Method for preparing terephthalate diester by catalyzing depolymerization of polyethylene terephthalate (PET)

Abstract

Disclosed in the present invention is a method for preparing a terephthalate diester by catalyzing the depolymerization of polyethylene terephthalate (PET). Treating PET or a composite system thereof in a carbonate diester without a catalyst or under the condition of using a salt substance as a catalyst realizes chemical depolymerization of the PET, thereby obtaining the PET monomer terephthalate diester and ethylene carbonate and realizing complete depolymerization of the PET in the composite. The present invention can realize the depolymerization of PET under mild conditions by means of the reaction between the carbonate diester and the PET, and further carry out the research and development of related technology for the chemical recovery of the PET monomer from a PET composite system or a PET mixed system. The method provided by the present invention has the advantages of high efficiency, greenness, mild reaction conditions, etc., can catalyze the depolymerization of PET to generate the monomer terephthalate diester, and has a relatively strong industrial application value.

Description

A method for catalytic depolymerization of polyethylene terephthalate (PET) to prepare terephthalic acid diester TECHNICAL FIELD

[0001] The present application belongs to the technical field of waste plastic recycling, and particularly relates to a method for catalytic depolymerization of polyethylene terephthalate (PET) to prepare terephthalic acid diester, and more particularly relates to a method for catalytic depolymerization of PET to prepare terephthalic acid diester without catalyst or salt. BACKGROUND

[0002] Polyethylene terephthalate is a kind of polymer obtained by polycondensation of terephthalic acid (ester) and ethylene glycol, and has excellent performance and has been widely used in various fields of production and life. With the rapid development of human society, the demand for PET is rapidly increasing, and the amount of waste PET is also increasing. The annual output of PET in China exceeds 50 million tons, and the impact of waste PET products on our ecological environment is becoming more and more serious. Therefore, this problem needs to be solved urgently. Chemical conversion of PET into useful substances is an important way to effectively solve this problem. At present, methods such as hydrolysis, alcoholysis, aminolysis, and hydrogenolysis can convert PET into its monomers and chemicals by depolymerization, providing an important means for its recycling. PET is often used in combination with other polymer materials or inorganic materials, so there are often problems of high reaction temperature and cross-contamination in the depolymerization process, making the chemical recycling of PET costly and difficult to implement.

[0003] The transesterification method is a commonly used method for depolymerization of polyesters, and the exchange reagent used is mainly alcohol, acid, and ester, and the method of using carbonate for transesterification has not been reported. SUMMARY

[0004] The present application provides a method for depolymerization of polyethylene terephthalate (PET) to prepare its monomer terephthalic acid diester. Through the reaction of diester carbonate and PET, the depolymerization of PET under mild conditions can be achieved, and further chemical recycling of PET monomers in PET composite systems or mixed systems can be carried out. TECHNICAL PROBLEM

[0005] Waste PET products have a more and more serious impact on our ecological environment, and in addition, PET is often used in combination with other polymer materials or inorganic materials, so there are often problems of high reaction temperature and cross-contamination in the depolymerization process, making the chemical recycling of PET costly and difficult to implement. TECHNICAL SOLUTION

[0006] The application aims to provide a method for preparing terephthalic acid diester monomer of PET by depolymerization.

[0007] The method for preparing terephthalic acid diester monomer of PET by depolymerization provided by the application comprises the following steps: treating PET or a composite system thereof in a carbonic acid diester without a catalyst or with a salt as a catalyst, realizing chemical depolymerization of PET, obtaining terephthalic acid diester monomer of PET and ethylene carbonate, and realizing complete depolymerization of PET in the composite system.

[0008] In the method, the salt is any one of inorganic metal salts of halide anions, ionic liquids of halide anions, and composite systems formed by the inorganic metal salts and the ionic liquids.

[0009] The inorganic metal salt of halide anions is at least one of NaCl, KCl, ZnCl2, FeCl3, CuCl2, SnCl4, ZrCl4, CrCl3, NaBr, KBr, ZnBr2, FeBr3, CuBr2, SnBr4, ZrBr4, CrBr, Nal, KI, ZnI2, FeI3, CuI2, ZrI4, and CrI.

[0010] The ionic liquid of halide anions comprises, but is not limited to, imidazolium cations, pyridinium cations, tetraalkylammonium cations, tetraalkylphosphonium cations, guanidinium cations, and organic alkali cations.

