Processes for treating polyester depolymerization product streams

Abstract

A method for treating a depolymerization product stream from a polyester depolymerization process, with the depolymerization product stream including (i) at least one target product; (ii) impurities and optionally (iii) depolymerization reagent. The method includes the steps of (a) separating said depolymerization product stream in a separating zone to produce at least one target product stream; and (b) distilling the target product stream in a target product refining zone including a target product dividing wall distillation column (DWG) to produce a DWG effluent stream set, said DWG effluent stream set comprising a target product-rich stream. A method for depolymerizing polyester is also described.

Description

PROCESSES FOR TREATING POLYESTER 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 or glycolysis, and purification of the target 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, diethylene glycol, triethylene glycol, propanediol isomers, butanediol isomers, pentaerythritol, trimethylol ethane, trimethylol propane, and mixtures thereof. A product stream from a glycolysis depolymerization process may include for example unreacted depolymerization reagent such as ethylene glycol, diethylene glycol, triethylene glycol, or mixtures thereof. An exemplary 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) and 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 as a depolymerization reagent 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 feedstream and may be target products for certain 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 issues 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, 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 through methanolysis, glycolysis or alcoholysis, it is well known that depolymerization product streams will typically include a number of other chemical species in addition to one or more target products. As an initial matter, the feedstock for polyester 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 product 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 a polyester 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 stream 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 polyester depolymerization reactor or generate undesirable by-products.

[0010] A depolymerization product stream may include additional materials that could impact recovery of target products. For example, incidental chemical species may be generated during depolymerization and be present in EG and DMT product streams even though said streams are functionally equivalent to virgin EG and DMT produced by traditional chemical synthesis routes. Further, catalysts utilized in the depolymerization reaction may also be present in the depolymerization product streams and act as a catalyst for undesirable product stream component reaction as well as an independent contaminant source. Catalytically active species may also enter the depolymerization process with the feedstock components. Catalytically active species include salts, oxides, or complexes of Ti, Sb, Fe, Zn, Mn, Ge, Sn, Ni, Co, Mn and 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 moreuseful or commercially valuable components of the reaction product stream 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 depolymerization product stream from a polyester depolymerization process, with the depolymerization product stream including (i) at least one target product; (ii) impurities and optionally (iii) depolymerization reagent. The method of the present invention includes the steps of (a) separating said depolymerization product stream in a separating zone to produce at least one target product stream; and (b) distilling the target product stream in a target product refining zone including a target product dividing wall distillation column (DWC) to produce a DWC effluent stream set, said DWC effluent stream set comprising a target product-rich stream.

[0013] In another aspect, the present invention relates to method for depolymerizing a polyester. The method of this aspect of the present invention includes the steps of (a) depolymerizing a polyester in a depolymerization zone to form to a depolymerization product stream comprising (i) target product; (ii) impurities; and optionally (iii) depolymerization reagent; (b) separating the depolymerization product stream in a separating zone to produce at least one target product stream; and (b) distilling the target product stream in a target product refining zone including a target product dividing wall distillation column (DWC) to produce a DWC effluent stream set, said DWC effluent stream set comprising a target product-rich stream.

[0014] Further aspects of the invention are as disclosed and claimed herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a graphic depiction of an embodiment of the present invention directed to a method for treating a depolymerization product stream from a polyester depolymerization process;

[0016] Figure 2 is a graphic depiction of an embodiment of a refining step and related refining zone elements of an aspect of the method of the present invention;

[0017] Figures 3a, 3b and 3c are schematic depictions of various embodiments of dividing wall distillation columns (DWCs) that may be useful in the methods of the present invention; and

[0018] Figure 4 is a graphic depiction of an embodiment of the present invention directed to a method for depolymerizing polyester.DETAILED DESCRIPTION

[0019] 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 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-propane diol, and / or diethylene glycol, or combinations thereof and aliphatic polyesters such as PLA, polyglycolic acid, polycaprolactones, and polyethylene adipates; Polyesters and polyester manufacture are generallywell 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.

[0020] 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 for example 2-ethylhexanol as the depolymerizing alcohol; glycolysis depolymerization; pyrolysis depolymerization; hydrolysis depolymerization; and hydrogenolysis depolymerization.

[0021] A “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. Specifically contemplated as depolymerization product streams are all streams generated in a depolymerization process upstream from, in sequence with or downstream from a 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, and particularly preceding, those steps or system elements described herein.

