Gas separation membranes, methods of making and using the same

Abstract

The application relates to the field of membrane separation technology, and discloses a gas separation membrane and a preparation method and application thereof. The gas separation membrane has a mutual transmission network-like pore structure, so that the gas separation membrane has high gas selectivity and permeation coefficient at the same time, and can realize high-selectivity separation of gas pairs such as He / N2, He / CH4, H2 / CO2, H2 / N2, H2 / CH4, CO2 / N2 and CO2 / CH4.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to a gas separation membrane, its preparation method, and its application. Background Technology

[0002] Gas membrane separation is a "green technology". Compared with traditional separation technologies such as adsorption, absorption and cryogenic separation, membrane separation technology has the advantages of high separation efficiency, low energy consumption and simple operation. It is a mainstream technology for gas separation in the future and has broad application prospects in the fields of natural gas helium removal, hydrogen purification and decarbonization.

[0003] Based on the different materials used in gas separation membranes, they can be classified into organic membranes, inorganic membranes, and organic-inorganic hybrid membranes. Organic membranes have become the most attractive material in the gas separation membrane industry due to their diverse preparation materials, simple manufacturing methods, good processability, ease of scale-up production, and good mechanical stability. Currently, organic materials such as polyimide (PI), cellulose acetate (CA), polysulfone (PS), polycarbonate (PC), polydimethylsiloxane (PDMS), and polybenzimidazole have been developed for use in the preparation of gas separation membranes.

[0004] Polybenzimidazole (PBI) is a heterocyclic polymer with an imidazole ring in its main chain. It is an advanced engineering plastic with excellent mechanical, thermal, and chemical stability, making it important in high-temperature resistant filter fabrics, flame-retardant protective clothing, spacesuits, aircraft interiors, fire-retardant fillers, microelectronics, and separation membranes. In the field of separation membranes, PBI can be used to prepare reverse osmosis membranes, ultrafiltration membranes, nanofiltration membranes, proton exchange membranes, and gas separation membranes. Its advantages are particularly evident in harsh operating environments. The rigidity of the PBI molecular chain and the presence of intermolecular hydrogen bonds enable it to effectively separate small molecule gases, achieving the separation of gas pairs such as He / N2, He / CH4, H2 / CO2, H2 / N2, H2 / CH4, CO2 / N2, and CO2 / CH4. However, PBI has a relatively low gas permeability coefficient, which needs further improvement. One effective method is to prepare porous membranes. Currently, the most common method for preparing porous PBI gas separation membranes is solvent-inducible phase separation, resulting in sponge-like or finger-like pore structures.

[0005] The literature (Highly selective asymmetric polybenzimidazole-4,4'-(hexafluoroisopropylidene)bis(benzoic acid) hollow fiber membranes for hydrogen separation) reports a dry-wet spinning method for preparing PBI hollow fiber gas separation membranes. The prepared hollow fiber membranes exhibit finger-like pores. Under optimal conditions, the membranes show separation performance of only 43.4, 2.52, and 17.2 for H2 / N2, H2 / CO2, and CO2 / N2, respectively, indicating poor performance for small molecule gases. The literature (Fabrication of Polybenzimidazole / Palladium Nanoparticles Hollow Fiber Membranes for Hydrogen Purification) reports a method for preparing PBI / palladium nanoparticle bilayer hollow fiber membranes using a combination of non-solvent-induced phase separation and complexation-induced phase separation. Although the final bilayer composite membrane exhibits good hydrogen permeability and selectivity, the expensive palladium nanoparticle layer primarily plays a role in transporting and separating hydrogen.

[0006] Existing publicly available technologies for preparing porous PBI gas separation membranes exhibit low selectivity, requiring the coating of a dense layer onto the surface of the PBI porous membrane to enhance its selectivity, resulting in a complex preparation process. This invention aims to provide a novel method for preparing porous PBI membranes that improves gas permeability while retaining the high selectivity of PBI. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of poor separation selectivity, low gas permeability coefficient, and low permeability coefficient of existing separation membranes, and to provide a gas separation membrane, its preparation method, and its application. The gas separation membrane has an interconnected network pore structure, which enables the gas separation membrane to have both high gas selectivity and high permeability coefficient.

