A high-efficiency alcoholysis method for waste polyester

Abstract

The present invention discloses a method for efficiently degrading waste polyester. The method comprises the following steps: adding a waste polyester raw material and a presolvent in a certain proportion to a depolymerization kettle, subjecting the waste polyester surface to swelling treatment, and then adding tannic acid and ammonium molybdate to water and mixing to obtain a mixed solution. A carbon material is then impregnated with acetone and washed to obtain a MoO2-loaded carbon material methanolysis catalyst. The waste polyester and presolvent mixture is then cooled to room temperature, and methanol and the catalyst are added. The mixture reacts for a period of time, cools, and is then filtered and dried to obtain dimethyl methylate (DMT), which is then weighed to determine the actual DMT yield. The present invention provides a highly efficient, green, and economical degradation method for degrading waste polyester under mild conditions. The method has the advantages of low pollution, strong controllability, simple catalyst preparation, and low cost. This method provides a new approach for the efficient alcoholysis of PET and has broad market application prospects.

Description

Technical Field

[0001] The invention relates to a high-efficiency methanolysis method for waste polyester, belonging to the field of waste polyester recycling. Background Art

[0002] Polyethylene terephthalate (PET), a key raw material, is widely used in the production of beverage bottles, textiles, garments, sheet materials, and other products due to its high strength and chemical stability. With the widespread use of polyester materials, the amount of polyester waste generated has also increased rapidly. Because polyester is highly chemically inert, it is difficult to degrade in natural storage or by microorganisms, resulting in not only a huge waste of resources but also serious environmental pollution. Therefore, recycling to achieve a virtuous cycle of resources and improve environmental quality has become a key issue in the polyester industry.

[0003] Currently, there are two methods for recycling waste polyester: physical and chemical. The physical method primarily involves converting waste polyester and its products into recycled chips through simple physical treatments such as direct blending, co-blending, and granulation. This method is simple, has low investment costs, and offers rapid returns. However, the performance of the recycled product is somewhat inferior to that of virgin polyester, and after repeated physical recycling, it cannot be reused. The chemical method, on the other hand, utilizes depolymerizing agents to depolymerize polyester into small molecules, which can be reused for polymerization or the production of other chemical products. Chemical recycling methods primarily include alcoholysis, hydrolysis, and aminolysis. Alcoholysis is the most widely used method in industrial applications due to its high efficiency and low reaction by-products. However, due to technical requirements and high recycling costs, it has not been widely adopted. To this end, Publication No. CN115594581A discloses a "Method for Chemically Recycling Waste Textiles to Prepare Regenerated Dimethyl Terephthalate (DMT) and Its Application in the Preparation of Flame-Retardant Polyester Chips." Using waste polyester textiles as raw materials, the method employs ethylene glycol depolymerization and methanol transesterification to produce regenerated DMT, which is then used as a raw material to synthesize copolyester chips with excellent flame retardancy. CN109134244B discloses a "Method for Degrading Waste Polyester." After initial alcoholysis of the polyester with a diol, the initial alcoholysis product is subjected to deep alcoholysis and transesterification using a mixture of diol and methanol to produce high-purity dimethyl terephthalate. Publication No. CN112646135B discloses a "Method for Continuously Preparing Spinnable-Grade Colorless Regenerated Polyester from Colored Waste Polyester Textiles." The colored waste polyester textiles are crushed and melted to produce a waste polyester melt. The waste polyester melt is then subjected to continuous medium-pressure methanolysis with methanol (an alcoholysis agent) and an alcoholysis catalyst to produce the alcoholysis product.

[0004] While these alcoholysis catalytic systems offer good depolymerization efficiency, they still face significant technical barriers. Methanolysis requires harsh reaction conditions of high temperature and pressure, which accelerates equipment damage and significantly increases costs, making it inconsistent with green economy policy requirements.

