Polyimide hollow fiber gas separation membrane and preparation method thereof

Abstract

The invention discloses a polyimide hollow fiber gas separation membrane and a preparation method thereof, and the polyimide hollow fiber gas separation membrane is prepared by reasonably designing a precursor structure and accurately regulating spinning parameters. The prepared polyimide hollow fiber gas separation membrane is compact in surface, free of holes and defects and excellent in mechanical property, and has a high-flux and high-selectivity gas separation effect, especially for hydrogen. Wherein the hollow fiber spinning solution is obtained by mixing a polyimide polymer, a high-boiling-point solvent, a low-boiling-point solvent and a non-solvent, and the polyimide polymer is synthesized by carrying out condensation polymerization on a dianhydride monomer, a diamine monomer containing a benzimidazole group and other diamine monomers. The preparation method provided by the invention is simple, convenient and easy to operate, avoids tedious procedures and additional economic investment brought by subsequent processes (polydimethylsiloxane coating and crosslinking modification), and has a wide application prospect.

Description

Technical Field

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

[0002] Hydrogen plays an important role in synthetic fuel production, transportation and power supply. Its high "energy / mass" ratio makes it particularly suitable for heavy-duty, long-distance road freight, marine and aviation applications. In addition, hydrogen is essential for replacing coal and natural gas in fossil fuel-intensive industrial processes such as steelmaking. Hydrogen mainly comes from fossil fuel-related processes such as natural gas steam reforming, petrochemical refineries, purge gas recovery, etc. 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, has outstanding technical advantages and application prospects in hydrogen recovery due to its low investment, low energy consumption, simple operation and no pollution. Separation membranes have various forms, such as flat membranes, tubular membranes, and hollow fiber membranes. Hollow fiber membranes are hollow membranes with a fiber-like appearance and self-supporting function. Hollow fiber membranes have the advantages of high packing density, large specific surface area, good pressure resistance, and simple membrane component structure. The corresponding hollow fiber membrane separation process has the characteristics of low energy consumption, small device size, easy operation, high efficiency, and no secondary pollution, and is being used more and more widely.

[0004] Studies have shown that polyimide has excellent thermal stability and can be used in high temperature environments for a long time. It is widely used in aerospace, microelectronics, organic solvent nanofiltration and gas separation membranes due to its excellent mechanical properties, low dielectric properties, chemical stability and fatigue resistance. Polyimide is usually obtained by dehydration polycondensation of dianhydride and diamine. It has many advantages such as good thermal stability, dimensional stability and chemical stability. It is one of the most widely used engineering plastics. In particular, aromatic polyimide containing a large number of benzene rings in the molecular chain has excellent physical and chemical properties. Currently, commercially used aromatic polyimides include Matrimid, Kapton, P84, Ultem, etc. In addition, researchers have developed other high-performance polyimides, the most representative of which is polyimide containing hexafluoroisopropyl (6FDA). 6FDA has a large steric hindrance, which hinders the stacking of polyimide molecular chains, increases the free volume of the polymer, and improves the gas permeability coefficient. At the same time, the polarity of 6FDA enhances the solubility of polyimide in common polar solvents (such as DMF, NMP), making it easy to process into flat membranes or hollow fiber membranes. Most 6FDA-based polyimide membranes have good gas permeability coefficients and selectivity.

[0005] Large-scale gas separation applications in industry require separation membranes with high permeability to improve yield. Therefore, commercial membranes usually have two characteristics. First, they have an asymmetric structure, which is generally composed of a thicker porous support layer and a dense thin selective layer (<1μm). The asymmetric structure greatly reduces the gas transmission resistance. The permeability and selectivity of the membrane are mainly controlled by the thin selective layer, while the support layer only plays a mechanical support role, and the resistance to molecular transmission can be ignored. Secondly, most commercial membranes are processed in the form of fibers with hollow structures. The structure of hollow fiber membranes satisfies the above two characteristics well. In addition, 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 is filled with fibers with a diameter of 100 μm, and the membrane area can be as high as 300 m 2 For spiral wound membrane modules and flat membrane modules of equivalent size, the membrane area is only 20-40m 2 . Typical hollow fiber membranes are made from a small number 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 expected to have a thin selective layer to improve productivity. The rapid aggregation of polymer molecules and the irregular stacking of polymer chains often lead to defects in the thin selective layer, and the thinner the selective layer, the more defects are produced, resulting in a serious loss of selectivity of the membrane and making it unusable. The 6FDA-based polyimide hollow fiber membrane synthesized by the prior art is used to separate hydrogen and methane, but there are still the following problems: (1) The thickness of the hollow fiber selective layer is relatively large, and a high hydrogen and methane permeation flux cannot be achieved; (2) The hollow fiber membrane cannot have both high gas permeation flux and gas selectivity; (3) The hollow fiber does not have good mechanical properties and cannot ensure stability during operation. Summary of the invention

[0006] In order to solve the above technical problems, the purpose of the present invention is to provide a polyimide hollow fiber gas separation membrane and a preparation method thereof. By reasonably designing the precursor structure and precisely controlling the spinning parameters, a polyimide hollow fiber gas separation membrane with high flux and high selectivity gas separation effect, a dense, non-porous and defect-free surface and excellent mechanical properties is prepared.

