Polybenzimidazole gas separation membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of special polymer functional membranes, and discloses a polybenzimidazole gas separation membrane as well as a preparation method and application thereof, the polybenzimidazole gas separation membrane has an interpenetrating network-shaped pore structure, and the polybenzimidazole gas separation membrane has a nanoscale pore structure. The pore size distribution of the nanoscale pore structure is 0.1-30 nm, and the average pore size of the nanoscale pore structure is 1-80 nm. The polybenzimidazole gas separation membrane has an interpenetrating network-shaped pore structure and a nanoscale pore structure, so that the polybenzimidazole gas separation membrane has relatively high gas selectivity and permeability coefficient and also has relatively good mechanical properties.

Description

Polybenzimidazole gas separation membrane, its preparation method and application Technical Field

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

[0002] Nanoporous polymer membranes possess the advantages of large specific surface area, low density, high stability, and good processability, combining the strengths of both porous membranes and polymer materials. They have wide applications in gas separation, water treatment, catalyst supports, sensors, and proton exchange membranes. However, current methods for preparing porous polymer membranes suffer from problems such as wide pore size distribution, inability to control pore size, cumbersome preparation processes, and environmental pollution from waste emissions.

[0003] Polybenzimidazole (PBI) is a class of heterocyclic polymers containing imidazole rings in its main chain repeating units, exhibiting excellent thermal stability, mechanical strength, and chemical resistance. Due to the semi-trapezoidal structure of PBI and the presence of imidazole nitrogen atoms in the main chain, the polymer possesses high chain rigidity and intermolecular hydrogen bonds, resulting in a high intermolecular packing density and good hydrogen permeation selectivity. PBI also exhibits good thermal stability, with a thermal decomposition temperature as high as 550℃ and a glass transition temperature exceeding 400℃, allowing for prolonged use at high temperatures up to 250℃. Therefore, it can be used in high-temperature hydrogen separation applications.

[0004] Currently, common methods for preparing porous polymer membranes include solvent-inducing phase separation, pore formation by porogens, solvent evaporation-induced pore formation, polymer pyrolysis, and block copolymer self-assembly. Among these, solvent-inducing phase separation has attracted widespread research interest due to its ease of large-scale production. However, when using common aprotic solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone to prepare polybenzimidazole porous membranes, the phase separation rate is fast, and the prepared porous membranes have an asymmetric structure with finger-like or sponge-like pores and micron-sized pores. The porous structure serves as the support layer, while the dense surface layer plays a separating role. Therefore, the requirements for the surface structure are quite stringent, and the film formation process requires precise control.

[0005] Therefore, developing polybenzimidazole membrane materials with nanoporous structures, adjustable pore sizes and uniform size distribution, and simple preparation methods is of great significance in the field of gas separation. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of poor separation selectivity, low gas permeability coefficient, and poor mechanical stability of existing separation membranes, and to provide a polybenzimidazole gas separation membrane, its preparation method, and its application. This gas separation membrane has an interpenetrating network pore structure and a nanoscale pore structure, which makes the gas separation membrane have high gas selectivity and permeability coefficient, as well as good mechanical properties.

[0007] To achieve the above objectives, the first aspect of the present invention provides a polybenzimidazole gas separation membrane, wherein the polybenzimidazole gas separation membrane has an interpenetrating network pore structure and a nanoscale pore structure, wherein the pore size distribution of the nanoscale pore structure is 0.1-30 nm and the average pore size of the nanoscale pore structure is 1-80 nm.

[0008] A second aspect of the present invention provides a method for preparing a polybenzimidazole gas separation membrane, wherein the method comprises:

[0009] S1. Polybenzimidazole and a protic solvent are mixed and degassed to obtain a casting solution;

[0010] S2. After coating the casting solution onto the substrate to form a thin layer of casting solution, it is then immersed in a non-solvent to solidify into a film. After separating the film from the substrate, a nascent porous film is obtained.

[0011] S3. The nascent porous membrane is sequentially immersed in an alkaline solution and a washing solution to obtain a porous membrane;

[0012] S4. The porous membrane is dried to obtain a polybenzimidazole gas separation membrane.

[0013] A third aspect of the present invention provides a polybenzimidazole gas separation membrane prepared by the method described above.

[0014] The fourth aspect of the present invention provides an application of the aforementioned polybenzimidazole gas separation membrane in gas separation.

[0015] Through the above technical solutions, the nanoporous polybenzimidazole membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0016] (1) The porous membrane with the nanoporous structure has an interpenetrating network pore structure, which makes the gas separation membrane have high gas selectivity and permeability coefficient, and can achieve high selective separation of gas pairs such as He / N2, He / CH4, H2 / CO2, H2 / N2, H2 / CH4, CO2 / N2, and CO2 / CH4.

[0017] (2) This preparation method uses a protic solvent as the casting liquid. By utilizing the good solubility between the protic solvent and the polymer, the phase separation rate is slowed down, and a PBI membrane with a nanoporous structure is prepared. This makes the gas porous membrane not only highly selective, but also highly permeable and mechanically stable. Furthermore, when non-solvent-induced phase separation is used, the phase separation rate is slow, which can form a pore structure of nanoscale size.

