A method for alkylating polyester materials with the participation of carbonate or carboxylate

Abstract

The present invention discloses a method for alkylating polyester materials in which carbonate or carboxylate participates, and relates to comprehensive utilization of waste resources and cascade utilization of raw materials. The product of the method of the present invention is carboxylate and ethylene carbonate or diol. Taking PET as an example, the method uses multiple types of green ionic liquid catalysts, multiple types of carbonate or carboxylate such as dimethyl carbonate (DMC) or dimethyl malonate as methyl sources, and realizes the directional upgrading of PET to DMT under methanol-free conditions, and then DMC captures the generated ethylene glycol in situ, and forms five-membered cyclic ethylene carbonate through dehydration and cyclization. The present invention can be used for the depolymerization upgrading of waste PET materials, and other aromatic or alkyl carboxylic acid compounds (benzoic acid, p-methylbenzoic acid, 4-formylbenzoic acid, cyclohexanoic acid and n-pentanoic acid), similar polyesters and polycarbonates (polyethylene succinate, polyethylene adipate and polyethylene 2,5-furandicarboxylate) are also suitable for the recovery strategy of the present invention.

Description

Technical Field

[0001] The present invention relates to a method for alkylating polyester materials with the participation of carbonate or carboxylic acid esters, and relates to the comprehensive utilization of waste resources and the cascade utilization of raw materials. More specifically, the present invention relates to a direct methylation reaction of PET with the participation of dimethyl carbonate, and obtains dicarboxylic acid esters and five-membered cyclic ethylene carbonate with high yield. Background Art

[0002] Dimethyl terephthalate (DMT) is one of the most important polyester monomers. It is mainly used to synthesize polyester fibers, resins, films, polyester paints and engineering plastics, and has extremely high recycling value. The degradation preparation route of PET-based plastics to DMT usually occurs through the methanolysis of PET. In the reaction, methanol acts as a nucleophilic agent to attack the C=O bond in the polyester, thereby achieving the cleavage of the CO bond and obtaining DMT and ethylene glycol. Due to its low water solubility, the derived DMT is easy to extract and purify from the reaction system, making it a cost-effective option for treating complex PET-based waste. However, general methanolysis requires higher temperatures (generally ≥200°C) and excess methanol as a solvent to promote the slow decomposition of PET depolymerization, and the yield of the product DMT is only between 80-85%. Therefore, it is worth paying attention to the selection of other methylating agents and the development of a mild and efficient directed preparation strategy for waste PET to DMT. In addition, the ethylene glycol produced in the reaction is also difficult to separate and recover due to its high boiling point and is usually abandoned. However, the ethylene glycol unit of PET also has great potential for conversion into high-value chemicals, and has been used as a precursor material to convert small molecule carboxylic acids and light olefins with higher added value. Therefore, how to provide an effective PET methylation catalytic system, a targeted upgrading and recycling strategy for ethylene glycol during the depolymerization process, and a means to reduce the recycling cost of the catalyst in the catalytic system are problems that need to be solved urgently by those skilled in the art.

[0003] Ionic liquids are a type of excellent green catalyst that is non-volatile, thermally stable, and highly soluble. They are also designable and have been widely used in the fields of separation and catalysis. However, such catalysts have not been widely used in the coupled depolymerization pathway of PET.

[0004] Ethylene carbonate (EC) is an organic solvent with excellent performance. It can dissolve a variety of polymers and is widely used in organic synthesis. Generally, ethylene carbonate can be obtained by the nucleophilic reaction of ethylene glycol and dimethyl carbonate. Due to the stable five-membered ring structure of ethylene carbonate, it can promote the equilibrium of PET depolymerization reaction to proceed in the forward direction. Therefore, DMC can be used to capture the EG component from the waste PET in a directional manner, thereby solving the problem of ethylene glycol separation and achieving high-value conversion of ethylene glycol. At the same time, dimethyl carbonate is also an efficient methylation reagent and is widely used in the methylation reaction of aniline, carboxylic acid, phenol or alcohol. Compared with other methylation reagents (such as diazomethane, trimethylsilyldiazomethane, dimethyl sulfate and iodomethane), dimethyl carbonate has low toxicity and has the advantages of green safety. It can also be used in PET methylation reactions. This high-value recovery strategy helps to fully utilize PET waste at the molecular level, and to a certain extent helps to alleviate the consumption of petroleum resources and improve the recycling value of PET waste. Summary of the invention

[0005] The present invention aims at the needs of depolymerization and product-oriented upgrading of PET waste plastics and the shortcomings of the prior art, and provides a method for depolymerization and upgrading of polyester to carboxylate mediated by carbonate or carboxylate. Taking PET as a typical representative, the method uses green ionic liquid to catalyze the transesterification reaction of PET and DMC, and the ethylene glycol generated is captured in situ by DMC, and then dehydrated and cyclized to form a five-membered cyclic ethylene carbonate.

