A hydrolyzed polyacrylonitrile-based zeolitic imidazolate framework membrane for ammonia separation and a method of making the same

Abstract

The application discloses a kind of hydrolytic polyacrylonitrile-based zeolite imidazolate framework membrane for ammonia separation and preparation method thereof, comprising the following steps: S1, metal compound, organic ligand and solvent are mixed according to specific proportion, reaction, form ZIF-7 material, and it is dissolved in DMF, form ZIF-7 solution;S2, polyacrylonitrile and polyvinylpyrrolidone are dissolved in DMF solution, obtain PAN casting solution, then PAN casting solution is poured on clean smooth glass plate, immerse in deionized water, obtain PAN membrane, immerse in NaOH, HCl solution in succession, prepare HPAN membrane, and immerse in ZIF-7 solution;S3, HPAN membrane is used as support layer to divide metal compound solution and organic ligand solution, in the reaction process, metal compound solution and organic ligand solution diffuse towards opposite direction, reaction occurs on the surface of HPAN membrane support layer, and finally form the required framework membrane.The framework membrane obtained by the application has high efficient ammonia separation effect, when separating synthetic ammonia residual gas, ammonia permeability is as high as 2561.7 GPU, ammonia / nitrogen and ammonia / hydrogen selectivity are as high as 630.1 and 147.8 respectively.

Description

Technical Field

[0001] The present invention relates to the technical field of gas separation membranes, and in particular to a hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane for ammonia separation and a preparation method thereof. Background Art

[0002] Ammonia (NH3) plays a vital role in the chemical industry, with important applications in agricultural fertilizers, pharmaceuticals, organic compounds, and polymer material synthesis. To date, the vast majority of NH3 is still produced through the traditional Haber-Bosch process, which produces NH3 through a catalytic reaction between nitrogen (N2) and hydrogen (H2) under high temperature and high pressure conditions. It is important to note that the NH3 synthesis conversion rate of the Haber-Bosch process is relatively low, at only 10-20%, and is generally collected by physical cooling and liquefaction. However, approximately 3% of NH3 still remains in the circulating gas, reducing synthesis efficiency and affecting production capacity. Therefore, recovering low-concentration NH3 is crucial.

[0003] Membrane separation technology has the advantages of energy sustainability, simple operation and easy control, environmental protection, and high efficiency, and has great application potential in the field of gas separation. Membrane materials are the core of membrane separation technology. Ideal membrane materials should have high permeability, high selectivity, and high stability. Currently, the membrane materials widely used in commercial applications are traditional polymer materials, but they have problems such as small free volume within the membrane, discontinuous channels, and easy swelling. In addition, due to the "trade-off" effect between permeability and selectivity, it is difficult to significantly improve performance. Compared with discontinuous mixed matrix membranes prepared by blending, dense and defect-free metal-organic framework membranes prepared by interfacial polymerization and reverse diffusion methods can take advantage of the pore structure in gas separation. Summary of the Invention

[0004] To address the low ammonia selectivity and permeation flux of existing ammonia separation membranes, the present invention provides a hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane for ammonia separation and its preparation method. This functionalized ZIF-7 membrane exhibits high flux, excellent separation performance, and high stability. Using a functionalized zeolite imidazole framework (ZIF-7-NH2, ZIF-7-COOH, ZIF-7-SO3H, ZIF-7-Cl, ZIF-7-Br) as a selective layer, an ultrathin, defect-free, pure-phase functionalized ZIF-7 membrane is produced on a hydrolyzed polyacrylonitrile (HPAN) support layer.

[0005] The present invention adopts the following technical solutions:

[0006] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane for ammonia separation comprises a porous support layer and a zeolite imidazole framework membrane deposited on the porous support layer by a reverse diffusion method.

[0007] Preferably, the porous support layer is a hydrolyzed polyacrylonitrile-based (HPAN) membrane; and the zeolitic imidazolate framework membrane is a functionalized ZIF-7 membrane.

[0008] Preferably, the pore size of the porous support layer is 20-50 nm.

