Hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane for ammonia separation and preparation method of hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane

Abstract

The preparation method comprises the following steps: S1, mixing and reacting a metal compound, an organic ligand and a solvent according to a specific ratio to form a ZIF-7 material, and dissolving the ZIF-7 material in DMF (Dimethyl Formamide) to form a ZIF-7 solution; s2, polyacrylonitrile and polyvinylpyrrolidone are dissolved in a DMF solution to obtain a PAN membrane casting solution, then the PAN membrane casting solution is poured on a clean and smooth glass plate, the glass plate is soaked in deionized water to obtain a PAN membrane, the PAN membrane is sequentially soaked in NaOH and HCl solutions to prepare an HPAN membrane, and the HPAN membrane is soaked in a ZIF-7 solution; s3, the HPAN membrane serves as a supporting layer to divide the metal compound solution and the organic ligand solution, in the reaction process, the metal compound solution and the organic ligand solution are diffused in the opposite directions and react on the surface of the supporting layer of the HPAN membrane, and finally the needed framework membrane is formed. The obtained frame membrane has an efficient ammonia separation effect, and when the frame membrane is used for separating synthesis ammonia residual gas, the ammonia permeability reaches up to 2561.7 GPU, and the ammonia / nitrogen selectivity and the ammonia / hydrogen selectivity respectively reach up to 630.1 and 147.8.

Description

Technical Field

[0001] The 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 an important role in the chemical industry and has important applications in the fields of agricultural fertilizers, pharmaceuticals, organic compounds and polymer material synthesis. So far, most NH3 is still produced through the traditional Haber-Bosch process, which produces NH3 through the catalytic reaction of nitrogen (N2) and hydrogen (H2) under high temperature and high pressure conditions. It must be noted that the NH3 synthesis conversion rate of the Haber-Bosch process is low, only 10-20%, and is generally collected by physical cooling and liquefaction. However, about 3% of NH3 will still remain in the circulating gas, reducing the synthesis efficiency and affecting production capacity. Therefore, it is very important to recover low-concentration NH3.

[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. At present, the membrane materials widely used in commercial applications are traditional polymer materials, but there are problems such as small free volume in 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 the performance. Compared with the discontinuous mixed matrix membrane prepared by blending, the preparation of dense and defect-free metal organic framework membranes by interfacial polymerization and reverse diffusion methods can give full play to the advantages of pore structure in gas separation. Summary of the invention

[0004] Aiming at the problems of low ammonia selectivity and low ammonia permeation flux of ammonia separation membranes in the prior art, the present invention provides a hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane for ammonia separation and a preparation method thereof, wherein the functionalized ZIF-7 membrane has the characteristics of high flux, good separation performance and high stability. The functionalized zeolite imidazole framework (ZIF-7-NH2, ZIF-7-COOH, ZIF-7-SO3H, ZIF-7-Cl, ZIF-7-Br) is used as a selective layer to produce an ultra-thin, defect-free, pure-phase functionalized ZIF-7 membrane on a hydrolyzed polyacrylonitrile (HPAN) support layer.

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

[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 (HPAN) membrane; and the zeolite imidazole framework membrane is a functionalized ZIF-7 membrane.

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

[0009] A method for preparing a hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane for ammonia separation comprises the following steps:

[0010] S1. Preparation of functionalized ZIF-7 solution: metal compound, organic ligand and solvent are mixed in a specific molar ratio, reacted at a specific temperature to form a functionalized ZIF-7 material, and centrifuged, and the obtained product is vacuum dried at 60° C. for 12 h for activation treatment, and then the functionalized ZIF-7 powder is dissolved in DMF to form a functionalized ZIF-7 solution for standby use;

[0011] S2. Preparation of hydrolyzed polyacrylonitrile (HPAN) membrane: dissolving polyacrylonitrile and polyvinyl pyrrolidone 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 it with a scraper, and then immediately immersing it in deionized water to obtain a PAN membrane, and finally immersing the PAN membrane in a NaOH solution for 1-2 hours, and then immersing it in a HCl solution for 10-15 hours to obtain an HPAN membrane, and then immersing the HPAN membrane in the functionalized ZIF-7 solution in step S1;

[0012] 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 (HbIm) ligand solution functionalized with -NH2, -COOH, -SO3H, -Cl, -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, i.e., a hydrolyzed polyacrylonitrile-based zeolite imidazole framework 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 functionalized ZIF-7 / PAN membrane is removed. Finally, the obtained functionalized ZIF-7 / PAN membrane is rinsed and soaked with DMF and stored in ethanol for standby use.

