Method of depolymerizing a polyester of dicarboxylic acid

Abstract

There is provided a method of depolymerizing a polyester of a dicarboxylic acid, the method comprising: (a-i) depolymerizing a polyester of a dicarboxylic acid source in the presence of: (i) a mono-base system; and (ii) a solvent system comprising three or more different solvents, to obtain a product comprising a mono-salt of a monoester of the dicarboxylic acid and / or derivatives thereof.

Description

[0001] METHOD OF DEPOLYMERIZING A POLYESTER OF DICARBOXYLIC ACID

[0002] TECHNICAL FIELD

[0003] The present disclosure relates broadly to a method of depolymerizing a polyester of a dicarboxylic acid to obtain a product comprising a mono-salt of a monoester of the dicarboxylic acid and / or derivatives thereof.

[0004] BACKGROUND

[0005] Polyesters derived from dicarboxylic acids, e g., polyethylene terephthalate (PET) are the most widely used thermoplastics, with an annual production of 80.9 million tons in 2021. Their widespread utilization in packaging and textile industries, notably in the production of manufacturing bottles (e.g., for beverages and personal care items) and containers (e.g., for storing food, fruits, and eggs), is attributed to their exceptional physical properties / attributes, transparency, and thermal stability.

[0006] However, this extensive application leads to the generation of substantial quantity of PET waste worldwide annually. To promote environmental sustainability / protection and resource conservation, it is imperative to recycle or upcycle waste polyesters derived from dicarboxylic acids (e.g., PET) into valuable fine chemicals.

[0007] A key technological challenge to recycle or upcycle waste polyesters derived from dicarboxylic acids (e.g., PET) is to develop an efficient method for recycling or upcycling waste PET back into its monomers or fine chemicals. Among these, terephthalic acid (TPA) and dimethyl terephthalate (DMT) are two important monomers used in the production of virgin PET resin in current industries. Currently, there are three known methods to recycle / upcycle waste PET, including (1 ) hydrolysis into TPA, (2) methanolysis into DMT, and (3) glycolysis into bis-(2-hydroxyethyl) terephthalate (BHET). Despite their utility, however, these recycling and / or upcycling methods suffer from several limitations and are far from desirable. In particular, current techniques require high reaction temperatures (e.g., up to 183° C or more), making the processes energyconsuming and energy-intensive. Additionally, the known methods typically require high consumption of base (e.g., NaOH) and / or a large amount of acid (e.g., hydrochloric acid) in the acidification step, therefore resulting in an overall high material and operational costs. Current methods also encounter issues with slow and long reaction time (e g., of 24 hours). Furthermore, the desired products are often obtained with low selectivity and the final product mixture often includes oligomers or various by-products, reducing process efficiency and complicating downstream purification.

[0008] In view of the above, there is a need to address or at least ameliorate the above-mentioned problems. In particular, there is a need to provide a simple, efficient and environmentally sustainable method for recycling and upcycling polyesters derived from dicarboxylic acids.

[0009] SUMMARY

[0010] In one aspect, there is provided a method of depolymerizing a polyester of a dicarboxylic acid, the method comprising:

[0011] (a-i) depolymerizing a polyester of a dicarboxylic acid source in the presence of:

[0012] (i) a mono-base system; and

[0013] (ii) a solvent system comprising three or more different solvents, to obtain a product comprising a mono-salt of a monoester of the dicarboxylic acid and / or derivatives thereof. In one embodiment, the polyester of a dicarboxylic acid source comprises waste polyester of a dicarboxylic acid.

[0014] In one embodiment, the polyester of a dicarboxylic acid comprises a structure that is represented by general formula (1 ): wherein

[0015] A is optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocycloalkyl, optionally substituted heterocycloalkenyl, optionally substituted heteroaryl, or combinations thereof;

[0016] R1is optionally substituted alkylene, optionally substituted cycloalkylene, optionally substituted alkenylene, optionally substituted alkynylene, or combinations thereof; and n > 1.

[0017] In one embodiment, A comprises 1 ,4-disubstituted benzene and the polyester of a dicarboxylic acid comprises a structure that is represented by general formula (2): wherein

[0018] R2is optionally substituted alkylene, optionally substituted cycloalkylene, optionally substituted alkenylene, optionally substituted alkynylene, or combinations thereof; Ra, Rb, Rcand Rdare each independently hydrogen, halogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy, or combinations thereof; and n > 1.

[0019] In one embodiment, the depolymerizing in (a-i) comprises a plurality of alcoholysis and hydrolysis reactions.

[0020] In one embodiment, the depolymerizing in (a-i) comprises the following reaction: wherein A is optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocycloalkyl, optionally substituted heterocycloalkenyl, optionally substituted heteroaryl, or combinations thereof;

[0021] R1is optionally substituted alkylene, optionally substituted cycloalkylene, optionally substituted alkenylene, optionally substituted alkynylene, or combinations thereof;

[0022] R4and R4’ are each independently optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, or combinations thereof; and

[0023] M is a metal or ammonium-containing group; and n > 1.

[0024] In one embodiment, the mono-salt of a monoester of the dicarboxylic acid comprises a structure that is represented by general formula (3): wherein

[0025] A is optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocycloalkyl, optionally substituted heterocycloalkenyl, optionally substituted heteroaryl, or combinations thereof;

[0026] R3is optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, or combinations thereof; and M is a metal or ammonium-containing group. In one embodiment, A comprises 1 ,4-disubstituted benzene and the mono-salt of a monoester of the dicarboxylic acid comprises a structure that is represented by general formula (4): wherein

[0027] R4is optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, or combinations thereof;

[0028] R1 a, R1b, R1 cand R1dare each independently hydrogen, halogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy, or combinations thereof; and

[0029] M is a metal or ammonium-containing group.

[0030] In one embodiment, M is an alkali metal selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) or francium (Fr).

[0031] In one embodiment, the mono-base system is configured to concurrently serve as a catalyst as well as a reactant in the depolymerization reaction.

[0032] In one embodiment, the mono-base system comprises an inorganic base.

[0033] In one embodiment, the inorganic base comprises an Arrhenius base selected from the group consisting of metal hydroxides, alkali metal hydroxides, alkaline earth metal hydroxides, ammonium-containing hydroxides and combinations thereof. In one embodiment, the solvent system comprises three or more different solvents selected from the group consisting of:

[0034] (a) an aprotic solvent;

[0035] (b) a protic solvent; and

[0036] (c) a hydrocarbon compound.

[0037] In one embodiment, the aprotic solvent is selected from the group consisting of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), acetonitrile (ACN), acetone (ACE), methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, cyclohexanone, 2-pentanone (also known as methyl propyl ketone), 3-pentanone (also known as diethyl ketone), diethyl ether, methyl tert-butyl ether (MTBE), tert-amyl methyl ether (TAME), cyclopentyl methyl ether (CPME), methoxybenzene (also known as anisole), ethoxybenzene, sulfolane (also known as tetramethylene sulfone), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMA), a,a-trifluorotoluene (TFT), dichloromethane (DCM), chlorobenzene, and combinations thereof.

[0038] In one embodiment, the protic solvent is selected from the group consisting of methanol, ethanol, n-propanol, / sopropanol, n-butanol, ferf-butanol, allyl alcohol, propargyl alcohol, and combinations thereof.

[0039] In one embodiment, the hydrocarbon compound is selected from the group consisting of n-pentane, n-hexane, n-heptane, n-octane, 2-methylpentane, 3- methylpentane, cyclohexane, benzene, toluene, xylene, 1 ,2-dimethylbenzene, 1 ,3-dimethylbenzene, 1 ,4-dimethylbenzene, and combinations thereof.

[0040] In one embodiment, the volume ratio of the aprotic solvent to the protic solvent is from 1 : 10 to 50: 1 . In one embodiment, the volume ratio of the aprotic solvent plus the protic solvent to the hydrocarbon compound is from 1 :1 to 75:1 .

[0041] In one embodiment, the molar ratio of the mono-base to the number of repeating units in polyester is 0.1 to 2.

[0042] In one embodiment, the method further comprises:

[0043] (a-ii) reacting the product comprising the mono-salt of a mono ester of the dicarboxylic acid with a base to obtain a solution comprising di-alkali metal salt of the dicarboxylic acid.

[0044] In one embodiment, the method further comprises:

[0045] (a-iii) reacting the solution comprising the di-alkali metal salt of the dicarboxylic acid obtained from (a-ii) with an oxidant / oxidizing agent to obtain a decoloured solution comprising the di-alkali metal salt of the dicarboxylic acid.

[0046] In one embodiment, the method further comprises:

[0047] (a-iv) reacting the solution obtained from (a-ii) or (a-iii) with an acid to obtain a dicarboxylic acid.

[0048] In one embodiment, the dicarboxylic acid comprises a structure that is represented by general formula (8): wherein

[0049] R3a, R3b, R3cand R3dare each independently hydrogen, halogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy, or combinations thereof.

[0050] In one embodiment, the dicarboxylic acid is selected from the group comprising terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,5-furandicarboxylic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, 1 ,4-cyclohexanedicarboxylic acid, acetylene dicarboxylic acid, and combinations thereof.

[0051] In one embodiment, the method further comprises:

[0052] (a-v) isolating ethylene glycol from the solution obtained from step (a-i).

[0053] DEFINITIONS

[0054] The term “polyester” as used herein is to be interpreted broadly to refer to a polymer which contains one or more ester linkage(s) that connect(s) monomeric units in said polymer.

[0055] The term "polymer" as used herein refers to a chemical compound comprising repeating units and is created through a process of polymerization. The units composing the polymer are typically derived from monomers and / or macromonomers. A polymer typically comprises repetition of a number of constitutional units.

[0056] The terms “monomer” or “macromonomer” as used herein refer to a chemical entity that may be covalently linked to one or more of such entities to form a polymer.

[0057] The term "bond" refers to a linkage between atoms in a compound or molecule. The bond may be a single bond, a double bond, or a triple bond. In the definitions of a number of substituents below, it is stated that “the group may be a terminal group or a bridging group”. This is intended to signify that the use of the term is intended to encompass the situation where the group is a terminal group / moiety as well as the situation where the group is a linker between two other portions of the molecule. Using the term “alkyl” having 1 carbon atom as an example, it will be appreciated that when existing as a terminal group, the term “alkyl” having 1 carbon atom may mean -CHs and when existing as a bridging group, the term “alkyl” having 1 carbon atom may mean -CH2- or the like.

[0058] The terms "alkyl" or “alkylene” as a group or part of a group refers to a straight or branched aliphatic hydrocarbon group having 1 to 20 carbon atoms, 1 to 10 carbon atoms, 1 to 6 carbon atoms, or 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms. Examples of suitable straight and branched alkyl substituents include methyl, ethyl, n-propyl, 2-propyl, isopropyl, n- butyl, isobutyl, sec-butyl, t-butyl, hexyl, amyl, 1 ,2-dimethylpropyl, 1 ,1 - dimethylpropyl, pentyl, isopentyl, hexyl, 4-methylpentyl, 1 -methylpentyl, 2- methylpentyl, 3-methylpentyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl, 1 ,2- dimethylbutyl, 1 ,3-dimethylbutyl, 1 ,2,2-trimethylpropyl, 1 , 1 ,2-trimethylpropyl, 2- ethylpentyl, 3-ethylpentyl, heptyl, 1 -methylhexyl, 2,2-dimethylpentyl, 3,3- dimethylpentyl, 4,4-dimethylpentyl, 1 ,2-dimethylpentyl, 1 ,3-dimethylpentyl, 1 ,4- dimethylpentyl, 1 ,2,3-trimethylbutyl, 1 , 1 ,2-trimethylbutyl, 1 ,1 ,3-trimethylbutyl, 5- methylheptyl, 1 -methylheptyl, octyl, nonyl, decyl and the like. The group may be a terminal group or a bridging group.

[0059] The terms "alkenyl" or “alkenylene” as a group or part of a group denotes an aliphatic hydrocarbon group containing at least one carbon-carbon double bond and which may be straight or branched having 2 to 20 carbon atoms, 2 to 10 carbon atoms, 2 to 6 carbon atoms, or 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms in the chain. The group may contain a plurality of double bonds and the orientation about each double bond is independently E or Z. Exemplary alkenyl groups include, but are not limited to, ethenyl, vinyl, allyl, 1 -methylvinyl, 1 -propenyl, 2-propenyl, 2-methyl-1 -propenyl, 2-methyl-1 -propenyl, 1-butenyl, 2-butenyl, 3-butentyl, 1 ,3-butadienyl, 1 -pentenyl, 2-pententyl, 3-pentenyl, 4-pentenyl, 1 ,3-pentadienyl, 2,4-pentadienyl, 1 ,4- pentadienyl, 3-methyl-2-butenyl, 1 -hexenyl, 2-hexenyl, 3-hexenyl, 1 ,3- hexadienyl, 1 ,4-hexadienyl, 2-methylpentenyl, 1 -heptenyl, 2-heptentyl, 3- heptenyl, 1 -octenyl, 2-octenyl, 3-octenyl, 1 -nonenyl, 2-nonenyl, 3-nonenyl, 1 - decenyl, 2-decenyl, 3-decenyl and the like. The group may be a terminal group or a bridging group.

[0060] The terms "alkynyl" or “alkynylene” as a group or part of a group denotes an aliphatic hydrocarbon group containing at least one carbon-carbon triple bond and which may be straight or branched having 2 to 20 carbon atoms, 2 to 10 carbon atoms, 2 to 6 carbon atoms, or 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms in the chain. The group may contain a plurality of triple bonds. Exemplary alkynyl groups include, but are not limited to, acetylenyl, propynyl, 1-butynyl, 2-butynyl, 3-butynyl, 1 -pentynyl, 2-pentynyl, 3- methyl-1 -butynyl, 4-pentynyl, 1 -hexynyl, 2-hexynyl, 5-hexynyl, 1 -heptynyl, 2- heptynyl, 6-heptynyl, 1 -octynyl, 2-octynyl, 7-octynyl, 1 -nonynyl, 2-nonynyl, 8- nonynyl, 1 -decynyl, 2-decynyl, 9-decynyl and the like. The group may be a terminal group or a bridging group.

[0061] The term “cyclic” as used herein broadly refers to a structure where one or more series of atoms are connected to form at least one ring. The term includes, but is not limited to, both saturated and unsaturated 5-membered and saturated and unsaturated 6-membered rings. Examples of groups having a cyclic structure include, but are not limited to, cyclopentane, cyclopentene, cyclohexane, cyclohexene, benzene and the like. The term “cyclic” as used herein includes “heterocyclic”.

[0062] The term “heterocyclic” as used herein broadly refers to a structure where two or more different kinds of atoms are connected to form at least one ring. For example, a heterocyclic ring may be formed by carbon atoms and at least another atom (i.e. heteroatom) selected from oxygen (O), nitrogen (N) or (NR) and sulfur (S), where R is independently a hydrogen or an organic group. The term also includes, but is not limited to, saturated and unsaturated 5-membered, and saturated and unsaturated 6-membered rings. Examples of groups having a heterocyclic structure include, but are not limited to furan, thiophene, 1 H-pyrrole, 2H-pyrrole, 1 -pyrroline, 2-pyrroline, 3-pyrroline, 1-pyrazoline, 2-pyrazoline, 3- pyrazoline, 2-imidazoline, 3-imidazoline, 4-imidazoline, pyrazole, imidazole, oxazole, isoxazole, thiazole, isothiazole, 1 ,2,3-triazole, 1 ,2,4-triazole, 1 ,2,3- oxadiazole, disubstituted 1 ,2,4-oxadiazole, 1 ,2,5-oxadiazole, 1 ,3,4-oxadiazole,

[0063] 1 .2.3-thiadiazole, 1 ,2,4-thiadiazole, 1 ,2,5-thiadiazole, 1 ,3,4-thiadiazole, tetra hydrofuran, tetrahydrothiophene, pyrrolidine, 1 ,3-dioxolane, 1 ,2-oxathiolane,

[0064] 1.3-oxathiolane, pyrazolidine, imidazolidine, pyridine, pyridazine, pyrimidine, pyrazine, 1 ,2-oxazine, 1 ,3-oxazine, 1 ,4-oxazine, thiazine, 1 ,2,3-triazine, 1 ,2,4- triazine, 1 ,3,5-triazine, 2H-pyran, 4H-pyran, 2-pyrone, 4-pyrone, 1 ,4-dioxin, 2H- thiopyran, 4H-thiopyran, tetrahydropyran, thiane, piperidine, 1 ,4-dioxane, 1 ,2- dithiane, 1 ,3-dithiane, 1 ,4-dithiane, 1 ,3,5-trithiane, piperazine, morpholine, thiomorpholine and the like.

[0065] The term "aryl" as a group or part of a group denotes (i) an optionally substituted monocyclic, or fused polycyclic, aromatic carbocycle (ring structure having ring atoms that are all carbon) preferably having from 5 to 20, or 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms per ring. Examples of aryl groups include but are not limited to phenyl, tolyl, xylyl, naphthyl, anthracenyl, phenanthrenyl, fluorenyl, indenyl or indanyl and the like.

[0066] The term "heteroaryl" as a group or part of a group refers to groups containing an aromatic ring (preferably a 5- or 6- membered aromatic ring) having one or more carbon atoms (for example 1 to 6 carbon atoms) in the ring replaced by a heteroatom. Suitable heteroatoms may include nitrogen (N) or (NH), oxygen (O) and sulfur (S). Examples of heteroaryl include but are not limited to thiophene, benzothiophene, benzofuran, benzimidazole, benzoxazole, benzothiazole, benzisothiazole, naphtha[2,3-b]thiophene, furan, isoindolizine, xantholene, phenoxatine, pyrrole, imidazole, pyrazole, pyridine, pyrazine, pyrimidine, pyridazine, tetrazole, indole, isoindole, 1 H-indazole, purine, quinoline, isoquinoline, phthalazine, naphthyridine, quinoxaline, cinnoline, carbazole, phenantridine, acridine, phenazine, thiazole, isothiazole, phenothiazine, oxazole, isooxazole, furazane, phenoxazine, 2-, 3- or 4-pyridyl, 2-, 3-, 4-, 5-, or 8-quinolyl, 1 -, 3- 4-, or 5-isoquinolinyl 1-, 2-, or 3-indolyl, and 2-, or 3-thienyl and the like. The group may be a terminal group or a bridging group.

[0067] The term "heteroalkylene" as used herein refers to alkylene having one or more -CH2- replaced with a heteroatom selected from 0, NR, Si, P or S, where R is hydrogen or alkyl as defined herein. The term "heteroalkylene" can be linear, branched or cyclic and containing up to 500 carbon atoms.

