RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Application No.

63/041,816, filed on June 19, 2020, the disclosure of which is hereby incorporated by reference in its entirety

FIELD

[0002] The present disclosure relates generally to processes for improving the catalyst performance in methods for recycling polyesters, such as methods for recycling polyethylene terephthalate.

TECHNICAL BACKGROUND

[0003] Polyester is used in a variety of applications such as in films, bottles, and food containers. Current techniques allow colorless, transparent polyethylene terephthalate (PET) containers, such as bottles for soft drinks, to be recycled economically. In the recycling process, PET containers are sorted into different colors and baled. Baled containers made from clear and green PET are washed, flaked, and dried to form clean PET flakes. If necessary, the clean, clear PET flakes can be processed by mechanical means to remove any impurities (i.e., any component other than clean, clear PET flake and/or green PET flake), although each additional processing step increases the recycling cost and thereby lowers the economic value of recycling the PET.

[0004] The recycling of clean PET flakes can include depolymerization to break the ester bonds of the PET and reduce the polymer to smaller, soluble components. Such depolymerization can occur using several known reaction pathways, including, for example, via methanolysis or ethanolysis. Often, a strong base such as hydroxide is utilized as well.

[0005] Methods for depolymerizing plastics often suffer from impurities in the recycling stream. For example, impurities such as other recycle polymers and water can affect the depolymerization reaction and lead to decreased yields. A common solution employed in the purification of the polymer stream is to remove undesirable constituents before depolymerization; however, such solution can be costly and render impure streams unprofitable to recycle. Accordingly, there is a distinct need to develop robust methods for recycling plastics, including polyesters such as polyethylene terephthalate, that enable the efficient and economical recycling of diverse feed streams. SUMMARY

[0006] The inventors have found an efficient method for depolymerizing polyesters through contacting a polyester-containing feedstock with at least one alcohol in the presence of a depolymerization catalyst and at least one acid or acid precursor, selected from a mineral acid, an organic acid an anhydride and an ester. Surprisingly, the addition of acidic species has been found to mitigate the effect of water on the depolymerization reaction.

[0007] Thus, in one aspect, the disclosure provides a method for forming a di(Ci-C ₆ alkyl) terephthalate from a polyethylene terephthalate-containing feedstock. Such method includes: in a reaction mixture, contacting a polyethylene terephthalate-containing feedstock with at least one C1-C6 alcohol in the presence of a depolymerization catalyst and at least one acid or acid precursor, each being a mineral acid or an organic acid, anhydride or ester, present in a total amount of at least 0.01 wt% based on the weight of the reaction mixture, to form a reaction product stream comprising ethylene glycol and di(Ci-C ₆ alkyl) terephthalate.

[0008] The inventors have found that the method of the disclosure can tolerate presence of various impurities in the feedstock, such as water. In certain embodiments, water is present in the reaction mixture in an amount of at least 0.1 wt%, e.g., at least 0.5 wt%.

[0009] Other aspects of the disclosure will be apparent to those skilled in the art in view of the description that follows.

DETAILED DESCRIPTION

[0010] The present disclosure is concerned with efficient methods of recycling polyesters such as polyethylene terephthalate. High-pressure, high-temperature alcoholysis (e.g., methanolysis) is a common approach to depolymerizing polyethylene terephthalate (PET). In a typical reaction, a PET feed is contacted with methanol in the presence of a depolymerization catalyst at a high temperature and pressure to generate dimethyl terephthalate and ethylene glycol. Often, the PET flake contains substantial moisture, either endogenously or from a prior washing or separation step. Additionally, the alcohol employed may also contain moisture that is difficult to remove. The presence of small amounts of water can rapidly deactivate certain depolymerization catalysts, leading to markedly lower yields. One solution is to subject the reactants to rigorous drying prior to depolymerization. Another solution is to substantially increase the catalyst loading to offset deactivation. Each of these solutions, however, is costly and undesirable, potentially rendering the recycling of certain plastics uneconomical.

[0011] The present inventors have unexpectedly found that addition of small amounts of an acid (e.g., a carboxylic acid) or an acid-precursor (e.g., an anhydride or ester) can maintain catalyst activity even in the presence of significant water content. Without wishing to be bound by theory, it is believed that water can disadvantageously produce metal hydroxide species insoluble in MeOH by reaction between the depolymerization catalyst and water. These insoluble metal hydroxides are hypothesized to have poor catalytic activity and produce very poor depolymerization yields. Small amounts of acid added to the reaction mixture have been surprisingly found to increase the reaction yield; without intending to be bound by theory, it is believed that the acid combats the formation of these hydroxide species. Indeed, yields can be increased to levels comparable to reactions conducted in anhydrous conditions. In contrast to rigorous drying procedures of the feedstock prior to depolymerization or increased catalyst usage, the addition of small amounts of acid provides an economical pathway to the recycling of polyesters containing substantial moisture contents.

[0012] Accordingly, one aspect of the disclosure provides a method to form a di(Ci-C ₆ alkyl) terephthalate from a polyethylene terephthalate-containing feedstock. Such method includes: in a reaction mixture contacting the polyethylene terephthalate containing feedstock with at least one C1-C6 alcohol in the presence of

(a) a depolymerization catalyst and

(b) at least one acid or acid precursor, selected from a mineral acid, an organic acid, an anhydride and an ester, said acid or acid precursor being present in an amount of at least 0.01 wt% based on weight of the reaction mixture, to form a reaction product stream comprising ethylene glycol and di(Ci-C ₆ alkyl) terephthalate.

[0013] As described elsewhere in the disclosure, the inventors have advantageously determined that addition of an acid or acid-precursor to the reaction mixture has a beneficial effect on the yield. The acid or the acid-precursor can be directly added to the reaction mixture. It is preferred that the added acid and the metal salt of the added acid are soluble in the reaction mixture in presence of water i.e. form a homogeneous solution in C1-C6 alcohol in the presence of water. Mixtures of the acid with the acid-precursor are also contemplated.

[0014] In certain embodiments as otherwise described herein, the at least one acid or acid precursor is at least one organic acid. Such organic acid can be, for example, a carboxylic acid.

