Silicon-containing copolyimide hollow fiber carbon molecular sieve membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of membrane separation, in particular to a silicon-containing copolyimide hollow fiber carbon molecular sieve membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: in an inert atmosphere, mixing diamine, dianhydride and an aprotic polar solvent, and carrying out condensation polymerization to obtain a copolymerized polyamide acid solution; mixing the copolymerized polyamide acid solution, a dehydrating agent and a catalyst, and carrying out imidization reaction to obtain copolymerized polyimide; spinning the copolyimide to obtain a hollow fiber membrane; and carrying out heat treatment on the hollow fiber membrane in an inert atmosphere to obtain the hollow fiber carbon molecular sieve membrane. The selectivity and separability of the membrane are further improved through a heat treatment or carbonization process, the hollow fiber carbon molecular sieve membrane has good heat stability and can be used for a long time in a high-temperature environment, the membrane material is simple in preparation process, low-cost production can be achieved, the energy efficiency of the membrane material in the gas separation process is high, and the membrane material is suitable for industrial production. And the operation cost can be reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane separation technology, and particularly relates to a silicon-containing co-polyimide hollow fiber carbon molecular sieve membrane and a preparation method and application thereof. BACKGROUND

[0002] With the continuous advancement of industrialization, there is an increasing demand for efficient and low-cost gas separation technology worldwide. Traditional gas separation methods, such as adsorption and absorption, face problems such as high energy consumption and high operating costs in the separation process of large-scale gas mixtures. Compared with traditional methods, membrane separation technology has become a research and application hotspot due to its advantages of simple operation, low energy consumption, high separation efficiency, etc.

[0003] Among them, carbon molecular sieve membrane (CMSM) is widely used in gas separation field due to its excellent thermal stability, chemical stability and plasticization resistance. The pore structure of carbon molecular sieve membrane is closely related to the size and shape of gas molecules, and its separation performance mainly depends on factors such as membrane pore structure and free volume (FFV). Generally, carbon molecular sieve membrane is prepared by high-temperature carbonization process, which converts polymer precursor materials into membranes with highly microporous structure. However, traditional polyimide membranes are prone to membrane pore collapse during high-temperature carbonization process, resulting in a decrease in gas separation performance, especially when the membrane is used for a long time in a high-pressure environment, its permeation performance and selectivity will often deteriorate. Although various methods have been used to improve the stability of the membrane, such as cross-linking and filling modification, the trade-off between selectivity and flux is still a technical bottleneck, that is, while improving the permeability, the selectivity of the membrane is often reduced.

[0004] In order to improve this problem, researchers have proposed various modification strategies, one of which is to post-treat polyimide (PI) membranes with siloxane-based materials. Siloxane (Si-O-Si) groups have excellent thermal stability, mechanical strength and gas barrier properties, and the addition of siloxane to polyimide membranes can effectively improve the thermal stability of the membranes, improve the gas separation performance of the membranes, and slow down the collapse of the pore structure.

[0005] Studies have found that siloxane can form a more dense cross-linked structure between polyimide molecular chains, which can maintain a more stable pore structure during high-temperature carbonization process. This structure not only helps to improve the selectivity of the gas, but also improves the anti-aging ability of the membrane and prolongs the service life of the membrane. In addition, the introduction of siloxane groups can also optimize the microporous structure of the membrane, thereby effectively improving the separation ability of small molecule gases (such as H2, CO2).

[0006] Although the siloxane-modified polyimide material has excellent gas separation performance after carbonization, excessive or uneven distribution of siloxane during high-temperature carbonization can cause undesirable changes in the pore structure of the carbon molecular sieve membrane, resulting in poor gas separation performance. Therefore, how to accurately control the content of siloxane and optimize its distribution in the polyimide membrane is a key problem in the current research field of carbon molecular sieve membranes. SUMMARY

[0007] The purpose of the present application is to provide a method for preparing a copolymerized polyimide with accurate control of siloxane content, as well as a method for preparing a hollow fiber carbon molecular sieve membrane using such a precursor and its application. By preparing a copolymerized polyimide containing siloxane diamine, the siloxane functional group can be uniformly distributed in the polyimide backbone. During the subsequent carbonization process, the pore structure can be accurately controlled to obtain a high-performance hollow fiber carbon molecular sieve membrane. This technology provides a new approach for developing efficient and stable gas separation membranes and lays the foundation for future industrial applications.

[0008] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions: One of the technical solutions of the present application provides a method for preparing a hollow fiber carbon molecular sieve membrane, comprising the following steps: (1) mixing diamine, dianhydride and aprotic polar solvent under an inert atmosphere to carry out polycondensation reaction, obtaining a copolymerized polyamide acid solution; (2) mixing the copolymerized polyamide acid solution, dehydrating agent and catalyst to carry out imidization reaction, obtaining a copolymerized polyimide; (3) spinning the copolymerized polyimide to obtain a hollow fiber membrane; (4) heat treating the hollow fiber membrane under an inert atmosphere to obtain a hollow fiber carbon molecular sieve membrane.