[0005] Therefore, it is urgent to overcome the problems existing in the regeneration process of waste polyester by alcoholysis, and based on the methanol depolymerization characteristics of waste polyester textiles, develop a method that can still efficiently depolymerize waste polyester under mild methanolysis reaction conditions, thereby reducing environmental pollution and preparation costs. This is the focus of research and breakthroughs in the field of recycled polyester.

[0006] The degradation of PET is a surface-controlled process. Since the PET crystal structure is highly densified and it is a dense solid, its specific surface area is low, which will greatly reduce its degradation rate and increase the difficulty of depolymerization. If PET can be converted into a "sponge-like" form in some way, the specific surface area of ​​PET will be greatly increased, thereby increasing the degradation rate of PET. Studies have shown that polar aprotic solvents have a good swelling effect on PET, causing the PET surface to foam and produce a large number of gaps, increasing its specific surface area, thereby effectively reducing the crystallinity of PET, weakening the interaction between PET chains, and laying a good preliminary foundation for depolymerization; in addition, the addition of polar aprotic solvents will increase the mass transfer coefficient of methanol, enhance the mass transfer process of the reaction, thereby promoting the contact between methanol and PET, making the reaction easier to proceed. Molybdenum dioxide is a transition metal oxide with high electrical conductivity, high melting point, and high chemical stability. It has efficient charge transfer characteristics. The free electron density in the valence band of molybdenum dioxide is high, which increases the Mo 4+ The catalytic activity of Mo 4+ It can protonate the carbonyl oxygen in PET, making the carbonyl group more electrophilic and more susceptible to nucleophilic attack by methanol. Furthermore, carbon atom substitution can introduce higher charge and spin density into MoO2, enhancing its catalytic activity. Heteroatom doping can induce lattice distortion and changes in electron density, thereby activating the material's catalytic active sites. Experimental results show that a co-catalytic methanolysis system using polar aprotic solvents as presolvents and cosolvents and MoO2-supported carbon materials as catalysts is highly effective in the alcoholysis of PET and can cause its depolymerization at room temperature and pressure, making it a green, economical, and low-cost catalytic system. Summary of the Invention

[0007] In order to solve the shortcomings of traditional PET alcoholysis catalytic systems such as low catalytic efficiency, poor repeatability, and poor economy and environmental protection, the present invention provides a green and economical degradation method that can degrade waste polyester with high efficiency under mild conditions. It has the advantages of low pollution, strong controllability, and low cost investment. It provides a new idea for the efficient alcoholysis of PET and has great application prospects.

[0008] The specific technical solution adopted by the present invention to solve the above technical problems is:

[0009] A high-efficiency alcoholysis method for waste polyester comprises the following steps: (1) adding the waste polyester raw material and pre-solvent into a depolymerization kettle in a certain proportion, reacting at a certain temperature for a period of time, and performing swelling treatment on the surface of the waste polyester; (2) preparing an alcoholysis catalyst, adding tannic acid and ammonium molybdate into water respectively, and after fully dissolving, slowly pouring the ammonium molybdate solution into the tannic acid solution under the action of magnetic stirring to obtain a mixed solution; placing a carbon material in an acetone solution for immersion, rinsing with distilled water and drying after the end, adding the treated carbon material into the mixed solution, ultrasonicating for a period of time, and then placing it in a tube furnace for calcination, taking it out after a period of time, washing and drying, and obtaining a MoO2-loaded carbon material methanolysis catalyst. (3) depolymerizing the waste polyester, after cooling the mixed solution of the waste polyester and pre-solvent to room temperature (25°C), adding a certain amount of methanol and the above catalyst, stirring and heating, reacting for a period of time, cooling the depolymerization solution to room temperature, filtering and drying to obtain DMT, and weighing to obtain the actual yield of DMT.

[0010] The waste polyester raw materials are one or more of waste bottle flakes, waste textiles and waste films.

[0011] The pre-solvent is one or more of cyclopentyl methyl ether, sulfolane and dimethyl carbonate.