[0011] The ionic liquid of halide anions is at least one of 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), 1-butyl-3-methylimidazolium bromide ([BMIM]Br), 1-butyl-3-methylimidazolium iodide ([BMIM]I), 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl), 1-ethyl-3-methylimidazolium bromide ([EMIM]Br), and 1-ethyl-3-methylimidazolium iodide ([EMIM]I).

[0012] The carbonic acid diester is at least one of dimethyl carbonate and diethyl carbonate.

[0013] The PET and the composite system thereof comprise at least one of all samples, real objects, and mixed systems or composite systems containing a PET component.

[0014] The method is operated as follows: a sample containing PET (PET or a composite system thereof) is placed in a carbonic acid diester without a catalyst or with a salt as a catalyst, heated for a certain time, cooled, and separated to obtain terephthalic acid diester monomer and ethylene carbonate.

[0015] The molar ratio of the carbonic acid diester to the PET structural unit can be 1:1-25:1, specifically 10:1-15:1, 10:1, 15:1 or 20:1.

[0016] The molar content of the salt in the carbonic acid diester is 1%-20%, specifically 1%.

[0017] The reaction temperature is 50-250 DEG C and the reaction time is 0.5-36 h when the salt is added as a catalyst.

[0018] The reaction temperature is 170-250 DEG C and the reaction time is 15-36 h when no catalyst is used.

[0019] The carbonic acid diester is dimethyl carbonate, and the obtained terephthalic acid diester is dimethyl terephthalate.

[0020] The carbonic acid diester is diethyl carbonate, and the obtained terephthalic acid diester is diethyl terephthalate.

[0021] The method further comprises the following steps: filtering and separating the unreacted solid; then cooling to precipitate the terephthalic acid diester, filtering to obtain the terephthalic acid diester; further, collecting the excess carbonic acid diester and the generated ethylene carbonate in sequence by a conventional reduced pressure distillation method, and recycling the catalyst.

[0022] The product obtained by the above method is terephthalic acid diester and ethylene carbonate.

[0023] The recycled catalyst can be reused, and the obtained ethylene carbonate can be used to react with methanol or ethanol to generate the carbonic acid diester required for depolymerization of PET.

[0024] Regarding the separation of the product after the reaction, different separation methods can be used according to the catalyst used. Advantages

[0025] The present application can realize depolymerization of PET under mild conditions by the reaction of carbonic acid diester and PET, and further realize related technical research and development of PET monomer chemical recycling in PET composite systems or mixed systems. The method provided by the present application has the advantages of high efficiency, greenness, mild reaction conditions, etc., can catalyze PET to depolymerize to generate its monomer terephthalic acid diester, and has strong industrial application value. BRIEF DESCRIPTION OF DRAWINGS

[0026] Fig. 1 is a solid nuclear magnetic C spectrum of a polyester-cotton blended product (composition: 65% PET, 35% cotton) in Example 5 of the present application and the solid nuclear magnetic C spectrum of the residue after the reaction. 13 Fig. 2 is a solid nuclear magnetic H spectrum of the polyester-cotton blended product (composition: 65% PET, 35% cotton) in Example 5 of the present application and the solid nuclear magnetic H spectrum of the residue after the reaction. Embodiment of the present application

[0027] The application will be described in further detail below with specific reference to the embodiments. The examples given are only to illustrate the application and are not intended to limit the scope of the application. The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, instruments, etc. used in the following examples are commercially available unless otherwise specified.

[0028] Example 1, Ionic liquid N 4444 Cl catalyzed PET depolymerization to dimethyl terephthalate

[0029] A 0.96 g PET powder sample, 0.27 g tetrabutylammonium chloride (N 4444 Cl), 9 g dimethyl carbonate were added into a 25 mL round bottom flask and stirred at 120 °C for 2 hours. Then, dimethyl terephthalate was precipitated and separated by filtration and drying, obtaining 0.93 g dimethyl terephthalate (yield 95.9%, 1 H NMR (400 MHz, CDCl3, 25 °C): / ppm = 8.10 (s, 4H), 3.95 (s, 6H); 13 C NMR (101 MHz, CDCl3, 25 °C): / ppm = 166.57, 134.21, 129.84, 52.69). The filtrate was distilled under reduced pressure, obtaining 0.43 g vinyl carbonate (yield 97.7%, 1 H NMR (400 MHz, CDCl3, 25 °C): / ppm = 4.57 (s, 4H); 13 C NMR (101 MHz, CDCl3, 25 °C): / ppm = 155.12, 64.40.

