Foamed zinc loaded ZIF-8 material and application thereof in PET degradation

Abstract

The invention discloses a preparation method of a foam Zn (at) ZIF-8 material and application of the foam Zn (at) ZIF-8 material in PET degradation, the Zn (at) ZIF-8 material is prepared and synthesized through a hydrothermal method, foam zinc serves as a substrate, and due to the fact that the foam zinc has the high-strength metal characteristic and a stable three-dimensional network structure, the foam zinc has the high-strength metal characteristic and the stable three-dimensional network structure; then ZIF-8 is introduced to fill gaps, so that the catalyst has ultrahigh porosity and a stable bimetal and multi-active-center-site mutual synergistic structure, the activity of a reactant ethylene glycol is improved, meanwhile, collection and distribution of the reactant and a product are accelerated, the catalytic efficiency is improved, and the product purity is improved; meanwhile, due to the fact that ultrahigh pores of the catalyst have very strong adsorption performance, the whiteness of the product BHET can be greatly improved; and the catalyst has excellent cyclic utilization performance, and keeps the original catalytic activity after being recycled for multiple times.

Description

Technical Field

[0001] The present invention belongs to the field of resource recycling, and particularly relates to a preparation method of a foam Zn@ZIF-8 material and its application in PET degradation. Background Art

[0002] At present, the recycling methods of waste polyethylene terephthalate (PET) mainly include physical methods and chemical methods. Physical recycling methods are mostly "downcycling", and the value of recycled PET is low, and generally can only be recycled one or two times. Chemical recycling methods degrade PET into monomers or oligomers, which can eliminate the raw material limitations of recycled PET, and the obtained products have high quality, wide uses, and there are no limitations on downcycling and the number of recycling times. At present, the main PET chemical recycling methods include: hydrolysis method, methanol alcoholysis method, ethylene glycol alcoholysis method and other chemical depolymerization methods.

[0003] The research on PET ethylene glycol alcoholysis catalysts at home and abroad mainly focuses on ionic liquids, metal acetate catalysts, and metal oxide catalysts. Compared with acetate and ionic liquid catalysts, metal oxide catalysts have high purity, low catalyst cost, and are easy to separate and recycle compared with new ionic liquid catalysts. Although MOF composite catalysts are widely used in various catalytic fields, the most critical problem at present is still the need to solve the PET catalytic efficiency problem (the problem of difficult coordination and distribution control of multiple active center sites during the conversion process) and the problem of catalyst pore carbon deposition.

[0004] At present, the vast majority of MOFs in the existing reports on MOFs are microporous MOFs (pore diameter < 2nm). Their inherent small pore diameter hinders the diffusion of macromolecules and limits their interaction with active sites within the MOF structure. In contrast, mesoporous MOFs have larger pore diameters (pore diameter is 2 - 50nm), and the performance of mesoporous MOFs is often better than that of microporous MOFs in practical applications. This is because mesoporous MOFs can provide pore channel structures with different shape sizes, which is conducive to mass transfer and transportation of substances. Although the specific surface area of mesoporous MOFs is smaller than that of microporous MOFs, the larger pore space and structural hierarchy are conducive to the mass transfer and penetration of larger molecules, as well as the functionalization of more complex functional groups. What strategy to adopt to expand the pore diameter of MOF materials to prepare new mesoporous MOFs has become a very challenging topic in the current MOF research field. For a long time, people have explored many new methods to synthesize mesoporous MOFs. These methods include ligand extension method, mixed ligand method, soft template method, and hard template method, etc.

[0005] The present invention synthesizes a composite catalyst Zn@ZIF-8 by loading ZIFs on a foam metal material using the hard template method. This not only introduces multiple metal active sites to greatly improve the catalytic activity of the catalyst, but also utilizes the large pores of the foam metal to alleviate the problem of easy carbon deposition on the catalyst. Moreover, the product has high purity and good whiteness, making it easier for industrial application. The ZIFs in the catalyst have a tetrahedral three-dimensional network structure, can be prepared using any metal as the metal source, the pore size of the obtained metal framework can be adjusted, and the coordination mode can also be adjusted. Most of the active sites are exposed, making the loading more convenient, and it is favored by researchers due to its good thermal stability, chemical stability, and adsorption performance. The large-pore foam metal and PU cotton, etc., all have an ultra-high porosity and a very small bulk density, and are often used as catalytic supports. Moreover, compared with other large-pore materials, the strength and stiffness of the foam metal have been greatly improved. Loading ZIF-8 on the foam metal support not only has the microporous characteristics of ZIF-8, but also exhibits mesoporous and macroporous structures. The developed hierarchical pore structure helps to accelerate the dispersion of reactants and products, improve the catalytic efficiency, and can alleviate the problem of carbon deposition in the catalyst pores due to its macroporous structure. Summary of the Invention

[0006] Aiming at the defects or deficiencies of the prior art, the present invention provides a preparation method of a foam Zn@ZIF-8 material and its application in PET degradation.

