PBI composite membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of separation membranes, and discloses a PBI composite membrane as well as a preparation method and application thereof. The composite membrane comprises a supporting body and a compact layer covering one side or two sides of the outer surface of the supporting body, the supporting body is a polybenzimidazole porous layer, and the compact layer is made of polybenzimidazole. The polybenzimidazole composite membrane disclosed by the invention has a relatively high separation coefficient and a good mechanical property.

Description

Technical Field

[0001] The present invention relates to the technical field of separation membranes, and in particular to a PBI composite membrane and a preparation method and application thereof. Background Art

[0002] Polybenzimidazole (PBI) is a heterocyclic polymer containing an imidazole ring in the main chain. It is an advanced engineering plastic. PBI has good mechanical stability, thermal stability and chemical stability. It has important applications in high temperature resistant filter fabrics, flame retardant protective clothing, space suits, aircraft interiors, fireproof 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 obvious under harsh operating conditions. The rigidity of the PBI molecular chain and the presence of intermolecular hydrogen bonds enable it to separate small molecule gases well, and can achieve the separation of gas pairs such as He / N2, He / CH4, H2 / CO2, H2 / N2, H2 / CH4, CO2 / N2, and CO2 / CH4, which has extremely important application value in the field of gas separation. However, the permeability of the PBI membrane is low, and a porous membrane needs to be made in the actual use process. In the prior art, the preparation of polybenzimidazole porous membranes usually adopts a non-solvent induced phase separation method.

[0003] The literature (Highly selective asymmetric polybenzimidazole-4,4′-(hexafluoroisopropylidene)bis(benzoic acid) hollow fiber membranes for hydrogen separation) reported a dry-jet-wet spinning method for preparing PBI hollow fiber gas separation membranes. The prepared hollow fiber membranes have finger-like pores. The membranes prepared under optimal conditions have H2 / N2, H2 / CO2 and CO2 / N2 separation performances of only 43.4, 2.52 and 17.2, respectively, and the separation performance for small molecule gases is not good.

[0004] The literature (Fabrication of Polybenzimidazole / Palladium Nanoparticles HollowFiber Membranes for Hydrogen Purification) reports a method for preparing PBI / palladium nanoparticle double-layer hollow fiber membranes by combining non-solvent induced phase separation with complex induced phase separation. Although the final double-sided composite membrane exhibits good hydrogen permeability and selectivity, it is mainly the expensive palladium nanoparticle layer that plays the role of transporting and separating hydrogen.

[0005] The literature (Asymmetric polybenzimidazole membranes with thin selective skinlayer containing ZIF-8for H2 / CO2 separation at pre-combustion capture conditions) reports a method for preparing an asymmetric PBI porous hydrogen separation membrane containing an ultra-thin selective layer of ZIF-8. The method first requires the preparation of a P84 porous support layer, then the PBI / ZIF-8 mixed solution is coated on the support layer, the PBI / ZIF-8 selective layer is prepared by non-easily induced phase separation, and finally a layer of PDMS is coated on the membrane surface by dip coating. Although the prepared membrane has good hydrogen permeability and selectivity, the main effects on the selectivity are the ZIF-8 and PDMS layers.

[0006] The PBI porous gas separation membrane prepared by the existing public technology has low selectivity, and usually requires PDMS to be coated on the surface of the PBI porous membrane to repair defects, resulting in the failure to fully exert the intrinsic excellent hydrogen selectivity of PBI; in addition, the PBI membrane prepared by the non-solvent phase conversion method is often very brittle, and the mechanical properties need to be further improved. Summary of the invention

[0007] The purpose of the present invention is to overcome the defects of the polybenzimidazole porous membrane prepared by non-solvent induced phase separation in the prior art, such as the surface defects are easy to appear, or the material strength and elongation at break are insufficient, and the high-pressure gas separation membrane cannot be prepared. A PBI composite membrane and its preparation method and application are provided. The polybenzimidazole composite membrane has a high separation coefficient and good mechanical properties.

[0008] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a polybenzimidazole composite membrane, wherein the composite membrane comprises a support body and a dense layer covering one or both sides of the outer surface of the support body, the support body is a polybenzimidazole porous layer, and the material of the dense layer is polybenzimidazole.

[0009] A second aspect of the present invention provides a method for preparing a polybenzimidazole composite film, wherein the preparation method comprises:

[0010] (1) dissolving polybenzimidazole in a first polar organic solvent and subjecting the solvent to vacuum degassing to obtain a polybenzimidazole casting solution;

[0011] (2) coating the polybenzimidazole casting solution onto a substrate, and preparing a polybenzimidazole porous support layer by a non-solvent induced phase separation method;

[0012] (3) immersing the polybenzimidazole porous support layer in an acid solution for protonation to obtain a protonated polybenzimidazole porous support layer;

[0013] (4) dissolving polybenzimidazole in a second polar organic solvent to obtain a polybenzimidazole solution; and coating the polybenzimidazole solution on one or both sides of the outer surface of the protonated polybenzimidazole porous support layer to prepare a polybenzimidazole composite membrane.