[0007] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0008] The first aspect of the present invention provides a polyimide polymer, the structural formula of the polyimide polymer 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 condensation polymerization reaction is carried out between a dianhydride monomer and a diamine monomer 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 subjected to a spinning process, water immersion, multiple solvent exchanges, and a drying treatment to obtain the polyimide hollow fiber gas separation membrane.

[0020] The present invention provides a method for preparing a high-strength and high-selectivity polyimide hollow fiber gas separation membrane. The polyimide polymer is synthesized by a dianhydride monomer and a diamine monomer containing a benzimidazole (PABZ) group and other diamine monomers through a polycondensation reaction. The diamine monomer containing a benzimidazole (PABZ) group contains abundant hydrogen bonds and π-π effects, and the molecular chains are tightly stacked, which is beneficial to improving the screening ability of the membrane material. In the present invention, in order to make the surface of the polyimide hollow fiber membrane non-porous, by increasing the concentration of polyimide, the polymer chain has a certain entanglement, and when phase separation occurs, the hollow fiber membrane skin can quickly enter the gel region without crossing the two-phase region to form a dense structure. By adding a low-boiling point solvent, the polyimide polymer solution is rapidly volatilized in the air gap, the concentration of the polyimide polymer on the surface of the hollow fiber is increased, which is beneficial to the formation of a surface defect-free structure, thereby obtaining a surface non-porous polyimide hollow fiber membrane. The hollow fiber membrane made by spinning polyimide polymers has the advantages of high mechanical strength, high permeability flux, good thermal stability and good gas separation effect, especially for hydrogen.

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

[0022] Furthermore, in step (1), the dianhydride monomer is selected from 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA); and 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] Furthermore, in step (1), the solvent is selected from one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide.

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

[0025] In a specific embodiment, in step (1), equimolar amounts of diamine monomer and dianhydride monomer are put into a three-necked flask, stirred and dissolved in a solvent under a nitrogen environment, and fully dissolved and reacted to form a viscous high molecular weight polyamic acid, followed by azeotropic distillation to obtain a polyimide polymer solution, which is precipitated and dried to obtain a polyimide polymer.

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

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

[0028] Furthermore, 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 ether, acetone, tetrahydrofuran, petroleum ether and dichloromethane, preferably tetrahydrofuran; and 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] Furthermore, in step (2), based on the total weight of all substances used in step (2), the amount of the polyimide polymer is 15-35wt%, the amount of the high boiling point solvent is 45-65wt%, the amount of the low boiling point solvent is 1-15wt%, and the amount of the non-solvent is 1-15wt%.

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

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

[0032] Furthermore, steps (1) and (2) are carried out in a three-necked flask, and the degassing treatment in step (3) is carried out in a liquid tank. Since the viscosity of the hollow fiber spinning solution is relatively large, the hollow fiber spinning solution needs to be squeezed out of the three-necked flask into the liquid tank by nitrogen pressurization. Preferably, the pressure of the nitrogen pressurization is 1-5 bar.

[0033] Furthermore, in step (3), the degassing treatment is carried out for 6-12 hours at a temperature of 20-30°C.

[0034] Furthermore, 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] Furthermore, in step (3), the volume ratio of the organic solvent to water is (6-8):(2-4), such as 8:2, 7:3, 6:4.

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

[0037] Furthermore, in step (3), the distance of the air gap refers to the distance between the spinneret and the coagulation bath, that is, the distance of the membrane liquid and the core liquid from the spinneret to the coagulation bath. During this air gap stage, the low boiling point solvent evaporates rapidly, causing the concentration of the polyimide hollow fiber membrane epidermis polymer to increase rapidly, forming a cortex. Then, it is immersed in the coagulation bath water to complete phase separation and solidification (i.e., the core liquid present in the cortex is replaced with the water in the coagulation bath at this stage).

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

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

[0040] Furthermore, in step (3), the membrane liquid is transported 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 collecting wheel to collect the yarn, and the collecting speed of the collecting 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 liquid and solvent.

[0043] Furthermore, in step (3), the solvent for the 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 treatment is: air-drying for 22-24 hours.

[0045] Furthermore, in step (3), after the drying treatment, an annealing treatment at 180-280° C. is also included.

