Hollow fiber gas separation membrane, preparation method therefor and use thereof

Abstract

The present invention relates to the technical field of separation membranes. Disclosed are a hollow fiber gas separation membrane, a preparation method therefor and the use thereof. The hollow fiber membrane is characterized in that the central birefringence index of the hollow fiber membrane is △n0, and the central birefringence index of the region of the outermost 20% wall thickness of the hollow fiber membrane is △n1, wherein △n1 / △n0≥2 and satisfies one or both of the following: 1×10-3≤△n1≤1.8×10-2; and 0.5×10-3≤△n0≤4.0×10-3. When being used for gas separation, in particular He / N2 separation, the hollow fiber membrane has both high He / N2 selectivity and high He permeability.

Description

Hollow fiber gas separation membrane, its preparation method and application Technical Field

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

[0002] Membrane separation technology utilizes the differences in permeability of various gases in different membrane materials to achieve separation. It is an emerging "green technology" that has attracted widespread research interest due to its advantages such as simple equipment, low fixed investment, and low energy consumption. Gas separation membrane technology has developed rapidly in recent decades and has wide applications in fields such as natural gas purification, hydrogen extraction, organic vapor recovery, and air separation.

[0003] Polymer membranes, due to their excellent permeation selectivity and processability, are suitable for large-scale fabrication and are currently the most widely used and researched membrane materials in industry. Polymers currently used to prepare commercial gas separation membrane modules include cellulose acetate, polysulfone, polyethersulfone, polyphenylene ether, polyamide, and polyimide. Compared to other membrane configurations (plates and frames, spiral wound, etc.), hollow fiber configurations offer the highest surface area to volume ratio and, through a thin separation layer, maximize productivity. Furthermore, hollow fiber membranes offer the advantage of easy integration; therefore, gas separation membranes are generally presented in the form of hollow fiber membrane modules.

[0004] Hollow fiber membranes are generally prepared by stretching or phase inversion methods, involving numerous process parameters that are greatly affected by actual operating conditions. In existing technologies, even with the same polymer raw materials and spinning solution formulation, different processes and conditions can produce membranes with drastically different performance. Therefore, how to mass-produce defect-free hollow fibers with excellent gas separation performance is a key problem that needs to be solved in the production of high-performance gas separation membranes. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem that existing gas separation membranes cannot simultaneously improve gas permeability and selectivity. To this end, this invention provides a hollow fiber membrane in which the birefringence index increases progressively from the inner wall to the outer wall, enabling the hollow fiber membrane to exhibit both high He / N2 selectivity and high He permeability when used for gas separation, particularly He / N2 separation.

[0006] The first aspect of this invention provides a hollow fiber membrane, preferably a hollow fiber separation membrane, more preferably a hollow fiber gas separation membrane, wherein the central birefringence index of the hollow fiber membrane is Δn0, and the central birefringence index of the outermost 20% wall thickness region of the hollow fiber membrane is Δn1, wherein Δn1 / Δn0 ≥ 2, and satisfies one or both of the following: 1 × 10⁻⁶-3 ≤△n1≤1.8×10 -2 ; 0.5×10 -3 ≤△n0≤4.0×10 -3 .

[0007] A second aspect of the present invention provides a method for preparing a hollow fiber membrane, wherein the preparation method includes:

[0008] S1. The spinning casting solution and the core solution are extruded from the double-ring spinneret at rates v11 and v12 in mL / min, respectively. After passing through the air gap, they undergo phase transformation in the coagulation bath under the first stretching condition to obtain the primary film.

[0009] S2. Under the second stretching condition, the nascent membrane is subjected to a second stretching, and then washed and dried to obtain the hollow fiber membrane.

[0010] Wherein, the rate of the first stretch in m / min is v2, the rate of the second stretch in m / min is v3, the tension of the second stretch in N is F, and the following conditions are met: 1 m / mL ≤ v2 / v11 ≤ 15 m / mL, 1 < v3 / v2 ≤ 1.3, 0.005 N ≤ F ≤ 0.2 N.

[0011] A third aspect of the present invention provides a hollow fiber membrane prepared by the above-described preparation method.

[0012] A fourth aspect of the present invention provides an application of the above-mentioned hollow fiber membrane in gas separation.

[0013] Through the above technical solutions, the hollow fiber membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0014] In the hollow fiber membrane provided by the present invention, the birefringence index increases in a progressive manner along the direction from the inner wall to the outer wall of the hollow fiber membrane. By controlling Δn1 / Δn0 and Δn1 and / or Δn0 to meet specific ranges, the hollow fiber membrane is used for gas separation, especially for He / N2 separation, and has both high He / N2 selectivity and high He permeability.

[0015] In the hollow fiber membrane preparation method provided by the present invention, the microstructure of the hollow fiber membrane is regulated by controlling v2 / v11, v3 / v2 and F to meet specific ranges. This is reflected in Δn1 / Δn0 and Δn1 and / or Δn0 meeting specific ranges, thereby enabling the hollow fiber membrane to have a balanced gas permeability and selectivity, and a low defect rate. The prepared hollow fiber membrane has both high He permeability and high He / N2 selectivity. Attached Figure Description

[0016] Figure 1 is an optical microscope photograph of the cross-section of the hollow fiber membrane of Embodiment 3 of the present invention.

[0017] Figure 2 is an optical microscope photograph of the cross-section of the hollow fiber membrane of Comparative Example 1 of the present invention.

[0018] Figure 3 is an optical microscope photograph of the cross-section of the hollow fiber membrane of Comparative Example 2 of the present invention.

[0019] Figure 4 is a scanning electron microscope image of a cross section of the hollow fiber membrane of Embodiment 1 of the present invention.

[0020] Figure 5 is a schematic diagram of the method for calculating the birefringence index at various points in a hollow fiber membrane.

[0021] Figure 6 is a schematic diagram of the hollow fiber membrane gas separation performance testing device. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] The first aspect of this invention provides a hollow fiber membrane, wherein the central birefringence index of the hollow fiber membrane is Δn0, and the central birefringence index of the outermost 20% wall thickness region of the hollow fiber membrane is Δn1, wherein Δn1 / Δn0 ≥ 2. For example, Δn1 / Δn0 can be ≥ 2.2, ≥ 2.4, ≥ 2.5, ≥ 2.6, ≥ 2.8, or ≥ 3. Δn1 / Δn0 can be within a range from any point among 2, 2.2, 2.4, 2.5, 2.6, 2.8, and 3 to any point among 8, 7.5, 7, 6.5, 6, 5.5, and 5. It covers the range between any two of the above values, as long as the lower limit is less than the upper limit.

