Novel Cardo-based polyimide carbon molecular sieve membrane for separating CO2 / CH4 and preparation method of novel Cardo-based polyimide carbon molecular sieve membrane

Abstract

The invention belongs to the technical field of gas separation membranes, and discloses a novel Cardo-based polyimide carbon molecular sieve membrane for CO2 / CH4 separation and a preparation method thereof.The carbon molecular sieve membrane is prepared in an improved carbonization mode, a synthesized carbon molecular sieve membrane precursor is a polyimide membrane with-CF3 and fluorenyl, and the carbon molecular sieve membrane precursor is a polyimide membrane with-CF3 and fluorenyl. And meanwhile, a diamine monomer with high steric hindrance is introduced for copolymerization, so that the pore distribution and gas separation performance of the carbonized carbon molecular sieve membrane are improved. The preparation method comprises the following steps: firstly, preparing a flat sheet membrane with a smooth surface from various prepared polyimides in a solvent evaporation manner, and then carbonizing a polymer membrane with high free volume and high rigidity in an improved carbonization manner, so that the polymer membrane has micropore-ultramicropore pore channel distribution and excellent gas separation performance; the method has a good industrial prospect in the field of CO2 / CH4 separation.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas separation membranes, and relates to a polyimide carbon molecular sieve membrane with high CO2 / CH4 selectivity, a preparation method and application thereof in natural gas separation. Background Art

[0002] Climate warming is a global challenge facing mankind. The global carbon budget shows that the global average carbon dioxide concentration reached 417.2ppm in 2021, an astonishing 50% increase compared to the pre-industrial level in 1750. It is worth noting that a carbon dioxide concentration exceeding 450ppm means a critical threshold that will trigger a sudden change in climate and environment. Therefore, it is extremely important to seek effective technologies to separate and recycle carbon dioxide before it is emitted into the atmosphere. The traditional thermally driven CO2 separation methods currently used face challenges such as high cost, high energy consumption and environmental pollution.

[0003] In contrast, membrane separation is much more cost-effective and energy-efficient. It is estimated that membrane separation saves about 90% of energy compared to thermal distillation processes, making it a key contemporary separation technology. Among the various membrane materials that have been reported, polyimide exhibits easy fabrication, high thermal stability, and chemical stability, making it a prominent class of CO2 separation membrane materials. However, conventional polyimide membranes have low permeability due to their tight chain stacking, and are limited by the "trade-off" effect between their permeability and selectivity, making it difficult to break through the so-called Robeson upper limit. Therefore, improving the separation performance of polyimide membranes to break through the upper limit has become an important focus of current research.

[0004] The design and modification of polymer structure is considered to be an effective strategy to improve the gas separation performance of polyimide membranes. Studies have shown that the introduction of bulky rigid groups can effectively inhibit chain stacking, increase the free volume fraction (FFV), and improve its gas separation performance. Although the performance of this polymer membrane is relatively outstanding among many polyimide membrane materials, it only barely reaches the 2008 upper limit in the separation upper limit diagram, and there is still a gap with the performance requirements of actual industrial applications (Fan F., Sun Y., Zhao Q., et al. Fluorinated-cardo-based Co-polyimide membranes with enhanced selectivity for CO2 separation [J]. Separation and Purification Technology, 2023, 324.). The preparation of carbon molecular sieve membrane by polymer post-modification pyrolysis is also an effective way to improve performance. Carbon molecular sieve membrane (CMSM) is made by high-temperature pyrolysis of polymer precursors in an inert or vacuum atmosphere. CMSM combines the characteristics of polymer membranes and inorganic membrane materials, that is, polymer precursors can be processed into membranes of any geometric shape and customized thickness. At the same time, after carbonization, it can break through the "trade-off" limitation of polymer membranes by virtue of its narrow pore size distribution (close to the pore size distribution of inorganic crystalline materials) and excellent particle size screening performance. However, the research on carbon membranes is still in its infancy. Exploring the relationship between precursor materials and performance and finding excellent polymer materials are still the current research focus. (Liu Z., Qiu W., Quan W., et al. Advanced carbon molecular sieve membranes derived from molecularly engineered cross-linkable copolyimide for gas separations [J]. Nature Materials, 2022, 22 (1): 109-116.). Summary of the invention

[0005] In order to solve the problem that the gas separation performance of traditional polyimide membranes is relatively general due to the "trade-off" trade-off effect, the present invention provides a series of novel Cardo-based polyimide carbon molecular sieve membranes and preparation methods by high-temperature pyrolysis of polyimide precursor membranes. The present invention introduces F atoms and other diamine monomers into the polyimide precursor to explore the effects of different structures on the separation performance of carbon molecular sieve membranes. The carbon molecular sieve membranes finally obtained have high CO2 / CH4 selectivity and high CO2 permeability.