[0009] The second technical solution of the present application provides a hollow fiber carbon molecular sieve membrane prepared by the above-mentioned preparation method.

[0010] The third technical solution of the present application provides a gas separation assembly comprising the above-mentioned hollow fiber carbon molecular sieve membrane; the assembly is used for the gas separation process selected from any one of the following: separation of helium and methane, separation of hydrogen and methane, separation of carbon dioxide and methane, separation of helium and nitrogen, separation of oxygen and nitrogen, and separation of hydrogen sulfide and methane.

[0011] Compared with the prior art, the present application has the following beneficial effects: High gas separation performance: by modifying the polyimide material, the prepared membrane has high gas permeability and selectivity, and is particularly suitable for the separation of small molecule gases.

[0012] Excellent thermal stability: The polyimide hollow fiber membrane has good thermal stability, can be used for a long time in high temperature environment, and meets the requirements of industrial applications.

[0013] Realization of carbon molecular sieve structure: Through a heat treatment or carbonization process, the selectivity and separation performance of the membrane are further improved.

[0014] Environmentally friendly and cost-effective: The membrane material preparation process is simple, can realize low-cost production, and has high energy efficiency in the gas separation process, which helps to reduce operating costs. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Equation for the synthesis of copolymerized polyimide by condensation polymerization of diamine monomer and dianhydride monomer in the preparation example of the present application.

[0016] Figure 2 PI-A copolymerized polyimide in the preparation example of the present application 1 H-NMR spectrum (DMSO-d6).

[0017] Figure 3 Infrared spectra of two copolymerized polyimides in the preparation example of the present application, wherein a represents PI-A and b represents PI-B.

[0018] Figure 4 SEM image of the copolymerized polyimide hollow fiber membrane in Example 7 of the present application.

[0019] Figure 5 Tg-DSC graph of the copolymerized polyimide membrane prepared in Example 1 and Example 2 of the present application, wherein (a) is Example 1 and (b) is Example 2.

[0020] Figure 6 Upbound graph of the copolymerized polyimide hollow fiber carbon molecular sieve membrane in Example 5 and Example 6 of the present application. DETAILED DESCRIPTION

[0021] The various illustrative embodiments of the present application will now be described in detail below, which should not be considered limiting to the present application, but rather as a description of certain aspects, features, and embodiments of the present application.

[0022] It should be understood that the terms described in the present application are only for the description of the specific embodiments, and are not used to limit the present application. In addition, for the numerical range in the present application, it should be understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Each smaller range between any stated value or stated range and any other stated value or intermediate value within the stated range is also included in the present application. The upper limit and the lower limit of these smaller ranges can be independently included or excluded from the range.

[0023] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as those of a person of ordinary skill in the art to which the application pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, preferred methods and materials are described. All documents mentioned herein are incorporated by reference to disclose and describe in full the methods and / or materials which are described therein. In case of conflict between the content of the specification and that of any document incorporated herein by reference, the content of the specification prevails.

[0024] Many modifications and variations of the present application described in the specification are possible without departing from the scope or spirit of the application. Other implementations of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application. The specification and examples are illustrative only.

[0025] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", and the like are open-ended terms that are intended to permit but not limit the inclusion of elements or the number of elements, as well as the possibility that one or more other elements can be added or otherwise included.

[0026] The raw materials used in the present application can be obtained commercially or prepared by prior art.

[0027] The room temperature described in the present application is 25±2℃.

[0028] The present application provides a preparation method of hollow fiber carbon molecular sieve membrane, comprising the following steps: (1) mixing diamine, dianhydride and aprotic polar solvent under inert atmosphere, and performing polycondensation reaction to obtain copolymer polyamide acid solution;

[0030] (2) mixing the copolymer polyamide acid solution, dehydrating agent and catalyst, and performing imidization reaction to obtain copolymer polyimide; (3) spinning the copolymer polyimide to obtain hollow fiber membrane; (4) performing heat treatment on the hollow fiber membrane under inert atmosphere to obtain hollow fiber carbon molecular sieve membrane.

