MOF (Metal Organic Framework)-based magnetic supported catalyst as well as preparation and use methods thereof

Abstract

The invention discloses an MOF-based magnetic supported catalyst as well as a preparation method and application thereof, and belongs to the technical field of supported catalysts as well as preparation and application thereof. The preparation method comprises the following steps: S1, carrying out dispersion treatment on Fe3O4 nanoparticles and nitrate of transition metal in water to obtain a treatment solution A; s2, dissolving an organic ligand in water to obtain a treatment solution B; s3, dropwise adding the treating fluid B into the treating fluid A, and performing dispersion treatment to obtain treating fluid C; and S4, carrying out centrifugal treatment on the treatment liquid C, and washing and drying a precipitate obtained by the centrifugal treatment to obtain the MOF-based magnetic supported catalyst. The catalyst has relatively ideal PET conversion rate, BHET yield and catalyst recovery rate.

Description

Technical Field

[0001] The invention belongs to the technical field of supported catalysts and their preparation and application, and particularly relates to a MOF-based magnetic supported catalyst with short preparation cycle, good catalytic performance and high recovery rate. Background Art

[0002] While glycolysis technology can depolymerize polymer chains in current PET chemical recycling processes, key technical bottlenecks remain, including insufficient reaction efficiency, demanding process conditions, high costs for precious metal catalysts, and suboptimal product selectivity. Addressing these challenges, developing novel catalyst systems with high catalytic activity, excellent selectivity, and favorable economics is crucial for establishing a sustainable plastics recycling economy.

[0003] In the research and practice of waste PET degradation, a variety of catalysts have been proven to effectively promote PET depolymerization reactions.

[0004] For example, the Chinese invention patent CN117696101A discloses a method for preparing a loaded mesoporous molecular sieve catalyst and its application in degrading PET plastics. Although this method achieves high-value conversion of PET plastics under mild conditions and effectively improves the BHET yield, it still has defects such as the inability to separate and recover the catalyst and the long preparation process.

[0005] For example, Chinese invention patent CN116237052A discloses a method for preparing a hollow nano-aggregate microsphere catalyst and its application in polyester degradation. This catalyst can effectively lower the decomposition temperature and increase the target monomer yield, but it has problems such as a complex preparation process (requiring spray drying) and a long catalyst recovery time (3 minutes).

[0006] Metal-organic framework (MOF) materials, due to their excellent physicochemical properties, including high surface area, tunable pore structure, and abundant active sites, have broad application prospects in catalysis, gas adsorption, separation and purification, and chemical sensing. Currently, the development of efficient MOF-based catalysts and the highly selective depolymerization of PET by optimizing active sites has become an important research direction in the field of plastics recycling.

[0007] For example, Chinese invention patent CN118684870A discloses a method for the synthesis and application of a bimetallic organic framework catalyst. Using a bimetallic MOF as a catalyst (at a dosage of 0.5% of the molar amount of terephthalic acid), this method enables a closed cycle of polyester polymerization, depolymerization, and recycling. However, this method suffers from the low purity of the hydrogenation depolymerization product. Improving this purity requires increasing the catalyst content to 5% of the molar amount of terephthalic acid, significantly increasing process costs. Summary of the Invention

[0008] To address the above technical issues, this application further improves MOF-based supported catalysts and their preparation methods, in order to solve the above technical problems. One of the objectives of the present invention is to provide a method for preparing a MOF-based magnetic supported catalyst, a second objective is to provide a corresponding catalyst, and a third objective is to provide a method for using the catalyst.

[0009] The specific technical solution is described below:

[0010] A method for preparing a MOF-based magnetic supported catalyst comprises the following steps:

[0011] S1: Dispersing Fe3O4 nanoparticles and transition metal nitrates in water to obtain treatment solution A;

[0012] S2: dissolving the organic ligand in water to obtain treatment solution B;

[0013] S3: adding the treatment liquid B dropwise into the treatment liquid A and performing a dispersion treatment to obtain the treatment liquid C;

[0014] S4: centrifuging the treatment liquid C, washing and drying the precipitate obtained by the centrifugal treatment, and obtaining a MOF-based magnetic supported catalyst.

