will be required to achieve the desired separation. The column can be operated to increase the purity of the desired compound and increase the separation of impure compounds by changing the operating pressure, feed position, and reflux ratio.

[0181] In one embodiment of the present disclosure, the reflux ratio of the distillation column (206) in step B is 2 to 8, for example, 5.

[0182] The light fraction (207) comprises about 90% to 99.5% by weight of acetonitrile. In some embodiments, the light fraction comprises an amount of acetonitrile in the range of 96% to 99.5% by weight of acetonitrile, e.g., 96.5% to 99.5% by weight, 97% to 99.5% by weight, 97.5% to 99.5% by weight, or 98% to 99.5% by weight of acetonitrile, based on the total weight of the distillate. In terms of the upper limit, the feed stream may comprise less than 99.5% by weight of acetonitrile, e.g., less than 99%, less than 98.5%, less than 98%, less than 97.5%, less than 97%, less than 96.5%, less than 96%, less than 95.5%, or less than 95% by weight of acetonitrile. In terms of the lower limit, the feed stream can comprise greater than 90 wt% acetonitrile, e.g., greater than 91 wt%, greater than 92 wt%, greater than 93 wt%, greater than 94 wt%, greater than 95 wt%, greater than 95.5 wt%, greater than 96 wt%, greater than 96.5 wt%, greater than 97 wt%, greater than 97.5 wt%, greater than 98 wt%, greater than 98.5 wt%, or greater than 99 wt% acetonitrile.

[0183] Impurities having a boiling point between the acetonitrile azeotrope boiling point and the acetonitrile boiling point will be withdrawn together with the low boiling impurities, the acetonitrile azeotrope and acetonitrile. The light fraction (207) is withdrawn from the upper portion from column (206), for example, from the top of the column. Azeotrope formers include toluene, ethanol, water and acrylonitrile. This fraction further contains high boiling hydrophobic impurities such as toluene. This occurs because such high boiling hydrophobic impurities can form hydrophobic-hydrophobic interactions with acetonitrile, thereby being dragged overhead during distillation. The fraction (207) taken from the top of the column thus contains acetonitrile and binary and ternary azeotropes such as acetonitrile / diethylamine, acrylonitrile / water, acetonitrile / diisopropylamine, toluene / water / acrylonitrile, toluene / water / acetonitrile, diisopropylamine / water / acetonitrile, diethylamine / toluene / water, acetonitrile / water, acetonitrile / toluene, toluene / water, or ethanol / water, or mixtures thereof. The acetonitrile fraction (207) further contains low-boiling N-containing impurities such as diethylamine, diisopropylamine, or acrylonitrile, or mixtures thereof.

[0184] The acetonitrile fraction (207) produced in step B may also contain ethanol as an impurity. In some embodiments, the acetonitrile fraction (207) contains a relatively low content of ethanol. In one embodiment, the light fraction (207) contains an amount of ethanol in the range of 0.5 wt.% to 3 wt.% ethanol, e.g., 0.6 wt.% to 3 wt.%, 0.7 wt.% to 3 wt.%, 0.8 wt.% to 3 wt.% ethanol, based on the total weight of the distillate (207). On the upper end, the feedstock stream may contain less than 3 wt.% ethanol, e.g., less than 2.8 wt.%, less than 2.6 wt.%, less than 2.4 wt.%, less than 2.2 wt.%, less than 2 wt.%, less than 1.5 wt.% ethanol. In terms of the lower limit, the feedstock stream may contain greater than 0.5 wt.% ethanol, e.g., greater than 0.6 wt.%, greater than 0.7 wt.%, greater than 0.8 wt.%, greater than 0.9 wt.%, greater than 1 wt.%, greater than 1.2 wt.%, greater than 1.5 wt.%, greater than 1.7 wt.%, greater than 2 wt.%, or greater than 2.5 wt.% ethanol.

[0185] In some embodiments, the acetonitrile fraction (207) contains an amount of toluene in the range of 0.2 wt% to 5 wt% toluene, e.g., 0.5 wt% to 5 wt%, 1 wt% to 5 wt%, 1.5 wt% to 5 wt%, 2 wt% to 5 wt%, 2.5 wt% to 5 wt%, 3 wt% to 5 wt%, 3.5 wt% to 5 wt% toluene. In terms of upper limits, the light acetonitrile fraction (207) may contain less than 5 wt% toluene, e.g., less than 4.5 wt%, less than 4 wt%, less than 3.5 wt% toluene, less than 3 wt%, less than 2.5 wt%, less than 2 wt%, less than 1.5 wt%, less than 1 wt%, or less than 0.5 wt% toluene. In terms of the lower limit, the light-boiling acetonitrile fraction (207) can contain more than 0.2 wt.% toluene, e.g., more than 0.5 wt.%, more than 0.8 wt.%, more than 1 wt.%, more than 1.2 wt.%, more than 1.5 wt.%, more than 1.8 wt.%, more than 2 wt.%, more than 2.2 wt.%, more than 2.5 wt.%, more than 2.8 wt.%, more than 3 wt.%, more than 3.2 wt.%, more than 3.5 wt.%, more than 3.8 wt.%, more than 4 wt.%, or more than 4.5 wt.% toluene.

[0186] In some embodiments, the light acetonitrile fraction (207) contains an amount of acrylonitrile in the range of 1 to 200 ppm, e.g., 5 to 180 ppm, 50 to 150 ppm acrylonitrile. In terms of upper limits, the light acetonitrile stream may contain less than 200 ppm acrylonitrile, e.g., less than 180 ppm, less than 150 ppm, less than 120 ppm, less than 100 ppm, less than 75 ppm, less than 50 ppm, or less than 20 ppm acrylonitrile. In terms of the lower limit, the light-boiling acetonitrile fraction (207) can contain more than 1 ppm acrylonitrile, e.g., more than 5 ppm, more than 10 ppm, more than 20 ppm, more than 30 ppm, more than 40 ppm, more than 50 ppm, more than 60 ppm, more than 70 ppm, more than 80 ppm, more than 90 ppm, more than 100 ppm, more than 120 ppm, or more than 150 ppm acrylonitrile.

[0187] In some embodiments, the light acetonitrile fraction (207) contains an amount of diethylamine ranging from 5 to 300 ppm, e.g., 10 to 300 ppm, 20 to 280 ppm, 50 to 250 ppm diethylamine. In terms of upper limits, the light acetonitrile stream may contain less than 300 ppm diethylamine, e.g., less than 280 ppm, less than 250 ppm, less than 230 ppm, less than 210 ppm, less than 200 ppm, less than 180 ppm, less than 150 ppm, less than 130 ppm, less than 100 ppm, or less than 50 ppm diethylamine. In terms of the lower limit, the light-boiling acetonitrile fraction (207) may contain more than 5 ppm diethylamine, e.g., more than 20 ppm, more than 50 ppm, more than 75 ppm, more than 100 ppm, more than 120 ppm, more than 150 ppm, more than 175 ppm, more than 200 ppm, more than 250 ppm diethylamine.

[0188] In some embodiments, the light acetonitrile fraction (207) contains diisopropylamine in an amount ranging from 10 to 600 ppm, e.g., 50 to 550 ppm, 75 to 500 ppm, 100 to 400 ppm diisopropylamine. In terms of upper limits, the light acetonitrile fraction (207) may contain less than 600 ppm diisopropylamine, e.g., less than 550 ppm, less than 500 ppm, less than 450 ppm, less than 400 ppm, less than 350 ppm, less than 300 ppm, less than 250 ppm, less than 200 ppm, or less than 150 ppm diisopropylamine. In terms of the lower limit, the low-boiling acetonitrile fraction (207) may contain more than 10 ppm diisopropylamine, for example, more than 50 ppm, more than 75 ppm, more than 100 ppm, more than 150 ppm, more than 175 ppm, more than 200 ppm, more than 250 ppm, more than 300 ppm, more than 350 ppm, more than 400 ppm, more than 550 ppm, or more than 500 ppm diisopropylamine.

[0189] The light acetonitrile fraction (207) exits as a vapor and is passed through a condenser to produce a condensate, a portion of which is then returned to the column as a reflux stream and the remainder is removed as product, e.g., condensate, from an upper portion of the column, e.g., overhead.

[0190] The heavy boiling organic impurities withdrawn from the distillation column as the bottoms product (208) are considered waste and are discarded. In some embodiments, the heavy boiling organic impurities include at least one of 1-methylimidazole, imidazole, 2,6-lutidine, acetic acid, dimethylformamide, ETT, PADS, pyridine, and toluene, or mixtures thereof.

[0191] The light acetonitrile fraction (203) of step A is then fed to a water feed section (209) where it is mixed with the light acetonitrile fraction (207) from the organic purification step B together with water.

[0192] Second Distillation Zone The light streams (203, 207) from the aqueous and organic distillation steps A and B, respectively, are fed to a feed water section (209), where the light streams (203, 207) from steps A and B are combined. The resulting acetonitrile composition can be further enriched with water before being fed into a further distillation column (212) (step C). The light streams (203, 207) can be fed to the feed water section (209) independently, one after the other, for example in any order or with a ratio ranging from 0 to 100%, or simultaneously.

[0193] Depending on the amount of water present from the first distillation zone from the aqueous waste stream (203), the water present in this stream may function as an entrainer, thus eliminating the need for further enrichment with water, whereby the acetonitrile distillate (203) from the aqueous purification step is mixed with the acetonitrile distillate (207) from the organic purification step and water is added. Thus, in an alternative embodiment, the acetonitrile distillate (203) from the aqueous purification step is already enriched with enough water to produce a water-enriched acetonitrile stream suitable for the separation of low-boiling impurities and azeotrope formers. The water-enriched acetonitrile stream (201a) as a direct result of the mixing of the acetonitrile distillates (203, 207) is then fed directly into the third distillation column (212) and process step D is carried out without the further water feed of step C.

[0194] The amount of water present in the feed water zone (209) by combining the purified aqueous and organic acetonitrile feedstocks (203, 207) can be readily determined by one skilled in the art. For example, the amount of water present can be determined by computer simulation based on design specifications. The simulation can be performed by a well-known commercially available simulation package, Aspen Plus (Aspen Technology, Inc., Massachusetts, USA), to simulate the composition of the feed to the column including water content. In one embodiment, step C, e.g., step C1, further comprises determining the amount of water present, e.g., by using a process simulation software package such as Aspen software, to determine if additional water needs to be added to the feed water zone (209).

[0195] The amount of water present by simply adding the acetonitrile distillate of step A (203) and the acetonitrile distillate of step B (207) is less than 20% by weight, such as less than 15% by weight, such as less than 10% by weight, for example about 8% by weight.

[0196] In an alternative embodiment, step C comprises feeding the acetonitrile distillate (203) of step A and the acetonitrile distillate (207) of step B to a water feed zone (209) where they are combined to enrich the mixture with water. The amount of water added results in a water content of 10% to 30% by weight in the water-enriched acetonitrile stream (210). The amount of water added is preferably greater than 0.24 times the amount of acetonitrile and impurities in the feed stream, but can be as low as 0.05 times or as high as 0.50 times the total amount of acetonitrile and impurities present. The amount of water that may be required for this step is lower compared to step C1 of the process of the second aspect, since the light acetonitrile fraction (207) from the organic purification step B is mixed with the light acetonitrile fraction (203) from the aqueous purification of step A.

[0197] The resulting water-enriched acetonitrile stream (210, 201a) comprises about 60-90 wt% acetonitrile, e.g., 76 wt%. In one embodiment, the water-enriched acetonitrile stream (210, 201a) comprises an amount of acetonitrile ranging from 65 wt% to 90 wt% acetonitrile, e.g., 65 wt% to 85 wt% acetonitrile, based on the total weight of the respective stream (210, 210a). On the upper end, the water-enriched acetonitrile stream (210, 210a) may comprise less than 90 wt% acetonitrile, e.g., less than 85 wt%, less than 80 wt%, less than 75 wt%, or less than 70 wt% acetonitrile. On the lower end, the water-enriched acetonitrile stream (210, 210a) may comprise more than 65 wt% acetonitrile, e.g., more than 70 wt%, more than 75 wt%, more than 80 wt%, or more than 85 wt% acetonitrile.

[0198] In one embodiment of step C, the lighter streams (203, 207) from the aqueous and organic distillation steps A and B are also mixed with a recycled acetonitrile stream (221), which is a by-product of further processing steps, e.g., pressure swing distillation steps, e.g., steps F1 and F2. The recycled acetonitrile stream (221) comprises a composition at or approaching the acetonitrile / water azeotropic composition at the operating conditions of column (219) of step F2. This stream further comprises ethanol, which accumulates in the system. The amount of ethanol present will vary depending on the feed concentration and flow rate of this stream compared to the feed stream (213) entering the pressure swing distillation steps, e.g., steps F1 and F2.

[0199] The recycled acetonitrile stream (221) may contain acetonitrile in the range of 70-76 wt.%, e.g., 75 wt.%, acetonitrile, 0-3 wt.%, e.g., 1.3 wt.%, ethanol, and water in the range of 24-30 wt.%, e.g., 24 wt.%, based on the total content of the stream.

[0200] Recycling 10-30% of this stream allows ethanol to be purged from the process in the form of an ethanol / water azeotrope. The recycle step ensures optimal removal of ethanol from the process. The resulting water-enriched acetonitrile stream (210, 201a) is then fed into a distillation column (212) to carry out step D.

[0201] The idea of ​​recycling back to oligonucleotide synthesis can be used independently to regenerate acetonitrile using a batch or continuous process. The internal circulation in the regeneration process can also be done batchwise as needed. The advantage of continuous is that much less storage capacity is required, so the equipment is much cheaper, the process can be automated, and much less storage capacity is required.

[0202] In some embodiments, the water-enriched acetonitrile stream (210, 201a) comprises about 60-90% acetonitrile by weight. In one embodiment, the water-enriched acetonitrile stream (210, 201a) comprises an amount of acetonitrile in the range of 65%-90% acetonitrile by weight, e.g., 65%-85% acetonitrile by weight, based on the total weight of the respective stream (210, 201a). In terms of the upper limit, the water-enriched acetonitrile stream (210, 201a) may comprise less than 90% acetonitrile by weight, e.g., less than 85%, less than 80%, less than 75%, or less than 70% acetonitrile by weight. In terms of the lower limit, the water-enriched acetonitrile stream (210, 201a) may comprise more than 65% acetonitrile by weight, e.g., more than 70%, more than 75%, more than 80%, or more than 85% acetonitrile by weight.

[0203] In some embodiments, the water-enriched acetonitrile stream (210, 201a) contains up to 1 wt.% ethanol. In further embodiments, the stream (210, 201a) contains up to 20 ppm pyridine. In further embodiments, the stream (210, 201a) contains up to 50 ppm toluene.

[0204] The acetonitrile-rich stream (210, 201a) is then fed into a distillation column (212). The acetonitrile-rich feed (210, 201a) is distilled and separated into an acetonitrile bottoms product (213) and a lower boiling fraction (214) comprising a lower boiling azeotrope. All of the impurities in the feed are separated from the upper part of the column (212), e.g., overhead, as a binary or ternary azeotrope. The lower boiling azeotrope fraction (214) can be directed to organic waste. In one embodiment, at least a portion of the lower boiling azeotrope fraction (214) is first mixed with other organic impurities, e.g., from the previous distillation step A (208), e.g., in a separate mixing section (223), before being directed to organic waste.

[0205] In some embodiments, the distillation of step D operates at a pressure in the range of 100 to 980 mbar, preferably 900 to 980 mbar. In terms of the lower limit, the distillation column (212) may operate at a pressure greater than 100 bar, e.g., greater than 200 mbar, greater than 300 mbar, greater than 400 mbar, greater than 500 mbar, greater than 600 mbar, greater than 700 mbar, or greater than 800 mbar. In terms of the upper limit, the distillation column (212) may operate at a pressure less than 980 mbar, e.g., less than 950 mbar, less than 900 mbar, or less than 800 mbar.

[0206] Generally, the distillation column (212) contains structured packing or physical trays or plates whose purpose is to provide sufficient surface area to promote intimate contact between the liquid and vapor phases moving in a countercurrent direction inside the column. The height of the packing within the column, along with the hydraulic properties of the gas and liquid, determines the number of separation stages contained within the column. The number of stages required for a particular separation is determined by the complexity of the separation required. In general, it can be said that the closer the boiling points between the compound of interest and other accompanying compounds, the more stages will be required to achieve the desired separation. The column can be operated to increase the purity of the desired compound and increase the separation of impure compounds by changing the operating pressure, feed position, and reflux ratio.

[0207] In one embodiment of the present disclosure, the reflux ratio of the distillation column (212) in step D is 5 to 40, for example, 30.

[0208] A lower boiling azeotropic fraction (214) comprising at least one of acetonitrile / diethylamine, acetonitrile / diisopropylamine, toluene / water / acrylonitrile, toluene / water / acetonitrile, diisopropylamine / water / acetonitrile, acetonitrile / water, acetonitrile / toluene, toluene / water, and ethanol / water, or mixtures thereof. The lower boiling azeotropic fraction (214) may further comprise at least one N-containing compound, such as diethylamine, diisopropylamine, and acrylonitrile, or mixtures thereof.

[0209] The lower boiling azeotropic fraction is withdrawn as a vapor from an upper portion of the distillation column (212), e.g., overhead, and passed through a condenser to produce a condensate (214).

[0210] The acetonitrile produced as bottoms product (213) comprises about 60-90% acetonitrile by weight. In one embodiment, the acetonitrile bottoms product (213) comprises an amount of acetonitrile ranging from 65% to 90% acetonitrile by weight, e.g., 65% to 85% acetonitrile by weight, based on the total weight of the recovered acetonitrile bottoms product (213). On the upper end, the feed stream can comprise less than 90% acetonitrile by weight, e.g., less than 85%, less than 80%, less than 75%, or less than 70% acetonitrile by weight. On the lower end, the feed stream can comprise more than 65% acetonitrile by weight, e.g., more than 70%, more than 75%, more than 80%, or more than 85% acetonitrile by weight.

[0211] In some embodiments, the acetonitrile bottoms product (213) comprises up to 1 wt.% ethanol. In further embodiments, the acetonitrile bottoms product (213) comprises up to 20 ppm pyridine. In further embodiments, the acetonitrile bottoms product (213) comprises up to 50 ppm toluene.

[0212] The lower boiling azeotropic fraction (214) that is withdrawn from the upper portion of the distillation column (212), e.g., overhead, is considered waste and is discarded.

[0213] Thereby, a purified acetonitrile stream (213) is obtained, ensuring that the acetonitrile stream reaching the distillation column in the third distillation section has a reduced water and impurity content and is as rich as possible in acetonitrile.

[0214] Second and third aspects of the present disclosure Third Distillation Zone The third distillation zone may be called the dehydration zone and includes the same steps, e.g., steps F1 and F2, for both the second and third aspects of the present disclosure, unless otherwise specified. The acetonitrile streams (110, 216) from the previous two zones are combined in the feed to this zone. Along with acetonitrile and water, the feed (110, 216) contains residual amounts of other organic impurities, particularly toluene, acrylonitrile and ethanol, originating from distillation zones 1 and 2. In distillation zone 3, separation of water from acetonitrile may be achieved using a so-called pressure swing distillation system of two distillation columns (117, 120, 216, 219) operating at two different pressures (e.g., 0.2 and 5 bar). This system utilizes the difference between the two pressures in the azeotropic composition to generate a pure water waste from this zone and a pure acetonitrile product stream. The impurities mentioned above form a light azeotrope with water and acetonitrile, and a stream enriched in these impurities may be removed from the process at a location different from the aqueous and acetonitrile product streams from the process. If the water content in the product stream is not low enough, a further step of separation can be added which can remove the residual water as an azeotrope, or it can be removed by adsorption onto a stationary phase. The resulting acetonitrile has an assay purity of at least 99.90%, for example by gas chromatography, and a water content of less than 30 ppm.

