Large area gas separation membrane and method of making same

Abstract

The application discloses a large-area gas separation membrane and a preparation method thereof, and belongs to the technical field of membrane separation. The technical scheme is characterized by comprising the following preparation steps: S1, dissolving zinc nitrate in a solvent, then adding sodium hydroxide alcohol solution, and reacting under ultrasonic conditions to obtain a zinc hydroxide solution, wherein the molar ratio of the zinc nitrate to the sodium hydroxide is 1:2; S2, then adding a solvent in which terephthalic acid is dissolved, performing ultrasonic reaction for 1-2 hours, then performing suction filtration on the reaction solution to separate white precipitates, washing the white precipitates with ethanol for multiple times, and then vacuum drying to obtain a filler; S3, adding the filler obtained in the step S2 into a solvent, uniformly dispersing the filler, then adding polyimide, uniformly stirring the polyimide to obtain a dispersion liquid, pouring the dispersion liquid into a watch glass, heating at 50-60 DEG C, evaporating the solvent to obtain a thin film, and then vacuum drying the thin film to obtain a gas separation membrane, wherein the addition amount of the filler is 3-6% of the mass of the polyimide, so that the efficiency of carbon dioxide separation is improved.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a large-area gas separation membrane and its preparation method. Background Technology

[0002] Gas separation membrane technology has been widely used in air separation and purification, carbon dioxide recovery from combustion exhaust gas, and natural gas purification due to its outstanding advantages such as low energy consumption, convenient operation, and no environmental pollution. As the core of gas separation membrane technology, the performance of gas separation membrane material directly affects the preparation, separation performance, and long-term performance of gas separation membrane.

[0003] Currently, commonly used gas separation membranes are classified into three main categories: organic membranes, inorganic membranes, and mixed matrix membranes. Mixed matrix membranes are composed of dispersed fillers and continuous polymer matrix blends. Compared with traditional organic and inorganic membranes, mixed matrix membranes combine the advantages of organic and inorganic membrane materials. Common metal-organic framework fillers cannot simultaneously meet the conditions of large size and ultrathinness, making it difficult to construct an effective transport path for carbon dioxide inside the gas separation membrane material, resulting in poor carbon capture performance. Summary of the Invention

[0004] To improve the efficiency of carbon dioxide separation, this invention provides a large-area gas separation membrane and its preparation method.

[0005] The objective of this invention is to provide a method for preparing a large-area gas separation membrane, using the following technical solution:

[0006] A method for preparing a large-area gas separation membrane includes the following preparation steps:

[0007] S1. Dissolve zinc nitrate in a solvent, then add sodium hydroxide alcohol solution, and react under ultrasonic conditions to obtain zinc hydroxide solution, wherein the molar ratio of zinc nitrate to sodium hydroxide is 1:2;

[0008] S2. Then, a solvent containing terephthalic acid is added and the mixture is subjected to ultrasonic reaction for 1-2 hours. The reaction solution is then filtered to separate the white precipitate, which is washed multiple times with ethanol and then dried under vacuum to obtain the filler.

[0009] S3. Add the filler obtained in step S2 to the solvent and disperse it evenly. Then add polyimide and stir evenly to obtain a dispersion. Pour it onto a watch glass and heat it at 50-60°C to evaporate the solvent and obtain a film. Then vacuum dry the film to obtain a gas separation membrane. The amount of filler added is 3-6% of the mass of polyimide.

[0010] By adopting the above technical solution, the addition of filler in this application increases the free volume within the gas separation membrane and provides additional gas diffusion paths, thereby increasing the carbon dioxide permeability coefficient. When the amount of filler added is 3-6% of the mass of polyimide, it not only ensures the uniform dispersion of the filler within the membrane and guarantees the mass transfer channels for carbon dioxide within the membrane, thus improving the separation performance of the gas separation membrane for carbon dioxide and nitrogen, but when the amount of filler added exceeds 6% of the mass of polyimide, the filler is prone to agglomeration within the membrane and enhances the crystallinity of the membrane, thereby reducing some mass transfer channels in the gas separation membrane that were originally available for gas molecules to pass through, thus reducing the gas separation performance of the gas separation membrane.

