Neutral hydrolysis of polyethylene terephthalate using phase transfer catalysis

Abstract

Methods for the neutral hydrolysis of polymers comprising polyethylene terephthalate units are described, along with catalytic systems for such methods.

Description

NeutralPhase TransferField

[0001] The present invention is concerned with hydrolysis of polymers, such as polyethylene terephthalate, using phase transfer catalysis under neutral reaction conditions. BACKGROUND

[0002] It has been estimated that from 1950 to 2015, 6.3 x 1012kg of plastics have been synthesised – with a recycle rate of just ca. 9%. It has further been estimated, that without intervention, by 205012 x 1013kg of these polymers will either be in landfill or out polluting the natural world, therefore (until replacement of traditional plastics with sustainable materials is widespread) improvement in both the rate and efficiency of recycling is needed to reduce both the dependence on oil-derived virgin plastic and the contribution its synthesis / disposal makes to the current climatological and ecological emergency.

[0003] Poly(ethylene terephthalate) (PET) polyester is a major constituent in certain beverage bottles, textile fibres and food tray / pharmaceutical packaging which in 2021 accounted for 12% of worldwide solid waste. Of the commonly bulk-manufactured plastics, PET has the highest greenhouse gas (GHG) emissions associated with its production (up to 4.5 kg GHG / kg PET) yet is one of the most amenable to various ‘recycling’ methodologies - which can be broadly be categorised as either incineration, mechanical- or chemical recycling. Incineration solves the landfill problem and can recover energy from the materials but has been determined after a recent study by the European Commission’s Joint Research Centre to be less preferable from a climate change impact perspective. Mechanical recycling is operationally more facile yet amplifies existing degradation and produces recycled PET of lower value and quality, while chemical recycling via depolymerisation requires efficient process chemistry on large scales (frequently at high temperatures), however it can produce pure monomers which can be repolymerised to pristine PET for any application – thereby reducing reliance on fossil fuel-derived virgin PET. In addition, in the case of PET, a recent analysis found that CO2 emission savings at end of life treatment are considerably lower for chemical recycling than for mechanical. Chemical recycling methodologies include (inter alia) aminolysis, alcoholysis, glycolysis and hydrolysis. Hydrolysis may be conducted under basic, neutral or acidic conditions.

[0004] Hydrolytic PET depolymerization involves the reaction of the polymer in either a basic, neutral, or acidic aqueous solution. The products of PET hydrolysis are terephthalic acid (TPA) and ethylene glycol (EG). One major disadvantage of hydrolytic depolymerization is the large volumes of inorganic salt and aqueous waste that are generated, along with the high corrosivity of the basic and acidic systems. It has been estimated that, on an industrial scale, 20–5 kg of inorganic salt waste. It would be desirable to develop methods for PET depolymerization with less inorganic salt waste, and less water waste.

[0005] Alkaline hydrolysis of PET generally involves using a metal hydroxide catalyst, such as sodium hydroxide or potassium hydroxide, with a concentration between 4 and 20 % w / w at elevated temperature and pressure (e.g.225˚C, and 17 atm). The product of alkaline hydrolysis using sodium hydroxide of PET is disodium terephthalate and ethylene glycol. Treatment of the disodium terephthalate with acid results in the formation of terephthalic acid (TPA).

[0006] Acidic hydrolysis of PET generally involves the use of highly concentrated acid solutions. Reaction parameters that influence PET hydrolysis using mineral acids include acid concentration, reaction temperature, pressure, PET particle size and PET particle shape. Increasing acid concentration and reaction temperature results in an increase in PET depolymerization, and a decrease in PET particle size will also increase reaction rate of PET conversion due to increased surface area per volume.

[0007] Neutral hydrolysis of PET generally involves depolymerization in an excess of water or steam at a reaction temperature between about 115 and 420°C and at a pressure in the range of from 10 to 420 atm. TPA may be recovered from unreacted PET by acidification and filtration after hydrolysis. It has been reported that when PET is in the molten state at temperatures above 245°C, the reaction proceeds faster. Neutral hydrolysis therefore represents an energy intensive process for PET depolymerization. Furthermore, in neutral hydrolysis, organic solvents are generally not used, which is advantageous from an environmental standpoint. However, a negative consequence of neutral hydrolysis, is that treatment with acid as occurs in acid hydrolysis or treatment with base, as occurs in alkaline hydrolysis may remove impurities, which are remain as contaminants in neutral hydrolysis. Thus, while neutral hydrolysis is proposed as a green path for PET depolymerization as the reaction occurs in water or steam, the severe reaction conditions required to effect depolymerization, including high temperature, pressure, and the requirement for highly resistant reactors, have resulted in the technique being too costly as a commercial PET recycling methodology.

[0008] Stanica-Ezeanu et al. (Sci Rep. 2021, 11, 4431) report on natural depolymerization of waste PET by neutral hydrolysis in marine water, concluding that temperature of the water plays a pivotal role in reaction rate.

[0009] Zhang et al. (J. App. Polym. Sci.2013, 127, 2790-2795) report on the use of a dual functional phase transfer tungsten catalyst, [(CH3)3N(C16H33)]3[PW12O40], in the hydrolysis of PET.

[0010] Zhang (Eur. Polym. J.2014, 60, 1-5) also studied the kinetics of hydrolysis of PET catalysed by the aforementioned tungsten catalyst.

[0011] Sadbe et al. employed PEG 400 as a catalyst in the hydrolysis of PET. The reaction conditions with initial molar ratio of 55 mol water / mol PET, reaction time 30 min, PEG 400 catalyst concentration 2.0 × 10-5mol / cm3at 240°C, and 3.2 MPa autogenous pressure gave the best yield and conversion of PET. The yield and purity of TPA were found to be 90 and 99.1%, respectively. The synergetic effect of catalyst and pressure generated by water helps increase the conversion and yield of TPA. The addition of PEG 400 as catalyst was reported as accelerating depolymerization process by 15 min reaction time in comparison with supercritical and metal acetate depolymerization.

[0012] It would be desirable to provide improved methods and catalysts for the hydrolysis of polymers comprising polyethylene terephthalate units, such polyethylene terephthalate, under neutral conditions. It would be desirable to provide methods for the hydrolysis of polymers comprising polyethylene terephthalate, which are effective for larger flakes / particles / items of polyethylene terephthalate, for example, such that flakes / particles / items of >2 mm, preferably >5 mm, as well as smaller sized flakes / particles items could be effectively depolymerized / hydrolysed. Furthermore, it would be desirable to provide methods for hydrolysis of polymers comprising polyethylene terephthalate units, such as polyethylene terephthalate, with lower environmental impact, for example, methods which require less water. The catalysts and methods disclosed herein address these needs. SUMMARY

[0013] In one aspect, the present invention provides a method for hydrolysis of poly(ethylene terephthalate) comprising: combining poly(ethylene terephthalate), water, and a catalyst, and heating for a time sufficient to hydrolyze at least in part the poly(ethylene terephthalate), wherein the catalyst is a phase transfer catalyst having the formula (III):Formula (III)wherein each Y+has the formula IV:Formula (IV) wherein X1 is N or P, wherein each of R1, R2, R3and R4is independently selected from C1-C20 aliphatic, wherein together R1, R2, R3and R4comprise at least 16 carbon atoms, and wherein at least two of R1, R2, R3and R4are independently selected from C2-C20aliphatic, optionally, wherein the reaction is carried out at a pH in the range of from pH 6 to 8.

[0014] The reaction is carried out without the addition of strong acid or base traditionally required for hydrolysis of esters i.e. the reaction is carried out neutral pH, for example, a pH in the range of from pH 6 to 8, optionally, in the range of from pH 6.2 to pH 7.8, further optionally, in the range of from pH 6.5 to pH 7.5.

[0015] Each Y suitably comprises at least 24 carbon atoms, optionally, at least 28 carbon atoms, further optionally, at least 32 carbon atoms. Suitably, each Y comprises 32 carbon atoms.

[0016] Each of R1, R2, R3and R4of each Y may independently be selected from C1-C20alkyl, and at least two of R1, R2, R3and R4are independently selected from C2-C20alkyl.

[0017] For example, at least two of R1, R2, R3and R4of each Y may be independently selected from C4-C18 alkyl, optionally, from C4-C16 alkyl.

[0018] Suitably, two or three of R1, R2, R3and R4of each Y may be C4-C16alkyl, optionally, C4-C10alkyl, for example, two or three of R1, R2, R3and R4of each Y may independently be selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl.

[0019] Each of R1, R2, R3and R4of each Y may be the same i.e. R1= R2= R3= R4,. optionally, wherein each of R1, R2, R3and R4of each Y is C4-C10 alkyl, optionally, wherein each of R1, R2, R3and R4of each Y is butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl.

[0020] R1may be C1alkyl, optionally, methyl, and two or three of R2, R3and R4may independently be C6-C16 alkyl, optionally, C6-C12 alkyl.

[0021] For example, R1may be C1 alkyl, optionally, methyl, and three of R2, R3and R4are independently C6-C16alkyl, optionally, C6-C12alkyl.

[0022] R1may be C1alkyl, optionally, methyl, and three of R2, R3and R4may be the same and selected from C6-C12 alkyl. Optionally, R2, R3and R4are the same and are selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl.

[0023] Optionally, the the catalyst of formula (III) is selected from compound 18, compound 19 or compound 20 as shown below:.

[0024] The catalyst of formula III may be employed in an amount 2.5 mol% or less, more suitably, in an amount of 1.5 mol% or less, even more suitably in an amount of 1 mol% or less, most suitably in an amount of 0.5 mol% or less per mole of monomeric repeating unit of polyethylene terephthalate.