[0006] The specific technical solutions adopted by the present invention are as follows:

[0007]

[0008] In a first aspect, the present invention provides a method for alkylating polyester materials with the participation of carbonate or carboxylate, comprising:

[0009] S1, placing the raw material to be alkylated, the alkylating agent, the ionic liquid catalyst and the reaction solvent in a reaction kettle to form a reaction system;

[0010] The raw material to be alkylated is a crushed polyester material, and the polyester material includes polyethylene terephthalate, polyethylene succinate, polyethylene adipate and polyethylene 2,5-furandicarboxylate;

[0011] The alkylating agent is a carbonate raw material or a carboxylate raw material, the carbonate raw material includes dimethyl carbonate, diethyl carbonate, dibutyl carbonate or dimethyl pyrocarbonate, and the carboxylate raw material includes dimethyl malonate or dimethyl methylmalonate;

[0012] The ionic liquid catalyst is an imidazole-type ionic liquid [Emim][OAc] or [Bmim][OAc], and the structural formula is as follows:

[0013]

[0014] The reaction solvent includes N-methylpyrrolidone, dimethyl sulfoxide, toluene, N,N-dimethylformamide, tetrahydrofuran, acetonitrile or 1,4-dioxane;

[0015] S2, placing the reactor containing the reaction system at a depolymerization temperature of 120-160° C. for 4-8 hours of depolymerization reaction, cooling to room temperature after the reaction is completed, and obtaining a depolymerization product containing the dicarboxylic acid ester corresponding to the raw material to be alkylated.

[0016] In a second aspect, the present invention provides a method for alkylating a carboxylic acid compound raw material with the participation of a carbonate or a carboxylate, comprising:

[0017] S1, placing the raw material to be alkylated, the alkylating agent, the ionic liquid catalyst and the reaction solvent in a reaction kettle to form a reaction system;

[0018] The raw material to be alkylated is a carboxylic acid compound raw material, and the carboxylic acid compound raw material is an aromatic or alkyl carboxylic acid compound including benzoic acid, p-toluic acid, 4-formylbenzoic acid, cyclohexanoic acid and n-pentanoic acid;

[0019] The alkylating agent is a carbonate raw material or a carboxylate raw material, the carbonate raw material includes dimethyl carbonate, diethyl carbonate, dibutyl carbonate or dimethyl pyrocarbonate, and the carboxylate raw material includes dimethyl malonate or dimethyl methylmalonate;

[0020] The ionic liquid catalyst is an imidazole-type ionic liquid [Emim][OAc] or [Bmim][OAc], and the structural formula is as follows:

[0021]

[0022] The reaction solvent includes N-methylpyrrolidone, dimethyl sulfoxide, toluene, N,N-dimethylformamide, tetrahydrofuran, acetonitrile or 1,4-dioxane;

[0023] S2, placing the reactor containing the reaction system at a depolymerization temperature of 120-160° C. for 4-8 hours of depolymerization reaction, cooling to room temperature after the reaction is completed, and obtaining a depolymerization product containing methyl carboxylate corresponding to the raw material to be alkylated.

[0024] As a preferred embodiment of the first and second aspects, in the reaction system, the amount of the alkylating agent added is 4 to 6 times the amount of the raw material to be alkylated, based on molar amount.

[0025] As a preferred embodiment of the first and second aspects, in the reaction system, the amount of the ionic liquid catalyst added is 10 to 25 mol % of the raw material to be alkylated.

[0026] As a preferred embodiment of the first and second aspects, in the reaction system, the amount of the N-methylpyrrolidine solvent added is 3 to 6 mL / mmol of the raw material to be alkylated.

[0027] As a preferred embodiment of the first aspect, the polyester material is waste made of polyethylene terephthalate.

