System and method for PET glycolysis based on perovskite composite oxide

Abstract

The invention discloses a system and a method for performing PET glycolysis based on perovskite composite oxide. The system comprises a glycolysis device, a coarse filtration unit, a magnetic recovery unit, a thermal regeneration unit, a suction filtration unit, a rotary evaporation unit and a cooling crystallization unit. The perovskite structure catalyst is used for PET glycolysis, catalytic depolymerization of waste PET particles can be achieved under normal pressure, the monomer yield is 89.7%, separation and recovery of the catalyst and products can be achieved through the magnetic decantation process, and directional recovery of the PET particles is achieved. The catalyst has the advantages of cheap and easily available raw materials and simple preparation process, is more suitable for large-scale production and application compared with other precious catalysts, and can improve the economic benefit of the whole depolymerization process. Meanwhile, the yield of the PET monomer can be controlled by changing the amount of the ethylene glycol, the amount of the catalyst, the reaction temperature and the reaction time, the optimal reaction condition and the highest monomer yield of the catalyst are obtained by using a response surface analysis method, and the selection of reaction conditions in subsequent industrial application is facilitated.

Description

Technical Field

[0001] The present invention relates to a method for preparing a perovskite composite oxide catalyst and its application in the depolymerization of PET ester bonds to recover monomers, and uses factorial experiments to determine the optimal reaction conditions for the process of this catalyst. Background Art

[0002] Plastics have changed people's daily lives and brought many benefits to society. Currently, humans produce approximately 430 million tons of plastics per year, and two-thirds of them soon become waste. Every year, a large amount of plastic waste flows into aquatic ecosystems, polluting lakes, rivers, and oceans. Polyethylene terephthalate (PET) is one of the most widely used polyester-based plastics, with applications ranging from food and beverage packaging to the textile and construction industries, and has characteristics such as light weight, high transparency, high rigidity, chemical stability, and safety. Since PET is a petroleum-derived product, the recycling of PET helps to reduce the consumption of fossil fuels. Therefore, the efficient recycling of waste PET is an urgent need in today's society.

[0003] The glycolysis of post-consumer PET waste is carried out in the presence of a transesterification catalyst. So far, researchers have reported various homogeneous and heterogeneous catalysts. Although homogeneous catalysts have been reported to show high catalytic performance, there are still disadvantages such as separability, recyclability, low selectivity, and product purity. Therefore, there is an urgent need for commercial applications to catalyze the PET glycolysis reaction through heterogeneous catalysts. So far, many heterogeneous catalysts have been used for PET glycolysis, including metal oxides, metal-organic frameworks (MOF), carbonaceous compounds, magnetic nanoparticles, and zeolites. Compared with traditional homogeneous catalysts, heterogeneous catalysts have many desirable properties such as high melting points, strong mechanical properties, and regeneration potential, making them a more practical industrial choice.

[0004] The Lewis acidity of transition metal iron in ferrite plays a catalytic role in the glycolysis process, increasing the reaction rate and reducing the reaction conditions. The magnetism can be used for catalyst recovery and regeneration. Therefore, iron-based catalysts are cheap, widely available, have superior mechanical properties, environmentally friendly and stable thermodynamic properties, and significant magnetic properties. They have been widely used in the research of the glycolysis process and have broad industrial application prospects. Currently, the main ones used for the glycolysis recovery of polymer PET are Fe 3 O 4 、γ-Fe 2 O 3 and spinel ferrite compounds, obtaining a relatively high monomer yield and being able to be recovered in the system through magnetism.

[0005] The recycling of polymers has many advantages. There is an urgent need for a catalyst system that is simple, efficient, green, easy to regulate, and structurally stable, which can improve the depolymerization efficiency of PET, and the catalyst can be reused multiple times and is easy to regenerate. This is of great significance for future environmental sustainable development and efficient resource utilization.