[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] Beneficial effects of the present invention:

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

[0049] 2. The hollow fiber preparation rate of the present invention is relatively fast, which can greatly improve the efficiency of membrane fiber preparation and prepare a hollow fiber membrane with a dense and non-porous surface. The membrane is applied to the field of gas separation and exhibits extremely excellent gas separation performance, wherein the optimal hydrogen flux is between 270-300GPU, the optimal carbon dioxide flux is between 70-80GPU, and the optimal methane flux is between 3.25-3.55GPU. It has a high H2 / CH4 gas selectivity and can be applied to many actual production processes (natural gas separation, petrochemical refineries, purge gas recovery, etc.), which has important guiding significance for polyimide spinning. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A schematic flow chart of a method for preparing a polyimide hollow fiber gas separation membrane provided by the present invention.

[0051] Figure 2 The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 1 is shown in Figure 1; wherein, a is a scanning electron microscope cross-sectional overall view, b is a scanning electron microscope cross-sectional enlarged view, and c is a scanning electron microscope cortical view.

[0052] Figure 3 The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 2; wherein a is a scanning electron microscope cross-section overall view, b is a scanning electron microscope cross-section magnified view, and c is a scanning electron microscope cortical view.

[0053] Figure 4 The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 3; wherein a is a scanning electron microscope cross-section overall view, b is a scanning electron microscope cross-section magnified view, and c is a scanning electron microscope cortical view.

[0054] Figure 5 The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 4 is shown in Figure 4; wherein, a is a scanning electron microscope cross-sectional overall view, b is a scanning electron microscope cross-sectional enlarged view, and c is a scanning electron microscope cortical view.

[0055] Figure 6 The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 5 is shown in Figure 5; wherein, a is a scanning electron microscope cross-sectional overall view, b is a scanning electron microscope cross-sectional enlarged view, and c is a scanning electron microscope cortical view.

[0056] Figure 7The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 6; wherein a is a scanning electron microscope cross-section overall view, b is a scanning electron microscope cross-section magnified view, and c is a scanning electron microscope cortical view.

[0057] Figure 8 The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 7 is shown in Figure 1; wherein, a is a scanning electron microscope cross-sectional overall view, b is a scanning electron microscope cross-sectional enlarged view, and c is a scanning electron microscope cortical view.

[0058] Fig. 9 This is a morphology picture of the polyimide hollow fiber gas separation membrane prepared in Example 8; wherein, a is a scanning electron microscope cross-section overall picture, b is a scanning electron microscope cross-section magnified picture, and c is a scanning electron microscope cortical picture.

[0059] Fig.10 The morphology of the polyimide hollow fiber gas separation membrane prepared in Example 9; wherein a is a scanning electron microscope cross-section overall view, b is a scanning electron microscope cross-section magnified view, and c is a scanning electron microscope cortical view.

[0060] Fig.11 This is a morphology picture of the polyimide hollow fiber gas separation membrane prepared in Comparative Example 2; wherein a is a scanning electron microscope cross-section overall picture, b is a scanning electron microscope cross-section magnified picture, and c is a scanning electron microscope cortex picture.

[0061] Fig.12 The morphology of the polyimide hollow fiber gas separation membrane prepared in Comparative Example 3 is shown in Figure 3; wherein, a is a scanning electron microscope cross-sectional overall view, b is a scanning electron microscope cross-sectional enlarged view, and c is a scanning electron microscope cortical view.

[0062] Fig.13 This is a morphology picture of the polyimide hollow fiber gas separation membrane prepared in Comparative Example 4; wherein a is a scanning electron microscope cross-section overall picture, b is a scanning electron microscope cross-section magnified picture, and c is a scanning electron microscope cortex picture.

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

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

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

[0066] Fig.17 It is a tensile strength curve diagram of the polyimide hollow fibers prepared in Examples 1-9 and Comparative Examples 2-4. DETAILED DESCRIPTION

[0067] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

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

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

[0070] (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;

[0071] (3) Degassing the hollow fiber spinning solution to obtain a membrane solution; mixing an organic solvent with water to obtain a core solution; subjecting the membrane solution and the core solution to a spinneret, an air gap, and a coagulation bath treatment in sequence to obtain a hollow fiber; subjecting the hollow fiber to a spinning process, water immersion, multiple solvent exchanges, and drying treatments in sequence to obtain the polyimide hollow fiber gas separation membrane.

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

[0073] (1) Under nitrogen-filled sealed conditions, dianhydride monomer, diamine monomer and solvent are mixed and stirred for 20-24 hours until polyimide is uniformly obtained, and then a water separator and a reflux condenser are placed on 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°C, and the reaction is continued for 4-5 hours to obtain a polyimide polymer.

