Process for the preparation of diols

Abstract

This invention provides a method for separating diols from a product stream. The method includes the following steps: i) separating the product stream containing three or more C2-C6 diols, C3-C6 sugar alcohols, and C4-C6 polyols having at least three hydroxyl groups, as well as a catalyst, to produce a first stream containing the three or more C2-C6 diols; ii) separating the first stream containing the three or more C2-C6 diols into a) a second stream containing the first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, and b) a third stream containing two or more diols; iii) hydrogenating the second stream containing the first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups to provide a purified diol stream.

Description

TECHNICAL FIELD

[0001] The present invention relates to a purification process for preparing diols meeting product specifications for color bodies and radiation transmission, more particularly to a purification process for preparing monoethylene glycol (MEG) meeting product specifications for color bodies and radiation transmission. BACKGROUND

[0002] Ethylene glycol and propylene glycol are valuable materials with a variety of commercial applications, for example as heat transfer media, antifreeze agents, and precursors to polymers such as polyethylene terephthalate (PET). On an industrial scale, ethylene glycol and propylene glycol are typically prepared by hydrolysis of the corresponding alkylene oxides, which are oxidation products of ethylene and propylene produced from fossil fuels. Ethylene glycol has a wide range of uses, including this very important use as a basic raw material for the production of polyesters, which are used to produce polyester fibers, ethylene glycol in this context often being referred to as fiber-grade ethylene glycol product.

[0003] In recent years, there has been an increasing focus on producing chemicals, including diols, from renewable feedstocks such as sugar materials. Current processes for converting sugars to diols center around hydrogenation / hydrogenolysis processes, as described in Angew. Chem. Int. Ed. 2008, 47, 8510-8513. For example, US 2011 / 312050 describes a continuous process for catalytic production of polyols from cellulose, in which cellulose is contacted with hydrogen, water, and a catalyst to produce an effluent stream comprising at least one polyol.

[0004] CN 102643165 relates to a catalytic process for reacting a sugar in aqueous solution with hydrogen in the presence of a catalyst to produce a polyol.

[0005] As with many chemical processes, the product streams in these reactions contain a number of desired materials, diluents, by-products, and other undesired materials. In order to provide a high value process, the desired product or products must be able to be obtained from the product stream in high purity, with a high percentage recovery of each product and with as little energy and complex equipment used as possible.

[0006] One measure used to measure the quality of fiber-grade ethylene glycol product is UV light transmission at 220 nm, as this affects the gloss and color of downstream polyester products. The prior art teaches the use of ion exchange resins as catalysts to refine and purify ethylene glycol, for example US Patent 6,242,655 describes a process using a strongly acidic cation exchange resin as catalyst, in which the content of aldehyde groups in the ethylene glycol product is reduced from 20 ppm to 5 ppm or less after treatment. However, a drawback of the prior art process is that the content of aldehyde groups in the ethylene glycol product can only be removed to a maximum of about 2 ppm, but at this point the UV light transmission at 220 nm of the ethylene glycol product is still not at a very desirable value.

[0007] Therefore, improving the UV transmittance of carbohydrate-based ethylene glycol products and further ensuring product quality would be beneficial. An improved method is needed that is suitable for recovering high-purity glycols, preferably meeting UV transmittance standards. Summary of the Invention

[0008] This invention provides a method for separating diols from a product stream. The method includes the following steps: i) separating the product stream containing three or more C2-C6 diols, C3-C6 sugar alcohols, and C4-C6 polyols having at least three hydroxyl groups, as well as a catalyst, to produce a first stream containing the three or more C2-C6 diols; ii) separating the first stream containing the three or more C2-C6 diols into a) a second stream containing the first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, and b) a third stream containing two or more diols; iii) hydrogenating the second stream containing the first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups to provide a purified diol stream. Attached Figure Description

[0009] The method of the present invention can be better understood by referring to the following preferred embodiments and the accompanying drawings referenced therein, wherein:

[0010] Figure 1 A block flowchart of one embodiment of the method of the present invention is shown;

[0011] Figure 2 A block flowchart illustrating an alternative embodiment of the method of the present invention is shown; and

[0012] Figure 3 A UV transmission specification for an embodiment of the present invention is shown. Detailed Implementation

[0013] The following description of the variations is illustrative in nature and is in no way intended to limit the scope of this disclosure, its application, or its uses. The descriptions and examples given herein are for the purpose of illustrating various embodiments of this disclosure and should not be construed as limiting the scope and applicability of this disclosure.

