Process for recovering poly (alkylene terephthalate)

Abstract

A simple process for preparing dimethyl terephthalate is provided, the process comprising treating a polyester stream with a C4-C14 alkanol in the presence of an esterification or transesterification catalyst to depolymerize the polyester. Cooling this mixture allows removal of insoluble materials followed by transesterification to obtain recovered dimethyl terephthalate (r-DMT) and recovered ethylene glycol (r-EG).

Description

Technical Field

[0001] The present invention relates to the field of polyester recycling, particularly the recycling of poly(ethylene terephthalate) (PET). Background Art

[0002] The recycling of plastics has become an important issue faced by society. PET is a type of polyester and is one of the most widely recycled plastics. Most of its recycling is essentially mechanical, where the polyester is physically separated from other plastics, cleaned, and reprocessed into recycled PET (r-PET). The utility of mechanical recycling is limited because each heating cycle causes some degradation of the PET. An alternative to mechanical recycling is chemical recycling, where the polyester is chemically broken down into its constituent monomers. This allows for the purification of these monomers, which can then be repolymerized into PET or other polyesters, resulting in polymers identical to new materials.

[0003] Chemical recycling can be classified by the depolymerizing agent used. For example, the depolymerizing agent can include water, methanol, and ethylene glycol. If the depolymerization reactant is water, the product is terephthalic acid and ethylene glycol. If it is methanol, the product is dimethyl terephthalate and ethylene glycol. If it is ethylene glycol, the product is bis(2-hydroxyethyl) terephthalate (BHET) or its oligomers (depending on how much ethylene glycol is used). The key issue for the success of polyester chemical recycling is whether monomers of sufficient purity for repolymerization can be generated economically. This can pose varying degrees of challenges depending on the monomer target selected.

[0004] Terephthalic acid can be used as a monomer because it is the most widely used substance for preparing polyesters such as PET. Neutral or acid-catalyzed hydrolysis has poor kinetics and requires very harsh conditions. Therefore, caustic hydrolysis is often used. However, alkaline hydrolysis produces disodium terephthalate, which must be protonated to obtain the desired acid. For each mole of terephthalic acid, protonation generates two equivalents of salts such as sodium chloride, and this salt must be treated or recycled, which results in additional costs. Additionally, purifying terephthalic acid to a quality sufficient to prepare polymers can be challenging.

[0005] Bis(2-hydroxyethyl) terephthalate (BHET) is an attractive alternative depolymerization monomer target, particularly for PET preparation, because it is the actual monomer for polymerizing into PET. The glycolysis of PET into BHET has been widely studied, and recent advancements include technologies such as volatile amine catalysts, magnetic ionic liquid catalysts, and microwave technology. Although BHET can be used for chemical recycling, purifying BHET to polymer-grade purity is challenging and typically involves resource-intensive multi-stage processing.

[0006] For many polymer manufacturers, dimethyl terephthalate (DMT) is not usually the most desirable recycled monomer target because these manufacturers are not configured to handle the methanol by-products released during repolymerization. However, if the facility is designed to handle methanol, DMT can be an attractive target because this molecule is relatively easy to purify. Methanolysis of PET has received a great deal of attention in the past. The main problem with direct methanolysis of polyesters, including PET, is the high temperatures required for sufficient polyester reactivity. These temperatures are significantly higher than the boiling point of methanol and require high pressures (usually involving the use of supercritical methanol) or the use of superheated methanol vapor to achieve methanolysis.

[0007] Accordingly, improved methods for the depolymerization of PET and the separation of recycled DMT (r-DMT) would be of great interest. SUMMARY OF THE INVENTION

[0008] Regardless of the method used in chemical recycling, a particular problem in the depolymerization of waste PET is the removal of non-polyester impurities. These are generally insoluble solid materials that are not related to the polyester and can therefore be most effectively removed by filtration. Unfortunately, direct methanolysis yields DMT in solid form (melting point 145 °C), so filtration of the mixture requires high temperatures. In addition, although the melting point of BHET is lower (106 °C), glycolysis generally produces a large amount of BHET dimers and trimers (melting point > 200 °C) unless an undesirably large excess of ethylene glycol is used (which results in an increase in reactor volume and EG recovery loop), so filtration of these usually viscous mixtures also requires a significantly elevated temperature. In addition to the challenges of high-temperature and high-viscosity processing, these elevated temperatures required for filtration may tend to soften or even liquefy some of the impurities in the waste PET feedstock and may therefore be difficult to remove.

[0009] In various aspects as described herein, the present invention provides for the generation of a depolymerization mixture in low-viscosity liquid form at low temperatures (below 100 °C), which allows for the simple and early removal of these impurities by solid-liquid separation (SLS) such that they do not affect further processing. Solid-liquid separation refers to a variety of techniques known to those skilled in the art, including decantation, filtration, centrifugation, etc. In addition, the present invention also provides a method that combines high concentration, relatively low temperature, a simple recovery loop, and produces high-purity r-DMT and recycled ethylene glycol (r-EG). DETAILED DESCRIPTION

[0010] The present invention provides a method for recycling polyesters, the method comprising two chemical steps: (1) depolymerizing the polyester with a higher carbon monohydric alcohol, and subsequently (2) converting the depolymerization mixture into recycled DMT (r-DMT) and recycled ethylene glycol (r-EG). In other words, the method involves the polyester reacting with a higher alcohol (i.e., C4 -C 14 The catalytic reaction (using an esterification or transesterification catalyst) depolymerizes the poly(ethylene terephthalate) (PET), removes solid impurities via SLS, and converts the depolymerized mixture to obtain r-DMT and r-EG. Thus, the method of the present invention has the advantages of a relatively low depolymerization temperature (and thus lower energy use), high yield, and high purity of r-DMT. In particular, the purity of the resulting r-DMT can reduce or eliminate the need for further purification of the r-DMT so produced.

[0011] Accordingly, in a first aspect, the present invention provides a method for preparing dimethyl terephthalate, the method comprising:

[0012] a. In the presence of an esterification or transesterification catalyst, at a temperature sufficient to depolymerize at least a portion of the poly(ethylene terephthalate), treating the poly(ethylene terephthalate) with an alkanol to obtain a first reaction mixture product comprising di-C-alkyl terephthalate; followed by 2 -C 4 b. Treating in the presence of methanol with a transesterification catalyst to provide a second reaction mixture product comprising dimethyl terephthalate, -C-ol, and ethylene glycol, followed by 4 -C 14 c. Separating the dimethyl terephthalate. 2 -C 4 In certain embodiments, the poly(ethylene terephthalate) 4 -C 14 alkyl ester

[0013] b. Treating in the presence of methanol with a transesterification catalyst to provide a second reaction mixture product comprising dimethyl terephthalate, -C-ol, and ethylene glycol, followed by 4 -C 14 c. Separating the dimethyl terephthalate.

[0014] c. Separating the dimethyl terephthalate.

[0015] In certain embodiments, the poly(ethylene terephthalate) 2 -C 4) The alkylene ester may also contain additional diol and / or diacid residues and includes, for example, polyethylene terephthalate (PET), CHDM-modified PET, IPA-modified PET, DEG-modified PET, diol-modified PET, NPG-modified PET, PDO-modified PET, BDO-modified PET, HDO-modified PET, MP diol-modified PET, isosorbide-modified PET, PTMG-modified PET, PEG-modified PET, poly(cyclohexylene dimethylene terephthalate) (PCT), a copolyester containing CHDM, a copolyester containing isosorbide, or combinations thereof. In other embodiments, the poly(phenylene) alkylene ester may include polyethylene terephthalate (PET) which contains residues of CHDM, IPA, DEG, NPG, PDO, BDO, HDO, MP diol, isosorbide, PTMG, PEG, or combinations thereof. 2 -C 4 ) The alkylene ester may include polyethylene terephthalate (PET) which contains residues of CHDM, IPA, DEG, NPG, PDO, BDO, HDO, MP diol, isosorbide, PTMG, PEG, or combinations thereof.

[0016] In certain embodiments, the esterification or transesterification catalyst for part a is selected from such known catalysts as, for example, Lewis acids and Lewis bases. Exemplary Lewis base catalysts include alkali metal alkoxides, alkali metal carbonates, or alkali metal bicarbonates, where the alkali metal is selected from lithium, sodium, potassium, or cesium. Exemplary Lewis acid catalysts include metal acetates, titanium alkoxides, and tin substances such as stannous oxalate, monobutyltin oxide, and monobutyltin tris(2-ethylhexanoate). In certain embodiments, the metal acetate is selected from alkali metal acetates and transition metal acetates. In certain embodiments, the catalysts mentioned above include potassium carbonate, potassium bicarbonate, potassium acetate, titanium(IV) isopropoxide, and monobutyltin tris(2-ethylhexanoate). In certain embodiments, based on the PET repeating unit, the amount of catalyst used in the depolymerization reaction (step a above) is between about 0.001 equivalents and about 0.1 equivalents, or between about 0.005 equivalents and about 0.075 equivalents, or between about 0.005 equivalents and about 0.05 equivalents.

[0017] In step a. above, in certain embodiments, the temperature is between about 100 °C and about 250 °C, about 125 °C and about 250 °C, or about 150 °C and about 220 °C. The temperature can be advantageously selected to provide a desired reaction rate while minimizing reaction by-products and while taking advantage of the simplicity of the equipment setup. In this regard, at ambient pressure, it may be convenient to conduct the method at the boiling point of the lowest boiling component of the mixture. In other cases, such as when using lower carbon alcohols, it may be more convenient to conduct the method at elevated pressure to increase the boiling point of the mixture and accelerate the reaction rate. In certain embodiments, the reaction pressure can be in the range of about 0 psig to about 500 psig (pounds per square inch gauge).

[0018] Generally, the time required to complete step a. depends on the temperature, the particular monohydric alcohol selected, and the amount of catalyst used. In certain embodiments, the reaction time is between about 0.5 hour and about 10 hours, or between about 1 hour and about 8 hours, or between about 1 hour and about 6 hours.

[0019] Advantageously, the low-viscosity depolymerized product mixture obtained from step a. can be cooled to between about 20 °C and about 100 °C prior to SLS. Cooling facilitates separation by ensuring that impurities have the opportunity to fully solidify and by using standard equipment rather than high-temperature SLS equipment. Thus, in certain embodiments, the temperature prior to SLS is between about 20 °C and about 100 °C, or between about 30 °C and about 80 °C, or between about 40 °C and about 70 °C. SLS can be carried out using standard techniques known in the art, such as vacuum filtration, centrifugation, or pressure filtration. As is known in the art, there may be cases where a filter aid is required. In some cases, it may be more desirable to decant the liquid phase rather than filter the mixture. As used herein, the terms "isolating" or "isolation" refer to known methods of separating solid and liquid materials, such as the SLS methods described above.

[0020] The second step (b.) involves converting the depolymerized mixture of higher alcohols to dimethyl terephthalate (DMT) and ethylene glycol (EG) using base-catalyzed low-temperature transesterification with methanol. In certain embodiments, this step includes mixing the depolymerized mixture with methanol; adding a transesterification catalyst at an initial temperature between about 40 °C and about 70 °C; holding at this initial temperature for an initial period of time; cooling to a final temperature of about 30 °C or lower during a second period of time; holding at this final temperature for a third period of time to obtain a final DMT slurry; and isolating the DMT, for example, by solid-liquid separation such as filtration.

[0021] The amount of methanol used in this step of the method is not critical, but is typically an amount sufficient to maintain a fluid slurry of solid DMT in the mixture at the final temperature. Generally, based on the starting polyester substrate, the amount of methanol can be between about 5 equivalents and about 50 equivalents, or between about 5 equivalents and about 36 equivalents, or between about 5 equivalents and about 24 equivalents.