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

[0075] (3) Degassing the hollow fiber spinning solution to obtain a membrane solution; mixing an organic solvent with water to obtain a core solution; subjecting the membrane solution and the core solution to a spinneret, an air gap, and a coagulation bath treatment in sequence to obtain a hollow fiber; subjecting the hollow fiber to a spinning process, water immersion, multiple solvent exchanges, and drying treatments in sequence to obtain the polyimide hollow fiber gas separation membrane.

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

[0077] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0078] In the following embodiments, the diamine monomer was purchased from Aladdin with a purity of 98%; the solvent was purchased from Beijing Inokai 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 Inokai 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 schematic diagram of the process is as follows Figure 1 As shown, the specific steps include:

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

[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 the substances used in the step (2), the amount of the polyimide is 15wt%, the amount of the NMP is 65wt%, the amount of the THF is 10wt%, and the amount of the C2H5OH is 10wt%.

[0083] (3) The hollow fiber spinning solution is degassed in a liquid tank at 25°C for 12 hours to obtain a membrane solution, which is then transported to the spinneret with the prepared core solution (a mixture of NMP and water, with a volume fraction ratio of NMP to water of 6:4) by a gear pump, a pressure pump, and a syringe to control the speed. The membrane solution is extruded from the liquid tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, with a nitrogen pressurization pressure of 2 bar), and then sequentially passed through an air gap of 5 cm and a 25°C coagulation bath treatment to obtain a hollow fiber. The hollow fiber is sequentially subjected to a spinning process (filament collection by a collection wheel, with a collection speed of 30 m / min), water immersion for 12 hours, solvent exchange with ethanol and n-hexane for 3 times, and air-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 tested by scanning electron microscopy is shown in FIG. Figure 2 As shown in the figure, the membrane liquid forms a support layer and a selection layer, the support layer is inside and the selection layer is outside, and the core liquid plays a role in adjusting the structure and maintaining the hollow structure. Figure 2 It can be seen that the polyimide hollow fiber gas separation membrane is composed of a support layer with finger-like pores and a selection layer. The thickness of the selection layer is about 120 nm, and the surface is dense and non-porous.

[0085] Example 2

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

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

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

[0089] (3) The hollow fiber spinning solution is degassed in a liquid tank at 25°C for 12 hours to obtain a membrane solution, which is then transported to the spinneret with the prepared core solution (a mixture of NMP and water, with a volume fraction ratio of NMP to water of 7:3) by a gear pump, a pressure pump, and a syringe to control the speed. The membrane solution is extruded from the liquid tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, with a nitrogen pressurization pressure of 2 bar), and then sequentially passed through an air gap of 5 cm and a 25°C coagulation bath treatment to obtain a hollow fiber. The hollow fiber is sequentially subjected to a spinning process (filament collection by a collection wheel, with a collection speed of 50 m / min), water immersion for 12 hours, solvent exchange with ethanol and n-hexane for 3 times, and air-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 tested by scanning electron microscopy is shown in FIG. Figure 3 As shown, from Figure 3 It can be seen that the polyimide hollow fiber gas separation membrane is composed of a support layer with finger-like pores and a selection layer. The thickness of the selection layer is about 332 nm, and the surface is dense and non-porous.

[0091] Example 3

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

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

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

[0095] (3) The hollow fiber spinning solution is degassed in a liquid tank at 25°C for 12 hours to obtain a membrane solution, which is then transported to a spinneret through a gear pump, a pressure pump, and a syringe to control the speed of the prepared core solution (a mixture of NMP and water, with a volume fraction ratio of NMP to water of 8:2). The membrane solution is squeezed from the liquid tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, with a nitrogen pressurization pressure of 2 bar), and then sequentially passed through an air gap of 5 cm and a 25°C coagulation bath treatment to obtain a hollow fiber. The hollow fiber is sequentially subjected to a spinning process (filament collection by a collection wheel at a collection speed of 50 m / min), water immersion for 12 hours, solvent exchange with ethanol and n-hexane for 3 times, and air-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 tested by scanning electron microscopy is shown in FIG. Figure 4 As shown, from Figure 4 It can be seen that the polyimide hollow fiber gas separation membrane is composed of a sponge-like support layer and a selection layer. The thickness of the selection layer is about 4.5 μm, and the surface is dense and non-porous.