[0014] The third aspect of the present invention provides a polybenzimidazole composite film prepared by the above-mentioned preparation method.

[0015] A fourth aspect of the present invention provides an application of the aforementioned polybenzimidazole composite membrane in the separation and purification of helium / nitrogen, helium / methane, hydrogen / nitrogen, hydrogen / carbon dioxide, hydrogen / methane, carbon dioxide / nitrogen or carbon dioxide / methane.

[0016] Through the above technical solution, the present invention can provide the following beneficial effects:

[0017] (1) The PBI multilayer composite membrane prepared by the present invention has a high separation coefficient and good mechanical properties. The layers are tightly bonded, and the thickness of the dense layer can be adjusted according to the actual effect;

[0018] (2) The multilayer composite membrane prepared by the present invention improves the gas flux while maintaining gas selectivity, and can achieve the separation of gas pairs such as He / N2, He / CH4, H2 / CO2, H2 / N2, H2 / CH4, CO2 / N2, CO2 / CH4, etc., and can be used in the fields of helium and hydrogen purification and natural gas decarbonization. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a SEM electron microscope image of the upper surface S2-1 of the polybenzimidazole composite membrane prepared in Example 2 of the present invention;

[0020] Figure 2 1 is a SEM electron microscope image of the entire cross section S2-2 and the local cross section S2-3 near the upper surface of the polybenzimidazole composite membrane prepared in Example 2 of the present invention;

[0021] Figure 3 is a SEM electron microscope image of the polybenzimidazole composite membrane prepared in Example 5 of the present invention;

[0022] Figure 4 is a SEM electron microscope image of the polybenzimidazole composite membrane prepared in Comparative Example 1 of the present invention;

[0023] Figure 5 This is a SEM electron microscope image of the polybenzimidazole composite membrane prepared in Comparative Example 3 of the present invention.

[0024] Description of Reference Numerals

[0025] S2-1 is the upper surface of the polybenzimidazole composite film prepared in Example 2;

[0026] S2-2 is the entire section (cross section) of the polybenzimidazole composite membrane prepared in Example 2;

[0027] S2-3 is an enlarged view of the cross section of the polybenzimidazole composite membrane prepared in Example 2;

[0028] S5-1 is the upper surface of the polybenzimidazole composite film prepared in Example 5;

[0029] S5-2 is the entire cross-sectional surface of the polybenzimidazole composite membrane prepared in Example 5;

[0030] S5-3 is an enlarged view of the cross section of the polybenzimidazole composite membrane prepared in Example 5;

[0031] D1-1 represents the upper surface of the polybenzimidazole composite film prepared in Comparative Example 1;

[0032] D1-2 represents the entire cross section of the polybenzimidazole composite membrane prepared in Comparative Example 1;

[0033] D3-1 represents the upper surface of the polybenzimidazole composite film prepared in Comparative Example 3;

[0034] D3-2 represents the entire cross section of the polybenzimidazole composite film prepared in Comparative Example 3. DETAILED DESCRIPTION

[0035] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0036] As mentioned above, the first aspect of the present invention provides a polybenzimidazole composite membrane, wherein the composite membrane includes a support body and a dense layer covering one or both sides of the outer surface of the support body, the support body is a polybenzimidazole porous layer, and the material of the dense layer is polybenzimidazole.

[0037] The inventors of the present invention have found that the coating layer can effectively repair the surface defects of the porous support layer and enhance the gas selectivity and mechanical properties of the PBI porous membrane; in addition, by protonating the porous support layer, the solubility of polybenzimidazole can be changed, preventing the solvent from destroying the support layer structure when the dense layer is coated, and the thickness of the dense layer can be limited.

[0038] According to the present invention, the average size of the pores in the polybenzimidazole porous layer is between 10-2000 nm, preferably 20-500 nm.

[0039] According to the present invention, the porosity of the polybenzimidazole porous layer is 10-90%, preferably 30-60%.

[0040] According to the present invention, the thickness of the polybenzimidazole porous layer is 30-300 um, preferably 50-150 um.

[0041] According to the present invention, the thickness of the dense layer is 0.01-10 um, preferably 0.1-5 um.

[0042] According to the present invention, the number average molecular weight of the polybenzimidazole is 50,000-300,000, preferably 50,000-287,000.

[0043] According to the present invention, the polybenzimidazole comprises one or more of the structural units represented by formulae (A1) to (A8);

[0044]

[0045]

[0046] Preferably, the polybenzimidazole comprises one or more structural units represented by formulae (A5) to (A8).

[0047] According to the present invention, in the PBI multi-layer composite membrane of the present application, the structures of the polybenzimidazoles in the porous layer and the dense layer are the same.

[0048] According to the present invention, the polybenzimidazole multilayer composite film has a breaking strength of 17.3-49.4 MPa, preferably 28.4-49.4 MPa; and a breaking elongation of 4.33-27.10%, preferably 16.97-27.10%.