[0215] The reduction of the water content of the acetonitrile stream fed to the third distillation zone is achieved by the use of pressure swing distillation, the first distillation being carried out below atmospheric pressure, e.g. 0.20 bar. The percentage of water in the acetonitrile / water azeotrope is reduced at low pressure and increased at high pressure. It is preferred to carry them out in separate columns. Thus, it is preferred to carry out the low pressure distillation in a first distillation column (117, 216) and then the higher pressure distillation in a second distillation column (120, 219). The second distillation is carried out at a higher pressure than the first distillation, e.g. above atmospheric pressure, e.g. 5 bar.

[0216] Thus, in one embodiment, the method according to the first aspect of the present disclosure comprises: F1) introducing the acetonitrile-rich stream (110) into a fourth distillation column (117) and distilling it at less than atmospheric pressure to remove water therefrom, wherein acetonitrile is withdrawn as a vapor from said fourth distillation column and condensed to produce a fourth distillate (118) and water is produced as fourth distillation column bottoms (119); F2) introducing the fourth distillate (118) into a fifth distillation column (120) and carrying out a second distillation at a pressure above atmospheric pressure, for example 5 bar, to produce a lower boiling fraction (122) which is withdrawn via the upper part of the fifth distillation column (120) and acetonitrile which is produced as the fifth distillation column bottoms (121).

[0217] The acetonitrile withdrawn from the distillation column in step F2 (121) is greater than 99.90% pure, based on the total content of the acetonitrile stream (121), as measured by GC. Preferably, the acetonitrile withdrawn from the distillation column in step F2 (121) is greater than 99.90% pure, as measured by GC, and contains less than 30 ppm water.

[0218] In one embodiment, the method according to the second aspect of the present disclosure comprises: F1) introducing the acetonitrile bottoms product (213) from the distillation of step D into a fourth distillation column (216) and distilling it at subatmospheric pressure (e.g., 0.2 bar) to remove water therefrom, wherein acetonitrile is withdrawn as a vapor from said fourth distillation column (216) and condensed to produce a fourth distillate (217) and water is produced as fourth distillation column bottoms (218); F2) introducing the fourth distillate (217) into a fifth distillation column (219) and carrying out a second distillation at a pressure above atmospheric pressure, for example 5 bar, to produce a lower boiling fraction (221) which is withdrawn via the upper part of the fifth distillation column (219) and acetonitrile which is produced as the fifth distillation column bottoms (220).

[0219] The acetonitrile withdrawn from the column in step F2 (220) is greater than 99.90% pure, based on the total content of the acetonitrile stream (220), as measured by GC. Preferably, the acetonitrile withdrawn from the distillation column in step F2 (220) is greater than 99.90% pure, as measured by GC, and contains less than 30 ppm water.

[0220] In one embodiment, the acetonitrile bottoms product (213) of step D is first fed into a further mixing zone (215), whereby it is mixed with a recycled acetonitrile stream (221) (step E), the recycled acetonitrile stream (221) being a by-product of a further processing step, e.g., a pressure swing distillation step. In one embodiment, the recycled acetonitrile stream (221) is a by-product of step F2, e.g., it is the lower boiling fraction (221) from distillation step F2.

[0221] In one embodiment, the distillation of step F1 for the process according to the second and third aspects of the present disclosure operates at a pressure in the range of 50 to 980 mbar, preferably 50 to 200 mbar, for example 200 mbar. In terms of the lower limit, the distillation of step F1 may operate at a pressure greater than 50 mbar, for example greater than 100 mbar, greater than 150 mbar, or greater than 175 mbar, or greater than 200 mbar. In terms of the upper limit, the distillation of step F1 may operate at a pressure less than atmospheric pressure, for example less than 980 mbar, less than 900 mbar, or less than 800 mbar, less than 700 mbar, less than 600 mbar, less than 500 mbar, less than 400 mbar, less than 300 bar, or less than 200 mbar.

[0222] Generally, the distillation column (117, 216) contains structured packing or physical trays or plates whose purpose is to provide sufficient surface area to promote intimate contact between the liquid and vapor phases moving in a countercurrent direction inside the column. The height of the packing within the column, along with the hydraulic properties of the gas and liquid, determines the number of separation stages contained within the column. The number of stages required for a particular separation is determined by the complexity of the separation required. In general, it can be said that the closer the boiling points between the compound of interest and other accompanying compounds, the more stages will be required to achieve the desired separation. The column can be operated to increase the purity of the desired compound and increase the separation of impure compounds by changing the operating pressure, feed position, and reflux ratio.

[0223] In one embodiment of the present disclosure, the reflux ratio of the distillation column (117, 216) in step F1 is 0.05 to 1, for example, 0.1.

[0224] Acetonitrile and the lighter fractions (118, 217) in step F1, which contain the azeotropic acetonitrile composition and excess water or approach the azeotropic composition, and impurities such as ethanol, are withdrawn as condensate from the upper portion of the column (117, 216), e.g., overhead. The water withdrawn as the bottoms product (119, 218) is considered waste and is discarded.

[0225] In some embodiments, the light acetonitrile fraction (118, 217) withdrawn through the upper portion of the distillation column (117, 216) in step F1, for example from the top, contains an amount of acetonitrile in the range of 75% to 92% by weight of acetonitrile, based on the total weight of the acetonitrile fraction. In terms of the upper limit, the light acetonitrile fraction (118, 217) may contain less than 92% by weight of acetonitrile, for example, less than 90% by weight, less than 85% by weight, less than 80% by weight. In terms of the lower limit, the light acetonitrile fraction (118, 217) may contain more than 75% by weight of acetonitrile, for example, more than 80% by weight, more than 85% by weight, or more than 90% by weight of acetonitrile.

[0226] In some embodiments, the light acetonitrile fraction (118, 217) of step F1 contains an amount of water in the range of 8% to 28% by weight of water, based on the total weight of the acetonitrile fraction. In terms of the upper limit, the light acetonitrile fraction (118, 217) may contain less than 28% by weight of water, for example, less than 25% by weight, less than 23% by weight, less than 20% by weight, less than 15% by weight, or less than 10% by weight. In terms of the lower limit, the light acetonitrile fraction (118, 217) may contain more than 8% by weight of water, for example, more than 10% by weight, more than 15% by weight, more than 20% by weight, or more than 25% by weight.

[0227] In some embodiments, the light acetonitrile fraction (118, 217) contains an amount of ethanol in the range of 0.2% to 3% by weight of ethanol, based on the total weight of the acetonitrile fraction. On the upper end, the light acetonitrile fraction (118, 217) may contain less than 3% by weight of ethanol, e.g., less than 2% by weight, less than 1.5% by weight, less than 1% by weight, less than 0.8% by weight, less than 0.5% by weight, or less than 0.3% by weight. On the lower end, the light acetonitrile fraction (118, 217) may contain more than 0.2% by weight of ethanol, e.g., more than 0.5% by weight, more than 1% by weight, or more than 2% by weight of ethanol.

[0228] Thereby, it is ensured that the streams (118, 217) arriving at the higher pressure distillation columns (120, 219) have a reduced water content and are as rich as possible in acetonitrile. During the distillation of step F2, which is carried out at a higher pressure than the distillation of step F1, the water content of the azeotrope increases and reaches about 23% by weight at 5 bar. The remaining water can therefore be distilled off in the form of an acetonitrile / water azeotrope (122, 221). This azeotrope (122) is preferably recycled to the acetonitrile feedstock, for example in step C1, in the first distillation zone of the process according to the first embodiment, for example for the distillation of step D1, or more preferably via the feed water zone (109).

[0229] According to a second aspect of the present disclosure, the azeotrope (221) is preferably recycled to the acetonitrile feedstock, e.g., in the second distillation zone of the process for distillation of step D, or more preferably via the feed water zone (209), whereby the lighter streams (203, 207) from the aqueous and organic distillation steps A and B are combined, e.g., in step C.

[0230] Thus, in one embodiment, any impurities present in the acetonitrile stream (118, 217) that form a light azeotrope with water and acetonitrile can be withdrawn from the upper portion of the distillation column (120, 219), e.g., overhead, and recycled together with the remaining acetonitrile and water, e.g., via step C1 to step D1, or, e.g., via step C back to step D, and fed back to the distillation process of the present disclosure.

[0231] In a further embodiment of the first aspect, the impurities (122) from the pressure swing distillation steps, e.g., F1 and F2, are recycled back to step D1 via the feed water section (109) of step C1, where the feed is enriched with water to produce an azeotrope with a lower boiling point compared to acetonitrile, which is introduced into step D1.

[0232] In a separate embodiment of the first aspect, the impurities (122, 221) from the pressure swing distillation steps, e.g., F1 and F2, can be purged and sent to waste.

[0233] In some embodiments, the distillation of step F2 for the process according to the second and third aspects of the present disclosure operates at a pressure above atmospheric pressure or in the range of 3 to 8 bar, preferably at 5 bar. In terms of the lower limit, the distillation of step F2 may operate at a pressure above 3 bar, such as above 4, above 4.5, or above 5 bar. In terms of the upper limit, the distillation of step F2 may operate at a pressure below 8 bar, such as below 7 bar, below 6 bar, or below 5.5 bar.

[0234] Generally, distillation columns (120, 219) contain structured packing or physical trays or plates whose purpose is to provide sufficient surface area to promote intimate contact between the liquid and gas phases moving in a countercurrent direction inside the column. The height of the packing within the column, along with the hydraulic properties of the gas and liquid, determines the number of separation stages contained within the column. The number of stages required for a particular separation is determined by the complexity of the separation required. In general, it can be said that the closer the boiling points between the compound of interest and other accompanying compounds, the more stages will be required to achieve the desired separation. The column can be operated to increase the purity of the desired compound and increase the separation of impure compounds by changing the operating pressure, feed position, and reflux ratio.

[0235] In one embodiment of the present disclosure, the reflux ratio of the distillation column (120, 219) in step F2 is 0.05 to 1, for example, 0.25.

[0236] The acetonitrile withdrawn as bottoms product (121, 220) from the higher pressure distillation column of step F2 is 99.90% ultra pure (measured by area % by GC analysis) based on the total content of the acetonitrile stream (121, 220). Preferably, the acetonitrile bottoms product (121, 220) also has a water content of less than 30 ppm.

[0237] In some embodiments, the acetonitrile bottoms product (121, 220) comprises an amount of acetonitrile ranging from 99.90% to 99.99% (area %) acetonitrile as measured by gas chromatography analysis. On the upper end, the acetonitrile bottoms product (121, 220) may comprise less than 99.99% acetonitrile, e.g., less than 99.98%, less than 99.95%, less than 99.92% acetonitrile. On the lower end, the acetonitrile bottoms product (121, 220) may comprise more than 99.90% acetonitrile, e.g., more than 99.92%, more than 99.95%, or more than 99.98% acetonitrile. Preferably, the acetonitrile bottoms product (121, 220) also has a water content of less than 30 ppm.

[0238] In some embodiments, the acetonitrile bottoms product (121, 220) contains an amount of water in the range of 10 to 30 ppm water based on the total weight of the acetonitrile fraction. On the upper limit, the acetonitrile bottoms product (121, 220) can contain less than 30 ppm water, e.g., less than 28 ppm, less than 25 ppm, less than 23 ppm, less than 20 ppm, less than 18 ppm, less than 15 ppm, or less than 12 ppm water. On the lower limit, the acetonitrile bottoms product (121, 220) can contain more than 10 ppm water, e.g., more than 12 ppm, more than 15 ppm, more than 20 ppm water.

[0239] In some embodiments, the acetonitrile bottoms product (121, 220) may contain relatively small amounts of organic impurities. In some embodiments, the acetonitrile bottoms product (121, 220) may contain residual ethanol as an impurity, for example, in an amount ranging from 1 to 10 ppm ethanol based on the total weight of the acetonitrile fraction. On the upper limit, the feed stream may contain less than 10 ppm ethanol, for example, less than 9 ppm, less than 8 ppm, less than 7 ppm, less than 6 ppm, less than 5 ppm, less than 4 ppm, less than 3 ppm, or less than 2 ppm ethanol. On the lower limit, the feed stream may contain more than 1 ppm ethanol, for example, more than 3 ppm, more than 5 ppm, or more than 8 ppm ethanol.

[0240] In one embodiment, the acetonitrile bottoms product (121, 220) contains an amount of pyridine in the range of 1 to 5 ppm pyridine, based on the total weight of the acetonitrile fraction. On the upper limit, the acetonitrile bottoms product may contain less than 5 ppm pyridine, e.g., less than 4 ppm, less than 3 ppm, or less than 2 ppm pyridine. On the lower limit, the feed stream may contain more than 1 ppm pyridine, e.g., more than 2 ppm, more than 3 ppm, or more than 4 ppm pyridine.

[0241] In some embodiments, the acetonitrile bottoms product (121, 220) may contain toluene as an impurity. In one embodiment, the acetonitrile bottoms product contains an amount of toluene in the range of 1 to 10 ppm toluene based on the total weight of the acetonitrile fraction toluene. On the upper limit, the acetonitrile bottoms product may contain less than 10 ppm toluene, e.g., less than 8 ppm, less than 7 ppm, less than 6 ppm, less than 5 ppm, less than 4 ppm, less than 3 ppm, less than 2 ppm toluene. On the lower limit, the acetonitrile bottoms product may contain more than 1 ppm toluene, e.g., more than 2 ppm, more than 3 ppm, more than 4 ppm, more than 5 ppm, more than 6 ppm, more than 7 ppm, more than 8 ppm, more than 9 ppm toluene.

[0242] In order to be reused in oligonucleotide manufacturing, an acetonitrile purity of at least 99.90% must be achieved. Additionally, a water content of less than 30 ppm is desirable. Otherwise, the impurity levels are too high to be suitable for reuse in industrial or manufacturing oligonucleotide processes.

[0243] Thus, if the water content in the product stream from the pressure swing distillation process is not low enough, a further stage of separation may be added which can remove the residual water as an azeotrope, or it may be removed by adsorption onto a stationary phase, e.g., molecular sieves.

[0244] Thus, in a further embodiment of the present disclosure, the method according to the second or third aspect of the present disclosure further comprises feeding the acetonitrile bottom product (121, 220) of step F2 to a water adsorption zone (124, 225) and contacting the acetonitrile bottom product (121, 220) with a water reducing adsorbent to produce highly purified acetonitrile exiting the adsorption zone. The water reducing adsorbent may be a molecular sieve. Further details and embodiments of the adsorbent are described in

[0033] to

[0038] of WO2015126713A1. In a preferred embodiment, the molecular sieve has a pore size of 3 angstroms. A pore size of 3 angstroms is very efficient for separation because water has a smaller size and acetonitrile has a larger size. The acetonitrile exiting the adsorption zone has a purity of at least 99.90% and a water content of less than 30 ppm, as measured, for example, by gas chromatography.

[0245] Fourth aspect of the present disclosure In a fourth embodiment, there is provided a method for recovering and / or purifying acetonitrile from waste acetonitrile (301, 302) generated during oligonucleotide synthesis, comprising: A') introducing into a first mixing zone (303) and combining therein an organic waste feedstock (301) comprising acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile, and an aqueous waste feedstock (302) comprising acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile, to form an acetonitrile waste feedstock comprising said impurities; or introducing an organic waste feedstock (301) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a first mixing zone (303) and enriching with water to produce a water-enriched acetonitrile stream containing said impurities; B') introducing the acetonitrile waste feedstock or the water-enriched acetonitrile stream into a first distillation column (304) to separate acetonitrile and a first set of impurities having a boiling point lower than acetonitrile from a second set of impurities having a boiling point higher than acetonitrile, wherein acetonitrile and the first set of impurities are withdrawn as vapor from the first distillation column and condensed to produce a first distillate (306) and the second set of impurities is produced as first distillation column bottoms (305); C') optionally introducing the first distillate (306) containing acetonitrile and low boiling impurities into a water feed section (307) and enriching it with water to produce a water-enriched acetonitrile stream (307a); D') introducing the water-enriched acetonitrile stream (306, 307a) into a second distillation column (308) and separating the acetonitrile from low-boiling impurities, wherein acetonitrile is produced as second distillation column bottoms (309); Includes; A method is thereby provided whereby recovered and / or purified acetonitrile is obtained.

[0246] The second distillation column bottoms (309) produced as a result of the second distillation step D' comprises an acetonitrile / water azeotrope.

[0247] Further processing steps may be used to reduce the water content of the acetonitrile product to less than 30 ppm. In one embodiment of the fourth aspect of the present disclosure, the method comprises: E') introducing the second distillation column bottoms product (309) of step D' into a third distillation column (311) to separate acetonitrile from the acetonitrile / water azeotrope, wherein acetonitrile is produced as third distillation column bottoms (312).

[0248] The introduction of the organic and aqueous waste feedstocks of the alternative embodiment of step A' may be carried out independently, e.g., one after the other in any order or in ratios ranging from 0 to 100%, or simultaneously. Since the waste streams are generated in the same proportions from the main synthesis / purification section of the process, the steps may be initiated simultaneously, but this is not required.

[0249] The method of the fourth aspect of the present disclosure incorporates pressure swing distillation technology across all three columns to recover acetonitrile with a water content of less than 30 ppm. The system includes three distillation columns (304, 308, 311) operating at low pressure, e.g., 20-500 mbar, e.g., 200 mbar, medium pressure, e.g., 200 mbar to 2 bar, e.g., 960 mbar, and high pressure, e.g., 2 bar to 5 bar, e.g., 5 bar.

[0250] The distillation step B' is carried out in the so-called first distillation zone (Figure 3, zone 1). In one embodiment, the acetonitrile waste containing aqueous and organic impurities (303) entering this zone is separated into a stream (306) enriched in acetonitrile and containing water and ethanol as well as light-boiling organic impurities. The acetonitrile-water azeotrope is the overhead distillation and excess water is removed from the base of the column (305) together with the higher boiling components that do not form binary or ternary azeotropes. The heavy components include acetic acid, acetic anhydride, N-dimethylformamide, 1-methylimidazole, dichloroacetic acid, 2,6-lutidine, 5-ethylthio-1H-tetrazole and pyridine. Two components that have individual higher boiling points compared to acetonitrile but are not separated in this step are toluene and diisopropylamine, since they form low-boiling binary and ternary azeotropes with acetonitrile and water. This section is operated to maximize the yield of acetonitrile in the form of an azeotrope while removing as much excess water as possible from the process.