[0068] The term "halogen" represents chlorine, fluorine, bromine or iodine. The term "halide" represents chloride, fluoride, bromide or iodide. The term "halo" represents chloro, fluoro, bromo or iodo.

[0069] The term "amine group" or the like is intended to broadly refer to a group containing -NR2, where R is independently a hydrogen or an organic group. The group may be a terminal group or a bridging group.

[0070] The term "amide group" or the like is intended to broadly refer to a group containing -C(=O)NR2, where R is independently a hydrogen or an organic group. The group may be a terminal group or a bridging group.

[0071] The term “optionally substituted,” when used to describe a chemical structure or moiety, refers to the chemical structure or moiety wherein one or more of its hydrogen atoms is optionally substituted with a chemical moiety or functional group such as alcohol, alkoxy, alkanoyloxy, alkoxycarbonyl, alkenyl, alkyl (e g., methyl, ethyl, propyl, t-butyl), alkynyl, alkylcarbonyloxy (-OC(O)alkyl), amide (-C(O)NH-alkyl- or -alkylNHC(O)alkyl), amine (such as alkylamino, arylamino, arylalkylamino), aryl, aryloxy, azo, carbamoyl (-NHC(O)O-alkyl- or -OC(O)NH-alkyl), carbamyl (e.g., CONH2, as well as CONH-alkyl, CONH-aryl, and CONH-arylalkyl), carboxyl, carboxylic acid, cyano, ester, ether (e.g., methoxy, ethoxy), halo, haloalkyl (e.g., -CCI3, -CFs, -C(CF3)s), heteroalkyl, isocyanate, isothiocyanate, nitrile, nitro, phosphodiester, sulfide, sulfonamido (e.g., SO2NH2), sulfone, sulfonyl (including alkylsulfonyl, arylsulfonyl and arylalkylsulfonyl), sulfoxide, thiol (e.g., sulfhydryl, thioether) or urea (-NHCONH-alkyl-).

[0072] The term "dicarboxylic acid" as used herein refers to an organic compound comprising two carboxyl functional groups (-COOH) covalently bonded to a carbon-based backbone, which may be linear, branched, alicyclic, or aromatic. The carboxyl groups may be positioned at terminal or non-terminal locations within the molecular structure. Dicarboxylic acids may include, but are not limited to, aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, and aromatic dicarboxylic acids such as phthalic acid and terephthalic acid. The term encompasses both naturally occurring and synthetically derived compounds, including their salts, esters, and derivatives, unless the context otherwise requires.

[0073] The term "waste" as used herein refers to any material, substance, or byproduct that is unwanted, unusable, or discarded as a result of industrial, commercial, domestic, medical, agricultural, or biological processes, including but not limited to solids, liquid, sludge or particulate matter, regardless of whether such material retains residual utility or value.

[0074] The term “particle” as used herein broadly refers to a discrete entity or a discrete body. The particle described herein can include an organic, an inorganic, a composite particle or a biological particle. The particle used described herein may also be a macro-particle that is formed by an aggregate of a plurality of subparticles or a fragment of a small object. The particle of the present disclosure may be spherical, substantially spherical, or non-spherical, such as irregularly shaped particles or ellipsoidally shaped particles. The term “size” when used to refer to the particle broadly refers to the largest dimension of the particle. For example, the term “size” when used in the context of nanoparticle can refer to the diameter of the nanoparticle although it is not limited as such. In various embodiments, when the particle is substantially spherical, the term “size” can refer to the diameter of the particle; or when the particle is substantially non- spherical, the term “size” can refer to the largest length of the particle.

[0075] The term "micro" as used herein is to be interpreted broadly to include dimensions from about 1 micron to about 1000 microns, about 1 micron to less than about 1000 microns, about 1 micron to about 900 microns, about 1 micron to about 800 microns, about 1 micron to about 700 microns, about 1 micron to about 600 microns, about 1 micron to about 500 microns, about 1 micron to about 400 microns, about 1 micron to about 300 microns, about 1 micron to about 200 microns, or from about 1 micron to about 100 microns.

[0076] The term "nano" as used herein is to be interpreted broadly to include dimensions in a nanoscale, i.e., less than about 1000 nm, about 1 nm to less than about 1000 nm, about 1 nm to about 900 nm, about 1 nm to about 800 nm, about 1 nm to about 700 nm, about 1 nm to about 600 nm, about 1 nm to about 500 nm, about 1 nm to about 400 nm, about 1 nm to about 300 nm, about 1 nm to about 200 nm, or from about 1 nm to about 100 nm. Accordingly, the term “nanostructures”, “nanoparticles”, “nanomaterials” and the like as used herein may include structures that have at least one dimension in the range of no more than said range. The term “nanostructures”, “nanoparticles", “nanomaterials” and the like as used herein may include structures that have at least one dimension that is no more than about 100 nm, no more than about 90 nm, no more than about 80 nm, no more than about 70 nm, no more than about 60 nm, no more than about 50 nm, no more than about 40 nm, no more than about 30 nm, no more than about 20 nm, or no more than about 10 nm.

[0077] The term “nanostructure” as used herein broadly refers to an arrangement of interrelated elements in a system having at least one dimension in the nanoscale. The nanostructure described herein can include a nanoparticle, nanorod, nanofiber, nanoneedle, nanoplate, nanotube, and the like. The term “size” when used in the context of nanoparticle can refer to the diameter of the nanoparticle although it is not limited as such.

[0078] The term “particle” as used herein broadly refers to a discrete entity or a discrete body. The particle described herein can include an organic, an inorganic, a composite particle or a biological particle. The particle used described herein may also be a macro-particle that is formed by an aggregate of a plurality of subparticles or a fragment of a small object. The particle of the present disclosure may be spherical, substantially spherical, or non-spherical, such as irregularly shaped particles or ellipsoidally shaped particles. The term “size” when used to refer to the particle broadly refers to the largest dimension of the particle. For example, when the particle is substantially spherical, the term “size” can refer to the diameter of the particle; or when the particle is substantially non-spherical, the term “size” can refer to the largest length of the particle.

[0079] The terms "coupled" or "connected" as used in this description are intended to cover both directly connected or connected through one or more intermediate means, unless otherwise stated.

[0080] The term "associated with", used herein when referring to two elements refers to a broad relationship between the two elements. The relationship includes, but is not limited to a physical, a chemical or a biological relationship. For example, when element A is associated with element B, elements A and B may be directly or indirectly attached to each other or element A may contain element B or vice versa.

[0081] The term "adjacent" used herein when referring to two elements refers to one element being in close proximity to another element and may be but is not limited to the elements contacting each other or may further include the elements being separated by one or more further elements disposed therebetween. The term "and / or", e.g., "X and / or Y" is understood to mean either "X and Y" or "X or Y" and should be taken to provide explicit support for both meanings or for either meaning.

[0082] Further, in the description herein, the word “substantially” whenever used is understood to include, but not restricted to, "entirely" or “completely” and the like. In addition, terms such as "comprising", "comprise", and the like whenever used, are intended to be non-restricting descriptive language in that they broadly include elements / components recited after such terms, in addition to other components not explicitly recited. For example, when “comprising" is used, reference to a “one” feature is also intended to be a reference to “at least one” of that feature. Terms such as “consisting”, “consist”, and the like, may in the appropriate context, be considered as a subset of terms such as "comprising", "comprise", and the like. Therefore, in embodiments disclosed herein using the terms such as "comprising", "comprise", and the like, it will be appreciated that these embodiments provide teaching for corresponding embodiments using terms such as “consisting”, “consist", and the like. Further, terms such as "about", "approximately" and the like whenever used, typically means a reasonable variation, for example a variation of + / - 5% of the disclosed value, or a variance of 4% of the disclosed value, or a variance of 3% of the disclosed value, a variance of 2% of the disclosed value or a variance of 1 % of the disclosed value.

[0083] Furthermore, in the description herein, certain values may be disclosed in a range. The values showing the end points of a range are intended to illustrate a preferred range. Whenever a range has been described, it is intended that the range covers and teaches all possible sub-ranges as well as individual numerical values within that range. That is, the end points of a range should not be interpreted as inflexible limitations. For example, a description of a range of 1% to 5% is intended to have specifically disclosed sub-ranges 1 % to 2%, 1 % to 3%, 1 % to 4%, 2% to 3% etc., as well as individually, values within that range such as 1 %, 2%, 3%, 4% and 5%. It is to be appreciated that the individual numerical values within the range also include integers, fractions and decimals. Furthermore, whenever a range has been described, it is also intended that the range covers and teaches values of up to 2 additional decimal places or significant figures (where appropriate) from the shown numerical end points. For example, a description of a range of 1 % to 5% is intended to have specifically disclosed the ranges 1.00% to 5.00% and also 1.0% to 5.0% and all their intermediate values (such as 1.01 %, 1.02% ... 4.98%, 4.99%, 5.00% and 1.1 %, 1.2% ... 4.8%, 4.9%, 5.0% etc.,) spanning the ranges. The intention of the above specific disclosure is applicable to any depth / breadth of a range.

[0084] Additionally, when describing some embodiments, the disclosure may have disclosed a method and / or process as a particular sequence of steps. However, unless otherwise required, it will be appreciated that the method or process should not be limited to the particular sequence of steps disclosed. Other sequences of steps may be possible. The particular order of the steps disclosed herein should not be construed as undue limitations. Unless otherwise required, a method and / or process disclosed herein should not be limited to the steps being carried out in the order written. The sequence of steps may be varied and still remain within the scope of the disclosure.

[0085] Furthermore, it will be appreciated that while the present disclosure provides embodiments having one or more of the features / characteristics discussed herein, one or more of these features / characteristics may also be disclaimed in other alternative embodiments and the present disclosure provides support for such disclaimers and these associated alternative embodiments.

[0086] It will also be appreciated that where priority is claimed to an earlier application, the full contents of the earlier application are also taken to form part of the present disclosure and may serve as support for embodiments disclosed herein. DESCRIPTION OF EMBODIMENTS

[0087] Exemplary, non-limiting embodiments of a method of depolymerizing a polyester of a dicarboxylic acid are disclosed hereinafter.

[0088] There is provided a method of depolymerizing a polyester of a dicarboxylic acid (or polyester) into depolymerization / recycled / upcycled / degradation product(s). The polyester of a dicarboxylic acid may be derived from a polyester containing source which includes but is not limited to polyester-based waste, polyester waste, waste polyester, unwanted polyester, waste polyester of a dicarboxylic acid, unwanted polyester of a dicarboxylic acid or the like. In various embodiments, the method comprises recycling / upcycling / breaking down (e.g., chemical recycling / upcycling / breaking down) waste polyester into valuable products / chemicals. Advantageously, in various embodiments, the method disclosed herein allows waste polyester to be recycled / upcycled / converted directly into forms that are useful on their own or useful as feedstocks for further applications.

[0089] In various embodiments, the polyester of a dicarboxylic acid source is provided in the form of a solid, e.g., in the form of an article. The polyester of a dicarboxylic acid source may be a packaging material (such as protective / food packaging, bottle, box, film, mold, fabric, textile, container, lid, tray, disposable cutlery), polyethylene terephthalate (PET) waste, PET post-consumer products, mixed / blended fabrics of PET-cotton or PET-cotton-spandex or PET-cotton- nylon, multi-layer films of PET-PE or PET-PP, mixed plastic waste of PET with other plastics such as polyethylene (PE), propylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polyethylene furanoate (PEF), poly(butylene adipate) (PBA), poly(butylene succinate) (PBS), and poly(butylene sebacate) (PBSb), and block copolymer of polyesters, the like or combinations thereof. The polyester of a dicarboxylic acid may be obtained or derived from a source such as a waste source containing unwanted polyester of a dicarboxylic acid. The polyester of a dicarboxylic acid source may also comprise additives, impurities, chemicals, materials, components and / or contaminants such as dyes, plasticizers, pigments, colouring agents, printing inks, fillers such as titanium oxide or zinc oxide, flame retardants, lubricants, adhesives, paper, cotton, fabric, nylon, spandex, cellulose material, polyethylene (PE), propylene (PP), or the like or combinations thereof, which may be present in amounts of at least about 1 wt%, at least about 5 wt%, at least about 10 wt%, at least about 15 wt%, at least about 20 wt%, at least about 25 wt%, at least about 30 wt%, at least about 35 wt%, at least about 40 wt%, at least about 45 wt%, at least about 50 wt%, at least about 55 wt%, at least about 60 wt%, at least about 65 wt%, or at least 70 wt%. Advantageously, in various embodiments, the polyester of a dicarboxylic acid source does not require pre-treatment, e.g., chemical / physical steps to remove said additives, impurities, chemicals, materials, components, and / or any other contaminants (e.g., dirt or food waste) present in the source. Even more advantageously, the presence of additives, impurities, chemicals, materials, components, and / or contaminants in the polyester of a dicarboxylic acid source does not substantially prevent / deter the method from working efficiently and / or effectively. In various embodiments, the method disclosed herein allows the polyester of a dicarboxylic acid source to be recycled / upcycled / converted successfully into depolymerization products, even in the presence of additives, impurities, chemicals, materials, components, and / or contaminants. Advantageously, in various embodiments, the method is minimally affected by presence of additives and dyes. Advantageously, in various embodiments, the efficiency, product / conversion yield and / or selectivity of the method (or depolymerization step) is not impeded by presence of additives and / or dyes. In various embodiments therefore, the method is substantially devoid of a pre-treatment step to remove additives, impurities, chemicals, materials, components, and / or any other contaminants (e.g., dirt or food waste) from the polyester of a dicarboxylic acid source. It will, however, be appreciated that the polyester of a dicarboxylic acid source may be inspected for non-polyester of a dicarboxylic acid components / parts / contam inants and processed to remove such components / parts / contaminants prior to use. For example, a polyester-based packaging may be inspected and processed to remove parts such as food waste before use. In various embodiments, the polyester of a dicarboxylic acid is substantially non-biodegradable (e.g., PET, PBT, the like, or combinations thereof) or substantially biodegradable (e.g., PBA, PBS, the like, or combinations thereof). In various embodiments, the polyester of a dicarboxylic acid is substantially non-biodegradable.

[0090] In various embodiments, the method further comprises, prior to the depolymerizing / degrading / recycling / upcycling step, a pre-depolymerizing, and / or a simple pre-treatment step to reduce the original size (and / or increase the surface area) of the polyester of a dicarboxylic acid source. The predepolymerizing step and / or the pre-treatment step may comprise a step of cutting / breaking / ripping / tearing the polyester of a dicarboxylic acid source into smaller pieces / chunks. It will be appreciated that, in various embodiments, the pre-depolymerizing step and / or the pre-treatment step is / are not a strict requirement of the method although said step increases the rate of conversion / reaction due to the larger exposed surface area (as a result of cutting / breaking / ripping / tearing / cutting the source).

[0091] In various embodiments, there is provided a method of depolymerizing a polyester of a dicarboxylic acid, the method comprising:

[0092] (a-i) depolymerizing a polyester of a dicarboxylic acid source under suitable conditions.

[0093] In various embodiments, the depolymerizing in step (a-i) is performed in the presence of:

[0094] (i) a mono-base system (or single base system); and

[0095] (ii) a solvent system comprising three or more different solvents.

[0096] Advantageously, in various embodiments, the method is designed or configured to depolymerize / convert / recycle / upcycle polyester of a dicarboxylic acid source into the desired depolymerization products with increased / enhanced / improved / high efficiency, yield and / or selectivity. The method (or depolymerizing step) may be tailored as desired to obtain target product with high product / conversion yield (up to 100%, e.g., 92%) and / or high product selectivity (e g., up to 99.5%). Without being bound by theory, it is believed that the mono-base system works synergistically with the solvent system, and such a synergistic interaction favourably promotes the depolymerization step (a-i). In various embodiments, when the mono-base system is present together with the solvent system, the base contained in the mono-base system reacts or interacts with the solvent system to generate species or ions (e.g., active species or ions) that participate in the depolymerization reaction, thereby facilitating a plurality / series of alcoholysis and hydrolysis reactions to take place at the polyester. Advantageously, the synergistic interaction between the mono-base system and solvent system allows for high depolymerization rate, depolymerization efficiency, depolymerization yield and / or depolymerization selectivity to be achieved. Advantageously, the synergistic interaction between the mono-base system and solvent system also allows the method to be performed under mild conditions. In various embodiments, the method is substantially devoid of harsh conditions such as high reaction temperature and / or pressure.

[0097] In various embodiments, the base system comprises / consists / consist essentially of one (or a single) base. Accordingly, in various embodiments, the base system does not have more than one base. In various embodiments, the base system comprises a mono-base system.

[0098] In various embodiments, the mono-base system comprises an inorganic base. Advantageously, in various embodiments, the mono-base system is configured to concurrently serve as a catalyst as well as a reactant in the depolymerization reaction. In various embodiments, the mono-base system (or inorganic base) acts / serves / behaves as a catalyst and / or promotes / increases / enhances the rate / speed of the depolymerization reaction. In various embodiments, the mono-base system (or inorganic base) also acts / serves / behaves as a reactant and / or participates in the depolymerization reaction. Advantageously, in various embodiments therefore, the mono-base system comprises dual functionality.

[0099] In various embodiments, the inorganic base comprises an Arrhenius base. In various embodiments, the Arrhenius base may include but is not limited to metal hydroxides, alkali metal hydroxides, alkaline earth metal hydroxides, ammonium-containing hydroxides (e.g., ammonium hydroxide and quaternary ammonium hydroxides), the like and combinations thereof. In various embodiments, the metal contained in the Arrhenius base (or inorganic base) is selected from an alkali metal (e g., lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr)) or an alkaline earth metal (e.g., beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra)).

[0100] In various embodiments, the alkali metal hydroxides are selected from the group consisting of potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), the like, and combinations thereof.

[0101] In various embodiments, the quaternary ammonium hydroxides comprise tetra-alkylammonium hydroxides. For example, the quaternary ammonium hydroxides may be selected from the group consisting of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, the like, and combinations thereof.

[0102] In various embodiments, the solvent system comprises three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, or ten or more different solvents. For example, the solvent system may comprise a tri-solvent system, tetra-solvent system, penta-solvent system, hexa-solvent system, hepta-solvent system, or octa-solvent system. In various embodiments, the solvent system comprises three or more different solvents selected from the group consisting of:

[0103] (a) an aprotic solvent (or polyester-swelling solvent);

[0104] (b) a protic solvent (or base-reacting solvent); and

[0105] (c) a hydrocarbon compound (or product-precipitating solvent).

