Hollow fiber separation membrane, method for producing the same, and use thereof

Abstract

The application relates to the technical field of membrane separation materials, and discloses a hollow fiber separation membrane and a preparation method and application thereof. The separation membrane comprises a support body, a functional layer coated on the outer surface of the support body, and a connecting layer embedded in the support body; the support body is a hollow fiber microporous membrane; the connecting layer has a porous structure; the material of the functional layer is polybenzimidazole, and the number average molecular weight of the polybenzimidazole is 50,000-300,000; the novel hollow fiber separation membrane has a high separation coefficient and good mechanical properties.

Description

Technical Field

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

[0002] Helium and hydrogen are gases with relatively small molecules, and both are essential resources for human survival and development. Helium is chemically extremely stable and possesses unique properties such as strong diffusivity, good thermal conductivity, low solubility, and low latent heat of vaporization, making it a very important industrial gas. Due to its unique properties, helium is widely used in cryogenics, aerospace, electronics, biomedicine, and nuclear facilities, and is one of the essential basic materials for national security and the development of high-tech industries. Currently, there is no technology to synthesize helium; it is mainly obtained by purifying associated gas from natural gas and shale gas extraction. Natural gas and shale gas helium extraction processes are divided into cryogenic processes and non-cryogenic processes. Cryogenic processes are currently the most commonly used method in industrial applications. Generally, industrial processes with temperatures below -100℃ are classified as cryogenic processing. In the case of natural gas processing, cryogenic processing of natural gas, in order of decreasing processing temperature, includes ethane recovery (-100℃), natural gas liquefaction (-160℃), natural gas denitrification (-190℃), natural gas helium extraction (-190℃), and helium liquefaction (-269℃). Among them, helium extraction from natural gas and helium liquefaction are typical cryogenic processes with the lowest refrigeration separation temperature in the cryogenic processing of natural gas, and have the following characteristics:

[0003] (1) As the refrigeration temperature continues to decrease, the energy consumption per unit of refrigeration capacity increases dramatically. This puts forward higher and more stringent requirements for how to refrigerate efficiently, how to make reasonable and efficient use of refrigeration capacity, and the design, manufacturing and operation of equipment.

[0004] (2) Natural gas is a multi-component mixture, and low-temperature phase equilibrium is the basis for cryogenic helium extraction from natural gas. Due to the limitations of the freezing point and solubility of substances, as the refrigeration temperature decreases, more substances will cause low-temperature blockage, which puts forward higher requirements on how to purify, separate and prevent low-temperature blockage.

[0005] (3) The enrichment and concentration of trace hydrogen in natural gas places higher demands on the effective dehydrogenation process, and the presence of trace neon has a significant impact on the quality classification of helium and the effective separation or purification of neon. These substances are not often considered in conventional natural gas analysis, which requires accurate and quantitative analysis of trace substances in natural gas to ensure effective control of the entire process.

[0006] (4) The equipment mainly uses non-ferrous metals such as stainless steel, aluminum, and copper, requiring good low-temperature resistance and involving issues such as transitional bonding of different materials and multi-layer vacuum shielding insulation. This places higher demands on high-vacuum equipment, helium leak detection, materials, and processes. Membrane separation helium purification and refining technology avoids various phase transition processes and violent chemical reactions, has low energy consumption, small equipment size, and high safety. It is suitable for my country's dispersed helium resources and complex application conditions, and is a key technology to solve my country's helium resource shortage. Hydrogen is a carrier of clean energy and also a secondary energy source. It cannot be directly mined and needs to be produced through other energy sources. The vast majority of commercial hydrogen in the world is produced from fossil fuels. The products of hydrogen production from fossil fuels contain gases such as N2, CO, CH4, and CO2, which need to be separated and purified. With the increasing global demand for clean and efficient energy, the production and refining of hydrogen are receiving more and more attention.

[0007] In summary, to meet the demand for helium and hydrogen resources for economic development, there is an urgent need to develop efficient, green, safe, and reliable methods for helium and hydrogen purification. Membrane separation technology offers advantages such as mild operating conditions and miniaturized equipment, while the demand for core materials, especially high-end membrane materials, is particularly pressing.

[0008] CN113318609A discloses a method for manufacturing a rigid network microporous hydrogen separation membrane with high permeability and selectivity. This method utilizes a conjugated microporous polymer to prepare a novel hydrogen separation membrane. The membrane maintains high permeability, and its rigid network structure ensures high gas permeability. Furthermore, it can be prepared using a solution method, facilitating production and reducing costs. However, this membrane has limited selectivity for hydrogen and cannot produce high-purity hydrogen or helium products.

[0009] CN112142980B discloses a hyperbranched polybenzimidazole-polysiloxane block copolymer, its preparation method, and its application. The block copolymer is formed by the combination of soft segments of PDMS and hard segments of HBPBI, and hydrophobic segments of PDMS and hydrophilic segments of HBPBI, thus creating a soft... Hard, intimate The sparse phase separation structure constructs a proton transport channel through the phase separation structure of two chain segments. The hyperbranched structure of HBPBI can accommodate more phosphate, ultimately achieving high proton conductivity. However, the material has insufficient strength and elongation at break, and cannot be used to prepare high-pressure gas separation membranes.

[0010] US Patent 20160375410A1 discloses a method for preparing PBI asymmetric hollow fiber membranes and their applications. This patent uses a solvent-free phase-induced separation technique to prepare the PBI asymmetric hollow fiber membrane, which has a flux of 10⁸ GPU at 250°C, a separation coefficient of 23.7 for H₂ / CO₂, and a separation coefficient of 129 for H₂ / N₂. However, this membrane is prone to defects during phase transformation, significantly affecting its selectivity and preventing it from achieving the true separation effect of PBI.

[0011] Therefore, it is of great significance to develop membrane materials with dense functional layers, easy preparation, and the ability to achieve the highest separation effect of PBI. Summary of the Invention

[0012] The purpose of this invention is to overcome the problems of existing technologies, such as the easy occurrence of surface defects in hollow fiber membranes prepared by non-solvent-induced phase separation, or insufficient material strength and elongation at break, which prevent the preparation of high-pressure gas separation membranes. This invention provides a novel hollow fiber separation membrane, its preparation method, and its application. The novel hollow fiber separation membrane has a high separation coefficient and good mechanical properties.

[0013] To achieve the above objectives, the first aspect of the present invention provides a novel hollow fiber separation membrane, wherein the separation membrane includes a support, a functional layer covering the outer surface of the support, and a connecting layer embedded in the support; the support is a hollow fiber microporous membrane, the connecting layer has a porous structure, the functional layer is made of polybenzimidazole, and the number average molecular weight of the polybenzimidazole is 50,000 to 300,000.

[0014] A second aspect of the present invention provides a method for preparing a novel hollow fiber separation membrane, wherein the method comprises:

[0015] (1) Polybenzimidazole, acid, optional volatile solvent and optional additive are contacted and mixed to obtain casting solution; the number average molecular weight of the polybenzimidazole is 50,000 to 300,000.

[0016] (2) A spinneret for preparing the primary membrane and the connecting layer is used; a hollow fiber microporous membrane is used as the support;

[0017] (3) The casting liquid is extruded and enters the spinneret. The casting liquid is then scraped onto the support by a scraper. At the same time, the support is stretched from bottom to top through the inside of the spinneret to obtain a nascent film covering the support, and some casting liquid penetrates into the inside of the support.