[0012] The carbon material is one or more of carbon nanotubes, porous activated carbon, and graphite flakes.

[0013] As a further preferred embodiment, the mass of the waste polyester raw material in step (2) is 2.0-7.0 g, the volume of the pre-solvent is 5-35 mL, the reaction time is 1-3 h, and the reaction temperature is 30-60° C.

[0014] As a further preference, in step (3), the molar ratio of tannic acid to ammonium molybdate is 1:1-3, the mass ratio of ammonium molybdate to carbon material is one or more of 2:1, 4:1, and 6:1, the ultrasonic time is 40-60 min, and the calcination temperature is 500-700° C., and the time is 2-4 h.

[0015] As further preferred, in step (3), the mass of the added catalyst is 0.5-2 g, the volume of methanol is 5-45 mL, the alcoholysis temperature is 30-60° C. (lower than the boiling point of methanol), and the alcoholysis time is 5-10 h.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) The pre-solvent / co-solvent is one or more of cyclopentyl methyl ether, cyclopentane sulfone, and dimethyl carbonate, all of which are new polar solvents that are both environmentally friendly and high-performance. They can efficiently treat the surface of PET and can replace polar aprotic solvents such as tetrahydrofuran, methyltetrahydrofuran, methyl tert-butyl ether, and dioxane.

[0018] (2) The catalyst is novel, simple to prepare, low-cost, and can be easily separated after macroscopic processing. It is an efficient and economical catalyst.

[0019] (3) The presolvent in the catalytic system has a good swelling effect on PET, which can increase its specific surface area and weaken the interaction between PET chains. In addition, the addition of polar aprotic solvent will increase the mass transfer coefficient of methanol and enhance the mass transfer process of the reaction, thereby promoting the contact between methanol and PET, so that the depolymerization reaction can be carried out efficiently under normal temperature and pressure conditions, solving the current problems of harsh methanol decomposition reaction conditions and high investment costs. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with specific examples. These examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, after reading the content taught by the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalents also fall within the scope defined by the appended claims of the application.

[0021] Example 1:

[0022] (1) Pre-dissolved surface treatment of waste polyester: 4 g of waste polyester and 10 mL of cyclopentyl methyl ether were put into a depolymerization reactor and reacted at 30 ° C for 1 hour to swell the surface of the waste polyester.

[0023] (2) Preparation of alcoholysis catalyst: Tannic acid and ammonium molybdate with a molar ratio of 1:1 are added to water respectively. After they are fully dissolved, the ammonium molybdate solution is slowly poured into the tannic acid solution under the action of magnetic stirring to obtain a mixed solution; porous activated carbon with a mass ratio of 1:2 to ammonium molybdate is placed in an acetone solution for immersion, and then rinsed with distilled water and dried. The treated porous activated carbon is added to the above-mentioned mixed solution and ultrasonicated. After 50 minutes, it is placed in a tubular furnace and calcined at a temperature of 600°C. After 3 hours, it is taken out, washed and dried to obtain a MoO2-loaded carbon material methanolysis catalyst.

[0024] (3) Depolymerization of waste polyester: After the mixture of waste polyester and pre-solvent was cooled to room temperature (25°C), 10 mL of methanol and 0.5 g of the above catalyst were added, stirred and heated to 30°C. After reacting for 5 h, the actual DMT yield and PET depolymerization rate were obtained by weighing.

[0025] Example 2:

[0026] (1) Pre-dissolved surface treatment of waste polyester: 4 g of waste polyester and 10 mL of cyclopentyl methyl ether were put into a depolymerization reactor and reacted at 45 °C for 1 h to swell the surface of the waste polyester.