[0018] (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

[0019] Figure 1 is a cross-sectional morphology diagram of the gas separation membrane prepared in Example 1;

[0020] Figure 2 is a partially enlarged view of the cross-sectional morphology of the gas separation membrane prepared in Example 1;

[0021] Figure 3 is a cross-sectional morphology diagram of the gas separation membrane prepared in Example 3;

[0022] Figure 4 is a partially enlarged view of the cross-sectional morphology of the gas separation membrane prepared in Example 3;

[0023] Figure 5 shows the surface morphology of the gas separation membrane prepared in Comparative Example 1;

[0024] Figure 6 is a cross-sectional morphology of the gas separation membrane prepared in Comparative Example 1;

[0025] Figure 7 shows the surface morphology of the gas separation membrane prepared in Comparative Example 2;

[0026] Figure 8 is a cross-sectional morphology diagram of the gas separation membrane prepared in Comparative Example 2. Detailed Implementation

[0027] 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.

[0028] As mentioned above, in order to achieve the above objectives, the first aspect of the present invention provides a polybenzimidazole gas separation membrane, wherein the polybenzimidazole gas separation membrane has an interpenetrating network pore structure and a nanoscale pore structure, wherein the pore size distribution of the nanoscale pore structure is 0.1-30 nm and the average pore size of the nanoscale pore structure is 1-80 nm.

[0029] According to the present invention, preferably, the pore size distribution of the nanoscale pore structure is 0.2-30 nm, more preferably 0.2-25 nm, more preferably 0.5-20 nm, and even more preferably 0.57-19 nm.

[0030] According to the present invention, preferably, the average pore size of the nanoscale pore structure is 2-50 nm, more preferably 3-20 nm, and even more preferably 5-18 nm.

[0031] The inventors of this invention have discovered that the gas separation membrane in this invention has an interpenetrating network pore structure with an internal nanoporous structure. This pore structure can maintain or even further improve the gas selectivity of the gas separation membrane while increasing its permeability coefficient, especially achieving highly selective separation of gas pairs such as He / N2, He / CH4, H2 / CO2, H2 / N2, H2 / CH4, CO2 / N2, and CO2 / CH4.

[0032] According to the present invention, the porosity of the gas separation membrane is 3-30%, preferably 3-22%, more preferably 5-15%, and even more preferably 5.98-14.82%. In the present invention, the porosity of the gas separation membrane meets the above range, which can further improve the permeability coefficient of the gas separation membrane.

[0033] According to the present invention, the permeability coefficient of the gas separation membrane is 5-30 Barrer, preferably 10-20 Barrer, and more preferably 10.56-18.75 Barrer. It should be noted in this invention that the permeability coefficient of the gas separation membrane refers to its permeability coefficient relative to helium (He).

[0034] 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.

[0035] Additionally, it should be noted that the unit of permeability coefficient in this invention is "Barrer" (1 Barrer = 7.5 × 10⁻⁶). -18 m 3 (STP)m / (m 2 ·s·Pa).

[0036] A second aspect of the present invention provides a method for preparing a polybenzimidazole gas separation membrane, wherein the method comprises:

[0037] S1. Polybenzimidazole and a protic solvent are mixed and degassed to obtain a casting solution;

[0038] S2. After coating the casting solution onto the substrate to form a thin layer of casting solution, it is then immersed in a non-solvent to solidify into a film. After separating the film from the substrate, a nascent porous film is obtained.

[0039] S3. The nascent porous membrane is sequentially immersed in an alkaline solution and a washing solution to obtain a porous membrane;

[0040] S4. The porous membrane is dried to obtain a polybenzimidazole gas separation membrane.

[0041] The inventors discovered that current methods for preparing PBI porous membranes mainly involve non-solvent-induced phase separation using aprotic organic solvents. This results in membranes with high permeability but poor selectivity and mechanical properties. This invention provides a novel type of solvent for preparing PBI porous membranes: protic solvents. By utilizing the excellent solubility between protic solvents and polymers, the rate of phase separation is slowed down, allowing the preparation of PBI membranes with a nanoporous structure. This results in gas-porous membranes that exhibit high selectivity, high permeability, and high mechanical stability.

[0042] In this invention, the method is simple to prepare and the process is stable. The porosity of polybenzimidazole can be controlled by changing the type of protic solvent, the mass fraction of non-solvent and polymer, and it is easy to carry out industrial implementation.

[0043] According to the present invention, a casting solution is obtained by uniformly mixing, dissolving, and degassing a mixture containing polybenzimidazole and a protic solvent. The mixing, dissolution, and degassing methods and conditions are not specifically required and can be conventional methods in the art. Preferably, the mixing conditions include stirring at 40-80°C for 24-72 hours; more preferably, stirring at 60-75°C for 24-36 hours. The stirring conditions are not specifically limited and can be conventionally selected by those skilled in the art.

[0044] Furthermore, the degassing can be conventional centrifugal degassing, vacuum degassing, or ultrasonic degassing in the art. In this invention, vacuum degassing is preferred, and more preferably, vacuum degassing is performed at room temperature to -0.1 MPa.

[0045] According to the present invention, the protic solvent is selected from at least one of methanesulfonic acid, formic acid, acetic acid, sulfuric acid, hydrochloric acid, phosphoric acid, and polyphosphoric acid; preferably, the protic solvent is selected from at least one of methanesulfonic acid, formic acid, acetic acid, and hydrochloric acid; more preferably, the protic solvent is methanesulfonic acid; in the present invention, the above-mentioned specific protic solvent is selected, which has good solubility for polybenzimidazole, ensuring that the low-concentration casting solution has good film-forming properties, and the film-forming rate is slow, ensuring that the pore size is in the nanometer range, and is not prone to defects.