[0015] In some embodiments, in step S1, the transition metal nitrate is selected from one of zinc nitrate dihydrate, copper nitrate hexahydrate, and cobalt nitrate hexahydrate.

[0016] In a preferred embodiment, the molar ratio of the transition metal nitrate to the metal in the Fe3O4 nanoparticles is (2-4):1.

[0017] In a preferred embodiment, in step S2, the organic ligand is 2-methylimidazole.

[0018] In a preferred embodiment, the present invention is characterized in that the molar ratio of 2-methylimidazole to the transition metal nitrate is (3-5):1.

[0019] In a preferred embodiment, the molar ratio of the transition metal nitrate to the metal in the Fe3O4 nanoparticles is 3:1, and the molar ratio of 2-methylimidazole to the transition metal nitrate is 4:1.

[0020] A MOF-based magnetic supported catalyst is prepared by the preparation method described in any of the above technical solutions.

[0021] In a further embodiment, the supported catalyst is used for the depolymerization of PET.

[0022] A method for applying a MOF-based magnetic supported catalyst comprises the following steps:

[0023] S1: Put PET into a reaction vessel containing ethylene glycol and catalyst for alcoholysis;

[0024] S2: The catalyst in the alcoholysis solution is recovered by an external magnetic field, and the recovered catalyst is cleaned and dried for later use;

[0025] S3: adding water to the alcoholysis solution after the catalyst is recovered and heating the solution until the solution is completely dissolved, cooling the solution, and filtering the solution to obtain a filtrate;

[0026] S4: refrigerating and crystallizing the filtrate to obtain a solid-liquid mixture containing BHET crystals, filtering the solid-liquid mixture to obtain a solid phase as crude BHET;

[0027] The catalyst is the above-mentioned MOF-based magnetic supported catalyst.

[0028] In a preferred embodiment, the mass ratio of PET to catalyst is 1:(0.05-0.2).

[0029] In summary, the technical solution of the present invention has the following main beneficial effects:

[0030] Compared with the existing technology, the MOF-based magnetic supported catalyst prepared in the embodiment achieves a major breakthrough in PET degradation technology by using different metals (Zn, Cu, Co) to optimize the MOF pore structure and combining it with the loading technology of magnetic Fe3O4 particles. It provides an efficient and economical solution for the green recycling of PET plastics and has broad prospects for industrial application, as follows:

[0031] The metal ions in this supported catalyst can form directional coordination bonds with the carbonyl oxygen atoms in the PET molecular chain, increasing the polarization of the C=O bond and significantly reducing the activation energy of the alcoholysis reaction. Its catalytic activity is higher than that of traditional heterogeneous catalysts.

[0032] The supported catalyst has a large specific surface area, providing more active sites, stabilizing the transition state during the reaction, reducing the reaction activation energy, and thus improving the reaction efficiency;

[0033] The supported catalyst has a hierarchical pore structure, and reactants are adsorbed and enriched on the catalyst surface, increasing the collision frequency, thereby limiting the occurrence of catalytic side reactions and improving catalyst activity and product selectivity.

[0034] This supported catalyst has both high catalytic performance and magnetic recovery characteristics. Magnetic nano-Fe3O4 gives the catalyst excellent magnetic response characteristics. By combining MOF materials with magnetic substances, a magnetic MOF catalyst is obtained. It not only has excellent catalytic performance but can also be quickly separated and recovered by an external magnetic field.

[0035] Compared with the core-shell structure catalysts of the same type, the supported catalyst of the present invention has the advantage of a short preparation cycle (usually less than 15 h);

[0036] For the depolymerization process of PET, the alcoholysis reaction needs to be carried out at a high temperature of around 200°C. Under such reaction conditions, the core-shell catalyst of the same type has inherent advantages due to its special structure. The material located in the "core" position (such as Fe3O4 particles) is in a relatively stable state and is not easily deactivated. The metal catalytic component in the "shell" position is tightly bound to the surrounding of the "core" and is not easily lost.