[0009] A method for preparing a hydrolyzed polyacrylonitrile-based zeolitic imidazolate framework membrane for ammonia separation, comprising the following steps:

[0010] S1, preparation of a functionalized ZIF-7 solution: mixing a metal compound, an organic ligand, and a solvent according to a specific molar ratio, reacting at a specific temperature to form a functionalized ZIF-7 material, and centrifuging the functionalized ZIF-7 material to obtain a product, which is activated by vacuum drying at 60°C for 12 h, and then dissolving the functionalized ZIF-7 powder in DMF to form a functionalized ZIF-7 solution for use;

[0011] S2, preparation of a hydrolyzed polyacrylonitrile (HPAN) membrane: dissolving polyacrylonitrile and polyvinylpyrrolidone in a DMF solution, heating and stirring to obtain a PAN casting solution, then pouring the PAN casting solution onto a clean and smooth glass plate, repeatedly scraping with a doctor blade, then immediately immersing in deionized water to obtain a PAN membrane, and finally immersing the PAN membrane in a NaOH solution for 1-2 h, and then immersing in an HCl solution for 10-15 h to obtain a HPAN membrane, and immersing the HPAN membrane in the functionalized ZIF-7 solution of step S1;

[0012] S3, preparation of a functionalized ZIF-7 / PAN membrane: using a self-made two-chamber reaction tank, the HPAN membrane soaked in the functionalized ZIF-7 solution in step S2 is used as a support layer to separate Zn(NO3)2·6H2O solution and imidazole ligand solution with -NH2, -COOH, -SO3H, -Cl, -Br functionalization and HbIm ligand solution, during the reaction process, the metal compound solution and the organic ligand solution will diffuse in opposite directions, and react on the surface of the HPAN membrane support layer, finally forming a dense and defect-free functionalized ZIF-7 / PAN membrane, i.e. a hydrolyzed polyacrylonitrile-based zeolitic imidazolate framework membrane. In order to prevent the membrane from being quenched and causing cracks, the oven should be naturally cooled to room temperature before taking out the device and removing the functionalized ZIF-7 / PAN membrane. Finally, the prepared functionalized ZIF-7 / PAN membrane is washed and soaked with DMF and stored in ethanol for use.

[0013] In step S1, the metal compound is zinc nitrate hexahydrate (Zn(NO3)2·6H2O), the organic ligand is a benzimidazole-based mixed ligand, and the solvent is deionized water; the molar ratio of zinc nitrate hexahydrate (Zn(NO3)2·6H2O), benzimidazole, solvent, and DMF is (1-3):(1-4):(10-20):10.

[0014] Preferably, the organic ligand is a mixture of benzimidazole and a functionalized imidazole ligand in a molar ratio of 1:4-4:1, wherein the functionalized imidazole ligand is one of 2-aminoimidazole, 2-methylimidazole-4,5-dicarboxylic acid, 2-phenylbenzimidazole-5-sulfonic acid, 5-chlorobenzimidazole-2-thiol and 2-bromo-6-nitrobenzimidazole.

[0015] In step S1, the reaction temperature is 80-120° C., and the reaction time is 12-48 hours.

[0016] In step S2, the mass ratio of polyacrylonitrile to polyvinyl pyrrolidone is (3-6):1, and the mass concentration of polyacrylonitrile in the DMF solution is 10%-15%.

[0017] In step S2, the molar ratio of the HPAN membrane to the functionalized ZIF-7 solution is 1:5.

[0018] The concentration of the NaOH solution in step S2 is 0.2-1.2M; the concentration of the HCl solution is 0.2-1.2M.

[0019] The heating temperature in step S2 is 60-80°C.

[0020] The reverse diffusion reaction in step S3 is carried out at 80° C. for 24-48 hours.