[0251] In step B', an acetonitrile fraction is withdrawn from the upper portion of the distillation column (304), for example, overhead. The acetonitrile fraction exits as a vapor and is passed through a condenser to produce a condensate (306). A portion of the condensate is then returned to the column as a reflux stream, and the remainder is withdrawn as product. The acetonitrile fraction (306) contains acetonitrile and light-boiling impurities, for example, acetonitrile / water azeotropes and binary and ternary azeotropes containing toluene and diisopropylamine. The acetonitrile fraction may further contain ethanol. For example, heavy impurities having a boiling point higher than acetonitrile are withdrawn as distillation column bottoms (305). The heavy-boiling impurities (305) include water, non-volatile salts, and organic residues. The bottoms product (305) is considered waste and is discarded.

[0252] For all columns used in the process of the present disclosure, a heat source may be provided at the base of the column to vaporize the acetonitrile and light boiler fraction still present at the base of the column and provide a vapor stream for heat exchange further up the column. In one embodiment, the heat source is a reboiler.

[0253] Process step C' is carried out in the so-called second distillation zone (Figure 3, zone 2).

[0254] Step C' comprises introducing the distillate (306) from step B' into a water feed section (307) and enriching said distillate (307) with water to produce a water-enriched acetonitrile stream. To separate azeotrope-forming agents with acetonitrile, such as toluene or diisopropylamine, an entrainer (e.g., water) can be added to the feed, which forms azeotropes with these compounds at lower boiling points compared to acetonitrile, making them easier to separate from acetonitrile. To the inventors' surprise, water unexpectedly reduces acetonitrile losses from the process, since the azeotrope is mainly impurities, rich in water, and has a lower acetonitrile content. The amount of water added compared to acetonitrile can be more than 0.24 w / w, but can range from 0.05 to 0.40 w / w or more, based on the amount of acetonitrile and impurities present in the stream. Since the light acetonitrile fraction (306) from step B' is the result of mixing of the aqueous and organic waste streams in step A', the amount of water required for this step is less compared to step C1 of the process of the first embodiment. The amount of water added is relative to the amount of acetonitrile and impurities that ensures stable column operation.

[0255] The lower boiling azeotrope of the water-enriched acetonitrile stream of step C' comprises at least one of acetonitrile, water, ethyl acetate, toluene, ethanol, diethylamine, diisopropylamine, and acrylonitrile, or mixtures thereof. For example, the lower boiling azeotrope of step C' comprises at least one of ethyl acetate / water, ethyl acetate / acetonitrile, ethyl acetate / water / acetonitrile, acetonitrile / water, acrylonitrile / water, acetonitrile / toluene, acetonitrile / diethylamine, acetonitrile / diisopropylamine, toluene / water, ethanol / water, toluene / water / acrylonitrile, toluene / water / acetonitrile, diisopropylamine / water / acetonitrile, diethylamine / toluene / water, or mixtures thereof.

[0256] Depending on the amount of water present in the first mixing zone (303) from the aqueous waste stream (302), the water present in the mixing zone (303) may be sufficient to act as an entrainer, thus eliminating the need for a further step C', whereby the acetonitrile distillate (306) is enriched with water (307) to produce a water-enriched acetonitrile stream, making step C' optional. Thus, in an alternative embodiment, the lower boiling azeotrope present in step C' is present in the acetonitrile stream (306) from step B', in which case the mixing zone (303) functions as a feed water zone.

[0257] The amount of water present in the mixing zone (303) by combining the aqueous and organic waste streams (301, 302) can be easily determined by one skilled in the art. For example, the amount of water present can be determined by computer simulation based on design specifications. The simulation can be performed by a well-known commercially available simulation package, Aspen Plus (Aspen Technology, Inc., Massachusetts, USA), to simulate the composition of the feed to the column including water content. In one embodiment, step A' further comprises determining the amount of water present in the acetonitrile waste feedstock by using a process simulation software package, such as, for example, Aspen software, to determine if additional water needs to be added to the water supply zone (307).

[0258] In an alternative embodiment, the organic waste feedstock (301) containing acetonitrile and said organic impurities is fed into the water supply section (303) and enriched directly with water to produce a water-enriched acetonitrile stream containing said impurities without the need for an additional aqueous waste stream feed.

[0259] The acetonitrile stream (306) is then fed directly into a second distillation column (308) where process steps D' and E' take place.

[0260] The water-enriched acetonitrile feed is distilled and separated into an acetonitrile bottoms product (309) and an overhead fraction (310) containing a lower boiling azeotrope, the latter having a higher acetonitrile concentration than the water-enriched acetonitrile stream from step C'. The lower boiling azeotrope (310) is withdrawn from the upper portion of the distillation column (308), e.g., overhead. Such lower boiling azeotrope fraction may be directed to waste, thereby ensuring that the resulting purified acetonitrile product or stream reaching the column where the distillation of step E' takes place has a reduced water content and is as rich in acetonitrile as possible.

[0261] Distillation step E' comprises introducing the acetonitrile bottom product from step D' into a third distillation column (311) and distilling said acetonitrile bottom product (309) to remove remaining water or organic impurities, such as ethanol, therefrom to produce an overhead fraction (313) comprising a lower boiling azeotrope relative to acetonitrile, and an acetonitrile bottom product (312). Thus, remaining water can be distilled off in the form of an acetonitrile / water azeotrope. Such lower boiling azeotrope fraction (313) can be recycled back to step A' (316) and fed into the first mixing zone (303). In one embodiment, at least a portion of said lower boiling azeotrope fraction (313) is first purged (314), i.e., removed from the system, before being recycled to step A' (316). In another embodiment, the lower boiling azeotropic fraction (313) is purged (314) and sent to waste (315).

[0262] The acetonitrile (312) produced in step E' can be produced with a purity of at least 99.90% containing less than 30 ppm water. A yield of about 85% has been calculated.

[0263] Advantageously, the above process steps A'-D' provide an improved acetonitrile recovery and / or purification process. Such a process can successfully remove high boiling hydrophobic organic and inorganic aqueous impurities from acetonitrile waste streams, such as those produced during oligonucleotide synthesis. The acetonitrile produced according to steps A'-D' is 99.90% (area%) pure by gas chromatography analysis. Such recovered acetonitrile can be conveniently directly reused in oligonucleotide production.

[0264] The amount of acetonitrile that can be regenerated in the process using steps A'-E' corresponds to 70-90% of the total acetonitrile consumed in the oligonucleotide synthesis process.

[0265] If the water content in the acetonitrile product stream (312) from step E' is not low enough, a further step of separation can be added which can remove the residual water as an azeotrope, or it can be removed by adsorption onto a stationary phase, for example molecular sieves. The details of this further drying step are the same as those described herein for the first, second and third aspects of the present disclosure.

[0266] The disclosed method can also be used to purify acetonitrile waste streams, for example, from oligonucleotide synthesis, to produce purified acetonitrile suitable for reuse in various industrial or manufacturing processes, particularly oligonucleotide manufacturing. In some embodiments, the purified acetonitrile obtained according to the methods disclosed herein is suitable for reuse as an inter-step wash solution in oligonucleotide synthesis performed with inter-step acetonitrile washes. In some embodiments, the purified acetonitrile is suitable as a reaction solvent during oligonucleotide synthesis steps. In one embodiment, the purified acetonitrile is at least 99.90% pure, for example, as measured by gas chromatography. In a preferred embodiment, the purified acetonitrile is at least 99.90% pure and contains less than 30 ppm water, for example, as measured by gas chromatography.

[0267] In one embodiment, the waste acetonitrile according to any one of the first, second, third and fourth aspects of the present disclosure is on an industrial scale. In one embodiment, the amount of waste acetonitrile is at least 10 kg, preferably at least 100 kg, at least 1000 kg or at least 10,000 kg. In further embodiments, the acetonitrile is recovered on a gram or kilogram scale or more.

[0268] In a further embodiment, the method according to any one of the first, second, third and fourth aspects of the present disclosure is carried out batchwise. In another embodiment, the method according to any one of the first, second, third and fourth aspects of the present disclosure is carried out continuously.

[0269] In a further embodiment, there is provided a method for synthesizing an oligonucleotide, comprising the steps of: A *) introducing an organic waste feedstock (105, 205) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a distillation column (106, 206) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the distillation column and condensed to produce a distillate (107, 207) and the second set of organic impurities is produced as a second distillation column bottoms (108, 208); B * ) introducing the distillate (107, 207) into a water feed section (109, 209) to produce a water-enriched acetonitrile stream (111, 210, 210a); C * ) introducing the water-enriched acetonitrile stream (111, 210, 210a) into a second distillation column (112, 212) and separating the first set of organic impurities from the acetonitrile, wherein acetonitrile is produced as second distillation column bottoms (113, 213); thereby obtaining recovered and / or purified acetonitrile; D * ) optionally, further treating the second distillation column bottoms (113, 213) to reduce the water content of the acetonitrile to less than 30 parts per million; E * ) using at least a portion of the recovered and / or purified acetonitrile in a process for synthesizing oligonucleotides and / or for washing oligonucleotides or support-bound oligonucleotides with a portion of the recovered and / or purified acetonitrile. Provided herein is a method comprising recovering and / or purifying acetonitrile by

[0270] The recovered acetonitrile can be immediately reused in oligonucleotide production or stored until ready for use.

[0271] In a further embodiment, there is provided a method for synthesizing an oligonucleotide, comprising the steps of: A1) introducing an aqueous waste feedstock (101) containing acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile into a first distillation column (102) and separating the acetonitrile and the first set of impurities from the second set of impurities, wherein the acetonitrile and the first set of impurities are withdrawn as vapor from the first distillation column and condensed to produce a first distillate (103) and the second set of impurities is produced as first distillation column bottoms (104); B1) introducing an organic waste feedstock (105) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a second distillation column (106) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the second distillation column and condensed to produce a second distillate (107), and the second set of organic impurities are produced as second distillation column bottoms (108); C1) introducing the second distillate (107) into a water supply section (109) and enriching it with water to produce a water-enriched acetonitrile stream (111); D1) introducing the water-enriched acetonitrile stream (111) into a third distillation column (112) and separating the first set of organic impurities from the acetonitrile, the acetonitrile being produced as third distillation column bottoms (113); E1) feeding the first distillate (103) of step A1 and the third distillation column bottoms (113) of step D1 to a mixing zone (116) where they are combined to produce an acetonitrile-enriched stream (110); thereby obtaining recovered and / or purified acetonitrile; F1a) optionally further treating the acetonitrile-rich stream (110) to reduce the water content of the acetonitrile to less than 30 parts per million; G1) using at least a portion of the recovered and / or purified acetonitrile in a process for synthesizing oligonucleotides and / or for washing oligonucleotides or support-bound oligonucleotides with a portion of the recovered and / or purified acetonitrile; Provided herein is a method comprising recovering and / or purifying acetonitrile by

[0272] The recovered acetonitrile can be immediately reused in oligonucleotide production or stored until ready for use.

[0273] In a further embodiment, there is provided a method for synthesizing an oligonucleotide, comprising the steps of: A) introducing an aqueous waste feedstock (201) containing acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile into a first distillation column (202) and separating the acetonitrile and the first set of impurities from the second set of impurities, wherein the acetonitrile and the first set of impurities are withdrawn as a vapor from the first distillation column and condensed to produce a first distillate (203) and the second set of impurities is produced as first distillation column bottoms (204); B) introducing an organic waste feedstock (205) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a second distillation column (206) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the second distillation column and condensed to produce a second distillate (207), and the second set of organic impurities are produced as second distillation column bottoms (208); C) feeding the first distillate (203) of step A and the second distillate (207) of step B to a water supply area (209); C1) combining therein to produce a water-enriched acetonitrile stream (210a); or C2) combining therein and enriching with water to produce a water-enriched acetonitrile stream (210); D) introducing the water-enriched acetonitrile stream (210, 201a) into a third distillation column (212) and separating the first set of impurities from the acetonitrile, wherein acetonitrile is produced as third distillation column bottoms (213); thereby obtaining recovered and / or purified acetonitrile; E) optionally, further treating the third distillation column bottoms (213) to reduce the water content of the acetonitrile to less than 30 parts per million; F) using at least a portion of the recovered and / or purified acetonitrile in a process for synthesizing oligonucleotides and / or for washing oligonucleotides or support-bound oligonucleotides; and recovering and / or purifying acetonitrile by

[0274] The recovered and / or purified acetonitrile can be immediately reused in oligonucleotide production or stored until ready for use.

[0275] Further processing of the acetonitrile-rich stream (110) or the third distillation column bottoms (213) to reduce the water content of the acetonitrile to less than 30 parts per million may further include introducing the acetonitrile-rich stream (110) or the third distillation column bottoms (213) into a fourth distillation column (117, 216), where the water content of the acetonitrile-rich stream is reduced by the use of pressure swing distillation, as described above, to recover acetonitrile having a water content of less than 30 parts per million.

[0276] In one embodiment, the pressure swing distillation is carried out as described above. F1) introducing the acetonitrile-rich stream (110) or the third distillation column bottoms (213) into a fourth distillation column (117, 216) and distilling it at less than atmospheric pressure to remove water therefrom, wherein acetonitrile is withdrawn as a vapor from said fourth distillation column and condensed to produce a fourth distillate (118, 217) and water is produced as the fourth distillation column bottoms (119, 218); F2) introducing the fourth distillate (118, 217) into a fifth distillation column (120, 219) and carrying out a second distillation at a pressure above atmospheric pressure, for example 5 bar, to produce a lower boiling fraction (122, 221) which is withdrawn via the upper part of the fifth distillation column (120, 219) and acetonitrile which is produced as the fifth distillation column bottoms (121, 220); Includes.

[0277] In yet another embodiment, there is provided a method for synthesizing an oligonucleotide, comprising the steps of: A') introducing into a first mixing zone (303) and combining therein an organic waste feedstock (301) comprising acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile, and an aqueous waste feedstock (302) comprising acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile, to form an acetonitrile waste feedstock comprising said impurities; or introducing an organic waste feedstock (301) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a first mixing zone (303) and enriching with water to produce a water-enriched acetonitrile stream containing said impurities; B') introducing the acetonitrile waste feedstock or the water-enriched acetonitrile stream into a first distillation column (304) to separate acetonitrile and a first set of impurities having a boiling point lower than acetonitrile from a second set of impurities having a boiling point higher than acetonitrile, wherein acetonitrile and the first set of impurities are withdrawn as vapor from the first distillation column and condensed to produce a first distillate (306) and the second set of impurities is produced as first distillation column bottoms (305); C') optionally introducing the first distillate (306) containing acetonitrile and low boiling impurities into a water feed section (307) and enriching it with water to produce a water-enriched acetonitrile stream (307a); D') introducing the water-enriched acetonitrile stream (306, 307a) into a second distillation column (308) and separating the acetonitrile from low-boiling impurities, wherein acetonitrile is produced as second distillation column bottoms (309); thereby obtaining recovered and / or purified acetonitrile; E') optionally introducing the second distillation column bottoms product (309) of step D' into a third distillation column (311) to separate acetonitrile from the acetonitrile / water azeotrope, wherein acetonitrile is produced as third distillation column bottoms (312); F') using at least a portion of the recovered and / or purified acetonitrile in a process for synthesizing oligonucleotides and / or for washing oligonucleotides or support-bound oligonucleotides. and recovering and / or purifying acetonitrile by

[0278] Advantageously, by recovering and / or purifying acetonitrile from waste acetonitrile generated during an oligonucleotide synthesis process by using a method according to the first, second, third or fourth aspect of the present disclosure (including embodiments thereof disclosed herein), an oligonucleotide product, e.g., a therapeutic oligonucleotide, may be successfully synthesized without adversely affecting the quality, yield and / or purity of said product.

[0279] All the above embodiments relating to the method for recovering and / or purifying acetonitrile from waste acetonitrile according to the first, second, third or fourth aspect of the present disclosure are equally applicable to and may be combined with the disclosed method for synthesizing oligonucleotides.

[0280] Additionally, all of the above and following embodiments relating to the method for recovering and / or purifying acetonitrile from waste acetonitrile of the present disclosure are equally applicable to: Acetonitrile of the present disclosure; Use of the present disclosure; and The system of the present disclosure.

[0281] As used herein, references to first, second and third distillation zones in the present disclosure are for illustrative purposes only and are not intended to impose any technical limitations on the operation or location of the distillation zones within the methods or systems disclosed herein.

[0282] Acetonitrile of the present disclosure In a further aspect, provided herein is an acetonitrile (or acetonitrile composition) for use in oligonucleotide manufacturing, having a purity of at least 99.90%, e.g., as measured by gas chromatography, and the acetonitrile is recovered from oligonucleotide synthesis waste, e.g., according to any one of the methods disclosed herein.Preferably, the acetonitrile has a purity of at least 99.90% and less than 30 parts per million water, e.g., as measured by gas chromatography.Ideally, oligonucleotide, e.g., DNA or RNA, synthesis grade acetonitrile should have a purity of at least 95% (area %) by GC, e.g., at least 99.90% (area %) acetonitrile, and contain about 50 ppm or less water.Oligonucleotide synthesis grade acetonitrile is typically used as a detergent, reaction solvent, and diluent in oligonucleotide synthesis processes.Oligonucleotide synthesis grade acetonitrile is also used in the manufacture of therapeutic oligonucleotides.The acetonitrile of the present disclosure is preferably obtained from the method of the present disclosure, e.g., according to any one of the first, second, third, and fourth aspects and embodiments thereof. For example, the acetonitrile of the present disclosure, obtained from the method of the present disclosure, for example, according to any one of the first, second, third and fourth aspects and its embodiments, has a purity of at least 99.90%, for example, as measured by gas chromatography.Preferably, the acetonitrile has a purity of at least 99.90% and less than 30 ppm water, for example, as measured by gas chromatography, and is therefore suitable for use / reuse in oligonucleotide production.

[0283] The recovered acetonitrile may contain trace amounts of organic impurities, such as pyridine, ethanol, toluene, acrylonitrile, or mixtures thereof. In one embodiment, the acetonitrile contains 1 to 10 ppm of ethanol, for example, as measured by gas chromatography. In one embodiment, the acetonitrile contains 1 to 5 ppm of pyridine, for example, as measured by gas chromatography. In one embodiment, the acetonitrile contains 1 to 10 ppm of toluene, for example, as measured by gas chromatography.

[0284] Uses of the Disclosure In a further aspect, there is provided a use of acetonitrile for oligonucleotide synthesis, wherein the acetonitrile has a purity of at least 99.90%, for example, as measured by gas chromatography, and the acetonitrile is recovered from oligonucleotide synthesis waste.Preferably, the acetonitrile has a purity of at least 99.90%, for example, as measured by gas chromatography, and less than 30 ppm water.Since oligonucleotide, for example, DNA or RNA synthesis grade acetonitrile must have a purity of at least 95% (area %), for example, at least 99.90%, as measured by GC, and contain about 50 ppm or less water, such recovered acetonitrile according to the method disclosed herein can advantageously be used or reused in oligonucleotide production, and subsequently recovered.The recovered acetonitrile of the present disclosure is preferably obtained from the method of the present disclosure, for example, according to any one of the first, second, third and fourth aspects and their embodiments. For example, the acetonitrile of the present disclosure, obtained from the method of the present disclosure according to any one of the first, second, third and fourth aspects and its embodiments, has a purity (area%) of at least 99.90% as measured by GC.Preferably, the acetonitrile obtained from the method of the present disclosure has a purity (area%) of at least 99.90% as measured by gas chromatography, and less than 30 ppm water, thereby being suitable for use / reuse in oligonucleotide production.