[0024] In this invention, when Δn1 / Δn0 of the hollow fiber membrane meets the above-mentioned range, it indicates that the birefringence index increases progressively along the direction from the inner wall to the outer wall of the hollow fiber membrane, and there is a certain degree of difference between the birefringence index of the outermost region of the membrane and the birefringence index of the central region of the membrane. This indicates that the orientation degree of the outer side of the hollow fiber membrane is greater than that of the inner side, and the degree of orientation differs to a certain extent, enabling the hollow fiber membrane to be used for gas separation, especially He / N2 separation, while possessing both high He / N2 selectivity and high He permeability.

[0025] Furthermore, △n1 / △n0≥2.5, preferably, 3≤△n1 / △n0≤6.

[0026] According to the present invention, the central birefringence index Δn1 of the outermost 20% wall thickness region of the hollow fiber membrane is 1×10⁻⁶. -3 -1.8×10 -2 For example, Δn1 can be calculated from 1×10 -3 1.2×10 -3 1.4×10 -3 1.5×10 -3 1.6×10 -3 1.8×10 -3 2×10 -3 2.2×10 -3 2.4×10 -3 2.5×10 -3 3×10 -3 4×10 -3 From any point in to 1.8 × 10 -2 1.6×10 -2 1.5×10 -2 1.4×10 -2 1.2×10 -2 1×10 -2 9×10 -3 The range of any point in the range. This encompasses the range between any two of the above values, provided the lower limit is less than the upper limit.

[0027] In this invention, when the central birefringence index of the outermost 20% wall thickness region of the hollow fiber membrane meets the above-mentioned range, it indicates that the outermost region has an optimal degree of orientation, thereby forming an optimal molecular channel structure, which can further improve the gas permeability and selectivity of the hollow fiber membrane.

[0028] Furthermore, the central birefringence index Δn1 of the outermost 20% wall thickness region of the hollow fiber membrane is 2 × 10⁻⁶. -3 -1.6×10 -2 Preferably, 2.5 × 10 -3 -1.2×10 -2 .

[0029] According to the present invention, the central birefringence index Δn0 of the hollow fiber membrane is 0.5 × 10⁻⁶. -3 -4.0×10 -3 For example, Δn0 can be 0.5 × 10 -3 0.6×10 -3 0.7×10 -3 0.8×10 -3 0.9×10 -3 1×10 -3Any point in the range up to 4.0 × 10 -3 3.9×10 -3 3.8×10 -3 3.7×10 -3 3.6×10 -3 3.5×10 -3 3×10 -3 The range of any point in the range. This encompasses the range between any two of the above values, provided the lower limit is less than the upper limit.

[0030] In this invention, when the central birefringence index of the hollow fiber membrane meets the above range, it indicates that the overall structure of the hollow fiber membrane has not been overstretched. This can improve the gas permeability and selectivity of the hollow fiber membrane while ensuring that the hollow fiber membrane is not prone to defects and has high strength.

[0031] Furthermore, the central birefringence index of the hollow fiber membrane is 0.6 × 10⁻⁶. -3 -3.8×10 -3 Preferably, 0.8 × 10 -3 -3.5×10 -3 .

[0032] In this invention, the birefringence index is measured at room temperature (approximately 23°C) using a polarizing microscope (Olympus BX51) with a Berek compensator, in accordance with the method of ASTM D4093-23.

[0033] Cut a section of hollow fiber to a length of 0.5-1.5 cm and immerse it in white oil (standard wetting oil from Olympus, refractive index n). e =1.518 (23℃) until the fiber becomes translucent, and a sample with observable light transmission effect is obtained.

[0034] According to ASTM D4093-23, place the sample at the center of the polarizing microscope's field of view (the point to be observed should be at the exact center), find the extinction point (the angle at which the brightness of the observation point is lowest), and then rotate the stage 45° on the horizontal plane to achieve the diagonal position. Install the Berek compensator, and rotate the compensator knob until the brightness of the observation point reaches its lowest point. Read the compensation angle θ, and calculate the optical path difference θλ / π. The birefringence index = optical path difference / distance traveled by light in the medium. The formula for calculating the birefringence index is: Δn = θλ / πt

[0035] In the formula, λ is the wavelength of the incident light (589.3 nm for sodium light), and t is the distance the light travels in the medium.

[0036] The specific method for calculating the birefringence index at various points on the hollow fiber membrane is shown in Figure 5. In Figure 5, the average outer diameter of the hollow fiber membrane is D, the average inner diameter is d, and the average wall thickness is L = (Dd) / 2. The line aa passes through the center point of the hollow fiber membrane, and the line bb passes through a point at a radial distance of 0.1L from the outer wall and is perpendicular to the diameter at that point.

[0037] The central birefringence index Δn0 of the hollow fiber membrane is measured along the line connecting aa, where the optical path difference is / (Dd).

[0038] In this invention, the average inner diameter and average outer diameter of the hollow fiber membrane are measured using a polarizing microscope.

[0039] According to the present invention, the average wall thickness of the hollow fiber membrane is 50-200 μm. For example, the average wall thickness of the hollow fiber membrane can be in the range from any point among 50, 55, 60, 65, 70 μm to any point among 200, 180, 160, 150, 140, 120, 100 μm.

[0040] In this invention, when the average wall thickness of the hollow fiber membrane meets the above-mentioned range, it can ensure that the hollow fiber membrane has sufficient mechanical strength to support the overall structure, ensure that the membrane structure remains intact and is not prone to defects during actual application, and improve the service life of the hollow fiber membrane.

[0041] Furthermore, the hollow fiber membrane has an average wall thickness of 60-120 μm.

[0042] According to the present invention, the average outer diameter of the hollow fiber membrane is 300-700 μm. For example, the average outer diameter of the hollow fiber membrane can be in the range from any point among 300, 350, 400, 450 μm to any point among 700, 650, 600, 550 μm.

[0043] In this invention, when the average outer diameter of the hollow fiber membrane meets the above-mentioned range, the hollow fiber membrane has membrane filaments of moderate thickness and a suitable effective separation area, which makes it easy to subsequently bundle and fill into component units and ensure the separation performance of the component units.

[0044] Furthermore, the hollow fiber membrane has an average outer diameter of 350-600 μm.