[0022] In certain embodiments, a basic catalyst is used in the transesterification step of the method. Exemplary catalysts include metal 1 -C 14 alkoxides, metal carbonates, and metal hydroxides. In certain embodiments, the metal is an alkali metal such as lithium, sodium, and potassium. In other embodiments, the catalyst is selected from sodium hydroxide or potassium hydroxide, sodium methoxide or potassium methoxide, sodium or potassium 2-ethylhexanoate, or potassium carbonate. In certain embodiments, based on the starting polyester substrate, the amount of catalyst can be from about 0.005 equivalents to about 0.2 equivalents, or between about 0.01 equivalents and about 0.10 equivalents, or between about 0.02 equivalents and about 0.075 equivalents, where more catalyst generally provides a faster reaction.

[0023] In certain embodiments, the initial temperature of the transesterification step of the method is between about 40 °C and 70 °C, or between about 40 °C and about 65 °C. In one embodiment, the initial temperature is between about 50 °C and about 65 °C.

[0024] In certain embodiments, the first period of time at the initial temperature is from about 15 minutes to about 120 minutes, or from about 15 minutes to about 90 minutes, or from about 15 minutes to about 60 minutes. The cooling time is not particularly critical and can generally occur within 5 minutes to 75 minutes, or 15 minutes to 60 minutes, or 15 minutes to 45 minutes. The time at the final temperature is not critical and can be from 0 hours to 24 hours, or from 0 minutes to 120 minutes, or from 0 minutes to 60 minutes. These times can be varied to some extent by the catalyst loading.

[0025] The second step (step b.) of the method (i.e., transesterification) can be carried out at atmospheric pressure or near atmospheric pressure. Conditions above atmospheric pressure, while not necessary, do not have a negative impact on the method. During the method, conditions below atmospheric pressure may cause methanol evaporation, which would be undesirable, but can also contribute to cooling the mixture if the methanol evaporation is well controlled.

[0026] Using the above conditions, a slurry of DMT in methanol can be obtained, and DMT can be conveniently and effectively separated by solid-liquid separation. The method of SLS can be any conventional method known in the art - vacuum filtration, centrifugation, pressure filtration, etc. Usually, additional methanol is used to transfer the solid DMT to the filter, and this methanol also helps to remove any residual diol and monoalcohol from the solid. Therefore, the DMT obtained by this method is of high purity, usually having, for example, <0.5% non-volatile impurities, and the overall single-pass yield of PET usually exceeds 80%.

[0027] Another embodiment of the method involves separating the liquid components after separating DMT. These components are typically methanol, higher monoalcohols, ethylene glycol, and residual soluble terephthalate substances. One embodiment of the separation method involves sequentially distilling the liquid components in the resulting filtrate, thereby purifying them and allowing the solvents and raw materials to be recycled into the method. This is particularly advantageous for shorter monoalcohols such as n-butanol, isobutanol, and hexanol, since the boiling points of the liquid substances are well separated. This sequential distillation allows methanol, alcohol, and ethylene glycol to be recovered separately in high purity. In particular, the ethylene glycol from this distillation has a low color. The residual terephthalate ends up in the distillation pot residue and can thus be recycled into the method.

[0028] Another embodiment of the separation method is effective for higher boiling monoalcohols such as decanol, dodecanol, and tetradecanol. In this embodiment, methanol and ethylene glycol can be separated by sequential distillation, while the monoalcohol and terephthalate residue remain in the base, which allows the latter mixture to be recycled into the method at any time.

[0029] Another embodiment of the separation method involves distillation and extraction and is particularly applicable to intermediate range monoalcohols where the boiling point of the alcohol is close to that of ethylene glycol (e.g., 2-ethylhexanol, n-octanol). In this embodiment, methanol is removed by distillation and the residue is treated with water. The amount of water is not critical and can vary between 0.1 to 5 parts / part residue, or 0.1 to 1 part, or 0.25 to 0.75 parts / part residue. This water treatment results in two layers that can be easily separated. The top layer is almost pure monoalcohol, which contains most of the terephthalate residue; this material can be recycled into the method. The bottom layer contains water and ethylene glycol as well as a small amount of monoalcohol. This residual monoalcohol can be removed as a water azeotrope during water distillation. The overall recovery of monoalcohol is usually above 95%. Further distillation can give high purity colorless EG from the DMT filtrate in an almost quantitative yield.

[0030] Additional advantages of the present invention include the ability to utilize plastic waste streams obtained by conventional separation or mechanical recycling of various plastics. In this regard, the robust methods described herein are capable of separating such undesired materials from the desired recycled materials.

[0031] As used herein, the term "waste plastic stream" refers to a heterogeneous waste plastic stream containing various polymers and plastics. The waste plastic stream can include materials recycled as manufacturing scrap, industrial waste, post-consumer waste, or combinations thereof. In certain embodiments, the recycled polyester can be a previously used product that has been used and / or discarded. In certain embodiments, the waste plastic stream can be from various sources and / or in various forms, including but not limited to textiles, carpets, thermoformed materials, bottles, pellets, and films. Additionally, the waste plastic stream can include one or more foreign substances. In certain embodiments, the one or more foreign substances can include but are not limited to polyesters other than poly(ethylene terephthalate), polyvinyl chloride (PVC), polyvinyl acetal, polyvinyl butyral (PVB), polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), cotton, polyolefins, polyethylene, polypropylene, polystyrene, polycarbonate, spandex, natural fibers, cellulose esters, polyacrylates, polymethacrylates, polyamides, nylons, poly(lactic acid), polydimethylsiloxane, polysilanes, calcium carbonate, titanium dioxide, inorganic fillers, dyes, pigments, color toners, colorants, plasticizers, binders, flame retardants, metals, aluminum, and iron, or combinations thereof. In various aspects, relative to the weight of the poly(ethylene terephthalate) alkylene ester, the one or more foreign substances can be present in the polyester composition in an amount of from about 0.01 wt% to about 50 wt%, from about 0.01 wt% to about 40 wt%, from about 0.01 wt% to about 30 wt%, from about 0.01 wt% to about 20 wt%, from about 0.01 wt% to about 15 wt%, from about 0.01 wt% to about 10 wt%, from about 0.01 wt% to about 7.5 wt%, from about 0.01 wt% to about 5 wt%, from about 0.01 wt% to about 2.5 wt%, from about 0.01 wt% to about 1.0 wt%. 2 -C 4 ) alkylene ester, the one or more foreign substances can be present in the polyester composition in an amount of from about 0.01 wt% to about 50 wt%, from about 0.01 wt% to about 40 wt%, from about 0.01 wt% to about 30 wt%, from about 0.01 wt% to about 20 wt%, from about 0.01 wt% to about 15 wt%, from about 0.01 wt% to about 10 wt%, from about 0.01 wt% to about 7.5 wt%, from about 0.01 wt% to about 5 wt%, from about 0.01 wt% to about 2.5 wt%, from about 0.01 wt% to about 1.0 wt%.

[0032] Thus, waste plastic streams are typically obtained by recycling methods that involve collecting and optionally separating plastic materials by polymer type, typically followed by forming molten waste plastic and forming new intermediate products (e.g., pellets or sheets) and / or new final products. Generally, mechanical recycling does not substantially alter the chemical structure of the recycled plastics.

[0033] Thus, in a second aspect, the present invention provides a method for preparing dimethyl terephthalate, the method comprising:

[0034] a. in the presence of an esterification or transesterification catalyst, at a temperature sufficient to depolymerize at least a portion of the poly(ethylene terephthalate), with C 4 -C 14An alkanol treats a waste plastic stream comprising poly(ethylene terephthalate) to obtain a first reaction mixture product comprising di-C 4 -C 14 alkyl terephthalate; followed by

[0035] b. treating with a transesterification catalyst in the presence of methanol to provide a second reaction mixture product comprising dimethyl terephthalate, C 4 -C 14 alcohol and ethylene glycol, followed by

[0036] c. separating the dimethyl terephthalate.

[0037] This second aspect of the invention can also utilize the various embodiments as set forth above in the first aspect.

[0038] Key advantages of the method of the present invention include the ability to depolymerize polyesters with higher monohydric alcohols at low alcohol to PET ratios and still provide a non-tacky depolymerization mixture that can undergo SLS at low temperatures, thereby effectively removing the solid inorganic contaminants and non-PET plastics initially present in the waste plastic stream, such as those described above. In addition, the method is carried out at a relatively low overall temperature, uses an inexpensive catalyst with a short reaction time, and has low energy consumption. Generally, the r-DMT produced by this method is usually obtained from PET with non-volatile impurities of <0.5% in a yield of 80% or higher. In fact, even closely related impurities such as dimethyl isophthalate can be removed from dimethyl terephthalate by the present invention. The present invention allows for the direct production of DMT with sufficient purity (or with minimal subsequent purification) to allow its direct use in polyester production. In addition, the monohydric alcohol reactant is easily recovered, with a high overall recovery rate, and r-EG with good sensory properties (low color and odor) is obtained in high purity and high yield.

[0039] Example

[0040] Example 1: Depolymerization of PET and n-butanol at a ratio of 2.5:1

[0041] In a 300 mL autoclave, granulated post-consumer PET bottle flakes (50.0 g; 0.276 mol) and potassium carbonate (1.01 g; 0.0072 mol; 0.028 eq) were slurried in n-butanol (125 g; 1.686 mol; 6.55 eq). The autoclave was pressurized with 500 psig of nitrogen, then vented and sealed. Stirring was started and the interior of the autoclave was heated to 200 °C to generate an autogenous pressure of approximately 120 psig. The vessel was further pressurized to 500 psig and stirred at 200 °C for four hours. The mixture was cooled to ambient temperature and poured into a bottle from the autoclave (there was little remaining in the autoclave). The non-viscous mixture was filtered to remove insolubles, and the filtrate was bottled. The insoluble residue was dried to give 0.60 g. HPLC analysis of the filtrate showed the presence of 71% dibutyl terephthalate, and the acid value of the material analyzed was 1.67. The theoretical content of the filtrate was 1.46 mmol total terephthalate per gram. HPLC (150 × 4.6 mm ZORBAX SB-C8 column, 85:15 (v:v) methanol: water (containing 0.1% trifluoroacetic acid) for 6 minutes, gradient to 100% methanol over 1 minute, 100% methanol for 3 minutes, detection at 220 nm): dibutyl terephthalate, t R 4.53 minutes; butyl EG mixed esters, t R 2.25 minutes.

[0042] Example 2: Depolymerization of PET and n-butanol at a ratio of 2:1

[0043] In a 300 mL autoclave, granulated post-consumer PET bottle flakes (50.0 g; 0.276 mol) and potassium carbonate (1.01 g; 0.0072 mol; 0.028 eq) were slurried in n-butanol (100 g; 1.349 mol; 5.24 eq). The autoclave was pressurized with 500 psig of nitrogen, then vented and sealed. Stirring was started and the interior of the autoclave was heated to 200 °C to generate an autogenous pressure of approximately 120 psig. The vessel was further pressurized to 500 psig and stirred at 200 °C for four hours. The mixture was cooled to ambient temperature and poured into a bottle from the autoclave (there was little remaining in the autoclave). The non-viscous mixture was filtered to remove insolubles, and the filtrate was bottled. The insoluble residue was dried to give <1 g. HPLC analysis of the filtrate showed the presence of 70% dibutyl terephthalate, and the acid value of the material analyzed was 1.58. The theoretical content of the filtrate was 1.72 mmol total terephthalate per gram.

[0044] Example 3: Transesterification of the PET butanolysis mixture with methanol using sodium methoxide

[0045] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET butanolysis mixture prepared as in Example 2 (1.72 mmol / g; 40.0 g; 0.069 mol) was slurried in 50.2 mL of methanol (1.238 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (787 μL; 0.0034 mol; 0.05 equivalents; 0.34 equivalents of active catalyst based on the acid value) was added. The mixture was stirred at 250 rpm at 50 °C, and precipitation accompanied by exotherm was observed starting from 4.5 minutes. After heating at 50 °C for 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 45 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to obtain 9.70 g of white powdered DMT, which had a purity > 99.9 wt% as determined by HPLC, indicating a total yield of 73% from PET. Analysis of the filtrate showed that it contained 5.5% of the expected yield of DMT and small amounts (each < 0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), 2-hydroxyethyl methyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0046] 1 H NMR(CDCl 3 ): δ 8.11 (s, 4H); 3.96 (s, 3H).