[0022] The phrase “target depolymerization product” or “target product” is used herein to describe the compound(s) or material(s) on which the monomeric unit(s) of the depolymerized polymer is based. Specific non-limiting examples may include DMT and glycols such EG as when the depolymerized polyester is PET; diols such as cis- or trans-cyclohexane- 1 ,4-dimethanol (CHDM) or mixtures thereof, cis- or trans- cyclohexane-1 ,3-dimethanol (CHDM)or mixtures thereof, cis- or trans-cyclobutane-2,2,4,4-tetramethyl-1 ,3-dimethanol (TMCD) or mixtures thereof, diethylene glycol (DEG), neopentylglycol, 1 ,3-propanediol, 1 ,4-butanediol, and triethylene glycol and mixtures of DEG and EG.

[0023] “Impurities” as the term is used herein includes any materials present in a depolymerization product steam other than target depolymerization target products and depolymerization reagents. Specific non-limiting examples of impurities may include 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 side reactions 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 depolymerization product, materials with a boiling point higher than the boiling point of a target depolymerization product, materials that form azeotropes with one or more target products or 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.

[0024] “Depolymerization agents”, also referred to as depolymerization reagents, 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 reagents 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. Depolymerization reagents may include materials with a boiling point lower than the boiling point of a target depolymerization product, materials with a boiling point higher than the boiling point of a target depolymerization product, materials that form azeotropes with one or more target products or 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 may not be effectively separable 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. In one non-limiting example to illustrate, methanol (which is useful as a depolymerization reagent in methanolysis depolymerization processes) has a lower boiling point than target products DMT and EG. In another non-limiting example to illustrate, 2-ethyl hexanol (which is useful as a depolymerization agent in alcoholysis depolymerization processes) has a lower boiling point than target product DMT and forms an azeotrope with target product EG. In another non-limiting example to illustrate, ethylene glycol (which may be a target product and is useful as a depolymerization agent in glycolysis depolymerization processes) forms an azeotrope with target product DMT.

[0025] 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” mayinclude 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.

[0026] 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; a method for depolymerizing polyester; a system for treating a depolymerization product stream from a polyester methanolysis depolymerization process; and a polyester depolymerization system. 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.

[0027] The present invention, in a first aspect, is directed to a method for a treating a depolymerization product stream from a polyester depolymerization process. With primary reference to Figure 1 but also Figure 4, the method includes the step of distilling a depolymerization product stream 10, or a substream 12 thereof, in a target product refining zone 14 that may include one or more target product dividing wall distillation columns (DWC) 15 to produce a target product DWC effluent stream set 20, 21 and 22. In some embodiments, depolymerization product stream 10 may be a stream sourced directly from a depolymerization process and may include two or more target products; however, it is understood that stream 10 may be processed or refined after emanating from a depolymerization process, for example to separate thestream 10 into separate substreams 12 and 13, for example in a separating zone 11 , each before entering a target product refining zone. Substreams 12 and 13 may therefore be referred to a target product streams 12 and 13 or target product recovery streams 12 and 13 insofar as they may be further refined or processed to maximize recovery of a target product therefrom. In one example, in embodiments wherein a target product includes ethylene glycol (EG), substream 12 may also be referred to as EG product stream or EG recovery stream 12. Similarly, in embodiments wherein a target product includes dimethyl terephthalate (DMT), substream 13 may also be referred to as DMT product stream or DMT recovery stream 13. In one or more exemplary embodiments wherein the depolymerization stream 10 includes two or more target products, the separate depolymerization streams 12 and 13 may each include a different target product. In one or more exemplary embodiments wherein the depolymerization stream 10 includes target additives, one or more of the separate depolymerization substreams 12 and 13 may each include target additives. In one non-limiting example, separate depolymerization product substream 12 may include the target product EG while separate depolymerization product stream 13 may include the target product DMT. In such embodiments, stream 12 may be described as an EG recovery stream while stream 13 may be described as a DMT recovery stream.

[0028] In one non-limiting embodiment depicted in Figures 1 and 4, a depolymerization product stream 10 sourced from a depolymerization process may be separated into one or more separate depolymerization product substreams 12 and 13 in a separating zone 11 prior to a step of distilling in a target product refining zone that includes a distillation column. In such embodiments, the method of the present invention may include a step of separating said depolymerization product stream into 2 or more separate depolymerization product substreams and distilling at least one of said substreams in a separate target product refining zone that includes a target product DWC to generate separate target product effluent stream sets.

