Ionic liquid catalyst for recycling polyethylene glycol terephthalate as well as preparation method and application of ionic liquid catalyst
The ionic liquid catalyst prepared by biheterocyclic organic alkali and 4-hydroxypiperidine is efficiently depolymerized under mild conditions, solving the high temperature, high energy consumption and pollution problems of existing catalysts, and achieving efficient and environmentally friendly PET Recycle.
Patent Information
- Application Number
- CN202411166794.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-23
- Publication Date
- 2024-12-27
AI Technical Summary
During the PET depolymerization process, existing catalysts have problems such as high reaction temperature, large energy consumption, heavy metal pollution and low thermal stability, especially non-metallic catalysts have long reaction time, low monomer conversion rate and poor thermal stability.
The ionic liquid catalyst prepared by reacting biheterocyclic organic bases with 4-hydroxypiperidine is used to carry out PET depolymerization under mild conditions, avoiding the use of metal ions, and increasing the heat of the catalyst by optimizing the reaction conditions. stability.
The efficient depolymerization of PET is achieved, and the monomer yield reaches 85.2%, which reduces the reaction temperature, improves the thermal stability and environmental protection of the catalyst, simplifies the process flow, and reduces the recovery cost.
Smart Images
Figure CN119192060A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a catalyst and a preparation method thereof, in particular to a catalyst for recovering polyethylene terephthalate and a preparation method and application thereof. Background Art
[0002] Polyethylene terephthalate (PET) is a material with excellent performance and has been widely used in various industries. This is accompanied by the generation and accumulation of a large amount of waste PET materials, which are difficult to degrade due to their biological and chemical resistance and remain in the natural environment for a long time. Mechanical recycling and landfill as conventional physical recycling methods cannot solve the PET recycling problem from the root. Chemical recycling is the only effective way to fundamentally solve the problem of plastic recycling.
[0003] Among chemical recycling methods, hydrolysis, alcoholysis, diollysis and amination are the four common depolymerization pathways. Among them, diollysis is favored as an ideal industrial recycling pathway for plastics in the future due to its relatively mild reaction conditions and simple process flow. However, the process of diollysis usually requires the addition of catalysts to reduce the activation energy of the reaction to achieve the purpose of efficient recycling of PET. Various catalysts have been studied in this process and have played a huge role.
[0004] However, metal catalysts also bring many problems. For example, the reaction temperature of metal catalysts is high, and they are also accompanied by high pressure, which brings heavy energy loss; the large-scale use of heavy metal ions pollutes water quality, has great biological toxicity, and also brings huge pressure to the environment. Non-metallic catalysts, as greener and more environmentally friendly catalysts, can effectively reduce the reaction energy barrier in terms of reaction, so that the reaction can be carried out under mild conditions; the reaction operation is simple and highly designable. However, the main problems of non-metallic catalysts at present are that it takes a long time for the reaction to reach equilibrium and the monomer conversion rate is low; the thermal stability is not high, and the reaction is easy to denature at the reaction temperature of depolymerizing PET. Summary of the invention
[0005] In order to overcome the problems existing in the background technology, the present invention provides an ionic liquid catalyst and a preparation method thereof, which are used for depolymerizing waste polyethylene terephthalate.
[0006] In order to achieve the above object, the present invention adopts the following technical solution:
[0007] 1. An ionic liquid catalyst for recycling polyethylene terephthalate:
[0008] The ionic liquid catalyst is mainly prepared by the reaction of a bicyclic organic base and 4-hydroxypiperidine and is a transparent light yellow liquid.
[0009] The bicyclic organic base is one or more of 1,5,7-triazabicyclo[4.4.0]dec-5-ene TBD, 1,5-diazabicyclo[4.3.0]-5-nonene DBN, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene MTBD and 1,8-diazabicyclo[5.4.0]undec-7-ene DBU;
[0010] The molar ratio of the bicyclic organic base to 4-hydroxypiperidine is 1:1.
