Hollow fiber gas separation membrane, method of making and use thereof

Abstract

The application discloses a hollow fiber gas separation membrane and a preparation method and application thereof. The preparation method uses oxadiazoline as a chemical crosslinking agent, dissolves the oxadiazoline with ethanol, soaks the hollow fiber in the oxadiazoline solvent, and reacts for a period of time at a certain temperature to complete the crosslinking. The application uses oxadiazoline as a crosslinking agent to perform chemical crosslinking on a series of different hollow fiber membranes in a 6FDA (hexafluorodiphthalic anhydride) and DABA (3,5-diaminobenzoic acid) system, reduces the cost, maintains the support layer of the fiber from collapsing, improves the gas separation performance of the fiber, improves the plasticization resistance and mechanical strength of the hollow fiber membrane, and obtains a polyimide hollow fiber gas separation membrane with high mechanical strength and high CO2 plasticization resistance.

Description

Technical Field

[0001] This invention relates to the field of membrane preparation technology, and in particular to a hollow fiber gas separation membrane, its preparation method, and its application. Background Technology

[0002] As an emerging clean energy source, natural gas is gradually gaining widespread application and attention in various fields of production and daily life due to its advantages such as high calorific value, clean products, and convenient transportation.

[0003] Biogas contains a large amount of methane, as well as impurities such as carbon dioxide and helium. The presence of large amounts of carbon dioxide and helium may reduce the calorific value of biogas and increase compression and transportation costs, thus limiting the economic viability of biogas for direct power generation at the production site. By removing these impurities, the purified gas is expected to contain high-quality methane, which can facilitate its use in a variety of applications (Bioresource Technology Reports, 2018, 1:79-88).

[0004] In recent years, membrane technology has played an increasingly important role in the field of gas separation, especially hollow fiber membranes, which have attracted widespread attention due to their advantages such as simple operation, small footprint, low energy consumption, flexible design, and high separation efficiency.

[0005] Polyimide membranes based on 6FDA exhibit excellent He / CH4 and CO2 / CH4 separation performance, along with good thermal and chemical stability. Specifically, the CO2 / CH4 selectivity of the 6FDA-DABA system reaches 62.2 at 35°C and 100 psi, while the He / CH4 selectivity of the 6FDA-mPDA-DABA-TFDB system exceeds 200 at the same temperature, surpassing most commercial polyimide membranes. Furthermore, DABA, with its carboxyl group, possesses high chemical reactivity and can undergo cross-linking under specific conditions, significantly enhancing its resistance to plasticization. Therefore, the 6FDA-DABA system has attracted increasing attention in fields such as natural gas separation and flue gas purification.

[0006] Currently, the traditional crosslinking method for 6FDA-DABA hollow fiber membranes is the thermally induced decarboxylation crosslinking method. The advantage of this method is that it is simple to operate, does not affect the processing performance of the material, and the prepared hollow fibers have good plasticization resistance and thermal stability. However, because this method requires heat treatment of the fiber at high temperature for a long time, the support layer of the fiber will collapse, which will significantly reduce the gas separation performance of the fiber and, in severe cases, reduce the mechanical properties of the fiber, seriously affecting its application in the field of gas separation.

[0007] Therefore, a new method for preparing hollow fiber membranes in the 6FDA-DABA system is needed. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a method for preparing a gas separation membrane. This invention uses dioxazoline as a crosslinking agent to chemically crosslink a hollow fiber membrane based on a 6FDA-DABA system, significantly reducing the crosslinking temperature and cost while preparing a fiber membrane with high permeability and selectivity, as well as practical mechanical strength and excellent resistance to plasticization.

[0009] A further technical problem to be solved by the present invention is to provide a gas separation membrane prepared by the above preparation method and its application.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for preparing a hollow fiber gas separation membrane, wherein the preparation method uses dioxazoline as a chemical crosslinking agent, dissolves dioxazoline in ethanol, immerses hollow fibers in dioxazoline solvent, and reacts at a certain temperature for a period of time to complete crosslinking;

[0012] The chemical structural formula of the dioxazoline is as follows:

[0013] .