[0006] CN202410136323.7 discloses a bimetallic catalyst CoMo@SiO for degrading PET 2 (the molar ratio of Co to Mo is 1:1), which points out the mechanism of the action of transition metals on the cleavage of ester bonds in PET degradation. Based on the design strategy of frustrated Lewis acid-base pairs of bimetallic catalysts, two transition metals are coordinated and anchored on the carrier by a complexing agent, and the synergistic effect of the two metal sites is utilized to improve the catalytic reaction rate and the selectivity of the catalytic reaction. However, the preparation process of this catalyst is complex and not conducive to large-scale preparation; at the same time, if a high catalytic effect is to be achieved, the ratio of metal ions needs to be strictly controlled.

[0007] In order to solve the problems existing in the current glycolysis method for recycling waste PET polyester, such as low BHET yield and purity, metal residues, and long reaction time, CN202310075211.0 discloses a method for recycling waste PET polyester by using ionic liquids as catalysts. However, it should be noted that all kinds of ionic liquids used in this patent are soluble in ethylene glycol, which has great disadvantages in the subsequent recycling and reuse of catalysts. Therefore, considering all aspects, heterogeneous catalysts are the mainstream in current industrial large-scale applications. Summary of the Invention

[0008] In order to efficiently depolymerize PET particles to obtain product monomers, the present invention provides a novel-structured, environmentally friendly, efficient, and simple-to-prepare ferrite perovskite composite oxide catalyst. Compared with zinc acetate, sodium carbonate, and ionic liquid catalysts, the prepared catalyst is more easily recycled and reused in the reaction system. At the same time, the stable chemical structure of the catalyst reduces the leaching rate of iron ions and can better improve the product quality. At the same time, the perovskite structure ensures the excellent regulability of the catalyst, and the catalytic effect can be adjusted by changing the B-site ions. Based on the influence of reaction conditions on the whole system, the response surface analysis method is used to calculate the optimal reaction conditions to reduce the operating cost of actual industrial applications.

[0009] The technical solution of the present invention:

[0010] A system for PET glycolysis based on perovskite composite oxides, comprising a glycolysis device, a coarse filtration unit, a magnetic recovery unit, a thermal regeneration unit, a suction filtration unit, a rotary evaporation unit, and a cooling crystallization unit.

[0011] The glycolysis device is filled with perovskite composite oxide and solvent. The outlet of the glycolysis device is connected to the inlet of the coarse filtration unit. The coarse filtration unit is provided with a solid outlet and a filtrate outlet. The filtrate outlet is connected to the inlet of the magnetic recovery unit. The catalyst outlet of the magnetic recovery unit is connected to the inlet of the glycolysis device or the thermal regeneration unit. The outlet of the thermal regeneration unit is connected to the glycolysis device. The oligomer and monomer outlet of the magnetic recovery unit is connected to the suction filtration unit. The filtrate outlet of the suction filtration unit is connected to the inlet of the rotary evaporation unit. The outlet of the rotary evaporation unit is connected to the inlet of the cooling crystallization unit.

[0012] A method for PET glycolysis based on perovskite composite oxide is as follows: Feed the raw material PET particles into the glycolysis device filled with perovskite composite oxide and solvent. The perovskite composite oxide serves as a catalyst for glycolysis of PET. An inert gas is introduced into the glycolysis device, and corresponding reaction temperature, reaction time, addition amount of solvent, and catalyst dosage are set for the glycolysis device to carry out the glycolysis reaction on PET. After the reaction is completed, the reaction solution is fed into the coarse filtration unit. The solid after coarse filtration is unreacted PET, and the filtrate contains the catalyst, as well as a mixture of oligomers and monomers (ethylene terephthalate monomers). Among them, the catalyst recovered by the magnetic recovery unit determines its destination according to the number of times of recycling in the whole system. If it is judged to be deactivated, it is first introduced into the thermal regeneration unit for regeneration and then recycled back to the glycolysis device. If it is judged not to be deactivated, it is directly introduced into the glycolysis device. The mixture of oligomers and monomers after the magnetic recovery unit passes through the suction filtration unit, and the obtained solid is oligomers. The filtrate enters the cooling crystallization unit after evaporation by the rotary evaporation unit for cooling to obtain ethylene terephthalate BHET.