[0045] In this invention, along the direction from the inner wall to the outer wall of the hollow fiber membrane, the hollow fiber membrane may sequentially include: a porous layer; an optional transition layer; and a dense layer, wherein the porosity of the porous layer, the transition layer, and the dense layer decreases, and the birefringence index increases. Functionally, the porous layer mainly serves a supporting role and can also be called a porous support layer; the dense layer mainly serves a separating role and can also be called a separating layer.

[0046] In this invention, the dense layer and the optional transition layer constitute the outer shell layer.

[0047] According to the present invention, the average thickness of the outer shell layer is 10-60 μm. For example, the average thickness of the outer shell layer can be in the range of any point from 10, 15, 20, 25 μm to any point from 60, 55, 50, 45 μm. Alternatively or additionally, the average thickness of the outer shell layer is ≥20% and ≤60% of the wall thickness of the hollow fiber membrane. For example, the average thickness of the outer shell layer is in the range of any point from 20%, 25%, 30%, 35% to 60%, 55%, 50%, 45% of the wall thickness of the hollow fiber membrane.

[0048] In this invention, when the thickness of the outer shell layer meets the above-mentioned range, it indicates that the thickness of the highly oriented structural region in the hollow fiber gas separation membrane is moderate, which is also beneficial to improving the gas permeability and selectivity of the hollow fiber gas separation membrane.

[0049] Further, the average thickness of the outer shell layer is 20-45 μm. Alternatively or additionally, the average thickness of the outer shell layer is ≥20% and ≤50% of the wall thickness of the hollow fiber membrane.

[0050] In this invention, the average thickness of the outer shell layer is measured at room temperature (approximately 23°C) using a polarizing microscope (Olympus BX51) with a Berek compensator, in accordance with the method of ASTM D4093-23.

[0051] Cut a section of hollow fiber to a length of 0.5-1.5 cm and immerse it in white oil (standard wetting oil from Olympus, refractive index n). e =1.518 (23℃) until the fiber becomes translucent, and a sample with observable light transmission effect is obtained.

[0052] According to ASTM D4093-23, when observing samples under a polarized microscope with white light in a dark field, the interference color sequence exhibited by the samples is consistent with the increasing order of optical path difference. A typical interference color sequence is, for example, black-gray-white-yellow-orange-red-transitional color-blue-blue-green-green-yellow-orange-red. With similar thicknesses, the optical path difference of the material is positively correlated with its molecular orientation. Therefore, the higher the orientation, the later the corresponding interference color appears in the sequence. Based on this principle, layering is determined: from the outer wall of the sample, the color region with the latest interference color (i.e., the largest optical path difference) and forming a significant brightness / color difference with adjacent areas is defined as the outer shell layer.

[0053] According to the present invention, the material for forming the hollow fiber membrane is not limited and can be any polymer conventionally used in the art for preparing hollow fiber membranes, such as at least one selected from polyimide, polysulfone, polyethersulfone, and polybenzimidazole, preferably polyimide. Preferably, the material used to form the hollow fiber membrane is a polymer with a He / N2 selectivity greater than 70, selected from at least one selected from polyimide, polysulfone, polyethersulfone, and polybenzimidazole. Preferably, the material used to form the hollow fiber membrane is polyimide with a He / N2 selectivity greater than 70. The He / N2 selectivity of the polymer is measured according to GB-T40260-2021 "Test Method for Gas Permeability Performance of Polymer Membrane Materials".

[0054] According to the present invention, the hollow fiber membrane has substantially the same material in all its portions. That is, the hollow fiber membrane is chemically substantially homogeneous and is prepared using a polymer or polymer blend having a single composition.

[0055] A second aspect of the present invention provides a method for preparing a hollow fiber membrane, characterized in that the preparation method includes the following steps:

[0056] S1. The spinning casting solution and the core solution are extruded from the double-ring spinneret at rates v11 and v12 in mL / min, respectively. After passing through the air gap, they undergo phase transformation in the coagulation bath under the first stretching condition to obtain the primary film.

[0057] S2. Under the second stretching condition, the nascent membrane is subjected to a second stretching, and then washed and dried to obtain the hollow fiber membrane.

[0058] Wherein, the rate of the first stretch in m / min is v2, the rate of the second stretch in m / min is v3, the tension of the second stretch in N is F, and the following conditions are met: 1 m / mL ≤ v2 / v11 ≤ 15 m / mL, 1 < v3 / v2 ≤ 1.3, 0.005 N ≤ F ≤ 0.2 N.

[0059] In the preparation method provided by this invention, the microstructure of the hollow fiber membrane is controlled by controlling v2 / v11, v3 / v2, and F to meet specific ranges. As a result, the birefringence index of the hollow fiber membrane increases along the direction from the inner wall to the outer wall, and Δn1 / Δn0 and Δn1 and / or Δn0 meet specific ranges. This results in the hollow fiber membrane having a balanced gas permeability and selectivity, and a low defect rate. The hollow fiber membrane also has high He permeability and high He / N2 selectivity.

[0060] In a preferred embodiment of the present invention, 2m / mL≤v2 / v11≤13m / mL, preferably, 4m / mL≤v2 / v11≤12m / mL; 1<v3 / v2≤1.25, preferably, 1<v3 / v2≤1.1; 0.01N≤F≤0.18N, preferably, 0.01≤F≤0.14N.

[0061] According to the present invention, 0.1 mL / min ≤ v11 ≤ 10 mL / min; 0.1 mL / min ≤ v12 ≤ 5 mL / min.

[0062] In this invention, when the control rate v11 or v12 meets the above range, the streamline will not fluctuate while ensuring uniform and continuous material output, so that the cross-sectional morphology of the final hollow fiber membrane is a regular concentric circle or ellipse, and the inner and outer diameters and thicknesses are uniform.

[0063] In this invention, the extrusion rates v11 of the spinning casting solution from the double-ring spinneret and v12 of the core solution from the double-ring spinneret can be the same or different. The condition that needs to be met is 1≤v11 / v12≤10, preferably 2≤v11 / v12≤6.

[0064] In one specific embodiment of the present invention, 0.5 mL / min ≤ v11 ≤ 5 mL / min, more preferably, 0.5 mL / min ≤ v11 ≤ 3.5 mL / min.

[0065] In one specific embodiment of the present invention, 0.1 mL / min ≤ v12 ≤ 3.5 mL / min, more preferably, 0.1 mL / min ≤ v12 ≤ 1.2 mL / min.

