Preparation method of amino-modified bimetallic ZIF / polyimide-based mixed matrix membrane

Abstract

The invention belongs to the field of preparation and application of membrane materials, and discloses a preparation method of an amino-modified bimetallic ZIF-based mixed matrix membrane. Zinc salt and cobalt salt react with 2-methylimidazole and an organic ligand containing an amino benzimidazole ring structure, and a novel zeolite imidazole framework material is synthesized. The obtained amino-modified bimetallic ZIF material is physically blended with polyimide to prepare a mixed matrix membrane with different filler loading capacities for gas separation. Cobalt ions are introduced into amino-functionalized ZIF-8, so that the flexibility of a metal-ligand bond is effectively limited, the aperture of ZIF is reduced, the gating effect is inhibited, and the gas separation performance is remarkably improved while good interfacial compatibility is kept. The method provides important potential for improving the performance and application of the mixed matrix membrane in a gas separation technology.

Description

Technical Field

[0001] The present invention belongs to the field of preparation and application of membrane materials, and discloses a preparation method of an amino-modified bimetallic ZIF / polyimide-based mixed matrix membrane. Background Art

[0002] As a clean energy, hydrogen energy has attracted much attention due to its high energy density and zero-emission characteristics in fuel cells, and plays a key role in industrial decarbonization fields such as fuel cells and ammonia synthesis. China has included hydrogen energy in the key points of its energy strategy. However, the removal of impurities such as CH4, N2, and CO2 during the preparation of high-purity hydrogen is still a major technical challenge. Compared with other hydrogen purification technologies, the gas membrane separation technology has core advantages such as low energy consumption, high efficiency, small floor area, and easy amplification, and is an efficient energy-saving and environmentally friendly hydrogen separation technology. Among various gas separation membrane materials, mixed matrix membranes (MMMs) can synergistically improve gas permeability and separation selectivity by organically combining the advantages of polymer membranes and porous inorganic fillers.

[0003] Metal-organic framework materials (MOFs) are widely used as fillers for mixed matrix membranes (MMMs) due to their extremely high specific surface area and porosity. Among the ZIF series of materials, ZIF-8 has a six-membered ring pore size of 0.34 nm, which is suitable for the separation of gas pairs such as CO2 (0.33 nm) / CH4 (0.38 nm), CO2 / N2 (0.364 nm), etc., making it one of the most widely studied MOF materials (Park K.Y., Ni Z., Adrien P.C., et al. Exceptional chemical and thermal stability of zeolitic imidazolate frameworks[J]. PNAS, 2006, 103(27):10186-10191). Experimental studies have shown that there is a "gating effect" in the six-membered ring window of ZIF-8: under the action of pressure or guest molecules, the imidazole ring will undergo spatial rotation, resulting in an effective pore size larger than 0.34 nm, which has an adverse effect on the screening effect of gas pairs with significant differences in molecular dynamic sizes such as CO2 / CH4 and CO2 / N2 (Moggach, S., Bennett, T. and Cheetham, A. (2009), The Effect of Pressure on ZIF-8: Increasing Pore Size with Pressure and the Formation of a High-Pressure Phase at 1.47 GPa. Angewandte Chemie International Edition, 48:7087-7089). To improve the gas pair selectivity of ZIF-based mixed matrix membranes, it is necessary to modify or post-treat ZIF-8 to inhibit its "gating effect".

[0004] Therefore, the present invention intends to introduce Co 2+ ions into ZIF-8-NH2 by the "solvothermal method" to reduce the flexibility of the Zn-N bond by forming a stronger Co-N bond, thereby inhibiting the "gating effect". Summary of the Invention

[0006] In order to overcome the "gating effect" of ZIF-8 in the mixed matrix membrane and improve its separation performance, the present invention proposes a method for preparing an amino-modified bimetallic ZIF-based mixed matrix membrane. This method uses the solvothermal method to introduce Co 2+ ions into ZIF-8-NH2 to reduce the pore size by restricting the flexibility of the metal-ligand bond, thereby inhibiting the "gating effect". The modified Zn / Co-ZIF-NH2 is incorporated into the polyimide matrix as a filler.