[0025] Optionally, the method may further comprise a purification step. Optionally, the purification step involves one or more of washing, filtering, and base / acid treatment. For example, a purification step may further comprise dissolution in aqueous NaOH followed by filtering and reprecipitation of terephthalic acid using dilute mineral acids such as H2SO4 or HCl. Suitably, the purification step involves washing with organic solvent, such as acetone, ethyl acetate, dichloromethane and / or chloroform.

[0026] The hydrolysis reaction may be carried out under pressure. For example, the method may be carried out at a pressure of from 5 to 30 atm, suitably, from 10 to 25 atm, for example, from 12 to 20 atm, optionally, at approx.15 atm.

[0027] The hydrolysis reaction i.e. the method of the invention, may be carried out at a temperature in the range of from 100 to 300°C, optionally, in the range of from 150 to 250°C, further optionally in the range of from 180 to 230°C.

[0028] For example, the hydrolysis reaction may be carried out at a pressure of from 5 to 30 atm, and at a temperature in the range of from 100 to 300°C. Optionally, the hydrolysis reaction may be carried out at a pressure in the range of from 10 to 25 atm, and at a temperature in the range of from 150 to 250°C. Further optionally, the hydrolysis reaction may be carried out at a pressure in the range of from 12 to 20 atm, and at a temperature in the range of from 180 to 230°C.

[0029] Optionally, wherein the hydrolysis reaction is carried out in an autoclave.

[0030] Suitably, the (initial) step of combining polyethylene terephthalate, water, and a catalyst, comprises combining polyethylene terephthalate with water in a concentration of 50 to 300 g / L, preferably in a concentration of 80 to 250 g / L, such as from 80 g / L to 220 g / L, for example 80 g / L to 150 g / L.

[0031] Advantageously, the method of the present invention involves neutral hydrolysis of polymers comprising polyethylene terephthalate units, such as neutral hydrolysis of PET. Brief description of the drawings

[0032] FIG.1 shows1H NMR spectrum of catalyst compound 19.

[0033] FIG.2 shows13C NMR spectrum of catalyst compound 19.

[0034] FIG.3 shows31P NMR spectrum of catalyst compound 19.

[0035] FIG.41H NMR spectrum of compound 20.

[0036] FIG.513C NMR spectrum of compound 20.

[0037] FIG 631P NMR spectrum of compound 20. DETAILED DESCRIPTION

[0038] As outlined above, the invention is concerned with the neutral hydrolysis of polymers comprising one or more polyethylene terephthalate unit, such as polyethylene terephthalate. Advantageously, the methods described herein provide the hydrolysis product terephthalic acid in high yield, and without the requirement for expensive heavy metal catalysts, such as the tungsten catalyst employed by Zhang et al. discussed above. A further advantage of the methods of the present invention is that the reactions can be carried out at high concentration, with low volumes of water being employed to effect hydrolysis. This is considerably advantageousfrom an environmental standpoint. Furthermore, in contrast to some methods for neutral hydrolysis reported in the literature, the reaction conditions in terms of temperature and pressure required to effect hydrolysis / depolymerisation of the PET units in the method of the present invention is milder, with effective hydrolysis achieved at a temperature of around 200°C.

[0039] Two classes of catalyst were employed in the present development work. Catalyst Classes

[0040] Two classes of catalyst were employed in our investigations, which we have broadly categorized as Catalyst System A and Catalyst System B.

[0041] Catalyst System A comprise a combination of a phase transfer catalyst system including a combination of a quaternary ammonium salt or a quaternary phosphonium salt, and a metal salt of the terephthalate dianion, e.g. disodium terephthalate.

[0042] Catalyst System B comprises a diphosphonium salt or diammonium salt of the terephthalate dianion. A representative diphosphonium salt of the diterephthalate dianion is

[0043] Catalyst System A

[0044] As outlined above, catalyst system A involves the use of a binary catalytic system which include the presence of 2 molar equivalents of a quaternary ammonium or quaternary phosphonium salt, per 1 molar equivalent of a dimetal salt of the terephthalate dianion. The person skilled in the art will appreciate that at least 2 molar equivalents of the quaternary ammonium or quaternary phosphonium salt, may be employed per 1 molar equivalent of a dimetal salt of the terephthalate dianion.

[0045] Using Catalyst System A as defined herein, the method for hydrolysing a polymer comprising polyethylene terephthalate units, such as polyethylene terephthalate, involves: combining a polymer comprising polyethylene terephthalate units, such as PET, water, and a catalyst, and heating for a time sufficient to hydrolyse at least in part the polyethylene terephthalate, wherein the catalyst comprises: (i) a phase transfer catalyst having a formula selected from: Formula (I)wherein X1is N or P, wherein A1- is an anion, wherein each of R1, R2, R3and R4is independently selected from C1-C20 aliphatic, wherein together R1, R2, R3and R4comprise at least 16 carbon atoms, and wherein at least two of R1, R2, R3and R4are independently selected from C2-C20aliphatic; and (i) a compound of formula (II):wherein Z+is a cation.

[0046] Suitably, for each molar equivalent of the compound of formula (II), 2 molar equivalents of compound of formula (I) are added.

[0047] Advantageously, the method does not involve the addition of strong acid or strong base as is required in acidic or alkaline hydrolysis of PET. For example, thehydrolysis / depolymerization reaction of the present invention to produce terephthalic acid from PET takes place without the addition of strong acid such as HCl, HBr, HNO3or H2SO4, and without the addition of strong base such as NaOH, KOH, Mg(OH)2, Ca(OH)2etc. during the hydrolysis reaction.

[0048] Suitably, the reaction is carried out at a pH in the range of from pH 6 to 8, optionally, in the range of from pH 6.2 to pH 7.8, further optionally, in the range of from pH 6.5 to pH 7.5.

[0049] Each Z+is suitably an alkali metal cation. Optionally, each Z+is independently selected from Na+, K+Li+, Rb+and Cs+., Preferably each Z+is the same. More preferably each Z+is Na+.

[0050] Suitably, the the compound of formula (I) comprises at least 24 carbon atoms, optionally, at least 28 carbon atoms, further optionally, at least 32 carbon atoms.

[0051] Suitably, A1- is selected from Cl-, Br-, F-, I-, BF4-, OMs-, and CF3C(O)O-, preferably Cl-, Br-, or I-.

[0052] Each of R1, R2, R3and R4may be independently selected from C1-C20alkyl.

[0053] For example, each of R1, R2, R3and R4may be may be independently selected from C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl, C10 alkyl, C11 alkyl, C12 alkyl, C13 alkyl, C14 alkyl, C15 alkyl, C16 alkyl, C17 alkyl, C18 alkyl, C19 alkyl, and C20 alkyl.

[0054] At least two of R1, R2, R3and R4may be independently selected from C2-C20 alkyl.

[0055] For example, at least two of R1, R2, R3and R4may be may be independently selected from C2alkyl, C3alkyl, C4alkyl, C5alkyl, C6alkyl, C7alkyl, C8alkyl, C9alkyl, C10alkyl, C11alkyl, C12 alkyl, C13 alkyl, C14 alkyl, C15 alkyl, C16 alkyl, C17 alkyl, C18 alkyl, C19 alkyl, and C20 alkyl.

[0056] Each of R1, R2, R3and R4may be independently selected from C1-C20 alkyl, and at least two of R1, R2, R3and R4are independently selected from C2-C20alkyl.

[0057] For example, each of R1, R2, R3and R4may be may be independently selected from C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl, C10 alkyl, C11 alkyl, C12 alkyl, C13 alkyl, C14 alkyl, C15 alkyl, C16 alkyl, C17 alkyl, C18 alkyl, C19 alkyl, and C20 alkyl; and at least two of R1, R2, R3and R4may be may be independently selected from C2alkyl, C3alkyl, C4alkyl, C5alkyl, C6alkyl, C7alkyl, C8alkyl, C9alkyl, C10alkyl, C11alkyl, C12alkyl, C13alkyl, C14 alkyl, C15 alkyl, C16 alkyl, C17 alkyl, C18 alkyl, C19 alkyl, and C20 alkyl.

[0058] Some or each of R1, R2, R3and R4may be selected from C4-C18 alkyl, optionally, from C4-C16alkyl.

[0059] For example, at least two of R1, R2, R3and R4may be independently selected from C4-C18 alkyl. Optionally, at least two of R1, R2, R3and R4is selected from C4-C16 alkyl.

[0060] For example, two of R1, R2, R3and R4may be butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl or octadecyl.

[0061] Suitably, two of R1, R2, R3and R4are butyl, pentyl, hexyl or octyl. Optionally, two of R1, R2, R3and R4are butyl, hexyl or octyl.

[0062] Optionally, at least three of R1, R2, R3and R4may be independently selected from C4-C18alkyl. Optionally, at least three of R1, R2, R3and R4is selected from C4-C16alkyl.

[0063] For example, three of R1, R2, R3and R4may be butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl or octadecyl.

[0064] Suitably, three of R1, R2, R3and R4are butyl, pentyl, hexyl or octyl. Optionally, three of R1, R2, R3and R4are butyl, hexyl or octyl.

[0065] In some catalysts, each of R1, R2, R3and R4is the same, i.e. R1= R2= R3= R4.

[0066] Each of R1, R2, R3and R4may be C4-C10 alkyl.

[0067] For example, each of R1, R2, R3and R4may be independently selected from C4 alkyl, C5alkyl, C6alkyl, C7alkyl, C8alkyl, C9alkyl, and C10alkyl.

[0068] Suitably, each of R1, R2, R3and R4may be butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl.