[0014] The preparation method of the gas separation membrane specifically includes the following steps:

[0015] S1: Preparation of crosslinking agent: Dissolve dioxazoline in ethanol to obtain a crosslinking agent solution, wherein the solid content of the crosslinking agent solution is 3%~5%;

[0016] S2: The hollow fiber membrane is immersed in a crosslinking agent solution at 60~80℃ for 20~24h to obtain the gas separation membrane.

[0017] Preferably, after step S2, the cross-linked hollow fiber membrane is further cleaned and dried. Specifically, the chemically cross-linked wet fiber is immersed in ethanol at 50-60°C for 40-48 hours, then immersed in isooctane at 65-75°C for 10-12 hours to remove the solvent from the fiber; and then thoroughly dried at 100-120°C.

[0018] The hollow fiber membrane is made of a polyimide polymer, which has the following structure as shown in general formula (I):

[0019] (I)

[0020] Where n represents the degree of polymerization of different components of the polymer, and n is an integer from 100 to 200; x represents the molar ratio of the DABA part, and x is an integer from 0 to 100; the weight-average molecular weight of the polymer is between 20,000 and 50,000.

[0021] The R1 group is one or more of the following groups;

[0022] ;

[0023] The R2 group comprises any one or more of the following structures:

[0024] .

[0025] The polyimide polymer is a copolymer of a crystalline aromatic diamine and an aromatic dianhydride.

[0026] The hollow fiber membrane is prepared as follows:

[0027] S01: First, the monomer is dissolved in p-chlorophenol to obtain a monomer solution with a solid content of 15-20 wt%, and then heated to 90-120°C under a nitrogen atmosphere; wherein the monomer includes an aromatic diamine and an aromatic dianhydride, and the molar ratio of the aromatic diamine to the aromatic dianhydride is 0.95-1:1-1.1;

[0028] S02: Add isoquinoline catalyst to the monomer solution, then heat to 190~200℃ and stir to allow the reaction to proceed for a certain time; after the reaction is complete, pour the reaction solution into methanol or ethanol to obtain a fibrous polymer; the mass of the catalyst is 0.05~0.1% of the total mass of the monomer; the reaction time is 12~24h;

[0029] S03: After multiple precipitation and washing, the solvent in the polymer is removed. The obtained polymer is dried in a vacuum drying oven at 120~130℃ for 20~24h and then weighed. The dried polymer is polyimide.

[0030] S04: The dried polymer is dissolved in a polar solvent at 90~100℃ to obtain a polymer solution. The polymer solution is filtered through a metal mesh, and then spun to obtain the hollow fibers. The solid content of the polymer solution is controlled at 15~20wt%, and the rotational viscosity of the polymer solution at 100~105℃ is controlled at 280~350 poise. The spinning process specifically involves extruding the hollow fibers through a hollow fiber membrane spinning nozzle and passing the extruded hollow fibers through a nitrogen atmosphere. Subsequently, a phase inversion is carried out in an ethanol aqueous solution condensation bath at a temperature of -10~-5℃ to produce a hollow fiber membrane.

[0031] Preferably, the aromatic diamine includes DABA, and the aromatic dianhydride includes 6FDA.

[0032] More preferably, the aromatic diamine further includes any one or more of the following compounds:

[0033] 2,2'-Di(trifluoromethyl)diaminobiphenyl, 2,2',5,5'-tetrachlorodiphenylamine, p-diaminobiphenyl, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 2,3,5,6-tetramethyl-1,4-phenylenediamine, 3,6-diaminocarbazole, 3,6-diamino-9-ethylcarbazole;

[0034] The aromatic dianhydride further includes any one or more of the following compounds:

[0035] BPDA: PMDA: .

[0036] In step S04, the solid content of the polymer solution is controlled at 15-20 wt%, and the rotational viscosity of the polymer solution at 100-105°C is 280-350 poise.

[0037] A hollow fiber gas separation membrane is prepared by the above-mentioned method for preparing hollow fiber gas separation membranes.