[0047] HPLC (150×4.6 mm Zorbax SB-C8 column, 75:25 (v:v) methanol:water (containing 0.1% trifluoroacetic acid) for 5 minutes, gradient to 100% methanol over 1 minute, hold at 100% methanol for 4 minutes, detection at 220 nm): BHET, t R 1.75 minutes; MHET, t R 2.1 minutes; DMI, t R 2.75 minutes; DMT, t R 2.87 minutes.

[0048] Example 4: Transesterification of the PET butanolysis mixture with methanol using sodium hydroxide

[0049] In a 300 mL three-neck round-bottom flask equipped with a top-mounted stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET butanolysis mixture prepared as in Example 2 (1.72 mmol / g; 40.0 g; 0.069 mol) was slurried in 50.2 mL of methanol (1.238 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / -2 °C), 50% aqueous sodium hydroxide solution (168 μL; 0.255 g; 0.0032 mol; 0.046 equivalents; 0.030 equivalents of active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed starting from five minutes. After heating at 50 °C for 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 45 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 9.70 g of white powdered DMT, which had a purity >99.9 wt% as determined by HPLC, indicating a total yield of 66% from PET. Analysis of the filtrate showed that it contained 5.5% of the expected yield of DMT and small amounts (each <0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), 2-hydroxyethyl methyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0050] Example 5: Depolymerization of PET and n-butanol at a ratio of 1.5:1

[0051] In a 1 L autoclave, granulated bottle-grade waste PET (250.0 g; 1.287 mol) and potassium carbonate (4.98 g; 0.036 mol; 0.028 equivalents) were slurried in n-butanol (375 g; 5.06 mol; 3.93 equivalents). The autoclave was pressurized with 500 psig of nitrogen, then vented and sealed. Stirring was started and the interior of the autoclave was heated to 200 °C to generate an autogenous pressure of approximately 120 psig. The vessel was further pressurized to 500 psig and stirred at 200 °C for four hours. The mixture was cooled to ambient temperature and poured into a bottle from the autoclave (there was little remaining in the autoclave). The non-sticky mixture was filtered to remove insolubles. Analysis of the filtrate viscosity showed that the viscosity decreased from 8.6 cP at 25 °C to 4.2 cP at 60 °C. HPLC analysis of the filtrate showed the presence of 59% dibutyl terephthalate, and the acid value of the analyzed material was 1.36. The theoretical content of the filtrate was 2.06 mmol total terephthalate per gram.

[0052] Example 6: Transesterification of the PET butanolysis mixture with methanol using sodium methoxide

[0053] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET butanolysis mixture prepared as in Example 5 (2.06 mmol / g; 35.0 g; 0.072 mol) was slurried in 61.5 mL of methanol (1.518 mol; 21.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction mixture equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (632 μL; 0.0028 mol; 0.038 equivalent; 0.30 equivalent active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed starting from five minutes. After heating at 50 °C for 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 45 minutes and then stirred at ambient temperature for 2 hours. The resulting precipitate was filtered, washed with methanol, and air-dried to obtain 11.78 g of white powdery DMT, which had a purity >99.9 wt% as determined by HPLC, indicating a total yield from PET of 84%. Analysis of the filtrate showed that it contained 3.3% of the expected yield of DMT and small amounts (each <0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), 2-hydroxyethyl methyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0054] Example 7: Transesterification of the PET butanolysis mixture with methanol using sodium hydroxide

[0055] In a 1 L jacketed reactor equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET butanolysis mixture prepared as in Example 5 (2.06 mmol / g; 150.0 g; 0.309 mol) was slurried in 264 mL of methanol (6.504 mol; 21.0 equivalents). The jacket was heated until the internal temperature equilibrated at 50 °C (+ / -2 °C). A 50% aqueous sodium hydroxide solution (688 μL; 0.0129 mol; 0.042 equivalent; 0.30 equivalent active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 200 rpm, and precipitation accompanied by exotherm was observed starting from 6.5 minutes. After heating at 50 °C for 60 minutes, heating was stopped, and the mixture was cooled to ambient temperature within 90 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to obtain 49.17 g of white powdery DMT, which had a purity of 99.7 wt% as determined by HPLC, indicating a total yield from PET of 82%. Analysis of the filtrate showed that it contained 3.3% of the expected yield of DMT and small amounts (each <0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), 2-hydroxyethyl methyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0056] The resulting filtrate (407.57 g) was concentrated under reduced pressure to remove most of the methanol, resulting in a slurry, which was filtered. The precipitate (1.58 g after drying) was analyzed to be >99.8% DMT (2.6% yield). The liquid was distilled through a Vigreux column at atmospheric pressure to obtain 84.03 g of a distillate boiling at 62 °C to 80 °C. This distillate was analyzed to be 80.6% methanol and 19.4% butanol. The remainder was further distilled at atmospheric pressure to obtain an overlapping fraction (8.88 g, boiling at 80 °C to 110 °C) and a fraction boiling at 110 °C to 113 °C (58.1 g), which was analyzed to be 98.5% butanol, 1.3% methanol, and 0.2% EG. The pressure was reduced to 30 mm Hg, and an overlapping fraction boiling at 36 to 107 °C (4.83 g) was taken, which was analyzed to be 65.3 wt% butanol and 15.3 wt% EG. The final fraction (5.19 g) was distilled at 109 °C to 110 °C / 30 mm Hg and was analyzed to be 97.0 wt% EG and 1.2 wt% butanol. All fractions were colorless.

[0057] Example 8: Depolymerization of PET and n-butanol at a ratio of 1.25:1

[0058] In a 300 mL autoclave, granulated bottle-grade waste PET (50.0 g; 0.276 mol) and potassium carbonate (1.01 g; 0.0072 mol; 0.028 eq) were slurried in n-butanol (62.5 g; 0.843 mol; 3.27 eq). The autoclave was pressurized with 500 psig nitrogen, then vented and sealed. Stirring was started and the interior of the autoclave was heated to 200 °C to generate an autogenous pressure of approximately 120 psig. The vessel was further pressurized to 500 psig and stirred at 200 °C for four hours. The mixture was cooled to ambient temperature and poured from the autoclave into a bottle (there was little remaining in the autoclave). The non-sticky mixture was filtered to remove insolubles. HPLC analysis of the filtrate showed the presence of 61% dibutyl terephthalate, and the acid value of the material analyzed was 1.4. The theoretical content of the filtrate was 2.27 mmol total terephthalate per gram.

[0059] Example 9: Depolymerization of PET and 2-ethylhexanol at a ratio of 10:1

[0060] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium carbonate (0.50 g; 3.6 mmol; 0.028 eq) were slurried in 2-ethylhexanol (250 g; 1920 mmol; 14.8 eq). The interior of the flask was heated to 185 °C and maintained for 1 hour after complete dissolution of the PET. The mixture was cooled to 60 °C and filtered, and the filtrate (235.45 g) was bottled. HPLC analysis of the filtrate showed the presence of a mixed ester of 91% bis(2-ethylhexyl) terephthalate and 8% 2-ethylhexyl 2-hydroxyethyl terephthalate. The theoretical content of the filtrate was 0.47 mmol total terephthalate per gram.

[0061] HPLC (150×4.6 mm Zorbax SB-C8 column, 90:10 (v:v) methanol:water (containing 0.1% trifluoroacetic acid) for 11 minutes, gradient to 100% methanol over 4 minutes, detection at 250 nm): bis(2-ethylhexyl) terephthalate, t R 9.95 minutes; mixed ester, t R 2.64 minutes.

[0062] Example 10: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET = 10:1) with methanol

[0063] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, a PET 2-ethylhexanolysis mixture prepared as in Example 9 (0.47 mmol / g; 50 g; 0.024 mol) was slurried in 22.9 mL of methanol (0.565 mol; 24.0 eq). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / -2 °C), 50% aqueous sodium hydroxide solution (26 μL; 0.0005 mol; 0.02 eq) was added. The mixture was stirred at 50 °C at 250 rpm for 5 minutes, and an additional 0.02 eq of 50% sodium hydroxide was added. After 10 minutes, an additional 0.04 eq of 50% sodium hydroxide was added, and after 15 minutes, a 25% methanol solution of sodium methoxide (0.02 eq) was added. The mixture was stirred at 50 °C for a total of 45 minutes with no precipitation, then cooled to ambient temperature over 30 minutes, during which precipitation occurred. An additional 0.05 eq of a methanol solution of sodium methoxide was added, and the mixture was stirred at ambient temperature for four hours. The resulting precipitate was filtered, washed with methanol, and air-dried to give 1.78 g of white powdered DMT, which was determined by HPLC to have a purity of 96.2 wt%, indicating a total yield from PET of 37%.

[0064] Example 11: Depolymerization of PET and 2-ethylhexanol at a ratio of 5:1

[0065] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium carbonate (0.50 g; 3.6 mmol; 0.028 eq) were slurried in 2-ethylhexanol (125 g; 960 mmol; 7.38 eq). The interior of the flask was heated to 185 °C and held for 1 hour after complete dissolution of the PET. The mixture was cooled to 60 °C and filtered, and the filtrate was bottled. HPLC analysis of the filtrate showed the presence of a mixed ester of 82% bis(2-ethylhexyl) terephthalate and 16% 2-ethylhexyl 2-hydroxyethyl terephthalate. The theoretical content of the filtrate was 0.86 mmol total terephthalate per gram.

[0066] Example 12: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET = 5:1) with methanol

[0067] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 11 (0.86 mmol / g; 50.0 g; 0.043 mol) was slurried in 42.1 mL of methanol (1.039 mol; 24.0 eq). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (198 μL; 0.0009 mol; 0.02 eq) was added. The mixture was stirred at 50 °C at 250 rpm for 5 minutes with no precipitation, and an additional 0.03 eq of the methanol solution of 25% sodium methoxide was added. Precipitation accompanied by exotherm was observed between 30 and 45 minutes. After heating at 50 °C for a total of 120 minutes, the heating bath was removed and the mixture was cooled to ambient temperature within 45 minutes and then stirred at ambient temperature for 2 hours. The resulting precipitate was filtered, washed with methanol, and air-dried to give 5.68 g of white powdery DMT, which was determined by HPLC to have a purity of 97.8 wt%, indicating a total yield from PET of 66%. Analysis of the filtrate showed that it contained 11.1% of the expected yield of DMT and small amounts (each < 0.5%) of 2-hydroxyethyl terephthalate (MHET) and dimethyl isophthalate (DMI).

[0068] Example 13: Depolymerization of PET and 2-ethylhexanol at a ratio of 2.5:1

[0069] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium carbonate (0.50 g; 3.6 mmol; 0.028 eq) were slurried in 2-ethylhexanol (62.5 g; 480 mmol; 3.69 eq). After the PET was completely dissolved, the interior of the flask was heated to 185 °C and maintained for 1 hour. The mixture was cooled to 60 °C and filtered, and the filtrate was bottled. HPLC analysis showed the presence of a mixed ester of 69% bis(2-ethylhexyl) terephthalate and 25% 2-ethylhexyl 2-hydroxyethyl terephthalate.