[0007] Technical solution of the present invention:

[0008] A preparation method of an amino-modified bimetallic ZIF / polyimide-based mixed matrix membrane comprises the following steps:

[0009] (1) Preparation of ZIF material: At room temperature, an organic ligand containing benzimidazole, an organic ligand of 2-methylimidazole and base A are dissolved in solvent A, and heated and stirred to obtain a mixed ligand solution; a soluble zinc salt and a soluble cobalt salt are respectively dissolved in solvent B to prepare a zinc ion solution and a cobalt ion solution. After a certain period of time, the zinc ion solution and the cobalt ion solution are mixed to obtain a metal ion solution; after the mixed ligand solution is cooled to room temperature, the metal ion solution is added dropwise to the mixed ligand solution under stirring conditions; after reacting at room temperature for a certain time, the reaction solution is centrifuged and washed; finally, the dried product is obtained to obtain an amino-modified bimetallic ZIF material;

[0010] (2) Preparation of the mixed matrix membrane: The amino-modified bimetallic ZIF material is ground and dried, and then dried for a second time; subsequently, the amino-modified bimetallic ZIF material is dispersed in organic solvent B, and polyimide is added to obtain a casting solution, and an amino-modified bimetallic ZIF / polyimide-based mixed matrix membrane is prepared by the solvent evaporation method.

[0011] The organic ligand containing benzimidazole is 2-(4-aminophenyl)-5-aminobenzimidazole, 2-aminobenzimidazole or 6-aminobenzimidazole.

[0012] The polyimide is one of 6FDA-DAM or 6FDA-DAM / DABA (the molar ratio of the two diamine monomers DAM and DABA is 0.1-10:1).

[0013] The solvent A is N,N-dimethylformamide, N,N-dimethylacetamide or methanol.

[0014] The solvent B is N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.

[0015] The base A is sodium formate, triethylamine or sodium hydroxide.

[0016] In step (1), the soluble zinc salt is zinc nitrate or zinc chloride.

[0017] In step (1), the soluble cobalt salt is cobalt nitrate or cobalt chloride.

[0018] In step (1), the molar ratio of the soluble zinc salt to the soluble cobalt salt is 1:0.5-2.

[0019] In step (1), the molar ratio of the organic ligand containing aminobenzimidazole to 2-methylimidazole is 1:5-12.

[0020] In step (1), the molar ratio of alkali A to the aminobenzimidazole-containing organic ligand is 1-5:1.

[0021] In step (1), the molar ratio of the soluble zinc salt to the aminobenzimidazole-containing organic ligand is 1-10:1.

[0022] In step (1), the stirring temperature is 60-70 °C and the stirring time is 2-3 hours.

[0023] In step (1), the reaction time at room temperature is 2-4 hours.

[0024] In step (2), the mass fraction of the casting solution is 8-10 wt%, wherein the mass fraction of the amino-modified bimetallic ZIF material is 0.8-4 wt%, and the mass fraction of polyimide in the casting solution is 4.8-12 wt%.

[0025] Advantages of the present invention: The preparation method of the present invention effectively reduces the pore size and inhibits the "gating effect" by introducing Co into ZIF-8-NH2. At the same time, the use of the aminobenzimidazole-containing organic ligand significantly improves the interfacial compatibility between the ZIF material and the polyimide matrix through strong hydrogen bonding. The above-mentioned synergistic effect significantly improves the gas separation performance of the amino-modified bimetallic ZIF-based mixed matrix membrane. 2+ The gas separation performance of the amino-modified bimetallic ZIF-based mixed matrix membrane is significantly improved by the above-mentioned synergistic effect. Specific embodiments

[0026] The following further illustrates the specific embodiments of the present invention in combination with the technical solutions.

[0027] Gas permeability test: The permeability test of the gas separation membrane in the present invention is carried out by the constant volume variable pressure method, the test temperature is 35 °C, and the test pressure is 2 bar.