[0038] The aforementioned applications of hollow fiber gas separation membranes include: purification of helium from natural gas; separation of helium and radon; and purification of methane from biogas.

[0039] When the hollow fiber gas separation membrane of the present invention is applied to CO2 removal from flue gas and biogas, the specific operation is as follows:

[0040] Approximately 1000-10000 hollow fiber membranes of suitable length, prepared by the method of this invention, are bundled together. The two sides of the fiber bundle are fixed to a tube sheet with resin, and an opening is made at one end of each fiber to allow air intake. The membrane module is then assembled in this way. The membrane module is then connected to a container containing a mixed gas inlet, a permeate gas outlet, and a non-permeate gas outlet, thus isolating the space connecting the interior of the hollow fiber membrane from the space connecting the exterior of the hollow fiber membrane. In such a gas separation membrane module, the mixed gas is input from the mixed gas inlet into the interior of the hollow fiber membrane or into the space communicating with the exterior, but is not limited to this. When the mixed gas comes into contact with the hollow fiber membrane, specific gas components contained in the mixed gas selectively permeate through the membrane. The permeate gas exits from the permeate gas outlet, and the non-permeate gas that does not permeate the membrane exits from the non-permeate gas outlet. Gas separation is achieved in this way. Elements of a gas separation membrane module are prepared in this manner.

[0041] The components are inserted into a stainless steel container to form a membrane separation assembly. The flue gas or biogas material to be separated is passed into the outside of the gas separation membrane under a pressure of 300 psi, and CH4 after He and CO2 removal is obtained at the product gas outlet.

[0042] The beneficial effects of this invention are as follows:

[0043] (1) In this invention, dioxazoline is used as a crosslinking agent to chemically crosslink a series of different hollow fiber membranes in the 6FDA (hexafluorodianhydride) and DABA (3,5-diaminobenzoic acid) system, which reduces costs, keeps the fiber support layer from collapsing, improves the gas separation performance of the fiber, and improves the anti-plasticization performance and mechanical strength of the hollow fiber membrane, thus obtaining a polyimide hollow fiber gas separation membrane with high mechanical strength and high CO2 plasticization resistance.

[0044] (2) The polyimide hollow fiber gas separation membrane obtained by the present invention has advantages such as high strength and anti-plasticization during the gas separation process. It has good thermal stability, improves the permeability while maintaining good selectivity for He / CH4, CO2 / N2 and CO2 / CH4, and plays an important role in the field of natural gas methane purification. Attached Figure Description

[0045] Figure 1 The graph shows the changes in permeation flux and selectivity of the hollow fiber gas separation membranes prepared in Examples 1, 3, and the comparative examples under pure gas conditions and different feed pressures.

[0046] Figure 2 Thermogravimetric curves of the hollow fiber gas separation membranes prepared in Examples 1, 4, 5 and the comparative examples are shown.

[0047] Figure 3The tensile strength curves are for the hollow fiber gas separation membranes prepared in Examples 1, 3, 6 and the comparative examples. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0049] Unless otherwise specified, the raw materials and equipment used in the embodiments of the present invention are all commercially available.

[0050] Example 1:

[0051] (1) At room temperature, DABA, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 6FDA, BPDA (biphenyl-3,3',4,4'-tetracarboxylic acid dianhydride), and PMDA (pyromellitic dianhydride) were first dissolved in p-chlorophenol to obtain a monomer solution. The molar ratio of each raw material in the monomer solution was BPDA:6FDA:PMDA:DABA:2,2'-bis(trifluoromethyl)diaminobiphenyl = 1:1:1:1.5:1.5, and the solid content of the solution was 18wt%. Then, the temperature was raised to 120℃ under a nitrogen atmosphere.

[0052] (2) After the monomer is completely dissolved in the solvent, a small amount of isoquinoline catalyst is added to the monomer solution, and then the temperature is raised to 190°C. The polymerization reaction is promoted by stirring. The polymerization is initiated at 190°C and then reacted at this temperature for 24 hours. After the reaction is completed, the solution is poured into methanol or ethanol to obtain fibrous polymer.