[0031] In step (1) of the present application, the diamine monomer is dissolved in aprotic polar solvent under 0℃ and inert atmosphere, and after stirring and dissolving in ice water mixture, dianhydride is added, and polycondensation reaction is performed under room temperature to obtain viscous copolymer polyamide acid solution. In the present application, the diamine is a mixture of 1,3-phenylenediamine and siloxane diamine; the proportion of 1,3-phenylenediamine in diamine is 0-100 mol%; the proportion of siloxane diamine in diamine is 0-100 mol%, and the molar ratio of 1,3-phenylenediamine and siloxane diamine is preferably 2-4:1, for example, it can be 2:1, 3:1 or 4:1, etc. The dianhydride includes one or more of p-phenylenediamine dianhydride, benzophenone tetracarboxylic dianhydride, biphenyl tetracarboxylic dianhydride, hexafluoroisopropyl phthalic anhydride, benzophenone tetracarboxylic dianhydride and oxo-bis-phthalic anhydride; The aprotic polar solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

[0031] In the application, the temperature of the polycondensation reaction is -20-35℃, for example, -20℃, -10℃, 0℃, 10℃, 20℃ or 35℃, etc., and the time is 2-48 h, for example, 2 h, 6 h, 12 h, 24 h or 48 h, etc.; the solid content of the copolymerized polyamide acid solution is 10-40%, for example, 10%, 20%, 30% or 40%, etc. In step (2) of the application, the imidization reaction is carried out by adding a dehydrating agent and a catalyst to the copolymerized polyamide acid solution, the polymer is allowed to settle in methanol after the reaction is completed, and the polymer is washed with methanol for 24 h and dried to obtain the copolymerized polyimide.

[0032] In the application, the dehydrating agent is acetic anhydride; the catalyst is pyridine or triethylamine; the molar ratio of the diamine and the dianhydride is 1-7:1; the molar ratio of the dehydrating agent and the diamine is 1-5:1; and the molar ratio of the catalyst and the diamine is 1-2.5:1.

[0033] The temperature of the imidization reaction is 15-50℃, for example, 15℃, 25℃, 35℃, 45℃ or 50℃, etc., and the time is 2-48 h, for example, 2 h, 6 h, 12 h, 24 h or 48 h, etc.; and the drying temperature is 100-250℃, for example, 100℃, 150℃, 200℃ or 250℃, etc., and the time is 48 h.

[0034] In the application, the copolymerized polyimide has the following general structure formula I: Formula I; In formula I, m represents the number of repeating units, and m is 20-500; In formula I, n represents the number of repeating units, and n is 20-500; In formula I, Ar is a connecting unit of dianhydride anhydride groups, each Ar is the same or different; the dianhydride anhydride groups are derived from a dianhydride monomer, and the dianhydride monomer is one or more of p-phenylenediamine dianhydride (PMDA), benzophenone tetracarboxylic dianhydride (MPDA), biphenyl tetracarboxylic dianhydride (BPDA), hexafluoroisopropyl phthalic anhydride (6FDA), benzophenone tetracarboxylic dianhydride (BTDA) and oxo-bis-phthalic anhydride (ODPA).

[0035] The structures of each dianhydride monomer are as follows: (1) PMDA (2) MPDA (3) BPDA (4) 6FDA (5) BTDA (6) ODPA Step (3) of the present invention is to spin copolyimide to prepare hollow fiber membrane.

[0036] In this invention, the polyimide needs to be co-polymerized with a solvent before spinning to prepare a spinning solution; the solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran, methanol, ethanol, butanol and acetone, preferably a mixture of N-methylpyrrolidone and tetrahydrofuran, or a mixture of N-methylpyrrolidone and N,N-dimethylformamide; the mass fraction of the spinning solution is 15-40%, for example, it can be 15%, 20%, 25%, 30%, 35% or 40%, etc.

[0037] In some embodiments of the present invention, the spinning method is a dry-wet process. The spinning solution is transferred into a spinning tank maintained at a constant temperature and vacuum degassed for 12 hours. The core solution is supplied by a horizontal flow pump, and dry nitrogen is used as the spinning driving force. The dry-wet process allows the spinning solution to form a primary film after passing through the spinning nozzle. After entering the coagulation bath, the film is gelled and solidified. The hollow fiber membrane is washed in running water for 24 hours to remove residual solvent. The hollow fiber membrane is dried using a solvent replacement method. Hollow fibers soaked in water for 12 hours are carefully transferred into a beaker containing methanol and stirred for 30 minutes, three times (the methanol is replaced each time). Then, hexane is used to replace the methanol three times, 30 minutes each time.

[0038] In this invention, the spinning parameters include: the temperature of the spinning solution is 15~70℃, for example, it can be 15℃, 20℃, 30℃, 40℃, 50℃, 60℃ or 70℃, etc.; the temperature of the coagulation bath is 15~70℃, for example, it can be 15℃, 20℃, 30℃, 40℃, 50℃, 60℃ or 70℃, etc.; and the flow rate of the spinning solution is 2~50. The flow rate can be 0.5~50 mL / min, for example, 0.5 mL / min, 1 mL / min, 1 mL / min, 20 mL / min, 30 mL / min, 40 mL / min or 50 mL / min; the core fluid flow rate can be 0.5 mL / min, for example, 0.5 mL / min, 1 mL / min, 5 mL / min, 10 mL / min, 20 mL / min, 30 mL / min, 40 mL / min or 50 mL / min; the wire drawing rate can be 5~50 m / min, for example, 5 m / min, 8 m / min, 10 m / min, 20 m / min, 30 m / min, 40 m / min or 50 m / min; and the wire winding rate can be 5~50 m / min, for example, 5 m / min, 8 m / min, 10 m / min, 20 m / min, 30 m / min, 40 m / min or 50 m / min. The solvent used in the core fluid is an aqueous solution of one or a mixture of two of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone, with a concentration of 0-100%.