[0015] A variety of organic acids are known in the art, and identified by the inventors as useful in the methods of the disclosure. Carboxylic acids are particular preferred in the present invention, and preferably the at least one organic acid is a C2-C7 carboxylic acid (e.g., (C1-C6 alkyl)COOH). Suitable non-limiting examples include acetic acid, propionic acid, butyric acid, isobutyric acid, pentanoic acid, and 2-ethyl butyric acid. In particular embodiments, the at least one organic acid is acetic acid.

[0016] The organic acid may also be a poly-carboxylic acid (e.g., a dicarboxylic acid or tricarboxylic acid), such as a C2-C7 dicarboxylic acid or tricarboxylic acid. In certain embodiments, the at least one organic acid is citric acid or fumaric acid.

[0017] The organic acid may be further substituted. For example, the organic acid may be halogenated (e.g., fluorinated). Thus in certain embodiments, the at least one organic acid may be of the formula (C1-C6 haloalkyl)COOH, such as trifluoroacetic acid.

[0018] Aromatic acids may also be suitable for the methods of the disclosure, and in certain embodiments, the acid is an aryl carboxylic acid. Examples of suitable aryl carboxylic acids include, but are not limited to, benzoic acid, and p-toluic acid.

[0019] In certain other embodiments, the acid is a sulphonic or phosphonic acid, for example an aryl sulfonic acid, such as phenyl sulfonic acid.

[0020] Mineral acids may also be suitable for use in the methods of the disclosure. For example, in certain embodiments, the at least one acid or acid precursor is at least one mineral acid. Numerous mineral acids are known in the art. Examples of suitable mineral acids include, but are not limited to, hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, nitric acid, and boric acid.

[0021] Utilization of an acid-precursor (e.g., a substance that reacts to form an acid, such as reacts with water to form an acid) may be especially beneficial in certain embodiments. Acid-precursors which are organic anhydrides and esters have the added benefit of consuming water in a hydrolysis reaction to form an organic acid such as a carboxylic acid. As a result, the acid-precursors may advantageously be used in lower amounts than a pure organic acid if so desired. Organic anhydrides are advantageous as one equivalent of organic anhydride reacts with one equivalent of water to form two equivalents of organic acid. As such, they can both remove water from the reaction mixture and also provide organic acid.

[0022] In certain embodiments as otherwise described herein, the at least one acid or acid precursor includes at least one organic anhydride. Suitable anhydrides include those derived from carboxylic acids as otherwise described herein. In certain embodiments, the at least one organic anhydride is an anhydride of a C2-C7 carboxylic acid (e.g., of formula (C1-C6 alkyl)C02-C0(Ci-C ₆ alkyl)). Examples of suitable organic anhydrides include, but are not limited to, acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, pentanoic anhydride, and 2-ethylbutyric anhydride. In certain embodiments, the at least one organic anhydride is acetic anhydride. The at least one organic anhydride may be substituted. For example, the organic anhydride may be halogenated (e.g., fluorinated). Thus in certain embodiments, the anhydride may be of formula (C1-C6 haloalkyl)C02-CO(Ci-C ₆ haloalkyl), such as trifluoroacetic anhydride.

[0023] In certain embodiments, the at least one acid or acid precursor includes at least one organic ester. One equivalent of an organic ester is known to react with water to form a carboxylic acid and an alkoxide. Accordingly, organic esters may be used to reduce the water content and also generate carboxylic acids. In certain embodiments as otherwise described herein, the at least one mineral acid, organic acid, anhydride or ester is at least one organic ester. For example, the at least one organic ester may be a C2-C7 carboxylate C1-C6 alkyl ester (e.g., of formula (C1-C6 alkyl)C02(Ci-C ₆ alkyl)). Preferred esters are Ci to C3 alkyl esters, particularly of C2-C4 carboxylic acids, such as of acetic acid and propionic acid. Examples of suitable organic methyl esters include, but are not limited to, methyl acetate and methyl propionate. In certain embodiments, the at least one organic ester is methyl acetate. The at least one organic ester may also be an arylate C1-C6 alkyl ester, such as methyl benzoate. In other embodiments, the at least one organic ester includes an ester-containing polymer. For example, a polymer which includes pendant ester side chains can release carboxylic acids upon reaction with water, leaving an alcohol group in place of the ester on the polymer. Examples of suitable polymers include, but are not limited to, polymers of the class of poly(vinyl ester), such as poly(vinyl acetate) and poly(vinyl propionate), as well as copolymers such as ethylene-vinyl acetate, vinyl acetate- acrylic acid. Accordingly, in certain embodiments as otherwise described herein, the at least one organic ester is poly(vinyl acetate). [0024] The person of ordinary skill in the art, based on the disclosure herein, can select an appropriate acid or acid precursor, depending, e.g., on amount of water in the feed, identity of the depolymerization catalyst, and desired purification method used in separating desired products from the product stream.

[0025] Based on the disclosure herein, the amount of the at least one acid or acid precursor added to the reaction mixture can be selected by the skilled person in order to optimize reaction yield, cost, or other parameters. In certain embodiments as otherwise described herein, the at least one acid or acid precursor is present in the reaction mixture in an amount of at least 0.005 wt%, or at least 0.008 wt%, or at least 0.01 wt%, or at least 0.02 wt% (e.g., at least 0.05 wt%, or at least 0.1 wt%, or least 0.15 wt%, or at least 0.2 wt%, or at least 0.3 wt%, or at least 0.5 wt%, or at least 0.75 wt%, or at least 1 wt%). In certain embodiments, the at least one acid or acid precursor is present in the reaction mixture in an amount of no more than 5 wt%, or no more than 3 wt% (e.g., no more than 2 wt%, or no more than 1.5 wt%, or no more than 1 wt%, or no more than 0.8 wt%, or no more than 0.6 wt%, or no more than 0.5 wt%). (As used herein, wherein more than one acid or acid precursor is present, the “amounts present” relate to the total amount of acid and acid precursor present.)