[0008] To achieve the above objectives, the first aspect of the present invention provides a gas separation membrane, characterized in that the gas separation membrane has an interconnected network-like pore structure.

[0009] A second aspect of the present invention provides a method for preparing a gas separation membrane, characterized in that the method comprises:

[0010] S1. A casting solution containing polybenzimidazole and a pore-forming agent is scraped onto a substrate to form a film, and the film is separated from the substrate to obtain a polymer film.

[0011] S2. Protonate the above polymer film to obtain a protonated polymer film.

[0012] S3. Remove the pore-forming agent from the above protonated polymer film to obtain the gas separation membrane;

[0013] The mass ratio of the polybenzimidazole to the porogen is 3:7-9:1.

[0014] A third aspect of the present invention provides a gas separation membrane prepared by the preparation method provided in the second aspect.

[0015] The fourth aspect of the present invention provides an application of the gas separation membrane described in the first aspect and the gas separation membrane described in the third aspect of the present invention in gas separation.

[0016] Through the above technical solutions, the gas separation membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0017] (1) The gas separation membrane has an interconnected network pore structure, which enables the gas separation membrane to have both high gas selectivity and permeability coefficient, and can achieve highly selective separation of gas pairs such as He / N2, He / CH4, H2 / CO2, H2 / N2, H2 / CH4, CO2 / N2, and CO2 / CH4.

[0018] (2) In this preparation method, polybenzimidazole is blended with a pore-forming agent of a polymer material to prepare a polymer film. The first solvent is used to protonate the polybenzimidazole to change its solubility. The second solvent is used to etch the pore-forming agent in the polymer film to prepare a polybenzimidazole film with an interpenetrating network pore structure, i.e., the gas separation membrane. The polybenzimidazole component in the mixed membrane is protonated so that the structure formed by the polybenzimidazole component is not destroyed during the etching process, thus ensuring that the gas separation membrane has an interpenetrating network pore structure. This makes the gas separation membrane have both high gas selectivity and permeability coefficient.

[0019] (3) The preparation method is simple to operate and easy to carry out industrial implementation. It can also be used in the purification of helium and hydrogen and the decarbonization of natural gas. Attached Figure Description

[0020] Figure 1 This is a surface morphology diagram of the gas separation membrane prepared in Example 4;

[0021] Figure 2 This is a cross-sectional morphology diagram of the gas separation membrane prepared in Example 4. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] The first aspect of the present invention provides a gas separation membrane, characterized in that the gas separation membrane has an interconnected network-like pore structure.

[0024] In this invention, the gas separation membrane has an interconnected network pore structure. This interconnected network pore structure can maintain or even further improve the gas selectivity of the gas separation membrane while increasing its permeability coefficient. In particular, it can achieve highly selective separation of gas pairs such as He / N2, He / CH4, H2 / CO2, H2 / N2, H2 / CH4, CO2 / N2, and CO2 / CH4.

[0025] According to the present invention, the porosity of the gas separation membrane is 10-70%.

[0026] In this invention, the porosity of the gas separation membrane meets the above-mentioned range, which can further improve the permeability coefficient of the gas separation membrane.

[0027] Furthermore, the porosity of the gas separation membrane is 17-50%.

[0028] According to the present invention, the permeability coefficient of the gas separation membrane is 9-30 Barrer.

[0029] In this invention, when the permeability coefficient meets the above-mentioned range, the gas separation membrane can maintain a high gas selectivity at the permeability coefficient.

[0030] According to the present invention, the permeability coefficient of the gas separation membrane is 9-15 Barrer.

[0031] In this invention, when the permeability coefficient meets the above-mentioned range, the selective separation of gas by the gas separation membrane can be further improved.

[0032] A second aspect of the present invention provides a method for preparing a gas separation membrane, characterized in that the method comprises:

[0033] S1. A casting solution containing polybenzimidazole and a pore-forming agent is scraped onto a substrate to form a film, and the film is separated from the substrate to obtain a polymer film.

