Tannic acid modified zeolite imidazate framework material catalyst as well as preparation method, use method and application thereof

Abstract

The invention discloses a tannic acid modified zeolite imidazate framework material catalyst as well as a preparation method, a use method and application thereof, and belongs to the technical field of functional catalytic materials. The invention provides a tannic acid modified zeolite imidazate framework material catalyst. The tannic acid modified zeolite imidazate framework material catalyst comprises tannic acid molecules and a zeolite imidazate framework material, phenolic hydroxyl groups in the tannic acid molecules and metal ions in the zeolite imidazate framework material form coordination connection. The invention further provides application of the tannic acid modified zeolite imidazate framework material catalyst as a PET glycolysis catalyst to improvement of PET depolymerization efficiency. The catalyst disclosed by the invention integrates the advantages of a hierarchical pore structure and surface functionalization characteristics, shows excellent product selectivity while keeping high catalytic activity, and provides an innovative solution for efficient ethylene glycol alcoholysis of PET (Polyethylene Terephthalate).

Description

Technical Field

[0001] This invention belongs to the field of functional catalytic materials technology, specifically relating to the preparation of a tannic acid-modified zeolite imidazole ester framework catalyst for PET glycolysis, and its application in chemical processes. Background Technology

[0002] Polyethylene terephthalate (PET), as an important general-purpose plastic, is widely used in packaging, fibers, and textiles. However, its massive consumption has led to serious problems of white pollution and resource waste. In PET chemical recycling processes, glycolysis technology is considered one of the most promising pathways to achieving a circular economy for plastics due to its ability to efficiently convert waste PET into the high-value monomer diethyl terephthalate (BHET). However, this process still faces technical bottlenecks such as low reaction efficiency, demanding conditions, high cost of precious metal catalysts, and poor product selectivity. Therefore, developing novel catalyst systems that combine high activity, excellent selectivity, and good economic efficiency is of great significance for achieving efficient resource recycling of PET.

[0003] Currently, research on PET glycolysis catalysts mainly focuses on homogeneous systems (such as zinc acetate and titanium sulfate). These catalysts selectively activate carbonyl oxygen atoms in the PET molecular chain through metal ions. Although they exhibit catalytic activity in the reaction, they suffer from fundamental drawbacks such as difficulty in separation from the reaction system, product contamination, and inability to be reused. To overcome these technical challenges, the research and development of heterogeneous catalytic systems has become crucial.

[0004] Zeolitic imidazolate frameworks (ZIFs), especially ZIF-8, have attracted much attention due to their high specific surface area, tunable pore structure, and abundant active sites. However, ZIF-8 still has certain limitations in practical catalytic applications. For example, Chinese invention patent application CN117126050A discloses the application of Fe3O4@ZIF-8 magnetic core-shell particles in PET degradation. Although this method can effectively improve the whiteness of the product and has excellent recycling performance, it still suffers from problems such as long preparation time (reaction at 200℃ for 8 hours in a reactor) and low PET degradation rate. Chinese invention patent application CN120346840A discloses a zinc foam-supported ZIF-8 material and its application in PET degradation. This catalyst can effectively solve the problem of easy carbon deposition in the catalyst and has high product purity, but this method has drawbacks such as complex preparation process (requiring pretreatment of zinc foam) and low BHET monomer yield (<80%).

[0005] These reports indicate that the intrinsic specific surface area of ​​ZIF-8 has not been fully utilized in actual reactions, and its catalytic performance still has room for improvement. In existing technologies, due to the lack of effective means to control the degree of tannic acid etching, the prepared materials generally suffer from problems such as structural disorder and uneven distribution of active sites. Summary of the Invention

[0006] To address the shortcomings of existing technologies and to solve problems such as poor accessibility of catalyst active sites, low mass transfer efficiency, low recovery rate, and insufficient catalytic performance in current PET recycling processes, this invention aims to design and provide a tannic acid-modified zeolite imidazole ester (ZIF) framework catalyst and its application in the ethylene glycol alcoholysis reaction of PET. This catalyst combines the advantages of a hierarchical porous structure and surface functionalization characteristics, exhibiting excellent product selectivity while maintaining high catalytic activity, thus providing an innovative solution for the efficient ethylene glycol alcoholysis of PET.