[0028] As a preferred embodiment of the first aspect, the waste is in the form of discarded bottles, discarded films, and colored ropes made of polyethylene terephthalate.

[0029] As a preferred embodiment of the first aspect, the waste needs to be pre-crushed into centimeter-sized flakes, particles or powders before being added to the reactor, which can ensure the resource utilization effect of waste PET materials, targeted upgrading and obtain dimethyl terephthalate and ethylene carbonate with high yield.

[0030] As a preference for the first aspect, when the alkylating agent is a carbonate raw material, the depolymerization product is dicarboxylic acid ester and vinyl carbonate.

[0031] As a preference for the first aspect, when the alkylating agent is a carboxylic acid ester raw material, the depolymerization product is a dicarboxylic acid ester and ethylene glycol.

[0032] As a preferred embodiment of the first and second aspects, the ionic liquid catalyst is preferably [Emim][OAc].

[0033] As a preference of the first and second aspects above, the depolymerization temperature is preferably 140°C.

[0034] As a preference for the first and second aspects above, the depolymerization time is preferably 6 hours.

[0035] Compared with the prior art, some embodiments of the present invention have the following beneficial effects:

[0036] (1) The ionic liquid catalyst used in the present invention has the advantages of high efficiency and greenness, and can promote the methylation reaction of PET with the participation of DMC and prepare high-purity DMT and realize the directional upgrading and recovery of ethylene glycol.

[0037] (2) The methylation and depolymerization strategy for waste plastic PET developed by the present invention has the advantages of mild conditions and high catalytic efficiency, and can achieve complete conversion of PET under standard reaction conditions. The strategy has a wide range of applications, and the types of waste PET raw materials are varied. Various types of waste PET materials, such as various types of PET waste bottles, PET matrix waste films, PET colored ropes and PET non-woven fabrics, can all be efficiently upgraded and converted in a short time.

[0038] (3) The PET waste plastic matrix material of the present invention can be replaced by various polyesters and polycarbonates with similar structures, such as polyethylene succinate, polyethylene adipate and polyethylene 2,5-furandicarboxylate, which to a certain extent shows the high applicability of the strategy and further broadens the scope of waste plastic treatment materials. Under the premise of ensuring high depolymerization efficiency and rapid reaction time, the corresponding conversion can be completed to obtain dicarboxylic acid esters, ethylene glycol and vinyl carbonate. DETAILED DESCRIPTION

[0039] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, a detailed description is given below through specific embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0040] The present invention provides a method for alkylating polyester materials with the participation of carbonate or carboxylate, wherein the method uses a green ionic liquid catalyst to catalyze the methylation reaction of polyester materials with the participation of an alkylating agent, thereby achieving alkylation and obtaining a high-value product. The alkylating agent and the polyester material are respectively exemplified by DMC and PET, and the DMC captures the generated ethylene glycol in situ, and the five-membered ethylene carbonate is formed by dehydration and cyclization.

[0041] The specific method of alkylation of polyester materials involving carbonate or carboxylate is as follows:

[0042] S1, placing the raw material to be alkylated, i.e., crushed polyester material, an alkylating agent (carbonate raw material or carboxylate raw material), an ionic liquid catalyst and a reaction solvent in a reaction kettle to form a reaction system;

[0043] S2, placing the reactor containing the reaction system at a depolymerization temperature of 120-160° C. for 4-8 hours of depolymerization reaction, cooling to room temperature after the reaction is completed, and obtaining a depolymerization product corresponding to the polyester material.

[0044] In the above reaction, the specific depolymerization product is related to the type of alkylating agent used: when the alkylating agent is a carbonate raw material, the depolymerization products of the depolymerization reaction in which the carbonate raw material participates are dicarboxylic acid ester and ethylene carbonate; when the alkylating agent is a carboxylate raw material, the depolymerization products of the depolymerization reaction in which the carboxylate raw material participates are dicarboxylic acid ester and ethylene glycol.