[0018] (4) The nascent membrane is stretched and heated to form a polybenzimidazole functional layer with a dense structure; and a non-solvent is injected into the support body through a central tube as a core liquid to induce non-solvent-induced phase separation of the portion of the casting liquid that has penetrated into the support body to generate a porous connecting layer; and then the membrane is washed with water to obtain a novel hollow fiber separation membrane.

[0019] A third aspect of the present invention provides a novel hollow fiber separation membrane prepared by the method described above.

[0020] The fourth aspect of the present invention provides a novel hollow fiber separation membrane as described above for separating and purifying helium / nitrogen, helium / methane, hydrogen / nitrogen, or hydrogen / methane.

[0021] Through the above technical solution, the present invention has the following beneficial effects:

[0022] (1) Adopt acid Polybenzimidazole was dissolved in a volatile solvent and the phase transformation of the polybenzimidazole material was achieved by solvent evaporation in the coating layer to prepare an outer functional layer with separation properties.

[0023] (2) The internal support reinforcement improves the mechanical properties of the gas separation membrane, which can meet the requirements of high temperature, high pressure and high flow rate gas separation systems for the mechanical properties of membrane fibers, and expands the application range of gas separation membranes;

[0024] (3) The casting solution penetrates into the support and a connecting layer with a microporous structure is obtained by non-solvent phase separation induced by the core liquid, thus avoiding the detachment of the functional layer;

[0025] (4) The thickness of the external functional layer can be controlled during the spinning process by means of the present invention;

[0026] (5) The hollow fiber membrane obtained is protonated by using acid as solvent during polymer dissolution to control the accumulation of molecular chains during membrane formation and inhibit the formation of intermolecular hydrogen bonds, thus preparing a separation membrane with both high separation coefficient and high permeation flux. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the spinneret structure used in the preparation of the primary membrane and the connecting layer according to the present invention;

[0028] Figure 2 This is a schematic diagram of the primary membrane and connecting layer prepared according to the present invention, as well as the film scraping process;

[0029] Figure 3 This is a cross-sectional electron microscope image of the novel hollow fiber separation membrane prepared in Example 1 of this invention.

[0030] Figure 4This is an electron microscope image of the functional layer of the novel hollow fiber separation membrane prepared in Example 1 of this invention;

[0031] Figure 5 This is an electron microscope image of the inner surface cross-section of the novel hollow fiber separation membrane prepared in Example 1 of this invention;

[0032] Figure 6 This is an electron microscope image of the outer surface of the novel hollow fiber separation membrane prepared in Example 1 of this invention;

[0033] Figure 7 This is an electron microscope image of the inner surface of the novel hollow fiber separation membrane prepared in Example 1 of this invention. Detailed Implementation

[0034] 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.

[0035] As mentioned above, the first aspect of the present invention provides a novel hollow fiber separation membrane, wherein the separation membrane includes a support, a functional layer covering the outer surface of the support, and a connecting layer embedded in the support; the support is a hollow fiber microporous membrane, the connecting layer has a porous structure, the functional layer is made of polybenzimidazole, and the number average molecular weight of the polybenzimidazole is 50,000 to 300,000.

[0036] The inventors of this invention discovered that polybenzimidazole (PBI) is a class of heterocyclic polymers with an imidazole ring in its main chain. These polymers possess excellent chemical stability, thermal stability, hydrolytic stability, and mechanical stability. As a polymer material, PBI exhibits good processability, and PBI membranes are easy to encapsulate with reasonable preparation costs. PBI is particularly suitable for preparing separation membranes required for hydrogen or helium purification. Furthermore, the inventors of this invention, on the one hand, use organic acids and volatile solvents to create a hollow fiber composite membrane whose surface functional layer is composed of protonated polybenzimidazole, resulting in a high separation coefficient; on the other hand, employing high-temperature, high-pressure membrane scraping and high-temperature, low-pressure drying methods promotes solvent evaporation, resulting in a well-dense polybenzimidazole functional layer, preventing defect formation, and achieving better separation performance. In addition, the internal support reinforcement method improves the mechanical properties of the gas separation membrane, which can meet the requirements of high temperature, high pressure and high flow rate gas separation systems for the mechanical properties of membrane fibers, thus expanding the application range of gas separation membranes; and a connecting layer with a microporous structure is obtained through core liquid-induced non-solvent phase separation, which avoids the shedding of functional layers.

[0037] According to the present invention, in a preferred embodiment, the number-average molecular weight of the polybenzimidazole is 50,000 to 287,000, and in a more preferred embodiment, the number-average molecular weight of the polybenzimidazole is 56,000 to 200,000.

[0038] According to the present invention, in a preferred embodiment, the polybenzimidazole comprises one or more of the structural units shown in formulas (A1) to (A8);

[0039] (A1);

[0040] (A2);

[0041] (A3);

[0042] (A4);

[0043] (A5);

[0044] (A6);

[0045] (A7);

[0046] , (A8).

[0047] According to the present invention, in a preferred embodiment, the polybenzimidazole comprises one or more of the structural units shown in formulas (A5) to (A8).

[0048] According to the present invention, the support may be a fiber braided tube or a hollow fiber microporous membrane prepared by means of a polymer material that cannot be dissolved by acid B through methods such as thermally induced phase separation and melt stretching; the hollow fiber microporous membrane is selected from one or more of fiber braided tubes, polypropylene microporous membranes, polyethylene microporous membranes and inorganic microporous membranes, preferably, the hollow fiber microporous membrane is a polypropylene microporous membrane or a polyethylene microporous membrane prepared by thermally induced phase separation.

[0049] According to the present invention, the average thickness of the hollow fiber separation membrane is 50-2000 μm, preferably 150-1000 μm, and more preferably 180-500 μm.

[0050] According to the present invention, the porosity of the support is 30-90%, preferably 50-80%.

[0051] According to the present invention, the average thickness (outer diameter) of the support is 100-2000 μm, preferably 300-1800 μm, and more preferably 500-1500 μm.

[0052] According to the present invention, the average thickness of the functional layer is 100-40000 nm, preferably 200-5000 nm.

[0053] According to the present invention, the average thickness of the connecting layer is 20-2000 μm, preferably 50-1500 μm, and more preferably 200-1000 μm.

[0054] In this invention, it should be noted that the connecting layer has the same cross-sectional diameter as the support body.

[0055] According to the present invention, the connecting layer is obtained by non-solvent-induced phase separation of an acid solution containing polybenzimidazole.

[0056] According to the present invention, the tensile strength of the separation membrane is 10-500 MPa; preferably, the tensile strength of the separation membrane is 50-180 MPa; more preferably, the tensile strength of the separation membrane is 52-155 MPa.

[0057] According to the present invention, at a test pressure of 0.1 MPa and a temperature of 100°C, the flux of pure helium is 3-480 GPU, the flux of pure hydrogen is 3-80 GPU, the flux of nitrogen is 0.01-0.7 GPU, and the flux of methane is 0.01-0.7 GPU; preferably, the flux of pure helium is 3.48-477.5 GPU, the flux of pure hydrogen is 3.03-79.6 GPU, the flux of nitrogen is 0.016-0.68 GPU, and the flux of methane is 0.0135-0.6 GPU.

