Method for catalyzing polyester depolymerization by alkoxide

Abstract

The invention discloses a method for catalyzing polyester depolymerization by alkoxide. The method comprises the following steps: carrying out chemical depolymerization reaction on polyester or a polyester-containing composite material in diester carbonate in the absence of a catalyst or in the presence of an organic salt as a catalyst, wherein the organic salt comprises metal organic salt and organic anion ionic liquid; anions in the metal organic salt and the organic anion ionic liquid are independently selected from the following anions: alcohol anions, phenol anions, mercaptan anions and thiophenol anions. The method has the advantages of high efficiency, greenness, mild reaction conditions and the like, polyester can be depolymerized to generate the polyester monomer, a new method is provided for chemical conversion of waste polyester plastic, and the method has high industrial application value.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of waste plastic recycling, and particularly relates to a method for preparing monomers by catalytic polyester depolymerization, and more particularly relates to a method for catalytic polyester depolymerization without catalyst or alcohol (phenol / thiol / sulfenol) salt substance. BACKGROUND

[0002] Polyesters have excellent properties and have been widely used in various fields of production and life. With the rapid development of human society, the demand for polyesters is rapidly increasing, and the amount of waste polyesters is also increasing. Therefore, it is urgent to solve this problem.

[0003] Chemical methods for converting them into useful substances are an important way to effectively solve this problem. At present, methods such as hydrolysis, alcoholysis, aminolysis, and acidolysis can depolymerize polyesters into monomers and chemicals, providing an important means for their recycling. However, there are often problems such as high reaction temperature and cross-contamination in the process of polyester depolymerization, making the chemical recycling of polyesters costly and difficult to implement. Therefore, new methods for depolymerizing polyesters are urgently needed. To our knowledge, there is no published content on using carbonic diesters to depolymerize polyesters. SUMMARY

[0004] In view of the defects of the prior art, the present application provides a new method for catalytic polyester depolymerization. This method has the advantages of high efficiency, greenness, and mild reaction conditions, and can generate monomers from polyesters, having strong industrial application value.

[0005] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0006] The method for catalytic polyester depolymerization provided by the present application comprises the following steps: under the condition of no catalyst or with an organic salt as a catalyst, polyesters or composite materials containing polyesters are subjected to chemical depolymerization reaction in carbonic diesters;

[0007] The organic salt includes metal organic salt and / or organic anion type ionic liquid.

[0008] The anions in the metal organic salt and the organic anion type ionic liquid are independently selected from the following anions: alcohol anion, phenol anion, thiol anion, and sulfenol anion.

[0009] The above steps can achieve the depolymerization of polyesters under mild conditions, and the polyesters are depolymerized into corresponding monomers and small molecular compounds, providing a new method for the chemical recycling of polyesters in waste polyester products.

[0010] Further, in the method, the reaction condition of the chemical depolymerization reaction is that the reaction is carried out at a temperature of room temperature to 220°C for 0.5 to 36 hours. The room temperature refers to 15 to 30°C.

[0011] Further, in the method, the alcohol anion, the phenol anion, the thiol anion and the thiophenol anion are all anions formed by losing a proton from the corresponding compound (alcohol, phenol, thiol, thiophenol).

[0012] The alcohol anion has a general formula of R1O - , wherein R1 represents a substituted or unsubstituted alkyl group, and further can be a substituted or unsubstituted C1-C8 straight chain or branched alkyl group, wherein the substituent of the substituted or unsubstituted alkyl group is selected from any of the following groups: halogen (such as F, Cl, Br, etc.), hydroxyl, phenyl, etc.

[0013] Specifically, the alcohol anion includes but is not limited to a methanol anion (methoxy anion), an ethanol anion (ethoxy anion), a trifluoroethanol anion (trifluoroethoxy anion), a propanol anion (propoxy anion), an isopropanol anion (isopropoxy anion), a n-butanol anion (n-butoxy anion), a t-butanol anion (t-butoxy anion), a benzyl alcohol anion (benzyloxy anion), etc.

[0014] The phenol anion has a general formula of ArO - , wherein Ar represents an aryl group, and further can be a phenyl group; specifically, the phenol anion can be a phenol anion, etc.

[0015] The thiol anion has a general formula of R1S - , wherein R1 represents an alkyl group, and further can be a C1-C4 straight chain or branched alkyl group; specifically, the thiol anion can be an ethanethiol anion (ethanethioxy anion).

[0016] The thiophenol anion has a general formula of ArS - , wherein Ar represents an aryl group, and further can be a phenyl group; specifically, the thiophenol anion can be a thiophenol anion.

[0017] Further, in the method, the metal organic salt is a salt formed by the combination of a metal cation and an organic anion through an ionic bond; wherein the metal cation includes but is not limited to lithium ion, sodium ion, potassium ion, calcium ion, magnesium ion, etc.