[0014] The terminology and wording used herein are for descriptive purposes and should not be construed as limiting the scope. Language such as “including,” “contains,” “has,” “includes,” or “involves,” and variations thereof, is intended to be broad and encompass the subjects listed thereafter, equivalents, and additional subjects not listed.

[0015] Furthermore, as used herein, any reference to “one embodiment” or “implementation” means that a particular element, feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment. The phrase “in one embodiment” appearing in various places in the specification does not necessarily refer to the same embodiment.

[0016] The embodiments described herein depict methods for separating diols from a product stream. In some embodiments, the product stream originates from a carbohydrate hydrogenolysis process. Such product streams from a hydrogenolysis process of a carbohydrate-containing feedstock contain certain desired diols as well as byproducts containing diols and other materials. Carbohydrates include sugars, including monosaccharides such as glucose, fructose, and xylose; disaccharides such as sucrose; and polysaccharides such as starch, cellulose, and hemicellulose.

[0017] The product stream may contain three or more C2-C6 diols. Preferably, the separated diols and the three or more C2-C6 diols in the product stream are selected from C2-C6 diols. As used herein, the term diol has its usual meaning, i.e., a diol in which two hydroxyl groups are present on adjacent carbon atoms. Preferably, the diol is ethylene glycol (MEG) and the product stream contains MEG and 1,2-butanediol (1,2-BDO), or the diol is propylene glycol (MPG) and the product stream contains MPG and 2,3-pentanediol. Most preferably, the diol is ethylene glycol (MEG) and the product stream contains MPG and 1,2-butanediol (1,2-BDO). The product stream may also contain three or more C2-C6 diols and one or more components selected from C3-C6 sugar alcohols and C4-C6 polyols having at least three hydroxyl groups in their molecules, as well as an optional catalyst.

[0018] Three or more C2 to C6 diol product streams may be derived from any diol process, such as, but not limited to, oil routes, i.e., direct or process hydration, hydrogenation of oxalate esters, or hydrogenolysis of carbohydrate-containing feedstocks. In other embodiments, the product stream may be any diol stream that does not meet product specifications regarding chromophores and radiation transmission.

[0019] Typically, the product stream from a hydrogenolysis process of a carbohydrate-containing feedstock contains at least MEG, MPG, and 1,2-BDO as diols. Other diols, such as 2,3-BDO, pentanediol, hexanediol, and heptanediol, may also be present.

[0020] In addition to three or more C2-C6 diols, the product stream from the hydrogenolysis of carbohydrates can contain any composition of oxygenated compounds, hydrocarbons, catalysts, degradation products, and gases. The types and concentrations of compounds depend on the carbohydrate-containing feedstock and various hydrogenation and hydrogenolysis conversion conditions, including catalysts, reaction conditions such as temperature, pressure, and carbohydrate concentration.

[0021] In one embodiment, the product stream comprises at least a mixture containing MEG and 1,2-BDO. Other materials, such as MPG and other light diols, may be present in the mixture containing MEG and 1,2-BDO. In this embodiment, the mixture containing MEG and 1,2-BDO preferably has a MEG:1,2-BDO weight ratio of at least 3:2. More preferably, the MEG:1,2-BDO weight ratio is at least 5:1. Most preferably, the MEG:1,2-BDO weight ratio is at least 20:1.

[0022] In another embodiment, the product stream comprises at least a mixture containing MPG and 2,3-pentanediol. Other materials, such as light diols, may be present in the mixture containing MPG and 2,3-pentanediol. In this embodiment, the mixture containing MPG and 2,3-pentanediol preferably has an MPG:2,3-pentanediol weight ratio of at least 3:2. More preferably, the MPG:2,3-pentanediol weight ratio is at least 5:1. Most preferably, the MPG:2,3-pentanediol weight ratio is at least 20:1.