[0066] According to the present invention, the air gap is 1-35cm.

[0067] In this invention, when the air gap is controlled to meet the above range, the stability of the streamline can be controlled, ensuring that the streamline will not be disturbed by the environment due to excessively high gap, and ultimately ensuring that the hollow fiber membrane produced has a uniform morphology and few defects.

[0068] Furthermore, the air gap is 5-10cm.

[0069] According to the present invention, 0.6 m / min ≤ v2 ≤ 60 m / min.

[0070] In this invention, when the rate v2 of the first stretching is controlled to meet the above range, the nascent membrane fibers entering the coagulation bath are subjected to uniform and appropriate stretching and elongation while undergoing phase separation and solvent exchange, ultimately ensuring that the hollow fiber membrane formed has an outer shell layer of appropriate thickness and that the birefringence index of the outer shell layer is higher than that of the inner layer.

[0071] Furthermore, 5 m / min ≤ v2 ≤ 25 m / min.

[0072] In this invention, there is no particular limitation on v2 / v12, as long as v2 and v12 each meet the requirements of this invention. Preferably, 4≤v2 / v12≤60, and more preferably 15≤v2 / v12≤45.

[0073] In this invention, there is no particular limitation on the second stretching rate v3, as long as v3 / v2 can meet the requirements of this invention.

[0074] According to the present invention, the inner diameter R1 of the double-ring spinneret is 0.1-0.4 mm; the outer diameter R2 of the double-ring spinneret is 0.4-0.7 mm.

[0075] In this invention, when the inner diameter R1 and outer diameter R2 of the double-ring spinneret are controlled to meet the above-mentioned range, the outflow area of ​​the spinning solution can be controlled between the inner diameter R1 and the outer diameter R2, thereby making the hollow fiber membrane have the required inner and outer diameters and wall thickness.

[0076] Furthermore, the inner diameter R1 of the double-ring spinneret is 0.15-0.3 mm; the outer diameter R2 of the double-ring spinneret is 0.5-0.7 mm.

[0077] According to the present invention, the temperature of the double-ring spinneret is 45-85°C.

[0078] In this invention, when the temperature of the spinneret is controlled to meet the above-mentioned range, it can be ensured that the spinning solution passing through the spinneret has a suitable viscosity, thereby enabling the spinning solution to be uniformly extruded from the spinneret without fluctuation in the flow line, thus ensuring the quality stability of the hollow fiber membrane.

[0079] Furthermore, the temperature of the double-ring spinneret is 55-65℃.

[0080] According to the present invention, the temperature of the coagulation bath is 15-40°C.

[0081] In this invention, when the temperature of the coagulation bath is controlled within the above-mentioned range, it can be ensured that the hollow fibers entering the coagulation bath undergo phase separation and solvent exchange at a moderate speed, ultimately resulting in a nascent hollow fiber membrane with uniform morphology and a certain strength.

[0082] Furthermore, the temperature of the coagulation bath is 25-35°C.

[0083] In this invention, there are no particular limitations on the spinning casting solution, as long as it is a conventional spinning casting solution in the art that can be used to prepare hollow fiber membranes.

[0084] In this invention, the solid content of the spinning casting solution is 20-35 wt%.

[0085] In this invention, the spinning casting solution includes a polymer material, a diluent, and optionally additives;

[0086] Based on the total weight of the spinning casting solution, the content of polymer material is 20-35 wt%, the content of diluent is 58-80 wt%, and the content of additive is 0-7 wt%.

[0087] In this invention, the polymer material is selected from at least one of polyimide, polysulfone, polyethersulfone, and polybenzimidazole, preferably polyimide. More preferably, the polymer material is a polymer selected from at least one of polyimide, polysulfone, polyethersulfone, and polybenzimidazole with a He / N2 selectivity greater than 70. More preferably, the polymer material is a polyimide with a He / N2 selectivity greater than 70.

[0088] In this invention, the weight-average molecular weight of the polymer material is 50,000-250,000 g / mol.

[0089] In this invention, the diluent is at least one of the following: high-boiling-point solvents, such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, etc.; low-boiling-point solvents, such as ethanol, tetrahydrofuran, etc.; monobasic acids (mainly used for polybenzimidazole), such as hydrochloric acid, hydrofluoric acid, methanesulfonic acid, nitric acid, formic acid, acetic acid, etc. Preferably, the diluent is selected from at least one of N-methylpyrrolidone, tetrahydrofuran, and ethanol.

[0090] In this invention, the additive is a pore-forming agent such as polyvinylpyrrolidone, polyethylene oxide, polyvinyl alcohol, polyethylene glycol, polypropylene glycol, glycerin, etc., and / or an inorganic salt such as lithium nitrate, lithium chloride, calcium chloride, sodium chloride, potassium chloride, etc.

[0091] In this invention, there is no particular limitation on the core liquid, as long as it is a conventional core liquid in the art that can be used to prepare hollow fiber membranes.

[0092] In this invention, the core fluid comprises a good solvent diluent and a non-solvent for the polymer material, wherein, based on the total weight of the core fluid, the content of the good solvent diluent is 50-90 wt%, and the content of the non-solvent is 10-50 wt%.

[0093] In this invention, the good solvent diluent for the polymer material is a conventional good solvent used for the polymer material in the art.

[0094] In this invention, the good solvent diluent is at least one of the following: high-boiling-point solvents, such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, etc.; low-boiling-point solvents, such as ethanol, tetrahydrofuran, etc.; monobasic acids (mainly used for polybenzimidazole), such as hydrochloric acid, hydrofluoric acid, methanesulfonic acid, nitric acid, formic acid, acetic acid, etc. For example, the good solvent diluent for the polyimide is N-methylpyrrolidone.

[0095] In this invention, the non-solvent is a small-molecule polar solvent, such as water, methanol, ethanol, isopropanol, n-butanol, etc.

[0096] A third aspect of the present invention provides a hollow fiber membrane prepared by the above-described preparation method.

[0097] A fourth aspect of the present invention provides the application of the above-described hollow fiber membrane in gas separation, preferably in the separation of He and N2.

[0098] The present invention will be described in detail below through embodiments.