[0007] The catalyst of this invention possesses both synergistic catalytic active sites and a hierarchical pore confinement structure. Through the synergistic catalytic effect of abundant phenolic hydroxyl groups on its surface and the ZIF framework, the catalyst significantly enhances its activation ability for carbonyl groups in the PET molecular chain; it lowers the reaction energy barrier by enhancing substrate C=O bond polarization; and it achieves efficient mass transfer through its pore structure, while the confinement effect enables rapid desorption. Ultimately, this results in a simultaneous and significant improvement in catalytic activity and product selectivity during the PET glycolysis reaction. This invention provides a novel catalytic material and feasible technical solution for the efficient chemical recovery of PET, possessing high activity, excellent stability, and good economic benefits.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] On the one hand, the present invention provides a tannic acid-modified zeolite imidazole ester framework catalyst, comprising tannic acid molecules and zeolite imidazole ester framework material;

[0010] The metal ion in the zeolite imidazole ester framework material is zinc metal ion;

[0011] The phenolic hydroxyl groups in the tannic acid molecule coordinate with the zinc metal ions in the zeolite imidazole ester framework material.

[0012] The catalyst is a tannic acid-modified zeolite imidazole ester framework material, wherein the zeolite imidazole ester framework material is ZIF-8.

[0013] The zinc ions in ZIF-8 possess moderate Lewis acidity, which effectively polarizes the PET carbonyl group while preventing side reactions. Furthermore, the strength of its Zn-N bonds and its tetrahedral geometry allow it to maintain structural integrity under catalytic conditions. Other metal ions cannot simultaneously meet these conditions, thus failing to achieve the goals of this invention.

[0014] Secondly, the present invention provides a method for preparing a tannic acid-modified zeolite imidazole ester framework catalyst, comprising the following steps:

[0015] The zeolite imidazole ester framework material was dissolved in water to obtain the first solution;

[0016] Dissolve tannic acid in water to obtain a second solution;

[0017] The second solution was slowly added dropwise to the first solution, and the mixture was ultrasonically treated at room temperature. The precipitate was collected by centrifugation, washed, and dried to obtain a tannic acid-modified zeolite imidazole ester framework catalyst.

[0018] The preparation method is characterized in that the mass ratio of the zeolite imidazole ester skeleton material to tannic acid is 1~3:1;

[0019] The ultrasonic treatment time is 20-40 minutes.

[0020] In the preparation method described above, the concentration of the first solution is 8~12 mg / mL;

[0021] The concentration of the second solution is 3~6 mg / mL.

[0022] The preparation method described above, when the zeolite imidazole ester skeleton material is ZIF-8, the specific preparation method of ZIF-8 is as follows:

[0023] Dissolve zinc acetate dihydrate in water to obtain solution A;

[0024] Dissolve 2-methylimidazole in water to obtain solution B;

[0025] Solution A and solution B were rapidly mixed, stirred at room temperature, centrifuged, the precipitate was collected, washed, and dried to obtain ZIF-8;

[0026] The molar ratio of zinc acetate dihydrate to 2-methylimidazole is 1:4~8.

[0027] Thirdly, the present invention provides the application of the tannic acid-modified zeolite imidazole ester framework material catalyst as a PET glycolysis catalyst.

[0028] Fourthly, the present invention provides a method for depolymerizing PET, comprising the following steps:

[0029] PET was placed in a reaction vessel containing ethylene glycol and the tannic acid-modified zeolite imidazole ester framework material catalyst as described in claim 1, and an alcoholysis reaction was carried out to obtain an alcoholysis liquid.

