A polyimide hollow fiber gas separation membrane and its preparation method

Abstract

This invention discloses a polyimide hollow fiber gas separation membrane and its preparation method. By rationally designing the precursor structure and precisely controlling the spinning parameters, a polyimide hollow fiber gas separation membrane with a dense, non-porous, and defect-free surface and excellent mechanical properties is prepared, exhibiting high-throughput and high-selectivity gas separation effects, especially for hydrogen. The hollow fiber spinning solution is obtained by mixing a polyimide polymer with a high-boiling-point solvent, a low-boiling-point solvent, and a non-solvent. The polyimide polymer is synthesized from dianhydride monomers, diamine monomers containing benzimidazole groups, and other diamine monomers through a polycondensation reaction. The preparation method provided by this invention is simple and easy to operate, avoiding the cumbersome procedures and additional economic investment associated with subsequent processes (polydimethylsiloxane coating and crosslinking modification), and has broad application prospects.

Description

Technical Field

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

[0002] Hydrogen plays a vital role in the production, transportation, and power supply of synthetic fuels. Its high energy-to-mass ratio makes it particularly suitable for heavy-duty, long-haul road freight, maritime transport, and aviation applications. Furthermore, in fossil fuel-intensive industries such as steelmaking, hydrogen is crucial for replacing coal and natural gas. Hydrogen primarily originates from fossil fuel-related processes, such as natural gas steam reforming, petrochemical refineries, and purge gas recovery. The separation of hydrogen and methane is one of the key steps in these hydrogen production processes.

[0003] Gas separation, as a membrane separation technology, boasts significant technological advantages and promising application prospects in hydrogen recovery due to its low investment, low energy consumption, simple operation, and pollution-free nature. Separation membranes come in various forms, such as flat sheet membranes, tubular membranes, and hollow fiber membranes. Hollow fiber membranes, with their fibrous shape and self-supporting structure, offer advantages such as high packing density, large specific surface area, good pressure resistance, and simple membrane module structure. Consequently, hollow fiber membrane separation processes exhibit low energy consumption, small device size, ease of operation, high efficiency, and no secondary pollution, leading to their increasingly widespread application.

[0004] Studies have shown that polyimides possess excellent thermal stability, allowing for long-term use in high-temperature environments. Their superior mechanical properties, low dielectric constant, chemical stability, and fatigue resistance make them widely used in aerospace, microelectronics, organic solvent nanofiltration, and gas separation membranes. Polyimides are typically obtained through the dehydration condensation reaction of dianhydrides and diamines, exhibiting excellent thermal stability, dimensional stability, and chemical stability, making them one of the most widely used engineering plastics. Aromatic polyimides, in particular, containing a large number of benzene rings in their molecular chains, possess excellent physicochemical properties. Currently commercially available aromatic polyimides include Matrimid, Kapton, P84, and Ultem. In addition, researchers have developed other high-performance polyimides, the most representative of which is the polyimide containing hexafluoroisopropyl (6FDA). 6FDA exhibits significant steric hindrance, hindering the stacking of polyimide molecular chains, increasing the free volume of the polymer, and improving the gas permeability coefficient. Meanwhile, the polarity of 6FDA enhances the solubility of polyimide in common polar solvents (such as DMF and NMP), making it easy to process into flat sheet membranes or hollow fiber membranes. 6FDA-based polyimide membranes generally exhibit good gas permeability and selectivity.

[0005] Large-scale gas separation applications in industry require separation membranes with high permeability to improve yield. Therefore, commercial membranes typically possess two characteristics. First, they have an asymmetric structure, generally composed of a thick porous support layer and a dense, thin selective layer (<1 μm). This asymmetric structure significantly reduces gas transport resistance; the membrane's permeability and selectivity are primarily controlled by the thin selective layer, while the support layer only provides mechanical support, with negligible resistance to molecular transport. Second, most commercial membranes are processed in the form of hollow fibers. The structure of hollow fiber membranes perfectly satisfies the above two characteristics. Furthermore, hollow fiber membranes have the advantages of self-supporting properties and high packing density. For example, a hollow fiber membrane module with a diameter of 20 cm and a length of 1 m filled with fibers of 100 μm diameter can achieve a membrane area of ​​up to 300 m². 2 For equivalent-sized spiral-wound membrane modules and flat-sheet membrane modules, the membrane area is only 20-40 m². 2 Typical hollow fiber membranes are made from small quantities of commercially available and well-studied polymers, such as cellulose acetate and polyethersulfone. However, most polymers are difficult to prepare into usable hollow fiber gas separation membranes. This is mainly because in practical applications, hollow fiber membranes are desired to have a thin selectivity layer to improve productivity. Rapid aggregation of polymer molecules and irregular stacking of polymer chains often lead to defects in the thin selectivity layer, and the thinner the selectivity layer, the more defects are generated, resulting in a severe loss of membrane selectivity and rendering it unusable. The 6FDA-based polyimide hollow fiber membrane synthesized by existing technology for separating hydrogen and methane still has the following problems: (1) the selectivity layer of the hollow fiber is relatively thick, which cannot achieve high permeation fluxes for hydrogen and methane; (2) the hollow fiber membrane cannot simultaneously possess high gas permeation flux and gas selectivity; (3) the hollow fiber does not have good mechanical properties, which cannot ensure stability during operation. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a polyimide hollow fiber gas separation membrane and its preparation method. By rationally designing the precursor structure and precisely controlling the spinning parameters, a polyimide hollow fiber gas separation membrane with high throughput and high selectivity, a dense, non-porous, and defect-free surface, and excellent mechanical properties is prepared.

[0007] The above-mentioned objective of this invention is achieved through the following technical solution:

[0008] The first aspect of this invention provides a polyimide polymer, the structural formula of which is shown in formula (I):

[0009]

[0010] Among them, 0 < x < 100, 0 ≤ y < 100, and both x and y are integers.

[0011] R1 is selected from the following structural groups:

[0012]

[0013] R2 is selected from the following structural groups:

[0014]

[0015] Furthermore, the weight-average molecular weight of the polyimide polymer is 30,000 - 1,500,000, preferably 30,000 - 70,000.

[0016] The second aspect of the present invention provides a method for preparing a polyimide hollow fiber gas separation membrane, comprising the following steps:

[0017] (1) Under an inert environment, a dianhydride monomer and a diamine monomer are subjected to a polycondensation reaction in a solvent to obtain the polyimide polymer described in the first aspect;

[0018] (2) The polyimide polymer is mixed with a high-boiling-point solvent, a low-boiling-point solvent, and a non-solvent to obtain a hollow fiber spinning solution;

[0019] (3) The hollow fiber spinning solution is subjected to a defoaming treatment to obtain a membrane solution; an organic solvent and water are mixed to obtain a core solution; the membrane solution and the core solution are successively passed through a spinneret, an air gap, and a coagulation bath treatment to obtain hollow fibers; the hollow fibers are successively passed through a spinning process, water immersion, multiple solvent exchanges, and drying treatment to obtain the polyimide hollow fiber gas separation membrane.