[0013] Preferably, the perovskite composite oxide is prepared by the sol-gel method.

[0014] Preferably, the perovskite composite oxide CaFeO 3 is in the form of particles with a particle size range of 40.08 ± 10.81 μm.

[0015] Preferably, the preparation method of the perovskite composite oxide includes the following steps:

[0016] Fe(NO 3 ) 3 ·9H 2 O and Ca(NO 3 ) 2 are heated and mixed with citric acid in a ratio of 1 - 1.2:1 - 1.2:1 - 1.2, then placed in an oven for drying, and then ground and calcined to obtain the perovskite composite oxide CaFeO 3 .

[0017] Preferably, the temperature of the heating and mixing is 90 - 95 °C; the time of the heating and mixing is 30 - 35 min until the solution becomes a gel.

[0018] Preferably, the temperature of the oven drying is 105 - 110 °C; the time of the oven drying is 35 - 36 h.

[0019] Preferably, the calcination is divided into two stages. The calcination temperature in the first stage is 320 - 350 °C; the calcination time is 0.4 - 0.5 h. The calcination temperature in the second stage is 820 - 850 °C; the calcination time is 1.5 - 2 h.

[0020] Preferably, the solvent is ethylene glycol, diethylene glycol, propylene glycol and 1,4 - butanediol. Most preferably, it is ethylene glycol.

[0021] Preferably, a magnetic stirrer is provided in the glycolysis device to form a shear flow field, and a continuous depolymerization reaction is carried out under this shear flow field to obtain the depolymerization product BHET.

[0022] Preferably, the temperature of the glycolysis reaction in the glycolysis device is 120 - 196 °C.

[0023] Preferably, the mass ratio of the catalyst added in the glycolysis device to the mass of PET contained in the dissolution solution is 0.005 - 0.02.

[0024] Preferably, the time of the glycolysis device is 60 - 240 min.

[0025] Preferably, in the glycolysis device, when the solvent is ethylene glycol, the mass ratio of ethylene glycol to PET is 5 - 10.

[0026] Preferably, a condensation reflux device is provided on the glycolysis device to recover the ethylene glycol volatilized due to temperature rise.

[0027] In a specific embodiment of the present invention, the PET product is a product mainly composed of PET, including but not limited to any one of bottle - grade PET, film - grade PET, fiber - grade PET, etc.

[0028] The main active ingredient of the perovskite composite oxide catalyst provided by the present invention is CaFeO 3 , CaFeO 3 During the catalytic process, Fe - O 6 species are easily formed, effectively increasing the catalytic activity of the catalyst.

[0029] In principle, the present invention is applicable to CaFeO 3There are no special restrictions on the appearance, and those skilled in the art can select and adjust according to the actual situation and product requirements. In order to better improve the catalytic performance and stability of the catalyst, CaFeO is preferably 3 nanoparticle structure.

[0030] In the present invention, due to the polyester characteristics of PET, it depolymerizes to form the monomer ethylene terephthalate in the presence of ethylene glycol and a catalyst. The reaction process is the breaking of the ester bond of PET. The catalyst used needs to combine with the carbonyl oxygen of the polymer chain to make the ester group form more carbocations, combine with the hydroxyl group of ethylene glycol, complete the chain-breaking process, and gradually depolymerize to obtain the product monomer. In the experimental device built in the present invention, the final product is dissolved in ethylene glycol.

[0031] In addition, unless otherwise specified, any range described in the present invention includes the end values and any numerical value between the end values, as well as any sub-range composed of any numerical value between the end values or the end values. The preparation methods in the present invention are all conventional methods unless otherwise specified. The raw materials used can be obtained from public commercial channels or prepared according to the existing technology unless otherwise specified. The percentages are mass percentages unless otherwise specified, and the solutions are aqueous solutions unless otherwise specified.