[0106] In various embodiments, it will be appreciated that the three or more solvents do not necessarily need to each come from (a), (b) and (c) above respectively, although they may do so. For example, three different solvents may all be broadly protic solvents but are different in their specific identities or the first may be an aprotic solvent, the second may be a protic solvent and the third may be a hydrocarbon compound. In various embodiments, the three or more solvents comprises at least an aprotic solvent, a protic solvent and a hydrocarbon compound.

[0107] In various embodiments, the solvent system comprises three different solvents, for e.g., the solvent system may be a tri-solvent system.

[0108] In various embodiments, the protic solvent (or base-reacting solvent) in the solvent system reacts or interacts with the inorganic base (e.g., dissociated hydroxide ions from the inorganic base) in the mono-base system to produce alkoxide ions, thereby generating / forming a solution of alkoxide ions and hydroxide ions (existing in equilibrium). Advantageously, the combination of protic solvent (or base-reacting solvent) and inorganic base supplies / provides a source or pool of alkoxide ions and hydroxide ions for a plurality / series of alcoholysis and hydrolysis reactions to take place in the depolymerizing step. Therefore, in various embodiments, the solvent system comprises at least a protic solvent.

[0109] In various embodiments, the aprotic solvent (or polyester-swelling solvent) swells the polyester of a dicarboxylic acid, and improves interaction between the polyester of a dicarboxylic acid and alkoxide ions, thereby facilitating / enhancing / accelerating / speeding up the alcoholysis reaction. Therefore, in various embodiments, the solvent system comprises at least an aprotic solvent.

[0110] In various embodiments, the hydrocarbon compound (or productprecipitating solvent) facilitates / enhances / accelerates / speeds up the hydrolysis reaction and / or precipitation speed of a target product that comprises limited solubility in the reaction mixture (e.g., a mono-salt of a monoester of the dicarboxylic acid), thereby enhancing reaction rate and increasing product / conversion yield. Therefore, in various embodiments, the solvent system comprises at least a hydrocarbon compound.

[0111] In various embodiments, the polyester-swelling solvent comprises an aprotic solvent selected from the group consisting of polar aprotic organic solvents, non-polar aprotic organic solvents and combinations thereof.

[0112] In various embodiments, the polyester-swelling solvent comprises a polar aprotic organic solvent which includes but is not limited to tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), acetonitrile (ACN), acetone (ACE), methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, cyclohexanone, 2-pentanone (also known as methyl propyl ketone), 3-pentanone (also known as diethyl ketone), diethyl ether, methyl tert-butyl ether (MTBE), tertamyl methyl ether (TAME), cyclopentyl methyl ether (CPME), methoxybenzene (also known as anisole), ethoxybenzene, sulfolane (also known as tetramethylene sulfone), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMA), a,a- trifluorotoluene (TFT), the like, and combinations thereof.

[0113] In various embodiments, the polyester-swelling solvent comprises a nonpolar aprotic organic solvent which includes but is not limited to dichloromethane (DCM), chlorobenzene, diethyl ether, the like, and combinations thereof. In various embodiments, the base-reacting solvent comprises a protic solvent selected from saturated alcohols, unsaturated alcohols, linear alcohols, branched alcohols or combinations thereof.

[0114] In various embodiments, the base-reacting solvent comprises an alcohol which includes but is not limited to methanol, ethanol, n-propanol, / sopropanol, n-butanol, tert-butanol, allyl alcohol, propargyl alcohol, the like, and combinations thereof.

[0115] In various embodiments, the product-precipitating solvent comprises a hydrocarbon compound selected from aliphatic hydrocarbon, aromatic hydrocarbon or combinations thereof. The hydrocarbon compound may be optionally substituted, for e g., one or more of hydrogen atoms in the hydrocarbon compound may be optionally substituted with a chemical moiety or functional group such as alkyl.

[0116] In various embodiments, the product-precipitating solvent comprises an optionally substituted aliphatic hydrocarbon such as alkanes (e.g., a linear alkane, or a branched alkane, or a cycloalkane) which includes but is not limited to optionally substituted pentane, optionally substituted hexane, optionally substituted heptane, optionally substituted octane, optionally substituted cyclohexane, n-pentane, n-hexane, n-heptane, n-octane, 2-methylpentane, 3- methylpentane, cyclohexane, the like, and combinations thereof.

[0117] In various embodiments, the product-precipitating solvent comprises an optionally substituted aromatic hydrocarbon which includes but is not limited to optionally substituted benzene, optionally substituted toluene, xylene (e.g., 1 ,2- dimethylbenzene, 1 ,3-dimethylbenzene, 1 ,4-dimethylbenzene), the like, and combinations thereof.

[0118] In various embodiments, the method comprises a step of chemically converting / depolymerizing / recycling / upcycling / breaking down a polyester of a dicarboxylic acid source. In various embodiments, the method or the step of depolymerizing the polyester into depolymerization / degradation product(s) comprises cleavage of the polymeric ester chains present in the polyester into shorter / smaller / simpler chains, small organic molecules, the like, or combinations thereof. For example, the polyester of a dicarboxylic acid source may be converted / depolymerized / recycled / upcycled / broken down into one or more of the following:

[0119] (1 ) a diester of the dicarboxylic acid;

[0120] (2) a mono-salt of a monoester of the dicarboxylic acid;

[0121] (3) a mono-acid of a monoester of the dicarboxylic acid;

[0122] (4) a di-alkali metal salt of the dicarboxylic acid; and

[0123] (5) a dicarboxylic acid.

[0124] In various embodiments, the method (or depolymerizing step) is designed to be custom izable / tunable to obtain specific depolymerization product(s) from the depolymerization of the polyester of a dicarboxylic acid. For example, the method (or depolymerizing step) may be configured to selectively produce a “mono-salt of a monoester of the dicarboxylic acid” (or “alkali metal salt of a monoester of the dicarboxylic acid”). The method (or depolymerizing step) may also be configured to selectively produce a “mono-acid of a monoester of the dicarboxylic acid”. The method (or depolymerizing step) may also be configured to selectively produce a “di-alkali metal salt of the dicarboxylic acid”. The method (or depolymerizing step) may also be configured to selectively produce a “dicarboxylic acid”. In various embodiments, the depolymerization products comprise both direct products obtained (e g., a mono-salt of a monoester of dicarboxylic acid) and by-products formed (e.g., a di-alkali metal salt of dicarboxylic acid). In various embodiments, the depolymerization products may include but is not limited to “mono-salt of a monoester of the dicarboxylic acid” (or “alkali metal salt of a monoester of the dicarboxylic acid”), “mono-acid of a monoester of the dicarboxylic acid”, “di-alkali metal salt of the dicarboxylic acid”, “dicarboxylic acid” or the like. In various embodiments, the depolymerization products comprise a product comprising a mono-salt of a monoester of the dicarboxylic acid, a product comprising a mono-acid of a monoester of the dicarboxylic acid, a product comprising a di-alkali metal salt of the dicarboxylic acid, a dicarboxylic acid or derivatives thereof.

[0125] In various embodiments, the method and / or step (a-i) achieves a conversion / yield (of the mono-salt of a monoester of dicarboxylic acid) of at least about 50.0%, at least about 55.0%, at least about 60.0%, at least about 65.0%, at least about 70.0%, at least about 75.0%, at least about 80.0%, at least about 81 .0%, at least about 82.0%, at least about 83.0%, at least about 84.0%, at least about 85.0%, at least about 86.0%, at least about 87.0%, at least about 88.0%, at least about 89.0%, at least about 90.0%, at least about 91.0%, at least about 92.0%, at least about 93.0%, at least about 94.0%, at least about 95.0%, at least about 96.0%, at least about 97.0%, at least about 98.0%, at least about 99.0%, at least about 99.1 %, at least about 99.2%, at least about 99.3%, at least about 99.4%, at least about 99.5%, at least about 99.6%, at least about 99.7%, at least about 99.8%, at least about 99.9%, or about 100.0%.

[0126] In various embodiments, the method and / or step (a-i) achieves a selectivity (of the mono-salt of a monoester of dicarboxylic acid) of at least about 60.0%, at least about 65.0%, at least about 70.0%, at least about 75.0%, at least about 80.0%, at least about 81.0%, at least about 82.0%, at least about 83.0%, at least about 84.0%, at least about 85.0%, at least about 86.0%, at least about 87.0%, at least about 88.0%, at least about 89.0%, at least about 90.0%, at least about 91.0%, at least about 92.0%, at least about 93.0%, at least about 94.0%, at least about 95.0%, at least about 96.0%, at least about 97.0%, at least about 98.0%, at least about 99.0%, at least about 99.1 %, at least about 99.2%, at least about 99.3%, at least about 99.4%, at least about 99.5%. In various embodiments, the selectivity percentage / value refers to the ratio of the amount of the direct product obtained (i.e. mono-salt of a monoester of dicarboxylic acid) relative to the by-products formed (e g., di-alkali metal salt of dicarboxylic acid). In various embodiments, the step of depolymerizing (a-i) is custom izable / tunable to obtain the desired product(s) by altering the reaction conditions. For example, the reaction conditions employed for the step of PET depolymerization can be designed / adjusted to obtain a single specific product (e.g., mono-salt of a monoester of the dicarboxylic acid) in high selectivity and / or high product / conversion yield.

[0127] In various embodiments, the depolymerizing step (a-i) comprises one or more of the following steps: mixing, stirring, and / or heating the mixture comprising:

[0128] (a) polyester of a dicarboxylic acid source;

[0129] (b) mono-base system; and

[0130] (c) solvent system (e.g., tri-solvent system).

[0131] In various embodiments, the molar ratio of the inorganic base to the number of repeating units in the polyester is about 0.1 to 2, about 0.2 to 1 .9, about 0.3 to 1 .8, about 0.4 to 1 .7, about 0.5 to 1 .6, about 0.6 to 1.5, about 0.7 to 1 .4, about 0.8 to 1 .3, about 0.8 to 1 .5, about 0.9 to 1 .2, about 1 .0 to 1 .1 , or about 1 .05. In various embodiments, the molar ratio of the number of repeating units in polyester to the inorganic base is about 1 :1.

[0132] In various embodiments, the volume ratio of the aprotic solvent (or polyester-swelling solvent) to the protic solvent (or base-reacting solvent) is from about 1 :10 to about 50:1 , from about 1 :8 to about 40:1 , from about 1 :6 to about 30: 1 , from about 1 :4 to about 20: 1 , from about 1 :3 to about 15: 1 , from about 1 :2 to about 10: 1 , or from about 1 : 1 to about 5: 1 .

[0133] In various embodiments, the volume ratio of the aprotic solvent (or polyester-swelling solvent) plus the protic solvent (or base-reacting solvent) to the hydrocarbon compound (or product-precipitating solvent) is from about 1 :1 to about 75:1 , from about 2:1 to about 70:1 , from about 3:1 to about 65:1 , from about 4:1 to about 60:1 , from about 4:1 to about 55:1 , from about 4:1 to about 50:1 , from about 5:1 to about 45:1 , from about 6:1 to about 40:1 , from about 7:1 to about 35: 1 , from about 8: 1 to about 30:1 , from about 9: 1 to about 25:1 , from about 10:1 to about 20: 1 , or from about 12:1 to about 18: 1 .

[0134] In various embodiments, the volume ratio of the polyester-swelling solvent to the base-reacting solvent to the product-precipitating solvent is about 0.5-0.8 : 0.2-0.5 : 0.1 -0.2. In various embodiments, the volume ratio of the polyester- swelling solvent to the base-reacting solvent to the product-precipitating solvent is about 0.5-0.7 : 0.3-0.4 : 0.1 -0.2, or about 0.5-0.6 : 0.3-0.4 : 0.1 -0.2.

[0135] In various embodiments, the step (a-i) of depolymerizing is performed at a temperature that is at least about 10.0°C, at least about 15.0°C, at least about 20.0°C, at least about 25.0°C, at least about 30.0°C, at least about 35.0°C, at least about 40.0°C, at least about 45.0°C, at least about 50.0°C, at least about 55.0°C, at least about 60.0°C, at least about 65.0°C, at least about 70.0°C, at least about 75.0°C, at least about 80.0°C, at least about 85.0°C, or at least about 90.0°C. The step of depolymerization may be performed at a temperature from about 10.0°C to about 90.0°C, from about 15.0°C to about 85.0°C, from about 20.0°C to about 80.0°C, from about 25.0°C to about 75.0°C, from about 30.0°C to about 70.0°C, from about 35.0°C to about 65.0°C, from about 40.0°C to about 60.0°C, from about 45.0°C to about 55.0°C, or about 50.0°C. The step of depolymerization may be carried out at a temperature of more than about 23°C to no more than about 55°C.

[0136] In various embodiments, the step (a-i) of depolymerizing is performed over a time duration of at least about 10 minutes, at least about 15 minutes, at least about 20 minutes, at least about 25 minutes, at least about 30 minutes, at least about 35 minutes, at least about 40 minutes, at least about 45 minutes, at least about 50 minutes, at least about 55 minutes, at least about 1 hour, at least about 2 hours, at least about 3 hours, at least about 4 hours, at least about 5 hours, at least about 6 hours, at least about 7 hours, at least about 8 hours, at least about 9 hours, or at least about 10 hours. The step of depolymerization may be performed over a time duration of from about 10 minutes to about 10 hours, from about 15 minutes to about 9 hours, from about 20 minutes to about 8 hours, from about 25 minutes to about 7 hours, from about 30 minutes to about 6 hours, from about 35 minutes to about 5 hours, from about 40 minutes to about 4 hours, from about 45 minutes to about 3 hours, from about 50 minutes to about 2 hours, or from about 55 minutes to about 1 hour.

[0137] In various embodiments, the step (a-i) of depolymerizing achieves a high yield of at least about 84.5% and a high selectivity of at least about 90% at a temperature of about 40°C, over a time period of about 1 hour.

[0138] In various embodiments, the polyester of a dicarboxylic acid comprises a structure that is represented by general formula (1 ): wherein

[0139] A is optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocycloalkyl, optionally substituted heterocycloalkenyl, optionally substituted heteroaryl, or combinations thereof;

[0140] R1is optionally substituted alkylene, optionally substituted cycloalkylene, optionally substituted alkenylene, optionally substituted alkynylene, or combinations thereof; and n > 1.

[0141] In various embodiments, n is an integer that is at least about 30, at least about 300, or at least about 3,000. In various embodiments, n is an integer > 30. For example, n > 35, n > 40, n > 45, n > 50, n > 55, n > 60, n > 65, n > 70, n > 75, n > 80, n > 85, n > 90, n > 95, n > 100, n > 150, n > 200, n > 250, n > 300, n > 350, n > 400, n > 450, n > 500, n > 550, n > 600, n > 650, n > 700, n > 750, n > 800, n > 850, n > 900, n > 950, n > 1 ,000, n > 1 ,500, n > 2,000, n > 2,500, or n > 3,000. In various embodiments, n is a value that is from about 50 to about 3,000, from about 75 to about 2,750, from about 100 to about 2,500, from about 125 to about 2,250, from about 150 to about 2,000, from about 175 to about 1 ,750, from about 200 to about 1 ,500, from about 225 to about 1 ,250, from about 250 to about 1 ,000, from about 275 to about 750, from about 300 to about 500, from about 325 to about 475, from about 350 to about 450, or about 400.

[0142] In various embodiments, the average molecular weight (Mw) of the polyester of a dicarboxylic acid is from about 5,000 to about 500,000, from about 6,000 to about 450,000, from about 7,000 to about 400,000, from about 8,000 to about 350,000, from about 9,000 to about 300,000, from about 10,000 to about 250,000, from about 15,000 to about 200,000, from about 20,000 to about 150,000, from about 25,000 to about 100,000, from about 30,000 to about 95,000, from about 35,000 to about 90,000, from about 40,000 to about 85,000, from about 45,000 to about 80,000, from about 50,000 to about 75,000, from about 55,000 to about 70,000, or from about 60,000 to about 65,000.

[0143] In various embodiments, the average molecular mass (Mn) of the polyester of a dicarboxylic acid is from about 5,000 to about 500,000, from about 6,000 to about 450,000, from about 7,000 to about 400,000, from about 8,000 to about 350,000, from about 9,000 to about 300,000, from about 10,000 to about 250,000, from about 15,000 to about 200,000, from about 20,000 to about 150,000, from about 25,000 to about 100,000, from about 30,000 to about 95,000, from about 35,000 to about 90,000, from about 40,000 to about 85,000, from about 45,000 to about 80,000, from about 50,000 to about 75,000, from about 55,000 to about 70,000, or from about 60,000 to about 65,000.

[0144] In various embodiments, A comprises an optionally substituted 5- membered ring. For example, A may be selected from pyrrole, thiophene, furan, pyrazole, imidazole, imidazoline, oxazole, isoxazole, thiazole, isothiazole, triazole, oxadiazole, thiadiazole, tetrazole, the like or combinations thereof. For example, A may be an optionally substituted furan ring (e.g., di-substituted furan such as 2,3-disubstituted furan, 2,4-disubstituted furan, 2,5-disubstituted furan or 3,4-disubstituted furan). In various embodiments, A comprises an optionally substituted 6-membered ring. For example, A may be selected from benzene, toluene, phenol, aniline, nitrobenzene, chlorobenzene, benzoic acid, pyridine, phosphorine, pyrimidine, pyrazine, pyridazine, 1 ,3,5-triazine, 1 ,2,4-triazine, 1 ,2,3-triazine, oxazine, thiazine, quinoline, isoquinoline, the like or combinations thereof.

[0145] In various embodiments, A comprises an optionally substituted 6- membered ring. For example, A may be an optionally substituted benzene ring (e.g., di-substituted benzene such as 1 ,2-disubstituted benzene, 1 ,3- disubstituted benzene or 1 ,4-disubstituted benzene).

[0146] In various embodiments, A comprises 1 ,4-disubstituted benzene. In such embodiments, the polyester of a dicarboxylic acid comprises a structure that is represented by general formula (2): wherein

[0147] R2is optionally substituted alkylene, optionally substituted cycloalkylene, optionally substituted alkenylene, optionally substituted alkynylene, or combinations thereof;

[0148] Ra, Rb, Rcand Rdare each independently hydrogen, halogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy, or combinations thereof; and n > 1.