[0018] Specifically, the metal organic salt includes but is not limited to lithium methoxide, sodium methoxide, potassium methoxide, magnesium methoxide, calcium methoxide, lithium ethoxide, sodium ethoxide, potassium ethoxide, magnesium ethoxide, calcium ethoxide, sodium propanol, sodium isopropanol, sodium n-butanol, sodium t-butanol, sodium phenol, potassium phenol, sodium trifluoroethanol, sodium ethanethiol, sodium thiophenol, etc.

[0019] Furthermore, in the above method, the organic anionic ionic liquid is formed by the combination of cations and organic anions through ionic bonds, and is liquid at or near room temperature; wherein, the anions include, but are not limited to, alcohol anions, phenolic anions, etc.; the cations include, but are not limited to, imidazole cations, pyridinium cations, tetraalkylammonium cations, tetraalkylphosphine cations, guanidinium cations, alkylpiperidine cations, alkylpyridine cations, alkylpyrrole cations, etc.; wherein, the alkyl groups in the tetraalkylammonium cation, tetraalkylphosphine cation, alkylpiperidine cation, alkylpyridine cation, and alkylpyrrole cation are all independently selected from C1-C8 straight-chain or branched alkyl groups;

[0020] Specifically, the organic anionic liquid includes, but is not limited to, [N 1111 ]OCH3 (tetramethylammonium methanol salt), [N 4444 ]OCH3 (tetrabutylammonium methoxide), [P 4444 [OCH3 (tetrabutylphosphine methanol), [Py] 14 [OCH3 (N-butyl-N-methylpyrrole methanol salt), [PP] 14 ]OCH3 (N-butyl-N-methylpiperidine methanol salt), [N 4444 ]OCH2CH3 (tetrabutylammonium ethanolate), [N 4444 [OPh](Tetrabutylammonium phenolate).

[0021] Furthermore, in the above method, the diester carbonate may be selected from at least one of: dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, dibutyl carbonate, and diphenyl carbonate (DPC).

[0022] Further, in the above method, the polyester includes polyethylene terephthalate (PET), polypropylene terephthalate (PPT), polybutylene terephthalate (PBT), polyethylene succinate (PES), polybutylene adipate (PBA), polyethylene adipate (PEA), polyethylene 2,5-furandiate (PEF), polybutylene succinate (PBS), polybutylene adipate / terephthalate (PBAT), polylactic acid (PLA), polycaprolactone (PCL), etc.; the polyester-containing composite system includes, but is not limited to, at least one of all samples, physical objects, or mixtures thereof containing polyester components.

[0023] Furthermore, the polyester can be polyester textiles, polyester plastic products, etc.

[0024] Further, in the above method, the reaction system of the reaction can further comprise an additive, which can be selected from at least one of carbonates, sulfates, phosphates, hydrogen phosphates, nitrates. Specifically, the additive includes but is not limited to Na2SO4, NaNO3, NaH2PO4, Na2HPO4, [P 4444 ]H2PO4, [P 4444 ]NO3, ZnSO4, ZnCO3, etc. In the metal salt catalytic system, the addition of an appropriate amount of additive can shorten the reaction time; in the ionic liquid catalytic system, the addition of an appropriate amount of additive can reduce the amount of ionic liquid catalyst.

[0025] Further, the molar ratio of the additive to the polyester structural unit can be 0.01:1 to 0.5:1, and specifically can be 0.02:1, 0.05:1, etc.

[0026] Further, in the above method, the molar ratio of the carbonic diester to the polyester structural unit can be 1:1 to 25:1, and specifically can be 10:1 to 15:1, 10:1, 15:1, or 20:1, etc.

[0027] Further, in the above method, the molar ratio of the organic salt to the polyester structural unit can be 1% to 20%, and specifically can be 1%, 5%, 10%, or 20%, etc.

[0028] Further, in the above method, under the condition of no catalyst, the reaction conditions of the chemical depolymerization reaction are as follows: the reaction is carried out at a temperature of 170 to 220°C (specifically, such as 200°C to 220°C, 170°C, 200°C, or 220°C, etc.) for 12 to 36 hours.

[0029] Further, in the above method, when an organic salt is added as a catalyst, the reaction temperature can be 50 to 220°C, and the reaction time can be 0.5 to 24 hours.