[0011] Preferably, the mass ratio of terephthalic acid to sodium hydroxide is (60-70):1.

[0012] Preferably, in step S2, the filler is added to ethanol containing 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, and the mixture is stirred and reacted at 55-65°C for 20-24 hours. The product is then centrifuged, washed, and vacuum dried to obtain the nanocomposite filler.

[0013] Preferably, the mass ratio of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate to the filler is 1:(1-2).

[0014] Preferably, the concentration of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate in ethanol is 0.02-0.04 g / ml.

[0015] By adopting the above technical solution, the nanocomposite filler obtained after modification of the filler with 1-ethyl-3-methylimidazolium trifluoromethanesulfonate increases the interaction between the inorganic filler and the organic polymer matrix, thereby improving the affinity between the two. This increases the average distance between polymer chain segments in the nanocomposite filler, which is conducive to the passage of carbon dioxide gas. Furthermore, the trifluoromethyl, sulfonic acid, and imidazole groups in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate have a strong affinity for carbon dioxide, increasing the carbon dioxide gas transfer sites in the gas separation membrane. The affinity of the trifluoromethyl, sulfonic acid, and imidazole groups for carbon dioxide can promote the dissolution of carbon dioxide in the gas separation membrane, thereby strengthening the dissolution-diffusion mechanism of the gas separation membrane. This achieves an increase in carbon dioxide permeability while maintaining high selectivity.

[0016] Preferably, the solvent in both steps S1 and S2 is N,N-dimethylformamide.

[0017] Preferably, the vacuum drying conditions for the thin film in step S3 are drying at 140-150°C for 30-32 hours.

[0018] Preferably, the polyimide in step S3 is obtained by the following method:

[0019] S1. Add 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane to N,N-dimethylformamide and stir to dissolve to form a solution with a concentration of 0.3-0.5 g / ml. Then add 0.4-0.5 parts by weight of pyridine and 0.5-0.7 parts by weight of trimethylchlorosilane and react for 15-20 minutes.

[0020] S2. Add 1.2-1.5 parts by weight of hexafluorodianhydride and 2-4 parts by weight of N,N-dimethylformamide under ice-water bath conditions and react for 15-20 hours.

[0021] S3. Add 2-2.5 parts by weight of acetic anhydride and 1.5-2.2 parts by weight of pyridine to the solution obtained in step S2. Stir the reaction at room temperature for 6-8 hours, wash and filter with methanol, and then dry under vacuum to obtain polyimide.

[0022] The second objective of this invention is to provide a gas separation membrane obtained by the preparation method of the large-area gas separation membrane described above.

[0023] In summary, the present invention has the following beneficial effects:

[0024] The addition of filler in this application increases the free volume within the gas separation membrane and provides additional gas diffusion paths, thereby improving the carbon dioxide permeability coefficient. In particular, the nanocomposite filler obtained by modifying the filler with 1-ethyl-3-methylimidazolium trifluoromethanesulfonate increases the interaction between the inorganic filler and the organic polymer matrix, thereby improving the affinity between the two. This increases the average distance between polymer chain segments in the nanocomposite filler, which facilitates the passage of carbon dioxide gas. Furthermore, the trifluoromethyl, sulfonic acid, and imidazole groups in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate have strong interactions with carbon dioxide, increasing the carbon dioxide gas transfer sites in the gas separation membrane. Therefore, the nanocomposite filler enhances the rapid transfer of carbon dioxide gas in the gas separation membrane.

[0025] The polyimide material obtained by the preparation method of this application, when used in combination with composite nanomaterials, greatly improves the carbon dioxide gas permeability. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the embodiments.

[0027] The raw materials used in the preparation examples, embodiments, and comparative examples of this application are all commercially available.

[0028] Preparation Example 1

[0029] A polyimide, comprising the following preparation steps:

[0030] S1. Add 9g of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane to 30ml of N,N-dimethylformamide and stir to dissolve to form a solution with a concentration of 0.3g / ml. Then add 4g of pyridine and 5g of trimethylchlorosilane and react for 15 minutes.