[0285] The recovered acetonitrile used in the present disclosure may contain trace amounts of organic impurities, such as pyridine, ethanol, toluene, acrylonitrile, or mixtures thereof. In one embodiment, the acetonitrile contains 1 to 10 ppm of ethanol, for example, as measured by gas chromatography. In one embodiment, the acetonitrile contains 1 to 5 ppm of pyridine, for example, as measured by gas chromatography. In one embodiment, the acetonitrile contains 1 to 10 ppm of toluene, for example, as measured by gas chromatography. The recovered acetonitrile may contain 1 to 10 ppm of ethanol, 1 to 5 ppm of pyridine, and 1 to 10 ppm of toluene, for example, as measured by gas chromatography.

[0286] Thus, the present disclosure provides a method of using the recovered acetonitrile produced according to the method disclosed herein in the manufacture of oligonucleotides. In one embodiment, the oligonucleotides produced using the recovered and / or purified acetonitrile are RNA. In one embodiment, the oligonucleotides are DNA. In one embodiment, the oligonucleotides include both RNA and DNA.

[0287] In a further embodiment of the present disclosure, the oligonucleotides produced using the recovered and / or purified acetonitrile are modified oligonucleotides. In one embodiment, the modification is at the 2' position of the sugar moiety and is selected from the group consisting of 2'-F, 2'-OMe, 2'-MOE, and 2'-amino, or the oligonucleotide comprises a PMO, LNA, PNA, BNA, or SPIEGELMER. In one embodiment, the modification is at the nucleobase and is selected from the group consisting of 5-methylpyrimidine, 7-deazaguanosine, and abasic nucleotides. In one embodiment, the modification is at the backbone and is selected from the group consisting of phosphorothioate, phosphoroamidate, and phosphorodiamidate.

[0288] In one embodiment, the oligonucleotides produced using recovered and / or purified acetonitrile are antisense oligonucleotides. In one embodiment, the oligonucleotides are siRNA. In one embodiment, the oligonucleotides are aptamers. In one embodiment, the oligonucleotides are miRNAs. In one embodiment, the oligonucleotides are gapmers.

[0289] In one embodiment, the oligonucleotides produced using the recovered and / or purified acetonitrile are 10-200 nucleotides in length. In a further embodiment of the present disclosure, the oligonucleotides are 15-30 nucleotides in length. In one embodiment of the present disclosure, the products are 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 nucleotides in length. In one embodiment of the present disclosure, the oligonucleotides are 20 nucleotides in length, a "20-mer." In one embodiment of the present disclosure, the oligonucleotides are 21 nucleotides in length, a "21-mer." In one embodiment of the present disclosure, the oligonucleotides are 22 nucleotides in length, a "22-mer." In one embodiment of the present disclosure, the oligonucleotides are 23 nucleotides in length, a "23-mer." In one embodiment of the present disclosure, the oligonucleotides are 24 nucleotides in length, a "24-mer." In one embodiment of the present disclosure, the oligonucleotides are 25 nucleotides in length, a "25-mer." In one embodiment of the present disclosure, the oligonucleotides are 26 nucleotides in length, a "26-mer." In one embodiment of the present disclosure, the oligonucleotides are 27 nucleotides in length, a "27-mer." In one embodiment of the disclosure, the oligonucleotide is 28 nucleotides long, a "28-mer." In one embodiment of the disclosure, the oligonucleotide is 29 nucleotides long, a "29-mer." In one embodiment of the disclosure, the oligonucleotide is 30 nucleotides long, a "30-mer."

[0290] In one embodiment of the present disclosure, the oligonucleotide produced using the recovered and / or purified acetonitrile is a therapeutic oligonucleotide. In one embodiment of the present disclosure, the oligonucleotide is a single-stranded therapeutic oligonucleotide. In one embodiment of the present disclosure, the oligonucleotide is a double-stranded therapeutic oligonucleotide.

[0291] In one embodiment, the oligonucleotide produced using the recovered and / or purified acetonitrile is inclisilane. In another embodiment, the oligonucleotide produced using the recovered and / or purified acetonitrile is peracarsen.

[0292] The oligonucleotides of the oligonucleotide synthesis waste stream from which acetonitrile is recovered and / or purified according to the methods disclosed herein can be the same or different oligonucleotides as those produced according to the present disclosure. Thus, the oligonucleotides of the oligonucleotide synthesis waste stream can be any of the oligonucleotides described above.

[0293] As described herein, the amount of acetonitrile recovered according to the method disclosed herein is particularly suitable for large-scale and industrial production of oligonucleotides, particularly the oligonucleotides disclosed herein.In the context of this disclosure, large-scale production of oligonucleotides refers to production at a scale of 1 liter or more.Alternatively or additionally, in the context of this disclosure, large-scale production of oligonucleotides refers to production at a gram scale of product, particularly production of 10 grams or more of product.In one embodiment of this disclosure, the amount of oligonucleotide product produced is gram scale.In one embodiment of this disclosure, the amount of product produced is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100 grams or more. In one embodiment of the present disclosure, the amount of oligonucleotide product produced is 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 grams or more. In one embodiment of the present disclosure, the amount of oligonucleotide product produced is 500 grams or more. In one embodiment of the present disclosure, the amount of oligonucleotide product produced using recovered acetonitrile is in kilogram scale. In one embodiment of the present disclosure, the amount of oligonucleotide product produced using recovered acetonitrile is 1 kg or more. In one embodiment of the present disclosure, the amount of oligonucleotide product produced using recovered acetonitrile is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 kg or more.

[0294] In certain embodiments, the recovered acetonitrile is used in the industrial scale manufacture of oligonucleotides.

[0295] System of the present disclosure In a further embodiment, a system for purifying and / or recovering acetonitrile from waste acetonitrile (105, 205, 301) generated during an oligonucleotide manufacturing process is provided, comprising: a first distillation column (106, 206, 304) configured to receive the acetonitrile organic waste stream (105, 205, 301) and produce a first distillate (107, 207, 306) comprising acetonitrile and a first set of organic impurities, the first distillation column (106, 206, 304) having a condenser coupled to an upper portion of the first distillation column; and a second distillation column (112, 212, 308) configured to receive the first distillate (107, 207, 306), separate the first set of organic impurities from the acetonitrile, and produce purified acetonitrile as a second distillation column bottoms; The system, the first distillate (107, 207, 306) is first enriched with water before reaching the second distillation column (112, 212, 308) so as to obtain purified and / or recovered acetonitrile; or The system is provided further comprising a water supply area (109, 209, 303, 307) arranged such that the organic waste acetonitrile (301) is enriched with water before reaching the first distillation column (304), thereby obtaining purified and / or recovered acetonitrile.

[0296] By incorporating a water feed zone into the disclosed system and method, separation of azeotrope formers with acetonitrile, such as toluene, acrylonitrile, ethanol, ethyl acetate, and low boiling amines that are difficult to successfully separate from acetonitrile to produce acceptable purity profiles, can be achieved. Thus, by using water as an entrainer, successful partitioning and classification of organic waste from the acetonitrile process stream can be achieved. The first set of organic impurities includes azeotrope formers and impurities with boiling points lower than acetonitrile, as described herein.

[0297] The water supply zone (109, 209, 303, 307) is configured to receive water, either by direct addition of water or from another source, such as an acetonitrile process stream that contains water.

[0298] The light acetonitrile stream (107, 207, 306) can be fed to a feed water section (109, 209, 307), whereby the acetonitrile stream containing light impurities (107, 207, 306) is enriched with water to produce a water-enriched acetonitrile stream (111, 210, 210a, 307a). Water can be added directly to the first distillate (107, 207, 306) or can be added to the first distillate (107, 207, 306) as a component of a further acetonitrile process stream, e.g. present in the acetonitrile distillate from the aqueous purification step. Alternatively, water can be added as described above to the incoming acetonitrile organic waste process stream (301), e.g. present in the acetonitrile aqueous waste stream (302), prior to entering the first distillation column (304).

[0299] Thus, the addition of water via the acetonitrile process stream eliminates the need for further enrichment with water.

[0300] The water-enriched acetonitrile stream (111, 201, 210a, 307a) is then fed to a second distillation column (112, 212, 308). The acetonitrile bottoms product (113, 213, 309) produced from the second distillation column can then be collected or further processed. For example, the acetonitrile bottoms product produced from distillation column (112) can be combined with the light acetonitrile stream (103) from the aqueous purification step as described herein, or can be subjected to further purification steps, as needed, to reduce the water content to less than 30 ppm.

[0301] In a further aspect, there is provided a system (100) for purifying and / or recovering acetonitrile from waste acetonitrile (101, 105) generated during an oligonucleotide manufacturing process according to the first aspect of the present disclosure, comprising: a first distillation column (102) configured to receive an aqueous acetonitrile waste stream (101) and produce a first distillate (103) comprising acetonitrile and a first set of impurities, the first distillation column (102) having a condenser connected to an upper portion of the first distillation column (102), e.g., connected to an overhead stream; a second distillation column (106) configured to receive the acetonitrile organic waste stream (105) and produce a second distillate (107) comprising acetonitrile and the first set of impurities, the second distillation column (106) having a condenser connected to an upper portion of the second distillation column (106), e.g., connected to an overhead stream; and a third distillation column (112) configured to receive the second distillate (107) and separate the first set of organic impurities from the acetonitrile and produce purified acetonitrile as a third distillation column bottoms; A system (100) is provided, the system further comprising: a water feed section (109) arranged such that the second distillate (107) is first enriched with water before reaching the third distillation column (112) so as to obtain purified and / or recovered acetonitrile; and a mixing section (116) configured to mix the first distillate (103) from the first distillation column (102) and the third distillation column bottoms (113) from the third distillation column (112), e.g., before entering the fourth distillation column (117).

[0302] The feedwater section (109) may be located at any point such that the second distillate (107) is first enriched with water before reaching the third distillation column (112). For example, the feedwater section (109) is located between the second and third distillation columns (106, 112).

[0303] In one embodiment, a system (100) as depicted in FIG. 1 is provided.

[0304] FIG. 1 shows an acetonitrile purification / recycle system in one embodiment of the present disclosure. According to the present disclosure, the acetonitrile organic waste stream is directed to the lower part of the first distillation column. As an example, the feedstock is low-grade acetonitrile from oligonucleotide synthesis waste. Low-grade acetonitrile can be provided from other sources, such as, but not limited to, HPLC waste and pharmaceutical manufacturing waste. As mentioned above, oligonucleotide synthesis waste typically contains many components that can vary from process to process. It is understood that the acetonitrile feedstock can contain more or fewer components.

[0305] The first distillation zone may be referred to as the organic purification zone and includes at least two distillation columns (106, 112). The organic waste stream fed to this zone contains a combination of acetonitrile, 2,6-lutidine, acetic anhydride, dichloroacetic acid, pyridine, toluene, 1-methylimidazole, 5-ethylthio-1H-tetrazole and lesser amounts of diethylamine, diisopropylamine, acetic acid, 5-ethylthio-1H-tetrazole, N,N-dimethylformamide, organic iodine and sulfur compounds, as well as residual oligonucleotide building blocks and trace amounts of water. The heavy organics produced as bottoms products in the first distillation column are considered waste. The concentration of the compounds in the solution may be present in concentrations ranging from negligible to up to 30% by weight. Many of these compounds are difficult to separate from acetonitrile because they have very similar volatility to acetonitrile within certain concentration ranges or because they form azeotropes with acetonitrile. Several purification steps in this first distillation zone may be used to separate acetonitrile from other organic impurities present. A first stage may be used to initially separate the heavy fraction of compounds from acetonitrile, light boilers and azeotrope formers. This stage may be designed to take advantage of minimal differences in the relative volatility of the compounds being separated to increase the purity of the acetonitrile stream.

[0306] Generally, the distillation columns (106), (112) contain structured packing or physical trays or plates whose purpose is to provide sufficient surface area to promote intimate contact between the liquid and vapor phases moving in a countercurrent direction inside the column. The height of the packing within the column, along with the hydraulic properties of the gas and liquid, determines the number of separation stages contained within the column. The number of stages required for a particular separation is determined by the complexity of the separation required. In general, it can be said that the closer the boiling points between the compound of interest and other accompanying compounds, the more stages will be required to achieve the desired separation. The column can be operated to increase the purity of the desired compound and increase the separation of impure compounds by changing the operating pressure, feed position, and reflux ratio.

[0307] Columns (106, 112) are used as distillation towers to effect separation as shown with reference to FIG. 1 and described below. Based on the boiling points of known binary azeotropes and the nominal pure components, substantially all of the acetonitrile, acetonitrile / water azeotrope, toluene, toluene / water azeotrope, and toluene / acetonitrile azeotrope are rectified to produce column outlet vapor. Upon exiting column (106), the vapor is condensed in a condenser to produce distillate (107).

[0308] The light fraction (107) from this stage, containing most of the acetonitrile, may then be fractionated in further stages, for example in a second distillation column (112) to produce a substantially pure acetonitrile product stream (113) and a more volatile light waste stream (114). Typically, the distillation column (112) includes structured packing or physical trays or plates, the purpose of which is to provide sufficient surface area to promote intimate contact between the liquid and gas phases moving in a countercurrent direction inside the column. The height of the packing within the column, along with the hydraulic properties of the gas and liquid, determines the number of separation stages contained within the column. The number of stages required for a particular separation is determined by the complexity of the separation required. In general, it may be said that the closer the boiling points between the compound of interest and other accompanying compounds, the more stages are required to effect the desired separation. The column may be operated to increase the purity of the desired compound and increase the separation of impure compounds by varying the operating pressure, feed position, and reflux ratio.

[0309] To separate azeotrope-forming agents with acetonitrile, such as toluene, acrylonitrile or ethanol, an entrainer such as water can be added to the feedstock (107), which forms azeotropes with these compounds with lower boiling points compared to acetonitrile, making them easier to separate from acetonitrile. Thus, the light acetonitrile stream (107) is then fed to a water feed zone (109), which then feeds a water-enriched acetonitrile stream (111) to a further distillation column (112). The acetonitrile bottom product (113) produced from the distillation column (112) can then be fed into a third distillation zone. The acetonitrile bottom product produced from the distillation column (112) is mixed with the light-boiling stream (103) from the second distillation zone.

[0310] The second distillation section may be referred to as the inorganic aqueous purification section. Acetonitrile waste entering this section is separated into a lighter stream (103) enriched in acetonitrile and containing some water and ethanol. The heavier portion (102) contains non-volatile salts and organic residues from the main process purification as aqueous solutions. This section is operated to maximize the yield of acetonitrile in the form of an azeotrope while removing as much excess water as possible from the process.

[0311] Generally, the column (102) includes structured packing or physical trays or plates, the purpose of which is to provide sufficient surface area to promote intimate contact between the liquid and gas phases moving in a countercurrent direction inside the column. The height of the packing within the column, along with the hydraulic properties of the gas and liquid, determines the number of separation stages contained within the column. The number of stages required for a particular separation is determined by the complexity of the separation required. In general, it may be said that the closer the boiling points between the compound of interest and other accompanying compounds, the more stages will be required to achieve the desired separation. The column can be operated to increase the purity of the desired compound and increase the separation of impure compounds by varying the operating pressure, feed position, and reflux ratio.

[0312] In a further aspect, there is provided a system (200) for purifying and / or recovering acetonitrile from waste acetonitrile (201, 205) generated during an oligonucleotide manufacturing process according to the second aspect of the present disclosure, comprising: a first distillation column (202) configured to receive the aqueous acetonitrile waste stream (201) and produce a first distillate (203) comprising acetonitrile and a first set of impurities, the first distillation column (202) having a condenser coupled to an upper portion of the first distillation column (202), e.g., coupled to an overhead stream; a second distillation column (206) configured to receive the acetonitrile organic waste stream (205) and produce a second distillate (207) comprising acetonitrile and the first set of impurities, the second distillation column (206) having a condenser connected to an upper portion of the second distillation column (206), e.g., connected to an overhead stream; and a third distillation column (212) configured to receive the first and second distillates (203, 207), separate the first set of impurities from the first and second distillates, and produce purified acetonitrile as a third distillation column bottoms (213); A system (200) is provided, the system further comprising a water feed section (209) arranged such that the first and second distillates (203, 207) are first mixed and enriched with water before reaching the third distillation column (212) so as to obtain purified and / or recovered acetonitrile.

[0313] The feedwater section (209) may be located at any point such that the first and second distillates (203, 207) are first mixed and enriched with water before reaching the third distillation column (212). For example, the feedwater section (209) is located between the first and third (202, 212) or second and third distillation columns (206, 212).

[0314] In one embodiment, a system (200) as depicted in FIG. 2 is provided.

[0315] FIG. 2 shows an acetonitrile purification / recycle system in one embodiment of the present disclosure. According to the present disclosure, two waste streams (201, 205), e.g., aqueous and organic waste streams, originating from the purification region and oligonucleotide synthesis section of the oligonucleotide process enter the first distillation zone. The first distillation zone can be called the dual aqueous and organic purification zone and includes at least two distillation columns (202, 206). Process steps A and B are carried out in the so-called first distillation zone (FIG. 2), where the organic and inorganic aqueous purification steps are carried out. The goal is to separate as many heavy boilers as possible from acetonitrile and any other light boilers in the feed stream. The bottom products (204, 208) from each section are sent to waste. The details of the light fraction (207, 203) are the same as those for the light fraction (107, 103) as disclosed above.

[0316] The details of the distillation towers (202, 206) are the same as those described above for the columns (102, 106).

[0317] Upon exiting the columns (202, 206), the vapor is condensed in a condenser to produce a distillate (203, 207).

[0318] The light fractions (203, 207) are combined in a feedwater section (209) to produce an acetonitrile feedstock (210), which is enriched with water and introduced into the light ends column (212) in the second distillation section (FIG. 2). The light ends column (212) produces an acetonitrile bottoms product (213).

[0319] The system (100, 200) may further include a dehydration zone that includes a third distillation zone.

[0320] In one embodiment of the system (100), the acetonitrile streams from the previous two sections (103, 113) are combined in the feed to this section, for example in a mixing section (116). Along with acetonitrile and water, the feed contains residual amounts of other organics, particularly toluene, acrylonitrile and ethanol, originating from distillation sections 1 and 2.

[0321] In distillation zone 3 of the system (100, 200), separation of water from acetonitrile can be achieved using a so-called pressure swing distillation system of two distillation columns operating at two different pressures (e.g., 0.2 and 5 bar). This system exploits the difference between the two pressures in the azeotropic composition to produce a pure water waste from this zone and a pure acetonitrile product stream. The impurities mentioned above form light-boiling azeotropes with water and acetonitrile, and a stream enriched in these impurities can be removed from the process at a location different from the aqueous and acetonitrile product streams from the process. The mixed acetonitrile feedstock (116, 215) from distillation zones 1 and 2 enters the first distillation column (117, 216) of the third distillation zone. The acetonitrile stream entering this column is enriched in acetonitrile and separated into a light-boiling stream (118, 217) containing an acetonitrile / water azeotrope. The distillation is carried out below atmospheric pressure, e.g., 0.20 bar. Water is withdrawn as bottom product (119, 218) and sent to aqueous waste. The light acetonitrile stream (118, 217) is fed to a second distillation column (120, 219) whereby a second distillation is carried out at a pressure above atmospheric pressure, e.g., 5 bar, to produce lower boiling impurities (122, 221) withdrawn from the top of the second distillation column (120, 219) and high purity acetonitrile (121, 220) withdrawn from the distillation column bottom. The lower boiling impurities (122, 221) may comprise at least one of ethanol, water, an ethanol / water azeotrope and an acetonitrile / water azeotrope, or mixtures thereof.