[0020] This invention provides a method for preparing a high-strength, high-selectivity polyimide hollow fiber gas separation membrane. The polyimide polymer is synthesized by a condensation reaction of a dianhydride monomer, a diamine monomer containing a benzimidazole (PABZ) group, and other diamine monomers. The diamine monomer containing the benzimidazole (PABZ) group contains abundant hydrogen bonds and π-π interactions, resulting in tightly stacked molecular chains, which is beneficial for improving the sieving capacity of the membrane material. In this invention, to achieve a non-porous surface on the polyimide hollow fiber membrane, the concentration of polyimide is increased, causing a certain degree of polymer chain entanglement. During phase separation, the membrane surface can rapidly enter the gel region without crossing the two-phase region, forming a dense structure. By adding a low-boiling-point solvent, the polyimide polymer solution is rapidly evaporated in the air gap, increasing the concentration of polyimide polymer on the hollow fiber surface, which is beneficial for forming a defect-free surface structure, thereby obtaining a non-porous polyimide hollow fiber membrane. Hollow fiber membranes made by spinning polyimide polymers have advantages such as high mechanical strength and high permeation flux in gas separation processes, good thermal stability, and good gas separation performance, especially for hydrogen.

[0021] Furthermore, in step (1), nitrogen is used to create an inert environment.

[0022] Further, in step (1), the dianhydride monomer is selected from 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA); the diamine monomer is selected from one or more of 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ), 2,3,5,6-tetramethyl-1,4-phenylenediamine and 3,5-diaminobenzoic acid (DABA).

[0023] Further, in step (1), the solvent is selected from one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide.

[0024] Further, in step (1), based on the total weight of all substances used in step (1), the amount of the diamine is 5-15 wt%, the amount of the dianhydride is 5-15 wt%, and the amount of the solvent is 80-90 wt%.

[0025] In a specific embodiment, in step (1), equimolar amounts of diamine monomer and dianhydride monomer are added to a three-necked flask and stirred and dissolved in a solvent under nitrogen atmosphere. The reaction is fully dissolved to form a viscous high molecular weight polyamic acid. Subsequently, a polyimide polymer solution is obtained by azeotropic distillation, and the precipitated polyimide polymer is dried to obtain a polyimide polymer.

[0026] Further, the diamine monomer, dianhydride monomer and solvent are mixed and stirred for 20-24 hours until homogeneous to obtain polyamic acid.

[0027] Furthermore, the polyamic acid is further heated to react and obtain polyimide polymers for 4-5 hours.

[0028] Further, in step (2), the high-boiling-point solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide, preferably N-methylpyrrolidone; the low-boiling-point solvent is selected from one or more of diethyl ether, acetone, tetrahydrofuran, petroleum ether and dichloromethane, preferably tetrahydrofuran; the non-solvent is selected from one or more of methanol, ethanol, glycerol, n-butanol, isopropanol, n-hexane, water, propionic acid and ethylene glycol, preferably ethanol.

[0029] Further, in step (2), based on the total weight of all substances used in step (2), the amount of the polyimide polymer is 15-35 wt%, the amount of the high-boiling-point solvent is 45-65 wt%, the amount of the low-boiling-point solvent is 1-15 wt%, and the amount of the non-solvent is 1-15 wt%.

[0030] Preferably, in step (2), based on the total weight of all substances used in step (2), the amount of the polyimide polymer is 20-30 wt%, the amount of the high-boiling-point solvent is 45-55 wt%, the amount of the low-boiling-point solvent is 10-15 wt%, and the amount of the non-solvent is 5-10 wt%.

[0031] Furthermore, in step (2), the mixing time is 12-24 hours.

[0032] Further, steps (1) and (2) are carried out in a three-necked flask, and the degassing treatment in step (3) is carried out in a feed tank. Because the hollow fiber spinning solution has a high viscosity, it is necessary to pressurize it with nitrogen to squeeze the hollow fiber spinning solution from the three-necked flask into the feed tank. Preferably, the pressure of the nitrogen pressurization is 1-5 bar.

[0033] Furthermore, in step (3), the degassing treatment takes 6-12 hours and the temperature is 20-30°C.

[0034] Further, in step (3), the organic solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide, preferably N-methylpyrrolidone.

[0035] Further, in step (3), the volume ratio of the organic solvent to water is (6-8):(2-4), such as 8:2, 7:3, or 6:4.

[0036] Furthermore, in step (3), the spinneret has a concentric circle structure, the core liquid passes through the inner circle of the spinneret, and the film liquid passes through the outer circle of the spinneret.

[0037] Further, in step (3), the distance of the air gap refers to the distance between the spinneret and the coagulation bath, that is, the distance the membrane liquid and the core liquid move from the spinneret to the coagulation bath. During this air gap stage, the low-boiling-point solvent evaporates rapidly, causing the polymer concentration on the polyimide hollow fiber membrane skin to rise rapidly, forming a skin layer. Then, it is immersed in the coagulation bath water to complete phase separation and solidification (that is, the core liquid present in the skin layer is replaced by water in the coagulation bath during this stage).

[0038] Furthermore, in step (3), the distance of the air gap is 3-10cm; the temperature of the coagulation bath treatment is 10-35℃.

[0039] Furthermore, in step (3), the core liquid is extruded by a pressure pump and a syringe at a certain pressure and speed, and the speed is controlled to deliver it to the spinneret. The flow rate of the core liquid is 0.03-0.2 mL / min.

[0040] Furthermore, in step (3), the membrane solution is delivered to the spinneret by a gear pump, and the speed of the gear pump is 30-50 r / min.

[0041] Furthermore, in step (3), the spinning process uses a take-up wheel to take up the yarn, and the take-up speed of the take-up wheel is 30-70m / min.

[0042] Furthermore, in step (3), the water soaking time is 12-24 hours, and the purpose of water soaking is to remove excess core fluid and solvent.

[0043] Furthermore, in step (3), the solvent used for solvent exchange is ethanol-n-hexane solvent, and the number of solvent exchanges is 5-6 times. The purpose of multiple solvent exchanges is to remove residual solvent and water.

[0044] Furthermore, in step (3), the specific operation of the drying process is: air drying for 22-24 hours.

[0045] Furthermore, in step (3), the drying process further includes an annealing process at 180-280°C.

[0046] The third aspect of the present invention provides a polyimide hollow fiber gas separation membrane prepared by the method described in the second aspect.

[0047] The beneficial effects of this invention are:

[0048] 1. The preparation method provided by the present invention is simple and easy to operate, avoiding the cumbersome procedures and additional economic investment brought about by subsequent processes (polydimethylsiloxane coating and crosslinking modification). The prepared polyimide hollow fiber gas separation membrane has a dense, non-porous and defect-free surface, good mechanical strength, and high throughput and high selectivity.

[0049] 2. This invention provides a faster rate of hollow fiber preparation, which can greatly improve the efficiency of membrane fiber preparation and produce a dense, non-porous hollow fiber membrane. When applied to the field of gas separation, this membrane exhibits excellent gas separation performance, with the optimal hydrogen flux between 270-300 GPU, the optimal carbon dioxide flux between 70-80 GPU, and the optimal methane flux between 3.25-3.55 GPU. It also has high H2 / CH4 gas selectivity and can be applied to many practical production processes (natural gas separation, petrochemical refineries, purge gas recovery, etc.), which has important guiding significance for polyimide spinning. Attached Figure Description

[0050] Figure 1 This is a schematic flowchart illustrating a method for preparing a polyimide hollow fiber gas separation membrane provided by the present invention.