[0030] Cold water was added to the alcoholysis solution to form a mixture. The mixture was then heated in an oil bath and kept warm until completely dissolved. After cooling, the mixture was filtered, the filtrate was collected, and the crystals were refrigerated and filtered again to obtain the crude product BHET.

[0031] The method for depolymerizing PET, wherein the mass ratio of PET to ethylene glycol is 1:4~6;

[0032] The mass ratio of PET to tannic acid-modified zeolite imidazole ester framework catalyst is 1:0.05~0.2.

[0033] The depolymerization method for PET, wherein the alcoholysis reaction conditions are: reaction temperature 190~205℃, reaction time 110~130 min;

[0034] The conditions for the cold crystallization are: temperature 3~6℃, time 12~24h.

[0035] Preferably, 100 mL of cold water is added to the alcoholysis solution.

[0036] Preferably, the alcoholysis solution with added cold water is heated to 100°C.

[0037] Preferably, the alcoholysis solution with added cold water is heated for 60 minutes.

[0038] The tannic acid-modified ZIF catalyst provided by this invention possesses abundant surface phenolic hydroxyl functional groups and a tunable pore structure, providing a large number of highly active sites for the PET alcoholysis reaction. These active sites can strongly coordinate with reactant molecules, effectively stabilizing the reaction transition state, significantly reducing the activation energy of the alcoholysis reaction, and thus greatly improving the reaction efficiency. The hierarchical porous and hollow structure constructed through a controllable etching strategy significantly improves the reaction mass transfer performance and greatly enhances the accessibility of active sites. The catalyst's unique hierarchical pore system not only facilitates the rapid adsorption and diffusion of reactants but also enriches reactant molecules through spatial confinement effects, increasing local concentration and effective collision frequency, thereby synergistically enhancing catalytic activity and selectivity for the target product BHET.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. In the tannic acid-modified ZIF catalyst of the present invention, the metal nodes and the phenolic hydroxyl functional groups provided by tannic acid produce a synergistic catalytic effect, which can directionally coordinate the carbonyl oxygen atoms in the PET molecular chain, significantly enhance the C=O bond polarization, and greatly reduce the energy barrier of alcoholysis reaction. Its catalytic activity is significantly better than that of unmodified ZIF material.

[0041] 2. The tannic acid-modified ZIF catalyst of this invention is constructed with a controllable etching strategy, which has the characteristics of multi-level channels and hollow structure, greatly improving the mass transfer efficiency between reactants and products, significantly improving the availability of active sites, enabling a highly active and selective PET degradation process, and providing more sufficient contact and reaction pathways for PET macromolecules.

[0042] 3. The tannic acid-modified ZIF catalyst of this invention has a pore confinement effect, which allows the target product BHET to diffuse smoothly away from the active site after its formation, thus avoiding side reactions at the active site.

[0043] 4. The tannic acid-modified ZIF catalyst of this invention has a milder acidity. This mild acidic environment can effectively catalyze transesterification reactions, but is insufficient to catalyze side reactions such as dehydration or self-polymerization of ethylene glycol, thereby improving the selectivity and yield of the target product BHET.

[0044] 5. The present invention uses a water-solvent method to synthesize ZIF-8. The ZIF-8 synthesized by this method contains some defect sites that are passivated in situ by water molecules or hydroxyl groups, thereby significantly enhancing the material's resistance to hydrolysis and structural integrity in a high-temperature alcohol-water environment.

[0045] 6. The method of this invention first synthesizes ZIF-8 nanoparticles using a room temperature and pressure method, then combines them with a tannic acid solution under stirring at a certain temperature. Utilizing the coordination interaction between the phenolic hydroxyl groups in the tannic acid molecules and the zinc ions in the ZIF-8 framework, a TA@ZIF-8 composite catalyst was successfully prepared. This method is simple, has mild reaction conditions, is low in cost, and is environmentally friendly. The resulting composite material was applied to the glycolysis reaction of PET, and the results showed that the TA@ZIF-8 composite catalyst exhibited excellent catalytic activity and could effectively promote the depolymerization of PET macromolecules. This invention provides a novel catalytic material with practical application prospects for the efficient chemical recycling of PET. Attached Figure Description

[0046] Figure 1 This is a flowchart of the synthesis process of the catalyst of the present invention.