[0322] The resulting acetonitrile (121, 220) has an assay purity of at least 99.90%, based on the total content of acetonitrile (121, 220), as measured by GC. If the water content in the product stream is not low enough, a further stage of separation can be added which can remove the residual water as an azeotrope, or it can be removed in the drying section (124, 225), for example by adsorption onto a stationary phase (124, 225). The resulting acetonitrile has an assay purity of at least 99.90% and a water content of less than 30 ppm. The details of the distillation column in the third distillation section are the same as those used in the first and second sections.

[0323] In a further aspect, there is provided a system (300) for purifying and / or recovering acetonitrile from waste acetonitrile (301, 302) generated during an oligonucleotide manufacturing process according to the third aspect of the present disclosure, comprising: a first distillation column (304) configured to receive the mixed acetonitrile aqueous and organic waste stream and produce a first acetonitrile distillate (306) comprising acetonitrile and a first set of impurities, the first distillation column (304) having a condenser coupled to an upper portion of the first distillation column (304), e.g., coupled to an overhead stream; a second distillation column (308) configured to receive the first acetonitrile distillate (306) and produce a second acetonitrile distillate (309) comprising an acetonitrile / water azeotrope, the second distillation column (308) having a condenser coupled to an upper portion of the second distillation column (308), e.g., coupled to an overhead stream; and a third distillation column (311) configured to receive the second acetonitrile distillate (309) and separate the acetonitrile from the acetonitrile / water azeotrope to produce acetonitrile as a third distillation column bottoms (312); The system is configured such that the first acetonitrile distillate (306) is first enriched with water (307) before reaching the second distillation column (308); and / or A system (300) is provided which further comprises a water feed zone (303, 307) arranged such that the organic waste acetonitrile (301) is first enriched with water by mixing the aqueous acetonitrile and organic waste streams (303) before reaching the first distillation column (304) to obtain purified and / or recovered acetonitrile.

[0324] The feed water section (307) may be located at any point such that the first acetonitrile distillate (306) is first enriched with water before reaching the second distillation column (308). For example, the feed water section (307) may be located between the first and second distillation columns (306, 308). Alternatively, sufficient water from the mixing of the acetonitrile aqueous and organic waste streams may be present to act as an entrainer prior to entering the first distillation column (304). Thus, in this embodiment, the mixing section (303) may also function as a feed water section.

[0325] In one embodiment, a system (300) as depicted in FIG. 3 is provided.

[0326] Figure 3 shows an acetonitrile purification / recycle system according to one embodiment of the present disclosure. According to the present disclosure, two waste streams (301, 302), e.g., aqueous and organic waste streams, originating from the purification and oligonucleotide synthesis sections of the oligonucleotide process enter into a mixing zone (303) where they are combined to produce an acetonitrile waste feedstock containing aqueous and organic impurities with lower and higher boiling points compared to acetonitrile. Details of the aqueous and organic acetonitrile waste streams are equivalent to those described for the systems representing the methods according to the first, second, third and fourth embodiments of the present disclosure.

[0327] The combined acetonitrile waste feedstock is then introduced into the first distillation section, which comprises a first distillation column (304). Process step B' is carried out in the so-called first distillation section (FIG. 3), where the initial purification steps take place. The goal is for as many of the heavy boilers as possible to be separated from the acetonitrile and any other light boilers in the feed stream. The bottom product (305) is sent to waste. Details of the light fraction (306) are described under the third aspect of this disclosure for the process section for step B'.

[0328] Upon exiting the column (304), the vapor is condensed in a condenser to produce a distillate (306).

[0329] The light acetonitrile fraction (306) is sent to a feed water section (307) to produce an acetonitrile feedstock which is enriched with water and introduced into a second distillation column (308) in a second distillation section (FIG. 3). The second distillation column (212) produces an acetonitrile bottoms product (309) which comprises an acetonitrile / water azeotrope.

[0330] The acetonitrile bottoms product (309) of the second distillation zone is then introduced into a third distillation column (311) in a third distillation zone (FIG. 3). The third distillation column separates the acetonitrile from the acetonitrile / water azeotrope and remaining lower boiling point impurities (313) to produce purified acetonitrile as a third distillation column bottoms product (312). The lower boiling point impurities (313) can include at least one of ethanol, water, an ethanol / water azeotrope, and an acetonitrile / water azeotrope, or mixtures thereof.

[0331] In the distillation system (300), separation of impurities from acetonitrile can be achieved using a so-called pressure swing distillation system of three distillation columns operating at three different pressures (e.g., low, medium and high pressure, e.g., 200 mbar, 960 mbar and 5 bar).

[0332] The resulting acetonitrile (312) has an assay purity of at least 99.90% based on the total acetonitrile content as measured by GC. If the water content in the product stream is not low enough, a further stage of separation can be added that can remove the residual water as an azeotrope, or it can be removed in a drying section (124, 225), for example, by adsorption onto a stationary phase (124, 225). The resulting acetonitrile has an assay purity of at least 99.90% and a water content of less than 30 ppm.

[0333] The details of the distillation columns (304, 308, 311) of the first, second and third distillation sections of system (300) are equivalent to those disclosed for systems (100, 200), i.e. (102, 106, 112, 202, 206, 212).

[0334] The condensers of the distillation columns present in any one of the systems disclosed herein are typically connected to the upper portion of said distillation columns as is standard in the art. In one embodiment, one or more or all of the condensers of the distillation columns (102, 106, 112, 117, 120, 202, 206, 212, 216, 219, 304, 308, 311) are connected via an overhead stream.

[0335] Enumerated embodiments Embodiment 1. A method for recovering and / or purifying acetonitrile from waste acetonitrile (105, 205, 301) generated during oligonucleotide synthesis, comprising: A *) introducing an organic waste feedstock (105, 205, 301) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a distillation column (106, 206, 304) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the distillation column and condensed to produce a distillate (107, 207, 306) and the second set of organic impurities is produced as a second distillation column bottoms (108, 208, 305); B * ) introducing the distillate (107, 207, 306) into a water feed section (109, 209, 307) to produce a water-enriched acetonitrile stream (111, 210, 210a, 307a); C * ) introducing the water-enriched acetonitrile stream (111, 210, 210a, 307a) into a second distillation column (112, 212, 308) and separating the first set of organic impurities from the acetonitrile, which is produced as second distillation column bottoms (113, 213, 309); Includes; Thereby, recovered and / or purified acetonitrile is obtained.

[0336] Embodiment 2. Water is used in step B * is added to the distillate (107, 207, 306) to produce a water-enriched acetonitrile stream (111, 210, 307a).

[0337] Embodiment 3. Step B * 2. The method of claim 1, wherein the distillate (207) of is combined with an acetonitrile stream containing water to produce a water-enriched acetonitrile stream (210a).

[0338] Embodiment 4. The method of embodiment 3, wherein the acetonitrile stream containing water is obtained from distillation of aqueous waste feedstock generated during oligonucleotide synthesis.

[0339] Embodiment 5. The method of embodiment 4, wherein the distillation comprises introducing an aqueous waste feedstock (201) containing acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile into a distillation column (202) and separating the acetonitrile and the first set of impurities from the second set of impurities, wherein the acetonitrile and the first set of impurities are withdrawn from the distillation column as a vapor and condensed to produce a distillate (203), and the second set of impurities are produced as distillation column bottoms (204).

[0340] Embodiment 6. Step B * The distillate (207) of step B is combined with an acetonitrile stream containing water according to any one of embodiments 3 to 5, and the water is * 2. The method of embodiment 1, wherein a water-enriched acetonitrile stream (210) is further added at

[0341] Embodiment 7. Step A * The method according to any one of the above embodiments, wherein the distillation column operates in the range of 50 to 980 mbar, for example, 100 to 300 mbar.

[0342] Embodiment 8. Step C * The method according to any one of the above embodiments, wherein the distillation column operates in the range of 100 to 980 mbar, for example, 900 to 980 mbar.

[0343] Embodiment 9. Step C * The method of any one of the above embodiments, further comprising mixing the distillate (107, 207) with a recycled acetonitrile stream (122, 221) comprising an acetonitrile / water azeotrope and ethanol, the recycled acetonitrile stream (122, 221) being a by-product of a further processing step, the recycled acetonitrile stream (122, 221) comprising acetonitrile, water and ethanol.

[0344] Embodiment 10. The method of any one of the above embodiments, wherein the distillation column bottoms (113, 213) is further treated to reduce the water content of the acetonitrile to less than 30 parts per million.

[0345] Embodiment 11. A method for recovering and / or purifying acetonitrile from waste acetonitrile (101, 105) generated during, for example, oligonucleotide synthesis, for example, solid phase oligonucleotide synthesis, comprising: A1) introducing an aqueous waste feedstock (101) containing acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile into a first distillation column (102) and separating the acetonitrile and the first set of impurities from the second set of impurities, wherein the acetonitrile and the first set of impurities are withdrawn as vapor from the first distillation column and condensed to produce a first distillate (103) and the second set of impurities is produced as first distillation column bottoms (104); B1) introducing an organic waste feedstock (105) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a second distillation column (106) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the second distillation column and condensed to produce a second distillate (107), and the second set of organic impurities are produced as second distillation column bottoms (108); C1) introducing the second distillate (107) into a water supply section (109) and enriching it with water to produce a water-enriched acetonitrile stream (111); D1) introducing the water-enriched acetonitrile stream (111) into a third distillation column (112) and separating the first set of organic impurities from the acetonitrile, the acetonitrile being produced as third distillation column bottoms (113); E1) feeding the first distillate (103) of step A1 and the third distillation column bottoms (113) of step D1 to a mixing section (116) in which they are combined to produce an acetonitrile-rich stream (110); Includes; Thereby, recovered and / or purified acetonitrile is obtained.

[0346] Embodiment 12. The method of embodiment 11, wherein steps A1 and B1 are carried out in parallel.

[0347] Embodiment 13. The method according to any one of embodiments 11 and 12, wherein steps A1 and B1 are carried out sequentially.

[0348] Embodiment 14. The method of any one of embodiments 11 to 13, wherein the first set of aqueous impurities in step A1 comprises at least one of ethanol and water, or a mixture thereof.

[0349] Embodiment 15. The method of any one of embodiments 11 to 14, wherein the distillation column of step B1 operates in the range of 50 to 980 mbar, for example, 100 to 300 mbar.

[0350] Embodiment 16. The method of any one of embodiments 11 to 15, wherein the distillation column of step A1 operates in the range of 200 to 980 mbar, for example, 400 to 500 mbar.

[0351] Embodiment 17. The method of any one of embodiments 11 to 16, wherein the distillation column of step D1 operates in the range of 100 to 980 mbar, for example 900 to 980 mbar.

[0352] Embodiment 18. The method of any one of embodiments 11 to 17, wherein step C1 further comprises mixing the distillate (107) with a recycled acetonitrile stream (221) comprising an acetonitrile / water azeotrope and ethanol, the recycled acetonitrile stream (221) being a by-product of a further processing step.

[0353] Embodiment 19. The method according to any one of embodiments 11 to 18, wherein the reflux ratio in step B1 is 2 to 8, for example, 5.

[0354] Embodiment 20. The method of any one of embodiments 11-19, wherein the third distillation column bottoms (113) of step D1 comprises acetonitrile and an acetonitrile / water azeotrope.

[0355] Embodiment 21. The method according to any one of embodiments 11 to 20, wherein the reflux ratio in step D1 is 5 to 40, for example 30.

[0356] Embodiment 22. The method of any one of embodiments 11 to 21, wherein the first distillate (103) of step A1 comprises an acetonitrile / water azeotrope.

[0357] Embodiment 23. The method according to any one of embodiments 11 to 22, wherein the reflux ratio in step A1 is 0.25 to 2, for example, 1.

[0358] Embodiment 24. The method of any one of embodiments 11 to 23, wherein the first distillate (103) of step A1 comprises 60 to 80% by weight of acetonitrile.

[0359] Embodiment 25. The method of any one of embodiments 11 to 24, wherein the first distillate (103) of step A1 comprises 20 to 40% by weight of water.

[0360] Embodiment 26. The method according to any one of embodiments 11 to 25, wherein the water-enriched acetonitrile stream (111) of step C1 comprises 5 to 40 wt.% acetonitrile.

[0361] Embodiment 27. The method of any one of embodiments 11 to 26, wherein the amount of water added in step C1 is a ratio of 0.05 to 0.40 (w / w) or more, based on the total amount of acetonitrile and impurities present in the stream.

[0362] Embodiment 28. The method of any one of embodiments 11 to 27, wherein the third distillation column bottoms (113) of step D1 comprises 60 to 90% by weight acetonitrile.

[0363] Embodiment 29. The method of any one of embodiments 11 to 28, wherein the third distillation column bottoms (113) of step D1 further comprises ethanol as an impurity.

[0364] Embodiment 30. The method of embodiment 29, wherein the concentration of ethanol as an impurity is 1 to 10 parts per million.

[0365] Embodiment 31. The method of any one of embodiments 11 to 30, wherein the acetonitrile-rich stream (110) of step E1 is further treated to reduce the water content of the acetonitrile to less than 30 parts per million.

[0366] Embodiment 32. A method for recovering and / or purifying acetonitrile from waste acetonitrile (201, 205) generated during, for example, oligonucleotide synthesis, for example, solid phase oligonucleotide synthesis, comprising: A) introducing an aqueous waste feedstock (201) containing acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile into a first distillation column (202) and separating the acetonitrile and the first set of aqueous impurities from the second set of aqueous impurities, wherein the acetonitrile and the first set of aqueous impurities are withdrawn as a vapor from the first distillation column and condensed to produce a first distillate (203) and the second set of aqueous impurities is produced as first distillation column bottoms (204); B) introducing an organic waste feedstock (205) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a second distillation column (206) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as a vapor from the second distillation column and condensed to produce a second distillate (207), and the second set of organic impurities are produced as second distillation column bottoms (208); C) feeding the first distillate (203) of step A and the second distillate (207) of step B to a water supply area (209); C1) combining therein to produce a water-enriched acetonitrile stream (210a); or C2) combining therein and enriching with water to produce a water-enriched acetonitrile stream (210); D) introducing the water-enriched acetonitrile stream (210, 201a) into a third distillation column (212) and separating the first set of organic and aqueous impurities from the acetonitrile, wherein acetonitrile is produced as third distillation column bottoms (213); Includes; Thereby, recovered and / or purified acetonitrile is obtained.

[0367] Embodiment 33 The method of embodiment 32, wherein steps A and B are carried out in parallel.

[0368] Embodiment 34. The method of embodiment 32, wherein steps A and B are carried out sequentially.

[0369] Embodiment 35. The method of any one of embodiments 32 to 34, wherein the distillation column of step A operates in the range of 200 to 980 mbar, for example, 400 to 500 mbar.

[0370] Embodiment 36. The method of any one of embodiments 32 to 35, wherein the distillation column of step B operates in the range of 50 to 980 mbar, for example, 100 to 300 mbar.

[0371] Embodiment 37. The method of any one of embodiments 32 to 36, wherein the distillation column of step D operates in the range of 100 to 980 mbar, for example, 900 to 980 mbar.

[0372] Embodiment 38. The method of any one of embodiments 32 to 37, wherein step C further comprises mixing the first and second distillates (203, 207) with a recycled acetonitrile stream (221) comprising an acetonitrile / water azeotrope and ethanol, the recycled acetonitrile stream (221) being a by-product of a further processing step.

[0373] Embodiment 39. The method of any one of embodiments 32-38, wherein the first set of aqueous impurities in step A comprises at least one of ethanol and water, or a mixture thereof.

[0374] Embodiment 40. The method of any one of embodiments 32-39, wherein the first distillate (203) of Step A comprises an acetonitrile / water azeotrope.

[0375] Embodiment 41. The method of any one of embodiments 32 to 40, wherein the reflux ratio in step A is 0.25 to 2, for example, 1.

[0376] Embodiment 42 The method of any one of embodiments 32 to 41, wherein the reflux ratio in step B is 2 to 8, for example, 5.

[0377] Embodiment 43. The method of any one of embodiments 32-42, wherein the third distillation column bottoms (213) of Step D comprises acetonitrile and an acetonitrile / water azeotrope.

[0378] Embodiment 44. The method of any one of embodiments 32 to 43, wherein the reflux ratio in step D is 5 to 40, for example 30.

[0379] Embodiment 45. The method of any one of embodiments 32 to 44, wherein the first distillate (203) of step A comprises 60 to 80% by weight acetonitrile.

[0380] Embodiment 46. The method of any one of embodiments 32 to 45, wherein the first distillate (203) of step A comprises 20 to 40% by weight water.

[0381] Embodiment 47. The method of any one of embodiments 32 to 46, wherein the amount of water added in step C is a ratio of 0.05 to 0.40 (w / w) or more, based on the total amount of acetonitrile and impurities present in the stream.

[0382] Embodiment 48. The method of any one of embodiments 32 to 47, wherein the water-enriched acetonitrile stream (210, 210a) of step C comprises 60 to 90% by weight acetonitrile.

[0383] Embodiment 49. The method of any one of embodiments 32 to 48, wherein the third distillation column bottoms (213) of Step D comprises 60 to 90% by weight acetonitrile.

[0384] Embodiment 50. The method of any one of embodiments 32-49, wherein the third distillation column bottoms (213) of step D further comprises ethanol as an impurity.

[0385] Embodiment 51. The method of embodiment 50, wherein the concentration of ethanol as an impurity is 1 to 10 parts per million.

[0386] Embodiment 52. The method of any one of the preceding embodiments, wherein the acetonitrile-rich stream (110) or the distillation column bottoms (113, 213) is further treated to reduce the water content of the acetonitrile to less than 30 parts per million.

[0387] Embodiment 53. The method of embodiment 52 when dependent on any one of embodiments 11 to 52, further comprising the steps of introducing the acetonitrile-rich stream (110) or the distillation column bottoms (113, 213) into a fourth distillation column (117, 216) and reducing the water content of the acetonitrile-rich stream by use of pressure swing distillation to recover acetonitrile having a water content of less than 30 parts per million.

[0388] Embodiment 54. The pressure swing distillation comprises: F1) introducing the acetonitrile-rich stream (110) or the distillation column bottoms (113, 213) into a distillation column (117, 216) and removing water therefrom by distillation at less than atmospheric pressure, wherein acetonitrile is withdrawn from said distillation column as a vapor and condensed to produce a distillate (118, 217) and water is produced as distillation column bottoms (119, 218); F2) introducing the distillate (118, 217) into a distillation column (120, 219) and carrying out a second distillation at a pressure above atmospheric pressure, for example 5 bar, to produce a lower boiling fraction (122, 221) which is withdrawn from the upper part of the distillation column (120, 219) and acetonitrile which is produced as distillation column bottoms (121, 220); 54. The method of embodiment 53, comprising:

[0389] Embodiment 55. The method of embodiment 54, wherein the reflux ratio in step F1 is 0.05 to 1, for example, 0.1.

[0390] Embodiment 56 The method according to any one of embodiments 54 and 55, wherein the reflux ratio in step F2 is 0.05 to 1, for example, 0.25.