[0030] Example 2, Metal salt ZnCl2 catalyzed PET depolymerization to dimethyl terephthalate

[0031] A 0.96 g PET powder sample, 0.13 g zinc chloride (ZnCl2), 9 g dimethyl carbonate were added into a 25 mL round bottom flask and stirred at 120 °C for 12 hours. Then, dimethyl terephthalate was precipitated and separated by filtration and drying, obtaining 0.92 g dimethyl terephthalate (yield 94.8%). The filtrate was distilled under reduced pressure, obtaining 0.42 g vinyl carbonate (yield 95.5%).

[0032] Example 3, Ionic liquid N 4444Preparation of dimethyl terephthalate from PET plastic bottle recycling catalyzed by Cl

[0033] 0.96 g of PET plastic bottle fragments, 0.27 g of tetrabutylammonium chloride (N 4444 Cl), 9 g of dimethyl carbonate were added into a 25 mL round bottom flask and stirred at 120 °C for 4 hours. Then, dimethyl terephthalate was precipitated and separated by filtration and drying, obtaining 0.93 g of dimethyl terephthalate (yield 95.9%). The filtrate was distilled under reduced pressure, obtaining 0.43 g of ethylene carbonate (yield 97.7%).

[0034] Example 4, Ionic liquid N 4444 Preparation of methyl terephthalate from PET textile recycling catalyzed by Cl

[0035] 0.97 g of PET textile fragments (composition: 100% PET), 0.28 g of tetrabutylammonium chloride (N 4444 Cl), 8 g of dimethyl carbonate were added into a 25 mL round bottom flask and stirred at 140 °C for 1 hour. Then, dimethyl terephthalate was precipitated and separated by filtration and drying, obtaining 0.94 g of dimethyl terephthalate (yield 95.9%). The filtrate was distilled under reduced pressure, obtaining 0.41 g of ethylene carbonate (yield 92.2%).

[0036] Example 5, Ionic liquid N 4444 Preparation of dimethyl terephthalate from polyester-cotton textile recycling catalyzed by Cl

[0037] 1.48 g of PET textile fragments (composition: 65% polyester, 35% cotton fiber), 0.38 g of tetrabutylammonium chloride (N 4444 Cl), 10 g of dimethyl carbonate were added into a 25 mL round bottom flask and stirred at 130 °C for 2 hours. Then, the unreacted solid was separated by filtration, washed and dried, obtaining 0.52 g of solid, which was cellulose (Figure 1). Subsequently, the filtrate was cooled, dimethyl terephthalate was precipitated and separated by filtration and drying, obtaining 0.93 g of dimethyl terephthalate (yield 96.0%). The filtrate was distilled under reduced pressure, obtaining 0.42 g of ethylene carbonate (95.5%).

[0038] Example 6, Ionic liquid N 4444 Preparation of dimethyl terephthalate from polyester-cotton textile recycling catalyzed by Cl

[0039] 2.02 g of PET textile fragments (composition: 47.5% polyester, 47.5% cotton fiber, 5% spandex), 0.27 g of tetrabutylammonium chloride (N 4444Cl), 9 g of dimethyl carbonate were added to a 25 mL round bottom flask and stirred at 130 °C for 10 hours. Then, the unreacted solid was separated by filtration, washed, dried and 1.06 g of solid was obtained with a composition of cellulose and spandex. Subsequently, the filtrate was cooled and dimethyl terephthalate was precipitated, filtered and dried to obtain 0.94 g of dimethyl terephthalate (yield 96.9%). The filtrate was distilled under reduced pressure to obtain 0.43 g of ethylene carbonate (yield 97.7%).

[0040] Example 7, Ionic liquid N 4444 I catalyzed PET depolymerization to dimethyl terephthalate

[0041] A sample of 0.97 g of PET powder, 0.37 g of tetrabutylammonium iodide (N 4444 I), 8 g of dimethyl carbonate were added to a 25 mL round bottom flask and stirred at 110 °C for 2 hours. Then, dimethyl terephthalate was precipitated by cooling, filtered and dried to obtain 0.45 g of dimethyl terephthalate (yield 45.9%). The filtrate was distilled under reduced pressure to obtain 0.22 g of ethylene carbonate (yield 49.5%).

