Hollow fiber seperation membrane, preparation method therefor and application thereof

Abstract

The present invention relates to the technical field of membrane separation, and discloses a hollow fiber separation membrane, a preparation method therefor and an application thereof. The hollow fiber separation membrane comprises a supporting body, a functional layer and a connecting layer between the supporting body and the functional layer, wherein at least part of the connecting layer is embedded into the supporting body. The hollow fiber separation membrane has a high separation coefficient and good mechanical properties.

Description

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

[0001] The present invention relates to the field of membrane technology, and in particular to a novel hollow fiber separation membrane, a preparation method thereof, and applications thereof. Background Art

[0002] Helium and hydrogen are gases with relatively small molecular weights and are both very important industrial gases.

[0003] Helium is primarily produced by purifying associated gas from natural gas and shale gas extraction. Helium extraction processes from natural gas and shale gas are categorized as cryogenic or non-cryogenic. Cryogenic processes are currently a common method used in industrial production. Industrial processes with temperatures below -100°C are generally classified as cryogenic processes. Natural gas helium extraction and helium liquefaction are typical cryogenic processes with the lowest refrigeration separation temperatures within natural gas cryogenic processing. Cryogenic helium extraction processes are energy-intensive and require complex equipment. Membrane separation helium purification and refining technology avoids various phase transitions and violent chemical reactions, resulting in low energy consumption, compact equipment, and high safety.

[0004] Hydrogen is a clean energy carrier and a secondary energy source. Hydrogen produced from fossil fuels contains gases such as N2, CO, CH4, and CO2, which require separation and purification. With the growing global demand for clean, efficient energy, the production and refining of hydrogen are gaining increasing attention.

[0005] To meet the demand for helium and hydrogen, there is an urgent need to develop efficient, green, safe, and reliable methods for purifying helium and hydrogen. Membrane separation technology is in particularly urgent need of core membrane materials, especially high-end membrane materials.

[0006] CN113318609A discloses a method for manufacturing a rigid network microporous hydrogen separation membrane with high permeability and selectivity. However, the membrane disclosed in this application has limited selectivity for hydrogen and cannot produce high-purity hydrogen or helium products.

[0007] CN112142980B discloses a hyperbranched polybenzimidazole-polysiloxane block copolymer, its preparation method, and applications. The block copolymer combines the soft segment of PDMS with the hard segment of HBPBI, and the hydrophobic segment of PDMS with the hydrophilic segment of HBPBI, forming a soft-hard, hydrophilic-hydrophobic phase separation structure. This phase separation of the two segments creates a proton transport channel, and the hyperbranched structure of HBPBI can accommodate more phosphoric acid, ultimately achieving high proton conductivity. However, the material's strength and elongation at break are insufficient, making it unsuitable for use in high-pressure gas separation membranes.

[0008] US20160375410A1 discloses a method for preparing a PBI asymmetric hollow fiber membrane and its application. This patent utilizes a non-solvent-induced phase separation technique to prepare the membrane, achieving a flux of 108 GPU at 250°C, an H2 / CO2 separation factor of 23.7, and an H2 / N2 separation factor of 129. However, the membrane is prone to defects during the phase inversion process, significantly affecting selectivity and failing to achieve the true separation effect of PBI.

[0009] Therefore, it is of great significance to develop membrane materials with dense functional layers, easy preparation, and the ability to exhibit high separation effects of PBI.

[0010] Summary of the Invention

[0011] The present invention aims to overcome the problems of prior art hollow fiber membranes prepared by non-solvent-induced phase separation, such as the tendency for surface defects to occur, insufficient material strength and elongation at break, and the inability to produce high-pressure gas separation membranes. The present invention provides a novel hollow fiber separation membrane, a preparation method, and applications thereof. The hollow fiber separation membranes of the present invention exhibit a high separation coefficient and excellent mechanical properties.

[0012] In order to achieve the above-mentioned purpose, one aspect of the present application provides a hollow fiber separation membrane, characterized in that the separation membrane includes a support body, a functional layer and a connecting layer located between the support body and the functional layer, wherein at least a portion of the connecting layer is embedded in the support body.

[0013] According to some embodiments, in the hollow fiber separation membrane of the present application, the connecting layer and the functional layer comprise the same polymer; preferably, the connecting layer and the functional layer comprise the same polymer and the connecting layer and the functional layer are formed by the same casting solution; more preferably, the connecting layer and the functional layer comprise the same polymer, the connecting layer and the functional layer are formed by the same casting solution, and the connecting layer and the functional layer are formed by non-solvent induced phase separation and thermally induced phase separation, respectively. According to some embodiments, the connecting layer has a porous structure (porous). According to some embodiments, the connecting layer is porous and the functional layer is dense.

[0014] On the other hand, the present invention provides a hollow fiber separation membrane, wherein the separation membrane includes a support body, a functional layer attached to 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.

[0015] One aspect of the present application provides a method for preparing a hollow fiber separation membrane, characterized in that the method comprises:

[0016] (1) preparing a casting solution containing a polymer;

[0017] (2) coating the casting solution on a support, wherein a portion of the casting solution penetrates into the support to obtain a primary film coated on the support;

[0018] (3) heating the primary film to form a functional layer; and

[0019] (4) injecting a core liquid into the support body to cause the casting liquid that penetrates into the support body to undergo non-solvent induced phase separation to generate a connecting layer.

[0020] Optionally, the method for preparing the hollow fiber separation membrane of the present invention further comprises heating after forming the connecting layer to remove substantially all of the solvent.

[0021] Another aspect of the present invention provides a method for preparing a hollow fiber separation membrane, wherein the method comprises:

[0022] (1) mixing polybenzimidazole, an acid (solvent), an optional volatile solvent, and an optional additive to obtain a casting solution; wherein the number average molecular weight of the polybenzimidazole is 50,000 to 300,000;

[0023] (2) extruding the casting liquid, the extruded casting liquid enters a spinneret, and using a scraper to scrape the casting liquid onto a support, while the support is pulled upward through the interior of the spinneret to obtain a primary film attached to the support, and a portion of the casting liquid penetrates into the support;

[0024] (3) The primary membrane is subjected to a heat treatment to form a polybenzimidazole functional layer with a dense structure; and a non-solvent is injected into the support body through the core tube as a core liquid, so that the portion of the casting liquid infiltrated into the support body undergoes non-solvent-induced phase separation to form a connecting layer with a porous structure; and then the membrane is fully dried to obtain a hollow fiber separation membrane.

[0025] One aspect of the present invention provides a hollow fiber separation membrane prepared by the aforementioned method.

[0026] Another aspect of the present invention provides use of the hollow fiber separation membrane of the present invention in separating and purifying helium / nitrogen, helium / methane, hydrogen / nitrogen, or hydrogen / methane.

[0027] Another aspect of the present invention provides a method for purifying helium from a gas containing helium, the method comprising performing membrane separation using the hollow fiber separation membrane of the present application or the hollow fiber separation membrane prepared by the method of the present application.

[0028] Through the above technical solution, the present invention can provide the following beneficial effects:

[0029] (1) preparing an outer functional layer with separation performance by achieving phase transformation of polybenzimidazole material through volatilization of the solvent in the coating layer;

[0030] (2) The use of 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 the membrane fibers, thereby expanding the application range of the gas separation membrane;

[0031] (3) The casting liquid is allowed to penetrate into the support, and the core liquid induces non-solvent phase separation to obtain a connecting layer with a porous structure, thereby preventing the functional layer from falling off;

[0032] (4) During the spinning process, the thickness of the external functional layer can be controlled by the method described in the present invention.