[0006] The main contents of the present invention are: synthesizing a novel polyimide precursor, wherein the dianhydride is selected from 6FDA, wherein the bulky -C(CF3)2- can effectively destroy the chain stacking and increase the free volume fraction of the polymer membrane; the diamine Ar1 is selected from a variety of cardo-based monomers FFDA, BAMF, and FDA; the diamine Ar2 is DAM with high steric hindrance and 6FAP with -OH, so as to obtain copolymerized polyimide membranes with different free volume fractions. Subsequently, the polyimide membranes with different structures are pyrolyzed and carbonized to obtain a carbon molecular sieve membrane with a microporous-ultramicroporous structure, so as to improve the size screening ability of the gas separation membrane.

[0007] The technical solution of the present invention:

[0008] A novel Cardo-based polyimide carbon molecular sieve membrane for CO2 / CH4 separation, which contains the following repeating unit structure:

[0009]

[0010] Wherein, m, n are the polymerization degree of polyimide, m, n = 400-800, and are positive integers.

[0011] Ar1 is any one of the following diamine structures, which is FFDA or BAMF:

[0012]

[0013] Ar2 is any one of the following diamine structures, DAM or 6FAP:

[0014]

[0015] A method for preparing a novel Cardo-based polyimide carbon molecular sieve membrane for CO2 / CH4 separation, comprising the following steps:

[0016] (1) Preparation of Cardo-based polyimide polymer: Under the protection of nitrogen gas, monomer Ar1 and monomer Ar2 are mixed in a reactor at a certain molar ratio, and meta-cresol is used as a reaction solvent to dissolve; then dianhydride monomer 6FDA is added, and the reaction solvent is supplemented to keep the total solute concentration of the reaction system at a certain concentration; after 6FDA is completely dissolved, a catalyst is added and the reaction system is raised to a certain temperature, and after a certain reaction time to complete polymerization, the reaction is cooled and collected in a washing solvent to obtain a white powder, which is washed several times and then transferred to a vacuum drying oven and dried at a certain temperature for a certain time to obtain a Cardo-based polyimide polymer;

[0017] (2) Preparation of Cardo-based polyimide precursor film: dissolving the obtained Cardo-based polyimide polymer in a non-polar solvent to obtain a casting solution of a certain concentration, stirring the casting solution to clarify it, casting it into a smooth culture dish through a filter membrane, and naturally evaporating it until a film is formed, and transferring the film to a vacuum drying oven at a certain temperature until the solvent is completely evaporated to obtain a Cardo-based polyimide precursor film with uniform thickness;

[0018] (3) Preparation of Cardo-based polyimide carbon molecular sieve membrane: The Cardo-based polyimide precursor membrane is sandwiched between two smooth corundum sheets, and heated under the protection of nitrogen gas according to a certain carbonization procedure to obtain a new Cardo-based polyimide carbon molecular sieve membrane with uniform thickness and smooth surface.

[0019] In step (1):

[0020] The molar ratio of the diamine monomers Ar1 and Ar2 is 0.5 to 1;

[0021] The total solute concentration of the reaction system is 10-40wt%;

[0022] The dianhydride monomer is 6FDA, and the structure is as follows:

[0023]

[0024] The catalyst is isoquinoline;

[0025] The reaction system temperature is 180-190°C and the reaction time is 8-12 hours;

[0026] The washing solvent is one of water, methanol and ethanol, and the washing times are 3-5 times;

[0027] The vacuum drying temperature is 180-200° C., and the vacuum drying time is 12-18 hours.

[0028] In step (2):

[0029] The non-polar solvent is THF;

[0030] The concentration of the casting solution is 1-10wt%;

[0031] The vacuum drying temperature is 80-100° C., and the vacuum drying time is 24-48 hours.

[0032] In step (3):

[0033] The carbonization temperature is 500-900° C., and the carbonization time is 1-3 hours.