[0034] S2. Protonate the above polymer film to obtain a protonated polymer film.

[0035] S3. Remove the pore-forming agent from the above protonated polymer film to obtain the gas separation membrane;

[0036] The mass ratio of the polybenzimidazole to the porogen is 3:7-9:1.

[0037] In this invention, the inventors discovered that current methods for preparing porous PBI membranes primarily involve non-solvent-induced phase separation, resulting in membranes with high permeability but poor selectivity. This invention provides a novel method: solvent etching. By using a solvent to etch gas transport channels with an interconnected network pore structure into a dense PBI membrane, the gas separation membrane exhibits both high selective separation performance and a high permeability coefficient.

[0038] In this invention, the mass ratio of the polybenzimidazole to the porogen satisfies the above-mentioned range, which enables the gas separation membrane to improve its permeation performance while ensuring high separation selectivity.

[0039] Furthermore, the method is simple to prepare and has a stable process. The pore structure of polybenzimidazole can be controlled by changing the type, molecular weight and addition ratio of the pore-forming agent, making it easy to carry out industrial-scale implementation.

[0040] In this invention, there is no particular limitation on the substrate, which can be a conventional substrate in the art, such as a glass plate, a steel plate, a polytetrafluoroethylene sheet, etc.

[0041] In this invention, the plate-film separation can be achieved by the following method: drying the substrate coated with casting solution and then immersing it in water to peel the film off the substrate surface.

[0042] Furthermore, the drying method and conditions can be conventional means in the art. In this invention, drying at 70-200°C for 2-8 hours is preferred.

[0043] The inventors of this invention discovered through research that by first drying the substrate coated with casting solution at atmospheric pressure and 70-110°C, and then drying it at a vacuum of -0.1MPa to 0MPa and 110-200°C, better technical results can be obtained.

[0044] According to the present invention, the mass ratio of the polybenzimidazole to the porogen is 1-9:1.

[0045] The polybenzimidazole comprises the structural unit shown in formula (1):

[0046]

[0047] Wherein, R1 is selected from the structural unit shown in equation a, equation b, equation c or equation d;

[0048]

[0049] In this invention, the inventors discovered that when the polybenzimidazole contains the structural unit shown in formula (1), the viscosity of the resulting casting solution can meet the coating requirements, making it easy to coat, and the prepared PBI porous membrane has good mechanical properties.

[0050] According to the present invention, the method further includes: mixing polybenzimidazole, a pore-forming agent and a first organic solvent, and then degassing to obtain the casting solution.

[0051] In this invention, there are no specific requirements for the methods and conditions of mixing, dissolving, and degassing; they can be conventional methods in the art. Preferably, the mixing conditions include stirring at 40-80°C for 24-72 hours.

[0052] Furthermore, the degassing can be conventional methods in the art, such as centrifugal degassing, vacuum degassing, and ultrasonic degassing.

[0053] According to the present invention, the solid content of the casting solution is 5-30 wt%.

[0054] In this invention, the solid content of the casting solution meets the above-mentioned range, making it easier to control the thickness of the polymer film during the preparation process.

[0055] Furthermore, the solid content of the casting solution is 8-20 wt%.

[0056] According to the present invention, the number average molecular weight of the polybenzimidazole is 50,000-300,000.

[0057] In this invention, the number-average molecular weight of the polybenzimidazole meets the above-mentioned range, the polymer has good solubility, and the prepared polymer has good mechanical properties.

[0058] Furthermore, the number-average molecular weight of the polybenzimidazole is 50,000-200,000.

[0059] According to the present invention, the pore-forming agent is selected from at least one of polyimide, polyethersulfone, polyetherimide, polysulfone, and polyethylene oxide.

[0060] According to the present invention, the number average molecular weight of the porogen is 3000-100000.

[0061] In this invention, the number-average molecular weight of the pore-forming agent meets the above-mentioned range, is well miscible with polybenzimidazole, and can effectively etch polymer films to obtain an interconnected network pore structure.

[0062] Furthermore, the number-average molecular weight of the porogen is 20,000-100,000.

[0063] According to the present invention, the first organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone.

