High-permeability carbon molecular sieve gas separation membrane as well as preparation method and application thereof

Abstract

The invention discloses a high-permeability carbon molecular sieve gas separation membrane as well as a preparation method and application thereof, and belongs to the technical field of polymer functional materials and membrane separation. The preparation method specifically comprises the following steps: by taking a dianhydride monomer, a diamine monomer and a three-dimensional polyamine monomer as raw materials, regulating the crosslinking degree by regulating the molar ratio of the dianhydride monomer to the three-dimensional polyamine monomer, synthesizing a polyimide precursor film with a complex net structure in situ by adopting a one-step method, and then removing a residual solvent in the precursor film, thereby obtaining the polyimide film with the complex net structure. And performing carbonization treatment on the high-permeability carbon molecular sieve gas separation membrane (CMSMs) in an inert atmosphere to prepare the high-permeability carbon molecular sieve gas separation membrane (CMSMs), according to the preparation method, a special three-dimensional structure monomer is introduced into a polyimide precursor membrane, so that polymer chain accumulation can be inhibited, pore channel collapse in a carbonization process is reduced, and accurate regulation and control on the pore size and distribution of the carbon molecular sieve membrane are realized; the prepared carbon molecular sieve membrane shows high permeability and excellent selectivity in a gas separation system, and has excellent plasticizing resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer functional materials and membrane separation, and particularly relates to a high-permeability carbon molecular sieve gas separation membrane and a preparation method and application thereof. Background Art

[0002] As the "dual carbon" strategy of achieving carbon peak and carbon neutrality becomes a global consensus, traditional high-energy separation technologies face enormous challenges, and new, low-energy, continuous, and modular separation methods are urgently needed. Gas separation membrane technology, with its outstanding advantages such as low energy consumption, ease of operation, and environmental friendliness, is considered a core alternative to traditional technologies. It has been widely used in air separation and purification, recovery of carbon dioxide from combustion exhaust gases, and natural gas purification.

[0003] In gas separation membrane technology, gases are separated through polymer membranes based on their different permeation rates. Separation performance is dependent on factors such as the gas molecules, the membrane's structural properties, and the interaction between the gas and the membrane. Different gases have different solubility and diffusion abilities within the separation membrane, thereby achieving gas separation. In the field of gas separation membranes, polymer membranes are widely used due to their low cost and ease of processing. However, polymer membranes also have numerous drawbacks, such as poor thermal stability, insufficient chemical resistance, and susceptibility to plasticization by condensed gases. Furthermore, the trade-off between the material's permeability and selectivity limits the performance of polymer membranes for gas separation, making it difficult to simultaneously achieve high permeability and high selectivity. Therefore, developing new high-performance membrane materials to overcome these limitations has become a key research direction. Among these, carbon molecular sieve (CMS) membranes have become a research hotspot due to their ideal combination of separation performance, chemical stability, and plasticization resistance for gas-liquid separation.

[0004] Carbon molecular sieve (CMS) membranes are prepared by pyrolyzing polymer precursors in a specific atmosphere, with the pyrolysis temperature depending on the polymer precursor. By modifying the structure of the polymer precursor, the carbon structure and pore structure of the CMS membrane can be controlled. Methods for modifying the polymer precursor include: (i) crosslinking copolymerization; (ii) designing polymer precursors with specific structures; and (iii) mixing the polymer with inorganic materials. In the process of exploring and optimizing the structure of polymer precursors, crosslinking the polymer precursors through chemical crosslinking or thermally induced crosslinking reactions is a very effective method to enhance the thermal stability and mechanical strength of the polymer, while also improving the gas separation performance of the CMS membrane.

[0005] For example, the Chinese patent with publication number CN115945079A and application date of December 29, 2022 discloses a preparation method and application of a fluorine-containing cross-linkable polyimide-based carbon molecular sieve membrane, using 4,4' (hexafluoroisopropylene) diphthalic anhydride as a dianhydride monomer, 3,5' diaminobenzoic acid and 4,4' diaminodiphenyl ether as common diamine monomers to copolymerize into a polyamic acid solution to make a casting liquid, and after standing and degassing, a polyamic acid film is made by coating, and the polyamic acid film is imidized to prepare a polyimide membrane as a polymer precursor membrane of the carbon molecular sieve membrane, which is placed in a programmed temperature carbonization furnace with a protective atmosphere and calcined at high temperature to obtain a fluorine-containing cross-linkable polyimide-based carbon molecular sieve membrane. The carbon molecular sieve membrane is used for CO2 / N2 and CO2 / CH4 separation, and has a high CO2 permeability coefficient and CO2 / N2, CO2 / CH4 separation factor.