[0039] Step (4) of this invention involves heat-treating the hollow fiber membrane under an inert atmosphere to obtain a hollow fiber carbon molecular sieve membrane.

[0040] In this invention, the heat treatment is performed using a programmed temperature rise method, and the process parameters for the programmed temperature rise include: First stage: The temperature is increased from room temperature to 300°C at a rate of 4~6°C / min (preferably 5°C / min) and held at 300°C for 1~3 hours; this process ensures that the membrane is heated uniformly under an argon atmosphere, avoiding any oxidation reaction.

[0041] The second stage involves heating from 300°C to 400°C at a rate of 2-6°C / min (preferably 2°C / min) and holding at 400°C for 1-3 hours to minimize thermal stress during the temperature rise process and prevent film deformation or uneven carbonization.

[0042] The third stage involves heating from 400℃ to 500-800℃ (e.g., 500℃, 550℃, 600℃, 650℃, 700℃, or 800℃) at a rate of 0.2-2℃ / min (preferably 2℃ / min), and holding at 500-800℃ for 1-3 hours. This stage primarily completes the carbonization reaction of the membrane. Organic groups in the polyimide membrane are gradually removed, polymer chains break down, and the membrane transforms into a membrane with a carbon molecular sieve structure. During this process, the membrane's pore structure gradually forms, significantly improving gas separation performance.

[0043] In this invention, after the heat treatment, the tubular furnace is gradually cooled to room temperature. An argon atmosphere is maintained during the cooling process to prevent external oxygen from contacting the membrane surface and causing an oxidation reaction. The cooling rate is controlled to be less than 2°C per minute to avoid structural damage to the membrane due to excessive temperature differences. By precisely controlling the heating, temperature maintenance, and cooling processes, a stable hollow fiber carbon molecular sieve membrane with excellent gas separation performance is ultimately obtained.

[0044] The present invention also provides a hollow fiber carbon molecular sieve membrane prepared by the above-described preparation method.

[0045] This invention provides a copolyimide membrane modified with siloxane diamine. This membrane material can effectively suppress pore collapse during carbonization, maintaining high porosity and structural stability, thereby significantly improving the selectivity and flux of gas separation. Specifically, by introducing siloxane diamine into the polyimide matrix, a flexible cross-linked network can be formed at the molecular level, effectively enhancing the membrane's thermal stability, mechanical strength, and anti-aging ability.

[0046] The present invention also provides a gas separation assembly comprising the hollow fiber carbon molecular sieve membrane described above; the assembly is used for a gas separation process selected from any of the following: separation of helium and methane, separation of hydrogen and methane, separation of carbon dioxide and methane, separation of helium and nitrogen, separation of oxygen and nitrogen, and separation of hydrogen sulfide and methane.

[0047] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0048] Preparation Example 1 Under 0°C conditions, the mixture was first purged under a N2 atmosphere for about 15 minutes. Then, 0.134 mol of the diamine monomer 1,3-phenylenediamine (MPD) and 0.067 mol of 1,3-bis(3-aminopropyl)tetramethyldisilane (APTMDS) were dissolved in 360 g of N-methylpyrrolidone (NMP) and stirred in an ice-water mixture to dissolve. Then, 0.2 mol of hexafluoroisopropylphthalic anhydride (6FDA) dianhydride monomer was added and stirred at room temperature for 24 hours to form a viscous polyamic acid solution. Imidization was carried out by adding 1 mol of acetic anhydride and 0.5 mol of pyridine to a polyamic acid solution. After reacting at room temperature for 24 hours, the polymer was precipitated in methanol, washed with methanol for 24 hours, and then dried in a vacuum oven at 100-250°C for 48 hours to obtain polyimide, denoted as PI-B.

[0049] Preparation Example 2 The only difference from Example 1 is that 0.268 mol MPD and 0.067 mol APTMDS were dissolved in 360 g NMP. The polyimide prepared in this example is denoted as PI-A.

[0050] Example 1 Dissolve 1.00 g of PI-A in DMF and stir until completely dissolved. The solid content of the casting solution is 8.0 wt%. Filter the solution through a 0.45 μm polytetrafluoroethylene filter membrane. Pour the filtered solution into a flat glass petri dish and place it in a vacuum oven at 50 °C for 24 h. Then raise the temperature to 150 °C and place it for another 24 h to obtain a dense polyimide film with uniform thickness and a smooth surface, with a film thickness between 70 and 80 μm.