[0064] In this invention, the first organic solvent is selected from the above-mentioned types, which enables the gas separation membrane to have an interconnected network-like pore structure.

[0065] According to the present invention, the protonation treatment includes: immersing the polymer film in an acid solution for the first time.

[0066] In this invention, it is preferable to dry the polymer film before the first immersion. The drying method and conditions are conventional in the art. For example, in this application, it is preferable to dry the film at 60-70°C with forced air for 2-3 hours, followed by drying in a vacuum oven at 150-160°C for 8-10 hours. This can reduce deformation during the drying process and improve the success rate of preparing the gas separation membrane.

[0067] In this invention, the protonation treatment ensures that the PBI component structure is not damaged during solvent etching, thus guaranteeing the high selectivity of the gas separation membrane.

[0068] In this invention, after the first soaking is completed, conventional operations such as washing and drying are also performed, and the conditions can be conventional conditions in the art.

[0069] According to the present invention, the acid solution is a monoprotic acid solution.

[0070] Furthermore, the acid solution is selected from at least one of methanesulfonic acid solution, hydrochloric acid solution, and acetic acid solution.

[0071] According to the present invention, the concentration of the acid solution is 0.2-6 mol / L, preferably 1-3 mol / L.

[0072] According to the present invention, the conditions for the first soaking include soaking at 20-50°C for 1-7 days.

[0073] According to the present invention, the pore-forming agent removal includes: immersing the protonated polymer film in a second organic solvent.

[0074] In this invention, it is preferable to dry the protonated polymer film before the second immersion, wherein the drying method and drying conditions are conventional in the art.

[0075] In this invention, the removal of the pore-forming agent enables the gas separation membrane to have an interconnected network pore structure, thereby improving the permeability coefficient while ensuring the high selectivity of the gas separation membrane.

[0076] According to the present invention, the second organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone.

[0077] According to the present invention, the conditions for the second soaking include: a temperature of 20-80°C and a time of 2-24 hours.

[0078] In this invention, the inventors discovered that by replacing the second organic solvent every 6-10 hours during the second soaking, a gas separation membrane with a more complete interconnected network pore structure can be obtained, further improving the gas permeability coefficient.

[0079] In this invention, after the second soaking is completed, the polymer film is soaked in the extractant for the third time.

[0080] In this invention, the third immersion is to remove impurities such as the second organic solvent remaining in the polymer film.

[0081] According to the present invention, the extractant is selected from at least one of methanol, ethanol, isopropanol and deionized water.

[0082] In this invention, there are no particular limitations on the conditions for the third soaking, as long as it can remove impurities such as the second organic solvent.

[0083] In this invention, after the third soaking is completed, the polymer film is dried in a conventional manner to obtain the gas separation membrane.

[0084] In one specific embodiment of the present invention, the gas separation membrane is prepared according to the following steps:

[0085] S1. Add polybenzimidazole (number average molecular weight of 50,000-300,000) and porogen (number average molecular weight of 3,000-100,000) to an Erlenmeyer flask. The mass ratio of polybenzimidazole to porogen is 3:7-9:1. Then add the first organic solvent. Stir at 40-80℃ for 24-72 hours. After cooling to room temperature, filter and degas under vacuum to obtain the casting solution with a solid content of 5-30 wt%.

[0086] S2. Coat the casting solution evenly onto the substrate surface, dry at 70-200℃ for 2-8 hours, cool to room temperature, immerse in deionized water until the film naturally peels off from the substrate surface, absorb the moisture from the film surface, and continue drying at 70-200℃ for 2-8 hours to obtain a polymer film.

[0087] S3. The polymer film is first immersed in an acid solution of 0.2-6 mol / L at 20-50℃ for 1-7 days, then washed and dried at 70-200℃ for 2-8 hours to obtain a protonated polymer film.

[0088] S4. The protonated polymer film is immersed in a second organic solvent at 20-80℃ for 2-24 hours to etch the protonated polymer film and dissolve the pore-forming agent component. After etching, the film is immersed in an extractant to remove the second organic solvent remaining in the film. Then, it is dried in a ventilated environment at room temperature to obtain a gas separation membrane.