[0032] The beneficial effects of the present invention are as follows:

[0033] (1) The perovskite composite oxide catalyst of ferrite provided by the present invention can achieve the glycolysis of waste PET particles under atmospheric pressure, and the conversion rate of PET to high-value-added chemicals is 89.7%. It has a higher yield compared with other ionic salt catalysts. Moreover, the catalyst structure is stable and easy to recycle, and it can recover the initial catalytic effect by thermal regeneration at 850 °C, which is suitable for large-scale production applications.

[0034] (2) The perovskite composite oxide catalyst of ferrite provided by the present invention is used in the PET glycolysis process. The reason for the improved depolymerization effect compared with other Lewis acids is the presence of more strong acid sites. At the same time, it has strong paramagnetism and can be recovered in the system through the magnetic decantation process. Therefore, the product can be separated by simple rotary evaporation. Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is a process flow chart of using the catalyst prepared by this patent to promote the glycolysis of PET to obtain the product.

[0037] Figure 2 For the CaFeO prepared in Example 1 3 XRD spectrum of the catalyst.

[0038] Figure 3 For the CaFeO prepared in Example 1 3 Microstructure diagram of the catalyst, where (a)-(d) are CaFeO 3 SEM image of the catalyst, (e) is CaFeO 3 Particle size distribution diagram of the catalyst.

[0039] Figure 4 For the CaFeO prepared in Example 1 3 Hysteresis loop diagram of the catalyst.

[0040] Figure 5 For the CaFeO prepared in Example 1 3 Comparison diagram of the depolymerization effects of the catalyst and different conventional catalysts.

[0041] Figure 6 For the CaFeO prepared in Example 1 3 Comparison diagram of the yields of the catalyst under different reaction conditions, where (a) is the comparison diagram of the monomer yields at different temperatures, (b) is the comparison diagram of the monomer yields at different reaction times, (c) is the comparison diagram of the monomer yields at different catalyst addition amounts, and (d) is the comparison diagram of the monomer yields at different ethylene glycol addition amounts.

[0042] Figure 7 After the glycolysis reaction process of PET particles is completed, for the ethylene glycol terephthalate in the product 1 HNMR spectrum.

[0043] Figure 8 For the CaFeO prepared in Example 1 3 Effect diagram of the repeated use of the catalyst. Among them, (a) is the diagram of the number of catalyst cycles and monomer yield, (b) is the initial morphology of the catalyst, (c) is the surface morphology diagram of the catalyst after the first cycle, (d) is the surface morphology diagram of the catalyst after the second cycle, and (e) is the surface morphology diagram of the catalyst after passing through the thermal regeneration unit. Detailed implementation manners

[0044] The present invention will be described in detail below in conjunction with the embodiments, so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following embodiments.

[0045] For all raw materials of the present invention, there is no special limitation on their purity. The present invention preferably adopts analytical purity or the purity requirements conventional in the field of PET depolymerization.

[0046] All raw materials of the present invention, their sources and abbreviations belong to the conventional sources and abbreviations in the art, and are clear and definite in the fields of their related uses. Those skilled in the art can purchase them from the market or prepare them by conventional methods according to the abbreviations and corresponding uses.

[0047] To illustrate the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments and the accompanying drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0048] Example 1

[0049] Preparation of catalyst:

[0050] Weigh Fe(NO 3 ) 3 ·9H 2 O and Ca(NO 3 ) 2 according to the molar ratio of 1:1, dissolve them in distilled water and adjust the pH to 7, and stir and react in a water bath at 75 °C for 30 min; then, add C 3 ) 2 with a molar ratio of 1:1 to Ca(NO 6 H 8 O 7 ·H 2 O, continue to stir for 10 min and then heat in a water bath at 95 °C to make the solution become a gel; then, place it in an oven at 110 °C and dry for 36 h to obtain a dry gel, and obtain a precursor after self-propagating combustion; finally, grind the precursor and pre-calcine it at 350 °C for 0.5 h, and then calcine it at 850 °C for 2 h to obtain the product, i.e., perovskite-type CaFeO 3 . The particle size range is 40.08 ± 10.81 μm.

