Processes for treating polyester methanolysis depolymerization product streams

Abstract

A method for treating a methanolysis depolymerization product stream from a polyester methanolysis depolymerization process wherein the methanolysis depolymerization product stream includes DMT, EG, impurities and methanol. The method includes (i) refining the methanolysis depolymerization product stream in a DMT refining zone to produce a DMT product stream and an EG product stream; (ii) refining said EG product stream in an EG refining zone to produce an EG target stream and EG refining zone effluent; and (iii) recovering methanol from at least one of said depolymerization product stream, said DMT refining zone and said EG refining zone in a methanol recovery zone; wherein at least one of steps (i), (ii) and (iii) is at least partially conducted in the presence of a refining solvent. A method for depolymerizing polyester; a system for treating a depolymerization product stream from a polyester depolymerization process; and a polyester depolymerization system are also described.

Description

PROCESSES FOR TREATING POLYESTER METHANOLYSIS DEPOLYMERIZATION PRODUCT STREAMSFIELD OF THE INVENTION

[0001] The present invention generally relates to the field of polyester recycle processes and more particularly to a polyester recycle process that includes depolymerization of polyester for example via methanolysis and purification of the depolymerization reaction products to provide useful chemical compounds.BACKGROUND OF THE INVENTION

[0002] Polyesters are often viewed as the world’s most purchased and diversely utilized class of polymers, with published world production volumes (including recycling) recently reported to be well in excess of 75 million tons. This level of commercial success is likely attributable in part to polyesters’ attractive combination of relative cost, manufacturability and competitive performance attributes. Polyester’s physical, chemical and thermal properties make them useful and desirable for a wide variety of end-use applications. Polyethylene terephthalate (PET) is probably one of the most popular types of polyester for many end-uses. With the continuing commercial success of polyesters generally and PET specifically has come efforts to recover materials from post-consumer, post-industrial, scrap and other sources and re-use those materials as an alternative to basic disposal methods such as landfills.

[0003] In some known recycle methods, recycled PET is blended with virgin materials. This approach has been used, for example, to prepare blends of virgin poly(butylene terephthalate) (“PBT”) with recycled PET to yield a PBT-based product with recycle content (see, for example, U.S. Patent Application Publication No. 2009 / 0275698). Such blends, however, can be generally immiscible and produce a material that is relatively opaque. Blending, therefore, is not a uniformly satisfactory method to provide commercially acceptable end products with recycle content.

[0004] In other recycle methods, polyesters are depolymerized to form the monomer units originally used in its manufacture. Glycolysis is one commercially utilized method of depolymerizing polyesters. Glycolysis may be generally described as a transesterification-based depolymerization process wherein the depolymerization agent or reagent is a transesterification agent such as a glycol, or more broadly a polyol, exemplified by ethylene glycol (EG), diethylene glycol, triethylene glycol, propanediol isomers, butanediol isomers, pentaerythritol, trimethylol ethane, trimethylol propane, and mixtures thereof. In one or more embodiments, the depolymerization product stream may include unreacted depolymerization reagent comprising for example ethylene glycol, diethylene glycol, triethylene glycol, or mixtures thereof. A typical glycolysis process can be illustrated with particular reference to the glycolysis of PET, in which waste PET is dissolved in and reacted with a glycol, typically ethylene glycol, to form a mixture of dihydroxyethyl terephthalate and low molecular weight terephthalate oligomers. This mixture can be subjected to a transesterification reaction, usually in the presence of an ester exchange catalyst, with a lower alcohol such as methanol to form dimethyl terephthalate (DMT), ethylene glycol (EG), and other monomers, again depending upon the composition of the waste or scrap polyester feedstock. Representative examples of glycolysis methods are disclosed in U.S. Pat. Nos. 3,257,335; 3,907,868; 6,706,843; and 7,462,649, the contents and disclosure of which are hereby incorporated herein by reference.

[0005] Methanolysis is another known and commercially practiced polyester depolymerization method. In methanolysis, the polyester is reacted with methanol to produce a depolymerized polyester mixture comprising polyester oligomers, dimethyl terephthalate (“DMT”), and ethylene glycol (“EG”). Methanolysis may be generally described as a transesterification-based depolymerization process wherein the depolymerization agent or reagent is a transesterification agent that includes methanol. In addition to DMT and EG, other monomers such as, for example, 1 ,4-cyclohexanedimethanol (“CHDM”) and diethylene glycol may also be present depending on the composition of the polyester in the methanolysis feed stream and may be target products forcertain polyester depolymerization processes. Some representative methods for the methanolysis of PET are described in U.S. Pat. Nos. 3,037,050; 3,321,510; 3,776,945; 5,051,528; 5,298,530; 5,414,022; 5,432,203; 5,576,456 and 6,262,294, the contents and disclosure of which are incorporated herein by reference. A representative methanolysis process is also illustrated in U.S. Pat. No. 5,298,530, the contents and disclosure of which is incorporated herein by reference. The ‘530 patent describes a process for the recovery of ethylene glycol and dimethyl terephthalate from scrap polyester. The process includes the steps of dissolving scrap polyester in oligomers of ethylene glycol and terephthalic acid or dimethyl terephthalate and passing super-heated methanol through this mixture. The oligomers can comprise any low molecular weight polyester polymer of the same composition as that of the scrap material being employed as the starting component such that the scrap polymer will dissolve in the low molecular weight oligomer. The dimethyl terephthalate and the ethylene glycol are recovered from the methanol vapor stream that flows from the depolymerization reactor.

[0006] Alcoholysis, another useful polyester depolymerization process particularly useful in depolymerization of poly(C2-C4 alkylene) terephthalates such as polyethylene terephthalate (PET), may be generally described as a transesterification-based depolymerization process wherein the depolymerization agent or reagent is a transesterification agent such as a C4 to C14 alkanol., exemplified by 1 -butanol, 2-ethylhexanol and 2-methylpentanol. In one or more embodiments, the depolymerization product stream may include unreacted depolymerization reagent including C2 to C12 alkanol or including one or more of 1 -butanol, 2-ethylhexanol, 2-methylpentanol and 2-ethylhexanol.

[0007] Recycled / reclaimed target products from depolymerization, including for example EG and DMT, are commercially valuable materials in manufacture of polyesters (such as PET) with recycle content and are typically the primary target products for commercial depolymerization processes and systems. These products are also useful chemical intermediates for other products, as exemplified in U.S. Published Patent Application No. U.S.2013 / 0041053, assigned to the assignee of the present invention, the contents and disclosure of which are incorporated herein by reference, which describes a process wherein DMT formed from a polyester depolymerization process may be hydrogenated to 1,4 CHDM. Similarly, Bis(2-Hydroxyethyl) terephthalate (BHET) produced via glycolysis depolymerization may be used as a raw material for both dimethyl terephthalate (“DMT”) based and terephthalic acid (“TPA”)-based PET production processes without major modification of the production facility.

[0008] Though EG and DMT are typically the primary target products generated through depolymerization of polyesters (in particular PET) through methanolysis, glycolysis or alcoholysis, it is well known that depolymerization product streams will typically include a number of other chemical species. As an initial matter, the feedstock for depolymerization may as a practical commercial matter contain various other components in addition to virgin polyester polymers per se. For example, the feedstock may include colored polyesters (that may supply colorants / pigments / dyes or reaction products thereof to the depolymerization feed and effluent streams); plasticized polyesters (that may supply various plasticizers or reaction products thereof to the depolymerization feed and effluent streams) and previously recycled polyesters. Variations in the number and type of polyester resins present in depolymerization feedstocks can generate related variations in depolymerization reaction products that may impact the recovery of specific target depolymerization products. Depending on the specific type of polyester(s) fed to a depolymerization process, products such as dimethyl isophthalate may be present in product streams that, while separately useful and possibly a target depolymerization product in its own right, nonetheless must be separated from the EG and DMT target products. Other examples of useful target products include diols such as cis- or trans-cyclohexane-1 ,4-dimethanol (CHDM) or mixtures therein, cis- or trans- cyclohexane-1 ,3-dimethanol (CHDM) or mixtures therein, cis- or trans-cyclobutane-2, 2,4,4-tetramethyl-1 ,3-dimethanol (TMCD) or mixtures therein, diethylene glycol, neopentylglycol, 1 ,3-propanediol, 1 ,4-butanediol, and triethylene glycol.

[0009] Feedstocks may also contain non-polyester polymer materials that may for example pass through the depolymerization process or generate (and / or catalyze the formation of) undesirable by-products. For example, Bisphenol-A may be present in a depolymerization product stream when polycarbonate materials are present in the feed stream and diesters of adipic acid such dimethyl adipate may be present in the depolymerization product streams when the feed stream includes polyamide materials. Depolymerization feedstocks may also include contaminants such as dirt, glass, paper and other non-polymer materials that may also pass through the depolymerization reactor or generate undesirable by-products.

[0010] A depolymerization product stream may include additional materials which could impact recovery of target products. For example, the depolymerization reaction itself may also generate undesirable or less desirable side-species in the product streams. Further, catalysts utilized in the depolymerization reaction may also be present in the depolymerization product streams, acting as catalyst for undesirable product stream component reactions as well as an independent contaminant source. Catalytically active species may also enter the depolymerization process with the feedstock components. Undesirable catalytically active species may include one or more salts, oxides, or complexes of Ti, Sb, Fe, Zn, Mn, Ge, Sn, Ni, Co, Mn, Mo.

[0011] Separation and subsequent disposal of side-species, byproducts and contaminants from methanolysis and glycolysis depolymerization product streams can be expensive, capital-intensive, time-consuming and environmentally problematic. Further, while the commercial value or utility of at least some of the side species may be changed or improved by conversion to other more useful or valuable compounds; however, this conversion almost certainly adds additional processing steps (and therefore cost) to the process and must be managed to avoid negative impacts on target product conversion, yield and purity. In the end, the presence of one or more of these contaminants, side species and the like negatively impacts the use and recovery of the more useful or commercially valuable components of the depolymerization product stream (that may be referred to as target products or target depolymerizationproducts) such as EG and DMT. A continuing and unmet need therefore exists for a method to treat the product streams of a polyester depolymerization process to provide high conversion and yield of target products such as EG and DMT with quality and purity levels that are comparable to virgin materials and commercially suitable for use in the manufacture of polymers and other chemical compounds with recycle content.SUMMARY OF THE INVENTION

[0012] In a first aspect, the present invention relates to a method for treating a methanolysis depolymerization product stream from a polyester methanolysis depolymerization process wherein the methanolysis depolymerization product stream includes DMT, EG, impurities and methanol. The method of this aspect of the present invention includes (i) refining the methanolysis depolymerization product stream in a DMT refining zone to produce a DMT product stream and an EG product stream; (ii) refining said EG product stream in an EG refining zone to produce an EG target stream and EG refining zone effluent; and (iii) recovering methanol from at least one of said depolymerization product stream, said DMT refining zone and said EG refining zone in a methanol recovery zone; wherein at least one of steps (i), (ii) and (iii) is at least partially conducted in the presence of a refining solvent.

[0013] In another aspect, the present invention relates to method for methanolysis depolymerization of polyester. The method of this aspect of the present invention includes the steps of (a) depolymerizing a polyester via methanolysis to form a methanolysis depolymerization product stream comprising DMT, EG, impurities and methanol; (b) refining said methanolysis depolymerization product stream in a DMT refining zone to produce a DMT product stream and an EG product stream; (c) refining said EG product stream in an EG refining zone to produce an EG target stream and EG refining zone impurities effluent; and (d) recovering methanol from at least one of said depolymerization product stream, said DMT refining zone and said EG refining zone in a methanol recovery zone; wherein at least one of steps (a), (b), (c) and (d) is at least partially conducted in the presence of a refining solvent.

[0014] In another aspect, the present invention relates to a system for treating a methanolysis depolymerization product stream from a polyester methanolysis depolymerization process. The system of this aspect of the present invention includes a depolymerization product stream including DMT, EG, impurities and methanol; a DMT refining zone; an EG refining zone; and a methanol recovery zone; where at least one of the DMT refining zone, the EG refining zone and the methanol recovery zone include a refining solvent.

[0015] In another aspect, the present invention relates to a system for depolymerizing polyester via methanolysis. In this aspect, the system of the present invention includes a methanolysis depolymerization zone generating a depolymerization product stream including DMT, EG, impurities and methanol; a DMT refining zone; and EG refining zone; and a methanol recovery zone; where at least one of the DMT refining zone, the EG refining zone and the methanol recovery zone include a refining solvent.

[0016] Further aspects of the invention are as disclosed and claimed herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figures 1a, 1b and 1c are graphic depictions of the present invention as directed to methods and systems for treating a depolymerization product stream from a polyester methanolysis depolymerization process;

[0018] Figures 2a and 2b are graphic depictions of exemplary DMT refining zones useful in methods and systems of the present invention;

[0019] Figure 3a and 3b are graphic depictions of exemplary methanol recovering zones useful in methods and systems of the present invention;

[0020] Figure 4a and 4b are graphic depictions of exemplary EG refining zones useful in methods and systems of the present invention; and

[0021] Figures 5a, 5b and 5c are graphic depictions of the present invention as directed to a method for depolymerizing polyester and a polyester depolymerization system.DETAILED DESCRIPTION

[0022] The term “polyester” as used herein is meant to generally include without limitation homopolyesters as well as copolyesters, terpolyesters and the like and are typically prepared by reacting a difunctional carboxylic acid or its ester, often a dicarboxylic acid, or mixtures of such acids or esters, with a difunctional hydroxyl compound, often a diol or glycol, or mixtures of such diols or glycols. Alternatively, the difunctional carboxylic acid may be a hydroxy carboxylic acid and the difunctional hydroxyl compound may be an aromatic nucleus bearing 2 hydroxyl substituents such as, for example, hydroquinone. Examples include polyesters having repeating aromatic or cyclic units such as those containing a repeating terephthalate or naphthalate units such as polyethylene terephthalate (PET) and PEN, or those containing repeating furanate repeating units, and although within the definition of PET, it is worth mentioning also those polyesters having repeating terephthalate units and one or more residues or moieties of TMCD (2,2,4,4-tetramethyl-1 ,3-cyclobutanediol), CHDM (cyclohexanedimethanol), propylene glycol, or NPG (neopentylglycol), isosorbide, isophthalic acid, 1,4-butanediol, 1 ,3-propanediol, and / or diethylene glycol, or combinations thereof and aliphatic polyesters such as PLA, polyglycolic acid, polycaprolactones, and polyethylene adipates; Polyesters and polyester manufacture are generally well known and are exemplified in for example U.S. Patent Nos. 2,891 ,930 and 2,720,502, assigned to a legacy assignee of the present invention, the contents and disclosure of which are incorporated herein by reference.

[0023] A “polyester depolymerization process” as the phrase is used herein includes any method, process or system for treatment of polyester-containing feedstocks under conditions to produce or generate one or more oligomers or monomers from which the polyester may be formed. Non-limiting examples include without limitation methanolysis depolymerization; alcoholysis depolymerization, e.g., using 2-ethylhexanol as the depolymerizing alcohol; glycolysis depolymerization; pyrolysis depolymerization; hydrolysis depolymerization; and hydrogenolysis depolymerization.