[0089] A third aspect of the present invention provides a gas separation membrane prepared by the preparation method provided in the second aspect.

[0090] The fourth aspect of the present invention provides an application of the gas separation membrane described in the first aspect and the gas separation membrane described in the third aspect of the present invention in gas separation.

[0091] The present invention will be described in detail below through embodiments. In the following embodiments,

[0092] The gas separation membrane was measured by the n-butanol absorption method;

[0093] The microstructure of the gas separation membrane was measured using a Hitachi S-4800 high-resolution field emission scanning electron microscope.

[0094] The permeability coefficient was measured using a gas permeation tester via the pressure difference method.

[0095] Selectivity is obtained by dividing the permeability coefficients of different gases;

[0096] PBI membrane, purchased from Shanghai Shengjun Technology Co., Ltd.

[0097] All other chemical reagents were purchased from Beijing Innocare Technology Co., Ltd.

[0098] The following examples and comparative examples illustrate the prepared gas separation membranes.

[0099] Example 1

[0100] S1. Add 1g of polybenzimidazole (number average molecular weight of 57,000, R1 selected from formula c) and 1g of polyimide (number average molecular weight of 87,000) to an Erlenmeyer flask. The mass ratio of polybenzimidazole to porogen is 1:1. Then add 18g of the first organic solvent N,N-dimethylacetamide. Stir at 75°C for 24h. After cooling to room temperature, filter and degas under vacuum to obtain the casting solution with a solid content of 10wt%.

[0101] S2. The casting solution is uniformly coated onto the surface of a glass plate, dried at 75°C under normal pressure for 4 hours, and then dried in a vacuum oven at -0.1MPa and 120°C for 8 hours. After cooling to room temperature, the film is soaked in deionized water until it peels off naturally from the surface of the glass plate. The moisture on the surface of the film is absorbed with absorbent paper and then dried in a vacuum oven at -0.1MPa and 120°C for 8 hours to obtain a polymer film.

[0102] S3. The polymer film was first immersed in a 2 mol / L methanesulfonic acid solution at 20℃ for 24 hours. After being taken out, the film surface was repeatedly rinsed with deionized water. After the water on the film surface was dried with absorbent paper, it was placed in a vacuum oven at -0.1 MPa and 120℃ for 8 hours to obtain a protonated polymer film.

[0103] S4. The protonated polymer film is immersed in the second organic solvent N,N-dimethylacetamide at 20°C for a second time, so that N,N-dimethylacetamide etches the protonated polymer film and dissolves the polyimide component of the mixed film. N,N-dimethylacetamide is replaced every 8 hours, and the immersion lasts for a total of 24 hours. After etching, the film is immersed in ethanol for a third time to remove the second organic solvent remaining in the film. Then, it is placed at room temperature and dried in a ventilated environment to obtain a gas separation membrane, which is labeled as S1.

[0104] Examples 2-4

[0105] Consistent with Example 1, except that the second organic solvent N,N-dimethylacetamide in step S4 was replaced with N-methylpyrrolidone, dimethyl sulfoxide and N,N-dimethylformamide respectively, and the same type of second organic solvent was replaced every 8 hours to obtain gas separation membranes, which were labeled as S2-S4.

[0106] Example 5

[0107] Consistent with Example 1, except that the number average molecular weight of the polyimide was 2000, a gas separation membrane was obtained and labeled as S5.

[0108] Example 6

[0109] Similar to Example 1, except that the amount of polybenzimidazole was 0.6g and the amount of polyimide was 1.4g, i.e., the mass ratio of polybenzimidazole to porogen was 3:7, and the solid content of the casting solution was 10wt%, and a gas separation membrane was finally obtained and labeled as S6.

[0110] Example 7

[0111] Similar to Example 1, except that the amount of polybenzimidazole was 0.8g and the amount of polyimide was 1.2g, i.e., the mass ratio of polybenzimidazole to porogen was 4:6, and the solid content of the casting solution was 10wt%, and a gas separation membrane was finally obtained and labeled as S7.