[0013] In step S1, the metal compound is zinc nitrate hexahydrate (Zn(NO3)2·6H2O), the organic ligand is a benzimidazole 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 the 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 in the present invention is The ZIF-7 was used as the composite membrane selection layer. The pore size of ZIF-7 was reduced by functionalization of organic ligands, and the pore size of ZIF-7 was reduced 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 bonding 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 by 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 selection 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 method of the present invention uses functionalized ZIF-7 as the selective layer, and its ultra-thin and porous structure can greatly shorten the gas transmission path, reduce the gas permeation resistance, and increase the gas flux of the membrane. The method has low raw material cost and simple experimental operation. DETAILED DESCRIPTION

[0026] The present invention can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. Instead, these embodiments are provided so that the present disclosure will be thorough and complete and will fully convey the concept of the present invention to those skilled in the art. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0027] Embodiment 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 treatment 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 polyvinyl pyrrolidone were dissolved in DMF solution at a mass ratio of 6:1, heated and stirred at 80°C to obtain 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 0.6M NaOH solution for 2 hours, and then immersed in a 0.6M HCl solution for 10 hours to obtain an HPAN membrane, and the HPAN membrane was immersed in the functionalized ZIF-7 solution of step S1 at a molar ratio of 1:5.

[0031] S3, Synthesis of 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 oven at 80°C, the metal salt solution and the mixed ligand solution diffused in opposite directions. The conditions for the reverse diffusion reaction were 80°C for 24 hours, and then the reaction occurred on the surface of the HPAN membrane support layer, and finally a dense and defect-free functionalized ZIF-7-SO3H(20) / PAN membrane was formed. 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 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 later use.

[0032] A gas separation device was used to separate the mixed gas containing ammonia, nitrogen and hydrogen, and 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 780.3GPU, and the ammonia / nitrogen and ammonia / hydrogen selectivities were 440.5 and 85.7, respectively.

[0033] Embodiment 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: dissolve polyacrylonitrile and polyvinyl pyrrolidone in DMF solution at a mass ratio of 5:1, heat and stir at 60°C to obtain PAN casting solution, then pour the PAN casting solution onto a clean and smooth glass plate, scrape it flat with a scraper, and then immediately immerse it in deionized water to obtain a PAN membrane, finally immerse the PAN membrane in a 0.2M NaOH solution for 2h, and then immerse it in a 1.2M HCl solution for 12h to obtain an HPAN membrane, and then immerse the HPAN membrane in the functionalized ZIF-7 solution of step S1 at a molar ratio of 1:5.

[0037] S3, Synthesis of ZIF-7-SO3H(50) / 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. During the reaction in an oven at 80℃, the metal salt solution and the mixed ligand solution diffused in opposite directions. The conditions for the reverse diffusion reaction were 48h at 80℃, and then the reaction occurred on the surface of the HPAN membrane support layer, and finally a dense and defect-free functionalized ZIF-7-SO3H(50) / PAN membrane was formed. 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 taken out and the ZIF-7-SO3H(50) / PAN membrane is removed. Finally, the prepared ZIF-7-SO3H(50) / PAN membrane is rinsed and soaked with DMF and stored in ethanol for later use.

[0038] A gas separation device was used to separate a mixed gas containing ammonia, nitrogen and hydrogen, and 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] Embodiment 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: Dissolve Zn(NO3)2·6H2O (2 mmol) in 10 mL of deionized water, and then dissolve benzimidazole (1 mmol) and 2-phenylbenzimidazole-5-sulfonic acid (4 mmol) in 10 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 100°C for 24 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(80) powder, and dissolve the functionalized ZIF-7-SO3H(80) powder 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 polyvinyl pyrrolidone were dissolved in DMF solution at a mass ratio of 3:1, heated and stirred at 70°C to obtain 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 1.2M NaOH solution for 1 hour, and then immersed in a 0.2M HCl solution for 15 hours to obtain an HPAN membrane, and the HPAN membrane was immersed in the functionalized ZIF-7 solution of step S1 at a molar ratio of 1:5.

[0043] S3, Synthesis of ZIF-7-SO3H(80) / 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. During the reaction in an oven at 80℃, the metal salt solution and the mixed ligand solution diffused in opposite directions. The conditions for the reverse diffusion reaction were 48h at 80℃, and then the reaction occurred on the surface of the HPAN membrane support layer, and finally a dense and defect-free functionalized ZIF-7-SO3H(80) / PAN membrane was formed. 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 taken out and the ZIF-7-SO3H(80) / PAN membrane is removed. Finally, the prepared ZIF-7-SO3H(80) / PAN membrane is rinsed and soaked with DMF and stored in ethanol for later use.