[0051] Figure 2 shows the XRD pattern of the CaFeO 3 catalyst prepared in this example. From this pattern, it can be seen that the present invention successfully prepared CaFeO 3 .

[0052] Figure 3 shows the microstructural diagram of the CaFeO 3 catalyst prepared in this example. The figure shows that the surface of the CaFeO 3 catalyst is a porous structure and has a large specific surface area.

[0053] Figure 4 shows the CaFeO 3The hysteresis loop diagram of the catalyst shows that the catalyst is paramagnetic at room temperature.

[0054] Comparative Example 1

[0055] Compare the glycolytic catalytic performance of different catalysts on PET

[0056] Use different catalysts to catalyze the glycolysis of PET. The specific method is as follows: Add 2 g of PET particles and the catalyst into a glass device in a nitrogen atmosphere, and add the catalyst of the present invention and commercial catalysts Zn(Ac) 2 , Na 2 CO 3 , Fe 2 O 3 , Fe 3 O 4 Each 0.02 g, then add 15 g of ethylene glycol. The solution and solid particles are heated under normal pressure in the presence of a complex metal catalyst. The heating temperature is 196 °C. At the same time, a magnetic stirrer is used to form a shear flow field. Under this shear flow field, a continuous depolymerization reaction is carried out for 120 min. The obtained depolymerized solution is made up to 1000 mL with methanol, and the yield of the product BHET is analyzed by HPLC. All experiments are carried out under normal pressure.

[0057] The monomer yields of different catalysts for PET glycolysis are as Figure 5 shown. By comparison, it can be seen that the CaFeO 3 of the present invention has the best catalytic performance for PET glycolysis. Especially compared with the yield without adding a catalyst, the yield of the catalyst of the present invention is about 89% higher than that without a catalyst, while the commonly used homogeneous zinc acetate and sodium carbonate catalysts are only about 80% and 60%, respectively, and the effect of the commonly used ferrite catalyst is more than 70%, which is also lower than the effect of the catalyst prepared by the present invention. The reason for the analysis is that the surface morphology of the catalyst prepared by the present invention is a porous structure, which has a larger specific surface area to contact with the reactants. At the same time, the high valence state of iron ions will also form a higher Lewis acidity, increasing the binding force with the carbonyl oxygen, thereby greatly improving the yield of BHET.

[0058] Example 2

[0059] Test the optimal reaction conditions

[0060] Use the CaFeO 3 catalyst prepared in Example 1 to catalyze the glycolysis process of PET, and analyze the yield of the product BHET by HPLC. Screen out the optimal depolymerization conditions. The specific method is as follows:

[0061] 2.1 Reaction temperature. The temperature of the reaction system was controlled at 120 °C, 160 °C, and 196 °C respectively. The reaction time in the system was 180 min, the addition amount of EG was 15 g, the addition amount of catalyst was 0.025 g, and the PET particles were 2 g. The yield of BHET monomer was measured by HPLC. The results are shown in Figure 6 as shown in (a) of it. From this curve, it can be seen that the reaction temperature has a great influence on the glycolysis reaction process of PET. The higher the reaction temperature, the higher the yield of BHET monomer. Therefore, the highest yield of BHET is reached at 196 °C.

[0062] 2.2 Reaction time. According to the above method, the reaction time was controlled at 60 min, 150 min, 180 min, and 240 min respectively. The reaction temperature in the system was 196 °C, the addition amount of EG was 15 g, the addition amount of catalyst was 0.025 g, and the PET particles were 2 g. The yield of BHET monomer was measured by HPLC. The results are shown in Figure 6 as shown in (b) of it. From the analysis of this figure, it can be seen that the longer the reaction time, the higher the monomer yield. However, the time cannot be extended blindly. When the time is extended to a certain value, further extension of the time has little effect on the reaction. Therefore, the highest yield of BHET is reached at 180 min.