[0047] Figure 2 This is a TEM image of the TA@ZIF-8-2 (30 min) catalyst of the present invention.

[0048] Figure 3 The infrared spectrum of the TA@ZIF-8-2 (30 min) catalyst of this invention.

[0049] Figure 4 This is the BET plot of the TA@ZIF-8-2 (30 min) catalyst of the present invention. Detailed Implementation

[0050] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this application is not limited to these embodiments.

[0051] Example 1: Preparation of the tannic acid-modified zeolite imidazole ester framework catalyst of the present invention

[0052] (1) Preparation of ZIF-8:

[0053] 1.1 g of zinc acetate dihydrate was uniformly dispersed in 50 mL of deionized water to obtain solution A1;

[0054] Dissolve 3.3 g of 2-methylimidazole in 50 mL of deionized water to obtain solution B1; at this time, the molar ratio of zinc acetate dihydrate to 2-methylimidazole is 1:8.

[0055] Solution A1 was quickly poured into solution B1 and stirred at room temperature for 24 h. The solution was then centrifuged for 10 min, the precipitate was collected, washed three times with deionized water, and dried under vacuum at 60 °C for 12 h to obtain ZIF-8.

[0056] (2) Preparation of catalyst TA@ZIF-8-2 (30 min):

[0057] The synthesis process flow diagram of the catalyst of this invention is as follows: Figure 1 As shown.

[0058] 300 mg ZIF-8 was uniformly dispersed in 30 mL of deionized water to obtain solution A2;

[0059] Dissolve 150 mg of tannic acid (TA) in 30 mL of deionized water to obtain solution B2; at this time, the mass ratio of ZIF-8 to TA is 2:1.

[0060] Solution B2 was slowly added dropwise to solution A2 at a rate of 2 mL / min, and the mixture was sonicated at room temperature for 30 min. The precipitate obtained by centrifugation for 10 min was then washed three times with deionized water and dried under vacuum at 60℃ for 12 h to obtain the catalyst: TA@ZIF-8-2 (30 min). TEM, IR, and BET images of the TA@ZIF-8-2 (30 min) catalyst are shown below. Figure 2 , 3 As shown in Figure 4. TEM: A uniform and complete ZIF-8@TA core-shell structure was successfully constructed; IR: At 1072 cm⁻¹. −1 The strong absorption peak at is related to the stretching vibration of the CO bond in the phenolic hydroxyl group of tannic acid, indicating that tannic acid was successfully introduced; BET: a broad peak appears in the 2-10 nm range. TA etching causes the micropores to be destroyed and reorganized into mesopores, indicating that a micropore-mesopore hierarchical structure was successfully constructed.

[0061] Example 2:

[0062] The difference from Example 1 is that only the sonication time at room temperature was changed to 20 min. Catalyst TA@ZIF-8-2 was prepared (20 min).

[0063] Example 3:

[0064] The difference from Example 1 is that only the sonication time at room temperature was changed to 40 min. Catalyst TA@ZIF-8-2 was prepared (40 min).

[0065] Example 4:

[0066] The difference from Example 1 is that only the mass of ZIF-8 added was changed to 150 mg, at which point the mass ratio of ZIF-8 to TA was 1:1. Catalyst TA@ZIF-8-1 was prepared (30 min).

[0067] Example 5:

[0068] The difference from Example 1 is that only the mass of ZIF-8 added was changed to 450 mg, at which point the mass ratio of ZIF-8 to TA was 3:1. TA@ZIF-8-3 was prepared (30 min).