[0049] According to the present invention, the selectivity of the polybenzimidazole multilayer composite membrane for He / N2 is 100.4-164.7, the selectivity for He / CH4 is 179.5-296.4, the selectivity for H2 / N2 is 117-208.1, the selectivity for H2 / CH4 is 209.2-374.6, the selectivity for CO2 / N2 is 28.78-44.44, the selectivity for CO2 / CH4 is 51.49-80, and the selectivity for H2 / CO2 is 4.064-4.819. The multilayer composite membrane prepared by the present invention improves the gas flux while maintaining the gas selectivity, and can achieve the separation of gas pairs such as He / N2, He / CH4, H2 / CO2, H2 / N2, H2 / CH4, CO2 / N2, and CO2 / CH4.

[0050] A second aspect of the present invention provides a method for preparing a polybenzimidazole composite film, wherein the preparation method comprises:

[0051] (1) dissolving polybenzimidazole in a first polar organic solvent and subjecting the solvent to vacuum degassing to obtain a polybenzimidazole casting solution;

[0052] (2) coating the polybenzimidazole casting solution onto a substrate, and preparing a polybenzimidazole porous support layer by a non-solvent induced phase separation method;

[0053] (3) immersing the polybenzimidazole porous support layer in an acid solution for protonation to obtain a protonated polybenzimidazole porous support layer;

[0054] (4) dissolving polybenzimidazole in a second polar organic solvent to obtain a polybenzimidazole solution; and coating the polybenzimidazole solution on one or both sides of the outer surface of the protonated polybenzimidazole porous support layer to prepare a polybenzimidazole composite membrane.

[0055] According to the present invention, the first polar organic solvent and the second polar organic solvent are the same or different, and each is selected from one or more of N,N-dimethylformimide, N,N-dimethylacetimide, N-methylpyrrolidone and dimethyl sulfoxide.

[0056] According to the present invention, in step (1), polybenzimidazole is dissolved in a first polar organic solvent, and after the polybenzimidazole is completely dissolved, vacuum degassing is performed to obtain a polybenzimidazole casting solution; wherein the vacuum degassing conditions include: room temperature, vacuuming to -0.1 MPa.

[0057] According to the present invention, in step (1), based on the total weight of the polybenzimidazole casting solution, the content of the polybenzimidazole is 6-16wt%, and the content of the first polar organic solvent is 84-94wt%; preferably, based on the total weight of the polybenzimidazole casting solution, the content of the polybenzimidazole is 10-14wt%, and the content of the first polar organic solvent is 86-90wt%.

[0058] According to the present invention, in step (2), the polybenzimidazole casting solution prepared in step (1) is uniformly coated on the substrate, and the polybenzimidazole porous support layer is prepared by a non-solvent induced phase separation method; in addition, in step (2) of the present invention, it also includes soaking the polybenzimidazole porous support layer in deionized water and / or ethanol and then drying it, wherein the soaking time can be 1-6 hours, and the drying treatment can be dried in a vacuum oven at a temperature of 25-120°C, preferably dried in a vacuum oven at 80-120°C.

[0059] According to the present invention, in step (2), the non-solvent induced phase separation includes steam induced phase separation and / or immersion precipitation phase separation.

[0060] According to the present invention, the steam-induced phase separation comprises placing the substrate coated with the polybenzimidazole casting solution in a constant temperature and humidity chamber to perform water vapor-induced phase separation.

[0061] According to the present invention, the humidity is 20-95%, the temperature is 25-80°C, and the constant temperature and humidity time is 0.5-8h; preferably, the humidity is 50-80%, the temperature is 40-80°C, and the constant temperature and humidity time is 0.5-4h.

[0062] According to the present invention, the immersion precipitation phase separation comprises immersing the substrate coated with the polybenzimidazole casting solution in a coagulation bath for phase separation.

[0063] According to the present invention, the temperature of the coagulation bath is 25-80° C., and the immersion time is 0.5-6 h; preferably, the temperature of the coagulation bath is 25-50° C., and the immersion time is 0.5-2 h.

[0064] According to the present invention, the coagulation bath comprises one or more of deionized water, ethanol and isopropanol.

[0065] According to the present invention, the coating may be performed by one or more of blade coating, dip coating, spin coating and spray coating.

[0066] According to the present invention, in step (3), the polybenzimidazole porous support layer is placed in an acid solution at room temperature for protonation to obtain a protonated polybenzimidazole porous support layer; preferably, in step (3), the protonated polybenzimidazole porous support layer is further washed and then dried, wherein the washing can be performed with deionized water, and the drying can be performed in a vacuum oven at a temperature of 25-120°C, preferably in a vacuum oven at a temperature of 80-120°C.

[0067] According to the present invention, in step (4), polybenzimidazole is dissolved in a second polar organic solvent, cooled to room temperature, filtered, and vacuum degassed to obtain a polybenzimidazole solution; in the present invention, based on the total weight of the polybenzimidazole solution, the content of the polybenzimidazole is 0.5-5wt%, and the content of the second polar organic solvent is 95-99.5wt%; preferably, based on the total weight of the polybenzimidazole solution, the content of the polybenzimidazole is 1-3wt%, and the content of the second polar organic solvent is 97-99wt%.