[0046] According to the present invention, the non-solvent is selected from at least one of deionized water, methanol, ethanol, isopropanol, n-butanol, acetone and tetrahydrofuran, preferably, the non-solvent is selected from at least one of deionized water, ethanol and isopropanol; in the present invention, the selection of the non-solvent from the above types enables the gas separation membrane to have a nanoscale interpenetrating network pore structure.

[0047] According to the present invention, the plate-film separation can be carried out 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, thereby achieving plate-film separation.

[0048] According to the present invention, the first washing liquid is an alkaline solution, preferably an alkaline aqueous solution, and more preferably sodium hydroxide and / or sodium bicarbonate.

[0049] According to the present invention, the molar concentration of the alkaline solution is 0.01-1 mol / L; preferably, the molar concentration of the alkaline solution is 0.1-0.5 mol / L.

[0050] And / or, the washing solution is selected from at least one of deionized water, methanol, ethanol, isopropanol, n-butanol, acetone, cyclohexane, and n-heptane, preferably deionized water.

[0051] According to the present invention, the weight ratio of the polybenzimidazole to the protic solvent is 1:(9-99), preferably 1:(9-49), and more preferably 1:(10-49). In the present invention, the mass ratio of the polybenzimidazole to the protic solvent satisfies the above range, which enables the gas separation membrane to improve its permeation performance while ensuring high separation selectivity.

[0052] According to the present invention, the solid content of the casting solution is 1-10 wt%, preferably 2-8 wt%. In the present invention, the solid content of the casting solution meets the above range, making it easier to coat and control the thickness of the polymer film during the preparation process.

[0053] According to the present invention, the polybenzimidazole comprises one or more of the structural units shown in formulas (A1) to (A8);

[0054]

[0055] In this invention, the inventors discovered that when the polybenzimidazole includes one or more of the structural units shown in formulas (A5) to (A8), it is easy to coat and the prepared PBI porous membrane has good mechanical properties.

[0056] According to the present invention, preferably, the polybenzimidazole has the structural unit shown in formula (A5):

[0057]

[0058] When the polybenzimidazole has the structural unit shown in formula (A5), it is easier to coat and the prepared PBI porous membrane has better mechanical properties.

[0059] According to the present invention, the number-average molecular weight of the polybenzimidazole is 20,000-300,000, preferably 20,000-200,000, more preferably 47,000-148,200, for example, any combination between 47,000, 54,000, 57,000, 74,800, and 148,200. In the present invention, the number-average molecular weight of the polybenzimidazole satisfies the above range, the polymer has good solubility, and the prepared polymer has good mechanical properties.

[0060] According to the present invention, the conditions for the coating include: a temperature of 20-100°C, preferably 50-80°C.

[0061] According to the present invention, the impregnation conditions include: a temperature of 20-80°C and a time of 0.5-24h, preferably 2-6h.

[0062] According to the present invention, the conditions for soaking in alkaline solution include: soaking at 20-50°C for 0.5-72 hours; preferably, soaking at room temperature (20-40°C) for 24-30 hours.

[0063] According to the present invention, the soaking conditions in the washing solution include: soaking at 20-80°C for 6-72 hours; preferably, soaking at 60-80°C for 24-32 hours; more preferably, changing the washing solution (preferably deionized water) every 8 hours.

[0064] 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.

[0065] In this invention, the drying method and conditions can be conventional means in the art. Preferably, the drying conditions are: drying at 20-150℃ with forced air for 2-8 hours, followed by drying in a vacuum oven at 100-200℃ for another 8-10 hours. This can reduce deformation during the drying process and improve the success rate of preparing gas separation membranes.

[0066] The inventors of this invention have discovered through research that, more preferably, the porous membrane is first dried at 20-50°C under forced air conditions for 2-3 hours, and then second dried at a vacuum degree of -0.1MPa to 0MPa, preferably at a vacuum degree of -0.1MPa, and at 100-150°C, preferably at 100-120°C, to achieve better technical results.

[0067] In one specific embodiment of the present invention, the membrane with the nanoporous structure is prepared according to the following steps:

[0068] S1. Add polybenzimidazole (number average molecular weight of 20,000-500,000) and a protic solvent to an Erlenmeyer flask. The mass ratio of polybenzimidazole to solvent is 1:99-10:90. Stir at 40-80℃ for 24-72 hours. After degassing, a casting solution is obtained with a solid content of 1-10 wt%.

[0069] S2. The casting solution is uniformly coated onto the substrate surface, and after being immersed in a non-solvent solution at 20-80℃ to solidify into a film, it is detached from the substrate surface. The immersion continues for 0.5-24 hours to obtain the initial porous membrane.

[0070] S3. The nascent porous membrane is first soaked and washed in an alkaline solution of 0.01-1 mol / L at 20-50℃ for 0.5-72 h. After removal, it is soaked in a second washing solution at 20-80℃ for 6-72 h.

[0071] S4. The porous membrane obtained in S3 is dried to obtain a gas separation membrane.

[0072] A third aspect of the present invention provides a polybenzimidazole gas separation membrane prepared by the method described above.

[0073] The fourth aspect of the present invention provides an application of the aforementioned polybenzimidazole gas separation membrane in gas separation.

[0074] The present invention will be described in detail below through embodiments.