[0058] According to the present invention, at a test pressure of 0.1 MPa and a temperature of 100°C, the separation coefficient of hydrogen / nitrogen is 110-235, and the separation coefficient of hydrogen / methane is 125-260; preferably, the separation coefficient of hydrogen / nitrogen is 110-234.1, and the separation coefficient of hydrogen / methane is 129.1-256.7.

[0059] According to the present invention, at a test pressure of 0.1 MPa and a temperature of 100°C, the separation coefficient of helium / nitrogen is 140-190, and the separation coefficient of helium / methane is 170-175; preferably, the separation coefficient of helium / nitrogen is 141.4-187.5, and the separation coefficient of helium / methane is 170-173.8.

[0060] A second aspect of the present invention provides a method for preparing a novel hollow fiber separation membrane, wherein the method comprises:

[0061] (1) Polybenzimidazole, acid, optional volatile solvent and optional additive are contacted and mixed to obtain casting solution; the number average molecular weight of the polybenzimidazole is 50,000 to 300,000.

[0062] (2) A spinneret for preparing the primary membrane and the connecting layer is used; a hollow fiber microporous membrane is used as the support;

[0063] (3) The casting liquid is extruded and enters the spinneret. The casting liquid is then scraped onto the support by a scraper. At the same time, the support is stretched from bottom to top through the inside of the spinneret to obtain a nascent film covering the support, and some casting liquid penetrates into the inside of the support.

[0064] (4) The nascent membrane is stretched and heated to form a polybenzimidazole functional layer with a dense structure; and a non-solvent is injected into the support body through a central tube as a core liquid to induce non-solvent-induced phase separation of the portion of the casting liquid that has penetrated into the support body to generate a porous connecting layer; and then the membrane is washed with water to obtain a novel hollow fiber separation membrane.

[0065] According to the present invention, in a preferred embodiment, the number-average molecular weight of the polybenzimidazole is 50,000 to 287,000, and in a more preferred embodiment, the number-average molecular weight of the polybenzimidazole is 56,000 to 200,000.

[0066] According to the present invention, the polybenzimidazole comprises one or more of the structural units shown in formulas (A1) to (A8);

[0067] (A1);

[0068] (A2);

[0069] (A3);

[0070] (A4);

[0071] (A5);

[0072] (A6);

[0073] (A7);

[0074] , (A8).

[0075] According to the present invention, in a preferred embodiment, the polybenzimidazole comprises one or more of the structural units shown in formulas (A5) to (A8).

[0076] According to the present invention, the polybenzimidazole and the support are as described above, and will not be repeated here. Furthermore, in the present invention, the support can be modified before film formation.

[0077] The inventors of this invention discovered that, in a preferred embodiment, the use of an organic acid and a volatile solvent causes the polybenzimidazole to protonate during dissolution, inhibiting the formation of intermolecular hydrogen bonds and increasing the flexibility of the polymer molecular chains. This allows the polymer to pack more tightly during film formation, resulting in a hollow fiber composite membrane with a high separation coefficient. Furthermore, employing high-temperature, high-pressure film scraping and high-temperature, normal-pressure drying promotes solvent evaporation, resulting in a well-dense polybenzimidazole functional layer, preventing defect formation, and achieving better separation performance. Additionally, the use of internal support reinforcement improves the mechanical properties of the gas separation membrane, meeting the requirements of high-temperature, high-pressure, and high-flow-rate gas separation systems for membrane fiber mechanical properties, thus expanding the application range of gas separation membranes. Finally, a microporous connecting layer is obtained through core liquid-induced non-solvent-induced phase separation, preventing the functional layer from detaching.

[0078] According to the present invention, the acid is a monobasic acid; preferably, the acid is selected from one or more of hydrochloric acid, hydrofluoric acid, and methanesulfonic acid; more preferably, the acid is methanesulfonic acid. During the film-forming process, the organic acid induces protonation, inhibits the formation of hydrogen bonds between polymer molecules, reduces polymer rigidity, and allows the polymer molecular chains to be more tightly packed, thereby increasing the separation performance of small molecule gases such as hydrogen and helium.

[0079] According to the present invention, the non-solvent is one or more of water, ethanol and tetrahydrofuran.

[0080] According to the present invention, the volatile solvent is ethanol and / or tetrahydrofuran.

[0081] According to the present invention, the additive is selected from one or more of lithium nitrate, calcium chloride, sodium chloride, potassium chloride, polyethylene glycol and polyethylene oxide; preferably, the additive is selected from lithium nitrate and / or potassium chloride.

[0082] According to the present invention, based on the total weight of the casting solution, the amount of polybenzimidazole is 4-18 wt%, the amount of acid is 77-90 wt%, the amount of volatile solvent is 0-10 wt%, and the amount of additive is 0-5 wt%; preferably, based on the total weight of the casting solution, the amount of polybenzimidazole is 8-15 wt%, the amount of acid is 80-90 wt%, the amount of volatile solvent is 1-5 wt%, and the amount of additive is 1-2 wt%.

[0083] In this invention, it should be noted that the sum of the components of polybenzimidazole, acid, volatile solvent and optional additives is 100wt%.

[0084] According to the present invention, polybenzimidazole A can be added to acid B and simultaneously mixed with a volatile solvent and additives. During the mixing process, the solution can be dissolved by stirring and heating to obtain a casting solution. The mixing conditions include a temperature of 25-160°C and a time of 2-72 hours. Preferably, the temperature is 80-160°C and the time is 12-48 hours. The stirring can be a conventional choice for those skilled in the art and is not particularly limited here. In a preferred case, the stirring rate is 20-500 rpm.

[0085] According to the present invention, a casting solution is scraped onto the surface of a support at a certain temperature and pressure to obtain a nascent film of a certain thickness. The scraping conditions include: a temperature of 100-240°C, preferably 110-180°C; and, in this invention, the pressure is not specifically limited, but preferably 10-2000 kPa, and more preferably 500-1200 kPa. In this invention, during the scraping process, the film thickness (the gap between the scraper and the outer wall of the support) is 10-100 μm.

[0086] According to the present invention, in step (3), the extruded casting liquid is introduced into the spinneret, wherein the casting liquid is in contact with the support inside the spinneret for 1-15 seconds, preferably 1-10 seconds; in the present invention, the pressure is not specifically limited, preferably the pressure is atmospheric pressure to 0.2 MPa, more preferably the pressure is 0.02-0.1 MPa.

[0087] In this invention, Figure 1 This is a schematic diagram of the spinneret structure used in the preparation of the primary membrane and the connecting layer according to the present invention; Figure 2 This is a schematic diagram of the primary membrane and connecting layer prepared according to the present invention, as well as the membrane scraping process.

[0088] from Figure 1 and Figure 2It can be seen that the spinneret structure used in this invention for preparing the nascent membrane includes a support body, a support body positioner, an annular scraper, a base membrane positioner, and a core tube. The base membrane positioner surrounds a cavity formed around the support body, which is used to store casting solution. The cavity has a casting solution inlet and an outlet; preferably, the casting solution outlet is higher than the casting solution inlet. One end of the cavity is connected to the support body positioner to form a closed end, and the other end of the cavity is provided with the annular scraper. The diameter of the annular scraper is smaller than the width of the support body positioner, and the gap formed by the difference can be used to form the nascent membrane. The core tube is built into the support body, forming a core fluid channel inside the support body. Core fluid is injected into the core fluid channel through the core tube, and non-solvent-induced phase separation by the core fluid yields a connecting layer with a microporous structure, preventing the functional layer from detaching.