[0097] Example 4

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

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

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

[0101] (3) The hollow fiber spinning solution is degassed in a liquid tank at 25°C for 12 hours to obtain a membrane solution, which is then transported to the spinneret with the prepared core solution (a mixture of NMP and water, with a volume fraction ratio of NMP to water of 8:2) by a gear pump, a pressure pump, and a syringe to control the speed. The membrane solution is extruded from the liquid tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, with a nitrogen pressurization pressure of 4 bar), and then sequentially passed through an air gap of 3 cm and a 25°C coagulation bath treatment to obtain a hollow fiber. The hollow fiber is sequentially subjected to a spinning process (filament collection by a collection wheel, with a collection speed of 70 m / min), water immersion for 12 hours, solvent exchange with ethanol and n-hexane for 3 times, and air-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 tested by scanning electron microscopy is shown in FIG. Figure 5 As shown, from Figure 5 It can be seen that the polyimide hollow fiber gas separation membrane is composed of a support layer with finger-like pores and a selection layer. The thickness of the selection layer is about 700 nm, and the surface is dense and non-porous.

[0103] Example 5

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

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

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

[0107] (3) The hollow fiber spinning solution is degassed in a liquid tank at 25°C for 12 hours to obtain a membrane solution, which is then transported to the spinneret through a gear pump, a pressure pump, and a syringe to control the speed of the prepared core solution (a mixture of NMP and water, with a volume fraction ratio of NMP to water of 8:2). The membrane solution is extruded from the liquid tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, with a nitrogen pressurization pressure of 4 bar), and then sequentially passed through an air gap of 3 cm and a 25°C coagulation bath treatment to obtain a hollow fiber. The hollow fiber is sequentially subjected to a spinning process (filament collection by a collection wheel, with a collection speed of 70 m / min), water immersion for 12 hours, solvent exchange with ethanol and n-hexane for 3 times, and air drying for 24 hours, and then 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 tested by scanning electron microscopy is shown in FIG. Figure 6 As shown, from Figure 6 As can be seen from the figure, the polyimide hollow fiber gas separation membrane is composed of a support layer with finger-like pores and a selection layer, and the thickness of the selection layer is about 800 nm.

[0109] Example 6

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

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

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

[0113] (3) The hollow fiber spinning solution is degassed in a liquid tank at 25°C for 12 hours to obtain a membrane solution, which is then transported to the spinneret with the prepared core solution (a mixture of NMP and water, with a volume fraction ratio of NMP to water of 8:2) by a gear pump, a pressure pump, and a syringe to control the speed. The membrane solution is extruded from the liquid tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, with a nitrogen pressurization pressure of 4 bar), and then sequentially subjected to an air gap of 3 cm and a 25°C coagulation bath treatment to obtain a hollow fiber. The hollow fiber is sequentially subjected to a spinning process (filament collection by a collection wheel, with a collection speed of 70 m / min), water immersion for 12 hours, solvent exchange with ethanol and n-hexane for 3 times, and air drying for 24 hours, and then 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 measured by scanning electron microscopy is shown in FIG. Figure 7 As shown, from Figure 7 It can be seen that the polyimide hollow fiber gas separation membrane is composed of a support layer with finger-like pores and a selection layer, and the thickness of the selection layer is about 850 nm.

[0115] Example 7

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

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

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

[0119] (3) The hollow fiber spinning solution is degassed in a liquid tank at 25°C for 12 hours to obtain a membrane solution, which is then transported to the spinneret through a gear pump, a pressure pump and a syringe to control the speed of the prepared core solution (a mixture of NMP and water, with a volume fraction ratio of NMP to water of 8:2). The membrane solution is squeezed from the liquid tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, the pressure of nitrogen pressurization is 4 bar), and then sequentially passed through an air gap of 3 cm and a 25°C coagulation bath treatment to obtain a hollow fiber. The hollow fiber is sequentially subjected to a spinning process (filament collection by a collection wheel, with a collection speed of 70 m / min), water immersion for 12 hours, solvent exchange with ethanol and n-hexane for 3 times, and air drying for 24 hours, and then 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 measured by scanning electron microscopy is as follows: Figure 8 As shown, from Figure 8 It can be seen that the polyimide hollow fiber gas separation membrane is composed of a support layer with finger-like pores and a selection layer, and the thickness of the selection layer is about 1.07 μm.

[0121] Example 8

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

[0123] (1) In a three-necked flask, in an ice bath and under nitrogen protection, 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,3,5,6-tetramethyl-1,4-phenylenediamine and 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) are stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP) under nitrogen environment. Based on the total weight of all the substances used in step (1), the molar ratio of 6FDA, Bn4CH3 and PABZ is 5:3:2, a total of 20wt%, and the amount of ultra-dry NMP is 80wt%. The mixture is reacted for 24h under stirring to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and then the temperature was gradually increased to 200°C and reacted at a constant temperature for 5 hours to obtain PI-Im-Bn4CH3 polyimide (weight average molecular weight of 35,000). After precipitation and washing with methanol, it was dried in a vacuum oven at 120°C for 24 hours.