[0023] In one embodiment, a method for separating diols from the aforementioned product stream is described. The method includes the steps of: (i) separating a product stream containing three or more C2-C6 diols, C3-C6 sugar alcohols, and C4-C6 polyols having at least three hydroxyl groups, along with a catalyst, to produce a first stream containing three or more C2-C6 diols; (ii) separating the first stream containing three or more C2-C6 diols into a) a second stream containing the first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, and b) a third stream containing two or more diols; and (iii) hydrogenating the second stream containing the first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups to provide a high-purity diol stream. In some embodiments, the high-purity diols meet product specifications regarding chromophores and radiation transmission.

[0024] Preferably, the separation step (i) of the above method is an evaporation step (i). Preferably, the evaporation step includes providing a product stream to a distillation column or flash unit. The separation step provides a first stream containing three or more C2-C6 diols. In some embodiments, when the separation step is the evaporation step (i), the evaporation can occur at a temperature in the range of about 120°C to about 250°C, preferably in the range of about 150°C to about 230°C, more preferably in the range of about 180°C to about 210°C, and most preferably below 200°C, the temperature being measured as the temperature of the bulk liquid in the reboiler (bottom of the column). In some embodiments, the evaporation step (i) can occur at a pressure in the range of about 0.1 kPa to about 2000 kPa. In some embodiments, the evaporation step (i) can have a theoretical plate number varying in the range of about 1 to about 140, or it can be a flash vessel without trays or packing, which may be equipped with a demister to remove entrained droplets in the gas phase.

[0025] The separation step (ii) of the above method includes separating the first stream into a second stream and a third stream. The second stream contains a first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, and the third stream contains two or more diols.

[0026] Separation step (ii) can be carried out in one or two distillation columns. In embodiments using a single distillation column, the single distillation column is operated at a temperature in the range of 100°C to 300°C and a pressure in the range of 0.1 kPa to 2000 kPa to produce a second stream as a bottom stream containing a first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, and a third stream as a top stream containing two or more diols, which are removed from the distillation column. In some embodiments, the third stream may be an azeotrope of MEG and 1,2-BDO or an azeotrope of MPG and 2,3-BDO. The second stream is fed to the hydrogenation step (iii) disclosed above. The third stream is subjected to one or more fractionation steps to produce the desired product as a pure product stream.

[0027] A single distillation column can be any suitable type of column known in the art, and can be equipped with trays or structured or unstructured packing. The theoretical number of trays can vary from 3 to 140, and can be easily determined by those skilled in the art based on simple economic optimization experiments.

[0028] In embodiments using two distillation columns, a first feed stream containing three or more C2-C6 diols is provided to a first distillation column, which is an extractive distillation column. The extractive distillation column can be any suitable type of column known in the art and can be equipped with trays or structured or unstructured packing. The theoretical plate number can vary from 3 to 140 and can be readily determined by those skilled in the art based on simple economic optimization experiments.

[0029] The extractant is fed into the extractive distillation at or above the location where the first feed stream is provided. Preferably, the extractant is provided at or below the top of the first distillation column on several trays.

[0030] The extractant is selected from C3-C6 sugar alcohols, C4-C6 polyols having at least three hydroxyl groups in their molecules, and mixtures thereof. Sugar alcohols have the general formula HOCH2(CHOH)nCH2OH. Suitable sugar alcohols include glycerol, erythritol, threitol, araitol, xylitol, ribitol, mannitol, sorbitol, galactitol, and idotitol. Although some of these sugar alcohols may be solids at room temperature, under the pressure and composition suitable for the extractant mixture, they are used as liquids at suitable temperature and pressure in the method of the present invention. In one embodiment, the extractant is glycerol, which may be at least 50 w / w% of the extractant feed mixture entering the distillation column.

[0031] Polyols that can be used as extractants include glycerol, pentaglycerol, pentaerythritol, hexanetriol, hexanetriol, and hexanepentol.

[0032] Preferably, the amount of extractant added is such that the weight ratio of the feed containing the extractant to the mixture containing at least one C2-C7 diol is from about 1:2 to about 20:1. In some embodiments, based on the total weight of the feed / mixture, the weight ratio of the feed containing the extractant to the mixture containing at least one C2-C7 diol is at least 0.05:1, more preferably at least 0.1:1, and even more preferably at least 0.25:1. Preferably, based on the total weight of the feed / mixture, the weight ratio of the feed containing the extractant to the first mixture containing at least one C2-C7 diol is at most 10:1, more preferably at most 5:1, even more preferably 2:1, and even more preferably at most 1.5:1.

