Hollow fiber gas separation membrane as well as preparation method and application thereof

Abstract

The invention discloses a hollow fiber gas separation membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: taking dioxazoline as a chemical cross-linking agent, dissolving the dioxazoline in ethanol, soaking hollow fibers in a dioxazoline solvent, and reacting for a period of time at a certain temperature to complete cross-linking. According to the invention, dioxazoline is used as a cross-linking agent to perform chemical cross-linking on a series of different hollow fiber membranes under a 6FDA (hexafluorodianhydride) and DABA (3, 5-diaminobenzoic acid) system, so that the cost is reduced, a supporting layer of the fiber is prevented from collapsing, the gas separation performance of the fiber is improved, and the plasticizing resistance and mechanical strength of the hollow fiber membrane are improved; the polyimide hollow fiber gas separation membrane with high mechanical strength and high CO2 plasticizing resistance is obtained.

Description

Technical Field

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

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

[0003] Biogas contains significant amounts of methane, as well as impurities such as carbon dioxide and helium. The presence of these impurities can reduce the calorific value of biogas and increase compression and transportation costs, limiting the economic viability of generating electricity directly from biogas at the point of production. By removing these impurities, the purified gas is expected to contain high-quality methane, facilitating 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 easy 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, as well as good thermal and chemical stability. The CO2 / CH4 selectivity of the 6FDA-DABA system can reach 62.2 at 35°C and 100 psi, while the He / CH4 selectivity of the 6FDA-mPDA-DABA-TFDB system can reach over 200 at 35°C and 100 psi, exceeding that of most commercial polyimide membranes. Furthermore, DABA, which contains carboxyl groups and is highly chemically active, can undergo cross-linking under specific conditions, significantly improving its resistance to plasticization. Consequently, the 6FDA-DABA system has attracted increasing attention in areas such as natural gas separation and flue gas purification.

[0006] Currently, the traditional cross-linking method for 6FDA-DABA system hollow fiber membranes is the heat-induced decarboxylation cross-linking method. The advantages of this method are simple operation, no impact on the processing performance of the material, and the prepared hollow fibers have good plasticization resistance and thermal stability. However, since this method requires heat treatment of the fibers at high temperatures for a long time, the fiber support layer will collapse, significantly reducing the fiber's gas separation performance. In severe cases, it will reduce the fiber's mechanical properties, seriously affecting its application in the field of gas separation.

[0007] Therefore, it is necessary to provide a new method for preparing a 6FDA-DABA system hollow fiber membrane. Summary of the Invention

[0008] In order to solve the above technical problems, the present invention provides a method for preparing a gas separation membrane. The present invention uses dioxazoline as a cross-linking agent to chemically cross-link the hollow fiber membrane of the 6FDA-DABA system, greatly reducing the cross-linking temperature and reducing the cost while preparing a fiber membrane with high permeability and selectivity while having practical mechanical strength and excellent anti-plasticization ability.

[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] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A method for preparing a hollow fiber gas separation membrane, wherein the preparation method uses bisoxazoline as a chemical crosslinking agent, dissolves bisoxazoline in ethanol, soaks the hollow fiber in the bisoxazoline 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 method for preparing the cross-gas separation membrane specifically comprises the following steps:

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

[0016] S2: Soaking the hollow fiber membrane in a crosslinking agent solution at 60-80° C. for 20-24 hours to obtain the gas separation membrane.

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

[0018] Wherein, the hollow fiber membrane is made of a polyimide polymer, and the polyimide polymer has the following structure represented by the general formula (I):

[0019] (I)

[0020] Wherein, n represents the degree of polymerization of different components of the polymer, n is an integer of 100-200, x represents the molar ratio of the DABA portion, x is an integer of 0-100, and 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 includes any one or more of the following structures:

[0024] .

[0025] Wherein, the polyimide polymer is a crystalline copolymer of aromatic diamine and aromatic dianhydride.

[0026] Wherein, the preparation method of the hollow fiber membrane is as follows:

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

[0028] S02: adding an isoquinoline catalyst to the monomer solution, then heating to 190-200° C. and stirring to react for a certain time; after the reaction is completed, pouring 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 12-24 hours;

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

[0030] S04: Dissolving the dried polymer in a polar solvent at 90-100°C to obtain a polymer solution, filtering the polymer solution through a wire mesh, and then spinning the polymer solution to obtain the hollow fiber. The solid content of the polymer solution is controlled to be 15-20 wt%, and the rotational viscosity of the polymer solution at 100-105°C is controlled to be 280-350 poise. The spinning process specifically comprises extruding the extruded hollow fiber through a hollow fiber membrane spinning nozzle, passing the extruded hollow fiber body through a nitrogen atmosphere, and then phase-inverting the extruded hollow fiber body in a coagulation bath of ethanol aqueous solution at a temperature of -10--5°C to produce the hollow fiber membrane.

