Polyimide hollow fiber membranes, their preparation methods and applications

Abstract

This invention relates to the field of gas membrane separation, and discloses a polyimide hollow fiber membrane, its preparation method, and its application. The polyimide forming the polyimide hollow fiber membrane has the structure shown in Formula I; wherein X is derived from a diamine monomer with the structure shown below; Y is derived from at least one diamine monomer with the structure shown in the group below; Ar1 ​​is derived from a dianhydride monomer with the structure shown below; and Ar2 is derived from at least one dianhydride monomer with the structure shown in the group below. The polyimide forming this hollow fiber membrane introduces structural units containing fluorine and ether bonds into a rigid structure, which significantly improves the solubility of the polyimide. This results in a polyimide hollow fiber membrane that, while maintaining good gas separation performance, also possesses good toughness, exhibiting excellent separation performance and mechanical stability when used for helium separation.

Description

Technical Field

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

[0002] As a strategic resource, helium plays an irreplaceable role in various industrial fields such as magnetic resonance imaging, nanotechnology, aerospace, nuclear magnetic resonance, leak detection, and chromatography. Currently, over 90% of helium is extracted from natural gas, but the concentration of helium in most natural gas is below 0.5% or even below 0.1%, making the separation of helium using conventional methods such as cryogenics and pressure swing adsorption extremely energy-intensive. For extracting helium from low-concentration helium-containing natural gas, membrane gas separation technology is the most economical method.

[0003] Membrane gas separation technology is a novel gas separation technology developed in recent decades, and it has been successfully applied in many fields such as high-purity helium production, hydrogen recovery, natural gas purification, air separation, and organic vapor recovery. As the core of membrane separation technology, the separation membrane directly determines the effectiveness of the technology. Polymer membrane materials, due to their diverse structures, ease of processing and industrialization, and good mechanical, chemical, and thermal stability, have become the most researched and widely used type of membrane material in industry. Currently, the polymer materials used to prepare gas separation membranes mainly include polyimide, polybenzimidazole, polysulfone, cellulose acetate, and polypyrrole. Aromatic polyimide materials are favored by researchers due to their rich structures and good gas separation performance. Gas separation membranes are generally used in the production field in the form of hollow fiber membrane modules. Therefore, in addition to good gas separation performance, mechanical strength and chemical corrosion resistance are also very important properties of gas separation membrane materials. Solvent exchange is required during membrane preparation, that is, immersing the nascent hollow fiber membrane in water to displace the solvent. However, the imine ring in polyimide materials is easily hydrolyzed, and the solvent replacement process causes a decrease in its molecular weight. The prepared membrane fibers are fragile and easily broken, making it difficult to prepare membrane modules and achieve long-term stable application. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of poor spinnability and fragile and easily broken membrane fibers of aromatic polyimides in the prior art, and to provide a polyimide hollow fiber membrane, its preparation method and application. The polyimide forming the polyimide hollow fiber membrane introduces structural units containing fluorine and ether bonds into a rigid structure, which can significantly improve the solubility of polyimide. This allows the polyimide hollow fiber membrane formed by the polyimide to have good toughness while ensuring good gas separation performance. When used for helium separation, it has good separation performance and mechanical stability.

[0005] To achieve the above objectives, a first aspect of the present invention provides a polyimide hollow fiber membrane, wherein the polyimide forming the polyimide hollow fiber membrane has the structure shown in Formula I;

[0006]

[0007] Wherein, X comes from a diamine monomer with the structure shown below;

[0008]

[0009] Y is derived from at least one diamine monomer with the structure shown in the following group;

[0010]

[0011] Ar1 is derived from a dianhydride monomer with the structure shown below;

[0012]

[0013] Ar2 is derived from at least one dianhydride monomer with the structure shown in the following group;

[0014]

[0015] A second aspect of the present invention provides a method for preparing a polyimide hollow fiber membrane, wherein the preparation method includes:

[0016] S1. In the presence of a protective atmosphere, diamine monomer I, diamine monomer II, dianhydride monomer I, dianhydride monomer II are mixed with an organic solvent and subjected to a polycondensation reaction to obtain a polyamic acid solution. Then, an imidization reaction is carried out to obtain polyimide.

[0017] S2. The polyimide obtained in step S1, a good solvent A for the polyimide, a poor solvent B for the optional polyamide imide, and a non-solvent C are mixed to obtain a casting solution.

[0018] S3. The casting solution and the core solution are extruded to obtain a nascent fiber membrane. The nascent fiber membrane is then passed through an air bath and a coagulation bath in sequence, and after being wound up, it is exchanged and dried to obtain the polyimide hollow fiber membrane.

[0019] Among them, diamine monomer I is

[0020] Diamine monomer II is selected from at least one of the following diamine monomers;

[0021]

[0022] Dianone monomer I is

[0023] Dianone monomer II is selected from at least one of the following dianone monomers;

[0024]

[0025] A third aspect of the present invention provides a polyimide hollow fiber membrane prepared by the above-described preparation method.

[0026] A fourth aspect of the present invention provides an application of the above-mentioned polyimide hollow fiber membrane in helium separation.

[0027] Through the above technical solutions, the polyimide hollow fiber membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0028] In this invention, structural units containing hexafluoroisopropane and ether bonds are introduced into the rigid structure of the polyimide forming the polyimide hollow fiber membrane. The large volume of hexafluoroisopropane reduces the packing density of the rigid molecular chains, thereby increasing the free volume of the polyimide hollow fiber membrane. This avoids the problems of slow gas permeation rate and poor polymer solubility caused by the tight packing of rigid polyimide chains. The ether bonds can increase the flexibility of the polymer chain segments, further increase the solubility of the polymer, improve the toughness of the polyimide molecular chains, and ensure the gas separation performance of the polyimide hollow fiber membrane.