[0028] Example 1

[0029] Synthesis of 6FDA-DAM: Under nitrogen and ice-water bath conditions, 3 g of 6FDA and 1.02 g of DAM were dissolved in 12 mL of N-methyl-2-pyrrolidone. After 4 hours, the reactor was taken out and reacted at room temperature for 24 hours. 0.5 mL of pyridine and 5 mL of acetic anhydride were added, and the reaction continued at room temperature for 24 hours. Finally, the product was washed and dried to obtain a white solid 6FDA-DAM.

[0030] Synthesis of Zn / Co-ZIF-NH₂: Dissolve 0.54 g of 2-aminobenzimidazole, 2.96 g of 2-methylimidazole and 0.20 g of sodium formate in 100 mL of methanol, and react at 70 °C for 2 hours. Meanwhile, dissolve 1.488 g of zinc nitrate hexahydrate and 1.46 g of cobalt nitrate hexahydrate in 50 mL of N,N-dimethylformamide (DMF) respectively, and mix them after a short interval. Dropwise add the obtained metal salt solution into the imidazole mixture and react at room temperature for 2 hours. After the reaction is completed, wash the product thoroughly with methanol and dry it to obtain purple Zn / Co-ZIF-NH₂ powder.

[0031] Preparation of mixed matrix membrane: Disperse 0.04 g of Zn / Co-ZIF-NH₂ in 4.96 g of N,N-dimethylformamide (DMF) to prepare 5 g of Zn / Co-ZIF-NH₂ DMF suspension; dissolve 0.36 g of 6FDA-DAM polymer in 4.64 g of DMF to prepare 5 g of 6FDA-DAM DMF solution. After stirring the two solutions for 24 hours respectively, add the 6FDA-DAM DMF solution into the Zn / Co-ZIF-NH₂ DMF suspension and stir well. After the casting solution is degassed by ultrasonic treatment, dry it at 60 °C for 8 hours, and then dry it in a vacuum oven at 120 °C under vacuum for 12 hours.

[0032] Example 2

[0033] Synthesis of 6FDA-DAM: Dissolve 3 g of 6FDA and 1.02 g of DAM in 12 mL of N-methyl-2-pyrrolidone under nitrogen and ice-water bath conditions, take out the reactor after 4 hours, and react at room temperature for 24 hours. Add 0.5 mL of pyridine and 5 mL of acetic anhydride, and continue to react at room temperature for 24 hours. Finally, wash and dry to obtain white solid 6FDA-DAM product.

[0034] Synthesis of Zn / Co-ZIF-NH₂: Dissolve 0.54 g of aminobenzimidazole, 2.96 g of 2-methylimidazole and 0.20 g of sodium formate in 100 mL of methanol, and react at 70 °C for 2 hours. Meanwhile, dissolve 1.488 g of zinc nitrate hexahydrate and 1.46 g of cobalt nitrate hexahydrate in 50 mL of N,N-dimethylformamide (DMF) respectively, and mix them after a short interval. Dropwise add the obtained metal salt solution into the imidazole mixture and react at room temperature for 2 hours. After the reaction is completed, wash the product thoroughly with methanol and dry it to obtain purple Zn / Co-ZIF-NH₂ powder.

[0035] Preparation of mixed matrix membrane: 0.08 g of Zn / Co-ZIF-NH2 was dispersed in 4.92 g of N,N-dimethylformamide (DMF) to prepare 5 g of Zn / Co-ZIF-NH2 DMF suspension; 0.32 g of 6FDA-DAM polymer was dissolved in 4.68 g of DMF to prepare 5 g of 6FDA-DAM DMF solution. After the two solutions were stirred for 24 hours respectively, the 6FDA-DAM DMF solution was added to the Zn / Co-ZIF-NH2 DMF suspension and stirred thoroughly. After the casting solution was degassed by ultrasound, it was dried at 60 °C for 8 hours and then vacuum dried at 120 °C for 12 hours in a vacuum oven.

[0036] Example 3

[0037] Synthesis of 6FDA-DAM: 3 g of 6FDA and 1.02 g of DAM were dissolved in 12 mL of N-methyl-2-pyrrolidone under nitrogen and ice-water bath conditions. The reactor was taken out after 4 h and reacted at room temperature for 24 h. 0.5 mL of pyridine and 5 mL of acetic anhydride were added and the reaction continued at room temperature for 24 h. Finally, the product was washed and dried to obtain a white solid 6FDA-DAM product.