[0051] Example 2 Dissolve 1.00 g of PI-B in DMF and stir until completely dissolved. The solid content of the casting solution is 8.0 wt%. Filter the solution through a 0.45 PTFE membrane. Pour the filtered solution into a flat glass petri dish and place it in a vacuum oven at 50°C for 24 h. Then, raise the temperature to 150°C and place it for another 24 h to obtain a dense polyimide film with uniform thickness and a smooth surface, with a film thickness between 70 and 80 μm.

[0052] Test Example 1 Gas permeation tests were conducted on PI-A and PI-B dense membranes using the isovolute pressure rise method [Macromolecules 2024, 57, 1370-1382]. The test results are shown in Table 1.

[0053] Table 1 Gas permeation test results of PI-A and PI-B dense membranes

[0054] Example 3 The dried PI-A polyimide was dissolved in a mixed solvent of NMP and THF and stirred at room temperature for 24 hours to obtain a spinning solution. The spinning solution was transferred to a spinning tank maintained at a constant temperature and vacuum degassed for 12 hours. The core solution was supplied by a horizontal flow pump, using dry nitrogen as the spinning driving force. A dry-wet method was used to pass the membrane solution through the spinning nozzle to form a nascent membrane, which was then placed in a coagulation bath and gelled to solidify into a membrane. The hollow fiber membrane was washed in running water for 24 hours to remove residual solvent. The hollow fiber membrane was dried using a solvent displacement method. Hollow fibers soaked in water for 12 hours were carefully transferred to a beaker containing methanol and stirred for 30 minutes, three times (replacing methanol each time). Then, hexane was used to replace the methanol three times, 30 minutes each time. The membrane was dried at room temperature for 12 hours to obtain the PI-A hollow fiber membrane.

[0055] Example 4 The dried PI-B polyimide was dissolved in a mixed solvent of NMP and THF and stirred at room temperature for 24 hours to obtain a spinning solution. The spinning solution was transferred to a spinning tank maintained at a constant temperature and vacuum degassed for 12 hours. The core solution was supplied by a horizontal flow pump, using dry nitrogen as the spinning driving force. A dry-wet method was used to pass the membrane solution through the spinning nozzle to form a nascent membrane, which was then placed in a coagulation bath and gelled to solidify into a membrane. The hollow fiber membrane was washed in running water for 24 hours to remove residual solvent. Drying of the hollow fiber membrane was achieved using a solvent displacement method. Hollow fibers soaked in water for 12 hours were carefully transferred to a beaker containing methanol and stirred for 30 minutes, three times (replacing the methanol each time). Then, hexane was used to replace the methanol three times, 30 minutes each time. The membrane was dried at room temperature for 12 hours to obtain the PI-B hollow fiber membrane.

[0056] The spinning parameters for Examples 3 and 4 were set as shown in Table 2 below.

[0057] Table 2 Spinning parameters

[0058] Test Example 2 The hollow fiber membranes prepared in Examples 3 and 4 were used as components for gas permeability testing using the isovolute pressure rise method [Macromolecules 2024, 57, 1370−1382]. The test results are shown in Table 3. Table 3 Gas permeation test results of PI-A hollow fiber membrane and PI-B hollow fiber membrane

[0059] The mechanical properties of the membranes were tested using an INSTRON 3343 electronic universal testing machine according to ASTM D882-12. After measurement, the tensile strength and elongation at break were calculated from the stress-strain curve data provided by the instrument. The mechanical properties of each membrane are the average of three independent experimental results.

[0060] Table 4. Test results of mechanical properties of PI-A hollow fiber membrane and PI-B hollow fiber membrane.

[0061] Example 5 The dense membrane prepared in Example 1 was placed in a tube furnace and heated under an argon protective atmosphere. First, the furnace temperature was gradually increased to 300°C at a heating rate of 2°C / min and held at 300°C for 2 hours. Then, the temperature was gradually increased to 400°C at a heating rate of 2°C / min and held at 400°C for 1 hour. Finally, the temperature was increased to 550°C at a heating rate of 1°C / min and held at 550°C for 1 hour after stabilizing at 550°C. After carbonization was completed, the tube furnace was gradually cooled to room temperature while maintaining an argon atmosphere. The cooling rate was controlled to within 2 degrees per second to obtain the PI-A carbon molecular sieve flat sheet membrane.