[0024] A “methanolysis depolymerization product stream”, as the phrase is used herein, includes any stream generated in the course of or in conjunction with a method, process or system for depolymerizing polyester via methanolysis. Specifically contemplated as methanolysis depolymerization product streams are all streams generated in a depolymerization process upstream from, in sequence with or downstream from a methanolysis depolymerization reaction. Depolymerization product streams expressly include without limitation streams that have been or will be subject to separation, purification, crystallization, precipitation, filtration, centrifugation, sedimentation, leaching, solid-liquid separation, hydrocyclonization, drying, distillation, extractive distillation, azeotropic distillation, reactive distillation, extraction, decantation, evaporation, adsorption, pervaporation, membrane permeation, flotation, further reaction or similar processing steps in the course of or in conjunction a method, process or system for depolymerization of polyester in addition to those steps or system elements described herein.

[0025] The phrase “target product” is used herein to describe the compound(s) or material(s) on which the oligomeric or monomeric unit(s) of the depolymerized polyester is based. Specific non-limiting examples may include dimethyl terephthalate (DMT), dimethyl isophthalate (DMI), or mixtures of DMT and DMI, and glycols such ethylene glycol (EG) as when the depolymerized polyester is PET; diols such as cis- or trans-cyclohexane- 1 ,4-dimethanol (CHDM) or mixtures therein, cis- or trans- cyclohexane-1 ,3-dimethanol (CHDM) or mixtures therein, cis- or trans-cyclobutane-2,2,4,4-tetramethyl-1 ,3-dimethanol (TMCD) or mixtures therein, diethylene glycol (DEG), neopentylglycol, 1 ,3-propanediol, 1 ,4-butanediol, triethylene glycol, and mixtures of DEG and EG.

[0026] “Impurities” as the term is used herein includes any materials present in a depolymerization product steam other than target products and depolymerization reagents. Specific non-limiting examples of impurities may include colorants such as dyes and pigments; catalysts, including residual depolymerization catalyst and polymerization catalyst present in feedstock; reaction products (other than target depolymerization products) from other sidereactions that may occur in either the purposeful depolymerization reaction or other downstream steps; solvents; oligomers; residual reactants; and the like. In one or more embodiments, impurities may include materials with a boiling point lower than the boiling point of a target product, materials with a boiling point higher than the boiling point of a target product, materials that form azeotropes with one or more target products a combination thereof. As is appreciated by those skilled in the art, azeotropes are constant boiling mixtures of volatile species, i.e., a mixture in which the vapor and liquid phase compositions are equal. As such, azeotropic mixtures cannot be separated by simple fractional distillation, as distillative separation techniques rely on enhancement of the composition of one component in the vapor phase relative to the composition of the same component in the liquid phase.

[0027] ““Depolymerization reagents”, also referred to as depolymerization agents, include reactants or reagents that are purposefully added to a depolymerization zone for the depolymerization of polyester, often in stoichiometric excess, with a depolymerization reagent that is present in the depolymerization product stream as residual or unreacted from the depolymerization process referred to as an “unreacted” depolymerization reagent. Typical depolymerization agents are C1 to C16 alkanols, such as methanol, ethanol, 1 -propanol, 2-propanol, 1 -butanol and C4 isomers, cyclohexanol, 1 -hexanol and C6 isomers, 1 -octanol, 2-ethylhexanol and C8 isomers, benzyl alcohol, methyl benzyl alcohols, detergent alcohols; C2-C16 diols or glycols such as ethylene glycol, diethylene glycol, triethylene glycol, 1 ,4-CHDM and isomers, 1,4-benzenedimethanol and isomers, neopentyl glycol; C4 to C12 polyols such as trimethylol propane, trimethylol ethane, glycerol, pentaerythritol. Preferred depolymerization reagents are methanol, ethylene glycol, diethylene glycol and 2-ethylhexanol. In the example wherein depolymerization in a depolymerization zone is methanolysis depolymerization, a depolymerization reagent includes methanol.

[0028] The term “zone” is intended to describe a collection of one or more interconnected unit operations and related devices assembled to contribute to achievement of a related system or method purpose or purposes.In non-limiting examples relevant to the present invention, a “depolymerization zone” may include a reacting or depolymerizing operation employing suitable apparatus or systems such as a reactor or depolymerizer; a “refining zone” may include one or more unit operations to refine a stream such as separating, extracting, distilling, evaporating, condensing, decanting, crystallizing, filtering and the like employing suitable apparatus such as a extractor, distillation column, evaporator, condenser, decanter, crystallizer, filter and the like. A “recovery zone” may include one or more unit operations to recover and / or recycle one or more stream components such as separating, extracting, distilling, evaporating, condensing, decanting, crystallizing, filtering and the like employing suitable apparatus such as a extractor, distillation column, evaporator, condenser, decanter, crystallizer, filter and the like.

[0029] The present invention is described herein with respect to various interrelated aspects and embodiments, including but not limited to a method for treating a depolymerization product stream from a polyester depolymerization process and a method for depolymerizing polyester. One of ordinary skill will understand and appreciate that elements or features used to describe one aspect or embodiment may be applicable and useful in describing other embodiments. Accordingly, descriptions and disclosure relating to elements or features of an aspect or embodiment of the present invention are hereby expressly relied on to describe and support those elements or features in other aspects or embodiments.

[0030] The present invention, in a first aspect, is directed to a method for a treating a methanolysis depolymerization product stream from a polyester methanolysis depolymerization process. The method includes (i) refining a methanolysis depolymerization product stream in a DMT refining zone to produce a DMT product stream and an EG product stream; (ii) refining the EG product stream in an EG refining zone to produce EG target stream and an impurities purge stream; and (iii) recovering methanol from at least one of the depolymerization product stream, the DMT refining zone and said EG refining zone, wherein at least one of refining step (i), refining step (ii) and recovering step (iii) is at least partially conducted in the presence of a refining solvent.

[0031] In one or more embodiments, refining step (i) of this aspect of the method of the present invention is at least partially conducted in the presence of a refining solvent. In one or more embodiments, refining step (ii) of this aspect of the method of the present invention is at least partially conducted in the presence of a refining solvent. In one or more embodiments, recovering step (iii) of this aspect of the method of the present invention is at least partially conducted in the presence of a refining solvent. In one or more embodiments, refining step (i) and refining step (ii) of this aspect of the method of the present invention are at least partially conducted in the presence of a refining solvent. In one or more embodiments, refining step (ii) and recovering step (iii) of this aspect of the method of the present invention are at least partially conducted in the presence of a refining solvent. In one or more embodiments, refining step (i) and recovering step (iii) of this aspect of the method of the present invention are at least partially conducted in the presence of a refining solvent. In one or more embodiments, refining step (i), refining step (ii) and recovering step (iii) of this aspect of the method of the present invention are at least partially conducted in the presence of a refining solvent.

[0032] Figures 1a, 1b and 1c provide general flow-chart diagrams of non-limiting embodiments of the method and system of the invention for illustration though it will be appreciated that other embodiments are contemplated. In some embodiments, and with reference to Figures 1a, 1b and 1c, a methanol recovery step (iii) may be performed in one or both of a DMT refining zone 40 and EG refining zone 100 and a methanol recovery step (iii) may include recovering methanol from one or both of DMT refining zone 40 and EG refining zone 100. Again, with reference to Figure 1a, depolymerization product stream 5 may serve as feed to, and may be processed in DMT refining zone 40 which may generate and from which may emanate DMT product stream 22 and EG product stream 32. EG product stream 32 may serve as feed for EG refining zone 100 which may generate and from which may emanate EG target stream 110 and EG refining zone impurities effluent 72.

[0033] In some embodiments, and as depicted in FIG 1b, a methanol recovery step (iii) may be performed at least in part in a methanol recovery zone80 that may be downstream from a DMT refining zone 40 and / or may be between DMT refining zone 40 and EG refining zone 100. Again, with reference to Figure 1b, depolymerization product stream 5 may serve as feed to, and may be processed in DMT refining zone 40 which may generate and from which may emanate DMT product stream 22 and EG product stream 32. EG product stream 32 may serve as feed for methanol recovery zone 80 which may generate and from which may emanate EG refining zone feed 32’ which feeds EG refining zone 100 which may generate and from which may emanate EG target stream 110 and EG refining zone impurities effluent 72. In such embodiments, the methanol recovering step (iii) of the method of the present invention may include recovering methanol from the EG product stream 32. In general, and as demonstrated in the non-limiting embodiments depicted in the Figures, numbering or lettering of steps and zones (for example (i), (ii) and (iii) or (a), (b) and (c)) is not intended to and does not necessarily indicate a sequence or order for such steps or zones.

[0034] In some embodiments and as depicted in Figure 1c, a methanol recovery zone 80 may be upstream from DMT refining zone 40 with DMT refining zone 40 between methanol recovery zone 80 and EG refining zone 100. Again with reference to Figure 1c, depolymerization product stream 5 may serve as feed to, and may be processed in, methanol recovery zone 80 from which may emanate a modified depolymerization product stream 5’ which may also be described as a methanol recovery exit stream insofar as it has yet to be refined in either DMT refining zone 40 or EG refining zone 100, or which is labeled as solvent-rich stream 96 in Figure 3b. Modified depolymerization product stream 5’ may serve as feed for a DMT refining zone 40 which may generate and from which may emanate DMT product stream 22 and EG product stream 32. EG product stream 32 may in turn serve as feed for EG refining zone 100 which may generate and from which may emanate EG target stream 110 and EG refining zone impurities effluent 72. In such embodiments, the methanol recovering step (iii) of the method of the present invention may include recovering methanol from the depolymerization product stream 5.

[0035] Though the step of recovering methanol may be performed in what is referred to as a methanol recovery zone, it will be appreciated that methanol may also be recovered from one or more of EG refining zone 100 and DMT refining zone 40 and additionally from methanol recovery zone 80. Accordingly, as depicted in FIGs 1a, 1b and 1c, each of DMT refining zone 40 and EG refining zone 100 as well as any methanol recovery zone 80 may include methanol recovery streams emanating therefrom as shown generally as element 4 in Figures 1 a through 1 c.

[0036] In one or more embodiments, the methanolysis depolymerization product stream 5 may generally include DMT, EG, impurities and methanol. In one or more embodiments, the depolymerization process is a methanolysis depolymerization process and the depolymerization product stream is a methanolysis depolymerization product stream formed from a methanolysis depolymerization process. For avoidance of doubt, the phrase ’’depolymerization product stream” as used herein is intended to broadly include product streams generated from a depolymerization zone or depolymerization reactor, including product streams which have been subjected to one or more processing or refining steps such as, for example, separation, purification, crystallization, precipitation, filtration, centrifugation, sedimentation, leaching, solid-liquid separation, hydrocyclonization, drying, distillation, extractive distillation, azeotropic distillation, reactive distillation, extraction, decantation, evaporation, adsorption, pervaporation, membrane permeation, flotation, further reaction or similar processing steps, prior to refining step of the method of the present invention. One of ordinary skill will appreciate that polyester depolymerization processes, and depolymerization product stream compositions, will vary widely depending on a number of factors such as for example feedstock content and purity, processing parameters and presence or absence of post-depolymerization processing such as separation, purification, crystallization, precipitation, filtration, centrifugation, sedimentation, leaching, solid-liquid separation, hydrocyclonization, drying, distillation, extractive distillation, azeotropic distillation, reactive distillation, extraction, decantation,evaporation, adsorption, pervaporation, membrane permeation, flotation, further reaction or similar processing steps.

[0037] In one or more embodiments, a refining solvent may be present in the one or more of refining step (i), refining step (ii) and recovering step (iii) of this aspect of the method of the present invention. The presence of refining solvent in a given step or a corresponding zone as described herein may be established by one or more approaches. In one or more embodiments, a refining solvent may be purposefully added to or present in one or more of refining step (i), refining step (ii) and recovering step (iii). In one or more embodiments, a refining solvent may be present as a residual component of a feed stream or supply stream or a recycle stream to one or more of refining step (i), refining step (ii) and recovering step (iii) of this aspect of the method of the present invention. In one or more embodiments, a refining solvent may be purposefully added to and present in one or more of DMT refining zone, methanol recovery zone and EG refining zone. In one or more embodiments, a refining solvent may be present as a residual component of a feed stream or supply stream or a recycle stream to one or more of refining step (i), refining step (ii) and recovering step (iii). In one or more embodiments, a refining solvent may be present as a residual component of a feed stream or supply stream or a recycle stream to or in one or more of DMT refining zone, methanol recovery zone and EG refining zone. In one more embodiments, the refining solvent may adjust solubilities of certain chemical species, act as an extracting agent which may form a second liquid phase and provide a medium for liquid-liquid interphase mass transfer, and / or break azeotropes present in the various zones and related unit operations and devices and consequently may improve recovery and purity of target products such as DMT and EG and expand the range of process operational parameters. In one or more embodiments, refining solvents are hydrophobic.

[0038] Suitable refining solvents may include one or more of C6 to C15 aromatics; C5 to C12 esters; C7 to C20 alkanes; C6 to C20 ethers; C6 to C15 ketones; C6 to C15 chlorinated aromatics; and C6 to C20 chloroalkanes. Specific examples of suitable refining solvents include ethylbenzene, cumene,diisopropylbenzene, mesitylene and isomers, m-xylene, o-xylene, p-xylene, and mixtures thereof , mixtures of primarily C9-C11 aromatics such as Aromatic 150 or Solvesso™ 150 , mixtures of primarily C12-C15 aromatics commonly known as Aromatic 200 or Solvesso™ 200 sold commercially by Exxon Mobil™ mixtures of iso alkanes commonly known as Isopar solvents, such as Isopar™ C, Isopar™ G, Isopar™ H, Isopar™ L, and Isopar™ M. motor gasoline, kerosene, white mineral spirits, chlorobenzene, dichlorobenzene isomers, either individually or as mixtures, methyl propyl ketone (MPK), methyl amyl ketone (MAK), methyl isoamyl ketone (MIAK), di-isobutyl ketone (DIBK), methyl iso-butyl ketone (MIBK), di-isopropyl ketone (DIPK), methyl isopropyl ketone (MIPK), diamyl ketone (DAK), di-isoamyl ketone (DIAK), dipropyl ketone (DPK), mixtures of C11 ketones such as commercially available from Eastman Chemical, mixtures of C7 ketones such as commercially available from Eastman Chemical, isophorone, mixtures of C9 ketones such as commercially available from Eastman Chemical, dibutyl ether, dipropyl ether, n-heptane and isomers and mixtures thereof, hexane and isomers and mixtures thereof, cyclohexane, methyl cyclohexane, n-octane and isomers, n-octane and isomers and mixtures thereof, n-decane and isomers and mixtures thereof, n-undecane and isomers, n-dodecane and isomers and mixtures thereof. In one or more embodiments, the refining solvent may be substantially immiscible with at least one of EG and DMT. The refining solvent may be substantially immiscible with other glycols such as diethylene glycol, triethylene glycol, (i.e., the refining solvent and said glycols may form two liquid phases when mixed and allowed to quiescently de-mix under process conditions). Mixtures of two or more refining solvents are also contemplated, including for example a mix of Aromatic 150 and a C7 to C9 ketone and a mix of Aromatic 200 with a C9 ketone.