[0068] According to the present invention, in step (3), the acid solution is a monoacid; preferably, the monoacid is selected from one or more of hydrochloric acid, formic acid, acetic acid, benzoic acid and methanesulfonic acid; the concentration of the monoacid is 0.1-7 mol / L, preferably 0.1-3 mol / L, more preferably 0.5-3 mol / L.

[0069] According to the present invention, the protonation conditions include: the soaking time is 0.5-72h, preferably 2-12h.

[0070] According to the present invention, in step (4), the polybenzimidazole solution is coated on one or both sides of the outer surface of the protonated polybenzimidazole porous support layer and then dried. The drying process can be carried out in a vacuum oven at a temperature of 25-120°C, preferably in a vacuum oven at a temperature of 80-120°C.

[0071] The third aspect of the present invention provides a polybenzimidazole composite film prepared by the above-mentioned preparation method.

[0072] The fourth aspect of the present invention provides an application of the aforementioned polybenzimidazole composite membrane in the separation and purification of helium / nitrogen (He / N2), helium / methane (He / CH4), hydrogen / nitrogen (H2 / N2), hydrogen / methane (H2 / CH4), hydrogen / carbon dioxide (H2 / CO2), carbon dioxide / nitrogen (CO2 / N2) or carbon dioxide / methane (CO2 / CH4).

[0073] The present invention will be described in detail below through examples.

[0074] In the following examples and comparative examples:

[0075] Surface morphology test: SEM-4800 was used to characterize the surface and cross section of the film, where the cross section was obtained by quenching the film in liquid nitrogen, and all samples were gold-sprayed before testing.

[0076] The test method of permeation rate (GPU): Under a specific temperature, the test instrument designed by the laboratory is used to measure the gas flow rate per unit membrane area per unit time under a specific pressure difference. Among them, 1GPU = 10 -6 cm 3 (STP) / (cm 2 ·s·cmHg).

[0077] The separation coefficient α is a dimensionless quantity used to characterize the selective permeability of gas components in a membrane. The separation coefficient is the ratio of the permeation rates of two gases in a membrane.

[0078] Mechanical strength test method: Instron 3342 was used to characterize the breaking strength and breaking elongation of the film. The size of the film was 1 cm×4 cm, and the stretching rate was 5 cm / min.

[0079] Pore ​​size and specific surface area test: The membrane pore size and porosity were tested using the N2 adsorption method.

[0080] OPBI (ether-containing PBI, corresponding to structure A5) was purchased from Shanghai Shengjun Plastic Technology Co., Ltd.

[0081] Example 1

[0082] This embodiment is intended to illustrate the polybenzimidazole composite membrane prepared by the method of the present invention.

[0083] (1) Preparation of casting solution:

[0084] (Polybenzimidazole casting solution for preparing porous layer) 0.6 g of polybenzimidazole (polybenzimidazole has a number average molecular weight of 64,000 and has a structural unit shown in formula (A5)) is added to a conical flask, followed by adding 9.4 g of N,N-dimethylacetimide, and the polymer is completely dissolved after mechanical stirring at 75° C. for 24 hours to prepare a 6 wt % polybenzimidazole casting solution, which is then cooled to room temperature and vacuumed to -0.1 MPa for vacuum degassing to obtain a polybenzimidazole casting solution for preparing a porous layer, which is then used for standby use;

[0085] (2) Preparation of polybenzimidazole porous support layer:

[0086] The polybenzimidazole casting solution for preparing the porous layer is uniformly coated on the surface of the glass plate, and then immersed in isopropanol at room temperature for 1 hour, and then moved to deionized water for 0.5 hour, and the film falls off the surface of the glass plate. After the film is further immersed in ethanol at room temperature for 2 hours, the ethanol on the surface of the film is dried with absorbent paper, and then placed in a vacuum oven at 80°C for 2 hours, and then heated to 100°C and continued to be dried for 8 hours to obtain a polybenzimidazole porous support layer;

[0087] (3) Protonation of the polybenzimidazole porous support layer:

[0088] The polybenzimidazole porous support layer was immersed in a 0.5 mol / L methanesulfonic acid solution at room temperature for 8 h, and the membrane surface was repeatedly rinsed with deionized water after being taken out, and the moisture on the membrane surface was absorbed with absorbent paper and then placed in a vacuum oven at 120° C. for 8 h to obtain a protonated polybenzimidazole porous support layer;

[0089] (4) Preparation of polybenzimidazole dense selective layer:

[0090] Polybenzimidazole casting solution for dense layer preparation: 0.1 g polybenzimidazole (polybenzimidazole has a number average molecular weight of 64,000 and has a structural unit shown in formula (A5)) is added to a conical flask, followed by adding 9.9 g N,N-dimethylacetimide, and the polymer is completely dissolved after mechanical stirring at 75° C. for 24 hours to prepare a 1 wt % polybenzimidazole solution, which is filtered after cooling to room temperature, and evacuated to -0.1 MPa for vacuum degassing for later use;

[0091] The polybenzimidazole casting liquid with a solid content of 1 wt% for preparing a dense layer is evenly scraped onto the upper surface of the protonated polybenzimidazole porous support layer, and then placed in a vacuum oven at 100°C for drying for 12 hours to obtain a polybenzimidazole multilayer composite membrane, labeled as S1; in addition, the parameter characterization and performance of the obtained polybenzimidazole multilayer composite membrane are shown in Table 1-2.