[0075] In the following examples and comparative examples:

[0076] The microstructure of the gas separation membrane was measured using a Hitachi S-4800 or FEI nano450 high-resolution field emission scanning electron microscope.

[0077] Testing of average pore size, pore size distribution, and porosity: The average pore size, pore size distribution, and porosity of the membrane were tested using the N2 adsorption method. Specifically: the experimental sample was prepared, and nitrogen gas was introduced into the sample to achieve a certain gas content. The sample was placed in a constant temperature and pressure device to maintain it under constant temperature and pressure conditions. The specific surface area of ​​the sample was measured by continuously adjusting the pressure (P / P0) and specific volume (Vv0). The average pore size, pore size distribution, and porosity of the sample were calculated using the formula of BET's law.

[0078] The permeability coefficient was measured using a gas permeation tester via the pressure difference method.

[0079] Selectivity is obtained by dividing the permeability coefficients of different gases;

[0080] PBI membrane, purchased from Shanghai Shengjun Technology Co., Ltd. and the Institute of Chemistry, Chinese Academy of Sciences;

[0081] All other chemical reagents were purchased from Beijing Innocare Technology Co., Ltd.

[0082] Example 1

[0083] This embodiment illustrates a nanoporous polybenzimidazole gas separation membrane prepared using the method of the present invention.

[0084] (S1) Preparation of casting solution:

[0085] 0.8 g of polybenzimidazole (with a number-average molecular weight of 74,800 and structural units as shown in formula (A5)) was added to an Erlenmeyer flask, followed by 9.2 g of methanesulfonic acid. After mechanical stirring at 75°C for 24 h, the polymer was completely dissolved, and an 8 wt% polybenzimidazole casting solution was prepared. The solution was cooled to room temperature and vacuumed to -0.1 MPa to remove bubbles, yielding the polybenzimidazole casting solution, which was then placed in an oven at 60°C for later use.

[0086] (S2) Preparation of primary porous membrane:

[0087] Polybenzimidazole casting solution was uniformly coated onto the surface of a glass plate, and then immersed in deionized water at room temperature for 0.5 h to solidify into a film. After separation of the plate and the film, a primary porous membrane was obtained.

[0088] (S3) Preparation of porous membranes:

[0089] The nascent porous membrane was transferred to a 0.1 mol / L sodium hydroxide aqueous solution and soaked at room temperature for 24 hours. Then the membrane was transferred to deionized water and soaked at 80°C for another 24 hours. The deionized water was changed every 8 hours to obtain the porous membrane.

[0090] (S4) Preparation of polybenzimidazole gas separation membrane:

[0091] After removing the porous membrane, the surface moisture was absorbed with absorbent paper and then dried in a 50℃ forced-air oven for 2 hours, followed by drying in a 100℃ vacuum oven for 8 hours to obtain a dry membrane (polybenzimidazole gas separation membrane), labeled as S1.

[0092] In addition, the parameter characterization and performance of the polybenzimidazole porous membrane are shown in Tables 1-3.

[0093] Example 2

[0094] This embodiment illustrates a nanoporous polybenzimidazole gas separation membrane prepared using the method of the present invention.

[0095] (S1) Preparation of casting solution: Same as in Example 1;

[0096] (S2) Preparation of primary porous membrane:

[0097] The polybenzimidazole casting solution was uniformly coated onto the surface of a glass plate, and then immersed in ethanol at room temperature for 1 hour to solidify into a film. After separation of the plate and film, a primary porous membrane was obtained.

[0098] (S3) Preparation of porous membranes:

[0099] The nascent porous membrane was transferred to a 0.1 mol / L sodium bicarbonate aqueous solution and soaked at room temperature for 24 hours. Then the membrane was transferred to deionized water and soaked at 80°C for another 24 hours. The deionized water was changed every 8 hours to obtain the porous membrane.

[0100] (S4) Preparation of polybenzimidazole gas separation membrane:

[0101] After removing the porous membrane, the surface moisture was absorbed with absorbent paper and then dried in a 50℃ forced-air oven for 2 hours, followed by drying in a 100℃ vacuum oven for 8 hours to obtain a dry membrane (polybenzimidazole gas separation membrane), labeled as S2.

[0102] In addition, the parameter characterization and performance of the polybenzimidazole porous membrane are shown in Tables 1-3.

[0103] Example 3

[0104] This embodiment illustrates a nanoporous polybenzimidazole gas separation membrane prepared using the method of the present invention.

[0105] (S1) Preparation of casting solution: Same as in Example 1;

[0106] (S2) Preparation of primary porous membrane:

[0107] The polybenzimidazole casting solution was uniformly coated onto the surface of a glass plate, and then immersed in deisopropanol at room temperature for 1 hour to cure it into a film. After separating the plate and the film, the nascent porous membrane was obtained.

[0108] (S3) Preparation of porous membranes:

[0109] The nascent porous membrane was transferred to a 0.1 mol / L sodium bicarbonate aqueous solution and soaked at room temperature for 24 hours. Then the membrane was transferred to deionized water and soaked at 80°C for another 24 hours. The deionized water was changed every 8 hours to obtain the porous membrane.

[0110] (S4) Preparation of polybenzimidazole gas separation membrane:

[0111] After removing the porous membrane, the surface moisture was absorbed with absorbent paper and then dried in a 50℃ forced-air oven for 2 hours, followed by drying in a 100℃ vacuum oven for 8 hours to obtain a dry membrane (polybenzimidazole gas separation membrane), labeled as S3.

