Process for purification of recovered glycol from chemical recycling of waste polyester

Abstract

To provide a process for purifying polyester-grade ethylene glycol from crude ethylene glycol containing at least a first component and a second component that have a boiling point below that of ethylene glycol.SOLUTION: A process includes the steps of: (a) providing a stream of crude ethylene glycol by depolymerizing polyethylene terephthalate in a chemical recycling process; (b) introducing the crude ethylene glycol stream into a first distillation column for distilling the first component and removing the first component from the process; (c) withdrawing a first stream from the lower portion of the first distillation column and feeding the first stream into a second distillation column for distilling the second component and removing the second component from the process; (d) withdrawing a second stream from the lower portion of the second distillation column and feeding the second stream into a third distillation column; and (e) recovering polyester-grade ethylene glycol from the third distillation column.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates generally to a process for the recovery of polyester grade ethylene glycol from a crude ethylene glycol product stream produced from colored post-consumer recycled resins, and more generally to a process for the recovery of pure ethylene glycol of 99.9% or greater purity from a crude ethylene glycol product stream produced by the depolymerization of colored post-consumer recycled resins, such as polyethylene terephthalate (PET), via a chemical recycling process. [Background technology]

[0002] Polyethylene terephthalate, commonly known as PET, is a highly versatile and essential material in the packaging industry. Due to its excellent physical and chemical properties, PET is widely used in single and multiple use products such as food and beverage containers.

[0003] PET is a polycrystalline polyester formed by the esterification of terephthalic acid (TPA) with ethylene glycol (EG) or the transesterification of dimethyl terephthalate (DMT) with ethylene glycol (EG). The synthesis of PET involves two reaction steps for either process. The first step is the production of the intermediate monomer bis(2-hydroxyethyl) terephthalate (BHET) with the release of a small molecule, either water (esterification of TPA with EG) or methanol (transesterification of DMT with EG). The second step is the polycondensation of BHET with the release of EG under high vacuum to produce PET in the melt phase.

[0004] In an attempt to conserve petrochemicals and energy feedstocks, several PET recycling methods have been developed. These PET recycling methods can be classified into four groups: primary, secondary, tertiary (chemical) and quaternary. Primary recycling, also known as re-extrusion, refers to the "in-plant" recycling of scrap materials that has similar characteristics to the original product and requires non-contaminated scrap. Secondary recycling, also known as mechanical recycling, involves separating the polymer from its contaminants and reprocessing it into granules by sorting and separating the waste, removing contaminants, reducing the size by crushing and grinding, extruding with heat, and modifying. Tertiary or chemical recycling involves the transformation of the PET polymer chains, such as depolymerization, i.e., breaking the ester bonds and reducing the polymer to its monomeric components. Quaternary recycling is the recovery of the energy content from the waste by incineration.

[0005] Recycling bottles made of PET to form bottles made of PET is preferred because it increases its added value. Such recycling is commonly known as "bottle-to-bottle recycling" as opposed to recycling bottles made of PET to fiber-grade PET to produce apparel. To carry out bottle-to-bottle recycling, the recycled PET must meet the requirements for bottle processing (glass transition and melting temperature, melt viscosity, melt stiffness, recrystallization rate, thermal stability), as well as food contact approval (decontamination, color, haze). As a high level of decontamination is required for recycled PET for food packaging applications, bottle-to-bottle recycling must be a chemical recycling process that includes depolymerization. Depolymerization can be done by hydrolysis, glycolysis or methanolysis to form monomers and / or oligomers. Chemical recycling is the only acceptable process according to the principles of sustainable development, as it leads to the formation of raw materials (monomers) to manufacture PET.

[0006] The decontamination capability of the chemical recycling process is an important objective function for recycling PET for food packaging applications. The removal of various contaminants needs to be considered during the process. The object of the present invention is to provide a process for purifying ethylene glycol and recovering polyester-grade purified ethylene glycol. Another object of the process is to purify ethylene glycol and recover polyester-grade purified ethylene glycol from a crude ethylene glycol product stream containing contaminants, such as those formed during the chemical recycling process, without introducing any added components, such as catalysts, into the process.

[0007] Various methods have been disclosed in the literature for depolymerizing post-consumer polyester into its constituent monomers such as ethylene glycol and terephthalic acid, naphthalenedicarboxylic acid or derivatives thereof so that they can be reused.

[0008] For example, U.S. Patent No. 3,367,847 discloses a process for purifying ethylene glycol recovered from a process for producing linear polyester films and fibers made from ethylene glycol and terephthalic acid. In the process, the ethylene glycol is first freed from the sodium salt of terephthalic acid, and then fractionally distilled to remove high-boiling and low-boiling impurities. The distilled ethylene glycol is then treated with activated carbon to remove impurities that adversely affect ultraviolet light transmission.