[0006] A Chinese patent with publication number CN116328558A and application date of March 20, 2023 discloses the synthesis of polyamic acid using dianhydride and diamino crown ether as monomer raw materials; the polyamic acid is subjected to a chemical imidization reaction or a thermal imidization reaction to synthesize polyimide, which is used as a precursor and pyrolyzed at 800°C to prepare CMSM, which solves the problem of insufficient permeability selectivity of thin film materials such as polyimide, and the difficulty in controlling the pore size of polyimide due to its thermal expansion effect during the high-temperature carbonization process.

[0007] At present, some progress has been made in exploring the relationship between the structure of modified polymer precursors and the performance of derived CMS membranes through cross-linking. However, due to various research, carbon molecular sieve gas separation membranes have not yet been adopted by industry. Therefore, it is still of great significance to continue to strengthen the preparation and mechanism research of carbon molecular sieve membranes to promote the preparation and application of membranes. Based on the characteristics of CMS membranes, a series of new cross-linked polymer precursors were designed by in-situ cross-linking in one step, and then carbon molecular sieve gas separation membranes with significantly improved permeability and anti-plasticization properties were prepared. They have important practical value and application prospects in industrial fields such as natural gas purification and carbon capture and storage (CCS). Summary of the Invention

[0008] In order to solve the problems existing in the prior art, the present invention provides a high-permeability carbon molecular sieve gas separation membrane and its preparation method and application. The introduction of special three-dimensional structural monomers into the polyimide precursor membrane can not only inhibit the accumulation of polymer chains, but also reduce the pore collapse during the carbonization process, thereby realizing precise control of the pore size and distribution of the carbon molecular sieve membrane.

[0009] The technical solutions of the present invention are as follows:

[0010] One of the objectives of the present invention is to provide a method for preparing a high-permeability carbon molecular sieve gas separation membrane, which uses a dianhydride monomer, a diamine monomer, and a three-dimensional polyamine monomer as raw materials, adjusts the molar ratio of the dianhydride monomer to the three-dimensional polyamine monomer to control the crosslinking degree, adopts a one-step in-situ synthesis of a polyimide (PI) precursor membrane, then removes the residual solvent in the precursor membrane, and carbonizes it under an inert atmosphere to prepare the high-permeability carbon molecular sieve gas separation membrane (CMSMs);

[0011] Wherein, the three-dimensional polyamine monomer is selected from any one of 2,6,13(14)-triaminotriptycene TAT, tris(4-aminophenyl)methane TAMP, and tetrakis(4-aminophenyl)methane TAPM.

[0012] Furthermore, the addition amount of the three-dimensional polyamine monomer is 1-30% of the mole fraction of the dianhydride monomer; the mole fraction of the dianhydride monomer is the sum of the mole fractions of the diamine monomer and the three-dimensional polyamine monomer.

[0013] Furthermore, the mole fraction of the dianhydride monomer must be equal to the sum of the mole fractions of the diamine monomer and the three-dimensional polyamine monomer.

[0014] Furthermore, the method specifically includes the following steps:

[0015] S1, dissolving a dianhydride monomer, a diamine monomer, and a three-dimensional polyamine monomer in an organic solvent in proportion, and stirring under an inert atmosphere to form a casting solution;

[0016] S2, placing the casting solution in an oven to volatilize and form a film, thereby obtaining a polyimide PI precursor film;

[0017] S3, removing the residual solvent in the precursor film by stripping and high temperature;

[0018] S4. Carbonizing the precursor membrane under an inert atmosphere to obtain the high permeability carbon molecular sieve gas separation membrane.

[0019] Furthermore, the dianhydride monomer in S1 is selected from hexafluorodianhydride 6FDA, pyromellitic dianhydride

[0020] Any one of PMDA, 3,3',4,4'-benzophenonetetracarboxylic dianhydride BTDA, 4,4'-biphenyltetracarboxylic dianhydride BPDA, and 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride DSDA.