[0053] (3) After repeated precipitation and washing, the solvent in the fibrous polymer was removed, and the obtained polymer was dried in a vacuum drying oven at 120°C for 24 hours; the amount of catalyst used was 0.05 wt% of the total monomer mass;

[0054] (4) Dissolve the dried polymer in a polar solvent at 90°C, control the solid content of the solution at 15wt%, and control the rotational viscosity of the solution at 100~105°C at 280~350 poise. Filter the polyimide solution with a metal mesh, then extrude it through a hollow fiber membrane spinning nozzle, and pass the extruded hollow fiber through a nitrogen atmosphere. Subsequently, in a condensation bath of ethanol aqueous solution, a phase inversion is carried out at -10°C to produce wet fiber.

[0055] (5) Soak the wet fiber in a 5% dioxazoline ethanol solution at 80°C for 24 hours; complete the chemical cross-linking of the hollow fiber to obtain the chemically cross-linked wet fiber;

[0056] (6) The chemically cross-linked wet fibers were immersed in ethanol at 50°C for 40 hours, and then immersed in isooctane at 65°C for 12 hours to remove the solvent from the fibers; and then thoroughly dried at 120°C. The final product is a hollow fiber gas separation membrane made of polyimide.

[0057] Example 2:

[0058] (1) At room temperature, DABA, 2,2',5,5'-tetrachlorodiphenylamine, 6FDA, BPDA (biphenyl-3,3',4,4'-tetracarboxylic acid dianhydride), and PMDA (pyromellitic dianhydride) were first dissolved in p-chlorophenol to obtain a monomer solution. The molar ratio of each raw material in the monomer solution was BPDA:6FDA:DABA:2,2',5,5'-tetrachlorodiphenylamine = 1:1:0.8:1.2, the solid content of the solution was 20wt%, and the solid content of the solution was 18wt%. Then, the temperature was raised to 90℃ under a nitrogen atmosphere.

[0059] (2) After the monomer is completely dissolved in the solvent, a small amount of isoquinoline catalyst is added to the monomer solution, and then the temperature is raised to 190°C. The polymerization reaction is promoted by stirring, and the polymerization is initiated at 200°C. The reaction is then carried out at this temperature for 12 hours. After the reaction is completed, the solution is poured into methanol or ethanol to obtain fibrous polymer.

[0060] (3) After repeated precipitation and washing, the solvent in the fibrous polymer was removed, and the resulting polymer was dried in a vacuum drying oven at 130°C for 20 h; the amount of catalyst used was 0.1 wt% of the total monomer mass;

[0061] (4) Dissolve the dried polymer in a polar solvent at 100°C, control the solid content of the solution to 20wt%, and control the rotational viscosity of the solution at 100~105°C to 280~350 poise. Filter the polyimide solution with a metal mesh, then extrude it through a hollow fiber membrane spinning nozzle, and pass the extruded hollow fiber through a nitrogen atmosphere. Subsequently, in a condensation bath of ethanol aqueous solution, a phase inversion is carried out at -5°C to produce wet fiber.

[0062] (5) Soak the wet fiber in a 3% dioxazoline ethanol solution at 60°C for 20 hours to complete the chemical cross-linking of the hollow fiber and obtain the chemically cross-linked wet fiber.

[0063] (6) The chemically cross-linked wet fibers were immersed in ethanol at 60°C for 48 hours, and then immersed in isooctane at 75°C for 10 hours to remove the solvent from the fibers; and then thoroughly dried at 100°C. The final product is a hollow fiber gas separation membrane made of polyimide.

[0064] Example 3:

[0065] The experimental steps in this embodiment are the same as in Embodiment 1. The difference is that the molar ratio of the raw materials in the monomer solution is 6FDA:PMDA:DABA:2,2',5,5'-tetrachlorodiphenylamine = 1:1:1:1, and the solid content of the solution is 18wt%.