[0026] As discussed above, water can disadvantageously produce metal hydroxide salts by reaction between the depolymerization catalyst and water. The present method reduces hydroxide content by limiting the amount of water. Accordingly, in certain embodiments as otherwise described herein, hydroxide species corresponding to the depolymerization catalyst are present in the reaction mixture in an amount no more than 100 ppm, e.g., no more than 50 ppm or no more than 20 ppm. In certain embodiments, hydroxide species corresponding to the depolymerization catalyst are present the reaction mixture at a concentration of no more than 10 ppm.

[0027] The amount of the acid or acid precursor present may be selected relative to the amount of water present in the reaction mixture. In certain embodiments as otherwise described herein, the at least one acid or acid precursor is present in the amount of between 5 % by weight and 500 % by weight based on the weight of the water present in the reaction mixture (e.g., between 50 % by weight and 400 % by weight, or between 80 % by weight and 350 % by weight, or between 5 % by weight and 100 % by weight). In certain embodiments, the at least one acid (e.g. carboxylic acid), anhydride or ester may be provided so as to be approximately stoichiometric with the amount of water in the reaction mixture. For example, there may be at least 0.1 equivalents of the at least one acid or acid precursor for each equivalent of water (e.g., at least 0.2 equivalents, or at least 0.5 equivalents, or at least 0.75 equivalents, or at least 1 equivalent). In certain embodiments as otherwise described herein, there may be at most 5 equivalents of the at least one acid or acid precursor for each equivalent of water (e.g., at most 4 equivalents, or at most 2 equivalents, or at most 1 equivalent, or at most 0.75 equivalents, or at most 0.5 equivalents, or at most 0.3 equivalents).

[0028] Accordingly, in certain embodiments as otherwise described herein, the method as otherwise described herein further comprises: determining the amount of water present in the reaction mixture, and determining the amount of the at least one mineral acid, organic acid, anhydride or ester to provide to the reaction mixture based on the amount of water in the reaction mixture. Of course, this is not necessary; in many embodiments, the person of ordinary skill in the art will be able to use sufficient acid or acid precursor based on the moisture specification of the feedstock.

[0029] The water may be present in the reaction mixture in a variety of amounts depending on the endogenous water content of solvents and reactants, especially the feedstock selected for recycling and the pre-treatment (if any) performed on the feedstock. Accordingly, in an embodiments as otherwise described herein, water is present in the reaction mixture in an amount of at least 0.05 wt%, or at least 0.1 wt% (e.g., at least 0.5 wt%, or at least 0.75 wt%. In certain embodiments as otherwise described herein, water is present in the reaction mixture in an amount of at least 1 wt%, e.g., at least 1.5 wt%, or at least 2 wt%, or at least 3 wt%, or at least 5 wt%. In certain embodiments of the methods as otherwise described herein, water is present in the reaction mixture in an amount of no more than 10 wt%, e.g., no more than 7.5 wt%. In certain embodiments, water is present in the reaction mixture in an amount of no more than 5 wt%, e.g., or no more than 4 wt%, or no more than 3 wt%, or no more than 2 wt%.

[0030] A significant source of water introduced into the reaction mixture can be water admixed with the polyester to be depolymerized. Accordingly, in certain embodiments as otherwise described herein, the PET-containing feedstock includes at least 0.1 wt% water. In certain embodiments, the PET-containing feedstock includes at least 0.5 wt% water (e.g., at least 1 wt% water). In certain embodiments, the PET-containing feedstock includes at least 5 wt% water, e.g., at least 10 wt% water. In certain embodiments, the PET-containing feedstock includes no more than 20 wt% water, or no more than 15 wt% water, or no more than 10 wt% water, or no more than 5 wt% water, or no more than 3 wt% water, or no more than 2 wt% water, or no more than 1 wt% water. In certain embodiments, the PET-containing feedstock is anhydrous, or substantially anhydrous (e.g., contains less than 1000 ppm water, or less than 100 ppm water, or less than 20 ppm water), and the water is introduced into the reaction mixture by other means. Controlling the moisture content of the PET-containing feedstock can be an effective method to controlling the moisture content of the reaction mixture. However, certain advantageous embodiments of the methods of the disclosure allow the use of PET-containing feedstock which has not been rigorously dried. Accordingly, in certain embodiments, the PET- containing feedstock is not pre-dried. In other embodiments, the method further comprises: before contacting the PET-containing feedstock with the at least one C1-C6 alcohol, drying the PET-containing feedstock to a water content of no more than 10 wt% water, or no more than 5 wt% water, or no more than 3 wt% water, or no more than 1 wt% water. The PET-containing feedstock may be dried in a limited fashion to reduce energy consumption. Accordingly, in certain embodiments the method further comprises: before contacting the PET-containing feedstock with the at least one C1-C6 alcohol, drying the PET-containing feedstock to a water content of at least 0.1 wt% water, or at least 0.5 wt% water (e.g., at least 1 wt% water, at least 5 wt% water, at least 10 wt% water). In certain embodiments, the method as otherwise described herein further comprises: determining the amount of water present in the PET-containing feedstock, and determining the amount of the at least one mineral acid, organic acid, anhydride or ester to provide to the reaction mixture based on the amount of water in the reaction mixture.