[0042] Example 8, Ionic liquid N 4444 Br catalyzed PET depolymerization to dimethyl terephthalate

[0043] A sample of 0.95 g of PET powder, 0.32 g of tetrabutylammonium bromide (N 4444 Br), 9 g of dimethyl carbonate were added to a 25 mL round bottom flask and stirred at 120 °C for 2 hours. Then, dimethyl terephthalate was precipitated by cooling, filtered and dried to obtain 0.69 g of dimethyl terephthalate (yield 71.9%). The filtrate was distilled under reduced pressure to obtain 0.30 g of ethylene carbonate (yield 68.9%).

[0044] Example 9, Ionic liquid P 4444 Cl catalyzed PET depolymerization to dimethyl terephthalate

[0045] A sample of 0.97 g of PET powder, 0.29 g of tetrabutylphosphonium chloride (P 4444 Cl), 8 g of dimethyl carbonate were added to a 25 mL round bottom flask and stirred at 120 °C for 2 hours. Then, dimethyl terephthalate was precipitated by cooling, filtered and dried to obtain 0.90 g of dimethyl terephthalate (yield 91.8%). The filtrate was distilled under reduced pressure to obtain 0.37 g of ethylene carbonate (yield 83.2%).

[0046] Example 10, Ionic liquid P 4444Br-catalyzed depolymerization of PET to prepare dimethyl terephthalate

[0047] 0.96 g of PET powder sample and 0.40 g of tetrabutylphosphine bromide (P 4444 Br) and 9 g of dimethyl carbonate were added to a 25 mL round-bottom flask and stirred at 120 ºC for 2 hours. Then, the mixture was cooled, and dimethyl terephthalate precipitated out. The precipitate was filtered and dried to obtain 0.76 g of dimethyl terephthalate (yield 78.4%). The filtrate was distilled under reduced pressure to obtain 0.36 g of ethylene carbonate (yield 81.8%).

[0048] Example 11, Ionic liquid P 4444 I. Catalytic depolymerization of PET to prepare dimethyl terephthalate

[0049] 0.97 g of PET powder sample and 0.36 g of tetrabutylphosphine iodide (P 4444 1) 7 g of dimethyl carbonate was added to a 25 mL round-bottom flask and stirred at 140 ºC for 2 hours. Then, the mixture was cooled, and dimethyl terephthalate precipitated out. The precipitate was filtered and dried to obtain 0.47 g of dimethyl terephthalate (yield 48.0%). The filtrate was distilled under reduced pressure to obtain 0.23 g of ethylene carbonate (yield 51.7%).

[0050] Example 12: Preparation of dimethyl terephthalate from PET by catalytic depolymerization of ionic liquid BMImCl

[0051] 1.0 g of PET powder sample, 0.20 g of 1-butyl-3-methylimidazolium chloride (BMImCl), and 8 g of dimethyl carbonate were added to a 25 mL round-bottom flask and stirred at 110 ºC for 6 hours. After cooling, dimethyl terephthalate precipitated out, was filtered, and dried to obtain 0.81 g of dimethyl terephthalate (yield 80.2%). The filtrate was distilled under reduced pressure to obtain 0.38 g of ethylene carbonate (yield 82.9%).

[0052] Example 13: Preparation of dimethyl terephthalate from PET by NaCl-catalyzed depolymerization

[0053] 0.94 g of PET powder sample, 0.06 g of sodium chloride (NaCl), and 8 g of dimethyl carbonate were added to a 25 mL round-bottom flask and stirred at 180 ºC for 24 hours. After cooling, dimethyl terephthalate precipitated out, was filtered, and dried to obtain 0.78 g of dimethyl terephthalate (yield 82.1%). The filtrate was distilled under reduced pressure to obtain 0.32 g of ethylene carbonate (yield 74.3%).

[0054] Example 14, Ionic Liquid N4444 Cl-catalyzed PET depolymerization to dimethyl terephthalate

[0055] A 0.95 g PET powder sample, 0.36 g tetrabutylammonium chloride (N 4444 Cl), 9 g dimethyl carbonate were added to a 25 mL round bottom flask and stirred at 80 °C for 12 hours. Then, it was cooled and dimethyl terephthalate precipitated, filtered and dried, obtaining 0.30 g of dimethyl terephthalate (yield 42.2%). The filtrate was distilled under reduced pressure, obtaining 0.14 g of ethylene carbonate (yield 38.5%).