[0031] S2. Add 12g of hexafluorodianhydride and 20g of N,N-dimethylformamide under ice-water bath conditions and react for 15h.

[0032] S3. Add 20g of acetic anhydride and 15g of pyridine to the solution obtained in step S2, stir and react at room temperature for 6 hours, wash and filter with methanol, and then dry under vacuum to obtain polyimide.

[0033] Preparation Example 2

[0034] A polyimide, comprising the following preparation steps:

[0035] S1. Add 16g of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane to 40ml of N,N-dimethylformamide and stir to dissolve to form a solution with a concentration of 0.4g / ml. Then add 4.5g of pyridine and 6g of trimethylchlorosilane and react for 20 minutes.

[0036] S2. Add 13g of hexafluorodianhydride and 30g of N,N-dimethylformamide under ice-water bath conditions and react for 18h.

[0037] S3. Add 22g of acetic anhydride and 18g of pyridine to the solution obtained in step S2, stir and react at room temperature for 7 hours, wash and filter with methanol, and then dry under vacuum to obtain polyimide.

[0038] Preparation Example 3

[0039] A polyimide, comprising the following preparation steps:

[0040] S1. Add 25g of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane to 50ml of N,N-dimethylformamide and stir to dissolve to form a solution with a concentration of 0.5g / ml. Then add 5g of pyridine and 7g of trimethylchlorosilane and react for 20 minutes.

[0041] S2. Add 15g of hexafluorodianhydride and 4g of N,N-dimethylformamide under ice-water bath conditions and react for 20h.

[0042] S3. Add 25g of acetic anhydride and 22g of pyridine to the solution obtained in step S2, stir the reaction at room temperature for 8 hours, wash and filter with methanol, and then dry under vacuum to obtain polyimide.

[0043] Example 1

[0044] A method for preparing a large-area gas separation membrane includes the following preparation steps:

[0045] S1. Dissolve 3.86g of zinc nitrate hexahydrate in 6ml of N,N-dimethylformamide solution, then add sodium hydroxide alcohol solution (dissolve 1.04g of sodium hydroxide in 3ml of methanol), and react under ultrasonic conditions to obtain zinc hydroxide solution. The molar ratio of zinc nitrate to sodium hydroxide is 1:2.

[0046] S2. Then, N,N-dimethylformamide solution containing terephthalic acid was added (62.4 g of terephthalic acid was dissolved in 1.9 L of N,N-dimethylformamide) and the mixture was sonicated for 1 hour. The reaction solution was then filtered to separate the white precipitate, washed repeatedly with ethanol, and then vacuum dried to obtain the filler. The mass ratio of terephthalic acid to sodium hydroxide was 60:1.

[0047] S3. Take 0.15g of the filler obtained in step S2 and add it to 50ml of N,N-dimethylformamide and disperse it evenly. Then add 5g of the polyimide obtained in Preparation Example 1 and stir evenly to obtain a dispersion. Pour it onto a watch glass and heat it at 50°C to evaporate the solvent and obtain a film. Then vacuum dry the film at 140°C for 30 hours to obtain a gas separation membrane. The amount of filler added is 3% of the mass of polyimide.

[0048] Example 2

[0049] A method for preparing a large-area gas separation membrane includes the following preparation steps:

[0050] S1. Dissolve 3.86g of zinc nitrate hexahydrate in 6ml of N,N-dimethylformamide solution, then add sodium hydroxide alcohol solution (dissolve 1.04g of sodium hydroxide in 3ml of methanol), and react under ultrasonic conditions to obtain zinc hydroxide solution. The molar ratio of zinc nitrate to sodium hydroxide is 1:2.

[0051] S2. Then, N,N-dimethylformamide solution containing terephthalic acid was added (67.6 g of terephthalic acid was dissolved in 1.95 L of N,N-dimethylformamide) and the mixture was sonicated for 1 hour. The reaction solution was then filtered to separate the white precipitate, washed repeatedly with ethanol, and then vacuum dried to obtain the filler. The mass ratio of terephthalic acid to sodium hydroxide was 65:1.