[0069] For example: Each of R1, R2, R3and R4may be butyl, or pentyl, or hexyl, or heptyl or octyl. Suitably, when each of R1, R2, R3and R4is the same, each of R1, R2, R3and R4is butyl, hexyl, octyl or decyl.

[0070] For example, the compound of formula (I) may be:, wherein A- is an anion selected from Cl-, Br- or I-.

[0071] In some catalysts, each of R2, R3and R4are the same and are selected from C4- C12alkyl.

[0072] For example, each of R2, R3and R4are the same and are selected from C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl, C10 alkyl, C11 alkyl, and C12 alkyl.

[0073] Optionally, each of R2, R3and R4are the same and are selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl. Suitably, each of R2, R3and R4are the same and are selected from butyl, hexyl, octyl, and decyl.

[0074] In some catalysts, R1is C1 alkyl, optionally, methyl.

[0075] For example, in some catalysts R1is C1 alkyl, optionally, methyl, and two or three of R2, R3and R4are independently C6-C16alkyl, optionally, C6-C12alkyl, such as C6-C10alkyl. For example, two or three of R2, R3and R4are independently selected from C6alkyl, C7alkyl, C8alkyl, C9 alkyl, C10 alkyl, C11 alkyl, C12 alkyl, C13 alkyl, C14 alkyl, C15 alkyl, and C16 alkyl.

[0076] Optionally, R1is methyl, and two of R2, R3and R4are independently C6-C16 alkyl.

[0077] Optionally, R1is methyl, and two of R2, R3and R4are independently C6-C12alkyl.

[0078] Optionally, R1is methyl, and two of R2, R3and R4are independently C6-C10alkyl.

[0079] Optionally, R1is methyl, and three of R2, R3and R4are independently C6-C16 alkyl.

[0080] Optionally, R1is methyl, and three of R2, R3and R4are independently C6-C12alkyl.

[0081] Optionally, R1is methyl, and three of R2, R3and R4are independently C6-C10 alkyl.

[0082] Optionally, R1is methyl and two or three of R2, R3and R4may be hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, or hexadecyl.

[0083] Suitably, R1is methyl and two of R2, R3and R4are the same and are selected from hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, or hexadecyl.

[0084] Suitably, R1is methyl and three of R2, R3and R4are the same and are selected from hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, or hexadecyl.

[0085] For example, R1may be methyl and R2, R3and R4are octyl, nonyl or decyl.

[0086] For example, R1may be methyl, and R2, R3and R4are the same and are each octyl, nonyl or decyl.

[0087] For example, the catalyst may be a catalyst as shown below:, where A- is an anion, such as Cl-, I- or Br-.

[0088] For example, the catalyst may be catalyst 5 or 6 shown below:.

[0089] The catalyst may be catalyst 14 or catalyst 15 as shown below:.

[0090] In some catalysts, R1is C1 alkyl, optionally, methyl and R2is C1 alkyl, optionally, methyl.

[0091] Suitably, R1and R2may each be methyl, and R3and R4may independently be selected from C6-C16alkyl, such as C8-C16alkyl, for example, C10-C16alkyl.

[0092] Optionally, R1and R2are each methyl, and R3and R4are the same and selected from C6-C16 alkyl, optionally, C8-C16 alkyl, suitably, C10-C16 alkyl.

[0093] Optionally, R1and R2are methyl, and R3and R4are the same and are selected from hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, or hexadecyl.

[0094] For example, R1and R2may be methyl, and R3and R4are the same and are octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, or hexadecyl.

[0095] For example, the catalyst may be catalyst 12 or 13 as shown below:

[0096] Some representative compounds of formula (I) are shown below:

[0097] Some representative compounds of formula (I) are shown below:.

[0098] Suitably, the using Catalyst System A, the method of the invention suitably employs one or more of phase transfer catalyst compounds 2-6, wherein X1 is P, or one or more of phase transfer catalyst compounds 9, 12, 13, 14 or 15.

[0099] Suitably, in the method of the invention, the phase transfer catalyst of formula (I) is employed in an amount of 10 mol% or less, preferably in an amount of 5 mol% or less, suitably, in an amount of 2.5 mol% or less, more suitably, in an amount of 1.5 mol% or less relative, most suitably in an amount of 1 mol% or less per mole of monomeric repeating unit of polyethylene terephthalate.

[0100] The method may further comprise a purification step. Optionally, the purification step involves one or more of washing, filtering, and base / acid treatment. For example, a purification step may further comprise dissolution in aqueous NaOH followed by filtering and reprecipitation of terephthalic acid using dilute mineral acids such as H2SO4 or HCl. Suitably, the purification step involves washing with organic solvent, such as acetone, ethyl acetate, dichloromethane and / or chloroform.

[0101] The method may further comprising a subsequent addition (after hydrolysis) of acid, suitably, a Bronsted acid.

[0102] The acid may be selected from aqueous HCl, H2SO4, HNO3, CH3COOH, and HBr.

[0103] As unreacted PET and TPA are both insoluble in the reaction mixture, one way to separate the PET from the TPA is to add aqueous NaOH, to deprotonate the TPA, and render it soluble in water, followed by filtration to remove the unreacted PET, and subsequent acid treatment (e.g. with aqueous HCl) of the filtrate to reprecitipitate the TPA. Advantageously, as TPA is insoluble in solvents such as acetone, and the catalyst is soluble in acetone, acetone may be employed to remove the catalyst from the TPA. Catalyst System B

[0104] In contrast to catalyst system A, which involves the addition of two different species i.e. a binary catalyst system, catalyst system B involves the addition of individual catalytic species that comprise a terephthalate dianion and quaternary phosphonium or quaternary ammonium cations.

[0105] Using Catalyst System B as defined herein, the method for hydrolysing a polymer comprising polyethylene terephthalate units, such as polyethylene terephthalate, involves:combining a polymer comprising polyethylene terephthalate units, such as PET, water, and a catalyst, and heating for a time sufficient to hydrolyse at least in part the polyethylene terephthalate, wherein the catalyst is a phase transfer catalyst having the formula (III):wherein each Y+has the formula IV:Formula (IV) wherein X1is N or P, wherein each of R1, R2, R3and R4is independently selected from C1-C20 aliphatic, wherein together R1, R2, R3and R4comprise at least 16 carbon atoms, and wherein at least two of R1, R2, R3and R4are independently selected from C2-C20aliphatic.

[0106] Advantageously, the method does not involve the addition of strong acid or strong base as is required in acidic or alkaline hydrolysis of PET. For example, the hydrolysis / depolymerization reaction of the present invention to produce terephthalic acid from PET takes place without the addition of strong acid such as HCl, HBr, HNO3or H2SO4, and without the addition of strong base such as NaOH, KOH, Mg(OH)2, Ca(OH)2 etc.

[0107] Suitably, the reaction is carried out at a pH in the range of from pH 6 to 8, optionally, in the range of from pH 6.2 to pH 7.8, further optionally, in the range of from pH 6.5 to pH 7.5.

[0108] Each Y suitably comprises at least 24 carbon atoms, optionally, at least 28 carbon atoms, further optionally, at least 32 carbon atoms.

[0109] Each of R1, R2, R3and R4of each Y may be independently selected from C1-C20 alkyl.

[0110] For example, each of R1, R2, R3and R4of each Y may be may be independently selected from C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl, C10 alkyl, C11 alkyl, C12 alkyl, C13 alkyl, C14 alkyl, C15 alkyl, C16 alkyl, C17 alkyl, C18 alkyl, C19 alkyl, and C20alkyl.

[0111] At least two of R1, R2, R3and R4of each Y may be independently selected from C2-C20alkyl.

[0112] For example, at least two of R1, R2, R3and R4of each Y may be may be independently selected from C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl, C10alkyl, C11alkyl, C12alkyl, C13alkyl, C14alkyl, C15alkyl, C16alkyl, C17alkyl, C18alkyl, C19alkyl, and C20alkyl.

[0113] Each of R1, R2, R3and R4of each Y may be independently selected from C1-C20 alkyl, and at least two of R1, R2, R3and R4are independently selected from C2-C20 alkyl.

[0114] For example, each of R1, R2, R3and R4of each Y may be may be independently selected from C1alkyl, C2alkyl, C3alkyl, C4alkyl, C5alkyl, C6alkyl, C7alkyl, C8alkyl, C9alkyl, C10alkyl, C11 alkyl, C12 alkyl, C13 alkyl, C14 alkyl, C15 alkyl, C16 alkyl, C17 alkyl, C18 alkyl, C19 alkyl, and C20 alkyl; and at least two of R1, R2, R3and R4of each Y may be may be independently selected from C2alkyl, C3alkyl, C4alkyl, C5alkyl, C6alkyl, C7alkyl, C8alkyl, C9alkyl, C10alkyl, C11alkyl, C12alkyl, C13alkyl, C14alkyl, C15alkyl, C16alkyl, C17alkyl, C18alkyl, C19alkyl, and C20alkyl.

[0115] Some or each of R1, R2, R3and R4may be selected from C4-C18alkyl, optionally, from C4-C16 alkyl.

[0116] For example, at least two of R1, R2, R3and R4of each Y may be independently selected from C4-C18alkyl. Optionally, at least two of R1, R2, R3and R4is selected from C4-C16alkyl.

[0117] For example, two of R1, R2, R3and R4may be independently selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl or octadecyl.

[0118] Suitably, two of R1, R2, R3and R4of each Y are butyl, pentyl, hexyl or octyl. Optionally, two of R1, R2, R3and R4are butyl, hexyl or octyl.

[0119] Optionally, at least three of R1, R2, R3and R4of each Y may be independently selected from C4-C18alkyl. Optionally, at least three of R1, R2, R3and R4of each Y is selected from C4-C16alkyl.