[0063] 2.3 Addition amount of EG. According to the above method, the mass ratio of the addition amount of EG was controlled at EG:PET = 5, 7.5, 10 respectively. The reaction temperature in the system was 196 °C, the reaction time was 180 min, the addition amount of catalyst was 0.025 g, and the PET particles were 2 g. The yield of BHET monomer was measured by HPLC. The results are shown in Figure 6 as shown in (c) of it. From the analysis of this figure, it can be seen that excessive EG promotes the glycolysis process of PET. Through the swelling effect, it promotes the entry of ethylene glycol molecules into the interior of PET particles, and its higher concentration shifts the equilibrium to the product monomer side. However, excessive ethylene glycol will reduce the yield of PET monomer. Therefore, the highest yield of BHET is reached when EG:PET is 7.5.

[0064] 2.4 Addition amount of catalyst. According to the above method, the mass ratio of the addition amount of catalyst was controlled at catalyst:PET = 0.005, 0.0125, 0.02 respectively. The reaction temperature in the system was 196 °C, the reaction time was 180 min, the addition amount of EG was 15 g, and the PET particles were 2 g. The yield of BHET monomer was measured by HPLC. The results are shown in Figure 6As shown in (d) of this figure, it can be analyzed from this figure that when the amount of the catalyst increases to 0.0125 g, the conversion rate of PET and the yield of BHET increase sharply. The significant increase in the conversion of PET and the yield of BHET is attributed to the more active sites provided by the catalyst, which can accelerate the glycolysis process. The further increase in the amount of the catalyst only causes a slight increase in the conversion rate of PET. Therefore, the optimal addition amount of the catalyst is 0.0125 when the catalyst:PET ratio is considered.

[0065] Example 3

[0066] Investigation on the stability of the catalyst

[0067] Add 2 g of PET particles and the catalyst into a glass device in a nitrogen atmosphere, and add CaFeO prepared by the present invention as the catalyst 3 with an amount of 0.025 g. Then add 15 g of ethylene glycol. The solution and solid particles are heated to 196 °C under normal pressure and in the presence of the composite metal catalyst, and at the same time, a magnetic stirrer is used to form a shear flow field. Under this shear flow field, a continuous depolymerization reaction is carried out. After the reaction is completed in 180 min, a magnet is used to recover the catalyst in the reaction solution, and then the catalyst is placed in an oven at 100 - 105 °C for drying for the next experiment. This recycling process is carried out three times, and the products and the catalyst are analyzed. The effect of the catalyst in the cyclic reaction is as Figure 8 shown. Among them, SEM is used to characterize the surface morphology of the catalyst before and after deactivation.

[0068] The deactivated catalyst is thermally regenerated. After the catalyst is dried, it is placed in a muffle furnace and pre-calcined at 340 - 350 °C for 0.5 h, and then calcined at 820 - 850 °C for 3 - 4 hours and taken out for a new cycle of the PET glycolysis process. The obtained results are as Figure 8 shown.

[0069] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made on the basis of the above description. It is impossible to list all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A system for PET glycolysis based on perovskite composite oxides, characterized in that: It includes a glycolysis device, a coarse filtration unit, a magnetic recovery unit, a thermal regeneration unit, a suction filtration unit, a rotary evaporation unit, and a cooling crystallization unit; The glycolysis device is filled with perovskite composite oxide and solvent, the outlet of the glycolysis device is connected to the inlet of the coarse filtration unit, the coarse filtration unit is provided with a solid outlet and a filtrate outlet, the filtrate outlet is connected to the inlet of the magnetic recovery unit, the catalyst outlet of the magnetic recovery unit is connected to the glycolysis device or the inlet of the thermal regeneration unit, the outlet of the thermal regeneration unit is connected to the glycolysis device, the oligomer and monomer outlets of the magnetic recovery unit are connected to the suction filtration unit, the filtrate outlet of the suction filtration unit is connected to the inlet of the rotary evaporation unit, and the outlet of the rotary evaporation unit is connected to the inlet of the cooling crystallization unit.