[0066] Example 4:

[0067] The experimental steps in this embodiment are the same as in Example 1. The difference lies in the molar ratio of the raw materials in the monomer solution: BPDA:6FDA:PMDA:DABA:2,2',5,5'-tetrachlorodiphenylamine = 1:1:1:1.15:1.7, and the solid content of the solution is 15wt%.

[0068] Example 5:

[0069] The experimental steps in this embodiment are the same as in Example 1. The difference lies in the molar ratio of the raw materials in the monomer solution: BPDA:6FDA:PMDA:DABA:p-diaminobiphenyl = 1:1:1:1.5:1.5, and the solid content of the solution is 18wt%.

[0070] Example 6:

[0071] The experimental steps in this embodiment are the same as in Embodiment 1. The difference lies in the molar ratio of the raw materials in the monomer solution: BPDA:6FDA:PMDA:DABA:p-diaminobiphenyl = 1:1:1:1.2:1.8, and the solid content of the solution is 18wt%. The remaining experimental and application steps are the same as in Embodiment 1.

[0072] Example 7:

[0073] The experimental steps in this embodiment are the same as in Example 1. The difference is that the molar ratio of the raw materials in the monomer solution is 6FDA:DABA:4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl = 3:1.5:1.5, and the solid content of the solution is 18wt%.

[0074] Example 8:

[0075] The experimental steps in this embodiment are the same as in Example 1. The difference is that the molar ratio of the raw materials in the monomer solution is 6FDA:DABA:4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl = 3:1.2:1.8, and the solid content of the solution is 15wt%.

[0076] Example 9:

[0077] The experimental steps in this embodiment are the same as in Example 1. The difference is that the molar ratio of the raw materials in the monomer solution is 6FDA:DABA:4,4'-diamino-3,3'-dimethylbiphenyl = 3.3:1.5:1.35, and the solid content of the solution is 18wt%.

[0078] Example 10:

[0079] The experimental steps in this embodiment are the same as in Example 1. The difference lies in the molar ratio of the raw materials in the monomer solution: 6FDA:DABA:4,4'-diamino-3,3'-dimethylbiphenyl = 3:1.2:1.8, and the solid content of the solution is 18wt%.

[0080] Example 11:

[0081] The experimental steps in this embodiment are the same as in Embodiment 1. The difference is that the molar ratio of the raw materials in the monomer solution is BPDA:6FDA:PMDA:DABA = 1:1:1:3, and the solid content of the solution is 18wt%.

[0082] Example 12:

[0083] The experimental steps in this embodiment are the same as in Embodiment 1. The difference lies in the molar ratio of the raw materials in the monomer solution being BPDA:6FDA:PMDA:DABA = 1.2:1:0.8:3, and the solid content of the solution being 18wt%.

[0084] Example 13:

[0085] The experimental steps in this embodiment are the same as in Embodiment 1. The difference lies in the molar ratio of the raw materials in the monomer solution being BPDA:6FDA:PMDA:DABA = 0.8:1:1.2:3, and the solid content of the solution being 18wt%.

[0086] Example 14:

[0087] The experimental steps in this embodiment are the same as in Embodiment 1. The difference lies in the molar ratio of the raw materials in the monomer solution being BPDA:6FDA:PMDA:DABA = 0.5:1:1.5:3, and the solid content of the solution being 18wt%.

[0088] Example 15:

[0089] The experimental steps in this embodiment are the same as in Example 1. The difference is that the molar ratio of the raw materials in the monomer solution is BPDA:6FDA:PMDA:DABA:3,6-diamino-9-ethylcarbazole = 1:1:1:1.5:1.5, and the solid content of the solution is 18wt%.

[0090] Example 16:

[0091] The experimental steps in this embodiment are the same as in Example 1. The difference is that the molar ratio of the raw materials in the monomer solution is BPDA:6FDA:PMDA:DABA:3,6-diamino-9-ethylcarbazole = 1.2:1.1:1:1.5:1.5, and the solid content of the solution is 18wt%.