[0056] Example 15, ionic liquid N 4444 Cl-catalyzed PET depolymerization to dimethyl terephthalate

[0057] A 0.95 g PET powder sample, 0.25 g tetrabutylammonium chloride (N 4444 Cl), 7 g dimethyl carbonate were added to a 25 mL round bottom flask and stirred at 80 °C for 24 hours. Then, it was cooled and dimethyl terephthalate precipitated, filtered and dried, obtaining 0.55 g of dimethyl terephthalate (yield 57.3%). The filtrate was distilled under reduced pressure, obtaining 0.24 g of ethylene carbonate (yield 55.1%).

[0058] Example 16, ionic liquid N 4444 Cl-catalyzed PET depolymerization to diethyl terephthalate

[0059] A 0.94 g PET powder sample, 0.26 g tetrabutylammonium chloride (N 4444 Cl), 10 g diethyl carbonate were added to a 25 mL round bottom flask and stirred at 130 °C for 4 hours. Then, it was cooled and diethyl terephthalate precipitated, filtered and dried, obtaining 0.96 g of diethyl terephthalate (yield 88.3%, 1 H NMR (400 MHz, CDCl3, 25 °C): / ppm = 8.10 (s, 4H), 4.41 (q, 4H, J = 7.3), 1.41 (t, 6H, J = 7.0); 13 C NMR (101 MHz, CDCl3, 25 °C): / ppm = 166.02, 134.41, 129.69, 61.60, 14.51. The filtrate was distilled under reduced pressure, obtaining 0.33 g of ethylene carbonate (yield 76.6%).

[0060] Example 17, ionic liquid N4444 Cl catalyzed PET depolymerization to prepare diethyl terephthalate

[0061] A 0.99 g PET powder sample, 0.27 g tetrabutylammonium chloride (N 4444 Cl), 12 g diethyl carbonate were added into a 25 mL round bottom flask and stirred at 140 ºC for 1 hour. Then, diethyl terephthalate was precipitated out by cooling, filtered and dried to obtain 0.98 g diethyl terephthalate (yield 85.6%). The filtrate was distilled under reduced pressure to obtain 0.40 g ethylene carbonate (yield 88.2%).

[0062] Example 18, Ionic liquid P 4444 Cl catalyzed PET depolymerization to prepare diethyl terephthalate

[0063] A 0.97 g PET powder sample, 0.46 g tetrabutylphosphonium chloride (P 4444 Cl), 12 g diethyl carbonate were added into a 25 mL round bottom flask and stirred at 160 ºC for 1 hour. Then, diethyl terephthalate was precipitated out by cooling, filtered and dried to obtain 1.05 g diethyl terephthalate (yield 91.7%). The filtrate was distilled under reduced pressure to obtain 0.42 g ethylene carbonate (yield 92.6%).

[0064] Example 19, ZnCl2catalyzed PET / cotton textile recycling to prepare dimethyl terephthalate

[0065] A 1.48 g PET textile (composition: 65% polyester, 35% cotton fiber) pieces, 0.15 g ZnCl2, 8 g dimethyl carbonate were added into a 25 mL round bottom flask and stirred at 150 ºC for 5 hours. Then, the unreacted solid was separated by filtration, washed and dried to obtain 0.52 g solid, which was cellulose. Subsequently, the filtrate was cooled, dimethyl terephthalate was precipitated out, filtered and dried to obtain 0.94 g dimethyl terephthalate (yield 96.9%). The filtrate was distilled under reduced pressure to obtain 0.43 g ethylene carbonate (yield 97.7%).

[0066] Example 20, Ionic liquid N 4444 Cl catalyzed PET / cotton textile depolymerization to prepare diethyl terephthalate

[0067] A 1.48 g PET textile (composition: 65% polyester, 35% cotton fiber) pieces, 0.50 g N 4444Cl, 15 g of diethyl carbonate was added into a 25 mL round-bottom flask, and the reaction was stirred at 150 °C for 3 hours. Then, the unreacted solid was separated by filtration, washed, and dried to obtain 0.52 g of solid, which was cellulose. Subsequently, the filtrate was cooled, and diethyl terephthalate was precipitated and separated by filtration and drying to obtain 0.95 g of diethyl terephthalate (yield 97.9%). The filtrate was distilled under reduced pressure to obtain 0.41 g of ethylene carbonate (yield 93.2%).