[0070] Example 14: Depolymerization of PET and 2-ethylhexanol at a ratio of 2:1

[0071] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium carbonate (0.50 g; 3.6 mmol; 0.028 eq) were slurried in 2-ethylhexanol (50.0 g; 384 mmol; 2.95 eq). After the PET was completely dissolved, the interior of the flask was heated to 185 °C and maintained for 1 hour. The mixture was cooled to 60 °C and filtered, and the filtrate was bottled. Analysis of the viscosity of the filtrate showed that the viscosity decreased from 30.0 cP at 25 °C to 10.8 cP at 60 °C. HPLC analysis of the filtrate showed the presence of a mixed ester of 64% bis(2-ethylhexyl) terephthalate and 28% 2-ethylhexyl 2-hydroxyethyl terephthalate. The theoretical content of the filtrate was 1.72 mmol total terephthalate per gram.

[0072] Example 15: Transesterification of the PET 2-ethylhexanolysis mixture with methanol using sodium hydroxide

[0073] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 14 (1.72 mmol / g; 25 g; 0.043 mol) was slurried in 41.8 mL of methanol (1.032 mol; 24.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), 50% aqueous sodium hydroxide solution (236 μL; 0.0043 mol; 0.10 equivalent) was added. The mixture was stirred at 50 °C at 200 rpm for 60 minutes, during which precipitation was observed. The heating bath was then removed, and the mixture was cooled to ambient temperature over 45 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 5.07 g of white powdered DMT, which had a purity of 99.9 wt% as determined by HPLC, indicating a total yield from PET of 61%. Analysis of the filtrate showed that it contained 7.4% of the expected yield of DMT and small amounts (each < 0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), methyl 2-hydroxyethyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0074] Example 16: Depolymerization of PET and 2-ethylhexanol at a ratio of 1.5:1

[0075] In a 500 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (300.0 g; 1.56 mol) and potassium carbonate (6.04 g; 0.015 mol; 0.028 equivalent) were slurried in 2-ethylhexanol (450 g; 3.455 mol; 2.21 equivalents). After the PET had completely dissolved, the interior of the flask was heated to 185 °C and held for 1 hour. The mixture was cooled to 60 °C and filtered, and the filtrate (229.1 g) was bottled. The residual solid was washed with methanol and dried to give 2.5 g of insoluble residue. Analysis of the viscosity of the filtrate showed that the viscosity decreased from 43.8 cP at 25 °C to 14.7 cP at 60 °C. HPLC analysis of the filtrate showed the presence of 47% bis(2-ethylhexyl) terephthalate and 28% 2-ethylhexyl 2-hydroxyethyl terephthalate mixed esters, with the remainder being other esters and oligomers. The filtrate was analyzed at an acid value of 1.36, and the theoretical content of the filtrate was 2.06 mmol of total terephthalate esters per gram.

[0076] Example 17: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET = 1.5:1) with 24 equivalents of methanol using sodium methoxide catalyst

[0077] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.06 mmol / g; 25.0 g; 0.052 mol) was slurried in 50.2 mL of methanol (1.239 mol; 24.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction mixture equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (698 μL; 0.0031 mol; 0.059 equivalents; 0.050 equivalents of active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed within 20 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to obtain 8.53 g of DMT as a shiny white solid, which had a purity of 98.6 wt% as determined by HPLC and GC, indicating a total yield from PET of 84%. Analysis of the filtrate showed that it contained 3.0% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0078] Example 18: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET = 1.5:1) with 21 equivalents of methanol using sodium methoxide catalyst

[0079] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.06 mmol / g; 25.0 g; 0.052 mol) was slurried in 43.9 mL of methanol (1.084 mol; 21.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction mixture equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (698 μL; 0.0031 mol; 0.059 equivalents; 0.050 equivalents of active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed within 20 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to obtain 8.88 g of DMT as a shiny white solid, which had a purity of 99.9 wt% as determined by HPLC and GC, indicating a total yield from PET of 88%. Analysis of the filtrate showed that it contained 2.8% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0080] Example 21: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET = 1.5:1) with 18 equivalents of methanol using sodium methoxide catalyst

[0081] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.06 mmol / g; 25.0 g; 0.052 mol) was slurried in 37.7 mL of methanol (0.929 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (698 μL; 0.0031 mol; 0.059 equivalents; 0.050 equivalents of active catalyst based on the acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and a precipitate accompanied by exotherm was observed at 10 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.97 g of DMT as a shiny white solid, which had a purity of 95.2 wt% as determined by HPLC and GC, indicating a total yield from PET of 85%. Analysis of the filtrate showed that it contained 1.3% of the expected yield of DMT and small amounts (each < 0.5%) of bis(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0082] Example 23: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET = 1.5:1) with 15 equivalents of methanol using sodium methoxide catalyst

[0083] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.06 mmol / g; 25.0 g; 0.052 mol) was slurried in 31.3 mL of methanol (0.774 mol; 15.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (698 μL; 0.0031 mol; 0.059 equivalents; 0.050 equivalents of active catalyst based on the acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed at nine minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.53 g of DMT as a shiny white solid, which had a purity of 98.0 wt% as determined by HPLC and GC, indicating a total yield from PET of 83%. Analysis of the filtrate showed that it contained 1.6% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0084] Example 25: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET = 1.5:1) with 12 equivalents of methanol using sodium methoxide catalyst

[0085] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.06 mmol / g; 25.0 g; 0.052 mol) was slurried in 25.1 mL of methanol (0.620 mol; 12.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (698 μL; 0.0031 mol; 0.059 equivalents; 0.050 equivalents of active catalyst based on the acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed within 20 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.37 g of DMT as a shiny white solid, which had a purity of 99.7 wt% as determined by HPLC and GC, indicating a total yield from PET of 83%. Analysis of the filtrate showed that it contained 1.6% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0086] Example 27: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET = 1.5:1) with 18 equivalents of methanol using potassium carbonate catalyst

[0087] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.06 mmol / g; 25.0 g; 0.052 mol) was slurried in 37.7 mL of methanol (0.929 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), potassium carbonate (0.357 g; 0.0026 mol; 0.050 equivalents; 0.041 equivalents of active catalyst based on the acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and a precipitate accompanied by exotherm was observed at seven minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.66 g of DMT as a shiny white solid, which had a purity of 98.5 wt% as determined by HPLC and GC, indicating a total yield from PET of 85%. Analysis of the filtrate showed that it contained 2.5% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0088] Example 29: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET = 1.5:1) with 18 equivalents of methanol under cooling Example 31: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET = 1.5:1) with 18

[0089] In a 300 mL three-neck round-bottom flask equipped with a top-mounted stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.06 mmol / g; 25.0 g; 0.052 mol) was slurried in 37.7 mL of methanol (0.929 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (698 μL; 0.0031 mol; 0.059 equivalents; 0.050 equivalents of active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed at 10 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The mixture was then cooled in an ice bath at 0 °C to 5 °C for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 9.19 g of shiny white solid DMT, which had a purity of 96.0 wt% as determined by HPLC and GC, indicating a total yield from PET of 88%. Analysis of the filtrate showed that it contained 1.2% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0090] equivalents of methanol under cooling using potassium carbonate catalyst Example 33: Depolymerization of carpet PET and 2-ethylhexanol at a ratio of 1.5:1

[0091] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.06 mmol / g; 25.0 g; 0.052 mol) was slurried in 37.7 mL of methanol (0.929 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), potassium carbonate (0.357 g; 0.0026 mol; 0.050 equivalent; 0.041 equivalent active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and a precipitate accompanied by exotherm was observed at 15 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The mixture was then cooled in an ice bath at 0 °C to 5 °C for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 9.21 g of DMT as a shiny white solid, which was determined to be 93.6 wt% pure by HPLC and GC, indicating a total yield from PET of 86%. Analysis of the filtrate showed that it contained 1.2% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-ethylhexyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0092] Example 34: Transesterification of the PET 2-ethylhexanolysis mixture from carpet with 18 equivalents of meth

[0093] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated waste PET from carpets (87.0% PET; 25 g; 113.2 mmol) and potassium carbonate (0.44 g; 3.2 mol; 0.028 equivalent) were slurried in 2-ethylhexanol (37.5 g; 287.9 mmol; 2.54 equivalents). After the PET had completely dissolved, the interior of the flask was heated to 185 °C and held for 1 hour. The mixture was cooled to 60 °C and filtered, and the filtrate (48.39 g) was bottled. The residual solid was washed with methanol and dried to give 5 g of insoluble residue. HPLC analysis of the filtrate showed the presence of 58% bis(2-ethylhexyl) terephthalate and 33% 2-ethylhexyl 2-ethylhexylhydroxy terephthalate mixed esters, with the remainder being other esters and oligomers. The acid value of the filtrate was 2.48, and the theoretical content of the filtrate was 1.80 mmol total terephthalate per gram.

[0094] anol using sodium methoxide catalyst ​

[0095] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 25 (1.80 mmol / g; 43.0 g; 0.077 mol) was slurried in 56.4 mL of methanol (1.392 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction mixture equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (1.319 μL; 0.0058 mol; 0.075 equivalent; 0.050 equivalent active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed at 30 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 2 hours. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.97 g of DMT as a shiny white solid, which had a purity of 99.9 wt% as determined by HPLC and GC, indicating a total yield from PET of 81%. Analysis of the filtrate showed that it contained 9.4% of the expected yield of DMT and small amounts (each <0.5%) of bis(2-ethylhexyl) terephthalate (BHET) and dimethyl isophthalate (DMI).

[0096] Example 27: Depolymerization of automotive textile PET with 2-ethylhexanol

[0097] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, waste PET from automotive textiles (74.0% PET; 25.0 g; 96.3 mmol) and potassium carbonate (0.37 g; 2.7 mmol; 0.028 equivalent) were slurried in 2-ethylhexanol (27.8 g; 213.1 mmol; 2.21 equivalents). After the PET was completely dissolved, the interior of the flask was heated to 185 °C and held for 1 hour. The mixture was cooled to 60 °C and filtered, and the filtrate (29.38 g) was bottled. The residual solid was washed with methanol and dried to give 13.87 g of insoluble residue. HPLC analysis of the filtrate showed the presence of 49% bis(2-ethylhexyl) terephthalate and 24% 2-ethylhexyl 2-hydroxyethyl terephthalate mixed esters, with the remainder being other esters and oligomers. The acid value of the filtrate (29.38 g) was measured to be 1.40. The theoretical content of the filtrate was 2.06 mmol of total terephthalate per gram.

[0098] Example 28: Transesterification of the PET 2-ethylhexanolysis mixture from automotive textiles with 18 equivalents of methanol using a sodium methoxide catalyst

[0099] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 27 (2.06 mmol / g; 20.0 g; 0.0413 mol) was slurried in 30.1 mL of methanol (0.743 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction mixture equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (586 μL; 0.0026 mol; 0.062 equivalents; 0.05 equivalents of active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed at 10 minutes. After heating at 50 °C for a total of 45 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 6.32 g of DMT as a shiny white solid, which was determined to be 99.4 wt% pure by HPLC and GC, indicating a total yield from PET of 78%. Analysis of the filtrate showed that it contained 3.9% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-ethylhexyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0100] Example 29: Depolymerization of PET from a release liner with 2-ethylhexanol at a ratio of 1.5:1

[0101] In a 1 L three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, PET waste from a silicated release liner (98.0% PET; 150.0 g; 0.781 mol) and potassium carbonate (3.02 g; 0.022 mol; 0.028 equivalents) were slurried in 2-ethylhexanol (225.0 g; 1.728 mol; 2.21 equivalents). After the PET was completely dissolved, the interior of the flask was heated to 185 °C and held for 1 hour. The mixture was cooled to 60 °C and filtered to give 349.8 g of filtrate, which was taken directly. The residual solid was washed with methanol and dried to give 10.53 g of insoluble residue. HPLC area% analysis of the filtrate showed the presence of 58% bis(2-ethylhexyl) terephthalate, with the remainder being other esters and oligomers. The filtrate (59.7 g) had an acid value of 0.96. The theoretical content of the filtrate was 2.03 mmol of total terephthalate per gram.