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

[0125] (3) The hollow fiber spinning solution is degassed in a liquid tank at 25°C for 12 hours to obtain a membrane solution, which is then transported to the spinneret with the prepared core solution (a mixture of DMF and water, with a volume fraction ratio of DMF to water of 8:2) by a gear pump, a pressure pump, and a syringe to control the speed. The membrane solution is extruded from the liquid tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, the pressure of nitrogen pressurization is 4 bar), and then sequentially passed through an air gap of 5 cm and a 25°C coagulation bath treatment to obtain a hollow fiber. The hollow fiber is sequentially subjected to a spinning process (filament collection by a collection wheel, the collection speed is 60 m / min), water immersion for 12 hours, solvent exchange with ethanol and n-hexane 3 times, and air drying 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 tested by scanning electron microscopy is shown in FIG. Fig. 9 As shown, from Fig. 9 It can be seen that the polyimide hollow fiber gas separation membrane is composed of a support layer with finger-like pores and a selection layer, and the thickness of the selection layer is about 1 μm.

[0127] Example 9

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

[0129] (1) In a three-necked flask, in an ice bath and under nitrogen protection, 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) and 3,5-diaminobenzoic acid (DABA) are stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP) under nitrogen environment. Based on the total weight of all the substances used in the step (1), the molar ratio of 6FDA, PABZ and DABA is 5:3:2, a total of 20wt%, and the amount of ultra-dry NMP is 80wt%. The mixture is reacted for 24h under stirring to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and then the temperature was gradually increased to 200°C and reacted at a constant temperature 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°C for 24 hours.

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

[0131] (3) The hollow fiber spinning solution is degassed in a liquid tank at 25°C for 12 hours to obtain a membrane solution, which is then transported to a spinneret through a gear pump, a pressure pump, and a syringe to control the speed of the prepared core solution (a mixture of NMP and water, with a volume fraction ratio of NMP to water of 8:2). The membrane solution is extruded from the liquid tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, with a nitrogen pressurization pressure of 5 bar), and then sequentially passed through an air gap of 10 cm and a 25°C coagulation bath treatment to obtain a hollow fiber. The hollow fiber is sequentially subjected to a spinning process (filament collection by a collection wheel, with a collection speed of 70 m / min), water immersion for 12 hours, solvent exchange with ethanol and n-hexane for 3 times, and air-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 tested by scanning electron microscopy is shown in FIG. Fig.10 As shown, from Fig.10It can be seen that the polyimide hollow fiber gas separation membrane is composed of a support layer with finger-like pores and a selection layer, and the thickness of the selection layer is about 300 nm.

[0133] Comparative Example 1

[0134] A method for preparing a polyimide flat film comprises the following steps:

[0135] (1) In a three-necked flask, under an ice bath and nitrogen protection, 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) were stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP) under a nitrogen environment. Based on the total weight of all the substances used in step (1), the molar ratio of 6FDA to PABZ was 1:1, a total of 20wt%, and the amount of ultra-dry NMP was 80wt%. The mixture was reacted for 24h under stirring to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene was added to the flask, and then the temperature was gradually increased to 200°C and the reaction was carried out at a constant temperature for 5h 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 hours.

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

[0137] Comparative Example 2

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

[0139] (1) In a three-necked flask, in an ice bath and under nitrogen protection, 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2,3,5,6-tetramethyl-1,4-phenylenediamine are stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP) under a nitrogen environment. Based on the total weight of all the substances used in step (1), the molar ratio of 6FDA and 2,3,5,6-tetramethyl-1,4-phenylenediamine is 1:1, a total of 20wt%, and the amount of ultra-dry NMP is 80wt%. The mixture is reacted for 24h under stirring to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene is added to the flask, and then the temperature is gradually increased to 200°C and the reaction is carried out at a constant temperature for 5h to obtain PI-Bn4CH3 polyimide (weight average molecular weight is 32000), the structural formula is After precipitation and washing with methanol, it was 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 the mixture is uniform to obtain a hollow fiber spinning solution; based on the total weight of all the substances used in the step (2), the amount of the polyimide is 25wt%, the amount of the NMP is 55wt%, the amount of the THF is 10wt%, and the amount of the C2H5OH is 10wt%.

[0141] (3) The hollow fiber spinning solution is degassed in a liquid tank at 25°C for 12 hours to obtain a membrane solution, which is then transported to the spinneret with the prepared core solution (a mixture of NMP and water, with a volume fraction ratio of NMP to water of 8:2) by a gear pump, a pressure pump and a syringe to control the speed. The membrane solution is extruded from the liquid tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, the pressure of nitrogen pressurization is 2 bar), and then sequentially passed through an air gap of 2 cm and a 25°C coagulation bath treatment to obtain a hollow fiber. The hollow fiber is sequentially subjected to a spinning process (filament collection by a collection wheel, with a collection speed of 60 m / min), water immersion for 12 hours, solvent exchange with ethanol and n-hexane for 3 times, and air-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 tested by scanning electron microscopy is shown in FIG. Fig.11 As shown, from Fig.11 It can be seen that the polyimide hollow fiber gas separation membrane is composed of a support layer with finger-like pores and a selection layer, and the thickness of the selection layer is about 201 nm.