[0039] In one or more exemplary embodiments, the refining solvent may be characterized by a parameter referred to as “partition coefficient”. In general, the partition coefficient is the ratio of concentrations of a compound in a mixture of two immiscible solvents at equilibrium and therefore a comparison of the solubilities of the solute in these two liquids. Most commonly, one of thesolvents is hydrophilic (for example water, ethylene glycol, higher glycols, or combinations therein), while the second is hydrophobic (for example a non-glycolic C4 or higher species) . In such cases, the partition coefficient measures how hydrophilic ("water-loving") or hydrophobic ("water-fearing") a solute or chemical substance is. An equation for partition coefficient useful in the present invention is set forth in the Examples below and experimental data regarding partition coefficients of useful refining solvents is set forth in the related Tables. Partition coefficients for the refining solvents of the present invention may be greater than 0.6, with preferred partition coefficients being greater than 1.0 or greater than 1 .5.

[0040] In one or more exemplary embodiments, the refining solvent may be characterized by a parameter referred to as “selectivity”. In general, selectivity may be described as the ratio of the partition coefficient of a target product (usually DMT) or hydrophobic impurity in a refining solvent to the partition coefficient of hydrophilic target product (ethylene glycol) in a particular refining solvent. Selectivities for refining solvents of the present invention may be greater than 5, with preferred selectivities being greater than 10.

[0041] The amount of refining solvent present in a step or zone of this aspect of the method of the present invention may vary depending on a number of factors including without limitation type and purpose of step, stream component identity and amount, design of process equipment, and the like. In one or more embodiments, the refining solvent is present in an amount of from 0.02 / 1 to 4.0 / 1 or from 0.05 to 2.0 solvent to treated stream weight ratio based on the total weight of the material or stream being treated, wherein the stream may be selected from the group consisting of one or more of the depolymerization product stream and EG product stream.

[0042] In some embodiments, the method of the present invention may include a step of feeding a refining solvent, shown at 200 including refining solvent to one or more of DMT refining zone 40, methanol recovery zone 80 and EG refining zone 100. In one or more embodiments, the refining solvent may be combined with or mixed with or added to the depolymerization product stream 5 or the EG product stream 32. Accordingly, in one or moreembodiments, the method of the present invention includes mixing refining solvent feed with the depolymerization product stream or the EG product stream. It may be appreciated that the presence of the refining solvent in the various zones and / or steps may be established by one or more of (a) purposefully adding fresh refining solvent feed to a zone or step as depicted at 200; (b) adding refining solvent to a zone or step as a residual component of a process stream feeding into a zone or step; and (c) adding recycled refining solvent as a recycle stream (or component thereof) supplied to a zone or step. In one or more exemplary embodiments, the method may include purposefully adding fresh refining solvent to methanol recovering step (iii) in a methanol recovery zone. In one or more exemplary embodiments, the method may include (a) purposefully adding fresh refining solvent to methanol recovering step (iii) in a methanol recovery zone and (b) adding refining solvent to refining step (ii) in an EG refining zone by one or both of (i) as a residual component of a process stream and (ii) as a recycle stream (or component thereof).

[0043] In one or more embodiments, and as depicted for example in FIG 2a, a DMT refining zone 40 may include a condensing unit 45, a crystallizer 50, a solid-liquid separation unit 55, a DMT concentration unit 60 and a DMT refining column 65. Accordingly, in one or more embodiments, the refining step (i) may include (i)(a) processing a depolymerization product stream 5 may include methanol, ethylene glycol, DMT, DMI, and minor amounts of other terephthalyl and isophthalyl species, in condensing unit 45 wherein hot, vaporous depolymerization effluent (typically at 200 to 260°C), may be cooled, condensed, and methanol content adjusted (via partial condensation) to form a concentrated DMT stream 46, which may include 20 to 35 wt%, more typically 22 to 32 wt%, DMT fully dissolved in solution, at 85 to 100°C and a condensing unit methanol recovery stream 47, comprising greater than about 85 wt% methanol (MeOH), more typically 90 wt% MeOH or more; (i)(b) crystallizing DMT from said concentrated DMT stream 46 in a crystallizer 50 to produce crystallizer DMT stream 51 and a crystallizer recovery stream 52; (i)(c) separating said crystallizer DMT stream 51 in a solid-liquid separation unit 55 to recover DMT crystals 56 and produce solid-liquid separation liquors 57 whichmay in some embodiments be used as a component of feed 32 for EG refining zone 100 or feed for methanol recovery zone 80 ;(i)(d) melting DMT crystals in a DMT concentration unit 60 to produce DMT melt 61 and DMT concentrator overhead stream 62; and (i)(e) distilling said DMT melt 61 in a DMT refining column 65, which in some embodiments may be operated as a side-draw column, to produce a DMT product stream 68 which may be a side-draw stream 68, high boiler stream 67, and a DMT column overhead stream 69.

[0044] In one or more embodiments, and as depicted for example in FIG 2b, a DMT refining zone 40 may include a crystallizer 50, a solid-liquid separation unit 55, a DMT concentration unit 60 and a DMT refining column 65. The DMT refining zone 80 as depicted in Fig 2b may be particularly useful in the embodiment of the present invention depicted in Figure 1c, wherein methanol recovery zone 80 producing modified depolymerization stream 5’, also labeled as solvent-rich stream 69, may be upstream from DMT refining zone 40 with DMT refining zone 40 between methanol recovery zone 80 and EG refining zone 100. In such embodiments, the refining step (i) in a DMT refining zone 40 may include (i)(a) crystallizing DMT from a modified depolymerization stream 5’ to produce crystallizer DMT stream 51 and a crystallizer recovery stream 52; (i)(b) separating said crystallizer DMT stream 51 in a solid-liquid separation unit 55 to recover DMT crystals 56 and produce solid-liquid separation liquors 57 which may in some embodiments be used as feed 32 (or a component thereof) for EG refining zone 100 or methanol recovery zone 80; (i)(c) melting DMT crystals in a DMT concentration unit 60 to produce DMT melt 61 and DMT concentrator overhead stream 62; and (i)(e) distilling said DMT melt 61 in a DMT refining column 65, which in some embodiments may be operated as a side-draw column, to produce a DMT product stream 68 which may be a side-draw stream 68, high boiler stream 67, and a DMT column overhead stream 69. In embodiments where column 65 is not operated as a side-draw column, no side-draw stream 68 is produced and stream 69 may be labeled as a DMT product stream. In one or more embodiments, at least one said steps (i)(a) though (i)(e) are performed in the presence of a refining solvent. In one or more embodiments, the method mayinclude the step of feeding refining solvent feed that includes one or both of fresh or recycle refining solvent to one or more of condensing unit 45, crystallizer 50, solid-liquid separation unit 55, DMT concentration unit 60, and DMT refining column 65. Said refining solvent feed may serve to solubilize DMT and other high-melting materials contained in depolymerization product stream 5 and widen operating conditions. Side-draw stream 68 may in some embodiments serve as DMT product stream 22; however, it is to be understood that in some embodiments overhead stream 69 may serve as a DMT product stream 22. Solid-liquid separation liquors 57 may serve in some embodiments as a component or the entirety of EG refining zone EG product stream 32 and / or EG refining zone feed 32’; therefore, one or more of EG refining zone feed 32’ and EG product stream 32 may include solid-liquid separation liquors 57 from the DMT refining zone 40.

[0045] In one or more embodiments, DMT refining column 65 comprises a conventional fractional distillation column comprising from about 2 to about 20 theoretical stages, more typically from 4 to 16 theoretical stages, wherein said staging is implemented as sieve trays, bubble cap trays, valve trays, random or structured packing, or other staging methods known in the art. The DMT refining column may be operated preferentially under vacuum, for example less than 0.12 bara or less than 0.12 bara top pressure, with exemplary base temperatures of less than 260°C, more typically less than 240°C, a reflux ratio of 0.1 to 5.0, more typically 0.4 to 2.0, and a distillate to feed weight ratio of greater than 0.9, more typically greater than 0.95. In one exemplary embodiment, the products of said DMT refining column are a refined DMT material comprising greater than 99 wt%, more typically greater than 99.5% DMT as overhead stream 69, and a high boiling stream 67, wherein said high boiling stream may include one or more of DMT, 2-hydroxyethyl methyl terephthalate (MHET), monomethyl terephthalate (MHT), BHET, residual dyes and terephalate oligomers of glycols. In another exemplary embodiment, the products of said DMT refining column may include a refined DMT material comprising greater than 99 wt%, more typically greater than 99.5% DMT as side-draw stream 68, an overhead stream 69 comprising low-boiling impuritiesexemplified by methanol, ethylene glycol, and residual refining solvent, and a high boiling stream 67 as described above. In one or more embodiments, the distillation may be done in the presence of refining solvent, wherein said refining solvent may serve to solubilize DMT and other high-melting materials contained in DMT melt stream 61 and widen operating conditions. In one or more embodiments additional refining solvent may be added to the DMT refining column to form low-boiling azeotropes with water, ethylene glycol or other glycols to enhance their separability from DMT and improve recovery of said azeotropes into overhead stream 69. It may be advantageous in certain embodiments to collect overhead stream 69 in a vessel capable of handling liquid-liquid phase formation (e.g., a decanter vessel), wherein heterogeneous azeotropes such as water-refining solvent, ethylene glycol-refini ng solvent pairs may be advantageously separated into a refining solvent-rich layer and water or ethylene-glycol containing layer.

[0046] In one or more embodiments, the depolymerization process may produce a vaporous depolymerization product stream 5 or the depolymerization product stream may be in vapor form, such as for example when methanol is used as a depolymerization agent in a high temperature, vapor-stripping operation. In one or more embodiments, the condensing step of condensing unit 45 may involve total or partial condensation, or fractionation wherein the DMT concentration is adjusted to 20 to 35 wt%, more typically 22 to 27 wt% DMT in the underflow condensed liquid product. A vaporous depolymerization stream 5 (at a temperature of for example from 200 to 260°C), may be cooled, condensed, and methanol content may be adjusted (via partial condensation and / or fractionation for example) to form a concentrated DMT stream 46, which may include 20 to 35 wt%, more typically 22 to 32 wt%, DMT fully dissolved in solution, at 85 to 100°C, along with a mixture of about 8 to 15 wt% ethylene glycol and other glycols, 50 to 70 wt% methanol, and a condensing unit methanol recovery stream 47, comprising greater than about 85 wt% MeOH, more typically 90 wt% or more. Typical pressures for operation of condensing unit 45 may be from 0.9 bara to 5 bara, more typically from about 1 bara to 4 bara. In such an embodiment, the condensing unit 45 may include any meansknown in the art for removal of sensible and latent heat, such as indirect cooling methods exemplified by shell and tube or plate and frame heat exchangers, direct contact cooling, or combinations thereof, and may include a staged fractionation column to improve the purity of either stream 46 or 47. In an exemplary embodiment, condensing may be performed in the presence of, or condensing unit 45 may be operated with addition of, refining solvent 200, such that the majority of methanol is removed overhead into methanol recovery stream 47 and the majority of the refining solvent is recovered in the form a concentrated DMT stream 46, which may include 20 to 45 wt%, more typically 25 to 40 wt%, DMT fully dissolved in solution, at 60 to 120°C, along with a mixture of about 8 to 20 wt% ethylene glycol and other glycols, less than 10 wt% methanol, and 30 to 70 wt% refining solvent.

[0047] In one or more embodiments, concentrated DMT stream 46 may be processed in crystallizer 50 to produce crystallizer DMT stream 51 and optionally crystallizer recovery stream 52. More generally, methods for the crystallizing step may involve one or more of several methods known in the art to assist in, or result in, precipitation or crystallization of the target product DMT, with non-limiting examples including controlled indirect cooling via heat exchange of the crystallizer solution to reduce the solubility of DMT in the crystallizer solution; controlled direct cooling, i.e., evaporative cooling, of the crystallizer solution by boiling and removal from the crystallizer solution of methanol or another component added or present as an evaporative cooling agent, i.e. refining solvent; concentration of DMT via distillation, evaporation or other vapor-liquid equilibrium-based separation method, of at least a part of the methanol or refining solvent to increase the level of supersaturation of DMT; and addition into the crystallization solution of a recovery enhancement agent such as an anti-solvent component for DMT. Non-limiting examples of antisolvents for methanol-rich crystallizer solutions include water and ethylene glycol. Examples of antisolvents for refining-solvent-rich crystallizer solutions are hydrocarbons, such as alkanes. Crystallizer 50 may be operated in batch or continuous mode, with one or more crystallizer vessels in series with successively lower operating temperatures. A typical final crystallizer 50temperature may be from 15 to 30°C. In an exemplary embodiment of crystallizer 50, wherein the crystallization solution is methanol rich, the crystallizer may be operated batchwise, with a cooling profile controlled to prevent rapid nucleation, and wherein the crystallization profile entails cooling from about 90°C to 100°C to about 20 to 30°C by evaporative cooling of methanol and corresponding reduction in operating pressure to achieve said temperatures, for example a final pressure of about 0.17 bara is needed to achieve an final temperature of about 25°C. Typically about 10 to 20 wt% of methanol in the inlet concentrated DMT stream 46 may be removed via evaporative cooling, and may optionally be removed from the system via stream 52 or returned partially or in total to crystallizer 50. Preferably about 90% to 98% of the DMT content of concentrated DMT stream 46 may be recovered per pass after crystallization, with DMI, EG, and other contaminating species remaining in solution. In another exemplary embodiment of crystallizer 50, wherein the crystallization solution is refining-solvent-rich, the crystallizer is operated batchwise, with a cooling profile controlled to prevent rapid nucleation, and wherein the crystallization profile entails cooling from a first temperature of about 90°C to 120°C to a second temperature of about 20°C to 40°C by evaporative cooling or indirect heat exchange. Preferably about 85% to 95% of the DMT content of concentrated DMT stream 46 may be recovered per pass after crystallization, with DMI, EG, and other impurities or contaminants remaining in solution. DMI is highly soluble in aromatic refining solvents, typically above 40 wt% at 50°C, providing an efficient means of recycle and concentration of DMT and DMI-containing liquids to crystallizer 50 after downstream processing, and to improve overall DMT recovery.

[0048] In one or more embodiments, the step of separating the crystallizer DMT stream in a solid-liquid separation unit 55 may be performed using methods, devices or systems known in the art, such as filtration, centrifugation, hydroclonization, sedimentation, and the like. For embodiments in which solid-liquid separation unit 55 comprises filtration, said filtration may be implemented as plate and frame filters, rotary vacuum filters, rotary pressure filters, belt filters, and other means known in the art wherein the majority of solidDMT particles are separated from crystallization liquors. The separating step in solid-liquid separation unit 55 typically produces a mass of crude DMT crystals comprising typically 30% to 75% solids and the remainder residual crystallization liquors. The separating step in solid-liquid separation unit 55 typically may be performed at temperatures less than 60°C, more typically less than 40°C, at pressure between 0.2 bara and 10 bara. The crude DMT crystals produced via the separating step in solid-liquid separation unit 55, may be washed with a suitable wash solvent to produce DMT wet cake 56 and spent wash liquor which may or may not be combined with crystallization liquors to produce solid-liquid separation liquors 57. Typically, the wash solvent is selected to have relatively low solubility of DMT at wash temperature. A particularly exemplary wash solvent is methanol. Another exemplary wash solvent is the refining solvent, such as for example xylene or Aromatic 150. The wash solvent is typically applied to the crude DMT crystals at a wash solvent to crude DMT crystals mass ratio of 0.3 / 1 to 5 / 1, more typically 0.5 / 1 to 2 / 1 mass ratio. The washing may be accomplished in a single step or with multiple wash steps, with either fresh wash solvent applied in each washing step or in countercurrent manner (fresh solvent contacts the crystals in the last wash step, and the resulting spent wash liquor is fed back to the previous wash step) as is well known in the art. The wash steps typically are accomplished at temperatures less than 60°C, more typically less than 30°C, at pressure between 0.2 bara and 10 bara. The separating step in solid-liquid separation unit 55 and corresponding wash steps may be accomplished continuously or batchwise.