[0009] U.S. Pat. No. 3,491,161 discloses treating ethylene glycol contaminated with dimethyl terephthalate and other esters and impurities with a stoichiometric amount of ammonia to convert the ester impurities to the corresponding amides and alcohols and recover the ethylene glycol by distillation of the reaction mixture.

[0010] No. 4,028,195 discloses the recovery of ethylene glycol or 1,2-propylene glycol mixed with a lower alkane monoester of glycol and an azeotropic agent from conventional distillation. The glycol is introduced into a fractional distillation zone containing at least one aqueous solution of acetic acid and formic acid to suppress the formation of orthoesters, and purified glycol is recovered from the bottom of the zone.

[0011] US Patent No. 4,519,875 discloses the purification of ethylene glycol for fiber grade applications by removal of residual ethylene carbonate from which the glycol is derived. The effluent from the reactor in which ethylene carbonate is hydrolyzed is distilled to produce a low boiling fraction substantially containing ethylene glycol and water, and a high boiling fraction substantially containing ethylene glycol, higher glycols and catalyst. The high boiling fraction is recycled as reflux against the low boiling products to complete the hydrolysis of unreacted ethylene carbonate and reduce the ethylene carbonate content of the ethylene glycol to a very low level suitable for fiber grade applications.

[0012] U.S. Patent No. 4,830,712 discloses a process for recovering ethylene glycol from crude ethylene glycol having a normal boiling point lower than that of ethylene glycol and containing at least one component capable of forming an ultraviolet absorber in the presence of ethylene glycol. The purification process includes a fractional distillation zone having an upper, lower and middle section. In the middle section of the fractional distillation zone, the measured pH of the crude ethylene glycol stream is maintained below about 7.5. The middle section includes a diluent in a concentration sufficient to reduce the formation of ultraviolet absorbers. Ethylene glycol is withdrawn from the lower section of the fractional distillation zone.

[0013] U.S. Pat. No. 5,051,528 discloses a method for recovering ethylene glycol and dimethyl terephthalate from scrap polyethylene terephthalate resin by dissolving the scrap in oligomers of the same monomer and passing methanol through the solution.

[0014] US Patent No. 5,298,530 discloses a process for recovering components such as ethylene glycol and dimethyl terephthalate from scrap polyester, which includes the steps of (a) introducing ethylene glycol and terephthalic acid or dimethyl terephthalate oligomers into a first vessel and heating the oligomers, (b) introducing scrap polyester into the first vessel and forming a startup melt with the oligomers, (c) transferring the melt from the first vessel to a second vessel, (d) passing superheated methanol through the melt in the second vessel to form a final melt containing low molecular weight polyester and monomers, (e) transferring the final melt from the second vessel to the first vessel, and (f) recovering components from the second vessel.

[0015] US Patent No. 5,391,263 discloses the separation of ethylene glycol and diethylene glycol from dimethyl terephthalate by distillation of methyl benzoate or the methyl ester of p-toluic acid as an azeotropic agent.

[0016] US Patent No. 5,414,022 discloses a process and optimum conditions for depolymerizing polyester into its components and separating the components using an apparatus having a dissolver for containing polyester, a reactor for depolymerizing the polyester into its components, and a rectifier for separating the polyester components. The process includes the steps of (a) adding polyester to the dissolver and mixing the melt from the reactor with the liquid from the rectifier to shorten the chain length of the polyester, (b) transferring the polyester with the shortened chain length from the dissolver to the reactor, (c) passing superheated methanol through the reactor to depolymerize the polyester into its constituent monomers, (d) transferring the depolymerized product from the reactor to the rectifier, and (e) separating the depolymerized product in the rectifier into a gas phase containing the constituent monomers and a liquid phase containing high molecular weight materials.

[0017] U.S. Pat. No. 5,576,456 discloses a process for depolymerizing polyethylene terephthalate into its constituent monomers using a reactor in which the polyethylene terephthalate is a discontinuous phase in contact with a continuous phase of superheated methanol vapor.

[0018] U.S. Patent No. 5,672,780 discloses a process for removing dimethyl terephthalate contaminants from ethylene glycol, which includes distilling ethylene glycol in the presence of a transesterification catalyst and reacting the ethylene glycol with dimethyl terephthalate to form a compound that is less volatile than either ethylene glycol or dimethyl terephthalate, such as bis(2-hydroxyethyl) terephthalate.

[0019] U.S. Pat. No. 5,770,778 discloses a process for purifying ethylene glycol recovered from scrap polyester by contacting the recovered ethylene glycol with a first adsorbent having a high affinity for polar contaminants and a second adsorbent having a high affinity for non-polar contaminants.