[0031] Another source of the water introduced into the reaction mixture may be the at least one C1-C6 alcohol. Often, commercial feedstocks of alcohols contain significant amounts of water. Removal of this water can introduce significant capital costs and be energy-intensive. Accordingly, in certain embodiments as otherwise described herein, the at least one C1-C6 alcohol includes at least 0.1 wt% water, or at least 0.5 wt% water (e.g., at least 1 wt% water, at least 5 wt% water, at least 10 wt% water). In certain embodiments, the at least one C1-C6 alcohol includes no more than 20 wt% water, or no more than 15 wt% water, or no more than 10 wt% water, or no more than 5 wt% water, or no more than 2 wt% water, no more than 1 wt% water. In certain embodiments, the at least one C1-C6 alcohol is anhydrous, or substantially anhydrous (e.g., contains no more than 1000 ppm water, or no more than 100 ppm water, or no more than 20 ppm water), and the water is introduced into the reaction mixture by other means. Controlling the moisture content of the at least one C1-C6 alcohol can be an effective method to controlling the moisture content of the reaction mixture. Advantageously, in certain embodiments the methods of the disclosure allow the use of an at least one C1-C6 alcohol which has not been rigorously dried. Accordingly, in certain embodiments, the at least one C1-C6 alcohol is not pre-dried. In other embodiments, the method further comprises: before contacting the PET-containing feedstock with the at least one C1-C6 alcohol, drying the at least one C1-C6 alcohol to a water content of no more than 10 wt% water, or no more than 5 wt% water, or no more than 3 wt% water, or no more than 1 wt% water. The at least one C1-C6 alcohol may be dried in a limited fashion to reduce energy consumption. Accordingly, in certain embodiments the method further comprises: before contacting the PET-containing feedstock with the at least one C1-C6 alcohol, drying the at least one C1-C6 alcohol to a water content of at least 0.1 wt% water, or at least 0.5 wt% water (e.g., at least 1 wt% water, at least 5 wt% water, at least 10 wt% water). In certain embodiments, the method as otherwise described herein further comprises: determining the amount of water present in the at least one C1-C6 alcohol, and determining the amount of the at least one mineral acid, organic acid, anhydride or ester to provide to the reaction mixture based on the amount of water in the reaction mixture.

[0032] A variety of catalysts are known in the art for effecting the depolymerization of plastics such as polyesters. In certain embodiments as otherwise described herein, the depolymerization catalyst is a zinc chloride, zinc acetate, magnesium chloride, magnesium acetate, ammonium chloride, boron fluoride, boron chloride, boron bromide, titanium chloride, sodium acetate, lithium acetate, manganese acetate, cobalt acetate, palladium acetate and copper acetate. In certain embodiments as otherwise described herein, the depolymerization catalyst is an acetate, such as zinc acetate, magnesium acetate, sodium acetate, lithium acetate, manganese acetate, cobalt acetate, palladium acetate and copper acetate. In certain embodiments as otherwise described herein, the depolymerization catalyst is zinc acetate. In certain embodiments, the depolymerization catalyst is a metal- based compound in which the metal is selected from groups 1, 2, or 7-12 of the periodic table, or titanium oxyacetylacetonate. Mixtures of one or more of the above catalysts may also be used to optimize the method as presently disclosed.

[0033] An advantage of the presently-described methods is that catalyst deactivation may be avoided in feedstocks with significant water content. This allows the processing of high-water feedstocks without unduly increasing the amount of catalyst provided. Accordingly, in certain embodiments, the depolymerization catalyst is present in an amount of no more than 5 wt%, or no more than 3 wt% (e.g., no more than 2 wt%, or no more than 1 wt%, or no more than 0.5 wt%, or no more than 0.2 wt%, or no more than 0.1 wt%). In certain embodiments as otherwise described herein, the depolymerization catalyst is present in an amount of at least 0.0001 wt%, or at least 0.001 wt% (e.g., at least 0.002 wt%, or at least 0.005 wt%, or at least 0.01 wt%).

[0034] Without wishing to be bound by theory, it is presently believed that the depolymerization of polyester proceeds, as least in part, through the transesterification reaction between the polyester and at least one hydroxyl-containing compound. In certain embodiments as otherwise described herein, the hydroxyl-containing compound is at least one Ci-Ce alcohol. Examples of suitable C1-C6 alcohols that may be used include methanol, ethanol, propanol, isopropanol, and combinations thereof. In certain embodiments, a mixture of alcohols is used. In other embodiments, a single alcohol is used. For example, in certain embodiments, the at least one C1-C6 alcohol is selected from methanol, ethanol, propanol, isopropanol, and combinations thereof. In certain embodiments, the at least one C1-C6 alcohol includes methanol (e.g., is methanol).

[0035] The at least one C1-C6 alcohol may be obtained from a variety of sources. Of particular interest is the sourcing of the at least one C1-C6 alcohol from renewable resources. Accordingly, in certain embodiments, the at least one C1-C6 alcohol is obtained from a renewable source. For example, alcohols may be prepared from a variety of biomass sources, including grasses, sugarcane (e.g., sugarcane bagasse), waste streams (e.g., animal waste, human-generated waste), trees and wood, com, sorghum, barley, sugar beets, rice straw, and agricultural residues such as corn cobs and stocks, rice straw, sawdust, and wood chips. In certain embodiments, the method as otherwise described herein comprises obtaining the at least one C1-C6 alcohol from a renewable source (e.g., obtaining methanol from a renewable source, or obtain ethanol from a renewable source). For example, in certain embodiments, the at least one C1-C6 alcohol is methanol or ethanol, and the method further comprises obtaining methanol or ethanol at least partially derived from biomass.

[0036] The present method may be utilized to depolymerize and then recycle certain plastic-containing waste streams. Accordingly, in certain embodiments as otherwise described herein, the polyethylene terephthalate-containing feedstock is derived at least in part from a waste stream. In particular embodiments, the waste stream is at least partially post-consumer waste (e.g., at least 50%, or at least 75%, or at least 90% post-consumer waste). In other embodiments, the waste stream is industrial waste. In certain embodiments, the waste stream is from a mixture of sources, and optionally blended with a non-waste stream.

[0037] Plastic streams, especially those derived from waste streams, often include many other polymers. In certain embodiments, the polyethylene terephthalate-containing feedstock further comprises one or more other recycle polymers. For example, the polyethylene-containing feedstock may further comprise one or more polymers selected from the group consisting of polyvinyl chloride (PVC), high density polyethylene (HDPE), polyethylene (PE), glycol modified PET (PETG), polypropylene (PP), polystyrene (PS), polycarbonate (PC), nylon MXD6 (MXD6), nylon 6, nylon 6,6, nylon 12, ethylene vinyl alcohol (EVOH), poly (ethylene vinyl alcohol), polylactic acid (PLA), polyglycolic acid, poly(hydroxyalkanoate) (PHA), a synthetic rubber, poly(ethylene-2,5-furan dicarboxylic acid), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), poiyeyeiohexyienedimethyiene terephthalate (PCT), polyvinyl acetate (PVA), polybutylene succinate (PBS), polybutylene adipate terephthalate (PBAT), ethylene acrylic acid (EAA) ionomers, bioderived polymers or combinations thereof.