[0029] In general, the separating step may include one or more separating methods known in the art, such as for example, condensation,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, reaction or similar processing steps. One may appreciate that the specific methods employed in the separating step and the unit operations, devices and systems included in the separating zone 11 , may vary based on a number of factors, including without limitation depolymerization stream content, temperature and component form. In one or more exemplary embodiments, for example embodiments wherein depolymerization product stream 10 is in vapor form, separating zone 11 may include at least a condensing unit, crystallizer and a solid-liquid separation unit. Separating step may therefore include condensing depolymerization product stream vapor to form a depolymerization product stream liquid that includes dissolved target products; crystallizing a target product from the depolymerization product stream liquid to form target product solids in liquid; and separating target product solids from liquid. In an exemplary embodiment where depolymerization product stream includes EG and DMT target products in vapor form, the separating step may include condensing depolymerization product stream vapor to form a depolymerization product stream liquid that includes dissolved DMT and EG; crystallizing DMT from the depolymerization product stream liquid to form DMT solids in liquid; and separating DMT solids from liquid. In embodiments where the depolymerization product stream includes liquid with dissolved target products, the condensing unit may be omitted from the separation zone 11 and the separating step may include crystallizing a target product from the depolymerization product stream liquid to form target product solids in liquid and separating target product solids from liquid, In embodiments where the depolymerization product stream includes a liquid that includes a target product in dissolved form and a solid target product, the crystallizer may be omitted from the separating zone and the separating step may include separating target product solids from liquid. In one or more embodiments, the separating step and the separating zone may include further methods and unit operations, inparticular downstream from solids separating step and.or the solid / liquid separating unit, to further refine target product streams 12 prior to refining step (b) and refining zones 15 and 25 of the method of the present invention.

[0030] In one or more exemplary embodiments, the separating step may be performed in the presence of a refining solvent (described in more detail below) and the separating step may include feeding a refining solvent to the separating zone, such as shown as refining solvent feed 9. 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; (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.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.

[0031] In one or more exemplary embodiments, the depolymerization product stream includes (i) target product and (ii) impurities. In one or more exemplary embodiments, the depolymerization product stream optionally includes or includes (iii) depolymerization reagent. In one or more embodiments, the depolymerization product stream comprises at least two target products and said separating step (a) comprises separating said depolymerization product stream in a separating zone to produce at least two target product streams. In one or more embodiments, the depolymerization product stream is a methanolysis depolymerization product stream formed from a methanolysis depolymerization process. In one or more exemplaryembodiments, the depolymerization product stream may include depolymerization reagent such as for example methanol that remains unreacted after depolymerization. In one or more embodiments, the depolymerization product stream is a glycolysis depolymerization product stream formed from a glycolysis depolymerization process. In one or more embodiments, the depolymerization product stream may include unreacted depolymerization reagent comprising ethylene glycol, diethylene glycol, triethylene glycol, or combinations therein. In one or more embodiments, the depolymerization product stream is an alcoholysis depolymerization product stream formed from an alcoholysis depolymerization process. In one or more embodiments, the depolymerization product stream may include unreacted depolymerization reagent comprising 2-ethylhexanol. In one or more embodiments, the depolymerization product stream is a hydrogenolysis depolymerization product stream formed from a hydrogenolysis depolymerization process. In one or more embodiments, the depolymerization product stream is a pyrolysis depolymerization product stream formed from a pyrolysis depolymerization process. In one or more embodiments, the depolymerization product stream is a hydrolysis depolymerization product stream formed from a hydrolysis depolymerization process. In one or more embodiments, the target product a target product is selected from the group consisting of ethylene glycol (EG) and dimethyl terephthalate (DMT).

[0032] For avoidance of doubt, the phrase ’’depolymerization product stream” as used herein is intended to broadly include product streams generated from a depolymerization zone and / or a depolymerization reactor, including product streams from depolymerization zones or depolymerization reactors 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 or as part of the refining step of the method of thepresent invention. “Depolymerization product stream” is intended to expressly include the depolymerization product substreams described herein. One of ordinary skill will appreciate that polyester depolymerization processes, and depolymerization product stream compositions, may 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.