[0030] As a preferred, when a metal organic salt is added as a catalyst, the reaction temperature can be 120 to 180°C (specifically, such as 140°C to 180°C, 120°C, 140°C, 160°C, 170°C, or 180°C, etc.), and the reaction time can be 4 to 24 hours (specifically, such as 4 to 16 hours, 4 hours, 8 hours, 12 hours, 16 hours, or 24 hours, etc.); more preferably, when a metal organic salt is added as a catalyst, the reaction temperature can be 140 to 180°C, and the reaction time can be 8 to 16 hours;

[0031] As preferred, when an organic anion type ionic liquid is added as catalyst, the temperature of the reaction can be room temperature (15-30°C) to 60°C (specifically, 30°C to 60°C, 30°C, 40°C, 50°C or 60°C, etc.), and the time can be 0.5 to 6 hours (specifically, 2 to 6 hours, 0.5 hour, 2 hours, 4 hours or 6 hours, etc.). More preferably, when an alcohol anion type ionic liquid is added as catalyst, the temperature of the reaction can be room temperature (20-30°C) to 50°C, and the time can be 0.5 to 4 hours; and most preferably, when a methanol anion type ionic liquid is added as catalyst, the temperature of the reaction can be 20 to 30°C, and the time can be 0.5 to 2 hours.

[0032] As preferred, when a complex system formed by a metal organic salt and an organic anion ionic liquid is added as catalyst, the temperature of the reaction can be 20 to 40°C (specifically, 20 to 30°C), and the time can be 0.5 to 4 hours (specifically, 1 to 2 hours), wherein more preferably, the metal organic salt and the organic anion ionic liquid contain the same anion, which is preferably an alcohol anion (such as a methanol anion).

[0033] The polyester structural unit in the present application refers to the basic repeating unit constituting the polyester high molecular compound, the core of which is a structural fragment containing two ester groups connected by an ester bond (-O-CO-), which can be generally represented as -O-R-CO- (wherein R is an aliphatic or aromatic hydrocarbon group). Specifically, the polyester is formed by polyhydric alcohol (such as ethylene glycol) and polycarboxylic acid (such as terephthalic acid) through condensation polymerization reaction, in which water molecules are removed, and the remaining part is connected by an ester bond to form a high molecular chain, and this repeating structural fragment connected by an ester bond is the structural unit of the polyester.

[0034] Further, the specific operation of the above method is as follows: the polyester or the polyester-containing composite material is placed in a carbonic acid diester, heated to a set time under certain temperature conditions without catalyst or with the addition of an organic salt as catalyst, cooled, and the precipitate is separated to obtain the corresponding monomer.

[0035] The method further comprises the following operations: the unreacted solid is separated by filtration; and then the excess carbonic acid diester and the generated monomer are collected in sequence by separation methods such as conventional filtration, vacuum distillation, etc., and the catalyst is recovered.

[0036] The recovered catalyst can be reused.

[0037] Regarding the separation of the product after the reaction, it further includes using the corresponding separation method according to the different catalysts used.

[0038] The product obtained by the above method is described as follows by way of example:

[0039] PET is depolymerized in dimethyl carbonate (DMC) to obtain dimethyl terephthalate (DMT) and ethylene carbonate (EC);

[0040] PPT is depolymerized in DMC to obtain dimethyl terephthalate (DMT) and 2,4,8,10-oxa-3,9-carbonyl-undecane;

[0041] PBT is depolymerized in DMC to obtain dimethyl terephthalate (DMT) and 2,4,9,11-oxa-3,10-carbonyl-dodecane;

[0042] PEA is depolymerized in DMC to obtain dimethyl adipate and ethylene carbonate (EC);

[0043] PBA is depolymerized in DMC to obtain dimethyl adipate and 2,4,9,11-oxa-3,10-carbonyl-dodecane;

[0044] PEF is depolymerized in DMC to obtain dimethyl furan 2,5-dicarboxylate and ethylene carbonate (EC);

[0045] PES is depolymerized in DMC to obtain dimethyl succinate and ethylene carbonate (EC);

[0046] PBS is depolymerized in DMC to obtain dimethyl succinate and 2,4,9,11-oxa-3,10-carbonyl-dodecane;

[0047] PBAT is depolymerized in DMC to obtain dimethyl terephthalate (DMT), dimethyl adipate and 2,4,9,11-oxa-3,10-carbonyl-dodecane;

[0048] PLA is depolymerized in DMC to obtain methyl (2R)-2-((methoxycarbonyl)oxy)propanoate;

[0049] PCL is depolymerized in DMC to obtain 6-[(methoxycarbonyl)oxy ethyl ester)] adipate;

[0050] PET is depolymerized in diethyl carbonate (DEC) to obtain diethyl terephthalate and ethylene carbonate (EC);

[0051] PET is depolymerized in diphenyl carbonate (DPC) to obtain diphenyl terephthalate and ethylene carbonate (EC).

[0052] The present application realizes the depolymerization of polyester into ester monomers under mild conditions through the reaction of carbonic acid diester and polyester, and is suitable for the related technical research and development of polyester monomer chemical recycling in any polyester and its mixed system. The method provided by the present application has the advantages of high efficiency, greenness, mild reaction conditions, etc., and has strong industrial application value in the depolymerization of polyester into its monomers. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 Equation of depolymerization reaction of polyester in dimethyl carbonate and depolymerization products;

[0054] Figure 2 Equation of depolymerization reaction of polyester in diethyl carbonate and depolymerization products.