[0038] Numerous additives are also common in the manufacture of polyethylene terephthalate. Accordingly, these additives may be carried through in the polyethylene terephthalate-containing feedstock of the present method as otherwise described herein. [0039] The sources of polyethylene terephthalate may contain impurities from the manufacture, or as a consequence as being derived from a waste stream. In certain embodiments as otherwise described herein, the polyethylene terephthalate-containing feedstock further comprises one or more impurities. Examples of such impurities are paper, aluminum, steel, glass, wood, cardboard, cotton, labels (e.g., plastic labels or paper labels including a colorant), food waste, and combinations thereof. Aluminium is a particular impurity which can be found in polyethylene terephthalate-containing feedstocks, and raises a potential concern that the aluminium may interact detrimentally with the depolymerization catalyst, such as catalysts based on zinc acetate. We have found, however, that this is not the case, and no detrimental effect of aluminium has been observed. Thus, the present invention may be applied advantageously in polyethylene terephthalate-containing feedstocks which also comprise aluminium. The aluminium may be present in an amount of at least 0.01wt% aluminium and/or up to 1 wt% aluminium, such as up to 0.5wt%. The aluminium in such feedstocks may be present in any typical “form”, including aluminium film, foil or powder, or aluminium compounds, such as oxides and hydroxides.

[0040] Additives are also commonly introduced into polyethylene terephthalate- containing items to modify properties of interest. Accordingly, additives may also be present in the polyethylene terephthalate-containing feedstock as well. In certain embodiments as otherwise described herein, the polyethylene terephthalate-containing feedstock further comprises one or additives. Examples of such additives are pigments, colorants, UV stabilizers, UB absorbers, gas barrier and gas scavenging additives, acetaldehyde scavengers, slip agents, reheat agents, impact modifiers, filers, halogenated and halogen-free fire retardant additives, coatings (e.g., silicone coatings), inks, adhesives, nucleation agents, stabilizers, antioxidants or combinations thereof.

[0041] As described above, the depolymerization of polyester involves a transesterification reaction. When polyethylene terephthalate is the polyester and is reacted with a Ci-Ce alcohol, the reaction product stream comprises a di(Ci-C ₆ alkyl) terephthalate and ethylene glycol. For example, when the at least one C1-C6 alcohol includes methanol, the di(Ci-C ₆ alkyl) terephthalate includes dimethyl terephthalate. In certain embodiments, the di(Ci-C ₆ alkyl) terephthalate is dimethyl terephthalate.

[0042] The relative reactant concentrations may, based on the disclosure herein, be adjusted to improve the efficiency of the method of the present disclosure. In certain embodiments as otherwise described herein, the weight ratio of the at least one C1-C6 alcohol to the polyethylene terephthalate in the reaction mixture is at least 2 (e.g., at least 3, or at least 4, or at least 5). In certain embodiments, the weight ratio of the at least one Ci- Ce alcohol to the polyethylene terephthalate in the reaction mixture is no more than 10, or no more than 8, or no more than 6.

[0043] In certain embodiments as otherwise described herein, the polyethylene feedstock further comprises one or more other recycle polymers. Examples of possible other recycle polymers are polyolefins, nylons, polycarbonate, and/or bioderived polymers. [0044] In general, the method of the present disclosure is carried out at high temperature and high pressure. In certain embodiments as otherwise described herein, the reaction mixture is maintained at a temperature in the range of 100-350 °C. For example, in certain embodiments, the temperature is in the range of 120-325 °C, or 140-300 °C, or 160-280 °C, or 165-280 °C, or 170-260 °C. In certain embodiments as otherwise described herein, the reaction mixture is maintained at a pressure in the range of 2-80 bar, or 5-60 bar (e.g., 10-50 bar, or 15-45 bar, or 20-40 bar, or 25-30 bar).

[0045] The presently disclosed method allows for high yields of di(Ci-C ₆ alkyl) terephthalate. Accordingly, in certain embodiments as otherwise described herein, the method is performed such that the yield of di(Ci-C ₆ alkyl) terephthalate (e.g., dimethyl terephthalate) is at least 70%, or at least 75% (e.g., at least 85%, or at least 90%, or at least 95%).

EXAMPLES [0046] The Examples that follow are illustrative of specific embodiments of the methods of the disclosure, and various uses thereof. They are set forth for explanatory purposes only, and are not to be taken as limiting the scope of the disclosure.

Comparative Example 1. Baseline Depolymerization Reaction [0047] One equivalent of sorted, commercial PET flake was added to a batch reactor with five equivalents of methanol, 0.01 wt% zinc acetate, and no added water or acid. The mixture was reacted at 180 °C and approximately 25 bar for 60 minutes. The resulting yield of dimethyl terephthalate was 95%, and 0.22 wt% of unreacted PET was observed. Comparative Example 2. Depolymerization Reactions with Added Water Comparative Example 2a. [0048] A reaction was conducted as in Comparative Example 1 except with the addition of 0.5 wt% water. The resulting yield of dimethyl terephthalate was 33%, and 27.93 wt% unreacted PET was observed.

Comparative Example 2b.

[0049] A reaction was conducted as in Comparative Example 2a except with the addition of 1.0 wt% water Upon increasing the water loading to 1.0 wt%, the dimethyl terephthalate yield decreased to 8%, and 61.54 wt% unreacted PET was observed.

Comparative Example 3. Depolymerization Reactions with Added Water and Increased Catalyst Loading Comparative Example 3a.

[0050] Reaction was conducted as in Comparative Example 2a except catalyst loading was increased 8 times (i.e. to 0.08 wt% zinc acetate). The resulting yield of dimethyl terephthalate was 90%, with 3.9% of unreacted PET observed.

Comparative Example 3b.

[0051] Reaction was conducted as in Comparative Example 2a except catalyst loading was increased 11 times (i.e. to 0.11 wt% zinc acetate). The resulting yields of dimethyl terephthalate was 87%, with 3.2% of unreacted PET observed.