[0021] Furthermore, the diamine monomer is selected from any one of 4,4'-diaminodiphenyl ether (ODA), m-phenylenediamine, benzyl diamine, methyl-substituted benzyl diamine, and isopropyl benzyl diamine.

[0022] Furthermore, the organic solvent in S1 is m-cresol, N,N-dimethylacetamide

[0023] DMAc, dimethyl sulfoxide DMF, N, N-dimethylformamide DMSO; the use amount of the polymer composed of any one of the dianhydride monomer, the diamine monomer and the three-dimensional polyamine monomer and the organic solvent is 2-300 mg / mL.

[0024] Further, the film forming process temperature in the S2 oven is 100-180 DEG C.

[0025] Further, the temperature for removing residual solvent in the film in S3 is 60-80 DEG C.

[0026] Further, the inert atmosphere is nitrogen or argon.

[0027] Further, the carbonization temperature in S4 is 450-800 DEG C, the carbonization time is 1-5 h, and the oxygen content in the system during the carbonization process is less than 0.1 ppm.

[0028] Further, the carbonization temperature is 550 DEG C, and the carbonization time is 3 h.

[0029] The second object of the present application is to provide a high-permeability carbon molecular sieve gas separation membrane, which has an ultramicropore pore size distribution.

[0030] The oxygen O2 permeation rate is 700-4000 Barrer, and the O2 / N2 selectivity is 5-8.

[0031] The carbon dioxide CO2 permeation rate is 4200-22000 Barrer, and the CO2 / CH4 selectivity is 40-100.

[0032] The third object of the present application is to provide a high-permeability carbon molecular sieve gas separation membrane for use in gas separation.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] 1. Unlike the preparation method of the traditional carbon molecular sieve membrane, the present application discloses a new preparation strategy combining three-dimensional polyamine monomer crosslinking degree regulation and one-step in-situ synthesis, the core innovation is to introduce a special polyamine monomer with rigid three-dimensional structure, by accurately controlling the molar ratio of the monomer and the dianhydride monomer, the crosslinking degree of the polymer precursor is accurately adjusted. Compared with the small molecule crosslinking agent in the prior art, the design utilizes the steric hindrance effect of the three-dimensional monomer, effectively inhibits the accumulation of polymer chains, utilizes the synergistic effect of one-step film forming process and low temperature carbonization, and constructs an anti-collapse ultramicropore channel in the carbonization process. This method not only simplifies the production process of the carbon molecular sieve membrane, but also realizes the accurate control of the pore size and distribution of the CMSM membrane, and simultaneously improves the permeability and selectivity, lays a foundation for the functionalization and industrial continuous production of the gas separation carbon membrane.

[0035] 2. The cross-linked network formed by the three-dimensional monomers in the carbon molecular sieve gas separation membrane of the present invention effectively inhibits carbonization shrinkage, concentrates the pore size distribution in the ultra-micropore range, significantly improves the specific surface area and optimizes the gas transmission channel, so that it has the characteristics of high permeability, high selectivity and strong stability. The carbon molecular sieve gas separation membrane shows advantages in performance and stability in industrial gas separation. The oxygen O2 permeability is 700-4000 Barrer and the O2 / N2 selectivity is 8-5; the carbon dioxide CO2 permeability is 4200-22000 Barrer and the CO2 / CH4 selectivity is 100-40. The mixed gas separation performance has exceeded the Robeson upper limit in 2018. At the same time, the carbon molecular sieve gas separation membrane also has good anti-plasticization ability, and is suitable for industrial scenarios such as O2 / N2 separation, CO2 / CH4 separation, natural gas decarbonization and purification, and shows good application potential in the gas separation industry.

[0036] 3. The carbon molecular sieve gas separation membrane preparation method provided by the present invention is simple to operate and has industrial potential. This preparation method not only involves low-cost raw materials, but also can precisely control the pore size range of the carbon membrane to meet production requirements by regulating the cross-linking degree of the polymer precursor. The preparation process only requires two steps: the preparation of the casting solution and the carbonization step. The carbonization step can be directly connected to the membrane production line, and oxygen content control is achieved through the circulation of a standard inert gas. This significantly improves the performance of the gas separation membrane while effectively reducing production costs, providing a reference solution for the industrial development of gas separation membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the general structure of the polyimide PI precursor film prepared by the method of the present invention;