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

[0032] The more preferred aromatic diamine further includes any one or more of the following compounds:

[0033] 2,2'-Bis(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 also 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 to be 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 the hollow fiber gas separation membrane.

[0038] The hollow fiber gas separation membrane is used for the purification of helium in natural gas; or the hollow fiber gas separation membrane is used for the separation of helium and radon; or the hollow fiber gas separation membrane is used for the purification of methane in biogas.

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

[0040] Approximately 1,000 to 10,000 hollow fiber membranes of moderate length, prepared by the method of the present invention, are bundled together. Both sides of the fiber bundle are fixed to a tube sheet with resin, and one end of the fibers is opened to maintain air flow. This method completes the assembly of the membrane assembly. The membrane assembly is then connected to a container equipped with a mixed gas inlet, a permeate gas outlet, and a non-permeate gas outlet. This ensures that the space connecting the hollow fiber membranes to the interior is isolated from the space connecting the hollow fiber membranes to the exterior. In this gas separation membrane assembly, a mixed gas is introduced from the mixed gas inlet into the hollow fiber membranes or into a space connected to the exterior, but not limited thereto. When the mixed gas contacts the hollow fiber membranes, specific gas components contained in the mixed gas selectively permeate the membranes. The permeated gas is discharged from the permeate gas outlet, while the non-permeate gas that has not permeated the membrane is discharged from the non-permeate gas outlet. Gas separation is achieved in this manner. Components of a gas separation membrane assembly are prepared in this manner.

[0041] The element is inserted into a stainless steel container to make 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 300psi, and CH4 after depletion of He and CO2 is obtained at the product gas outlet.

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

[0043] (1) The present invention uses dioxazoline 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, thereby reducing costs, maintaining the fiber support layer from collapsing, improving the fiber's gas separation performance, and improving the hollow fiber membrane's plasticization resistance and mechanical strength, thereby obtaining a polyimide hollow fiber gas separation membrane with high mechanical strength and high resistance to CO2 plasticization.

[0044] (2) The polyimide hollow fiber gas separation membrane obtained by the present invention has the advantages of high strength and plasticization resistance in the gas separation process, good thermal stability, and improves the permeability while maintaining good selectivity for He / CH4, CO2 / N2 and CO2 / CH4, playing an important role in the field of natural gas methane purification. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Graphs showing changes in permeation flux and selectivity of hollow fiber gas separation membranes prepared in Example 1, Example 3 and the comparative example under pure gas conditions and different feed pressures.

[0046] Figure 2 These are the thermogravimetric curves of the hollow fiber gas separation membranes prepared in Example 1, Example 4, Example 5 and the comparative example.

[0047] Figure 31 and 2 are tensile strength curves of the hollow fiber gas separation membranes prepared in Example 1, Example 3, Example 6, and the comparative example. DETAILED DESCRIPTION

[0048] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may 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 commercially available.

[0050] Example 1:

[0051] (1) At room temperature, DABA, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 6FDA, BPDA (biphenyl-3,3',4,4'-tetracarboxylic dianhydride), and PMDA (pyromellitic dianhydride) were dissolved in p-chlorophenol to obtain a monomer solution. The molar ratio of the raw materials 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 18 wt%. The solution was then heated to 120 °C 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 and stirred to promote the polymerization reaction. 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 a fibrous polymer;

[0053] (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; the amount of catalyst used was 0.05wt% of the total weight of the monomer;

[0054] (4) The dried polymer is dissolved in a polar solvent at 90°C, the solid content of the solution is controlled to be 15 wt%, and the rotational viscosity of the solution at 100-105°C is controlled to be 280-350 poise. The polyimide solution is filtered with a wire mesh and then extruded through a hollow fiber membrane spinning nozzle. The extruded hollow fiber body is passed through a nitrogen atmosphere and then phase-inverted in an ethanol aqueous solution coagulation bath at a temperature of -10°C to produce wet fibers.

[0055] (5) Soaking the wet fiber in a dioxazoline ethanol solution with a solid content of 5% at 80° C. for 24 hours to complete the chemical crosslinking of the hollow fiber to obtain a chemically crosslinked 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 dried thoroughly at 120°C. Finally, a hollow fiber gas separation membrane made of polyimide was obtained.