[0033] Extractive distillation in the first distillation column is carried out at a temperature of 50°C to 300°C, preferably 100°C to 250°C, and a pressure of 0.1 kPa to 2000 kPa. Typically, a pressure of at least 1 kPa is preferred for economic reasons, and more preferably at least 5 kPa for the same reason. The pressure is at most 2000 kPa, preferably at most 200 kPa, and more preferably at most 120 kPa. It will be apparent to those skilled in the art that suitable conditions can be achieved by varying the temperature and pressure relative to each other.

[0034] From the extractive distillation column, the stream containing the first diol and possible unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, as well as the extractant, is removed as the bottom stream, and the top stream containing two or more diols is removed from the top of the column.

[0035] The top stream, containing two or more C2-C7 diols, is removed from the first distillation column above the extractant feed point. In the separation of MEG and 1,2-BDO, the top stream will contain 1,2-BDO; in the separation of MPG and 2,3-pentanediol, the top stream will contain 2,3-pentanediol. Preferably, the top stream is removed from the first distillation column as a condensed overhead stream. The top stream may contain other diols, such as MPG, 2,3-BDO, pentanediol, hexanediol, and heptanediol. Preferably, the top stream is subjected to one or more fractionation steps to produce the desired product as a pure product stream.

[0036] The bottom stream from the first distillation column, containing a first diol and possibly unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, along with an extractant, is fed to a second distillation column. The second distillation column produces a top stream containing a first diol (preferably MEG) and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, and a bottom stream containing an extractant. This distillation is preferably carried out at the same or lower pressure as the extractive distillation step (in the first distillation column) to limit the temperature in the reboiler and avoid or minimize potential product degradation. Distillation in the second distillation column is carried out at a temperature of 120°C to 300°C, preferably 150°C to 250°C. Typically, for economic reasons, it is preferred that the second distillation column be at a pressure of at least 1 kPa, and more preferably at least 5 kPa for the same reason. The pressure is at most 2000 kPa, preferably at most 200 kPa, and more preferably at most 120 kPa. It will be apparent to those skilled in the art that suitable conditions can be achieved by varying the temperatures and pressures associated with each other. In some embodiments where the first diol is MEG, it is suitable that the diol content of the top feed stream comprises at least 95% by weight MEG, preferably at least 98% by weight MEG, more preferably at least 99% by weight MEG, even more preferably at least 99.5% by weight MEG, and most preferably at least 99.9% by weight MEG.

[0037] The third stream, which is the bottom feed stream removed from the second distillation column, is the used extractant stream. At least a portion of the used extractant stream can then be recycled back to the first distillation column as at least a portion of an additional feed containing extractant. Any remaining heavy materials already present in the product stream containing three or more C2-C6 diols may also be present in the extractant stream to be recycled. If the product stream containing three or more C2-C6 diols originates from the hydrogenolysis of a carbohydrate-containing feedstock, such heavy materials may be sugar alcohols in terms of their structure, boiling point, and other physical properties, and can be recycled along with the remainder of the extractant stream.

[0038] A portion of the used extractant stream can be removed as effluent to prevent the accumulation of heavy materials. In this embodiment, fresh extractant is supplied to the first distillation column to replenish the required amount of extractant. The fresh extractant should be supplied to the first distillation column at or above the height of the used extractant stream. Optionally, at least a portion of the recirculated stream may undergo further processing steps to further improve its purity.

[0039] Following separation step (ii), a second stream comprising the first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups is fed to the hydrogenation step (iii) disclosed above to remove any impurities, such as oxygen-containing compounds, that may prevent the first diol from passing through the product specifications regarding chromaticity and radiation transmission.

[0040] In some embodiments, the hydrogenation step (iii) can be carried out by any suitable manner known to those skilled in the art. In some embodiments, the hydrogenation reaction is carried out at a temperature ranging from about 20°C to about 300°C and a pressure ranging from about 0.5 bar to about 250 bar. In one arrangement, hydrogenation can be carried out according to the method described in U.S. Patent 6,137,016, which is incorporated herein by reference. The hydrogenation step provides a high-purity diol stream that meets product specifications regarding chromophore and UV radiation transmittance. For example, the standard test for UV transmittance of MEG is ASTM E2193. Those skilled in the art will be able to determine the standard test for UV transmittance of other diols of interest.