[0092] Example 17:

[0093] The experimental steps of this embodiment are the same as those of Example 1. The difference is that the molar ratio of the raw materials in the monomer solution is BPDA:6FDA:PMDA:DABA:3,6-diamino-9-ethylcarbazole:2,2',5,5'-tetrachlorodiphenylamine = 1:1:1:1:1:1, and the solid content of the solution is 18wt%.

[0094] Example 18:

[0095] The experimental steps of this embodiment are the same as those of Example 1. The difference is that the molar ratio of the raw materials in the monomer solution is BPDA:6FDA:PMDA:DABA:3,6-diamino-9-ethylcarbazole:2,2',5,5'-tetrachlorodiphenylamine = 1:1:1:0.8:0.8:1.4, and the solid content of the solution is 18wt%.

[0096] Comparative example:

[0097] This example uses a polymer system of DABA, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 6FDA, BPDA (biphenyl-3,3',4,4'-tetracarboxylic dianhydride), and PMDA (pyromellitic dianhydride polyimide) as a comparative example:

[0098] (1) At room temperature, DABA, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 6FDA, BPDA (biphenyl-3,3',4,4'-tetracarboxylic acid dianhydride), and PMDA (pyromellitic dianhydride polyimide) were first dissolved in p-chlorophenol to obtain a monomer solution. The molar ratio of each raw material in the monomer solution was BPDA:6FDA:PMDA:DABA:2,2'-bis(trifluoromethyl)diaminobiphenyl = 1:1:1:1.5:1.5, and the solid content of the solution was 18wt%. Then, the temperature was raised to 120℃ under a nitrogen atmosphere.

[0099] (2) After the monomer is completely dissolved in the solvent, a small amount of isoquinoline catalyst is added to the monomer solution, and then the temperature is raised to 190°C. The polymerization reaction is promoted by stirring. The polymerization is initiated at 190°C and then reacted at this temperature for 24 hours. After the reaction is completed, the solution is poured into methanol or ethanol to obtain fibrous polymer.

[0100] (3) After multiple precipitation and washing, the solvent in the fibrous polymer was removed, and the obtained polymer was dried in a vacuum drying oven at 120°C for 24 hours; wherein the molar ratio of diamine to dianhydride in the reaction system was maintained at 1:1, and the amount of catalyst was 0.05 wt% of the total monomer mass;

[0101] (4) Dissolve the dried polymer in a polar solvent at 90~100℃, control the solid content of the solution at 15~20wt%, and control the rotational viscosity of the solution at 100~105℃ at 280~350 poise. Filter the polyimide solution with a metal wire mesh, and then extrude it through a hollow fiber membrane spinning nozzle. Pass the extruded hollow fiber body through a nitrogen atmosphere, and then carry out phase inversion in an ethanol aqueous solution condensation bath at a temperature of -10~-5℃ to produce wet fiber.

[0102] (5) Immerse the wet fiber in ethanol at 50-60°C for 40-48 hours, then immerse it in isooctane at 65-75°C for 10-12 hours to remove the solvent from the fiber; and dry it thoroughly at 100-120°C.

[0103] The resulting hollow fiber gas separation membrane is applied to the CH4 purification of natural gas and biogas. The specific application method is as follows: Approximately 105 hollow fiber membranes of suitable length, prepared by the method of this invention, are bundled together; these hollow fibers are tightly packed (fill rate approximately 50%), and both ends of the fiber bundle are embedded in thermosetting epoxy resin, fixed in a tube sheet, with an opening at one end of each fiber to allow gas inlet. This method completes the assembly of the membrane module. The membrane module is then connected to a container containing a mixed gas inlet, a permeate gas outlet, and a non-permeate gas outlet, thus isolating the space connecting the interior of the hollow fiber membrane from the space connecting the exterior. In such a gas separation membrane module, the mixed gas is input from the mixed gas inlet into the interior of the hollow fiber membrane or into the space communicating with the exterior, but is not limited to this. When the mixed gas comes into contact with the hollow fiber membrane, specific gas components contained in the mixed gas selectively permeate through the membrane. The permeate gas exits from the permeate gas outlet, and the non-permeate gas that does not permeate the membrane exits from the non-permeate gas outlet. A gas separation element is thus prepared.