[0062] Example 6 The dense flat sheet membrane prepared in Example 2 was placed in a tube furnace and heated under an argon protective atmosphere. First, the furnace temperature was gradually increased to 300°C at a heating rate of 2°C / min and held at 300°C for 1 hour. Then, the temperature was gradually increased to 400°C at a heating rate of 2°C / min and held at 400°C for 1 hour. Finally, the temperature was increased to 550°C at a heating rate of 1°C / min and held at 550°C for 1 hour after stabilizing at 550°C. After carbonization was completed, the tube furnace was gradually cooled to room temperature while maintaining an argon atmosphere. The cooling rate was controlled to within 2 degrees per second to obtain the PI-B carbon molecular sieve flat sheet membrane.

[0063] Test Example 3 The carbon molecular sieve flat sheet membranes prepared in Examples 5 and 6 were assembled into modules for gas permeation testing. First, hollow fibers were used to fabricate membrane modules. Each module consisted of an aluminum alloy base and hollow fibers bonded together on one side with epoxy resin AB glue, and the other side sealed with quick-drying epoxy resin. Each module contained 10-20 hollow fibers, approximately 10 cm in length. During testing, high-pressure gas was introduced into the outer side of the hollow fiber membrane, and permeation was measured on the cavities of the hollow fibers. The test results are as follows. Table 5 Gas permeation test results of PI-A carbon molecular sieve flat sheet membrane and PI-B carbon molecular sieve flat sheet membrane.

[0064] Example 7 The hollow fiber membrane prepared in Example 3 was placed in a tube furnace and heated under an argon protective atmosphere. First, the furnace temperature was gradually increased to 300°C at a heating rate of 2°C / min and held at 300°C for 1 hour. Then, the temperature was gradually increased to 400°C at a heating rate of 2°C / min and held at 400°C for 1 hour. Finally, the temperature was increased to 550°C at a heating rate of 1°C / min and held at 550°C for 1 hour to obtain a hollow fiber carbon molecular sieve membrane, denoted as PI-A-550.

[0065] Example 8 The hollow fiber membrane prepared in Example 4 was placed in a tube furnace and heated under an argon protective atmosphere. First, the furnace temperature was gradually increased to 300°C at a heating rate of 2°C / min and held at 300°C for 1 hour. Then, the temperature was gradually increased to 400°C at a heating rate of 2°C / min and held at 400°C for 1 hour. Finally, the temperature was increased to 550°C at a heating rate of 1°C / min and held at 550°C for 1 hour to obtain a hollow fiber carbon molecular sieve membrane, denoted as PI-B-550.

[0066] Test Example 4 The hollow fiber carbon molecular sieve membranes prepared in Examples 7 and 8 were assembled into a device and subjected to gas permeation testing. The test results are as follows: Table 6. Gas permeation test results of the hollow fiber carbon molecular sieve membranes prepared in Examples 7 and 8.

[0067] The anti-plasticization test was conducted according to the method described in "Influence of previous history on physical aging in thin glassy polymer films as gas separation membranes" (Polymer Volume 51, Issue 16, 22 July 2010, Pages 3784-3792), and the test results are shown in Table 7.

[0068] Table 7. Anti-plasticization test of hollow fiber carbon molecular sieve membranes prepared in Examples 7 and 8.

[0069] SEM image of the copolyimide hollow fiber membrane in Example 7 is shown below. Figure 4As shown, (a) clearly presents the cross-sectional structure of the hollow fiber carbon molecular sieve membrane, which has a dense skin layer and a support layer with finger-like pores, typical of asymmetric hollow fiber membranes. (b) shows the portion of the hollow fiber membrane near the outer skin layer, where the skin layer is dense and defect-free. (c) A skin layer thickness of approximately 3 micrometers can be observed, containing silica particles. (d) Clearly shows aggregates of silica particles with relatively uniform particle size.

[0070] Example 9 The hollow fiber membrane prepared in Example 3 was placed in a tube furnace and initially heated under an argon protective atmosphere. First, the furnace temperature was gradually increased to 300°C at a heating rate of 2°C / min, and held at 300°C for 1 hour. Then, the temperature was gradually increased to 400°C at a heating rate of 2°C / min, and held at 400°C for 1 hour. Finally, the temperature was increased to 650°C at a heating rate of 1°C / min. After the temperature stabilized at 650°C, it was maintained at this temperature for 1 hour to obtain the hollow fiber carbon molecular sieve membrane, denoted as PI-A-650.

[0071] Example 10 The hollow fiber membrane prepared in Example 4 was placed in a tube furnace and initially heated under an argon protective atmosphere. First, the furnace temperature was gradually increased to 300°C at a heating rate of 2°C / min, and held at 300°C for 1 hour. Then, the temperature was gradually increased to 400°C at a heating rate of 2°C / min, and held at 400°C for 1 hour. Finally, the temperature was increased to 650°C at a heating rate of 1°C / min. After the temperature stabilized at 650°C, it was maintained at this temperature for 1 hour to obtain the hollow fiber carbon molecular sieve membrane, denoted as PI-B-650.