[0092] Example 2

[0093] This embodiment is intended to illustrate the polybenzimidazole composite membrane prepared by the method of the present invention.

[0094] A polybenzimidazole composite membrane was prepared in the same manner as in Example 1, except that in step (1), the polybenzimidazole casting solution for preparing the porous layer was prepared by adding 1.2 g of polybenzimidazole (polybenzimidazole having a number average molecular weight of 64,000 and a structural unit represented by formula (A5)) into a conical flask, followed by adding 8.8 g of N,N-dimethylacetimide to prepare a 12 wt % polybenzimidazole casting solution.

[0095] The result is a polybenzimidazole multilayer composite membrane, labeled as S2; in addition, the parameter characterization and performance of the polybenzimidazole multilayer composite membrane are shown in Table 1-4.

[0096] Figure 1 is a SEM electron microscope image of the upper surface S2-1 of the polybenzimidazole composite membrane prepared in Example 2 of the present invention, Figure 2 2 is a SEM electron microscope image of the entire cross section S2-2 and the local cross section S2-3 near the upper surface of the polybenzimidazole composite membrane prepared in Example 2 of the present invention; Figure 1 and Figure 2 It can be seen that the prepared porous layer has a uniform pore size distribution, the dense layer is bonded to the upper surface of the porous layer, and the thickness of the dense layer is about 4 um.

[0097] Example 3

[0098] This embodiment is intended to illustrate the polybenzimidazole composite membrane prepared by the method of the present invention.

[0099] A polybenzimidazole composite membrane was prepared in the same manner as in Example 1, except that in step (1), the polybenzimidazole casting solution for preparing the porous layer was prepared by adding 1.6 g of polybenzimidazole (polybenzimidazole having a number average molecular weight of 64,000 and having a structural unit represented by formula (A5)) into a conical flask, followed by adding 8.4 g of N,N-dimethylacetimide to prepare a 16 wt % polybenzimidazole casting solution.

[0100] The result is a polybenzimidazole multilayer composite membrane, labeled as S3; in addition, the parameter characterization and performance of the polybenzimidazole multilayer composite membrane are shown in Table 1-4.

[0101] Example 4

[0102] This embodiment is intended to illustrate the polybenzimidazole composite membrane prepared by the method of the present invention.

[0103] (1) Preparation of casting solution:

[0104] (Polybenzimidazole casting solution for porous layer preparation) 2.4 g of polybenzimidazole (polybenzimidazole has a number average molecular weight of 64,000 and has a structural unit shown in formula (A5)) is added to a conical flask, followed by adding 17.6 g of N,N-dimethylacetimide. After mechanical stirring at 75°C for 24 hours, the polymer is completely dissolved and a 12 wt% casting solution is prepared. The solution is cooled to room temperature and evacuated to -0.1 MPa for vacuum degassing and set aside.

[0105] (2) Preparation of polybenzimidazole porous support layer: Prepare according to the method of Example 1.

[0106] (3) Protonation of the polybenzimidazole porous support layer: The specific steps are the same as those in Example 1.

[0107] (4) Preparation of polybenzimidazole dense selective layer:

[0108] The preparation of the casting solution for preparing the dense layer is the same as that in Example 1.

[0109] The protonated polybenzimidazole porous support layer was immersed in a PBI casting solution with a solid content of 1 wt% for 10 seconds, then taken out and placed in a vacuum oven at 100°C for drying for 12 hours to obtain a polybenzimidazole multilayer composite membrane, labeled S4; in addition, the parameter characterization and performance of the obtained polybenzimidazole multilayer composite membrane are shown in Tables 1-4.

[0110] Example 5

[0111] This embodiment is intended to illustrate the polybenzimidazole composite membrane prepared by the method of the present invention.

[0112] A polybenzimidazole composite membrane was prepared in the same manner as in Example 4, except that in step (4), a layer of PBI casting solution with a solid content of 1 wt% was applied to the upper surface of the protonated polybenzimidazole porous support layer by spin coating, and the membrane was dried in a vacuum oven at 100°C for 12 h to obtain a polybenzimidazole multilayer composite membrane, which was labeled as S5. In addition, the parameter characterization and performance of the obtained polybenzimidazole multilayer composite membrane are shown in Tables 1-4.

[0113] Figure 3 is a SEM electron microscope image of the polybenzimidazole composite membrane prepared in Example 5 of the present invention. Figure 3 It can be seen that the prepared porous layer has a uniform pore size distribution, the dense layer is bonded to the upper surface of the porous layer, and the thickness of the dense layer is about 4 μm.