[0041] The high-purity diols used herein refer to diols with a purity of at least 99% by weight, preferably at least 99.5% by weight, more preferably at least 99.6% by weight, and most preferably at least 99.9% by weight. A qualified diol stream will meet product specifications regarding chromophores and radiation transmittance. Preferably, in embodiments where the qualified diol is a MEG, the qualified MEG is suitable for use as a fiber-grade MEG. Fiber-grade MEGs must meet the transmittance requirements at four different wavelengths (in nm) as shown in Table 1 below:

[0042] Table 1. Specifications of Fiber Grade MEG

[0043]

[0044]

[0045] Any suitable hydrogenation catalyst can be used and can be determined by those skilled in the art. The hydrogenation catalyst is preferably a hydrogenation catalyst containing IUPAC updated Group 7, 8, 9, 10, and 11 metals. Suitable catalysts containing IUPAC updated Group 7, 8, 9, 10, and 11 metals typically contain about 0.1 wt% to about 2 wt% of IUPAC updated Group 7, 8, 9, 10, and 11 metals. Examples of IUPAC updated Group 7, 8, 9, 10, and 11 metals include nickel, palladium, platinum, rhodium, iridium, rhenium, etc., and mixtures of two or more thereof. The IUPAC updated Group 7, 8, 9, 10, and 11 metals are deposited on an inert support, such as graphite, alumina, silica-alumina, silica, zirconium oxide, thorium oxide, diatomaceous earth, etc. A particularly preferred catalyst is a nickel catalyst. It may contain, for example, about 10 wt% to about 60 wt% or more of nickel. Another type is a carbon-supported palladium catalyst, which preferably contains about 0.1% to about 4% palladium by weight.

[0046] Although hydrogenation can be carried out in the gas phase, it can be conveniently performed as a liquid-phase reaction using a catalyst slurry or, more preferably, a fixed-bed catalyst. When operating with a fixed-bed catalyst, the catalyst particles preferably have a particle size in the range of about 0.5 mm to about 5 mm. The particles can be any convenient shape, such as spherical, pellet, annular, or saddle-shaped.

[0047] When using a fixed-bed catalyst, the reactor can be a shell-and-tube reactor, which can operate isothermally. However, it is preferably an adiabatic reactor. Using an adiabatic reactor is advantageous because its capital cost is much lower than that of a shell-and-tube reactor, and it is generally easier to load the selected catalyst.

[0048] Hydrogenation can be carried out under any suitable reaction conditions. In one arrangement, hydrogenation can be carried out at elevated temperatures, for example, from about 30°C to about 170°C. The feed temperature of the hydrogenation zone can be from about 50°C to about 125°C. Hydrogenation can be carried out at elevated pressures. Suitable pressures include, for example, from about 50 psia (about 3.45 bar) to about 2000 psia (about 137.90 bar), preferably from about 150 psia (about 10.34 bar) to about 1000 psia (about 68.95 bar).

[0049] A second feed stream comprising a first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups can be supplied to the hydrogenation reactor at a liquid hourly space velocity of about 0.1 h⁻¹ to about 4.0 h⁻¹, preferably about 0.5 h⁻¹ to about 1.5 h⁻¹.

[0050] The inert diluent can be mixed with the feed before entering the hydrogenation zone. In one arrangement, the inert diluent can be a recycled material from the outlet of the hydrogenation zone. In this arrangement, the ratio of inert diluent to fresh feed is preferably in the range of about 1:1 to about 1000:1.

[0051] Now turn to the attached image. Figure 1 A block flowchart illustrating one embodiment of the method of the present invention is shown. The method 100 for separating diols from a product stream includes supplying a product stream 101 to a first separation unit 102 having three or more C2-C6 diols, C3-C6 sugar alcohols, and C4-C6 polyols having at least three hydroxyl groups in their molecules, as well as a catalyst as feed. The separation unit 102 may be a flash distillation unit or a distillation column. The separation unit 102 produces a heavy stream 104 from the product stream 101 and a first stream 103 comprising three or more C2-C6 diols and possible unsaturated hydrocarbons and / or one or more compounds having carbonyl groups.