[0029] The fluorinated polyimide hollow fiber membrane prepared by this invention has a tensile strength greater than or equal to 25 MPa, an elongation at break greater than or equal to 30%, a He / Ne selectivity greater than or equal to 4, a He / N2 selectivity greater than or equal to 55, and a He / CH4 selectivity greater than or equal to 91, and is suitable for the preparation of high-purity helium. Attached Figure Description

[0030] Figure 1 This is a cross-sectional SEM image of the polyimide hollow fiber membrane prepared in Example 1.

[0031] Figure 2 This is a magnified SEM image of a cross-section of the polyimide hollow fiber membrane prepared in Example 1.

[0032] Figure 3 This is a SEM image of the outer surface of the polyimide hollow fiber membrane prepared in Example 1. Detailed Implementation

[0033] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0034] A first aspect of the present invention provides a polyimide hollow fiber membrane, wherein the polyimide forming the hollow fiber membrane has the structure shown in Formula I;

[0035]

[0036] Wherein, X comes from a diamine monomer with the structure shown below;

[0037]

[0038] Y is derived from at least one diamine monomer with the structure shown in the following group;

[0039]

[0040]

[0041] Ar1 is derived from a dianhydride monomer with the structure shown below;

[0042]

[0043] Ar2 is derived from at least one dianhydride monomer with the structure shown in the following group;

[0044]

[0045] In this invention, structural units containing hexafluoroisopropane and ether bonds are introduced into the rigid structure of the polyimide forming the polyimide hollow fiber membrane. The large volume of hexafluoroisopropane reduces the packing density of the rigid molecular chains, thereby increasing the free volume of the polyimide hollow fiber membrane. This avoids the problems of slow gas permeation rate and poor polymer solubility caused by the tight packing of rigid polyimide chains. The ether bonds can increase the flexibility of the polymer chain segments, further increase the solubility of the polymer, improve the toughness of the polyimide molecular chains, and ensure the gas separation performance of the polyimide hollow fiber membrane.

[0046] In one specific embodiment of the present invention, Y originates from a diamine monomer.

[0047]

[0048] In one specific embodiment of the present invention, Ar2 is derived from the dianhydride monomer.

[0049] According to the present invention, the ratio of n:(m+n) is 0.2-0.8:1.

[0050] In this invention, the inventors discovered that when the ratio of polyimide n:(m+n) meets the above-mentioned range, the prepared polymer has both good strength and toughness, and the hollow fiber membrane prepared thereby is both pressure resistant and can resist repeated high-pressure gas impacts.

[0051] In one specific embodiment of the present invention, the ratio of n:(m+n) is 0.4-0.8:1.

[0052] According to the present invention, the polyimide has a number-average molecular weight of 1 × 10⁻⁶. 4 -100×10 4 g / mol.

[0053] According to the present invention, the polyimide has a molecular weight distribution of 1-5.

[0054] In this invention, when the number-average molecular weight and / or molecular weight distribution of the polyimide meets the above-mentioned range, the polyimide simultaneously possesses good processability and film-forming properties, and good mechanical properties.

[0055] Furthermore, the polyimide has a number-average molecular weight of 3 × 10⁻⁶. 4 -25×10 4 g / mol.

[0056] Furthermore, the polyimide has a molecular weight distribution of 1-3.

[0057] A second aspect of the present invention provides a method for preparing a polyimide hollow fiber membrane, wherein the preparation method includes the following steps:

[0058] S1. In the presence of a protective atmosphere, diamine monomer I, diamine monomer II, dianhydride monomer I, dianhydride monomer II are mixed with an organic solvent and subjected to a polycondensation reaction to obtain a polyamic acid solution. Then, an imidization reaction is carried out to obtain polyimide.

[0059] S2. The polyimide obtained in step S1, a good solvent A for the polyimide, a poor solvent B for the optional polyamide-imide, and a non-solvent C for the optional polyimide are mixed to obtain a casting solution.

[0060] S3. The casting solution and the core solution are extruded to obtain a nascent fiber membrane. The nascent fiber membrane is then passed through an air bath and a coagulation bath in sequence, and after being wound up, it is exchanged and dried to obtain the polyimide hollow fiber membrane.

[0061] Among them, diamine monomer I is

[0062] Diamine monomer II is selected from at least one of the following diamine monomers;

[0063]

[0064] Dianone monomer I is

[0065] Dianone monomer II is selected from at least one of the following dianone monomers;

[0066]

[0067] In this invention, the polyimide hollow fiber membrane prepared by the above preparation method has high tensile strength, excellent elongation at break and good gas separation performance, making the membrane fibers strong and tough, and able to resist pressure and repeated impacts from high-pressure gases.

[0068] In one specific embodiment of the present invention, the dianhydride monomer II is selected from at least one of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride (α-ODPA), and 4,4'-biphenyl ether dianhydride (ODPA).

[0069] In one specific embodiment of the present invention, the diamine monomer II is selected from at least one of 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP), toluene diamine (m-PDA), 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA), 2-(4-aminophenyl)-5-aminobenzoxazole (APBOA), and 9,9-dimethylfluorene-2,7-diamine (SA-1).

[0070] According to the present invention, the molar ratio of diamine monomer to dianhydride monomer is 0.9-1.1:1, preferably 0.95-1.05:1.

[0071] According to the present invention, the molar ratio of diamine monomer I to dianhydride monomer is 0.2-0.8:1.

[0072] In this invention, when the molar ratio of diamine monomer I (HFBAPP) and dianhydride monomer is controlled to meet the above-mentioned range, the prepared polyimide has both good processability and mechanical stability, which can meet the preparation requirements of hollow fiber membrane, and makes the prepared hollow fiber membrane have good compressive and tensile strength.

[0073] In this invention, the molar ratio of diamine monomer I to dianhydride monomer refers to the case where the types of diamine monomer I and diamine monomer II are different. When the types of diamine monomer I and diamine monomer II are the same, it is sufficient to make the molar ratio of diamine monomer to dianhydride monomer 0.9-1.1:1, preferably 0.95-1.05:1.

[0074] Furthermore, the molar ratio of diamine monomer I to dianhydride monomer is 0.4-1:1.