[0051] Figure 2 The images show the morphology of the polyimide hollow fiber gas separation membrane prepared in Example 1; where a is an overall cross-sectional view under a scanning electron microscope, b is a magnified cross-sectional view under a scanning electron microscope, and c is a skin layer image under a scanning electron microscope.

[0052] Figure 3 The image shows the morphology of the polyimide hollow fiber gas separation membrane prepared in Example 2; where a is an overall cross-sectional view under a scanning electron microscope, b is a magnified cross-sectional view under a scanning electron microscope, and c is a skin layer image under a scanning electron microscope.

[0053] Figure 4 The images show the morphology of the polyimide hollow fiber gas separation membrane prepared in Example 3; where a is an overall cross-sectional view under a scanning electron microscope, b is a magnified cross-sectional view under a scanning electron microscope, and c is a skin layer image under a scanning electron microscope.

[0054] Figure 5 The image shows the morphology of the polyimide hollow fiber gas separation membrane prepared in Example 4; where a is an overall cross-sectional view under a scanning electron microscope, b is a magnified cross-sectional view under a scanning electron microscope, and c is a skin layer image under a scanning electron microscope.

[0055] Figure 6 The image shows the morphology of the polyimide hollow fiber gas separation membrane prepared in Example 5; where a is an overall cross-sectional view under a scanning electron microscope, b is a magnified cross-sectional view under a scanning electron microscope, and c is a skin layer image under a scanning electron microscope.

[0056] Figure 7The image shows the morphology of the polyimide hollow fiber gas separation membrane prepared in Example 6; where a is an overall cross-sectional view under a scanning electron microscope, b is a magnified cross-sectional view under a scanning electron microscope, and c is a skin layer image under a scanning electron microscope.

[0057] Figure 8 The image shows the morphology of the polyimide hollow fiber gas separation membrane prepared in Example 7; where a is an overall cross-sectional view under a scanning electron microscope, b is a magnified cross-sectional view under a scanning electron microscope, and c is a skin layer image under a scanning electron microscope.

[0058] Figure 9 The image shows the morphology of the polyimide hollow fiber gas separation membrane prepared in Example 8; where a is an overall cross-sectional view under a scanning electron microscope, b is a magnified cross-sectional view under a scanning electron microscope, and c is a skin layer image under a scanning electron microscope.

[0059] Figure 10 The image shows the morphology of the polyimide hollow fiber gas separation membrane prepared in Example 9; where a is an overall cross-sectional view under a scanning electron microscope, b is a magnified cross-sectional view under a scanning electron microscope, and c is a skin layer image under a scanning electron microscope.

[0060] Figure 11 The image shows the morphology of the polyimide hollow fiber gas separation membrane prepared in Comparative Example 2; where a is an overall cross-sectional view under a scanning electron microscope, b is a magnified cross-sectional view under a scanning electron microscope, and c is a skin layer image under a scanning electron microscope.

[0061] Figure 12 The image shows the morphology of the polyimide hollow fiber gas separation membrane prepared in Comparative Example 3; where a is an overall cross-sectional view under a scanning electron microscope, b is a magnified cross-sectional view under a scanning electron microscope, and c is a skin layer image under a scanning electron microscope.

[0062] Figure 13 The image shows the morphology of the polyimide hollow fiber gas separation membrane prepared in Comparative Example 4; where a is an overall cross-sectional view under a scanning electron microscope, b is a magnified cross-sectional view under a scanning electron microscope, and c is a skin layer image under a scanning electron microscope.

[0063] Figure 14 The infrared spectrum of PI-Im polyimide in Example 1 (left image) and 1 H NMR spectrum (right image).

[0064] Figure 15 The infrared spectrum (left) of PI-Im-BN4CH3 polyimide in Example 8 and 1 HNMR image (right).

[0065] Figure 16 The infrared spectrum (left) of PI-Im-COOH polyimide in Example 9 and 1 H NMR spectrum (right image).

[0066] Figure 17 The tensile strength curves of the polyimide hollow fibers prepared in Examples 1-9 and Comparative Examples 2-4 are shown. Detailed Implementation

[0067] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0068] This invention provides a method for preparing a polyimide hollow fiber gas separation membrane, comprising the following steps:

[0069] (1) Under an inert environment, dianhydride monomer and diamine monomer undergo a polycondensation reaction in a solvent to obtain the polyimide polymer described in the first aspect;

[0070] (2) The polyimide polymer is mixed with a high-boiling-point solvent, a low-boiling-point solvent and a non-solvent to obtain a hollow fiber spinning solution;

[0071] (3) The hollow fiber spinning solution is degassed to obtain a membrane solution; an organic solvent is mixed with water to obtain a core solution; the membrane solution and the core solution are sequentially passed through a spinneret, an air gap and a coagulation bath to obtain hollow fibers; the hollow fibers are sequentially passed through a spinning process, water immersion, multiple solvent exchanges and drying to obtain the polyimide hollow fiber gas separation membrane.

[0072] In a specific embodiment, the preparation method includes the following steps:

[0073] (1) Under sealed conditions with nitrogen purging, the dianhydride monomer, diamine monomer, and solvent are mixed and stirred for 20-24 hours until homogeneous to obtain polyimide. Then, a water separator and reflux condenser are attached to a three-necked flask, and anhydrous toluene is added to the three-necked flask and the water separator. The reaction temperature is gradually increased to 190-200℃, and the reaction is continued for 4-5 hours to obtain polyimide polymers.

[0074] (2) Mix the polyimide polymer with a high-boiling-point solvent, a low-boiling-point solvent and non-solvent B for 12-24 hours, and stir until uniform to obtain a hollow fiber spinning solution;

[0075] (3) The hollow fiber spinning solution is degassed to obtain a membrane solution; an organic solvent is mixed with water to obtain a core solution; the membrane solution and the core solution are sequentially passed through a spinneret, an air gap and a coagulation bath to obtain hollow fibers; the hollow fibers are sequentially passed through a spinning process, water immersion, multiple solvent exchanges and drying to obtain the polyimide hollow fiber gas separation membrane.

[0076] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0077] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0078] In the following examples, the diamine monomer was purchased from Aladdin with a purity of 98%; the solvent was purchased from Beijing Innocare with a purity of 98%; the dianhydride was purchased from Aladdin with a purity of 99%; the high-boiling-point solvent was purchased from Beijing Innocare with a purity of 98%; the low-boiling-point solvent was purchased from Sinopharm with analytical grade; the non-solvent was purchased from Sinopharm with analytical grade; and P84 was purchased from HP Polymer GmbH.