[0099] The thickness, average outer diameter, average inner diameter, and birefringence of the hollow fiber membrane were measured using a polarizing microscope (Olympus BX51) at room temperature (approximately 23°C). A 0.5-1.5 cm section of hollow fiber was cut and immersed in white oil (a standard impregnation oil from Olympus, with a refractive index n). e =1.518 (23℃) until the fiber becomes translucent, obtaining a sample where the light transmission effect can be observed. The birefringence index was determined according to ASTM D4093-23, and the specific calculation method is as described above. Each measurement result was taken at three different locations on the film and the arithmetic mean was taken.

[0100] The morphology of the hollow fiber membrane was measured using a scanning electron microscope (SEM, Hitachi S-4800). After quenching the hollow fiber membrane in liquid nitrogen, a layer of gold was sputtered onto the surface before testing.

[0101] The permeability coefficient of the hollow fiber membrane to He and the He / N2 separation coefficient were measured using the differential pressure method. The test setup was self-made and is shown in Figure 6 (1 is a gas cylinder, 2 is a hollow fiber membrane module, 3 is a volumetric flow meter, and 4 is a pressure gauge). The specific method was a constant pressure-variable volume test: at 23℃, a certain pressure was applied to the feed side of the hollow fiber membrane module, while the permeate side was vented to the atmosphere, creating a pressure difference between the feed side and the permeate side. The volumetric flow meter was used to read the volume of gas permeated per unit time. Five tests were performed, and the average value was recorded. The gas permeability (GPU, 1*10⁻⁶) is calculated. -6 cm 3 / (cm 2 The formula for calculating *s*cmHg is as follows:

[0102] Where Q is the gas volumetric flow rate (cm³). 3 s -1 A is the total outer surface area of ​​the membrane (cm²). 2 ), where Δp is the pressure difference across the membrane (cmHg).

[0103] The formula for calculating gas selectivity is as follows:

[0104] Where P i and P j The permeability is denoted by two different gases.

[0105] At least one set of measurements were performed under both internal pressure (with the inner cavity of the hollow fiber membrane as the feed side and the outer cavity as the permeation side) and external pressure (with the outer cavity of the hollow fiber membrane as the feed side and the inner cavity as the permeation side).

[0106] All raw materials used in the embodiments and comparative examples of this invention (except for polyimide) are commercially available products. N-methylpyrrolidone, ethanol, tetrahydrofuran, lithium nitrate, and n-hexane were all from Beijing Innocare Technology Co., Ltd.

[0107] Preparation Example 1

[0108] Preparation of spinning casting solution A1: 27 wt% polyimide (preparation example 10 with structural formula ZL202210717238.0, the polyimide with a selectivity of 160.4 for He / N2) resin, 53 wt% N-methylpyrrolidone, 10 wt% ethanol, 7 wt% tetrahydrofuran, and 3 wt% lithium nitrate additive were added to a kettle equipped with a stirring device. The mixture was heated to 50°C and stirred for 48 hours under nitrogen protection. After standing at a constant temperature for 24 hours to remove bubbles, a uniform spinning casting solution A1 was obtained.

[0109] Preparation Example 2

[0110] Preparation of spinning casting solution: Add 26 wt% polyimide (preparation example 4 with structural formula ZL202210717238.0, the polyimide has a selectivity of 104.9 for He / N2) resin, 54 wt% N-methylpyrrolidone, 13 wt% ethanol, and 7 wt% tetrahydrofuran to a kettle equipped with a stirring device, heat to 50°C, stir for 48 hours under nitrogen protection, and let stand at a constant temperature for 24 hours to remove bubbles, to obtain a uniform spinning casting solution A2.

[0111] Preparation Example 3

[0112] Preparation of core fluid: Mix 80 wt% N-methylpyrrolidone with 20 wt% water to obtain the core fluid.

[0113] Example 1

[0114] S1. A metering pump is used to deliver the spinning casting solution A1 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate v11 = 1.56 mL / min, and the core solution is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate v12 = 0.3 mL / min. The spinneret temperature is 60℃. The spinning casting solution and the core solution are simultaneously extruded through the spinneret, pass through a 5 cm air gap, and enter a 30℃ water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 10 m / min to obtain the primary membrane.

[0115] S2. After the primary membrane is stretched a second time at a rate of v3 = 10.12 m / min and a tension of F = 0.03 N at the rear end of the coagulation bath, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber membrane M1.

[0116] Figure 4 shows a cross-sectional scanning electron microscope image of the hollow fiber membrane M1. As can be seen from Figure 4, the membrane surface is a dense layer, the interior is a porous layer, and there is a transition layer near the surface. The approximate locations of the dense layer and the transition layer are schematically shown in the figure.

[0117] Example 2

[0118] S1. A metering pump is used to deliver the spinning casting solution A1 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate v11 = 2.08 mL / min, and the core solution is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate v12 = 0.5 mL / min. The spinneret temperature is 60℃. The casting solution and the core solution are simultaneously extruded through the spinneret, pass through a 10 cm air gap, and enter a 30℃ water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 22 m / min to obtain the primary membrane.

[0119] S2. After the primary membrane is stretched a second time at a rate of v3 = 23.16 m / min and a tension of F = 0.09 N at the rear end of the coagulation bath, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber membrane M2.

[0120] Example 3

[0121] S1. A metering pump is used to deliver the spinning casting solution A1 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate v11 = 2.6 mL / min, and the core solution is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate v12 = 0.6 mL / min. The spinneret temperature is 60℃. The spinning casting solution and the core solution are simultaneously extruded through the spinneret, pass through a 5 cm air gap, and enter a 30℃ water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 12 m / min to obtain the primary membrane.

[0122] S2. After the primary membrane is stretched a second time at the rear end of the coagulation bath at a rate of v3 = 13.16 m / min and a tension of F = 0.14 N, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber composite separation membrane M3.

[0123] Figure 1 shows the cross-sectional structure of the hollow fiber membrane M3 under an optical microscope. As can be seen from Figure 1, the membrane is hollow, with uniform inner and outer diameters and thickness. Under polarized light, it exhibits birefringence and moderate brightness. The color from the center to the inner wall is a relatively uniform dark orange, with a clear black boundary on the inner side caused by the wetting liquid (white oil). From the inner wall to the outer wall, the color transitions from dark orange to bright yellow. The light transmission effect is more significant in the bright yellow area on the outer side than on the inner side; this bright yellow area (area A) is identified as the outer shell layer. Measurements show that the birefringence index of the outer shell layer is significantly higher than that of the inner layer (area B), further supporting this assessment.