[0020] US Patent No. 6,472,557 discloses a process for producing high quality TPA suitable for PET feedstock from recycled polyester, which includes the steps of depolymerizing polyester to form DMT, separating the DMT from the secondary material, and hydrolyzing the DMT to form TPA.

[0021] US Patent No. 6,706,843 discloses a process for separating and recovering dimethyl terephthalate and ethylene glycol from polyester waste containing foreign matter. The polyester waste is treated in ethylene glycol containing a polyester depolymerization catalyst. The solid foreign matter fraction is removed by floating it on the surface of the resulting reaction liquid, and the remaining solid foreign matter fraction is removed from the remaining solution fraction. The remaining solution fraction is concentrated by distillation, and distilled ethylene glycol is recovered. The distillation residue is mixed with an ester exchange reaction catalyst and methanol. The resulting reaction mixture is recrystallized and separated into a DMT cake and a mixed liquid by centrifugation, and high-purity DMT is recovered by distilling the cake. The remaining mixed liquid is distilled to recover methanol, and the distillation residue is distilled to recover EG. Summary of the Invention

[0022] According to one embodiment of the present invention, a process for purifying polyester grade ethylene glycol from crude ethylene glycol containing at least a first component and a second component having a boiling point lower than that of ethylene glycol includes the steps of: (a) providing a crude ethylene glycol stream by depolymerizing polyethylene terephthalate in a chemical recycle process; (b) introducing the crude ethylene glycol stream into a first distillation column and distilling the first component to remove the first component from the process; (c) withdrawing the first stream from a bottom of the first distillation column and feeding the first stream to a second distillation column and distilling the second component to remove the second component from the process; (d) withdrawing the second stream from a bottom of the second distillation column and feeding the second stream to a third distillation column; and (e) recovering polyester grade ethylene glycol from the third distillation column.

[0023] In accordance with another embodiment of the present invention, a process for purifying polyester grade ethylene glycol from crude ethylene glycol includes methanol as a first component.

[0024] In accordance with yet another embodiment of the present invention, a process for purifying polyester grade ethylene glycol from crude ethylene glycol includes water as a second component.

[0025] In yet another embodiment of the present invention, in the process for purifying polyester grade ethylene glycol from crude ethylene glycol, the purity of the ethylene glycol is 99.9%.

[0026] In yet another embodiment of the present invention, in the process for purifying polyester grade ethylene glycol from crude ethylene glycol, the purity of the methanol is 99.9%.

[0027] In yet another embodiment of the present invention, in a process for purifying polyester grade ethylene glycol from crude ethylene glycol, the polyester grade ethylene glycol contains less than 0.01 wt % of a chain terminator.

[0028] In accordance with yet another embodiment of the present invention, a process for purifying polyester grade ethylene glycol from crude ethylene glycol includes a partial condenser.

[0029] In a process for purifying polyester grade ethylene glycol from crude ethylene glycol according to yet another embodiment of the present invention, the first distillation column operates at a temperature of less than 56° C. and a pressure of 110 mm Hg.

[0030] In a process for purifying polyester grade ethylene glycol from crude ethylene glycol according to yet another embodiment of the present invention, the second distillation column operates at a temperature range of 56° C. to 196° C. and a pressure of 110 mm Hg.

[0031] In a process for purifying polyester grade ethylene glycol from crude ethylene glycol according to yet another embodiment of the present invention, the third distillation column operates at a temperature range of 197° C. to less than 202° C. and a pressure of 110 mm Hg.

[0032] In yet another embodiment of the present invention, in the process for purifying polyester grade ethylene glycol from crude ethylene glycol, no other components such as catalysts are introduced.

[0033] In accordance with yet another embodiment of the present invention, a process for purifying polyester grade ethylene glycol from crude ethylene glycol includes the steps of: (1) providing crude ethylene glycol from a process of depolymerizing polyethylene terephthalate (PET) to form terephthalate; (2) mixing the polyethylene terephthalate (PET) with a first solvent, which is methanol, to obtain a first mixture; (3) adding a glycoside to the first mixture; (4) adding a second solvent, which is methanol; and (5) mixing the first mixture to obtain a crude ethylene glycol from the process of depolymerizing polyethylene terephthalate to form terephthalate. The process includes a step (5) of evaporating or distilling the ethylene glycol; a step (6) of introducing the crude ethylene glycol stream into a first distillation column and distilling a first component to remove the first component from the process; a step (7) of withdrawing a first stream from a bottom of the first distillation column and feeding the first stream to a second distillation column and distilling a second component to remove the second component from the process; a step (8) of withdrawing a second stream from a bottom of the second distillation column and feeding the second stream to a third distillation column; and a step (9) of recovering polyester grade ethylene glycol from the third distillation column.