[0007] To achieve the above object, the present invention adopts the following technical solutions: The preparation of a foam Zn@ZIF-8 material includes the following steps: (1) Making small round pieces from the foam Zn using a hole puncher; (2) Loading the foam Zn into a beaker, ultrasonically oscillating it with deionized water and methanol for a certain period of time respectively and then drying it; (3) Mixing 2-methylimidazole, zinc acetate anhydrous, and methanol in a mass ratio of 13:6:316 for hydrothermal reaction to obtain a synthesis solution of ZIF-8, (4) Adding the pretreated foam Zn and the synthesis solution of ZIF-8 into a reaction kettle, standing and reacting at a certain temperature for a certain period of time, then separating the synthesized foam Zn@ZIF-8 from the reaction system using a metal filter screen, washing it with methanol, and drying it.

[0008] Further, in step (1), the specifications of the small round pieces of foam Zn are a diameter of 6 mm and a thickness of about 2 mm.

[0009] Further, in step (2), the ultrasonic oscillation time of the foam Zn in deionized water is 15 - 30 min, depending on the quantity of the foam Zn, and the ultrasonic oscillation time in methanol is 15 min.

[0010] Further, the drying temperature in step (2) is 50 °C and the time is 30 min.

[0011] Further, the synthesis solution of ZIF-8 in step (3) consists of 1.2 g of anhydrous zinc acetate, 2.6 g of 2-methylimidazole and 80 mL of methanol.

[0012] Further, the temperature of the hydrothermal reaction in step (3) is 70 °C and the time is 10 min.

[0013] Further, in step (4), the addition amount of foamed Zn in one reaction kettle is 0.77 - 0.79 g (10 pieces), and the addition amount of the ZIF-8 synthesis solution is 60 times the mass of foamed Zn.

[0014] Further, the temperature of the static heating reaction in step (4) is 150 °C and the time is 5 h.

[0015] Further, in step (4), it is washed 3 times with methanol.

[0016] Further, the drying temperature in step (4) is 150 °C and the time is 15 min.

[0017] The application of the foamed Zn@ZIF-8 material in PET degradation, the specific application method is using ethylene glycol as the solvent and the Zn@ZIF-8 as the catalyst to carry out alcoholysis on PET.

[0018] Furthermore, in the alcoholysis, the dosage of Zn@ZIF-8 is 2.8% - 8.4% of the mass of PET, and the dosage of ethylene glycol is 3 - 6 times the mass of PET; the temperature of the alcoholysis is 180 °C - 205 °C and the time is 10 min - 40 min.

[0019] The foamed Zn@ZIF-8 material provided by the present invention has an ultra-high porosity, high strength and three-dimensional spatial structure, can provide bimetallic sites to bond with oxygen atoms in the structure of polyethylene terephthalate (PET), and its electron-withdrawing effect is stronger, making the carbon atom in the carbonyl group more easily attacked by the oxygen atom in ethylene glycol to form a transition state, and then generating the product bis(2-hydroxyethyl) terephthalate (BHET), and can realize the permanent recycling of PET.

[0020] Compared with the prior art, the remarkable advantages of the present invention are as follows: 1. The foamed Zn@ZIF-8 catalyst is a multi-metal catalyst with high selectivity and high catalytic activity, making the PET catalytic depolymerization product BHET have good whiteness and high industrial feasibility. (The degradation temperature is below 200 °C, the degradation rate is over 95% within 40 min, and the monomer yield is over 75%).

[0021] 2. The catalyst has a stable structure with synergistic bimetallic and multi-active center sites, which can improve the activity of the reactant ethylene glycol while accelerating the dispersion and collection of the reactants and products, thus enhancing the catalytic efficiency.