[0149] In various embodiments, A comprises optionally substituted fused polycyclic aryl group(s) selected from the group consisting of optionally substituted naphthalene, optionally substituted anthracene, optionally substituted phenanthrene, optionally substituted fluorene, the like or combinations thereof. For example, A may be an optionally substituted naphthalene (e.g., di-substituted naphthalene such as 1 ,2-disubstituted naphthalene, 1 ,3-disubstituted naphthalene, 1 ,4-disubstituted naphthalene, 1 ,5-disubstituted naphthalene, 1 ,6- disubstituted naphthalene, 1 ,7-disubstituted naphthalene, 1 ,8-disubstituted naphthalene, 2,3-disubstituted naphthalene, 2,6-disubstituted naphthalene, or 2,7-disubstituted naphthalene).

[0150] In various embodiments, A is optionally substituted alkyl (or alkylene), optionally substituted alkenyl (or alkenylene), optionally substituted cycloalkyl (or cycloalkylene), optionally substituted cycloalkenyl (or cycloalkenylene), optionally substituted alkynyl (or alkynylene), optionally substituted aryl (or arylene), optionally substituted heterocycloalkyl (or heterocycloalkylene), optionally substituted heterocycloalkenyl (or heterocycloalkenylene), optionally substituted heteroaryl (or heteroarylene), or combinations thereof.

[0151] In various embodiments, A is selected from optionally substituted alkylene, optionally substituted alkenylene or optionally substituted alkynylene. In various embodiments, A is optionally substituted alkylene. For example, A may be selected from methanediyl, ethanediyl, propane-1 ,3-diyl, propane-1 ,2-diyl, butane-1 ,4-diyl, 2-methylpropane-1 ,3-diyl, 1 -methylpropane-1 ,3-diyl, 1 ,1 - dimethylethanediyl, hexane-1 ,6-diyl, 1 ,2-dimethylpropane-1 ,3-diyl, 1 ,1 - dimethylpropane-1 ,3-diyl, pentane-1 ,5-diyl, 3-methylbutane-1 ,4-diyl, 4- methylpentane-1 ,5-diyl, 1-methylpentane-1 ,5-diyl, 2-methylpentane-1 ,5-diyl, 3- methylpentane-1 ,5-diyl, 2,2-dimethylbutane-1 ,4-diyl, 3,3-dimethylbutane-1 ,4- diyl, 1 ,2-dimethylbutane-1 ,4-diyl, 1 ,3-dimethylbutane-1 ,4-diyl, 1 ,2,2- trimethylpropane-1 ,3-diyl, 1 ,1 ,2-trimethylpropane-1 ,3-diyl, 2-ethylpentane-1 ,5- diyl, 3-ethylpentane-1 ,5-diyl, heptane-1 ,7-diyl, 1 -methylhexane-1 ,6-diyl, 2,2- dimethylpentane-1 ,5-diyl, 3,3-dimethylpentane-1 ,5-diyl, 4,4-dimethylpentane- 1 ,5-diyl, 1 ,2-dimethylpentane-1 ,5-diyl, 1 ,3-dimethylpentane-1 ,5-diyl, 1 ,4- dimethylpentane-1 ,5-diyl, 1 ,2,3-trimethylbutane-1 ,4-diyl, 1 , 1 ,2-trimethylbutane- 1 ,4-diyl, 1 ,1 ,3-trimethylbutane-1 ,4-diyl, 5-methylheptane-1 ,7-diyl, 1 - methylheptane-1 ,7-diyl, octane-1 , 8-diyl, nonane-1 ,9-diyl, decane-1 , 10-diyl, or the like or combinations thereof. In various embodiments, A comprises -CzH2z- where z is an integer > 1 . For example, A may be -CzH2z-, where z > 1 , z > 2, z

[0152] > 3, z > 4, z > 5, z > 6, z > 7, z > 8, z > 9, z > 10, z > 11 , z > 12, z > 13, z > 14, z

[0153] > 15, z > 16, z > 17, z > 18, z > 19, or z > 20. In various embodiments, A may be -C2H4-, -C4H8-, or -C8H16-. In various embodiments, A is selected from optionally substituted alkynylene. In various embodiments, A comprises - CzH2z-4- , where z is an integer > 2. For example, A may be -CzH2z-4-, where z > 2, z > 3, z > 4, z > 5, z > 6, z > 7, z > 8, z > 9, z > 10, z > 11 , z > 12, z > 13, z > 14, z > 15, z > 16, z > 17, z > 18, z > 19, or z > 20. In various embodiments, A may be -C=C-, -C3H2-, or -C4H4-.

[0154] In various embodiments, A is selected from optionally substituted cycloalkylene. In various embodiments, A is selected from optionally substituted cyclopropane, optionally substituted cyclobutane, optionally substituted cyclopentane, optionally substituted cyclohexane, optionally substituted cycloheptane, optionally substituted cyclooctane or optionally substituted cyclotridecane. For example, A may be an optionally substituted cyclohexane (e.g., di-substituted cyclohexane such as 1 ,2-disubstituted cyclohexane, 1 ,3- disubstituted cyclohexane or 1 ,4-disubstituted cyclohexane).

[0155] In various embodiments, R1and R2are each independently selected from optionally substituted alkylene, optionally substituted alkenylene or optionally substituted alkynylene. In various embodiments, R1and R2are each optionally substituted alkylene. For example, R1and / or R2may be selected from methanediyl, ethanediyl, propane-1 , 3-diyl, propane-1 ,2-diyl, butane-1 ,4-diyl, 2- methylpropane-1 , 3-diyl, 1 -methylpropane-1 , 3-diyl, 1 ,1 -dimethylethanediyl, hexane-1 ,6-diyl, 1 ,2-dimethylpropane-1 , 3-diyl, 1 , 1 -dimethylpropane-1 , 3-diyl, pentane-1 ,5-diyl, 3-methylbutane-1 ,4-diyl, 4-methylpentane-1 ,5-diyl, 1 - methylpentane-1 ,5-diyl, 2-methylpentane-1 ,5-diyl, 3-methylpentane-1 ,5-diyl, 2,2- dimethylbutane-1 ,4-diyl, 3,3-dimethylbutane-1 ,4-diyl, 1 ,2-dimethylbutane-1 ,4- diyl, 1 ,3-dimethylbutane-1 ,4-diyl, 1 , 2, 2-trimethylpropane-1 , 3-diyl, 1 ,1 ,2- trimethylpropane-1 , 3-diyl, 2-ethylpentane-1 ,5-diyl, 3-ethylpentane-1 ,5-diyl, heptane-1 ,7-diyl, 1 -methylhexane-1 ,6-diyl, 2, 2-dimethylpentane-1 ,5-diyl, 3,3- dimethylpentane-1 ,5-diyl, 4,4-dimethylpentane-1 ,5-diyl, 1 ,2-dimethylpentane- 1 ,5-diyl, 1 ,3-dimethylpentane-1 ,5-diyl, 1 ,4-dimethylpentane-1 ,5-diyl, 1 ,2,3- trimethylbutane-1 ,4-diyl, 1 ,1 ,2-trimethylbutane-1 ,4-diyl, 1 , 1 ,3-trimethylbutane- 1 ,4-diyl, 5-methylheptane-1 ,7-diyl, 1 -methylheptane-1 ,7-diyl, octane-1 ,8-diyl, nonane-1 ,9-diyl, decane-1 , 10-diyl, or the like or combinations thereof. In various embodiments, R1and / or R2comprises -CxH2x-, where x is an integer > 1. For example, R1and / or R2may be -CxH2x-, where x > 1 , x > 2, x > 3, x > 4, x > 5, x > 6, x > 7, x > 8, x > 9, x > 10, x > 11 , x > 12, x > 13, x > 14, x > 15, x > 16, x > 17, x > 18, x > 19, or x > 20. In various embodiments, R1and / or R2is / are ethyl (or ethylene). For example, R1and / or R2may be -C2H4-. In various embodiments, R1and / or R2is / are propyl (or propylene). For example, R1and / or R2may be -C3H6-. In various embodiments, R1and / or R2is / are butyl (or butylene). For example, R1and / or R2may be -C4H8-. In various embodiments, R1= R2.

[0156] In various embodiments, Ra, Rb, Rcand Rdare all H.

[0157] In various embodiments, the polyester of a dicarboxylic acid comprises a polyester derived from a dicarboxylic acid selected from the group consisting of terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,5- fu rand icarboxy lie acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, 1 ,4-cyclohexanedicarboxylic acid, acetylene dicarboxylic acid, and combinations thereof. In various embodiments, the polyester of a dicarboxylic acid comprises polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polyethylene furanoate (PEF), poly(butylene adipate) (PBA), poly(butylene succinate) (PBS), and poly(butylene sebacate) (PBSb), the like, or combinations thereof.

[0158] In various embodiments, the mono-salt of a monoester of the dicarboxylic acid is represented by general formula (3): wherein

[0159] A is optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocycloalkyl, optionally substituted heterocycloalkenyl, optionally substituted heteroaryl, or combinations thereof;

[0160] R3is optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, or combinations thereof; and M is a metal or ammonium-containing group.

[0161] In various embodiments, A comprises 1 ,4-disubstituted benzene. In such embodiments, the mono-salt of a monoester of the dicarboxylic acid is represented by general formula (4): wherein R4is optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, or combinations thereof;

[0162] R1 a, R1b, R1 cand R1dare each independently hydrogen, halogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy, or combinations thereof; and

[0163] M is a metal or ammonium-containing group.

[0164] In various embodiments, R3and R4are each independently selected from optionally substituted alkyl, optionally substituted alkenyl or optionally substituted alkynyl. The alkyl, alkenyl may have at least 1 , at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 11 , at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, or at least 20 carbon atoms. In various embodiments, R3and R4are each independently selected from -CyH2y+i or -CyH2y-i, where y is an integer > 1 , y > 2, y > 3, y > 4, y > 5, y > 6, y > 7, y > 8, y > 9, y > 10, y > 11 , y > 12, y > 13, y > 14, y > 15, y > 16, y > 17, y > 18, y > 19, or y > 20. For example, R3and / or R4may be selected from methyl, ethyl, n-propyl, 2-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, f-butyl, hexyl, amyl, 1 ,2-dimethylpropyl, 1 ,1 -dimethylpropyl, pentyl, isopentyl, hexyl, 4-methylpentyl, 1 -methylpentyl, 2-methylpentyl, 3-methylpentyl,

[0165] 2.2-dimethylbutyl, 3,3-dimethylbutyl, 1 ,2-dimethylbutyl, 1 ,3-dimethylbutyl, 1 ,2,2- trimethylpropyl, 1 , 1 ,2-trimethylpropyl, 2-ethylpentyl, 3-ethylpentyl, heptyl, 1 - methylhexyl, 2,2-dimethylpentyl, 3,3-dimethylpentyl, 4,4-dimethylpentyl, 1 ,2- dimethylpentyl, 1 ,3-dimethylpentyl, 1 ,4-dimethylpentyl, 1 ,2,3-trimethylbutyl,

[0166] 1 .1 .2-trimethylbutyl, 1 ,1 ,3-trimethylbutyl, 5-methylheptyl, 1 -methylheptyl, octyl, nonyl, decyl or the like or combinations thereof. In various embodiments, R3and R4may contain one or more C=C double bond(s). For example, R3and / or R4may be selected from ethenyl (vinyl), allyl (2-propenyl), 1 -propenyl, 1-butenyl, 2- butenyl (cis and trans), isobutenyl, 1 -pentenyl, 2-pentenyl (cis and trans), 3- pentenyl, isopentenyl, 1 -hexenyl, 2-hexenyl (cis and trans), 3-hexenyl, 1 - heptenyl, 2-heptenyl, 3-heptenyl, 1 -octenyl, 2-octenyl, 3-octenyl, 1-nonenyl, 2- nonenyl, 3-nonenyl, 1 -decenyl, 2-decenyl, 3-decenyl, 1 -undecenyl, 2-undecenyl, 1 -dodecenyl, 2-dodecenyl, 1 -tridecenyl, 2-tridecenyl, 1 -tetradecenyl, 2- tetradecenyl, 1 -pentadecenyl, 2-pentadecenyl, 1 -hexadecenyl, 2-hexadecenyl,

[0167] 1 -heptadecenyl, 2-heptadecenyl, 1 -octadecenyl (oleyl), 2-octadecenyl, 1 - nonadecenyl, 2-nonadecenyl, 1 -eicosenyl, 2-eicosenyl, or the like or combinations thereof. The alkynyl may have at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 11 , at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, or at least 20 carbon atoms. In various embodiments, R3and R4are each independently selected from -CyH2y-3, where y is an integer > 2, y > 2, y > 3, y > 4, y > 5, y > 6, y > 7, y > 8, y > 9, y > 10, y > 11 , y > 12, y > 13, y > 14, y > 15, y > 16, y > 17, y > 18, y > 19, or y > 20. In various embodiments, R3and R4may contain one or more C=C triple bond(s). For example, R3and / or R4may be selected from ethynyl (acetylide), 1 -propynyl, 2-propynyl (propargyl), 1 -butynyl,

[0168] 2-butynyl, 1 -pentynyl, 2-pentynyl, 3-pentynyl, 1 -hexynyl, 2-hexynyl, 3-hexynyl, 1 - heptynyl, 2-heptynyl, 3-heptynyl, 1 -octynyl, 2-octynyl, 3-octynyl, 4-octynyl, 1 - nonynyl, 2-nonynyl, 3-nonynyl, 4-nonynyl, 1 -decynyl, 2-decynyl, 3-decynyl, 4- decynyl, 5-decynyl, 1 -undecynyl, 2-undecynyl, 3-undecynyl, 4-undecynyl, 5- undecynyl, 1 -dodecynyl, 2-dodecynyl, 3-dodecynyl, 4-dodecynyl, 5-dodecynyl, 6- dodecynyl, 1 -tridecynyl, 2-tridecynyl, 3-tridecynyl, 4-tridecynyl, 5-tridecynyl, 6- tridecynyl, 1 -tetradecynyl, 2-tetradecynyl, 3-tetradecynyl, 4-tetradecynyl, 5- tetradecynyl, 6-tetradecynyl, 7 -tetradecynyl, 1 -pentadecynyl, 2-pentadecynyl, 3- pentadecynyl, 4-pentadecynyl, 5-pentadecynyl, 6-pentadecynyl, 7-pentadecynyl, 1 -hexadecynyl, 2-hexadecynyl, 3-hexadecynyl, 4-hexadecynyl, 5-hexadecynyl, 6-hexadecynyl, 7-hexadecynyl, 8-hexadecynyl, 1 -heptadecynyl, 2-heptadecynyl,

[0169] 3-heptadecynyl, 4-heptadecynyl, 5-heptadecynyl, 6-heptadecynyl, 7- heptadecynyl, 8-heptadecynyl, 1 -octadecynyl, 2-octadecynyl, 3-octadecynyl, 4- octadecynyl, 5-octadecynyl, 6-octadecynyl, 7-octadecynyl, 8-octadecynyl, 9- octadecynyl, 1 -nonadecynyl, 2-nonadecynyl, 3-nonadecynyl, 4-nonadecynyl, 5- nonadecynyl, 6-nonadecynyl, 7-nonadecynyl, 8-nonadecynyl, 9-nonadecynyl, 1 - eicosynyl, 2-eicosynyl, 3-eicosynyl, 4-eicosynyl, 5-eicosynyl, 6-eicosynyl, 7- eicosynyl, 8-eicosynyl, 9-eicosynyl, 10-eicosynyl, the like or combinations thereof. In various embodiments, R3and / or R4are each independently selected from -CH3, -C2H5, -CH2CH=CH2, -C3H7, -CH(CH3)2, -C4H9, -C(CH3)3, or -CH2C=CH.

[0170] In various embodiments, the identity of R3and / or R4in general formula (3), (4), (11 ), (12) and (13) corresponds to the type of alcoholysis involved (or the type of protic solvent / base-reacting solvent used) in depolymerization. For example, if methanolysis is performed (or methanol is used as the protic solvent) during depolymerization, then R3and / or R4may be methyl. If ethanolysis is performed (or ethanol is used as the protic solvent) during depolymerization, then R3and / or R4may be ethyl. If n-propanolysis is performed (or n-propanol is used as the protic solvent) during depolymerization, then R3and / or R4may be r?-propyl. If / ’sopropanolysis is performed (or / sopropanol is used as the protic solvent) during depolymerization, then R3and / or R4may be / sopropyl. If n-butanolysis is performed (or n-butanol is used as the protic solvent) during depolymerization, then R3and / or R4may be n-butyl. If fert-butanolysis is performed (or tert-butanol is used as the protic solvent) during depolymerization, then R3and / or R4may be fert-butyl. If allyl alcoholysis is performed (or allyl alcohol is used as the protic solvent) during depolymerization, then R3and / or R4may be allyl. If propargyl alcoholysis is performed (or propargyl alcohol is used as the protic solvent) during depolymerization, then R3and / or R4may be propargyl.

[0171] In various embodiments, M is an alkali metal. For example, M may be selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), francium (Fr), the like, or combinations thereof. In various embodiments, M is an alkaline earth metal. For example, M may be selected from beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), the like, or combinations thereof.

[0172] In various embodiments, M is an ammonium-containing group. For example, M may be selected from ammonium (NH4) or quaternary ammonium, e.g., tetra-alkylammonium such as tetramethylammonium, tetraethylammonium, tetrabutylammonium, the like, and combinations thereof.

[0173] In various embodiments, the identity of M in general formula (3), (4), (5), (6) and (12) corresponds to the type of base (or more particularly, the cation present in said base) used in depolymerization. For example, if potassium hydroxide is used as the inorganic base during depolymerization, then M may be potassium (K). If sodium hydroxide is used as the inorganic base during depolymerization, then M may be sodium (Na). If lithium hydroxide is used as the inorganic base during depolymerization, then M may be lithium (Li). If ammonium hydroxide is used as the inorganic base during depolymerization, then M may be ammonium (NF ). If tetra-alkylammonium hydroxide is used as the inorganic base during depolymerization, then M may be tetra-alkylammonium, e g., tetramethylammonium, tetraethylammonium, tetrabutylammonium hydroxide, the like, or combinations thereof.

[0174] In various embodiments, A, R1 a, R1 b, R1cand R1dcontain one or more features and / or share one or more properties that are similar to those already described above.