[0034] In yet another embodiment of the present invention, in a process for purifying polyester grade ethylene glycol from crude ethylene glycol, the crude ethylene glycol contains one or more of methanol, ethylene glycol, water, diethylene glycol, cyclohexanedimethanol (CHDM), BHET, bis(2-hydroxymethyl)isophthalate (BHEI), methyl terephthalaldehyde, 2-methoxyethanol, 2-butoxyethanol, 2-(2-methoxyethoxy)ethanol, dyes, and pigments. [Brief description of the drawings]

[0035] The present invention is illustrated and described herein with reference to various drawing figures, in which like reference numbers represent respective like method steps and / or system components.

[0036] [Figure 1] FIG. 1 is a schematic diagram showing the process of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The present invention may be more readily understood by reference to the following detailed embodiments of the invention in conjunction with the accompanying drawings, which form a part of this disclosure. It is to be understood that the invention is not limited to the specific apparatus, methods, conditions, or parameters described and / or illustrated herein, and that the terminology used herein is for the purpose of describing specific embodiments by way of example only, and is not intended to limit the invention as claimed. It is to be understood that any and all patents and other publications identified herein are incorporated by reference as if set forth herein.

[0038] Also, as used in the specification, including the appended claims, the singular forms "a," "an," and "the" include the plural and a reference to a particular numerical value includes at least that particular numerical value unless the context clearly indicates otherwise. Ranges may be expressed herein as from "about" or "approximately" one particular value, and / or to "about" or "approximately" another particular value. When such a range is expressed, another embodiment includes the one particular value and / or the other particular value. Similarly, when values ​​are expressed as approximations, by use of "about," it will be understood that the particular value forms another embodiment.

[0039] Ranges and limits referred to herein should be understood to include all ranges that fall within the stated limits (i.e., subranges). For example, the range of about 100 to about 200 also includes the ranges of 110 to 150, 170 to 190, 153 to 162, and 145.3 to 149.6. Furthermore, the limit of about 7 or less includes the limits of about 5 or less, 3 or less, and about 4.5 or less, as well as ranges within that limit, such as about 1 to about 5 and about 3.2 to about 6.5.

[0040] The present invention is directed to a process for purifying and recovering polyester grade purified ethylene glycol from crude ethylene glycol obtained from a chemical recycling process. The resulting polyester grade ethylene glycol produced from the present invention is obtained from polyester waste containing polyethylene terephthalate as a major component along with heterogeneous components and contaminants. The polyethylene terephthalate is depolymerized in a chemical recycling process by mixing the polyethylene terephthalate with a mixture containing methanol and a catalyst, so that dimethyl terephthalate and crude ethylene glycol can be recovered. The crude ethylene glycol can be produced according to the process described in U.S. Patent Publication No. 2019 / 0390035, entitled "Terephthalic Acid Esters Formation," which also discloses the use of catalysts such as alkoxides, sodium methoxide, sodium glycoxide, and any combination thereof.

[0041] In order to recover polyester grade ethylene glycol, it is necessary to remove further contaminants that become incorporated into the crude ethylene glycol by reaction with the catalyst during the depolymerization process. According to the present invention, there is provided a process for recovering polyester grade ethylene glycol from crude ethylene glycol when the crude ethylene glycol contains contaminants, some of which are the result of the catalyst used in the depolymerization process. According to the present invention, there is provided a process for recovering polyester grade ethylene glycol from crude ethylene glycol that does not include the step of adding components such as catalysts to the purification system. According to the present invention, there is provided a process for recovering greater than 99.9 wt% polyester grade ethylene glycol and less than 0.01 wt% chain stoppers from crude ethylene glycol that contains contaminants that are the result of the catalyst used in the depolymerization process.

[0042] The term chain terminator refers to any monoacid / monoester species that can react successfully with a diol in the formulation (in the case of mono-substituted acid or ester based species) and persist or remain in the polymer matrix after isolating the polymer, or any material with a single alcohol functionality that can react successfully with a diacid / diester in the formulation (in the case of mono-substituted alcohol based species) and persist or remain in the polymer matrix after isolating the polymer.

[0043] With specific reference to the drawings, a process for recovering polyester grade ethylene glycol from crude ethylene glycol is illustrated in FIG. 1 and generally designated by reference numeral 10. Process 10 involves purifying crude ethylene glycol produced from the depolymerization of post-consumer recycled resins, including colored post-consumer recycled resins such as PET. The crude ethylene glycol is obtained by a chemical recycling process that depolymerizes the resin or PET. There are three main methods for PET chemical recycling, depending on the hydroxyl group-containing molecule added, namely glycol for glycolysis, methanol for methanolysis, and water for hydrolysis. These methods are described in more detail below.