[0038] Synthesis of Zn / Co-ZIF-NH2: 0.54 g of aminobenzimidazole, 2.96 g of 2-methylimidazole and 0.20 g of sodium formate were dissolved in 100 mL of methanol and reacted at 70 °C for 2 h. At the same time, 1.488 g of zinc nitrate hexahydrate and 1.46 g of cobalt nitrate hexahydrate were dissolved in 50 mL of N,N-dimethylformamide (DMF) respectively and mixed after a short interval. The obtained metal salt solution was added dropwise to the imidazole mixture and reacted at room temperature for 2 h. After the reaction was completed, the product was washed thoroughly with methanol and dried to obtain purple Zn / Co-ZIF-NH2 powder.

[0039] Preparation of mixed matrix membrane: 0.12 g of Zn / Co-ZIF-NH2 was dispersed in 4.88 g of N,N-dimethylformamide (DMF) to prepare 5 g of Zn / Co-ZIF-NH2 DMF suspension; 0.28 g of 6FDA-DAM polymer was dissolved in 4.72 g of DMF to prepare 5 g of 6FDA-DAM DMF solution. After the two solutions were stirred for 24 hours respectively, the 6FDA-DAM DMF solution was added to the Zn / Co-ZIF-NH2 DMF suspension and stirred thoroughly. After the casting solution was degassed by ultrasound, it was dried at 60 °C for 8 hours and then vacuum dried at 120 °C for 12 hours in a vacuum oven.

[0040] Example 4

[0041] Synthesis of 6FDA-DAM: 3 g of 6FDA and 1.02 g of DAM were dissolved in 12 mL of N-methyl-2-pyrrolidone under nitrogen and an ice-water bath. After 4 h, the reactor was taken out and reacted at room temperature for 24 h. 0.5 mL of pyridine and 5 mL of acetic anhydride were added, and the reaction continued at room temperature for 24 h. Finally, the product was washed and dried to obtain a white solid 6FDA-DAM product.

[0042] Synthesis of Zn / Co-ZIF-NH2: 0.54 g of aminobenzimidazole, 2.96 g of 2-methylimidazole and 0.20 g of sodium formate were dissolved in 100 mL of methanol and reacted at 70 °C for 2 h. Meanwhile, 1.488 g of zinc nitrate hexahydrate and 1.46 g of cobalt nitrate hexahydrate were respectively dissolved in 50 mL of N,N-dimethylformamide (DMF), and the two were mixed after a short interval. The obtained metal salt solution was added dropwise to the imidazole mixture and reacted at room temperature for 2 h. After the reaction was completed, the product was washed thoroughly with methanol and dried to obtain purple Zn / Co-ZIF-NH2 powder.

[0043] Preparation of mixed matrix membrane: 0.16 g of Zn / Co-ZIF-NH2 was dispersed in 4.84 g of N,N-dimethylformamide (DMF) to prepare a 5 g Zn / Co-ZIF-NH2 DMF suspension; 0.24 g of 6FDA-DAM polymer was dissolved in 4.76 g of DMF to prepare a 5 g 6FDA-DAM DMF solution. After the two solutions were stirred for 24 h respectively, the 6FDA-DAM DMF solution was added to the Zn / Co-ZIF-NH2 DMF suspension and stirred thoroughly. After the casting solution was degassed by ultrasound, it was dried at 60 °C for 8 h and then vacuum dried at 120 °C in a vacuum oven for 12 h.

[0044] Example 5

[0045] Synthesis of 6FDA-DAM:DABA: 3 g of 6FDA, 0.4109 g of DABA and 0.6086 g of DAM were dissolved in 12 mL of N-methyl-2-pyrrolidone (NMP) under nitrogen and an ice-water bath. After 4 h, the reactor was taken out and reacted at room temperature for 24 h. 0.5 mL of pyridine and 5 mL of acetic anhydride were added, and the reaction continued at room temperature for 24 h. Finally, the product was washed and dried to obtain a pale yellow solid 6FDA-DAM:DABA product.