[0175] In various embodiments, the step of depolymerizing comprises a plurality / series of alcoholysis and hydrolysis reactions. The plurality / series of alcoholysis and hydrolysis reactions may occur at the carbonyl group(s) and / or ester group(s) / linkage(s) of the polyester. In various embodiments, the alcoholysis and hydrolysis reactions may occur in a series / sequence of cascade / tandem / domino / consecutive reactions. That is, the depolymerization may proceed first with an alcoholysis reaction, followed by a hydrolysis reaction. In various embodiments, the alcoholysis and hydrolysis reactions may occur concurrently. That is, the depolymerization may proceed with both an alcoholysis reaction and a hydrolysis reaction occurring at the same time. In various embodiments, the depolymerizing step comprises the following reaction:

[0176] (13) (12) wherein

[0177] A is optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocycloalkyl, optionally substituted heterocycloalkenyl, optionally substituted heteroaryl, or combinations thereof;

[0178] R1is optionally substituted alkylene, optionally substituted cycloalkylene, optionally substituted alkenylene, optionally substituted alkynylene, or combinations thereof;

[0179] R4and R4’ are each independently optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, or combinations thereof; and

[0180] M is a metal or ammonium-containing group; and n > 1. In various embodiments, the polyester of a dicarboxylic acid is represented by general formula (10). In various embodiments, the polyester of a dicarboxylic acid (i.e. , represented by general formula (10)) is converted into a diester of the dicarboxylic acid (i.e., represented by general formula (11 )). In various embodiments, the conversion of general formula (10) into general formula (11 ) comprises alcoholysis. In various embodiments, the diester of the dicarboxylic acid (i.e., represented by general formula (11 ) is converted into a mono-salt of a monoester of the dicarboxylic acid (i.e. represented by general formula (12)). In various embodiments, the conversion of general formula (12) into general formula (13) comprises hydrolysis. In various embodiments, the mono-salt of a monoester of the dicarboxylic acid (i.e. represented by general formula (12) is converted into a mono-acid of a monoester of the dicarboxylic acid (i.e., represented by general formula (13)). In various embodiments, the conversion of general formula (12) into general formula (13) comprises acidification. The acidification may be performed in the presence of an acid e.g., inorganic / mineral acid such as hydrochloric acid (HCI), sulfuric acid (H2SO4) and boric acid.

[0181] In various embodiments therefore, there is provided a method of producing alkali metal salt of a mono-ester of dicarboxylic acid via alternating alcoholysishydrolysis depolymerization / depolymerizing / recycling / upcycling / breaking down of a polyester of a dicarboxylic acid under suitable conditions to obtain a product comprising a mono-salt of a monoester of the dicarboxylic acid (e.g., M-METT) or derivatives thereof (e g., TPA). In various embodiments, there is provided a method of alternating alcoholysis-hydrolysis depolymerization of a polyester of a dicarboxylic acid (e.g., a polyester of terephthalic acid such as polyethylene terephthalate). In various embodiments, there is provided a method of selectively converting a polyester of a dicarboxylic acid (e.g., a polyester of terephthalic acid such as polyethylene terephthalate) into a monoester of a dicarboxylic acid (e.g., a monoester of terephthalic acid such as monoalkyl terephthalate) and / or its derivatives thereof. In various embodiments, there is provided a method of preparing / producing a monoester of a dicarboxylic acid (e.g., a monoester of terephthalic acid such as monoalkyl terephthalate) and / or its derivatives thereof via alternating alcoholysis-hydrolysis depolymerization of a polyester of a dicarboxylic acid (e g., a polyester of terephthalic acid such as polyethylene terephthalate). In various embodiments, there is provided a method of producing an alkali metal salt of a monoester of a dicarboxylic acid via alternating alcoholysis-hydrolysis depolymerization of a polyester of a dicarboxylic acid. In various embodiments, there is provided a method of producing an alkali metal salt of a monoester of terephthalic acid via alternating alcoholysis-hydrolysis depolymerization of PET. In various embodiments, there is provided a method of producing K-MMT via alternating methanolysis-hydrolysis depolymerization of PET.

[0182] In various embodiments, there is provided a method of alternating alcoholysis-hydrolysis depolymerization of a polyester of a dicarboxylic acid, selectively producing an alkali metal salt of a monoester of a dicarboxylic acid. In various embodiments, there is provided a method of alternating alcoholysishydrolysis depolymerization of a PET, selectively producing an alkali metal salt of a monoester of terephthalic acid. In various embodiments, there is provided a method of alternating ethanolysis-hydrolysis depolymerization of PET, selectively producing an alkali metal salt of a monoethyl terephthalate (Metal-MET, where Metal = K, Na, Li). In various embodiments, there is provided a method of alternating methanolysis-hydrolysis depolymerization of PET, selectively producing an alkali metal salt of a monomethyl terephthalate (Metal-MMT, where Metal = K, Na, Li).

[0183] In various embodiments, R4’ is selected from optionally substituted alkyl, optionally substituted alkenyl or optionally substituted alkynyl. The alkyl, alkenyl may have at least 1 , at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 11 , at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, or at least 20 carbon atoms. In various embodiments, R4’ is selected from -CyH2y+i or -CyH2y-i, where y is an integer > 1 , y > 2, y > 3, y > 4, y > 5, y > 6, y > 7, y > 8, y > 9, y > 10, y > 11 , y > 12, y > 13, y > 1 , y > 15, y > 16, y > 17, y > 18, y > 19, or y > 20. For example, R4’ may be selected from methyl, ethyl, n-propyl, 2-propyl, isopropyl, n- butyl, isobutyl, sec-butyl, f-butyl, hexyl, amyl, 1 ,2-dimethylpropyl, 1 ,1 - dimethylpropyl, pentyl, isopentyl, hexyl, 4-methylpentyl, 1 -methylpentyl, 2- methylpentyl, 3-methylpentyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl, 1 ,2- dimethylbutyl, 1 ,3-dimethylbutyl, 1 ,2,2-trimethylpropyl, 1 , 1 ,2-trimethylpropyl, 2- ethylpentyl, 3-ethylpentyl, heptyl, 1 -methylhexyl, 2,2-dimethylpentyl, 3,3- dimethylpentyl, 4,4-dimethylpentyl, 1 ,2-dimethylpentyl, 1 ,3-dimethylpentyl, 1 ,4- dimethylpentyl, 1 ,2,3-trimethylbutyl, 1 , 1 ,2-trimethylbutyl, 1 ,1 ,3-trimethylbutyl, 5- methylheptyl, 1 -methylheptyl, octyl, nonyl, decyl or the like or combinations thereof. In various embodiments, R4’ may contain one or more C=C double bond(s). For example, R4’ may be selected from ethenyl (vinyl), allyl (2 -propenyl), 1 -propenyl, 1-butenyl, 2-butenyl (cis and trans), isobutenyl, 1 -pentenyl, 2- pentenyl (cis and trans), 3-pentenyl, isopentenyl, 1 -hexenyl, 2-hexenyl (cis and trans), 3-hexenyl, 1 -heptenyl, 2-heptenyl, 3-heptenyl, 1 -octenyl, 2-octenyl, 3- octenyl, 1 -nonenyl, 2-nonenyl, 3-nonenyl, 1 -decenyl, 2-decenyl, 3-decenyl, 1 - undecenyl, 2-undecenyl, 1 -dodecenyl, 2-dodecenyl, 1 -tridecenyl, 2-tridecenyl, 1 - tetradecenyl, 2-tetradecenyl, 1 -pentadecenyl, 2-pentadecenyl, 1 -hexadecenyl, 2- hexadecenyl, 1 -heptadecenyl, 2-heptadecenyl, 1 -octadecenyl (oleyl), 2- octadecenyl, 1 -nonadecenyl, 2-nonadecenyl, 1 -eicosenyl, 2-eicosenyl, or the like or combinations thereof. The alkynyl may have at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 11 , at least 12, at least 13, at least 1 , at least 15, at least 16, at least 17, at least 18, at least 19, or at least 20 carbon atoms. In various embodiments, R4’ is selected from - CyH2y-3, where y is an integer > 2, y > 2, y > 3, y > 4, y > 5, y > 6, y > 7, y > 8, y > 9, y > 10, y > 11 , y > 12, y > 13, y > 14, y > 15, y > 16, y > 17, y > 18, y > 19, or y > 20. In various embodiments, R4’ may contain one or more C=C triple bond(s). For example, R4’ may be selected from ethynyl (acetylide), 1 -propynyl, 2-propynyl (propargyl), 1 -butynyl, 2-butynyl, 1 -pentynyl, 2-pentynyl, 3-pentynyl, 1 -hexynyl, 2- hexynyl, 3-hexynyl, 1 -heptynyl, 2-heptynyl, 3-heptynyl, 1 -octynyl, 2-octynyl, 3- octynyl, 4-octynyl, 1-nonynyl, 2-nonynyl, 3-nonynyl, 4-nonynyl, 1 -decynyl, 2- decynyl, 3-decynyl, 4-decynyl, 5-decynyl, 1 -undecynyl, 2-undecynyl, 3- undecynyl, 4-undecynyl, 5-undecynyl, 1 -dodecynyl, 2-dodecynyl, 3-dodecynyl, 4- dodecynyl, 5-dodecynyl, 6-dodecynyl, 1 -tridecynyl, 2-tridecynyl, 3-tridecynyl, 4- tridecynyl, 5-tridecynyl, 6-tridecynyl, 1 -tetradecynyl, 2 -tetradecynyl, 3- tetradecynyl, 4-tetradecynyl, 5-tetradecynyl, 6-tetradecynyl, 7-tetradecynyl, 1 - pentadecynyl, 2-pentadecynyl, 3-pentadecynyl, 4-pentadecynyl, 5-pentadecynyl, 6-pentadecynyl, 7-pentadecynyl, 1 -hexadecynyl, 2-hexadecynyl, 3-hexadecynyl,

[0184] 4-hexadecynyl, 5-hexadecynyl, 6-hexadecynyl, 7-hexadecynyl, 8-hexadecynyl,

[0185] 1 -heptadecynyl, 2-heptadecynyl, 3-heptadecynyl, 4-heptadecynyl, 5- heptadecynyl, 6-heptadecynyl, 7-heptadecynyl, 8-heptadecynyl, 1 -octadecynyl,

[0186] 2-octadecynyl, 3-octadecynyl, 4-octadecynyl, 5-octadecynyl, 6-octadecynyl, 7- octadecynyl, 8-octadecynyl, 9-octadecynyl, 1 -nonadecynyl, 2-nonadecynyl, 3- nonadecynyl, 4-nonadecynyl, 5-nonadecynyl, 6-nonadecynyl, 7-nonadecynyl, 8- nonadecynyl, 9-nonadecynyl, 1 -eicosynyl, 2-eicosynyl, 3-eicosynyl, 4-eicosynyl,

[0187] 5-eicosynyl, 6-eicosynyl, 7-eicosynyl, 8-eicosynyl, 9-eicosynyl, 10-eicosynyl, the like or combinations thereof. In various embodiments, R4= R4’.

[0188] In various embodiments, A, R1, R4, M and n contain one or more features and / or share one or more properties that are similar to those already described above.

[0189] In various embodiments, the mono-base system and solvent system (e.g., tri-solvent system) work synergistically to increase / enhance rate, efficiency, product / conversion yield and / or selectivity of the depolymerization reaction. In various embodiments, the inorganic base contained in the mono-base system (e.g., dissociated hydroxide ions from the inorganic base) reacts with the protic solvent to produce alkoxide ions, which in turn attack the carbonyl group(s) or ester group(s) / linkage(s) of the polyester.

[0190] In various embodiments, the method further comprises:

[0191] (a-ii) reacting the product comprising the alkali metal salt of mono-ester of the dicarboxylic acid with a base to obtain a solution comprising di-alkali metal salt of the dicarboxylic acid. In various embodiments, the step (a-ii) comprises hydrolysis of the alkali metal salt of mono-ester of the dicarboxylic acid (with a base). In various embodiments, step (a-ii) comprises producing di-alkali metal salt of the dicarboxylic acid. The base may include but is not limited to metal hydroxides, alkali metal hydroxides, alkaline earth metal hydroxides, ammonium-containing hydroxides (e.g., ammonium hydroxide and quaternary ammonium hydroxides), the like and combinations thereof. In various embodiments, the base is separately provided to the reaction mixture, and is not a base from step (a-i) or produced as a byproduct from step (a-i).

[0192] In various embodiments, the di-alkali metal salt of the dicarboxylic acid comprises a structure that is represented by general formula (5): wherein

[0193] A is optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocycloalkyl, optionally substituted heterocycloalkenyl, optionally substituted heteroaryl, or combinations thereof; and each of M is a metal or ammonium-containing group that may be same or different.

[0194] In various embodiments, A is 1 ,4-disubstituted benzene. In such embodiments, the di-alkali metal salt of the dicarboxylic acid comprises a structure that is represented by general formula (6): wherein

[0195] R2a, R2b, R2cand R2dare each independently hydrogen, halogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy, or combinations thereof; and each of M is a metal or ammonium-containing group that may be same or different.

[0196] In various embodiments, R2a, R2b, R2cand R2dare all H.

[0197] In various embodiments, the method further comprises:

[0198] (a-iii) reacting the solution comprising the di-alkali metal salt of the dicarboxylic acid obtained from step (a-ii) with an oxidant / oxidizing agent to obtain a decoloured (e.g., light colored or substantially colorless) solution comprising the di-alkali metal salt of the dicarboxylic acid.

[0199] In various embodiments, the step (a-iii) comprises the degradation / removal / oxidation of dye(s) from the solution (e.g., decolorization).

[0200] In various embodiments, the oxidant / oxidizing agent includes but is not limited to sodium hypochlorite (NaOCI), calcium hypochlorite (Ca(CI0)2), H2O2, Na.?O~. K2O2. CaO2:MgCh, SrCfe, ZnO2, benzoyl peroxide, tert-butyl hydroperoxide (tBuOOH), the like, and combinations thereof.

[0201] In various embodiments, the method further comprises:

[0202] (a-iv) reacting the solution obtained from step (a-ii) or (a-iii) with an acid to obtain a dicarboxylic acid.

[0203] In various embodiments, the acid includes but is not limited to inorganic / mineral acid, organic acid and combinations thereof. For example, the acid may be hydrochloric acid (HCI), sulfuric acid (H2SO4), phosphoric acid (H3PO4), acetic acid, formic acid, citric acid, oxalic acid, the like, and combinations thereof.

[0204] In various embodiments, the dicarboxylic acid comprises a structure that is represented by general formula (7): wherein

[0205] A is optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocycloalkyl, optionally substituted heterocycloalkenyl, optionally substituted heteroaryl, or combinations thereof.

[0206] In various embodiments, A comprises 1 ,4-disubstituted benzene. In such embodiments, the di-alkali metal salt of the dicarboxylic acid comprises a structure that is represented by general formula (8): wherein

[0207] R3a, R3b, R3cand R3dare each independently hydrogen, halogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy, or combinations thereof.

[0208] In various embodiments, R3a, R3b, R3cand R3dare all H.

[0209] In various embodiments, the dicarboxylic acid is selected from the group comprising terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,5-furandicarboxylic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, 1 ,4-cyclohexanedicarboxylic acid, acetylene dicarboxylic acid, or combinations thereof.

[0210] In various embodiments, the method further comprises: (a-v) isolating ethylene glycol from the solution obtained from step (a-i).

[0211] In various embodiments, ethylene glycol is contained in organic solvents used in / present in step (a-i) after the mono-salt of a monoester of the dicarboxylic acid (e.g. K-MMT) is isolated by filtration. It will be appreciated that as steps (a- ii), (a-iii) and / or (a-iv) are carried out / performed in water, there is no ethylene glycol present / involved or formed in these steps. In various embodiments, the method further comprises:

[0212] (b-i) a step of isolating the mono-salt of a monoester of the dicarboxylic acid after step (a-i);

[0213] (b-ii) a step of isolating the dicarboxylic acid after step (a-iv); and (b-iii) a step of isolating the ethylene glycol after step (a-i).

[0214] In various embodiments, the isolating step comprises one or more of the following steps: cooling, heating, drying, purifying, centrifuging, quenching, dissolving, washing, filtering, precipitating, extracting, distilling, drying, and / or decanting the desired products to remove impurities such as unreacted materials (e.g., un-depolymerized polymers such as PE, PP or un-depolymerized cotton, fabric etc), residual dyes, excess reactants, excess solvents etc.

[0215] In various embodiments, the step(s) of cooling, heating, drying, purifying, centrifuging, quenching, dissolving, washing, filtering, precipitating, distilling, drying, and / or decanting is / are repeated at least 1 time, at least 2 times, at least 3 times, at least 4 times, at least 5 times, at least 6 times, at least 7 times, at least 8 times, at least 9 times, or at least 10 times with a washing medium (e.g., organic solvents). The washing medium may be an organic solvent such as DCM, methanol, ethanol, acetone, acetonitrile, THF or ethyl acetate.

[0216] Advantageously, embodiments of the method allow polyester of dicarboxylic acid to be recycled / upcycled / converted into depolymerization products, without the need for expensive and / or tedious / complex / sophisticated / harsh chemical upcycling / recycling / recovering techniques that require high energy input. In various embodiments, the method does not require and / or is substantially devoid of the use of expensive and / or complex / sophisticated equipment that requires high energy input. Advantageously, in various embodiments, the method utilizes a simple and straightforward experimental set-up. In various embodiments, the method is cost- effective (i.e. has a low production cost). Advantageously, embodiments of the method disclosed herein have a high production yield, high scalability and / or high versatility (e.g., can be used for a wide range of waste polyester).

[0217] Advantageously, in various embodiments, the method is substantially devoid of / does not require a pre-treatment / pre-processing step to convert the polyester source into powder / dust / particle form via physical / mechanical means (e.g., powderization, pulverization, grinding and / or crushing), prior to the oxidizing / degrading / depolymerization step. While it should be appreciated that such pre-treatment / pre-processing are not strictly required in various embodiments of the method, it is still possible to still carry out such steps to increase the surface area of the polyester for reaction, which can increase the degradation speed.

[0218] Advantageously, embodiments of the method are less energy-intensive as compared to known methods; minimally affected by additives such as dyes commonly present in plastic waste; easy to perform as it is carried out in air under atmospheric pressure; requires reasonably low reaction temperature; and / or provides / achieves comparable yields to currently reported literatures within similar or shorter reaction time.

[0219] In various embodiments, the present technology is different from methods in that focus on producing DMT as a direct product of PET depolymerization. In contrast, embodiments of the present technology are capable of producing K-MMT as a direct product of PET depolymerization.

[0220] In various embodiments, the present technology is different from methods known in the art in the depolymerization mechanism. In various embodiments, the mechanism involved in the present technology comprises “alternating methanolysis-hydrolysis of PET”, which is completely different from a traditional methanolysis of PET. In various embodiments, the present technology is different from methods that use a bi-solvent system as a reaction medium. In contrast, embodiments of the present technology comprise the utilization of a solvent system with three or more different solvents e g. a tri-solvent system as the reaction medium.