[0027] (2) Preparation of alcoholysis catalyst: Tannic acid and ammonium molybdate with a molar ratio of 1:1 are added to water respectively. After they are fully dissolved, the ammonium molybdate solution is slowly poured into the tannic acid solution under the action of magnetic stirring to obtain a mixed solution; porous activated carbon with a mass ratio of 1:2 to ammonium molybdate is placed in an acetone solution for immersion, and then rinsed with distilled water and dried. The treated porous activated carbon is added to the above-mentioned mixed solution and ultrasonicated. After 50 minutes, it is placed in a tubular furnace and calcined at a temperature of 600°C. After 3 hours, it is taken out, washed and dried to obtain a MoO2-loaded carbon material methanolysis catalyst.

[0028] (3) Depolymerization of waste polyester: After the mixture of waste polyester and pre-solvent was cooled to room temperature (25°C), 10 mL of methanol and 0.5 g of the above catalyst were added, stirred and heated to 30°C. After reacting for 5 h, the actual DMT yield and PET depolymerization rate were obtained by weighing.

[0029] Example 3:

[0030] (1) Pre-dissolved surface treatment of waste polyester: 4 g of waste polyester and 10 mL of cyclopentane sulfone were put into a depolymerization reactor and reacted at 45 ° C for 1 hour to swell the surface of the waste polyester.

[0031] (2) Preparation of alcoholysis catalyst: Tannic acid and ammonium molybdate with a molar ratio of 1:1 are added to water respectively. After they are fully dissolved, the ammonium molybdate solution is slowly poured into the tannic acid solution under the action of magnetic stirring to obtain a mixed solution; porous activated carbon with a mass ratio of 1:2 to ammonium molybdate is placed in an acetone solution for immersion, and then rinsed with distilled water and dried. The treated porous activated carbon is added to the above-mentioned mixed solution and ultrasonicated. After 50 minutes, it is placed in a tubular furnace and calcined at a temperature of 600°C. After 3 hours, it is taken out, washed and dried to obtain a MoO2-loaded carbon material methanolysis catalyst.

[0032] (3) Depolymerization of waste polyester: After the mixture of waste polyester and pre-solvent was cooled to room temperature (25°C), 10 mL of methanol and 0.5 g of the above catalyst were added, and the mixture was stirred and heated to 30°C. After the reaction was carried out for 10 h, the actual DMT yield and PET depolymerization rate were obtained by weighing.

[0033] Example 4:

[0034] (1) Pre-dissolved surface treatment of waste polyester: 4 g of waste polyester and 10 mL of cyclopentyl methyl ether were put into a depolymerization reactor and reacted at 45 °C for 1 h to swell the surface of the waste polyester.

[0035] (2) Preparation of alcoholysis catalyst: Tannic acid and ammonium molybdate with a molar ratio of 1:1 are added to water respectively. After they are fully dissolved, the ammonium molybdate solution is slowly poured into the tannic acid solution under the action of magnetic stirring to obtain a mixed solution; porous activated carbon with a mass ratio of 1:2 to ammonium molybdate is placed in an acetone solution for immersion, and then rinsed with distilled water and dried. The treated carbon material is added to the above-mentioned mixed solution and ultrasonicated. After 50 minutes, it is placed in a tubular furnace and calcined at a temperature of 600°C. After 3 hours, it is taken out, washed and dried to obtain a MoO2-loaded carbon material alcoholysis catalyst.

[0036] (3) Depolymerization of waste polyester: After the mixture of waste polyester and pre-solvent was cooled to room temperature (25°C), 10 mL of methanol and 0.5 g of the above catalyst were added, and the mixture was stirred and heated to 45°C. After the reaction was carried out for 5 h, the actual DMT yield and PET depolymerization rate were obtained by weighing.

[0037] Example 5:

[0038] (1) Pre-dissolved surface treatment of waste polyester: 4 g of waste polyester and 10 mL of cyclopentyl methyl ether were put into a depolymerization reactor and reacted at 45 °C for 1 h to swell the surface of the waste polyester.