[0391] Embodiment 57. The method of any one of embodiments 54 to 56, wherein the distillate (118, 217) comprises acetonitrile and an acetonitrile / water azeotrope.

[0392] Embodiment 58. The method of any one of embodiments 54-57, wherein the lower boiling fraction of step F2 comprises at least one of ethanol, water, an ethanol / water azeotrope, and an acetonitrile / water azeotrope, or mixtures thereof.

[0393] Embodiment 59. The method of any one of embodiments 54-58, wherein acetonitrile produced as the distillation column bottoms (121, 220) of step F2 is passed through a water reducing adsorbent (124, 225).

[0394] Embodiment 60. The method of embodiment 59, wherein the water-reducing adsorbent (124, 225) is a molecular sieve.

[0395] Embodiment 61. The method of any one of the preceding embodiments, wherein the recovered acetonitrile has a purity of at least 99.90% as measured by gas chromatography and, optionally, a water content of less than 50 parts per million, for example less than 30 parts per million.

[0396] Embodiment 62. The method of any one of embodiments 52 to 61, further comprising recycling at least a portion of said lower boiling fraction (122, 221) from further processing of the acetonitrile-rich stream (110) or the distillation column bottoms (113, 213).

[0397] Embodiment 63. The method of any one of embodiments 52 to 62, further comprising recycling at least a portion of the lower boiling fraction (122, 221) from the distillation column (120, 219) of step F2.

[0398] Embodiment 64. The method of embodiment 63, wherein the lower boiling fraction (122, 221) is fed back to step F1.

[0399] Embodiment 65. The method of any one of embodiments 63 and 64, wherein the lower boiling fraction (122, 221) is first purged (123, 222) and then recycled.

[0400] Embodiment 66. The method of any one of embodiments 63 to 65, wherein the lower boiling fraction (122) is recycled to step D1 via the water feed section in step C1.

[0401] Embodiment 67. The process according to embodiment 66, wherein at least a portion of the lower boiling fraction (122, 221) is fed back to the distillation column (117, 216) of step F1.

[0402] Embodiment 68. The method of any one of embodiments 54 to 67, wherein the lower boiling fraction (122, 221) is fed back to the distillation column (117, 216) of step F1 via the mixing section (215) of step E or the mixing section (116) of step E1.

[0403] Embodiment 69. The method of embodiment 68, wherein at least a portion of the lower boiling fraction (122, 221) is recycled back to the distillation of step D1 or step D, and a higher proportion is sent back to the mixing zone (116, 215).

[0404] Embodiment 70. The method of embodiment 69, wherein at least a portion of the lower boiling fraction (221) is recycled back to the feedwater section (209) of step C.

[0405] Embodiment 71. The method of any one of embodiments 54 to 61, wherein the lower boiling fraction (122, 221) of step F2 is sent to waste.

[0406] Embodiment 72. The method of embodiment 71, wherein the lower boiling fraction (122, 221) is first purged (123, 222) and then sent to waste.

[0407] Embodiment 73. The method of any one of embodiments 54 to 72, wherein the distillation of step F1 is carried out at a pressure in the range of 50 to 980 mbar, such as 50 to 200 mbar, such as 200 mbar.

[0408] Embodiment 74. The method of any one of embodiments 54 to 73, wherein the distillation of step F2 is carried out at a pressure in the range of 3 to 8 bar, such as 5 bar.

[0409] Embodiment 75. A method for recovering and / or purifying acetonitrile from waste acetonitrile (301, 302) generated during oligonucleotide synthesis, comprising: A') introducing into a first mixing zone (303) and combining therein an organic waste feedstock (301) comprising acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile, and an aqueous waste feedstock (302) comprising acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile, to form an acetonitrile waste feedstock comprising said impurities; or introducing an organic waste feedstock (301) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a first mixing zone (303) and enriching with water to produce a water-enriched acetonitrile stream containing said impurities; B') introducing the acetonitrile waste feedstock or the water-enriched acetonitrile stream into a first distillation column (304) to separate acetonitrile and a first set of impurities having a boiling point lower than acetonitrile from a second set of impurities having a boiling point higher than acetonitrile, wherein acetonitrile and the first set of impurities are withdrawn as vapor from the first distillation column and condensed to produce a first distillate (306) and the second set of impurities is produced as first distillation column bottoms (305); C') optionally introducing the first distillate (306) containing acetonitrile and low boiling impurities into a water feed section (307) and enriching it with water to produce a water-enriched acetonitrile stream (307a); D') introducing the water-enriched acetonitrile stream (306, 307a) into a second distillation column (308) and separating the acetonitrile from low-boiling impurities, wherein acetonitrile is produced as second distillation column bottoms (309); Includes; Thereby, recovered and / or purified acetonitrile is obtained.

[0410] Embodiment 76. The method of embodiment 75, wherein the second distillation column bottoms comprises an acetonitrile / water azeotrope.

[0411] Embodiment 77. The method of embodiment 76, further comprising the step of: E') introducing the second distillation column bottoms product (309) of step D' into a third distillation column (311) to separate acetonitrile from the acetonitrile / water azeotrope, wherein acetonitrile is produced as third distillation column bottoms (312).

[0412] Embodiment 78. The method of any one of embodiments 75 to 77, wherein step A' further comprises mixing the acetonitrile waste feedstock with a recycled acetonitrile stream (316) comprising an acetonitrile / water azeotrope and ethanol, the recycled acetonitrile stream (316) being a by-product of a further processing step.

[0413] Embodiment 79. The method of any one of embodiments 75-78, wherein the second distillation column bottoms (309) or the third distillation column bottoms (312) are further treated to reduce the water content of the acetonitrile to less than 30 parts per million.

[0414] Embodiment 80. The method of any one of embodiments 75-79, wherein the distillation of step B' is carried out at a lower pressure than the distillation of step D', and optionally, the distillation of step D' is carried out at a lower pressure than the distillation of step E'.

[0415] Embodiment 81. The method of any one of embodiments 75 to 80, wherein the distillation column of step B' operates in the range of 50 to 980 mbar, for example, 100 to 300 mbar.

[0416] Embodiment 82. The method of any one of embodiments 75 to 81, wherein the distillation column of step D' operates in the range of 50 to 980 mbar, for example, 100 to 300 mbar.

[0417] Embodiment 83. The method of any one of embodiments 77 to 82, wherein the distillation column of step E' operates in the range of 50 to 980 mbar, for example, 100 to 300 mbar.

[0418] Embodiment 84. The method of any one of embodiments 77 to 83, wherein the recovered acetonitrile (312) is passed through a water reducing adsorbent.

[0419] Embodiment 85. The method of embodiment 84, wherein the water-reducing adsorbent is a molecular sieve.

[0420] Embodiment 86. The method of any one of embodiments 75-85, wherein the first distillate (306) of Step B' comprises an acetonitrile / water azeotrope.

[0421] Embodiment 87. The method of any one of embodiments 75 to 86, wherein the reflux ratio in step B' is from 0.25 to 8, for example, from 0.25 to 2 or from 2 to 8, and / or the reflux ratio in step D' is from 5 to 40, for example, 30.

[0422] Embodiment 88. The method of any one of embodiments 75-87, wherein the second distillation column bottoms (309) of step D' comprises acetonitrile and an acetonitrile / water azeotrope.

[0423] Embodiment 89. The method of any one of embodiments 75 to 88, wherein the amount of water added in step C' is a ratio of 0.05 to 0.40 (w / w) or more, based on the total amount of acetonitrile and impurities present in the stream.

[0424] Embodiment 90. The method of any one of embodiments 11 to 89, wherein acetonitrile and the first set of aqueous impurities are withdrawn in step A1, step A or step B' from an upper portion of the distillation column (102, 202, 304), e.g., from the top of the column.

[0425] Embodiment 91. Step A * The method of any one of the above embodiments, wherein the first set of organic impurities in Step B1, Step B or Step B' comprises an azeotrope former, the azeotrope former comprising at least one of toluene, ethyl acetate, ethanol, diethylamine, diisopropylamine and acrylonitrile, or a mixture thereof.

[0426] Embodiment 92. Step A * The method of any one of the preceding embodiments, wherein the first set of organic impurities of step B1, step B or step B' comprises at least one of diethylamine, diisopropylamine, ethyl acetate and acrylonitrile, or a mixture thereof.

[0427] Embodiment 93. Step A * The method of any one of the preceding embodiments, wherein the second set of organic impurities of step B1, step B or step B' comprises at least one of toluene, acetic acid, acetic anhydride, dichloroacetic acid and N-containing compounds, or mixtures thereof.

[0428] Embodiment 94. The method of embodiment 93, wherein the N-containing compound is selected from imidazole, 1-methylimidazole, 2,6-lutidine, dimethylformamide, pyridine, acrylonitrile, diisopropylamine, diethylamine, phenylacetyl (disulfide), and 5-(ethylthio)-1H-tetrazole.

[0429] Embodiment 95. The method of any one of the previous embodiments, wherein the water-enriched acetonitrile stream (111, 210, 210a, 303a, 307a) comprises acetonitrile and azeotropes having a lower boiling point relative to acetonitrile.

[0430] Embodiment 96. The method of embodiment 95, wherein the lower boiling azeotrope comprises at least one of acetonitrile, water, toluene, ethanol, diethylamine, diisopropylamine, and acrylonitrile, or mixtures thereof.

[0431] Embodiment 97. The method of any one of embodiments 95 and 96, wherein the lower boiling azeotrope comprises at least one of acetonitrile / water, acetonitrile / toluene, acetonitrile / diethylamine, acetonitrile / diisopropylamine, toluene / water, ethanol / water, toluene / water / acrylonitrile, toluene / water / acetonitrile, and diisopropylamine / water / acetonitrile, or mixtures thereof.

[0432] Embodiment 98. The method of any one of embodiments 77 to 97, further comprising recycling at least a portion of the lower boiling fraction (313) from the third distillation column (311).

[0433] Embodiment 99. The method of embodiment 98, wherein at least a portion of the lower boiling fraction (313) is fed back to the mixing zone (303).

[0434] Embodiment 100. The method of embodiment 99, wherein at least a portion of said lower boiling fraction (313) is first purged (314) before being fed back to the mixing zone (303).

[0435] Embodiment 101. The method of any one of embodiments 77 to 97, wherein the lower boiling fraction (313) is purged (314) and sent to waste (315).

[0436] Embodiment 102. The method of any one of the preceding embodiments, wherein the recovered acetonitrile has a purity (area %) of at least 99.90% as measured by gas chromatography.

[0437] Embodiment 103. The method of any one of the above embodiments, wherein the waste acetonitrile is on an industrial scale.

[0438] Embodiment 104. The method of any one of the above embodiments, wherein the waste acetonitrile is at least 10 kg, preferably at least 100 kg, at least 1000 kg or at least 10,000 kg.

[0439] Embodiment 105. The method of any one of the preceding embodiments, wherein acetonitrile is recovered on a gram or kilogram scale, or higher.

[0440] Embodiment 106. The method of any one of the above embodiments, wherein the method is carried out in batch mode.

[0441] Embodiment 107. The method according to any one of embodiments 1 to 105, wherein the method is carried out continuously.

[0442] Embodiment 108. The method according to any one of the above embodiments, wherein the oligonucleotide synthesis is a solid-phase oligonucleotide synthesis.

[0443] Embodiment 109. The method of any one of the above embodiments, wherein the oligonucleotide is RNA.

[0444] Embodiment 110. The method of any one of embodiments 1 to 108, wherein the oligonucleotide is DNA.

[0445] Embodiment 111. The method of any one of embodiments 1 to 108, wherein the oligonucleotide comprises both RNA and DNA.

[0446] Embodiment 112. The method of any one of the above embodiments, wherein the oligonucleotide is a modified oligonucleotide.

[0447] Embodiment 113. The method of embodiment 112, wherein the modification is at the 2' position of the sugar moiety and is selected from the group consisting of 2'-F, 2'-OMe, 2'-MOE, and 2'-amino, or the oligonucleotide comprises a PMO, LNA, PNA, BNA, or SPIEGELMER.

[0448] Embodiment 114. The method according to any one of embodiments 112 and 113, wherein the modification is in the nucleobase and is selected from the group consisting of 5-methylpyrimidine, 7-deazaguanosine and abasic nucleotides.

[0449] Embodiment 115. The method according to any one of embodiments 112 to 114, wherein the modifications are in the backbone and are selected from the group consisting of phosphorothioates, phosphoramidates and phosphorodiamidates.

[0450] Embodiment 116. The method of any one of embodiments 112 to 115, wherein the oligonucleotide is selected from the group consisting of an antisense oligonucleotide, an aptamer, an siRNA, an miRNA, and a gapmer.

[0451] Embodiment 117. The method of any one of embodiments 112 to 116, wherein the oligonucleotide is an antisense oligonucleotide.

[0452] Embodiment 118. The method of any one of embodiments 112 to 116, wherein the oligonucleotide is a siRNA.

[0453] Embodiment 119. The method of any one of the above embodiments, wherein the oligonucleotide is between 10 and 200 nucleotides in length.

[0454] Embodiment 120. The method of any one of the above embodiments, wherein the oligonucleotide is 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30 nucleotides in length.

[0455] Embodiment 121. The method of any one of the above embodiments, wherein the oligonucleotide is an 18-mer, 19-mer, 20-mer, 21-mer, 22-mer, 23-mer, 24-mer, 25-mer, 26-mer, 27-mer, 28-mer, 29-mer or 30-mer.

[0456] Embodiment 122. The method of any one of the above embodiments, wherein the oligonucleotide is a therapeutic oligonucleotide.

[0457] Embodiment 123. The method of any one of the above embodiments, wherein the oligonucleotide is a single-stranded therapeutic oligonucleotide.

[0458] Embodiment 124. The method of any one of the above embodiments, wherein the oligonucleotide is a double-stranded therapeutic oligonucleotide.

[0459] Embodiment 125. The method according to any one of embodiments 1 to 109, 112 to 117, 119 to 122 and 124, wherein the oligonucleotide is an inclisilan.

[0460] Embodiment 126. The method according to any one of embodiments 1 to 109, 112 to 116 and 118 to 123, wherein the oligonucleotide is peracarsen.

[0461] Embodiment 127. Acetonitrile (or an acetonitrile composition) for use in oligonucleotide production, having a purity of at least 99.90% as measured by gas chromatography, the acetonitrile being recovered from oligonucleotide synthesis waste.

[0462] Embodiment 128. The acetonitrile of embodiment 127, wherein the acetonitrile has less than 30 parts per million water.

[0463] Embodiment 129. The acetonitrile of any one of embodiments 127 and 128, wherein the acetonitrile further contains 1 to 5 parts per million pyridine, as measured, for example, by gas chromatography.

[0464] Embodiment 130. The acetonitrile of any one of embodiments 127 to 129, wherein the acetonitrile further comprises 1 to 10 parts per million of ethanol, as measured, for example, by gas chromatography.

[0465] Embodiment 131. The acetonitrile of any one of embodiments 127 to 130, wherein the acetonitrile further comprises 1 to 10 parts per million toluene, as measured, for example, by gas chromatography.

[0466] Embodiment 132. Acetonitrile obtained by the method according to any one of embodiments 1 to 126.

[0467] Embodiment 133. The acetonitrile of embodiment 132, wherein the acetonitrile has a purity of at least 99.90%.

[0468] Embodiment 134. The acetonitrile of any one of embodiments 132 and 133, wherein the acetonitrile has a purity of at least 99.90% and less than 30 parts per million water as measured by gas chromatography.

[0469] Embodiment 135. The acetonitrile of any one of embodiments 132 to 134, wherein the acetonitrile further comprises 1 to 5 parts per million pyridine, as measured, for example, by gas chromatography.

[0470] Embodiment 136. The acetonitrile of any one of embodiments 132 to 135, wherein the acetonitrile further comprises 1 to 10 parts per million toluene, as measured, for example, by gas chromatography.

[0471] Embodiment 137. The acetonitrile of any one of embodiments 132 to 136, wherein the acetonitrile further comprises 1 to 10 parts per million of ethanol, as measured, for example, by gas chromatography.

[0472] Embodiment 138. A method for synthesizing oligonucleotides, comprising recovering and / or purifying acetonitrile from waste acetonitrile according to any one of embodiments 1 to 126, and The method comprises using at least a portion of the recovered and / or purified acetonitrile in a process for synthesizing oligonucleotides and / or for washing oligonucleotides or support-bound oligonucleotides.

[0473] Embodiment 139. The method of embodiment 138, wherein the method comprises solid phase oligonucleotide synthesis.

[0474] Embodiment 140. The method according to any one of claims 138 and 139, wherein the oligonucleotide to be synthesized is defined according to any one of embodiments 109 to 126.

[0475] Embodiment 141. A system for purifying and / or recovering acetonitrile from waste acetonitrile (105, 205, 301) generated during an oligonucleotide manufacturing process, comprising: a first distillation column (106, 206, 304) configured to receive the acetonitrile organic waste stream (105, 205, 301) and produce a first distillate (107, 207, 306) comprising acetonitrile and a first set of impurities, the first distillation column (106, 206, 304) having a condenser coupled to an upper portion of the first distillation column; and a second distillation column (112, 212, 308) configured to receive the first distillate (107, 207, 306), separate the first set of organic impurities from the acetonitrile, and produce purified acetonitrile as a second distillation column bottoms; The system, the first distillate (107, 207, 306) is first enriched with water before reaching the second distillation column (112, 212, 308) so as to obtain purified and / or recovered acetonitrile; or The system further comprises a water feed zone (109, 209, 303, 307) arranged such that waste acetonitrile (301) is enriched with water before reaching the first distillation column (304) so ​​as to obtain purified and / or recovered acetonitrile.

[0476] Embodiment 142. A system (100) for purifying and / or recovering acetonitrile from waste acetonitrile (101, 105) generated during an oligonucleotide manufacturing process, e.g., a solid-phase oligonucleotide manufacturing process, comprising: a first distillation column (102) configured to receive an aqueous acetonitrile waste stream (101) and produce a first distillate (103) comprising acetonitrile and a first set of impurities, the first distillation column (102) having a condenser connected to an upper portion of the first distillation column (102), e.g., connected to an overhead stream; a second distillation column (106) configured to receive the acetonitrile organic waste stream (105) and produce a second distillate (107) comprising acetonitrile and the first set of impurities, the second distillation column (106) having a condenser connected to an upper portion of the second distillation column (106), e.g., connected to an overhead stream; and a third distillation column (112) configured to receive the second distillate (107) and separate the first set of organic impurities from the acetonitrile and produce purified acetonitrile as a third distillation column bottoms; The system (100) further includes a water feed section (109) arranged such that the second distillate (107) is first enriched with water before reaching the third distillation column (112) so as to obtain purified and / or recovered acetonitrile; and a mixing section (116) configured to mix the first distillate (103) from the first distillation column (102) and the third distillation column bottoms (113) from the third distillation column (112).