[0112] In addition, the parameter characterization and performance of the polybenzimidazole porous membrane are shown in Tables 1-3.

[0113] Example 4

[0114] This embodiment illustrates a nanoporous polybenzimidazole gas separation membrane prepared using the method of the present invention.

[0115] (S1) Preparation of casting solution:

[0116] 0.2 g of polybenzimidazole (with a number-average molecular weight of 148,200 and structural units as shown in formula (A5)) was added to an Erlenmeyer flask, followed by 9.8 g of methanesulfonic acid. After mechanical stirring at 75°C for 36 h, the polymer was completely dissolved, and a 2 wt% polybenzimidazole casting solution was prepared. The solution was cooled to room temperature and vacuumed to -0.1 MPa to remove bubbles, yielding the polybenzimidazole casting solution, which was then placed in an oven at 60°C for later use.

[0117] (S2) Preparation of primary porous membrane:

[0118] Polybenzimidazole casting solution was uniformly coated onto the surface of a glass plate, and then immersed in deionized water at room temperature for 0.5 h to solidify into a film. After separation of the plate and the film, a primary porous membrane was obtained.

[0119] (S3) Preparation of porous membranes:

[0120] The nascent porous membrane was transferred to a 0.1 mol / L sodium hydroxide ethanol solution and soaked at room temperature for 24 hours. Then the membrane was transferred to deionized water and soaked at 80°C for another 24 hours. The deionized water was changed every 8 hours to obtain the porous membrane.

[0121] (S4) Preparation of polybenzimidazole gas separation membrane:

[0122] After removing the porous membrane, the surface moisture was absorbed with absorbent paper and then dried in a 50℃ forced-air oven for 2 hours, followed by drying in a 120℃ vacuum oven for 12 hours to obtain a dry membrane (polybenzimidazole gas separation membrane), labeled as S4.

[0123] In addition, the parameter characterization and performance of the polybenzimidazole porous membrane are shown in Tables 1-3.

[0124] Example 5

[0125] This embodiment illustrates a nanoporous polybenzimidazole gas separation membrane prepared using the method of the present invention.

[0126] (S1) Preparation of casting solution:

[0127] 0.2 g of polybenzimidazole (with a number-average molecular weight of 148,200 and structural units as shown in formula (A5)) was added to an Erlenmeyer flask, followed by 9.8 g of methanesulfonic acid. After mechanical stirring at 75°C for 36 h, the polymer was completely dissolved, and a 2 wt% polybenzimidazole casting solution was prepared. The solution was cooled to room temperature and vacuumed to -0.1 MPa to remove bubbles, yielding the polybenzimidazole casting solution, which was then stored at room temperature for later use.

[0128] (S2) Preparation of primary porous membrane:

[0129] Polybenzimidazole casting solution was uniformly coated onto the surface of a glass plate, and then immersed in deionized water at room temperature for 0.5 h to solidify into a film. After separation of the plate and the film, a primary porous membrane was obtained.

[0130] (S3) Preparation of porous membranes:

[0131] The nascent porous membrane was transferred to a 0.5 mol / L sodium bicarbonate aqueous solution and soaked at room temperature for 24 hours. Then the membrane was transferred to deionized water and soaked at 80°C for another 24 hours. The deionized water was changed every 8 hours to obtain the porous membrane.

[0132] (S4) Preparation of polybenzimidazole gas separation membrane:

[0133] After removing the porous membrane, the surface moisture was absorbed with absorbent paper and then dried in a 50℃ forced-air oven for 2 hours, followed by drying in a 120℃ vacuum oven for 12 hours to obtain a dry membrane (polybenzimidazole gas separation membrane), labeled as S5.

[0134] In addition, the parameter characterization and performance of the polybenzimidazole porous membrane are shown in Tables 1-3.

[0135] Example 6

[0136] This embodiment illustrates a nanoporous polybenzimidazole gas separation membrane prepared using the method of the present invention.

[0137] (S1) Preparation of casting solution:

[0138] 1.0 g of polybenzimidazole (with a number-average molecular weight of 47,000 and structural units as shown in formula (A5)) was added to an Erlenmeyer flask, followed by 9.0 g of methanesulfonic acid. After mechanical stirring at 75°C for 24 h, the polymer was completely dissolved, and a 10 wt% polybenzimidazole casting solution was prepared. The solution was cooled to room temperature and vacuumed to -0.1 MPa to remove bubbles, thus obtaining the polybenzimidazole casting solution, which was then stored at room temperature for later use.

[0139] (S2) Preparation of primary porous membrane:

[0140] The polybenzimidazole casting solution was uniformly coated onto the surface of a glass plate, and then immersed in ethanol at room temperature for 1 hour to solidify into a film. After separation of the plate and film, a primary porous membrane was obtained.

[0141] (S3) Preparation of porous membranes:

[0142] The nascent porous membrane was transferred to a 0.5 mol / L sodium bicarbonate aqueous solution and soaked at room temperature for 24 h. Then the membrane was transferred to ethanol and soaked at 50 °C for another 24 h. The ethanol was replaced every 8 h to obtain the porous membrane.

[0143] (S4) Preparation of polybenzimidazole gas separation membrane:

[0144] After removing the porous membrane, the ethanol on the membrane surface was absorbed with absorbent paper and then dried in a 50°C forced-air oven for 2 hours, followed by drying in a 100°C vacuum oven for 8 hours to obtain a dry membrane (polybenzimidazole gas separation membrane), labeled as S6.