[0102] Example 30: Transesterification of the PET 2-ethylhexanolysis mixture from a release liner with 18 equivalents of methanol using a sodium methoxide catalyst

[0103] In a 1 L three-neck round-bottom flask equipped with a top-mounted stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 29 (349.8 g; maximum 0.781 mol) was slurried in 380 mL of methanol (9.37 mol; 12.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (10.71 mL; 0.047 mol; 0.06 equivalents) was added. The mixture was stirred at 50 °C at 250 rpm, and a precipitate accompanied by exotherm was observed at four minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 132.65 g of shiny white solid DMT, which had a purity of 91.0 wt% as determined by HPLC, indicating a total yield from PET of 80%. Analysis of the filtrate showed that it contained 2.4% of the expected yield of DMT and small amounts (each <0.5%) of mono(2-ethylhexyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0104] The filtrate from the DMT filtration was stripped of methanol under reduced pressure and at 40 °C. The residue (259.33 g) was treated with 64.93 g of water. The layers were mixed well and allowed to settle. The layers were separated and analyzed. The top layer mainly contained 2-EH alcohol (83.45%) and small amounts of ethylene glycol (2.72%) and terephthalates. The bottom layer contained water, ethylene glycol (34.27%), and small amounts of 2-ethylhexanol (0.67%). The bottom layer was distilled successively, first removing water and the water / 2-ethylhexanol azeotrope at atmospheric pressure and then distilling ethylene glycol (17.9 g) under vacuum. The purity of the distilled ethylene glycol was determined to be 98.0%, and the APHA color was 4.5. Analysis for silicon showed that the crystallized DMT had 104 ppm Si and the distilled EG had 646 ppm Si.

[0105] Example 31: Depolymerization of PET with 2-ethylhexanol at a ratio of 1.25:1

[0106] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium carbonate (0.50 g; 3.6 mmol; 0.028 eq) were slurried in 2-ethylhexanol (31.3 g; 240 mmol; 1.84 eq). After the PET was completely dissolved, the interior of the flask was heated to 185 °C and held for 1 hour. The mixture was cooled to 60 °C and filtered, and the filtrate was bottled (46.06 g). HPLC analysis of the filtrate showed the presence of 41% bis(2-ethylhexyl) terephthalate and 28% 2-ethylhexyl 2-hydroxyethyl terephthalate mixed esters, with the remainder being other esters and oligomers.

[0107] Example 32: Depolymerization of PET with 2-ethylhexanol at a ratio of 1.5:1 using tributyltin tris(2-ethylhexanoate) catalyst Example 33: Transesterification of the PET 2-ethylhexanolysis mixture prepared with tributyltin tris(2-ethylhexanoate) (2-EH:PET is

[0108] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and butyltin tris(2-ethylhexanoate) 4102 (PMC), 1.57 g; 2.6 mmol; 0.02 eq) were slurried in 2-ethylhexanol (37.5 g; 288 mmol; 2.21 eq). The interior of the flask was heated to 185 °C and held for 2 hours after the PET was completely dissolved (dissolution took 3.5 hours). The mixture was cooled to 60 °C and filtered, and the filtrate was bottled (66.11 g). HPLC analysis of the filtrate showed the presence of 53% bis(2-ethylhexyl) terephthalate and 30% 2-ethylhexyl 2-hydroxyethyl terephthalate mixed esters, with the remainder being other esters and oligomers. The theoretical content of the filtrate was 2.03 mmol total terephthalate per gram.

[0109] 1.5:1) Example 34: Depolymerization of PET with 2-ethylhexanol at a ratio of 1.5:1 using titanium tetraisopropoxide catalyst

[0110] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, a PET 2-ethylhexanolysis mixture (2.03 mmol / g; 25.0 g; 0.051 mol) with an acid value of 1.95 prepared as in Example 32 was slurried in 37.0 mL of methanol (0.914 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (778 μL; 0.0034 mol; 0.067 equivalents; 0.050 equivalents of active catalyst based on the acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed at 12 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 45 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 7.95 g of shiny white solid DMT, which had a purity of 99.4 wt% as determined by HPLC and GC, indicating a total yield from PET of 81%. Analysis of the filtrate showed that it contained 5.9% of the expected yield of DMT and small amounts (each <0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), 2-hydroxyethyl methyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0111] Transesterification

[0112] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and titanium tetraisopropoxide (0.38 g; 1.3 mmol; 0.01 equivalents) were slurried in 2-ethylhexanol (37.5 g; 288 mmol; 2.21 equivalents). After the PET was completely dissolved, the interior of the flask was heated to 185 °C and maintained for 2 hours. The mixture was cooled to 60 °C and filtered, and the filtrate was bottled (58.6 g). HPLC analysis of the filtrate showed the presence of 51% bis(2-ethylhexyl) terephthalate and 29% 2-ethylhexyl 2-hydroxyethyl terephthalate mixed esters, with the remainder being other esters and oligomers. The theoretical content of the filtrate was 2.07 mmol of total terephthalate per gram.

[0113] Example 35: Using Ti(OiPr) 4 ester of the PET 2-ethylhexanolysis mixture (2-EH:PET = 1.5:1) prepared Example 36: Depolymerization of PET with 2-ethylhexanol at a ratio of 1.5:1 using sodium bicarbonate catalyst

[0114] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture (2.07 mmol / g; 25.0 g; 0.052 mol) with an acid value of 1.61 prepared as in Example 34 was slurried in 37.8 mL of methanol (0.932 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction mixture equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (756 μL; 0.0033 mol; 0.064 equivalents; 0.050 equivalents of active catalyst based on the acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed within 20 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 45 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to obtain 8.37 g of DMT as a shiny white solid, which was determined to be 99.9 wt% pure by HPLC and GC, indicating a total yield of 83% from PET. Analysis of the filtrate showed that it contained 4.3% of the expected yield of DMT and small amounts (each <0.5%) of bis(2-ethylhexyl) terephthalate (BHET) and dimethyl isophthalate (DMI).

[0115] Example 37: Transesterification of the PET 2-ethylhexanolysis mixture prepared with sodium bicarbonate (2-EH:PET is 1.5:1)

[0116] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and sodium bicarbonate (0.31 g; 3.6 mmol; 0.028 equivalents) were slurried in 2-ethylhexanol (37.5 g; 288 mmol; 2.21 equivalents). The interior of the flask was heated to 185 °C and stirred for a total of 6 hours (2.5 hours were required to dissolve the PET). The mixture was cooled to 60 °C and filtered to remove insoluble gel-like material (3.27 g), and the filtrate was bottled (50.87 g). HPLC analysis of the filtrate showed the presence of 56% bis(2-ethylhexyl) terephthalate and 31% 2-ethylhexyl 2-hydroxyethyl terephthalate mixed esters, with the remainder being other esters and oligomers. The theoretical content of the filtrate was 2.07 mmol of total terephthalate per gram, and the acid value of the filtrate was 1.08.

[0117] Example 38: Depolymerization of PET with 2-ethylhexanol at a ratio of 1.5:1 using potassium bicarbonate catalyst Example 39: Transesterification of the PET 2-ethylhexanolysis mixture prepared with potassium bicarbonate (2-EH:PET is 1.5:1)

[0118] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 36 (2.07 mmol / g; 25.0 g; 0.052 mol) was slurried in 37.8 mL of methanol (0.932 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction mixture equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (702 μL; 0.0031 mol; 0.059 equivalents; 0.050 equivalents of active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed at seven minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 90 minutes. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.69 g of shiny white solid DMT, which was determined by HPLC and GC to have a purity > 99.9 wt%, indicating a total yield from PET of 86%. Analysis of the filtrate showed that it contained 2.9% of the expected yield of DMT and small amounts (each < 0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), methyl 2-hydroxyethyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0119] Example 40: Depolymerization of PET with 1-hexanol at a ratio of 2:1

[0120] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium bicarbonate (0.36 g; 3.6 mmol; 0.028 equivalents) were slurried in 2-ethylhexanol (37.5 g; 288 mmol; 2.21 equivalents). The interior of the flask was heated to 185 °C and stirred for a total of 6 hours (2 hours were required to dissolve the PET). The mixture was cooled to 60 °C and filtered (insoluble material < 1 g), and the filtrate was bottled (66.11 g). HPLC analysis of the filtrate showed the presence of 55% bis(2-ethylhexyl) terephthalate and 33% 2-ethylhexyl 2-hydroxyethyl terephthalate mixed esters, with the remainder being other esters and oligomers. The theoretical content of the filtrate was 2.07 mmol of total terephthalate per gram, and the acid value of the filtrate was 1.37.

[0121] Example 41: Transesterification of the PET hexanolysis mixture (hexanol:PET is 2:1) with methanol Example 42: Depolymerization of PET with 1-octanol at a ratio of 1.5:1

[0122] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 38 (2.07 mmol / g; 25.0 g; 0.052 mol) was slurried in 37.8 mL of methanol (0.932 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (731 μL; 0.0032 mol; 0.062 equivalents; 0.050 equivalents of active catalyst based on the acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed at 7.5 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 2 hours. The resulting precipitate was filtered, washed with methanol, and air-dried to give 7.74 g of shiny white solid DMT, which was determined by HPLC and GC to have a purity > 99.9 wt%, indicating a total yield from PET of 77%. Analysis of the filtrate showed that it contained 2.3% of the expected yield of DMT and small amounts (each < 0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), 2-hydroxyethyl methyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0123] Example 43: Transesterification of the PET octanolysis mixture (octanol:PET is 1.5:1) with methanol

[0124] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium carbonate (0.50 g; 3.6 mmol; 0.028 equivalents) were slurried in 1-hexanol (50 g; 489 mmol; 3.76 equivalents). After the PET was completely dissolved, the interior of the flask was heated to 157 °C and held for 1 hour. The mixture was cooled to 60 °C and filtered, and the precipitate was washed and dried to give 2.90 g. The filtrate was bottled (66.18 g). HPLC analysis of the filtrate showed the presence of 65% dihexyl terephthalate, with the remainder being other esters and oligomers. The theoretical content of the filtrate was 1.72 mmol of total terephthalate per gram.

[0125] Example 44: Depolymerization of PET with 1-decanol at a ratio of 2:1

[0126] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET hexanolysis mixture prepared as in Example 40 (1.72 mmol / g; 25.0 g; 0.043 mol) was slurried in 41.9 mL of methanol (1.034 mol; 24.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (492 μL; 0.0022 mol; 0.05 equivalents) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed at seven minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 2 hours. The resulting precipitate was filtered, washed with methanol, and air-dried to give 5.90 g of white solid DMT, which had a purity of 98.3 wt% as determined by GC, indicating a total yield from PET of 69%. Analysis of the filtrate showed that it contained 15.0% of the expected yield of DMT and small amounts (each < 0.5%) of bis(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0127] Example 45: Transesterification of the PET decanolysis mixture (decanol:PET is 2:1) with methanol

[0128] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium carbonate (0.50 g; 3.6 mmol; 0.028 equivalents) were slurried in 1-octanol (37.5 g; 288 mmol; 2.21 equivalents). The interior of the flask was heated to 190 °C and stirred for 1.5 hours to completely dissolve the PET, and it was maintained under these conditions for an additional 1 hour. The mixture was cooled to 60 °C and filtered, and the precipitate was washed and dried to give 1.52 g. The filtrate was bottled (52.74 g). HPLC analysis of the filtrate showed the presence of 61% dioctyl terephthalate, with the remainder being other mixed esters and oligomers. The theoretical content of the filtrate was 2.06 mmol total terephthalate per gram.