[0104] The components are inserted into a stainless steel container to form a membrane separation assembly. Under a pressure of 300 psi, the flue gas or biogas to be separated is passed into the external hole side of the gas separation membrane, and the de-CO2 flue gas or biogas is obtained at the product gas outlet.

[0105] Performance testing:

[0106] (1) Methods for determining the flux and selectivity of hollow fiber membranes

[0107] A permeation performance evaluation element with an effective length of 20 mm was fabricated using approximately 10 hollow fiber membranes, a stainless steel tube, and an epoxy resin-based adhesive. This element was inserted into a stainless steel container to form a pencil-shaped assembly. The temperature was kept constant at 35°C, and pure CO2 gas was introduced at a fixed rate into the exterior of the hollow fibers of the pencil-shaped assembly. The gas preceding the hollow fiber membrane element was considered the upstream gas, and the gas passing through the element was considered the downstream gas. The upstream gas pressure was kept constant, and the change in downstream gas pressure over time was measured. The CO2 permeation flux was calculated using a formula; the CH4 permeation flux was tested in the same manner. The CO2 / CH4 selectivity was obtained by comparing the two.

[0108] Replace the pure gas in the above method with a CH4 / CO2 mixture containing 50% CH4, and test it using the same method to obtain the flux of the mixed gas. Measure the ratio of the two gases in the mixed gas to obtain the selectivity of CO2 / CH4 in the mixed gas.

[0109] (2) Measurement of rotational viscosity

[0110] The rotational viscosity of the polyamide solution was measured at 100°C using a rotational viscometer (rotor shear rate: 1.75 / s).

[0111] Table 1

[0112]

[0113] Table 1 shows the gas permeation performance of different embodiments and comparative examples. It can be seen that, compared with the thermally induced decarboxylation crosslinking of the comparative example, the gas separation membrane of the fiber treated by the low-temperature chemical crosslinking method has a significantly improved permeation flux, while the selectivity is also maintained at a very high level.

[0114] Figure 1 The high-temperature dimensional stability of the gas separation membranes prepared in Examples 1, 3 and the comparative example under nitrogen conditions shows that, compared with the comparative example, the hollow fiber gas separation membranes prepared in Examples 1 and 3 have higher high-temperature dimensional stability.

[0115] Figure 2 Thermogravimetric curves of the gas separation membranes prepared in Examples 1, 4, 5, and the comparative examples are shown. Figure 2 The high-temperature resistance of the membrane of the present invention can be clearly seen from the thermogravimetric curve. The membrane only begins to lose weight gradually above 400°C, indicating that the membrane prepared by the present invention can remain stable at a high temperature of 400°C and can meet almost all harsh application temperatures.

[0116] Figure 3 The tensile strength curves are for the gas separation membranes prepared in Examples 1, 3, 6 and the comparative example. Figure 3This indicates that the mechanical properties of the chemically cross-linked gas separation membrane are far superior to those of the membrane prepared by thermally induced decarboxylation cross-linking. This ensures that no fiber breakage will occur during spinning, and the membrane is more robust and durable, greatly expanding the application fields of polyimide gas separation membranes.

[0117] This invention uses dioxazoline as a crosslinking agent. Dioxazoline is dissolved in ethanol, and the hollow fiber membrane with carboxyl groups undergoes chemical crosslinking at a low temperature below 80°C. This significantly improves the hollow fiber membrane's resistance to plasticization and aging, as well as its gas separation performance. Compared with traditional thermally induced crosslinking methods, the chemical crosslinking method operates at a lower temperature, preventing the collapse of the hollow fiber membrane's support layer and maximizing the membrane's gas separation performance. Simultaneously, the low-temperature crosslinking significantly saves energy required for heating the thermal crosslinking temperature, greatly reducing crosslinking costs. This membrane exhibits high strength and resistance to plasticization during gas separation, possesses good thermal stability, and maintains good selectivity for CO2 / N2, CO2 / CH4, and He / CH4 while improving permeability. It plays an important role in areas such as CO2 removal from flue gas and biogas, and the separation of natural gas, helium, and methane.