[0120] For example, three of R1, R2, R3and R4of each Y may be butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl or octadecyl.

[0121] Suitably, three of R1, R2, R3and R4of each Y are butyl, pentyl, hexyl or octyl. Optionally, three of R1, R2, R3and R4of each Y are butyl, hexyl or octyl.

[0122] In some catalysts, two or three of R1, R2, R3and R4of each Y are C4-C16 alkyl, optionally, C4-C10 alkyl, for example, wherein two or three of R1, R2, R3and R4of each Y are independently selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl.

[0123] In some catalysts, each of R1, R2, R3and R4of each Y is the same, i.e. R1= R2= R3= R4.

[0124] Each of R1, R2, R3and R4of each Y may be C4-C10 alkyl.

[0125] For example, each of R1, R2, R3and R4may be independently selected from C4 alkyl, C5alkyl, C6alkyl, C7alkyl, C8alkyl, C9alkyl, and C10alkyl.

[0126] Suitably, each of R1, R2, R3and R4may be butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl.

[0127] For example: each of R1, R2, R3and R4may be butyl, or pentyl, or hexyl, or heptyl or octyl. Suitably, when each of R1, R2, R3and R4is the same, each of R1, R2, R3and R4is butyl, hexyl, octyl or decyl.

[0128] For example, in formula (IV) X1 may be P, and each R1, R2, R3and R4may be butyl, hexyl or octyl. Suitably, the catalyst is compound 18 or 19 as shown below:.

[0129] In some catalysts, each of R2, R3and R4are the same and are selected from C4- C12alkyl.

[0130] For example, each of R2, R3and R4are the same and are selected from C4alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl, C10 alkyl, C11 alkyl, and C12 alkyl.

[0131] Optionally, each of R2, R3and R4are the same and are selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl. Suitably, each of R2, R3and R4are the same and are selected from butyl, hexyl, octyl, and decyl.

[0132] In some catalysts, R1is C1alkyl, optionally, methyl.

[0133] For example, in some catalysts R1is C1 alkyl, optionally, methyl, and two or three of R2, R3and R4are independently C6-C16 alkyl, optionally, C6-C12 alkyl, such as C6-C10 alkyl. For example, two or three of R2, R3and R4are independently selected from C6alkyl, C7alkyl, C8alkyl, C9alkyl, C10alkyl, C11alkyl, C12alkyl, C13alkyl, C14alkyl, C15alkyl, and C16alkyl.

[0134] Optionally, R1is methyl, and two of R2, R3and R4are independently C6-C16 alkyl.

[0135] Optionally, R1is methyl, and two of R2, R3and R4are independently C6-C12 alkyl.

[0136] Optionally, R1is methyl, and two of R2, R3and R4are independently C6-C10 alkyl.

[0137] Optionally, R1is methyl, and three of R2, R3and R4are independently C6-C16alkyl.

[0138] Optionally, R1is methyl, and three of R2, R3and R4are independently C6-C12 alkyl.

[0139] Optionally, R1is methyl, and three of R2, R3and R4are independently C6-C10 alkyl.

[0140] Optionally, R1is methyl and two or three of R2, R3and R4may be hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, or hexadecyl.

[0141] Suitably, R1is methyl and two of R2, R3and R4are the same and are selected from hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, or hexadecyl.

[0142] Suitably, R1is methyl and three of R2, R3and R4are the same and are selected from hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, or hexadecyl.

[0143] For example, in formula (IV), X1 may be P, R1may be methyl, and each of R2, R3and R4may be the same and be selected from hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl.

[0144] Suitably, the catalyst may be compound 20 as shown below:.

[0145] In some catalysts, each R1is C1 alkyl, optionally, methyl and each R2is C1 alkyl, optionally, methyl.

[0146] Suitably, each R1and R2may each be methyl, and each R3and R4may independently be selected from C6-C16alkyl, such as C8-C16alkyl, for example, C10-C16alkyl.

[0147] Optionally, R1and R2of each Y are each methyl, and R3and R4of each Y are the same and selected from C6-C16 alkyl, optionally, C8-C16 alkyl, suitably, C10-C16 alkyl.

[0148] Optionally, each R1and R2are methyl, and each R3and R4are the same and are selected from hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, or hexadecyl.

[0149] For example, R1and R2may be methyl, and R3and R4are the same and are octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, or hexadecyl.

[0150] For Catalyst System B, X1 is preferably P.

[0151] Optionally, the catalyst of formula (III) is selected from compounds 18, 19 and 20 shown below:.

[0152] Suitably, using Catalyst System B, the method of the invention suitably employs one or more of phase transfer catalysts of formula (III) where X1is P, and at least three of R2, R3and R4are the same, and are selected from butyl, hexyl, octyl or decyl. Suitably, or one or more of phase transfer catalyst compounds 18, 19 or 20 are employed.

[0153] The phase transfer catalyst of formula (III) may be employed in an amount of 10 mol% or less, preferably in an amount of 5 mol% or less, suitably, in an amount of 2.5 mol% or less, more suitably, in an amount of 1.5 mol% or less relative, most suitably in an amount of 1 mol% or less per mole of monomeric repeating unit of polyethylene terephthalate. Preferably, the phase transfer catalyst of formula (III) is employed in an amount of 1 mol% or less.

[0154] The method may further comprise a purification step. Optionally, the purification step involves one or more of washing, filtering, and base / acid treatment. For example, a purification step may further comprise dissolution in aqueous NaOH followed by filtering and reprecipitation of terephthalic acid using dilute mineral acids such as H2SO4 or HCl. Suitably, the purification step involves washing with organic solvent, such as acetone, ethyl acetate, dichloromethane and / or chloroform.

[0155] The method may further comprising a subsequent addition (after hydrolysis) of acid, suitably, a Bronsted acid.

[0156] The acid may be selected from aqueous HCl, H2SO4, HNO3,CH3COOH, and HBr.

[0157] As unreacted PET and TPA are both insoluble in the reaction mixture, one way to separate the PET from the TPA is to add aqueous NaOH, to deprotonate the TPA, and render it soluble in water, followed by filtration to remove the unreacted PET, and subsequent acid treatment (e.g. with aqueous HCl) of the filtrate to reprecitipitate the TPA. Advantageously, asTPA is insoluble in solvents such as acetone, and the catalyst is soluble in acetone, acetone may be employed to remove the catalyst from the TPA. General Aspects of the Method

[0158] The method is suitably carried out under pressure. For example, the reaction may be carried out at a pressure in the range of from 5 to 30 atm, suitably, from 10 to 25 atm, for example, from 12 to 20 atm, optionally, from 12 to 18 atm, such as at approx.15 atm.

[0159] The method (i.e. hydrolysis reaction) is suitably carried out at a temperature of 150°C or higher, suitably, 180°C or higher.

[0160] The method (i.e. hydrolysis reaction) is suitably carried out at a temperature in the range of from 100 to 300°C, optionally, in the range of from 150 to 250°C, further optionally in the range of from 180 to 230°C.

[0161] For example, the hydrolysis reaction (using either catalyst system A or catalyst system B) may be carried out at a pressure of from 5 to 30 atm, and at a temperature in the range of from 100 to 300°C. Optionally, the hydrolysis reaction may be carried out at a pressure in the range of from 10 to 25 atm, and at a temperature in the range of from 150 to 250°C. Further optionally, the hydrolysis reaction may be carried out at a pressure in the range of from 12 to 20 atm, and at a temperature in the range of from 180 to 230°C.

[0162] The (initial) step of combining polyethylene terephthalate, water, and a catalyst, comprises combining polyethylene terephthalate with water in a concentration of 50 to 300 g / L, preferably in a concentration of 80 to 250 g / L, such as from 80 g / L to 220 g / L, for example 80 g / L to 150 g / L.

[0163] Optionally, the method (using either catalyst system A or catalyst system B) may further comprise a purification step. Optionally, the purification step involves one or more of washing, filtering, and base / acid treatment. For example, a purification step may further comprise dissolution in aqueous NaOH followed by filtering and reprecipitation of terephthalic acid using dilute mineral acids such as H2SO4or HCl. Suitably, the purification step involves washing with organic solvent, such as acetone, ethyl acetate, dichloromethane and / or chloroform.

[0164] As outlined above, unreacted PET and TPA are both insoluble in the reaction mixture, one way to separate the PET from the TPA is to add aqueous NaOH, to deprotonate the TPA, and render it soluble in water, followed by filtration to remove the unreacted PET, and subsequent acid treatment (e.g. with aqueous HCl) of the filtrate to reprecitipitate the TPA.Advantageously, as TPA is insoluble in solvents such as acetone, and the catalyst is soluble in acetone, acetone may be employed to remove the catalyst from the TPA.

[0165] While the examples disclosed herein employ a hydrothermal autoclave reactor, other reactors are envisaged. For example, it is considered that the reactions would also proceed well under microwave conditions, and / or using ultrasound.

[0166] Suitably the reaction is carried out in a hydrothermal autoclave. Alternative reaction systems are also envisaged. For example, using microwave irradiation, or ultrasound is also envisaged, and / or carrying out the reaction in other forms of pressurised reactors.

[0167] The catalysts disclosed herein have utility in depolymerizing polymers comprising PET units, such as PET. Optionally, the PET may have a density in the range of from 1.30 g / cm3to 1.45 g / cm3, such as from 1.38 g / cm3to 1.41 g / cm3. EXAMPLES

[0168] The invention will be more readily appreciated by a review of the examples, which follow.

[0169] The following examples were conducted to identify optimal catalytic systems for neutral hydrolysis of PET.