[0052] S3. Take 0.2g of the filler obtained in step S2 and add it to 50ml of N,N-dimethylformamide and disperse it evenly. Then add 5g of the polyimide obtained in Preparation Example 1 and stir evenly to obtain a dispersion. Pour it onto a watch glass and heat it at 55°C to evaporate the solvent and obtain a film. Then vacuum dry the film at 150°C for 32 hours to obtain a gas separation membrane. The amount of filler added is 4% of the mass of polyimide.

[0053] Example 3

[0054] A method for preparing a large-area gas separation membrane includes the following preparation steps:

[0055] S1. Dissolve 3.86g of zinc nitrate hexahydrate in 6ml of N,N-dimethylformamide solution, then add sodium hydroxide alcohol solution (dissolve 1.04g of sodium hydroxide in 3ml of methanol), and react under ultrasonic conditions to obtain zinc hydroxide solution. The molar ratio of zinc nitrate to sodium hydroxide is 1:2.

[0056] S2. Then, N,N-dimethylformamide solution containing terephthalic acid was added (72.8g of terephthalic acid was dissolved in 2L of N,N-dimethylformamide) and the mixture was sonicated for 1 hour. The reaction solution was then filtered to separate the white precipitate, washed repeatedly with ethanol, and then vacuum dried to obtain the filler. The mass ratio of terephthalic acid to sodium hydroxide was 70:1.

[0057] S3. Take 0.3g of the filler obtained in step S2 and add it to 50ml of N,N-dimethylformamide and disperse it evenly. Then add 5g of the polyimide obtained in Preparation Example 1 and stir evenly to obtain a dispersion. Pour it onto a watch glass and heat it at 60°C to evaporate the solvent and obtain a film. Then vacuum dry the film at 150°C for 30 hours to obtain a gas separation membrane. The amount of filler added is 6% of the mass of polyimide.

[0058] Example 6

[0059] A method for preparing a large-area gas separation membrane includes the following preparation steps:

[0060] S1. Dissolve 3.86g of zinc nitrate hexahydrate in 6ml of N,N-dimethylformamide solution, then add sodium hydroxide alcohol solution (dissolve 1.04g of sodium hydroxide in 3ml of methanol), and react under ultrasonic conditions to obtain zinc hydroxide solution. The molar ratio of zinc nitrate to sodium hydroxide is 1:2.

[0061] S2. Then, N,N-dimethylformamide solution containing terephthalic acid was added (67.6 g of terephthalic acid was dissolved in 1.95 L of N,N-dimethylformamide) and the mixture was sonicated for 1 hour. The reaction solution was then filtered to separate the white precipitate, washed repeatedly with ethanol, and then vacuum dried to obtain the filler. The mass ratio of terephthalic acid to sodium hydroxide was 65:1.

[0062] S3. Take 5g of the filler obtained in step S2 and add it to ethanol containing 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (5g of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate is dissolved in 250ml of ethanol, that is, the mass ratio of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate to filler is 1:1). Stir and react at 55℃ for 20 hours. Then, centrifuge and wash the product and vacuum dry it to obtain the nanocomposite filler.

[0063] S4. Take 0.2g of the nanocomposite filler obtained in step S3 and add it to 50ml of N,N-dimethylformamide and disperse it evenly. Then add 5g of the polyimide obtained in Preparation Example 1 and stir evenly to obtain a dispersion. Pour it onto a petri dish and heat it at 55°C to evaporate the solvent and obtain a film. Then vacuum dry the film at 150°C for 32 hours to obtain a gas separation membrane. The amount of nanocomposite filler added is 4% of the mass of polyimide.

[0064] Example 7

[0065] A method for preparing a large-area gas separation membrane includes the following preparation steps:

[0066] S1. Dissolve 3.86g of zinc nitrate hexahydrate in 6ml of N,N-dimethylformamide solution, then add sodium hydroxide alcohol solution (dissolve 1.04g of sodium hydroxide in 3ml of methanol), and react under ultrasonic conditions to obtain zinc hydroxide solution. The molar ratio of zinc nitrate to sodium hydroxide is 1:2.