[0112] Example 8

[0113] Similar to Example 1, except that the amount of polybenzimidazole was 2g, the amount of polyimide was 2g, the mass of the first organic solvent N,N-dimethylacetamide was 96g, that is, the mass ratio of polybenzimidazole to porogen was 1:1, the solid content of the casting solution was 4wt%, and a gas separation membrane was finally obtained and labeled as S8.

[0114] Example 9

[0115] Similar to Example 1, except that the amount of polybenzimidazole was 1.6g and the amount of polyimide was 0.4g, i.e., the mass ratio of polybenzimidazole to porogen was 8:2, and the solid content of the casting solution was 10wt%, and a gas separation membrane was finally obtained and labeled as S9.

[0116] Example 10

[0117] S1. Add 1g of polybenzimidazole (number average molecular weight of 124,000, R1 selected from formula d) and 1g of polyethersulfone (number average molecular weight of 42,000) to an Erlenmeyer flask. The mass ratio of polybenzimidazole to porogen is 1:1. Then add 23g of the first organic solvent N,N-dimethylacetamide. Stir at 75°C for 24h. After cooling to room temperature, filter and degas under vacuum to obtain the casting solution with a solid content of 8wt%.

[0118] S2, Simultaneous Instance 1;

[0119] S3, Same as Example 1;

[0120] S4. Same as in Example 1, a gas separation membrane is obtained and labeled as S1.

[0121] Example 11

[0122] Similar to Example 10, except that in step S3, the polymer film was first soaked in a 2 mol / L methanesulfonic acid solution at 20°C for 7 days to obtain a gas separation membrane, which was labeled as S11.

[0123] Example 12

[0124] Similar to Example 10, except that in step S4, the second immersion is: the protonated polybenzimidazole mixed membrane is immersed in the second organic solvent N,N-dimethylacetamide at 20°C for 24 hours, without replacement of the second organic solvent, to prepare a gas separation membrane, which is labeled as S12.

[0125] Comparative Example 1

[0126] Similar to Example 1, except that no pore-forming agent, polyimide, was added, resulting in a non-porous polybenzimidazole homogeneous membrane, labeled D1.

[0127] Comparative Example 2

[0128] Similar to Example 1, except that protonation treatment was not performed, and the polymer film was immersed in a second organic solvent to dissolve the polybenzimidazole, making it impossible to prepare the film.

[0129] Comparative Example 3

[0130] Consistent with Example 1, except that no pore-forming agent removal treatment was performed, resulting in a non-porous mixed film of polybenzimidazole and polyimide, labeled D3.

[0131] Comparative Example 4

[0132] Similar to Example 1, except that the amount of polybenzimidazole was 0.4g and the amount of polyimide was 1.6g, i.e., the mass ratio of polybenzimidazole to porogen was 2:8, and the solid content of the casting solution was 20wt%. When the protonated membrane was immersed in the second solvent, the membrane completely dissolved and a porous membrane could not be formed.

[0133] Comparative Example 5

[0134] The method is consistent with that of Example 1, except that the polybenzimidazole has a number-average molecular weight of 57,000, and R1 is selected from the following structural units:

[0135]

[0136] It was found that it could not be dissolved in N,N-dimethylacetamide, making subsequent film formation impossible.

[0137] Table 1

[0138] S1 46.07 S2 45.71 S3 45.22 S4 44.37 S5 46.38 S6 55.7 S7 66.75 S9 17.6 S10 47.65 S11 45.72 S12 37.6 D1 - D3 -

[0139] Table 1 shows that the gas separation membranes prepared in Examples 1-12 have suitable porosity, with the porosity of Examples 1-4 and 9-11 being within the preferred range. Although the porosity of the gas separation membrane in Example 5 is also within the preferred range, its performance is poor in subsequent applications due to the small number of interconnected network pores.

[0140] Table 2

[0141]

[0142]

[0143] As can be seen from Table 2, Embodiments 1-12 of the present invention have good technical effects, while Embodiments 1-4 and 9-11, which satisfy the preferred scheme, have significantly better effects. Taking helium separation as an example, the permeability coefficient is significantly improved compared with the dense membrane D1, and the selectivity for He in He / N2 is also slightly improved.