[0079] Example 1

[0080] A method for preparing a polyimide hollow fiber gas separation membrane, the process flow diagram is shown below. Figure 1 As shown, the specific steps include:

[0081] (1) In a three-necked flask, under ice bath and nitrogen protection, 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) and 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) were stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP). Based on the total weight of all substances used in step (1), the molar ratio of 6FDA and PABZ was 1:1, totaling 20 wt%, and the amount of ultra-dry NMP was 80 wt%. The mixture was reacted with stirring for 24 h to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and the temperature was gradually increased to 200 °C and kept constant for 5 h to obtain PI-Im polyimide (weight average molecular weight of 65200). After precipitation and washing with methanol, it was dried in a vacuum oven at 120 °C for 24 h.

[0082] (2) The polyimide is mixed with NMP, tetrahydrofuran (THF) and ethanol (C2H5OH) for 24 hours and stirred until uniform to obtain a hollow fiber spinning solution; based on the total weight of all substances used in step (2), the amount of polyimide is 15wt%, the amount of NMP is 65wt%, the amount of THF is 10wt%, and the amount of C2H5OH is 10wt%.

[0083] (3) The hollow fiber spinning solution is degassed in a feed tank at 25°C for 12 hours to obtain a membrane solution. This membrane solution is then mixed with a prepared core solution (a mixture of NMP and water, with a volume ratio of NMP to water of 6:4) and fed to the spinneret via a gear pump, a pressure pump, and a syringe, respectively, with controlled speeds. The membrane solution is extruded from the feed tank to the spinneret for spinning by nitrogen pressurization (using a nitrogen pressurization tank at a pressure of 2 bar). The membrane solution is then passed through a 5 cm air gap and a 25°C coagulation bath to obtain hollow fibers. The hollow fibers are then subjected to a spinning process (take-up using a take-up wheel at a take-up speed of 30 m / min), soaked in water for 12 hours, subjected to solvent exchange with ethanol and n-hexane three times, and dried for 24 hours to obtain the polyimide hollow fiber gas separation membrane.

[0084] The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 1, as tested by scanning electron microscopy, is shown in the figure below. Figure 2 As shown, the membrane fluid forms a support layer and a selective layer, with the support layer on the inside and the selective layer on the outside. The core fluid plays a role in adjusting the structure and maintaining the hollow structure. Figure 2 As can be seen from the image, the polyimide hollow fiber gas separation membrane consists of a support layer with finger-shaped pores and a selective layer. The selective layer is approximately 120 nm thick and has a dense, non-porous surface.

[0085] Example 2

[0086] A method for preparing a polyimide hollow fiber gas separation membrane specifically includes the following steps:

[0087] (1) In a three-necked flask, under ice bath and nitrogen protection, 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) and 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) were stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP). Based on the total weight of all substances used in step (1), the molar ratio of 6FDA and PABZ was 1:1, totaling 20 wt%, and the amount of ultra-dry NMP was 80 wt%. The mixture was reacted with stirring for 24 h to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and the temperature was gradually increased to 200 °C and kept constant for 5 h to obtain PI-Im polyimide (weight average molecular weight of 65200). After precipitation and washing with methanol, it was dried in a vacuum oven at 120 °C for 24 h.

[0088] (2) The polyimide is mixed with NMP, THF and C2H5OH and stirred for 24 hours until uniform to obtain a hollow fiber spinning solution; based on the total weight of all substances used in step (2), the amount of polyimide is 15wt%, the amount of NMP is 65wt%, the amount of THF is 10wt%, and the amount of C2H5OH is 10wt%.

[0089] (3) The hollow fiber spinning solution is degassed in a feed tank at 25°C for 12 hours to obtain a membrane solution. This membrane solution is then mixed with a prepared core solution (a mixture of NMP and water, with a volume ratio of NMP to water of 7:3) and fed to the spinneret via a gear pump, a pressure pump, and a syringe, respectively, with controlled speeds. The membrane solution is extruded from the feed tank to the spinneret for spinning under nitrogen pressure (nitrogen pressurization tank, with a nitrogen pressure of 2 bar). The membrane solution is then passed through a 5 cm air gap and a 25°C coagulation bath to obtain hollow fibers. The hollow fibers are then subjected to a spinning process (take-up by a take-up wheel at a take-up speed of 50 m / min), soaked in water for 12 hours, subjected to solvent exchange with ethanol and n-hexane three times, and dried for 24 hours to obtain the polyimide hollow fiber gas separation membrane.

[0090] The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 2, as tested using scanning electron microscopy, is shown in the figure below. Figure 3 As shown, from Figure 3 As can be seen, the polyimide hollow fiber gas separation membrane consists of a support layer with finger-shaped pores and a selective layer. The selective layer is approximately 332 nm thick and has a dense, non-porous surface.

[0091] Example 3

[0092] A method for preparing a polyimide hollow fiber gas separation membrane specifically includes the following steps:

[0093] (1) In a three-necked flask, under ice bath and nitrogen protection, 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) and 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) were stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP). Based on the total weight of all substances used in step (1), the molar ratio of 6FDA and PABZ was 1:1, totaling 20 wt%, and the amount of ultra-dry NMP was 80 wt%. The mixture was reacted with stirring for 24 h to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and the temperature was gradually increased to 200 °C and kept constant for 5 h to obtain PI-Im polyimide (weight average molecular weight of 65200). After precipitation and washing with methanol, it was dried in a vacuum oven at 120 °C for 24 h.

[0094] (2) The polyimide is mixed with NMP, THF and C2H5OH and stirred for 24 hours until uniform to obtain a hollow fiber spinning solution; based on the total weight of all substances used in step (2), the amount of polyimide is 35wt%, the amount of NMP is 45wt%, the amount of THF is 15wt% and the amount of C2H5OH is 5wt%.

[0095] (3) The hollow fiber spinning solution is degassed in a feed tank at 25°C for 12 hours to obtain a membrane solution. This membrane solution is then mixed with a prepared core solution (a mixture of NMP and water, with a volume ratio of NMP to water of 8:2) and fed to the spinneret via a gear pump, a pressure pump, and a syringe, respectively, with controlled speeds. The membrane solution is extruded from the feed tank to the spinneret for spinning by nitrogen pressurization (using a nitrogen pressurization tank at a pressure of 2 bar). The membrane solution is then passed through a 5 cm air gap and a 25°C coagulation bath to obtain hollow fibers. The hollow fibers are then subjected to a spinning process (take-up using a take-up wheel at a take-up speed of 50 m / min), soaked in water for 12 hours, subjected to solvent exchange with ethanol and n-hexane three times, and dried for 24 hours to obtain the polyimide hollow fiber gas separation membrane.

[0096] The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 3, as tested using scanning electron microscopy, is shown in the figure below. Figure 4 As shown, from Figure 4 As can be seen, the polyimide hollow fiber gas separation membrane consists of a sponge-like support layer and a selective layer. The selective layer is approximately 4.5 μm thick and has a dense, non-porous surface.

[0097] Example 4

[0098] A method for preparing a polyimide hollow fiber gas separation membrane specifically includes the following steps:

[0099] (1) In a three-necked flask, under ice bath and nitrogen protection, 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) and 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) were stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP). Based on the total weight of all substances used in step (1), the molar ratio of 6FDA and PABZ was 1:1, totaling 20 wt%, and the amount of ultra-dry NMP was 80 wt%. The mixture was reacted with stirring for 24 h to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and the temperature was gradually increased to 200 °C and kept constant for 5 h to obtain PI-Im polyimide (weight average molecular weight of 65200). After precipitation and washing with methanol, it was dried in a vacuum oven at 120 °C for 24 h.