[0067] S2. Then, N,N-dimethylformamide solution containing terephthalic acid was added (67.6 g of terephthalic acid was dissolved in 1.95 L of N,N-dimethylformamide) and the mixture was sonicated for 1 hour. The reaction solution was then filtered to separate the white precipitate, washed repeatedly with ethanol, and then vacuum dried to obtain the filler. The mass ratio of terephthalic acid to sodium hydroxide was 65:1.

[0068] S3. Take 10g of the filler obtained in step S2 and add it to ethanol containing 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (5g of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate was dissolved in 125ml of ethanol, i.e., the mass ratio of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate to filler is 1:2). Stir and react at 65℃ for 24 hours. Then, centrifuge and wash the product, and vacuum dry it to obtain the nanocomposite filler.

[0069] S4. Take 0.2g of the nanocomposite filler obtained in step S3 and add it to 50ml of N,N-dimethylformamide and disperse it evenly. Then add 5g of the polyimide obtained in Preparation Example 1 and stir evenly to obtain a dispersion. Pour it onto a petri dish and heat it at 55°C to evaporate the solvent and obtain a film. Then vacuum dry the film at 150°C for 32 hours to obtain a gas separation membrane. The amount of nanocomposite filler added is 4% of the mass of polyimide.

[0070] Comparative Example 1

[0071] A method for preparing a large-area gas separation membrane differs from Example 2 in that the amount of filler added is 2% of the mass of polyimide, i.e., the amount of filler added is 0.1g and the amount of polyimide added is 5g, while the rest are the same as in Example 2.

[0072] Comparative Example 2

[0073] A method for preparing a large-area gas separation membrane differs from Example 2 in that the amount of filler added is 7% of the mass of polyimide, i.e., the amount of filler added is 0.35g and the amount of polyimide added is 5g, while the rest are the same as in Example 2.

[0074] The performance testing was conducted on the gas separation membranes obtained in the above embodiments and comparative examples to detect the permeation of carbon dioxide and nitrogen, wherein the volume ratio of carbon dioxide to nitrogen was 1:1. The testing was conducted according to the standard GB / T40260-2021 "Test Method for Gas Permeation Performance of Polymer Membrane Materials". The test results are shown in Table 1.

[0075] Table 1. Results of Gas Separation Membrane Permeation Performance Test

[0076] project <![CDATA[P 二氧化碳 ]]> <![CDATA[P 氮气 ]]> <![CDATA[α 二氧化碳 / 氮气 ]]> Example 1 27.32 1.79 15.25 Example 2 28.86 1.78 16.21 Example 3 28.41 1.80 15.78 Example 4 29.65 1.78 16.65 Example 5 28.94 1.75 16.54 Example 6 30.45 1.73 17.58 Example 7 30.36 1.74 17.41 Comparative Example 1 21.41 2.03 10.54 Comparative Example 2 20.56 2.11 9.76

[0077] The permeability coefficients for carbon dioxide and nitrogen in the table above are in Barrers.

[0078] As can be seen from Table 1, when the gas separation membranes obtained in Examples 1-3 of this application separate and detect a mixture of carbon dioxide and nitrogen, the permeability coefficient of carbon dioxide shows a trend of first increasing and then decreasing. This indicates that when the amount of each substance added in this application is within the range defined in this application, the selectivity of the gas separation membrane for carbon dioxide can be effectively improved.

[0079] Compared with Example 2, when the polyimide used was the polyimide obtained in Preparation Example 2 and Preparation Example 3, the carbon dioxide permeability coefficient in Examples 4 and 5 was better than that in Example 2, and the separation coefficient α between carbon dioxide and nitrogen was also better. 二氧化碳 / 氮气 It is also higher than the separation coefficient α of carbon dioxide and nitrogen in Example 2. 二氧化碳 / 氮气 It is evident that the amount of each substance added in Preparation Example 2 and Preparation Example 3 can further improve the selectivity of the gas separation membrane for carbon dioxide.