[0011] 2. A method for preparing an ionic liquid catalyst, the method comprising:
[0012] 1) At room temperature, a bicyclic organic base is placed in a solvent, mixed and stirred to dissolve to obtain a mixed solution;
[0013] 2) adding 4-hydroxypiperidine to the mixed solution prepared in step 1), heating and magnetically stirring the mixture for a period of time, and reacting the mixture under a nitrogen atmosphere to obtain a reaction solution;
[0014] 3) The reaction solution obtained in step 2) is subjected to rotary evaporation to remove the solvent, and the product is separated and purified to obtain the product, and then the product is placed in a vacuum oven and dried for a period of time to obtain an ionic liquid catalyst. The obtained ionic liquid catalyst is a transparent light yellow liquid.
[0015] The bicyclic organic base is one or more of 1,5,7-triazabicyclo[4.4.0]dec-5-ene TBD, 1,5-diazabicyclo[4.3.0]-5-nonene DBN, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene MTBD and 1,8-diazabicyclo[5.4.0]undec-7-ene DBU;
[0016] The molar ratio of the bicyclic organic base to 4-hydroxypiperidine is 1:1;
[0017] In the step 2), the heating temperature is 60-80°C and the reaction time is 3-12 hours;
[0018] In the step 3), the product is placed in a vacuum oven and dried for 12 to 24 hours.
[0019] In the step 1), the bicyclic organic base is 1,5,7-triazabicyclo[4.4.0]dec-5-ene TBD;
[0020] The molar ratio of the bicyclic organic base to 4-hydroxypiperidine is 1:1;
[0021] In the step 2), the heating temperature is 60°C and the reaction time is 12 hours;
[0022] In the step 3), the product is placed in a vacuum oven and dried for 24 hours.
[0023] The ionic liquid catalyst of the present invention can be used in the recovery of polyethylene terephthalate.
[0024] 3. A method for recovering polyethylene terephthalate using an ionic liquid catalyst, the method comprising the following steps:
[0025] An ionic liquid catalyst and polyethylene terephthalate are sequentially added to an ethylene glycol solution, and then a depolymerization reaction is carried out under a nitrogen atmosphere, and the final products obtained are bis(hydroxyethyl) terephthalate monomers and dimers and other oligomeric polymer insolubles. The degree of polymerization of the polymer in the oligomeric polymer insolubles is low, usually not higher than 10, so that the polyethylene terephthalate is recovered and processed.
[0026] The above products include bis(hydroxyethyl)terephthalate, dimer and oligomer with a polymerization degree of greater than 3 and less than or equal to 10.
[0027] The mass ratio of the ionic liquid catalyst, ethylene glycol and polyethylene terephthalate is 4-10:400-1000:100; the depolymerization reaction conditions are: the pressure is standard atmospheric pressure, the reaction temperature is 150-180°C, preferably the reaction temperature is 170°C, the reaction time is 10-70 minutes, and the preferred reaction time is 70 minutes.
[0028] The mass ratio of the ionic liquid catalyst, ethylene glycol and polyethylene terephthalate is 8:1000:100.
[0029] After the depolymerization reaction is completed, the reactants are cooled to room temperature, deionized water is added to the reactants to dissolve them, and the temperature is increased and then stirred, and then unreacted polyethylene terephthalate and filtrate are obtained by suction filtration. The unreacted polyethylene terephthalate is dried and weighed, and the filtrate is concentrated by rotary evaporation and then cooled at 0°C, and then suction filtered to obtain the recovered bis(hydroxyethyl) terephthalate.
[0030] Compared with the background technology, the beneficial effects of the present invention are as follows:
[0031] The present invention uses a mixed reaction of a bicyclic organic base and 4-hydroxypiperidine to prepare an ionic liquid catalyst, which is applied to the depolymerization of waste polyethylene terephthalate materials. The catalyst does not have any metal ions involved in the reaction and is a green and environmentally friendly catalyst. The method for depolymerizing PET using the catalyst can not only achieve efficient depolymerization of PET, but also reduce the reaction temperature. Under optimal conditions, PET is completely depolymerized and a monomer yield of 85.2% similar to that of a metal catalyst is obtained. In addition, the catalyst described in the present invention is green, harmless and easy to prepare, which reduces the cost compared to some non-metallic catalysts and improves thermal stability compared to common non-metallic catalysts. The depolymerization experimental process is simple and the recovery cost is low. In the future, experiments can be carried out in the pilot stage to lay the foundation for commercial depolymerization of PET. It is an efficient means to solve the problem of plastic pollution and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Figure 1 It is the thermogravimetric curve of the raw material TBD and 4-hydroxypiperidine and the corresponding synthesized ionic liquid catalyst. DETAILED DESCRIPTION
[0033] In order to more conveniently and comprehensively understand the present invention, the present invention is further described below in conjunction with specific embodiments.