[0100] (2) The polyimide is mixed with NMP, THF and C2H5OH and stirred for 24 hours until uniform to obtain hollow fiber spinning solution; based on the total weight of all substances used in step (2), the amount of polyimide is 30wt%, the amount of NMP is 50wt%, the amount of THF is 13wt% and the amount of C2H5OH is 7wt%.

[0101] (3) The hollow fiber spinning solution is degassed in a feed tank at 25°C for 12 hours to obtain a membrane solution. This membrane solution is then mixed with a prepared core solution (a mixture of NMP and water, with a volume ratio of NMP to water of 8:2) and fed to the spinneret via a gear pump, a pressure pump, and a syringe, respectively, with controlled speeds. The membrane solution is extruded from the feed tank to the spinneret for spinning by nitrogen pressurization (using a nitrogen pressurization tank at a pressure of 4 bar). The membrane solution is then passed through a 3 cm air gap and a 25°C coagulation bath to obtain hollow fibers. The hollow fibers are then subjected to a spinning process (take-up using a take-up wheel at a take-up speed of 70 m / min), soaked in water for 12 hours, subjected to solvent exchange with ethanol and n-hexane three times, and dried for 24 hours to obtain the polyimide hollow fiber gas separation membrane.

[0102] The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 4, as tested using scanning electron microscopy, is shown in the figure below. Figure 5 As shown, from Figure 5 As can be seen, the polyimide hollow fiber gas separation membrane consists of a support layer with finger-shaped pores and a selective layer. The selective layer is approximately 700 nm thick and has a dense, non-porous surface.

[0103] Example 5

[0104] A method for preparing a polyimide hollow fiber gas separation membrane specifically includes the following steps:

[0105] (1) In a three-necked flask, under nitrogen protection, 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) and 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) were stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP). Based on the total weight of all substances used in step (1), the molar ratio of 6FDA and PABZ was 1:1, totaling 20 wt%, and the amount of ultra-dry NMP was 80 wt%. The mixture was reacted with stirring for 24 h to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and the temperature was gradually increased to 200 °C and kept constant for 5 h to obtain PI-Im polyimide (weight average molecular weight of 65200). After precipitation and washing with methanol, it was dried in a vacuum oven at 120 °C for 24 h.

[0106] (2) The polyimide is mixed with NMP, THF and C2H5OH and stirred for 24 hours until uniform to obtain hollow fiber spinning solution; based on the total weight of all substances used in step (2), the amount of polyimide is 30wt%, the amount of NMP is 50wt%, the amount of THF is 13wt% and the amount of C2H5OH is 7wt%.

[0107] (3) The hollow fiber spinning solution is degassed in a feed tank at 25°C for 12 hours to obtain a membrane solution. This membrane solution is then mixed with a prepared core solution (a mixture of NMP and water, with a volume ratio of NMP to water of 8:2) and fed to the spinneret via a gear pump, a pressure pump, and a syringe, respectively, with controlled speeds. The membrane solution is extruded from the feed tank to the spinneret for spinning under nitrogen pressure (nitrogen pressurization tank, with a nitrogen pressure of 4 bar). The membrane solution is then passed through a 3 cm air gap and a 25°C coagulation bath to obtain hollow fibers. The hollow fibers are then subjected to a spinning process (take-up by a take-up wheel at a take-up speed of 70 m / min), soaked in water for 12 hours, subjected to solvent exchange with ethanol and n-hexane three times, and dried for 24 hours. Finally, the membrane is annealed in a vacuum environment at 180°C for 0.5 hours to obtain the polyimide hollow fiber gas separation membrane.

[0108] The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 5, as tested using scanning electron microscopy, is shown in the figure below. Figure 6 As shown, from Figure 6 As can be seen, the polyimide hollow fiber gas separation membrane consists of a support layer with finger-shaped pores and a selective layer, with the selective layer having a thickness of approximately 800 nm.

[0109] Example 6

[0110] A method for preparing a polyimide hollow fiber gas separation membrane specifically includes the following steps:

[0111] (1) In a three-necked flask, under nitrogen protection, 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) and 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) were stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP). Based on the total weight of all substances used in step (1), the molar ratio of 6FDA and PABZ was 1:1, totaling 20 wt%, and the amount of ultra-dry NMP was 80 wt%. The mixture was reacted with stirring for 24 h to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and the temperature was gradually increased to 200 °C and kept constant for 5 h to obtain PI-Im polyimide (weight average molecular weight of 65200). After precipitation and washing with methanol, it was dried in a vacuum oven at 120 °C for 24 h.

[0112] (2) The polyimide is mixed with NMP, THF and C2H5OH and stirred for 24 hours until uniform to obtain hollow fiber spinning solution; based on the total weight of all substances used in step (2), the amount of polyimide is 30wt%, the amount of NMP is 50wt%, the amount of THF is 13wt% and the amount of C2H5OH is 7wt%.

[0113] (3) The hollow fiber spinning solution is degassed in a feed tank at 25°C for 12 hours to obtain a membrane solution. This membrane solution is then mixed with a prepared core solution (a mixture of NMP and water, with a volume ratio of NMP to water of 8:2) and fed to the spinneret via a gear pump, a pressure pump, and a syringe, respectively, with controlled speeds. The membrane solution is extruded from the feed tank to the spinneret for spinning under nitrogen pressure (nitrogen pressurization tank, with a nitrogen pressure of 4 bar). The membrane solution is then passed through a 3 cm air gap and a 25°C coagulation bath to obtain hollow fibers. The hollow fibers are then subjected to a spinning process (take-up by a take-up wheel at a take-up speed of 70 m / min), soaked in water for 12 hours, subjected to solvent exchange with ethanol and n-hexane three times, and dried for 24 hours. Finally, the membrane is annealed in a vacuum environment at 230°C for 0.5 hours to obtain the polyimide hollow fiber gas separation membrane.

[0114] The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 6, as tested by scanning electron microscopy, is shown in the figure below. Figure 7 As shown, from Figure 7 As can be seen from the image, the polyimide hollow fiber gas separation membrane consists of a support layer with finger-shaped pores and a selective layer, with the selective layer having a thickness of approximately 850 nm.

[0115] Example 7

[0116] A method for preparing a polyimide hollow fiber gas separation membrane specifically includes the following steps:

[0117] (1) In a three-necked flask, under nitrogen protection, 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) and 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) were stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP). Based on the total weight of all substances used in step (1), the molar ratio of 6FDA and PABZ was 1:1, totaling 20 wt%, and the amount of ultra-dry NMP was 80 wt%. The mixture was reacted with stirring for 24 h to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and the temperature was gradually increased to 200 °C and kept constant for 5 h to obtain PI-Im polyimide (weight average molecular weight of 65200). After precipitation and washing with methanol, it was dried in a vacuum oven at 120 °C for 24 h.

[0118] (2) The polyimide is mixed with NMP, THF and C2H5OH and stirred for 24 hours until uniform to obtain hollow fiber spinning solution; based on the total weight of all substances used in step (2), the amount of polyimide is 30wt%, the amount of NMP is 50wt%, the amount of THF is 13wt% and the amount of C2H5OH is 7wt%.