[0055] Figure 3 NMR hydrogen spectrum of product DMT obtained in Example 1 in DMSO-d6.

[0056] Figure 4 NMR hydrogen spectrum of product EC obtained in Example 1 in DMSO-d6. DETAILED DESCRIPTION

[0057] The application will be further described in conjunction with the specific embodiments, and the examples given are only for the purpose of illustrating the application, but not for limiting the scope of the application. The examples provided below can serve as a guide for further improvement by those of ordinary skill in the art, and do not in any way constitute a limitation on the application.

[0058] The experimental methods in the following examples are all conventional methods, and are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions, unless otherwise specified. The materials, reagents, etc. used in the following examples can be obtained commercially, unless otherwise specified.

[0059] Example 1-12, depolymerization of PET in dimethyl carbonate without catalyst or methoxy anion metal salt catalyst

[0060] Experimental procedure: 0.96 g (about 5 mmol of polyester structural unit) of PET plastic bottle pieces, 0.5 mmol of methoxy anion metal salt, 9 g (about 100 mmol) of dimethyl carbonate were added to a 100 mL pressure-resistant reaction tube, then the reaction tube was placed in a heating device set to a certain temperature, and the reaction was carried out for a certain period of time, then ice water bath cooling was carried out, and immediately needle-like crystals of dimethyl terephthalate (DMT) were precipitated, the dimethyl terephthalate solid was obtained by filtration, the filtrate was further rotary evaporated to remove unreacted dimethyl carbonate, and the filtrate was filtered, which was another product, ethylene carbonate, and the solid was the methoxy anion metal salt catalyst, which could be recycled.

[0061] The solid product obtained was identified by structure as DMT (dimethyl terephthalate), as shown in the NMR hydrogen spectrum of product DMT obtained in Example 1 in DMSO-d6. Figure 3 The NMR hydrogen spectrum of product DMT obtained in Example 1 in DMSO-d6.

[0062] The liquid product obtained was identified by structure as EC (ethylene carbonate), as shown in the NMR hydrogen spectrum of product EC obtained in Example 1 in DMSO-d6. Figure 4The resulting product EC is shown in the nuclear magnetic resonance hydrogen spectrum in DMSO-d6.

[0063] Table 1 Reaction conditions and reaction results of Examples 1-12

[0064]

[0065]

[0066] Examples 13-23, metal salt of ethoxy anion, phenol anion, thiophenol anion catalyze dimethyl carbonate depolymerization of PET

[0067] Experimental procedure: 0.96 g (about 5 mmol of polyester structural units) of 100% PET textile, 0.5 mmol of metal salt, 9 g (about 100 mmol) of dimethyl carbonate are added to a 100 mL pressure-resistant reaction tube, then the reaction tube is placed in a heating device set to a temperature, and the reaction is carried out for a certain period of time, then it is cooled in an ice water bath, and immediately dimethyl terephthalate needle-shaped crystals are precipitated, the dimethyl terephthalate solid is filtered, the filtrate is further rotary evaporated to remove unreacted dimethyl carbonate, filtered, and the filtrate is the other product, ethylene carbonate, and the solid is the metal salt of alkoxide catalyst, which can be recycled.

[0068] Table 2 Reaction conditions and reaction results of Examples 13-23

[0069] Example Ethoxy anion metal salt Temperature / °C Time / h DMT yield / % EC yield / % 13 NaOCH2CH3 160 12 97 92 14 Mg(OCH2CH3)2 160 12 90 84 15 NaOCH2CH3 180 8 94 92 16 Mg(OCH2CH3)2 180 8 90 87 17 NaOCH2CH3 140 24 92 86 18 Mg(OCH2CH3)2 140 24 89 86 19 NaOCH2CH3 120 24 68 60 20 Mg(OCH2CH3)2 120 24 60 56 21 Sodium phenolate 170 16 97 85 22 Sodium ethanethiolate 170 16 96 83 23 Sodium thiophenolate 170 16 98 84

[0070] Examples 24-30, alcohol (phenol) ionic liquid catalyzes dimethyl carbonate depolymerization of PET

[0071] Experimental procedure: 0.96 g (about 5 mmol of polyester structural units) of PET plastic bottle pieces, 0.5 mmol of alcohol (phenol) ionic liquid, 9 g (about 100 mmol) of dimethyl carbonate are added to a 100 mL pressure-resistant reaction tube, then the reaction tube is placed in a heating device set to a temperature, and the reaction is carried out for a certain period of time, then it is cooled in an ice water bath, and immediately dimethyl terephthalate needle-shaped crystals are precipitated, a saturated sodium chloride solution is added to separate the ionic liquid catalyst, the upper clear liquid is separated to recover the catalyst, the lower layer is filtered to obtain dimethyl terephthalate solid, and the filtrate is further rotary evaporated to remove unreacted dimethyl carbonate, and the remaining is the other product, ethylene carbonate.