[0022] 3. The bimetallic organic framework Zn@ZIFs catalyst not only maintains the activity of the solid catalyst but also endows the catalyst with a high-strength three-dimensional spatial structure, enabling the continuous production of the PET alcoholysis process and the rapid separation and recovery of products. Description of the Drawings

[0023] Figure 1 This is the appearance diagram of the foam Zn@ZIF-8 material of the present invention.

[0024] Figure 2 This is the SEM scanning electron micrograph of the foam Zn@ZIF-8 material of the present invention.

[0025] Figure 3 This is the XRD scan diagram of the foam Zn@ZIF-8 material of the present invention.

[0026] Figure 4 This is the infrared scan diagram of the foam Zn@ZIF-8 material of the present invention.

[0027] Figure 5 This is the appearance diagram of the BHET monomer obtained after the foam Zn@ZIF-8 material of the present invention is used for PET alcoholysis.

[0028] Figure 6 This is the infrared scan diagram of the BHET monomer obtained after the foam Zn@ZIF-8 material of the present invention is used for PET alcoholysis. Detailed Description of the Invention

[0029] The present invention is illustrated by the following examples, but the present invention is not limited to the following examples. Without departing from the scope of the overall purpose, various changes and implementations are included in the technical scope of the present invention.

[0030] A kind of foam Zn@ZIF-8, its preparation includes the following steps: (1) Use a punch to make the foam Zn into small round pieces with a diameter of 6 mm and a thickness of about 2 mm; (2) Put the foam Zn into a beaker, first ultrasonically oscillate in deionized water for 15 - 30 min according to the amount of the foam Zn, and then ultrasonically oscillate in methanol for 15 min, and then dry it in an oven at 50 °C; (3) Mix 2.6 g of 2-methylimidazole, 1.2 g of anhydrous zinc acetate, and 80 mL of methanol, and carry out a hydrothermal reaction at 70 °C for 10 min to obtain the synthesis solution of ZIF-8; (4) The pretreated foamed Zn and ZIF-8 synthesis solution were added to the reaction kettle at a mass ratio of 1:60. After standing and reacting at 150 °C for 5 h, the synthesized foamed Zn@ZIF-8 was separated from the reaction system using a metal filter screen, washed 3 times with methanol, and then dried in an oven at 150 °C for 15 min.

[0031] Example 1 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol, and 0.085 g of foamed Zn@ZIF-8 were successively added to a 100 mL three-necked flask equipped with a thermometer, a stirring rotor, and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 180 °C. After refluxing for 30 min, the unreacted PET raw materials were separated by hot filtration and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water, and drying, a white solid BHET was obtained. After calculation, the degradation rate of PET was 29.7%, and the yield of monomer BHET was 25.3%.

[0032] Example 2 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol, and 0.085 g of foamed Zn@ZIF-8 were successively added to a 100 mL three-necked flask equipped with a thermometer, a stirring rotor, and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 185 °C. After refluxing for 30 min, the unreacted PET raw materials were separated by hot filtration and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water, and drying, a white solid BHET was obtained. After calculation, the degradation rate of PET was 46.4%, and the yield of monomer BHET was 39.5%.

[0033] Example 3 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.085 g of foam Zn@ZIF-8 were successively added to a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 190 °C. After 30 min of condensation reflux reaction, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, a white solid BHET was obtained. After calculation, the degradation rate of PET was 64.8%, and the yield of monomer BHET was 52.6%.

[0034] Example 4 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.085 g of foam Zn@ZIF-8 were successively added to a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 195 °C. After 30 min of condensation reflux reaction, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, a white solid BHET was obtained. After calculation, the degradation rate of PET was 88.8%, and the yield of monomer BHET was 68.5%.

[0035] Example 5 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.085 g of foam Zn@ZIF-8 were successively added to a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 200 °C. After 30 min of condensation reflux reaction, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, a white solid BHET was obtained. After calculation, the degradation rate of PET was 98.6%, and the yield of monomer BHET was 78.2%.

[0036] Example 6 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.085 g of foam Zn@ZIF-8 were successively added into a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 205 °C. After refluxing for 30 min, the unreacted PET raw materials were separated by hot filtration and dried and weighed. Then a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, white solid BHET was obtained. After calculation, the degradation rate of PET was 99.6%, and the yield of monomer BHET was 76.7%.