[0052] Use of such high catalyst loadings as used in Comparative Examples 3a and 3b was deemed costly and impractical.

Effect of acid and water addition on zinc species precipitation out of solution [0053] Comparative Examples 2a and 2b show that the presence of water results in significant decreases in the dimethyl terephthalate yield and significant increases in the amounts of unreacted PET. Without wishing to be bound by theory, it is presently believed that the active Zn catalyst needs to be in solution, and that it precipitates and/or deactivates in the presence of water and the absence of acid. To study this, a small scale dissolution study was conducted by separately adding combinations of water, and various acids to a zinc acetate solution in methanol. The resulting mixture was visually observed for any precipitation and subsequently an aliquot of the sample was passed through a filter to remove any precipitated material. The resulting liquid was tested for total zinc concentration via ICP (Inductively Coupled Plasma) analysis.

[0054] Table 1 shows the results of this study. Water was consistently added at about 0.3 g quantity to each solution. The amounts of acids were as follows: acetic acid of 0.014g, benzoic acid of 0.012g, and trifluoroacetic acid of 0.006 g. The addition of acids in combination with water shows that the entirety of zinc complex was retained in the solution vs. -30% loss when adding water alone, therefore avoiding the disadvantage of reduced catalyst content for the reaction.

Table 1. Summary of Experimental Conditions and Results Example 4. Depolymerization Reactions with Added Water and Acetic Acid Example 4a

[0055] A reaction was conducted as in Comparative Example 2a with 0.5 wt% water added, except acetic acid was added to the reaction mixture at a loading of 0.03 wt% acetic acid. The yield of dimethylterephthalate was 79%, and 2.7 wt% unreacted PET was observed.

Example 4b

[0056] A reaction was conducted as in Comparative Example 4a except acetic acid was added to the reaction mixture at an increased loading of 0.17 wt% acetic acid. A dimethyl terephthalate yield of 91% was observed, and only 1.6 wt% unreacted PET was observed. Example 4c

[0057] A reaction was conducted as in Comparative Example 4b but increasing the temperature to 200 °C. This resulted in a dimethyl terephthalate yield of 97% and a mere 1.2% unreacted PET observed. Table 2. Summary of Reaction Conditions and Yields

[0058] As shown in Table 2, addition of small amounts of acetic acid to the reaction mixture can offset decreasing yields caused by water in the reaction mixture, allowing high-yield depolymerization reactions to be conducted even in conditions that are far from anhydrous. Addition of even as little as 0.03 wt% acetic acid was found to significantly improve the reaction yield. Indeed, with the addition of only 0.17 wt% acetic acid, at the same 180 °C temperature, the yield remarkably increased from less than 33% to 91% in feeds having 0.5 wt% water content. Tolerance to aluminium impurities in rPET feedstock

[0059] A series of reactions was conducted on clean flaked PET material using a zinc acetate depolymerization catalyst, and where aluminum in the form of foil, powder, hydroxide or deposited as a layer in a film was present at levels between 0.05 and 0.5 wt%. Reactions were conducted at 180°C and residence times of 30 and 60 minutes as shown in Table 3, which also shows the respective yields from these experiments.

Table 3. Summary of Reaction Conditions and Yields

[0060] These results illustrate that the addition of aluminum to the feedstock in these various forms does not result in any detrimental effect on the yield.

[0061] Various exemplary embodiments of the disclosure include, but are not limited to the enumerated embodiments listed below, which can be combined in any number and in any combination that is not technically or logically inconsistent.

[0062] Embodiment 1 provides a method for forming a di(Ci-C ₆ alkyl) terephthalate from a polyethylene terephthalate-containing feedstock, the method comprising: in a reaction mixture contacting a polyethylene terephthalate-containing (PET- containing) feedstock with at least one C1-C6 alcohol in the presence of a depolymerization catalyst and at least one acid or acid precursor, each being a mineral acid, or an organic acid, anhydride or ester, present in a total amount in the range of at least 0.01 wt% based on weight of the reaction mixture, to form a reaction product stream comprising ethylene glycol and di(Ci-C ₆ alkyl) terephthalate. [0063] Embodiment 2 provides the method according to embodiment 1, wherein water is present in the reaction mixture in an amount of at least 0.1 wt%, e.g., at least 0.5 wt%. [0064] Embodiment 3 provides the method according to embodiment 1, wherein water is present in the reaction mixture in an amount of at least 1 wt%, e.g., at least 2 wt%.

[0065] Embodiment 4 provides the method according to any of embodiments 1-3, wherein water is present in the reaction mixture in an amount of no more than 5 wt%, e.g., no more than 4 wt%, or no more than 3 wt%.

[0066] Embodiment 5 provides the method of any of embodiments 1-4, wherein the polyethylene terephthalate-containing feedstock comprises water in an amount of at least 0.1 wt% water and no more than 20 wt% water.

[0067] Embodiment 6 provides the method according to any of embodiments 1-5, wherein hydroxide species corresponding to the depolymerization catalyst are present in the reaction mixture in an amount no more than 100 ppm, e.g., no more than 50 ppm, or no more than 20 ppm, or no more than 10 ppm.

[0068] Embodiment 7 provides the method according to any of embodiments 1-6, wherein the at least acid or acid precursor includes at least one organic acid, e.g., a carboxylic acid.

[0069] Embodiment 8 provides the method according to embodiment 7, wherein the at least one organic acid is a C2-C7 carboxylic acid (e.g., (C1-C6 alkyl)COOH, such as acetic acid, propionic acid, butyric acid, isobutyric acid, pentanoic acid, 2-ethylbutyric acid, or (C1-C6 haloalkyl)COOH, such as trifluoroacetic acid).

[0070] Embodiment 9 provides the method according to embodiment 7, wherein the organic acid is an aryl carboxylic acid (e.g., benzoic acid or p-toluic acid).

[0071] Embodiment 10 provides the method according to embodiment 7, wherein the organic acid is citric acid or fumaric acid.