[0034] The embodiments of the present invention are as follows:
[0035] Example 1
[0036] Add 50 mL of solvent and 2.78 g of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) into a three-necked flask, stir thoroughly to dissolve, add 2.02 g of 4-hydroxypiperidine, heat in a 60°C oil bath and stir magnetically for 3 hours, and the reaction is carried out under a nitrogen atmosphere. After the reaction is completed, the solution is purified and separated, and the solvent is removed by rotary evaporation. The product is placed in a vacuum oven and dried overnight to obtain catalyst A.
[0037] The results of thermogravimetric testing of the raw materials 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 4-hydroxypiperidine (4-HOP) and the synthesized ionic liquid catalyst in this example are as follows: Figure 1 As shown in the figure, it can be seen that the thermal stability of the prepared ionic liquid catalyst is significantly improved, which is greater than the raw material itself, ultimately reflecting the excellent thermal stability of the catalyst under the treatment of the scheme of the present invention.
[0038] Example 2
[0039] Add 50 mL of solvent and 2.48 g of 1,5-diazabicyclo[4.3.0]-5-nonene (DBN) to a three-necked flask, stir thoroughly to dissolve, add 2.02 g of 4-hydroxypiperidine, heat in a 60°C oil bath and stir magnetically for 3 hours, and the reaction is carried out under a nitrogen atmosphere. After the reaction is completed, the solution is purified and separated, and the solvent is removed by rotary evaporation. The product is placed in a vacuum oven and dried overnight to obtain catalyst B.
[0040] Example 3
[0041] Add 50 mL of solvent and 3.06 g of 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) to a three-necked flask, stir thoroughly to dissolve, add 2.02 g of 4-hydroxypiperidine, heat in an oil bath at 60°C and stir magnetically for 3 hours, and react under a nitrogen atmosphere. After the reaction is completed, the solution is purified and separated, and the solvent is removed by rotary evaporation. The product is placed in a vacuum oven and dried overnight to obtain catalyst C.
[0042] Example 4
[0043] Add 50 mL of solvent and 3.04 g of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) into a three-necked flask, stir thoroughly to dissolve, add 2.02 g of 4-hydroxypiperidine, heat in an oil bath at 60°C and stir magnetically for 3 hours, and the reaction is carried out under a nitrogen atmosphere. After the reaction is completed, the solution is purified and separated, and the solvent is removed by rotary evaporation. The product is placed in a vacuum oven and dried overnight to obtain catalyst D.
[0044] Example 5
[0045] 20g of ethylene glycol EG, 0.16g of catalyst A, and 2g of waste PET bottle slices were added to a 250mL glass four-necked flask in sequence. The flask was placed in a heating jacket with a temperature sensor for heating and mechanical stirring with a stirrer. The speed was 100rpm, and the temperature was controlled at 170°C. The reaction process was placed in a nitrogen atmosphere and the reaction time was 70min. After the reaction was completed, it was cooled to room temperature, about 400ml of deionized water was added for dissolution, and the temperature was raised to 70°C, stirred thoroughly, and then filtered to separate the unreacted PET for drying and weighing. The filtrate was concentrated to 100ml by rotary evaporation, cooled at 0°C for 12h, and then filtered to obtain a white needle-shaped solid bis(hydroxyethyl) terephthalate BHET, which was dried and weighed. The PET depolymerization rate was calculated to be 100% and the BHET yield was 85.2%. This condition was subsequently proved to be the optimal condition for depolymerization.
[0046] Example 6
[0047] 20g EG, 0.16g catalyst B, and 2g waste PET bottle slices were added to a 250mL glass four-necked flask in sequence. The flask was placed in a heating jacket with a temperature sensor for heating and mechanical stirring with a stirrer. The speed was 100rpm, and the temperature was controlled at 170°C. The reaction process was placed in a nitrogen atmosphere and the reaction time was 70min. After the reaction was completed, it was cooled to room temperature, about 400ml of deionized water was added for dissolution, and the temperature was raised to 70°C, fully stirred, and then filtered, the unreacted PET was separated and dried and weighed, and the filtrate was concentrated to 100ml by rotary evaporation, cooled at 0°C for 12h, and then filtered to obtain a white needle-shaped solid BHET, which was dried and weighed. The PET depolymerization rate was calculated to be 100% and the BHET yield was 82.5%.