[0057] Example 2:

[0058] (1) At room temperature, DABA, 2,2',5,5'-tetrachlorodiphenylamine, 6FDA, BPDA (biphenyl-3,3',4,4'-tetracarboxylic dianhydride), and PMDA (pyromellitic dianhydride) were first dissolved in p-chlorophenol to obtain a monomer solution, wherein the molar ratio of the raw materials in the monomer solution was BPDA:6FDA:DABA:2,2',5,5'-tetrachlorodiphenylamine = 1:1:0.8:1.2, and the solid content of the solution was 20 wt % and 18 wt %, respectively. The mixture was then heated to 90°C 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 and stirred to promote the polymerization reaction. The polymerization is initiated at 200°C and then reacted at this temperature for 12 hours. After the reaction is completed, the solution is poured into methanol or ethanol to obtain a fibrous polymer;

[0060] (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 130°C for 20 h; the amount of catalyst used was 0.1 wt% of the total weight of the monomer;

[0061] (4) The dried polymer is dissolved in a polar solvent at 100°C, the solid content of the solution is controlled to be 20 wt%, and the rotational viscosity of the solution at 100-105°C is controlled to be 280-350 poise. The polyimide solution is filtered with a wire mesh and then extruded through a hollow fiber membrane spinning nozzle. The extruded hollow fiber body is passed through a nitrogen atmosphere and then phase-inverted in an ethanol aqueous solution coagulation bath at a temperature of -5°C to produce wet fibers.

[0062] (5) Soaking the wet fiber in a 3% solid content dioxazoline ethanol solution at 60° C. for 20 h to complete the chemical crosslinking of the hollow fiber to obtain a chemically crosslinked 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 dried thoroughly at 100°C. Finally, a hollow fiber gas separation membrane made of polyimide was obtained.

[0064] Example 3:

[0065] The experimental steps of this example are the same as those of Example 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 18 wt%.

[0066] Example 4:

[0067] The experimental steps of this example 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:2,2',5,5'-tetrachlorodiphenylamine = 1:1:1:1.15:1.7, and the solid content of the solution is 15 wt%.

[0068] Embodiment 5:

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

[0070] Example 6:

[0071] The experimental procedures of this example 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: p-diaminobenzidine = 1:1:1:1.2:1.8, and the solid content of the solution is 18 wt%. The remaining experimental and application procedures are the same as those of Example 1.

[0072] Embodiment seven:

[0073] The experimental steps of this example are the same as those of 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 18 wt%.

[0074] Embodiment 8:

[0075] The experimental steps of this example are the same as those of 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 15 wt%.

[0076] Embodiment 9:

[0077] The experimental steps of this example are the same as those of 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 18 wt%.

[0078] Embodiment 10:

[0079] The experimental steps of this example are the same as those of 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 = 3:1.2:1.8, and the solid content of the solution is 18 wt%.

[0080] Example 11:

[0081] The experimental steps of this example are the same as those of Example 1, except 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 18 wt%.

[0082] Example 12:

[0083] The experimental steps of this example are the same as those of Example 1, except that the molar ratio of the raw materials in the monomer solution is BPDA:6FDA:PMDA:DABA=1.2:1:0.8:3, and the solid content of the solution is 18 wt%.

[0084] Example 13:

[0085] The experimental steps of this example 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=0.8:1:1.2:3, and the solid content of the solution is 18 wt%.

[0086] Example 14:

[0087] The experimental steps of this example 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=0.5:1:1.5:3, and the solid content of the solution is 18 wt%.

[0088] Embodiment 15:

[0089] The experimental steps of this example 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 = 1:1:1:1.5:1.5, and the solid content of the solution is 18 wt%.

[0090] Example 16:

[0091] The experimental steps of this example 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 = 1.2:1.1:1:1.5:1.5, and the solid content of the solution is 18 wt%.

[0092] Embodiment 17:

[0093] The experimental steps of Example 1 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 18 wt%.

[0094] Embodiment 18:

[0095] The experimental steps of Example 1 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 18 wt%.

[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 dianhydride), and PMDA (pyromellitic dianhydride polyimide) were first dissolved in p-chlorophenol to obtain a monomer solution, wherein 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 18 wt %. The solution was then heated to 120 °C 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 and stirred to promote the polymerization reaction. 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 a fibrous polymer;

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

[0101] (4) The dried polymer is dissolved in a polar solvent at 90-100°C, the solid content of the solution is controlled to be 15-20 wt%, and the rotational viscosity of the solution at 100-105°C is controlled to be 280-350 poise. The polyimide solution is filtered with a wire mesh and then extruded through a hollow fiber membrane spinning nozzle. The extruded hollow fiber body is passed through a nitrogen atmosphere and then phase-inverted in an ethanol aqueous solution coagulation bath at a temperature of -10--5°C to produce wet fibers.