[0118] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0119] The parts of this invention not described in detail are well-known in the art. The above embodiments are provided merely for the purpose of describing the invention and are not intended to limit its scope. The scope of the invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principles of the invention should be covered within its scope.

Claims

1. A method for preparing a hollow fiber gas separation membrane, characterized in that, The preparation method of the hollow fiber gas separation membrane specifically includes the following steps: S1: Preparation of crosslinking agent: Dissolve dioxazoline in ethanol to obtain a crosslinking agent solution, wherein the solid content of the crosslinking agent solution is 3%~5%; wherein the chemical structural formula of dioxazoline is as follows: ; S2: Immerse the hollow fiber membrane in a crosslinking agent solution at 60~80℃ for 20~24h; the hollow fiber membrane is made of polyimide polymer, which is a copolymer of crystalline aromatic diamine and aromatic dianhydride; the aromatic diamine includes DABA, and the aromatic dianhydride includes 6FDA. S3: The hollow fiber gas separation membrane can be obtained by cleaning and drying the soaked hollow fiber membrane.

2. The method for preparing the hollow fiber gas separation membrane according to claim 1, characterized in that: The polyimide polymer has the structure shown in general formula (Ⅰ): （Ⅰ） Where n represents the degree of polymerization of different components of the polymer, and n is an integer between 100 and 200; x represents the molar ratio of the DABA part, and x is an integer greater than 0 and less than 100; the weight-average molecular weight of the polymer is between 20,000 and 50,000. The R1 group is one or more of the following groups; ； The R2 group comprises any one or more of the following structures: 。 3. The method for preparing the hollow fiber gas separation membrane according to claim 2, characterized in that, The hollow fiber membrane is prepared as follows: S01: First, the monomer is dissolved in p-chlorophenol to obtain a monomer solution with a solid content of 15-20 wt%, and then heated to 90-120°C under a nitrogen atmosphere; wherein the monomer includes an aromatic diamine and an aromatic dianhydride, and the molar ratio of the aromatic diamine to the aromatic dianhydride is 0.95-1:1-1.

1. S02: Add isoquinoline catalyst to the monomer solution, then heat to 190~200℃ and stir to allow the reaction to proceed for a certain period of time; After the reaction is complete, the reaction solution is poured into methanol or ethanol to obtain a fibrous polymer. S03: After multiple precipitation and washing, the solvent in the polymer is removed. The obtained polymer is dried in a vacuum drying oven at 120~130℃ for 20~24h and then weighed. The dried polymer is polyimide. S04: The dried polymer is dissolved in a polar solvent at 90~100℃ to obtain a polymer solution, the polymer solution is filtered, and then the polymer solution is spun to obtain the hollow fiber membrane.

4. The method for preparing the hollow fiber gas separation membrane according to claim 3, characterized in that, The aromatic diamine further includes any one or more of the following compounds: 2,2'-Di(trifluoromethyl)diaminobiphenyl, 2,2',5,5'-tetrachlorodiphenylamine, p-diaminobiphenyl, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 2,3,5,6-tetramethyl-1,4-phenylenediamine, 3,6-diaminocarbazole, 3,6-diamino-9-ethylcarbazole; The aromatic dianhydride further includes any one or more of the following compounds: ； 。 5. The method for preparing the hollow fiber gas separation membrane according to claim 3, characterized in that, In step S04, the solid content of the polymer solution is controlled at 15-20 wt%, and the rotational viscosity of the polymer solution at 100-105°C is 280-350 poise.

6. A hollow fiber gas separation membrane, characterized in that, It is prepared by the method of any one of claims 1 to 5 for preparing hollow fiber gas separation membrane.

7. The application of the hollow fiber gas separation membrane according to claim 6, characterized in that, The hollow fiber gas separation membrane is used for the purification of helium in natural gas; or for the separation of helium and radon; or for the purification of methane in biogas.

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