[0037] The catalyst prepared in the embodiment of the present invention does not have a core-shell structure, but a supported structure. The embodiment of the present invention verifies that under the premise of this supported structure and being used in a high-temperature catalytic environment of about 200°C, the catalyst can still maintain the magnetic activity of the Fe3O4 particles, which is convenient for the subsequent catalyst recovery. The metal catalytic components of the catalyst are also not easily lost, and have a high catalyst recovery rate.

[0038] Further or more detailed beneficial effects will be described in conjunction with specific examples in the specific implementation manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a SEM (scanning electron microscope) photograph of the catalyst prepared in Example 1;

[0040] Figure 2 is a TEM (transmission electron microscope) photograph of the catalyst prepared in Example 1;

[0041] Figure 3 This is the pore size distribution diagram of the catalyst prepared in Example 1. DETAILED DESCRIPTION

[0042] The present invention will be further explained with reference to the following embodiments:

[0043] The core technical problem faced by the technical solution of the embodiment of this application comes from the inventor's accurate understanding of the existing technology. Therefore, how to provide an efficient, economical and industrially applicable solution for the green recycling of PET plastics is a technical problem that the inventor urgently needs to solve.

[0044] It should be noted that the embodiments do not constitute a limitation on the scope of protection of the claims of the present invention. Based on the technical concepts provided / proven by the embodiments, all technical solutions that can be reasonably anticipated by technical personnel in the relevant technical field should be included in the scope of protection of the claims of the present invention.

[0045] Details are as follows:

[0046] Preparation Examples 1 to 3 are specific implementation methods for preparing the catalyst.

[0047] Preparation Example 1 :

[0048] Fe3O4@Zn-MOF: 100 mg of Fe3O4 and 300 mg of zinc nitrate dihydrate were uniformly dispersed in 50 mL of deionized water (solution A). The particle size of Fe3O4 particles was distributed between 50 and 80 nm.

[0049] Dissolve 550 mg of 2-methylimidazole in 50 mL of deionized water (Solution B).

[0050] Solution B was slowly added to solution A at a rate of 2 mL / min and ultrasonicated at room temperature for 40 min.

[0051] The solution was centrifuged for 10 min to obtain a precipitate, which was washed three times in deionized water and dried under vacuum at 60°C for 12 h to obtain a MOF-based magnetic supported catalyst: Fe3O4@Zn-MOF.

[0052] The SEM photo, TEM photo and pore size distribution diagram of the Fe3O4@Zn-MOF are respectively shown in the appendix of the specification. Figures 1-3 It can be seen that it has a loaded structure and a high specific surface area, as well as a hierarchical pore structure, which is conducive to the adsorption and enrichment of reactants on the catalyst surface, increasing the collision frequency, and improving the catalyst activity and product selectivity.

[0053] Preparation Example 2 :

[0054] Fe3O4@Cu-MOF: 100 mg of Fe3O4 and 350 mg of copper nitrate hexahydrate were uniformly dispersed in 50 mL of deionized water (solution A). The particle size of Fe3O4 particles was distributed between 50 and 80 nm.

[0055] Dissolve 550 mg of 2-methylimidazole in 50 mL of deionized water (Solution B).

[0056] Solution B was slowly added to solution A at a rate of 2 mL / min and ultrasonicated at room temperature for 40 min.

[0057] The solution was centrifuged for 10 min to obtain a precipitate, which was washed three times in deionized water and dried in vacuum at 60°C for 12 h to obtain a MOF-based magnetic supported catalyst: Fe3O4@Cu-MOF.

[0058] Preparation Example 3 :

[0059] Fe3O4@Co-MOF: 100 mg of Fe3O4 and 520 mg of cobalt nitrate hexahydrate were uniformly dispersed in 80 mL of deionized water (Solution A). The particle size of Fe3O4 particles ranged from 50 to 80 nm.

[0060] Dissolve 550 mg of 2-methylimidazole in 50 mL of deionized water (Solution B).

[0061] Solution B was slowly added to solution A at a rate of 2 mL / min and ultrasonicated at room temperature for 40 min.