[0075] According to the present invention, the molar ratio of dianhydride monomer I to dianhydride monomer is 0.2-0.8:1.

[0076] In this invention, when the molar ratio of dianhydride monomer I to dianhydride monomer is controlled to meet the above-mentioned range, the resulting polyimide has both good film-forming processability and good gas permeability.

[0077] Furthermore, the molar ratio of dianhydride monomer I to dianhydride monomer is 0.4-0.8:1.

[0078] In this invention, the organic solvent in step S1 is selected from one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO).

[0079] In this invention, the amount of organic solvent used is such that the total solid content of diamine monomer I, diamine monomer II, dianhydride monomer I, and dianhydride monomer II in the mixed solution is 10-25 wt%.

[0080] According to the present invention, the conditions for the polycondensation reaction include: a reaction temperature of 0-30°C and a reaction time of 6-36 h.

[0081] Furthermore, the conditions for the polycondensation reaction include: a reaction temperature of 0-30°C and a reaction time of 12-24 hours.

[0082] In this invention, there is no particular limitation on the type of protective atmosphere, and conventional protective atmospheres in the art, such as nitrogen, can be used.

[0083] According to the present invention, the imidization reaction is carried out in the presence of a catalyst and a dehydrating agent.

[0084] In this invention, there is no particular limitation on the types of catalysts and dehydrating agents. Conventional types of dehydrating agents and catalysts in the art can be used. For example, the catalyst is selected from at least one of isoquinoline, pyridine and 3-methylpyridine; and the dehydrating agent is acetic anhydride.

[0085] In this invention, there is no particular limitation on the amount of the catalyst or the dehydrating agent, and conventional amounts in the art can be used. Preferably, the molar ratio of the catalyst to the dianhydride monomer is 1.5-6:1, more preferably 2.5-1.5:1; the molar ratio of the dehydrating agent to the dianhydride monomer is 1.5-6:1, more preferably 2.5-1.5:1.

[0086] According to the present invention, the conditions for the imidization reaction include: a reaction temperature of 10-60°C and a reaction time of 12-48 h.

[0087] Furthermore, the conditions for the imidization reaction include: a reaction temperature of 20-60°C and a reaction time of 24-36 h.

[0088] In this invention, the preparation method further includes: pouring the product obtained by imidization into a precipitant to precipitate, washing and drying it to obtain the polyimide copolymer.

[0089] In this invention, there is no particular limitation on the type of precipitant, as long as it can cause polyimide to precipitate from the solution after the amidation reaction. For example, it can be at least one selected from methanol, ethanol, water and acetone.

[0090] In one specific embodiment of the present invention, the precipitant is a mixed solvent of ethanol and water, wherein the volume ratio of ethanol to water is 9:1 to 1:1.

[0091] In this invention, there are no particular limitations on the drying conditions, as long as the polyimide copolymer can be fully dried. In one specific embodiment of this invention, the drying is carried out under vacuum conditions at 120-180°C.

[0092] According to the present invention, based on the total weight of the casting solution, the content of polyimide is 16-35 wt%, the content of good solvent A of polyimide is 40-80 wt%, the content of poor solvent B of polyimide is 0-40 wt%, and the content of non-solvent C of polyimide is 0-15 wt%.

[0093] In this invention, when the casting solution contains the above-mentioned components and the content of each component meets the above-mentioned range, the viscosity of the casting solution can meet the requirements of spinning, and the prepared hollow fiber has a dense selective layer.

[0094] Furthermore, based on the total weight of the casting solution, the content of polyimide is 20-35 wt%, the content of good solvent A for polyimide is 40-80 wt%, the content of poor solvent B for polyimide is 5-20 wt%, and the content of non-solvent C for polyimide is 0-7 wt%.

[0095] In this invention, the good solvent A for polyimide refers to a solvent that can achieve a solubility of polyimide of 30 wt% or more.

[0096] In one specific embodiment of the present invention, the good solvent A of the polyimide is selected from at least one of DMAc, NMP, DMF, and DMSO.

[0097] In this invention, the unsuitable solvent B for polyimide refers to a solvent that can dissolve or swell polyimide and has a solubility of less than 20 wt% for polyimide.

[0098] In one specific embodiment of the present invention, the undesirable solvent B of the polyimide is selected from at least one of THF, CH2Cl2, and CHCl3.

[0099] In this invention, the non-solvent C of the polyimide refers to a solvent that does not dissolve or swell the polyimide at all.

[0100] In one specific embodiment of the present invention, the non-solvent C of the polyimide is selected from at least one of ethanol, methanol, and deionized water.

[0101] In one specific embodiment of the present invention, the mixing in step S2 is carried out under heating conditions.

[0102] In this invention, mixing polyimide, a good solvent A for polyimide, optionally a poor solvent B for polyamide-imide, and optionally a non-solvent C for polyimide under heating conditions enables the polymer to dissolve more quickly.

[0103] Furthermore, the heating temperature is 40-80℃.

[0104] In this invention, in order to ensure that the components are fully and uniformly mixed, preferably, the mixing in step S2 is carried out under stirring conditions.

[0105] According to the present invention, in step S3, the core fluid is selected from at least one of deionized water, ethanol and NMP.

[0106] In one specific embodiment of the present invention, the core fluid is a mixture of deionized water and NMP, wherein the volume ratio of the deionized water to the NMP is 1:1 to 1:9.

[0107] According to the present invention, the height of the air bath is 2-20cm.

[0108] In this invention, when the height of the air bath is controlled to meet the above-mentioned range, the undesirable solvent can be fully evaporated, forming a dense selective layer.

[0109] Furthermore, the height of the air bath is 8-15cm.

[0110] According to the present invention, the coagulation bath is deionized water, and the coagulation bath temperature is 20-60℃, preferably 30-40℃.

[0111] According to the present invention, the exchange is carried out in a water bath.

[0112] In one specific embodiment of the present invention, the exchange time is 1-72 hours, preferably 8-12 hours.