[0038] Figure 2 Schematic diagram of the products of the membranes prepared in Examples 1-4 and the carbon molecular sieve gas separation membranes prepared in Examples 8-11 of the present invention;

[0039] Figure 3 FT-IR schematic diagrams of all films prepared in Examples 1-14 of the present invention;

[0040] Figure 4 Schematic diagrams of TGA and DTG of all films prepared in Examples 1-14 of the present invention;

[0041] Figure 5 Schematic diagram of BET of all films prepared in Examples 1-14 of the present invention;

[0042] Figure 6 Schematic diagram of pure gas separation performance of all membranes prepared in Examples 1-14 of the present invention;

[0043] Figure 7 Schematic diagram of the pressure-dependent separation performance of the membranes prepared in Examples 3 and 7 of the present invention for CO2 / CH4 (50 / 50) mixed gas. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with preferred embodiments. The endpoints of the ranges and any values ​​disclosed in the present invention 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 individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0045] Unless otherwise specified, the experimental methods in the following examples are conventional methods and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions.

[0046] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0047] Example 1

[0048] This embodiment provides a method for preparing an SPI-0 film, comprising the following steps:

[0049] S1. Dissolve 444.2 mg of 6FDA and 108.1 mg of m-phenylenediamine (mPD) in 2 mL of m-cresol and stir to form a homogeneous system using a magnetic stirrer.

[0050] S2. After the viscosity increases, add 8 mL of m-cresol and stir evenly. Add dropwise to a Petri dish with a diameter of 60 mm, place in an oven at 140°C and let it stand for 12 hours to evaporate, to obtain a membrane with a thickness of 100 μm.

[0051] Example 2

[0052] This embodiment provides a TAT-based in-situ cross-linked SPI-1% membrane, the preparation method of which includes the following steps:

[0053] S1. Dissolve 444.2 mg of 6FDA, 3 mg of TAT, and 106.5 mg of m-phenylenediamine (mPD) in 2 mL of m-cresol and stir to form a homogeneous system using a magnetic stirrer.

[0054] S2. Before the film is gelled, 8 mL of m-cresol is added and stirred evenly. The film is then added dropwise to a 60 mm diameter culture dish and placed in an oven at 140°C for 12 h to evaporate, thereby obtaining a 110 μm thick membrane.

[0055] Example 3

[0056] This embodiment provides a TAT-based in situ cross-linked SPI-5% membrane, the preparation method of which includes the following steps:

[0057] S1. Dissolve 444.2 mg of 6FDA, 15 mg of TAT, and 100 mg of m-phenylenediamine (mPD) in 2 mL of m-cresol and stir with a magnetic stirrer to form a homogeneous system.

[0058] S2. Before the film is gelled, 8 mL of m-cresol is added and stirred evenly. The film is then added dropwise to a 60 mm diameter culture dish and placed in an oven at 140°C for 12 h to evaporate, thereby obtaining a 110 μm thick membrane.

[0059] Example 4

[0060] This embodiment provides a TAT-based in-situ cross-linked SPI-10% membrane, the preparation method of which comprises the following steps:

[0061] S1. Dissolve 444.2 mg of 6FDA, 15 mg of TAT, and 100 mg of m-phenylenediamine (mPD) in 2 mL of m-cresol and stir with a magnetic stirrer to form a homogeneous system.

[0062] S2. Before the film is gelled, 8 mL of m-cresol is added and stirred evenly. The film is then added dropwise to a 60 mm diameter culture dish and placed in an oven at 140°C for 12 h to evaporate, thereby obtaining a 110 μm thick membrane.

[0063] Example 5

[0064] This embodiment provides a one-step in-situ cross-linking polymer membrane, the preparation method of which comprises the following steps:

[0065] S1. Dissolve 444.2 mg of 6FDA and 334.3 mg of 2,2-bis(4-aminophenyl)hexafluoropropane 6FA in 3 mL of m-cresol and stir to form a homogeneous system using a magnetic stirrer.

[0066] S2. After the viscosity increases, add 9 mL of m-cresol and stir evenly. Draw 4 mL of the casting solution and drop it into a Petri dish with a diameter of 60 mm. Place it in an oven at 140°C and let it evaporate for 12 hours to obtain a membrane with a thickness of 60 μm.