[0129] Example 46: Depolymerization of PET with a mixture of octanol and decanol at an alcohol:PET ratio of 2:1

[0130] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET octanolysis mixture prepared as in Example 42 (2.06 mmol / g; 25.0 g; 0.052 mol) was slurried in 37.7 mL of methanol (0.929 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (708 μL; 0.0031 mol; 0.06 equivalents) was added. The mixture was stirred at 50 °C at 250 rpm, and a precipitate accompanied by exotherm was observed at three minutes. The mixture was heated at 50 °C for a total of 60 minutes, during which time the mixture became a very thick slurry, then the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 5.90 g of white powdery DMT, which had a purity of 99.8 wt% as determined by GC, indicating a total yield from PET of 92%. Analysis of the filtrate showed that it contained 2.5% of the expected yield of DMT and small amounts (each < 0.5%) of bis(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0131] Example 47: Transesterification of the PET octanolysis / decanolysis mixture (alcohol:PET is 2:1) with methanol

[0132] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium carbonate (0.50 g; 3.6 mmol; 0.028 equivalents) were slurried in 1-decanol (50.0 g; 315.9 mmol; 2.43 equivalents). The interior of the flask was heated to 190 °C and stirred for 3 hours to dissolve the PET almost completely. The mixture was cooled to 65 °C and filtered through a warm sintered funnel. The filtrate was bottled and solidified (70.74 g) after cooling to ambient temperature. The theoretical content of the filtrate was 1.72 mmol of total terephthalate per gram.

[0133] Example 48: Depolymerization of PET with dodecanol at a ratio of 1.5:1

[0134] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET glycolysis mixture prepared as in Example 44 (1.72 mmol / g; 30.0 g; 0.052 mol) was slurried in 37.7 mL of methanol (0.930 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (709 μL; 0.0031 mol; 0.06 equivalents) was added. The mixture was stirred at 250 rpm at 50 °C, and precipitation accompanied by heat evolution was observed within four minutes. The mixture was heated at 50 °C for a total of 60 minutes, during which time the mixture became a very thick slurry, then the heating bath was removed, and the mixture was cooled to ambient temperature within 45 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.62 g of white powdered DMT, which had a purity of 99.3 wt% as determined by LC, indicating a total yield from PET of 85%. Analysis of the filtrate showed that it contained 4.6% of the expected yield of DMT and small amounts (each <0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), 2-hydroxyethyl methyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0135] Example 49: Transesterification of the PET dodecanolysis mixture (dodecanol:PET is 1.5:1) with methanol

[0136] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium carbonate (0.50 g; 3.6 mmol; 0.028 equivalents) were slurried in a 55:45 mixture of 1-octanol (27.5 g; 211 mmol; 1.62 equivalents) and 1-decanol (22.5 g; 142.2 mmol; 1.09 equivalents). The flask was heated to reflux (178 °C to 182 °C) and stirred for 3 hours, at which point no appreciable PET remained. The mixture was cooled to 65 °C, and the mixture was filtered through a preheated (50 °C) sintered funnel with filter paper. The precipitate was very small, and the filtrate was bottled (71.44 g). The theoretical content of the filtrate was 1.72 mmol of total terephthalate per gram.

[0137] Example 50: Depolymerization of PET with tetradecanol at a ratio of 2:1

[0138] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET octanolysis / decanolysis mixture prepared as in Example 46 (1.72 mmol / g; 30.0 g; 0.052 mol) was slurried in 37.7 mL of methanol (930 mmol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction solution equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (709 μL; 0.0031 mol; 0.06 equivalents) was added. The mixture was stirred at 50 °C at 250 rpm, and a precipitate accompanied by heat evolution was observed at 3.5 minutes. The mixture was heated at 50 °C for a total of 60 minutes, during which time the mixture became a thick slurry. Then the heating bath was removed, and the mixture was cooled to ambient temperature within 45 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.44 g of white powdered DMT, which had a purity of 99.8 wt% as determined by HPLC and GC, indicating a total yield from PET of 84%. Analysis of the filtrate showed that it contained 4.0% of the expected yield of DMT and small amounts (each <0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), methyl 2-hydroxyethyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0139] Example 51: Transesterification of the PET tetradecanolysis mixture (tetradecanol:PET is 2:1) with methanol

[0140] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium carbonate (0.50 g; 3.6 mmol; 0.028 equivalents) were slurried in 1-dodecanol (37.5 g; 201 mmol; 1.55 equivalents). The interior of the flask was heated to 190 °C and stirred for 6 hours, at which time a small amount of PET was observed. The mixture was cooled to 70 °C, and the liquid was decanted from the residue to give 52.32 g, which solidified at ambient temperature. HPLC analysis of the decanted material showed the presence of 50% dilauryl terephthalate, with the remainder being other mixed esters and oligomers. The theoretical content of the filtrate was 2.06 mmol of total terephthalate per gram.

[0141] Example 52: Depolymerization of PET with a mixture of dodecanol and tetradecanol at a ratio of 2:1

[0142] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET dodecanolysis mixture prepared as in Example 48 (2.06 mmol / g; 25.0 g; 0.052 mol) was slurried in 43.9 mL of methanol (1.084 mol; 21.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction slurry had equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (708 μL; 0.0031 mol; 0.06 equivalents) was added. The mixture was stirred at 50 °C at 250 rpm for 60 minutes. The mixture remained a slurry throughout the holding time, although the consistency of the slurry did change. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 45 minutes and then stirred overnight at ambient temperature. The resulting precipitate was filtered, washed with methanol, and air-dried to give 9.44 g of DMT as a shiny white solid, which was determined to be 99.4 wt% pure by HPLC and GC, indicating a total yield from PET of 94%. Analysis of the filtrate showed that it contained 0.3% of the expected yield of DMT and small amounts (each <0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), methyl 2-hydroxyethyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0143] Example 53: Transesterification of the PET dodecanolysis / tetradecanolysis mixture (alcohol:PET is 2:1) with methanol

[0144] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium carbonate (0.50 g; 3.6 mmol; 0.028 equivalents) were combined with 1-tetradecanol (50.0 g; 201 mmol; 1.55 equivalents). The interior of the flask was heated to 190 °C and stirred for 2 hours, at which point a small amount of PET was observed and the reaction appeared to have stopped. The mixture was cooled to 75 °C and stirring was stopped. The liquid was decanted from the residue, and the liquid immediately solidified to a waxy solid (64.98 g). The theoretical content of the filtrate was 1.72 mmol of total terephthalate per gram.

[0145] Example 54: Depolymerization of PET with 2-ethylhexanol using sodium acetate catalyst

[0146] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET tetradecanolysis mixture prepared as in Example 50 (1.72 mmol / g; 30.0 g; 0.052 mol) was slurried in 37.7 mL of methanol (930 mol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction slurry had equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (709 μL; 0.0031 mol; 0.06 equivalents) was added. The mixture was stirred at 50 °C at 250 rpm for 60 minutes. The mixture remained a slurry throughout the holding period, but the consistency of the slurry did change, becoming thicker. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 45 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 12.44 g of DMT as a white solid, which was determined to be 73.8 wt% pure by HPLC and GC, indicating a total yield from PET of 91%. Analysis of the filtrate showed that it contained small amounts (each <0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), methyl 2-hydroxyethyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0147] ​

[0148] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 130.1 mmol) and potassium carbonate (0.50 g; 3.6 mmol; 0.028 equivalents) were slurried in a 70:30 mixture of dodecanol (35.0 g; 188 mmol; 1.44 equivalents) and tetradecanol (15.0 g; 70.0 mmol; 0.54 equivalents). The interior of the flask was heated to 190 °C and stirred for 4 h, at which point a small amount of PET was observed. The mixture was cooled to 75 °C and stirring was stopped. The liquid was decanted from the residue to give 70.69 g, and the liquid solidified into a solid at approximately 40 °C. The theoretical content of the filtrate was 1.72 mmol of total terephthalate per gram.

[0149] ​

[0150] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET dodecanolysis / tetradecanolysis mixture prepared as in Example 52 (1.72 mmol / g; 30.0 g; 0.052 mol) was slurried in 37.7 mL of methanol (930 mmol; 18.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction slurry had equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (709 μL; 0.0031 mol; 0.06 equivalents) was added. The mixture was stirred at 50 °C at 250 rpm. After approximately two minutes, the mixture became a clear solution, and a precipitate accompanied by exotherm was observed at 4.5 minutes. The mixture was heated at 50 °C for a total of 60 minutes, during which time the mixture became a very thick slurry, then the heating bath was removed, and the mixture was cooled to ambient temperature within 45 minutes and then stirred at ambient temperature for 2 hours. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.76 g of white powdered DMT, which was determined by HPLC and GC to have a purity of 98.2 wt%, indicating a total yield from PET of 86%. Analysis of the filtrate showed that it contained 4.7% of the expected yield of DMT and small amounts (each <0.5%) of bis(2-hydroxyethyl) terephthalate (BHET), methyl 2-hydroxyethyl terephthalate (MHET), and dimethyl isophthalate (DMI).

[0151] ​

[0152] In a 250 mL three-necked round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 0.1276 mol) and sodium acetate (0.52 g; 0.0064 mol; 0.05 equivalents) were slurried in 2-ethylhexanol (37.5 g; 0.2879 mol; 2.26 equivalents). The interior of the flask was heated to 185 °C and maintained for 10 hours (1 hour after complete dissolution of PET). The filtrate was analyzed by HPLC area% and found to have an acid by-product content of 2.36%, and the theoretical content of the filtrate was 2.02 mmol total terephthalate per gram.

[0153] Example 55: Transesterification of the PET 2-ethylhexanolysis mixture (sodium acetate catalyst) with 12 equivalents of methanol using sodium methoxide catalyst Example 56: Depolymerization of PET with 2-ethylhexanol using 2.5 mol% potassium acetate catalyst

[0154] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 54 (2.02 mmol / g; 15.00 g; 0.0304 mol) was slurried in 14.8 mL of methanol (0.365 mol; 12.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (257 μL; 0.0011 mol; 0.037 equivalents) was added. The mixture was stirred at 50 °C at 250 rpm, and a precipitate accompanied by exotherm was observed at 9.5 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 20 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 4.72 g of DMT as a shiny white solid, which had a purity of 98.7 wt% as determined by HPLC and GC, indicating a total yield from PET of 79%. Analysis of the filtrate showed that it contained 13% of the expected yield of DMT and small amounts (each < 0.5%) of bis(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0155] Example 57: Transesterification of the PET 2-ethylhexanolysis mixture (2.5 mol% potassium acetate catalyst) with 12 equivalents of methanol using sodium methoxide catalyst

[0156] In a 250 mL three-necked round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (98.1% PET; 20.39 g; 0.1041 mol) and potassium acetate (0.255 g; 0.0026 mol; 0.025 equivalents) were slurried in 2-ethylhexanol (30.6 g; 0.2349 mol; 2.26 equivalents). The interior of the flask was heated to 185 °C and maintained for 3 hours (1 hour after complete dissolution of PET). The filtrate was analyzed by HPLC area%, and the acid by-product content was 2.62%, and the theoretical content of the filtrate was 2.03 mmol total terephthalate per gram.

[0157] Example 58: Depolymerization of PET with 2-ethylhexanol using 2.0 mol% potassium acetate catalyst Example 59: Transesterification of the PET 2-ethylhexanolysis mixture (2.0 mol% potassium acetate catalyst) with 12 equivalents of methanol using sodium methoxide catalyst

[0158] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 56 (2.03 mmol / g; 25.00 g; 0.0508 mol) was slurried in 24.7 mL of methanol (0.609 mol; 12.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (580 μL; 0.0025 mol; 0.05 equivalents) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by heat evolution was observed at 5 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 2 hours. The resulting precipitate was filtered, washed with methanol, and air-dried to give 9.18 g of DMT as a shiny white solid, which had a purity of 99.4 wt% as determined by HPLC and GC, indicating a total yield from PET of 93%. Analysis of the filtrate showed that it contained 1.2% of the expected yield of DMT and small amounts (each <0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0159] Example 60: Depolymerization of PET with 2-ethylhexanol using 1.5 mol% potassium acetate catalyst

[0160] In a 250 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (98.1% PET; 20.39 g; 0.1041 mol) and potassium acetate (0.204 g; 0.0021 mol; 0.02 equivalents) were slurried in 2-ethylhexanol (30.6 g; 0.2349 mol; 2.26 equivalents). The interior of the flask was heated to 185 °C and maintained for 3 hours (1 hour after complete dissolution of PET). The filtrate was analyzed by HPLC area%, and the acid by-product content was 2.40%, and the theoretical content of the filtrate was 2.03 mmol total terephthalate per gram.