[0072] Table 3 Reaction conditions and reaction results of Examples 24-30

[0073] Example Methoxy anion ionic liquid Temperature / °C Time / h DMT yield / % EC yield / % 24 [[N 1111 ]OCH3]] 30 2 95 88 25 [[N 4444 ]OCH3]] 30 2 93 87 26 [[P 4444 ]OCH3]] 30 2 92 85 27 [[Py 14 ]OCH3]] 30 2 90 88 28 [[PP 14 ]OCH3]] 30 2 94 89 29 [[N 4444 ]OCH2CH3]] 50 2 96 80 30 [[N 4444 ][OPh]]]> 60 6 80 74

[0074] Examples 31-35, composite catalytic system catalyzes PET depolymerization in DMC

[0075] Experimental procedure: 0.96 g (about 5 mmol of substance containing polyester structural units), PET, 0.5 mmol of alcohol (phenol) ionic liquid, 0.5 mmol of alcohol (phenol) metal salt, 9 g (about 100 mmol) of dimethyl carbonate were added into a 100 mL pressure-resistant reaction tube, then the reaction tube was placed in a heating device set at a certain temperature, reacted for a certain time, then cooled in an ice water bath, and immediately needle-like dimethyl terephthalate crystals were precipitated. A saturated sodium chloride solution was added to separate the ionic liquid catalyst, the upper clear liquid was separated to recover the catalyst, and the lower layer was filtered to obtain dimethyl terephthalate (DMT) solid. The filtrate was further rotary evaporated to remove unreacted dimethyl carbonate, filtered, and the filtrate was another product, ethylene carbonate (EC). The solid was an alcohol (phenol) metal salt catalyst that could be recycled.

[0076] Table 4 Reaction conditions and reaction results of examples 31-35

[0077] Example Catalyst 1 Catalyst 2 Temperature / °C Time / h DMT yield / % EC yield / % 31 [[N 1111 ]OCH3]] NaOCH3 30 1 93 88 32 [[N 4444 ]OCH3]] NaOCH3 30 1 95 85 33 [[P 4444 ]OCH3]] NaOCH3 30 1 96 81 34 [[Py 14 ]OCH3]] NaOCH3 30 1 91 83 35 [[PP 14 ]OCH3]]> NaOCH3 30 1 92 87

[0078] Examples 36-43, DMC depolymerization of PET catalyzed by composite catalyst system containing additives

[0079] Experimental procedure: 0.96 g (about 5 mmol of substance containing polyester structural units), PET, 0.25 mmol of alcohol (phenol) ionic liquid or 0.25 mmol of alcohol (phenol) metal salt, 0.25 mmol of additive, 9 g (about 100 mmol) of dimethyl carbonate were added into a 100 mL pressure-resistant reaction tube, then the reaction tube was placed in a heating device set at a certain temperature, reacted for a certain time, then cooled in an ice water bath, and immediately needle-like dimethyl terephthalate crystals were precipitated. A saturated sodium chloride solution was added to separate the ionic liquid (if no ionic liquid was used, this step could be omitted), the upper clear liquid was separated to recover the catalyst, and the lower layer was filtered to obtain dimethyl terephthalate solid. The filtrate was further rotary evaporated to remove unreacted dimethyl carbonate, filtered, and the filtrate was another product, ethylene carbonate. The solid was an alcohol (phenol) metal salt and / or metal salt additive that could be recycled (if no metal salt was used, this step could be omitted).

[0080] Table 5 Reaction conditions and reaction results of examples 36-43

[0081] Example Catalyst Additive Temperature / °C Time / h DMT yield / % EC yield / % 36 NaOCH3 Na2SO4 160 6 94 81 37 NaOCH3 NaNO3 160 6 92 83 38 NaOCH3 NaH2PO4 160 6 93 82 39 NaOCH3 Na2HPO4 160 6 91 84 40 [[P 4444 ]OCH3]] [[P 4444 ]H2PO4]]> 30 2 94 81 41 [[P 4444 ]OCH3]] [[P 4444 ]NO3]]> 30 2 93 82 42 [[P 4444 ]OCH3]] ZnSO4 30 2 91 83 43 [[P 4444 ]OCH3]] ZnCO3 30 2 92 87

[0082] Example 44, NaOCH3 catalyzed depolymerization of PET in diethyl carbonate (DEC)

[0083] Experimental procedure: 0.96 g (about 5 mmol of substance containing polyester structural units), PET, 0.5 mmol of sodium methoxide, 12 g (about 100 mmol) of diethyl carbonate were added to a 100 mL pressure-resistant reaction tube, then the reaction tube was placed in a heating device at 160 °C for 16 hours, then cooled in an ice water bath, immediately there were needle-like crystals of diethyl terephthalate precipitated, the diethyl terephthalate solid was obtained by filtration, the filtrate was further rotary evaporated to remove the unreacted diethyl carbonate, the remaining was another product, ethylene carbonate, and the solid was sodium methoxide, which could be recycled. Weighed and calculated, the yield of diethyl terephthalate (92%) and the yield of ethylene carbonate (81%) were obtained.