[0046] Synthesis of Zn / Co-ZIF-NH2: Dissolve 0.54 g of aminobenzimidazole, 2.96 g of 2-methylimidazole and 0.20 g of sodium formate in 100 mL of methanol and react at 70 °C for 2 hours. Meanwhile, dissolve 1.488 g of zinc nitrate hexahydrate and 1.46 g of cobalt nitrate hexahydrate in 50 mL of N,N-dimethylformamide (DMF) respectively, and mix them after a short interval. Dropwise add the obtained metal salt solution into the imidazole mixture and react at room temperature for 2 hours. After the reaction is completed, wash the product thoroughly with methanol and dry it to obtain purple Zn / Co-ZIF-NH2 powder.

[0047] Preparation of mixed matrix membrane: Disperse 0.04 g of Zn / Co-ZIF-NH2 in 4.96 g of N,N-dimethylformamide (DMF) to prepare 5 g of Zn / Co-ZIF-NH2 DMF suspension; dissolve 0.36 g of 6FDA-DAM:DABA polymer in 4.64 g of DMF to prepare 5 g of 6FDA-DAM:DABA DMF solution. After stirring the two solutions for 24 hours respectively, add the 6FDA-DAM:DABA DMF solution into the Zn / Co-ZIF-NH2 DMF suspension and stir well. After the casting solution is degassed by ultrasonic treatment, dry it at 60 °C for 8 hours, and then dry it under vacuum at 120 °C in a vacuum oven for 12 hours.

[0048] Example 6

[0049] Synthesis of 6FDA-DAM:DABA: Dissolve 3 g of 6FDA, 0.4109 g of DABA and 0.6086 g of DAM in 12 mL of N-methyl-2-pyrrolidone (NMP) under nitrogen and ice-water bath conditions. Take out the reactor after 4 hours and react at room temperature for 24 hours. Add 0.5 mL of pyridine and 5 mL of acetic anhydride and continue to react at room temperature for 24 hours. Finally, wash and dry to obtain a pale yellow solid 6FDA-DAM:DABA product.

[0050] Synthesis of Zn / Co-ZIF-NH2: Dissolve 0.54 g of aminobenzimidazole, 2.96 g of 2-methylimidazole and 0.20 g of sodium formate in 100 mL of methanol and react at 70 °C for 2 hours. Meanwhile, dissolve 1.488 g of zinc nitrate hexahydrate and 1.46 g of cobalt nitrate hexahydrate in 50 mL of N,N-dimethylformamide (DMF) respectively, and mix them after a short interval. Dropwise add the obtained metal salt solution into the imidazole mixture and react at room temperature for 2 hours. After the reaction is completed, wash the product thoroughly with methanol and dry it to obtain purple Zn / Co-ZIF-NH2 powder.

[0051] Preparation of mixed matrix membrane: 0.08 g of Zn / Co-ZIF-NH2 was dispersed in 4.92 g of N,N-dimethylformamide (DMF) to prepare 5 g of Zn / Co-ZIF-NH2 DMF suspension; 0.32 g of 6FDA-DAM:DABA copolymer was dissolved in 4.68 g of DMF to prepare 5 g of 6FDA-DAM:DABA DMF solution. After the two solutions were stirred for 24 hours respectively, the 6FDA-DAM:DABA DMF solution was added to the Zn / Co-ZIF-NH2 DMF suspension and stirred thoroughly. After the casting solution was degassed by ultrasonic treatment, it was dried at 60 °C for 8 hours and then vacuum dried at 120 °C for 12 hours in a vacuum oven.

[0052] Example 7

[0053] Synthesis of 6FDA-DAM:DABA: 3 g of 6FDA, 0.4109 g of DABA and 0.6086 g of DAM were dissolved in 12 mL of N-methyl-2-pyrrolidone (NMP) under nitrogen and ice-water bath conditions. The reactor was taken out after 4 h and reacted at room temperature for 24 h. 0.5 mL of pyridine and 5 mL of acetic anhydride were added, and the reaction continued at room temperature for 24 h. Finally, the product was washed and dried to obtain a light yellow solid 6FDA-DAM:DABA product.