[0221] In various embodiments, the present technology is different from methods that use NaOCHs as a catalyst to promote methanolysis of PET (and is not consumed during the reaction). In contrast, embodiments of the present technology comprise the utilization of a base (e.g., KOH) as the catalyst, which also participates in the reaction as a reactant (and is thus consumed during the reaction).

[0222] Advantageously, embodiments of the present technology comprising a solvent system with three or more different solvents e.g. a tri-solvent system improve yield while retaining high selectivity to K-MMT. Such technical advantages / effects / outcomes are unexpected, unpredictable and cannot be derived in an obvious manner from known methods in the art.

[0223] In various embodiments, the present technology is different from methods that focus on producing TPA as a direct product of PET depolymerization. In contrast, embodiments of the present technology are capable of producing K-MMT as a direct product of PET depolymerization.

[0224] In various embodiments, the present technology is different from methods known in the art in the depolymerization mechanism. In various embodiments, the mechanism involved in the present technology comprises “alternating methanolysis-hydrolysis of PET”, which is completely different from a traditional hydrolysis of PET and also completely different from a traditional methanolysis of PET. In various embodiments, the present technology is different from methods that use acidic ionic liquid as a catalyst. In contrast, embodiments of the present technology comprise the utilization of KOH as the catalyst, which also participates in the reaction as a reactant.

[0225] In various embodiments, the present technology is different from methods known in the art in the temperature employed during the reaction. Advantageously, in various embodiments, PET depolymerization of the present technology is carried out at low temperatures (e.g., 40°C - 55 °C) below the boiling point of solvents. On the other hand, known methods in the art are required to perform / carry out PET depolymerization at a high temperature of 180 °C, which consumes more energy.

[0226] In various embodiments, the present technology is different from methods known in the art in the pressure employed during the reaction. Advantageously, in various embodiments, PET depolymerization of the present technology is carried out at atmospheric pressure. On the other hand, methods known in the art are required to perform / carry out PET depolymerization in an autoclave under relatively high pressure because the reaction temperature is above the boiling point of solvents.

[0227] Advantageously, embodiments of the present technology comprising a solvent system with three or more different solvents e.g. a tri-solvent system improves yield while retaining high selectivity to K-MMT. Such technical advantages / effects / outcomes are unexpected, unpredictable and cannot be derived in an obvious manner from known methods in the art.

[0228] In various embodiments, the present technology is different from methods that focus on producing DMT as a direct product. In contrast, embodiments of the present technology are capable of producing K-MMT as a direct product. In various embodiments, the present technology is different methods that use K2CO3 as a catalyst (and is not consumed during the reaction). In contrast, embodiments of the present technology comprise the utilization of KOH as the catalyst, which also participates in the reaction as a reactant (and is thus consumed during the reaction).

[0229] In various embodiments, the present technology is different from methods known in the art in the depolymerization rate. Advantageously, embodiments of the present technology are capable of achieving more than 90% yield in 2 hours. In contrast, methods in the art require a longer reaction time (e.g., at least 24 hours) to achieve a yield of above 90%.

[0230] Advantageously, embodiments of the present technology comprising a solvent system with three or more different solvents e.g. a tri-solvent system improves yield while retaining high selectivity. Such technical advantages / effects / outcomes are unexpected, unpredictable and cannot be derived in an obvious manner from the art.

[0231] In various embodiments, the present technology is different from methods that carry out PET depolymerization in a bi-solvent system comprising a PET- swelling solvent and a base-reacting solvent. In contrast, embodiments of the present technology are carried out in a solvent system with three or more different solvents e.g. a tri-solvent system comprising a PET-swelling solvent, a base-reacting solvent, and a product-precipitating solvent. Advantageously, the present application has shown that embodiments of the present technology comprising a solvent system with three or more different solvents e.g. a trisolvent system (containing the product-precipitating solvent) improve yield while retaining high selectivity. Such technical advantages / effects / outcomes are unexpected, unpredictable and cannot be derived in an obvious manner from methods known in the art. In various embodiments, the present technology is different from methods that focus on transforming waste PET into carbon nanotubes. In contrast, embodiments of the present technology aim to develop a new depolymerization method to transform waste PET into fine chemicals (e.g., K- MMT, MMT, and TPA).

[0232] In various embodiments, the present technology is different from methods known in the art in the reaction condition employed. Advantageously, in various embodiments, PET depolymerization of the present technology is carried out at low temperatures (e.g., 40°C - 55 °C). On the other hand, methods known in the art (e.g., those that focuses on synthesis of carbon nanotubes from PET) are required to perform / carry out PET depolymerization at a high temperature of 800 °C, which consumes much more energy.

[0233] In various embodiments, the present technology is different from methods known in the art in the decolorization process. In various embodiments, the inventor found the dyes in PET are released and dissolved into solvents after depolymerization, and thus most of the dyes are removed by dissolving into solvents. In various embodiments, the residual dyes in the obtained fine chemicals are decomposed by oxidation using an oxidant. On the other hand, methods known in the art are carried out such that all dyes in PET are decomposed by oxidation using an oxidant before the high-temperature reaction.

[0234] Advantageously, embodiments of the present technology comprising a solvent system with three or more different solvents e.g. a tri-solvent system improves yield while retaining high selectivity to K-MMT. Such technical advantages / effects / outcomes are unexpected, unpredictable and cannot be derived in an obvious manner from methods known in the art.

[0235] In various embodiments, the present technology is a sustainable PET recycling and upcycling technology (SPRUT). Advantageously, in various embodiments, the present technology can be applied to industrial applications, as increasing the isolated yield while retaining high selectivity to produce K-MMT is useful on an industrial scale.

[0236] In various embodiments, the present application also comprises one or more of the following features:

[0237] (Feature 1 ) A process of selectively producing alkali metal salt of mono-ester terephthalate by alternating alcoholysis-hydrolysis depolymerization of waste PET, wherein the process comprises:

[0238] I. A tri-solvent medium comprising a PET-swelling solvent, a basereacting solvent, and a product-precipitating solvent.

[0239] II. An inorganic base of alkali metals or ammonium hydroxide.

[0240] (Feature 2) The process of feature 1 , wherein the selectivity to alkali metal salt of mono-ester terephthalate against di-metal salt of terephthalate is above 80%, preferably above 90%, and further preferably above 95%.

[0241] (Feature 3) The process of features 1 and 2, wherein the alkali metal salt of mono-ester terephthalate is potassium mono-methyl terephthalate, sodium mono-methyl terephthalate, lithium mono-methyl terephthalate, potassium monoethyl terephthalate, sodium mono-ethyl terephthalate, lithium mono-ethyl terephthalate, potassium mono-allyl terephthalate, sodium mono-allyl terephthalate, lithium mono-allyl terephthalate, and the mixture of them.

[0242] (Feature 4) The process of feature 1 , wherein the waste PET feedstocks are post-consumer colourless and colored PET wastes (PET bottles, PET boxes, PET films, industrial PET molds, PET fabrics / textiles), and mixed / blended fabrics of PET-cotton or PET-cotton-spandex or PET-cotton-nylon, multi-layer films of PET-PE or PET-PP, mixed plastic waste of PET with other plastics such as PE, PP, polyvinyl chloride (PVC), polystyrene (PS), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polyethylene furanoate (PEF), poly(butylene adipate) (PBA), poly(butylene succinate) (PBS), and poly(butylene sebacate) (PBSb), and block copolymer of polyesters.

[0243] (Feature 5) The process of feature 1 , wherein the inorganic base is selected from the group of alkali metal hydroxide, consisting of KOH (potassium hydroxide), NaOH (sodium hydroxide), LiOH (lithium hydroxide), ammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and mixtures thereof.

[0244] (Feature 6) The process of features 1 -5, wherein the mole ratio of the inorganic base to the repeating unit of PET is from 0.80 to 1 .5, preferably 0.90 to 1 .2.

[0245] (Feature 7) The process of feature 1 , wherein the PET-swelling solvent is chosen from a group of aprotic solvents, which may either be nonpolar or polar. Dichloromethane (DCM) serves as a representative nonpolar aprotic solvent, while examples of polar aprotic solvents include tetra hydrofuran (THF), 2- methyltetrahydrofuran (2-MeTHF), acetonitrile (ACN), acetone (ACE), methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, cyclohexanone, 2-pentanone (also known as methyl propyl ketone), 3-pentanone (also known as diethyl ketone), diethyl ether, methyl tert-butyl ether (MTBE), tertamyl methyl ether (TAME), cyclopentyl methyl ether (CPME), methoxybenzene (also known as anisole), ethoxybenzene, sulfolane (also known as tetramethylene sulfone), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMA), a,a- trifluorotoluene (TFT), and various combinations thereof.

[0246] (Feature s) The process of feature 1 , wherein the base-reacting solvent is a protic solvent, selected from a group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, allyl alcohol, and propargyl alcohol. (Feature 9) The process of feature 1 , wherein the product-precipitating solvent is selected from a group consisting of pentane, hexane, heptane, octane, benzene, toluene, and mixtures thereof.

[0247] (Feature 10) The process of features 1 , 7 and 8, wherein the volume ratio of the aprotic solvent to the protic solvent is from 1 :1 to 10:1 .

[0248] (Feature 11 ) The process of features 1 , and 7-9, wherein the volume ratio of the aprotic solvent plus protic solvent to product-precipitating solvent is from 4:1 to 50:1.

[0249] (Feature 12) The process of features 1 -11 , wherein said alternating depolymerizing is performed at a temperature ranging from 10 °C to 90 °C, preferably from 25 °C to 65 °C.

[0250] (Feature 13) The process of features 1 -12, wherein said depolymerizing is undertaken for a time period from 10 minutes to 10 hours or from 30 minutes to 5 hours.

[0251] (Feature 14) The process of features 1 -13, wherein further comprising the hydrolysing of the metal salt of mono-ester terephthalate to di-metal salt terephthalate at room temperature in water with a base selected from the group consisting of potassium hydroxide, sodium hydroxide, and lithium hydroxide.

[0252] (Feature 15) The process of features 1 -14, wherein further comprising the degradation of residual dyes in the aqueous solution of di-metal salt terephthalate with an oxidant selected from the group comprising sodium hypochlorite (NaOCI), calcium hypochlorite (Ca(CIO)2), H2O2, Na2O2, K2O2, CaO2, MgO2, SrCh, ZnO2, benzoyl peroxide, tert-butyl hydroperoxide (tBuOOH), etc., and any combination of them. (Feature 16) The process of features 26 and 27, wherein further comprising the acidification of di-metal salt of terephthalate to produce terephthalic acid at room temperature by the addition of the acid solution selected from the group consisting of hydrochloric acid (HCI), sulfuric acid (H2SO4), phosphoric acid (H3PO4), acetic acid, formic acid, citric acid and mixtures thereof.

[0253] (Feature 17) A process to transform colored waste PET to white TPA monomer, comprising five steps:

[0254] I. Conduct the alternating alcoholysis-hydrolysis depolymerization of colored waste PET to M-METT (alkali metal salt of mono-ester terephthalate) using an inorganic base in a tri-solvent medium.

[0255] II. Isolation of M-METT by filtration and washing the crude M-METT with organic solvents to remove the dyes which are released from the colored PET after depolymerization.

[0256] III. Dissolve M-METT in water, then add stoichiometric (equimolar) amount of MOH (KOH or NaOH or LiOH) to transform it into M2-TPA.

[0257] IV. An oxidant is added to the K2-TPA aqueous solution to degrade the residual dyes, resulting in a pale-colored or colorless K2-TPA solution.

[0258] V. An acid (such as H2SO4 or HCI) is added to the K2-TPA solution, producing a white TPA monomer, which is isolated by filtration.

[0259] (Feature 18) The process of feature 17, wherein the alkali metal salt of monoester terephthalate is potassium mono-methyl terephthalate, sodium monomethyl terephthalate, lithium mono-methyl terephthalate, potassium mono-ethyl terephthalate, sodium mono-ethyl terephthalate, lithium mono-ethyl terephthalate, potassium mono-allyl terephthalate, sodium mono-allyl terephthalate, lithium mono-allyl terephthalate, and the mixture of them.

[0260] (Feature 19) The process of feature 17, wherein the waste PET feedstocks are post-consumer colored PET wastes ( PET bottles, PET boxes, PET films, industrial PET molds, PET fabrics / textiles), and mixed / blended fabrics of PET- cotton or PET-cotton-spandex or PET-cotton-nylon, multi-layer films of PET-PE or PET-PP, mixed plastic waste of PET with other plastics such as PE, PP, polyvinyl chloride (PVC), polystyrene (PS), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polyethylene furanoate (PEF), poly(butylene adipate) (PBA), poly(butylene succinate) (PBS), and poly(butylene sebacate) (PBSb), and block copolymer of polyesters.

[0261] (Feature 20) The process of feature 17, wherein the inorganic base is selected from the group of alkali metal hydroxide, consisting of KOH (potassium hydroxide), NaOH (sodium hydroxide), LiOH (lithium hydroxide), and mixtures thereof.

[0262] (Feature 21 ) The process of feature 17, wherein the tri-solvent medium comprises a PET-swelling solvent, a base-reacting solvent, and a productprecipitating solvent.

[0263] (Feature 22) The process of features 17 and 21 , wherein the PET-swelling solvent is chosen from a group of aprotic solvents, which may either be nonpolar or polar. Dichloromethane (DCM) serves as a representative nonpolar aprotic solvent, while examples of polar aprotic solvents include tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), acetonitrile (ACN), acetone (ACE), methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, cyclohexanone, 2-pentanone (also known as methyl propyl ketone), 3-pentanone (also known as diethyl ketone), diethyl ether, methyl tert-butyl ether (MTBE), tertamyl methyl ether (TAME), cyclopentyl methyl ether (CPME), methoxybenzene (also known as anisole), ethoxybenzene, sulfolane (also known as tetramethylene sulfone), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMA), a,a- trifluorotoluene (TFT), and various combinations thereof.

[0264] (Feature 23) The process of features 17 and 21 , wherein the base-reacting solvent is a protic solvent, selected from a group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, allyl alcohol, and propargyl alcohol.

[0265] (Feature 24) The process of features 17 and 21 , wherein the productprecipitating solvent is selected from a group consisting of pentane, hexane, heptane, octane, benzene, toluene, and mixtures thereof.

[0266] (Feature 25) The process of features 17, 19 and 20, wherein the mole ratio of the inorganic base to the repeating unit of PET is from 0.80 to 1 .5, preferably from 0.90 to 1.1.

[0267] (Feature 26) The process of features 17, 21 -23, wherein the volume ratio of the aprotic solvent to the protic solvent is from 1 :1 to 10:1 .

[0268] (Feature 27) The process of features 17, 21 -24, wherein the volume ratio of the aprotic solvent plus protic solvent to product-precipitating solvent is from 4:1 to 50:1.

[0269] (Feature 28) The process of features 17-27, wherein said alternating depolymerizing is performed at a temperature ranging from 10 °C to 90 °C, preferably from 25 °C to 65 °C.

[0270] (Feature 29) The process of features 17-28, wherein said alternating depolymerizing is undertaken for a time period from 10 minutes to 10 hours or from 30 minutes to 5 hours.

[0271] BRIEF DESCRIPTION OF FIGURES

[0272] FIG. 1 is a schematic diagram 100 showing a method of depolymerizing a polyester of a dicarboxylic acid (derived from a polyester of a dicarboxylic acid source) into depolymerization product(s) in accordance with various embodiments disclosed herein. EXAMPLES

[0273] Example embodiments of the disclosure will be better understood and readily apparent to one of ordinary skill in the art from the following examples, tables and if applicable, in conjunction with the figures. It should be appreciated that other modifications related to structural, and / or chemical changes may be made without deviating from the scope of the invention. Example embodiments are not necessarily mutually exclusive as some may be combined with one or more embodiments to form new example embodiments. The example embodiments should not be construed as limiting the scope of the disclosure.

[0274] The following examples describe the development of a new process to produce K-MMT by “alternating methanolysis-hydrolysis” depolymerization of waste PET promoted by an inorganic base in a tri-solvent medium comprising a PET-swelling solvent, a base-reacting solvent, and a product-precipitating solvent. In the following examples, the inorganic base used is an alkali hydroxide, selected from the group consisting of KOH, NaOH, LiOH, or a mixture of them. The PET-swelling solvent used is DCM, the base-reacting solvent used is methanol, and the product-precipitating solvent used is hexanes. As will be shown in the examples, the PET depolymerization with stoichiometric (equimolar) amount of KOH in a tri-solvent medium of DCM (60 vol%), methanol (30 vol%), and hexanes (10 vol%), advantageously afforded 92.4% isolated yield and high selectivity of K-MMT (K-MMT : K2-TPA= 99.2 : 0.8, molar ratio) at 40 °C for a reaction time of 3 hours, demonstrating the potential for industrial applications.

[0275] Therefore, a process has been developed that allows selective production of alkali metal salt of mono-ester terephthalate (M-METT) against the di-metal salt of terephthalate by alternating alcoholysis-hydrolysis depolymerization of waste PET, and further transformation of M-METT into terephthalic acid (TPA). 1. Main Concepts schematic of the depolymerization method

[0276] The examples deploy a method of depolymerizing a polyester of a dicarboxylic acid (derived from a polyester of a dicarboxylic acid source) in accordance with various embodiments disclosed herein and as illustrated in FIG. 1. As shown in the schematic diagram 100, the method comprises a step 102 of alcoholysis, a step 104 of hydrolysis (e.g., monohydrolysis) and a step 106 of acidification (e.g., in the presence of a mineral acid). Step 102 may be methanolysis (e.g., by using methanol as choice of a protic solvent or basereacting solvent in the tri-solvent system) or ethanolysis (e.g., by using ethanol as choice of a protic solvent or base-reacting solvent in the tri-solvent system).

[0277] In step 102, a polyester of a dicarboxylic acid source “A” (e.g., polyethylene terephthalate scrap) is subjected to alcoholysis, which results in the production of an intermediate “B” in-situ. In various embodiments, the intermediate “B” comprises a diester of the dicarboxylic acid. In step 104, the intermediate “B” undergoes dissolution and hydrolysis (e.g., monohydrolysis), and converts into a mono-salt of a monoester of the dicarboxylic acid “C”. Due to its limited solubility in the solvent system, “C” precipitates out as a solid. In step 106, “C” is subjected to acidification, and converts into a mono-acid of a monoester of the dicarboxylic acid “D”. Step 106 may be carried out using sulfuric acid (as mineral acid) at room temperature.