[0044] A gas separation device was used to separate the mixed gas containing ammonia, nitrogen and hydrogen, and 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 2561.7GPU, 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 polyvinyl pyrrolidone were dissolved in a DMF solution, heated and stirred (stirred at 50-70°C for 20-24 h) to obtain a PAN casting solution; the PAN casting solution was poured onto a clean and smooth glass plate, repeatedly scraped with a scraper, and then immediately immersed in deionized water, and then the PAN membrane was immersed in a NaOH solution for 2 h, and then immersed in a HCl solution for 10 h to obtain an HPAN membrane.

[0047] A gas separation device was used to separate a mixed gas containing ammonia, nitrogen and hydrogen, and the permeabilities of the three gases were tested and the ammonia / nitrogen and ammonia / hydrogen selectivities were calculated. The results showed that the ammonia permeability of the HPAN membrane was 600.2 GPU, and the ammonia / nitrogen and ammonia / hydrogen selectivities were 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] Embodiment 4:

[0050] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared by 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] Embodiment 5:

[0052] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared by 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] Embodiment 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] Embodiment 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] Embodiment 8:

[0058] 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 12 h, and similar results were obtained.

[0059] Embodiment 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] Embodiment 10:

[0062] 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 120° C. for 24 h, and similar results were obtained.

[0063] Embodiment 11:

[0064] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared by 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] Embodiment 12:

[0066] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared by a method similar to that of 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] Embodiment 13:

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

[0069] Embodiment 14:

[0070] A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane was prepared by a method similar to that of 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 the functionalized ZIF-7 membrane by the reverse diffusion method. ZIF-7, through the functionalization of organic ligands, not only makes the pore size of ZIF-7 and hydrogen The functionalized ZIF-7 membrane has a pore size between the gas pairs to be separated, which is beneficial to the transmission and separation of gases 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.

[0072] The hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane obtained by the present invention has a highly efficient 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 greatly reducing the cost of membrane preparation and facilitating its large-scale application.

[0074] Anything not described in the present invention is applicable to the prior art.

[0075] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. However, the obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane for ammonia separation, 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.

2. The hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane for ammonia separation according to claim 1, characterized in that: The porous support layer is a hydrolyzed polyacrylonitrile (HPAN) membrane; and the zeolite imidazole framework membrane is a functionalized ZIF-7 membrane.

3. The hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane for ammonia separation according to claim 2, characterized in that: The pore size of the porous support layer is 20nm-50nm.

4. 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: metal compound, organic ligand and solvent are mixed in a specific molar ratio, reacted at a specific temperature to form a functionalized ZIF-7 material, and centrifuged, and the obtained product is vacuum dried at 60° C. for 12 h for activation treatment, and then the functionalized ZIF-7 powder is dissolved in DMF to form a functionalized ZIF-7 solution for standby use; S2. Preparation of hydrolyzed polyacrylonitrile (HPAN) membrane: dissolve polyacrylonitrile and polyvinyl pyrrolidone in DMF solution, heat and stir to obtain PAN casting solution, then pour the PAN casting solution onto a clean and smooth glass plate, scrape it flat with a scraper, and then immediately immerse it in deionized water to obtain a PAN membrane, finally immerse the PAN membrane in NaOH solution for 1-2 hours, and then immerse it in HCl solution for 10-15 hours to obtain an HPAN membrane, and immerse the HPAN membrane in the functionalized ZIF-7 solution in 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 (HbIm) ligand solution 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, i.e., a hydrolyzed polyacrylonitrile-based zeolite imidazole framework membrane.

5. The preparation method according to claim 4, characterized in that: In step S1, the metal compound is zinc nitrate hexahydrate (Zn(NO3)2·6H2O), the organic ligand is a benzimidazole 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.

6. The preparation method according to claim 5, characterized in that: 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.

7. The preparation method according to claim 5, characterized in that: In the step S1, the reaction temperature is 80-120° C. and the reaction time is 12-48 hours.

8. The preparation method according to claim 4, characterized in that: 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%; the molar ratio of the HPAN membrane to the functionalized ZIF-7 solution is 1:

5.

9. The preparation method according to claim 4, characterized in that: 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.

10. The preparation method according to claim 4, characterized in that: The heating temperature in step S2 is 60-80°C.

11. The preparation method according to claim 4, characterized in that: The reverse diffusion reaction in step S3 is carried out at 80° C. for 24-48 hours.