[0045] In addition, in the subsequent embodiments, the raw materials in the above reaction system are as follows: the polyester material is one of polyethylene terephthalate (PET), polyethylene succinate, polyethylene adipate and polyethylene 2,5-furandicarboxylate; the aromatic or alkyl carboxylic acid compound is benzoic acid, p-toluic acid, 4-formylbenzoic acid, cyclohexane acid and n-pentanoic acid; the alkylating agent is a carbonate raw material (including dimethyl carbonate, diethyl carbonate, dibutyl carbonate or dimethyl pyrocarbonate) or a carboxylic acid ester raw material (including dimethyl malonate or dimethyl methyl malonate); methyl ester); the reaction solvent is N-methylpyrrolidone, dimethyl sulfoxide, toluene, N,N-dimethylformamide, tetrahydrofuran, acetonitrile, 1,4-dioxane; the ionic liquid catalyst is an imidazole-type ionic liquid [Emim][OAc] or [Bmim][OAc], and the structural formulas of the two and the structural formulas of other ionic liquids [Emim][Cl], [Emim][Br], [Emim][I], [Emim][MeSO3], [Emim][BF4] used as comparison in the subsequent embodiments are as follows:

[0046]

[0047] In addition, if the polyester material is PET, pure PET or PET waste can be used. If waste is used as raw material, the waste can be in the form of PET waste bottles, PET matrix waste film and PET colored rope, but the waste must be pre-crushed into centimeter-level flakes, particles or powder before adding it to the reactor.

[0048] In the subsequent examples, the dosage ratios of the raw materials in the above reaction system are as follows: in terms of molar amount, the amount of the alkylating agent added is 4 to 6 times the amount of the raw material to be alkylated; the amount of the ionic liquid catalyst added is 10 to 25 mol% of the raw material to be alkylated; and the amount of the N-methylpyrrolidine solvent added is 3 to 6 mL / mmol of the raw material to be alkylated.

[0049] Of course, based on the same inventive concept, in addition to the crushed polyester material, the raw material to be alkylated in the aforementioned steps S1 to S2 of the present invention can also be replaced by a carboxylic acid compound raw material, and the carboxylic acid compound raw material can be an aromatic carboxylic acid compound or an alkyl carboxylic acid compound, such as benzoic acid, p-methylbenzoic acid, 4-formylbenzoic acid, cyclohexanoic acid and n-pentanoic acid. Therefore, in other embodiments, the present invention also provides a method for alkylating a carboxylic acid compound raw material with the participation of a carbonate or carboxylic acid ester, which is basically the same as the method for alkylating a polyester material with the participation of a carbonate or carboxylic acid ester shown in the aforementioned S1 to S2, except that the polyester material is replaced by a carboxylic acid compound raw material, so that the corresponding depolymerization product will contain a corresponding high-value product, that is, the carboxylic acid methyl ester corresponding to the raw material to be alkylated.

[0050] The following examples are used to demonstrate the reaction results under different raw materials and parameters.

[0051] Example 1

[0052] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 grams of CR-pure PET powder (1 mmol), 0.36 grams of dimethyl carbonate (4 mmol), [Emim][OAc] (20 mol%, the molar percentage is calculated based on the molar amount of PET powder) and N-methylpyrrolidone (4 mL) were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 140°C and reacted at this temperature for 6 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the dilution was used to determine the yield by GC, with n-dodecane as the internal standard. The results showed that the PET decomposition rate of this embodiment was 100%, the yield of dimethyl terephthalate was 99%, and the yield of ethylene carbonate was 99%. 1 HNMR yield was 84%.

[0053] Example 2

[0054] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 g of CR-pure PET powder (1 mmol), 0.36 g of dimethyl carbonate (4 mmol), [Emim][OAc] (20 mol%, the molar percentage is calculated based on the molar amount of PET powder) and dimethyl sulfoxide (4 mL) were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 6 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was used to determine the yield by GC, with n-dodecane as the internal standard. The yield of dimethyl terephthalate was 74%, and that of ethylene carbonate was 74%. 1 H NMR yield was 62%.

[0055] Example 3

[0056] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 g of CR-pure PET powder (1 mmol), 0.36 g of dimethyl carbonate (4 mmol), [Bmim][OAc] (20 mol%, the molar percentage is calculated based on the molar amount of PET powder) and dimethyl sulfoxide (4 mL) were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 6 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was used to determine the yield by GC, with n-dodecane as the internal standard. The yield of dimethyl terephthalate was 60%, and that of ethylene carbonate was 60%. 1 H NMR yield was 51%.