[0054] Synthesis of Zn / Co-ZIF-NH2: 0.54 g of aminobenzimidazole, 2.96 g of 2-methylimidazole and 0.20 g of sodium formate were dissolved in 100 mL of methanol and reacted at 70 °C for 2 h. At the same time, 1.488 g of zinc nitrate hexahydrate and 1.46 g of cobalt nitrate hexahydrate were dissolved in 50 mL of N,N-dimethylformamide (DMF) respectively and mixed after a short interval. The obtained metal salt solution was added dropwise to the imidazole mixture and reacted at room temperature for 2 h. After the reaction was completed, the product was washed thoroughly with methanol and dried to obtain purple Zn / Co-ZIF-NH2 powder.

[0055] Preparation of mixed matrix membrane: 0.12 g of Zn / Co-ZIF-NH2 was dispersed in 4.88 g of N,N-dimethylformamide (DMF) to prepare 5 g of Zn / Co-ZIF-NH2 DMF suspension; 0.28 g of 6FDA-DAM:DABA copolymer was dissolved in 4.72 g of DMF to prepare 5 g of 6FDA-DAM:DABA DMF solution. After the two solutions were stirred for 24 hours respectively, the 6FDA-DAM:DABA DMF solution was added to the Zn / Co-ZIF-NH2 DMF suspension and stirred thoroughly. After the casting solution was degassed by ultrasonic treatment, it was dried at 60 °C for 8 hours and then vacuum dried at 120 °C for 12 hours in a vacuum oven.

[0056] Example 8

[0057] Synthesis of 6FDA-DAM:DABA: Under nitrogen and an ice-water bath, 3 g of 6FDA, 0.4109 g of DABA and 0.6086 g of DAM were dissolved in 12 mL of N-methyl-2-pyrrolidone (NMP). After 4 h, the reactor was taken out and reacted at room temperature for 24 h. 0.5 mL of pyridine and 5 mL of acetic anhydride were added, and the reaction continued at room temperature for 24 h. Finally, the product was washed and dried to obtain a pale yellow solid 6FDA-DAM:DABA product.

[0058] Synthesis of Zn / Co-ZIF-NH2: 0.54 g of aminobenzimidazole, 2.96 g of 2-methylimidazole and 0.20 g of sodium formate were dissolved in 100 mL of methanol and reacted at 70 °C for 2 h. Meanwhile, 1.488 g of zinc nitrate hexahydrate and 1.46 g of cobalt nitrate hexahydrate were respectively dissolved in 50 mL of N,N-dimethylformamide (DMF), and the two were mixed after a short interval. The obtained metal salt solution was added dropwise to the imidazole mixture and reacted at room temperature for 2 h. After the reaction was completed, the product was washed thoroughly with methanol and dried to obtain purple Zn / Co-ZIF-NH2 powder.

[0059] Preparation of mixed matrix membrane: 0.16 g of Zn / Co-ZIF-NH2 was dispersed in 4.84 g of N,N-dimethylformamide (DMF) to prepare a 5 g Zn / Co-ZIF-NH2 DMF dispersion; meanwhile, 0.24 g of 6FDA-DAM:DABA copolymer was dissolved in 4.76 g of DMF to prepare a 5 g 6FDA-DAM:DABA DMF solution. After the two systems were stirred for 24 h respectively, the 6FDA-DAM:DABA DMF solution was added to the ZIF-8-NH2 DMF dispersion and stirred well. After the obtained casting solution was degassed by ultrasonic treatment, it was dried at 60 °C for 8 h, and then vacuum dried at 120 °C in a vacuum oven for 12 h.

[0060] Control Example 1

[0061] Synthesis of 6FDA-DAM: Under nitrogen and an ice-water bath, 3 g of 6FDA and 1.02 g of DAM were dissolved in 12 mL of N-methyl-2-pyrrolidone. After 4 h, the reactor was taken out and reacted at room temperature for 24 h. 0.5 mL of pyridine and 5 mL of acetic anhydride were added, and the reaction continued at room temperature for 24 h. Finally, the product was washed and dried to obtain a white solid 6FDA-DAM product.