[0084] Example 45, NaOCH3 catalyzed depolymerization of PET in diphenyl carbonate (DPC)

[0085] Experimental procedure: 0.96 g (about 5 mmol of substance containing polyester structural units), PET, 0.5 mmol of sodium methoxide, 12 g (about 100 mmol) of diethyl carbonate were added to a 100 mL pressure-resistant reaction tube, then the reaction tube was placed in a heating device at 160 °C for 16 hours, then cooled in an ice water bath, immediately there were needle-like crystals of diethyl terephthalate precipitated, the diethyl terephthalate solid was obtained by filtration, the filtrate was further rotary evaporated to remove the unreacted diethyl carbonate, the remaining was another product, ethylene carbonate, and the solid was sodium methoxide, which could be recycled. Weighed and calculated, the yield of diethyl terephthalate (92%) and the yield of ethylene carbonate (81%) were obtained.

[0086] Examples 46-55, NaOCH3 catalyzed depolymerization of other polyesters in DMC

[0087] Experimental procedure: about 1 mmol of substance containing polyester structural units of different polyesters (PPT, PBT, PBA, PBS, PEA, PES, PEF, PBAT, PLA or PCL), 0.05 mmol of sodium methoxide, 900 mg (about 10 mmol) of DMC were added to a 15 mL pressure-resistant reaction tube, then the reaction tube was placed in a heating device at 160 °C for 2 hours, then cooled in an ice water bath, mesitylene was added as an internal standard, then the yield was determined by nuclear magnetic resonance analysis with internal standard method.

[0088] Example 46, depolymerization of PPT, yield of dimethyl terephthalate 99%, 2,4,8,10-oxa-3,9-carbonyl-undecane 95%.

[0089] Example 47, depolymerization of PBT, yield of dimethyl terephthalate 98%, 2,4,9,11-oxa-3,10-carbonyl-dodecane 93%.

[0090] Example 48 depolymerization of PBA, yield of dimethyl adipate 98%, 2,4,9,11-oxa-3,10- carbonyl-dodecane 90%.

[0091] Example 49 depolymerization of PBS, yield of dimethyl succinate 97%, 2,4,9,11-oxa-3,10- carbonyl-dodecane 89%.

[0092] Example 50 depolymerization of PEA, yield of dimethyl adipate 99%, ethylene carbonate 94%.

[0093] Example 51 depolymerization of PES, yield of dimethyl succinate 98%, ethylene carbonate 90%.

[0094] Example 52 depolymerization of PEF, yield of dimethyl furan 2,5-dicarboxylate 99%, ethylene carbonate 96%.

[0095] Example 53 depolymerization of PBAT, yield of dimethyl terephthalate 96%, dimethyl adipate 95%, 2,4,9,11-oxa-3,10-carbonyl-dodecane 91%.

[0096] Example 54 depolymerization of PLA, yield of methyl (2R)-2-((methoxycarbonyl)oxy)propanoate 98%.

[0097] Example 55 depolymerization of PCL, yield of adipic acid 6-[(methoxycarbonyl)oxy ethyl ester)] 97%.

[0098] Examples 56-65, [N 4444 ] [OCH3] catalyzed depolymerization of other polyesters in DMC

[0099] Procedure: about 1 mmol of different polyesters (PPT, PBT, PBA, PBS, PEA, PES, PEF, PBAT, PLA or PCL) containing the structural unit of the polyester, 0.05 mmol [N 4444 ] [OCH3], 900 mg (about 10 mmol) of DMC were added to a 15 mL pressure tube, then the reaction tube was placed in a heating device at 40°C for 2 hours, then cooled in an ice water bath, mesitylene was added as an internal standard, then the yield was determined by NMR analysis using the internal standard method.

[0100] Example 56 depolymerization of PPT, yield of dimethyl terephthalate 99%, 2,4,8,10-oxa-3,9- carbonyl-undecane 93%.

[0101] Example 57 depolymerization of PBT, with a yield of 99% dimethyl terephthalate and 94% 2,4,9,11-oxa-3,10-carbonyl-dodecane.

[0102] Example 58 depolymerization of PBA, with a yield of 98% dimethyl adipate and 91% 2,4,9,11-oxa-3,10-carbonyl-dodecane.

[0103] Example 59 depolymerization of PBS, with a yield of 97% dimethyl adipate and 91% 2,4,9,11-oxa-3,10-carbonyl-dodecane.