[0145] In addition, the parameter characterization and performance of the polybenzimidazole porous membrane are shown in Tables 1-3.

[0146] Example 7

[0147] This embodiment illustrates a nanoporous polybenzimidazole gas separation membrane prepared using the method of the present invention.

[0148] The polybenzimidazole gas separation membrane was prepared using the same method as in Example 1, except that:

[0149] (S1) Preparation of casting solution: Add 0.8g of polybenzimidazole (the number average molecular weight of polybenzimidazole is 74,800 and it has the structural unit shown in formula (A5)) to an Erlenmeyer flask, then add 9.2g of hydrochloric acid. After mechanical stirring at room temperature for 24h, the polymer is completely dissolved, and an 8wt% polybenzimidazole casting solution is prepared. Cool to room temperature, and vacuum degas at -0.1MPa to obtain the polybenzimidazole casting solution. Place it in an oven at 60℃ for later use.

[0150] (S2) Preparation of primary porous membrane: Same as in Example 1;

[0151] (S3) Preparation of porous membrane: Same as in Example 1;

[0152] (S4) Preparation of polybenzimidazole gas separation membrane: Same as in Example 1; the result is a dry membrane (polybenzimidazole gas separation membrane), labeled as S7.

[0153] In addition, the parameter characterization and performance of the polybenzimidazole porous membrane are shown in Tables 1-3.

[0154] Example 8

[0155] This embodiment illustrates a nanoporous polybenzimidazole gas separation membrane prepared using the method of the present invention.

[0156] The polybenzimidazole gas separation membrane was prepared using the same method as in Example 1, except that:

[0157] (S1) Preparation of casting solution: Replace "methanesulfonic acid" with "sulfuric acid";

[0158] (S2) Preparation of primary porous membrane: Same as in Example 1;

[0159] (S3) Preparation of porous membrane: Same as in Example 1;

[0160] (S4) Preparation of polybenzimidazole gas separation membrane: Same as in Example 1; the result is a dry membrane (polybenzimidazole gas separation membrane), labeled as S8.

[0161] In addition, the parameter characterization and performance of the polybenzimidazole porous membrane are shown in Tables 1-3.

[0162] Example 9

[0163] This embodiment illustrates a nanoporous polybenzimidazole gas separation membrane prepared using the method of the present invention.

[0164] The polybenzimidazole gas separation membrane was prepared using the same method as in Example 1, except that:

[0165] (S1) Preparation of casting solution: Add 0.1g of polybenzimidazole (the number average molecular weight of polybenzimidazole is 148,200 and it has the structural unit shown in formula (A5)) to an Erlenmeyer flask, and then add 9.9g of methanesulfonic acid. After mechanical stirring at 60°C for 24h, the polymer is completely dissolved, and a 1wt% polybenzimidazole casting solution is prepared. Cool to room temperature, and vacuum degas at -0.1MPa to obtain the polybenzimidazole casting solution. Place it in an oven at 60°C for later use.

[0166] (S2) Preparation of primary porous membrane: Same as in Example 1;

[0167] (S3) Preparation of porous membrane: Same as in Example 1;

[0168] (S4) Preparation of polybenzimidazole gas separation membrane: Same as in Example 1; the result is a dry membrane (polybenzimidazole gas separation membrane), labeled as S9.

[0169] In addition, the parameter characterization and performance of the polybenzimidazole porous membrane are shown in Tables 1-3.

[0170] Example 10

[0171] This embodiment illustrates a nanoporous polybenzimidazole gas separation membrane prepared using the method of the present invention.

[0172] The polybenzimidazole gas separation membrane was prepared using the same method as in Example 1, except that:

[0173] (S1) Preparation of casting solution: Add 1.0g of polybenzimidazole (the number average molecular weight of polybenzimidazole is 65,000 and it has the structural unit shown in formula (A7)) to an Erlenmeyer flask, and then add 9.0g of methanesulfonic acid. After mechanical stirring at 60℃ for 24h, the polymer is completely dissolved, and a 10wt% polybenzimidazole casting solution is prepared. Cool to room temperature, and vacuum degas at -0.1MPa to obtain the polybenzimidazole casting solution. Place it in an oven at 60℃ for later use.

[0174] (S2) Preparation of primary porous membrane: Same as in Example 1;

[0175] (S3) Preparation of porous membrane: Same as in Example 1;

[0176] (S4) Preparation of polybenzimidazole gas separation membrane: Same as in Example 1; the result is a dry membrane (polybenzimidazole gas separation membrane), labeled as S10.

[0177] In addition, the parameter characterization and performance of the polybenzimidazole porous membrane are shown in Tables 1-3.

[0178] Example 11

[0179] This embodiment illustrates a nanoporous polybenzimidazole gas separation membrane prepared using the method of the present invention.

[0180] The polybenzimidazole gas separation membrane was prepared using the same method as in Example 1, except that:

[0181] (S1) Preparation of casting solution: Add 0.5g of polybenzimidazole (the number average molecular weight of polybenzimidazole is 50,000 and it has the structural unit shown in formula (A2)) to an Erlenmeyer flask, and then add 9.5g of methanesulfonic acid. After mechanical stirring at 60℃ for 24h, the polymer is completely dissolved, and a 5wt% polybenzimidazole casting solution is prepared. Cool to room temperature, and vacuum degas at -0.1MPa to obtain the polybenzimidazole casting solution. Place it in an oven at 60℃ for later use.