[0062] Synthesis of ZIF-8-NH2: Dissolve 0.270g of aminobenzimidazole, 1.488g of 2-methylimidazole and 0.10g of sodium formate in 50mL of methanol solvent and react at 70℃ for 2h. Dissolve 1.488g of zinc nitrate hexahydrate in 50mL of DMF solvent and add dropwise to the imidazole solution. After reacting at room temperature for 4h, continue to react at 60℃ for 16h. The product is washed with methanol and dried to obtain white solid ZIF-8-NH2 powder.

[0063] Preparation of mixed matrix membrane: 0.12g ZIF-8-NH2 was dispersed in 4.88g N,N-dimethylformamide (DMF) to prepare 5g ZIF-8-NH2 DMF suspension; 0.28g 6FDA-DAM polymer was dissolved in 4.72g DMF to prepare 5g 6FDA-DAM DMF solution. After the two solutions were stirred for 24 hours, the 6FDA-DAM DMF solution was added to the ZIF-8-NH2DMF suspension and stirred thoroughly. After ultrasonic degassing, the casting solution was dried at 60℃ for 8 hours, and then vacuum dried in a vacuum oven at 120℃ for 12 hours.

[0064] Comparative Example 2

[0065] Synthesis of 6FDA-DAM: Dissolve 3g 6FDA and 1.02g DAM in 12mL N-methyl-2-pyrrolidone under nitrogen and ice-water bath conditions. Take out the reactor after 4 hours and react at room temperature for 24 hours. Add 0.5mL pyridine and 5mL acetic anhydride and continue to react at room temperature for 24 hours. Finally, wash and dry to obtain a white solid 6FDA-DAM product.

[0066] Synthesis of ZIF-67-NH2: 0.270 g of aminobenzimidazole, 1.488 g of 2-methylimidazole and 0.10 g of sodium formate were dissolved in 50 mL of methanol solvent and reacted at 70 °C for 2 h. 1.46 g of cobalt nitrate hexahydrate was dissolved in 50 mL of DMF solvent and added dropwise to the imidazole solution. After reacting at room temperature for 4 h, the reaction was continued at 60 °C for 16 h. The product was washed with methanol and dried to obtain a purple solid ZIF-67-NH2 powder.

[0067] Preparation of Mixed Matrix Membrane: 0.12 g of ZIF-67-NH2 was dispersed in 4.88 g of N,N-dimethylformamide (DMF) to prepare 5 g of ZIF-67-NH2 DMF suspension; 0.28 g of 6FDA-DAM polymer was dissolved in 4.72 g of DMF to prepare 5 g of 6FDA-DAM DMF solution. After the two solutions were stirred for 24 hours respectively, the 6FDA-DAM DMF solution was added to the ZIF-67-NH2 DMF suspension and stirred thoroughly. After the casting solution was degassed by ultrasonic treatment, it was dried at 60 °C for 8 hours and then dried in a vacuum oven at 120 °C under vacuum for 12 hours.