[0021] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0022] A. The pore size of the zeolite imidazole framework selected by the present invention is The ZIF-7 is used as the composite membrane selection layer, and the pore size of ZIF-7 is made smaller by functional modification of organic ligands, so as to be placed in the ammonia gas as much as possible. and hydrogen The functionalized ZIF-7 selective layer carries acidic functional groups such as -OH, -COOH, and -SO3H, which have good affinity for NH3. The hydrogen bond and Lewis acid-base synergy between the functionalized ZIF-7 membrane and NH3 significantly enhance the separation performance of NH3. In addition, the pore size of the functionalized ZIF-7 membrane is between the gas pairs to be separated, which is beneficial to the transmission and separation of the gas in the membrane. According to the preparation method of the present invention, the polyacrylonitrile-based zeolite imidazole framework membrane is hydrolyzed and ammonia separation is performed by membrane separation, which can achieve continuous, rapid, and low-energy separation of ammonia.

[0023] B. The hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane obtained in the present invention has a highly efficient ammonia separation effect. When separating the residual gas of synthetic ammonia, the ammonia permeability is as high as 2561.7 GPU, and the ammonia / nitrogen and ammonia / hydrogen selectivities are as high as 630.1 and 147.8, respectively.

[0024] C. The present invention combines the advantages of the functionalized ZIF-7 selective layer to achieve the synergistic effect of size screening and acid-base interaction; and the uniform and continuous functionalized ZIF-7 film prepared by the reverse diffusion method has good self-support and certain mechanical strength.

[0025] D. The present method uses functionalized ZIF-7 as the selective layer. Its ultra-thin, porous structure can significantly shorten the gas transmission path, reduce gas permeation resistance, and increase the gas flux of the membrane. This method has low raw material costs and simple experimental operation. DETAILED DESCRIPTION

[0026] The present invention may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the present invention to those skilled in the art. All other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort shall fall within the scope of protection of the present invention.

[0027] Example 1:

[0028] This embodiment provides a method for preparing a uniform and continuous ZIF-7-SO3H(20) thin film by using a reverse diffusion method, comprising the following steps:

[0029] S1. Preparation of functionalized ZIF-7-SO3H(20) solution: dissolve Zn(NO3)2·6H2O (2 mmol) in 5 mL of deionized water, and then dissolve benzimidazole (4 mmol) and 2-phenylbenzimidazole-5-sulfonic acid (1 mmol) in 5 mL of deionized water to prepare a mixed ligand solution; then, mix with Zn(NO3)2·6H2O (2 mmol) solution, react in an oven at 80°C for 48 h to obtain a milky white suspension, and after centrifugation, the obtained product is vacuum-dried at 60°C for 12 h for activation to obtain functionalized ZIF-7-SO3H(20) powder, and dissolve the functionalized ZIF-7-SO3H(20) powder in 10 mL of DMF to form a functionalized ZIF-7 solution for standby use;

[0030] S2. Preparation of hydrolyzed polyacrylonitrile (HPAN) membrane: polyacrylonitrile and polyvinylpyrrolidone were dissolved in DMF solution at a mass ratio of 6:1, heated and stirred at 80°C to obtain a PAN casting solution, and then the PAN casting solution was poured onto a clean and smooth glass plate, flattened with a scraper, and then immediately immersed in deionized water to obtain a PAN membrane. Finally, the PAN membrane was immersed in a 0.6 M NaOH solution for 2 h, and then immersed in a 0.6 M HCl solution for 10 h to obtain an HPAN membrane, and the HPAN membrane was immersed in the functionalized ZIF-7 solution in step S1 at a molar ratio of 1:5.

[0031] Synthesis of S3, ZIF-7-SO3H(20) / PAN membrane: Using a self-made two-chamber reaction cell, the hydrolyzed polyacrylonitrile (HPAN) membrane soaked in the functionalized ZIF-7 solution in S2 was used as a support layer to separate the Zn(NO3)2·6H2O solution and the mixed ligand solution of 2-phenylbenzimidazole-5-sulfonic acid and benzimidazole. In an 80℃ oven, the metal salt solution and the mixed ligand solution diffuse in opposite directions. The reverse diffusion reaction conditions are 80℃ for 24h, and then react on the surface of the HPAN membrane support layer, finally forming a dense and defect-free functionalized ZIF-7-SO3H(20) / PAN membrane. In order to prevent the membrane from being suddenly cooled and causing cracks in the membrane, the oven should be cooled naturally to room temperature before the device is taken out and the ZIF-7-SO3H(20) / PAN membrane is removed. Finally, the prepared ZIF-7-SO3H(20) / PAN membrane is rinsed and soaked with DMF and stored in ethanol for future use.