[0069] Example 6:

[0070] The tannic acid-modified zeolite imidazole ester framework catalyst was prepared using the same method as in Example 1. The only changes were: (1) the molar ratio of zinc acetate dihydrate to 2-methylimidazole was 1:4; (2) the concentration of ZIF-8 in solution A2 was 8 mg / mL; and (3) the concentration of tannic acid in solution B2 was 3 mg / mL.

[0071] Example 7:

[0072] The tannic acid-modified zeolite imidazole ester framework catalyst was prepared using the same method as in Example 1. The only changes were: (1) the molar ratio of zinc acetate dihydrate to 2-methylimidazole was 1:9; (2) the concentration of ZIF-8 in solution A2 was 12 mg / mL; and (3) the concentration of tannic acid in solution B2 was 6 mg / mL.

[0073] Comparative Example 1:

[0074] 1.1 g of zinc acetate dihydrate was uniformly dispersed in 50 mL of deionized water to obtain solution A;

[0075] Dissolve 3.3 g of 2-methylimidazole in 50 mL of deionized water to obtain solution B;

[0076] Solution A was quickly poured into solution B and stirred at room temperature for 24 h. The solution was then centrifuged for 10 min, the precipitate was collected, washed three times with deionized water, and dried under vacuum at 60 °C for 12 h to obtain the ZIF-8 catalyst.

[0077] Comparative Example 2:

[0078] In this comparative example, tannic acid (TA) was used as a catalyst.

[0079] Comparative Example 3:

[0080] The catalyst was prepared using the same method as in Example 1, except that the raw material ZIF-8 was replaced with ZIF-67.

[0081] Comparative Example 4:

[0082] The catalyst was prepared using the same method as in Example 1, except that the sonication time at room temperature was changed to 10 min.

[0083] Comparative Example 5:

[0084] The catalyst was prepared using the same method as in Example 1, except that the sonication time at room temperature was changed to 50 min.

[0085] Comparative Example 6:

[0086] The catalyst was prepared using the same method as in Example 1, except that the mass of ZIF-8 added was changed to 600 mg, at which point the mass ratio of ZIF-8 to TA was 4:1.

[0087] Comparative Example 7:

[0088] The catalyst was prepared using the same method as in Example 1, except that the mass of ZIF-8 added was changed to 75 mg, at which point the mass ratio of ZIF-8 to TA was 0.5:1.

[0089] Example 8: Application of the tannic acid-modified zeolite imidazole ester framework catalyst of the present invention

[0090] 1. Using the catalysts obtained in Examples 1-7 and Comparative Examples 1-3 respectively, the ethylene glycol alcoholysis of PET was carried out by the following method to finally obtain the crude product diethyl terephthalate (BHET).

[0091] The specific method is as follows:

[0092] 5 g of PET was added to a reaction vessel containing 25 g of ethylene glycol and 0.05 g of catalyst, and the alcoholysis reaction was carried out at 200 °C for 120 minutes under normal pressure. After the reaction, the resulting alcoholysis solution was clear and transparent, with no obvious impurities. Then, 100 mL of cold water was added to the alcoholysis solution, and a large amount of white flocculent precipitate immediately formed. The mixture was heated to 100 °C in an oil bath and held at that temperature for 60 minutes to completely dissolve the precipitate. After the solution cooled to 60 °C, it was hot-filtered, and the filtrate was collected. The filtrate was placed in a refrigerator at 5 °C for crystallization for 24 hours to obtain a solid-liquid mixture containing BHET crystals. Finally, the mixture was filtered at room temperature, and the resulting solid was the crude product, diethyl terephthalate.

[0093] Example 9:

[0094] The same method as in Example 8 was used to depolymerize PET using the catalyst of Example 1, except that the amount of catalyst TA@ZIF-8-2 (30 min) added in Example 1 was 0.035 g.