[0068] As shown in Table 1, in Comparative Examples 1, 2 and Example 3, different fillers (ZIF-8-NH2, ZIF-67-NH2 and Zn / Co-ZIF-NH2) were used, the filler loadings were the same, but the polymer types were the same. The performance comparison shows that the separation selectivity of the membrane in Comparative Example 1 was significantly lower than that in Example 3, and was also lower than that in Examples 1, 2 and 4 with lower filler loadings, but its permeability was higher. Comparative Example 2 used the same content and the same polymer, but different ZIF materials (using ZIF-67-NH2), and the permeability of its mixed matrix membrane was much lower than that in Example 3, and was also lower than that in Examples 1, 2 and 4 with lower filler loadings. Through the performance comparison between the comparative examples and the examples, it can be seen that the combination of 6FDA-DAM and Zn / Co-ZIF-NH2 can prepare a highly selective mixed matrix membrane. With the increase of the loading of Zn / Co-ZIF-NH2 in the mixed matrix membrane, the permeability and selectivity of the Zn / Co-ZIF-NH2 / 6FDA-DAM mixed matrix membrane were both improved. In addition, in Examples 4-8, the same filler (Zn / Co-ZIF-NH2) was used, but the polyimide was the copolymeric polyimide 6FDD. With the increase of the filler loading, the gas separation performance was enhanced, and its ideal selectivity was much higher than that in Examples 1-4, which indicates that the improvement of the gas separation performance of the mixed matrix membrane by Zn / Co-ZIF-NH2 mainly comes from its improvement of the selectivity of gas pairs and its better interfacial compatibility with polyimide. This further proves that Zn / Co-ZIF-NH2 has an excellent molecular sieving effect on gas pairs with large differences in molecular kinetic diameters.

[0069] Table 1 shows the gas permeability and selectivity of the gas separation membranes prepared in the comparative examples and the examples

[0070]

[0071]

Claims

1. A preparation method of an amino-modified bimetallic ZIF / polyimide-based mixed matrix membrane, characterized in that, The steps are as follows: (1) Preparation of ZIF material: At room temperature, an organic ligand containing benzimidazole, an organic ligand of 2-methylimidazole, and base A are dissolved in solvent A, and the mixture is heated and stirred to obtain a mixed ligand solution; a soluble zinc salt and a soluble cobalt salt are respectively dissolved in solvent B to prepare a zinc ion solution and a cobalt ion solution. After a certain period of time, the zinc ion solution and the cobalt ion solution are mixed to obtain a metal ion solution; after the mixed ligand solution is cooled to room temperature, the metal ion solution is added dropwise to the mixed ligand solution under stirring; after reacting at room temperature for a certain period of time, the reaction solution is centrifuged and washed; Finally, a dried product is obtained, which is an amino-modified bimetallic ZIF material; (2) Preparation of the mixed matrix membrane: The amino-modified bimetallic ZIF material is ground and dried, and then dried again; subsequently, the amino-modified bimetallic ZIF material is dispersed in organic solvent B, and polyimide is added to obtain a casting solution, and an amino-modified bimetallic ZIF / polyimide-based mixed matrix membrane is prepared by the solvent evaporation method.

2. The preparation method according to claim 1, wherein in step (1), the organic ligand containing benzimidazole is 2-(4-aminophenyl)-5-aminobenzimidazole, 2-aminobenzimidazole or 6-aminobenzimidazole; the solvent A is N,N-dimethylformamide, N,N-dimethylacetamide or methanol; the solvent B is N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide; the base A is sodium formate, triethylamine or sodium hydroxide; the soluble zinc salt is zinc nitrate or zinc chloride; the soluble cobalt salt is cobalt nitrate or cobalt chloride.

3. The preparation method according to claim 1, wherein in step (1), the molar ratio of the soluble zinc salt to the soluble cobalt salt is 1:0.5 - 2; the molar ratio of the organic ligand containing aminobenzimidazole to 2-methylimidazole is 1:5 - 12; the molar ratio of base A to the organic ligand containing aminobenzimidazole is 1 - 5:1; the molar ratio of the soluble zinc salt to the organic ligand containing aminobenzimidazole is 1 - 10:

1.

4. The preparation method according to claim 1, wherein in step (1), the stirring temperature is 60 - 70 °C, and the stirring time is 2 - 3 hours; the reaction time at room temperature is 2 - 4 hours.

5. The preparation method according to claim 1, wherein in step (2), the polyimide is 6FDA-DAM or 6FDA-DAM / DABA; wherein, in 6FDA-DAM / DABA, the molar ratio of the two diamine monomers DAM and DABA is 0.1 - 10:

1.

6. The preparation method according to claim 1, wherein in step (2), the mass fraction of the casting solution is 8 - 10 wt%, wherein the mass fraction of the amino-modified bimetallic ZIF material is 0.8 - 4 wt%, and the mass fraction of polyimide in the casting solution is 4.8 - 12 wt%.

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