[0067] Example 6

[0068] This embodiment provides a polymer membrane based on TAMP in situ cross-linking, and the preparation method thereof comprises the following steps:

[0069] S1. Dissolve 444.2 mg of 6FDA, 14.5 mg of tris(4-aminophenyl)methane TAMP, and 309.2 mg of 2,2-bis(4-aminophenyl)hexafluoropropane 6FA in 3 mL of m-cresol and stir to form a homogeneous system using a magnetic stirrer.

[0070] S2. Before it gels, add 9 mL of m-cresol and stir evenly. Draw 4 mL of the casting solution and drop it into a culture dish with a diameter of 60 mm. Place it in an oven at 140°C and let it evaporate for 12 hours to obtain a membrane with a thickness of 70 μm.

[0071] Example 7

[0072] This embodiment provides a polymer membrane based on in-situ cross-linking of TAPM, the preparation method of which comprises the following steps:

[0073] S1. Dissolve 444.2 mg of 6FDA, 19 mg of tetrakis(4-aminophenyl)methane TAPM, and 301.7 mg of 2,2-bis(4-aminophenyl)hexafluoropropane 6FA in 3 mL of m-cresol and stir to form a homogeneous system using a magnetic stirrer.

[0074] S2. Before it gels, add 9 mL of m-cresol and stir evenly. Draw 4 mL of the casting solution and drop it into a culture dish with a diameter of 60 mm. Place it in an oven at 140°C and let it evaporate for 12 hours to obtain a membrane with a thickness of 80 μm.

[0075] Example 8

[0076] This embodiment provides a method for preparing a high permeability SPI-O-CMS membrane, comprising the following steps:

[0077] S1. Dissolve 444.2 mg of 6FDA and 108.1 mg of m-phenylenediamine (mPD) in 2 mL of m-cresol and stir to form a homogeneous system using a magnetic stirrer.

[0078] S2. After the viscosity increases, add 8 ml of m-cresol and stir evenly. Then, add dropwise to a 60 mm diameter Petri dish and place in a 140°C oven for 12 h to evaporate, thereby obtaining a 100 μm thick SPI-0 precursor film.

[0079] S3, removing the residual m-cresol from the SPI-0 precursor membrane by Soxhlet extraction and drying in a vacuum oven at 80°C;

[0080] S4. The prepared SPI-0 precursor membrane was placed in a tube furnace and carbonized for 1 hour at 550°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve a cross-linking reaction, and finally a high-permeability gas separation SPI-0-CMS membrane with a thickness of 121 μm was obtained.

[0081] Example 9

[0082] This embodiment provides a method for preparing a high-permeability SPI-1%-CMS membrane, comprising the following steps:

[0083] S1. Dissolve 444.2 mg of 6FDA, 3 mg of TAT, and 106.5 mg of m-phenylenediamine (mPD) in 2 mL of m-cresol and stir to form a homogeneous system using a magnetic stirrer.

[0084] S2. Before the gelation, add 8 mL of m-cresol and stir evenly. Then, add the mixture dropwise to a 60 mm diameter Petri dish and place it in a 140°C oven for 12 h to evaporate. Then, a 110 μm thick SPI-1% precursor film is obtained.

[0085] S3, removing the residual m-cresol from the SPI-1% precursor membrane by Soxhlet extraction and drying in a vacuum oven at 80°C;

[0086] S4. The prepared SPI-1% precursor membrane is placed in a tube furnace and carbonized for 1 hour at 550°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve a cross-linking reaction, and finally a high-permeability gas separation SPI-1%-CMS membrane with a membrane thickness of 122 μm is obtained.

[0087] Example 10

[0088] This embodiment provides a method for preparing a high-permeability SPI-5%-CMS membrane, comprising the following steps:

[0089] S1. Dissolve 444.2 mg of 6FDA, 15 mg of TAT, and 100 mg of m-phenylenediamine (mPD) in 2 mL of m-cresol and stir with a magnetic stirrer to form a homogeneous system.

[0090] S2. Before the gelation, add 8 ml of m-cresol and stir evenly. Then, add dropwise to a 60 mm diameter Petri dish and place in a 140°C oven for 12 h to evaporate, thereby obtaining a 110 μm thick SPI-5% precursor membrane.

[0091] S3. Residual m-cresol in the SPI-5% precursor membrane was removed by Soxhlet extraction and drying in a vacuum oven at 80°C.