[0089] In this invention, when using Figure 2 The method for preparing the primary membrane and the connecting layer using the aforementioned apparatus includes:

[0090] First, a support is selected and fixed using a support positioner. Casting solution extruded from a twin-screw extruder or gear pump is injected through the casting solution inlet. An annular doctor blade is used for coating, while the support is simultaneously drawn upwards through the inside of the spinneret. Excess casting solution flows out through the casting solution outlet, and some of it permeates into the support. This process prepares a nascent membrane covering the support. A core tube is embedded inside the support, forming a core liquid channel within it. Core liquid is injected into the core liquid channel through the core tube, and non-solvent-induced phase separation induced by the core liquid yields a connecting layer with a microporous structure, preventing the functional layer from detaching.

[0091] According to the present invention, after the film is scraped, the hollow fiber is drawn and enters a heating device, so that the outer coating of the hollow fiber membrane is evaporated by hot air, ultimately forming a polybenzimidazole functional layer attached to the surface of the support. In this invention, the drawing conditions are not specifically limited, and can be performed on the guide roller at a winding speed of 100-4000 cm / min. The conditions for promoting solvent evaporation with hot air include a temperature of 80-300°C. The conditions for the heat treatment include: the equipment for the heat treatment is not specifically limited, and can be an oven, wherein the temperature is 100-280°C and the time is 2-24 hours; preferably, the temperature is 120-150°C and the time is 5-12 hours.

[0092] In this invention, the method further includes removing residual solvent from the prepared finished membrane by steps such as washing with water.

[0093] A third aspect of the present invention provides a novel hollow fiber separation membrane prepared by the method described above.

[0094] The fourth aspect of the present invention provides a novel hollow fiber separation membrane as described above for separating and purifying helium / nitrogen, helium / methane, hydrogen / nitrogen, or hydrogen / methane.

[0095] The present invention will be described in detail below through embodiments.

[0096] In the following examples and comparative examples:

[0097] Polybenzimidazole was purchased from Shanghai Shengjun Plastics Technology Co., Ltd., and other reagents were purchased from Inokai.

[0098] The test method for permeation rate (per GPU) is as follows: At 20℃ and a pressure difference of 0.1 MPa, the gas flow rate per unit time through a unit membrane area is measured. The separation coefficient α is dimensionless and is used to characterize the selective permeation ability of gas components in the membrane. The separation coefficient is the ratio of the permeation rates of the two gases in the membrane. The test results are shown in Table 3. Where 1 GPU = 10⁻⁶ cm⁻¹ 3 (STP) / (cm 2 ·s·cmHg).

[0099] Example 1

[0100] This embodiment illustrates the novel hollow fiber separation membrane prepared using the method of the present invention.

[0101] (1) Polybenzimidazole A5, ethanol, and hydrochloric acid were added to methanesulfonic acid and stirred thoroughly at 70°C for 24 hours to obtain a mixed solution (casting solution); the mass fraction of which was: polybenzimidazole 10wt%, ethanol 3wt%, hydrochloric acid 3wt%, and methanesulfonic acid 84wt%;

[0102] Polybenzimidazole A5 includes the following structural units:

[0103] (A5);

[0104] The number-average molecular weight of the polybenzimidazole A5 is 56,000.

[0105] (2) The mixture is mixed at 240°C to form a uniform spinning solution. The casting solution extruded by the twin-screw extruder enters the spinneret and is used as follows: Figure 1The spinneret shown has a nylon braided tube as its support. Concentric circular composite spinning technology is used to bring the casting solution into contact with the nylon braided tube inside the spinneret (spinneret cavity height 10cm) for 10 seconds. Subsequently, a ring-shaped doctor blade controls the thickness of the nascent polybenzimidazole membrane to 20μm. Simultaneously, the support is drawn upwards through the interior of the spinneret, resulting in a nascent polybenzimidazole membrane covering the support. Excess casting solution flows out through the casting solution outlet, and some of the casting solution permeates into the support.

[0106] (3) The nascent polybenzimidazole membrane is passed through an air bath of 100cm length and 100℃ and then through the first guide wheel. It is wound at a winding speed of 100cm / min for stretching and heating treatment to form a polybenzimidazole functional layer with a dense structure.

[0107] (4) Ethanol is introduced through the core tube to induce phase separation, which causes the portion of the casting liquid that has seeped into the support to undergo non-solvent-induced phase separation to generate a porous connecting layer; then the solvent in the nascent membrane is completely evaporated in an oven at 110°C, and the residual solvent is removed by water washing and other steps; as a result, a novel hollow fiber separation membrane is prepared.

[0108] In addition, the average thickness of the novel hollow fiber separation membrane is 400 μm; the thickness of the functional layer is 1-2 μm (1000-2000 nm), and the average thickness of the functional layer is 1500 nm. The thickness of the functional layer is detailed below. Figure 4 , Figure 4 This is a cross-sectional electron microscope image of the functional layer of the novel hollow fiber separation membrane prepared in Example 1 of this invention; from Figure 4 It can be seen that: the thickness of the functional layer of the outer PBI film; in addition, it should be noted that not all the areas shown are functional layers, a small part of the surface is a functional layer, with a thickness of only 1-2 μm; the outer diameter of the support is 1500 μm; the connecting layer is embedded in the support and has a thickness of 380 μm (since the connecting layer is embedded and attached to the support, the thickness of the support is generally the same as the thickness of the connecting layer. In Example 1, the connecting layer extends inward a little, therefore, the support is slightly thicker).

[0109] The novel hollow fiber separation membrane prepared has a tensile strength of 60 MPa. At 100℃ and 0.5 MPa test pressure, the pure helium flux is 3.48 GPU, the pure hydrogen flux is 3.03 GPU, and the nitrogen and methane fluxes are 0.016 GPU and 0.0135 GPU, respectively. The separation coefficients of hydrogen / nitrogen and hydrogen / methane reach 189 and 224, respectively.

[0110] in addition, Figure 3 This is a cross-sectional electron microscope image of the novel hollow fiber separation membrane prepared in Example 1 of this invention; from Figure 3 It can be seen that the functional layer is on the outer surface of the membrane, and the connecting layer is embedded in the support and is tightly bonded to the PBI membrane.

[0111] Figure 5 This is an electron microscope image of the inner surface cross-section of the novel hollow fiber separation membrane prepared in Example 1 of this invention; from Figure 5 It can be seen that the support is embedded inside the connecting layer, and the inner surface of the connecting layer has a microporous structure.

[0112] Figure 6 This is an electron microscope image of the outer surface of the novel hollow fiber separation membrane prepared in Example 1 of this invention; from Figure 6 It can be seen that the outer surface has a dense structure.

[0113] Figure 7 This is an electron micrograph of the inner surface of the novel hollow fiber separation membrane prepared in Example 1 of this invention; from Figure 7 It can be seen that the inner surface has a microporous structure.