[0113] According to the present invention, the preparation method further includes: post-treating the exchange-treated fiber membrane in solvent D and then drying it.

[0114] According to the present invention, the solvent D is selected from at least one of methanol, ethanol and n-hexane.

[0115] A third aspect of the present invention provides a polyimide hollow fiber membrane prepared by the above-described preparation method.

[0116] A fourth aspect of the present invention provides an application of the above-mentioned polyimide hollow fiber membrane in helium separation.

[0117] The present invention will be described in detail below through embodiments. In the following embodiments,

[0118] The molecular weight and molecular weight distribution of polyimide were determined using GPC.

[0119] All raw materials used in the examples and comparative examples are commercially available products.

[0120] Example 1

[0121] (1) Preparation of polyimide:

[0122] 18 L of N-methylpyrrolidone (NMP) was added to a dry reactor under a nitrogen atmosphere. 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP, 3.2 mol, diamine monomer I and diamine monomer II) was added and stirred until completely dissolved. The reaction system was cooled to 20 °C, and pre-mixed hexafluorodianhydride (6FDA, 2.56 mol, dianhydride monomer I) and 4,4'-biphenyl ether dianhydride (ODPA, 0.64 mol, dianhydride monomer II) were added. The reaction was carried out at 20 °C for 1 h, then the refrigerator was turned off, and the reaction was continued for 15 h to obtain polyimide acid. Acetic anhydride (11.52 m... A mixed solution of diamine monomer (11.52 mol) and pyridine (11.52 mol) was used to dehydrate polyimide. The dehydration reaction was carried out at room temperature for 24 hours to obtain a polyimide solution. The polyimide solution was then transferred to a mixed solution of ethanol and water, where the polyimide precipitated as fibers. The fibers were then washed with an alcohol-water mixture at 60°C under mechanical stirring for 24 hours, with the solution being changed three times during this period. After washing, the polyimide fibers were dried in a forced-air oven at 60°C for 24 hours, and then thoroughly dried in a vacuum oven at 150°C to obtain polyimide, denoted as PI-1. The molar ratio of diamine monomer to dianhydride monomer was 1:1, the molar ratio of dianhydride monomer I to dianhydride monomer II was 4:1, the molar ratio of dianhydride monomer I to dianhydride monomer was 0.8:1, the molar ratio of acetic anhydride to dianhydride monomer was 3.6:1, and the molar ratio of pyridine to dianhydride monomer was 3.6:1.

[0123] (2) Preparation of polyimide casting solution: PI-1, NMP, and tetrahydrofuran (THF) were added to the reaction vessel of the spinning machine at a mass ratio of 30:56:14. After stirring at 60°C for 24 h, the mixture was degassed under vacuum for 48 h to obtain the casting solution. Based on the total mass of the casting solution, the content of PI-1 was 30 wt%, the content of NMP (a good solvent for polyimide) was 56 wt%, and the content of THF (a poor solvent for polyimide) was 14 wt%.

[0124] (3) Preparation of polyimide hollow fiber membrane: The casting solution was extruded from the nozzle, and a mixed solution of water and NMP (wherein the volume content of NMP in the mixed solution was 70 vol%) was used as the core liquid. The nascent hollow fiber membrane was passed through the air for 15 cm and then entered a pure hydrogel bath (temperature 30℃). After being collected by a winding wheel, it was soaked in a water tank for 24 h to remove residual solvent, and then soaked in ethanol for 12 h. The membrane fibers were then hung to air dry to obtain a polyimide hollow fiber membrane, denoted as HFM-1.

[0125] Figure 1 This is a cross-sectional SEM image of the polyimide hollow fiber membrane prepared in Example 1; from Figure 1 It can be seen that the prepared hollow fiber membrane has a regular concentric circle structure. Figure 2 This is a magnified SEM image of a cross-section of the polyimide hollow fiber membrane prepared in Example 1; from Figure 2 It can be seen that the prepared hollow fiber membrane has sponge-like pores. Figure 3 This is a SEM image of the outer surface of the polyimide hollow fiber membrane prepared in Example 1. Figure 3 It can be seen that the outer surface of the prepared hollow fiber membrane is dense and defect-free.

[0126] Example 2

[0127] (1) Preparation of polyimide:

[0128] 16 L of N-methylpyrrolidone (NMP) was added to a dry reactor under a nitrogen atmosphere. 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP, 3.2 mol) was added and stirred until completely dissolved. The reaction system was cooled to 5 °C, and pre-mixed hexafluorodianhydride (6FDA, 1.28 mol) and 4,4'-biphenyl ether dianhydride (ODPA, 1.92 mol) were added. The reaction was carried out at 5 °C for 4 h, then the refrigerator was turned off, and the reaction was continued for 15 h to obtain polyimide acid. Acetic anhydride (11.52 mol) and pyridine (11.52 mol) were then added. A mixed solution of l) was used to dehydrate polyimide. The dehydration reaction was carried out at room temperature for 24 hours to obtain a polyimide solution. The polyimide solution was discharged into a mixed solution of ethanol and water. The polyimide precipitated out in fibrous form. It was then washed with an alcohol-water mixture at 60°C under mechanical stirring for 24 hours, with the solution being changed three times during the washing process. After washing, the polyimide fibers were dried in a forced-air oven at 60°C for 24 hours, and then thoroughly dried in a vacuum oven at 150°C to obtain polyimide, denoted as PI-2.

[0129] (2) Preparation of polyimide casting solution: PI-2, NMP, and tetrahydrofuran (THF) were added to the reaction vessel of the spinning machine at a mass ratio of 22:46.8:31.2. After stirring at 60°C for 48 h, the mixture was degassed under vacuum for 48 h to obtain the casting solution. Based on the total mass of the casting solution, the content of PI-2 was 22 wt%, the content of NMP (a good solvent for polyimide) was 46.8 wt%, and the content of THF (a poor solvent for polyimide) was 31.2 wt%.