[0170] To date, much of the investigations on PET depolymerization has employed smaller PET flakes, which have a larger surface area per gram of PET, and therefore represent more reactive, and less challenging substrates. In order to develop a platform for industrial application, we employed PET flakes of larger size, circa 5 mm square flakes, which is consistent with the output from mechanical PET recycling. Materials and Methods

[0171] The PET was derived from colourless water bottles purchased from a large supermarket chain. The average molecular weight for bottle grade PET ranges from 24000 to 36000 g mol-1. The density of the PET was in the range of from 1.38 to 1.41 g / cm3.

[0172] Once emptied of their contents and labels were removed, the PET bottles were cut into flakes of approx.5 mm square in size.

[0173] Sodium hydroxide pellets were purchased from Sigma Aldrich, and used without further purification.

[0174] Hydrochloric acid was purchased from Sigma Aldrich (37% conc.) and solutions thereof were prepared.

[0175] Phase transfer catalysts were purchased where available or synthesized in accordance with literature procedures, unless otherwise specified.

[0176] The hydrolysis reactions were carried out using a hydrothermal autoclave, for example, using an Acid digestion vessel available from Parr® Instrument Company, suitably Model 4749 general purpose acid digestion vessel may be used, using a 23 mL PTFE liner.

[0177] Proton Nuclear Magnetic Resonance (NMR) spectra were recorded on Bruker DPX 400 MHz and Bruker Avance II 600MHz spectrometers, using CDCl3 and DMSO-d6 as solvents, and referenced relative to residual CHCl3 (δ = 7.26 ppm) or DMSO (δ = 2.50 ppm). Carbon NMR spectra were recorded on the same instruments (101 MHz and 151 MHz respectively) with total proton decoupling. Phosphorus NMR spectra were recorded on the Bruker DPX400 machine (162 MHz). Infrared spectra were obtained on a Perkin Elmer Spectrum 100 FT-IR spectrometer equipped with a universal ATR sampling accessory. ESI mass spectra were acquired using a Waters Micromass LCT- time of flight mass spectrometer (TOF), interfaced to a Waters 2690 HPLC. The instrument was operated in either positive or negative mode as required. APCI experiments were carried out on a Bruker microTOF-Q III spectrometer interfaced to a Dionex UltiMate 3000 LC or direct insertion probe. Agilent tuning mix APCI-TOF was used to calibrate the system. Hydrolysis experiments were carried out with Radleys Carousel 12 Plus Reaction Station. HPLC grade water was purchased from Sigma-Aldrich and used as the reaction medium for the basic hydrolysis of PET. Colourless polyethylene terephthalate bottles were purchased from a local large supermarket chain and cut into flakes (ca.5 mm square). Unless otherwise noted, all commercially available compounds were used as provided, without any further purification.

[0178] Test System

[0179] The test system employed to assess the efficacy of various catalysts was as follows: ^ 1000 mg PET flakes (approx.5 mm square); ^ Catalyst: 5 mol% or less relative to the number of moles of monomeric units present in PET polymer, e.g. the number of monomeric units present in 0.5 g of PET is 2.6 mmol, which enables the calculation of the required amount of catalyst based on the mass of PET used;^ Water: 5mL, 10 mL or 15 mL (approx. pH 7); ^ Reactor: Hydrothermal Autoclave (Model 4749 Acid digestion vessel from Parr®, using 23 mL PTFE liner); ^ Stirring: ^ Temperature: 200°C; ^ Duration: 3 hours, 4 hours or 5 hours.

[0180] Scheme 1 below illustrates the test system, along with different catalyst classes investigated.Scheme 1: Consitions utilised in the PTC-catalysed neutral PET hydrolysis and the catalyst classes employed. Evaluation of Catalyst System A

[0181] Neutral hydrolysis of PET catalysed by catalyst system A using a combination of phosphonium phase transfer catalysts and disodium terephthalate were assessed. Table 1: Neutral hydrolysis of PET catalysed by catalyst system A (phosphonium ion- based)aIJ7Entry Phosphonium salt Phosphonium Disodium terephthalate Conversion Yield (%)bsalt loading loading (mol%) (%)a(mol%) 1 none 0 0 4.5 3.6 2 none 0 2.5 10 9.3 3 1 5 0 16.8 16.5 4 1 2 1 14.5c18.8 5 2 2 1 65.1 63.9 6 2 5 2.5 70.6 60.4 7 3d2 1 66.9 59.5 8 4 2 1 59.7 58.0 9 5 2 1 73.9 70.6 10 5 5 2.5 79.4 68.2 11 6 5 2.5 69.6 51.6 12e5 2 1 64.1 58.4 13f5 2 1 48.2 45.5 14g2 2 1 81.8 62.7 15h2 2 1 76.3 61.8 aConversion determined by dissolution of the crude in NaOH(aq.) and filtration of unreacted PET. bDetermined by1H NMR spectroscopic analysis of precipitated (aqueous HCl) TPA using 4- iodoanisole as an internal standard – data agrees with yields derived from the mass of TPA recovered within 1.5% in all cases. cConversion artificially deflated due to presence of catalyst in the recovered PET flakes. dCatalyst decomposition evident. e5 mL H2O used. f15 mL H2O used. g5 mL H2O used, 4 h reaction time. f15 mL H2O used, 4 h reaction time.

[0182] As disodium terephthalate forms a dianion in solution, two molar equivalents of the phase transfer catalyst are employed per mole of terephthalate.

[0183] In the absence of any catalyst (entry 1) conversion of the PET to TPA at 200 ˚C is minimal. Similarly, neither disodium TPA nor tetrabutylphosphonium bromide (entries 2 and 3 respectively) served as active catalysts when utilised alone. However, when used together (entry 4), superior (albeit low) product yields could be obtained than was the case when either catalyst component was employed alone at higher loadings. Increasing the lipohilicity of the phosphonium ion component (i.e. 2, entries 5 and 6) resulted in a dramatic improvement in product yield. Catalysis by binary systems involving phosphonium bromides with one longer chain yet no overall increase in the number of C-atoms per catalyst (i.e.3 and 4, entries 7-8) failed to provide TPA in higher yields. Returning to the tetraoctylphosphonium ion motif – it was posited that one shorter chain could allow more efficient ion metathesis / access to the PET surface. Accordingly, the methyltrioctylphosphonium iodide (5) was synthesised and evaluated in conjunction with disodium TPA; this catalyst system mediated the hydrolysis of PET in 71% yield (entry 9). Either increasing the catalyst loading or changing the anion associated with the phosphonium unit to chloride (i.e. 6) failed to improve catalyst efficacy (entries 10-11). We also investigated the effect of the water:PET ratio (entries 12-15). Increasing reaction concentration by decreasing the volume of water appears to increase conversion rate (entries 12 & 13).

[0184] Pleasingly catalyst recovery was possible by washing with acetone during the work up procedure.

[0185] Next we investigated whether quaternary ammonium salts would outperform the quaternary phosphonium salts in the binary catalyst system, catalyst system A. Table 2 Neutral hydrolysis of PET catalysed by catalyst system A (ammonium ion-based)aEntry Ammonium salt Ammonium salt Disodium terephthalate Conversion Yield (%)bloading (mol%) loading (mol%) (%)a1 7c2 1 12.3d17.9 2 8c2 1 20.1d24.939c2 1 72.7 63.04 10c2 1 52.7 45.7 5 11c2 1 49.2 51.46 12 2 1 69.0 63.5 7 13c2 1 71.3 62.0 8 14 2 1 64.8 60.2 9 15 2 1 66.1 62.4 10 16 2 1 18.2d20.2 11 17 2 1 17.9 17.7 aConversion determined by dissolution of the crude in NaOH(aq.) and filtration of unreacted PET. bDetermined by1H NMR spectroscopic analysis of precipitated (aqueous HCl) TPA using 4- iodoanisole as an internal standard – data agrees with yields derived from the mass of TPA recovered within 1.5% in all cases. cConversion artificially deflated due to presence of catalyst in the recovered PET flakes. dCatalyst decomposition evident.

[0186] While the same general trends regarding both lipophilicity and advantages associated with possessing at least one shorter substituent were observed – the ammonium ion- based catalysts did not outperform the phosphonium ion catalysts detailed in Table 1.

[0187] It was hypothesized that more effective catalysis could result if the ion metathesis step could be avoided. Consequently, rather than employing a binary catalytic system, as in catalyst system A, we decided to replace the metal cations of the diterephthalate anion, with quaternary phosphonium ions. Ionic liquid catalysts incorporating both the phosphonium ion and the terephthalate dianion 18-20 were synthesised and evaluated (Table 3). Pleasingly, catalyst 18 proved considerably superior to the corresponding binary catalyst system (entry 1) (with a 2.4 fold increase in yield observed). In addition, concentrating the reaction further, by reducing the volume of water, halving the quantity of catalyst used, and increasing the duration of reaction led to a conversion and yield of approximately 80% (see entry 5).

[0188] Table 3 Neutral hydrolysis of PET catalysed by catalyst system Ba     Entry Ionic liquid catalyst Loading (mol%) Conversion (%)aYield (%)b1 18 2.5 47.0 43.9 2 19 2.5 72.0 63.3 3 19 1 72.6 64.2 4 20 1 64.0 58.6 5c19 0.5 80.1 79.8aConversion determined by dissolution of the crude in NaOH(aq.) and filtration of unreacted PET.bDetermined by1H NMR spectroscopic analysis of precipitated (aqueous HCl) TPA using 4-iodoanisole as an internal standard – data agrees with yields derived from the mass of TPA recovered within 1.5% in all cases.c5 h reaction time.