[0278] In various embodiments, the “R” substituent in the ester (i.e. -C(=O)-O- R) present in “B”, “C” and “D” corresponds to the type of alcoholysis involved (or the type of protic solvent / base-reacting solvent used) in depolymerization. For example, if methanolysis is performed (or methanol is used as the protic solvent) during depolymerization, then R may be methyl. If ethanolysis is performed (or ethanol is used as the protic solvent) during depolymerization, then R may be ethyl. In various embodiments, when step 102 comprises methanolysis (e.g., methanol is used in tri-solvent system), polyethylene terephthalate scrap (i.e. A) is converted into dimethyl terephthalate (DMT) (i.e. B), which undergoes hydrolysis and is precipitated out in step 104 as alkali metal salt of mono-methyl terephthalate (M-MMT) (i.e. C). The alkali metal salt of mono-methyl terephthalate (M-MMT) is isolated from the reaction mixture of PET depolymerization. The M-MMT is then dissolved in water and subsequently acidified in step 106 to form monomethyl terephthalate (MMT) (i.e. D). In various embodiments, C comprises potassium salt of monomethyl terephthalate (K-MMT) when a potassium containing base is used in the mono-base system.

[0279] In various embodiments, when step 102 comprises ethanolysis (e.g., ethanol is used in tri-solvent system), polyethylene terephthalate scrap (i.e. A) is converted into diethyl terephthalate (DET) (i.e. B), which undergoes hydrolysis and is precipitated out in step 104 as alkali metal salt of mono-ethyl terephthalate (M-MET) (i.e. C). The alkali metal salt of mono-ethyl terephthalate (M-MET) is isolated from the reaction mixture of PET depolymerization. The M-MET is then dissolved in water and subsequently acidified in step 106 to form monoethyl terephthalate (MET) (i.e. D). In various embodiments, C comprises potassium salt of monoethyl terephthalate (K-MET) when a potassium containing base is used in the mono-base system.

[0280] The examples disclosed herein show that a highly selective, highly efficient and environmentally benign / sustainable methodology has been developed for converting waste polyester of a dicarboxylic acid into useful smaller molecules. The approach comprises use of a mono-base system and tri-solvent system under substantially mild and / or environmentally-benign conditions. Advantageously, the method allows waste polyester of a dicarboxylic acid (e.g., waste polyester of a dicarboxylic acid source) to be upcycled in a less energy- intensive (and therefore more cost and energy-efficient) manner and under environmentally-sustainable conditions. Advantageously, the method is less energy-intensive than current methods. The method / reaction is also easy to perform as it is carried out under mild reaction conditions. Advantageously, the method is able to degrade different types of polyester products, including coloured polyester products. Advantageously, in various embodiments, the method (or depolymerizing step) is minimally affected by presence of dyes in the source. In the following examples, it is shown that the presence of dyes in colored PET bottles and fabrics does not impede the efficiency of PET depolymerization in embodiments of the presently disclosed method.

[0281] Alternating Depolymerization of Waste PET

[0282] In the examples disclosed herein, alternating depolymerization of waste PET is demonstrated in tri-solvent medium. In particular, a process is developed to produce alkali metal salt of mono-ester terephthalates (M-METT) by alternating alcoholysis-hydrolysis depolymerization of waste PET, wherein the process comprises:

[0283] (1 ) A tri-solvent medium comprising a PET-swelling solvent, a base-reacting solvent, and a product-precipitating solvent; and

[0284] (2) An inorganic base (KOH, NaOH, LiOH, or NH4OH (ammonium hydroxide)).

[0285] Firstly, the process designed in accordance with various embodiments herein provides an alternating depolymerization of waste PET, i.e. alternating alcoholysis-hydrolysis depolymerization, that allows waste PET to be efficiently and selectively transformed into alkali metal salt of mono-ester terephthalate at mild conditions. The selectively is high up to more than 90%. Two examples of the alkali metal salt of mono-ester terephthalates are potassium salt of monomethyl terephthalate (K-MMT) and monoethyl terephthalate (K-MET), which are produced by alternating methanolysis-hydrolysis depolymerization of waste PET and alternating ethanolysis-hydrolysis depolymerization of waste PET, respectively.

[0286] Even more advantageously, the examples disclosed herein show that the process designed in accordance with various embodiments disclosed herein can convert waste PET into K-MMT with high selectivity (up to 99%) and high isolated yield (up to 92%) for a 3-hour run at 40 °C.

[0287] The process designed in accordance with various embodiments disclosed herein further includes transforming alkali metal salt of mono-ester terephthalate (M-METT), e g., K-MMT to dialkali metal salt of terephthalic acid (M2-TPA) in water and degrading or decomposing the residual dyes in the M2-TPA aqueous solution with an oxidant. This results in a pale-colored or colorless M2-TPA solution, to which acid may be finally added to convert M2-TPA into white terephthalic acid (TPA).

[0288] In various embodiments therefore, the present disclosure also provides for a process of transforming colored waste PET to white TPA product, comprising five steps as described below:

[0289] I. Conduct the alternating alcoholysis-hydrolysis depolymerization of colored waste PET to M-METT, promoted by an inorganic base in a trisolvent medium.

[0290] II. Isolation of M-METT by filtration and washing the crude K-METT (if M is potassium) with organic solvents to remove the dyes which are released from the colored PET after depolymerization.

[0291] III. Dissolve M-METT in water, then add a stoichiometric (equimolar) amount of inorganic base to transform M-METT into M2-TPA.

[0292] IV. Add an oxidant into the M2-TPA aqueous solution to degrade the residual dyes, resulting in a pale-colored or colorless M2-TPA solution.

[0293] V. Add an acid (such as H2SO4 or HCI) into the M2-TPA solution to convert M2-TPA to a white TPA monomer, which is isolated by filtration.

[0294] The waste PET feedstocks may include but are not limited to postconsumer PET bottles, PET boxes, PET films, industry PET moulds, PET fabrics / textiles, mixed / blended fabrics / textiles of PET-cotton or PET-cotton- spandex or PET-cotton-nylon, multi-layer films of PET-PP or PET-PE, mixed plastic waste of PET with other plastics such as PP, PE, polyvinyl chloride (PVC), polystyrene (PS), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polyethylene furanoate (PEF), poly(butylene adipate) (PBA), poly(butylene succinate) (PBS), and poly(butylene sebacate) (PBSb), and block copolymer of polyesters. These PET wastes can be colorless or colored, such as black, red, blue, and green.

[0295] The solvent used for PET-swelling may be chosen from a selection of aprotic solvents, which can be either nonpolar or polar. As an example of a nonpolar aprotic solvent, dichloromethane (DCM)may be employed. On the other hand, examples of polar aprotic solvents encompass tetrahydrofuran (THF), 2- methyltetrahydrofuran (2-MeTHF), acetonitrile (ACN), acetone (ACE), methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, cyclohexanone, 2-pentanone (also known as methyl propyl ketone), 3-pentanone (also known as diethyl ketone), diethyl ether, methyl tert-butyl ether (MTBE), tertamyl methyl ether (TAME), cyclopentyl methyl ether (CPME), methoxybenzene (also known as anisole), ethoxybenzene, sulfolane (also known as tetramethylene sulfone), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMA), ct,a- trifluorotoluene (TFT), and various combinations thereof.

[0296] The base-reacting solvent may be a protic solvent, selected from a group of alcohols comprising methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, allyl alcohol, propargyl alcohol, and any combination of them.

[0297] The product-precipitating solvent may be chosen from a group of alkanes comprising pentane, hexane, heptane, octane, benzene, toluene, and mixtures thereof.

[0298] The oxidant used to degrade the residual dyes in M2-TPA solution may be selected from the group comprising sodium hypochlorite (NaOCI), calcium hypochlorite (Ca(CIO)2), H2O2, Na2C>2, K2O2, CaO2, MgCh, SrC>2, ZnO2, benzoyl peroxide, ferf-butyl hydroperoxide (tBuOOH), or any combination of them. Mechanism of Alternating Depolymerization of Waste PET

[0299] The proposed depolymerization mechanism of the method of alternating depolymerization of waste PET in tri-solvent medium is illustrated using a specific example shown in FIG. 1 . As shown, methanol is used as a base-reacting solvent, which produces methoxide anions in the equilibrium, creating a solution that comprises both methoxide anions and hydroxide anions. DOM can swell PET resin to accelerate the methanolysis of PET (A) to produce the intermediate DMT (B). In the tri-solvent medium, DMT is soluble and one ester group of DMT is hydrolyzed to produce K-MMT (C). Because K-MMT has poor solubility in the trisolvent medium, K-MMT is precipitated out from the solution. The examples of product-precipitating solvents are hexane and heptane, which can enhance the precipitation of K-MMT and accelerate the monohydrolysis of DMT. Therefore, the tri-solvent medium leads to high isolated yields, while retaining high selectivity of 99%.

[0300] When alcohol is used as the protic solvent, the reaction is an “alternating alcoholysis-hydrolysis” of waste PET.

[0301] In the example shown in FIG. 1 , the PET-swelling solvent is DCM, the base-reacting solvent is methanol, and the product-precipitating solvent is hexanes. The inventors surprisingly found that the PET depolymerization with stoichiometric (equimolar) amount of KOH in a tri-solvent medium of DCM (60 vol%), methanol (30 vol%), and hexanes (10 vol%), afforded 92.4% isolated yield and high selectivity of K-MMT (K-MMT : K2TA= 99.2 : 0.8, molar ratio) at 40 °C for a reaction time of 3 hours.

[0302] In the example shown in FIG. 1 , K-MMT is readily acidified into MMT at r.t. in water. Both K-MMT and MMT are fine chemicals in the market. Additionally, K- MMT is readily hydrolyzed into K2-TPA at r.t. in water within 5 minutes. The K2- TPA aqueous solution is then acidified at r.t. in water to produce TPA for PET recycling. NaOH and LiOH can also promote the “alternating methanolysis- hydrolysis” depolymerization of waste PET, producing Na-MMT and Li-MMT, respectively.

[0303] According to the proposed mechanism shown in FIG. 1 , such a unique “alternating alcoholysis-hydrolysis” depolymerization of waste PET is a two-step “cascade alcoholysis-monohydrolysis” reaction in mechanism, which can also be called “concurrent alcoholysis-monohydrolysis” reaction, or “tandem alcoholysis- monohydrolysis” reaction, or “domino alcoholysis-monohydrolysis” reaction. When methanol is used as the protic solvent, it is a “cascade methanolysis- monohydrolysis” depolymerization of waste PET, producing K-MMT which is readily acidified into MMT at r.t. in water. When ethanol is used as the protic solvent, it is a “cascade ethanolysis-monohydrolysis” depolymerization of waste PET, producing K-MET which is readily acidified into MET at r.t. in water. The overall result is indicating an “alternating methanolysis-hydrolysis” depolymerization of waste PET.

[0304] Features of the proposed mechanism include:

[0305] 1. High selectivity

[0306] 2. High efficiency

[0307] 3. Require mild conditions

[0308] 4. Presence of a tri-solvent system

[0309] Role of Solvents

[0310] The solvent used for swelling PET, such as DCM, improves the interaction between PET and bases like methoxide ions, thereby speeding up the reaction. The base-reacting solvent, such as methanol, reacts with the inorganic base, such as KOH, to produce methoxide ions, resulting in a solution containing both methoxide ions and hydroxide ions. The solvent used for precipitating the product, such as hexane or heptane, quickens / fastens the precipitation of K-MMT from the reaction solution, thereby enhancing the reaction rate and increasing the isolated yield.

[0311] Summary of features of the Tri-solvent system:

[0312] Role of DCM -> (1 ) swelling PET; and (2) dissolving DMT better.

[0313] Role of methanol -> generating methoxide anions.

[0314] Role of hexane -> enhancing precipitation of K-MMT.

[0315] Isolation of Ethylene Glycol (EG) as the Second Product

[0316] The solid product K-MMT resulting from the depolymerization of PET can be separated from the reaction mixture through filtration and subsequently isolated. Another product of PET depolymerization, ethylene glycol, is a liquid that mixes well with the solvent blend. Ethylene glycol can be extracted by eliminating solvents with low boiling points and then purified through distillation under reduced pressure. It remains stable within the depolymerization concentrations.

[0317] Removal of Dyes When Using Colored Waste PET as Feedstock

[0318] It has been demonstrated in the examples disclosed herein that the presence of dyes in colored PET bottles and fabrics does not impede the efficiency of PET depolymerization. Hence, various colored PET bottles and fabrics can serve as suitable feedstock. For instance, depolymerization of black PET fabric proceeds rapidly, yielding a black slurry. The resulting K-MMT product is filtered and washed with DCM, resulting in a pale black powder and a black filtrate solution. Analysis revealed that, after PET depolymerization, the organic dyes were liberated and could be eliminated by washing K-MMT with organic solvents.

[0319] The obtained K-MMT is then dissolved in water, and equimolar amounts of KOH (or NaOH, or ammonium hydroxide) are introduced to convert K-MMT to K2-TPA, producing a pale black aqueous solution. An oxidizing agent is incorporated into the solution and stirred at room temperature to degrade or decompose any residual dyes, resulting in a pale-yellow or nearly colorless solution. The oxidizing agent is chosen from a range including sodium hypochlorite (NaOCI), calcium hypochlorite (Ca(CIO)2), HaCh, NasOa, K2O2, CaOa, MgCh, SrOa, ZnOa, benzoyl peroxide, tert-butyl hydroperoxide (tBuOOH), etc., and any combination thereof.

[0320] Following this, an acid solution (such as H2SO4 or HCI) is introduced to the obtained pale-yellow or nearly colorless solution to acidify K2-TPA and produce the white TPA monomer. Thus, a chemical process for producing white TPA from colored waste PET is also provided herein.

[0321] Using PET-containinq Plastic Mixture as Feedstock

[0322] In practical scenarios, plastic waste typically comprises a blend of PET alongside other materials such as PP, PE, cotton fabric, paper, nylon, and spandex. The method designed in accordance with various embodiments disclosed herein enables the selective depolymerization of PET while preserving the integrity of other components (PP, PE, cotton fabric, paper, nylon, spandex). Consequently, the unsorted mixtures of plastic waste can serve as viable feedstocks, allowing for the selective depolymerization of PET and its conversion into K-MMT, subsequently leading to TPA for PET recycling.

[0323] Unique features of the presently disclosed method

[0324] The method disclosed in accordance with various embodiments disclosed herein is different from methods that are performed in a bi-solvent medium.

[0325] In the embodiments of the presently disclosed method, a third solvent (such as hexanes) was added as a product-precipitating solvent, thus forming a tri-solvent medium, which leads to a higher isolated yield (85.4%) for a 1 -h run while retaining the high selectivity to K-MMT. Therefore, the embodiments of the presently disclosed method provide an improved depolymerization process to transform waste PET into K-MMT.

[0326] In addition, embodiments of the presently disclosed method also provide a process to remove the dyes of colored waste PET after depolymerization in two steps:

[0327] (1 ) After PET depolymerization, wash the crude K-MMT product with an organic solvent to remove the dyes that are released from colored PET waste.

[0328] (2) After K-MMT is transformed to K2-TPA in water, an oxidizing agent is added to the aqueous solution of K2-TPA to degrade the residual dyes, resulting in a pale-colored or nearly colorless K2-TPA solution. The acidification of the K2-TPA solution produces the white TPA product.

[0329] 2. Experiments and Results

[0330] 2.1. General Considerations

[0331] Preparation of waste PET scraps:

[0332] Various waste PET and PET-containing waste mixtures can be used as feedstocks, including but not limited to colorless and colored PET bottles, colorless and colored PET boxes, colorless and colored PET films, various colored PET fabrics or textiles, blended or mixed fabrics of PET with cotton, rayon, nylon, and spandex, etc.

[0333] Feedstock-1’. Colorless PET bottles were collected from various brands of postconsumer water bottles without undergoing any cleaning process. These bottles were manually cut into small pieces measuring approximately 1.5x1.5 cm and utilized as feedstock.

[0334] Feedstock-2’, mixed three scraps of colorless PET, PE, and PP bottles. Three plastics of colorless bottles (PET, PE, and PP) were cut into small scraps measuring approximately 1.5*1.5 cm and mixed as feedstock. The approximate weight ratio of PET to PE to PP is 2: 1 : 1 .

[0335] Feedstock-3: mixed scraps of three colored PET bottles (black, red and blue). These three colored PET bottles were cut into small pieces measuring approximately 1 .5*1 .5 cm and mixed as feedstock.

[0336] Feedstock-4: Scraps of white PET-cotton blended fabric (labelled as PET polyester 28% and cotton 72%) were cut into small fragments measuring approximately 1 .5*1 .5 cm. These small cuttings were then utilized as feedstock. Feedstock-5: Pieces of black PET fabric (labelled as 100% PET polyester) were cut into small scraps measuring approximately 1.5*1.5 cm using scissors. These small scraps were then used as feedstock.

[0337] Determination of Selectivity:

[0338] The molar ratio of K-MMT / K2-TPA is calculated by the integral area of the Ph-H peaks of K-MMT (7.92 ppm and 8.07 ppm), to the peak of the Ph-H of impurity K2-TPA (7.88 ppm) in the1H-NMR spectrum of the K-MMT product.

[0339] Solvents and Chemicals:

[0340] All the solvents and chemicals were purchased from the sources as provided below, and were used as received in all the examples and comparative examples.

[0341] Dichloromethane (DCM): >99.5%, Avantor Performance Materials.

[0342] Methanol: >99.9%, VWR Chemicals.

[0343] Hexanes: Assay (sum of 5 isomers, total hexanes plus methylcyclopentane) (by GC) >98.5%, Avantor Performance Materials. Potassium hydroxide (KOH): >85.0%, Merck KGaA.

[0344] Deuterium oxide (D2O, 99.96% D): Cambridge Isotope Laboratories

[0345] Nuclear Magnetic Resonance (NMR) Measurement:

[0346] 1H-NMR (500MHz) and13C-NMR (125MHz) spectra were recorded with JEOL 500MHz NMR spectrometer. 2.2. Experimental procedure for Comparative Example 1

[0347] Feedstock-1 (scraps of colorless PET bottles, 5 g, repeating unit 26.02 mmol), DCM (26.7 mL), methanol (13.3 mL), and KOH (1.72 g, 26.02 mmol) were added into a 100 mL RBF in order in air. The resulting mixture was vigorously stirred while heating to 40 °C in a silicon oil bath. A white slurry was obtained after 1 hour. The white solid powder was collected by filtration and washed with DCM (20 mL). No unreacted PET was observed. The white K-MMT product was first dried in air in fume hood overnight, then dried in an oven at 60 °C for 6 hours. The obtained K-MMT was characterized by1H and13C-NMR.