[0033] When polybenzimidazole is used as the polymer for preparing the casting solution, the polybenzimidazole is dissolved in an acid and, optionally, a volatile solvent. The resulting hollow fiber membrane uses the acid as the solvent, protonating the polymer during dissolution. This controls the accumulation of molecular chains during membrane formation and inhibits the formation of intermolecular hydrogen bonds, resulting in a separation membrane with both a high separation coefficient and a high permeate flux. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a schematic structural diagram of a spinneret used in preparing a primary membrane and a connecting layer according to the present invention;

[0035] FIG2 is a schematic diagram of a process for preparing a primary membrane and a connecting layer using the spinneret of FIG1 according to the present invention;

[0036] FIG3 is an electron micrograph of a cross-section of a hollow fiber separation membrane prepared in Example 1 of the present invention;

[0037] FIG4 is an electron micrograph of a cross-section of a functional layer of a hollow fiber separation membrane prepared in Example 1 of the present invention;

[0038] FIG5 is an electron micrograph of a cross-sectional view of the inner surface of the hollow fiber separation membrane prepared in Example 1 of the present invention;

[0039] FIG6 is an electron micrograph of the outer surface of the hollow fiber separation membrane prepared in Example 1 of the present invention;

[0040] FIG7 is an electron micrograph of the inner surface of the hollow fiber separation membrane prepared in Example 1 of the present invention;

[0041] FIG8 is an electron microscope image of the hollow fiber separation membrane prepared in Example 4 of the present invention;

[0042] FIG9 is an electron microscope image of the hollow fiber separation membrane prepared in Example 5 of the present invention;

[0043] Figure 10 is an electron microscope image of the hollow fiber separation membrane prepared in Comparative Example 1; and

[0044] FIG11 is a schematic diagram of a method for purifying helium from a helium-rich gas according to the present invention. DETAILED DESCRIPTION

[0045] The endpoints of the ranges and any values ​​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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0046] In this specification, reference to "one embodiment" or "some embodiments" means that the features, structures, or characteristics described in connection with the embodiment are included in at least one embodiment. In one or more embodiments, these features, structures, or characteristics can be combined in any suitable manner.

[0047] As mentioned above, the present invention provides a hollow fiber separation membrane, characterized in that the separation membrane includes a support body, a functional layer and a connecting layer located between the support body and the functional layer, wherein at least a portion of the connecting layer is embedded in the support body.

[0048] In the present invention, the support body is tubular and the wall of the support body has holes and / or gaps. At least a portion of the connecting layer is embedded in the holes and / or gaps of the wall of the support body.

[0049] In the present invention, the connecting layer and the functional layer comprise the same polymer. In some embodiments, the connecting layer and the functional layer are formed of the same polymer.

[0050] In some embodiments, the polymer included in or forming the tie layer and the functional layer is polybenzimidazole.

[0051] Preferably, in some embodiments, the tie layer and the functional layer comprise the same polymer and are formed from the same casting solution. More preferably, in some embodiments, the tie layer and the functional layer comprise the same polymer and are formed from the same casting solution, and are formed by non-solvent-induced phase separation and thermally induced phase separation, respectively.

[0052] Non-solvent induced phase separation and thermally induced phase separation are known in the art.

[0053] In the present invention, the functional layer is a selective dense layer, and the connecting layer is a layer for connecting the functional layer and the support.

[0054] In some embodiments, the present invention provides a hollow fiber separation membrane, wherein the separation membrane includes a support body, a functional layer attached to 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.

[0055] Polybenzimidazole (PBI) is a class of heterocyclic polymers containing imidazole rings in the backbone. These polymers exhibit excellent chemical, thermal, hydrolytic, and mechanical stability. As a polymer material, PBI offers excellent processability, making PBI membranes easy to encapsulate and cost-effective to manufacture. PBI is particularly well-suited for the preparation of separation membranes used for hydrogen or helium purification.

[0056] In the present invention, high-temperature, normal-pressure, or reduced-pressure drying is used to promote solvent volatilization, resulting in a polymer functional layer, such as a polybenzimidazole functional layer, having excellent density, avoiding the formation of defects, and achieving better separation performance. Furthermore, the present invention employs an internal support reinforcement method to improve the mechanical properties of the gas separation membrane, meeting the mechanical performance requirements of the membrane fibers in high-temperature, high-pressure, and high-flow rate gas separation systems, thereby expanding the application range of the gas separation membrane. In the present invention, a connecting layer with a porous structure is obtained by inducing non-solvent phase separation with a core liquid, thereby preventing the functional layer from shedding.

[0057] In the case where the functional layer contains polybenzimidazole, the present invention uses an organic acid and optionally a volatile solvent to prepare a casting solution, and the surface functional layer of the resulting hollow fiber composite membrane contains or is composed of protonated polybenzimidazole, thereby obtaining a higher separation coefficient.

[0058] In the present invention, the tie layer is obtained by non-solvent induced phase separation of the casting solution. In a preferred embodiment, the tie layer is obtained by non-solvent induced phase separation of an acid solution containing polybenzimidazole.

[0059] In the present invention, the functional layer and the tie layer may be formed from the same casting solution. In some embodiments, the functional layer and the tie layer are formed from the same primary film, wherein the tie layer is formed by non-solvent induced phase separation and the functional layer is formed by thermally induced phase separation.

[0060] In the present invention, the connecting layer has a porous structure. In the present invention, the functional layer is dense.

[0061] According to the present invention, preferably, the polymer contained in or forming the connecting layer and the functional layer is polybenzimidazole. The number average molecular weight of the polybenzimidazole may be 50,000 to 300,000; preferably, the number average molecular weight of the polybenzimidazole may be 56,000 to 200,000 or 80,000 to 287,000.

[0062] According to the present invention, preferably, the polybenzimidazole comprises one or more structural units represented by formulae (A1) to (A8);

[0063]

[0064] According to the present invention, preferably, the polybenzimidazole comprises one or more structural units represented by formulae (A5) to (A8).

[0065] According to the present invention, the support body can be a fiber braided tube or a hollow fiber membrane, preferably a hollow fiber microporous membrane. The hollow fiber microporous membrane can be a hollow fiber microporous membrane prepared by a method such as thermally induced phase separation, melt stretching, etc. from a polymer material that cannot be dissolved by an acid used to prepare a casting solution. The support body can be one or more selected from a fiber braided tube, a polypropylene hollow microporous membrane, a polyethylene hollow microporous membrane, and an inorganic hollow microporous membrane. Preferably, the hollow fiber microporous membrane is a polypropylene hollow microporous membrane or a polyethylene hollow microporous membrane prepared by a thermally induced phase separation method.

[0066] According to the present invention, the average thickness of the hollow fiber separation membrane may be 50-2000 μm or 100-2000 μm, preferably 150-1000 μm, and more preferably 180-500 μm.

[0067] According to the present invention, when the support is a hollow fiber microporous membrane, the porosity of the support can be 30-90%, preferably 50-80%. In some embodiments, the pore size of the support can be, for example, 10 nanometers to 20 micrometers. The porosity is measured by nitrogen adsorption.

[0068] According to the present invention, the average thickness of the tube wall of the support body may be 50-2000 μm or 100-2000 μm, preferably 300-1800 μm, and more preferably 500-1500 μm.