[0062] The solution was centrifuged for 10 min to obtain a precipitate, which was washed three times in deionized water and dried in vacuum at 60 °C for 12 h to obtain a MOF-based magnetic supported catalyst: Fe3O4@Co-MOF.

[0063] Examples 1 to 9 are specific implementations of the catalyst for PET depolymerization.

[0064] Example 1 :

[0065] 5 g of PET was added to a reaction vessel containing 25 g of ethylene glycol and 0.05 g of Fe3O4@Zn-MOF catalyst, and heated to 200°C under normal pressure for alcoholysis for 150 min. The alcoholysis solution was clear and transparent, with no impurities.

[0066] The alcoholysis depolymerization reaction equation is:

[0067] ;

[0068] The Fe3O4@Zn-MOF catalyst was recovered by attraction using an external magnetic field. The recovered catalyst was cleaned of residual alcoholysis liquid on its surface with ethanol and then dried. 100 mL of cold water was added to the alcoholysis liquid, resulting in the formation of a large amount of white flocculent material. The solution was heated to 110°C in an oil bath for 60 minutes. Once the solution was completely dissolved, the temperature was lowered to 60°C and filtered to obtain a filtrate. The filtrate was refrigerated at 5°C for 24 hours to allow crystallization. After crystallization, a solid-liquid mixture containing BHET crystals was obtained, which was filtered at room temperature. The filtered solid was crude BHET.

[0069] Example 2 :

[0070] The difference from Example 1 is that the catalyst used in this example is Fe3O4@Cu-MOF.

[0071] Example 3 :

[0072] The difference from Example 1 is that the catalyst used in this example is Fe3O4@Co-MOF.

[0073] Example 4 :

[0074] The difference from Example 1 is that the added amount of the catalyst Fe3O4@Zn-MOF is 0.025 g.

[0075] Example 5 :

[0076] The difference from Example 1 is that the added amount of the catalyst Fe3O4@Zn-MOF is 0.035 g.

[0077] Example 6 :

[0078] The difference from Example 1 is that the added amount of the catalyst Fe3O4@Zn-MOF is 0.075 g.

[0079] Example 7 :

[0080] The difference from Example 1 is that the added amount of the catalyst Fe3O4@Zn-MOF is 0.1 g.

[0081] Example 8 :

[0082] The difference from Example 1 is that the alcoholysis time is reduced to 100 min.

[0083] Example 9 :

[0084] The difference from Example 1 is that the alcoholysis time is increased to 200 min.

[0085] Comparative Example 1 :

[0086] The catalyst used is Zn-MOF, and its preparation method is as follows:

[0087] Dissolve 3.75 g of zinc nitrate dihydrate in 60 mL of deionized water to make solution A.

[0088] Dissolve 4.95 g of 2-methylimidazole in 60 mL of deionized water (Solution B).

[0089] Solution A was slowly added to solution B at a rate of 2 mL / min and ultrasonicated at room temperature for 40 min to obtain a milky white solution. The precipitate was washed three times in deionized water and dried in a vacuum at 60°C for 12 h to obtain Zn-MOF.

[0090] The specific implementation method applied to PET depolymerization is the same as that of Example 1, except that the catalyst is the above-mentioned Zn-MOF.

[0091] Comparative Example 2 :

[0092] The catalyst used is Cu-MOF, and its preparation method is as follows:

[0093] Dissolve 3.95 g of copper nitrate hexahydrate in 60 mL of deionized water to make solution A.

[0094] Dissolve 4.95 g of 2-methylimidazole in 60 mL of deionized water (Solution B).

[0095] Solution A was slowly added to solution B at a rate of 2 mL / min and ultrasonicated at room temperature for 40 min to obtain a blue solution. The precipitate was washed three times in deionized water and dried in a vacuum at 60°C for 12 h to obtain Cu-MOF.

[0096] The specific implementation method applied to PET depolymerization is the same as that of Example 1, except that the catalyst is the above-mentioned Cu-MOF.

[0097] Comparative Example 3 :

[0098] The catalyst used is Co-MOF, and its preparation method is as follows:

[0099] Dissolve 5.78 g of cobalt nitrate hexahydrate in 80 mL of deionized water to form solution A.