[0033] The method of this aspect of the present invention includes a step of distilling a depolymerization product stream or a substream thereof in a target product refining zone that includes at least one target product dividing wall distillation column to produce a first effluent stream set that includes a target product-rich stream. In a non-limiting embodiment depicted Figure 1, depolymerization product stream 10 is distilled in a target product refining zone 14 that includes a target product dividing wall distillation column (DWC) 15 to produce a DWC effluent stream set 20, 21 and 22 that includes a target productrich stream.

[0034] In one or more embodiments, and as depicted in Figures 1 and 4, a depolymerization product stream 10 may be separated in a separating zone 11 into depolymerization product substreams 12 and 13 and one or both of streams 12 and 13 may be distilled in separate target product refining zones 14 and 24 that each include a target product DWC (shown as 15 and 25). Accordingly, in one or more embodiments, the method of the present invention includes separating the depolymerization product stream in a separating zone into separate depolymerization product substreams and distilling at least one of said depolymerization product substreams in a target product refining zone that includes a target product dividing wall distillation column. In a non-limiting embodiment depicted in Figures 1 and 4, target product streams 12 and 13 areeach distilled in target product refining zones 14 and 24 that each include at least one target product dividing wall distillation column (DWC) 15 and 25 to produce a first DWC effluent stream set 20, 21 and 22 that includes a target product-rich stream and a second effluent stream set 30,31 and 32 that includes a target product-rich stream.

[0035] The separating step and therefore separating zone 11 may include one or more separating methods, systems and devices known in the art, such as for example, 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 one or more exemplary embodiments, the separating step may be performed in the presence of a refining solvent and the separating step may include feeding a refining solvent to the separating zone, such as shown as refining solvent feed 9. In general, a 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 method steps, 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. Suitable refining solvents may include one or more 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. Specific examples of suitable refining solvents include ethylbenzene, m-xylene, o-xylene, p-xylene, and mixtures therein, cumene, diisopropylbenzene, mesitylene and isomers, mixtures of primarily C9-C11 aromatics commonly known as Aromatic 150, mixtures of primarily C12-C15 aromatics commonly known as Aromatic 20, 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, MAK, MPK, MIAK, DIBK, DAK, DIAK, DPK,, mixtures of C11 ketones, mixtures of C7 ketones, isophorone, mixtures of C9 ketones, dibutyl ether, dipropyl ether, n-heptane and isomers and mixtures therein, hexane and isomers and mixtures therein, cyclohexane, methyl cyclohexane, n-octane and isomers, n-octane and isomers and mixtures therein, n-decane and isomers and mixtures therein, n-undecane and isomers, n-dodecane and isomers and mixtures therein.

[0036] 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.

[0037] 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; (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.

[0038] 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.

[0039] In general, the dividing wall distillation column may separate at least partially the depolymerization product stream components based on the volatility or boiling point of those individual components. In one or more embodiments, the depolymerization product stream contaminants includes so-called “light” components with boiling points less than a target depolymerization product and so-called “heavy” components with boiling points greater than a target depolymerization product. Accordingly, a DWC effluent stream set may include an intermediate component stream 20, a light component (or top) stream 21 and a heavy component (or bottoms) stream 22. Similarly, a DWC effluent stream set may include an intermediate component stream 30, a light component (or top) stream 31 and a heavy component (or bottoms) stream 32

[0040] Dividing wall distillation columns, also referred to as divided wall columns (DWCs) or dividing wall distillation columns, are generally known in art and are described for example in U.S. Patent Nos. 5,755,933; 6,958,111 ; and 8,968,524, the contents and disclosure of which are hereby incorporated herein by reference. As generally depicted in Figures 3a, 3b and 3c, dividing wall distillation columns such as depicted at 15 and 25 of Figures 1 and 4 may include (i) an exterior shell 67 defining a column interior 69 and (ii) a wall 68 or similar structure partitioning the column interior 69. Various partition wall configurations for dividing wall columns may be are suitable for the present invention, including without limitation a wall 68 extending longitudinally and centrally in the column as shown in FIG 3a, said configuration also known as a “middle wall column”; a wall 68 extending longitudinally from the top of the column 67 toward the center of the interior 69 as shown in FIG 3b; a wall 68 extending longitudinally from the bottom or base of the column 67 toward the center of the interior 69 as shown in FIG 3c; and annular walls extending circumferentially around the column interior and separating a central distillation zone from an annular distillation zone. Again with reference to Figures 3(a) to 3(c), embodiments wherein wall 68 extends longitudinally and centrally in the column (e.g., a middle wall column) may generate an intermediate component stream, shown generically as IS, that is a side-draw stream as shown in FIG 3a, wherein a “side-draw stream” is defined as a distillation column effluent stream drawn from the side of the distillation column at a physical location between the draw point of the light component (or top) stream and the draw point of the heavy component (or bottoms) stream; embodiments wherein wall 68 extends longitudinally from the top of the column 67 toward the center of theinterior 69 may generate an intermediate component stream IS emanating from the upper portion of the column as shown in FIG 3b; and embodiments wherein wall 68 extends longitudinally from the bottom or base of the column 67 toward the center of the interior 69 may generate an intermediate component stream IS emanating from the lower portion of the column as shown in FIG 3c.