[0161] Example 61: Transesterification of the PET 2-ethylhexanolysis mixture (1.5 mol% potassium acetate catalyst) with 12 equivalents of methanol using sodium methoxide catalyst Example 62: Depolymerization of PET with 2-ethylhexanol using 1.25 mol% potassium acetate catalyst

[0162] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 58 (2.03 mmol / g; 25.00 g; 0.0508 mol) was slurried in 24.7 mL of methanol (0.609 mol; 12.0 eq). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (580 μL; 0.0025 mol; 0.05 eq) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed at 5 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 45 minutes. The resulting precipitate was filtered, washed with methanol, and air-dried to give 9.02 g of shiny white solid DMT, which had a purity of 99.8 wt% as determined by HPLC and GC, indicating a total yield from PET of 91%. Analysis of the filtrate showed that it contained 3.6% of the expected yield of DMT and small amounts (each <0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0163] Example 63: Transesterification of the PET 2-ethylhexanolysis mixture (1.25 mol% potassium acetate catalyst) with 12 equivalents of methanol using sodium methoxide catalyst

[0164] In a 250 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (98.1% PET; 20.39 g; 0.1041 mol) and potassium acetate (0.153 g; 0.0016 mol; 0.015 eq) were slurried in 2-ethylhexanol (30.6 g; 0.2349 mol; 2.26 eq). The interior of the flask was heated to 185 °C and maintained for 4 hours (1 hour after complete dissolution of PET). The filtrate was analyzed by HPLC area%, and the acid by-product content was 2.08%, and the theoretical content of the filtrate was 2.04 mmol total terephthalate per gram.

[0165] Example 64: Depolymerization of PET with 2-ethylhexanol using 2 mol% potassium acetate catalyst, ratio of 2-EH alcohol to PET is 1.25:1 Example 65: Transesterification of the PET 2-ethylhexanolysis mixture (2.0 mol% potassium acetate catalyst; ratio of 2-EH alcohol to PET is 1.25:1) with 12 equivalents of methanol using sodium methoxide catalyst

[0166] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 60 (2.04 mmol / g; 25.00 g; 0.0510 mol) was slurried in 24.8 mL of methanol (0.612 mol; 12.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (583 μL; 0.0026 mol; 0.05 equivalents) was added. The mixture was stirred at 50 °C at 250 rpm, and a precipitate accompanied by exotherm was observed at 4.5 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 45 minutes. The resulting precipitate was filtered, washed with methanol, and air-dried to give 9.24 g of DMT as a shiny white solid, which was determined to be 99.9 wt% pure by HPLC and GC, indicating a total yield from PET of 93%. Analysis of the filtrate showed that it contained 2.9% of the expected yield of DMT and small amounts (each < 0.5%) of bis(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0167] Example 66: Depolymerization of PET with 2-ethylhexanol using 2 mol% potassium acetate catalyst, ratio of 2-EH alcohol to PET is 1:1

[0168] In a 250 mL three-necked round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (98.1% PET; 20.39 g; 0.1041 mol) and potassium acetate (0.128 g; 0.0016 mol; 0.0125 equivalents) were slurried in 2-ethylhexanol (30.6 g; 0.2349 mol; 2.26 equivalents). The interior of the flask was heated to 185 °C and maintained for 5 hours (1 hour after complete dissolution of PET). The filtrate was analyzed by HPLC area% and found to contain 1.58% acid by-products, and the theoretical content of the filtrate was 2.04 mmol total terephthalate per gram.

[0169] Example 67: Transesterification of the PET 2-ethylhexanolysis mixture (2.0 mol% potassium acetate catalyst; ratio of 2-EH alcohol to PET is 1:1) with 12 equivalents of methanol using sodium methoxide catalyst Example 68: Depolymerization of PET with 2-ethylhexanol using in-situ prepared 2.5 mol% potassium acetate catalyst

[0170] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 62 (2.04 mmol / g; 25.00 g; 0.0510 mol) was slurried in 24.8 mL of methanol (0.612 mol; 12.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction mixture equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (583 μL; 0.0026 mol; 0.05 equivalents) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed at 4.5 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 90 minutes. The resulting precipitate was filtered, washed with methanol, and air-dried to give 9.61 g of DMT as a shiny white solid, which had a purity of 99.7 wt% as determined by HPLC and GC, indicating a total yield from PET of 97%. Analysis of the filtrate showed that it contained 2.0% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0171] Example 69: Transesterification of the PET 2-ethylhexanolysis mixture (2.5 mol% in-situ potassium acetate catalyst) with 12 equivalents of methanol using sodium methoxide catalyst Example 70: Preparation of 5 mol% sodium 2-ethylhexanoate

[0172] In a 250 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 0.1276 mol) and potassium acetate (0.251 g; 0.0026 mol; 0.02 equivalents) were slurried in 2-ethylhexanol (31.3 g; 0.2399 mol; 1.88 equivalents). The interior of the flask was heated to 185 °C and maintained for 5 hours (1 hour after complete dissolution of PET). The flask was cooled to 60 °C and filtered. It filtered rapidly, and the filtrate was a free-flowing liquid. Analysis of the filtrate by HPLC area% showed an acid by-product content of 1.86% and an acid value of 1.03. The theoretical content of the filtrate was 2.26 mmol of total terephthalate per gram.

[0173] Example 71: Transesterification of the PET 2-ethylhexanolysis mixture with 12 equivalents of methanol using 5 mol% sodium 2-ethylhexanoate catalyst Example 72: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET is 1.5:1) with 12 equivalents of methanol using potassium carbonate catalyst

[0174] In a 300 mL three-necked round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 64 (2.26 mmol / g; 25.00 g; 0.0565 mol) was slurried in 27.5 mL of methanol (0.678 mol; 12.0 equivalents). The flask was placed in an oil bath set at 57 °C. Once the reaction mixture equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (491 μL; 0.0021 mol; 0.038 equivalents; 0.30 equivalents of active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and a precipitate accompanied by exotherm was observed at 5 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 9.86 g of DMT as a shiny white solid, which had a purity of 98.9 wt% as determined by HPLC and GC, indicating a total yield from PET of 89%. Analysis of the filtrate showed that it contained 2.6% of the expected yield of DMT and small amounts (each < 0.5%) of bis(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0175] Example 73: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET is 1.5:1) with 9 equivalents of methanol using sodium methoxide catalyst Example 74: Transesterification of the PET 2-ethylhexanolysis mixture (2-EH:PET is 1.5:1) with 9 equivalents of methanol using potassium carbonate catalyst

[0176] In a 250 mL three-necked round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (25.00 g; 0.1276 mol) and potassium acetate (0.251 g; 0.0026 mol; 0.02 equivalents) were slurried in 2-ethylhexanol (25 g; 0.1920 mol; 1.50 equivalents). The inside of the flask was heated to 185 °C and maintained for 6 hours (1 hour after complete dissolution of PET). The flask was cooled to 60 °C and filtered. It filtered rapidly, and the filtrate was a freely flowing liquid at room temperature but was a bit viscous at ambient temperature. Analysis of the filtrate by HPLC area% showed an acid by-product content of 1.88% and an acid value of 0.48. The theoretical content of the filtrate was 2.54 mmol of total terephthalate per gram.

[0177] ​ ​

[0178] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 66 (2.54 mmol / g; 25.00 g; 0.0635 mol) was slurried in 30.9 mL of methanol (0.762 mol; 12.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (479 μL; 0.0021 mol; 0.033 equivalents; 0.30 equivalents of active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation with exotherm was observed at 3.5 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 11.22 g of DMT as a shiny white solid, which had a purity of 94.3 wt% as determined by HPLC and GC, indicating a total yield from PET of 86%. Analysis of the filtrate showed that it contained 3.5% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0179] ​

[0180] In a 250 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, 2-ethylhexanol (30.6 g; 0.2349 mol; 2.26 equivalents), acetic acid (0.156 mL; 0.0027 mmol; 0.026 equivalents), and potassium hydroxide (45.9% aqueous solution; 0.318 g; 0.0026 mol; 0.025 equivalents) were combined. The mixture was stirred for 5 minutes, and granulated bottle flake waste PET (98.1% PET; 20.39 g; 0.1041 mol) was added. The interior of the flask was heated to 185 °C and maintained for 5 hours (1 hour after complete dissolution of PET). The filtrate was analyzed by HPLC area%, and the acid by-product content was 2.40%, and the theoretical content of the filtrate was 2.02 mmol of total terephthalate per gram.

[0181] ​ ​

[0182] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 68 (2.02 mmol / g; 25.00 g; 0.0505 mol) was slurried in 24.6 mL of methanol (0.606 mol; 12.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), a methanol solution of 25% sodium methoxide (577 μL; 0.0025 mol; 0.05 equivalents) was added. The mixture was stirred at 50 °C at 250 rpm, and a precipitate accompanied by exotherm was observed at 5.5 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 2 hours. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.54 g of DMT as a shiny white solid, which had a purity of 99.8 wt% as determined by HPLC and GC, indicating a total yield from PET of 87%. Analysis of the filtrate showed that it contained 4.0% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0183] ​

[0184] In a 250 mL three-neck round-bottom flask equipped with a magnetic stir bar, a thermocouple well, and a Dean-Stark separator with an air condenser having a nitrogen / vacuum inlet at the top, 2-ethylhexanol (50 g) and 50% sodium hydroxide (2.672 g; 0.0334 mol) were combined. The mixture was heated in a 120 °C oil bath and a vacuum was applied, slowly reducing the pressure from 200 mmHg to full vacuum (ca. 21 mmHg). The initial water-2-ethanol-hexanol azeotrope was collected in the Dean-Stark separator, followed by the collection of only ca. 3 mL of 2-ethylhexanol. The heat was removed, the mixture was cooled to ambient temperature, and the vacuum was released with nitrogen. 2-Ethylhexanol was added to the mixture to give a total weight of 50.73 g, giving a 10% clear colorless solution of sodium 2-ethylhexanoate in 2-ethylhexanol. The measured density was 0.82 g / mL.