[0119] (3) The hollow fiber spinning solution is degassed in a feed tank at 25°C for 12 hours to obtain a membrane solution. This membrane solution is then mixed with a prepared core solution (a mixture of NMP and water, with a volume ratio of NMP to water of 8:2) and fed to the spinneret via a gear pump, a pressure pump, and a syringe, respectively, with controlled speeds. The membrane solution is extruded from the feed tank to the spinneret for spinning under nitrogen pressure (nitrogen pressurization tank, with a nitrogen pressure of 4 bar). The membrane solution is then passed through a 3 cm air gap and a 25°C coagulation bath to obtain hollow fibers. The hollow fibers are then subjected to a spinning process (take-up by a take-up wheel at a take-up speed of 70 m / min), soaked in water for 12 hours, subjected to solvent exchange with ethanol and n-hexane three times, and dried for 24 hours. Finally, the membrane is annealed in a vacuum environment at 280°C for 0.5 hours to obtain the polyimide hollow fiber gas separation membrane.

[0120] The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 7, as tested using scanning electron microscopy, is shown in the figure below. Figure 8 As shown, from Figure 8 As can be seen, the polyimide hollow fiber gas separation membrane consists of a support layer with finger-shaped pores and a selective layer, with the selective layer having a thickness of approximately 1.07 μm.

[0121] Example 8

[0122] A method for preparing a polyimide hollow fiber gas separation membrane specifically includes the following steps:

[0123] (1) In a three-necked flask, under ice bath and nitrogen protection, 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA), 2,3,5,6-tetramethyl-1,4-phenylenediamine, and 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) were dissolved in ultra-dry N-methylpyrrolidone (NMP) with stirring. Based on the total weight of all substances used in step (1), the molar ratio of 6FDA, Bn4CH3, and PABZ was 5:3:2, totaling 20 wt%, and the amount of ultra-dry NMP was 80 wt%. The mixture was reacted with stirring for 24 h to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and the temperature was gradually increased to 200℃ and kept at a constant temperature for 5 hours to obtain PI-Im-Bn4CH3 polyimide (weight average molecular weight of 35000). After precipitation and washing with methanol, it was dried in a vacuum oven at 120℃ for 24 hours.

[0124] (2) The polyimide is mixed with DMF, THF and C2H5OH and stirred for 24 hours until uniform to obtain a hollow fiber spinning solution; based on the total weight of all substances used in step (2), the amount of polyimide is 23wt%, the amount of DMF is 59wt%, the amount of THF is 5wt%, and the amount of C2H5OH is 13wt%.

[0125] (3) The hollow fiber spinning solution is degassed in a feed tank at 25°C for 12 hours to obtain a membrane solution. This membrane solution is then mixed with a prepared core solution (a mixture of DMF and water, with a DMF to water volume ratio of 8:2) and fed to the spinneret via a gear pump, a pressure pump, and a syringe, respectively, with controlled speeds. The membrane solution is extruded from the feed tank to the spinneret for spinning under nitrogen pressure (nitrogen pressurization tank, with a nitrogen pressure of 4 bar). The membrane solution is then passed through a 5 cm air gap and a 25°C coagulation bath to obtain hollow fibers. The hollow fibers are then subjected to a spinning process (take-up by a take-up wheel at a take-up speed of 60 m / min), soaked in water for 12 hours, subjected to solvent exchange with ethanol and n-hexane three times, and dried for 24 hours to obtain the polyimide hollow fiber gas separation membrane.

[0126] The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 8, as tested using scanning electron microscopy, is shown in the figure below. Figure 9 As shown, from Figure 9 As can be seen, the polyimide hollow fiber gas separation membrane consists of a support layer with finger-shaped pores and a selective layer, with the selective layer having a thickness of approximately 1 μm.

[0127] Example 9

[0128] A method for preparing a polyimide hollow fiber gas separation membrane specifically includes the following steps:

[0129] (1) In a three-necked flask, under ice bath and nitrogen protection, 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA), 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ), and 3,5-diaminobenzoic acid (DABA) were dissolved in ultra-dry N-methylpyrrolidone (NMP) with stirring. Based on the total weight of all substances used in step (1), the molar ratio of 6FDA, PABZ, and DABA was 5:3:2, totaling 20 wt%, and the amount of ultra-dry NMP was 80 wt%. The mixture was reacted with stirring for 24 h to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and the temperature was gradually increased to 200℃ and kept constant for 5 hours to obtain PI-Im-COOH polyimide (weight average molecular weight of 35,000). After precipitation and washing with methanol, it was dried in a vacuum oven at 120℃ for 24 hours.

[0130] (2) The polyimide is mixed with NMP, THF and CH3OH and stirred for 24 hours until uniform to obtain a hollow fiber spinning solution; based on the total weight of all substances used in step (2), the amount of polyimide is 30wt%, the amount of NMP is 50wt%, the amount of THF is 12wt% and the amount of CH3OH is 8wt%.

[0131] (3) The hollow fiber spinning solution is degassed in a feed tank at 25°C for 12 hours to obtain a membrane solution. This membrane solution is then mixed with a prepared core solution (a mixture of NMP and water, with a volume ratio of NMP to water of 8:2) and fed to the spinneret via a gear pump, a pressure pump, and a syringe, respectively, with controlled speeds. The membrane solution is extruded from the feed tank to the spinneret for spinning by nitrogen pressurization (using a nitrogen pressurization tank at a pressure of 5 bar). The membrane solution is then passed through a 10 cm air gap and a 25°C coagulation bath to obtain hollow fibers. The hollow fibers are then subjected to a spinning process (take-up using a take-up wheel at a take-up speed of 70 m / min), soaked in water for 12 hours, subjected to solvent exchange with ethanol and n-hexane three times, and dried for 24 hours to obtain the polyimide hollow fiber gas separation membrane.

[0132] The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 9, as tested by scanning electron microscopy, is shown in the figure below. Figure 10 As shown, from Figure 10As can be seen, the polyimide hollow fiber gas separation membrane consists of a support layer with finger-shaped pores and a selective layer, with the selective layer having a thickness of approximately 300 nm.

[0133] Comparative Example 1

[0134] A method for preparing a polyimide flat sheet film specifically includes the following steps:

[0135] (1) In a three-necked flask, under ice bath and nitrogen protection, 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) and 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) were stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP). Based on the total weight of all substances used in step (1), the molar ratio of 6FDA and PABZ was 1:1, totaling 20 wt%, and the amount of ultra-dry NMP was 80 wt%. The mixture was reacted with stirring for 24 h to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and the temperature was gradually increased to 200 °C and kept constant for 5 h to obtain PI-Im polyimide (weight average molecular weight of 65200). After precipitation and washing with methanol, it was dried in a vacuum oven at 120 °C for 24 h.

[0136] (2) A certain amount of DMF solvent was added to PI-Im polyimide under stirring at 25°C to prepare a 5% polymer solution. The obtained polymer solution was then filtered through a polytetrafluoroethylene (PTFE) filter and poured into a flat glass mold. The solvent was slowly evaporated at 60°C for 36 h, and then further dried at 120°C for 24 h to remove residual solvent, resulting in a dense polyimide sheet film with a thickness of approximately 50–60 μm.