[0143] Comparative Example 3

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

[0145] (1) In a three-necked flask, under an ice bath and nitrogen protection, 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2,3,5,6-tetramethyl-1,4-phenylenediamine are stirred and dissolved in ultra-dry N-methylpyrrolidone (NMP) under a nitrogen environment. Based on the total weight of the amount of all substances used in the step (1), the molar ratio of the 6FDA and 2,3,5,6-tetramethyl-1,4-phenylenediamine is 1:1, a total of 20wt%, and the amount of ultra-dry NMP is 80wt%. The mixture is reacted for 24h under stirring to form a viscous high molecular weight polyamic acid (PAA). Subsequently, anhydrous toluene is added to the flask, and then the temperature is gradually increased to 200°C and the reaction is carried out at a constant temperature for 5h to obtain PI-Bn4CH3 polyimide (weight average molecular weight of 32000), which is precipitated and washed with methanol and then dried in a vacuum oven at 120°C for 24 hours.

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

[0147] (3) The hollow fiber spinning solution is degassed in a liquid tank at 25°C for 12 hours to obtain a membrane solution, which is then transported to the spinneret with the prepared core solution (a mixture of NMP and water, with a volume fraction ratio of NMP to water of 7:3) by a gear pump, a pressure pump and a syringe to control the speed. The membrane solution is squeezed from the liquid tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, the pressure of nitrogen pressurization is 3 bar), and then sequentially passed through an air gap of 6 cm and a 25°C coagulation bath treatment to obtain a hollow fiber. The hollow fiber is sequentially subjected to a spinning process (filament collection by a collection wheel, with a collection speed of 30 m / min), soaked in water for 12 hours, solvent exchanged with ethanol and n-hexane 3 times, and air-dried for 24 hours. The hollow fiber membrane is soaked in a methanol solution of copper ions at 40°C for 24 hours and air-dried to obtain the hollow fiber membrane.

[0148] The morphology of the polyimide hollow fiber gas separation membrane prepared in Comparative Example 3 tested by scanning electron microscopy is shown in FIG. Fig.12 As shown, from Fig.12 It can be seen that the polyimide hollow fiber gas separation membrane is composed of a support layer with finger-like pores and a selection layer, and the thickness of the selection layer is about 380 nm.

[0149] Comparative Example 4

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

[0151] (1) P84 is mixed with NMP, THF and C2H5OH and stirred for 24 hours until the mixture is uniform to obtain a hollow fiber spinning solution; based on the total weight of all the substances used in the 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 liquid tank at 25°C for 12 hours to obtain a membrane solution, which is then transported to the spinneret with the prepared core solution (a mixture of NMP and water, with a volume fraction ratio of NMP to water of 6:4) by a gear pump, a pressure pump and a syringe to control the speed. The membrane solution is extruded from the liquid tank to the spinneret for spinning by nitrogen pressurization (nitrogen pressurization tank, the pressure of nitrogen pressurization is 5 bar), and then sequentially passed through an air gap of 8 cm and a 25°C coagulation bath treatment to obtain a hollow fiber. The hollow fiber is sequentially subjected to a spinning process (filament collection by a collection wheel, with a collection speed of 40 m / min), water immersion for 12 hours, solvent exchange with ethanol and n-hexane for 3 times, and air-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 tested by scanning electron microscopy is shown in FIG. Fig.13 As shown, from Fig.13 It can be seen that the polyimide hollow fiber gas separation membrane is composed of a support layer with finger-like pores and a selection layer, and the thickness of the selection layer is about 1.47 μm.

[0154] Fig.14 The infrared spectrum (left) and nuclear magnetic hydrogen spectrum ( 1 HNMR) diagram (right), the characteristic absorption bands of benzimidazole structure and imide structure can be observed. 1298cm -1 The stretching vibration of benzimidazole NH is at 1781 cm -1 The symmetric stretching vibration of C=O of the imide ring is 1715 cm -1 The asymmetric stretching vibration of the imide ring C=O is 1368 cm -1 The stretching vibration of the imide ring-CNC is 716 cm -1 The imide ring is deformed.