[0049] In one or more embodiments, the method includes melting DMT crystals, for example crystals of a DMT wet cake, in a DMT concentration unit 60 to remove at least a portion of residual liquids contained therein. DMT concentration unit 60 may be operated batchwise or continuously. In one preferred embodiment, wherein the residual liquid comprises primarily methanol, DMT wet cake 56 may be conveyed to a previously heated mass of molten DMT in a process vessel (i.e., stirred tank or thermosyphon apparatus) and further heated to vaporize residual methanol via conveyance to an externalheat exchanger and recirculation into said heated mass. The process vessel may be fitted with a fractionation column, reflux condenser (partial or total), or both to accomplish condensation of vaporized residual methanol and subsequent removal as DMT concentrator overhead stream 62. Typically the process vessel and heat exchanger may be operated at 140 to 180°C, at 0.5 bara to 2 bara, and may result in reduction of methanol content of in DMT melt stream 61 to less than 5 wt%, more typically less than 2.5 wt%. In one or more embodiments, the melting step may be performed in the presence of refining solvent. Addition of refining solvent to DMT concentration unit 60 may be particularly advantageous when the residual liquid in the DMT wet cake 56 is methanol, with the refining solvent acting as an intermediate boiler and solubilizing agent for DMT and DMI, preventing fouling / freezing of DMT and DMI as methanol is removed from the mixture. In another preferred embodiment, wherein the residual liquid includes primarily refining solvent, DMT wet cake 56 is conveyed to a previously heated mass of molten DMT in a process vessel (i.e., stirred tank or thermosyphon apparatus) and further heated to vaporize refining solvent via conveyance to an external heat exchanger and recirculation into said heated mass. The process vessel may be fitted with a fractionation column, reflux condenser (partial or total), or both to accomplish condensation of vaporized methanol and subsequent removal as DMT concentrator overhead stream 62. Typically, the process vessel and heat exchanger may be operated at 140 to 200°C, at 0.1 bara to 1 .5 bara, and may result in reduction of refining solvent content in DMT melt stream 61 to less than 5 wt%, more typically less than 1 .5 wt%, more typically less than 1 wt%, and produce a DMT melt stream of greater than 95 wt%, more typically greater than 98% DMT. If ethylene glycol or other similar glycols are present in DMT wet cake 56, removal of refining solvent may also accomplish removal of said glycols via formation and distillation of refining solvent-glycol low-boiling azeotropes.

[0050] In one or more embodiments, the method includes distilling the DMT melt 61 in a DMT refining column 65, which in some embodiments may be a side-draw column, to produce side-draw stream 68, high boiler stream 67,and a DMT column overhead stream 69. In one or more embodiments, at least one of said steps (i)(a) though (i)(e) described herein are performed in the presence of a refining solvent. In one or more embodiments, the method may include the step of feeding refining solvent feed that includes one or both of fresh or recycle refining solvent to one or more of condensing unit 45, crystallizer 50, solid-liquid separation 55, DMT concentration unit 60, and DMT refining column 65. The refining solvent may serve to solubilize DMT and other high-melting materials contained in depolymerization product stream 5 and widen operating conditions. Further, in embodiments where ethylene glycol or other similar glycols are present in DMT melt stream 61, removal of refining solvent may also accomplish removal of said glycols via formation and distillation of refining solvent-glycol low-boiling azeotropes. Side-draw stream 68 may in some embodiments serve as DMT product stream 22; however, it is to be understood that in some embodiments overhead stream 69 may serve as DMT product stream 22.

[0051] In one or more embodiments, and as described in more detail in a non-limiting Example 4 below, DMT present in the methanolysis depolymerization may be in solid form (such that crystallization is not required). In such embodiments, DMT refining zone 40 may simply include a solid-liquid separation unit 55 forming DMT solids (wet cake) 56 and solid-liquid separation liquors 57.

[0052] In one or more embodiments, a methanol recovering step (iii) may be conducted in a methanol recovery zone 80. FIG 3a generally depicts a non-limiting embodiment of a methanol recovery zone 80, which may be utilized for example with the method / system depicted in Fig. 1b. In one or more embodiments, the methanol refining zone 80 may include one or more of methanol recovery column 85 and a liquid-liquid refining zone 90 that includes decanter 90a and refining solvent column 98. Methanol recovery zone 80 may be fed by methanol recovery zone feed 81 which may include one or more of depolymerization product stream 5, solid-liquid separation liquors 57, refining solvent-rich stream 96, refining solvent recycle stream 99 and / or refining solvent side-draw recycle stream 92. Accordingly, in one or more embodiments,recovering methanol step (iii) comprises (iiia) distilling a methanol recovery zone feed 81 including at least one of the depolymerization product stream 5 and the EG product stream 32 in the presence of the refining solvent in a methanol recovery column 85 to produce a methanol recovery stream 86 and an methanol-depleted column underflow 87 and (iiib) further processing said methanol-depleted column underflow 87 via a liquid-liquid equilibrium-based separation method in the presence of a refining solvent in liquid-liquid refining zone 90 to produce refining solvent-rich stream 96 and EG-rich stream 97 which, in embodiments wherein methanol recovery zone 80 is upstream from an EG refining zone 100, also serves as feed 32 for the EG refining zone 100 such that EG refining zone feed 32 may include EG-rich stream 97 from the methanol recovery zone 80. In one or more exemplary embodiments, EG-rich stream includes residual refining solvent that may be used to supply refining solvent to EG refining zone 100 so as to be present in refining step (ii). In one or more embodiments, the method may further include (iiid) refining at least a portion of one or both of the refining solvent-rich stream 96 and recycle stream 125 in a refining solvent column 98 to produce a refining solvent overhead stream 99 and refining solvent column bottoms stream 93. In one or more embodiments, the method may further include (iiie) refining one or both of the refining solvent-rich stream 96 and refining solvent recycle stream 125 in the refining solvent column 98 to produce a refining solvent overhead stream 99 and / or a refining solvent side-draw recycle stream 92. In some embodiments, the method may further include recycling at least a portion of one or more of the refining solvent-rich stream 96, the refining solvent recycle stream 99 and / or refining solvent side-draw recycle stream 92 to one or both of methanol recovery column 85 and liquid-liquid refining zone 90. As EG-rich stream 97 may serve as feed (or a component thereof) for EG refining zone 100, for convenience the stream may be referred to herein as EG refining zone feed 32 in applicable embodiments.

[0053] Referring to Figure 3a, in one or more embodiments, the refining solvent conveyed to methanol refining column via streams 99, 92, 96, or as part of 5, is fed at a ratio of 0.05 / to 1 / 1 mass ratio of refining solvent todepolymerization product stream 5 (with the mass of stream 5 calculated on a refining-solvent free basis, more typically 0.1 / 1 to 0.5 / 1 mass ratio). Preferably, more than 85%, more preferably more than 92% of the methanol included in stream 5 exits zone 80 in methanol recovery stream 86. Preferably, the methanol concentration in methanol-depleted column underflow 87 is less than 10 wt%, more preferably less than 6 wt%. Said methanol recovery column preferably operates at a bottom temperature of 100 to 135°C, at a top pressure of 0.7 bara to 2 bara, more preferably 110 to 125°C and less than 1 .2 bara. The purity of methanol recovery stream 86 is controlled by the staging and refluxing implemented in column 85, but typically is more than 90 wt% methanol, more typically is greater than 93 wt% methanol. Typical impurities in the methanol recovery stream 86 comprise water and refining solvent. Preferred reflux ratios are greater than 0.05 and less than 2.0, more preferably 0.1 to 0.8, with theoretical staging (excluding reboiler) preferably of 1 to 15 stages, more preferably 5 to 10 stages.

[0054] Again referring to Figure 3a, in one or more embodiments, refining solvent-rich stream 96 is purified in a refining solvent column 98 to produce a refining solvent overhead stream 99. In one or more embodiments, the method may further include (iiie) refining one or both of solvent recycle stream 125 and solvent-rich stream 96 in the refining solvent column 98 to produce a refining solvent overhead stream 99 and / or a refining solvent side-draw recycle stream 92. Said solvent recovery column 98 preferably operates at a bottom temperature of 160 to 245°C, at a top pressure of 0.1 bara to 1.2 bara, more preferably 180 to 220°C and less than 0.5 bara. When column 98 is run in sidedraw mode, stream 99 comprises low boilers exemplified as any remaining methanol, depolymerization impurities boiling less than the refining solvent, water, and possibly glycols. The purity of side-draw stream 92 or overhead stream 99 (when column 98 is operated without a side-draw 92) is controlled by the staging and refluxing implemented in column 98, but typically is more than 90 wt% refining solvent, more typically is greater than 95 wt% refining solvent. Typical impurities in the methanol recovery stream 86 comprise water and refining solvent. Preferred reflux ratios are greater than 0.05 and less than2.0, more preferably 0.3 to 0.1, with theoretical staging (excluding reboiler) preferably of 3 to 30 stages, more preferably 6 to 20 stages. Refining solvent column bottoms stream 93 typically comprises hydrophobic impurities less volatile than the refining solvent that partitioned into the refining solvent during decantation or extraction occurring in zone 90. Exemplary constituents of stream 93 are DMT, DMI, fatty acid esters such as plasticizers and other materials in the original depolymerization feedstock.

[0055] Again referring to Figure 3a, stream 92 may comprise water, ethylene glycol, and similar glycols that form two liquid phases with the refining solvent, wherein stream 92 may form two layers upon cooling and storage. In at least one embodiment, stream 92 may be conveyed to a liquid-liquid separation device to remove any hydrophilic layer prior to recycle to other unit operations. Solvent refining column 98 may also be implemented as two columns with streams 99 and 92 distillates in successive columns.

[0056] Liquid-liquid refining zone 90 comprises at least one method known in the art to exploit liquid-liquid phase equilibrium to effect purification of the EG target product via interaction with a refining solvent such as a hydrophobic refining solvent. The hydrophobic refining solvent is chosen such that it is immiscible with hydrophilic ethylene glycol and forms a refining solventrich stream and an EG-rich stream. EG purification results from preferential partitioning of hydrophobic impurities contained in methanol-depleted column underflow 87 into the hydrophobic refining solvent and away from the EG-rich phase. Non-limiting examples of hydrophobic impurities partitioned in zone 90 from EG-rich stream 97 include but are not limited to DMT, DMI, and other alkanol or alkoxy esters of terephthalic acid or isophthalic acid, 2-hydroxyethyl methyl terephthalate, methyl benzoate, methyl-para-toluate, 4-methylene-cyclohexanemethanol, fatty acid methyl esters such as methyl octanoate, methyl decanoate, methyl doecanoate, and the like, 1 ,4-dioxane, 2-methyl-1 ,3-dioxolane, methyl 4-vinylbenzoate, Methyl 4-cyanobenzoate, Methyl 4-acetylbenzoate, methyl 4-ethylbenzoate, diacid esters such as dimethyl adipate, acetals of methanol, C4 and higher aldol derivatives of acetaldehyde, such as crotonaldehyde, sorbaldehyde, octatrienal, alpha-methyl styrene andthe like. Many of these hydrophobic impurities are derived from non-PET components or plastics of the depolymerization feedstocks or by-products resulting from the depolymerization process reaction conditions. Moreover, many of these impurities form minimum boiling azeotropes with ethylene glycol, or are close boiling to ethylene glycol, and are difficult to separate efficiently from ethylene glycol by distillative separation methods.

[0057] The partitioning of hydrophobic impurities may be accomplished by equipment and techniques known in the art, such as one or more steps of decantation, counter-current multi-stage extraction, or fractional extraction, and implemented with equipment designs known in the art, such as mixer-settlers, unagitated configurations, such as bubble, baffled, packed or trayed multi-stage countercurrent extractors, or agitated extractors such as Kuhni, Karr, Scheibel, rotating disk, or centrifugal extractors. Referring to Figure 3a, in one exemplary embodiment, liquid-liquid liquid refining zone 90 comprises a single stage decanter 90a, wherein the total refining solvent (entering via streams 87 or 92) is fed at a mass ratio of 0.05 / 1 to 4 / 1 , more preferably 0.1 to 1 / 1 mass ratio of solvent to stream 87 (with the mass of stream 87 calculated on a refiningsolvent free basis), and is operated at a temperature of 40 to 120°C, more preferably 60 to 95°C, and a pressure sufficient to keep all components present largely in the liquid phase, for example 1 bara to 4 bara, more preferably 1 bara to 2 bara. Typically more than 70%, more typically more than 85% of all hydrophobic species may be extracted in a single stage decantation, with DMT / DMI recoveries typically above 75% to 90%.

[0058] FIG 3b generally depicts a non-limiting embodiment of a methanol recovery zone 80. In one or more embodiments, the methanol refining zone 80 may include one or more of methanol recovery column 85, liquid-liquid refining zone 90 that includes decanter 90a and extractor 95 and refining solvent column 98. Accordingly, in one or more embodiments, recovering methanol step (iii) comprises (iiia) distilling a methanol recovery zone feed 81 including at least one of the depolymerization product stream 5 and the EG product stream 32 (also referred to herein as solid-liquid separation liquors 57 or methanol recovery zone feed 57) in the presence of the refining solvent in amethanol recovery column 85 to produce a methanol recovery stream 86 and a two-phase methanol column underflow 87 and (iiib) decanting said 2-phase methanol column underflow 87 to produce a crude EG stream 88 and a refining solvent-rich stream 89. Decanting step (iii)(b) may be conducted in the presence of a refining solvent. In one or more embodiments, the method may further include (iiic) refining the crude EG stream 88 in the presence of said refining solvent in an extractor 95 to produce refining solvent-rich stream 96 and EG-rich stream 97 which, in embodiments wherein methanol recovery zone 80 is upstream from an EG refining zone 100, also serves as feed (or a feed component) for the EG refining zone 100 such that EG refining zone feed 32 may include EG-rich stream 97 from the liquid-liquid refining zone 90. In one or more embodiments, the method may further include (iiid) refining at least a portion of the extract 96 in a refining solvent column 98 to produce a refining solvent overhead stream 99. In one or more embodiments, the method may further include (iiie) refining one or more of the refining solvent-rich stream 89, solvent recycle stream 125 and refining solvent-rich stream 96 in the refining solvent column 98 to produce a refining solvent overhead stream 99, or a refining solvent side-draw recycle stream 92. In some embodiments, the method may further include feeding at least a portion of the refining solvent recycle stream 99 or refining solvent side-draw recycle stream 92, or both, to one or both of methanol recovery column 85 and extractor 95. As EG-rich stream 97 may serve as a feed for a refining step (ii) in a EG refining zone 100, for convenience the stream 97 may be referred to herein as EG refining zone feed in applicable embodiments.