[0048] Example 7
[0049] 20g EG, 0.16g catalyst C, and 2g waste PET bottle slices were added to a 250mL glass four-necked flask in sequence. The flask was placed in a heating jacket with a temperature sensor for heating and mechanical stirring with a stirrer. The speed was 100rpm, and the temperature was controlled at 170°C. The reaction process was placed in a nitrogen atmosphere and the reaction time was 70min. After the reaction was completed, it was cooled to room temperature, about 400ml of deionized water was added for dissolution, and the temperature was raised to 70°C, stirred thoroughly, and then filtered to separate the unreacted PET for drying and weighing. The filtrate was concentrated to 100ml by rotary evaporation, cooled at 0°C for 12h, and then filtered to obtain a white needle-shaped solid BHET, which was dried and weighed. The PET depolymerization rate was calculated to be 92.5% and the BHET yield was 71.8%.
[0050] Example 8
[0051] 20gEG, 0.16g catalyst D, and 2g waste PET bottle slices were added to a 250mL glass four-necked flask in sequence. The flask was placed in a heating jacket with a temperature sensor for heating and mechanical stirring with a stirrer. The speed was 100rpm, and the temperature was controlled at 170°C. The reaction process was placed in a nitrogen atmosphere and the reaction time was 70min. After the reaction was completed, it was cooled to room temperature, about 400ml of deionized water was added for dissolution, and the temperature was raised to 70°C, fully stirred, and then filtered, the unreacted PET was separated and dried and weighed, and the filtrate was concentrated to 100ml by rotary evaporation, cooled at 0°C for 12h, and then filtered to obtain a white needle-shaped solid BHET, which was dried and weighed. The PET depolymerization rate was calculated to be 98.5% and the BHET yield was 79.6%.
[0052] Example 9
[0053] 20g EG, 0.12g catalyst A, and 2g waste PET bottle slices were added to a 250mL glass four-necked flask in sequence. The flask was placed in a heating jacket with a temperature sensor for heating and mechanical stirring with a stirrer. The speed was 100rpm, and the temperature was controlled at 170°C. The reaction process was placed in a nitrogen atmosphere and the reaction time was 70min. After the reaction was completed, it was cooled to room temperature, about 400ml of deionized water was added for dissolution, and the temperature was raised to 70°C, fully stirred, and then filtered, the unreacted PET was separated and dried and weighed, and the filtrate was concentrated to 100ml by rotary evaporation, cooled at 0°C for 12h, and then filtered to obtain a white needle-shaped solid BHET, which was dried and weighed. The PET depolymerization rate was calculated to be 87.0% and the BHET yield was 72.5%.
[0054] Example 10
[0055] 20g EG, 0.16g catalyst A, and 2g waste PET bottle slices were added to a 250mL glass four-necked flask in sequence. The flask was placed in a heating jacket with a temperature sensor for heating and mechanical stirring with a stirrer. The speed was 100rpm, the temperature was controlled at 160°C, the reaction process was placed in a nitrogen atmosphere, and the reaction time was 70min. After the reaction was completed, it was cooled to room temperature, about 400ml of deionized water was added for dissolution, and the temperature was raised to 70°C, fully stirred, and then filtered, the unreacted PET was separated for drying and weighing, and the filtrate was concentrated to 100ml by rotary evaporation, cooled at 0°C for 12h, and then filtered to obtain a white needle-shaped solid BHET, which was dried and weighed. The PET depolymerization rate was calculated to be 85.0% and the BHET yield was 70.6%.
[0056] Embodiment 11
[0057] 20g EG, 0.16g catalyst A, and 2g waste PET bottle slices were added to a 250mL glass four-necked flask in sequence. The flask was placed in a heating jacket with a temperature sensor for heating and mechanical stirring with a stirrer. The speed was 100rpm, and the temperature was controlled at 170°C. The reaction process was placed in a nitrogen atmosphere and the reaction time was 50min. After the reaction was completed, it was cooled to room temperature, about 400ml of deionized water was added for dissolution, and the temperature was raised to 70°C, stirred thoroughly, and then filtered to separate the unreacted PET for drying and weighing. The filtrate was concentrated to 100ml by rotary evaporation, cooled at 0°C for 12h, and then filtered to obtain a white needle-shaped solid BHET, which was dried and weighed. The PET depolymerization rate was calculated to be 88.5% and the BHET yield was 73.8%.