[0104] Example 60 depolymerization of PEA, with a yield of 98% dimethyl adipate and 92% ethylene carbonate.

[0105] Example 61 depolymerization of PES, with a yield of 97% dimethyl succinate and 91% ethylene carbonate.

[0106] Example 62 depolymerization of PEF, with a yield of 98% dimethyl furan 2,5-dicarboxylate and 92% ethylene carbonate.

[0107] Example 63 depolymerization of PBAT, with a yield of 95% dimethyl terephthalate, 96% dimethyl adipate and 91% 2,4,9,11-oxa-3,10-carbonyl-dodecane.

[0108] Example 64 depolymerization of PLA, with a yield of 97% methyl (2R)-2-((methoxycarbonyl)oxy)propanoate.

[0109] Example 65 depolymerization of PCL, with a yield of 98% adipic acid 6-[(methoxycarbonyl)oxy ethyl ester)].

[0110] The application has been described in detail. Those skilled in the art will understand that they can make modifications and alterations to this application without departing from the spirit and scope of the application. Although specific embodiments of this application have been shown and described, it is to be understood that various modifications can be made by one skilled in the art without departing from the scope of this application. Accordingly, it is not intended that the application be limited, except as by the appended claims.

Claims

1. A method for catalytic depolymerization of a polyester, comprising the following steps: subjecting a polyester or a polyester-containing composite to a chemical depolymerization reaction in a carbonic acid diester in the absence of a catalyst or in the presence of an organic salt as a catalyst; wherein the organic salt comprises a metal organic salt and / or an organic anion ionic liquid; the anion of the metal organic salt and the organic anion ionic liquid is independently selected from at least one of the following anions: alcohol anion, phenol anion, thiol anion, thiophenol anion.

2. The method of claim 1, wherein: the reaction condition of the chemical depolymerization reaction is at a temperature of room temperature to 220℃ for 0.5 to 36 hours. 3.The method of claim 1 or 2, wherein: said alcohol anion, of general formula RO - , R representing a substituted or unsubstituted alkyl group, further a substituted or unsubstituted C1-C8 linear or branched alkyl group, wherein the substituents of said substituted or unsubstituted alkyl group are selected from any of the following groups: halogen, hydroxyl, phenyl; in particular, said alcohol anion is selected from at least one of the following: methanol anion, ethanol anion, trifluoroethanol anion, ethylene glycol monoanion, propanol anion, isopropanol anion, n-butanol anion, t-butanol anion, benzyl alcohol anion; and / or, the phenolate anion, of the general formula ArO - , Ar represents an aryl group, further a phenyl group; in particular, the phenolate anion is a phenolate anion; and / or, the thiol anion, of the general formula R1S - R1 represents an alkyl group, further a C1-C4 straight chain or branched alkyl group; in particular, the thiol anion is an ethanethiol anion; and / or, the thiophenolate anion, which has the general formula Ar1S - , Ar1 represents an aryl group, further a phenyl group; in particular, the thiophenolate anion is a phenylthiophenolate anion.

4. The method according to any one of claims 1-3, characterized by: the metal cation of the metal organic salt is selected from at least one of the following: lithium ion, sodium ion, potassium ion, calcium ion, magnesium ion; further, the metal organic salt is selected from at least one of the following: lithium methoxide, sodium methoxide, potassium methoxide, magnesium methoxide, calcium methoxide, lithium ethoxide, sodium ethoxide, potassium ethoxide, magnesium ethoxide, calcium ethoxide, sodium propanol, sodium isopropanol, sodium n-butanol, sodium tert-butanol, sodium phenoxide, potassium phenoxide, sodium trifluoroethanol, sodium ethanethiol, sodium thiophenol; and / or, the anion of the organic anion ionic liquid is selected from at least one of the following: alcohol anion, phenol anion, and the cation thereof is selected from at least one of the following: imidazolium cation, pyridinium cation, tetraalkylammonium cation, tetraalkylphosphonium cation, guanidinium cation, alkylpiperidine cation, alkylpyridine cation, alkylpyrrole cation, wherein the alkyl of the tetraalkylammonium cation, tetraalkylphosphonium cation, alkylpiperidine cation, alkylpyridine cation and alkylpyrrole cation is independently selected from C1-C8 linear or branched alkyl; Further, the organic anion ionic liquid is selected from at least one of: [N 1111 ]OCH3, [N 4444 ]OCH3, [P 4444 ]OCH3, [Py 14 ]OCH3, [PP 14 ]OCH3, [N 4444 ]OCH2CH3, [N 4444 ]OCH2CH3, and [OPh]. 5.The method of any one of claims 1-4, wherein: in the absence of a catalyst, the reaction condition of the chemical depolymerization reaction is at a temperature of 170-220℃ for 12-36 hours; in the presence of an organic salt as a catalyst, the reaction temperature is 50-220℃ and the reaction time is 0.5-24 hours; as preferred, in the presence of a metal organic salt as a catalyst, the reaction temperature is 120-180℃ and the reaction time is 4-24 hours;more preferably, the reaction temperature is 140-180℃ and the reaction time is 8-16 hours; as preferred, in the presence of an organic anion ionic liquid as a catalyst, the reaction temperature is 15-60℃ and the reaction time is 0.5-6 hours;more preferably, in the presence of an alcohol anion ionic liquid as a catalyst, the reaction temperature is 20-50℃ and the reaction time is 0.5-4 hours; as preferred, in the presence of a composite system formed by a metal organic salt and an organic anion ionic liquid as a catalyst, the reaction temperature is 20-40℃ and the reaction time is 0.5-4 hours, more preferably, the metal organic salt and the organic anion ionic liquid contain the same anion, especially preferred alcohol anion.