[0114] Example 6

[0115] This embodiment is intended to illustrate the polybenzimidazole composite membrane prepared by the method of the present invention.

[0116] (1) Preparation of casting solution: The specific steps are the same as those in Example 4.

[0117] (2) Preparation of polybenzimidazole porous support layer: The casting liquid was evenly coated on the surface of a glass plate, and then immersed in ethanol at room temperature for 1 hour. After that, the film was moved to deionized water and immersed for 0.5 hour. The film fell off the surface of the glass plate, and the film was continued to be immersed in ethanol at room temperature for 2 hours. After that, it was placed in a vacuum oven at 30°C and dried for 2 hours. After that, the temperature was increased to 100°C and continued to be dried for 8 hours to obtain a polybenzimidazole porous support layer.

[0118] (3) Protonation of the polybenzimidazole porous support layer: The specific steps are the same as those in Example 1.

[0119] (4) Preparation of polybenzimidazole dense selective layer: The specific steps are the same as those in Example 1, and the prepared multilayer composite membrane is marked as S6; in addition, the parameter characterization and performance of the obtained polybenzimidazole multilayer composite membrane are shown in Tables 1-4.

[0120] Example 7

[0121] (1) Preparation of casting solution: The specific steps are the same as those in Example 2.

[0122] (2) Preparation of polybenzimidazole porous support layer: The specific steps are the same as those in Example 2.

[0123] (3) Protonation of polybenzimidazole porous support layer: The polybenzimidazole porous support layer was immersed in a 5 mol / L methanesulfonic acid solution at room temperature for 8 h. After being taken out, the membrane surface was repeatedly rinsed with deionized water. The moisture on the membrane surface was absorbed with absorbent paper and then dried in a vacuum oven at 120°C for 8 h to obtain a protonated polybenzimidazole porous support layer.

[0124] (4) Preparation of a dense selective layer of polybenzimidazole: The specific steps are the same as those in Example 1. The prepared multilayer composite membrane is labeled as S7. In addition, the parameter characterization and performance of the obtained multilayer composite membrane are shown in Tables 1-4.

[0125] Example 8

[0126] 1.0 g of polybenzimidazole (polybenzimidazole has a number average molecular weight of 98,000 and has a structural unit shown in formula (A7)) is added to a conical flask, followed by 9.0 g of dimethyl sulfoxide. The polymer is completely dissolved after mechanical stirring at 75° C. for 24 hours to prepare a 10 wt % polybenzimidazole casting solution, which is cooled to room temperature and evacuated to -0.1 MPa for vacuum degassing for later use.

[0127] (2) Preparation of polybenzimidazole porous support layer:

[0128] The polybenzimidazole casting solution for preparing the porous layer is uniformly coated on the surface of the glass plate, and then immersed in isopropanol at room temperature for 1 hour, and then moved to deionized water for 0.5 hour, and the film falls off the surface of the glass plate. After the film is immersed in ethanol at room temperature for 2 hours, the ethanol on the surface of the film is dried with absorbent paper, and then placed in a vacuum oven at 30°C for 2 hours, and then heated to 100°C and continued to dry for 8 hours to obtain a polybenzimidazole porous support layer;

[0129] (3) Protonation of the polybenzimidazole porous support layer:

[0130] The polybenzimidazole porous support layer was immersed in a 0.5 mol / L methanesulfonic acid solution at room temperature for 8 h, and the membrane surface was repeatedly rinsed with deionized water after being taken out, and the moisture on the membrane surface was absorbed with absorbent paper and then placed in a vacuum oven at 120° C. for 8 h to obtain a protonated polybenzimidazole porous support layer;

[0131] (4) Preparation of polybenzimidazole dense selective layer:

[0132] (Polybenzimidazole casting solution for dense layer preparation) 0.1 g of polybenzimidazole (polybenzimidazole has a number average molecular weight of 98,000 and has a structural unit shown in formula (A7)) is added to a conical flask, followed by 9.9 g of dimethyl sulfoxide. The polymer is completely dissolved after mechanical stirring at 75° C. for 24 hours. The 1 wt % polybenzimidazole solution is cooled to room temperature, filtered, and vacuum degassed for later use.

[0133] The polybenzimidazole casting liquid with a solid content of 1 wt% for preparing a dense layer is evenly spin-coated on the upper surface of the protonated polybenzimidazole porous support layer, and then placed in a vacuum oven at 100°C and dried for 12 hours to obtain a polybenzimidazole multilayer composite membrane, labeled S8; in addition, the parameter characterization and performance of the obtained multilayer composite membrane are shown in Tables 1-4.

[0134] Comparative Example 1

[0135] (1) Preparation of casting solution: 1.2 g of polybenzimidazole (polybenzimidazole has a number average molecular weight of 64,000 and has a structural unit shown in formula (A5)) is added to a conical flask, followed by adding 8.8 g of N,N-dimethylacetimide. After mechanical stirring at 75° C. for 24 h, the polymer is completely dissolved to prepare a 12 wt % polybenzimidazole casting solution, which is cooled to room temperature and evacuated to -0.1 MPa for vacuum degassing for later use.