[0034] Beneficial effects of the present invention: The present invention prepares a series of customizable uniform carbon molecular sieve membranes through an improved carbonization method, explores the effect of the introduction of aromatic fluorine atoms on the separation performance during the carbonization process, and explores the effect of different free volume precursor polymer membranes on the gas separation performance after carbonization. And by adjusting the parameters, a new Cardo-based polyimide carbon molecular sieve membrane with excellent CO2 / CH4 separation performance is prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the comparison result of the performance and separation upper limit of the gas separation membrane prepared in the comparative example and the example. DETAILED DESCRIPTION

[0036] The specific implementation of the present invention is further described below in conjunction with the technical solution.

[0037] Example 1

[0038] A novel Cardo-based polyimide carbon molecular sieve membrane, wherein the polyimide is polymerized by a dianhydride monomer 6FDA and a diamine monomer FFDA in a ratio of 1:1, and the monomer structure is as follows:

[0039]

[0040] This embodiment provides a method for preparing a novel Cardo-based polyimide carbon molecular sieve membrane, which specifically includes the following steps:

[0041] Before the reaction, the reactor was purged with nitrogen for 30 minutes. After the purging, the nitrogen flow rate was reduced to 100 mL / min and continued until the reaction was completed. Then, 20 mmol FFDA was dissolved in a certain amount of m-cresol, and the dissolution was promoted by mechanical stirring. After it was completely dissolved until the solution was clear, 20 mmol 6FDA was slowly added. When 6FDA was completely dissolved, isoquinoline was added and the reaction temperature was raised to 185°C and maintained for 12 hours. After the reaction was completed, it was naturally cooled to room temperature, and the reaction solution was poured into methanol to precipitate a white filamentous product, which was then washed three times with methanol, each time for 12 hours. Finally, the product was placed in a vacuum oven at 185°C and dried for 18 hours before being taken out.

[0042] Take 0.15g of the product and dissolve it in 7.35g of THF solvent to prepare a casting solution with a solute concentration of 2wt%. After stirring for 24h to completely dissolve, ultrasonic degassing and cast it in a culture dish, evaporate naturally until a film is formed, and transfer the film to a vacuum drying oven at 80°C and dry it for 48 hours to obtain a uniform polyimide film with a film thickness of 45μm.

[0043] The obtained polyimide membrane was sandwiched between two smooth corundum plates to prevent high-temperature deformation, and then placed in a tubular furnace with continuous nitrogen purge, gradually heated to 600°C for pyrolysis for 2 hours, and naturally cooled to room temperature to obtain a 6FDA-FFDA-CMS600 polyimide carbon molecular sieve membrane with a thickness of 32 μm.

[0044] The obtained carbon molecular sieve membrane was tested for gas separation performance at 35°C and 2 bar, where P(CO2) = 15579.3 Barrer, P(CH4) = 432.5 Barrer, P(H2) = 15579.3 Barrer; selectivity α(CO2 / CH4) = 36.0, α(H2 / CH4) = 50.0.

[0045] Compared with Comparative Example 1, the difference is that aromatic F atoms are introduced into the precursor polymer membrane. Although the introduction of aromatic F atoms reduces the free volume fraction of the precursor membrane and the permeability decreases after carbonization, the pore-forming effect of HF gas molecules generated by CF during the carbonization process generates ultra-micropores, which can effectively screen gas molecules with large size differences. Therefore, the selectivity of CO2 / CH4 is increased by about 148.3%, and the selectivity of H2 / CH4 is increased by about 517.3%. The separation performance of this embodiment is closer to the application requirements of natural gas separation.

[0046] Example 2

[0047] This embodiment introduces a DAM monomer with high steric hindrance for copolymerization on the basis of embodiment 1, and provides a novel Cardo-based copolymerized polyimide carbon molecular sieve membrane. The polyimide is polymerized by a diamine monomer FFDA, DAM and a dianhydride monomer 6FDA in a ratio of 1:1:2. The monomer structure is as follows:

[0048]

[0049] This embodiment provides a method for preparing a novel Cardo-based copolymerized polyimide carbon molecular sieve membrane, which specifically comprises the following steps:

[0050] Before the reaction, the reactor was purged with nitrogen for 30 minutes. After the purging, the nitrogen flow rate was reduced to 100 mL / min and continued until the reaction was completed. Then, 10 mmol FFDA and 10 mmol DAM were dissolved in a certain amount of m-cresol, and the dissolution was promoted by mechanical stirring. After the solution was completely dissolved until it was clear, 20 mmol 6FDA was slowly added. When 6FDA was completely dissolved, isoquinoline was added and the reaction temperature was raised to 185°C and maintained for 12 hours. After the reaction was completed, it was naturally cooled to room temperature, and the reaction solution was poured into methanol to precipitate a white filamentous product, which was then washed three times with methanol, each time for 12 hours. Finally, the product was placed in a vacuum oven at 185°C and dried for 18 hours before being taken out.

[0051] Take 0.15g of the product and dissolve it in 7.35g of THF solvent to prepare a casting solution with a concentration of 2wt%. After stirring for 24h to completely dissolve, ultrasonic degassing and cast it in a culture dish, evaporate naturally until a film is formed, and transfer the film to a vacuum drying oven at 80°C and dry it for 48 hours to obtain a uniform polyimide film with a film thickness of 43μm.

[0052] The obtained polyimide membrane was sandwiched between two smooth corundum plates to prevent high-temperature deformation, and then placed in a tubular furnace with continuous nitrogen purge, gradually heated to 600°C for pyrolysis for 2 hours, and naturally cooled to room temperature to obtain a 6FDA-FFDA / DAM (1:1)-CMS600 polyimide carbon molecular sieve membrane with a thickness of 34 μm.

[0053] The obtained carbon molecular sieve membrane was tested for gas separation performance at 35°C and 2 bar, where P(CO2) = 20291.5 Barrer, P(CH4) = 262.0 Barrer, P(H2) = 29997.0 Barrer; selectivity α(CO2 / CH4) = 77.4, α(H2 / CH4) = 114.5.

[0054] Compared with Comparative Example 2, the introduction of aromatic F atoms in this embodiment still produces ultra-micropores with excellent sieving performance during the carbonization process of the high free volume fraction polymer membrane, enhancing the separation ability of gas molecules with large size differences. Among them, the selectivity of CO2 / CH4 is increased by about 201.2%, and the selectivity of H2 / CH4 is increased by about 319.4%. The separation performance of this embodiment far exceeds the research on carbon molecular sieve membranes for CO2 / CH4 separation in recent years.

[0055] Example 3

[0056] This embodiment provides a novel Cardo-based copolymerized polyimide carbon molecular sieve membrane, which differs from the embodiment 2 only in that Ar2 of the polyimide is no longer DAM with high steric hindrance, but 6FAP monomer containing -OH, and the polyimide is polymerized by a diamine monomer FFDA, 6FAP and a dianhydride monomer 6FDA in a ratio of 1:1:2, and the monomer structure is as follows:

[0057]

[0058] This embodiment provides a method for preparing a novel Cardo-based copolymerized polyimide carbon molecular sieve membrane, which specifically comprises the following steps:

[0059] Before the reaction, nitrogen was used to purge the reactor for 30 minutes. After the purge, the nitrogen flow rate was reduced to 100 mL / min and continued until the reaction was completed. Then, 10 mmol FFDA and 10 mmol 6FAP were dissolved in a certain amount of m-cresol, and mechanical stirring was used to promote dissolution. After complete dissolution until the solution was clear, 20 mmol 6FDA was slowly added. When 6FDA was completely dissolved, isoquinoline was added and the reaction temperature was raised to 185°C and maintained for 12 hours. After the reaction was completed, it was naturally cooled to room temperature, and the reaction solution was poured into methanol to precipitate a white filamentous product, which was then washed three times with methanol, each time for 12 hours. Finally, the product was placed in a vacuum oven at 185°C and dried for 18 hours before being taken out.

[0060] Take 0.15g of the product and dissolve it in 7.35g of THF solvent to prepare a casting solution with a concentration of 2wt%. After stirring for 24h to completely dissolve, ultrasonic degassing and cast it in a culture dish, evaporate naturally until a film is formed, and transfer the film to a vacuum drying oven at 80°C and dry it for 48 hours to obtain a uniform polyimide film with a film thickness of 43μm.