[0069] According to the present invention, the average thickness of the functional layer may be 100-50000 nm. Preferably, in some embodiments, the thickness of the functional layer may be 200-5000 nm.

[0070] According to the present invention, the average thickness of the connecting layer may be 20-2000 μm, preferably 50-1500 μm, and more preferably 20-1000 μm.

[0071] In the present invention, at least a portion of the connecting layer is embedded in at least a portion of the support. In some embodiments, the diameter of the connecting layer may be the same as the diameter of the support. In some embodiments, the connecting layer may span the outer surface of the support. In some embodiments, the connecting layer may span the inner surface of the support.

[0072] According to the present invention, the tie layer is formed from a casting solution by non-solvent induced phase separation. In some embodiments, the tie layer is formed from an acid solution containing polybenzimidazole by non-solvent induced phase separation.

[0073] The hollow fiber separation membrane of the present invention has excellent properties including, for example, breaking strength, flux, and separation factor.

[0074] According to the present invention, the separation membrane has a fracture strength of 10-500 MPa; preferably, the separation membrane has a fracture strength of 50-250 MPa; more preferably, the separation membrane has a fracture strength of 52-210 MPa.

[0075] According to the present invention, in some embodiments, the hollow fiber separation membrane of the present invention may have a pure helium flux of 0.8-480 GPU, a pure hydrogen flux of 0.8-580 GPU, a nitrogen flux of 0.01-0.7 GPU, and / or a methane flux of 0.01-0.7 GPU at 100°C and a test pressure of 0.5 MPa; preferably, the pure helium flux may be 3.48-477.5 GPU, the pure hydrogen flux may be 3.03-79.6 GPU, the nitrogen flux may be 0.016-0.68 GPU, and / or the methane flux may be 0.0135-0.6 GPU.

[0076] According to the present invention, in some embodiments, the hollow fiber separation membrane of the present invention may have a hydrogen / nitrogen separation coefficient of 110-300 or 110-235, and / or a hydrogen / methane separation coefficient of 125-360 or 125-260 at 100°C and a test pressure of 0.5 MPa; preferably, the hydrogen / nitrogen separation coefficient may be 110-234.1, and / or the hydrogen / methane separation coefficient may be 129.1-256.7.

[0077] According to the present invention, in some embodiments, the hollow fiber separation membrane of the present invention may have a helium / nitrogen separation coefficient of 140-390 or 140-190, and / or a helium / methane separation coefficient of 170-500 or 170-175 at 100°C and a test pressure of 0.5 MPa; preferably, the helium / nitrogen separation coefficient may be 141.4-187.5, and / or the helium / methane separation coefficient may be 170-173.8.

[0078] According to the present invention, in some embodiments, the hollow fiber separation membrane of the present invention can have a hydrogen / nitrogen separation factor of 200-550 and / or a hydrogen / methane separation factor of 200-860 at 25°C and 0.5 MPa test pressure.

[0079] According to the present invention, in some embodiments, the hollow fiber separation membrane of the present invention can have a helium / nitrogen separation factor of 240-900 and / or a helium / methane separation factor of 200-2000 at 25°C and 0.5 MPa test pressure.

[0080] The invention also provides a method for preparing the hollow fiber separation membrane.

[0081] According to some embodiments, the method for preparing a hollow fiber separation membrane of the present invention comprises:

[0082] (1) preparing a casting solution containing a polymer;

[0083] (2) coating the casting solution on a support, wherein a portion of the casting solution penetrates into the support to obtain a primary film coated on the support;

[0084] (3) heating the primary film to form a functional layer; and

[0085] (4) injecting a core liquid into the support body to cause the casting liquid that penetrates into the support body to undergo non-solvent induced phase separation to generate a connecting layer.

[0086] Casting solutions and their preparation are generally known in the art. For example, the casting solution can be prepared by dissolving a polymer in a solvent. The polymer can be any of the polymers mentioned above for hollow fiber separation membranes. Preferably, the polymer is polybenzimidazole. Those skilled in the art can select the solvent based on the type of polymer, etc. The solvent can be a single solvent or a mixture.

[0087] Optionally, the casting solution may further comprise one or more additives. Those skilled in the art may appropriately select the additives as needed.

[0088] In some embodiments, based on the total weight of the casting solution, the amount of the polymer is 4-18 wt %, the amount of the solvent is 77-90 wt %, and the amount of the additive is 0-5 wt %. Preferably, in some embodiments, based on the total weight of the casting solution, the amount of the polymer is 8-15 wt %, the amount of the solvent is 80-90 wt %, and the amount of the additive is 1-2 wt %.

[0089] After preparing the casting solution, the casting solution is applied to a support. The support may be any of the supports described above. Coating may be performed using various methods commonly known in the art. For example, the support may be pulled through the casting solution to coat the support.

[0090] According to the present invention, the casting solution penetrates at least a portion of the support. In some embodiments, the casting solution penetrates a portion of the wall of the tubular support, for example, it can penetrate 10% to 150% of the thickness of the support wall. In some embodiments, the casting solution can penetrate greater than or equal to 10%, greater than or equal to 15%, greater than or equal to 20%, greater than or equal to 25%, greater than or equal to 30%, greater than or equal to 35%, greater than or equal to 40%, greater than or equal to 45%, greater than or equal to 50%, greater than or equal to 60%, greater than or equal to 70%, greater than or equal to 80%, greater than or equal to 90%, greater than or equal to 100%, greater than or equal to 110%, etc. of the thickness of the support wall. Those skilled in the art can reasonably determine the extent of penetration of the casting solution into the support wall. The method of the present invention can enable the casting liquid that penetrates into the tube wall of the support body to basically maintain or maintain the penetration depth when it is converted into a connecting layer (so that the embedding depth of the obtained connecting layer in the support body is the same or basically the same as the penetration depth of the casting liquid), thereby ensuring that at least a portion of the connecting layer formed by the casting liquid in the final finished hollow fiber separation membrane is embedded in the support body.

[0091] After the casting solution is coated on the support, a primary film coated on the support is obtained.

[0092] The nascent film may then be heated to form a functional layer. In the present invention, heating the nascent film causes thermally induced phase separation, thereby forming an outermost functional layer.

[0093] The heating promotes the volatilization of the solvent in the casting solution to form the polymer functional layer. Those skilled in the art can select an appropriate heating temperature based on the solvent used. Alternatively, heating can be performed under normal pressure or reduced pressure. For example, hot air can be used for heating. In some embodiments, hot air can be used to volatilize the solvent. In the present invention, for example, the heating temperature can be 80-300°C.

[0094] In the method of the present invention, the thermally induced phase separation proceeds until only the outermost portion of the nascent membrane undergoes phase separation (forming a functional layer), but no phase separation occurs within the nascent membrane. In particular, the casting solution that has permeated the support remains in a liquid state and does not undergo thermally induced phase separation.

[0095] After the nascent membrane is heated to form the functional layer, a core liquid can be injected into the support (i.e., within the tubular support). This core liquid causes the casting liquid that has permeated the support to undergo non-solvent-induced phase separation to form a tie layer. In some embodiments, for example, the core liquid can be injected after the desired functional layer is obtained. In the present invention, the core liquid can be introduced at room temperature and normal pressure.

[0096] Those skilled in the art can select the core liquid according to the composition of the casting liquid, the material of the support, etc., as long as the casting liquid can undergo non-solvent-induced phase separation.