[0041] One of ordinary skill will appreciate that Figures 3a - 3c are intended primarily to depict and support the descriptions of various dividing wall and partition wall configurations for the dividing wall distillation columns utilized in the present invention without regard to specific placement within the process and / or specific feed streams, Accordingly, column feed streams and effluent streams are depicted generically in Figures 3a - 3c (F=feed, TS=top stream, IS=intermediate steam, BS=bottoms stream) and without numeric labeling. For consistency, these labels (F=feed, TS=top stream, IS=intermediate steam, BS=bottoms stream) have also been adopted in describing numbered streams.

[0042] In one or more embodiments, a target product-rich stream may be intermediate component stream 20. Though intermediate component stream 20 is depicted in Figures 1 and 4 as a side-draw stream which serves as a target product-rich stream, embodiments in which the light component (or top) stream 21 or the heavy component (or bottoms) stream 22 are a target productrich stream are expressly contemplated and are within the spirit and scope of the present invention. As a general matter, identification of the target productrich stream amongst the streams of the first effluent stream set may depend on a variety of factors, including for example identity and amount of the components of the depolymerization stream, identity of the target product(s), presence or absence of refining solvent and depolymerization reagent and dividing wall column design.

[0043] A target product refining zone may include multiple dividing wall distillation columns and, more broadly, multiple refining devices, systems and / or steps. Non-limiting examples of such include steps, devices or systems for separation, purification, distillation, crystallization, precipitation, filtration, centrifugation, sedimentation, leaching, solid-liquid separation, hydrocyclonization, drying, distillation, extractive distillation, azeotropicdistillation, 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 formation of the target productrich stream from the target product refining zone.

[0044] In one or more exemplary embodiments, the method of the present invention may further include distilling one or more streams of the DWC effluent stream set in a dividing wall distillation column, for example to recover (and for example to use as recycle) one or more target additives such as depolymerization reagent and, in applicable embodiments described herein, refining solvent. In an embodiments where the DWC effluent stream set includes intermediate component (IS) stream 20, a light component stream (or TS) 21 and a heavy component stream (BS) 22, and as generally depicted in Figure 2, the method may accordingly include distilling one or more of an intermediate component stream 20, light component stream 21 and a heavy component stream 22 in a dividing wall distillation column, preferably to recover one or more of depolymerization reagent and, in applicable embodiments described below, refining solvent.

[0045] In one or more exemplary embodiments, and as depicted in Figure 2, light component stream 21 may be a light component feed that feeds a dividing wall distillation column 55 to generate a light component column effluent set that includes light column effluent top stream 51, light column effluent intermediate stream 50 and light column effluent bottom stream 52. Accordingly, the method may further include a step of distilling one of more streams of the DWC effluent stream set, preferably the light component stream, in a dividing wall distillation column to produce a light component column effluent stream set. In one or more embodiments, the light component stream 21 comprises a target additive and the light component effluent set comprises a target additive-rich stream. In one or more embodiments, the light component stream comprises a target product the light component column effluent setcomprises a target additive-rich stream. The phrase “target additive” is intended to include depolymerization reagent and refining solvent. Accordingly, in one or more embodiments, the target additive is refining solvent and said light component effluent set comprises a refining solvent-rich stream. Similarly, in one or more embodiments, the target additive is depolymerization reagent and said light component effluent set comprises a depolymerization agent-rich stream. In many embodiments, a target additive-rich stream is an intermediate stream (IS) as depicted in Figures 3a-3c. In one or more embodiments, light column effluent intermediate stream 50 may be a target additive-rich stream, such as a refining solvent-rich stream or a depolymerization reagent stream, which may be recycled for example to one or more of target product DWC 15, separating zone 11 in certain embodiments discussed herein, and / or the polyester depolymerization process. Accordingly, the method of the present invention may further include a step of recycling a target additive or the target additive-rich stream to one or more (i) the polyester depolymerization step or depolymerization zone; (ii) the separating step or the separating zone 11, and (iii) the refining step, target product DWC 15 or refining zone 14. Further, the method may further include a step of recycling depolymerization agent or a depolymerization agent-rich stream to the polyester depolymerization step or the depolymerization zone 74. Further, the method may further include a step of recycling refining solvent or a refining solvent-rich stream to one or more of (i) the polyester depolymerization step or depolymerization zone; (ii) the separating step or the separating zone 11 ; and (iii) a target product DWC 15 or a refining zone.