[0137] Comparative Example 2

[0138] A method for preparing a polyimide hollow fiber gas separation membrane specifically includes the following steps:

[0139] (1) In a three-necked flask, under ice bath and nitrogen protection, 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) and 2,3,5,6-tetramethyl-1,4-phenylenediamine were dissolved in ultra-dry N-methylpyrrolidone (NMP) under nitrogen atmosphere with stirring. The molar ratio of 6FDA and 2,3,5,6-tetramethyl-1,4-phenylenediamine was 1:1, totaling 20 wt%, and the amount of ultra-dry NMP was 80 wt%. The mixture was reacted with stirring for 24 h to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and the temperature was gradually increased to 200 °C and maintained at this temperature for 5 h to obtain PI-Bn4CH3 polyimide (weight-average molecular weight 32000), with the following structural formula: After precipitation and washing with methanol, the product is dried in a vacuum oven at 120°C for 24 hours.

[0140] (2) The polyimide is mixed with NMP, THF and C2H5OH and stirred for 24 hours until uniform to obtain hollow fiber spinning solution; based on the total weight of all substances used in step (2), the amount of polyimide is 25wt%, the amount of NMP is 55wt%, the amount of THF is 10wt% and the amount of C2H5OH is 10wt%.

[0141] (3) The hollow fiber spinning solution is degassed in a feed tank at 25°C for 12 hours to obtain a membrane solution. This membrane solution is then mixed with a prepared core solution (a mixture of NMP and water, with a volume ratio of NMP to water of 8:2) and fed to the spinneret via a gear pump, a pressure pump, and a syringe, respectively, with the speed controlled. The membrane solution is extruded from the feed tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, with a nitrogen pressure of 2 bar). The membrane solution is then passed through a 2 cm air gap and a 25°C coagulation bath to obtain hollow fibers. The hollow fibers are then subjected to a spinning process (take-up by a take-up wheel at a take-up speed of 60 m / min), soaked in water for 12 hours, subjected to solvent exchange with ethanol and n-hexane three times, and dried for 24 hours to obtain the polyimide hollow fiber gas separation membrane.

[0142] The morphology of the polyimide hollow fiber gas separation membrane prepared in Comparative Example 2, as tested by scanning electron microscopy, is shown in the figure below. Figure 11 As shown, from Figure 11 As can be seen from the image, the polyimide hollow fiber gas separation membrane consists of a support layer with finger-shaped pores and a selective layer, with the selective layer having a thickness of approximately 201 nm.

[0143] Comparative Example 3

[0144] A method for preparing a polyimide hollow fiber gas separation membrane specifically includes the following steps:

[0145] (1) In a three-necked flask, under ice bath and nitrogen protection, 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) and 2,3,5,6-tetramethyl-1,4-phenylenediamine were dissolved in ultra-dry N-methylpyrrolidone (NMP) under nitrogen atmosphere with stirring. The molar ratio of 6FDA and 2,3,5,6-tetramethyl-1,4-phenylenediamine was 1:1, totaling 20 wt%, and the amount of ultra-dry NMP was 80 wt%. The mixture was stirred for 24 h to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and the temperature was gradually increased to 200 °C and kept constant for 5 h to obtain PI-Bn4CH3 polyimide (weight average molecular weight of 32,000). After precipitation and washing with methanol, it was dried in a vacuum oven at 120 °C for 24 h.

[0146] (2) The polyimide is mixed with NMP, THF and C2H5OH and stirred for 24 hours until uniform to obtain hollow fiber spinning solution; based on the total weight of all substances used in step (2), the amount of polyimide is 30wt%, the amount of NMP is 50wt%, the amount of THF is 10wt% and the amount of C2H5OH is 10wt%.

[0147] (3) The hollow fiber spinning solution is degassed in a feed tank at 25°C for 12 hours to obtain a membrane solution. This membrane solution is then mixed with a prepared core solution (a mixture of NMP and water, with a volume ratio of NMP to water of 7:3) and fed to the spinneret via a gear pump, a pressure pump, and a syringe, respectively, with the speed controlled. The membrane solution is extruded from the feed tank to the spinneret for spinning under nitrogen pressure (nitrogen pressurization tank, with a nitrogen pressure of 3 bar). The membrane solution is then passed through a 6 cm air gap and a 25°C coagulation bath to obtain hollow fibers. The hollow fibers are then subjected to a spinning process (take-up by a take-up wheel at a take-up speed of 30 m / min), soaked in water for 12 hours, subjected to solvent exchange with ethanol and n-hexane three times, and dried for 24 hours. The hollow fiber membrane is then soaked in a methanol solution of copper ions at 40°C for 24 hours and dried to obtain the hollow fiber membrane.

[0148] The morphology of the polyimide hollow fiber gas separation membrane prepared in Comparative Example 3, as tested by scanning electron microscopy, is shown in the figure below. Figure 12 As shown, from Figure 12 As can be seen from the image, the polyimide hollow fiber gas separation membrane consists of a support layer with finger-shaped pores and a selective layer, with the selective layer having a thickness of approximately 380 nm.

[0149] Comparative Example 4

[0150] A method for preparing a polyimide hollow fiber gas separation membrane specifically includes the following steps:

[0151] (1) P84 is mixed with NMP, THF and C2H5OH and stirred for 24h until uniform to obtain hollow fiber spinning solution; based on the total weight of all substances used in step (1), the amount of polyimide is 35wt%, the amount of NMP is 45wt%, the amount of THF is 15wt% and the amount of C2H5OH is 5wt%.

[0152] (2) The hollow fiber spinning solution is degassed in a feed tank at 25°C for 12 hours to obtain a membrane solution. This membrane solution is then mixed with a prepared core solution (a mixture of NMP and water, with a volume ratio of NMP to water of 6:4) and fed to the spinneret via a gear pump, a pressure pump, and a syringe, respectively, with the speed controlled. The membrane solution is extruded from the feed tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, with a nitrogen pressure of 5 bar). The membrane solution is then passed through an 8 cm air gap and a 25°C coagulation bath to obtain hollow fibers. The hollow fibers are then subjected to a spinning process (take-up by a take-up wheel at a take-up speed of 40 m / min), soaked in water for 12 hours, subjected to solvent exchange with ethanol and n-hexane three times, and dried for 24 hours to obtain the polyimide hollow fiber gas separation membrane.

[0153] The morphology of the polyimide hollow fiber gas separation membrane prepared in Comparative Example 4, as tested by scanning electron microscopy, is shown in the figure below. Figure 13 As shown, from Figure 13 As can be seen, the polyimide hollow fiber gas separation membrane consists of a support layer with finger-shaped pores and a selective layer, with the selective layer having a thickness of approximately 1.47 μm.