[0058] Comparative Example 1
[0059] 20g EG, 0.16g catalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), and 2g waste PET bottle slices were added to a 250mL glass four-necked flask in sequence. The flask was placed in a heating jacket with a temperature sensor for heating and mechanical stirring with a stirrer. The speed was 100rpm and the temperature was controlled at 170°C. The reaction process was placed in a nitrogen atmosphere and the reaction time was 60min. After the reaction was completed, it was cooled to room temperature, about 400ml of deionized water was added for dissolution, and the temperature was raised to 70°C, stirred thoroughly, and then filtered to separate the unreacted PET for drying and weighing. The filtrate was concentrated to 100ml by rotary evaporation, cooled at 0°C for 12h, and then filtered to obtain a white needle-shaped solid BHET, which was dried and weighed. The PET depolymerization rate was calculated to be 85.6% and the BHET yield was 63.5%.
[0060] Comparative Example 2
[0061] 20g EG, 0.16g catalyst 1,5-diazabicyclo[4.3.0]-5-nonene (DBN), and 2g waste PET bottle slices were added to a 250mL glass four-necked flask in sequence. The flask was placed in a heating jacket with a temperature sensor for heating and mechanical stirring with a stirrer. The speed was 100rpm and the temperature was controlled at 170°C. The reaction process was placed in a nitrogen atmosphere and the reaction time was 60min. After the reaction was completed, it was cooled to room temperature, about 400ml of deionized water was added for dissolution, and the temperature was raised to 70°C, stirred thoroughly, and then filtered to separate the unreacted PET for drying and weighing. The filtrate was concentrated to 100ml by rotary evaporation, cooled at 0°C for 12h, and then filtered to obtain a white needle-shaped solid BHET, which was dried and weighed. The PET depolymerization rate was calculated to be 82.2% and the BHET yield was 60.3%.
[0062] Comparative Example 3
[0063] 20gEG, 0.16g catalyst 4-hydroxypiperidine, and 2g waste PET bottle slices were added to a 250mL glass four-necked flask in sequence. The flask was placed in a heating jacket with a temperature sensor for heating and mechanical stirring with a stirrer. The speed was 100rpm, and the temperature was controlled at 170°C. The reaction process was placed in a nitrogen atmosphere and the reaction time was 60min. After the reaction was completed, it was cooled to room temperature, about 400ml of deionized water was added for dissolution, and the temperature was raised to 70°C, stirred thoroughly, and then filtered to separate the unreacted PET for drying and weighing. The filtrate was concentrated to 100ml by rotary evaporation, cooled at 0°C for 12h, and then filtered to obtain a white needle-shaped solid BHET, which was dried and weighed. The PET depolymerization rate was calculated to be 71.2% and the BHET yield was 48.5%.
[0064] It can be seen from Example 5 and Comparative Examples 1 to 3 that the prepared ionic liquid catalysts can effectively depolymerize PET. The best screened example is Example 5, which is also the example studied under the best conditions.
[0065] In summary of the above embodiments, the present invention uses the ionic liquid prepared by the bicyclic organic base and 4-hydroxypiperidine as a catalyst for depolymerizing waste PET materials, not only realizing the depolymerization reaction of PET under relatively mild conditions, but also the depolymerization reaction catalyst is efficient, easy to obtain, low-cost, and environmentally friendly. In addition, the catalyst has strong thermal stability and can meet the requirements of PET for reaction in the glycolysis temperature range for a long time.
[0066] The above embodiments are only used to explain the present invention and to clarify the examples made by the present invention, but are not intended to limit the scope of protection of the present invention. It should be pointed out that any equivalent changes or modifications made within the spirit and scope of protection of the present invention and the claims without departing from the principles of the present invention are deemed to be within the scope of protection of the present invention.