[0037] Example 7 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.085 g of foam Zn@ZIF-8 were successively added into a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 200 °C. After refluxing for 10 min, the unreacted PET raw materials were separated by hot filtration and dried and weighed. Then a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, white solid BHET was obtained. After calculation, the degradation rate of PET was 70.5%, and the yield of monomer BHET was 51.3%.

[0038] Example 8 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.085 g of foam Zn@ZIF-8 were successively added into a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 200 °C. After refluxing for 20 min, the unreacted PET raw materials were separated by hot filtration and dried and weighed. Then a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were separated by filtration. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, white solid BHET was obtained. After calculation, the degradation rate of PET was 91.1%, and the yield of monomer BHET was 70.3%.

[0039] Example 9 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.085 g of foam Zn@ZIF-8 were successively added to a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 200 °C. After refluxing for 30 min, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, white solid BHET was obtained. After calculation, the degradation rate of PET was 98.9%, and the yield of monomer BHET was 78.6%.

[0040] Example 10 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.085 g of foam Zn@ZIF-8 were successively added to a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 205 °C. After refluxing for 40 min, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, white solid BHET was obtained. After calculation, the degradation rate of PET was 99.9%, and the yield of monomer BHET was 75.6%.

[0041] Example 11 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.072 g of unloaded foam Zn were successively added to a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 200 °C. After refluxing for 30 min, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, white solid BHET was obtained. After calculation, the degradation rate of PET was 86.3%, and the yield of monomer BHET was 56.7%.

[0042] Example 12 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.085 g of foamed Zn@ZIF-8 were successively added into a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 200 °C. After refluxing for 30 min, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then placed in a refrigerator for refrigeration, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, white solid BHET was obtained. After calculation, the degradation rate of PET was 98.7%, and the yield of monomer BHET was 77.0%.

[0043] Example 13 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.17 g of foamed Zn@ZIF-8 were successively added into a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 200 °C. After refluxing for 30 min, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then placed in a refrigerator for refrigeration, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, white solid BHET was obtained. After calculation, the degradation rate of PET was 99.9%, and the yield of monomer BHET was 79.4%.

[0044] Example 14 Using PET particles as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.252 g of foamed Zn@ZIF-8 were successively added into a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 200 °C. After refluxing for 30 min, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then placed in a refrigerator for refrigeration, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, white solid BHET was obtained. After calculation, the degradation rate of PET was 98.8%, and the yield of monomer BHET was 75.7%.

[0045] Example 15 Using PET pellets as raw materials, 3.0 g of PET, 9.0 g of ethylene glycol and 0.085 g of foamed Zn@ZIF-8 were successively added to a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 200 °C. After refluxing for 30 min, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, a white solid BHET was obtained. After calculation, the degradation rate of PET was 99.6%, and the yield of monomer BHET was 75.8%.

[0046] Example 16 Using PET pellets as raw materials, 3.0 g of PET, 12.0 g of ethylene glycol and 0.085 g of foamed Zn@ZIF-8 were successively added to a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 200 °C. After refluxing for 30 min, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, a white solid BHET was obtained. After calculation, the degradation rate of PET was 99.9%, and the yield of monomer BHET was 79.4%.

[0047] Example 17 Using PET pellets as raw materials, 3.0 g of PET, 15.0 g of ethylene glycol and 0.085 g of foamed Zn@ZIF-8 were successively added to a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 200 °C. After refluxing for 30 min, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then refrigerated in a refrigerator, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, a white solid BHET was obtained. After calculation, the degradation rate of PET was 99.9%, and the yield of monomer BHET was 73.1%.

[0048] Example 18 Using PET particles as raw materials, 3.0 g of PET, 18.0 g of ethylene glycol and 0.085 g of foam Zn@ZIF-8 were successively added to a 100 mL three-necked flask equipped with a thermometer, a stirring rotor and a spherical condenser. Then, the three-necked flask was placed in an electric heating mantle, and the reaction temperature was controlled at 200 °C. After 30 min of condensation reflux reaction, the unreacted PET raw materials were filtered off while it was hot and dried and weighed. Then, a certain amount of boiling water was added to the filtrate, and the flocculent oligomers were filtered off. The filtrate was rotary evaporated to 25 mL and then placed in a refrigerator for refrigeration, and white needle-like crystals precipitated. After filtration, separation, washing with water and drying, white solid BHET was obtained. After calculation, the degradation rate of PET was 99.9%, and the yield of monomer BHET was 51.7%.