[0092] S4. The prepared SPI-5% precursor membrane is placed in a tube furnace and carbonized for 1 hour at 550°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve a cross-linking reaction, and finally a high-permeability gas separation SPI-5%-CMS membrane with a membrane thickness of 125 μm is obtained.

[0093] Example 11

[0094] This embodiment provides a method for preparing a high-permeability SPI-10%-CMS membrane, comprising the following steps:

[0095] S1. Dissolve 444.2 mg of 6FDA, 15 mg of TAT, and 100 mg of m-phenylenediamine (mPD) in 2 mL of m-cresol and stir with a magnetic stirrer to form a homogeneous system.

[0096] S2. Before the gelation, add 8 mL of m-cresol and stir evenly. Then, add the mixture dropwise to a 60 mm diameter Petri dish and place it in a 140°C oven for 12 h to evaporate. Then, a 110 μm thick SPI-10% precursor film is obtained.

[0097] S3. Residual m-cresol in the SPI-10% precursor membrane was removed by Soxhlet extraction and drying in a vacuum oven at 80°C.

[0098] S4. The prepared SPI-10% precursor membrane is placed in a tube furnace and carbonized for 1 hour at 550°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve a cross-linking reaction, and finally a high-permeability gas separation SPI-10%-CMS membrane with a membrane thickness of 124 μm is obtained.

[0099] Example 12

[0100] This embodiment provides a one-step in-situ cross-linking polymer membrane, the preparation method of which comprises the following steps:

[0101] S1. Dissolve 444.2 mg of 6FDA and 334.3 mg of 2,2-bis(4-aminophenyl)hexafluoropropane 6FA in 3 mL of m-cresol and stir to form a homogeneous system using a magnetic stirrer.

[0102] S2. After the viscosity increases, add 9 mL of m-cresol and stir evenly. Draw 4 mL of the casting solution and drop it into a Petri dish with a diameter of 60 mm. Place it in a 140°C oven and let it evaporate for 12 hours to obtain a precursor film with a thickness of 60 μm.

[0103] S3, removing the residual m-cresol from the precursor membrane by Soxhlet extraction and drying in a vacuum oven at 80°C;

[0104] S4. The obtained precursor membrane is placed in a tube furnace and carbonized for 1 hour at 750°C under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve a cross-linking reaction, and finally a high permeability gas separation carbon molecular sieve membrane with a membrane thickness of 90 μm is obtained.

[0105] Example 13

[0106] This embodiment provides a polymer membrane based on TAMP in situ cross-linking, and the preparation method thereof comprises the following steps:

[0107] S1. Dissolve 444.2 mg of 6FDA, 14.5 mg of TAMP, and 309.2 mg of 2,2-bis(4-aminophenyl)hexafluoropropane 6FA in 3 mL of m-cresol and stir to form a homogeneous system using a magnetic stirrer.

[0108] S2. Before the gel is formed, 9 mL of m-cresol is added and stirred evenly. 4 mL of the casting solution is dropped into a 60 mm diameter Petri dish and placed in a 140°C oven for 12 h to evaporate, thereby obtaining a precursor film with a thickness of 70 μm.

[0109] S3, removing the residual m-cresol from the precursor membrane by Soxhlet extraction and drying in a vacuum oven at 80°C;

[0110] S4. The prepared precursor membrane is placed in a tube furnace and carbonized for 1 hour at 750° C. under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve a cross-linking reaction, and finally a high-permeability gas separation carbon molecular sieve membrane with a membrane thickness of 100 μm is obtained.

[0111] Example 14

[0112] This embodiment provides a polymer membrane based on in-situ cross-linking of TAPM, the preparation method of which comprises the following steps:

[0113] S1. Dissolve 444.2 mg of 6FDA, 19 mg of TAPM, and 301.7 mg of 2,2-bis(4-aminophenyl)hexafluoropropane 6FA in 3 mL of m-cresol and stir to form a homogeneous system using a magnetic stirrer.

[0114] S2. Before the gel is formed, 9 mL of m-cresol is added and stirred evenly. 4 mL of the casting solution is dropped into a 60 mm diameter Petri dish and placed in a 140°C oven for 12 h to evaporate, thereby obtaining a precursor film with a thickness of 80 μm.