[0046] In one or more embodiments, and as depicted in Figure 2, heavy component stream 22 may be a heavy component feed that feeds a dividing wall distillation column 45 to generate a heavy component column effluent set 40, 41 and 42. Accordingly, the method may further include a step of distilling the heavy component stream in a dividing wall distillation column to produce a heavy component column effluent stream set. In one or more embodiments, the heavy component stream 22 includes target product and the heavy componenteffluent set 40, 41 and 42 includes a target product-rich stream or a target product-concentrated stream.

[0047] While Figure 2 generally illustrates the elements that may be present in a singular refining zone that is labeled in the Figure as refining zone 14, it should be understood and appreciated that, in embodiments that include a separating step with separating zone 11 to form substreams, multiple refining zones, depicted as elements 14 and 24 in Figures 1 and 4, may be present. The method steps and elements applicable to the singular refining zone 14 are expressly used herein to describe and support method steps and elements that may be present in the refining zones for embodiments with multiple refining zones as shown in Figures 1 and 4 at 14 and 24.

[0048] In general, in embodiments that may include a depolymerization product stream separating step that generates substreams in a separating zone and which may for each substream employ a refining zone with a target product dividing wall distillation column, dividing wall distillation columns may be utilized to treat various stream of effluent stream sets.

[0049] The use of additional dividing wall distillation columns 45 and 55 downstream of target product DWC 15 in refining zone 14 may be particularly useful in the recovery of target products as well as the recovery and reuse or recycling of depolymerization reagent ad / or, where present, refining solvent (depolymerization reagent and refining solvent may be collectively referred to as target additives). Accordingly, in one or more embodiments, the method of the present invention may further include a step of recycling the refining solventrich stream to one or both of the polyester depolymerization process and the target product DWC 15, or to the separating zone 11 in embodiments that include a separating step. Further, the method of the present invention may further include a step of recycling depolymerization reagent-rich stream to the polyester depolymerization process. In general, the method may include a step recycling a target additive-rich stream to one or more of the polyester depolymerization step or process, the target product DWC 15 and (in applicable embodiments) the separating zone 11 .

[0050] In one or more embodiments, the distilling step in a target product DWC 15 may be performed in the presence of a refining solvent, added via example via refining solvent feed 9. It may be appreciated that the presence of the refining solvent in the distilling step and the refining zone, as well as more generally the various zones and / or steps of the present invention, may be established by 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 (c) adding recycled refining solvent as a recycle stream (or component thereof) supplied to a zone or step. In one or more embodiments, the method may therefore include adding refining solvent to the target product DWC or to the refining zone. In one or more exemplary embodiments, the refining solvent may adjust solubilities of certain chemical species, extract species into separate liquid phases, and / or facilitate the separation of azeotropes present in the various zones and related unit operations and devices into component constituents, and consequently may improve recovery and purity of target products such as DMT and EG and expand the range of process operational parameters. Suitable refining solvents may include one or more 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. Specific examples of suitable refining solvents include ethylbenzene, m-xylene, o-xylene, p-xylene, and mixtures therein, cumene, diisopropylbenzene, mesitylene and isomers, mixtures of primarily C9-C11 aromatics commonly known as Aromatic 150, mixtures of primarily C12-C15 aromatics commonly known as Aromatic 20, 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, MAK, MPK, MIAK, DIBK, DAK, DIAK, DPK„ mixtures of C11 ketones, mixtures of C7 ketones, isophorone, mixtures of C9 ketones, dibutyl ether, dipropyl ether, n-heptane and isomers and mixtures therein, hexane and isomers and mixtures therein, cyclohexane, methyl cyclohexane, n-octane and isomers, n-octane and isomers and mixtures therein, n-decane and isomersand mixtures therein, n-undecane and isomers, n-dodecane and isomers and mixtures therein. 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. In some embodiments, at least one of DW effluent stream set 20, 21 and 22, in particular light component or top stream 21 , may described as a methanol recovery stream, at least a portion of which may be recycled to a polyester depolymerization step or depolymerization zone of a polyester depolymerization process in some embodiments as depicted in Figure 4.