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

[0103] The resulting hollow fiber gas separation membrane is used for CH4 purification from natural gas and biogas. A specific application method is as follows: approximately 105 hollow fiber membranes of appropriate length prepared by the method of the present invention are bundled together; these hollow fibers are densely packed (approximately 50% packing ratio), and the ends of the fiber bundle are embedded in a thermosetting polymer epoxy resin and fixed to a tube sheet. One end of each fiber is open to allow air inlet, completing the assembly of the membrane module. The membrane module is then connected to a container equipped with a mixed gas inlet, a permeate gas outlet, and a non-permeate gas outlet. This ensures that the space connecting the hollow fiber membranes to the interior is isolated from the space connecting the hollow fiber membranes to the exterior. In this gas separation membrane module, a mixed gas is introduced from the mixed gas inlet into the hollow fiber membranes or into the space connected to the exterior, but not limited thereto. When the mixed gas contacts the hollow fiber membranes, specific gas components contained in the mixed gas selectively permeate the membranes. The permeated gas is discharged from the permeate gas outlet, while the non-permeated gas that has not permeated the membrane is discharged from the non-permeate gas outlet. In this manner, a gas separation element is produced.

[0104] The element is inserted into a stainless steel container to make a membrane separation assembly. The flue gas or biogas material to be separated is passed into the external pore side of the gas separation membrane under a pressure of 300psi, and the flue gas or biogas after de-CO2 is obtained at the product gas outlet.

[0105] Performance testing:

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

[0107] A permeability 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 maintained at a constant 35°C, and pure CO2 gas was introduced into the hollow fibers of the pencil-shaped assembly at a constant rate. The gas immediately preceding the hollow fiber membrane element was designated as the upstream gas, while the gas passing through the element was designated as the downstream gas. The upstream pressure was maintained constant, and the downstream pressure was measured over time. The CO2 permeation flux was calculated using a formula; the CH4 permeation flux was measured in the same manner. The CO2 / CH4 selectivity was determined by comparing the two.

[0108] The pure gas in the above method is replaced with a CH4 / CO2 mixed gas with a 50% CH4 content, and the same method is used for testing to obtain the mixed gas flux. By measuring the ratio of the two gases in the mixed gas, the CO2 / CH4 selectivity in the mixed gas can be obtained.

[0109] (2) Measurement of rotational viscosity

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

[0111] Table 1

[0112] Table 1 shows the gas permeation performance of different examples and comparative examples. It can be seen that compared with the thermally induced decarboxylation crosslinking of the comparative example, the permeation flux of the gas separation membrane treated with the low-temperature chemical crosslinking method is greatly improved, while the selectivity is also maintained at a very high level.

[0113] Figure 1 The high-temperature dimensional stability of the gas separation membranes prepared in Example 1, Example 3 and the comparative example under nitrogen conditions shows that the hollow fiber gas separation membranes prepared in Example 1 and Example 3 have higher high-temperature dimensional stability than the comparative example.

[0114] Figure 2 The thermogravimetric curves of the gas separation membranes prepared in Example 1, Example 4, Example 5 and the comparative example are shown. Figure 2 The high temperature resistance of the membrane of the present invention can be clearly seen in the thermogravimetric curve. The membrane begins to gradually lose weight 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 stringent application temperatures.

[0115] Figure 3 1 and 2 are tensile strength curves of the gas separation membranes prepared in Example 1, Example 3, Example 6 and the comparative example. Figure 3This shows that the mechanical properties of the gas separation membrane after chemical cross-linking are much higher than those of the membrane prepared by thermally induced decarboxylation cross-linking, which can ensure that no filament breakage occurs during spinning, and the membrane is stronger and more durable, greatly broadening the application field of polyimide gas separation membranes.