[0124] Example 4

[0125] S1. A metering pump is used to deliver the spinning casting solution A2 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate of v11 = 1.56 mL / min, and the core solution is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate of v12 = 0.3 mL / min. The spinneret temperature is 60℃. The spinning casting solution and the core solution are simultaneously extruded through the spinneret, pass through a 5 cm air gap, and enter a 30℃ water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 11 m / min to obtain the primary membrane.

[0126] S2. After the primary membrane is stretched a second time at the rear end of the coagulation bath at a rate of v3 = 13.32 m / min and a tension of F = 0.18 N, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber membrane M4.

[0127] Example 5

[0128] S1. A metering pump is used to deliver the spinning casting solution A2 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate v11 = 2.6 mL / min, and the core solution is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate v12 = 0.6 mL / min. The spinneret temperature is 60℃. The spinning casting solution and the core solution are simultaneously extruded through the spinneret, pass through a 5 cm air gap, and enter a 27℃ water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 12 m / min to obtain the primary membrane.

[0129] S2. After the primary membrane is stretched a second time at a rate of v3 = 12.12 m / min and a tension of F = 0.01 N at the rear end of the coagulation bath, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber membrane M5.

[0130] Example 6

[0131] S1. A metering pump is used to deliver the spinning casting solution A2 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate of v11 = 6.5 mL / min, and the core solution is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate of v12 = 2 mL / min. The spinneret temperature is 60℃. The spinning casting solution and the core solution are simultaneously extruded through the spinneret, pass through a 5 cm air gap, and enter a 27℃ water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 36 m / min to obtain the primary membrane.

[0132] S2. After the primary membrane is stretched a second time at a rate of v3 = 40.2 m / min and a tension of F = 0.06 N at the rear end of the coagulation bath, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber membrane M6.

[0133] Comparative Example 1

[0134] S1. A metering pump is used to deliver the spinning casting solution A1 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate v11 = 1.56 mL / min, and the core solution is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate v12 = 0.3 mL / min. The spinneret temperature is 60℃. The spinning casting solution and the core solution are simultaneously extruded through the spinneret, pass through a 5 cm air gap, and enter a 30℃ water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 10 m / min to obtain the primary membrane.

[0135] S2. After the primary membrane is stretched a second time at the rear end of the coagulation bath at a rate of v3 = 8.52 m / min and a tension of F = 0 N, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber membrane DM1.

[0136] Figure 2 shows the cross-sectional structure of the hollow fiber membrane DM1 under an optical microscope. As can be seen from Figure 2, the membrane is hollow, with uniform inner and outer diameters and thickness. Under polarized light, it exhibits birefringence and light transmission, but with low brightness. The area from the center to the inner wall is grayish-black, indicating weak light transmission in this region. A relatively wide, opaque black area, created by the wetting liquid (white oil), is located on the inner side of the inner wall. The color transitions from light yellow to white from the inner wall to the outer wall, indicating a small overall optical path difference. Furthermore, the light transmission effects on the outer and inner sides are similar, suggesting the absence of a clearly defined outer shell layer. Measurements show that the birefringence indices are similar at various points from the inner to the outer wall, further supporting this assessment.

[0137] Comparative Example 2

[0138] S1. A metering pump is used to deliver the spinning casting solution A1 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate v11 = 1.56 mL / min, and the core solution is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate v12 = 0.3 mL / min. The spinneret temperature is 60℃. The spinning casting solution and the core solution are simultaneously extruded through the spinneret, pass through a 5 cm air gap, and enter a 30℃ water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 10 m / min to obtain the primary membrane.

[0139] S2. After the primary membrane is stretched a second time at the rear end of the coagulation bath at a rate of v3 = 13.32 m / min and a tension of F = 0.25 N, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber membrane DM2.

[0140] Figure 3 shows the cross-sectional structure of the hollow fiber membrane DM2 under an optical microscope. As can be seen from Figure 3, the membrane is hollow inside, with uniform inner and outer diameters and thickness, but there are pore defects on the right side of the membrane wall. Under polarized light, the membrane appears blue-green (with a large optical path difference), indicating a high overall birefringence index. The color transitions from deep purple to deep blue from the center to the inner wall, with an opaque black boundary created by the wetting liquid (white oil) on the inner side of the inner wall. The color transitions from blue-green to yellow to blue to orange from the inner wall to the outer wall, with the outermost color area being orange-red. A clear boundary is formed between this outer color area and the adjacent inner color area, and the light transmission effect is particularly significant. The orange area (area A) is identified as the outer shell layer. Measurements show that the birefringence index of the outer shell layer is very high, significantly higher than that of the inner layer (area B), further supporting the above judgment.

[0141] Comparative Example 3

[0142] S1. A metering pump is used to deliver the spinning casting solution A2 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate v11 = 2.6 mL / min, and the core solution is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate v12 = 0.6 mL / min. The spinneret temperature is 60℃. The spinning casting solution and the core solution are simultaneously extruded through the spinneret, pass through a 5 cm air gap, and enter a 30℃ water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 12 m / min to obtain the primary membrane.

[0143] S2. After the primary membrane is stretched a second time at a rate of v3 = 11.72 m / min and a tension of F = 0.01 N at the rear end of the coagulation bath, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber membrane DM3.

[0144] Comparative Example 4

[0145] S1. A metering pump is used to deliver the spinning casting solution A2 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate of v11 = 1.56 mL / min, and the core solution is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate of v12 = 0.3 mL / min. The spinneret temperature is 60℃. The spinning casting solution and the core solution are simultaneously extruded through the spinneret, pass through a 5 cm air gap, and enter a 30℃ water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 11 m / min to obtain the primary membrane.

[0146] S2. After the primary membrane is stretched a second time at the rear end of the coagulation bath at a rate of v3 = 13.32 m / min and a tension of F = 0.22 N, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber membrane DM4.

[0147] Comparative Example 5

[0148] S1. A metering pump is used to deliver the spinning casting solution A1 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate of v11 = 1.56 mL / min, and the core solution is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate of v12 = 0.3 mL / min. The spinneret temperature is 60℃. The spinning casting solution and the core solution are extruded through the spinneret at the same time, pass through a 5 cm air gap, and enter a 30℃ water coagulation bath for phase transformation. At the same time, they are stretched at a uniform speed of v2 = 24.6 m / min, resulting in fiber breakage and failure to form a complete and continuous hollow fiber membrane.