[0049] The above are only the preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

[0050] Figure 1 It is the appearance diagram of foam Zn@ZIF-8, and the surface morphology of the prepared foam Zn@ZIF-8 can be seen.

[0051] Figure 2 It is the SEM diagram of foam Zn@ZIF-8. The structure of foam Zn@ZIF-8 is a polyhedral crystal form, indicating that ZIF-8 is successfully loaded on foam Zn.

[0052] Figure 3 It is the XRD diagram of foam Zn@ZIF-8 and standard ZIF-8. By comparison, it can be obtained that foam Zn@ZIF-8 has the standard peaks of ZIF-8, proving that ZIF-8 is successfully loaded on foam Zn.

[0053] Figure 4 It is the infrared spectrum diagram of foam Zn@ZIF-8. At 2952 cm -1 and 3290 cm -1 The two peaks at the positions correspond to the stretching vibration peaks of the aliphatic and aromatic C-H bonds of imidazole. The in-plane bending specific absorption peak of the imidazole ring appears at 952 cm -1 All of these are consistent with the specific absorption peaks of ZIF-8 reported in the literature.

[0054] Figure 5 It is the product obtained by degrading PET, and the obtained monomer BHET is white needle-like crystals.

[0055] Figure 6 It is the infrared spectrum diagram of monomer BHET. The characteristic peak of BHET is at 899 cm -1 It is the characteristic peak of the bending vibration of the C-H bond in the benzene ring structure. At 1128 cm -1is the absorption peak of the stretching vibration of the C-O bond in the ester group. 1408 cm -1 is the peak of the stretching vibration of the C=C bond within the benzene ring, 1722 cm -1 is the peak of the stretching vibration of the C=O bond in the ester group. The stretching vibration of the aliphatic alkyl group results in peaks at 2930 cm -1 and 2956 cm -1 . At the position of 3302 cm -1 , a relatively broad hydroxyl stretching vibration peak is observed, indicating that the BHET product may contain moisture.

Claims

1. A preparation method of a foam Zn@ZIF-8 material, characterized in that: It includes the following steps: (1) Making small round pieces from the foamed Zn with a hole punch; (2) Loading the foamed Zn into a beaker, ultrasonically oscillating it with deionized water and methanol respectively for a period of time and then drying; (3) Mixing 2-methylimidazole with anhydrous zinc acetate and methanol for a hydrothermal reaction to obtain the synthesis solution of ZIF-8; (4) Adding the pretreated foamed Zn and the synthesis solution of ZIF-8 into a reaction kettle, standing and reacting at a certain temperature for a certain time, then separating the synthesized foamed Zn@ZIF-8 from the reaction system with a metal filter screen, washing it with methanol and then drying.

2. The preparation method according to claim 1, characterized in that: The specifications of the small round pieces of foamed Zn obtained in step (1) are a diameter of 6 mm and a thickness of 2 mm.

3. The preparation method according to claim 1, characterized in that: In step (2), the ultrasonic oscillation time of the foamed Zn in deionized water is 15 - 30 min, depending on the amount of the foamed Zn, and the ultrasonic oscillation time in methanol is 15 min, and then it is dried in an oven at 50 °C.

4. The preparation method according to claim 1, characterized in that: In step (3), the synthesis solution of ZIF-8 consists of 1.2 g of anhydrous zinc acetate, 2.6 g of 2-methylimidazole and 80 mL of methanol; the temperature of the hydrothermal reaction is 70 °C and the time is 10 min.

5. The preparation method according to claim 1, characterized in that: In step (4), the addition amount of the foamed Zn is 0.77 - 0.79 g, and the addition amount of the ZIF-8 synthesis solution is 60 times the mass of the foamed Zn; the temperature of the reaction kettle is 150 °C and the time is 5 h.

6. Use of the foam Zn@ZIF-8 material obtained by the preparation method according to any one of claims 1-5 in PET degradation, characterized in that: Its application method is specifically using ethylene glycol as the solvent and the foamed Zn@ZIF-8 as the catalyst to carry out alcoholysis on PET.

7. The application according to claim 6, characterized in that: The dosage of Zn@ZIF-8 is 2.8% - 8.4% of the mass of PET, and the dosage of ethylene glycol is 3 - 6 times the mass of PET; the temperature of the alcoholysis is 180 °C - 205 °C and the time is 10 min - 40 min.

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