[0061] The obtained polyimide membrane was sandwiched between two smooth corundum plates to prevent high-temperature deformation, and then placed in a tubular furnace with continuous nitrogen purge, gradually heated to 600°C for pyrolysis for 2 hours, and naturally cooled to room temperature to obtain a 6FDA-FFDA / 6FAP (1:1)-CMS600 polyimide carbon molecular sieve membrane with a thickness of 34 μm.

[0062] The obtained carbon molecular sieve membrane was tested for gas separation performance at 35°C and 2 bar, where P(CO2) = 3759.5 Barrer, P(CH4) = 60.3 Barrer, P(H2) = 4813.5 Barrer; selectivity α(CO2 / CH4) = 62.3, α(H2 / CH4) = 79.8.

[0063] In this embodiment, -OH forms a hydrogen bond with CF, making the chain stacking of the precursor more compact and the free volume fraction lower, so it has lower permeability and higher selectivity after carbonization. Compared with Comparative Example 3, 6FAP has side groups such as -CF3 and -OH, which are the same as CF in Example 2. During the carbonization process, a large number of ultra-micropores will be generated, which enhances the size screening ability and thus shows higher gas selectivity; while the mPDA-based copolymer in Comparative Example 3 also has a low free volume fraction, but the mPDA segment has no pore-forming effect of the side groups during the carbonization process, so the selectivity is lower than that of Example 3.

[0064] Comparative Example 1

[0065] This comparative example provides a Cardo-based polyimide carbon molecular sieve membrane, which differs from Example 1 only in that the raw material of the polyimide is a Cardo diamine monomer FDA that does not contain CF, and the other raw materials, dosages and implementation steps are the same as those in Example 1. The reaction structure is as follows:

[0066]

[0067] The obtained carbon molecular sieve membrane was tested for gas separation performance at 35°C and 2 bar, where P(CO2) = 31699.6 Barrer, P(CH4) = 2191.5 Barrer, P(H2) = 17764.7 Barrer; selectivity α(CO2 / CH4) = 14.5, α(H2 / CH4) = 8.1.

[0068] Comparative Example 2

[0069] This comparative example provides a Cardo-based copolyimide carbon molecular sieve membrane, which differs from Example 2 only in that the raw material of the polyimide is a Cardo diamine monomer FDA that does not contain CF, and the other raw materials, dosages and implementation steps are the same as those of Example 2. The reaction structure is as follows:

[0070]

[0071] The obtained carbon molecular sieve membrane was tested for gas separation performance at 35°C and 2 bar, where P(CO2) = 27390.1 Barrer, P(CH4) = 1067.2 Barrer, P(H2) = 29154.0 Barrer; selectivity α(CO2 / CH4) = 25.7, α(H2 / CH4) = 27.3.

[0072] Comparative Example 3

[0073] This comparative example provides a Cardo-based copolyimide carbon molecular sieve membrane, which differs from Example 3 only in that the comonomer in the raw material of the polyimide is no longer 6FAP containing -OH, but mPDA without a side group. Other raw materials, amounts and implementation steps are the same as those in Example 3. The reaction structure is as follows:

[0074]

[0075] The obtained carbon molecular sieve membrane was tested for gas separation performance at 35°C and 2 bar, where P(CO2) = 4077.2 Barrer, P(CH4) = 101.7 Barrer, P(H2) = 5734.5 Barrer; selectivity α(CO2 / CH4) = 40.1, α(H2 / CH4) = 56.4.

[0076] like Figure 1 As shown, the gas selectivity of the polyimide carbon molecular sieve membrane synthesized by the diamine monomer FFDA is greatly improved compared with FDA without aromatic F atoms, which is about 3 times that of comparative example 1 and exceeds the upper limit in 2019. Although the introduction of CF bonds reduces the free volume fraction of the polymer precursor, the HF gas molecules generated by the CF single bonds during the carbonization process form a large number of ultra-micropores, which enhance the size screening performance of the carbon molecular sieve membrane, proving that the introduction of aromatic F atoms can enhance the gas separation performance of the carbon molecular sieve membrane. Subsequently, on the basis of 6FDA-FFDA, a DAM monomer copolymer with high steric hindrance was introduced to enhance the FFV of the precursor copolymer membrane. After carbonization, the gas permeability of the membrane was greatly improved, and the permeability of CO2 was about 1.3 times that of Example 1, indicating that with the increase of the free volume fraction of the precursor membrane, the gas permeability of the carbon molecular sieve membrane can be significantly improved during the carbonization process. At the same time, compared with Comparative Example 2 without aromatic CF bonds, the selectivity of CO2 / CH4 was increased by about 201.2%, which also far exceeded the separation upper limit in 2019, proving that the introduction of aromatic F atoms can still improve the gas separation performance by virtue of the excellent pore-forming effect during the carbonization process of the copolymerized polyimide. In addition, Example 3 also introduces the copolymerized monomer 6FAP that reduces the FFV of the polyimide precursor membrane. Compared with Comparative Example 3, the pore-forming effect of the side groups in the copolymerized monomer is more excellent in the separation performance of the carbon molecular sieve membrane. In summary, all the examples significantly exceeded the latest 2019 separation upper limit, proving that this study prepared a new Cardo-based polyimide carbon molecular sieve membrane with excellent CO2 / CH4 separation performance by introducing aromatic F atoms into the precursor polymer.