[0072] Embodiment 11 provides the method according to embodiment 7 or embodiment 8, wherein the at least one C2-C7 carboxylic acid is acetic acid.

[0073] Embodiment 12 provides the method according to any of embodiments 1-6, wherein the at least one acid or acid precursor includes at least one organic anhydride. [0074] Embodiment 13 provides the method according to embodiment 12, wherein the at least one organic anhydride is an anhydride of a C2-C7 carboxylic acid (e.g., (C1-C6 alkyl)C02-C0(Ci-C ₆ alkyl), such as acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, pentanoic anhydride, 2-ethylbutyric anhydride, or (C1-C6 haloalkyl)C02-CO(Ci-C ₆ haloalkyl), such as trifluoroacetic anhydride).

[0075] Embodiment 14 provides the method according to any of embodiments 1-6, wherein the at least one acid or acid precursor includes at least one organic ester.

[0076] Embodiment 15 provides the method according to embodiment 14, wherein the at least one organic ester is a C2-C7 carboxylate C1-C6 alkyl ester (e.g., (C1-C6 alkyl)C02(Ci-C ₆ alkyl), such as methyl acetate, methyl propionate, etc., or (C1-C6 haloalkyl)C02(Ci-C ₆ alkyl), such as methyl trifluoroacetate).

[0077] Embodiment 16 provides the method according to embodiment 15, wherein the at least one organic ester is methyl acetate.

[0078] Embodiment 17 provides the method according to embodiment 14, wherein the at least one organic ester is an arylate C1-C6 alkyl ester (e.g., methyl benzoate).

[0079] Embodiment 18 provides the method of any of embodiments 1-6, wherein the at least one acid or acid precursor includes at least one mineral acid, such as hydrochloric acid, sulfuric acid, phosphoric acid, or nitric acid.

[0080] Embodiment 19 provides the method according to any of embodiments 1-18, wherein the at least one acid or acid precursor is present in the reaction mixture in a total amount of at least 0.005 wt%, e.g., at least 0.008 wt%.

[0081] Embodiment 20 provides the method according to any of embodiments 1-18, wherein the at least one acid or acid precursor is present in the reaction mixture in a total amount of at least 0.01 wt%.

[0082] Embodiment 21 provides the method according to any of embodiments 1-18, wherein the at least one acid or acid precursor is present in the reaction mixture in a total amount of at least 0.02 wt%, e.g., at least 0.05 wt%.

[0083] Embodiment 22 provides the method according to any of embodiments 1-18, wherein the at least one acid or acid precursor is present in the reaction mixture in a total amount of at least 0.1 wt%, e.g., at least 0.15 wt%.

[0084] Embodiment 23 provides the method according to any of embodiments 1-22, wherein the at least one acid or acid precursor is present in the reaction mixture in a total amount of no more than 2 wt%, e.g., no more than 1.5 wt%, or no more than 1 wt%.

[0085] Embodiment 24 provides the method according to any of embodiments 1-22, wherein the at least one acid or acid precursor is present in the reaction mixture in a total amount of no more than 0.8 wt%, e.g., no more than 0.6 wt%. [0086] Embodiment 25 provides the method according to any of embodiments 1-24, wherein the at least one acid or acid precursor is present in an amount of between 5 % by weight and 100 % by weight based on the weight of water present in the reaction mixture. [0087] Embodiment 26 provides the method according to any of embodiments 1-25, further comprising: determining the amount of water present in the reaction mixture; and determining the amount of the at least one mineral acid, organic acid, anhydride or ester to provide to the reaction mixture based on the amount of water in the reaction mixture.

[0088] Embodiment 27 provides the method according to any of embodiments 1-26, wherein the depolymerization catalyst is a zinc chloride, zinc acetate, magnesium chloride, magnesium acetate, ammonium chloride, boron trifluoride, boron trichloride, boron tribromide, titanium chloride, sodium acetate, lithium acetate, manganese acetate, cobalt acetate, palladium acetate and copper acetate, an ionic liquid, or a metal-based compound, wherein the metal is selected from groups 1, 2, or 7-12 of the periodic table, or titanium oxy acetyl acetonate .

[0089] Embodiment 28 provides the method according to any of embodiments 1-27, wherein the depolymerization catalyst is present in amount of no more than 2 wt% (e.g., no more than 1 wt%, or no more than 0.5 wt%, or no more than 0.2 wt%, or no more than 0.1 wt%).

[0090] Embodiment 29 provides the method according to any of embodiments 1-27, wherein the depolymerization catalyst is present in an amount of at least 0.001 wt%, e.g., at least 0.002 wt%, or at least 0.005 wt%.

[0091] Embodiment 30 provides the method according to any of embodiments 1-29, wherein the at least one C1-C6 alcohol is selected from methanol, ethanol, propanol, isopropanol, and combinations thereof.

[0092] Embodiment 31 provides the method according to any of embodiments 1-30, wherein the at least one C1-C6 alcohol includes methanol, e.g., is methanol.

[0093] Embodiment 32 provides the method according to any of embodiments 30 or embodiment 31, wherein the at least one C1-C6 alcohol is obtained from a renewable source.

[0094] Embodiment 33 provides the method of any of embodiments 1-28, wherein the method further comprises obtaining the at least one C1-C6 alcohol from a renewable source (e.g., obtaining methanol from a renewable source, or obtaining ethanol from a renewable source).

[0095] Embodiment 34 provides the method of any of embodiments 1-28, wherein the at least one C1-C6 alcohol is methanol or ethanol, and the method further comprises obtaining methanol or ethanol at least partially derived from biomass.

[0096] Embodiment 35 provides the method according to any of embodiments 1-34 wherein the di(Ci-C ₆ alkyl) terephthalate of the reaction product stream comprises dimethyl terephthalate.

[0097] Embodiment 36 provides the method according to any of embodiments 1-35, wherein a weight ratio of the at least one C1-C6 alcohol to the polyethylene terephthalate in the reaction mixture is a least 2, e.g., at least 3, or at least 4, or at least 5.

[0098] Embodiment 37 provides the method according to any of embodiments 1-35, wherein a weight ratio of the at least one C1-C6 alcohol to the polyethylene terephthalate in the reaction mixture is no more than 10, e.g., no more than 8, or no more than 6.