[0189] Advantageously, the catalytic systems described herein represent a marked improvement of prior art phase transfer catalytic systems for neutral hydrolysis of polymers comprising PET units, such as PET. The catalytic systems are effective in hydrolysing larger sized flakes of PET c.a.5 mm2which is consistent with the output of mechanical recycling of PET, and the reactions can be effected under less extreme conditions at a temperature of 200°C, thereby, reducing energy costs associated with the transformation. Moreover, the catalysts are effective at depolymerizing PET using low volumes of water, which is environmentally advantageous.Experimental Protocol Catalyst synthesis

[0190] Catalyst 5

[0191] A 25 mL round-bottomed flask equipped with a stirring bar was charged with triocylphosphine (2.52 mL, 10 mmol), acetonitrile (10 mL) and was cooled in an ice bath. Iodomethane (0.69 mL, 11 mmol) was added dropwise via syringe and the heterogeneous mixture was stirred at room temperature for 24 h. The solvent was removed under reduced pressure and the residue was washed with diethyl ether (2 x 5 mL). The resulting solid was dried in vacuo yielding 5 as a colourless gum (3.12 g, 52%). δH (400 MHz, DMSO-d6): 2.27–2.10 (m, 6H), 1.79 (d, J = 14.0, 3H), 1.56–1.17 (m, 36H), 0.93- 0.80 (m, 9H) ppm. δc (101 MHz, DMSO-d6): 31.2, 30.0 (d, J = 15.1), 28.3 (d, J = 18.8), 22.4, 22.0, 20.5, 19.1 (d, J = 51.2), 13.9, 3.2 (d, J = 51.2) ppm. δp (162 MHz, DMSO-d6): 33.2 ppm. HRMS (m / z – ESI+): Found: 385.3957 (M+) C25H54P+ Requires: 385.3958 vmax(neat) / cm-1: 2945, 2922, 2854, 1458, 1378, 1305, 1099, 1033, 943, 907, 770, 721

[0192] Catalyst 6

[0193] A 25 mL round-bottomed flask equipped with a stirring bar was charged with catalyst 5 (0.5716 g, 1 mmol), methanol (40 mL) and Amberlyst® IRA-900 chloride form (6 g) and shaken for 18 h at room temperature. The solution was then passed through a column containing Amberlyst® IRA-900 chloride form (6 g) and washed with methanol (3 x 40 mL). The solvent was removed under reduced pressure and the product was dried in vacuo yielding 6 as a yellow oil (0.4070 g, 97%). δH (400 MHz, DMSO-d6): 2.20–2.05 (m, 6H), 1.75 (d, J = 14.2, 3H), 1.51–1.20 (m, 36H), 0.87- 0.82 (m, 9H) ppm. δc(101 MHz, DMSO-d6): 31.7, 30.0 (d, J = 15.1), 28.7 (d, J = 18.8), 22.5, 21.0, 20.9, 19.5 (d, J = 51.2), 14.4, 3.7 (d, J = 51.2) ppm. δp (162 MHz, DMSO-d6): 32.2 ppm. nmax(neat) / cm-1: 2923, 2855, 1727, 1452, 1377, 1305, 1100, 1033, 944, 721

[0195] A 25 mL round-bottomed flask equipped with a stirring bar was charged with methylamine (2.0 mL, 2.0 M in THF, 4.0 mmol), acetonitrile (4 mL) and potassium carbonate (2.21 g, 16 mmol).1-Bromohexane (1.6 mL, 14.0 mmol) was added dropwise at room temperature. The flask was equipped with a condenser and the solution was heated under reflux for 24 h before themixture was filtered. The solvent was removed under reduced pressure and the product was triturated in diethyl ether. The product was dried in vacuo yielding 12 as a brown oil (0.53 g, 37%). δH (400 MHz, DMSO-d6): 3.23-3.13 (m, 6H), 2.93 (s, 3H), 1.69-1.53 (m, 6H), 1.39-1.21 (m, 18H), 0.88 (t, J = 6.3 Hz, 9H) ppm.(2 mL), dimethylamine (2.0 mL, 2.0 M solution in THF, 4.0 mmol) and potassium carbonate (2.21 g, 16.0 mmol).1-Bromoundecane (3.12 mL, 14.0 mmol) was diluted with anhydrous acetonitrile (2 mL) and added dropwise to the reaction mixture at room temperature. The flask was equipped with a condenser and the solution was heated under reflux for 24 h before the mixture was filtered. The residual white solid was washed with acetonitrile (3 x 5 mL) and the filtrate was concentrated under reduced pressure. The resulting oil was purified by flash chromatography (CH2Cl2 to CH2Cl2 / MeOH (9:1)) to yield 20 as a white solid (1.14 g, 66%). M.p.159-161 °C. δH (400 MHz, CDCl3): 3.57-3.46 (m, 4H), 3.41 (s, 6H), 1.74-1.63 (m, 4H), 1.43-1.20 (m, 32H), 0.87 (t, 6H, J = 6.8 Hz) ppm. δC (100 MHz, CDCl3): 64.0, 51.4, 32.0, 29.7, 29.6, 29.5, 29.4, 29.3, 26.4, 22.9, 22.8, 14.2 ppm. HRMS (m / z – ESI+): Found: 354.4098 (M+) C24H52N+Requires: 354.4094. νmax (neat) / cm-1: 2951, 2921, 2853, 1466, 1455, 889, 720.

[0198] Catalyst 19

[0199] A 25 mL round-bottomed flask equipped was charged with tetraoctylphosphonium bromide (1.1276 g, 2 mmol), methanol (30 mL) and Amberlyst® A26 hydroxide form (4.4 g) and shaken for 18 h at room temperature. The solution was then passed through a column containing Amberlyst® A26 hydroxide form (4.4 g) and washed with methanol (3 x 30 mL). The eluent solution was then charged with a stir bar and terephthalic acid (0.1661 g, 1 mmol) and stirred at room temperature for 18 h. The solvent was removed under reduced pressure and the product was dried in vacuo yielding 19 as a colourless gum (1.096 g, 97%). δH (400 MHz, DMSO-d6): 7.62 (s, 4H), 2.34-2.04 (m, 16H), 1.59-1.14 (m, 96H), 0.99-0.74 (m, 24H) ppm. δc(101 MHz, DMSO-d6): 169.0, 142.2, 127.9, 31.7, 30.0 (d, J = 15.5), 28.2 (d, J = 21.2), 22.02, 21.0, 20.9, 17.4 (d, J = 47.1), 14.4 ppm. δp (162 MHz, DMSO-d6): 33.8 ppm. HRMS (m / z – ESI+): Found: 483.5061 (M+) C32H68P+Requires: 483.5053 vmax(neat) / cm-1: 2923, 2854, 1581, 1464, 1350, 1116, 1017, 801, 754, 721

[0200] Catalyst 20

[0201] A 25 mL round-bottomed flask equipped with a stirring bar was charged with catalyst 5 (1.025 g, 2 mmol), methanol (30 mL) and Amberlyst® A26 hydroxide form (4.4 g) and shaken for 18 h at room temperature. The solution was then passed through a column containing Amberlyst® A26 hydroxide form (4.4 g) and washed with methanol (3 x 30 mL). The solution was then charged with a stir bar and terephthalic acid (0.1661g, 1 mmol) and stirred at room temperature for 18h. The solvent was removed under reduced pressure and the product was dried in vacuo yielding 20 as a white wax (0.897 g, 96%).

[0202] δH(400 MHz, DMSO-d6): 7.58 (s,4H), 2.20–2.07 (m, 12H), 1.76 (d, J = 14.3, 6H), 1.46–1.25 (m, 72H), 0.87-0.82 (m, 18H) ppm.

[0203] δc (101 MHz, DMSO-d6): 169.0, 142.2, 127.9, 31.7, 30.0 (d, J = 15.5), 28.7 (d, J = 18.3), 22.5, 21.0, 20.9, 19.5 (d, J = 47.6), 14.4, 3.5 (d, J = 53.4) ppm.

[0204] δp(162 MHz, DMSO-d6): 32.3 ppm.

[0205] nmax (neat) / cm-1: 3320, 2922, 2852, 2165, 1981, 1635, 1588, 1536, 1465, 1349, 1309, 1084, 1044, 1018, 995, 945, 890, 830, 800, 754, 723

[0206] Neutral PET hydrolysis procedure – Catalyst System A

[0207] A 23 mL Teflon® cup was charged with water (10 mL), disodium terephthalate (0.0109 g, 1 mol %),acatalyst (2 mol %, of a quaternary ammonium or phosphonium salt of catalyst system A) and polyethylene terephthalate flakes (ca. 5 mm squares, 1.000 g). The Teflon® cup was then sealed inside a batch hydrothermal autoclave before being placed into an oven pre-heated at 200 °C for 3 h. The batch hydrothermal autoclave was then placed on a ceramic tile for 16h. To the reaction mixture was then added sodium hydroxide (0.450 g) and water (6 mL). After 10 min the reaction mixture was filtered and washed with water (10 mL x 2).bThe filtrate was adjusted, with cooling, to pH 2-3 using dilute HCl and the precipitate was filtered. The residue was washed with water (10 mL) and the product was dried for 4 h in a vacuum oven at 60 °C.caMol% of catalyst is related to the number of moles of monomeric units (5.204 mmol) present in 1.000 g of polymer.bTo establish catalyst recyclability, the unreacted PET residue was subsequently washed with acetone (2 x 10mL) and the washings concentrated in vacuo.cYield calculated based on the mass of recovered TPA after acidification. Correction is made for the the additional TPA derived from protonation of the added disodium terephthalate upon workup. To evaluate purity and provide yield data based on an internal standard – samples of TPA post in vacuo drying were added to known amounts of 4-iodoanisole and yield was calculated by1H NMR spectroscopy. Spectroscopically obtained yields agreed with those derived from the mass of TPA within 1.1% in all cases. M.p. >300 ˚C δH(400 MHz, DMSO-d6): 13.26 (br s, 2H), 8.02 (s, 4H) ppm.