[0059] Referring to Figure 3b, in one or more embodiments, the refining solvent conveyed to methanol refining column via streams 99, 92, 96, or as part of 5, is fed at a ratio of 0.05 / to 1 / 1 mass ratio of solvent to depolymerization product stream 5 (with the mass of stream 5 calculated on a refining-solvent free basis, more typically 0.1 / 1 to 0.5 / 1 mass ratio. Preferably, more than 85%, more preferably more than 92% of the methanol contained in stream 5 exits zone 80 in methanol recovery stream 86. Preferably, the methanol concentration in methanol-depleted column underflow 87 is less than 10 wt%,more preferably less than 6 wt%. Said methanol recovery column preferably operates at a bottom temperature of 100 to 135°C, at a top pressure of 0.7 bara to 2 bara, more preferably 110 to 125°C and less than 1 .2 bara. The purity of methanol recovery stream 86 is controlled by the staging and refluxing implemented in column 85, but typically is more than 90 wt% methanol, more typically is greater than 93 wt% methanol. Typical impurities in the methanol recovery stream 86 comprise water and refining solvent. Preferred reflux ratios are greater than 0.05 and less than 2.0, more preferably 0.1 to 0.8, with theoretical staging (excluding reboiler) preferably of 1 to 15 stages, more preferably 5 to 10 stages.

[0060] Referring to Figure 3b, in one or more embodiments, refining solvent-rich stream 96 is purified in a refining solvent column 98 to produce a refining solvent overhead stream 99. In one or more embodiments, the method may further include (iiie) refining one or more of the refining solvent-rich stream 89, solvent recycle stream 125 and refining solvent-rich stream 96 in the refining solvent column 98 to produce a refining solvent overhead stream 99 and / or a refining solvent side-draw recycle stream 92. Said solvent recovery column 98 preferably operates at a bottom temperature of 160 to 245°C, at a top pressure of 0.1 bara to 1.2 bara, more preferably 180 to 220°C and less than 0.5 bara. When column 98 is operated in a side-draw mode, recycle refining solvent is primarily obtained via stream 92 and stream 99 comprises low boilers exemplified as any remaining methanol, depolymerization impurities boiling less than the refining solvent, water, and possibly glycols. When column 98 is not operated in side-draw mode, column 98 does not generate side-draw stream 92 and recycle refining solvent is primarily obtained via stream 99. The purity of side-draw stream 92 or overhead stream 99 (when column 98 is operated without a side-draw 92) is controlled by the staging and refluxing implemented in column 98, but typically is more than 90 wt% refining solvent, more typically is greater than 95 wt% refining solvent. Typical impurities in the methanol recovery stream 86 comprise water and refining solvent. Preferred reflux ratios are greater than 0.05 and less than 2.0, more preferably 0.3 to 0.1 , with theoretical staging (excluding reboiler) preferably of 3 to 30 stages, morepreferably 6 to 20 stages. Refining solvent column bottoms stream 93 typically comprises hydrophobic impurities less volatile than the refining solvent that partitioned into the refining solvent during decantation or extraction occurring in zone 90. Exemplary constituents of stream 93 are DMT, DMI, fatty acid esters such as plasticizers and other additives in the original depolymerization feedstock.

[0061] Referring to Figure 3b, stream 92 may comprise water, ethylene glycol, and similar glycols that form two liquid phases with the refining solvent, wherein stream 92 may form two layers upon cooling and storage. In at least one embodiment, stream 92 may be conveyed to a liquid-liquid separation device to remove any hydrophilic layer prior to recycle to other unit operations. Solvent refining column 98 may also be implemented as two columns with streams 99 and 92 distillates in successive columns.

[0062] Referring to Figure 3b, in one embodiment, liquid-liquid refining zone comprises a single stage decanter 90a followed by extractor 95. In decanter 90a the total refining solvent entering via streams 87 or 92 is fed at a mass ratio of 0.05 / 1 to 4 / 1 , more preferably 0.1 to 1 / 1 mass ratio of solvent to stream 87 (with the mass of stream 87 calculated on a refining-solvent free basis), and is operated at a temperature of 40 to 120°C, more preferably 60 to 95°C, and a pressure sufficient to keep all components present largely in the liquid phase, for example 1 bara to 4 bara, more preferably 1 bara to 2 bara. Typically more than 70%, more typically more than 85% of all hydrophobic species may be extracted in a single stage decantation, with DMT / DMI recoveries typically above 75% to 90%. Decanter 90a produces crude EG stream 88 and a refining solvent-rich stream 89.

[0063] Referring to Figure 3b, in one embodiment, crude EG stream 88 is countercurrently contacted with a relatively clean refining solvent stream which may be singly refining solvent recycle stream 99 and / or refining solvent side-draw recycle stream 92, or a combination therein, to produce an extract, referred to as refining solvent-rich stream 96 and a raffinate, referred to as EG-rich stream 97. The total refining solvent (entering via streams 99 or 92) is fed at a mass ratio of 0.1 / 1 to 4 / 1 , more preferably 0.20 to 1 / 1 mass ratio of solventto stream 88 (with the mass of stream 88 calculated on a refining-solvent free basis), and is operated at a temperature of 40 to 120°C, more preferably 60 to 95°C, and a pressure sufficient to keep all components present largely in the liquid phase, for example 1 bara to 4 bara, more preferably 1 bara to 2 bara. Typically more than 90%, more typically more than 98% of all hydrophobic species may be extracted in a single stage decantation, with DMT / DMI recoveries typically above 95 to 99% or more. Extractor 95 may be implemented as a counter-current multi-stage extraction, or fractional extraction, consisting of equipment designs known in the art, such as mixersettlers, unagitated configurations, such as bubble, baffled, packed or trayed multi-stage countercurrent extractors, or agitated extractors such as Kuhni, Karr, Scheibel, rotating disk, or centrifugal extractors. Extractor 95 preferably comprises two to 12 theoretical stages, more preferably three to seven theoretical stages.

[0064] In some embodiments, the method further includes refining an EG refining zone feed 32 in EG refining zone 100. In general, and as depicted for example in Figures 5a - 5c, the primary purpose of the EG refining zone 100 is to refine a feed to produce a refined EG stream set that includes a purge stream 72 comprising impurities, and an EG target stream 110 of low color and odor, and of sufficient purity to be acceptable for polyester production or other uses commercial or industrial uses. One of ordinary skill will appreciate that additional intermediate product streams, side streams, waste streams, recycle streams and the like may be generated in conjunction with formation of EG target stream 110 and impurities purge stream 72.

[0065] The color, odor, and purity specifications for EG target stream 110 may be achieved by including as elements of EG refining zone 100 one or more devices, systems, steps or unit operations that may promote, effect, support or facilitate a low color, low odor, high purity EG target stream through one or more of 1 ) recovery of the majority of residual refining solvent and methanol that enter the system; 2) removal of at least partially high boiling (relative to EG) impurities such as DEG, TEG, CHDM, hydrophilic terephthalate or isophthalate esters, as exemplified by bis-2-hydroxyethyl terephthalate (BHET); 3) removalof catalyst materials, as exemplified by antimony glycolate and related species; 4) removal of at least partially lower boiling (relative to EG) hydrophilic impurities such as 2-methoxyethanol, chloroethanol, ethanol, and amines, exemplified by dimethylamine, dimethylaminoethanol; and 5) removal of at least partially homogeneous low-boiling azeotropes formed with EG, as exemplified diethylene glycol monomethyl ether. Non-limiting examples of such unit operations may include fractional distillation, extractive distillation, azeotropic distillation, reactive distillation, extraction, decantation or other liquid-liquid based separation methods, evaporation, adsorption, pervaporation, membrane permeation, flotation, further reaction or complex formation, crystallization, precipitation, filtration, centrifugation, sedimentation, leaching, solid-liquid separation, hydrocyclonization, drying and the like. The EG target stream set may further include one or more of refining solvent recycle stream(s) 125 and methanol recycle stream(s) 165.

[0066] Figures 4a and 4b depict non-limiting examples of an EG refining zone 100. As depicted, EG refining zone 100 may include distillation columns 130 and 150, decanter 140, stripper 160 as shown in FIGs 4a and 4b. Referring to Figure 4a, in one exemplary embodiment, EG-rich stream 97 (also referenced as EG refining zone feed 32) is conveyed to EG low boiler distillation column 130, wherein species boiling lighter than EG are removed into low boiler distillate stream 132 and lights stripped EG stream 134 is removed as a bottoms product. Typically, low boiler distillate stream 132 comprises light components (compared to EG) which enter EG refining zone 100 via stream 97, such as residual refining solvent, water, residual methanol, and other hydrophilic impurities generated in the depolymerization zone and other sections of the process (exemplified as 2-methoxyethanol, ethanol, 2-chloroethanol, and the like). Light components in stream 132 may advantageously be fed to decanter 140, wherein a light refining solvent-rich liquid phase may be formed as refining solvent recycle stream 125, and from which a heavy hydrophilic componentrich phase may be removed as decanter hydrophilic stream 142. It may be understood by those of ordinary skill in the art that a unit operation such as decanter 140 may not produce a perfect separation of all hydrophobic materialsinto stream 125 and all hydrophilic materials into stream 142. As such, stream 142 may include small amounts of hydrophobic materials, and stream 125 may include small amounts of hydrophilic materials.

[0067] Stream 134 is further fed to EG high boiler column 150, wherein EG high boiler stream 158 is produced as a bottoms product and high boiler column distillate stream 152 as overhead takeoff. In embodiments where EG high boiler column 150 is operated as a two-product fractional distillation (i.e., no side-draw), high purity EG is produced via high boiler column distillate stream 152, EG target stream 110 and high boiler column distillate stream 152 are one in the same, and streams 156 and 153 do not exist. In other embodiments where EG high boiler column 150 is operated in side-draw mode, high purity EG is produced via intermediate draw-off stream 156, and intermediate draw-off stream 156 and EG target stream 110 are one in the same. Further, when EG product column is operated in side-draw mode, any remaining lights and EG azeotropes may be removed via high boiler column distillate stream 152, corresponding also to EG product column lights stream 153, and stream 154 does not exist. In one or more exemplary embodiments, all or portions of streams 153 and 158 may be removed from the process as part of impurities purge stream 72.

[0068] Decanter hydrophilic stream 142 may be further processed in stripper 160 wherein relatively clean water suitable for wastewater treatment or other process needs is produced as stripper underflow stream 166, and stripper distillate stream 162, comprising methanol and other strippable components are removed. In one or more embodiments, all or portions of stream 162 may be removed from the process as part of impurities purge stream 72 or alternatively recycled back into the process as methanol recycle stream 165. So-called “banding” impurities that form minimum boiling azeotropes with water (exemplified by p-dioxane, 2-methoxyethanol, 2-chloroethanol among others), tend to accumulate or “band” in stripper 160 and may be difficult to remove overhead without excessive water co-distillation, which dilutes the methanol in the distillate. In one or more exemplary embodiments, said banding impuritiesmay be advantageously removed via banding impurities stream 164, which may be removed from the process as part of impurities purge stream 72.

[0069] Depending on the contaminants in the polyester depolymerization feedstock and reaction conditions in the depolymerization zone, EG-rich stream 97 may be contaminated with substantial amounts of EG quality-degrading high boiling species and catalytically active metal species. As such, it may be advantageous to distill target product EG overhead and away from said EG quality-degrading high boiling species as early in the EG purification sequence as practical. Referring to Figure 4b, in an exemplary embodiment employing this principle of early distillation, EG refining zone 100 may include distillation columns 130 and 150, decanter 140, stripper 160, and evaporator 170.

[0070] In one or more embodiments and with reference to Figure 4a, EG low boiler column 130 is preferably operated at a bottom temperature of 170 to 225°C, at a bottom pressure of 0.3 bara to 1.5 bara, more preferably 180 to 215°C and 1.1 bara to 0.5 bara. The removal of EG low boilers is controlled by the staging and refluxing implemented in column 130, but typically is more than 90 % , more typically is greater than 98 % or more removal of feed low boilers into low boiler distillate stream 132. Preferred reflux ratios are greater than 0.05 and less than 2.0, more preferably 0.2 to 1.2, with theoretical staging (excluding reboiler) preferably of 8 to 45 stages, more preferably 12 to 35 stages.

[0071] In one or more embodiments with reference to Figure 4a, EG high boiler 150, is preferably operated at a bottom temperature of 170 to 245°C, at a bottom pressure of 0.1 bara to 1.0 bara, more preferably 180 to 225°C and 0.2 bara to 0.6 bara. The recovery of EG into the high boiler column distillate stream 152 (when not operated in side draw mode) is controlled by the staging and refluxing implemented in column 150, but typically is more than 90% of the EG brought into the column via lights stripped EG stream 134, more typically is greater than 95% or more recovery of target EG product into high boiler column distillate stream 152. Preferred reflux ratios are greater than 0.05 and less than 2.0, more preferably 0.3 to 1 .2, with theoretical staging (excluding reboiler) preferably of 8 to 45 stages, more preferably 12 to 35 stages. When column150 is operated in side-draw mode, typically is more than 90% of the EG brought into the column via lights stripped EG stream 134, more typically is greater than 95% or more recovery of target EG product into intermediate drawoff stream 156. In side-draw mode, typically only 5 to 15 wt% of the feed comprising lights stripped EG stream 134 may be removed as high boiler column distillate stream 152, and as such, the top reflux ratio may be quite high, with the top reflux ratio typically 1 to 40, more typically less than 20, and reflux ratio of intermediate draw stream 156 is 0.3 and less than 2.0, more preferably 0.5 to 1.2.

[0072] In one or more embodiments and with reference to Figure 4a, decanter 140 may be operated at a temperature of 20 to 70°C, pressure of 0.5 to 2 bara, and a residence time of 10 minutes to 2 hours.

[0073] In one or more embodiments as with reference to Figure 4a, stripper 160 is preferably operated at a bottom temperature of 90 to 120°C, at a bottom pressure of 0.5 bara to 1 .5 bara, more preferably 99 to 110°C and 0.65 bara to 1.1 bara. Preferred reflux ratios are greater than 1.0 and less than 8, more preferably 1.5 to 6.0, with theoretical staging (excluding reboiler) preferably of 5 to 25 stages, more preferably 8 to 20 stages.

[0074] With reference to Figure 4b, EG-rich stream 97 may be conveyed to EG high boiler column 150 wherein EG high boiler stream 158, comprising aforementioned EG quality-degrading high boiling species, is produced as a bottoms product and high boiler column distillate stream 152, comprising low boiling materials such as residual refining solvent, water, residual methanol, and other hydrophilic impurities generated in the depolymerization zone and other sections of the process (exemplified as 2-methoxyethanol, ethanol, 2-chloroethanol, and the like), and target EG, is produced or taken as an overhead product. In embodiments where EG high boiler column 150 is operated as a two-product fractional distillation (i.e., no side-draw), a mixture of low boilers and target product EG are produced as high boiler column distillate stream 152 and fed to EG low boiler column 130 via stream 154, whereas streams 153 and 156 do not exist. In other embodiments where EG high boiler column 150 is operated in a side-draw mode, then an EG-enriched intermediate draw-off stream 156 is conveyed to EG low boiler column for further purification, and low boiling materials are removed as high boiler column distillate stream 152, which is sent via stream 153 to decanter 140, with stream 154 non-existent. In one or more embodiments, all or portions of stream 158 may be removed from the process as part of impurities purge stream 72.