[0044] (Hydrolysis) Hydrolysis involves the depolymerization of PET into terephthalic acid (TPA) and ethylene glycol by adding water in an acidic, alkaline or neutral environment. The hydrolysis products are used to produce virgin PET or converted to expensive chemicals such as oxalic acid if required. Typically, concentrated sulfuric acid is used for acid hydrolysis, caustic soda for alkaline hydrolysis, and water or steam for neutral hydrolysis. Hydrolysis is slower than methanolysis and glycolysis since water is the weakest nucleophile among the three depolymerization agents (i.e., water, methanol, and ethylene glycol). It also always uses high temperature or pressure, or a combination of these. Another drawback of hydrolysis is that recovery of the TPA monomer is difficult and requires many steps to reach the required purity.

[0045] (Methanolysis) Methanolysis is the depolymerization of PET with methanol into dimethyl terephthalate (DMT) and ethylene glycol (EG).

[0046] (Glycolysis) Glycolysis is carried out using ethylene glycol to produce bis(2-hydroxyethyl) terephthalate (BHET) and other PET glycolates that can be used in the production of unsaturated resins, polyurethane foams, copolyesters, acrylic paints, and hydrophobic dyes. The BHET produced by glycolysis can be added to the unused BHET and the mixture can be used in either of the two PET production (DMT-based or TPA-based) lines. In addition to its flexibility, glycolysis is the simplest, oldest, and least capital-intensive process. For these reasons, PET glycolysis has attracted much attention. Many studies have been published on PET glycolysis, and reactions have been performed over a wide range of temperatures and times. Studies on the kinetics of PET glycolysis have shown that glycolysis without a catalyst (such as metal salts, zeolites, or ionic liquids) is very slow and complete depolymerization of PET to BHET cannot be achieved.

[0047] The crude EG stream 12 introduced into the process of the present invention may be produced by any PET chemical recycling process, but is preferably either methanolysis or glycolysis. In this example, the crude EG feed stream 12 was produced by the process described in U.S. Patent Publication No. 2019 / 0390035, entitled "Terephthalic Acid Esters Formation." The process disclosed in this patent application produces a crude EG feed stream 12 that may include the following components as set forth in Table 1a:

[0048] [Table 1a]

[0049] Crude EG stream 12 may also contain the additional components set forth in Table 1b below.

[0050] [Table 1b]

[0051] As shown in FIG. 1, the crude EG feed stream 12 is introduced into a first distillation column 14 designed to separate methanol (MeOH) from the crude EG feed stream 12. Depending on the operation of the first distillation column 14, the crude EG feed stream 12 may be vaporous, liquid, or a combination thereof. Preferably, the temperature of the EG feed stream 12 is from about 20° C. to about 100° C., more preferably from about 25° C. to about 95° C. Although the EG feed stream 12 is shown as a single stream in FIG. 1, it may be formed by two or more separate streams having different temperatures and flow rates. For example, when the EG feed stream is formed by a first stream and a second stream, the first stream may have a temperature of from about 20° C. to about 35° C. and a mass flow rate of from about 5,000 kg / hr to about 8,000 kg / hr, and the second stream may have a temperature of from about 80° C. to about 100° C. and a mass flow rate of from about 6,000 kg / hr to about 9,000 kg / hr.

[0052] First distillation column 14 is generally a cylindrical column having one or more separation stages and is fitted with trays, structured packing, or a combination of trays and structured packing. First distillation column 14 separates the higher boiling materials from the lower boiling methanol in the product stream. During operation, the lowest boiling materials in crude EG feed stream 12, which comprises primarily methanol and water, exit the top of first distillation column 14 via first distillation column gas stream 16. The methanol removed from first distillation column 14 is at least 99.9% pure.

[0053] The operating temperature of first distillation column 14 is preferably less than 56° C. at 110 mm Hg. Operation of first distillation column 14 below 56° C. at 110 mm Hg allows methanol to be distilled while removing ethylene glycol and heavies from the bottom of first distillation column 14. The temperature may be adjusted depending on the composition of the crude EG feed stream 12 introduced to first distillation column 14 to prevent thermal decomposition of the heavies and other components intended to be removed from the bottom of first distillation column 14.