[0052] The first feed stream 103 is fed to the distillation unit 105 to produce a second feed stream 106 comprising a first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, and a third feed stream 107 comprising two or more diols. In some embodiments, the distillation unit 105 may be one or two distillation columns.

[0053] A second feed stream 106, comprising a first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, is fed to a hydrogenation unit 108 to provide a high-purity diol feed stream 110.

[0054] Figure 2 A block flowchart illustrating an alternative embodiment of the method of the present invention is shown. The method 200 for separating diols from a product stream includes supplying a product stream 201 to a first separation unit 202 having three or more C2-C6 diols, C3-C6 sugar alcohols, and C4-C6 polyols having at least three hydroxyl groups in their molecules, as well as a catalyst as feed. The separation unit 202 may be a flash distillation unit or a distillation column. The separation unit 202 produces a heavy stream 230 from the product stream 201 and a first stream 203 comprising three or more C2-C6 diols and possible unsaturated hydrocarbons and / or one or more compounds having carbonyl groups.

[0055] The first feed stream 203 is fed to the first distillation unit 205 to produce a second feed stream 206 containing a first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, and a third feed stream 214 containing two or more diols.

[0056] The extractant stream 204 is also provided to the first distillation column 205 at or above the same height as the first feed stream 203. In some embodiments, the first distillation column 205 operates at a temperature ranging from 100°C to 300°C and a pressure ranging from 0.1 kPa to 2000 kPa. The bottom feed stream 206 is distilled in the second distillation column 215, which is operated to provide the first diol feed stream as the overhead stream 220. The remaining extractant is removed as the bottom feed stream 207 and can be recycled to provide the used extractant 208 to the first distillation column 205. The effluent stream 209 is removed from the extractant recirculation stream to prevent the accumulation of heavy materials.

[0057] The overhead stream 220, comprising a first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, is supplied to the hydrogenation reactor 208 to provide a high-purity diol stream 210.

[0058] Example

[0059] The implementation scheme is further illustrated by the following non-limiting examples.

[0060] Comparative Example 1 - Separation and Extractive Distillation of Mixed Diols

[0061] As described in WO2018 / 064245, a mixture of diols was obtained by the conversion of glucose, the entire disclosure of which is incorporated herein by reference. A total of 165.2 kg of reactor effluent was obtained from a reactor feed comprising a total of 19.6 kg of glucose and 145.6 kg of water.

[0062] Water and light components, such as trace amounts of methanol and ethanol, were removed in ten separate batches using rotary evaporation that simulated flash evaporation. 144.9 kg of liquid fraction, primarily water, was collected and discarded, leaving the organic fraction.

[0063] Subsequent rotary evaporation of the organic fraction yielded a mixed glycol fraction of 16.9 kg. Mass balances of ten individual batches indicated a loss of approximately 1.7 kg of glycol in the water fraction, while the mixed glycol fraction contained up to 2.4 kg of water. These mass balances demonstrate that a total of 14.5 kg of glycol was recovered from the obtained 16.9 kg mixed glycol fraction (89.5% w of the total mixed glycols produced).

[0064] Subsequent rotary evaporation of the mixed diol fraction yielded a residual fraction of 3.4 kg containing sorbitol, erythritol, glycerol, and residual catalyst. The residual fraction was not further analyzed in detail.

[0065] Table 1. Mass balance during the preparation and separation of mixed diols

[0066]

[0067]

[0068] The composition of the mixed glycol fraction was analyzed by GC, and the glycerol fraction was measured by LC (Table 2 - Feed). This mixed glycol fraction was used as the feed for extractive distillation.

[0069] The first 2-inch glass double-walled distillation column was used for extractive distillation with glycerol as the extractant. The first column had three sections, each approximately 167 cm high. The top section was empty, while the middle and bottom sections were filled with Sulzer Mellapak Y-500 Hastelloy, each with a total height of approximately 140 cm. The feed position was located two-thirds of the way from the top, between two filled sections. The extractant feed inlet was at the top of the first column. The theoretical height equivalent (HETP) of the trays was estimated to be 22 cm.