[0097] In the method of the present invention, optionally, the hollow fiber separation membrane can be heated to (substantially) remove all solvent after the connecting layer is generated. The heating can be carried out under normal pressure or reduced pressure. Those skilled in the art can select a suitable temperature for heating according to the solvent used. For example, hot air can be used for heating. In some embodiments, the same temperature as used in step (3) above can be used in this step. For example, the temperature can be 80-300°C.

[0098] In the method of the present invention, a dense functional layer and a porous connecting layer are formed from the same casting solution in two different ways, resulting in an integrated structure. This method allows the connecting layer to remain within (i.e., be embedded within) the support, thereby firmly connecting the functional layer to the support and preventing it from falling off. Furthermore, the method of the present application enables the connecting layer to remain porous, further facilitating a secure connection between the functional layer and the support.

[0099] The functional layer in the present invention is dense, but the tie layer is porous. As will be appreciated by those skilled in the art, a transition region may exist when transitioning from the dense functional layer to the porous tie layer. In this application, the transition region, if present, is considered part of the tie layer.

[0100] The hollow fiber separation membrane prepared by the method of the present invention also provides advantageous membrane properties, including, for example, flux and / or separation factor.

[0101] According to some embodiments, the method for preparing a hollow fiber separation membrane of the present invention comprises:

[0102] (1) mixing polybenzimidazole, an acid, an optional volatile solvent, and an optional additive to prepare a casting solution containing the polymer;

[0103] (2) coating the casting solution on a support, wherein a portion of the casting solution penetrates into at least a portion of the support, to obtain a primary film coated on the support;

[0104] (3) heating the primary film to form a functional layer; and

[0105] (4) injecting a core liquid into the support body to cause the casting liquid that penetrates into the support body to undergo non-solvent induced phase separation to generate a connecting layer.

[0106] According to some embodiments, the method for preparing a hollow fiber separation membrane of the present invention comprises:

[0107] (1) mixing polybenzimidazole, an acid, an optional volatile solvent, and an optional additive to obtain a casting solution; wherein the polybenzimidazole has a number average molecular weight of 50,000 to 300,000;

[0108] (2) using a spinneret for preparing the primary membrane and the connecting layer; using a hollow fiber microporous membrane as a support;

[0109] (3) extruding the casting liquid, the extruded casting liquid enters a spinneret, and using a scraper to scrape the casting liquid onto the support, while the support is pulled upward through the spinneret to obtain a primary film attached to the support, and part of the casting liquid penetrates into the interior of the support;

[0110] (4) The primary membrane is subjected to a heat treatment 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, so that the portion of the casting liquid infiltrated into the support body undergoes a non-solvent-induced phase separation to form a connecting layer with a porous structure; and then the hollow fiber separation membrane is obtained by a heat treatment to remove the solvent.

[0111] According to the present invention, preferably, the number average molecular weight of the polybenzimidazole is 50,000 to 300,000 or 50,000 to 287,000. More preferably, the number average molecular weight of the polybenzimidazole is 80,000 to 287,000 or 56,000 to 200,000.

[0112] According to the present invention, the polybenzimidazole comprises one or more structural units represented by formulae (A1) to (A8);

[0113]

[0114]

[0115] According to the present invention, preferably, the polybenzimidazole comprises one or more structural units represented by formulae (A5) to (A8).

[0116] According to the present invention, the polybenzimidazole and the support may be the same as those described above with respect to the hollow fiber separation membrane.

[0117] Optionally, in the present invention, the support may be modified prior to coating. The modification method is not particularly limited. For example, the modification may include blending the materials used to prepare the support, such as using a polymer blend; chemical treatment, physical deposition, UV irradiation, heat treatment, or mechanical treatment of the support, etc.

[0118] The inventors of the present invention have found that: preferably, by using a compound of an organic acid and a volatile solvent, polybenzimidazole is protonated during the dissolution process, which inhibits the formation of intermolecular hydrogen bonds, increases the flexibility of the polymer molecular chain, and makes the polymer more easily stacked during the film formation process, and the resulting hollow fiber composite membrane has a high separation coefficient. On the other hand, by using high-temperature and high-pressure scraping and high-temperature normal pressure / reduced pressure drying methods, the volatilization of the solvent is promoted, so that the polybenzimidazole functional layer obtains a good density, avoids the formation of defects, and obtains better separation performance. In addition, by using an internal support enhancement method, the mechanical properties of the gas separation membrane are improved, which can meet the requirements of high-temperature, high-pressure, high-flow rate gas separation systems for the mechanical properties of the membrane fibers, and expand the application range of the gas separation membrane. In addition, a connecting layer with a porous structure is obtained by inducing non-solvent phase separation through the core liquid, which avoids the shedding of the functional layer.

[0119] According to the present invention, in some embodiments, the acid is a monoprotic acid. Preferably, the acid is one or more selected from hydrochloric acid, hydrofluoric acid, and methanesulfonic acid. More preferably, the acid is methanesulfonic acid. It is believed that during the film formation process, the organic acid induces protonation, inhibiting the formation of hydrogen bonds between polymer molecules, reducing polymer rigidity, and enabling more dense packing of polymer molecular chains, thereby improving the separation performance of small molecules such as hydrogen and helium.

[0120] According to the present invention, the core liquid may be one or more of water, ethanol, methanol, isopropanol, acetone and tetrahydrofuran.

[0121] According to the present invention, the volatile solvent may be ethanol and / or tetrahydrofuran.

[0122] According to the present invention, the additive can be one or more selected from 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.

[0123] According to the present invention, in some embodiments, based on the total weight of the casting solution, the amount of polybenzimidazole is 4-18wt%, the amount of the acid is 77-90wt%, the amount of the volatile solvent is 0-10wt%, and the amount of the additive is 0-5wt%. Preferably, based on the total weight of the casting solution, the amount of polybenzimidazole is 8-15wt%, the amount of the acid is 80-90wt%, the amount of the volatile solvent is 1-5wt%, and the amount of the additive is 1-2wt%. In the present invention, it should be noted that the sum of the components of polybenzimidazole, acid, volatile solvent, and optional additives is 100wt%.

[0124] In some embodiments, polybenzimidazole can be added to the acid and a volatile solvent (if used) and an additive (if used) can be added to mix to obtain a casting solution. Optionally, stirring and heating can be performed during the mixing process. In some embodiments, the mixing conditions may include: a temperature of 25-160°C and a time of 2-72 hours; preferably, a temperature of 80-160°C and a time of 12-48 hours. There is no particular limitation on the stirring and it can be conventionally selected by those skilled in the art. Preferably, the stirring rate of the stirring can be 20-500 rpm.

[0125] After preparing the casting solution, the casting solution is applied to the surface of the support. In some embodiments, the casting solution can be scraped onto the surface of the support. According to the present invention, the casting solution can be scraped onto the surface of the support at a certain temperature and pressure to obtain a primary film with a certain thickness. The scraping conditions may include: a temperature of 60-250°C, preferably a temperature of 80-180°C. In the present invention, there is no specific limitation on the scraping pressure. Preferably, the pressure can be 10-2000KPa, more preferably, the pressure can be 500-1200KPa.