[0144] in, Figure 1 This is a surface morphology image of the gas separation membrane prepared in Example 4. Figure 2 This is a longitudinal section view of the gas separation membrane prepared in Example 4, combined with... Figure 1 and Figure 2 It can be seen that the prepared pores are interconnected network structures with uniform pore size distribution.

[0145] Furthermore, a comparison between Examples 1 and Examples 6-7 shows that when the ratio of polybenzimidazole to porogen is 1:(1-4), the prepared porous membrane exhibits higher selectivity for He / N2, He / CH4, H2 / N2, H2 / CH4, CO2 / N2, and CO2 / CH4, and the permeation coefficients of He, H2, and CO2 are significantly improved compared to the dense membrane. The solution etching method for preparing polybenzimidazole porous membranes can effectively improve their gas separation performance.

[0146] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a gas separation membrane, characterized in that, The method includes: S1. A casting solution containing polybenzimidazole and a pore-forming agent is scraped onto a substrate to form a film, and the film is separated from the substrate to obtain a polymer film. S2. Protonate the above polymer film to obtain a protonated polymer film. S3. Remove the pore-forming agent from the above protonated polymer film to obtain the gas separation membrane; The mass ratio of the polybenzimidazole to the porogen is 3:7-9:1, and the polybenzimidazole comprises the structural unit shown in formula (1): Equation (1) Wherein, R1 is selected from the structural unit shown in equation a, equation b, equation c or equation d; Formula a Formula b Formula c Formula d; The porogen is selected from at least one of polyimide, polyethersulfone, polyetherimide, polysulfone, and polyethylene oxide.

2. The method according to claim 1, wherein, The mass ratio of the polybenzimidazole to the porogen is 1-9:1; And / or, the method further includes: mixing polybenzimidazole, a pore-forming agent and a first organic solvent, and then degassing to obtain the casting solution; And / or, the solid content of the casting solution is 5-30 wt%.

3. The method according to claim 2, wherein, The solid content of the casting solution is 8-20 wt%.

4. The method according to claim 1, wherein, The number-average molecular weight of the polybenzimidazole is 50,000-300,000; And / or, the number-average molecular weight of the porogen is 3,000-100,000.

5. The method according to claim 2, wherein, The first organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

6. The method according to claim 4, wherein, The number-average molecular weight of the polybenzimidazole is 50,000-200,000; And / or, the number average molecular weight of the porogen is 20,000-100,000.

7. The method according to claim 1, wherein, The protonation treatment includes: immersing the polymer film in an acid solution for the first time.

8. The method according to claim 7, wherein, The acid solution is a monobasic acid solution; And / or, the concentration of the acid solution is 0.2-6 mol / L; And / or, the conditions for the first soaking include: soaking at 20-50°C for 1-7 days.

9. The method according to claim 8, wherein, The acid solution is selected from at least one of methanesulfonic acid solution, hydrochloric acid solution and acetic acid solution; And / or, the concentration of the acid solution is 1-3 mol / L.

10. The method according to claim 1, wherein, The removal of the pore-forming agent includes: immersing the protonated polymer film in a second organic solvent.

11. The method according to claim 10, wherein, The conditions for the second soaking include: a temperature of 20-80℃ and a time of 2-24 hours; And / or, the second organic solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

12. A gas separation membrane prepared by the method according to any one of claims 1-11.

13. The gas separation membrane according to claim 12, wherein, The gas separation membrane has an interconnected network-like pore structure.

14. The gas separation membrane according to claim 12, wherein the porosity of the gas separation membrane is 10-70%.

15. The gas separation membrane according to claim 14, wherein the porosity of the gas separation membrane is 17-50%.

16. The gas separation membrane according to claim 12, wherein, The permeability coefficient of the gas separation membrane is 9-30 Barrer.

17. The gas separation membrane according to claim 16, wherein, The permeability coefficient of the gas separation membrane is 9-15 Barrer.

18. The application of the gas separation membrane according to any one of claims 12-17 in gas separation.

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