[0116] The present invention uses dioxazoline as a cross-linking agent, dissolves dioxazoline in ethanol, and chemically cross-links the hollow fiber membrane with a carboxyl group under low temperature conditions below 80°C, which greatly improves the plasticization resistance and aging resistance of the hollow fiber membrane, and improves the gas separation performance of the hollow fiber membrane. Compared with the traditional thermal induced cross-linking method, the chemical cross-linking method has a low temperature and will not cause the collapse of the supporting layer of the hollow fiber membrane, thereby maximizing the gas separation performance of the fiber membrane. At the same time, low-temperature cross-linking can greatly save the energy required for the thermal cross-linking heating temperature, and greatly reduces the cross-linking cost. The membrane has advantages such as high strength and plasticization resistance in the gas separation process, has good thermal stability, improves permeability, and can also maintain good selectivity for CO2 / N2, CO2 / CH4 and He / CH4, and plays an important role in the fields of flue gas and biogas deCO2, natural gas helium methane separation, etc.

[0117] It will be easily understood by those skilled in the art 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 in the scope of protection of the present invention.

[0118] Portions not described in detail in this specification belong to the common knowledge in the art. The above examples are provided for the purpose of illustrating the present invention only and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. Various equivalent substitutions and modifications made without departing from the spirit and principles of the present invention are intended to be encompassed within the scope of the present invention.

Claims

1. A method for preparing a hollow fiber gas separation membrane, characterized in that: The preparation method uses dioxazoline as a chemical crosslinking agent, dissolves dioxazoline in ethanol, soaks the hollow fiber in the dioxazoline solvent, and reacts at a certain temperature for a period of time to complete crosslinking; Wherein, the chemical structural formula of the dioxazoline is as follows: 。 2. The method for preparing a hollow fiber gas separation membrane according to claim 1, wherein: The preparation method of the hollow fiber gas separation membrane specifically comprises the following steps: S1: preparing a crosslinking agent: dissolving dioxazoline in ethanol to obtain a crosslinking agent solution, wherein the solid content of the crosslinking agent solution is 3% to 5%; S2: Soak the hollow fiber membrane in the crosslinking agent solution at 60-80°C for 20-24 hours; S3: The soaked hollow fiber membrane is cleaned and dried to obtain the hollow fiber gas separation membrane.

3. The method for preparing a hollow fiber gas separation membrane according to claim 1, wherein: The hollow fiber membrane is made of a polyimide polymer, and the polyimide polymer has a structure represented by the following general formula (I): （Ⅰ） Wherein, n represents the degree of polymerization of different components of the polymer, n is an integer of 100-200, x represents the molar ratio of the DABA portion, x is an integer of 0-100, and 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 includes any one or more of the following structures: 。 4. The method for preparing a hollow fiber gas separation membrane according to claim 3, wherein: The polyimide polymer is a crystalline copolymer of aromatic diamine and aromatic dianhydride.

5. The method for preparing a hollow fiber gas separation membrane according to claim 4, wherein: The preparation method of the hollow fiber membrane is as follows: S01: first dissolving a monomer in p-chlorophenol to obtain a monomer solution, wherein the solid content of the monomer solution is 15-20 wt %, and then heating the solution to 90-120° C. under a nitrogen atmosphere; wherein the monomer comprises an aromatic diamine and an aromatic dianhydride, wherein the molar ratio of the aromatic diamine to the aromatic dianhydride is 0.95-1:1-1.1; S02: adding isoquinoline catalyst to the monomer solution, then heating to 190-200° C. and stirring to react for a certain time; After the reaction is completed, 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, and the obtained polymer is dried in a vacuum drying oven at 120-130° C. for 20-24 hours and then weighed. The dried polymer is polyimide; S04: dissolving the dried polymer in a polar solvent at 90-100° C. to obtain a polymer solution, filtering the polymer solution, and then spinning the polymer solution to obtain the hollow fiber membrane.

6. The method for preparing a hollow fiber gas separation membrane according to claim 5, wherein: The aromatic diamine includes DABA, and the aromatic dianhydride includes 6FDA.

7. The method for preparing a hollow fiber gas separation membrane according to claim 6, wherein: The aromatic diamine further comprises any one or more of the following compounds: 2,2'-Bis(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 also includes any one or more of the following compounds: ； 。 8. The method for preparing a hollow fiber gas separation membrane according to claim 6, wherein: In step S04 , the solid content of the polymer solution is controlled to be 15-20 wt %, and the rotational viscosity of the polymer solution at 100-105° C. is 280-350 poise.

9. A hollow fiber gas separation membrane, characterized in that: The hollow fiber gas separation membrane is prepared by the preparation method of any one of claims 1 to 8.

10. Use of the hollow fiber gas separation membrane according to claim 9, characterized in that: The hollow fiber gas separation membrane is used for purifying helium in natural gas; or the hollow fiber gas separation membrane is used for separating helium from radon; or the hollow fiber gas separation membrane is used for purifying methane in biogas.

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