[0126] In the present invention, during the doctor blade coating process, the thickness of the primary film, and thus the thickness of the functional layer, can be controlled by controlling the distance between the doctor blade and the outer wall of the support. In some embodiments, the thickness of the doctor blade (primary film) (the distance between the doctor blade and the outer wall of the support) can be 10-300 μm. Of course, those skilled in the art can adjust the distance between the doctor blade and the outer wall of the support according to the desired primary film thickness.

[0127] In some embodiments, the casting solution is extruded into a spinneret, wherein the casting solution contacts the support inside the spinneret. The contact time is not particularly limited. For example, the contact time may be 1-15 seconds, preferably 1-10 seconds. In the present invention, there is no particular limitation on the pressure. For example, the pressure may be 10-2000 kPa. For example, the pressure may be 0 to 0.2 MPa (gauge pressure). For example, the pressure may be 0.02-0.1 MPa (gauge pressure).

[0128] According to the present invention, after the casting solution is applied to the support (e.g., a scraper), the support with the nascent film attached thereto can be pulled and fed into a heating device. The solvent in the outer layer of the nascent film is volatilized by heating to form a polymer functional layer attached to the support, such as a polybenzimidazole functional layer. The heating can be performed, for example, by hot air. The heating can be performed under normal pressure or reduced pressure. For example, the heating can be performed at -0.1 to 0 MPa (gauge pressure). In some embodiments, the conditions for promoting solvent volatilization by heating can include: a temperature of 80-300°C. In some embodiments, hot air can be used for heating. Those skilled in the art can appropriately select the heating conditions based on the solvent used, the desired volatilization rate, etc. In the present invention, there is no specific limitation on the device used for heating; for example, it can be an oven. In some embodiments, the heating temperature can be 100-280°C for a time of 2-24 hours; preferably, the heating temperature is 120-150°C for a time of 5-12 hours.

[0129] After the outermost polymer functional layer is formed by heating, a core liquid can be injected into the support body; the core liquid causes the casting liquid that has penetrated into the support body to undergo non-solvent induced phase separation to form a connecting layer. The core liquid is, for example, the core liquid described above.

[0130] In the method of the present invention, the hollow fiber separation membrane may optionally be heated after forming the connecting layer to remove (substantially) all of the solvent. The heating may be performed under normal pressure or reduced pressure. A person skilled in the art can select a suitable temperature for heating based on the solvent used. For example, hot air may be used for heating. For example, the heating temperature may be 80-300°C.

[0131] In the present invention, optionally, the method may further comprise washing the prepared finished membrane, such as washing with water, washing with ethanol, etc., to remove residual solvent.

[0132] Figure 1 is a schematic diagram of the structure of a spinneret used in the preparation of primary membrane and connecting layer of the present invention. Figure 2 is a schematic diagram of the process of preparing primary membrane and connecting layer using the spinneret of Figure 1 of the present invention.

[0133] Referring to Figures 1 and 2, the spinneret includes a support positioner, an annular scraper, and a core tube. The support positioner surrounds the support and is located at one end of a casting liquid chamber for containing the casting liquid. The casting liquid chamber is provided with a casting liquid inlet and a casting liquid outlet. Preferably, the casting liquid outlet is higher than the casting liquid inlet. The support positioner is disposed at one end of the casting liquid chamber to form a closed end, and the annular scraper is disposed at the other end of the casting liquid chamber. The diameter of the annular scraper is greater than the width of the support positioner, and the difference between the diameters forms a gap that can be used to form a nascent membrane. Figure 1 also shows a support holder, which is used to hold the support and pull it through the casting liquid chamber. Figure 1 also shows the core tube. The core tube can be inserted into the interior of the support and injected with core liquid to form a core liquid flow channel within the support. After the core liquid is injected through the core tube, the core liquid induces non-solvent-induced phase separation to form a connecting layer with a porous structure, preventing the functional layer from falling off.

[0134] Referring to Figure 2, the process of preparing a nascent membrane and a connecting layer using the spinneret described in Figure 1 is described. First, a support is selected and secured using a support positioner. A casting solution extruded from a twin-screw extruder or gear pump is injected into a casting solution chamber through a casting solution inlet. The support is pulled upward through the casting solution chamber and coated with an annular scraper; some of the casting solution penetrates the support. After exiting the annular scraper, a nascent membrane is obtained, attached to the support. Excess casting solution flows out through a casting solution outlet. After exiting the annular scraper, the support with the nascent membrane attached is pulled and passed into a heating device. The outer layer of the nascent membrane is heated (e.g., with hot air) to promote solvent volatilization, forming a polymer functional layer, such as a polybenzimidazole functional layer, attached to the surface of the support. The core tube is then placed within the support, and a core solution is injected into the support through the core tube. The core solution induces non-solvent phase separation, resulting in a connecting layer with a porous structure from the casting solution that has penetrated the support. The connecting layer is embedded in the support body and is integrated with the functional layer, which prevents the functional layer from falling off.

[0135] The present invention also provides a hollow fiber separation membrane prepared by the above method. In some embodiments, the hollow fiber separation membrane of the present invention is prepared by the method of preparing a hollow fiber separation membrane of the present invention.

[0136] The hollow fiber separation membrane of the present invention can be used for gas separation. Therefore, the present invention also provides the use of the hollow fiber separation membrane of the present invention for separating helium / nitrogen, helium / methane, hydrogen / nitrogen, and / or hydrogen / methane. The hollow fiber separation membrane of the present invention can be used to separate gases using procedures generally known in the art.

[0137] The present invention also provides a method for purifying helium from a helium-rich gas, the method comprising using the hollow fiber separation membrane of the present invention to perform membrane separation on the gas.

[0138] In some embodiments, the method for purifying helium from helium-rich gas may include subjecting the helium-rich gas to a cryogenic condensation process, a catalytic dehydrogenation process, a membrane separation process, and a pressure swing adsorption impurity removal process to obtain purified helium. The membrane separation process includes using the hollow fiber separation membrane of the present invention.

[0139] In some embodiments, the method for purifying helium from helium-rich gas may include: subjecting the helium-rich gas to a cryogenic condensation process, catalytic dehydrogenation, membrane separation using a helium separation membrane, and pressure swing adsorption impurity removal treatment to obtain purified helium; wherein the condensation process comprises a temperature ≥ -220°C. The membrane separation process comprises using the hollow fiber separation membrane of the present invention.

[0140] The method for purifying helium of the present invention has the following advantages:

[0141] (1) The helium produced can have high purity, for example, reaching 4N grade (99.99%) or even higher; and the helium extraction efficiency can be greatly improved;

[0142] (2) The cryogenic process has high temperature, which reduces energy consumption.

[0143] In some embodiments, the condensation treatment conditions may include a temperature of ≥-220° C. In some embodiments, the condensation treatment conditions may include a temperature of -210° C. to -150° C. and a pressure of 0.2-10 MPa; preferably, the condensation treatment conditions include a temperature of -180° C. to -150° C. and a pressure of 3-10 MPa.

[0144] According to the present invention, there is no specific limitation on the gas containing helium and there is no specific limitation on the composition of the gas containing helium, and the method of the present invention has universal applicability. In some embodiments, the gas containing helium may include natural gas, oilfield associated gas, etc. In some embodiments, the gas containing helium may include helium, nitrogen, methane, hydrogen and carbon dioxide. In some embodiments, based on the total volume of the helium-rich gas, the helium content may be 5-40% by volume; preferably, the helium content may be 15-30% by volume.

[0145] According to the present invention, the helium-rich gas further contains optional oxygen and water, and based on the total volume of the helium-rich gas, the oxygen content is 0-8% by volume, and the water content is 0-2% by volume.