[0100] Dissolve 4.95 g of 2-methylimidazole in 60 mL of deionized water (Solution B).

[0101] Solution A was slowly added to solution B at a rate of 2 mL / min and ultrasonicated at room temperature for 40 min to obtain a pink solution. The precipitate was washed three times in deionized water and dried in a vacuum at 60°C for 12 h to obtain Co-MOF.

[0102] The specific implementation method applied to PET depolymerization is the same as that of Example 1, except that the catalyst is the above-mentioned Co-MOF.

[0103] Comparative Example 4 :

[0104] The only difference between the preparation method of the catalyst and that of Preparation Example 1 is that the particle size distribution of the Fe3O4 particles is between 10 and 20 nm;

[0105] The specific implementation method applied to PET depolymerization is the same as that in Example 1, the only difference being the catalyst.

[0106] The PET depolymerization effects corresponding to Examples 1 to 9 and Comparative Examples 1 to 4 are shown in Table 1 below:

[0107] Table 1 PET depolymerization effects corresponding to Examples 1 to 9 and Comparative Examples 1 to 4 serial number Catalyst recovery PET conversion rate BHET yield Catalyst recovery rate Is PET completely depolymerized? Example 1 Recycling completed within 28 seconds 100% 87.21% 98.14% yes Example 2 Recycling completed within 31 seconds 100% 80.32% 96.42% yes Example 3 Recovery completed within 30 seconds 100% 84.17% 97.31% yes Example 4 Recycling completed within 21 seconds 100% 78.85% 97.57% yes Example 5 Recycling completed within 24 seconds 100% 81.62% 97.86% yes Example 6 Recycling completed within 36 seconds 100% 80.75% 98.27% yes Example 7 Recycling completed within 24 seconds 100% 78.88% 98.15% yes Example 8 Recycling completed within 28 seconds 100% 84.49% 98.22% yes Example 9 Recycling completed within 29 seconds 100% 85.39% 97.06% yes Comparative Example 1 Centrifugal recovery of catalyst 100% 75.29% 90.48% yes Comparative Example 2 Centrifugal recovery of catalyst 100% 69.03% 89.79% yes Comparative Example 3 Centrifugal recovery of catalyst 100% 72.33% 90.23% yes Comparative Example 4 Recovery completed within 100 s 100% 85.35% 94.90% yes ,

[0108] From Table 1 we can see that:

[0109] The BHET yields in Examples 1 to 9 ranged from 78.85% to 87.21%, the catalyst recovery rates were all above 96%, and the catalyst recovery time was ≤36 seconds;

[0110] Specifically, in Example 1, Fe3O4 and Zn-MOF synergistically catalyzed a higher BHET yield;

[0111] In Example 2, since the catalytic performance of Cu ions is lower than that of Zn ions, the BHET yield is lower than that of Example 1;

[0112] In Example 3, since the catalytic performance of Co ions is lower than that of Zn ions and higher than that of Cu ions, the BHET yield is lower than that of Example 1 but higher than that of Example 2;

[0113] In Example 4, the BHET yield decreased due to the reduced catalyst content;

[0114] In Example 5, since the catalyst content is slightly higher than that in Example 4, the BHET yield is also slightly increased;

[0115] In Example 6, the increase in catalyst content promoted the occurrence of side reactions and reduced the BHET yield;

[0116] In Example 7, due to the high catalyst content, side reactions occurred and the catalyst agglomerates, and the BHET yield was further reduced;

[0117] In Example 8, due to the shorter reaction time, the BHET yield was lower than that of Example 1. However, due to the good catalytic effect of Zn ions, the BHET yield was still higher than that of the examples using other catalysts.

[0118] In Example 9, due to the long reaction time, BHET underwent transesterification under catalytic conditions, and the BHET yield decreased.

[0119] In Comparative Examples 1 to 3, due to the different selection of catalysts and the single catalytic active site, the BHET yield was lower than that of the corresponding examples; and the centrifugal recovery of the catalyst took a long time, the alcoholysis solution became viscous due to the drop in temperature, the catalyst separation effect deteriorated, and the catalyst recovery rate was lowered compared with the corresponding examples.