[0149] Comparative Example 6

[0150] S1. A metering pump is used to deliver the spinning casting solution A2 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate of v11 = 6.5 mL / min, and the core solution is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate of v12 = 2 mL / min. The spinneret temperature is 60℃. The spinning casting solution and the core solution are simultaneously extruded through the spinneret, pass through a 5 cm air gap, and enter a 27℃ water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 6 m / min to obtain the primary membrane.

[0151] S2. After the primary membrane is stretched a second time at the rear end of the coagulation bath at a rate of v3 = 6.72 m / min and a tension of F = 0.06 N, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber membrane DM6.

[0152] Although a continuous and complete fiber can be obtained, both the nascent membrane and DM6 are coiled and spiral in shape, and cannot form uniformly straightened hollow fibers. Therefore, it is impossible to accurately measure structural parameters and separation performance.

[0153] The v2 / v11, v2 / v12, and v3 / v2 in the embodiments and comparative examples are shown in Table 1.

[0154] Table 1

[0155] The average outer diameter, average wall thickness, average thickness of the outer shell layer, central birefringence index Δn0, and central birefringence index Δn1 of the outermost 20% wall thickness region of the hollow fiber membranes prepared in the examples and comparative examples were tested, and the results are shown in Table 2.

[0156] Table 2

[0157] Test case

[0158] The permeation coefficient of hollow fiber membrane to He and the separation coefficient of He / N2 were tested, and the results are shown in Table 3.

[0159] Table 3

[0160] As can be seen from Tables 1-3, the hollow fiber membranes provided in the embodiments of the present invention have relatively high Δn1 and Δn0, and Δn1 is more than twice that of Δn0. This indicates that in the hollow fiber membranes provided in the embodiments of the present invention, the birefringence index of the hollow fiber membrane shows a significant increasing change along the direction from the inner wall to the outer wall.

[0161] In this invention, by controlling the spinning casting solution rate v11, the first stretching rate v2, the second stretching rate v3, and the second stretching tension F to meet the requirements defined in this invention, the hollow fiber membrane obtained can have Δn1 and Δn0 that meet the requirements of this invention. That is, the overall orientation degree of the hollow fiber membrane and the orientation degree of the outermost region are both within the optimal range, thereby obtaining the most suitable molecular channel structure size and improving the diffusion rate and selectivity of gas in the membrane.

[0162] Furthermore, the hollow fiber membrane of this invention has a suitable wall thickness, thereby ensuring that the hollow fiber membrane has sufficient mechanical strength to support the overall structure, guaranteeing that the membrane structure remains intact and is less prone to defects during practical applications, and improving the service life of the hollow fiber membrane. In addition, the hollow fiber membrane of this invention has a suitable outer shell layer thickness, which also contributes to improving the permeability coefficient of He and the He / N2 separation coefficient of the hollow fiber membrane.

[0163] In contrast, in Comparative Example 1, the ratio of the second stretching rate v3 to the first stretching rate v2 is small, and no tension is applied during the second stretching; in Comparative Example 2, the ratio of the second stretching rate v3 to the first stretching rate v2 is high, and the tension of the second stretching is relatively high; in Comparative Example 3, the ratio of the second stretching rate v3 to the first stretching rate v2 is small; and in Comparative Example 4, the tension of the second stretching is relatively high. All of these situations result in the hollow fiber membrane's Δn1 and Δn0 not meeting the requirements of the present invention, that is, the overall orientation degree of the hollow fiber membrane or the orientation degree of the outermost layer is not within the optimal range, and the internal molecular channel structure size is not conducive to the selective diffusion of gas within the membrane, ultimately leading to an unfavorable reduction in the permeation coefficient of He and the He / N2 separation coefficient.

[0164] Example 7 (Selectivity of Polyimide)

[0165] Preparation of spinning casting solution A3: 27 wt% polyimide (polyimide of Preparation Example 8 in structural formula ZL202210717238.0, which has a selectivity of 83.57 for He / N2) resin, 53 wt% N-methylpyrrolidone, 10 wt% ethanol, 7 wt% tetrahydrofuran, and 3 wt% lithium nitrate additive were added to a kettle equipped with a stirring device. The mixture was heated to 50°C and stirred for 48 hours under nitrogen protection. After standing at a constant temperature for 24 hours to remove bubbles, a uniform spinning casting solution A3 was obtained.

[0166] S1. A metering pump is used to deliver the spinning casting solution A3 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate v11 = 1.56 mL / min, and the core solution (from preparation example 3) is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate v12 = 0.3 mL / min. The spinneret temperature is 60 °C. The spinning casting solution is extruded through the spinneret, passes through a 5 cm air gap, and enters a 30 °C water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 10 m / min to obtain the primary membrane.

[0167] S2. After the primary membrane is stretched a second time at a rate of v3 = 10.12 m / min and a tension of F = 0.03 N at the rear end of the coagulation bath, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber membrane M7.

[0168] The Δn1 of test M7 is 6.07 × 10⁻⁶. -3 △n0 is 1.83×10 -3 The external pressure helium permeability is 135.5 GPU, and the He / N2 separation coefficient is 89.7.

[0169] Comparative Example 7 (Selectivity of Polyimide)

[0170] Preparation of spinning casting solution A4: Add 27 wt% polyimide (polyimide of Preparation Example 17 in structural formula ZL202210717238.0, which has a selectivity of 50.67 for He / N2) resin, 53 wt% N-methylpyrrolidone, 10 wt% ethanol, 7 wt% tetrahydrofuran, and 3 wt% lithium nitrate additive to a kettle equipped with a stirring device. Heat to 50°C and stir for 48 hours under nitrogen protection. Let stand at a constant temperature for 24 hours to remove bubbles to obtain a uniform spinning casting solution A4.

[0171] S1. A metering pump is used to deliver the spinning casting solution A4 to the outer ring of the double-ring spinneret (outer diameter R2 is 0.6 mm) at a rate of v11 = 1.56 mL / min, and the core solution (from preparation example 3) is delivered to the inner ring of the double-ring spinneret (inner diameter R1 is 0.2 mm) at a rate of v12 = 0.3 mL / min. The spinneret temperature is 60 °C. The casting solution is extruded through the spinneret, passes through a 5 cm air gap, and enters a 30 °C water coagulation bath for phase transformation. At the same time, the membrane is stretched at a uniform speed of v2 = 10 m / min to obtain the primary membrane.