Claims
1. An ionic liquid catalyst for recovering polyethylene terephthalate, characterized in that: The ionic liquid catalyst is mainly prepared by the reaction of a bicyclic organic base and 4-hydroxypiperidine and is a transparent light yellow liquid.
2. The ionic liquid catalyst according to claim 1, characterized in that: The bicyclic organic base is one or more of 1,5,7-triazabicyclo[4.4.0]dec-5-ene TBD, 1,5-diazabicyclo[4.3.0]-5-nonene DBN, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene MTBD and 1,8-diazabicyclo[5.4.0]undec-7-ene DBU; The molar ratio of the bicyclic organic base to 4-hydroxypiperidine is 1:
1.
3. The method for preparing the ionic liquid catalyst according to any one of claims 1 to 2, characterized in that the method include: 1) At room temperature, a bicyclic organic base is placed in a solvent, mixed and stirred to dissolve to obtain a mixed solution; 2) adding 4-hydroxypiperidine to the mixed solution prepared in step 1), heating and magnetically stirring the mixture for a period of time, and reacting the mixture under a nitrogen atmosphere to obtain a reaction solution; 3) The reaction solution obtained in step 2) is subjected to rotary evaporation to remove the solvent, and the product is separated and purified to obtain the product, and then the product is placed in a vacuum oven and dried for a period of time to obtain an ionic liquid catalyst. The obtained ionic liquid catalyst is a transparent light yellow liquid.
4. The method for preparing the ionic liquid catalyst according to claim 3, characterized in that: The bicyclic organic base is one or more of 1,5,7-triazabicyclo[4.4.0]dec-5-ene TBD, 1,5-diazabicyclo[4.3.0]-5-nonene DBN, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene MTBD and 1,8-diazabicyclo[5.4.0]undec-7-ene DBU; The molar ratio of the bicyclic organic base to 4-hydroxypiperidine is 1:1; In the step 2), the heating temperature is 60-80°C and the reaction time is 3-12 hours; In the step 3), the product is placed in a vacuum oven and dried for 12 to 24 hours.
5. The method for preparing the ionic liquid catalyst according to claim 3, characterized in that: In the step 1), the bicyclic organic base is 1,5,7-triazabicyclo[4.4.0]dec-5-ene TBD; The molar ratio of the bicyclic organic base to 4-hydroxypiperidine is 1:1; In the step 2), the heating temperature is 60°C and the reaction time is 12 hours; In the step 3), the product is placed in a vacuum oven and dried for 24 hours.
6. Use of the ionic liquid catalyst according to any one of claims 1-2 or the ionic liquid catalyst prepared by the preparation method according to any one of claims 3-5, characterized in that: Application in recycling polyethylene terephthalate.
7. A method for recovering polyethylene terephthalate using the ionic liquid catalyst according to any one of claims 1 to 2, characterized in that: The method comprises the following steps: sequentially adding an ionic liquid catalyst and polyethylene terephthalate to an ethylene glycol solution, and then carrying out a depolymerization reaction under a nitrogen atmosphere, and finally obtaining products of bis(hydroxyethyl) terephthalate monomers and dimers and oligomer polymer insolubles, thereby recycling and treating the polyethylene terephthalate.
8. The method for recovering polyethylene terephthalate using an ionic liquid catalyst according to claim 7, characterized in that: The mass ratio of the ionic liquid catalyst, ethylene glycol and polyethylene terephthalate is 4-10:400-1000:100; the depolymerization reaction conditions are: the pressure is standard atmospheric pressure, the reaction temperature is 150-180°C, and the reaction time is 10-70 minutes.
9. The method for recovering polyethylene terephthalate using an ionic liquid catalyst according to claim 7, characterized in that: The mass ratio of the ionic liquid catalyst, ethylene glycol and polyethylene terephthalate is 8:1000:
100.
10. The method for recovering polyethylene terephthalate using an ionic liquid catalyst according to claim 7, characterized in that: After the depolymerization reaction is completed, the reactants are cooled to room temperature, deionized water is added to the reactants to dissolve them, and the temperature is increased and then stirred, and then unreacted polyethylene terephthalate and filtrate are obtained by suction filtration. The unreacted polyethylene terephthalate is dried and weighed, and the filtrate is concentrated by rotary evaporation and then cooled at 0°C, and then suction filtered to obtain the recovered bis(hydroxyethyl) terephthalate.