[0348] Obtained K-MMT 4.64 g, 83.8%. The selectivity of K-MMT against K2-TPA is 99.4%. The results are listed in table 1 .

[0349] 1H-NMR (500 MHz, D2O, ppm) of K-MMT: 3.95 (s, 3H, -CW3), 7.92 (d, 2H, ph-H, JC-H = 8Hz), 8.07 (d, 2H, ph-H, C-H = 8Hz).

[0350] 13C-NMR (125 MHz, D2O, ppm) of K-MMT: 52.80, 128.77, 129.39, 131.48, 141.16, 169.10, 174.80.

[0351] 2.3. Experimental procedure for Examples 1-5 (using Feedstock-1)

[0352] Feedstock-1 (scraps of colorless PET bottles, 5 g, repeating unit 26.02 mmol), a tri-solvent mixture containing required amounts of DCM, methanol, hexanes, and KOH (1 .72 g, 26.02 mmol) were added into a 100 mL RBF in order in air. The resulting mixture was vigorously stirred while heating to 40 °C in a silicon oil bath. A white slurry was obtained after a reaction time of 1 , 2, or 3 hours. The white solid was collected by filtration and washed with DCM (20 mL). No unreacted PET was observed. The white K-MMT product was first dried in air in a fume hood overnight, then dried in an oven at 60 °C for 6 hours. The obtained K-MMT was characterized by1H and13C-NMR. The isolated yields and selectivity are listed in table 1 .1H-NMR (500 MHz, D2O, ppm) of K-MMT: 3.95 (s, 3H, -CW3), 7.92 (d, 2H, ph-H, JC-H = 8Hz), 8.07 (d, 2H, ph-H, C-H = 8Hz).

[0353] 13C-NMR (125 MHz, D2O, ppm) of K-MMT: 52.80, 128.77, 129.39, 131.48, 141.16, 169.10, 174.80.

[0354] 2.4. Experimental procedure for Example-6 (using Feedstock-2)

[0355] In a 100 mL round-bottom flask, Feedstock-2 (comprising mixed scraps of colorless PET, PE, and PP totalling 10 g, consisting of 5 g PET, 26.0 mmol of PET-RU), DCM (30 mL), methanol (15 mL), hexanes (5 mL), and KOH (1.72 g, 26.0 mmol) were sequentially added in ambient air. The resulting mixture was vigorously stirred with a magnetic stirring bar at 40 °C while heated in a silicone oil bath. After three hours, a white slurry containing un-depolymerized PE and PP scraps was obtained. The white powder (K-MMT) and solid PE and PP scraps were collected via filtration and washed with DCM (25 mL). A sample of the K- MMT powder was taken and dried at 40 °C for 4 hours before analysis via1H- NMR, revealing a selectivity of 99.1 % to K-MMT against K2-TPA.

[0356] The resulting solid mixture comprised K-MMT powder, PE scraps, and PP scraps. The mixture underwent extraction with water (2*45 mL) followed by filtration. Un-depolymerized PE and PP scraps were collected, totalling 5 g in weight after drying, indicating the intact preservation of PE and PP plastics under depolymerization conditions. The filtrate constituted a K-MMT aqueous solution, to which KOH (1.72 g, 26.0 mmol) was added and stirred for 10 minutes at room temperature, facilitating the conversion of K-MMT to K2-TPA. Subsequently, the K2-TPA solution was acidified by the addition of 25 wt.% H2SO4 until reaching a pH of 2, resulting in a white slurry of TPA. The TPA white powder was isolated through filtration and further dried overnight in an oven at 60 °C.

[0357] Obtained TPA 4.0 g, yield 92.5%.

[0358] 1H-NMR (100 MHz, DMSO-d6, ppm) of TPA: 7.58 (s, 4H, Ph-H). Table 1. Results of PET depolymerization using Feedstock-1.

[0359] Note: Waste PET scraps (5 g, repeating unit 26.02 mmol). KOH (1.72 g, 26.02 mmol). Reaction temperature 40 °C. The yield is isolated yield as white K-MMT powder. The selectivity is the molar ratio of K-MMT to Kg-TPA.

[0360] 2.5. Experimental procedure for Example-7 (using Feedstock-3)

[0361] Feedstock-3 comprising mixed scraps of three colored PET bottles (5 g, PET-RU 26.0 mmol), along with DCM (24 mL), methanol (12 mL), hexanes (4 mL), and KOH (1 .72 g, 26.0 mmol) were sequentially added into a 100 mL roundbottom flask in ambient air. The resulting mixture underwent vigorous stirring with a magnetic stirring bar at 40 °C while heated in a silicone oil bath. After three hours of reaction time, a brown slurry was obtained. The K-MMT powder was then collected via filtration and washed with DCM (3x15 mL), yielding a pale brown powder (crude K-MMT) and a brown filtrate solution. This result indicated that, after PET depolymerization, most of the dyes were released and dissolved into the organic solution. A sample of the K-MMT powder was dried at 40 °C for 4 hours and subsequently analyzed via1H-NMR, demonstrating a selectivity of 99.0 % to K-MMT against K2-TPA.

[0362] The crude K-MMT product was dissolved in water (2><45 mL), producing a pale brown solution. Subsequently, KOH (1.72 g, 26.0 mmol) was added and stirred for 10 minutes at room temperature to convert K-MMT to K2-TPA. Sodium hypochlorite pentahydrate (0.4 g) was then added and stirred overnight at room temperature, resulting in a color change to pale yellow. Next, the K2-TPA solution was acidified by adding 25 wt.% H2SO4 until reaching a pH of 2, yielding a white slurry of TPA. Finally, the TPA white powder was isolated via filtration and subsequently dried overnight in an oven at 60 °C.

[0363] Obtained TPA 3.95 g, yield 91 .4%.

[0364] 1H-NMR (100 MHz, DMSO-de, ppm) of TPA: 7.58 (s, 4H, Ph-H).

[0365] 2.6. Experimental procedure for Example-8 (using Feedstock-4)

[0366] Feedstock-4 [scraps of white PET (28%)-cotton (72%) blended fabric, totalling 18.9 g containing 5 g PET, PET-RU at 26.0 mmol), along with DCM (60 mL), methanol (30 mL), hexanes (10 mL), and KOH (1.72 g, 26.0 mmol), were added sequentially into a 200 mL round-bottom flask in ambient air. The resulting mixture underwent vigorous stirring with an overhead mechanical stirrer at 40 °C by heating in a silicone oil bath. After three hours, a white slurry containing undepolymerized cotton fabric was obtained. The white powder (K-MMT) and cotton scraps were collected via filtration. A sample of the K-MMT powder was dried at 40 °C for 4 hours and subsequently analyzed via1H-NMR, revealing a selectivity of 98.8 % to K-MMT against K2-TPA.

[0367] The resulting mixture comprising K-MMT powder and undepolymerized cotton fabric underwent extraction with water (2><50 mL) and subsequent filtration. The un-depolymerized cotton fabric was collected, dried, and weighed, totalling 12.40 g. This indicated that the blended PET-cotton fabric lost 5.5 g of the PET component after depolymerization.

[0368] The filtrate constituted a K-MMT aqueous solution, to which KOH (1.81 g, 27.4 mmol) was added and stirred for 10 minutes at room temperature, converting K-MMT to K2-TPA. Subsequently, the K2-TPA solution was acidified by adding 25 wt.% H2SO4 until reaching a pH of 2, yielding a white slurry of TPA. The TPA white powder was isolated via filtration and subsequently dried overnight in an oven at 60 °C.

[0369] Obtained TPA 4.03 g, yield 93.3%.

[0370] 1H-NMR (100 MHz, DMSO-d6, ppm) of TPA: 7.58 (s, 4H, Ph-H).

[0371] 2.7. Experimental procedure for Example-9 (using Feedstock-5)

[0372] Feedstock-5 (scraps of black PET fabric, 5g, PET-RU 26.0 mmol), DCM (24 mL), methanol (12 mL), hexanes (4 mL), and KOH (1 .72 g, 26.0 mmol) were sequentially added into a 150 mL round-bottom flask in ambient air. The resulting mixture was vigorously stirred with an overhead mechanical stirrer at 40 °C via heating in a silicone oil bath. After three hours, a black slurry was obtained. A pale yellow powder (K-MMT) was collected via filtration and washed with DCM (3x15 mL). The filtrate is a black solution containing the black dyes. A sample of the K-MMT powder was taken and dried at 40 °C for 4 hours. It was then analyzed using 1 H-NMR, which demonstrated a selectivity of 99.0% for K-MMT against K2-TPA%.

[0373] The pale yellow K-MMT powder was dissolved in water (85 mL), yielding a pale yellow aqueous solution. KOH (1.72 g, 26.0 mmol) was then added and stirred for 10 minutes at room temperature, transforming K-MMT into K2-TPA in the aqueous solution. Sodium hypochlorite pentahydrate (0.3 g) was then added and stirred overnight at room temperature, resulting in a very pale yellow solution. Subsequently, the K2-TPA solution was acidified by adding 25 wt.% H2SO4 until reaching a pH of 2, affording a white slurry of TPA. The TPA white powder was isolated via filtration and dried overnight in an oven at 60 °C.

[0374] Obtained TPA 4.05 g, yield 93.8%.

[0375] 1H-NMR (100 MHz, DMSO-de, ppm) of TPA: 7.58 (s, 4H, Ph-H).

[0376] 3. Comparative Analysis

[0377] 3.1. Advantage of using product-precipitating solvent

[0378] Without using hexanes as the product-precipitating solvent, the isolated yield is 83.8% with a selectivity of 99.4% (Comparative Example 1 ). After 4 mL DCM was replaced with hexanes (DCM was reduced from 26.7 mL to 22.7 mL), while retaining the same volume of methanol (13.3 mL), the isolated yield was increased to 84.5% and maintaining the same selectivity of 99.4% (Example 2). Then, keeping hexanes volume at 4 mL, while changing the volume ratio of DCM : methanol to 2 : 1 , the isolated yield was increased to 85.4% with a selectivity of 99.4% (Example 3). After further prolonging the reaction to two and three hours, the isolated yield was increased to 89.8% and 92.4%, with a selectivity of 99.4% and 99.2%, respectively (Examples 3 and 4). In example 5, the hexanes volume was increased to 6 mL (15 vol%), the isolated yield was 91.0%, and retained a high selectivity of 99.3% for a reaction time of 2 hours (Example 5). The experimental results clearly showed that the PET depolymerization in a tri-solvent medium afforded higher isolated yields with high selectivity to K- MMT, demonstrating great potential for industrial applications.

[0379] 3.2. Selective depolymerization of PET and removal of dyes

[0380] Selective depolymerization of the PET component is achievable when utilizing unsorted plastics which contain PET, PE, and PP (Example-6), as well as PET-cotton blended fabrics (Example-8) as feedstocks. PE, PP, and cotton remain intact after PET depolymerization.

[0381] The presence of dyes in colored PET bottles and PET fabrics does not slow down the PET depolymerization process (Examples 7 and 9). After PET depolymerization, most of the dyes are liberated into the solvents. The residual dyes present in the crude K-MMT can be degraded using oxidants in aqueous solution. The oxidant is chosen from the group comprising sodium hypochlorite (NaOCI), calcium hypochlorite (Ca(CIO)2), H2O2. Na2O2, K2O2, CaO2, gO2, SrO2, ZnO2, benzoyl peroxide, tert-butyl hydroperoxide (tBuOOH), etc.. Thus, the present application provides an efficient process to produce white TPA monomer from colored and unsorted PET wastes.

[0382] It will be appreciated by a person skilled in the art that other variations and / or modifications may be made to the embodiments disclosed herein without departing from the spirit or scope of the disclosure as broadly described. For example, in the description herein, features of different exemplary embodiments may be mixed, combined, interchanged, incorporated, adopted, modified, included etc. or the like across different exemplary embodiments. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

Claims

1. CLAIMS1 . A method of depolymerizing a polyester of a dicarboxylic acid, the method comprising:(a-i) depolymerizing a polyester of a dicarboxylic acid source in the presence of:(i) a mono-base system; and(ii) a solvent system comprising three or more different solvents, to obtain a product comprising a mono-salt of a monoester of the dicarboxylic acid and / or derivatives thereof.

2. The method of claim 1 , wherein the polyester of a dicarboxylic acid source comprises waste polyester of a dicarboxylic acid.

3. The method of any one of the preceding claims, wherein the polyester of a dicarboxylic acid comprises a structure that is represented by general formula (1 ):whereinA is optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocycloalkyl, optionally substituted heterocycloalkenyl, optionally substituted heteroaryl, or combinations thereof;R1is optionally substituted alkylene, optionally substituted cycloalkylene, optionally substituted alkenylene, optionally substituted alkynylene, or combinations thereof; and4. The method of claim 3, wherein A comprises 1 ,4-disubstituted benzene and the polyester of a dicarboxylic acid comprises a structure that is represented by general formula (2):whereinR2is optionally substituted alkylene, optionally substituted cycloalkylene, optionally substituted alkenylene, optionally substituted alkynylene, or combinations thereof;Ra, Rb, Rcand Rdare each independently hydrogen, halogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy, or combinations thereof; and n > 1.

5. The method of any one of the preceding claims, wherein the depolymerizing in (a-i) comprises a plurality of alcoholysis and hydrolysis reactions.

6. The method of any one of the preceding claims, wherein the depolymerizing in (a-i) comprises the following reaction:(13) (12) whereinA is optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocycloalkyl, optionally substituted heterocycloalkenyl, optionally substituted heteroaryl, or combinations thereof;R1is optionally substituted alkylene, optionally substituted cycloalkylene, optionally substituted alkenylene, optionally substituted alkynylene, or combinations thereof;R4and R4’ are each independently optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, or combinations thereof; andM is a metal or ammonium-containing group; and n > 1.

7. The method of any one of the preceding claims, wherein the mono-salt of a monoester of the dicarboxylic acid comprises a structure that is represented by general formula (3):whereinA is optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted heterocycloalkyl, optionally substituted heterocycloalkenyl, optionally substituted heteroaryl, or combinations thereof;R3is optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, or combinations thereof; andM is a metal or ammonium-containing group.

8. The method of claim 7, wherein A comprises 1 ,4-disubstituted benzene and the mono-salt of a monoester of the dicarboxylic acid comprises a structure that is represented by general formula (4):whereinR4is optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, or combinations thereof;R1 a, R1 b, R1 cand R1dare each independently hydrogen, halogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy, or combinations thereof; andM is a metal or ammonium-containing group.

9. The method of any one of claims 6 to 8, wherein M is an alkali metal selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) or francium (Fr).

10. The method of any one of the preceding claims, wherein the mono-base system is configured to concurrently serve as a catalyst as well as a reactant in the depolymerization reaction.11 . The method of any one of the preceding claims, wherein the mono-base system comprises an inorganic base.

12. The method of claim 11 , wherein the inorganic base comprises an Arrhenius base selected from the group consisting of metal hydroxides, alkali metal hydroxides, alkaline earth metal hydroxides, ammonium- containing hydroxides and combinations thereof.

13. The method of any one of the preceding claims, wherein the solvent system comprises three or more different solvents selected from the group consisting of:(a) an aprotic solvent;(b) a protic solvent; and(c) a hydrocarbon compound.

14. The method of claim 13, wherein the aprotic solvent is selected from the group consisting of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2- MeTHF), acetonitrile (ACN), acetone (ACE), methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, cyclohexanone, 2- pentanone (also known as methyl propyl ketone), 3-pentanone (also known as diethyl ketone), diethyl ether, methyl tert-butyl ether (MTBE), tert-amyl methyl ether (TAME), cyclopentyl methyl ether (CPME), methoxybenzene (also known as anisole), ethoxybenzene, sulfolane (also known as tetramethylene sulfone), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMA), a,a-trifluorotoluene (TFT), dichloromethane (DCM), chlorobenzene, and combinations thereof.

15. The method of any one of claims 13 to 14, wherein the protic solvent is selected from the group consisting of methanol, ethanol, n-propanol, / sopropanol, n-butanol, tert-butanol, allyl alcohol, propargyl alcohol, and combinations thereof.

16. The method of any one of claims 13 to 15, wherein the hydrocarbon compound is selected from the group consisting of n-pentane, n-hexane, n-heptane, n-octane, 2-methylpentane, 3-methylpentane, cyclohexane, benzene, toluene, xylene, 1 ,2-dimethylbenzene, 1 ,3-dimethylbenzene, 1 ,4-dimethylbenzene, and combinations thereof.

17. The method of any one of claims 13 to 16, wherein the volume ratio of the aprotic solvent to the protic solvent is from 1 :10 to 50:1 .

18. The method of any one of claims 13 to 17, wherein the volume ratio of the aprotic solvent plus the protic solvent to the hydrocarbon compound is from 1 :1 to 75:1.

19. The method of any one of the preceding claims, wherein the molar ratio of the mono-base to the number of repeating units in polyester is 0.1 to 2.

20. The method of any one of the preceding claims, wherein the method further comprises:(a-ii) reacting the product comprising the mono-salt of a mono ester of the dicarboxylic acid with a base to obtain a solution comprising dialkali metal salt of the dicarboxylic acid.21 . The method of claim 20, wherein the method further comprises:(a-iii) reacting the solution comprising the di-alkali metal salt of the dicarboxylic acid obtained from (a-ii) with an oxidant / oxidizing agent to obtain a decoloured solution comprising the di-alkali metal salt of the dicarboxylic acid.

22. The method of any one of claims 20 to 21 , wherein the method further comprises:(a-iv) reacting the solution obtained from (a-ii) or (a-iii) with an acid to obtain a dicarboxylic acid.

23. The method of claim 22, wherein the dicarboxylic acid comprises a structure that is represented by general formula (8):whereinR3aR3bR3canc|R3dare each independently hydrogen, halogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy, or combinations thereof.

24. The method of claim 23, wherein the dicarboxylic acid is selected from the group comprising terephthalic acid, isophthalic acid, 2,6- naphthalenedicarboxylic acid, 2,5-furandicarboxylic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, 1 ,4- cyclohexanedicarboxylic acid, acetylene dicarboxylic acid, and combinations thereof.

25. The method of any one of the preceding claims, wherein the method further comprises: (a-v) isolating ethylene glycol from the solution obtained from step (a-i).

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