[0099] Embodiment 38 provides the method according to any of embodiments 1-37, wherein the polyethylene terephthalate-containing feedstock is derived from a waste stream (e.g., derived from post-consumer waste).

[00100] Embodiment 39 provides the method according to any of embodiments 1-38, wherein the polyethylene terephthalate-containing feedstock further comprises one or more other recycle polymers, selected from the group consisting of polyvinyl chloride (PVC), high density polyethylene (HDPE), polyethylene (PE), glycol modified PET (PETG), polypropylene (PP), polystyrene (PS), polycarbonate (PC), nylon MXD6 (MXD6), nylon 6, nylon 6,6, nylon 12, ethylene vinyl alcohol (EVOH), poly (ethylene vinyl alcohol), polylactic acid (PLA), polyglycolic acid, poly(hydroxyalkanoate) (PHA), a synthetic rubber, poly(ethylene-2,5-furan dicarboxylic acid), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polycyclohexylenedimethylene terephthalate (PCT), polyvinyl acetate (PVA), polybutylene succinate (PBS), polybutylene adipate terephthalate (PBAT), ethylene acrylic acid (EAA) ionomers, bioderived polymers or combinations thereof.

[00101] Embodiment 40 provides the method according to any of embodiments 1-39, wherein the polyethylene terephthalate-containing feedstock further contains at least 1% of isophthalic acid, at least 1% of 2,5 furandicarboxylic acid and/or at least 1% of other monomers that can cause controlled disruption of crystallinity. [00102] Embodiment 41 provides the method according to any of embodiments 1-40, wherein the polyethylene terephthalate-containing feedstock further comprises one or more of impurities, selected from the group consisting of paper, aluminum, steel, glass, wood, cardboard, cotton, labels, food waste, or combinations thereof.

[00103] Embodiment 42 provides the method according to any of embodiments 1-41, wherein the polyethylene terephthalate-containing feedstock further comprises one or more additives, selected from the group consisting of pigments and colorants, UV stabilizers, UB absorbers, gas barrier and scavenging additives, acetaldehyde scavengers, slip agents, reheat agents, impact modifiers, filers, halogenated and halogen-free fire retardant additives, silicone coating, inks, adhesives, nucleation agents, stabilizers, antioxidants or combinations thereof.

[00104] Embodiment 43 provides the method according to any of embodiments 1-42, wherein the reaction mixture is maintained at a temperature in the range of 100-350 °C (e.g., in the range of 120-325 °C, or 140-300 °C, or 160-280 °C).

[00105] Embodiment 44 provides the method according to any of embodiments 1-43, wherein the reaction mixture is maintained at a pressure in the range of 5-60 bar (e.g., 10- 50 bar, or 15-45 bar, or 20-40 bar).

[00106] Embodiment 45 provides the method according to any of embodiments 1-44, performed such that the yield of dimethyl terephthalate is at least 75%, e.g., at least 80%. [00107] Embodiment 46 provides the method according to any of embodiments 1-44, performed such that the yield of dimethyl terephthalate is at least 85%, e.g., at least 90%. [00108] Embodiment 47 provides the method according to any of embodiments 1-46, wherein the PET-containing feedstock is not pre-dried.

[00109] Embodiment 48 provides the method according to any of embodiments 1-46, further comprising before contacting the polyethylene terephthalate-containing feedstock with the at least one C1-C6 alcohol, drying the polyethylene terephthalate feedstock to a water content of less than 5 wt%, based on the weight of the polyethylene terephthalate-containing feedstock.

[00110] The particulars shown herein are by way of example and for purposes of illustrative discussion of certain embodiments of the present disclosure only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of various embodiments of the disclosure. In this regard, no attempt is made to show details associated with the methods of the disclosure in more detail than is necessary for the fundamental understanding of the methods described herein, the description taken with the examples making apparent to those skilled in the art how the several forms of the methods of the disclosure may be embodied in practice. Thus, before the disclosed processes and devices are described, it is to be understood that the aspects described herein are not limited to specific embodiments, apparatus, or configurations, and as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and, unless specifically defined herein, is not intended to be limiting.

[00111] The terms “a,” “an,” “the” and similar referents used in the context of describing the methods of the disclosure (especially in the context of the following embodiments and claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

[00112] All methods described herein can be performed in any suitable order of steps unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein is intended merely to better illuminate the methods of the disclosure and does not pose a limitation on the scope of the disclosure. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the methods of the disclosure.

[00113] Unless the context clearly requires otherwise, throughout the description and the claims, the words ‘comprise’, ‘comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. Words using the singular or plural number also include the plural and singular number, respectively. Additionally, the words “herein,” “above,” and “below” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of the application.

[00114] As will be understood by one of ordinary skill in the art, each embodiment disclosed herein can comprise, consist essentially of or consist of its particular stated element, step, ingredient or component. As used herein, the transition term “comprise” or “comprises” means includes, but is not limited to, and allows for the inclusion of unspecified elements, steps, ingredients, or components, even in major amounts. The transitional phrase “consisting of’ excludes any element, step, ingredient or component not specified. The transition phrase “consisting essentially of’ limits the scope of the embodiment to the specified elements, steps, ingredients or components and to those that do not materially affect the embodiment.

[00115] All percentages, ratios and proportions herein are by weight, unless otherwise specified.

[00116] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[00117] Groupings of alternative elements or embodiments of the disclosure are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims. [00118] Some embodiments of various aspects of the disclosure are described herein, including the best mode known to the inventors for carrying out the methods described herein. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The skilled artisan will employ such variations as appropriate, and as such the methods of the disclosure can be practiced otherwise than specifically described herein. Accordingly, the scope of the disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context. [00119] In closing, it is to be understood that the various embodiments herein are illustrative of the methods of the disclosures. Other modifications that may be employed are within the scope of the disclosure. Thus, by way of example, but not of limitation, alternative configurations of the methods may be utilized in accordance with the teachings herein. Accordingly, the methods of the present disclosure are not limited to that precisely as shown and described.