[0072] Test Example 5 The hollow fiber carbon molecular sieve membranes prepared in Examples 9 and 10 were assembled into an array for testing. The test results are as follows: Table 8. Gas permeation test results of the hollow fiber carbon molecular sieve membranes prepared in Examples 9 and 10.

[0073] Table 9. Thermal stability and high-temperature separation performance of the hollow fiber carbon molecular sieve membranes prepared in Examples 9 and 10.

[0074] Table 10 Aging performance test of hollow fiber carbon molecular sieve membrane prepared in Example 10

[0075] Example 11 Under 0°C conditions, the mixture was first purged under a N2 atmosphere for about 15 minutes. Then, 0.067 mol of 1,3-bis(3-aminopropyl)tetramethyldisilane (APTMDS) was dissolved in 360 g of N-methylpyrrolidone (NMP), and the solution was stirred in an ice-water mixture to dissolve it. Then, 0.2 mol of hexafluoroisopropylphthalic anhydride (6FDA) dianhydride monomer was added, and the mixture was stirred at room temperature for 24 hours to form a viscous polyamic acid solution. Imidization was carried out by adding 1 mol of acetic anhydride and 0.5 mol of pyridine to a polyamic acid solution. After reacting at room temperature for 24 hours, the polymer was precipitated in methanol, washed with methanol for 24 hours, and then dried in a vacuum oven at 100-250°C for 48 hours to obtain polyimide.

[0076] The dried polyimide was dissolved in a mixed solvent of NMP and THF and stirred at room temperature for 24 hours. The casting solution was transferred to a spinning tank maintained at a constant temperature and vacuum degassed for 12 hours. The core solution was supplied by a horizontal flow pump, with dry nitrogen as the spinning driving force. A dry-wet method was used to pass the membrane solution through the spinning nozzle to form a nascent membrane, which was then placed in a coagulation bath and gelled to solidify into a membrane. The hollow fiber membrane was washed in running water for 24 hours to remove residual solvent. The hollow fiber membrane was dried using a solvent displacement method. Hollow fibers soaked in water for 12 hours were carefully transferred to a beaker containing methanol and stirred for 30 minutes, three times (with methanol replaced each time). The methanol was then replaced with n-hexane three times, for 30 minutes each time. The membrane was dried at room temperature for 12 hours to obtain the hollow fiber membrane.

[0077] The prepared hollow fiber membrane was placed in a tube furnace and initially heated under an argon protective atmosphere. First, the furnace temperature was gradually increased to 300℃ at a heating rate of 2℃ / min, and held at 300℃ for 1 hour. Then, the temperature was gradually increased to 400℃ at a heating rate of 2℃ / min, and held at 400℃ for 1 hour. Finally, the temperature was increased to 650℃ at a heating rate of 1℃ / min. After the temperature stabilized at 650℃, it was maintained at this temperature for 1 hour to obtain the hollow fiber carbon molecular sieve membrane.

[0078] Example 12 Under 0°C conditions, the mixture was first purged under a N2 atmosphere for about 15 minutes. Then, 0.268 mol of 1,3-phenylenediamine (MPD) was dissolved in 360 g of N-methylpyrrolidone (NMP), and the solution was stirred in an ice-water mixture to dissolve it. Then, 0.2 mol of hexafluoroisopropylphthalic anhydride (6FDA) dianhydride monomer was added, and the mixture was stirred at room temperature for 24 hours to form a viscous polyamic acid solution. Imidization was carried out by adding 1 mol of acetic anhydride and 0.5 mol of pyridine to a polyamic acid solution. After reacting at room temperature for 24 hours, the polymer was precipitated in methanol, washed with methanol for 24 hours, and then dried in a vacuum oven at 100-250°C for 48 hours to obtain polyimide.

[0079] The dried polyimide was dissolved in a mixed solvent of NMP and THF and stirred at room temperature for 24 hours. The casting solution was transferred to a spinning tank maintained at a constant temperature and vacuum degassed for 12 hours. The core solution was supplied by a horizontal flow pump, with dry nitrogen as the spinning driving force. A dry-wet method was used to pass the membrane solution through the spinning nozzle to form a nascent membrane, which was then placed in a coagulation bath and gelled to solidify into a membrane. The hollow fiber membrane was washed in running water for 24 hours to remove residual solvent. The hollow fiber membrane was dried using a solvent displacement method. Hollow fibers soaked in water for 12 hours were carefully transferred to a beaker containing methanol and stirred for 30 minutes, three times (with methanol replaced each time). The methanol was then replaced with n-hexane three times, for 30 minutes each time. The membrane was dried at room temperature for 12 hours to obtain the hollow fiber membrane.