[0032] A gas separation device was used to separate a mixture of ammonia, nitrogen, and hydrogen. The permeabilities of the three gases were tested and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the pure ammonia permeability of the ZIF-7-SO3H(20) / PAN membrane was 780.3 GPU, and the ammonia / nitrogen and ammonia / hydrogen selectivities were 440.5 and 85.7, respectively.

[0033] Example 2:

[0034] This embodiment provides a method for preparing a uniform and continuous ZIF-7-SO3H(50) thin film by using a reverse diffusion method, comprising the following steps:

[0035] S1. Preparation of functionalized ZIF-7-SO3H(50) solution: dissolve Zn(NO3)2·6H2O (1 mmol) in 10 mL of deionized water, and then dissolve benzimidazole (1 mmol) and 2-phenylbenzimidazole-5-sulfonic acid (1 mmol) in 10 mL of deionized water to prepare a mixed ligand solution; then, mix with Zn(NO3)2·6H2O (1 mmol) solution, react in an oven at 80°C for 48 h to obtain a milky white suspension, and after centrifugation, the obtained product is vacuum-dried at 60°C for 12 h for activation treatment to obtain functionalized ZIF-7-SO3H(50) powder, and dissolve the functionalized ZIF-7-SO3H(50) powder in 10 mL of DMF to form a functionalized ZIF-7 solution for standby use;

[0036] S2. Preparation of hydrolyzed polyacrylonitrile (HPAN) membrane: polyacrylonitrile and polyvinylpyrrolidone were dissolved in DMF solution at a mass ratio of 5:1, heated and stirred at 60°C to obtain a PAN casting solution, and then the PAN casting solution was poured onto a clean and smooth glass plate, scraped flat with a spatula, and then immediately immersed in deionized water to obtain a PAN membrane. Finally, the PAN membrane was immersed in a 0.2M NaOH solution for 2 hours, and then immersed in a 1.2M HCl solution for 12 hours to obtain an HPAN membrane, and the HPAN membrane was immersed in the functionalized ZIF-7 solution in step S1 at a molar ratio of 1:5.

[0037] Synthesis of S3 and ZIF-7-SO3H(50) / PAN membrane: A self-made two-chamber reaction cell was used to separate the Zn(NO3)2·6H2O solution and the mixed ligand solution of 2-phenylbenzimidazole-5-sulfonic acid and benzimidazole in S2 by soaking the hydrolyzed polyacrylonitrile (HPAN) membrane soaked in the functionalized ZIF-7 solution as the support layer. During the reaction in an 80℃ oven, the metal salt solution and the mixed ligand solution diffused in opposite directions. The reverse diffusion reaction was carried out at 80℃ for 48h, and then reacted on the surface of the HPAN membrane support layer, finally forming a dense and defect-free functionalized ZIF-7-SO3H(50) / PAN membrane. In order to prevent the membrane from being suddenly cooled and cracked, the oven should be cooled naturally to room temperature before the device is removed and the ZIF-7-SO3H(50) / PAN membrane is removed. Finally, the prepared ZIF-7-SO3H(50) / PAN membrane was rinsed and soaked with DMF and stored in ethanol for future use.

[0038] A gas separation device was used to separate a mixture of ammonia, nitrogen, and hydrogen. The permeabilities of the three gases were tested and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the pure ammonia permeability of the ZIF-7-SO3H(50) / PAN membrane was 843.7 GPU, and the ammonia / nitrogen and ammonia / hydrogen selectivities were 519.5 and 104.3, respectively.