[0182] (S2) Preparation of primary porous membrane: Same as in Example 1;

[0183] (S3) Preparation of porous membrane: Same as in Example 1;

[0184] (S4) Preparation of polybenzimidazole gas separation membrane: Same as in Example 1; the result is a dry membrane (polybenzimidazole gas separation membrane), labeled as S11.

[0185] In addition, the parameter characterization and performance of the polybenzimidazole porous membrane are shown in Tables 1-3.

[0186] Comparative Example 1

[0187] (1) Preparation of casting solution:

[0188] 0.8 g of polybenzimidazole (with a number-average molecular weight of 74,800 and structural units as shown in formula (A5)) was added to an Erlenmeyer flask, followed by 9.2 g of N,N-dimethylacetamide. After mechanical stirring at 75°C for 24 h, the polymer was completely dissolved, and an 8 wt% polybenzimidazole casting solution was prepared. The solution was cooled to room temperature and vacuumed to -0.1 MPa to remove bubbles, yielding the polybenzimidazole casting solution, which was then placed in an oven at 60°C for later use.

[0189] (2) Preparation of porous membranes:

[0190] The polybenzimidazole casting solution was uniformly coated onto the surface of a glass plate. After immersion in deionized water at room temperature for 0.5 h, the membrane was transferred to deionized water and immersed for another 24 h at 80 °C, with the deionized water changed every 8 h. After removal, the membrane surface was dried with absorbent paper and then placed in a 50 °C forced-air oven for 2 h, followed by drying in a 100 °C vacuum oven for 8 h to obtain a dry membrane, labeled D1. The parameter characterization and properties of the obtained polybenzimidazole porous membrane are shown in Tables 1-3.

[0191] Comparative Example 2

[0192] (1) Preparation of casting solution:

[0193] 1.0 g of polybenzimidazole (with a number-average molecular weight of 47,000 and structural units as shown in formula (A5)) was added to an Erlenmeyer flask, followed by 9.0 g of N,N-dimethylacetamide. After mechanical stirring at 75°C for 24 h, the polymer was completely dissolved, and a 10 wt% polybenzimidazole casting solution was prepared. The solution was cooled to room temperature and vacuumed to -0.1 MPa to remove bubbles, yielding the polybenzimidazole casting solution, which was then stored at room temperature for later use.

[0194] (2) Preparation of porous membranes:

[0195] The polybenzimidazole casting solution was uniformly coated onto the surface of a glass plate. After immersion in ethanol at room temperature for 1 hour, the membrane was transferred to ethanol and immersed for another 24 hours at 50°C, with the ethanol being changed every 8 hours. After removal, the ethanol on the membrane surface was blotted dry with absorbent paper, and then dried in a 50°C forced-air oven for 2 hours, followed by drying in a 100°C vacuum oven for 8 hours to obtain a dry membrane, labeled D2. The parameters and properties of the obtained polybenzimidazole porous membrane are shown in Tables 1-3.

[0196] Comparative Example 3

[0197] The polybenzimidazole gas separation membrane was prepared using the same method as in Example 1, except that:

[0198] (S1) Preparation of casting solution: Add 0.05g of polybenzimidazole (the number average molecular weight of polybenzimidazole is 47,000, and it has the structural unit shown in formula (A5)) to an Erlenmeyer flask, then add 9.2g of methanesulfonic acid. After mechanical stirring at 75°C for 24h, the polymer is completely dissolved, and a 0.05wt% polybenzimidazole casting solution is prepared. Cool to room temperature, and vacuum degas at -0.1MPa to obtain the polybenzimidazole casting solution. Place it in an oven at 60°C for later use.

[0199] (S2) Preparation of primary porous membrane: Same as in Example 1;

[0200] (S3) Preparation of porous membrane: Same as in Example 1;

[0201] (S4) Preparation of polybenzimidazole gas separation membrane: Same as in Example 1; the result was a dry membrane (polybenzimidazole gas separation membrane), labeled as D3.

[0202] In addition, the parameter characterization and performance of the polybenzimidazole porous membrane are shown in Tables 1-3.

[0203] Table 1

[0204] Sample pore size distribution (nm) Average pore size (nm) Porosity (%) S1 0.80 -12.5 7.0 8.75 S2 0.78 -13.6 6.8 8.02 S3 0.77 -13.7 5.8 7.83 S4 1.30 -19.7 12.7 14.82 S5 0.99 -19.0 11.5 12.75 S6 0.57 -18.9 5.3 5.45 S7 0.85 -16.78.29.17S80.87-16.99.09.85S91.50-25.817.222.07S100.67-22.35.55.98S1 10.27-15.85.13.66D1280-75058278.90D2357-85262065.38D31.98-35.7020.127.50 surface

[0205] Table 1 shows that the gas separation membranes prepared in Examples 1-11 have suitable porosity.

[0206] Figure 1 is a cross-sectional morphology diagram of the gas separation membrane prepared in Example 1, and Figure 2 is a partially enlarged cross-sectional morphology diagram of the gas separation membrane prepared in Example 1. It can be seen from Figures 1 and 2 that the pores in the separation membrane prepared in Example 1 are nanoscale pores with uniform pore size distribution and dense, defect-free surface.