[0114] Example 2

[0115] This embodiment illustrates the novel hollow fiber separation membrane prepared using the method of the present invention.

[0116] (1) Polybenzimidazole A6, ethanol, tetrahydrofuran and methanesulfonic acid were mixed and stirred thoroughly at 80°C and 0.5 MPa for 24 hours to obtain a mixed solution (casting solution); the mass fraction of which was: polybenzimidazole 10wt%, ethanol 2wt%, tetrahydrofuran 2wt%, methanesulfonic acid 86wt%;

[0117] The polybenzimidazole A6 comprises the following structural units:

[0118] (A6);

[0119] The number-average molecular weight of the polybenzimidazole A6 is 72,000.

[0120] (2) The mixture is mixed at 180°C to form a uniform spinning solution. The casting solution, extruded by a gear pump, enters the spinneret and is used as follows: Figure 1 The spinneret shown has a support made of a polypropylene microporous membrane with a porosity of 67%. Concentric circular composite spinning technology is used to bring the casting solution into contact with the polypropylene microporous membrane (prepared by thermally induced phase separation) inside the spinneret (spinneret cavity height 10 cm) for 10 seconds. Subsequently, a ring-shaped doctor blade controls the thickness of the nascent polybenzimidazole membrane to 20 μm. Simultaneously, the support is drawn upwards through the interior of the spinneret, resulting in a nascent polybenzimidazole membrane covering the support. Excess casting solution flows out through the casting solution outlet, and some of the casting solution permeates into the support.

[0121] (3) The nascent polybenzimidazole membrane is passed through an air bath of 200cm length and 100°C and then through the first guide wheel. It is wound at a winding speed of 100cm / min for stretching and heating treatment to form a polybenzimidazole functional layer with a dense structure.

[0122] (4) Ethanol is introduced through the core tube to induce phase separation, causing the portion of the casting liquid that has seeped into the support to undergo non-solvent ethanol-induced phase separation to generate a porous connecting layer; then the solvent in the nascent membrane is completely evaporated in an oven at 100°C, and the residual solvent is removed by water washing and other steps; as a result, a novel hollow fiber separation membrane is prepared.

[0123] In addition, the average thickness of the novel hollow fiber separation membrane is 200 μm; the thickness of the membrane portion of the functional layer is 2000 nm; the outer diameter of the support is 1000 μm; and the connecting layer is embedded in the support with a thickness of approximately 200 μm.

[0124] The novel hollow fiber separation membrane prepared has a tensile strength of 155 MPa. At 100℃ and 0.5 MPa test pressure, the pure helium flux is 7.5 GPU, the pure hydrogen flux is 6.8 GPU, and the nitrogen and methane fluxes are 0.04 GPU and 0.04 GPU, respectively. The separation coefficients of helium / nitrogen and helium / methane are 187.5 and 170, respectively.

[0125] Example 3

[0126] This embodiment illustrates the novel hollow fiber separation membrane prepared using the method of the present invention.

[0127] (1) Polybenzimidazole A4 and methanesulfonic acid were mixed and stirred thoroughly at 150°C and 1.0 MPa for 24 hours to obtain a mixed solution (casting solution); the mass fraction of which was: polybenzimidazole 18 wt% and methanesulfonic acid 82 wt%;

[0128] The polybenzimidazole A4 comprises the following structural units:

[0129] (A4);

[0130] The number-average molecular weight of the polybenzimidazole A4 is 68,000.

[0131] (2) The mixture is heated to 100°C to form a uniform spinning solution. The casting solution, extruded by a gear pump, enters the spinneret. Then, the solution is used as follows: Figure 1The spinneret shown has a support made of a polypropylene microporous membrane with a porosity of 67%. Concentric circular composite spinning technology is used to bring the casting solution into contact with the polypropylene microporous membrane (prepared by thermally induced phase separation) inside the spinneret (spinneret cavity height 10cm). The contact time between the casting solution and the braided tube is 2 seconds. The thickness of the nascent polybenzimidazole membrane is controlled to 10μm by a ring-shaped doctor blade. Simultaneously, the support is drawn upwards through the interior of the spinneret to obtain a nascent polybenzimidazole membrane covering the support. Excess casting solution flows out through the casting solution outlet, and some of the casting solution permeates into the support.

[0132] (3) The nascent polybenzimidazole membrane is subjected to an air bath of 200cm length and 150°C, and then passed through the first guide wheel. It is then wound at a winding speed of 500cm / min for stretching and heat treatment to form a polybenzimidazole functional layer with a dense structure.

[0133] (4) Water is introduced through the core tube to induce phase separation, causing the portion of the casting liquid that has seeped into the support body to undergo non-solvent-induced phase separation to generate a porous connecting layer; then the solvent in the nascent membrane is completely evaporated in an oven at 120°C, and the residual solvent is removed by water washing and other steps; as a result, a novel hollow fiber separation membrane is prepared.

[0134] In addition, the average thickness of the novel hollow fiber separation membrane is 500 μm; the thickness of the membrane portion of the functional layer is 5000 nm (thick but not dense, thus resulting in a low separation coefficient and a high flux); the outer diameter of the support is 1390 μm; and the connecting layer is embedded in the support with a thickness of approximately 450 μm.

[0135] The novel hollow fiber separation membrane prepared has a tensile strength of 66 MPa. At 100℃ and 0.5 MPa test pressure, the pure helium flux is 33.1 GPU, the pure hydrogen flux is 30.5 GPU, and the nitrogen and methane fluxes are 0.21 GPU and 0.20 GPU, respectively. The separation coefficients of hydrogen / nitrogen and hydrogen / methane are 145.2 and 152.5, respectively.

[0136] Example 4

[0137] This embodiment illustrates the novel hollow fiber separation membrane prepared using the method of the present invention.

[0138] (1) Polybenzimidazole A8, ethanol and methanesulfonic acid are mixed and stirred thoroughly at 60°C and normal pressure for 24 hours to achieve uniform mixing; wherein the mass fraction is: polybenzimidazole 4wt%, ethanol 10wt%, methanesulfonic acid 86wt%, to prepare a mixed solution (casting solution); the polybenzimidazole A8 includes the following structural units:

[0139] (A8);

[0140] The number-average molecular weight of the polybenzimidazole A8 is 97,000.

[0141] (2) The mixture is heated to 80°C to form a uniform spinning solution. The casting solution extruded by this pump enters the spinneret and is used as follows: Figure 1 The spinneret shown has a polypropylene microporous membrane support with a porosity of 67%. Concentric circular composite spinning technology is used to bring the casting solution into contact with the polypropylene microporous membrane (prepared by thermally induced phase separation) inside the spinneret (spinneret cavity height 10cm). The contact time between the casting solution and the braided tube is 10s. The thickness of the nascent polybenzimidazole membrane is controlled to 100μm by a ring-shaped doctor blade. Simultaneously, the support is drawn upwards through the interior of the spinneret to obtain a nascent polybenzimidazole membrane covering the support. Excess casting solution flows out through the casting solution outlet, and some of the casting solution permeates into the support.

[0142] (3) The nascent polybenzimidazole membrane is passed through an air bath of 200cm length and 150°C and then through the first guide wheel. It is then wound at a winding speed of 100cm / min for stretching and heating treatment to form a polybenzimidazole functional layer with a dense structure.