[0070] A second 2-inch glass double-walled distillation column was used for ethylene glycol recovery and extractant recycling. The second column also had three sections, each approximately 167 cm high. The top section was empty, while the middle and bottom sections were filled with Sigma-Aldrich Pro-Pak distillation packing. The middle section had a packing height of 20 cm, while the bottom section had a packing height of 10 cm. The feed position was two-thirds of the way from the top, between the two filled sections. The HETP was estimated at 22 cm.

[0071] The first distillation column was operated at a pressure of 231 mbar (measured at the top of the column), a condenser temperature of 132°C, and a reboiler liquid temperature of 180°C. The mixed glycol feed rate was 50 g / h, and the glycerol feed rate was 130 g / h, resulting in a top product flow rate of 6 g / h and a bottom product flow rate of 178 g / h. Water was fed into the reboiler at a rate of 0.5 g / h. The top reflux rate gradually decreased over time, from 350 g / h to 32 g / h, indicating a gradual decrease in the reflux ratio.

[0072] The second distillation column operates at a pressure of 91 mbar (measured at the top of the column), a condenser temperature of 125°C, and a reboiler liquid temperature of 202°C. The feed to the second distillation column is the bottom product of the first distillation column at a flow rate of 178 g / h, resulting in a top flow rate of 43 g / h and a bottom extractant flow rate of 134 g / h. Water is fed into the reboiler at a flow rate of 0.5 g / h. The top reflux flow rate is 25 g / h.

[0073] Table 2 provides the composition of the top product in the first distillation column and the top product in the second distillation column.

[0074] Table 2. Composition of Example 1

[0075] Component Feed [g / kg] Top C-1 [g / kg] Top C-2 [g / kg] Ethylene glycol 808.7 364.4 994.7 Propylene glycol 46.7 446.9 0.0 1,2-Butanediol 31.1 186.0 0.0 1,2-Hexanediol 10.6 0.0 6.5 2,3-Pentanediol isomers 7.5 14.1 0.0 2,3-Butanediol isomers 4.2 16.7 0.0 x,y-Hexanediol isomers 2.8 5.0 0.0 Cyclic diol 1 2.3 3.5 0.0 Glycerol 2.0 0.0 0.0 2,5-Hexanediol 1.9 0.0 <0.5 1,2-Pentanediol 1.8 2.7 0.0 Cyclic diol 2 1.5 2.5 0.0 Isosorbide 1.3 0.0 0.0 Total 922 1042 998

[0076] The UV transmittance of MEG was measured using a Perkin Elmer Lambda 35UV-Vis spectrophotometer (serial number 502S10121302) according to the standard test method for UV transmittance of monoethylene glycol (ASTM E2193) (using UV spectrophotometry). The selling specifications for UV transmittance are 70% (220 nm); 90% (250 nm); 94% (275 nm); and 98% (350 nm). The measured UV transmittance was 54% (220 nm); 82% (250 nm); 82% (275 nm); and 97% (350 nm). Since the required UV transmittance selling specifications were not met, the top stream from C-2 was sent for further processing.

[0077] Example 2 - Separation and Extraction of Mixed Diols by Distillation / Hydrogenation

[0078] To provide a MEG sample very similar to the nonconforming product of Comparative Example 1, the UV transparency of commercially available fossil-based high-purity MEG (fiber grade) was evaluated according to ASTM E2193, and the measured UV transmittance was 90% (220 nm); 98% (250 nm); 99% (275 nm); and 100% (350 nm). As described in Comparative Example 1, this MEG sample underwent extractive distillation. The UV transparency of the obtained MEG was measured according to ASTM E2193. The measured UV transmittance was 64% (220 nm); 82% (250 nm); 82% (275 nm); and 99% (350 nm). The obtained UV transmittance closely matches the UV transmittance of the MEG sample obtained after extractive distillation in Comparative Example 1. While not bound by theory, this may indicate that the deviation in UV transparency relative to high-purity MEG is primarily due to the presence of components that may be formed during extractive distillation via glycerol and / or the thermal radiation of the MEG. There is no clear indication that the components produced during the conversion of sugar into diols caused significant contamination.

[0079] The MEG sample obtained after extractive distillation was hydrogenated. 85.92 g of MEG was charged into a Hastelloy 250 ml magnetically stirred Parr autoclave, and a slurry of 2.02 g Raney Nickel 2800 (Aldrich) and 12.12 g water was added. The autoclave was shut off, and the mixture was purged three times with nitrogen and three times with hydrogen. The temperature was then raised to 119 °C and maintained for 120 minutes. The total pressure was maintained at 77 barg by adjusting the hydrogen pressure.