[0068] Example 21, PET treatment in dimethyl carbonate without catalyst

[0069] A 0.96 g PET powder sample, 9 g of dimethyl carbonate was added into a 25 mL pressure-resistant reaction kettle, and the reaction was stirred at 180 °C for 24 hours, and the solid completely disappeared. Then, the filtrate was cooled, and dimethyl terephthalate was precipitated and separated by filtration and drying to obtain 0.94 g of dimethyl terephthalate (yield 96.9%). The filtrate was distilled under reduced pressure to obtain 0.41 g of ethylene carbonate (yield 93.2%).

[0070] Comparative Example, PET treatment in dimethyl carbonate without catalyst

[0071] A 0.96 g PET powder sample, 9 g of dimethyl carbonate was added into a 25 mL round-bottom flask, and the reaction was stirred at 120 °C for 10 hours. Then, the filtrate was cooled, and the solid sample was recovered by filtration and drying 0.96 g; the liquid was detected by nuclear magnetic hydrogen spectrum, and no product was found. It is indicated that the reaction cannot occur under the reaction condition.

[0072] Cross-reference to related applications:

[0073] This application claims priority to Chinese patent application (application number 202411261062.8) with a filing date of September 10, 2024, the entire contents of which are hereby incorporated by reference. Industrial applicability

[0074] The present application can realize PET depolymerization under mild conditions through the reaction of diester carbonate and PET, and further carry out related technical research and development of PET monomer chemical recycling in PET composite system or mixed system. The method provided by the present application has the advantages of high efficiency, green, mild reaction condition, etc., can catalyze PET depolymerization to generate its monomer diester terephthalate, and has strong industrial application value.

Claims

1. A method for preparing monomer terephthalic acid diester from polyethylene terephthalate (PET) by depolymerization, comprising the following steps: treating PET or its composite system in a carbonic acid diester without catalyst or with a salt as catalyst, realizing chemical depolymerization of PET, obtaining PET monomer terephthalic acid diester and ethylene carbonate, and realizing complete depolymerization of PET in the composite system.

2. The method of claim 1, wherein, The salt is any one of inorganic metal halide, ionic liquid of halide, and composite system formed by them.

3. The method of claim 1, wherein, The inorganic metal halide is at least one of NaCl, KCl, ZnCl2, FeCl3, CuCl2, SnCl4, ZrCl4, CrCl3, NaBr, KBr, ZnBr2, FeBr3, CuBr2, SnBr4, ZrBr4, CrBr, NaI, KI, ZnI2, FeI3, CuI2, ZrI4, and CrI. The ionic liquid of halide has a cation selected from at least one of imidazolium, pyridinium, tetraalkylammonium, tetraalkylphosphonium, guanidinium, and organic alkali.

4. The method of claim 1, wherein, The carbonic acid diester is at least one of dimethyl carbonate (DMC) and diethyl carbonate (DEC).

5. The method of claim 1, wherein, The PET and its composite system comprises at least one of all samples, objects, and mixed systems or composite systems containing PET components.

6. The method of claim 1, wherein, The method is operated by placing PET or its composite system in a carbonic acid diester without catalyst or with a salt as catalyst, heating for a certain time, cooling, and separating to obtain terephthalic acid diester monomer and ethylene carbonate.

7. The method of claim 6, wherein, The molar ratio of carbonic acid diester to PET structural unit is 1:1-25:

1. The molar content of the salt in the carbonic acid diester is 1%-20%.

8. The method of claim 6, wherein, When the salt is added as a catalyst, the reaction temperature is 50-250 °C, and the reaction time is 0.5-36 h. When there is no catalyst, the reaction temperature is 170-250 °C, and the reaction time is 15-36 h.

9. The method of claim 6, wherein, The method further comprises the following operations: filtering and separating unreacted solid; then cooling to precipitate terephthalic acid diester, filtering to obtain terephthalic acid diester; further, collecting excess carbonic acid diester and generated ethylene carbonate in sequence by conventional vacuum rectification method, and recovering the catalyst.

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