[0077] Table 1 Gas permeability and selectivity of gas separation membranes prepared in comparative examples and examples

[0078]

Claims

1. A novel Cardo-based polyimide carbon molecular sieve membrane for CO2 / CH4 separation, characterized in that: The novel Cardo-based polyimide carbon molecular sieve membrane contains the following repeating unit structure: Wherein, m, n are the polymerization degree of polyimide, m, n = 400-800, and are positive integers; Ar1 is any one of the following diamine structures, which is FFDA or BAMF: Ar2 is any one of the following diamine structures, DAM or 6FAP:

2. A method for preparing a novel Cardo-based polyimide carbon molecular sieve membrane for CO2 / CH4 separation, characterized in that: Here are the steps: (1) Preparation of Cardo-based polyimide polymer: Under the protection of nitrogen gas, monomer Ar1 and monomer Ar2 are mixed in a reactor at a certain molar ratio, and meta-cresol is used as a reaction solvent to dissolve; then dianhydride monomer 6FDA is added, and the reaction solvent is supplemented to keep the total solute concentration of the reaction system at a certain concentration; after 6FDA is completely dissolved, a catalyst is added and the reaction system is raised to a certain temperature, and after a certain reaction time to complete polymerization, the reaction is cooled and collected in a washing solvent to obtain a white powder, which is washed several times and then transferred to a vacuum drying oven and dried at a certain temperature for a certain time to obtain a Cardo-based polyimide polymer; (2) Preparation of Cardo-based polyimide precursor film: dissolving the obtained Cardo-based polyimide polymer in a non-polar solvent to obtain a casting solution of a certain concentration, stirring the casting solution to clarify it, casting it into a smooth culture dish through a filter membrane, and naturally evaporating it until a film is formed, and transferring the film to a vacuum drying oven at a certain temperature until the solvent is completely evaporated to obtain a Cardo-based polyimide precursor film with uniform thickness; (3) Preparation of Cardo-based polyimide carbon molecular sieve membrane: The Cardo-based polyimide precursor membrane is sandwiched between two smooth corundum sheets, and heated under the protection of nitrogen gas according to a certain carbonization procedure to obtain a new Cardo-based polyimide carbon molecular sieve membrane with uniform thickness and smooth surface.

3. The method for preparing the novel Cardo-based polyimide carbon molecular sieve membrane according to claim 2, characterized in that: In step (1): The molar ratio of the diamine monomers Ar1 and Ar2 is 0.5 to 1; The total solute concentration of the reaction system is 10-40wt%; The dianhydride monomer is 6FDA, and the structure is as follows: The catalyst is isoquinoline; The reaction system temperature is 180-190°C and the reaction time is 8-12 hours; The washing solvent is one of water, methanol and ethanol, and the washing times are 3-5 times; The vacuum drying temperature is 180-200° C., and the vacuum drying time is 12-18 hours.

4. The method for preparing the novel Cardo-based polyimide carbon molecular sieve membrane according to claim 2, characterized in that: In step (2): The non-polar solvent is THF; The concentration of the casting solution is 1-10wt%; The vacuum drying temperature is 80-100° C., and the vacuum drying time is 24-48 hours.

5. A method for preparing a novel Cardo-based polyimide carbon molecular sieve membrane for CO2 / CH4 separation, characterized in that: In step (3): The carbonization temperature is 500-900° C., and the carbonization time is 1-3 hours.

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