[0155] Fig.15 The infrared spectrum of PI-Im-BN4CH3 polyimide in Example 8 (left) and 1In the HNMR diagram (right), characteristic absorption bands of benzimidazole and imide structures can be observed. -1 The stretching vibration of benzimidazole NH is at 1787 cm -1 The symmetrical stretching vibration of the imide ring C=O is 1720 cm -1 The asymmetric stretching vibration of the imide ring C=O is 1349 cm -1 The stretching vibration of the imide ring-CNC is 719 cm -1 The deformation of the imide ring is at 2980cm -1 The chemical shift at 2.08 ppm in the NMR spectrum corresponds to the hydrogen atom in the methyl group.

[0156] Fig.16 The infrared spectrum of PI-Im-COOH polyimide in Example 9 (left) and 1 In the H NMR spectrum (right), characteristic absorption bands of benzimidazole and imide structures can be observed. -1 The stretching vibration of benzimidazole NH is at 1781 cm -1 The symmetric stretching vibration of C=O of the imide ring is 1715 cm -1 The asymmetric stretching vibration of the imide ring C=O is 368 cm -1 The stretching vibration of the imide ring-CNC is 716 cm -1 The imide ring is deformed at 3600-2900cm -1 The broad absorption band at is caused by the stretching vibration of carboxyl -OH and benzimidazole -NH. The chemical shifts at 7.9 and 8.2 ppm (j, k, l) in the NMR spectrum correspond to CH on the aromatic ring of DABA. 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 a 316L stainless steel membrane assembly, and both ends of the membrane assembly were sealed with epoxy resin to form an assembly for gas separation performance testing. The polyimide flat membrane prepared in Comparative Example 1 was 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, GPU = 1×10 -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 tester. The effective length of the sample was 50 mm and the tensile rate was 5 mm / min. The test results are shown in FIG. Fig.17 As shown, the tensile stress of Example 1 is 33.4Mpa, and the tensile strain is 22.8%. The tensile stress of Example 2 is 42.3Mpa, and the tensile strain is 16.2%. The tensile stress of Example 3 is 48.4Mpa, and the tensile strain is 18.6%. The tensile stress of Example 4 is 67Mpa, and the tensile strain is 27.3%. The tensile stress of Example 5 is 75.1Mpa, and the tensile strain is 16.2%. The tensile stress of Example 6 is 80Mpa, and the tensile strain is 12%. The tensile stress of Example 7 is 83.2Mpa, and the tensile strain is 8.2%. The tensile stress of Example 8 is 60.3Mpa, and the tensile strain is 24.6%. The tensile stress of Example 9 is 49.5Mpa, and the tensile strain is 24.6%. The tensile stress of Comparative Example 2 is 52Mpa, and the tensile strain is 13.3%. The tensile stress of Comparative Example 3 is 42.5Mpa, and the tensile strain is 18%. The tensile stress of Comparative Example 4 is 42 MPa, and the tensile strain is 13%.

[0165] Obviously, the above embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art should understand that other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A polyimide polymer, characterized in that: The structural formula of the polyimide polymer is shown in Formula (I): Wherein, 0 < x < 100, 0 ≤ y < 100, and both x and y are integers. R1 is selected from the following structural groups: R2 is selected from the following structural groups:

2. A method for preparing a polyimide hollow fiber gas separation membrane, characterized in that: It includes the following steps: (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 Claim 1; (2) The polyimide polymer is mixed with a high-boiling solvent, a low-boiling solvent, and a non-solvent to obtain a hollow fiber spinning solution; (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 a drying treatment to obtain the polyimide hollow fiber gas separation membrane.

3. The preparation method according to claim 2, characterized in that: In step (1), the dianhydride monomer is selected from 4,4'-(hexafluoroisopropylidene) diphthalic anhydride; the diamine monomer is selected from one or more of 2-(4-aminophenyl)-5-aminobenzimidazole, 2,3,5,6-tetramethyl-1,4-phenylenediamine, and 3,5-diaminobenzoic acid.

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

5. The preparation method according to claim 2 or 4, characterized in that: In step (2), based on the total weight of the amounts of all substances used in step (2), the amount of the polyimide polymer is 15-35 wt%, the amount of the high-boiling solvent is 45-65 wt%, the amount of the low-boiling solvent is 1-15 wt%, and the amount of the non-solvent is 1-15 wt%.

6. The preparation method according to claim 2, characterized in that: In step (3), the time for the defoaming treatment is 6-12 h, and the temperature is 20-30 °C.

7. The preparation method according to claim 2, characterized in that: In step (3), 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 °C.

8. The preparation method according to claim 2, characterized in that: In step (3), the spinning process uses a take-up wheel for take-up, and the take-up speed of the take-up wheel is 30-70 m / min.

9. The preparation method according to claim 2, characterized in that: In step (3), after the drying treatment, it further includes a step of annealing treatment at 180-280 °C.

10. A polyimide hollow fiber gas separation membrane prepared by the method according to any one of Claims 2-9.

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