[0146] According to the present invention, the helium-rich gas is condensed to achieve the effect of liquefying impurities such as nitrogen, methane, oxygen, and light hydrocarbons, and partially removes nitrogen, methane, oxygen, and CO2 to obtain a second mixed gas.

[0147] According to the present invention, the second mixed gas is subjected to catalytic dehydrogenation treatment to remove part of the hydrogen to obtain a third mixed gas.

[0148] According to the present invention, the conditions for the catalytic dehydrogenation treatment may include: a temperature of 60-120° C., preferably 60-110° C., and more preferably 62-106° C. The catalytic dehydrogenation treatment is carried out in the presence of oxygen and a catalyst, wherein the catalyst is a precious metal catalyst, preferably selected from Pt, Pb, Rh, Ru, or Au; more preferably, the catalyst is selected from Pt, Pb, or Au.

[0149] According to the present invention, the third mixed gas is subjected to the membrane separation treatment of the present invention to remove part of nitrogen, methane, oxygen and CO2 to obtain a fourth mixed gas.

[0150] According to the present invention, membrane separation utilizes the differences in permeability of the components in the feed gas during dissolution, diffusion, and desorption, driven by a pressure differential across the membrane, to achieve helium separation. The membrane separation process can include: pressure on the membrane separation positive pressure side > pressure on the membrane separation permeate side; the pressure on the membrane separation positive pressure side can be 0.2-10 MPa; preferably, 0.5-10 MPa; and more preferably, 3-10 MPa. Membrane separation offers the advantages of simple operation, low energy consumption, and low equipment construction and operating costs.

[0151] According to the present invention, membrane separation can be used to purify helium using one or more stages. In membrane separation, multi-stage membrane separation means that the permeate side gas is pressurized and then used as the feed gas again for separation using a membrane. This process can be 1-5 stages.

[0152] According to the present invention, the fourth mixed gas is subjected to adsorption and impurity removal treatment to remove part of nitrogen, methane, oxygen, hydrogen and CO2 to obtain purified helium; wherein, based on the total volume of the purified helium, the helium content can be 99.986-99.996 volume%.

[0153] According to the present invention, the conditions for the pressure swing adsorption impurity removal treatment include: an adsorption pressure of 0.2-15 MPa, preferably 10-15 MPa. In the present invention, the adsorbent used in the adsorption impurity removal treatment can be selected from one or more of activated carbon, molecular sieves, metal organic framework materials (MOFs), and activated alumina.

[0154] In this application, pressures are gauge pressures unless otherwise stated.

[0155] The present invention will be described in detail below through examples.

[0156] In the following examples and comparative examples:

[0157] Polybenzimidazole was purchased from Shanghai Shengjun Plastic Technology Co., Ltd.; other reagents were purchased from Beijing Yinuokai Technology Co., Ltd. Among them, ethanol 99.9%; hydrochloric acid 12 mol / L; methanesulfonic acid 99.0%; tetrahydrofuran 99.9%.

[0158] The test method of permeation rate (GPU): Under a specific temperature and a specific pressure difference, the gas flow rate per unit time per unit membrane area is measured. 1GPU = 10 -6 cm 3 (STP) / (cm 2 ·s·cmHg).

[0159] The separation coefficient, α, is a dimensionless quantity used to characterize the selective permeation of gas components through a membrane. The separation coefficient is the ratio of the permeation rates of two gases through a membrane.

[0160] The breaking strength was tested using Instron 3342 according to ASTM D882.

[0161] Example 1

[0162] This embodiment provides a hollow fiber separation membrane prepared by the method of the present invention.

[0163] (1) Polybenzimidazole A5, ethanol, and hydrochloric acid were added to methanesulfonic acid, and stirred at 70° C. and 0 MPa (gauge pressure) for 24 hours to obtain a mixed solution (casting solution); wherein the mass fractions were: polybenzimidazole 10 wt %, ethanol 3 wt %, hydrochloric acid 3 wt %, and methanesulfonic acid 84 wt %;

[0164] The structural unit of polybenzimidazole A5 is shown below:

[0165]

[0166] Wherein, the number average molecular weight of the polybenzimidazole A5 is 56,000;

[0167] (2) The mixed liquid is heated to 240° C. and extruded into a spinneret through a twin-screw extruder, using the spinneret shown in FIG1 ; the support is a polyester fiber braided tube; a concentric circle composite spinning technique is used to allow the casting liquid to contact the braided tube in the spinneret (the spinneret cavity height is 10 cm), the contact time is 10 s, and the pressure is 0.1 MPa; the support is pulled from bottom to top through the interior of the spinneret, and then passes through an annular scraper and controls the thickness of the polybenzimidazole primary film to be 200 μm, thereby obtaining a polybenzimidazole primary film attached to the support; excess casting liquid flows out through the casting liquid outlet, and part of the casting liquid penetrates into the support;

[0168] (3) pulling the polybenzimidazole primary film into a length of 100 cm in an air bath at 100° C., cutting the film, and placing the film in an air bath at 100° C. for 50 minutes to form a polybenzimidazole functional layer having a dense structure;

[0169] (4) Ethanol is introduced into the support tube through the central core tube to induce phase separation, thereby causing the portion of the casting liquid that has infiltrated into the support body to undergo non-solvent induced phase separation to form a connecting layer with a porous structure; then, the solvent in the primary membrane is completely volatilized in an oven at 110°C to prepare a finished membrane - a hollow fiber separation membrane.

[0170] The thickness of the functional layer of the prepared hollow fiber separation membrane was approximately 27-29 μm; see Figure 4, which is an electron micrograph of a cross-section of the functional layer of the hollow fiber separation membrane prepared in Example 1 of the present invention. The connecting layer was embedded within the support and had a thickness of approximately 380 μm. (In Example 1, the connecting layer also extended inward from the inner surface of the support, resulting in a slightly thicker support.) The embedded layer's thickness exceeded the support wall thickness.

[0171] The hollow fiber separation membrane prepared in this Example 1 has a breaking strength of 160 MPa. At 100°C and a test pressure of 0.5 MPa, the pure helium flux is 3.48 GPU, the pure hydrogen flux is 3.03 GPU, the nitrogen flux and the methane flux are 0.016 GPU and 0.0135 GPU, respectively. The separation coefficients of hydrogen / nitrogen and hydrogen / methane are 189 and 224, respectively.

[0172] Figure 3 is an electron microscope image of the cross section of the hollow fiber separation membrane prepared in Example 1 of the present invention; it can be seen from Figure 3 that the functional layer is on the outer surface of the membrane, the connecting layer is embedded in the support body, and is tightly bonded to the PBI membrane.

[0173] FIG5 is an electron microscope image of the inner surface cross section of the hollow fiber separation membrane prepared in Example 1 of the present invention. It can be seen from FIG5 that the support body is embedded in the interior of the connecting layer, and the inner surface of the connecting layer is a microporous structure.

[0174] FIG6 is an electron microscope image of the outer surface of the hollow fiber separation membrane prepared in Example 1 of the present invention; FIG6 shows that the outer surface has a dense structure.

[0175] FIG7 is an electron microscope image of the inner surface of the novel hollow fiber separation membrane prepared in Example 1 of the present invention; FIG7 shows that the inner surface is a connecting layer with a microporous structure.