[0054] First distillation column vapor stream 16 is cooled in first partial condenser 18 to partially condense most of the methanol. A purified methanol stream 20 is withdrawn from partial condenser 18, with most of the purified methanol leaving process 10 via stream 22. Stream 22 has a temperature of about 40° C. to about 65° C. and a mass flow rate of about 11,000 kg / hr to about 13,000 kg / hr. A portion of stream 20 containing purified methanol is recycled via methanol reflux stream 24 to the top of first distillation column 14, preferably at a location above where stream 30 is introduced. The temperature of methanol reflux stream 24 is lower than the temperature of first distillation column 14. Reintroducing methanol reflux stream 24 to the top of distillation column 14 allows for additional purification, which can increase the purity level of first distillation column vapor stream 16 and the efficiency of first distillation column 14.

[0055] High boiling material components, mainly including ethylene glycol, water, and heavies, exit the bottom of the first distillation column 14 via tail stream 26. The heavies may include diethylene glycol, cyclohexanedimethanol (CHDM), dyes and pigments, and bis(2-hydroxyethyl) terephthalate (BHET) / bis(2-hydroxyethyl) isophthalate (BHEI) mixed monomers. A first reboiler 28 is provided at the bottom of the first distillation column 14. A portion of the tail stream 26, stream 27, is introduced into the first reboiler 28 and receives thermal energy to vaporize the components of stream 27, which are then reintroduced into the first distillation column 14 via stream 30, while the remaining portion of the tail stream 26 is fed to the second distillation column 34. The tail stream 26 preferably has a temperature of about 135° C. to about 155° C. and a mass flow rate of about 1,000 kg / hr to about 2,500 kg / hr.

[0056] Tail stream 26, containing primarily ethylene glycol, water and heavies, enters a second distillation column 34 designed to separate the higher boiling materials from the lower boiling materials and remove the lower boiling materials from the top of second distillation column 34 via second distillation column vapor stream 36. Second distillation column 34 is typically a cylindrical column having one or more separation stages, fitted with trays, structured packing or a combination of trays and structured packing.

[0057] The operating temperature of second distillation column 34 is preferably from about 56° C. to about 196° C. at 110 mm Hg. Operation of second distillation column 34 in this temperature range allows water and other components having boiling points within this range to be distilled while ethylene glycol and heavies are removed from the bottom of second distillation column 34. The temperature may be adjusted depending on the composition of tail stream 26 fed to second distillation column 34 to prevent thermal decomposition of the heavies and other components intended to be removed from the bottom of second distillation column 34.

[0058] Second distillation column vapor stream 36 is cooled in second dephlegmator 38 to partially condense most of the water. Stream 40, containing primarily purified water, methanol, and small amounts of ethylene glycol, is withdrawn from second dephlegmator 38, with most of the purified water leaving process 10 via stream 42 at a temperature of about 75° C. to about 95° C. and a mass flow rate of about 80 kg / hr to about 100 kg / hr. A portion of stream 40 is recycled via water reflux stream 44 to the top of second distillation column 34, preferably at a location above where stream 50 is introduced. The temperature of water reflux stream 44 is lower than the temperature of second distillation column 34.

[0059] High boiling materials, primarily comprising ethylene glycol, diethylene glycol, and heavies such as CHDM, dyes and pigments, and BHET / BHEI, exit the bottom of second distillation column 34 via tail stream 46. A portion of tail stream 46, stream 52, is introduced into second reboiler 48, which receives thermal energy to vaporize the components of stream 52 and reintroduces them into second distillation column 34 via stream 50. The remaining portion of tail stream 46 is fed to third distillation column 54. Tail stream 46 has a temperature of about 145° C. to about 160° C. and a mass flow rate of about 1,000 kg / hr to about 2,500 kg / hr.

[0060] Tail stream 46, which contains primarily ethylene glycol, diethylene glycol, PET color, BHET / BHEI and other heavies, enters a third distillation column 54 designed to purify and separate the ethylene glycol from the other components of tail stream 46 and exits the top of third distillation column 54 via third distillation column vapor stream 56. Third distillation column 54 is typically a cylindrical column having one or more separation stages, which may be fitted with trays, structured packing or a combination of trays and structured packing.

[0061] The operating temperature of third distillation column 54 is preferably greater than or equal to 197° C. and less than 202° C. at 110 mm Hg. Operation of third distillation column 54 in this temperature range allows ethylene glycol to be distilled while heavies are removed from the bottom of third distillation column 54 and removed from process 10. The temperature may be adjusted depending on the composition of the tail stream 46 fed to third distillation column 54 to prevent thermal decomposition of the heavies and other components intended to be removed from the bottom of third distillation column 54.