[0136] (2) Preparation of polybenzimidazole porous support layer: The polybenzimidazole casting liquid is uniformly coated on the surface of the glass plate, and then immersed in isopropanol at room temperature for 1 hour, and then moved to deionized water and immersed for 0.5 hour. The film falls off the surface of the glass plate, and the film is continued to be immersed in ethanol at room temperature for 2 hours, and then placed in a vacuum oven at 30°C for 2 hours, and then heated to 100°C and continued to be dried for 8 hours to obtain a polybenzimidazole porous support layer, which is marked as D1; ​​in addition, the parameter characterization and performance of the obtained polybenzimidazole porous support layer are shown in Tables 1-4.

[0137] Figure 4 is a SEM electron microscope image of the polybenzimidazole composite membrane prepared in Comparative Example 1 of the present invention; Figure 4 It can be seen that the surface of the coated base film without passing through the dense layer has porous defects.

[0138] Comparative Example 2

[0139] (1) Preparation of casting solution: 0.6 g of polybenzimidazole (polybenzimidazole has a number average molecular weight of 64,000 and has a structural unit shown in formula (A5)) was added to a conical flask, followed by 9.4 g of N,N-dimethylacetimide. After mechanical stirring at 75°C for 24 h, the polymer was completely dissolved. The 6 wt% casting solution was cooled to room temperature, filtered, and evacuated to -0.1 MPa for vacuum degassing and set aside.

[0140] (2) Preparation of polybenzimidazole dense film: The casting liquid is evenly coated on the surface of the glass plate, dried in a 70°C forced air oven for 2 hours, then placed in a 100°C vacuum oven for drying for 10 hours, cooled to room temperature, and immersed in deionized water until the film falls off the surface of the glass plate. The moisture on the surface of the film is absorbed with absorbent paper, and then placed in a 100°C vacuum oven for drying for 2 hours to obtain a polybenzimidazole dense film, marked as D2; in addition, the parameter characterization and performance of the obtained polybenzimidazole dense film are shown in Tables 1-4.

[0141] Comparative Example 3

[0142] The polybenzimidazole membrane was prepared in the same manner as in Example 2, except that the porous support layer and the dense layer were made of different materials, that is, the porous layer was polybenzimidazole and the dense layer was commercial polyimide (P84).

[0143] The result is a polybenzimidazole membrane, labeled as D3; in addition, the parameter characterization and performance of the polybenzimidazole membrane are shown in Table 1-4.

[0144] Figure 5 is a SEM electron microscope image of the polybenzimidazole composite membrane prepared in Comparative Example 3 of the present invention; Figure 5 It can be seen that when the dense layer is made of polyimide, the dense layer cannot be closely attached to the surface of the porous support layer, and there is a gap between the support layer and the dense layer. During the test, the support layer and the dense layer are completely peeled off under pressure, which is prone to defects and cannot be tested for long-term gas permeability performance.

[0145] Comparative Example 4

[0146] This embodiment is intended to illustrate the polybenzimidazole composite membrane prepared by the method of the present invention.

[0147] (1) Preparation of casting solution: The specific steps are the same as those in Example 6.

[0148] (2) Preparation of polybenzimidazole porous support layer: The casting liquid was evenly coated on the surface of a glass plate, and the film was immersed in deionized water at room temperature for 1 hour. The film fell off the surface of the glass plate, and the film was continued to be immersed in ethanol at room temperature for 2 hours, and then placed in a vacuum oven at 30°C for 2 hours, and then heated to 100°C and continued to be dried for 8 hours to obtain a polybenzimidazole porous support layer.

[0149] (3) Protonation of the polybenzimidazole porous support layer: The specific steps are the same as those in Example 1.

[0150] (4) Preparation of polybenzimidazole dense selective layer: The specific steps are the same as those in Example 1. The prepared multilayer composite membrane is labeled as D4. In addition, the parameter characterization and performance of the obtained polybenzimidazole multilayer composite membrane are shown in Tables 1-4.

[0151] Table 1

[0152] sample Breaking strength(MPa) Elongation at break (%) S1 17.3 4.33 S2 36.0 17.88 S3 49.4 27.10 S4 33.9 18.01 S5 28.4 20.07 S6 30.1 17.11 S7 34.7 16.97 S8 32.7 21.00 D1 25.4 23.82 D2 105.5 13.62 D3 29.6 9.71 D4 - -

[0153] It can be seen from the results of the mechanical properties of the membrane in Table 1 that in Comparative Example 4, when the non-solvent is deionized water, due to the formation of a macroporous structure, the membrane is fixed on the fixture and ruptures under pressure, and it is impossible to test the effective breaking strength and breaking elongation, indicating that the mechanical strength of the membrane prepared with deionized water as the non-solvent is poor. Except for Comparative Example 4, the other membranes all show good mechanical properties. In addition, the ratio of Example 1 is not within the preferred range defined by the present invention, and as a result, the membrane of Example 1 has poor mechanical properties. When the gas separation performance test is performed, as the test proceeds, the edge of the membrane where the force is applied will be damaged. Therefore, the gas separation test was not performed, and because the gas separation performance is not good, the porosity characterization was not performed.