[0143] (4) Ethanol is introduced through the core tube to induce phase separation, which causes the portion of the casting liquid that has seeped into the support to undergo non-solvent-induced phase separation to generate a porous connecting layer; then the solvent in the nascent membrane is completely evaporated in an oven at 110°C, and the residual solvent is removed by water washing and other steps; as a result, a novel hollow fiber separation membrane is prepared.

[0144] In addition, the average thickness of the novel hollow fiber separation membrane is 300 μm; the thickness of the membrane portion of the functional layer is 500 nm; the outer diameter of the support is 780 μm; and the connecting layer is embedded in the support with a thickness of 1000 nm (1 μm).

[0145] The novel hollow fiber separation membrane prepared has a tensile strength of 61 MPa. At 100℃ and 0.5 MPa test pressure, the pure helium flux is 477.5 GPU, the pure hydrogen flux is 65.5 GPU, and the nitrogen and methane fluxes are 0.68 GPU and 0.60 GPU, respectively. The separation coefficients of hydrogen / nitrogen and hydrogen / methane are 110 and 129.1, respectively (low concentration, although there is easy volatility and dissolution, the functional layer is still relatively thin, resulting in low separation coefficient and high flux).

[0146] Example 5

[0147] This embodiment illustrates the novel hollow fiber separation membrane prepared using the method of the present invention.

[0148] (1) Polybenzimidazole A7, ethanol and methanesulfonic acid were mixed and stirred thoroughly at 60°C and normal pressure for 72 hours to obtain a mixed solution (casting solution); wherein the mass fraction was: polybenzimidazole 4wt%, ethanol 1wt%, methanesulfonic acid 96wt%;

[0149] The polybenzimidazole A7 comprises the following structural units:

[0150] (A7);

[0151] The number-average molecular weight of the polybenzimidazole A7 is 287,000.

[0152] (2) The mixture is heated to 80°C to form a uniform spinning solution, which is then extruded using a gear pump and used as follows: Figure 1 The spinneret shown has a polypropylene microporous membrane support with a porosity of 67%. Concentric circular composite spinning technology is used to bring the casting solution into contact with the polypropylene microporous membrane (prepared by thermally induced phase separation) inside the spinneret (spinneret cavity height 10cm). The contact time between the casting solution and the braided tube is 10s. The thickness of the nascent polybenzimidazole membrane is controlled to 100μm by a ring-shaped doctor blade. Simultaneously, the support is drawn upwards through the interior of the spinneret to obtain a nascent polybenzimidazole membrane covering the support. Excess casting solution flows out through the casting solution outlet, and some of the casting solution permeates into the support.

[0153] (3) The nascent polybenzimidazole membrane is passed through an air bath of 200cm length and 150°C and then through the first guide wheel. It is then wound at a winding speed of 100cm / min for stretching and heating treatment to form a polybenzimidazole functional layer with a dense structure.

[0154] (4) Ethanol is introduced through the core tube to induce phase separation, which causes the portion of the casting liquid that has seeped into the support to undergo non-solvent-induced phase separation to generate a porous connecting layer; then the solvent in the nascent membrane is completely evaporated in an oven at 110°C, and the residual solvent is removed by water washing and other steps; as a result, a novel hollow fiber separation membrane is prepared.

[0155] In addition, the average thickness of the novel hollow fiber separation membrane is 300 μm; the average thickness of the functional layer is 300 nm; the outer diameter of the support is 760 μm; and the connecting layer is embedded in the support with a thickness of 280 μm.

[0156] The novel hollow fiber separation membrane prepared has a tensile strength of 63 MPa. At 100℃ and 0.5 MPa test pressure, the pure helium flux is 88.9 GPU, the pure hydrogen flux is 76.1 GPU, and the nitrogen and methane fluxes are 0.66 GPU and 0.52 GPU, respectively. The separation coefficients of hydrogen / nitrogen and hydrogen / methane are 134.7 and 170.9, respectively.

[0157] Example 6

[0158] This embodiment illustrates the novel hollow fiber separation membrane prepared using the method of the present invention.

[0159] (1) Polybenzimidazole A1, tetrahydrofuran and methanesulfonic acid were mixed and stirred thoroughly at 60°C and normal pressure for 72 h to obtain a mixed solution (casting solution); wherein the mass fraction was: polybenzimidazole 8wt%, tetrahydrofuran 2wt%, methanesulfonic acid 90wt%;

[0160] The polybenzimidazole A1 comprises the following structural units:

[0161] (A1);

[0162] The number-average molecular weight of the polybenzimidazole A1 is 87,000.

[0163] (2) The mixture is heated to 80°C to form a uniform spinning solution. The casting solution, extruded by a gear pump, enters the spinneret. Then, the solution is used as follows: Figure 1 The spinneret shown has a support made of a 72% porosity polyethylene hydrophobic microporous membrane. Concentric circular composite spinning technology is used to bring the casting solution into contact with the polyethylene hydrophobic microporous membrane (obtained by melt spinning and stretching) inside the spinneret (spinneret cavity height 10cm) for 10 seconds. The thickness of the nascent polybenzimidazole membrane is controlled to 80μm by a ring-shaped doctor blade. Simultaneously, the support is stretched upwards through the interior of the spinneret, resulting in a nascent polybenzimidazole membrane covering the support. Excess casting solution flows out through the casting solution outlet, and some of the casting solution permeates into the support.

[0164] (3) The nascent polybenzimidazole membrane is passed through an air bath of 200cm length and 150°C and then through the first guide wheel. It is then wound at a winding speed of 100cm / min for stretching and heating treatment to form a polybenzimidazole functional layer with a dense structure.

[0165] (4) Tetrahydrofuran is introduced through the core tube to induce phase separation, causing the portion of the casting solution that has permeated into the support to undergo non-solvent tetrahydrofuran-induced phase separation to generate a porous connecting layer; then the solvent in the nascent membrane is completely evaporated in an oven at 110°C, and the residual solvent is removed by water washing and other steps; as a result, a novel hollow fiber separation membrane is prepared.

[0166] In addition, the average thickness of the novel hollow fiber separation membrane is 180 μm; the thickness of the functional layer is 500 nm; the outer diameter of the support is 500 μm; and the connecting layer is embedded in the support with a thickness of approximately 180-190 μm (average thickness is 185 μm).

[0167] The novel hollow fiber separation membrane prepared has a tensile strength of 52 MPa. At 100℃ and 0.5 MPa test pressure, the pure helium flux is 82.2 GPU, the pure hydrogen flux is 79.6 GPU, and the nitrogen and methane fluxes are 0.34 GPU and 0.31 GPU, respectively. The separation coefficients of hydrogen / nitrogen and hydrogen / methane are 234.1 and 256.7, respectively.

[0168] Example 7

[0169] This embodiment illustrates the novel hollow fiber separation membrane prepared using the method of the present invention.

[0170] (1) Polybenzimidazole A7, tetrahydrofuran and methanesulfonic acid were mixed and stirred thoroughly at 60°C and normal pressure for 24 hours to obtain a mixed solution (casting solution); wherein the mass fraction was: polybenzimidazole 8wt%, tetrahydrofuran 2wt%, methanesulfonic acid 90wt%;

[0171] The polybenzimidazole A7 comprises the following structural units:

[0172] (A7);

[0173] The number-average molecular weight of the polybenzimidazole A7 is 126,000.