[0057] Example 4

[0058] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 g of CR-pure PET powder (1 mmol), 0.36 g of dimethyl carbonate (4 mmol), ionic liquids ([Emim][Cl], [Emim][Br], [Mmim][I], [Emim][MeSO3], and [EMIm][BF4]) (20 mol%, the molar percentage being calculated based on the molar amount of PET powder) and dimethyl sulfoxide (4 mL) were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130° C. and reacted at this temperature for 6 h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with n-dodecane as the internal standard. The results showed that in this embodiment, when the ionic liquid was [Emim][Cl], the yield of dimethyl terephthalate was 24%. When the ionic liquids are [Emim][Br], [Emim][I], [Emim][MeSO3] and [EMIm][BF4], the yields of dimethyl terephthalate corresponding to each of them are 0%, and the yields of ethylene carbonate corresponding to each of them are 0%. 1 The H NMR yields were all 0%.

[0059] Example 5

[0060] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 g of CR-pure PET powder (1 mmol), 0.36 g of dimethyl carbonate (4 mmol), [Emim][OAc] (20 mol%, the molar percentage is calculated based on the molar amount of PET powder) and a solvent (dimethyl sulfoxide, toluene, N,N-dimethylformamide, tetrahydrofuran, acetonitrile, 1,4-dioxane) (4 mL) were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 140°C and reacted at this temperature for 6 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The obtained mixed solution was diluted with dichloromethane, and the yield of the diluted solution was determined by GC, with n-dodecane being used as the internal standard. The results showed that when the solvent in this embodiment was dimethyl sulfoxide, toluene, N,N-dimethylformamide, tetrahydrofuran, acetonitrile, and 1,4-dioxane, the corresponding PET decomposition rate was 100%, and the corresponding dimethyl terephthalate yields were 89%, 91%, 96%, 80%, 91% and 92%, respectively.

[0061] Example 6

[0062] Discarded PET plastic bottles (Coca-Cola, Pepsi-Cola and Nongfu Spring brands) were crushed in centimeters in advance, and then 0.192 grams of PET plastic bottles were crushed in centimeters (1mmol), 0.36 grams of dimethyl carbonate (4mmol), [Emim][OAc] (20mol%, the molar percentage is calculated based on the molar amount of the PET plastic bottle crushed material) and N-methylpyrrolidone (4mL) were added to an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple and a program temperature controller. After placing the autoclave reactor, stirring and heating were turned on. The reaction system was heated to 140°C and reacted at this temperature for 6h. After the reaction was completed, it was cooled to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the PET decomposition rate of the present embodiment was 100%, and the dimethyl terephthalate yield was 92%.

[0063] Example 7

[0064] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.102 g of polyethylene succinate (1 mmol), 0.36 g of dimethyl carbonate (4 mmol), [Emim][OAc] (20 mol%, the molar percentage is calculated based on the molar amount of polyethylene succinate) and N-methylpyrrolidone (4 mL) were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 180°C and reacted at this temperature for 1 hour. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was passed through1 The yield was determined by H NMR with mesitylene as the internal standard. The results showed that the decomposition rate of polyethylene succinate in this example was 100%, the yield of dimethyl succinate was 92%, and the yield of ethylene carbonate was 63%.

[0065] Example 8

[0066] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.172 g of polyethylene adipate (1 mmol), 0.36 g of dimethyl carbonate (4 mmol), [Emim][OAc] (20 mol%, the molar percentage is calculated based on the molar amount of polyethylene adipate) and N-methylpyrrolidone (4 mL) were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 180°C and reacted at this temperature for 6 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was passed through 1 The yield was determined by H NMR with mesitylene as the internal standard. The results showed that the decomposition rate of polyethylene adipate in this example was 100%, the yield of dimethyl adipate was 92%, and the yield of ethylene carbonate was 70%.

[0067] Example 9

[0068] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.172 g of polyethylene 2,5-furandicarboxylate (1 mmol), 0.36 g of dimethyl carbonate (4 mmol), [Emim][OAc] (20 mol%, the molar percentage is calculated based on the molar amount of polyethylene 2,5-furandicarboxylate) and N-methylpyrrolidone (4 mL) were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 180°C and reacted at this temperature for 6 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was passed through 1 The yield was determined by H NMR with mesitylene as the internal standard. The results showed that the decomposition rate of polyethylene 2,5-furandicarboxylate in this example was 100%, the yield of dimethyl 2,5-furandicarboxylate was 95%, and the yield of ethylene carbonate was 85%.