[0154] Table 2

[0155]

[0156] Table 3

[0157]

[0158] Table 4

[0159]

[0160] It can be seen from the above results that the porous composite membrane with a single dense layer prepared by the present invention has both good separation performance and selectivity, and the thickness of the dense layer has little effect on the separation performance. The smaller the thickness of the dense layer, the greater the gas flux.

[0161] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A polybenzimidazole composite film, characterized in that: The composite membrane comprises a support body and a dense layer covering one side or both sides of the outer surface of the support body. The support body is a polybenzimidazole porous layer, and the material of the dense layer is polybenzimidazole.

2. The composite film according to claim 1, wherein The average size of the pores in the polybenzimidazole porous layer is 10-2000 nm, preferably 20-500 nm; and / or, the porosity of the polybenzimidazole porous layer is 10-90%, preferably 30-60%; And / or, the thickness of the polybenzimidazole porous layer is 30-300 um, preferably 50-150 um.

3. The composite film according to claim 1, wherein The thickness of the dense layer is 0.01-10 um, preferably 0.1-5 um.

4. The composite film according to any one of claims 1 to 3, wherein The number average molecular weight of the polybenzimidazole is 50,000-300,000, preferably 50,000-287,000; And / or, the polybenzimidazole comprises one or more of the structural units represented by formulas (A1) to (A8); Preferably, the polybenzimidazole comprises one or more structural units represented by formulae (A5) to (A8).

5. A method for preparing a polybenzimidazole composite film, characterized in that: The preparation method comprises: (1) dissolving polybenzimidazole in a first polar organic solvent and subjecting the solvent to vacuum degassing to obtain a polybenzimidazole casting solution; (2) coating the polybenzimidazole casting solution onto a substrate, and preparing a polybenzimidazole porous support layer by a non-solvent induced phase separation method; (3) immersing the polybenzimidazole porous support layer in an acid solution for protonation to obtain a protonated polybenzimidazole porous support layer; (4) dissolving polybenzimidazole in a second polar organic solvent to obtain a polybenzimidazole solution; and coating the polybenzimidazole solution on one or both sides of the outer surface of the protonated polybenzimidazole porous support layer to prepare a polybenzimidazole composite membrane.

6. The preparation method according to claim 5, wherein: The first polar organic solvent and the second polar organic solvent are the same or different, and are each selected from one or more of N,N-dimethylformimide, N,N-dimethylacetimide, N-methylpyrrolidone and dimethyl sulfoxide.

7. The preparation method according to claim 5, wherein: In step (1), based on the total weight of the polybenzimidazole casting solution, the content of the polybenzimidazole is 6-16wt%, and the content of the first polar organic solvent is 84-94wt%; And / or, in step (4), based on the total weight of the polybenzimidazole solution, the content of the polybenzimidazole is 0.5-5wt%, and the content of the second polar organic solvent is 95-99.5wt%.

8. The preparation method according to claim 5, wherein: In step (2), the non-solvent induced phase separation includes steam induced phase separation and / or immersion precipitation phase separation; And / or, the steam-induced phase separation comprises placing the substrate coated with the polybenzimidazole casting solution in a constant temperature and humidity chamber to perform water vapor-induced phase separation; Preferably, the humidity is 20-95%, the temperature is 25-80°C, and the constant temperature and humidity time is 0.5-8h; And / or, the immersion precipitation phase separation comprises immersing the substrate coated with the polybenzimidazole casting solution in a coagulation bath for phase separation; Preferably, the temperature of the coagulation bath is 25-80°C, and the immersion time is 0.5-6h; Preferably, the coagulation bath comprises one or more of deionized water, ethanol and isopropanol.

9. The preparation method according to claim 5, wherein: In step (3), the acid solution is a monoprotic acid; Preferably, the monoacid is selected from one or more of hydrochloric acid, formic acid, acetic acid, benzoic acid and methanesulfonic acid; and / or, the concentration of the monoprotic acid is 0.1-7 mol / L; And / or, the protonation conditions include: the soaking time is 0.5-72h.

10. The preparation method according to any one of claims 5 to 9, wherein: In step (2), the method further comprises soaking the polybenzimidazole porous support layer in deionized water and / or ethanol and then drying the layer; And / or, in step (3), the process further comprises washing the protonated polybenzimidazole porous support layer and then drying it; And / or, in step (4), the method further comprises coating the polybenzimidazole solution on one side or both sides of the outer surface of the protonated polybenzimidazole porous support layer and then performing a drying process.

11. A polybenzimidazole composite film prepared by the preparation method according to any one of claims 5 to 10.

12. Use of the polybenzimidazole composite membrane according to any one of claims 1 to 4 and 11 in separation and purification of helium / nitrogen, helium / methane, hydrogen / carbon dioxide, hydrogen / nitrogen, hydrogen / methane, carbon dioxide / nitrogen or carbon dioxide / methane.

Images