[0130] (3) Preparation of polyimide hollow fiber membrane: The casting solution was extruded from a nozzle, and a mixture of water and NMP (wherein the volume content of NMP in the mixture was 70 vol%) was used as the core solution. The nascent hollow fiber membrane was passed through the air for 10 cm and then entered a pure hydrogel bath (temperature 30℃). After being collected by a winding wheel, it was soaked in a water tank for 24 h to remove residual solvent, and then soaked in ethanol for 12 h. The membrane fibers were then hung to air dry to obtain a polyimide hollow fiber membrane, denoted as HFM-2.

[0131] Example 3

[0132] (1) Preparation of polyimide:

[0133] 16 L of N-methylpyrrolidone (NMP) was added to a dry reaction vessel under a nitrogen atmosphere. 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP, 3.2 mol) was added and stirred until completely dissolved. The reaction system was cooled to 10 °C, and pre-mixed hexafluorodianhydride (6FDA, 2.56 mol) and 4,4'-biphenyl ether dianhydride (ODPA, 0.64 mol) were added. The reaction was carried out at 10 °C for 4 h, then the refrigerator was turned off, and the reaction was continued for 15 h to obtain polyimide acid. Acetic anhydride (11.52 mol) and pyridine (11.52 mol) were then added. A mixed solution of ethanol and water was used to dehydrate polyimide. The dehydration reaction was carried out at room temperature for 24 hours to obtain a polyimide solution. The polyimide solution was then discharged into a mixed solution of ethanol and water, and the polyimide precipitated out in fibrous form. The polyimide was then washed with an alcohol-water mixture at 60°C under mechanical stirring for 24 hours, with the solution being changed three times during the washing process. After washing, the polyimide fibers were dried in a forced-air oven at 60°C for 24 hours, and then thoroughly dried in a vacuum oven at 150°C to obtain polyimide, denoted as PI-3.

[0134] (2) Preparation of polyimide casting solution: PI-3, NMP, tetrahydrofuran (THF), and ethanol were added to the reaction vessel of the spinning machine at a mass ratio of 22:50:18:10. After stirring at 60°C for 24 h, the mixture was degassed under vacuum for 48 h to obtain the casting solution. Based on the total mass of the casting solution, the content of PI-3 was 22 wt%, the content of NMP (a good solvent for polyimide) was 50 wt%, the content of THF (a poor solvent for polyimide) was 18 wt%, and the content of ethanol (a non-solvent) was 10 wt%.

[0135] (3) Preparation of polyimide hollow fiber membrane: The casting solution was extruded from the nozzle, and a mixed solution of water and NMP (wherein the volume content of NMP in the mixed solution was 70 vol%) was used as the core liquid. The nascent hollow fiber membrane was passed through the air for 10 cm and then entered a pure hydrogel bath (temperature 30℃). After being collected by a winding wheel, it was soaked in a water tank for 24 h to remove residual solvent, and then soaked in ethanol for 12 h. The membrane fibers were then hung to air dry to obtain a polyimide hollow fiber membrane, denoted as HFM-3.

[0136] Example 4

[0137] (1) Preparation of polyimide:

[0138] 16 L of N-methylpyrrolidone (NMP) was added to a dry reactor under a nitrogen atmosphere. 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP, 2.56 mol, diamine monomer I) and m-phenylenediamine (m-PDA, 0.64 mol, diamine monomer II) were added and stirred until completely dissolved. The reaction system was cooled to 10 °C, and pre-mixed hexafluorodianhydride (6FDA, 2.56 mol) and 4,4'-biphenyl ether dianhydride (ODPA, 0.64 mol) were added. The reaction was carried out at 10 °C for 4 h, then the refrigerator was turned off, and the reaction continued for 15 h to obtain polyimide acid. Acetic anhydride (11... A mixed solution of 11.52 mol of ethanol and pyridine was used to dehydrate polyimide. The dehydration reaction was carried out at room temperature for 24 hours to obtain a polyimide solution. The polyimide solution was then discharged into a mixed solution of ethanol and water, and the polyimide precipitated out in fibrous form. The polyimide was then washed with an alcohol-water mixture at 60°C under mechanical stirring for 24 hours, with the solution being changed three times during the washing process. After washing, the polyimide fibers were dried in a forced-air oven at 60°C for 24 hours, and then thoroughly dried in a vacuum oven at 150°C to obtain polyimide, denoted as PI-4.

[0139] (2) Preparation of polyimide casting solution: PI-4, NMP, tetrahydrofuran (THF), and ethanol were added to the reaction vessel of the spinning machine in a mass ratio of 32:50:15:3. After stirring at 60°C for 48 h, the mixture was degassed under vacuum for 48 h to obtain the casting solution. Based on the total mass of the casting solution, the content of PI-4 was 32 wt%, the content of NMP (a good solvent for polyimide) was 50 wt%, the content of THF (a poor solvent for polyimide) was 15 wt%, and the content of non-solvents was 3 wt%.

[0140] (3) Preparation of polyimide hollow fiber membrane: The casting solution was extruded from a nozzle, and a mixed solution of water and NMP (wherein the volume content of NMP in the mixed solution was 70 vol%) was used as the core liquid. The nascent hollow fiber membrane was passed through the air for 8 cm and then entered a pure hydrogel bath. After being collected by a winding wheel, it was soaked in a water tank for 24 h to remove residual solvent, and then soaked in ethanol for 12 h. The membrane fibers were then hung to air dry naturally to obtain a polyimide hollow fiber membrane, denoted as HFM-4.