[0075] In EG low boiler distillation column 130, as shown in Figure 4b, species boiling lighter than EG may be removed into low boiler distillate stream 132 and lights stripped EG stream 134, comprising a high concentration of EG, may be removed as a bottoms product. Stripped EG stream 134 may typically be characterized by an APHA color of greater than 100, or greater than 200. In order to produce an acceptably low-color target EG product stream 110 (e.g., with an APHA color of less than 25, more typically less than 10), stripped EG stream 134 may be further processed in evaporator 170 as shown in FIG 4b. In one embodiment, said evaporator 170 may be implemented as the reboiler of EG low boiler distillation column 130, wherein a portion of the evaporator vapor produced by evaporator 170 is removed as a vapor draw as EG target product 110, and the remainder of the evaporator vapor provides boil-up stream 171 to EG low boiler column 130. The evaporator underflow stream 172, comprising typically greater than 70% EG, more typically greater than 90% EG, may be recycled to EG high boiler column 150 for further EG recovery, may be purged from the process, or removed as part of impurities purge stream 72. In another embodiment, evaporator 170 may be implemented as a separate secondary evaporator distinct from the reboiler of EG low boiler column 130, but with streams 171 , 172, and 110 as described above.

[0076] Typically, the low boiler distillate stream 132 of Figure 4b comprises light components (compared to EG) such as residual refining solvent, water, residual methanol, and other hydrophilic impurities generated in the depolymerization zone and other sections of the process (exemplified as 2-methoxyethanol, ethanol, 2-chloroethanol, and the like), which enter EG refining zone 100 via stream 97. Light components in stream 132 may advantageously be fed to decanter 140 in the presence of refining solvent,wherein a light refining solvent-rich liquid phase is formed as refining solvent recycle stream 125, and a heavy hydrophilic component-rich phase is removed as decanter hydrophilic stream 142. It may be understood by those of ordinary skill in the art that a unit operation such as decanter 140 may not produce a perfect separation of all hydrophobic materials into stream 125 and all hydrophilic materials into stream 142. As such, stream 142 may include small amounts of hydrophobic materials, and stream 125 may include small amounts of hydrophilic materials.

[0077] Decanter hydrophilic stream 142 may be further processed in stripper 160 wherein relatively clean water suitable for wastewater treatment or other process needs is produced as stripper underflow stream 166, and stripper distillate stream 162, comprising methanol and other strippable components are removed. In one or more embodiments all or portions of stream 162 may be removed from the process as part of impurities purge stream 72 or alternatively recycled back into the process as methanol recycle stream 165. Banding impurities that form minimum boiling azeotropes with water (exemplified by p-dioxane, 2-methoxyethanol, 2-chloroethanol among others), tend accumulate in stripper 160 and are difficult to remove overhead without excessive water codistillation, which dilutes the methanol in the distillate. In one or more exemplary embodiment, said banding impurities may be advantageously removed via banding impurities stream 164, which may be removed from the process as part of impurities purge stream 72.

[0078] In one or more embodiments and with reference to Figure 4b, EG low boiler column 130 is preferably operated at a bottom temperature of 160 to 235°C, at a bottom pressure of 0.20 bara to 1.5 bara, more preferably 175 to 225°C and 1.1 bara to 0.5 bara bottom pressure. The achievable removal of EG low boilers and purity of EG in the underflow is controlled by the staging and refluxing implemented in column 130, but typically is more than 90 % , more typically is greater than 98 % or more removal of feed low boilers into low boiler distillate stream 132 and lights stripped EG stream 134 comprises more than 99 wt%, more preferably more than 99.5 wt% EG target product. Preferred reflux ratios are greater than 0.5 and less than 3.0, more preferably 0.7 to 2.0,with theoretical staging (excluding reboiler) preferably of 10 to 45 stages, more preferably 20 to 35 stages.

[0079] In one or more embodiments and with reference to Figure 4b, EG high boiler 150 is preferably operated at a bottom temperature of 175 to 240°C, at a bottom pressure of 0.1 bara to 1.0 bara, more preferably 180 to 220°C and 0.2 bara to 0.6 bara. The recovery of EG into the high boiler column distillate stream 152 (when not operated in side-draw mode) is controlled by the staging and refluxing implemented in column 150, but typically is more than 90% of the EG brought into the column via lights stripped EG stream 134, more typically is greater than 95% or more recovery of target EG product into high boiler column distillate stream 152. Preferred reflux ratios are greater than 0.02 and less than 1 .5, more preferably 0.05 to 0.7, with theoretical staging (excluding reboiler) preferably of 10 to 35 stages, more preferably 15 to 30 stages. When column 150 is operated in a side-draw mode, typically is more than 90% of the EG brought into the column via streams 97 and 172, more typically is greater than 95% or more recovery of target EG product into intermediate draw-off stream 156. In side-draw mode, typically only 5 to 15 wt% of the feed comprising lights stripped EG stream 134 is removed as high boiler column distillate stream 152, and as such, the top reflux ratio may be quite high, typically 1 to 40, more typically less than 20.

[0080] In one or more embodiments and with reference to Figure 4b, decanter 140 may be operated at 20 to 70°C, pressure of 0.5 to 2 bara, and a residence time of 10 minutes to 2 hours.

[0081] In one or more embodiments and with reference to Figure 4b, stripper 160 is preferably operated at a bottom temperature of 90 to 120°C, at a bottom pressure of 0.5 bara to 1 .5 bara, more preferably 99 to 110°C and 0.65 bara to 1.1 bara. Preferred reflux ratios are greater than 1.0 and less than 8, more preferably 1.5 to 6.0, with theoretical staging (excluding reboiler) preferably of 5 to 25 stages, more preferably 8 to 20 stages.

[0082] EG refining zone 100 may include one or more further systems, devices or unit operations for refining, purifying or otherwise improving the purity of EG target stream 110. In a non-limiting example embodiment, EGrefining zone may include an evaporator and the step refining the EG product stream in an EG refining zone may include vaporizing EG. In a non-limiting example embodiment, EG refining zone may include an adsorber or absorber in one or multiple stages and the step of refining the EG product stream in an EG refining zone may include evaporating, adsorbing, absorbing, binding, reacting with, complexing or otherwise immobilizing at least some impurities. In a non-limiting example embodiment, EG refining zone may include a cyclodextrin and the step of refining the EG product stream in an EG refining zone may include forming an impurity / cyclodextrin complex. In a non-limiting example embodiment, EG refining zone may include a carboxylic acid selected from the group consisting of C4 to C12 monocarboxylic acids and C4 to C9 dicarboxylic or polycarboxylic acids and the step of refining the EG product stream in an EG refining zone may include forming an impurity / carboxylic acid reaction product. These further systems, devices or unit operations may be employed alone or in combinations of two or more.

[0083] In one or more embodiments, the methanol recovery zone 80 may be located downstream from DMT refining zone 40 and upstream from EG refining zone 100, or between DMT refining zone 40 and EG refining zone 100. In some embodiments, methanol recovery zone feed 81 may include solidliquid separation liquors 57 from the DMT refining zone 40. Further, as the EG refining zone 100 may be downstream from the methanol recovery zone 80 in some embodiments, EG refining zone feed 32 may include EG-rich stream 97 from methanol recovery zone 80. In one or more embodiments, step (iii) may therefore include refining a methanol recovery feed 81 in a methanol recovery zone 80 to produce at least a component of EG refining zone feed 32.

[0084] As noted above, in some embodiments, methanol recovery zone 80 is between DMT refining zone 40 and EG refining zone 100 - or, stated another way, is downstream from DMT refining zone 40 and upstream from EG refining zone 100. In such embodiments, methanol recovery zone feed 81 includes solid-liquid separation liquors 57 from the DMT refining zone 40 and EG refining zone feed 101 includes EG-rich stream 97 from the methanol recovery zone 80. Such embodiments do not and are not intended to limit thespirit and scope of the present invention. For example, in some embodiments, methanol recovery zone 80 may be upstream from DMT refining zone 40 and EG refining zone 100 as depicted in FIG 1 b. Stated another way, DMT refining zone 40 may be between methanol recovery zone 80 and EG refining zone 100 in such embodiments. In these embodiments, the method of the present invention includes a step of (iii) recovering methanol from the said depolymerization product stream 5 in a methanol recovery zone 10. In such embodiments, methanol recovery zone feed includes depolymerization product stream 5; DMT refining zone feed includes raffinate EG-rich stream 97 from the methanol recovery zone 80; and EG refining zone feed 101 includes solid-liquid separation liquors 57 from DMT refining zone. In some embodiments, EG refining zone feed 32 may also include crude EG stream 88 from methanol recovery zone 80.

[0085] An important feature of the present invention is that the presence of the refining solvent in the methanol recovering step (iii) or in the methanol recovery zone 80 may include a material reduction in the amount of, if not elimination of, the presence of, solids such as DMT-based solids coming out of solution or precipitating near or at the base or bottom of the methanol recovery column 85. Plugging can occur in the base of the methanol recovery zone generally and the methanol recovery column specifically during the refining step if dissolved solids precipitate or come out of solution and such phenomena may be correlated to a detrimental increase in operating temperature at the base of the methanol recove ry / target product refining zone. Accordingly, in one or more embodiments, the methanol recovery column 85 may have a base operating temperature of between 100°C to 135°C, preferably between 100°C to 125°C.

[0086] One of ordinary skill will appreciate that the detailed features of the distillation column(s) described herein such as scale / sizing, number of theoretical plates, presence, absence or location of side-draw and the like, as well as detailed features of the related distilling step such as for example temperatures, pressures and the like, may vary based on a number of factors such as depolymerization product stream flow rate, composition, temperature, choice and type of target depolymerization product and the like.

[0087] As generally described herein, zones 40, 80 and 100 may include multiple refining or recovery unit operations, devices, systems and / or steps. Non-limiting examples of such include unit operations, steps, devices or systems for separation, purification, crystallization, precipitation, filtration, centrifugation, sedimentation, leaching, solid-liquid separation, hydrocyclonization, drying, distillation, extractive distillation, azeotropic distillation, reactive distillation, extraction, decantation, evaporation, adsorption, pervaporation, membrane permeation, flotation, further reaction and the like. One of ordinary skill will appreciate that, with the presence such additional refining equipment, devices, systems and / or steps, further separate target product streams, intermediate product streams, side streams, waste streams and the like will be generated in conjunction with the method steps described herein. In embodiments wherein a zone includes multiple devices, unit operations or systems, the corresponding step being “conducted in the presence of“ a refining solvent means that refining solvent is present in at least one of said multiple devices, unit operations or systems of the subject zone or zones.

[0088] The method of the present invention in one or more embodiments may be useful in separating target products from one or more impurities while generating useful and cost-reducing recycle streams, and accordingly may be useful in providing a low-impurity, low-color target product from a depolymerization product stream. Other benefits and advantages may include one or more of (1) reduced overall energy usage to produce DMT and EG target products; (2) plugging reduction or prevention in various location s / steps of the method; (3) improved EG target product recovery; (4) improved color (e.g., APHA of 10 or less or 6 or less) and odor characteristics of EG target product and (5) improvements in DMT quality & yield.

[0089] One of ordinary skill will be appreciate that, in one or more embodiments, the method of the present invention may include other, optional and / or additional methods or process steps to useful for separating target products from one or more impurities prior to, subsequent to or as part of the described method. Such other, optional and / or additional methods or processsteps may for example include separation, purification, crystallization, distillation, extraction, evaporation, adsorption, further reaction or similar processing steps. Further, it should be understood that method step numbering does not necessarily represent a step sequence or a sequential operation, For example, in one or more embodiments, the method may include refining step (i) followed by methanol recovery step (iii) followed by refining step (ii).

[0090] An important feature of the methods and other aspects of the present invention may include low impurity levels of the final product streams (e.g., EG target stream 110 or DMT product stream 68) and / or intermediate streams upstream from the final product streams. In one or more embodiments, the EG product stream 110 may be characterized by an APHA color specification of less than 40, more preferably less than 12, most preferably less than 6. The present invention may achieve one or more of 1) significantly reducing the odor of a target product such as EG, removing in particular hydrophobic odor bodies and odor body precursors; 2) reduce APHA color of a target product such as EG (versus methods not taught by the instant invention) by at least 5 to 10 units (3) achieving APHA color at or below 12 when starting at about 20 to 40; and 4) improving the lifetime of adsorption beds.

[0091] Another important feature of the methods and other aspects of the present invention may include improvements in target product yields over historic polyester depolymerization methods.

[0092] Yet another important feature of the methods and other aspects of the present invention may include reduced energy consumption and related cost savings over historic polyester depolymerization methods.

[0093] The present invention, in a second aspect, is directed to method for methanolysis depolymerization of polyester. With reference to Figures 5a, 5b and 5c, the method of this aspect of the present invention includes (a) depolymerizing a polyester in a depolymerization zone 10 via methanolysis to form to a methanolysis depolymerization product stream 5 that includes DMT, EG, impurities and methanol; (b) refining said methanolysis depolymerization product stream in a DMT refining zone to produce a DMT product stream andan EG product stream, (c) refining said EG product stream in an EG refining zone to produce an EG target stream and one or more impurities purge streams; and (d) recovering methanol from at least one of said depolymerization product stream, said DMT refining zone, said EG product stream and said EG refining zone; wherein at least one of steps (a), (b) (c) and (d) is at least partially conducted in the presence of a refining solvent.

[0094] The method of this aspect of the present invention includes a step of depolymerizing a polyester, sourced from a polyester-containing feedstock 80 as shown in Figure 5a through 5c, in depolymerization zone 10 to form to a depolymerization product stream 5. In one or more embodiments, the depolymerization product stream includes DMT, EG, one or more impurities and methanol. In one or more embodiments, the step (a) includes depolymerizing polyester via methanolysis in a methanolysis depolymerization zone 10 to form depolymerization product stream 5. In general terms, depolymerization of polyesters such as polyethylene terephthalate (PET) results in breaking down of polymer chains into the monomeric units or materials that were originally polymerized to form the polyester. As well known in the art and described elsewhere herein, depolymerization of polyester via methanolysis may be exemplified by methanolysis depolymerization of PET, wherein PET is trans-esterified with methanol to produce DMT and EG. Depolymerization of polyester via glycolysis may be exemplified by glycolysis depolymerization of PET wherein PET may be dissolved in and reacted with ethylene glycol to form a mixture of dihydroxyethyl terephthalate and low molecular weight terephthalate oligomers and the mixture subjected to a transesterification reaction, usually in the presence of an ester exchange catalyst, with a lower alcohol such as methanol to form dimethyl terephthalate (DMT) and ethylene glycol (EG).