[0095] Example 10:

[0096] The same method as in Example 8 was used to depolymerize PET using the catalyst of Example 1, except that the amount of catalyst TA@ZIF-8-2 (30 min) added in Example 1 was 0.075 g.

[0097] The specific surface area of ​​the catalysts prepared in Examples 1-7 and Comparative Examples 1-3, as well as the effect of each catalyst on the PET ethylene glycol alcoholysis, PET conversion rate, and BHET yield were experimentally tested. The test methods and results are as follows:

[0098] 1. Testing method:

[0099] (1) PET conversion rate:

[0100] After the ethylene glycol alcoholysis reaction of PET is completed, the unreacted PET is separated by filtration and dried to constant weight at 60°C. The formula for calculating the PET conversion rate (1) is shown below:

[0101] ; Formula (1)

[0102] In the formula, W0 represents the initial mass of PET, and W1 represents the mass of unreacted PET.

[0103] (2) BHET yield:

[0104] Cold water was added to the alcoholysis solution, and the mixture was heated until the solution was completely dissolved. After cooling, the water-insoluble byproducts were separated by filtration. The resulting filtrate was stored in a refrigerator overnight. The white crystalline sample obtained after filtration was the main product, which was dried to a fixed weight. The yield of BHET can be calculated using Formula 2:

[0105] ; Formula (2)

[0106] In the formula, W BHET W0 and W0 represent the weight of the main product and the initial weight of the PET, respectively. MW BHET and MW PET These are the molecular weights of BHET (254 g / mol) and PET repeating units (192 g / mol), respectively.

[0107] 2. Test Results:

[0108] The effect data of the catalysts prepared in Examples 1-7 and Comparative Examples 1-3 on PET depolymerization are shown in Table 1 below:

[0109] Table 1. PET depolymerization effect corresponding to catalysts in Examples 1-7 and Comparative Examples 1-3

[0110] As can be seen from the data in Table 1:

[0111] The TA-modified ZIF-8 prepared in Examples 1-7 successfully constructed a hollow hierarchical porous structure while maintaining a high specific surface area. At the same time, TA was successfully anchored on the surface, providing a large number of phenolic hydroxyl groups, which played a synergistic catalytic role in the depolymerization of PET, resulting in a high BHET yield.

[0112] The TA-modified ZIF-8 prepared in Comparative Example 4, due to its shorter TA etching time, could not form a complete hierarchical hollow structure, resulting in a limited number of surface active sites and a lower BHET yield compared to Examples 1-5. The TA-modified ZIF-8 prepared in Comparative Example 5, due to its longer TA etching time, experienced a thinner shell and reduced strength in the hollow structure; excessive etching also reduced the total specific surface area, further lowering the BHET yield compared to Examples 1-5.

[0113] The TA-modified ZIF-8 prepared in Comparative Example 6, due to its low TA content, failed to form a rich hollow hierarchical porous structure, resulting in insufficient active sites, weak synergistic catalytic effect, and insignificant improvement in mass transfer, leading to a low BHET yield. The TA-modified ZIF-8 prepared in Comparative Example 7, due to its high TA content and excessive etching, caused the ZIF framework to collapse or its structure to be destroyed, resulting in a decrease in specific surface area and pore volume, poorer accessibility to active sites, and a reduced BHET yield.

[0114] Although the catalyst addition amounts in Examples 9 and 10 were not optimal, they still demonstrated good results. Catalyst content below this range may not provide adequate catalysis, resulting in low BHET yields; conversely, catalyst content exceeding this range may promote side reactions, and excessive catalyst particles may increase the viscosity of the system and cause particle agglomeration, leading to low BHET yields.