[0176] Example 2

[0177] This embodiment provides a hollow fiber separation membrane prepared by the method of the present invention.

[0178] (1) Polybenzimidazole A6, ethanol, tetrahydrofuran, and methanesulfonic acid were mixed and stirred at 80° C. and 0.5 MPa for 24 hours to obtain a mixed solution (casting solution); wherein the mass fractions of the mixed solution were: polybenzimidazole 10 wt %, ethanol 2 wt %, tetrahydrofuran 2 wt %, and methanesulfonic acid 86 wt %;

[0179] The structural unit of the polybenzimidazole A6 is shown below:

[0180]

[0181] Wherein, the number average molecular weight of the polybenzimidazole A6 is 72,000;

[0182] (2) The mixed liquid is heated to 180° C. and extruded into a spinneret through a gear pump, using the spinneret shown in FIG1 ; the support is a polypropylene microporous membrane obtained by thermally induced phase separation; a concentric circle composite spinning technique is used to make the casting liquid contact with the polypropylene microporous membrane in the spinneret (the spinneret cavity height is 10 cm), the contact time is 10 s, and the contact pressure is 0.4 MPa; the support is pulled from bottom to top through the inside of the spinneret, and then passes through an annular scraper and controls the thickness of the polybenzimidazole primary membrane to be 100 μm, thereby obtaining a polybenzimidazole primary membrane attached to the support; excess casting liquid flows out through the casting liquid outlet, and part of the casting liquid penetrates into the support;

[0183] (3) pulling the polybenzimidazole primary film in an air bath at 100° C. for 200 cm, cutting the film, and placing the film in an air bath at 100° C. for 40 minutes to form a polybenzimidazole functional layer having a dense structure;

[0184] (4) Ethanol is introduced into the inner tube of the support body through the central core tube to induce phase separation, thereby causing the portion of the casting liquid that has infiltrated into the support body to undergo non-solvent ethanol-induced phase separation to form a connecting layer with a porous structure; then the solvent in the primary membrane is completely evaporated in a 100°C oven; as a result, a finished membrane - a hollow fiber separation membrane is prepared.

[0185] The average thickness of the prepared hollow fiber separation membrane is about 200 μm; the thickness of the functional layer is about 2-5 μm; and the connecting layer is embedded in the support body and has a thickness of about 200 μm.

[0186] The prepared hollow fiber separation membrane has a breaking strength of 155 MPa. At 100°C and a test pressure of 0.5 MPa, the pure helium flux is 7.5 GPU, the pure hydrogen flux is 6.8 GPU, the nitrogen flux is 0.04 GPU, and the methane flux is 0.04 GPU. The separation coefficients of helium / nitrogen and helium / methane are 187.5 and 170, respectively.

[0187] Example 3

[0188] This embodiment provides a hollow fiber separation membrane prepared by the method of the present invention.

[0189] (1) Polybenzimidazole A4 and methanesulfonic acid were mixed and stirred at 150° C. and 1.0 MPa for 24 h to obtain a mixed solution (casting solution); wherein the mass fraction composition was: polybenzimidazole 18 wt % and methanesulfonic acid 82 wt %;

[0190] The structural unit of the polybenzimidazole A4 is shown below:

[0191]

[0192] Wherein, the number average molecular weight of the polybenzimidazole A4 is 68,000;

[0193] (2) The mixed liquid is heated to 100° C. and extruded into a spinneret through a gear pump, using the spinneret shown in FIG1 ; the support is a polypropylene microporous membrane (prepared by thermally induced phase separation); a concentric circle composite spinning technique is used to make the casting liquid contact with the support in the spinneret (the spinneret cavity height is 10 cm), the casting liquid and the braided tube are in contact for 2 s, and the contact pressure is 0.5 MPa; the support is pulled from bottom to top through the inside of the spinneret, passes through an annular scraper and controls the thickness of the polybenzimidazole primary membrane to be 100 μm, thereby obtaining a polybenzimidazole primary membrane attached to the support; excess casting liquid flows out through the casting liquid outlet, and part of the casting liquid penetrates into the support;

[0194] (3) pulling the polybenzimidazole primary film in an air bath at 150° C. for 200 cm and then cutting the film, and continuing to place the film in an air bath at 150° C. for 50 minutes to form a polybenzimidazole functional layer with a dense structure;

[0195] (4) Water is introduced into the support body through the central core tube to induce non-solvent induced phase separation of the nascent membrane that has not yet separated into phases, thereby promoting the non-solvent induced phase separation of the portion of the casting liquid that has infiltrated into the support body to form a connecting layer with a porous structure; then, the solvent in the nascent membrane is completely volatilized in a 120°C oven to obtain a finished membrane - a hollow fiber separation membrane.

[0196] The thickness of the functional layer of the prepared hollow fiber separation membrane is about 45 to 50 μm; the connecting layer is embedded in the support body and has a thickness of about 450 μm.

[0197] The prepared hollow fiber separation membrane has a breaking strength of 206 MPa; at 100°C and a test pressure of 0.5 MPa, the pure helium flux is 0.87 GPU, the pure hydrogen flux is 0.81 GPU, the nitrogen flux and the methane flux are 0.005 GPU and 0.004 GPU respectively; the separation coefficients of hydrogen / nitrogen and hydrogen / methane reach 162 and 202.5 respectively.

[0198] Example 4

[0199] This embodiment provides a hollow fiber separation membrane prepared by the method of the present invention.

[0200] (1) Polybenzimidazole A8, ethanol, and methanesulfonic acid were mixed and stirred at 60° C. and normal pressure for 24 h to obtain a uniform mixture; wherein the mass fraction composition was: polybenzimidazole 4 wt %, ethanol 10 wt %, and methanesulfonic acid 86 wt %, to prepare a mixed liquid (casting liquid); the structural unit of the polybenzimidazole A8 was as follows:

[0201]

[0202] Wherein, the number average molecular weight of the polybenzimidazole A8 is 97,000;

[0203] (2) The mixed liquid is heated to 80° C. and extruded into a spinneret through a gear pump, using the spinneret shown in FIG1 ; the support is a polypropylene fiber braided tube, which is obtained by weaving polypropylene fibers; a concentric circle composite spinning technique is used to make the casting liquid contact the support in the spinneret (the spinneret cavity height is 10 cm); the casting liquid and the braided tube are in contact for 10 seconds, and the contact pressure is 0.05 MPa; the support is pulled from bottom to top through the inside of the spinneret, passes through an annular scraper and controls the thickness of the polybenzimidazole primary film to be 100 μm, thereby obtaining a polybenzimidazole primary film attached to the support; excess casting liquid flows out through the casting liquid outlet, and part of the casting liquid penetrates into the support;

[0204] (3) When the length of the polybenzimidazole primary film reaches 200 cm, it is cut and placed in an air bath at 150° C. to dry for 10 minutes to form a polybenzimidazole functional layer with a dense structure;

[0205] (4) Then, ethanol is introduced into the support tube through the central core tube to induce phase separation, thereby causing the portion of the casting liquid that has infiltrated into the support body to undergo non-solvent induced phase separation to form a connecting layer with a porous structure; then, the solvent in the primary membrane is completely evaporated in an oven at 110°C; and a finished membrane - a hollow fiber separation membrane is prepared.

[0206] The thickness of the functional layer of the prepared hollow fiber separation membrane is 400-600nm, with a relatively obvious transition layer; the connecting layer is embedded in the support body, with a thickness of 200-400μm, and some of it penetrates the support body.