[0062] The third distillation column gas stream 56 contains greater than 99.9 wt% purified ethylene glycol, which is polyester grade ethylene glycol, and less than 0.01 wt% chain terminators. The chain terminators contained in the purified ethylene glycol contain 30 ppm or less of chain terminators. The chain terminators found in the crude EG stream 12 may be methyl terephthalaldehyde, 2-methoxyethanol, 2-butoxyethanol, and 2-(2-methoxyethoxy)ethanol, as shown in Tables 1a and 1b.

[0063] Third distillation column vapor stream 56 is cooled in third partial condenser 58 to partially condense most of the ethylene glycol. A cooled ethylene glycol stream 60 is withdrawn from third partial condenser 58, and most of the purified ethylene glycol leaves process 10 via stream 62. Stream 62 preferably has a temperature of from about 120° C. to about 150° C. and a mass flow rate of from about 1,000 kg / hr to about 2,000 kg / hr. A portion of cooled stream 60 is recycled via ethylene glycol reflux stream 64 to the top of third distillation column 54, preferably at a location above where stream 70 is introduced. The temperature of ethylene glycol reflux stream 64 is less than the temperature of third distillation column 54.

[0064] The ethylene glycol bottoms, consisting of ethylene glycol, diethylene glycol, and heavies such as CHDM, dyes, pigments, and the like, and the high boiling materials consisting primarily of methyl terephthalaldehyde and BHET / BHEI exit the bottom of the third distillation column 54 via third tail stream 66. A portion of the third tail stream 66, stream 67, is introduced into a third reboiler 68, which receives thermal energy to vaporize the components of stream 67 and reintroduces them into the third distillation column 54 via stream 70. The remaining components consisting of the ethylene glycol bottoms and heavies are discharged as waste and exit the process 10 via stream 72. Stream 72 preferably has a temperature of about 160° C. to about 180° C. and a mass flow rate of about 250 kg / hr to about 450 kg / hr.

[0065] The process 10 of the present invention includes in series a first distillation column 14, a second distillation column 34 and a third distillation column 54. No additional components, such as catalysts, are introduced into the process 10 to purify and recover purified polyester grade ethylene glycol.

[0066] By polyester grade ethylene glycol is meant high purity ethylene glycol suitable for use in the production of polyesters such as PET, especially PET bottles. EXAMPLES

[0067] The following examples are illustrative of the present invention, but are not intended, and should not be construed, as limiting the scope of the invention.

[0068] Example 1 Example 1 is based on laboratory conditions and has not been carried out on a commercial scale. The crude EG used in the crude EG feed stream was produced by the process described in U.S. Patent Publication No. 2019 / 0390035, entitled "Terephthalic Acid Esters Formation," incorporated herein. The crude EG was obtained from a process for depolymerizing polyethylene terephthalate (PET) to form terephthalate, the process comprising: (i) mixing polyethylene terephthalate (PET) with a first solvent, which is methanol, to obtain a first mixture; (ii) adding a glycoside to the first mixture; (iii) adding a second solvent, which is methanol; A mixing step (iv), and and (v) evaporating or distilling crude ethylene glycol from the terephthalate.

[0069] The crude ethylene glycol was fed to the first distillation column. The process column information for this example is shown in Table 2. The condenser utilized is a highly efficient inverted bell with a jacketed wall design and containing water as the heat transfer medium.

[0070] Distillation column information for Example 1 [Table 2]

[0071] During operation, the second and third distillation columns were operated at full reflux until each column was fully operational. Once fully operational, the reflux ratio of the first distillation column was reduced to 0.16 L / min and the second distillation column was reduced to 0.19 L / min. The column conditions were adjusted by controlling the reflux as a variable control. After completion of the process, the purified ethylene glycol stream after distillation in the third distillation column and exiting the third condenser was evaluated and found to contain 99.9 wt% ethylene glycol as shown in Table 3. Table 3 also shows other constituents in the purified ethylene glycol.

[0072] [Table 3]

[0073] Example 2 The crude EG used in the crude EG feed stream was produced by the process described in U.S. Patent Publication No. 2019 / 0390035, entitled "Terephthalic Acid Esters Formation," incorporated herein. The crude EG was obtained from a process for depolymerizing polyethylene terephthalate (PET) to form terephthalate, which process comprises: (i) mixing polyethylene terephthalate (PET) with a first solvent, which is methanol, to obtain a first mixture; (ii) adding a glycoside to the first mixture; (iii) adding a second solvent, which is methanol; A mixing step (iv), and and (v) evaporating or distilling crude ethylene glycol from the terephthalate. The components of the crude EG feed stream are shown above in Tables 1a and 1b. The process column information for this example is shown in Table 4, the condenser information in Table 5, and the reboiler information in Table 6.

[0074] Distillation column information for Example 2 [Table 4]

[0075] Condenser information for Example 2 [Table 5]

[0076] Reboiler Information for Example 2 [Table 6]

[0077] The components in the various streams corresponding to the reference numbers shown in FIG.