[0185] ​ ​

[0186] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.02 mmol / g; 25.00 g; 0.0505 mol) was slurried in 24.6 mL of methanol (0.606 mol; 12.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture equilibrated at 50 °C (+ / - 2 °C), 10% sodium 2-ethylhexanoate in 2-ethylhexanol prepared above (4.69 mL; 0.0025 mol; 0.05 equivalent) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by heat evolution was observed at 7.5 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.29 g of DMT as a shiny white solid, which had a purity of 99.8 wt% as determined by HPLC and GC, indicating a total yield from PET of 84%. Analysis of the filtrate showed that it contained 3.2% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0187] ​ ​

[0188] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.06 mmol / g; 25.0 g; 0.052 mol) was slurried in 25.1 mL of methanol (0.620 mol; 12.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture equilibrated at 50 °C (+ / - 2 °C), potassium carbonate (355 mg; 0.0047 mol; 0.047 equivalent; 0.040 equivalent active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by heat evolution was observed at 10 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.52 g of DMT as a shiny white solid, which had a purity of 99.5 wt% as determined by HPLC and GC, indicating a total yield from PET of 85%. Analysis of the filtrate showed that it contained 3.9% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0189] ​ ​

[0190] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.06 mmol / g; 25.0 g; 0.052 mol) was slurried in 18.8 mL of methanol (0.465 mol; 9.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / -2 °C), a methanol solution of 25% sodium methoxide (668 μL; 0.0029 mol; 0.057 equivalents; 0.050 equivalents of active catalyst based on the acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and precipitation accompanied by exotherm was observed at 5 minutes. After heating at 50 °C for a total of 70 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 30 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 9.47 g of DMT as a shiny white solid, which had a purity of 91.3 wt% as determined by HPLC and GC, indicating a total yield from PET of 86%. Analysis of the filtrate showed that it contained 1.6% of the expected yield of DMT and small amounts (each <0.5%) of bis(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0191] ​ ​

[0192] In a 300 mL three-neck round-bottom flask equipped with an overhead stirrer, a thermocouple, and an air condenser with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.03 mmol / g; 25.0 g; 0.0508 mol) was slurried in 18.51 mL of methanol (0.457 mol; 9.0 equivalents). The flask was placed in an oil bath set at 57 °C, and once the reaction mixture had equilibrated at 50 °C (+ / - 2 °C), potassium carbonate (379 mg; 0.0054 mol; 0.054 equivalents; 0.050 equivalents of active catalyst based on acid value) was added. The mixture was stirred at 50 °C at 250 rpm, and a precipitate accompanied by exotherm was observed at 15.5 minutes. After heating at 50 °C for a total of 60 minutes, the heating bath was removed, and the mixture was cooled to ambient temperature within 20 minutes and then stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 8.15 g of DMT as a shiny white solid, which was determined to be 99.5 wt% pure by HPLC and GC, indicating a total yield from PET of 80%. Analysis of the filtrate showed that it contained 13.8% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0193] Example 75: Depolymerization of PET with 2-ethylhexanol at a ratio of 1.5:1

[0194] In a 1 L three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated bottle flake waste PET (98.1% PET; 202.0 g; 1.03 mol) and potassium carbonate (3.99 g; 0.029 mol; 0.028 equivalents) were slurried in 2-ethylhexanol (303 g; 2.327 mol; 2.26 equivalents). After the PET had completely dissolved, the interior of the flask was heated to 185 °C and maintained for 1 hour. The mixture was cooled to 60 °C and filtered, and the filtrate (479.66 g) was bottled. The residual solid was washed with methanol and dried to give 12.22 g of insoluble residue. The theoretical content of the filtrate was 2.03 mmol of total terephthalate per gram.

[0195] Example 76: Transesterification of a PET 2-ethylhexanol depolymerization mixture (2-EH:PET is 1.5:1) with methanol using a sodium methoxide catalyst and evaporative cooling

[0196] In a 1 L jacketed reactor equipped with an overhead stirrer, a thermocouple, and successive water and dry ice condensers with a nitrogen inlet, the PET 2-ethylhexanolysis mixture prepared as in Example 16 (2.03 mmol / g; 212.00 g; 0.4295 mol) was slurried in 313 mL of methanol (7.73 mol; 18.0 equivalents). The flask was heated to an internal temperature of 50 °C (+ / -2 °C), and a methanol solution of 25% sodium methoxide (5.89 mL; 0.026 mol; 0.06 equivalents) was added. The mixture was stirred at 50 °C for 1 hour (precipitation was observed at 7.5 minutes), heating was stopped, and the mixture was evaporated and cooled to ambient temperature by reducing the pressure to approximately 300 mmHg for 39 minutes. The methanol (25 mL) that was not condensed and returned directly to the reactor was added back to the mixture, and then the mixture was stirred at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and dried in a vacuum oven at 75 °C for 2 hours to obtain 80.36 g of shiny white solid DMT, which had a purity of 92.7 wt% as determined by HPLC and GC, indicating a total yield from PET of 89%. Analysis of the filtrate showed that it contained 0.3% of the expected yield of DMT and small amounts (each <0.5%) of bis(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

[0197] Example 77: Depolymerization of PET with 2-ethylhexanol at a ratio of 1.5:1 by centrifugation

[0198] In a 250 mL three-neck round-bottom flask equipped with an overhead stirrer, a Dean-Stark separator with a condenser, and a nitrogen inlet, granulated waste carpet PET (87% PET, 25.00 g; 0.113 mol) and potassium acetate (278 mg; 0.0028 mol; 0.025 equivalents) were slurried in 2-ethylhexanol (32.6 g; 0.251 mol; 2.21 equivalents). The flask was heated to 185 °C and stirred for 3.5 hours (PET dissolution was observed at 2 hours). The mixture was then cooled to 60 °C, methanol (29.0 g; 0.905 mol; 8.0 equivalents) was added, and the resulting mixture was cooled to ambient temperature. The resulting brown slurry was transferred to a centrifuge tube and centrifuged at 3000 G for five minutes to obtain a liquid and dense particles. The liquid was decanted and an equal amount of methanol was added to the tube (total 14.5 g; 0.452 mol; 4.0 equivalents). The mixture was vortexed to suspend the solid, and then centrifuged at 3000 G for five minutes. The resulting liquid was decanted, leaving dense brown particles. The total weight of the particles was 4.26 g, and HPLC analysis showed that it contained approximately 3% total terephthalate esters. The concentrates and washings were combined to a total of 92.18 g.

[0199] Example 78: Transesterification of a PET 2-ethylhexanol depolymerization mixture (2-EH:PET is 1.5:1) with methanol from the centrifuged mixture ​

[0200] The PET 2-ethylhexanolysis mixture prepared in Example 77 (92.18 g; 0.113 mol maximum) was added to a 500 mL three-neck round-bottom flask equipped with an overhead stirrer and a thermocouple. The flask was heated to an internal temperature of 50 °C (+ / - 2 °C), and a methanol solution of 25% sodium methoxide (1.29 mL; 0.0057 mol; 0.05 eq) was added. The mixture was stirred at 50 °C for 1 hour (precipitation was observed at 8.5 minutes), heating was stopped, and the mixture was cooled to ambient temperature in about 30 minutes and then held at ambient temperature for 1 hour. The resulting precipitate was filtered, washed with methanol, and air-dried to give 17.27 g of DMT as a shiny white solid, which was determined to have a purity > 99.9 wt% by HPLC and GC, indicating a total yield from PET of 79%. Analysis of the filtrate showed that it contained 4.9% of the expected yield of DMT and small amounts (each < 0.5%) of mono(2-hydroxyethyl) terephthalate (MHET) and dimethyl isophthalate (DMI).

Claims

1. A method for preparing dimethyl terephthalate, the method comprises: a. In the presence of an esterification or transesterification catalyst, at a temperature sufficient to depolymerize at least a portion of the poly(terephthalic acid C 2 -C 4 alkylene ester), treat the poly(terephthalic acid (C 4 -C 14 alkylene) ester) with a C 2 -C 4 alkanol to obtain a first reaction mixture product comprising di-C 4 -C 14 alkyl terephthalate; followed by b. Treating in the presence of methanol with a transesterification catalyst to provide a second reaction mixture product comprising dimethyl terephthalate, C 4 -C 14 alcohol and ethylene glycol, followed by c. Separating the dimethyl terephthalate.

2. The method according to claim 1, wherein step a is carried out at a temperature of about 100 °C to about 250 °C.

3. The method according to claim 1, further comprising the step of cooling the first reaction mixture product to a temperature below about 100 °C; or further comprising the step of cooling the first reaction mixture product to a temperature of about 20 °C to about 100 °C.

4. The method according to claim 3, further comprising the step of removing insoluble materials present in the first reaction mixture product by filtration, centrifugation or decantation.

5. The method according to claim 1, wherein the poly(C 2 -C 4 alkylene) ester is poly(ethylene terephthalate).

6. The method according to claim 1, wherein the C 4 -C 14 alcohols are selected from n-butanol, isobutanol, hexanol, 2-ethylhexanol, n-octanol, decanol, dodecanol, tetradecanol, and mixtures thereof.

7. The method according to claim 1 or 6, wherein the C 4 -C 14 alcohols are selected from n-butanol and 2-ethylhexanol.

8. The method according to claim 1, wherein the esterification or transesterification catalyst in step a is selected from Lewis acids and Lewis bases; or wherein the esterification or transesterification catalyst in step a is selected from alkali metal C 1 -C 14 alkoxides, alkali metal carbonates, alkali metal bicarbonates, wherein the alkali metal is selected from lithium, sodium, potassium or cesium; or wherein the esterification or transesterification catalyst in step a is selected from alkali metal acetates, transition metal acetates and titanium C 1 -C 6 alkoxides; or wherein the esterification or transesterification catalyst in step a is selected from potassium carbonate, potassium bicarbonate, potassium acetate, tetra(isopropanol)titanium and monobutyltin tris(2-ethylhexanoate).

9. The method according to claim 1, wherein the esterification or transesterification catalyst is selected from stannous oxalate, monobutyltin oxide and monobutyltin tris(2-ethylhexanoate).

10. The method according to claim 1, wherein the transesterification catalyst in step b is selected from alkali metal C 1 -C 14 alkoxides, alkali metal hydroxides and alkali metal carbonates; or wherein the transesterification catalyst in step b is selected from potassium hydroxide, sodium hydroxide, sodium methoxide, potassium methoxide, sodium 2-ethylhexanoate and potassium carbonate.

11. The method according to claim 1 further comprises, after separating dimethyl terephthalate in c., subjecting the second reaction mixture product to distillation and / or extraction to obtain purified C 4 -C 14 -alkanols and purified ethylene glycol.

12. A method for preparing dimethyl terephthalate, the method comprises: a. In the presence of an esterification or transesterification catalyst, at a temperature sufficient to depolymerize at least a portion of the poly(ethylene alkylene terephthalate), treating the waste plastic stream comprising poly(ethylene terephthalate) with a C 4 -C 14 alkan-ol to obtain a first reaction mixture product comprising di-C 4 -C 14 alkyl terephthalate; followed by b. Treating in the presence of methanol with a transesterification catalyst to provide a second reaction mixture product comprising dimethyl terephthalate, C 4 -C 14 alcohol and ethylene glycol, followed by c. Separating the dimethyl terephthalate.

13. The method according to claim 12, wherein step a is carried out at a temperature of about 100 °C to about 250 °C.

14. The method according to claim 12, wherein the first reaction mixture product is cooled to a temperature of about 20 °C to about 100 °C.

15. The method according to claim 12, 13 or 14, further comprising the step of removing insoluble materials present in the first reaction mixture product by filtration, centrifugation or decantation.

16. The method according to claim 12, wherein the C 4 -C 14 alcohols are selected from n-butanol and 2-ethylhexanol.

17. The method according to claim 12, wherein the esterification or transesterification catalyst in step a is selected from alkali metal alkoxides, alkali metal carbonates, alkali metal bicarbonates, wherein the alkali metal is selected from lithium, sodium, potassium or cesium; or wherein the esterification or transesterification catalyst in step a is selected from alkali metal acetates, transition metal acetates and titanium C 1 -C 6 alkoxides; or wherein the esterification or transesterification catalyst in step a is selected from tin oxalate, monobutyltin oxide and monobutyltin tris(2-ethylhexanoate), potassium carbonate, potassium bicarbonate, potassium acetate, titanium tetraisopropoxide and monobutyltin tris(2-ethylhexanoate).

18. The method according to claim 12, wherein the transesterification catalyst in step b is selected from alkali metal C 1 -C 14 alcoholates, alkali metal hydroxides and alkali metal carbonates; or wherein the transesterification catalyst in step b is selected from potassium hydroxide, sodium hydroxide, sodium methoxide, potassium methoxide, sodium 2-ethylhexanoate and potassium carbonate.

19. The method according to claim 12 further comprises subjecting the second reaction mixture product to distillation and / or extraction after separating dimethyl terephthalate in c. to obtain purified C 4 -C 14 -alkanols and purified ethylene glycol.