[0141] Example 5

[0142] (1) Preparation of polyimide:

[0143] 16 L of N-methylpyrrolidone (NMP) was added to a dry reactor under nitrogen atmosphere. 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP, 2.56 mol) and 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA, 0.64 mol) were added and stirred until completely dissolved. The reaction system was cooled to 5 °C, and pre-mixed hexafluorodianhydride (6FDA, 1.92 mol) and 4,4'-biphenyl ether dianhydride (ODPA, 1.28 mol) were added. The reaction was carried out at 5 °C for 4 h, then the refrigerator was turned off, and the reaction continued for 24 h to obtain polyimide acid. Acetic anhydride (11... A mixed solution of diamine monomer (11.52 mol) and pyridine (11.52 mol) was used to dehydrate polyimide. The dehydration reaction was carried out at room temperature for 24 hours to obtain a polyimide solution. The polyimide solution was then transferred to a mixed solution of ethanol and water, where the polyimide precipitated as fibers. The fibers were then washed with an alcohol-water mixture at 60°C under mechanical stirring for 36 hours, with the solution being changed four times during this period. After washing, the polyimide fibers were dried in a 60°C forced-air oven for 24 hours, and then thoroughly dried in a 150°C vacuum oven to obtain polyimide, denoted as PI-5. The molar ratio of diamine monomer to dianhydride monomer was 1:1, the molar ratio of diamine monomer I to dianhydride monomer was 0.8:1, the molar ratio of acetic anhydride to dianhydride monomer was 3.6:1, and the molar ratio of pyridine to dianhydride monomer was 3.6:1.

[0144] (2) Preparation of polyimide casting solution: PI-5, NMP, and tetrahydrofuran (THF) were added to the reaction vessel of the spinning machine at a mass ratio of 30:60:10. After stirring at 60°C for 48 hours, the mixture was degassed under vacuum for 48 hours to obtain the casting solution. Based on the total mass of the casting solution, the content of PI-5 was 30 wt%, the content of NMP (a good solvent for polyimide) was 60 wt%, and the content of THF (a poor solvent for polyimide) was 10 wt%.

[0145] (3) Preparation of polyimide hollow fiber membrane: The casting solution was extruded from a nozzle, and a mixed solution of water and NMP (wherein the volume content of NMP in the mixed solution was 70 vol%) was used as the core liquid. The nascent hollow fiber membrane was passed through the air for 10 cm and then entered a pure hydrogel bath (temperature 30℃). After being collected by a winding wheel, it was soaked in a water tank for 24 h to remove residual solvent, and then soaked in ethanol for 24 h. After that, the membrane fibers were hung to air dry and naturally air-dried to obtain a polyimide hollow fiber membrane, denoted as HFM-5.

[0146] Example 6

[0147] (1) Preparation of polyimide:

[0148] 15 L of N-methylpyrrolidone (NMP) was added to a dry reactor under a nitrogen atmosphere. 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP, 1.92 mol) and 9,9-dimethylfluorene-2,7-diamine (SA-1, 1.28 mol) were added and stirred until completely dissolved. The reaction system was cooled to 5 °C, and pre-mixed hexafluorodianhydride (6FDA, 1.92 mol) and 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride (α-ODPA, 1.28 mol) were added. The reaction was carried out at 5 °C for 8 h, then the refrigerator was turned off, and the reaction continued for 24 h to obtain polyimide acid. Acetic anhydride was then added. A mixed solution of 11.52 mol of polyimide and pyridine (11.52 mol) was used to dehydrate polyimide. The dehydration reaction was carried out at room temperature for 24 hours to obtain a polyimide solution. The polyimide solution was then discharged into a mixed solution of ethanol and water, and the polyimide precipitated out in fibrous form. The polyimide was then washed with an alcohol-water mixture at 60°C under mechanical stirring for 12 hours, with the solution being changed three times during the washing process. After washing, the polyimide fibers were dried in a forced-air oven at 60°C for 24 hours, and then thoroughly dried in a vacuum oven at 150°C to obtain polyimide, denoted as PI-6.

[0149] (2) Preparation of polyimide casting solution: PI-6, NMP, THF, and ethanol were added to the reaction vessel of the spinning machine in a mass ratio of 32:48:15:5. After stirring at 60°C for 48 hours, the mixture was degassed under vacuum for 48 hours to obtain the casting solution. Based on the total mass of the casting solution, the content of PI-6 was 32 wt%, the content of NMP (a good solvent for polyimide) was 48 wt%, the content of THF (a poor solvent for polyimide) was 15 wt%, and the content of non-solvents was 5 wt%.

[0150] (3) Preparation of polyimide hollow fiber membrane: The casting solution was extruded from a nozzle, and a mixed solution of water and NMP (wherein the volume content of NMP in the mixed solution was 90 vol%) was used as the core liquid. The nascent hollow fiber membrane was passed through the air for 8 cm and then entered a pure hydrogel bath (temperature 30℃). After being collected by a winding wheel, it was soaked in a water tank for 24 h to remove residual solvent, and then soaked in ethanol for 12 h. The membrane fibers were then hung to air dry naturally to obtain a polyimide hollow fiber membrane, denoted as HFM-6.

[0151] Comparative Example 1

[0152] A hollow fiber membrane prepared using commercially available polyimide matrimonium as a raw material was named HFM-D1. [Data source: David Oana C., Gorri Daniel, Nijmeijer Kitty, et al. Hydrogen separation from multicomponent gas mixtures containing CO, N2 and CO2 using matrimonium-sasymmetric hollow fiber membranes[J]. Journal of Membrane Science, 2012,(419-420):49-56.]

[0153] Comparative Example 2

[0154] A hollow fiber membrane prepared using commercially available polyimide P84 as a raw material was named HFM-D2. [Data source: Sheng Lujie, Ren Jizhong, Hua Kaisheng, et al. The enhancement of mechanical properties of P84 hollow fiber membranes by thermally annealing below and above T] g [J].Journal of Membrane Science,2020,595:117580.】

[0155] Comparative Example 3:

[0156] The mechanical properties of the PVP gas separation membrane were named HFM-D3. [Data source: Jianjun Qin, Tai-Shung Chung. Effect of dope flow rate on the morphology, separation performance, thermal and mechanical properties of ultrafiltration hollow fibremembranes[J]. Journal of Membrane Science, 1999, 157(1):35-51]

[0157] Comparative Example 4

[0158] (1) Preparation of polyimide:

[0159] 16 L of N-methylpyrrolidone (NMP) was added to a dry reaction vessel under a nitrogen atmosphere. 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP, 2.56 mol, diamine monomer I) and m-phenylenediamine (m-PDA, 0.64 mol, diamine monomer II) were added and stirred until completely dissolved. The reaction system was cooled to 10 °C, and 4,4'-biphenyl ether dianhydride (ODPA, 3.2 mol) was added. The reaction was carried out at 10 °C for 4 h, then the refrigerator was turned off, and the reaction was continued for 15 h to obtain polyimide acid. Acetic anhydride (11.52 mol) and pyridine (11.52 mol) were then added. A 52 mol / L mixed solution was used to dehydrate polyimide acid. The dehydration reaction was carried out at room temperature for 24 hours to obtain a polyimide solution. The polyimide solution was then transferred to a mixture of ethanol and water, where the polyimide precipitated as fibers. The fibers were then washed with an alcohol-water mixture at 60°C under mechanical stirring for 24 hours, with the solution being changed three times during this period. After washing, the polyimide fibers were dried in a 60°C forced-air oven for 24 hours, and then thoroughly dried in a 150°C vacuum oven to obtain polyimide, denoted as PI-D4. The molar ratio of diamine monomer to dianhydride monomer was 1:1, the ratio of diamine monomer I to acid anhydride monomer was 0.8:1, the molar ratio of acetic anhydride to dianhydride monomer was 3.6:1, and the molar ratio of pyridine to dianhydride monomer was 3.6:1.

[0160] (2) Preparation of polyimide casting solution: PI-D4, NMP, tetrahydrofuran (THF), and ethanol were added to the reaction vessel of the spinning machine in a mass ratio of 32:50:15:3. After stirring at 60°C for 48 h, the mixture was degassed under vacuum for 48 h to obtain the casting solution. Based on the total mass of the casting solution, the content of PI-4 was 32 wt%, the content of NMP (a good solvent for polyimide) was 50 wt%, the content of THF (a poor solvent for polyimide) was 15 wt%, and the content of non-solvents was 3 wt%.

[0161] (3) Preparation of polyimide hollow fiber membrane: The casting solution was extruded from a nozzle, and a mixed solution of water and NMP (wherein the volume content of NMP in the mixed solution was 70 vol%) was used as the core liquid. The nascent hollow fiber membrane was passed through the air for 8 cm and then entered a pure hydrogel bath. After being collected by a winding wheel, it was soaked in a water tank for 24 h to remove residual solvent, and then soaked in ethanol for 12 h. The membrane fibers were then hung to air dry naturally to obtain a polyimide hollow fiber membrane, denoted as HFM-D4.

[0162] Comparative Example 5

[0163] (1) Preparation of polyimide:

[0164] 16 L of N-methylpyrrolidone (NMP) was added to a dry reactor under a nitrogen atmosphere. 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA, 3.2 mol) was added and stirred until completely dissolved. The reaction system was cooled to 5 °C, and pre-mixed hexafluorodianhydride (6FDA, 1.92 mol) and 4,4'-biphenyl ether dianhydride (ODPA, 1.28 mol) were added. The reaction was carried out at 5 °C for 4 h, then the refrigerator was turned off, and the reaction continued for 24 h to obtain polyimide acid. Acetic anhydride (11.52 mol) and pyridine (11.52 mol) were then added. A mixed solution was used to dehydrate polyimide. The dehydration reaction was carried out at room temperature for 24 hours to obtain a polyimide solution. This polyimide solution was then transferred to a mixture of ethanol and water, where the polyimide precipitated as fibers. The fibers were then washed with an ethanol-water mixture at 60°C under mechanical stirring for 36 hours, with the solution being changed four times during this period. After washing, the polyimide fibers were dried in a 60°C forced-air oven for 24 hours, and then thoroughly dried in a 150°C vacuum oven to obtain polyimide, denoted as PI-D4. The molar ratio of diamine monomer to dianhydride monomer was 1:1, the molar ratio of acetic anhydride to dianhydride monomer was 3.6:1, and the molar ratio of pyridine to dianhydride monomer was 3.6:1.

[0165] (2) Preparation of polyimide casting solution: PI-D4, NMP and tetrahydrofuran (THF) were added to the reaction vessel of the spinning machine in a mass ratio of 30:60:10. After stirring at 60°C for 48 hours, the casting solution gelled and could not be spun.

[0166] The molecular weight and molecular weight distribution of the polyimides in the examples and comparative examples were tested, and the results are shown in Table 1.

[0167] Table 1

[0168] sample n:(m+n) <![CDATA[Mn(×10 4 g / mol)]]> <![CDATA[Mw(×10 4 g / mol)]]> PDI PI-1 0.8:1 8.0 15.0 1.875 PI-2 0.4:1 13.7 26.1 1.905 PI-3 0.8:1 13.5 34.6 2.563 PI-4 0.8:1 10.6 23.4 2.208 PI-5 0.6:1 7.8 21.4 2.744 PI-6 0.6:1 6.2 14.0 2.258 PI-D4 0 11.5 22.8 1.983 PI-D5 0.6:1 5.8 13.0 2.241

[0169] Application test cases

[0170] The constant pressure, variable volume method was used to test the permeation rates of pure gases He, H2, Ne, N2, and CH4 through polyimide hollow fiber membranes using a gas separation instrument. First, the membrane fibers were encapsulated into modules, and the gas flow rate through the membrane fibers per unit time at a specific pressure was recorded. The gas permeability was then calculated using the following formula:

[0171]

[0172] Where P represents the gas permeability of the hollow fiber membrane, the unit is GPU (1 GPU = 10⁻⁶). -6 cm 3 (STP)cm -2 s -1 cmHg -1 ), where n represents the number of membrane fibers in each membrane module; Q represents the pure gas flow rate (cm). 3 / min); D is the outer diameter of the hollow fiber membrane (cm); l is the length of the hollow fiber membrane (cm); ΔP is the pressure difference between the inside and outside of the fiber test (cm Hg).