[0039] (2) Preparation of alcoholysis catalyst: Tannic acid and ammonium molybdate with a molar ratio of 1:1 are added to water respectively. After they are fully dissolved, the ammonium molybdate solution is slowly poured into the tannic acid solution under the action of magnetic stirring to obtain a mixed solution; porous activated carbon with a mass ratio of 1:2 to ammonium molybdate is placed in an acetone solution for immersion, and then rinsed with distilled water and dried. The treated carbon material is added to the above-mentioned mixed solution and ultrasonicated. After 50 minutes, it is placed in a tubular furnace and calcined at a temperature of 600°C. After 3 hours, it is taken out, washed and dried to obtain a MoO2-loaded carbon material alcoholysis catalyst.

[0040] (3) Depolymerization of waste polyester: After the mixture of waste polyester and pre-solvent was cooled to room temperature (25°C), 10 mL of methanol and 0.5 g of the above catalyst were added, and the mixture was stirred and heated to 60°C. After the reaction was carried out for 5 h, the actual DMT yield and PET depolymerization rate were obtained by weighing.

[0041] Example 6:

[0042] (1) Pre-dissolved surface treatment of waste polyester: 4 g of waste polyester and 10 mL of cyclopentyl methyl ether were put into a depolymerization reactor and reacted at 45 °C for 1 h to swell the surface of the waste polyester.

[0043] (2) Preparation of alcoholysis catalyst: Tannic acid and ammonium molybdate with a molar ratio of 1:1 are added to water respectively. After they are fully dissolved, the ammonium molybdate solution is slowly poured into the tannic acid solution under the action of magnetic stirring to obtain a mixed solution; porous activated carbon with a mass ratio of 1:2 to ammonium molybdate is placed in an acetone solution for immersion, and then rinsed with distilled water and dried. The treated carbon material is added to the above-mentioned mixed solution and ultrasonicated. After 50 minutes, it is placed in a tubular furnace and calcined at a temperature of 600°C. After 3 hours, it is taken out, washed and dried to obtain a MoO2-loaded carbon material alcoholysis catalyst.

[0044] (3) Depolymerization of waste polyester: After the mixture of waste polyester and pre-solvent was cooled to room temperature (25°C), 10 mL of methanol and 0.5 g of the above catalyst were added, stirred and heated to 45°C. After the reaction was carried out for 10 h, the actual DMT yield and PET depolymerization rate were obtained by weighing.

[0045] Example 7:

[0046] (1) Pre-dissolved surface treatment of waste polyester: 4 g of waste polyester and 10 mL of cyclopentyl methyl ether were put into a depolymerization reactor and reacted at 45 °C for 1 h to swell the surface of the waste polyester.

[0047] (2) Preparation of alcoholysis catalyst: Tannic acid and ammonium molybdate with a molar ratio of 1:1 are added to water respectively. After they are fully dissolved, the ammonium molybdate solution is slowly poured into the tannic acid solution under the action of magnetic stirring to obtain a mixed solution; porous activated carbon with a mass ratio of 1:2 to ammonium molybdate is placed in an acetone solution for immersion, and then rinsed with distilled water and dried. The treated carbon material is added to the above-mentioned mixed solution and ultrasonicated. After 50 minutes, it is placed in a tubular furnace and calcined at a temperature of 600°C. After 3 hours, it is taken out, washed and dried to obtain a MoO2-loaded carbon material alcoholysis catalyst.

[0048] (3) Depolymerization of waste polyester: After the mixture of waste polyester and pre-solvent was cooled to room temperature (25°C), 10 mL of methanol and 0.5 g of the above catalyst were added, and the mixture was stirred and heated to 45°C. After the reaction was carried out for 15 h, the actual DMT yield and PET depolymerization rate were obtained by weighing.

[0049] Example 8:

[0050] (1) Pre-dissolved surface treatment of waste polyester: 4 g of waste polyester and 10 mL of cyclopentyl methyl ether were put into a depolymerization reactor and reacted at 45 °C for 1 h to swell the surface of the waste polyester.