2. A method for glycolysis of PET based on perovskite composite oxides is carried out using the system for glycolysis of PET based on perovskite composite oxides according to claim 1, characterized in that: The specific process is as follows: the raw material PET particles are sent to a glycolysis device filled with perovskite composite oxide and a solvent, wherein the perovskite composite oxide is used as a catalyst to perform glycolysis on PET, an inert gas is introduced into the glycolysis device, and the corresponding reaction temperature, reaction time, amount of solvent added, and amount of catalyst are set for the glycolysis device to perform glycolysis on PET. After the reaction is completed, the reaction liquid is sent to a coarse filtration unit, and the solid after the coarse filtration is unreacted PET. The filtrate includes a catalyst and a mixture of oligomers and monomers; wherein the direction of the catalyst recovered by the magnetic recovery unit is determined according to the number of times the catalyst is recycled in the entire system. If it is judged to be inactivated, it is first passed into a thermal regeneration unit for regeneration and then circulated back to the glycolysis device. If it is judged not to be inactivated, it is directly passed into the glycolysis device; after the mixture of oligomers and monomers after the magnetic recovery unit passes through a suction filtration unit, the solid obtained is an oligomer, and the filtrate is evaporated by a rotary evaporation unit and then enters a cooling crystallization unit for cooling to obtain ethylene terephthalate BHET.

3. The method for PET glycolysis based on perovskite composite oxide according to claim 2, characterized in that: The perovskite composite oxide is prepared by a sol-gel method; the perovskite composite oxide CaFeO3 is in the form of particles with a particle size range of 40.08±10.81 μm.

4. The method for glycolysis of PET based on perovskite composite oxide according to claim 3, characterized in that: The preparation method of the perovskite composite oxide comprises the following steps: Fe(NO3)3·9H2O and Ca(NO3)2 are mixed with citric acid at a ratio of 1-1.2:1-1.2:1-1.2 by heating, and then put into an oven for drying, and then ground and calcined to obtain the perovskite composite oxide CaFeO3.

5. The method for PET glycolysis based on perovskite composite oxide according to claim 4, characterized in that: The heating and mixing temperature is 90-95°C; the heating and mixing time is 30-35 minutes, until the solution becomes a gel; the oven drying temperature is 105-110°C; the oven drying time is 35-36 hours; the calcination is divided into two stages, the calcination temperature of the first stage is 320-350°C; the calcination time is 0.4-0.5 hours; the calcination temperature of the second stage is 820-850°C; the calcination time is 1.5-2 hours.

6. The method for glycolysis of PET based on perovskite composite oxide according to claim 2, characterized in that: The solvent is ethylene glycol, diethylene glycol, propylene glycol and 1,4-butanediol.

7. The method for glycolysis of PET based on perovskite composite oxide according to claim 2, characterized in that: The temperature of the sugar depolymerization reaction in the glycolysis device is 120-196° C.; the time of the glycolysis device is 60-240 minutes.

8. The method for glycolysis of PET based on perovskite composite oxide according to claim 2, characterized in that: The ratio of the mass of the catalyst added to the glycolysis device to the mass of the PET contained in the dissolving solution is 0.005 to 0.

02.

9. The method for PET glycolysis based on perovskite composite oxide according to claim 2, characterized in that: In the glycolysis device, when ethylene glycol is used as the solvent, the mass ratio of ethylene glycol to PET is 5-10.

10. The method for PET glycolysis based on perovskite composite oxide according to claim 2, characterized in that: The glycolysis device is provided with a magnetic stirrer for forming a shear flow field under which a continuous depolymerization reaction is carried out to obtain a depolymerization product BHET; the glycolysis device is provided with a condensation reflux device for recovering ethylene glycol volatilized due to temperature increase.

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