[0078] Stream components of Example 2 [Table 7] TIFF2025061431000010.tif35170

[0079] As shown in Table 6, the purified ethylene glycol in stream 62 of Example 2 has a purity of 99.9 wt %, making it polyester grade ethylene glycol.

[0080] Although the invention has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those skilled in the art that other embodiments and examples may perform a similar function and / or achieve similar results, and all such equivalent embodiments and examples are within the spirit and scope of the invention and are intended to be encompassed by the following claims.

Claims

1. (a) providing a crude ethylene glycol stream by depolymerizing polyethylene terephthalate in a chemical recycling process; (b) introducing the crude ethylene glycol stream into a first distillation column and distilling a first component to remove the first component from the process; (c) withdrawing a first stream from a bottom of the first distillation column and feeding the first stream to a second distillation column to distill a second component and remove the second component from the process; (d) withdrawing a second stream from a bottom of the second distillation column and feeding the second stream to a third distillation column; and (e) recovering polyester grade ethylene glycol from the third distillation column.

2. 2. The process for purifying polyester grade ethylene glycol from crude ethylene glycol as recited in claim 1, wherein said first component is methanol.

3. 2. The process for purifying polyester grade ethylene glycol from crude ethylene glycol according to claim 1, wherein said second component is water.

4. 2. The process for purifying polyester grade ethylene glycol from crude ethylene glycol according to claim 1, wherein the purity of the ethylene glycol is 99.9%.

5. 3. The process for purifying polyester grade ethylene glycol from crude ethylene glycol according to claim 2, wherein the purity of the methanol is 99.9%.

6. 2. The process for purifying polyester grade ethylene glycol from crude ethylene glycol according to claim 1, wherein the polyester grade ethylene glycol contains less than 0.01 wt.% chain terminators.

7. 10. The process for purifying polyester grade ethylene glycol from the crude ethylene glycol of claim 1 further comprising a partial condenser.

8. 2. The process for purifying polyester grade ethylene glycol from crude ethylene glycol as set forth in claim 1, wherein said first distillation column operates at a temperature of less than 56° C. and a pressure of 110 mm Hg.

9. 2. The process for purifying polyester grade ethylene glycol from crude ethylene glycol as set forth in claim 1, wherein the second distillation column operates at a temperature range of greater than 56° C. to 196° C. and a pressure of 110 mm Hg.

10. 2. The process for purifying polyester grade ethylene glycol from crude ethylene glycol as set forth in claim 1, wherein the third distillation column operates at a temperature range of 197° C. to 202° C. and a pressure of 110 mm Hg.

11. 2. The process for purifying polyester grade ethylene glycol from crude ethylene glycol as set forth in claim 1, wherein no additional components such as catalysts are introduced into the process.

12. (i) mixing polyethylene terephthalate (PET) with a first solvent, which is methanol, to obtain a first mixture; (ii) adding a glycoside to the first mixture; (iii) adding a second solvent, which is methanol; mixing step (iv); and (a) providing crude ethylene glycol from a process for depolymerizing polyethylene terephthalate (PET) to form terephthalate, the process comprising step (v) of evaporating or distilling the crude ethylene glycol from the terephthalate; (b) introducing the crude ethylene glycol stream into a first distillation column and distilling a first component to remove said first component from said process; (c) withdrawing a first stream from a bottom of the first distillation column and feeding the first stream to a second distillation column to distill a second component and remove the second component from the process; (d) withdrawing a second stream from the bottom portion of the second distillation column and feeding the second stream to a third distillation column; and (e) recovering polyester grade ethylene glycol from said third distillation column.

13. 13. The process for purifying polyester grade ethylene glycol from crude ethylene glycol according to claim 12, wherein the crude ethylene glycol contains one or more of methanol, ethylene glycol, water, diethylene glycol, CHDM, BHET, BHEI, methyl terephthalaldehyde, pigments and dyes, 2-methoxyethanol, 2-butoxyethanol, and 2-(2-methoxyethoxy)ethanol.

14. 13. The process for purifying polyester grade ethylene glycol from crude ethylene glycol according to claim 12, wherein the first component is methanol.

15. 13. The process for purifying polyester grade ethylene glycol from crude ethylene glycol according to claim 12, wherein the second component is water.

16. 13. The process for purifying polyester grade ethylene glycol from crude ethylene glycol according to claim 12, wherein the purity of the ethylene glycol is 99.9%.

17. 13. The process for purifying polyester grade ethylene glycol from crude ethylene glycol as described in claim 12, wherein no additional components such as catalysts are introduced into the process.

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