[0080] Compared with Example 2, in Examples 6-7, after the filler in step S2 was modified with 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, the gas separation membrane obtained in Examples 6-7 showed further improved preferential selection performance for carbon dioxide and further improved carbon dioxide permeation coefficient. This may be because the modification of inorganic filler with 1-ethyl-3-methylimidazolium trifluoromethanesulfonate improved the dispersion performance of inorganic filler in organic polymer membrane, improved the interfacial compatibility between organic and inorganic filler, and the modification of filler with 1-ethyl-3-methylimidazolium trifluoromethanesulfonate could interfere with the arrangement and stacking of polymer chain segments, while providing additional carbon dioxide mass transfer channels, increasing the polymer chain spacing and carbon dioxide transfer sites in the gas separation membrane, and enhancing the diffusion process of carbon dioxide in the gas separation membrane.

[0081] Compared with Example 2, when the amount of filler added is not within the range defined in this application, the selectivity of the gas separation membranes obtained in Comparative Examples 1 and 2 for carbon dioxide is reduced, resulting in a decrease in the carbon dioxide permeation coefficient. It can be seen that when the amount of filler added is lower or higher than the range defined in this application, the carbon dioxide permeation performance will be reduced. The reason may be that when the content of filler is too high, it will agglomerate in the membrane and increase the crystallinity of the membrane, thereby reducing some mass transfer channels in the gas separation membrane that were originally available for gas molecules to pass through, thus reducing the gas separation performance of the gas separation membrane.

[0082] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a large area gas separation membrane, characterized by, It comprises the following preparation steps: S1, dissolving zinc nitrate in a solvent, then adding sodium hydroxide alcohol solution, and reacting under ultrasonic conditions to obtain a zinc hydroxide solution, the molar ratio of zinc nitrate to sodium hydroxide being 1:2; S2, then adding a solvent dissolving terephthalic acid and ultrasonically reacting for 1-2 hours, then separating the white precipitate by suction filtration, washing it with ethanol several times, and vacuum drying to obtain a filler, then adding the filler to ethanol dissolving 1-ethyl-3-methyl imidazole trifluoromethanesulfonate, stirring and reacting at 55-65°C for 20-24 hours, then centrifuging and washing the product, and vacuum drying to obtain a nanocomposite filler; S3, adding the filler obtained in step S2 to a solvent and dispersing uniformly, then adding polyimide and stirring uniformly to obtain a dispersion, pouring it onto a watch glass, heating at 50-60°C to evaporate the solvent, vacuum drying the film to obtain a gas separation membrane, wherein the amount of the filler added is 3-6% of the mass of the polyimide; The polyimide is obtained by the following method: S1, adding 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane to N,N-dimethylformamide and stirring to dissolve to form a solution with a concentration of 0.3-0.5 g / ml, then adding 0.4-0.5 parts by weight of pyridine and 0.5-0.7 parts by weight of trimethylchlorosilane and reacting for 15-20 minutes; S2, adding 1.2-1.5 parts by weight of hexafluorodiphthalic anhydride and 2-4 parts by weight of N,N-dimethylformamide and reacting for 15-20 hours under ice water bath conditions; S3, adding 2-2.5 parts by weight of acetic anhydride and 1.5-2.2 parts by weight of pyridine to the solution obtained in step S2, stirring at room temperature for 6-8 hours, washing with methanol, filtering, and vacuum drying to obtain polyimide.

2. The method of claim 1, wherein: The mass ratio of terephthalic acid to sodium hydroxide is (60-70):

1.

3. The method of claim 1, wherein: The mass ratio of 1-ethyl-3-methyl imidazole trifluoromethanesulfonate to the filler is 1:(1-2).

4. The method of claim 1, wherein: The concentration of 1-ethyl-3-methyl imidazole trifluoromethanesulfonate in ethanol is 0.02-0.04 g / ml.

5. The method of claim 1, wherein: The solvent in steps S1 and S2 is N,N-dimethylformamide.

6. The method of claim 1, wherein: The vacuum drying conditions of the film in step S3 are drying at 140-150°C for 30-32 hours.

7. A gas separation membrane obtained by the method of any one of claims 1-6.