[0051] In one or more embodiments, refining solvent may become contaminated with impurities, including impurities generated in the depolymerization zone 74 or refining zone 14, and it is necessary to purify the refining solvent for reuse, recycle or recovery. Typically said refining solvent may be contaminated by refining solvent impurities comprising high boiling, low boiling, and azeotropic impurities (relative to the refining solvent) and form a contaminated refining solvent stream. The refining solvent impurities may be removed in whole or part from the contaminated refining solvent stream by separation methods known in the art, including but not limited to distillation, crystallization, extraction, adsorption, and the like.

[0052] One of ordinary skill will appreciate that the detailed features of the various dividing wall distillation columns such as scale / sizing, number of theoretical plates, dividing wall location, 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. Similarly, other refining zone details such as physical location of the side-draw stream will vary based on similar factors.

[0053] One of ordinary skill will appreciate that, in the recovery of useful target products and target additives according to the methods and systems of the present invention, additional downstream purifying steps may be utilized. In one or more embodiments, the methods of the present invention may further include a step of purifying one or more of a target product-rich stream, a target product-concentrated stream and a target additive-rich stream. Examples of suitable purifying steps may include one or more of 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, reaction and the like. Such processing may be useful for example in achieving a specified target product quality specification.

[0054] The present invention, in a second aspect, is directed to method for depolymerizing a polyester. With primary reference to Figure 4 but also to Figure 1 , the method of this aspect of the present invention includes the steps of depolymerizing a polyester which may be a component of a depolymerization feed 70 in a depolymerization zone 74 to form to a depolymerization product stream 10 comprising (i) target product, (ii) impurities and optionally (iii) depolymerization reagent; and distilling said depolymerization product stream 10 or a substream thereof a target product refining zone 14 comprising at least one dividing wall distillation column 15 to produce a first effluent stream set. In embodiments wherein depolymerization product stream 10 includes depolymerization reagent, the method may further include recycling depolymerization reagent to the depolymerization zone, for example as shown in Figure 4 at 21.

[0055] The method of this aspect of the present invention includes a step of depolymerizing polyester, which may be sourced from a polyester-containing feedstock 70 as shown in Figure 4, in depolymerization zone 74 which in some embodiments may include depolymerization reactor 75, to form to a depolymerization product stream 10. In one or more embodiments, the depolymerization product stream 10 includes (i) a target product and (ii) one ormore impurities. In one or more embodiments, the target product is selected from the group consisting of dimethyl terephthalate (DMT) and ethylene glycol (EG). In one or more embodiments, the step includes depolymerizing polyester via methanolysis in a methanolysis zone to form to a methanolysis depolymerization product stream. In one or more embodiments, the step includes depolymerizing polyester via glycolysis in a glycolysis zone to form a glycolysis depolymerization product stream. In general terms, and as described in detail elsewhere herein, depolymerization of polyesters such as PET results in depolymerization of the polymer into oligomeric or monomeric units or materials that were originally polymerized to form the polyester, also referred to herein as target products.

[0056] Subsequent to the depolymerizing step to form the depolymerization product stream, the method of this aspect of the present invention may include steps and optional steps that substantially correspond to separating, distilling, refining, purifying, recycling and recovering 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 depolymerization process. Accordingly, and with reference to Figures 1 through 4, the method of this aspect of the present invention may further include of distilling the depolymerization product stream 10 in a target product refining zone 14 that includes a dividing wall distillation column 15 to produce a first effluent stream set. In one or more embodiments, the first effluent stream set includes a target depolymerization product-rich stream 20. In general, the dividing wall distillation column 15 separates at least partially the depolymerization product stream components based on the volatility or boiling point of those individual components. In one or more embodiments, the depolymerization product stream contaminants includes so-called “light” components with boiling points less than a target depolymerization product and so-called “heavy” components with boiling points greater than a target depolymerization product. Accordingly, the first effluent stream set may further include a light component (or top) stream 21 and a heavy component (or bottoms) stream 22.