[0051] (2) Preparation of alcoholysis catalyst: Tannic acid and ammonium molybdate with a molar ratio of 1:1 are added to water respectively. After they are fully dissolved, the ammonium molybdate solution is slowly poured into the tannic acid solution under the action of magnetic stirring to obtain a mixed solution; porous activated carbon with a mass ratio of 1:4 to ammonium molybdate is placed in an acetone solution for immersion, and then rinsed with distilled water and dried. The treated carbon material is added to the above-mentioned mixed solution and ultrasonicated. After 50 minutes, it is placed in a tubular furnace and calcined at a temperature of 600°C. After 3 hours, it is taken out, washed and dried to obtain a MoO2-loaded carbon material alcoholysis catalyst.

[0052] (3) Depolymerization of waste polyester: After the mixture of waste polyester and pre-solvent was cooled to room temperature (25°C), 10 mL of methanol and 0.5 g of the above catalyst were added, stirred and heated to 45°C. After the reaction was carried out for 10 h, the actual DMT yield and PET depolymerization rate were obtained by weighing.

[0053] Example 9:

[0054] (1) Pre-dissolved surface treatment of waste polyester: 4 g of waste polyester and 10 mL of cyclopentyl methyl ether were put into a depolymerization reactor and reacted at 45 °C for 1 h to swell the surface of the waste polyester.

[0055] (2) Preparation of alcoholysis catalyst: Tannic acid and ammonium molybdate with a molar ratio of 1:1 were added to water respectively. After they were fully dissolved, the ammonium molybdate solution was slowly poured into the tannic acid solution under the action of magnetic stirring to obtain a mixed solution; carbon nanotubes with a mass ratio of 1:6 to ammonium molybdate were placed in an acetone solution for immersion, and then rinsed with distilled water and dried. The treated carbon material was added to the above-mentioned mixed solution and ultrasonicated. After 50 minutes, it was placed in a tubular furnace and calcined at a temperature of 600°C. After 3 hours, it was taken out, washed and dried to obtain a MoO2-loaded carbon material alcoholysis catalyst.

[0056] (3) Depolymerization of waste polyester: After the mixture of waste polyester and pre-solvent was cooled to room temperature (25°C), 10 mL of methanol and 0.5 g of the above catalyst were added, stirred and heated to 45°C. After the reaction was carried out for 10 h, the actual DMT yield and PET depolymerization rate were obtained by weighing.

[0057] Comparative Example 1:

[0058] (1) Preparation of alcoholysis catalyst: Tannic acid and ammonium molybdate with a molar ratio of 1:1 are added to water respectively. After they are fully dissolved, the ammonium molybdate solution is slowly poured into the tannic acid solution under the action of magnetic stirring to obtain a mixed solution; porous activated carbon with a mass ratio of 6:1 to tannic acid is placed in an acetone solution for immersion, and then rinsed with distilled water and dried. The treated carbon material is added to the above-mentioned mixed solution and ultrasonicated. After 50 minutes, it is placed in a tubular furnace and calcined at a temperature of 600°C. After 3 hours, it is taken out, washed and dried to obtain a MoO2-loaded carbon material methanolysis catalyst.

[0059] (2) Depolymerization of waste polyester: 4 g of waste polyester, 10 mL of methanol and 0.5 g of the above catalyst were added to a depolymerization reactor, stirred and heated to 45 °C. After reacting for 10 h, the actual DMT yield and PET depolymerization rate were weighed to obtain the results.

[0060] Comparative Example 2:

[0061] (1) Pre-dissolved surface treatment of waste polyester: 4 g of waste polyester and 5 mL of cyclopentyl methyl ether were put into a depolymerization reactor and reacted at 45 °C for 1 h to swell the surface of the waste polyester.

[0062] (2) Depolymerization of waste polyester: After the mixture of waste polyester and pre-solvent was cooled to room temperature (25°C), 10 mL of methanol was added, stirred and heated to 45°C. After the reaction was carried out for 10 h, the actual DMT yield and PET depolymerization rate were obtained by weighing.