[0208] Neutral PET hydrolysis procedure – ionic liquid – catalyst system B

[0209] A 23 mL Teflon® cup was charged with water (10 mL), catalyst (1 mol %)aand polyethylene terephthalate flakes (ca.5 mm squares, 1.000 g). The Teflon® cup was then sealed inside a batch hydrothermal autoclave before being placed into an oven pre-heated at 200 °C for 3 h. The batch hydrothermal autoclave was then placed on a ceramic tile for 16 h. To the reaction mixture was then added sodium hydroxide (0.450 g) and water (6 mL). After 10 min the reaction mixture was filtered and washed with water (10 mL x 2).bThe filtrate was adjusted, with cooling, to pH 2-3 using dilute HCl and the precipitate was filtered. The residue was washed with water (10 mL) and the product was dried for 4 h in a vacuum oven at 60 °C.aMol% of catalyst is related to the number of moles of monomeric units (5.204 mmol) present in 1.000 g of polymer.bTo establish catalyst recyclability, the residue was washed with acetone (2 x 10mL) and the washings concentrated in vacuo.cYield calculated based on the mass of recovered TPA after acidification. To evaluate purity and provide yield data based on an internal standard – samples of TPA post in vacuo drying were added to known amounts of 4-iodoanisole and yield was calculated by1H NMR spectroscopy. Spectroscopically obtained yields agreed with those derived from the mass of TPA within 1.1% in all cases.

[0210] Suitably, the pressure within the autoclave during the hydrolysis reaction is in the range of from 10 to 25 atm, more suitably in the range of from 12 to 20 atm, such as from 12 to 18 atm, for example at approx.15 atm.

[0211] As outlined above, after the neutral hydrolysis reaction has been completed, a simple work-up procedure, involving treatment with base to deprotonate the TPA product, followed by protonation, leads to facile isolation of the TPA product, and isolation from the catalyst. However, an augmented work up procedure, involves washing the PET residue with acetone (e.g. 2 x 10 mL) and concentration of the filtrate in vacuo. This advantageously facilitates catalyst recycling.

[0212] The words “comprises / comprising” and the words “having / including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0213] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub- combination.Embodiments Catalyst System A - Embodiments 1. A method for hydrolysing polyethylene terephthalate comprising: combining poly(ethylene terephthalate), water, and a catalyst, and heating for a time sufficient to hydrolyse at least in part the poly(ethylene terephthalate), wherein the catalyst comprises: (ii) a phase transfer catalyst having a formula selected from: Formula (I)wherein X1is N or P, wherein A1- is an anion, wherein each of R1, R2, R3and R4is independently selected from C1-C20 aliphatic, wherein together R1, R2, R3and R4comprise at least 16 carbon atoms, and wherein at least two of R1, R2, R3and R4are independently selected from C2-C20aliphatic; and (iii) a compound of formula (II):wherein Z+is a cation, optionally, wherein the reaction is carried out a pH in the range of from pH 6 to 8.2. The method of embodiment 1, wherein the reaction is carried out a pH in the range of from pH 6.2 to pH 7.8, further optionally, in the range of from pH 6.5 to pH 7.5. 3. The method of embodiment 1 or 2, wherein each Z+is an alkali metal cation, optionally, each Z+is selected from Na+, K+, Li+, Rb+and Cs+, wherein optionally, each Z+is the same, and / or wherein each Z+is Na+or K+. 4. The method of any preceding embodiment, wherein the compound of formula (I) comprises at least 24 carbon atoms, optionally, at least 28 carbon atoms, further optionally, at least 32 carbon atoms. 5. The method of any preceding embodiment, wherein each of R1, R2, R3and R4is independently selected from C1-C20 aliphatic, optionally C1-C20 alkyl, and at least two of R1, R2, R3and R4are independently selected from C2-C20aliphatic, optionally C2-C20alkyl. 6. The method of any preceding embodiment, wherein at least two of R1, R2, R3and R4are independently selected from C4-C18 alkyl, optionally, from C4-C16 alkyl. 7. The method of any preceding embodiment, wherein two or three of R1, R2, R3and R4are C4-C16alkyl, optionally, C4-C10alkyl, for example, wherein two or three of R1, R2, R3and R4are independently selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl. 8. The method of any preceding embodiment, wherein each of R1, R2, R3and R4is the same. 9. The method of embodiment 8, wherein each of R1, R2, R3and R4is C4-C10alkyl, optionally, each of R1, R2, R3and R4is butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl. 10. The method of any one of embodiments 1 to 7, wherein each of R2, R3and R4are the same and are selected from C4-C12 alkyl, optionally, each of R2, R3and R4are the same and are selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl. 11. The method of any one of embodiments 1 to 7, wherein R1is C1alkyl, optionally, methyl. 12. The method of embodiment 11, wherein R1is C1 alkyl, optionally, methyl, and two or three of R2, R3and R4are independently C6-C16 alkyl, optionally, C6-C12 alkyl. 13. The method of embodiment 12, wherein R1is C1alkyl, optionally, methyl, and three of R2, R3and R4are independently C6-C16alkyl, optionally, C6-C12alkyl. 14. The method of embodiment 13, wherein R1is C1 alkyl, optionally, methyl, and three of R2, R3and R4are the same and are selected from C6-C12 alkyl, optionally, R2, R3and R4arethe same and are selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl. 15. The method of embodiment 11, wherein R1is C1alkyl, optionally, methyl and R2is C1alkyl, optionally, methyl. 16. The method of embodiment 15, wherein R1and R2are each methyl, and R3and R4are independently C6-C16alkyl. 17. The method of embodiment 15, wherein R1and R2are each methyl, and R3and R4are the same and selected from C6-C16 alkyl, optionally, C8-C16 alkyl, suitably, C10-C16 alkyl. 18. The method of any preceding embodiment wherein X1 is N. 19. The method of any one of embodiments 1 to 17, wherein X1is P. 20. The method of any preceding embodiment wherein A1- is selected from Cl-, Br-, F-, I-, BF4-, OMs-, and CF3C(O)O-, preferably Cl-, Br-, or I- 21. The method of any one of embodiments 1 to 3, wherein the compound of formula I is selected from:. 22. The method of any one of embodiments 1 to 3, wherein the compound of formula I is selected from:. The method of any preceding embodiment, wherein the phase transfer catalyst of formula (I) is employed in an amount of 10 mol% or less, preferably in an amount of 5 mol% or less, suitably, in an amount of 2.5 mol% or less, more suitably, in an amount of 1.5 mol%or less relative, most suitably in an amount of 1 mol% or less per mole of monomeric repeating unit of polyethylene terephthalate. 24. The method of any preceding embodiment, further comprising a purification step, optionally where the purification step involves one or more of washing, filtering, and base / acid treatment. 25. The method of embodiment 24, wherein the purification step involves washing with organic solvent, optionally, wherein the organic solvent is acetone, ethyl acetate, dichloromethane and / or chloroform. 26. The method of any preceding embodiment, further comprising a subsequent addition of acid, suitably, a Bronsted acid. 27. The method of embodiment 26, wherein the acid is selected from aqueous HCl, H2SO4, HNO3, CH3COOH, and HBr. Catalyst System B - Embodiments 28. A method for hydrolysis of poly(ethylene terephthalate) comprising: combining poly(ethylene terephthalate), water, and a catalyst, and heating for a time sufficient to hydrolyze at least in part the poly(ethylene terephthalate), wherein the catalyst is a phase transfer catalyst having the formula (III):wherein each Y+has the formula IV:Formula (IV) wherein X1is N or P, wherein each of R1, R2, R3and R4is independently selected from C1-C20aliphatic, wherein together R1, R2, R3and R4comprise at least 16 carbon atoms, and wherein at least two of R1, R2, R3and R4are independently selected from C2-C20 aliphatic, optionally, wherein the reaction is carried out a pH in the range of from pH 6 to 8. 29. The method of embodiment 28, wherein the reaction is carried out a pH in the range of from pH 6.2 to pH 7.8, further optionally, in the range of from pH 6.5 to pH 7.5. 30. The method of embodiment 28 or 29, wherein each Y comprises at least 24 carbon atoms, optionally, at least 28 carbon atoms, further optionally, at least 32 carbon atoms. 31. The method of any one of embodiments 28 to 30, wherein each of R1, R2, R3and R4of each Y is independently selected from C1-C20 alkyl, and at least two of R1, R2, R3and R4are independently selected from C2-C20alkyl. 32. The method of any one of embodiments 28 to 31, wherein at least two of R1, R2, R3and R4of each Y are independently selected from C4-C18 alkyl, optionally, from C4-C16 alkyl. 33. The method of any one of embodiments 28 to 32, wherein two or three of R1, R2, R3and R4of each Y are C4-C16alkyl, optionally, C4-C10alkyl, for example, wherein two or three of R1, R2, R3and R4of each Y are independently selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl. 34. The method of any one of embodiments 28 to 33, wherein each of R1, R2, R3and R4of each Y is the same. 35. The method of embodiment 34, wherein each of R1, R2, R3and R4of each Y is C4-C10alkyl, optionally, wherein each of R1, R2, R3and R4of each Y is butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl. 36. The method of any one of embodiments 28 to 33, wherein each of R2, R3and R4are the same and are selected from C4-C12alkyl, optionally, each of R2, R3and R4are the same and are selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl. 37. The method of any one of embodiments 28 to 33, wherein R1is C1 alkyl, optionally, methyl.38. The method of embodiment 37, wherein R1is C1 alkyl, optionally, methyl, and two or three of R2, R3and R4are independently C6-C16alkyl, optionally, C6-C12alkyl. 39. The method of embodiment 38, wherein R1is C1alkyl, optionally, methyl, and three of R2, R3and R4are independently C6-C16 alkyl, optionally, C6-C12 alkyl. 40. The method of embodiment 39, wherein R1is C1 alkyl, optionally, methyl, and three of R2, R3and R4are the same and are selected from C6-C12alkyl, optionally, R2, R3and R4are the same and are selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl. 41. The method of embodiment 37, wherein R1is C1 alkyl, optionally, methyl and R2is C1 alkyl, optionally, methyl. 42. The method of embodiment 41, wherein R1and R2are each methyl, and R3and R4are independently C6-C16 alkyl. 43. The method of embodiment 41, wherein R1and R2are each methyl, and R3and R4are the same and selected from C6-C16alkyl, optionally, C8-C16alkyl, suitably, C10-C16alkyl. 44. The method of any one of embodiments 28 to 43, wherein X is N. 45. The method of any one of embodiments 28 to 43, wherein X is P. 46. The method of any one of embodiments 28 to 30, wherein the catalyst of formula (III) is selected from:.of embodiments 28 to 46, wherein the catalyst of formula III is employed in an amount of 10 mol% or less, such as in an amount of 5 mol% or less,suitably, in an amount of 2.5 mol% or less, more suitably, in an amount of 1.5 mol% or less, even more suitably in an amount of 1 mol% or less, most suitably in an amount of 0.5 mol% or less per mole of monomeric repeating unit of polyethylene terephthalate. 48. The method of any one of embodiments 28 to 46, further comprising a purification step, optionally where the purification step involves one or more of washing, filtering, and / or base / acid treatment. 49. The method of embodiment 48, wherein the purification step involves washing with organic solvent, optionally, wherein the organic solvent is acetone, ethyl acetate, dichloromethane and / or chloroform. 50. The method of any preceding embodiment, further comprising a subsequent addition of acid, suitably, a Bronsted acid. 51. The method of embodiment 50, wherein the acid is selected from aqueous HCl, H2SO4, HNO3, CH3COOH, and HBr. 52. The method of any preceding embodiment, wherein the hydrolysis reaction is carried out under pressure, suitably, in the range of from 5 to 30 atm, optionally in the range of from 10 to 25 atm, such as from 12 to 20 atm, for example from 12 to 18 atm. 53. The method of any preceding embodiment, wherein the hydrolysis reaction is carried out at a temperature of 150°C or higher, suitably, 180°C or higher. 54. The method of any one of embodiments 1 to 52, wherein the hydrolysis reaction is carried out at a temperature in the range of from 100 to 300°C, optionally, in the range of from 150 to 250°C, optionally in the range of from 180 to 240°C. 55. The method of any preceding embodiment, wherein the hydrolysis reaction is carried out in an autoclave, such as in a hydrothermal autoclave. 56. The method of any preceding embodiment, wherein the (initial) step of combining polyethylene terephthalate, water, and a catalyst, comprises combining polyethylene terephthalate with water in a concentration of 50 to 300 g / L, preferably in a concentration of 80 to 250 g / L, such as from 80 g / L to 220 g / L, for example 80 g / L to 150 g / L. 57. The method of any preceding embodiment, wherein the hydrolysis reaction is carried out at a pressure in the range of from 10 to 25 atm, such as from 12 to 20 atm, and wherein the reaction is carried out at a temperature in the range of from 150 to 250°C, optionally in the range of from 180 to 240°C.58. The method of any one of embodiments 28 to 57, wherein the catalyst of formula III is employed in an amount of 2.5 mol% or less, more suitably, in an amount of 1.5 mol% or less, even more suitably in an amount of 1 mol% or less, most suitably in an amount of 0.5 mol% or less per mole of monomeric repeating unit of polyethylene terephthalate. 59. The method of embodiment 58, wherein the catalyst of formula III is employed in an amount of 1 mol% or less per mole of monomeric repeating unit of polyethylene terephthalate. 60. The method of any one of embodiments 28 to 59, wherein the catalyst of formula III is catalyst 19. 61. The method of any one of embodiments 1 to 21, wherein the compound of formula (I) is:wherein each A- is an anion selected from Cl-, Br- or I-. The method of any preceding embodiment, wherein the hydrolysis reaction is carried out at a pressure in the range of from 10 to 25 atm, such as from 12 to 20 atm, wherein the reaction is carried out at a temperature in the range of from 150 to 250°C, optionally in the range of from 180 to 240°C, and wherein the (initial) step of combining polyethylene terephthalate, water, and a catalyst, comprises combining polyethylene terephthalate with water in a concentration of from 80 to 250 g / L, optionally, in a concentration range of from 80 g / L to 220 g / L, for example 80 g / L to 150 g / L. The method of any preceding embodiment, wherein the hydrolysis reaction is carried out at a pressure in the range of from 12 to 20 atm, wherein the reaction is carried out at a temperature in the range of from 150 to 250°C, and wherein the (initial) step of combining polyethylene terephthalate, water, and a catalyst, comprises combining polyethylene terephthalate with water in a concentration of from 80 to 250 g / L. The method of embodiment 63, wherein the hydrolysis reaction is carried out at a pressure in the range of from 12 to 20 atm, wherein the reaction is carried out at a temperature in the range of from 180 to 240°C, and wherein the (initial) step of combining polyethylene terephthalate, water, and a catalyst, comprises combining polyethylene terephthalate with water in a concentration of from 80 g / L to 220 g / L. The method of any preceding embodiment, wherein the terephthalic acid formed from the hydrolysis reaction is further processed to form calcium terephthalate, optionally, wherein a metal-organic framework of calcium terephthalate is formed.