[0095] Subsequent to the depolymerization step, the method of this aspect of the present invention includes steps and optional steps that substantially correspond to steps of the preceding aspect of the method of the present invention, said aspect directed to a method for treating a depolymerization product stream from a polyester methanolysisdepolymerization process. As noted previously, the present invention is described herein with respect to various interrelated aspects and embodiments and one of ordinary skill will understand and appreciate that elements or features used to describe one aspect or embodiment may be applicable and useful in describing other embodiments. Accordingly, descriptions and disclosure relating to elements or features of an aspect or embodiment of the present invention are hereby expressly relied on to describe and support those elements or features in other aspects or embodiments. More particularly, descriptions and disclosure relating to elements or features of the method for treating a depolymerization product stream from a polyester depolymerization process as described herein are hereby expressly relied on to describe and support those elements or features in the method for depolymerizing a polyester as described herein, and vice versa.

[0096] The present invention, in a third aspect, is directed to a system for treating a depolymerization product stream from a polyester depolymerization process. With reference to Figures 1a, 1b and 1c, the system of this aspect of the present invention includes in fluid connection (a) a polyester depolymerization product stream 5 comprising EG, DMT, one or more impurities and methanol; (b) a DMT refining zone 40; (c) an EG refining zone 100; optionally (d) a methanol recovery zone 80, all fluidly connected to and downstream from the depolymerization product stream 5; and at least one methanol recovery stream 4 formed by and emanating from at least one of said depolymerization product stream, said DMT refining zone, said EG product stream and said EG refining zone. In one or more embodiments, at least one of the DMT refining zone 40, an EG refining zone 100 and methanol recovery zone 80 includes a refining solvent. As used herein, the term “fluidly connected to”, as used herein, is meant to include systems wherein the various zones are located so as to receive the product stream 5 or effluent from one or more preceding zones but without regard to sequence.

[0097] In one or more embodiments, the system of this aspect of the invention includes, in sequence, DMT refining zone 40 receiving depolymerization product stream 5; methanol recovery zone 80 and EG refiningzone 100 as depicted in FIG 5a. In one or more embodiments, the system of this aspect of the invention includes, in sequence, methanol recovery zone 80 receiving depolymerization product stream 5; DMT refining zone 40 and EG refining zone 100 as depicted in FIG 5b. “In sequence” is meant to describe systems wherein the recited zones in the indicated order but are not necessarily immediately successive with one immediately following the other. Stated another way, “in sequence” is intended to include all systems with the recited zones in the indicated order, regardless of the presence or absence of other, additional and / or optional elements between the recited elements.

[0098] The present invention, in a fourth aspect, is directed to a polyester depolymerization system. With reference to Figures 5a, 5b and 5c, the system of this aspect of the present invention includes in fluid connection (a) a polyester-containing depolymerization feed 1 ; (b) a polyester depolymerization zone or reactor 10 generating a depolymerization product stream 5 that includes DMT, EG, one or more impurities and methanol; (c) a DMT refining zone 40; (d) an EG refining zone 100; and optionally (e) a methanol recovery zone 80. In one or more embodiments, at least one of DMT refining zone 40, an EG refining zone 100 and methanol recovery zone 80 includes a refining solvent. As used herein, the term “fluidly connected to”, as used herein, is meant to include systems wherein the various zones are located so as to receive the product stream 5 or effluent from one or more preceding zones but without regard to sequence.

[0099] In one or more embodiments, the system of this aspect of the invention includes, in sequence, DMT refining zone 40 receiving depolymerization product stream 5; methanol recovery zone 80 and EG refining zone 100 as depicted in FIG 5b. In one or more embodiments, the system of this aspect of the invention includes, in sequence, methanol recovery zone 80 receiving feed that includes depolymerization product stream 5; DMT refining zone 40 and EG refining zone 100 as depicted in FIG 5c. “In sequence” is meant to describe systems wherein the recited zones in the indicated order but are not necessarily immediately successive with one immediately following the other. Stated another way, “in sequence” is intended to include all systems withthe recited zones in the indicated order, regardless of the presence or absence of other, additional and / or optional elements between the recited elements. The present invention is described herein with respect to various interrelated aspects and embodiments and one of ordinary skill will understand and appreciate that elements or features used to describe one aspect or embodiment may be applicable and useful in describing other aspects or embodiments. Accordingly, descriptions and disclosure relating to elements or features of an aspect or embodiment of the present invention are hereby expressly relied on to describe and support those elements or features in other aspects or embodiments. More particularly, descriptions and disclosure relating to elements or features of the method for treating a depolymerization product stream from a polyester depolymerization process as described herein are hereby expressly relied on to describe and support those elements or features in the method for depolymerizing a polyester as described herein, and vice versa. Similarly, descriptions and disclosure relating to elements or features of the system for treating a depolymerization product stream from a polyester depolymerization process as described herein are hereby expressly relied on to describe and support those elements or features in the method for depolymerizing a polyester as described herein, and vice versa. Further, descriptions and disclosure relating to elements or features of the methods as described herein are hereby expressly relied on to describe and support those elements or features in systems as described herein, and vice versa.

[0100] An important feature of the methods and systems of the present invention is the successful recovery of depolymerization target products such as DMT and EG at commercially attractive yields and with acceptable purity and color characteristics so as to be useful in the manufacture of polyesters such as PET with recycle content. Accordingly, a further aspect of the present invention may be a method for forming polyester with recycle content wherein the recycle content includes residues from DMT or EG recovered according to or using the methods or systems described herein. Similarly, a further aspect may be polyester with recycle content wherein therecycled content includes residues of DMT or EG recovered according to or using the methods or systems of the present invention.

[0101] The following examples, while provided to illustrate with specificity and detail the many aspects and advantages of the present invention, are not to be interpreted as in any way limiting its scope. Variations, modifications and adaptations which do depart of the spirit of the present invention are contemplated and may be readily appreciated by one of ordinary skill in the art.DESCRIPTION OF ANALYTICAL METHODSColorimetry test for target product (EG) color - APHA color test method protocol, ASTM D1209

[0102] APHA (American Public Health Association) Color, which is also referenced as PCS (Platinum Cobalt Scale) Color, requires the measurement in a spectrophotometer of light transmitted through a liquid sample in a cell. The cells may have clear, colorless, parallel entrance and exit windows. The internal distance between the faces of the cell may be user selectable, with exemplary distances ranging from 10 to 100 mm. The spectrophotometric measurement may be performed at wavelengths of between 430 and 510 nm. The instrument may be capable of mathematically converting the transmission measurement to the equivalent color measure using one or more platinum cobalt standards. A platinum cobalt stock solution can be prepared for example by dissolving 1.245 g of potassium chloroplatinate (K2PtCI6) and 1.00 g of cobalt chloride (CoCI2-H20) in water and adding 100 mL of hydrochloric acid (HCI) and diluting to 1 L with water. This stock solution may produce color equivalent to 500 APHA or PCS color units and may be subsequently diluted to appropriate concentrations for comparison to individual test solutions. This description conforms to the guidelines found in ASTM D5386, ASTM D1209 and ASTM D8005.Gas chromatography (GC Method)

[0103] Samples were prepared by weighing 30 milligrams of sample into an autosampler vial and diluting with 400 pL of an internal standard solution consisting of dodecane in pyridine. Samples were then derivatized by adding 450 pL N,0-Bis(trimethylsilyl)trifluoroacetamide (BSTFA) and heating at 80°C for 30 minutes. Aqueous samples required 1 .0-mL of BSTFA, and to solid and wet DMT samples, an additional 800 pL of pyridine was added to keep the sample in solution. Once prepared, samples were chromatographed simultaneously on 60m x 0.32mmlD x 1.00 micron 100% dimethylpolysiloxane and 60m x 0.32mmlD x 1.00 micron (14% cyanopropyl-phenyl)-methylpolysiloxane columns using temperature and pressure programming and flame ionization detection. Multipoint calibrations were performed for all components for which pure standards were available, with acceptable coefficients of determination exceeding 0.999.Depolymerization feedstocks used in Examples 4 to 28

[0104] A variety of polyester-containing materials were collected from multiple sources, including post-consumer, post-industrial, mechanical recycler / reclaimer and manufacturing trim, waste and off-spec outlets, and these were blended to form various feedstocks for a methanolysis depolymerization process. Mechanical reclaimer materials were those with higher than acceptable non-polyester content. All collected materials were primarily (95% or more) polyester but varied by size, physical form and contaminant type, size and form. Exemplary physical forms included particles, fines, flakes, pellets, strapping, extrudate, agglomerates and chunks. Exemplary contaminants included non-polyester polymers (PVC in particular); inorganics; paper (e.g., container labels); insoluble materials such as small metal items; and various textile materials, including fabrics. The feedstock blends used in the examples are summarized in Table A below. Each column specifies the weight percentage of each polyester source that was physically mixed together to create a feedstock blend. Table A percentages are by weight based on total feedstock weight.Table APolymerization Protocol (where applicable) for Examples 4-27

[0105] Experimental laboratory polymers were prepared utilizing the following polymerization method. Raw materials comprised virgin commercial-grade DMT, polymerization catalysts, and EG as supplied by the methods of the present invention. Heating was accomplished using a metal bath in contact with a heating mantle. Agitation was provided by a motorized stirring head (6 mm diameter stainless steel 6 rod with an anchor shaped agitator) which was placed in a 500 ml round-bottom flask containing raw materials. Vaporous reaction products were removed during the polymerization via a glass-side arm in the stirring head, and said vapors were condensed in a 500 mL vacuum flask cooled with dry ice. Vacuum was supplied by a standard lab vacuum pump connected to a dry ice trap, in turn connected to a vent on the vacuum flask. Prior to use, glassware was cleaned in a potassium hydroxide / isopropyl alcohol bath followed by a water wash, water rinse, and drying. The polymerization was carried out by heating the reaction and rampingvacuum down from atmospheric pressure to 0.002 bara, and ramping flask temperature from 220°C to 277°C, with a final hold time of 45 minutes. The resulting polymer was removed from heat, cooled, and recovered from the flask. The polymer was analyzed by a HunterLab colorimeter against a standard white background to determine B*.EXAMPLESExample 1 : Partition coefficients for refining solvents

[0106] In this set of experiments, various refining solvents were tested for their ability to partition dimethyl terephthalate (DMT) and dimethyl isophthalate (DMI) away from an ethylene glycol (EG)-rich (hydrophilic) phase and into a refining solvent (hydrophobic) phase. In each experiment, an equal mass of ethylene glycol to refining solvent were mixed and 0.25 wt% (based on total EG and solvent mass) of each of DMT and DMI were added. The resulting mixture was heated to 70°C with mixture to ensure all solid DMT and DMI melted. The mixture was then allowed to settle and phase separate at constant temperature. Both phases were sampled and analyzed by the above GC method to determine DMT, DMI, and EG content in both phases. Partition coefficients (Pc) and selectivities (S) were defined respectively as:Pc= wt% solute in organic phase / wt% solute in EG phaseS = Pcsolute / Pc EG

[0107] Results are given in Table 1 below.Table 1 : Example 1 ResultsExample 2 - partition into m-xylene vs EG and DEG phases

[0108] In this example the partition coefficient of several terephthalyl and isophthalyl esters of EG, methanol, and DEG between a hydrophobic refining solvent (m-xylene) phase and a hydrophilic (EG or DEG) phase were determined. 5 wt% (based on the total hydrophobic and hydrophilic materials) of a target product (as solute) was added to a 50-50 mixture of the hydrophilic and hydrophobic phases at 70°C. The resulting mixture was stirred and allowed to separate into clear phases at temperature. Samples of the two phases were taken and analyzed by the above GC method to determine the wt% of the solute and hydrophilic component in both phases, and these values were used to calculate partition coefficients and selectivities based on the above equations. Results are given in Table 2Table 2: Results for Example 2DMT = dimethyl ester of terephthalic acidMHT = monomethyl ester of terephthalic acidBHET = diester of terephthalic acid with EGDMI = dimethyl ester of isophthalic acidMHDI =methyl-DEG diester of isophthalic acidBHDT = diester of terephthalic acid with DEGBHDI = diester of isophthalic acid with DEGMHET =methyl-EG diester of terephthalic acidMHDT =methyl-DEG diester of terephthalic acidiMHET = methyl-EG diester of isophthalic acidExample 3 - Partition coefficients for Isopar L as a (hydrophobic) refining solvent

[0109] 1 wt% (based on total EG / lsopar L mass) each of methanol, DMT, MHET, and BHET were added to a 50 / 50 wt / wt ratio of Ethylene glycol and Isopar L in a Fischer-Porter glass pressure flask and heated to 90°C, stirred until all solids dissolved, and allowed to separate into clear phases at temperature. Samples of the two phases were taken and analyzed by the above GC method to determine the wt% of each constituent in each phases. These values were used to calculate partition coefficients and selectivities using the above equations. Results are given in Table 3.Table 3>Example 4. Depolymerization of Polyester depolymerization feedstock by Glycolysis / Methanolysis followed by refining of methanolysis depolymerization product

[0110] 1000 grams polyester feedstock 4 (Table A) was added to a stirred glass reactor containing 2000 grams of ethylene glycol and 3.0 grams of potassium carbonate. This mixture was heated to 190°C for 6 hours to depolymerize (glycolyze) the polyester content of the polyester feedstock. The depolymerization (glycolysis) product stream was filtered to remove small pieces of metal and other unsolubilized contaminants. The filtered depolymerization product stream was added to another stirred glass vessel, along with 1000 grams of methanol and 2.5 grams of 50 wt% aqueous caustic, and heated to 60°C for 30 minutes to form a methanolysis depolymerization product that included solid DMT and EG as well as methanol and impurities.

[0111] The methanolysis depolymerization product stream was then subject to refining step (i) in a DMT refining zone. Notably, the methanolysis depolymerization conditions facilitated formation of DMT in solid form such that DMT crystallization / solidification was not required to form a DMT product stream and an EG product stream from the DMT refining zone. In a DMT refining zone as generally depicted in FIG 2b (but without a crystallizer), the methanolysis depolymerization product was first cooled to room temperature, filtered, and washed with 1000 grams of methanol, concentrated,and distilled to recover solid DMT target product weighing 750 grams. Though fresh refining solvent was not purposefully added to the DMT refining zone for refining step (i), a minor (unmeasured) amount may have been present as a component of recycle streams. The resulting filtrate (dark in color) and wash liquids were then supplied to a methanol recovering step (iii) in a methanol recovery zone where it was subjected to a series of unit operations as follows (with reference to Figure 3b:

[0112] The combined filtrate / wash 57 was distilled in methanol distillation unit 85 to remove and recover methanol, with refining solvent (comprising mixed xylenes) initially added to the system via stream 200 then added to column 85 via recycle stream 92.

[0113] The underflow 87 from methanol distillation 85 was decanted (temperature of 80°C) at decanter 90a to separate the underflow into a crude EG-rich hydrophilic phase 88 and refining solvent-rich hydrophobic phase 89; and

[0114] The EG-rich hydrophilic phase 88 was further treated in a multi-stage countercurrent extractor 95 (5 theoretical stages, temperature of 80°C) with additional mixed xylene refining solvent (0.5 / 1 solvent to feed ratio) added to extractor 95 via recycle stream 92 or initially via stream 200 to produce an EG-rich raffinate 97 and solvent-rich extract 96. Stream 97 included at least 2% residual refining solvent such that refining solvent would be present for refining step (ii) in the downstream EG refining zone.