[0115] S3, removing the residual m-cresol from the precursor membrane by Soxhlet extraction and drying in a vacuum oven at 80°C;

[0116] S4. The obtained precursor membrane is placed in a tube furnace and carbonized for 1 hour at 750° C. under argon protection in an environment with an oxygen content of less than 0.1 ppm to achieve a cross-linking reaction, and finally a high-permeability gas separation carbon molecular sieve membrane with a membrane thickness of 110 μm is obtained.

[0117] Performance Testing

[0118] 1. Pure gas permeability and selectivity test

[0119] The diaphragms prepared in Examples 1-14 were packaged and placed in a constant volume pressure test apparatus. After the instrument was evacuated, the permeability to H2, He, N2, O2, CH4 and CO2 and the selectivity to ideal gases were tested by the time lag method at 30°C and an upstream pressure of 2 bar. The test data are shown in Table 1.

[0120] Table 1 Pure gas separation performance test results

[0121]

[0122] Note: Gas permeability and selectivity were measured at 35°C and 2 bar pressure, where 1 bar = 0.1 MPa.

[0123] According to the test results of all the above embodiments and Table 1, it can be seen that: with the increase in the molar ratio of the three-dimensional polyamine monomer, the degree of cross-linking is improved, the microstructure and gas transmission channels of the membrane are effectively regulated, and the introduction of the three-dimensional structure TAT effectively inhibits the accumulation of polymer chains. On this basis, the gas permeability of the membrane is gradually enhanced, and the selectivity is slightly reduced. For example, the permeability of CH4 and CO2 of the polymer membrane of Example 4 is more than twice that of Example 1. The permeability of CH4 and CO2 increases from 0.27 to 0.81 Barrer and 17.8 to 39.6 Barrer, respectively. At the same time, the CO2 / CH4 selectivity of SPI-10% decreases slightly with the increase in the amount of triamine monomer, from 65.9 to 48.9.

[0124] Furthermore, it was found that after pyrolysis, the permeability of the CMS membrane increased significantly with the increase in cross-linking degree. Compared with Example 8, the CO2 permeability of Example 11 increased significantly by 5 times, from 4285 to 21638 barrers. This is because after pyrolysis, the trifluoromethyl fluorine on the aliphatic group overflowed in the form of gas on the carbon membrane, generating more micropores. At the same time, the introduction of the three-dimensional structure effectively suppressed the collapse of the pores, giving the CMS membrane a looser structure, a larger specific surface area, and a higher micropore ratio, thereby accelerating the gas transmission rate.

[0125] 2. Mixed gas permeability and selectivity test

[0126] The membranes of Examples 3 and 10 were packaged and installed in a cross-flow constant volume pressure swing test device. First, the entire system was fully evacuated to remove residual gas in the system that would interfere with the test results. Then, compressed air with a pressure range of 1.5-2.8 MPa and 0.2-1.5 MPa was introduced as the gas source upstream of the test device, respectively. By monitoring the change in pressure in the downstream cavity of the membrane over time, the gas permeation amount per unit time was obtained. To further determine the composition of the permeated gas, downstream gas samples were collected after stable permeation, and gas chromatography was used for component analysis, thereby obtaining the permeation performance of each component gas in the membrane material. The corresponding gas permeation test results are shown in Table 2.

[0127] Table 2. Mixed gas separation performance test

[0128]

[0129] Note: The gas permeability and selectivity were measured at 35°C and a pressure of 2 15 bar, 1 bar = 0.1 MPa

[0130] Since the membrane materials prepared in Examples 3 and 10 showed excellent permeability and selectivity in the pure gas separation test, in order to better evaluate the value of the membrane in practical application, a pressure-dependent separation test was performed on CO2 / CH4(50 / 50) mixed gas. In the mixed gas permeation test, considering the obvious competitive adsorption effect between CO2 and CH4, the permeability and selectivity of the two gases decreased to some extent as the upstream gas pressure increased.

[0131]

[0132] The membrane of Example 3 had excellent plasticization resistance. When the CO2 / CH4mixed gas pressure increased to 15 bar, there was still no plasticization phenomenon. Compared with pure gas, the mixed gas CO2 permeability of the membrane was relatively low, because CO2 and CH4 competed for adsorption in the membrane micropores, reducing single gas transport. For example, under the condition of CO2 / CH4(50 / 50) mixed gas, the CO2 permeability decreased from 28.8 Barrer to 26.5 Barrer. The separation performance of the CMS membrane of Example 10 was very stable, and no plasticization occurred. When the upstream pressure increased from 2 to 15 bar, although the CO2 permeability decreased from 7030 to 6692 Barrer, the CO2 / CH4 selectivity was still 51.5, breaking through the upper limit line of CO2 / CH4 separation performance updated in 2018, indicating that the introduction of three-dimensional structure has great potential in the practical application of CMS membrane based on CO2 separation.