[0173] And according to α i / j =P i / P j The selectivity coefficients of He / Ne, He / N2, He / CH4, H2 / N2, and H2 / CH4 were calculated.

[0174] The mechanical properties of hollow fiber membranes were tested using a universal tensile testing machine. The initial test distance was set to 156 mm. During the test, the fixture was stretched at a constant speed of 50 mm / min. Each sample was tested 5 times, and the average value was taken after removing the extreme values. The results are shown in Tables 2 and 3.

[0175] Table 2

[0176] sample Fracture strength (MPa) Elongation at break (%) HFM-1 34.5 42.6 HFM-2 35.5 44.2 HFM-3 28.7 48.3 HFM-4 52.6 35.6 HFM-5 68.7 32.4 HFM-6 59.7 30.2 HFM-D3 2.8 43.8 HFM-D4 53.7 10.7

[0177] Table 3

[0178]

[0179]

[0180] As shown in Table 2, the elongation at break of the polyimide hollow fiber membrane provided by this invention is similar to that of the comparative example, but its tensile strength is approximately 10 times that of the comparative example. This indicates that the polyimide hollow fiber membrane provided by this invention possesses both excellent elongation at break and tensile strength. Compared to HFM-D4, the hollow fiber membrane HFM-4, made from polyimide PI-4 containing anhydride monomer I, has a significantly higher elongation at break, while its tensile strength is comparable, indicating that the hollow fiber membrane provided by this invention has better toughness.

[0181] As can be seen from Table 3, the separation performance of the polyimide hollow fiber membrane provided by the present invention is similar to or slightly higher than that of the hollow fiber membrane prepared by commercial membrane materials, and the permeability is much higher than that of the hollow fiber membrane prepared by Comparative Example 4, indicating that the polyimide hollow fiber membrane provided by the present invention has excellent gas separation performance.

[0182] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A polyimide hollow fiber membrane, characterized in that, The polyimide forming the hollow fiber membrane has the structure shown in Formula I; Wherein, X comes from a diamine monomer with the structure shown below; Y is derived from at least one diamine monomer with the structure shown in the following group; Ar1 is derived from a dianhydride monomer with the structure shown below; Ar2 is derived from at least one dianhydride monomer with the structure shown in the following group; 2. The polyimide hollow fiber membrane according to claim 1, wherein, The ratio of n:(m+n) is 0.2-0.8:

1.

3. The polyimide hollow fiber membrane according to claim 1 or 2, wherein, The polyimide has a number-average molecular weight of 1×10⁻⁶. 4 -100×10 4 g / mol, preferably 3×10 g / mol 4 -25×10 4 g / mol; Preferably, the polyimide has a molecular weight distribution of 1-5, more preferably 1-3.

4. A method for preparing a polyimide hollow fiber membrane, characterized in that, The preparation method includes the following steps: S1. In the presence of a protective atmosphere, diamine monomer I, diamine monomer II, dianhydride monomer I, dianhydride monomer II are mixed with an organic solvent and subjected to a polycondensation reaction to obtain a polyamic acid solution. Then, an imidization reaction is carried out to obtain polyimide. S2. The polyimide obtained in step S1, a good solvent A for the polyimide, a poor solvent B for the optional polyamide-imide, and a non-solvent C for the optional polyimide are mixed to obtain a casting solution. S3. The casting solution and the core solution are extruded to obtain a nascent fiber membrane. The nascent fiber membrane is then passed through an air bath and a coagulation bath in sequence, and after being wound up, it is exchanged and dried to obtain the polyimide hollow fiber membrane. Among them, diamine monomer I is Diamine monomer II is selected from at least one of the following diamine monomers; Dianone monomer I is Dianone monomer II is selected from at least one of the following dianone monomers; 5. The preparation method according to claim 4, wherein, The molar ratio of diamine monomer to dianhydride monomer is 0.9-1.1:1; Preferably, the molar ratio of diamine monomer I to dianhydride monomer is 0.2-1:1, more preferably 0.4-1:1; Preferably, the molar ratio of dianhydride monomer I to dianhydride monomer is 0.2-0.8:1, more preferably 0.4-0.8:1; Preferably, the conditions for the polycondensation reaction include: a reaction temperature of 0-30°C and a reaction time of 6-36 hours.

6. The preparation method according to claim 4 or 5, wherein, The iminolation reaction is carried out in the presence of a catalyst and a dehydrating agent; Preferably, the conditions for the imidization reaction include: a reaction temperature of 10-60°C and a reaction time of 12-48 h.

7. The preparation method according to any one of claims 4-6, wherein, Based on the total weight of the casting solution, the content of polyimide is 16-35 wt%, the content of good solvent A of polyimide is 40-80 wt%, the content of poor solvent B of polyimide is 0-40 wt%, and the content of non-solvent C of polyimide is 0-15 wt%. Preferably, the good solvent A is selected from at least one of DMAc, NMP, DMF, and DMSO; Preferably, the undesirable solvent B is selected from at least one of THF, CH2Cl2, and CHCl3; Preferably, the non-solvent C of the polyimide is selected from at least one of ethanol, methanol, and deionized water; Preferably, the mixing in step S2 is carried out under heating conditions, and preferably, the heating temperature is 40-80°C.

8. The preparation method according to any one of claims 4-7, wherein, In step S3, the core fluid is selected from at least one of deionized water, ethanol, and NMP; Preferably, the height of the air bath is 2-20cm; Preferably, the coagulation bath is deionized water, and the coagulation bath temperature is 20-60℃.

9. The preparation method according to any one of claims 4-8, wherein, The exchange is carried out in a water bath; Preferably, the stirring time is 1-72 hours; Preferably, the preparation method further includes: post-treating the exchange-treated fiber membrane in solvent E and then drying it; Preferably, the solvent E is selected from at least one of methanol, ethanol, and n-hexane.

10. A polyimide hollow fiber membrane prepared by any one of claims 4-9.

11. The application of the polyimide hollow fiber membrane according to any one of claims 1-3 and 10 in helium separation.

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