[0174] (2) The mixture is heated to 80°C to form a uniform spinning solution. The casting solution, extruded by a gear pump, enters the spinneret. Then, the solution is used as follows: Figure 1The spinneret shown has a support made of a 72% porosity polyethylene hydrophobic microporous membrane. Concentric circular composite spinning technology is used to bring the casting solution into contact with the polyethylene hydrophobic microporous membrane (obtained by melt spinning and stretching) inside the spinneret (spinneret cavity height 10cm) for 10 seconds. The thickness of the nascent polybenzimidazole membrane is controlled to 80μm by a ring-shaped doctor blade. Simultaneously, the support is stretched upwards through the interior of the spinneret, resulting in a nascent polybenzimidazole membrane covering the support. Excess casting solution flows out through the casting solution outlet, and some of the casting solution permeates into the support.

[0175] (3) The nascent polybenzimidazole membrane is passed through an air bath of 200cm length and 150°C and then through the first guide wheel. It is then wound at a winding speed of 100cm / min for stretching and heating treatment to form a polybenzimidazole functional layer with a dense structure.

[0176] (4) Tetrahydrofuran is introduced through the core tube to induce phase separation, causing the portion of the casting solution that has permeated into the support to undergo non-solvent tetrahydrofuran-induced phase separation to generate a porous connecting layer; then the solvent in the nascent membrane is completely evaporated in an oven at 110°C, and the residual solvent is removed by water washing and other steps; as a result, a novel hollow fiber separation membrane is prepared.

[0177] In addition, the average thickness of the novel hollow fiber separation membrane is 300 μm; the thickness of the functional layer is 500 nm; the outer diameter of the support is 700 μm; and the connecting layer is embedded in the support with a thickness of 310 μm.

[0178] The novel hollow fiber separation membrane prepared has a tensile strength of 52 MPa. At 100℃ and 0.5 MPa test pressure, the pure helium flux is 22.6 GPU, the pure hydrogen flux is 22.1 GPU, and the nitrogen and methane fluxes are 0.16 GPU and 0.13 GPU, respectively. The separation coefficients of helium / nitrogen and helium / methane are 141.4 and 173.8, respectively.

[0179] Comparative Example 1

[0180] (1) Polybenzimidazole A1 and methanesulfonic acid were mixed and stirred thoroughly at 150°C and 1.0 MPa for 24 hours to obtain a uniform mixture (casting solution); the mass fraction of which was: polybenzimidazole 10 wt%, methanesulfonic acid 90 wt%.

[0181] The polybenzimidazole A1 comprises the following structural units:

[0182] (A1);

[0183] The number-average molecular weight of the polybenzimidazole A1 is 68,000.

[0184] (2) The mixture is mixed at 140°C to form a uniform spinning solution. The casting solution, extruded by a gear pump, enters the spinneret and is used as follows: Figure 1 The spinneret shown employs concentric circle composite spinning technology, allowing the casting solution to contact the nylon braided tube inside the spinneret (spinneret cavity height 10cm). Spinning is carried out at 140℃, with the casting solution contacting the braided tube for 2s. The thickness of the nascent polybenzimidazole film is controlled to 30μm by an annular doctor blade. After passing through a 200cm long air bath at 150℃, the film passes through the first guide wheel and is wound at a winding speed of 500cm / min.

[0185] (3) The solvent in the nascent polybenzimidazole membrane (nascent membrane) is completely evaporated in a 200℃ oven, and the residual solvent is removed by water washing, ethanol cleaning and other steps to form the finished membrane - a new type of hollow fiber separation membrane.

[0186] The resulting novel hollow fiber separation membrane had an average thickness of 200 μm; the functional layer had a thickness of 800 nm; the outer diameter of the support was 600 μm; the connecting layer was not embedded in the support, and the functional layer was only attached to the outer surface of the support with a thickness of 2-5 μm. Due to the lack of a connecting layer, the functional layer had poor adhesion to the support, making it prone to detachment and reducing its lifespan. The functional layer was damaged when the internal pressure exceeded 0.04 MPa; under external pressure operation, after multiple pressure changes, the lifespan was only 2000-5000 hours.

[0187] In addition, the novel hollow fiber separation membrane has a tensile strength of 166 MPa. At 100°C and a test pressure of 0.5 MPa, the pure helium flux is 12.8 GPU, the pure hydrogen flux is 11.6 GPU, and the nitrogen and methane fluxes are 0.11 GPU and 0.10 GPU, respectively. The separation coefficients of hydrogen / nitrogen and hydrogen / methane are 105 and 116, respectively.

[0188] Comparative Example 2

[0189] (1) Polybenzimidazole A7 and methanesulfonic acid were mixed and stirred thoroughly at 150°C and 1.0 MPa for 24 hours to obtain a mixed solution (casting solution); the mass fraction of which was: polybenzimidazole 10 wt%, methanesulfonic acid 90 wt%;

[0190] The polybenzimidazole A7 comprises the following structural units:

[0191] (A7);

[0192] The number-average molecular weight of the polybenzimidazole A7 is 12.6.

[0193] (2) The mixed liquid is extruded through a gear pump and then processed using a method such as... Figure 1 The spinneret shown employs concentric circular composite spinning technology, allowing the casting solution to contact the nylon braided tube inside the spinneret (spinneret cavity height 10cm). Spinning is performed at 140℃, with the casting solution contacting the braided tube for 2s. The thickness of the nascent polybenzimidazole membrane is controlled to 30μm by a ring-shaped doctor blade. After a length of 200cm, the membrane enters a pure water coagulation bath and is wound at a winding speed of 5cm / min.

[0194] (3) Then, the solvent in the nascent membrane is transferred to the water in pure water, and the residual solvent is removed by water washing, ethanol cleaning and other steps to form the finished membrane - a new type of hollow fiber separation membrane.

[0195] The resulting novel hollow fiber separation membrane had an average thickness of 600 μm; the functional layer had a thickness of 500 nm; and the outer diameter of the support was 1400 μm. The connecting layer was not embedded within the support, thus failing to form a connecting layer. The functional layer was only attached to the outer surface of the support, with a thickness of 3-10 μm. Due to the lack of a connecting layer, the functional layer had poor adhesion to the support, making it prone to detachment and reducing its lifespan. The functional layer was damaged when the internal pressure exceeded 0.05 MPa.

[0196] In addition, the novel hollow fiber separation membrane has a tensile strength of 166 MPa. At 100°C and a test pressure of 0.5 MPa, the pure helium flux is 28.5 GPU, the pure hydrogen flux is 27.6 GPU, and the nitrogen and methane fluxes are 0.33 GPU and 0.27 GPU, respectively. The separation coefficients of hydrogen / nitrogen and hydrogen / methane are 83.7 and 102.2, respectively.

[0197] Comparative Example 3

[0198] (1) Polybenzimidazole A7 and N-methylpyrrolidone (NMP) were mixed and stirred thoroughly at 50°C and normal pressure for 24 hours to obtain a mixed solution (casting solution); wherein the mass fraction was: polybenzimidazole 10wt%, NMP 90wt%;

[0199] The polybenzimidazole A7 comprises the following structural units:

[0200] (A7);

[0201] The number-average molecular weight of the polybenzimidazole A7 is 12.6.