[0080] The resulting liquid was centrifuged to remove solid particles. The UV transparency of the liquid was measured according to ASTM E2193. The measured UV transmittance was 91% (220 nm); 99% (250 nm); 99% (275 nm); and 100% (350 nm).

[0081] No attempt was made to remove water from the catalyst slurry. Assuming water is completely transparent in the measured UV range, the obtained UV spectra were mathematically corrected for the presence of water to obtain the UV transmittance of the MEG. This mathematical correction resulted in slightly lower UV transparency, which was verified in separate experiments by diluting the MEG with water (results not shown). The corrected UV transmittance of the MEG was 90% (220 nm); 98% (250 nm); 99% (275 nm); and 100% (350 nm). Figure 3 ).

[0082] The MEG obtained after hydrogenation meets UV sales specifications. For example... Figure 3 As shown, the above tests meet or exceed the acceptable transmission percentage of fiber-grade MEG.

[0083] This invention offers numerous advantages over existing methods, which often encounter the problem that the glycol product does not meet the UV specifications for fiber-grade polymers and / or fibers. First, heavy (high-boiling) byproducts are removed by distillation in a first distillation column. Then, in a second distillation column, one or more extractants are used for selective extractive distillation of the first glycol. The strong interaction between the sugar alcohol and the first glycol can disrupt any azeotropics and affect the volatility of the glycol present, thereby separating them. In a third distillation column, a simple distillation of the first glycol from the extractant as the top product yields a stream containing the first glycol and unsaturated hydrocarbons and / or one or more compounds with carbonyl groups, which, after hydrogenation, meets UV sales specifications, providing a high-purity first glycol stream, suitable for immediate use as high-purity MEG for fiber-grade MEG, or after removal of trace compounds.

[0084] Although several embodiments of this disclosure have been described in detail above, those skilled in the art will readily understand that many modifications can be made without substantially departing from the teachings of this disclosure. Therefore, such modifications are intended to be included within the scope of this disclosure as defined in the claims.

Claims

1. A method for separating diols from a product stream, the method comprising the following steps: (i) Separating the product stream comprising three or more C2-C6 diols, C3-C6 sugar alcohols and C4-C6 polyols having at least three hydroxyl groups in the molecule, and a catalyst to produce a first stream comprising the three or more C2-C6 diols; (ii) Separating the first feed stream containing the three or more C2-C6 diols into a) a second feed stream comprising a first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups, and b) A third feed stream containing two or more diols; The separation of the first feed stream includes extractive distillation using an extractant, wherein the extractive distillation includes: - At a temperature ranging from 100°C to 300°C and a pressure ranging from 0.1 kPa to 2000 kPa, an intermediate stream comprising a first diol and unsaturated hydrocarbons and / or one or more compounds having carbonyl groups is extracted from the first stream using an extractant fed above the first stream; wherein the extractant is selected from C3-C6 sugar alcohols, C4-C6 polyols having at least three hydroxyl groups in their molecules, and mixtures thereof; and - Distill the intermediate stream to produce the second stream; (iii) Hydrogenating the second stream containing a first diol and an unsaturated hydrocarbon and / or one or more compounds having a carbonyl group to provide a purified diol stream.

2. The method of claim 1, wherein the product stream is or is derived from a product stream of a carbohydrate hydrogenolysis process, and wherein the product stream may further contain oxygen-containing compound impurities.

3. The method according to claim 1 or 2, wherein the separation in step (i) is evaporation.

4. The method according to claim 1 or 2, wherein the separation in step (i) is an evaporation performed in a distillation unit or a flash evaporation unit.

5. The method according to claim 1, wherein the extractant comprises glycerol.

6. The method of claim 1, wherein the amount of extractant added is such that, based on the total weight of the feed / mixture, the weight ratio of the extractant to the first feed stream is at least 1:2 and at most 20:

1.

7. The method according to claim 1 or 2, wherein the hydrogenation in step (iii) comprises a hydrogenation reaction carried out in the presence of a hydrogenation catalyst at a temperature in the range of 20°C to 300°C and a pressure in the range of 0.5 bara to 250 bara.

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