[0154] Figure 14 The infrared spectrum (left) and 1H NMR spectrum (1H NMR) of PI-Im polyimide in Example 1 are shown below. 1 The right-hand image (H NMR spectrum) shows the characteristic absorption bands of the benzimidazole and imide structures. (1298 cm⁻¹) -1 The point is the stretching vibration of benzimidazole NH4, 1781 cm. -1 The point is a symmetric stretching vibration of the imide ring C=O, 1715 cm⁻¹ -1 The vibration at point 1368 cm⁻¹ is an asymmetric stretching vibration of the imide ring C=O. -1 The stretching vibration of the imide ring-CNC is 716 cm⁻¹. -1 The part is a deformation of the imide ring.

[0155] Figure 15 The infrared spectrum (left) of PI-Im-BN4CH3 polyimide in Example 8 and 1The right-hand side of the 1H NMR spectrum shows the characteristic absorption bands of the benzimidazole and imide structures. (1298 cm⁻¹) -1 The point is the stretching vibration of benzimidazole NH4, 1787 cm. -1 The vibration at 1720 cm⁻¹ is a symmetric stretching vibration of the imide ring C=O. -1 The position is an asymmetric stretching vibration of the imide ring C=O, 1349 cm⁻¹ -1 The stretching vibration of the imide ring-CNC is 719 cm⁻¹. -1 The part is a deformation of the imide ring, 2980cm -1 The corresponding characteristic peak for methyl groups is shown at this location. The chemical shift at 2.08 ppm in the NMR spectrum corresponds to a hydrogen atom in the methyl group.

[0156] Figure 16 The infrared spectrum (left) of PI-Im-COOH polyimide in Example 9 and 1 The 1H NMR spectrum (right image) shows the characteristic absorption bands of the benzimidazole and imide structures. 1298 cm⁻¹ -1 The point is the stretching vibration of benzimidazole NH4, 1781 cm. -1 The point is a symmetric stretching vibration of the imide ring C=O, 1715 cm⁻¹ -1 The point is an asymmetric stretching vibration of the imide ring C=O, 368 cm⁻¹ -1 The stretching vibration of the imide ring-CNC is 716 cm⁻¹. -1 The area is a deformation of the imide ring, 3600-2900cm. -1 The broad absorption band at that position is caused by the stretching vibrations of the carboxyl-OH and benzimidazole-NH groups. The chemical shifts at 7.9 and 8.2 ppm (j,k,l) ​​in the NMR spectrum correspond to CH on the DABA aromatic ring. 1 The H NMR spectrum did not show the chemical shift of the carboxyl hydrogen (-OH) of DABA, which may be due to the abundant hydrogen bonds formed between -OH and C=N or C=O, resulting in a shielding effect.

[0157] Test Example 1

[0158] The polyimide hollow fiber gas separation membranes prepared in Examples 1-9 and Comparative Examples 2-4 were encapsulated in 316L stainless steel membrane modules. Both ends of the membrane modules were sealed with epoxy resin to form modules for gas separation performance testing. The polyimide flat sheet membrane prepared in Comparative Example 1 was also tested for gas separation performance. The test results are shown in Table 1.

[0159] Table 1

[0160]

[0161]

[0162] The unit of gas permeation flux is GPU, where GPU = 1 × 10⁻⁶. -6 cm 3 (STP) / cm 2 ·s·cmHg, Barrer=10 -10 [cm 3 (STP)·cm] / (cm 2 ·s·cmHg).

[0163] Test Example 2

[0164] The tensile strength and elongation at break of the polyimide hollow fibers prepared in Examples 1-9 and Comparative Examples 2-4 were measured using a tensile testing machine. The effective sample length was 50 mm, and the tensile rate was 5 mm / min. The test results are as follows: Figure 17 As shown, the tensile stress of Example 1 was 33.4 MPa and the tensile strain was 22.8%. The tensile stress of Example 2 was 42.3 MPa and the tensile strain was 16.2%. The tensile stress of Example 3 was 48.4 MPa and the tensile strain was 18.6%. The tensile stress of Example 4 was 67 MPa and the tensile strain was 27.3%. The tensile stress of Example 5 was 75.1 MPa and the tensile strain was 16.2%. The tensile stress of Example 6 was 80 MPa and the tensile strain was 12%. The tensile stress of Example 7 was 83.2 MPa and the tensile strain was 8.2%. The tensile stress of Example 8 was 60.3 MPa and the tensile strain was 24.6%. The tensile stress of Example 9 was 49.5 MPa and the tensile strain was 24.6%. The tensile stress of Comparative Example 2 was 52 MPa and the tensile strain was 13.3%. The tensile stress of Comparative Example 3 was 42.5 MPa and the tensile strain was 18%. The tensile stress of Comparative Example 4 was 42 MPa, and the tensile strain was 13%.

[0165] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. 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 claims of the present invention.

Claims

1. A method for producing a polyimide hollow fiber gas separation membrane, characterized by, The method comprises the following steps: (1) carrying out a polycondensation reaction of a dianhydride monomer and a diamine monomer in a solvent under an inert environment to obtain a polyimide polymer; The polyimide polymer has a structural formula as shown in formula (I): ， wherein 0 < x < 100, 0 ≤ y < 100, x and y are integers, R1is selected from the following structural groups: , R2is selected from the following structural groups: ; (2) mixing the polyimide polymer with a high-boiling-point solvent, a low-boiling-point solvent and a non-solvent to obtain a hollow fiber spinning solution; the polyimide polymer is used in an amount of 15-35 wt% based on the total weight of the amounts of all the substances used in step (2), the high-boiling-point solvent is used in an amount of 45-65 wt%, the low-boiling-point solvent is used in an amount of 1-15 wt%, and the non-solvent is used in an amount of 1-15 wt%; (3) carrying out a defoaming treatment on the hollow fiber spinning solution to obtain a membrane solution; mixing an organic solvent with water to obtain a core solution; the volume ratio of the organic solvent to water is (6-8):(2-4); sequentially passing the membrane solution and the core solution through a spinneret, an air gap and a coagulation bath to obtain a hollow fiber; the spinneret has a concentric circle structure, the core solution passes through the inner circle of the spinneret, and the membrane solution passes through the outer circle of the spinneret; the distance of the air gap is 3-10 cm; the temperature of the coagulation bath treatment is 10-35 ℃; sequentially carrying out a spinning process, water immersion, multiple solvent exchanges and a drying treatment on the hollow fiber to obtain the polyimide hollow fiber gas separation membrane.

2. The production method according to claim 1, characterized by, In step (2), the high-boiling-point solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide; the low-boiling-point solvent is selected from one or more of diethyl ether, acetone, tetrahydrofuran, petroleum ether and dichloromethane; and the non-solvent is selected from one or more of methanol, ethanol, glycerol, n-butanol, isopropyl alcohol, n-hexane, water, propionic acid and ethylene glycol.

3. The production method according to claim 1, characterized by, In step (3), the defoaming treatment is performed for 6-12 h at a temperature of 20-30 ℃.

4. The production method according to claim 1, characterized by, In step (3), the spinning process is performed by using a yarn take-up wheel, and the yarn take-up speed of the yarn take-up wheel is 30-70 m / min.

5. The production method according to claim 1, characterized by, In step (3), the drying treatment is further followed by a step of annealing treatment at 180-280 ℃.

6. A polyimide hollow fiber gas separation membrane prepared by the method of any one of claims 1-5.

Images