[0477] Embodiment 143. A system (200) for purifying and / or recovering acetonitrile from waste acetonitrile (201, 205) generated during an oligonucleotide manufacturing process, e.g., a solid-phase oligonucleotide manufacturing process, comprising: a first distillation column (202) configured to receive the aqueous acetonitrile waste stream (201) and produce a first distillate (203) comprising acetonitrile and a first set of impurities, the first distillation column (202) having a condenser coupled to an upper portion of the first distillation column (202), e.g., coupled to an overhead stream; a second distillation column (206) configured to receive the acetonitrile organic waste stream (205) and produce a second distillate (207) comprising acetonitrile and the first set of impurities, the second distillation column (206) having a condenser connected to an upper portion of the second distillation column (206), e.g., connected to an overhead stream; and a third distillation column (212) configured to receive the first and second distillates (203, 207), separate the first set of impurities from the first and second distillates, and produce purified acetonitrile as a third distillation column bottoms (213); The system (200) further comprises a water supply section (209) arranged such that the first and second distillates (203, 207) are first mixed, or are first mixed and enriched with water before reaching the third distillation column (212), thereby obtaining purified and / or recovered acetonitrile.

[0478] Embodiment 144. A system (300) for purifying and / or recovering acetonitrile from waste acetonitrile (301, 302) generated during an oligonucleotide manufacturing process, comprising: a first distillation column (304) configured to receive the mixed acetonitrile aqueous and organic waste stream and produce a first acetonitrile distillate (306) comprising acetonitrile and a first set of impurities, the first distillation column (304) having a condenser coupled to an upper portion of the first distillation column (304), e.g., coupled to an overhead stream; a second distillation column (308) configured to receive the first acetonitrile distillate (306) and produce a second acetonitrile distillate (309) comprising an acetonitrile / water azeotrope, the second distillation column (308) having a condenser coupled to an upper portion of the second distillation column (308), e.g., coupled to an overhead stream; and a third distillation column (311) configured to receive the second acetonitrile distillate (309) and separate the acetonitrile from the acetonitrile / water azeotrope to produce acetonitrile as a third distillation column bottoms (312); the system being enriched with water (307) before the first acetonitrile distillate (306) reaches the second distillation column (308); and / or The system (300) further comprises a water supply section (303, 307) arranged such that the organic waste acetonitrile (301) is enriched with water by mixing the aqueous acetonitrile and organic waste streams (303) before reaching the first distillation column (304), thereby obtaining purified and / or recovered acetonitrile.

[0479] Embodiment 145. The system (100) of embodiment 142 as shown in FIG. 1 .

[0480] Embodiment 146. The system (200) of embodiment 143, as shown in FIG. 2 .

[0481] Embodiment 147. The system (300) of embodiment 144 as shown in FIG. 3 .

[0482] Embodiment 148. The system (100, 200) according to any one of embodiments 142 and 143, further comprising at least a fourth distillation column (117, 216) configured to receive the third distillation column bottoms (113, 213) of the third distillation column (112, 212) and produce a fourth distillate (118, 217) comprising acetonitrile.

[0483] Embodiment 149. The system (100, 200) of embodiment 148, further comprising a fifth distillation column (120, 219) configured to receive a fourth distillate (118, 217) from the fourth distillation column (117, 216) and produce a fifth distillation column bottoms (121, 220) product comprising high purity acetonitrile.

[0484] Embodiment 150. A system (100, 200, 300) according to any one of embodiments 141 to 149, further comprising a drying section (124, 225), the drying section being configured to reduce the water content in the acetonitrile product to less than 30 parts per million.

[0485] Embodiment 151. The system (100, 200, 300) according to any one of embodiments 141 to 150, wherein the purified and / or recovered acetonitrile has a purity of at least 99.90% as measured by gas chromatography.

[0486] Embodiment 152. Use of acetonitrile for oligonucleotide synthesis, wherein the acetonitrile has a purity of at least 99.90% as measured by gas chromatography, and the acetonitrile is recovered from oligonucleotide synthesis waste, optionally wherein the oligonucleotide synthesis waste is solid-phase oligonucleotide synthesis waste.

[0487] Embodiment 153. The use according to embodiment 152, wherein the acetonitrile has less than 30 parts per million water.

[0488] Embodiment 154. The use according to any one of embodiments 152 and 153, wherein acetonitrile is defined according to any one of embodiments 127 to 137.

[0489] Embodiment 155. The use according to any one of embodiments 152 to 154, wherein the acetonitrile is obtained according to a method according to any one of embodiments 1 to 126.

[0490] Embodiment 156. The use according to any one of embodiments 152 to 155, wherein acetonitrile is used as a detergent and / or reaction solvent and / or diluent in oligonucleotide synthesis.

[0491] Embodiment 157. The use according to any one of embodiments 152 to 156, wherein the oligonucleotide synthesis is a solid-phase oligonucleotide synthesis.

[0492] Embodiment 158. The use according to any one of embodiments 152 to 157, wherein the oligonucleotide is RNA.

[0493] Embodiment 159. The use according to any one of embodiments 152 to 157, wherein the oligonucleotide is DNA.

[0494] Embodiment 160. The use according to any one of embodiments 152 to 157, wherein the oligonucleotide comprises both RNA and DNA.

[0495] Embodiment 161. The use according to any one of embodiments 152 to 160, wherein the oligonucleotide is a modified oligonucleotide.

[0496] Embodiment 162. The use according to embodiment 161, wherein the modification is at the 2' position of the sugar moiety and is selected from the group consisting of 2'-F, 2'-OMe, 2'-MOE, and 2'-amino, or the oligonucleotide comprises a PMO, LNA, PNA, BNA, or SPIEGELMER.

[0497] Embodiment 163. The use according to any one of embodiments 161 and 162, wherein the modification is in the nucleobase and is selected from the group consisting of 5-methylpyrimidine, 7-deazaguanosine and abasic nucleotides.

[0498] Embodiment 164. The use according to any one of embodiments 161 to 163, wherein the modifications are in the backbone and are selected from the group consisting of phosphorothioates, phosphoramidates and phosphorodiamidates.

[0499] Embodiment 165. The use according to any one of embodiments 161 to 164, wherein the oligonucleotide is selected from the group consisting of antisense oligonucleotides, aptamers, siRNAs, miRNAs, and gapmers.

[0500] Embodiment 166. The use according to any one of embodiments 161 to 165, wherein the oligonucleotide is an antisense oligonucleotide.

[0501] Embodiment 167. The use according to any one of embodiments 161 to 165, wherein the oligonucleotide is a siRNA.

[0502] Embodiment 168. The use according to any one of embodiments 158 to 167, wherein the oligonucleotide is 10 to 200 nucleotides in length.

[0503] Embodiment 169. The use according to any one of embodiments 158 to 168, wherein the oligonucleotide is 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30 nucleotides in length.

[0504] Embodiment 170. The use according to any one of embodiments 158 to 169, wherein the oligonucleotide is an 18-mer, 19-mer, 20-mer, 21-mer, 22-mer, 23-mer, 24-mer, 25-mer, 26-mer, 27-mer, 28-mer, 29-mer or 30-mer.

[0505] Embodiment 171. The use according to any one of embodiments 158 to 170, wherein the oligonucleotide is a therapeutic oligonucleotide.

[0506] Embodiment 172. The use according to any one of embodiments 158 to 171, wherein the oligonucleotide is a single-stranded therapeutic oligonucleotide.

[0507] Embodiment 173. The use according to any one of embodiments 158 to 171, wherein the oligonucleotide is a double-stranded therapeutic oligonucleotide.

[0508] Embodiment 174. The use according to any one of embodiments 152 to 158, 161 to 166, 168 to 171 and 173, wherein the oligonucleotide is an inclisilan.

[0509] Embodiment 175. The use according to any one of embodiments 152 to 158, 161 to 165 and 167 to 172, wherein the oligonucleotide is peracarsen.

[0510] Embodiment 176. The use according to any one of embodiments 152 to 175, wherein the oligonucleotide of the oligonucleotide synthesis waste is defined according to any one of embodiments 109 to 126.

[0511] Embodiment 177. The use according to any one of embodiments 152 to 176, wherein the oligonucleotide is produced on a gram or kilogram scale or higher. EXAMPLES

[0512] The following examples are offered by way of illustration.

[0513] Example 1 Several waste products are generated from the oligonucleotide synthesis process. The waste products are collected in three streams. One of these streams, the labeled organic waste, contains most of the acetonitrile, suitable for regeneration. Most of this stream contains many acetonitrile washes that are applied after each reaction step in the process to form oligonucleotides. The remaining two streams are less suitable for acetonitrile regeneration. One of these streams is a labeled chlorinated waste, containing mainly dichloroacetic acid and toluene, while the other stream is a labeled halogenated waste, containing mainly pyridine, iodine and water. Both of these streams contain very little acetonitrile and are less suitable for regenerating acetonitrile than the organic waste stream. Due to some backmixing during the reaction, the separation of these streams is incomplete, and it is not uncommon to find, for example, some pyridine, toluene or water in the organic waste stream.

[0514] To investigate the principles of acetonitrile regeneration using batch distillation, several batch experiments were performed combining various amounts of each of the above waste streams.

[0515] The batch distillation unit used for the experiments includes a 1 L jacketed glass reactor equipped with an agitator, a head plate containing several access points for filling the reactor with waste liquid and for fixing measuring probes such as a temperature probe and a pH meter to the reactor. A packed column of 500 mm height with an internal diameter of 30 mm is fixed to the head plate. The packing in the column is of structured packing type (DX packing) manufactured by Sulzer Chemtec. This packing results in 16 to 22 theoretical plates depending on the operating conditions used during these experiments. At the top of the packed column is placed a condenser fed with a glycol-water mixture at 5 °C to condense the vapors coming from the top of the packed section. At the base of the condenser is placed a reflux controller that controls the fraction of the condensate that is recycled to the packing and the fraction that is taken off as product to the distillate collection tank. A vacuum pump is connected to the unit to control the operating pressure on the condenser section.

[0516] The operating procedure for the batch experiments included the following steps. 1. Inerting the distillation unit with nitrogen. Turn on the coolant flow to the condenser at a temperature between 2.0°C and 5°C. 3. Set the reflux controller to full reflux. 4. Load the distillation unit with the distilled solution via the access point in the head plate. 5. Switch on the agitator and initially heat the jacket to 40°C. 6. Turn on the vacuum pump and reduce the pressure in the column to the desired set point. 7. Increase the jacket temperature until you notice the solution boiling. 8. Wait until all parts of the column contain distillate and the temperature inside the column stabilizes at a constant value. 9. Change the reflux ratio to the desired value and remove the distillate from the system. 10. Increase jacket temperature until desired distillate takeoff rate is reached. 11. Collect the distillate in the fraction.

[0517] During batch distillation, several distillate fractions are removed during each run and stored in bottles for analysis. The reactor contents are concentrated and only at the end are samples of the final bottoms residue taken for analysis. Distillation is continued until 80-85% of the original charge to the reactor has been distilled into fractions.

[0518] Table 1.1 shows that the fractions of each waste type were combined to produce the batch charge for each experiment. For example, in experiment 1.1, all of the waste streams were combined to produce the feedstock, while in experiment 1.3, all of the organic waste stream and only 20% of the available chlorination stream were combined to form the batch feedstock.

[0519] Each distillation experiment in Table 1.1 is carried out according to the procedure outlined above. Table 1.2 gives some details of the operating conditions of each experiment. Apart from experiment 1.1, which was carried out at 400 mbar, all other experiments are carried out at a pressure of 200 mbar. The reflux ratio is at a value of 3 from experiment 1.1 to experiment 1.6, and is then reduced to measure the effect of a lower reflux ratio on the purity of the distilled product. In Table 1.2, the number of theoretical separation stages obtained by the hydraulic conditions and the characteristics of the column packing during each experiment are also given.

[0520] Table 1.1 shows the composition of each batch charge to the distillation unit as determined by gas chromatography and expressed as area percent (Area%). The concentrations of toluene and pyridine are proportional to the amount of chlorinated and halogenated wastes, respectively, added to the feed. In Experiment 1.2, when neither chlorinated nor halogenated wastes are added to the feed, there is still residual contamination of both toluene and pyridine in the feed.

[0521] In Table 1.2 the water content in the feed to each run is shown, as well as the water content of the initial and final distillate cuts and the water content of the residue remaining in the batch reaction at the end of the run. The runs that included a portion of the halogenated waste stream show higher levels of water in the feed and distillate and final bottoms products, as would be expected based on the presence of water in the halogenated waste.

[0522] The pH values ​​of the same streams as above for water content are also shown in Table 1.2. Table 1.2 also shows the experimental time, the calculated number of stages and the operating pressure.

[0523] [Table 1.1]

[0524] [Table 1.2]

[0525] [Table 1.3]

[0526] The average composition of the distillate across all fractions from each run is shown in Table 1.3. The material balance from each step is calculated as well as the overall yield of acetonitrile from each run.

[0527] The above results demonstrate the following aspects of batch distillation of waste products resulting from the synthesis of oligonucleotides.

[0528] 1. In the absence of chlorinated waste streams in the starting solution, acetonitrile purities of greater than 99% are achieved. This is due to the presence of a binary toluene / acetonitrile azeotrope that results in the proportion of toluene present in the distillate proportional to the amount present in the feed.

[0529] At a reflux ratio of 2.3, even when all of the halogenated waste stream is included in the feed, only trace amounts of pyridine are measured in the distillate and purity of greater than 99% can be achieved in the distillate. If the reflux ratio is reduced to less than 1, the concentration of pyridine in the distillate increases.

[0530] 3. As expected, when halogenated waste is included in the feed mixture during batch charging, water is at its highest concentration in the feed, distillate and bottoms. Water present in the feed will concentrate in the distillate due to the presence of several low boiling binary azeotropes between acetonitrile and water and toluene and water.

[0531] The above examples demonstrate the importance of isolating waste streams to provide an initial feed containing high concentrations of acetonitrile to a process where the acetonitrile is regenerated.

[0532] The above examples also demonstrate that if the feedstock is contaminated with toluene and water, additional separation steps are necessary to reduce the concentrations of both to be able to meet the acetonitrile purity specifications of greater than 99.9% and water specifications of less than 30 parts per million.

[0533] Furthermore, the above examples demonstrate the following:

[0534] 1. The utility of using packed columns to improve the separation of these compounds that are difficult to separate due to the low relative volatility between the compounds and acetonitrile.

[0535] 2. The usefulness of reflux ratio as an operating parameter to improve the purity of distilled acetonitrile.

[0536] Having identified the need to use additional processing steps to separate acetonitrile from the azeotrope forming impurities and to dehydrate the final product, the following examples demonstrate that specific separation techniques may be used to maximize the yield and purity of the recycled product, using continuous distillation as opposed to batch distillation operating at steady state.

[0537] Example 2 Table 2.1 below shows the results of several sequential experiments using different combinations of waste streams derived from an oligonucleotide production process.

[0538] The same equipment as described in Example 1 was used for these experiments, except that the batch reactor was replaced with a jacketed wiped film evaporator. The wiped film evaporator is a vertical device with an aspect ratio of about 8 to 1 and an internal diameter of 50 mm. The central rotating shaft is fitted with plastic wipers that function to distribute the incoming fluid as a thin layer on the inside surface of the device. The central shaft has a variable speed motor, but typically operates at 120 to 160 revolutions per minute. The fraction of the feed evaporated in the wiped film evaporator is a function of the temperature of the fluid circulating through the jacket, the rotational speed of the shaft, the feed rate in the column, and the operating pressure. The residence time in the wiped film evaporator is on the order of a few seconds, and the hold-up is on the order of a few grams.

[0539] The vapors produced in the evaporator flow upward into a packed column located at the top of the evaporator. The condenser at the top of the packed column is equipped with a condenser and a reflux splitter. A fraction of the condensate is returned to the top of the packing and the remainder is returned to an external collection tank as product.

[0540] The feed composition for each experiment is shown in Table 2.1. In experiments where chlorinated waste is added to the organic feed, the concentration of toluene is increased in the entire feed compared to experiments where it is not added. In experiments where halogenated waste is added to the organic feed, the concentration of pyridine is increased. In feeds where both chlorinated and halogenated waste are added to the organic feed, both toluene and pyridine have higher overall concentrations in the feed. Only 10% of the chlorinated and halogenated waste streams are added to the organic waste stream because past experiments have demonstrated problems associated with toluene and pyridine in the feed stream. For this reason, only 10% was added to measure the impact of contamination.

[0541] The operating conditions for the experiments are shown in Table 2.2. All experiments were carried out at a constant pressure of 200 mbar. Experiments 2.1-2.4 are carried out at a reflux ratio of 3, while experiments 2.5 and 2.6 are performed at a reflux ratio of 4. Experiments 2.5 and 2.6 are repeats of experiments 2.3 and 2.4 to demonstrate the benefit of increasing the reflux ratio to reduce the level of pyridine contamination in the distillate.

[0542] [Table 2.1]

[0543] [Table 2.2]

[0544] In experiments where chlorinated wastes were included in the feed, the concentration of toluene in the distillate changed little even when the reflux ratio was increased from 3 to 4, while the concentration of pyridine decreased when the reflux ratio was increased. The concentration of 2,6-lutidine also decreased when the reflux ratio was increased. The concentrations of low boilers such as diisopropylamine and acrylonitrile partitioned between the distillate and bottoms. The overall low concentrations of both make precise quantification of the partitioning difficult, but even at a reflux ratio of 4, both were still present in the distillate, indicating the need for further stages of purification to reach acetonitrile purity above 99.90 area %.

[0545] [Table 2.3]

[0546] [Table 2.4]

[0547] As with the batch experiments, the distillate produced from the continuous distillation has a proportional concentration of toluene as measured in the feed. Even in experiments where no chlorinated waste is combined in the feed, toluene is still present in the distillate at low levels also proportional to the feed. The distillate is also contaminated with low levels of light boilers such as diisopropylamine and acrylonitrile. Two of the experiments show a purity of greater than 99.90 area % on a water free basis only, with yields of greater than 90% by weight, but the levels of impurities are unacceptable, with water also present in the distillate in amounts well in excess of 30 ppm by weight.

[0548] Similar conclusions can be expressed for this example as those expressed for batch distillation in Example 1. Additionally, the benefits of using continuous distillation to maintain a product stream with constant purity can be appreciated. The inherent advantages of continuous processing, such as less capital investment, less downtime, and higher yields, can be appreciated.

[0549] Example 3 In this example, the feedstock is processed through all steps of the organic side of the process set forth in claim 1 and subsequently dehydrated to produce a product suitable for recycling to an oligonucleotide synthesis reaction. The organic waste stream from the reaction sequence is processed through four process steps to purify acetonitrile. A description of the steps is provided in Table 1.

[0550] [Table 3.1]

[0551] The equipment used for reproduction is the same as that described in Examples 1 and 2 above.

[0552] The general operating conditions and parameters for each stage of operation are listed in Table 3.2 (distillation 3.1-3.3) and Table 2 (drying step 3.4).

[0553] [Table 3.2]

[0554] [Table 3.3]

[0555] The raw material is available in two parts and the composition of each part is shown in Table 3.4.

[0556] [Table 3.4]

[0557] Table 3.5 shows the composition of the distillate and bottom fractions from distillation 3.1. Feed 1 corresponds to distillates 3.1-3.3 and bottoms 3.1, feed 2 corresponds to distillates 3.4-3.6 and bottoms 3.2. The reflux ratio of the process is 5 and the number of theoretical separation stages is about 14. Under these conditions, the purity of acetonitrile increases from about 90.0 area % (feed) to 99.80 area % (distillate). The main impurities in the distillate are acrylonitrile, toluene, diisopropylamine and small amounts of pyridine. Virtually all of the heavy boilers (acetic acid, dichloroacetic acid, pyridine, 2,6-lutidine) are split into the bottom product. 22% of the feed is separated into the bottoms and 78% into the distillate. The overall mass balance for this process was 99.2 wt % and the yield of acetonitrile was 85.6 wt % (also summarized in Table 3.6).