[0115] In Comparative Example 1, the catalyst used was ZIF-8, which has a single catalytic active site, resulting in a lower BHET yield compared to the corresponding Example 1. In Comparative Example 2, when the TA catalyst was used to assist in the ethylene glycol alcoholysis of PET, significant PET residue remained in the resulting alcoholysis solution after the reaction. The unreacted PET was separated by filtration and dried to constant weight at 60°C, yielding approximately 2.93 g of unreacted PET. The remaining alcoholysis solution underwent recrystallization. In Comparative Example 2, the catalyst used was tannic acid. Tannic acid is rich in phenolic hydroxyl groups and has a certain degree of weak acidity, but its acidity is too weak and it lacks effective active sites, thus failing to effectively depolymerize PET. In Comparative Example 3, the Co in ZIF-67... 2+ Compared to Zn 2+ It possesses excessively strong Lewis acidity, which, while activating the carbonyl group of ester bonds, easily triggers side reactions such as excessive oxidation of ethylene glycol, reducing monomer selectivity. Furthermore, its low specific surface area, limited number of active sites, and low mass transfer efficiency result in catalytic performance inferior to ZIF-8.

Claims

1. A tannic acid-modified zeolite imidazole ester framework catalyst, characterized in that, It contains tannic acid molecules and zeolite imidazole ester framework materials; The metal ion in the zeolite imidazole ester framework material is zinc metal ion; The phenolic hydroxyl groups in the tannic acid molecule coordinate with the zinc metal ions in the zeolite imidazole ester framework material.

2. The tannic acid-modified zeolite imidazole ester framework catalyst as described in claim 1, characterized in that, The zeolite imidazole ester skeleton material is ZIF-8.

3. The preparation method of the tannic acid-modified zeolite imidazole ester framework catalyst as described in claim 1, characterized in that, Includes the following steps: The zeolite imidazole ester framework material was dissolved in water to obtain the first solution; Dissolve tannic acid in water to obtain a second solution; The second solution was slowly added dropwise to the first solution, and the mixture was ultrasonically treated at room temperature. The precipitate was collected by centrifugation, washed, and dried to obtain a tannic acid-modified zeolite imidazole ester framework catalyst.

4. The preparation method according to claim 3, characterized in that, The mass ratio of the zeolite imidazole ester skeleton material to tannic acid is 1~3:1; The ultrasonic treatment time is 20-40 minutes.

5. The preparation method according to claim 3, characterized in that, The concentration of the first solution is 8~12 mg / mL; The concentration of the second solution is 3~6 mg / mL.

6. The preparation method according to claim 3, characterized in that, When the zeolite imidazole ester skeleton material is ZIF-8, the specific preparation method of ZIF-8 is as follows: Dissolve zinc acetate dihydrate in water to obtain solution A; Dissolve 2-methylimidazole in water to obtain solution B; Solution A and solution B were rapidly mixed, stirred at room temperature, centrifuged, the precipitate was collected, washed, and dried to obtain ZIF-8; The molar ratio of zinc acetate dihydrate to 2-methylimidazole is 1:4~9.

7. The application of the tannic acid-modified zeolite imidazole ester framework catalyst as described in claim 1 as a PET depolymerization catalyst.

8. A method for depolymerizing PET, characterized in that, Includes the following steps: PET was placed in a reaction vessel containing ethylene glycol and the tannic acid-modified zeolite imidazole ester framework material catalyst as described in claim 1, and an alcoholysis reaction was carried out to obtain an alcoholysis liquid. Cold water was added to the alcoholysis solution to form a mixture. The mixture was then heated in an oil bath and kept warm until completely dissolved. After cooling, the mixture was filtered, the filtrate was collected, and the crystals were refrigerated and filtered again to obtain the crude product BHET.

9. A method for depolymerizing PET as described in claim 8, characterized in that, The mass ratio of PET to ethylene glycol is 1:4~6; The mass ratio of PET to tannic acid-modified zeolite imidazole ester framework catalyst is 1:0.007~0.

2.

10. A method for depolymerizing PET as described in claim 8, characterized in that, The conditions for the alcoholysis reaction are: reaction temperature 190~205℃, reaction time 110~130 min; The conditions for the cold crystallization are: temperature 3~6℃, time 12~24h.

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