[0207] Figure 3 is a cross-sectional morphology diagram of the gas separation membrane prepared in Example 3, and Figure 4 is a partial enlarged view of the cross-sectional morphology of the gas separation membrane prepared in Example 3. It can be seen from Figures 3 and 4 that the pores in the separation membrane prepared in Example 3 are nanoscale pores with uniform pore size distribution and dense, defect-free surface.

[0208] In summary, as shown in Figures 1 to 4, the prepared pores are nanoscale pores with uniform pore size distribution and dense, defect-free surfaces.

[0209] Figure 5 shows the surface morphology of the separation membrane prepared in Comparative Example 1, and Figure 6 shows the cross-sectional morphology of the separation membrane prepared in Comparative Example 1. It can be seen from Figures 5 and 6 that the porosity is relatively large and a dense surface layer has not been formed.

[0210] Figure 7 shows the surface morphology of the separation membrane prepared in Comparative Example 2, and Figure 8 shows the cross-sectional morphology of the separation membrane prepared in Comparative Example 2. It can be seen from Figures 7 and 8 that the porosity is relatively large and a dense surface layer has not been formed.

[0211] In summary, based on Figures 5 to 8, it can be seen that the porosity is relatively high and a dense surface layer has not been formed.

[0212] Table 2

[0213]

[0214] As shown in Table 2, the gas separation membranes prepared by the method of the present invention in Examples 1-11 exhibit high gas selectivity and permeability coefficient. Comparative Examples 1 and 2 have higher porosity and do not form a dense surface layer, making it impossible to obtain valid data.

[0215] Table 3

[0216] Sample breaking strength (MPa) Elongation at break (%) S1 12 2.6 17.9 S2 12 5.8 18.2 S3 14 3.5 17.6 S4 11 7.2 26.8 S5 11 2.3 23.7 S6 10 5.5 13.8 S7 13 2.7 11.2 S8 14 4.6 8.7 S9 10 1.2 10.2 S10 10 0.7 12.3 S1 19 2.1 11.5 D1 12.6 7.3 D2 25.1 17.1 D3 5 0.8 23.7 surface

[0217] As can be seen from the results in Table 3, the mechanical properties of the membranes prepared by the method of the present invention in Examples 1-11 are significantly better than those of the membranes prepared by using aprotic solvents as coagulation baths.

[0218] 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 polybenzimidazole gas separation membrane, characterized in that, The polybenzimidazole gas separation membrane has an interpenetrating network pore structure and a nanoscale pore structure. The pore size distribution of the nanoscale pore structure is 0.1-30 nm, and the average pore size of the nanoscale pore structure is 1-80 nm.

2. The polybenzimidazole gas separation membrane according to claim 1, wherein, The pore size distribution of the nanoscale pore structure is 0.2-30 nm, preferably 0.2-25 nm, more preferably 0.5-20 nm; and / or, the average pore size of the nanoscale pore structure is 2-50 nm, preferably 3-20 nm, more preferably 5-18 nm.

3. The polybenzimidazole gas separation membrane according to claim 1 or 2, wherein, The porosity of the polybenzimidazole gas separation membrane is 3-30%, preferably 5-15%; and / or the permeability coefficient of the polybenzimidazole gas separation membrane is 5-30 Barrer, preferably 10-20 Barrer.

4. A method for preparing a polybenzimidazole gas separation membrane, characterized in that, The method includes: S1, mixing polybenzimidazole and a protic solvent, degassing to obtain a casting solution; S2, coating the casting solution onto a substrate to form a thin layer of casting solution, then immersing it in a non-solvent to cure it into a film, and separating the film from the substrate to obtain a nascent porous membrane; S3, immersing the nascent porous membrane sequentially in an alkaline solution and a washing solution to obtain a porous membrane; S4, drying the porous membrane to obtain a polybenzimidazole gas separation membrane.

5. The method according to claim 4, wherein, The protic solvent is selected from at least one of methanesulfonic acid, formic acid, acetic acid, sulfuric acid, hydrochloric acid, phosphoric acid, and polyphosphoric acid; and / or, the non-solvent is selected from at least one of deionized water, methanol, ethanol, isopropanol, n-butanol, acetone, and tetrahydrofuran; and / or, the molar concentration of the alkaline solution is 0.01-1 mol / L; and / or, the washing liquid is selected from at least one of deionized water, methanol, ethanol, isopropanol, n-butanol, acetone, cyclohexane, and n-heptane.

6. The method according to claim 4, wherein, The weight ratio of the polybenzimidazole to the protic solvent is 1:(9-99), preferably 1:(9-49).

7. The method according to any one of claims 4-6, wherein, The polybenzimidazole comprises one or more of the structural units shown in formulas (A1) to (A8); Preferably, the polybenzimidazole has the structural unit shown in formula (A5):

8. The method according to claim 7, wherein, The number-average molecular weight of the polybenzimidazole is 20,000-500,000, preferably 30,000-300,000, and more preferably 50,000-250,000.

9. The method according to any one of claims 4-8, wherein, The conditions for coating include: a temperature of 20-100℃, preferably 50-80℃; and / or, the conditions for immersion include: a temperature of 20-80℃ for 0.5-24h; and / or, the conditions for soaking in an alkaline solution include: soaking at 20-50℃ for 0.5-72h; and / or, the conditions for soaking in a washing solution include: soaking at 20-80℃ for 6-72h.

10. A polybenzimidazole gas separation membrane prepared by the method according to any one of claims 4-9.

11. The application of the polybenzimidazole gas separation membrane according to any one of claims 1-3 and 10 in gas separation.

Images