[0057] Dividing wall distillation columns, also referred to as divided wall columns (DWCs) or dividing wall columns, are known in art and as generally depicted in Figures 3a, 3b and 3c. Dividing wall distillation columns include a column or vessel 65 with an exterior shell 67 defining a column interior 69 and a wall 68 or similar structure partitioning the column interior 69. Dividing wall distillation columns are described for example in U.S. Patent Nos. 5,755,933; 6,958,111 ; and 8,968,524, the contents and disclosure of which are hereby incorporated herein by reference. Various partition wall configurations for dividing wall columns are suitable for the present invention, including without limitation a wall 68 extending longitudinally and centrally in the column as shown in FIG 3a; a wall 68 extending longitudinally from the top of the column 67 toward the center of the interior 69 as shown in FIG 3b; a wall 68 extending longitudinally from the bottom or base of the column 67 toward the center of the interior 69 as shown in FIG 3c; and annular walls extending circumferentially around the column interior and separating a central distillation zone from an annular distillation zone.

[0058] One of ordinary skill will appreciate that the detailed features of the dividing wall distillation column such as scale / sizing, number of theoretical plates, dividing wall location, 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. Similarly, other refining zone details such as physical location of the side-draw stream will vary based on similar factors.

[0059] The steps described above for this aspect 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 depolymerization 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 orembodiment 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.

[0060] 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

THAT WHICH IS CLAIMED IS:

1. A method for treating a depolymerization product stream from a polyester depolymerization process, said depolymerization product stream comprising (i) at least one target product; (ii) impurities and optionally (iii) depolymerization reagent, said method comprising the steps of (a) separating said depolymerization product stream in a separating zone to produce at least one target product stream; and (b) distilling said target product stream in a target product refining zone comprising a target product dividing wall distillation column (DWC) to produce a DWC effluent stream set, said DWC effluent stream set comprising a target product-rich stream.

2. The method of claim 1 wherein said target product stream comprises ethylene glycol.

3. The method of claim 2 wherein said DWC comprises a column comprising a shell defining a column interior and a dividing wall partitioning the column interior.

4. The method of claim 3 wherein said dividing wall extends longitudinally and centrally within the column interior.

5. The method of claim 3 wherein said dividing wall extends longitudinally from the bottom or base of the column toward the center of said column interior.

6. The method of claim 3 wherein said dividing wall extends longitudinally from the top of the column toward the center of said column interior.

7. The method of claim 2 wherein at least one of said separating step (a) and distilling step (b) is performed in the presence of a refining solvent.

8. The method of claim 2 wherein said target product DWC effluent stream set comprises an intermediate component stream, a light component stream and a heavy component stream and said method further comprises a step of distilling said light component stream in a DWC to produce a light component column effluent set that comprises a target additive-rich stream.

9. The method of claim 8 wherein said target additive is refining solvent and said light component column effluent set comprises a refining solvent-rich stream.

10. The method of claim 9 further comprising recycling at least a position of said refining solvent-rich stream to at least one of said separating step (a) and said distilling step (b).

11. The method of claim 8 wherein said target additive is depolymerization reagent and said light component column effluent set comprises a depolymerization agent-rich stream.

12. The method of claim 11 further comprising recycling at least a position of said depolymerization agent-rich stream to said polyester depolymerization process.

13. The method of claim 8 further comprising recycling at least a portion of said target additive-rich stream to one or more of said polyester depolymerization process; separating step (a) and said distilling step (b).

14. The method of claim 1 wherein said depolymerization product stream comprises at least two target products and said separating step (a) comprises separating said depolymerization product stream in a separating zone to produce at least two target product streams.

15. The method of claim of 1 further comprising a step of purifying said target product-rich stream.

16. The method of claim 15 further comprising a step of purifying said target additive-rich stream.

17. A method for depolymerizing a polyester comprising the steps of (a) depolymerizing a polyester in a depolymerization zone to form to a depolymerization product stream comprising (i) target product; (ii) impurities; and optionally (iii) depolymerization reagent; (b) separating said depolymerization product stream in a separating zone to produce at least one target product stream; and (b) distilling the target product stream in a target product refining zone including a target product dividing wall distillation column (DWC) to produce a DWC effluent stream set, said DWC effluent stream set comprising a target product-rich stream.

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