[0080] The prepared hollow fiber membrane was placed in a tube furnace and initially heated under an argon protective atmosphere. First, the furnace temperature was gradually increased to 300℃ at a heating rate of 2℃ / min, and held at 300℃ for 1 hour. Then, the temperature was gradually increased to 400℃ at a heating rate of 2℃ / min, and held at 400℃ for 1 hour. Finally, the temperature was increased to 650℃ at a heating rate of 1℃ / min. After the temperature stabilized at 650℃, it was maintained at this temperature for 1 hour to obtain the hollow fiber carbon molecular sieve membrane.

[0081] Test Example 6 The hollow fiber carbon molecular sieve membranes prepared in Examples 11 and 12 were assembled into an array for testing. The test results are as follows: Table 11 Gas permeation test results of hollow fiber carbon molecular sieve membranes prepared in Examples 11 and 12

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a hollow fiber carbon molecular sieve membrane, characterized in that, Includes the following steps: (1) Under an inert atmosphere, diamine, dianhydride and aprotic polar solvent are mixed and subjected to a polycondensation reaction to obtain a copolyamic acid solution; (2) The copolyamic acid solution, dehydrating agent and catalyst are mixed and imidized to obtain copolyimide; (3) The copolyimide is spun to obtain a hollow fiber membrane; (4) The hollow fiber membrane is heat-treated under an inert atmosphere to obtain a hollow fiber carbon molecular sieve membrane.

2. The preparation method according to claim 1, characterized in that, The copolyimide has the general structural formula shown in Formula I: Formula I; In Equation I, m represents the number of repeating units, and the value of m ranges from 20 to 500; In Equation I, n represents the number of repeating units, and the value of n ranges from 20 to 500; In Formula I, Ar is the linking unit of the dianhydride group, and each Ar may be the same or different; the dianhydride group is derived from the dianhydride monomer, which is one or more of the following: pyromellitic dianhydride, tetraphenyl dianhydride, biphenyl dianhydride, hexafluoroisopropylphthalic anhydride, benzophenone tetracarboxylic anhydride, and oxobisphthalic anhydride.

3. The preparation method according to claim 1, characterized in that, Before spinning, the copolyimide needs to be mixed with a solvent to prepare a spinning solution; the solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran, methanol, ethanol, butanol and acetone; the mass fraction of the spinning solution is 15~40%.

4. The preparation method according to claim 3, characterized in that, The spinning parameters include: the temperature of the spinning solution is 15~70℃, the temperature of the coagulation bath is 15~70℃, the flow rate of the spinning solution is 2~50 mL / min, the flow rate of the core solution is 0.5~50 mL / min, the drawing rate is 5~50 m / min, and the winding rate is 5~50 m / min.

5. The preparation method according to claim 1, characterized in that, The heat treatment is performed using a programmed temperature rise method, and the process parameters for the programmed temperature rise include: First stage: Increase the temperature from room temperature to 300 ℃ at a rate of 4~6 ℃ / min, and hold at 300 ℃ for 1~3 h; Second stage: Increase the temperature from 300 ℃ to 400 ℃ at a rate of 2~6 ℃ / min, and hold at 400 ℃ for 1~3 h; The third stage: the temperature is increased from 400 ℃ to 500-800 ℃ at a rate of 0.2-2 ℃ / min, and then held at 500-800 ℃ for 1-3 h.

6. The preparation method according to claim 1, characterized in that, The diamine is a mixture of 1,3-phenylenediamine and siloxane diamine; the 1,3-phenylenediamine accounts for 0-100 mol% of the diamine; the siloxane diamine accounts for 0-100 mol% of the diamine. The dianhydride includes one or more of the following: pyromellitic dianhydride, tetraphenyl dianhydride, biphenyl dianhydride, hexafluoroisopropylphthalic anhydride, benzophenone tetracarboxylic anhydride, and oxobisphthalic anhydride. The aprotic polar solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

7. The preparation method according to claim 1, characterized in that, The dehydrating agent is acetic anhydride; the catalyst is pyridine or triethylamine; the molar ratio of the diamine to the dianhydride is 1~7:1; the molar ratio of the dehydrating agent to the diamine is 1~5:1; the molar ratio of the catalyst to the diamine is 1~2.5:

1.

8. The preparation method according to claim 1, characterized in that, The polycondensation reaction is carried out at a temperature of -20 to 35°C for 2 to 48 hours; the solid content of the polyamic acid solution is 10 to 40%. The imidization reaction is carried out at a temperature of 15-50°C for a time of 2-48 h.

9. A hollow fiber carbon molecular sieve membrane prepared by the preparation method according to any one of claims 1 to 8.

10. A gas separation membrane module, characterized in that, The assembly comprises the hollow fiber carbon molecular sieve membrane of claim 9; the assembly is used in a gas separation process selected from any one or more of the following: separation of helium and methane, separation of hydrogen and methane, separation of carbon dioxide and methane, separation of helium and nitrogen, separation of oxygen and nitrogen, and separation of hydrogen sulfide and methane.

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