Claims

Claims 1. A method for hydrolysis of poly(ethylene terephthalate) comprising: combining poly(ethylene terephthalate), water, and a catalyst, and heating for a time sufficient to hydrolyze at least in part the poly(ethylene terephthalate), wherein the catalyst is a phase transfer catalyst having the formula (III):Formula (III) wherein each Y+has the formula IV:Formula (IV) wherein X1is N or P, wherein each of R1, R2, R3and R4is independently selected from C1-C20 aliphatic, wherein together R1, R2, R3and R4comprise at least 16 carbon atoms, and wherein at least two of R1, R2, R3and R4are independently selected from C2-C20aliphatic, wherein the reaction is carried out at a pH in the range of from pH 6 to 8.

2. The method of claim 1, wherein the reaction is carried out a pH in the range of from pH 6.2 to pH 7.8, further optionally, in the range of from pH 6.5 to pH 7.5.

3. The method of claim 1 or 2, wherein each Y comprises at least 24 carbon atoms, optionally, at least 28 carbon atoms, further optionally, at least 32 carbon atoms.

4. The method of any preceding claim, wherein each of R1, R2, R3and R4of each Y is independently selected from C1-C20 alkyl, and at least two of R1, R2, R3and R4are independently selected from C2-C20 alkyl.

5. The method of any preceding claim, wherein at least two of R1, R2, R3and R4of each Y are independently selected from C4-C18alkyl, optionally, from C4-C16alkyl.

6. The method of any preceding claim, wherein two or three of R1, R2, R3and R4of each Y are C4-C16 alkyl, optionally, C4-C10 alkyl, for example, wherein two or three of R1, R2, R3and R4of each Y are independently selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl.

7. The method of any preceding claim, wherein each of R1, R2, R3and R4of each Y is the same, optionally, wherein each of R1, R2, R3and R4of each Y is C4-C10 alkyl, optionally, wherein each of R1, R2, R3and R4of each Y is butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl.

8. The method of any one of claims 1 to 6, wherein R1is C1 alkyl, optionally, methyl, and two or three of R2, R3and R4are independently C6-C16 alkyl, optionally, C6-C12 alkyl.

9. The method of claim 8, wherein R1is C1alkyl, optionally, methyl, and three of R2, R3and R4are independently C6-C16alkyl, optionally, C6-C12alkyl.

10. The method of claim 9, wherein R1is C1 alkyl, optionally, methyl, and three of R2, R3and R4are the same and are selected from C6-C12 alkyl, optionally, R2, R3and R4are the same and are selected from butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl.

11. The method of any preceding claim, wherein the catalyst of formula (III) is selected from compound 18, compound 19 or compound 20 as shown below:.

12. The method of any preceding claim, wherein the catalyst is employed in an amount 2.5 mol% or less, more suitably, in an amount of 1.5 mol% or less, even more suitably in an amount of 1 mol% or less, most suitably in an amount of 0.5 mol% or less per mole of monomeric repeating unit of polyethylene terephthalate.

13. The method of any preceding claim, further comprising a purification step, optionally where the purification step involves one or more of washing, filtering, and / or base / acid treatment, optionally, wherein the purification step involves washing with organic solvent, optionally, wherein the organic solvent is acetone, ethyl acetate, dichloromethane and / or chloroform.

14. The method of any preceding claim, wherein the hydrolysis reaction is carried out under pressure, and / or wherein the hydrolysis reaction is carried out at a temperature in the range of from 100 to 300°C, optionally, in the range of from 150 to 250°C; optionally, wherein the hydrolysis reaction is carried out in an autoclave.

15. The method of any preceding claim, wherein the (initial) step of combining polyethylene terephthalate, water, and a catalyst, comprises combining polyethylene terephthalate with water in a concentration of 50 to 300 g / L, preferably in a concentration of 80 to 250 g / L, such as from 80 g / L to 220 g / L, for example 80 g / L to 150 g / L. FRKelly

Images