[0558] [Table 3.5]

[0559] [Table 3.6]

[0560] The water content in the distillate stream from distillate 3.1 was adjusted by adding water to increase the concentration to about 2 wt.%. Water was added to act as an entrainer to remove toluene in the next step.

[0561] The distillate from step 3.1 is treated according to the operating conditions and parameters listed in Table 3.2. Four bottoms and one distillate fractions are collected from this step with compositions shown in Table 3.7.

[0562] Approximately 98% of the toluene, 50% of the acrylonitrile and 100% of the diisopropylamine are separated into the distillate along with some acetonitrile and most of the water. All of the pyridine in the feed is found in the bottoms product from the column. Overall, 15.82% of the feed is separated into the distillate and 81.09% into the bottoms. The overall mass balance for this process was 96.9 wt% and the acetonitrile yield was 83.8 wt% (also summarized in Table 3.7).

[0563] [Table 3.7]

[0564] The distillate from distillation 3.2 is processed according to the operating conditions and parameters listed in Table 3.2. Two bottoms and two distillate fractions are collected from this step, with compositions shown in Table 3.8. The water content in the product from this step is reduced from an average of 3786 ppmW to 378 ppmW in the bottoms product. Along with water, toluene and acrylonitrile are further reduced, while traces of diisopropylamine are also separated. All of the pyridine in the feed is found in the bottoms product from the column. Overall, 11.49% of the feed is separated into the distillate and 86.85% into the bottoms. The overall mass balance of this step was 98.3 wt.% and the yield of acetonitrile was 89 wt.% (also summarized in Table 3.6).

[0565] [Table 3.8]

[0566] The bottoms product from distillation 3 is pumped through a molecular sieve column according to the operating conditions and parameters in Table 3.3. The product is collected in four fractions, the compositions of which are shown in Table 3.9.

[0567] [Table 3.9]

[0568] This example shows that acetonitrile can be reliably recycled from an initial purity of 90 area % to greater than 99.90 area % purity, and the water content can also be reduced to less than 30 ppmW.

[0569] The amount of water added to the feed to distillation 2 is well below the optimum amount for removing low boiling azeotropes from the feed. In general, more water in the feed will increase the efficiency of removal of toluene, acrylonitrile and diisopropylamine. An amount of water in excess of the concentration that results in a water concentration from the bottom of the column exceeding the azeotrope at the column operating conditions is preferred. However, water concentrations below this are acceptable, but not guaranteed.

[0570] It will be appreciated that the limited number of stages available in the experimental column will not be sufficient to completely remove the remaining impurities shown in Table 3.9. More separation stages combined with more water will allow the concentrations of the light azeotrope formers shown in Table 3.9 to be reduced well below the values ​​shown in Table 3.9.

[0571] Example 4 In this example, acetonitrile is processed through all stages on the organic side of the process as well as the aqueous side of the process, and the products are combined and subsequently dehydrated to produce a product suitable for recycling into an oligonucleotide synthesis reaction.

[0572] The aqueous stream is processed through two stages of distillation (Distillation 4.1) and then combined with the product from Distillation 4.2 as set forth in Table 4.1. From here, the product is processed through two stages of dehydration (Distillations 4.3 and 4.4) to arrive at the product herein.

[0573] [Table 4.1A]

[0574] [Table 4.1B]

[0575] Aqueous acetonitrile containing waste from the process containing 8.34 wt% acetonitrile is processed through the same distillation column described in Example 1 to concentrate the acetonitrile in the feed to a concentration of 91.43 wt% in the distillate with 1.95 wt% ethanol. The product is retained for further processing through azeotropic distillation along with the product from the organic lights distillation step. The compositions of the feed, distillate and bottoms are shown in Table 4.2.

[0576] [Table 4.2]

[0577] The organic waste stream is distilled in a continuous distillation column similar to the process described in Example 2. The original feed containing 87.19 area % is concentrated to 99.70 area % in the distillate stream. The major impurities in the distillate are toluene with small amounts of pyridine, acrylonitrile and ethyl acetate. Most of the heavy boilers are retained in the bottoms product. It is possible to reduce the pyridine concentration in the distillate by either reducing the distillate cut, increasing the reflux ratio, or increasing the number of separation stages in the column. The compositions of the feed, distillate and bottoms are shown in Table 4.3.

[0578] [Table 4.3]

[0579] The concentration of water in the distillate from the heavies distillation stage is 0.28 wt%. To remove the toluene present in the distillate during the lights distillation stage, water is added to the distillate to reach a ratio of 30 times the concentration of toluene present. This ratio ensures that most of the toluene is purged from the process in the form of a ternary azeotrope with water and acetonitrile. While this ratio is well below the expected ratio used in a large-scale process, the absence of small-scale pressure swing distillation plants meant that the water in the process needed to be minimized to facilitate dehydration using a single azeotropic distillation step combined with a dehydration step using molecular sieves. The lights distillation stage feed and product stream concentrations are summarized in Table 4.4. The organic concentration values ​​are listed in the table on an anhydrous basis. All impurities in the feed stream, except pyridine, are enriched in the distillate phase and depleted in the bottoms product. All of the diisopropylamine is found in the distillate.

[0580] [Table 4.4]

[0581] The bottom product from the light distillation step is combined with the distillation product from the aqueous heavies distillation step to for...

Claims

1. A method for recovering and / or purifying acetonitrile from waste acetonitrile produced during oligonucleotide synthesis, comprising using water as an entrainer in a distillation step to separate the acetonitrile from one or more impurities in the waste acetonitrile.

2. The method described in claim 1, wherein the water promotes separation of one or more impurities by forming one or more azeotropes with the impurities, the one or more azeotropes having boiling points lower than the boiling point of acetonitrile.

3. The method described in claim 1, wherein the one or more impurities are one or more organic impurities.

4. A ＊ ) introducing an organic waste feedstock (105, 205) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a distillation column (106, 206) to separate the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as vapors from the distillation column and condensed to produce a distillate (107, 207), and the second set of organic impurities are produced as a second distillation column bottoms (108, 208); B ＊ ) introducing said distillate (107, 207) into a water feed zone (109, 209) to produce a water-enriched acetonitrile stream (111, 210, 210a); C ＊ ) introducing the water-enriched acetonitrile stream (111, 210, 210a) into a second distillation column (112, 212) and separating the first set of organic impurities from the acetonitrile, wherein acetonitrile is produced as second distillation column bottoms (113, 213); Including; 2. The method of claim 1, whereby recovered and / or purified acetonitrile is obtained. A') introducing an organic waste feedstock (301) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a first mixing zone (303) and enriching it with water to produce a water-enriched acetonitrile stream (303a) containing said impurities; B') introducing the water-enriched acetonitrile stream (303a) into a first distillation column (304) to separate the acetonitrile and the first set of organic impurities having a boiling point lower than that of acetonitrile from the second set of organic impurities having a boiling point higher than that of acetonitrile, wherein the acetonitrile and the first set of organic impurities are withdrawn as vapors from the first distillation column and condensed to produce a first distillate (306), and the second set of organic impurities are produced as first distillation column bottoms (305); C') introducing the first distillate (306) containing the acetonitrile and the first set of organic impurities from step B') into a water feed zone (307) and enriching it with water to produce a water-enriched acetonitrile stream (307a); D') introducing said first distillate (306) into a second distillation column (308) and separating said acetonitrile from said first set of organic impurities, said acetonitrile being produced as second distillation column bottoms (309); Including; 2. The method of claim 1, whereby recovered and / or purified acetonitrile is obtained.

6. A') introducing into a first mixing zone (303) and combining therein an organic waste feedstock (301) comprising acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile, and an aqueous waste feedstock (302) comprising acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile; B') introducing the acetonitrile waste feedstock into a first distillation column (304) to separate the acetonitrile and the first set of organic and aqueous impurities having a boiling point lower than that of acetonitrile from the second set of organic and aqueous impurities having a boiling point higher than that of acetonitrile, wherein the acetonitrile and the first set of organic and aqueous impurities are withdrawn as vapors from the first distillation column and condensed to produce a first distillate (306) and the second set of organic and aqueous impurities are produced as first distillation column bottoms (305); C') introducing said first distillate (306) containing acetonitrile and a first set of organic and aqueous impurities into a water feed zone (307) and enriching it with water to produce a water-enriched acetonitrile stream (307a); D') introducing the water-enriched acetonitrile stream (307a) into a second distillation column (308) and separating the acetonitrile from the first set of organic and aqueous impurities, wherein the acetonitrile is produced as second distillation column bottoms (309); Including; 2. The method of claim 1, whereby recovered and / or purified acetonitrile is obtained.

7. 5. The method of claim 4, wherein the second distillation column bottoms (309) comprises an acetonitrile / water azeotrope.

8. (i) Water is ＊ to produce a water-enriched acetonitrile stream (111, 210). (ii) Process B ＊ is combined with an acetonitrile stream containing water to produce a water-enriched acetonitrile stream (210a). (iii) The method of claim 4, wherein the acetonitrile stream containing water is obtained from the distillation of aqueous waste feedstock produced during oligonucleotide synthesis. (i) A method according to claim 4, comprising: A1) introducing an aqueous waste feedstock (101) containing acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile into a first distillation column (102) and separating the acetonitrile and first set of impurities from the second set of impurities, wherein the acetonitrile and first set of impurities are withdrawn as vapors from the first distillation column and condensed to produce a first distillate (103), and the second set of impurities are produced as first distillation column bottoms (104); B1) introducing an organic waste feedstock (105) containing acetonitrile, a first set of organic impurities having a boiling point lower than that of acetonitrile, and a second set of organic impurities having a boiling point higher than that of acetonitrile into a second distillation column (106) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as vapors from the second distillation column and condensed to produce a second distillate (107), and the second set of organic impurities are produced as second distillation column bottoms (108); C1) introducing said second distillate (107) into a water feed zone (109) and enriching it with water to produce a water-enriched acetonitrile stream (111); D1) introducing the water-enriched acetonitrile stream (111) into a third distillation column (112) and separating the first set of organic impurities from the acetonitrile, wherein the acetonitrile is produced as third distillation column bottoms (113); E1) feeding the first distillate (103) of step A1 and the third distillation column bottoms (113) of step D1 to a mixing zone (116) where they are combined to produce an acetonitrile-rich stream (110); Including; a process whereby recovered and / or purified acetonitrile is obtained, or (ii) The method according to claim 4, A) introducing an aqueous waste feedstock (201) containing acetonitrile, a first set of aqueous impurities having a boiling point lower than acetonitrile, and a second set of aqueous impurities having a boiling point higher than acetonitrile into a first distillation column (202) and separating the acetonitrile and first set of impurities from the second set of impurities, wherein the acetonitrile and first set of impurities are withdrawn as vapors from the first distillation column and condensed to produce a first distillate (203), and the second set of impurities are produced as first distillation column bottoms (204); B) introducing an organic waste feedstock (205) containing acetonitrile, a first set of organic impurities having a boiling point lower than acetonitrile, and a second set of organic impurities having a boiling point higher than acetonitrile into a second distillation column (206) and separating the acetonitrile and the first set of organic impurities from the second set of organic impurities, wherein the acetonitrile and the first set of organic impurities are withdrawn as vapors from the second distillation column and condensed to produce a second distillate (207), and the second set of organic impurities are produced as second distillation column bottoms (208); C) feeding the first distillate (203) of step A and the second distillate (207) of step B into a water supply area (209); C(i) combining therein to produce a water-enriched acetonitrile stream (210a); or C(ii) combining therein and enriching with water to produce a water-enriched acetonitrile stream (210); D) introducing the water-enriched acetonitrile stream (210, 210a) into a third distillation column (212) and separating the first set of impurities from the acetonitrile, wherein the acetonitrile is produced as third distillation column bottoms (213); Including; A method whereby recovered and / or purified acetonitrile is obtained.

10. a) Step A ＊ The distillation column operates in the range of 50 to 980 mbar, for example, 100 to 300 mbar. b) Process C ＊ The distillation column operates in the range of 100 to 980 mbar, for example, 900 to 980 mbar. c) the distillation column of step B1 operates in the range of 50 to 980 mbar, for example, 100 to 300 mbar; d) the distillation column of step A1 operates in the range of 200 to 980 mbar, for example, 400 to 500 mbar; e) the distillation column of step D1 operates in the range of 100 to 980 mbar, for example, 900 to 980 mbar; f) the distillation column of step A operates in the range of 200 to 980 mbar, for example, 400 to 500 mbar; g) the distillation column of step B operates in the range of 50 to 980 mbar, for example 100 to 300 mbar, and / or h) The process according to claim 9, wherein the distillation column of step D operates in the range of 100 to 980 mbar, for example 900 to 980 mbar.

11. Process C ＊ 11. The method of claim 10, wherein step C1 or step C further comprises mixing the distillate (107, 207) with a recycled acetonitrile stream (122, 221) comprising an acetonitrile / water azeotrope and ethanol, the recycled acetonitrile stream (122, 221) being a by-product of a further processing step.

12. 10. The method of claim 9, wherein the distillation column bottoms (113, 213, 309, 312) or the acetonitrile-rich stream (110) is further treated to reduce the water content of the acetonitrile to less than 30 parts per million.

13. 13. The method of claim 12, further comprising introducing the distillation column bottoms (113, 213) or the acetonitrile-rich stream (110) into a fourth distillation column (117, 216), wherein the water content of the acetonitrile-rich stream is reduced by use of pressure swing distillation to recover acetonitrile having a water content of less than 30 parts per million.

14. 10. The method of claim 1, wherein the recovered acetonitrile has a purity of at least 99.90% and a water content of less than 30 parts per million as measured by gas chromatography.

15. The method of claim 1 , wherein the oligonucleotide synthesis is solid phase oligonucleotide synthesis.

16. 16. The method of claim 15, wherein the oligonucleotide is an antisense oligonucleotide, an aptamer, an siRNA, an miRNA, or a gapmer.

17. A system for purifying and / or recovering acetonitrile from waste acetonitrile, comprising: (i) a first distillation column (106, 206, 304) configured to receive the acetonitrile organic waste stream (105, 205, 301) and produce a first distillate (107, 207, 306) comprising acetonitrile and a first set of organic impurities, the first distillation column (106, 206, 304) having a condenser coupled to an upper portion of the first distillation column; and a second distillation column (112, 212, 308) configured to receive the first distillate (107, 207, 306), separate a first set of organic impurities from the acetonitrile, and produce purified acetonitrile as a second distillation column bottoms; The system comprises: said first distillate (107, 207, 306) is first enriched with water before reaching said second distillation column (112, 212, 308) to obtain purified and / or recovered acetonitrile; or a system (105, 205, 301) further comprising a water supply area (109, 209, 303, 307) arranged such that the waste acetonitrile (301) is enriched with water before reaching the first distillation column (304) to obtain purified and / or recovered acetonitrile; or (ii) a first distillation column (102) configured to receive the aqueous acetonitrile waste stream (101) and produce a first distillate (103) comprising acetonitrile and a first set of impurities, the first distillation column (102) having a condenser coupled to an upper portion of the first distillation column (102); a second distillation column (106) configured to receive the acetonitrile organic waste stream (105) and produce a second distillate (107) comprising acetonitrile and a first set of impurities, the second distillation column (106) having a condenser coupled to an upper portion of the second distillation column (106); and a third distillation column (112) configured to receive the second distillate (107) and separate a first set of organic impurities from the acetonitrile to produce purified acetonitrile as a third distillation column bottoms; the system (100) further comprising a water feed zone (109) arranged such that the second distillate (107) is first enriched with water before reaching the third distillation column (112) to obtain purified and / or recovered acetonitrile; and a mixing zone (116) configured to mix the first distillate (103) from the first distillation column (102) and the third distillation column bottoms (113) from the third distillation column (112), or (iii) a first distillation column (202) configured to receive the aqueous acetonitrile waste stream (201) and produce a first distillate (203) comprising acetonitrile and a first set of impurities, the first distillation column (202) having a condenser coupled to an upper portion of the first distillation column (202); a second distillation column (206) configured to receive the acetonitrile organic waste stream (205) and produce a second distillate (207) comprising acetonitrile and a first set of impurities, the second distillation column (206) having a condenser coupled to an upper portion of the second distillation column (206); and a third distillation column (212) configured to receive the first and second distillates (203, 207), separate a first set of impurities from the first and second distillates, and produce purified acetonitrile as a third distillation column bottoms (213); the system (200) further comprising a water supply section (209) arranged such that the first and second distillates (203, 207) are first mixed and enriched with water before reaching the third distillation column (212) to obtain purified and / or recovered acetonitrile; or (iv) 1. A system (300) for purifying and / or recovering acetonitrile from waste acetonitrile (301, 302) generated during an oligonucleotide manufacturing process, comprising: a first distillation column (304) configured to receive the mixed acetonitrile aqueous and organic waste stream and to produce a first acetonitrile distillate (306) comprising acetonitrile and a first set of impurities, the first distillation column (304) having a condenser connected to an upper portion of the first distillation column (304), e.g., connected to an overhead stream; a second distillation column (308) configured to receive the first acetonitrile distillate (306) and produce a second acetonitrile distillate (309) comprising an acetonitrile / water azeotrope, the second distillation column (308) having a condenser connected to an upper portion of the second distillation column (308), e.g., connected to an overhead stream; and a third distillation column (311) configured to receive the second acetonitrile distillate (309) and separate acetonitrile from the acetonitrile / water azeotrope to produce acetonitrile as a third distillation column bottoms (312); the system is configured such that the first acetonitrile distillate (306) is first enriched with water (307) before reaching the second distillation column (308); and / or The system (300) further comprises a water supply area (303, 307) arranged such that the organic waste acetonitrile (301) is first enriched with water by mixing the aqueous acetonitrile and organic waste streams (303) before reaching the first distillation column (304) to obtain purified and / or recovered acetonitrile.

18. (i) at least a fourth distillation column (117, 216) configured to receive the third distillation column bottoms (113, 213) of the third distillation column (112, 212) and to produce a fourth distillate (118, 217) comprising acetonitrile; and (ii) a fifth distillation column (120, 219) configured to receive the fourth distillate (118, 217) from the fourth distillation column (117, 216) and to produce a fifth distillation column bottoms (121, 220) product comprising high purity acetonitrile; The system (100, 200) of claim 17, further comprising:

19. 20. The system of claim 17, further comprising a drying section configured to reduce the water content in the acetonitrile product to less than 30 parts per million.

20. 18. The system of claim 17, wherein the waste acetonitrile is industrial scale.

21. 10. A method for synthesizing oligonucleotides and / or for washing oligonucleotides or support-bound oligonucleotides, comprising recovering and / or purifying acetonitrile from waste acetonitrile according to claim 1 and using at least a portion of the recovered and / or purified acetonitrile in a process for synthesizing oligonucleotides and / or for washing oligonucleotides or support-bound oligonucleotides.

22. 1. Acetonitrile for use in oligonucleotide production, having a purity of at least 99.90% as measured by gas chromatography, said acetonitrile being recovered from oligonucleotide synthesis waste by the method of claim 1, and said impurities of said acetonitrile comprising pyridine and toluene.

Images