[0063] Comprehensive description

[0064] As shown in Table 1, a comprehensive analysis of the results of Examples 1 to 10 shows that the pre-dissolved catalytic methanol depolymerization system can efficiently depolymerize PET under mild reaction conditions; the results of Examples 1 and 2 show that increasing the temperature of the surface pretreatment reaction of waste polyester can increase the depolymerization rate of PET and the yield of DMT; the results of Examples 2 and 3 show that cyclopentyl methyl ether has a better pretreatment effect than cyclopentane sulfone, thereby increasing the depolymerization rate of PET and the yield of DMT; the results of Examples 2, 4, and 5 show that increasing the temperature of the catalytic depolymerization can increase the depolymerization rate of PET and the yield of DMT. yield; analysis of the results of Examples 5, 6, and 7 shows that increasing the catalytic depolymerization time can increase the depolymerization rate of PET and the yield of DMT; analysis of the results of Examples 6, 8, and 9 shows that increasing the carbon loading can increase the depolymerization rate of PET and the yield of DMT; analysis of the differences between the results of Comparative Examples 1 and 2 and the embodiment shows that when PET that has not undergone pre-dissolution surface treatment is subjected to catalytic methanol depolymerization, the PET depolymerization rate and DMT yield are greatly reduced. Only a methanol depolymerization system that combines pre-dissolution surface treatment with MoO2-loaded carbon material catalysis can achieve a good depolymerization effect.

[0065] Table 1

[0066]

Claims

1. A high-efficiency alcoholysis method for waste polyester, characterized in that: The following steps are involved: (1) Surface treatment of waste polyester pre-dissolved: put the waste polyester raw material and pre-solvent into the depolymerization kettle in a certain proportion, react at a certain temperature for a period of time, and perform swelling treatment on the surface of the waste polyester; (2) Preparation of alcoholysis catalyst: Tannic acid and ammonium molybdate are added to water respectively. After they are fully dissolved, the ammonium molybdate solution is slowly poured into the tannic acid solution under the action of magnetic stirring to obtain a mixed solution; the carbon material is placed in an acetone solution for immersion, and then rinsed with distilled water and dried. The treated carbon material is added to the above-mentioned mixed solution, ultrasonicated for a period of time, and then placed in a tube furnace for calcination. After a period of time, it is taken out, washed and dried to obtain a MoO2-loaded carbon material alcoholysis catalyst; (3) Depolymerization of waste polyester: After the mixture of waste polyester and pre-solvent is cooled to room temperature, a certain amount of methanol and the above-mentioned catalyst are added, stirred and heated, and after a period of reaction, the depolymerization liquid is cooled to room temperature, filtered and dried to obtain DMT; The waste polyester raw material is one or more of waste bottle flakes, waste textiles, or waste films; the presolvent is one or more of cyclopentyl methyl ether, cyclopentane sulfone, or dimethyl carbonate; and the carbon material is one or more of carbon nanotubes, porous activated carbon, or graphite flakes.

2. The efficient depolymerization method of waste polyester according to claim 1, characterized in that: The mass of the waste polyester raw material in step (2) is 2.0-7.0 g, the volume of the pre-solvent is 5-35 mL, the reaction time is 1-3 h, and the reaction temperature is 30-60° C.

3. The efficient depolymerization method of waste polyester according to claim 1, characterized in that: As described in step (3), the molar ratio of tannic acid to ammonium molybdate is 1:1-3, and the mass ratio of ammonium molybdate to carbon material is 2:1-6:1; the ultrasonic time is 40-60 min; the calcination temperature is 500-700°C, and the time is 2-4 h.

4. The efficient depolymerization method of waste polyester according to claim 1, characterized in that: As described in step (3), the mass of the added catalyst is 0.5-2 g, the volume of methanol is 5-45 mL, the alcoholysis temperature is 30-60° C., and the alcoholysis time is 5-10 h.

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