6. The method of any one of claims 1-5, wherein: The carbonic acid diester is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, diphenyl carbonate; And / or, the polyester is selected from at least one of polyethylene terephthalate (PET), polytrimethylene terephthalate (PPT), polybutylene terephthalate (PBT), polyethylene succinate (PES), polybutylene adipate (PBA), polyethylene adipate (PEA), polyethylene 2,5-furandicarboxylate (PEF), polybutylene succinate (PBS), polybutylene adipate terephthalate (PBAT), polylactic acid (PLA), polycaprolactone (PCL); the polyester-containing composite system is selected from at least one of all samples, physical objects or mixtures thereof containing a polyester component.

7. The method of any one of claims 1-6, wherein: The molar ratio of the carbonic acid diester to the polyester structural unit is 1:1-25:1; And / or, the molar ratio of the organic salt to the polyester structural unit is 1%-20%.

8. The method of any one of claims 1-7, wherein: An additive is further added to the reaction system of the reaction, and the additive is selected from at least one of carbonates, sulfates, phosphates, hydrogen phosphates, nitrates; Further, the additive is selected from at least one of Na2SO4, NaNO3, NaH2PO4, Na2HPO4, [P 4444 ]H2PO4, [P 4444 ]NO3, ZnSO4, ZnCO3. Further, the feeding molar ratio of the additive to the polyester structural unit is 0.01:1-0.5:

1.

9. The method of any one of claims 1-8, wherein: The specific operation steps of the method are as follows: the polyester or polyester-containing composite material is placed in the carbonic acid diester, heated to a set time under certain temperature conditions without a catalyst or by adding the organic salt as a catalyst, and cooled; Further, the method further includes the following operations: the unreacted solid is separated by filtration; then, the excess carbonic acid diester and the generated monomer are collected in sequence by a separation method of conventional filtration, reduced pressure distillation method, and the catalyst is recovered.

10. The method of any one of claims 1-9, wherein: The polyester is PET, which is depolymerized in dimethyl carbonate to obtain dimethyl terephthalate and ethylene carbonate; And / or, the polyester is PPT, which is depolymerized in dimethyl carbonate to obtain dimethyl terephthalate and 2,4,8,10-oxa-3,9-carbonyl-undecane; And / or, the polyester is PBT, which is depolymerized in dimethyl carbonate to obtain dimethyl terephthalate and 2,4,9,11-oxa-3,10-carbonyl-dodecane; And / or, the polyester is PEA, which is depolymerized in dimethyl carbonate to obtain dimethyl adipate and ethylene carbonate; And / or, the polyester is PBA, which is depolymerized in dimethyl carbonate to obtain dimethyl adipate and 2,4,9,11-oxa-3,10-carbonyl-dodecane; And / or, the polyester is PEF, which is depolymerized in dimethyl carbonate to obtain dimethyl furan 2,5-dicarboxylate and ethylene carbonate; And / or, the polyester is PES, which is depolymerized in dimethyl carbonate to obtain dimethyl succinate and ethylene carbonate; and / or, the polyester is PBS, which is depolymerized in dimethyl carbonate to give dimethyl succinate and 2,4,9,11-oxa-3,10-carbonyl-dodecane; and / or, the polyester is PBAT, which is depolymerized in dimethyl carbonate to give DMT, dimethyl adipate and 2,4,9,11-oxa-3,10-carbonyl-dodecane; and / or, the polyester is PLA, which is depolymerized in dimethyl carbonate to give methyl (2R)-2-((methoxycarbonyl)oxy)propanoate; and / or, the polyester is PCL, which is depolymerized in dimethyl carbonate to give 6-[(methoxycarbonyl)oxy ethyl ester)] adipate; and / or, the polyester is PET, which is depolymerized in diethyl carbonate to give diethyl terephthalate and ethylene carbonate; and / or, the polyester is PET, which is depolymerized in diphenyl carbonate to give diphenyl terephthalate and ethylene carbonate.

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