[0039] Example 3:

[0040] This embodiment provides a method for preparing a uniform and continuous ZIF-7-SO3H(80) thin film by using a reverse diffusion method, comprising the following steps:

[0041] S1. Preparation of functionalized ZIF-7-SO3H(80) solution: Zn(NO3)2·6H2O (2 mmol) was dissolved in 10 mL of deionized water, and then benzimidazole (1 mmol) and 2-phenylbenzimidazole-5-sulfonic acid (4 mmol) were dissolved in 10 mL of deionized water to prepare a mixed ligand solution; then, the solution was mixed with Zn(NO3)2·6H2O (2 mmol) solution and reacted in an oven at 100°C for 24 h to obtain a milky white suspension. After centrifugation, the obtained product was vacuum dried at 60°C for 12 h and activated to obtain functionalized ZIF-7-SO3H(80) powder. The functionalized ZIF-7-SO3H(80) powder was dissolved in 10 mL of DMF to form a functionalized ZIF-7 solution for standby use;

[0042] S2. Preparation of hydrolyzed polyacrylonitrile (HPAN) membrane: polyacrylonitrile and polyvinylpyrrolidone were dissolved in DMF solution in a mass ratio of 3:1, heated and stirred at 70°C to obtain a PAN casting solution, and then the PAN casting solution was poured onto a clean and smooth glass plate, scraped flat with a spatula, and then immediately immersed in deionized water to obtain a PAN membrane. Finally, the PAN membrane was immersed in a 1.2M NaOH solution for 1 hour, and then immersed in a 0.2M HCl solution for 15 hours to obtain an HPAN membrane. The HPAN membrane was then immersed in the functionalized ZIF-7 solution of step S1 at a molar ratio of 1:5.

[0043] Synthesis of S3 and ZIF-7-SO3H(80) / PAN membrane: A self-made two-chamber reaction cell was used to separate the Zn(NO3)2·6H2O solution and the mixed ligand solution of 2-phenylbenzimidazole-5-sulfonic acid and benzimidazole in S2 by soaking the hydrolyzed polyacrylonitrile (HPAN) membrane soaked in the functionalized ZIF-7 solution as the support layer. During the reaction in an 80℃ oven, the metal salt solution and the mixed ligand solution diffused in opposite directions. The reverse diffusion reaction conditions were 80℃ for 48h, and then the reaction occurred on the surface of the HPAN membrane support layer, eventually forming a dense and defect-free functionalized ZIF-7-SO3H(80) / PAN membrane. In order to prevent the membrane from being suddenly cooled and cracked, the oven should be cooled naturally to room temperature before the device is removed and the ZIF-7-SO3H(80) / PAN membrane is removed. Finally, the prepared ZIF-7-SO3H(80) / PAN membrane was rinsed and soaked with DMF and stored in ethanol for future use.

[0044] A gas separation device was used to separate a mixture of ammonia, nitrogen, and hydrogen. The permeabilities of the three gases were tested, and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the pure ammonia permeability of the ZIF-7-SO3H(80) / PAN membrane was as high as 2561.7 GPU, and the ammonia / nitrogen and ammonia / hydrogen selectivities were as high as 630.1 and 147.8, respectively.

[0045] Comparative Example 1:

[0046] 7.425 g of polyacrylonitrile and 1.345 g of polyvinylpyrrolidone were dissolved in a DMF solution and heated with stirring (stirring at 50-70°C for 20-24 h) to obtain a PAN casting solution. The PAN casting solution was poured onto a clean, smooth glass plate, repeatedly scraped flat with a spatula, and then immediately immersed in deionized water. The PAN membrane was then immersed in a NaOH solution for 2 h, and then immersed in an HCl solution for 10 h to obtain an HPAN membrane.

[0047] A gas separation device was used to separate a mixture of ammonia, nitrogen, and hydrogen. The permeabilities of the three gases were measured, and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the HPAN membrane had an ammonia permeability of 600.2 GPU, and ammonia / nitrogen and ammonia / hydrogen selectivities of 434.3 and 50.5, respectively.