[0202] (2) The mixed liquid is extruded through a gear pump and then processed using a method such as... Figure 1The spinneret shown employs concentric circular composite spinning technology, allowing the casting solution to contact the nylon braided tube inside the spinneret (spinneret cavity height 10cm). Spinning is performed at 60℃, with the casting solution contacting the braided tube for 2s. The thickness of the nascent polybenzimidazole membrane is controlled to 30μm by a ring-shaped doctor blade. After a length of 200cm, the membrane enters a pure water coagulation bath and is wound at a winding speed of 5cm / min.

[0203] (3) Then, the solvent in the nascent membrane is transferred into pure water to form the finished membrane. The residual solvent is then removed by washing with water and ethanol.

[0204] The resulting novel hollow fiber separation membrane had an average thickness of 150 μm; a functional layer thickness of 200 nm; and an outer diameter of 500 μm for the support. The connecting layer was not embedded within the support, and the functional layer was only attached to the outer surface of the support, with a thickness of 2-5 μm. Due to the lack of a connecting layer, the functional layer had poor adhesion to the support, making it prone to detachment and reducing its lifespan. The functional layer was damaged when the internal pressure exceeded 0.1 MPa.

[0205] In addition, the novel hollow fiber separation membrane has a tensile strength of 165 MPa. At 100°C and 0.5 MPa test pressure, the pure helium flux is 107 GPU, the pure hydrogen flux is 89.5 GPU, and the nitrogen and methane fluxes are 12.9 GPU and 11.4 GPU, respectively. The hydrogen / nitrogen and hydrogen / methane separation coefficients are 6.94 and 7.85, respectively.

[0206] 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 separation membrane, characterized in that, The separation membrane includes a support, a functional layer covering the outer surface of the support, and a connecting layer embedded in the support; the support is a hollow fiber microporous membrane, the connecting layer has a porous structure, the connecting layer is obtained by non-solvent-induced phase separation of an acid solution containing polybenzimidazole, the functional layer is made of polybenzimidazole, and the number average molecular weight of the polybenzimidazole is 50,000-300,000.

2. The separation membrane according to claim 1, wherein, The number-average molecular weight of the polybenzimidazole is 50,000 to 287,000.

3. The separation membrane according to claim 1 or 2, wherein, The polybenzimidazole comprises one or more of the structural units shown in formulas (A1) to (A8); ，（A1）； ，（A2）； ，（A3）； ，（A4）； ，（A5）； ，（A6）； ，（A7）； ，（A8）。 4. The separation membrane according to claim 3, wherein, The polybenzimidazole comprises one or more of the structural units shown in formulas (A5) to (A8); ，（A5）； ，（A6）； ，（A7）； ，（A8）。 5. The separation membrane according to claim 1, wherein, The hollow fiber microporous membrane is selected from one or more of the following: fiber braided tube, polypropylene microporous membrane, polyethylene microporous membrane, and inorganic microporous membrane. And / or, the average thickness of the hollow fiber separation membrane is 50-2000 μm; And / or, the average thickness of the support is 100-2000 μm; And / or, the average thickness of the functional layer is 100-40000 nm; And / or, the average thickness of the connecting layer is 20-2000 μm; And / or, the tensile strength of the separation membrane is 10-500 MPa; And / or, the separation membrane has a hydrogen / nitrogen separation coefficient of 110-235 and a hydrogen / methane separation coefficient of 125-260 at 100°C and 0.5MPa test pressure. And / or, the separation membrane has a helium / nitrogen separation coefficient of 140-190 and a helium / methane separation coefficient of 170-175 at 100°C and 0.5MPa test pressure.

6. A method for preparing a hollow fiber separation membrane, characterized in that, The method includes: (1) Polybenzimidazole, acid, volatile solvent and additive are mixed in contact to obtain a casting solution; the number average molecular weight of the polybenzimidazole is 50,000-300,000; wherein the acid is a monobasic acid; and based on the total weight of the casting solution, the amount of polybenzimidazole is 4-18 wt%, the amount of acid is 77-90 wt%, the amount of volatile solvent is 0-10 wt%, and the amount of additive is 0-5 wt%; (2) A spinneret for preparing the primary membrane and the connecting layer is used; a hollow fiber microporous membrane is used as the support; (3) The casting liquid is extruded and enters the spinneret. The casting liquid is then scraped onto the support by a scraper. At the same time, the support is stretched from bottom to top through the inside of the spinneret to obtain a nascent film covering the support, and some casting liquid penetrates into the inside of the support. (4) The nascent membrane is stretched and heated to form a polybenzimidazole functional layer with a dense structure; and a non-solvent is injected into the support body through a central tube as a core liquid to induce non-solvent-induced phase separation of the portion of the casting liquid that has penetrated into the support body to generate a porous connecting layer; and then the membrane is washed with water to obtain a hollow fiber separation membrane.

7. The method according to claim 6, wherein, The number-average molecular weight of the polybenzimidazole is 50,000 to 287,000.

8. The method according to claim 6 or 7, wherein, The polybenzimidazole comprises one or more of the structural units shown in formulas (A1) to (A8); ，（A1）； ，（A2）； ，（A3）； ，（A4）； ，（A5）； ，（A6）； ，（A7）； ，（A8）。 9. The method according to claim 8, wherein, The polybenzimidazole comprises one or more of the structural units shown in formulas (A5) to (A8); ，（A5）； ，（A6）； ，（A7）； ，（A8）。 10. The method according to claim 6, wherein, The hollow fiber microporous membrane is selected from one or more of the following: fiber braided tube, polypropylene microporous membrane, polyethylene microporous membrane, and inorganic microporous membrane. And / or, the volatile solvent is ethanol and / or tetrahydrofuran; And / or, the additive is selected from one or more of lithium nitrate, calcium chloride, sodium chloride, potassium chloride, polyethylene glycol, and polyethylene oxide; And / or, the non-solvent is one or more of water, ethanol and tetrahydrofuran.

11. The method according to claim 6, wherein, In step (1), the mixing conditions include: a temperature of 25-160°C and a time of 2-72 hours; And / or, the conditions for the scraping treatment include: a temperature of 100-240°C; And / or, the conditions for the heat treatment include: a temperature of 100-280°C; And / or, in step (3), the extruded casting liquid is introduced into the spinneret, wherein the casting liquid is in contact with the support inside the spinneret for 1-15 seconds.

12. The method according to claim 6, wherein, The spinneret used for preparing the primary membrane and connecting layer includes a support body, a support body positioner, an annular scraper, a base membrane positioner, and a core tube. The base film positioner surrounds the cavity formed by the support body; the cavity is used to store casting liquid, and the cavity is provided with a casting liquid inlet and a casting liquid outlet; one end of the cavity is connected to the support body positioner to form a closed end, and the other end of the cavity is provided with the annular scraper, the diameter of the annular scraper being smaller than the width of the support body positioner; The core tube is embedded inside the support.

13. A hollow fiber separation membrane prepared by the method according to any one of claims 6-12.

14. The use of a hollow fiber separation membrane according to any one of claims 1-5 and 13 in the separation and purification of helium / nitrogen, helium / methane, hydrogen / nitrogen, or hydrogen / methane.

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