[0115] The EG-rich raffinate (EG product stream) 97 was then ised as a feed supplying a refining step (ii) in an EG refining zone. There the EG-rich raffinate was distilled in two sequential distillation columns and passed through an evaporator as depicted in FIG 4b to remove components boiling higher (in the first column) and lower (in the second column) than EG.

[0116] After the sequential distillation operations, the resulting EG target product stream 110 was found to be 99.6 wt% EG by GC method 1 with an APHA color of 11 . The EG target product stream recovered EG at 93% of theoretical yield based on polyester feed. The EG from EG target productstream was used to make PET as per the Polymerization Protocol described above. The B* color of the resulting PET was 2.0Counterexample 5.

[0117] The glycolysis / methanolysis depolymerization procedure and DMT refining zone procedure of Example 4 were utilized to process polyester feedstock 4 and form a DMT product stream and an EG product stream from the DMT refining zone. The EG product stream was further refined in the absence of refining solvent, by first removing methanol in a methanol distillation, and further distilling the underflow of the methanol distillation in two columns to remove components boiling higher and lower than EG.

[0118] The resulting EG target product found to be 99.3 wt% EG by GC method 1 with an APHA color of 800. The EG target product was recovered at 87% of theoretical yield based on polyester feed. The EG target product was used to make PET as per the Polymerization Protocol described above. The B* color of the resulting PET was greater than 15.Examples 6 to 27 - depolymerization plus refining, EG target product recovery, polymerization to form PETMethanolysis Depolymerization procedure for Examples 6 to 27

[0119] Various polyester-containing blended feedstock materials as listed in Table A were each metered continuously into a stirred melting vessel operating at about 250 to 270°C and combined with recycled reactor underflow effluent to produce a melted polyester depolymerization feedstock feed stream. The melted polyester feed stream was co-fed into the bottom of a depolymerization reaction vessel along with a Lewis acid catalyst in methanol, and sparged with superheated methanol vapor. For each experimental run, the depolymerization reaction vessel was operated at an average temperature of approximately 260°C, 3 bara pressure, with an average liquid phase residence time of about 11 hours. The resulting methanolysis depolymerization product stream, comprising target products such as DMT, DMI, ethylene glycol and / or diethylene glycol, as well as depolymerization agent methanol, was removedfrom the depolymerization reaction vessel as a vaporous reactor overhead product. The recycled reactor underflow effluent was combined with the incoming polyester-containing feedstock material as described above. In the subject examples, the methanolysis depolymerization product stream was processed to recover ethylene glycol (EG) as primary target product.Refning steps for Examples 6 through 27

[0120] To refine the depolymerization product stream in a first refining step (refining step (i)) in a DMT refining zone, the vaporous depolymerization reactor overhead product was condensed, crystallized, concentrated and distilled as shown in FIG 2a to remove DMT as a solid crystalline material and generate an EG product stream (filtrate) 57 which was then further processed via a methanol recovering step (iii) in a methanol recovery zone 80.

[0121] For inventive examples, the methanol recovery zone 80 generally included the configuration and operations described above for Example 4 and depicted in FIG 3b, with mixed xylenes used as the refining solvent. The EG-rich raffinate from the methanol recovery zone, which for inventive examples is labeled 97, was then fed to an EG refining zone 100 for a refining step (ii). Stream 97 included at least 2% residual refining solvent such that refining solvent would be present for refining step (ii) in the downstream EG refining zone. In the EG refining zone, the EG-rich raffinate was distilled in two columns to remove components boiling higher than EG first, then lower than EG second (as depicted in FIG 4b). In some examples, the EG product from this distillation was flashed overhead in a continuous or batch evaporation step as described below. In some examples, the product from this flashing step was also passed through an adsorption bed filled with activated carbon. In some examples, EG product was used to manufacture polyester (PET) in accordance with the protocol set forth herein.

[0122] For counterexamples, none of the refining step (i) in the DMT refining zone; the methanol recovery step (iii) in the methanol recovery zone and refining step (ii) in the EG refining zone were performed in the presence of refining solvent. Further, methanol removal, and EG distillationwere carried out in the order as specified in Counterexample 5. In some counterexamples, the EG product from the Methanol-EG distillations was flashed overhead in a continuous or batch evaporation step as described below. In some counterexamples, the product from this flashing step was also passed through an adsorption bed filled with activated carbon. In some counterexamples, EG product was used to manufacture polyester in accordance with the protocol set forth herein.

[0123] Batch Evaporation. For those examples wherein refining step (ii) included batch evaporation, the evaporation operation was carried out with a 500ml round bottom glass flask fitted with an electrically driven heating mantle, thermocouple and thermocouple well, glass vacuum-jacketed take-off head, cooling water condenser, receiver flask, and vacuum pump with pressure controller. The EG-rich stream to be evaporated was charged to the flask, the system purged with nitrogen, sealed, evacuated to the desired operating pressure, then gradually heated to begin boiling. Heat was continuously applied until the desired fraction of the initial charge was taken overhead as the flashed product EG (EG-concentrated stream). The final temperature of the liquid in the flask was recorded as the batch flash temperature. The initial charge and the evaporation effluent were sampled and analyzed by the previously described GC method to determine purity and by the previously described APHA color method to determine color.

[0124] Continuous Evaporation. For those examples wherein refining step (ii) included continuous evaporation, the continuous evaporation operation was carried out with a 316 stainless steel vertical evaporator tube (2.5 cc nominal diameter, 45 centimeter fitted with an electrically driven band heater (800 Watt maximum output), thermocouple and thermocouple well, feed port connected via tubing to a control valve and mass flow controller in turn connected to a feed tank, a stainless steel take-off head, cooling water condenser, glass 10- liter receiver flask, and vacuum pump with pressure controller. The level in the evaporator was measured by a differential pressure device (DP cell) and controlled by varying the speed of the bottoms pump. The bottoms product was collected in a 5-liter stainless steel vessel. The EG-richstream to be evaporated was weighed and charged to a 50-liter 316 stainless steel feed tank, purged and pressurized with nitrogen. Initially a small fraction of the EG was pushed into the reboiler via the mass flow controller from the pressurized feed tank The system was evacuated to the desired pressure, and the band heater energized to begin heating the evaporator contents. Once the evaporator contents began to boil and flashed EG began to collect in the receiver, the control valve was opened to begin continuous feed flow. At this point feed was maintained, with the band heater wattage modulated to reach the desired depth of flash and the DP cell-bottoms pump controlling evaporator level. Typically, the evaporator was fed for 1 to 5 days continuously, with the continuous flash temperature and system pressure recorded overtime.

[0125] Adsorption. In some examples, the refining step (ii) in the EG refining zone included adsorption in an impurity adsorption zone. The impurity adsorption zone comprised an 1 .25 cm nomimal inside diameter glass tube packed with a dried adsorbent, which for applicable examples was an activated carbon product commercially available in undried form as GAC-1240. The dried adsorbent was prepared from the adsorbent material as received from the manufacturer by drying in a vacuum oven overnight (or until the recorded mass stabilized), purged with dried nitrogen, and held at 80°C, 0.25 bara pressure. The EG-concentrated stream was pumped through the adsorbent bed at room temperature and at a rate equivalent to approximately 3.5 cm / min superficial velocity, based on the cross sectional area of the tube. In all examples, the EG-concentrated stream was flowed through the adsorbent bed until the total mass of EG collected at the outlet of the bed was equivalent to 0.0025 grams of carbon per grams of low-impurity EG stream collected. Thus, for example, if the impurity adsorption zone was packed with 10 grams of adsorbent, then an EG-concentrated stream was fed through the bed until 4000 grams of low-impurity EG stream was collected (10 grams adsorbent / 4000 g low-impurity EG stream = 0.0025 g / g). The total combined adsorption zone effluent, a low-impurity EG stream, was then analyzed by the above-described APHA color method to determine color. An APHA color of 15or less is typically desirable for commercial application of EG to achieve a polymer with B* color less than 3 when said EG is used for polyester production.

[0126] In some examples the method included a further step of producing a polyester (PET) derived from EG present in the low-impurity EG stream (step (ii) effluent). The PET was produced in accordance with the polymerization protocol described herein and analyzed by the B* color method to determine color of the resulting polymer. A B* color of 3 or less is typically acceptable for most commercial applications.

[0127] Table 4 below sets forth details of the various experimental runs that were performed. APHA color results for EG streams as well as B* color results for polyesters, are also provided in Table 4.Table 4< < < > >> > >Table Key: * = counterexample / control runs; N / A = not applicable (polymer not made from recovered EG); CONT = continuous evaporation; BATCH = batch evaporation; RF=refining solvent (mixed xylene); MRZ=methanol recovery zone; EGRZ=EG recovery zone

[0128] In all Table 4 runs, EG yield (defined as the % of the EG in the combined filtrate / wash of step 1 that was recovered as EG target product after step 4) for the methods of the present invention was consistently 5 to 8 percentage points higher than control runs, with a typical average yield of about 96% for inventive examples and 89% for controls.

[0129] The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

1. THAT WHICH IS CLAIMED IS:1 . A method for treating a methanolysis depolymerization product stream from a polyester methanolysis depolymerization process wherein the methanolysis depolymerization product stream includes DMT, EG, impurities and methanol, said method comprising (i) refining the methanolysis depolymerization product stream in a DMT refining zone to produce a DMT product stream and an EG product stream; (ii) refining said EG product stream in an EG refining zone to produce an EG target stream and EG refining zone effluent; and (iii) recovering methanol from at least one of said depolymerization product stream, said DMT refining zone and said EG refining zone in a methanol recovery zone; wherein at least one of steps (i), (ii) and (iii) is at least partially conducted in the presence of a refining solvent.

2. The method of claim 1 wherein said refining solvent is selected from the group consisting of C6 to C15 aromatics, C7 to C20 alkanes, C6 to C20 ethers, C6 to C15 ketones, C6 to C15 chlorinated aromatics and C6 to C20 chloroalkanes.

3. The method of claim 1 wherein said refining solvent is selected from the group consisting of ethylbenzene, , cumene, diisopropylbenzene, mesitylene and isomers, m-xylene, o-xylene, p-xylene, and mixtures thereof, mixtures of primarily C9-C11 aromatics such as Aromatic 150 or Solvesso™ 150, mixtures of primarily C12-C15 aromatics commonly known as Aromatic 200 or Solvesso™ 200 sold commercially by Exxon Mobil™ mixtures of iso alkanes commonly known as Isopar solvents, such as Isopar™ C, Isopar™ G, Isopar™ H, Isopar™ L, and Isopar™ M, motor gasoline, kerosene, white mineral spirits, chlorobenzene, dichlorobenzene isomers, either individually or as mixtures, methyl propyl ketone (MPK), methyl amyl ketone (MAK), methyl isoamyl ketone (MIAK), di-isobutyl ketone (DIBK), methyl iso-butyl ketone (MIBK), di-isopropyl ketone (DIPK), methyl isopropyl ketone (MIPK), diamyl ketone (DAK), diisoamyl ketone (DIAK), dipropyl ketone (DPK), mixtures of C11 ketones such as commercially available from Eastman Chemical, mixtures of C7 ketonessuch as commercially available from Eastman Chemical, isophorone, mixtures of C9 ketones such as commercially available from Eastman Chemical, dibutyl ether, dipropyl ether, n-heptane and isomers and mixtures thereof, hexane and isomers and mixtures thereof, cyclohexane, methyl cyclohexane, n-octane and isomers, n-octane and isomers and mixtures thereof, n-decane and isomers and mixtures thereof, n-undecane and isomers, n-dodecane and isomers and mixtures thereof.

4. The method of claim 1 wherein said refining solvent is substantially immiscible with at least one of EG and DMT.

5. The method of claim 1 wherein said refining solvent comprises mixtures of primarily C9-C11 aromatics such as Aromatic 150 or Solvesso™ 150.

6. The method of claim 1 wherein at least refining step (i) is at least partially conducted in the presence of a refining solvent.

7. The method of claim 1 wherein at least refining step (ii) is at least partially conducted in the presence of a refining solvent.

8. The method of claim 1 wherein at least recovering step (iii) is at least partially conducted in the presence of a refining solvent.

9. The method of claim 1 wherein at least refining step (i) and refining step (ii) are at least partially conducted in the presence of a refining solvent.

10. The method of claim 1 wherein at least refining step (i) and recovering step (iii) are at least partially conducted in the presence of a refining solvent.11 . The method of claim 1 wherein at least refining step (ii) and recovering step (iii) are at least partially conducted in the presence of a refining solvent.

12. The method of claim 1 wherein refining step (i), refining step (ii) and recovering step (iii) are at least partially conducted in the presence of a refining solvent.

13. The method of claim 1 wherein said refining step (i) comprises (i)(a) processing said depolymerization product stream in a condensing unit to form a concentrated DMT stream and a condensing unit methanol recovery stream; (i)(b) crystallizing DMT from said concentrated DMT stream in a crystallizer to produce a crystallizer DMT stream and a crystallizer recovery stream; (i)(c) separating said crystallizer DMT stream in a solid-liquid separation unit to recover DMT crystals and produce solid-liquid separation liquors; (i)(d) melting said DMT crystals in a DMT concentration unit to produce DMT melt 61 and a DMT concentrator overhead stream 62; and (i)(e) distilling said DMT melt in a DMT refining column.

14. The method of claim 1 wherein said refining step (i) comprises (i)(a) crystallizing DMT from a modified depolymerization stream in a crystallizer to produce a crystallizer DMT stream and a crystallizer recovery stream; (i)(b) separating said crystallizer DMT stream in a solid-liquid separation unit to recover DMT crystals and produce solid-liquid separation liquors; (i)(c) melting said DMT crystals in a DMT concentration unit to produce DMT melt and a DMT concentrator overhead stream; and (i)(e) distilling said DMT melt in a DMT refining column.

15. A method for methanolysis depolymerization of polyester, said method comprising the steps of (a) depolymerizing a polyester via methanolysis to form a methanolysis depolymerization product stream comprising DMT, EG, impurities and methanol; (b) refining said methanolysis depolymerization product stream in a DMT refining zone to produce a DMT product stream and an EG product stream; (c) refining said EG product stream in an EG refining zone to produce an EG target stream and EG refining zone impurities effluent; and (d) recovering methanol from at least one of said depolymerization productstream, said DMT refining zone and said EG refining zone in a methanol recovery zone; wherein at least one of steps (a), (b), (c) and (d) is at least partially conducted in the presence of a refining solvent.

16. The method of claim 15 wherein said steps (a), (b), (c) and (d) are at least partially conducted in the presence of a refining solvent.

17. The method of claim 1 wherein said method includes one or more of (a) purposefully adding fresh refining solvent feed to a zone or step; (b) adding refining solvent to a zone or step as a residual component of a process stream feeding into a zone or step; and adding recycled refining solvent as a recycle stream (or component thereof) supplied to a zone or step.

18. The method of claim 17 comprising including purposefully adding fresh refining solvent feed to said recovering step (iii).

19. The method of claim 17 comprising adding refining solvent to said EG refining zone as a residual component of a process stream functioning as a feed to said EG refining zone.

Images