[0048] Combining Examples 1-3 and Comparative Example 1, it can be seen that the addition of functionalized ZIF-7-SO3H significantly improves the ammonia separation performance of the hydrolyzed polypropylene-based zeolite imidazole framework membrane. At the same time, with the increase of the -SO3H content, the synergistic effect of size screening and acid-base interaction is achieved, which significantly enhances the separation performance of NH3, is more conducive to the transmission and separation of ammonia in the membrane, and the ammonia permeability and ammonia selectivity of the hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane are simultaneously improved.

[0049] Example 4:

[0050] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared using a method similar to that of Example 3, except that the mass concentration of the casting solution was changed to 15%, and similar results were obtained.

[0051] Example 5:

[0052] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared using a method similar to that of Example 3, except that the mass concentration of the casting solution was changed to 10%, and similar results were obtained.

[0053] Example 6:

[0054] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared by a method similar to that in Example 3, except that the heating temperature of the casting solution was changed to 60° C. and the heating time was changed to 12 h, and similar results were obtained.

[0055] Example 7:

[0056] The hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared by a method similar to that in Example 3. When other parameters remained unchanged, zinc nitrate hexahydrate (Zn(NO3)2·6H2O), benzimidazole (HbIm), and DMF were added at a molar ratio of Zn(NO3)2·6H2O. 2+ :HbIm:DMF=3:2:10 mixture, similar results were obtained.

[0057] Example 8:

[0058] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared by a method similar to that of Example 3. With other parameters unchanged, the hydrothermal reaction conditions were changed to 100° C. for 12 h, and similar results were obtained.

[0059] Example 9:

[0060] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared by a method similar to that in Example 3. With other parameters unchanged, the hydrothermal reaction conditions were changed to 100° C. for 24 h, and similar results were obtained.

[0061] Example 10:

[0062] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared by a method similar to that of Example 3. With other parameters unchanged, the hydrothermal reaction conditions were changed to 120° C. for 24 h, and similar results were obtained.

[0063] Example 11:

[0064] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared using a method similar to that of Example 3, except that the organic ligand in ZIF-7 was changed to benzimidazole + 2-aminoimidazole, and similar results were obtained.

[0065] Example 12:

[0066] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared using a method similar to Example 3, except that the organic ligand in ZIF-7 was changed to benzimidazole + 2-methylimidazole-4,5-dicarboxylic acid, and similar results were obtained.

[0067] Example 13:

[0068] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared using a method similar to Example 3, except that the organic ligand in ZIF-7 was changed to benzimidazole + 5-chlorobenzimidazole-2-thiol, and similar results were obtained.

[0069] Example 14:

[0070] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared using a method similar to Example 3, except that the organic ligand in ZIF-7 was changed to benzimidazole + 2-bromo-6-nitrobenzimidazole, and similar results were obtained.

[0071] In summary, the present invention uses hydrolyzed polyacrylonitrile-based zeolite imidazole framework material as the selective layer and prepares functionalized ZIF-7 membrane by reverse diffusion method. ZIF-7, through the functional modification of organic ligands, not only makes the pore size of ZIF-7 and hydrogen The introduction of acidic functional groups (-COOH, -SO3H) facilitates the adsorption of ammonia. The hydrogen bonding and Lewis acid-base synergy between the functionalized ZIF-7 membrane and NH3 significantly enhances the separation performance of NH3. In addition, the pore size of the functionalized ZIF-7 membrane is between the gas pairs to be separated, which is beneficial for the transmission and separation of gases within the membrane. According to the preparation method of the present invention, the polyacrylonitrile-based zeolite imidazole framework membrane is hydrolyzed and ammonia separation is performed by membrane separation, which can achieve continuous, rapid, and low-energy separation of ammonia.

[0072] The hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane obtained by the present invention has a high-efficiency ammonia separation effect. When separating the residual gas of synthetic ammonia, the ammonia permeability can reach up to 2561.7 GPU, and the ammonia / nitrogen and ammonia / hydrogen selectivities are as high as 630.1 and 147.8, respectively.