[0069] Example 10

[0070] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 grams of CR purity PET powder (1mmol), methylating agents (dimethyl malonate, dimethyl methylmalonate, and dimethyl pyrocarbonate) (4mmol), [Emim][OAc] (20mol%, the molar percentage is calculated based on the molar amount of PET powder) and N-methylpyrrolidone (4mL) were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 140°C and reacted at this temperature for 6h. After the reaction was completed, it was cooled to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with n-dodecane as the internal standard. The results showed that when the methylating agents in this embodiment were dimethyl malonate, dimethyl methylmalonate, and dimethyl pyrocarbonate, the corresponding dimethyl terephthalate yields were 84%, 59%, and 99%, respectively.

[0071] Embodiment 11

[0072] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 grams of CR-pure PET powder (1 mmol), an alkylating agent (diethyl carbonate, dibutyl carbonate) (4 mmol), [Emim][OAc] (20 mol%, the molar percentage is calculated based on the molar amount of the PET powder) and N-methylpyrrolidone (4 mL) were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 140°C and reacted at this temperature for 6 hours. After the reaction was completed, the temperature was cooled to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with n-dodecane as the internal standard. The results showed that when the alkylating agent in this embodiment was diethyl carbonate and dibutyl carbonate, the yields of the corresponding product methyl carboxylate (diethyl terephthalate and dibutyl terephthalate, respectively) were 95% and 79%, respectively.

[0073] Embodiment 11

[0074] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 g of CR-purity aromatic or alkyl carboxylic acid compounds (benzoic acid, p-toluic acid, 4-formylbenzoic acid, cyclohexanoic acid and n-pentanoic acid) (1 mmol), dimethyl carbonate (4 mmol), [Emim][OAc] (20 mol%, the molar percentage is calculated based on the molar amount of the aromatic or alkyl carboxylic acid compound) and N-methylpyrrolidone (4 mL) were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 140°C and reacted at this temperature for 6 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluted solution was passed through 1The yield was determined by H NMR with mesitylene as the internal standard. The results showed that in this embodiment, when the carboxylic acid compounds were benzoic acid, p-toluic acid, 4-formaldehyde benzoic acid, cyclohexanoic acid and n-pentanoic acid, the corresponding carboxylic acid ester products were methyl benzoate, methyl p-toluic acid, methyl 4-formaldehyde benzoate, methyl cyclohexanecarboxylate and methyl n-pentanoate, and the corresponding yields were 99%, 98%, 95%, 99% and 93%, respectively.

[0075] The above examples show that not all ionic liquids can be used to catalyze the above depolymerization reaction. Compared with other ionic liquid catalysts, the two ionic liquid catalysts [Emim][OAc] and [Bmim][OAc] have extremely high catalytic performance in catalyzing the depolymerization and upgrading of polyester to carboxylic acid ester and vinyl carbonate.

[0076] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for alkylating polyester materials with the participation of carbonate or carboxylate, characterized in that: include: S1, placing the raw material to be alkylated, the alkylating agent, the ionic liquid catalyst and the reaction solvent in a reaction kettle to form a reaction system; The raw material to be alkylated is a crushed polyester material, and the polyester material includes polyethylene terephthalate, polyethylene succinate, polyethylene adipate and polyethylene 2,5-furandicarboxylate; The alkylating agent is dimethyl carbonate; The ionic liquid catalyst is an imidazole-type ionic liquid [Emim][OAc] or [Bmim][OAc], and the structural formula is as follows: ； The reaction solvent is N -Methylpyrrolidone; In the reaction system, the amount of the alkylating agent added is 4 to 6 times the amount of the raw material to be alkylated, the amount of the ionic liquid catalyst added is 10 to 25 mol% of the raw material to be alkylated, and the N - the amount of methylpyrrolidine solvent added is 3 to 6 mL / mmol of the raw material to be alkylated; S2, placing the reactor containing the reaction system at a depolymerization temperature of 120-160° C. for 4-8 hours of depolymerization reaction, cooling to room temperature after the reaction is completed, and obtaining a depolymerization product containing the dicarboxylic acid ester corresponding to the raw material to be alkylated.

2. The method according to claim 1, characterized in that The polyester material is waste of polyethylene terephthalate.

3. The method according to claim 2, characterized in that The waste is in the form of discarded bottles, discarded films, and colored bundles made of polyethylene terephthalate.

4. The method according to claim 2, characterized in that The waste must be crushed into centimeter-sized flakes, particles or powders before being added to the reactor.

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