[0172] S2. After the primary membrane is stretched a second time at a rate of v3 = 10.12 m / min and a tension of F = 0.03 N at the rear end of the coagulation bath, it is wound up by a winding machine, then washed in water, ethanol and n-hexane in sequence, and dried at room temperature to obtain hollow fiber membrane DM7.

[0173] The Δn1 of DM7 is 0.74 × 10⁻⁶. -3 △n0 is 0.22×10 -3 The external pressure helium permeability is 435.8 GPU, and the He / N2 separation coefficient is 25.4.

[0174] Comparative Example 8

[0175] A certain manufacturer produces polyimide hollow fiber membrane DM8.

[0176] The outer shell layer of DM8 is not clearly visible under an optical microscope, and Δn1 is 1.79 × 10⁻⁶. -3 △n0 is 1.73×10 -3 The external pressure helium permeability is 77.0 GPU, and the He / N2 separation coefficient is 52.4.

[0177] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A hollow fiber membrane, characterized in that, The central birefringence index of the hollow fiber membrane is Δn0. The central birefringence index of the outermost 20% wall thickness region of the hollow fiber membrane is Δn1. Where △n1 / △n0≥2, and satisfy one or both of the following: 1×10 -3 ≤△n1≤1.8×10 -2 ； 0.5×10 -3 ≤△n0≤4.0×10 -3 。 2. The hollow fiber membrane according to claim 1, wherein, △n1 / △n0≥2.5, preferably, 3≤△n1 / △n0≤6; and / or 2×10 -3 ≤△n1≤1.6×10 -2 Preferably, 2.5 × 10 -3 ≤△n1≤1.2×10 -2 ; and / or 0.6×10 -3 ≤△n0≤3.8×10 -3 Preferably, 0.8 × 10 -3 ≤△n0≤3.5×10 -3 .

3. The hollow fiber membrane according to claim 1 or 2, wherein, The hollow fiber membrane has a wall thickness of 50-200 μm, preferably 60-120 μm; and / or The hollow fiber membrane has an average outer diameter of 300-700 μm, preferably 350-600 μm.

4. The hollow fiber membrane according to any one of claims 1-3, wherein, The material forming the hollow fiber membrane is selected from at least one of polyimide, polysulfone, polyethersulfone, and polybenzimidazole, preferably polyimide, and more preferably polyimide with He / N2 selectivity greater than 70.

5. The hollow fiber membrane according to any one of claims 1-4, wherein, Along the direction from the inner wall to the outer wall of the hollow fiber membrane, the hollow fiber membrane sequentially comprises: -Porous layer; - Optional transition layer; and - Dense layer; The porosity of the porous layer, transition layer, and dense layer decreases, while the birefringence index increases.

6. The hollow fiber membrane according to claim 5, wherein, The dense layer and the optional transition layer constitute the outer shell layer, preferably, The average thickness of the outer shell layer is 10-60 μm, preferably 20-45 μm; and / or The average thickness of the outer shell layer is ≥20% and ≤60% of the wall thickness of the hollow fiber membrane, preferably ≥20% and ≤50%.

7. The hollow fiber membrane according to any one of claims 1-6, wherein, The hollow fiber membrane has substantially the same material in all its parts.

8. A method for preparing a hollow fiber membrane, characterized in that, The preparation method includes the following steps: S1. The spinning casting solution and the core solution are extruded from the double-ring spinneret at rates v11 and v12 in mL / min, respectively. After passing through the air gap, they undergo phase transformation in the coagulation bath under the first stretching condition to obtain the primary film. S2. Under the second stretching condition, the nascent membrane is subjected to a second stretching, and then washed and dried to obtain the hollow fiber membrane. Wherein, the rate of the first stretch in m / min is v2, the rate of the second stretch in m / min is v3, the tension of the second stretch in N is F, and the following conditions are met: 1 m / mL ≤ v2 / v11 ≤ 15 m / mL, 1 < v3 / v2 ≤ 1.3, 0.005 N ≤ F ≤ 0.2 N.

9. The preparation method according to claim 8, wherein, 2 m / mL ≤ v2 / v11 ≤ 13 m / mL, preferably, 4 m / mL ≤ v2 / v11 ≤ 12 m / mL; and / or 1 < v3 / v2 ≤ 1.25, preferably, 1 < v3 / v2 ≤ 1.1; and / or 0.01N≤F≤0.18N, preferably 0.01N≤F≤0.14N.

10. The preparation method according to claim 8 or 9, wherein, 0.1 mL / min ≤ v11 ≤ 10 mL / min, preferably 0.5 mL / min ≤ v11 ≤ 5 mL / min; and / or 0.1 mL / min ≤ v12 ≤ 5 mL / min, preferably 0.1 mL / min ≤ v12 ≤ 3.5 mL / min; and / or The air gap is 1-35cm, preferably 5-10cm; and / or 0.6 m / min ≤ v2 ≤ 60 m / min, preferably 5 m / min ≤ v2 ≤ 25 m / min.

11. The preparation method according to any one of claims 8-10, wherein, The inner diameter R1 of the double-ring spinneret is 0.1-0.4 mm; the outer diameter R2 of the double-ring spinneret is 0.4-0.7 mm; and / or The temperature of the double-ring spinneret is 45-85℃; and / or The temperature of the coagulation bath is 15-40℃.

12. The preparation method according to any one of claims 8-11, wherein, The spinning casting solution includes a polymer material, a diluent, and optional additives; preferably, Based on the total weight of the spinning casting solution, the polymer material content is 20-35 wt%, the diluent content is 58-80 wt%, and the additive content is 0-7 wt%; and / or The polymer material is selected from at least one of polyimide, polysulfone, polyethersulfone, and polybenzimidazole, preferably polyimide, more preferably polyimide with He / N2 selectivity greater than 70; and / or The diluent is selected from at least one of N-methylpyrrolidone, tetrahydrofuran, and ethanol.

13. The preparation method according to any one of claims 8-12, wherein, The core fluid comprises a good solvent diluent for the polymer material and a non-solvent; preferably, Based on the total weight of the core fluid, the content of the good solvent diluent is 50-90 wt%, and the content of the non-solvent is 10-50 wt%; and / or The good solvent diluent is N-methylpyrrolidone; and / or The non-solvent is water.

14. A hollow fiber membrane prepared by any one of claims 8-13.

15. The use of the hollow fiber membrane according to any one of claims 1-7 and 14 in gas separation, preferably He and N2 separation.

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