[0073] The raw materials for preparing the hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane of the present invention are either commercially available or can be synthesized at low cost, thereby significantly reducing the membrane production cost and facilitating its large-scale application.

[0074] Any matters not described in the present invention are applicable to the prior art.

[0075] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane for ammonia separation, characterized in that: The steps include: S1. Preparation of functionalized ZIF-7 solution: A metal compound, an organic ligand, and a solvent are mixed in a specific molar ratio and reacted at a specific temperature to form a functionalized ZIF-7 material. The resulting product is centrifuged and then dried in a vacuum at 60°C for 12 hours for activation. The functionalized ZIF-7 powder is then dissolved in DMF to form a functionalized ZIF-7 solution for later use. S2. Preparation of hydrolyzed polyacrylonitrile membrane: polyacrylonitrile and polyvinylpyrrolidone were dissolved in a DMF solution, heated and stirred to obtain a PAN casting solution, and then the PAN casting solution was poured onto a clean and smooth glass plate, scraped flat with a spatula, and then immediately immersed in deionized water to obtain a PAN membrane. Finally, the PAN membrane was immersed in a NaOH solution for 1-2 hours, and then immersed in an HCl solution for 10-15 hours to obtain an HPAN membrane, and the HPAN membrane was immersed in the functionalized ZIF-7 solution of step S1; S3. Preparation of functionalized ZIF-7 / PAN membrane: Using a homemade two-chamber reaction cell, the HPAN membrane soaked in the functionalized ZIF-7 solution in step S2 is used as a support layer to separate the Zn(NO3)2·6H2O solution and the imidazole ligand and benzimidazole ligand solutions functionalized with -NH2, -COOH, -SO3H, -Cl or -Br. During the reaction, the metal compound solution and the organic ligand solution will diffuse in opposite directions and react on the surface of the HPAN membrane support layer, eventually forming a dense and defect-free functionalized ZIF-7 / PAN membrane, namely, a hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane.

2. The preparation method according to claim 1, characterized in that In step S1, the metal compound is zinc nitrate hexahydrate, the organic ligand is a benzimidazole-based mixed ligand, and the solvent is deionized water; the molar ratio of zinc nitrate hexahydrate, benzimidazole, solvent, and DMF is 1-3:1-4:10-20:

10.

3. The preparation method according to claim 2, wherein: The organic ligand is a mixture of benzimidazole and a functionalized imidazole ligand in a molar ratio of 1:4-4:1, wherein the functionalized imidazole ligand is one of 2-aminoimidazole, 2-methylimidazole-4,5-dicarboxylic acid, 2-phenylbenzimidazole-5-sulfonic acid, 5-chlorobenzimidazole-2-thiol and 2-bromo-6-nitrobenzimidazole.

4. The preparation method according to claim 2, wherein: In step S1, the reaction temperature is 80-120° C., and the reaction time is 12-48 hours.

5. The preparation method according to claim 1, wherein: In step S2, the mass ratio of polyacrylonitrile to polyvinyl pyrrolidone is 3-6:1, the mass concentration of polyacrylonitrile in the DMF solution is 10%-15%; and the molar ratio of the HPAN membrane to the functionalized ZIF-7 solution is 1:

5.

6. The preparation method according to claim 1, wherein: The concentration of the NaOH solution in step S2 is 0.2-1.2M; the concentration of the HCl solution is 0.2-1.2M.

7. The preparation method according to claim 1, wherein: The heating temperature in step S2 is 60-80°C.

8. The preparation method according to claim 1, wherein: The reverse diffusion reaction in step S3 is carried out at 80° C. for 24-48 hours.

9. A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane for ammonia separation prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The invention comprises a porous supporting layer and a zeolite imidazole framework membrane deposited on the porous supporting layer by a reverse diffusion method; the porous supporting layer is a hydrolyzed polyacrylonitrile-based membrane; and the zeolite imidazole framework membrane is a functionalized ZIF-7 membrane.

10. The hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane for ammonia separation according to claim 9, characterized in that: The pore size of the porous supporting layer is 20 nm to 50 nm.