[0133] ​The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a high permeability carbon molecular sieve gas separation membrane, characterized in that: Using dianhydride monomers, diamine monomers and three-dimensional polyamine monomers as raw materials, the molar ratio of the dianhydride monomers to the three-dimensional polyamine monomers is adjusted to control the crosslinking degree, and a polyimide (PI) precursor membrane is synthesized in situ by a one-step method. The residual solvent in the precursor membrane is then removed and the membrane is carbonized under an inert atmosphere to prepare the high permeability carbon molecular sieve gas separation membrane (CMSMs). Wherein, the three-dimensional polyamine monomer is selected from any one of 2,6,13(14)-triaminotriptycene TAT, tris(4-aminophenyl)methane TAMP, and tetrakis(4-aminophenyl)methane TAPM.

2. The method for preparing a high permeability carbon molecular sieve gas separation membrane according to claim 1, characterized in that: The added amount of the three-dimensional polyamine monomer is 1-30% of the mole fraction of the dianhydride monomer; the mole fraction of the dianhydride monomer is the sum of the mole fractions of the diamine monomer and the three-dimensional polyamine monomer.

3. The method for preparing a high permeability carbon molecular sieve gas separation membrane according to claim 1, characterized in that: The specific steps include: S1, dissolving a dianhydride monomer, a diamine monomer, and a three-dimensional polyamine monomer in an organic solvent in proportion, and stirring under an inert atmosphere to form a casting solution; S2, placing the casting solution in an oven to volatilize and form a film, thereby obtaining a polyimide PI precursor film; S3, removing the residual solvent in the precursor film by stripping and high temperature; S4. Carbonizing the precursor membrane under an inert atmosphere to obtain the high permeability carbon molecular sieve gas separation membrane.

4. The method for preparing a high permeability carbon molecular sieve gas separation membrane according to claim 3, characterized in that: The dianhydride monomer in S1 is selected from any one of hexafluorodianhydride 6FDA, pyromellitic dianhydride PMDA, 3,3',4,4'-benzophenonetetracarboxylic dianhydride BTDA, 4,4'-biphenyltetracarboxylic dianhydride BPDA, and 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride DSDA; and the diamine monomer is selected from any one of 4,4'-diaminodiphenyl ether ODA, m-phenylenediamine, benzyl diamine, methyl-substituted benzyl diamine, and isopropyl benzyl diamine.

5. The method for preparing a high permeability carbon molecular sieve gas separation membrane according to claim 3, characterized in that: The organic solvent in S1 is any one of m-cresol, N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMF), and N,N-dimethylformamide (DMSO); the amount of the polymer composed of the dianhydride monomer, the diamine monomer, and the three-dimensional polyamine monomer and the organic solvent is 2-300 mg / mL.

6. The method for preparing a high permeability carbon molecular sieve gas separation membrane according to claim 3, characterized in that: The film forming process temperature in the S2 oven is 100-180°C.

7. The method for preparing a high permeability carbon molecular sieve gas separation membrane according to claim 3, characterized in that: The inert atmosphere is nitrogen or argon.

8. The method for preparing a high permeability carbon molecular sieve gas separation membrane according to claim 3, characterized in that: The carbonization temperature in S4 is 450-800° C., the carbonization time is 1-5 hours, and the oxygen content in the system is lower than 0.1 ppm during the carbonization process.

9. A high permeability carbon molecular sieve gas separation membrane prepared according to the method of any one of claims 1 to 8, characterized in that: The high permeability carbon molecular sieve gas separation membrane has an ultra-micropore size distribution; Oxygen O2 permeability is 700-4000 Barrer, O2 / N2 selectivity is 5-8; The carbon dioxide CO2 permeability is 4200-22000 Barrer, and the CO2 / CH4 selectivity is 40-100.

10. Use of the high permeability carbon molecular sieve gas separation membrane according to claim 9 in gas separation.

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