[0120] In the preparation process of the catalyst, comparative example 4 selected Fe3O4 particles with smaller particle size, resulting in a lower BHET yield compared with example 1 and a greatly increased recovery time. The reason may be that Fe3O4 particles with smaller particle size are easy to aggregate, blocking the MOF pores and reducing the active sites. In addition, the magnetic response of small-particle Fe3O4 particles is weak, and a long time of external magnetic field magnetic recovery is required.

[0121] The PET conversion, BHET yield, and catalyst recovery in Table 1 were calculated as follows:

[0122] After the reaction is completed, the unreacted PET is separated by filtration and dried at 60°C to constant weight. The PET conversion can be calculated by formula 1:

[0123]

[0124] Where W0 represents the initial mass of PET and W1 represents the mass of unreacted PET.

[0125] The white crystalline sample obtained by filtration is the main product, which is dried to a constant weight. The BHET yield is calculated as follows:

[0126]

[0127] Where W BHET and W0 represent the weight of the main product and the initial weight of PET, respectively. BHET and MW PET are the molecular weight of BHET (254 g / mol) and the repeating unit of PET (192 g / mol), respectively.

[0128] The catalyst recovery rate is calculated as follows:

[0129]

[0130] Where m0 represents the initial weight of the catalyst, and m1 represents the mass of the recovered catalyst.

[0131] Throughout this specification, reference to terms such as "embodiment," "basic embodiment," "preferred embodiment," "other embodiments," "example," "specific example," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0132] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0133] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for preparing a MOF-based magnetic supported catalyst, characterized in that: The steps include: S1: Dispersing Fe3O4 nanoparticles and transition metal nitrates in water to obtain treatment solution A; S2: dissolving the organic ligand in water to obtain treatment solution B; S3: adding the treatment liquid B dropwise into the treatment liquid A and performing a dispersion treatment to obtain the treatment liquid C; S4: centrifuging the treatment liquid C, washing and drying the precipitate obtained by the centrifugal treatment, and obtaining a MOF-based magnetic supported catalyst.

2. The preparation method according to claim 1, wherein: In step S1, the nitrate of the transition metal is selected from one of zinc nitrate dihydrate, copper nitrate hexahydrate and cobalt nitrate hexahydrate.

3. The preparation method according to claim 2, wherein: The molar ratio of transition metal nitrate to metal in Fe3O4 nanoparticles is (2~4):

1.

4. The preparation method according to claim 3, wherein: In step S2, the organic ligand is 2-methylimidazole.

5. The preparation method according to claim 4, characterized in that: The molar ratio of 2-methylimidazole to the transition metal nitrate is (3~5):

1.

6. The preparation method according to claim 5, characterized in that: The molar ratio of the transition metal nitrate to the metal in the Fe3O4 nanoparticles is 3:1, and the molar ratio of 2-methylimidazole to the transition metal nitrate is 4:

1.

7. A MOF-based magnetic supported catalyst, characterized in that: The method is prepared according to any one of claims 1 to 6.

8. The supported catalyst according to claim 7, wherein: The supported catalyst is applied to the depolymerization of PET.

9. A method for applying a MOF-based magnetic supported catalyst, characterized in that: The steps include: S1: Put PET into a reaction vessel containing ethylene glycol and catalyst for alcoholysis; S2: The catalyst in the alcoholysis solution is recovered by an external magnetic field, and the recovered catalyst is cleaned and dried for later use; S3: adding water to the alcoholysis solution after the catalyst is recovered and heating the solution until the solution is completely dissolved, cooling the solution, and filtering the solution to obtain a filtrate; S4: refrigerating and crystallizing the filtrate to obtain a solid-liquid mixture containing BHET crystals, filtering the solid-liquid mixture to obtain a solid phase as crude BHET; The catalyst is the MOF-based magnetic supported catalyst according to claim 7.

10. The application method according to claim 9, characterized in that: The mass ratio of PET to catalyst is 1:(0.05~0.2).

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