[0207] The prepared hollow fiber separation membrane has a breaking strength of 161 MPa; at 100°C and a test pressure of 0.5 MPa, the pure helium flux is 107 GPU, the pure hydrogen flux is 95 GPU, the nitrogen flux and the methane flux are 0.45 GPU and 0.41 GPU respectively; the separation coefficients of hydrogen / nitrogen and hydrogen / methane reach 211 and 231.7 respectively.

[0208] Figure 8 shows an electron microscope image of the hollow fiber separation membrane prepared in Example 4; from left to right and from top to bottom are images of the overall cross-section, the functional layer and the connecting layer, the enlarged functional layer and the connecting layer, the outer surface, the inner surface (the connecting layer is porous) and the cross-section of the support body.

[0209] Example 5

[0210] This embodiment provides a hollow fiber separation membrane prepared by the method of the present invention.

[0211] (1) Polybenzimidazole A7, ethanol, and methanesulfonic acid were mixed and stirred at 60° C. and normal pressure for 72 h to obtain a mixed solution (casting solution); wherein the mass fraction composition was: polybenzimidazole 4 wt %, ethanol 1 wt %, and methanesulfonic acid 95 wt %;

[0212] The structural unit of the polybenzimidazole A7 is shown below:

[0213]

[0214] Wherein, the number average molecular weight of the polybenzimidazole A7 is 287,000;

[0215] (2) The mixed liquid is heated to 80°C and extruded into a spinneret through a gear pump, using the spinneret shown in FIG1 ; the support is a polypropylene hollow fiber microporous membrane (average pore size 0.01 μm, porosity 65%, outer surface contact angle 75°C; the preparation method is as follows: 25% by mass of polypropylene resin, 0.5% maleic anhydride grafted polypropylene, 0.5% polyvinyl pyrrolidone and 74% soybean oil are stirred and heated at 185°C to obtain a homogeneous casting liquid; after vacuum degassing and filtration, the mixture is transported to a hollow spinneret with soybean oil as the inner core liquid, and enters the soybean oil for cooling and solidification; after acetone extraction, air The polypropylene hollow fiber microporous membrane is obtained after natural drying with air; a concentric composite spinning technique is used to contact a casting solution with a polypropylene microporous membrane (prepared by thermally induced phase separation) in a spinneret (the spinneret cavity height is 10 cm), the casting solution and the support are in contact for 10 seconds, and the contact pressure is 0.1 MPa; the support is pulled upward through the interior of the spinneret, passes through an annular scraper, and the thickness of the polybenzimidazole primary membrane is controlled to be 100 μm, thereby obtaining a polybenzimidazole primary membrane attached to the support; excess casting solution flows out through a casting solution outlet, and a portion of the casting solution penetrates into the support;

[0216] (3) After the polybenzimidazole primary film is pulled for 100 cm in an air bath at 150° C., it is cut and then dried in an air bath at 150° C. for 100 minutes to form a polybenzimidazole functional layer with a dense structure;

[0217] (4) Ethanol is introduced into the support tube through the central core tube to induce phase separation, thereby causing the portion of the casting liquid that has infiltrated into the support body to undergo non-solvent induced phase separation to form a connecting layer with a porous structure; then, the solvent in the primary membrane is completely evaporated in an oven at 110°C; and a finished membrane - a hollow fiber separation membrane is prepared.

[0218] The average thickness of the prepared hollow fiber separation membrane is about 350 μm; the average thickness of the functional layer is about 1.2 to 2.0 μm; and the connecting layer is embedded in the support body and has a thickness of about 30 μm.

[0219] The prepared hollow fiber separation membrane has a breaking strength of 63 MPa; at 100°C and a test pressure of 0.5 MPa, the pure helium flux is 88.9 GPU, the pure hydrogen flux is 76.1 GPU, the nitrogen flux and the methane flux are 0.66 GPU and 0.52 GPU respectively; the separation coefficients of hydrogen / nitrogen and hydrogen / methane reach 134.7 and 170.9 respectively.

[0220] Figure 9 shows an electron microscope image of the hollow fiber separation membrane prepared in Example 5; from left to right and from top to bottom are images of the overall cross-section, the functional layer and the connecting layer, the enlarged functional layer and the connecting layer, the outer surface, the inner surface and the cross-section of the support body.

[0221] Example 6

[0222] This embodiment provides a hollow fiber separation membrane prepared by the method of the present invention.

[0223] (1) polybenzimidazole A1, tetrahydrofuran, and methanesulfonic acid were mixed and stirred at 60° C. and normal pressure for 72 h to obtain a mixed solution (casting solution); wherein the mass fractions of the mixed solution were: polybenzimidazole 8 wt %, tetrahydrofuran 2 wt %, and methanesulfonic acid 90 wt %;

[0224] The structural unit of the polybenzimidazole A1 is shown below:

[0225]

[0226] Wherein, the number average molecular weight of the polybenzimidazole A1 is 87,000;

[0227] (2) The mixed liquid is heated to 80° C. and extruded into a spinneret through a gear pump, using the spinneret shown in FIG1 ; the support is a polyethylene microporous membrane (prepared by a melt-spinning stretching method; pore size 1-10 μm, porosity 65%-80%); a concentric circle composite spinning technique is used to bring the casting liquid into contact with the polyethylene microporous membrane in the spinneret (spinneret cavity height 10 cm), the contact time is 10 s, and the contact pressure is 0.2 MPa; the support is pulled from bottom to top through the interior of the spinneret, passes through an annular scraper and controls the thickness of the polybenzimidazole primary membrane to be 80 μm, thereby obtaining a polybenzimidazole primary membrane attached to the support; excess casting liquid flows out through the casting liquid outlet, and part of the casting liquid penetrates into the support;

[0228] (3) After the polybenzimidazole primary film is pulled for 100 cm in an air bath at 150° C., it is cut and placed in an air bath at 150° C. for drying for 100 minutes to form a polybenzimidazole functional layer with a dense structure;

[0229] (4) introducing tetrahydrofuran into the support body through the central core tube to induce phase separation, thereby causing the portion of the casting liquid infiltrated into the support body to undergo non-solvent tetrahydrofuran-induced phase separation to form a connecting layer with a porous structure; subsequently, the solvent in the primary membrane is completely volatilized in an oven at 110° C.; and a finished membrane - a hollow fiber separation membrane is prepared.

[0230] The thickness of the functional layer of the prepared hollow fiber separation membrane is about 2000 nm; the connecting layer is embedded in the support body and has a thickness of about 180-190 μm (with an average thickness of about 185 μm).

[0231] The prepared hollow fiber separation membrane has a breaking strength of 52 MPa; at 100°C and a test pressure of 0.5 MPa, the pure helium flux is 82.2 GPU, the pure hydrogen flux is 79.6 GPU, the nitrogen flux and the methane flux are 0.68 GPU and 0.55 GPU respectively; the separation coefficients of hydrogen / nitrogen and hydrogen / methane reach 120.61 and 144.7 respectively.

[0232] Example 7

[0233] This embodiment provides a hollow fiber separation membrane prepared by the method of the present invention.

[0234] (1) Polybenzimidazole A7, tetrahydrofuran, and methanesulfonic acid were mixed and stirred at 60° C. and normal pressure for 24 hours to obtain a mixed solution (casting solution); wherein the mass fraction composition was: polybenzimidazole 8 wt %, tetrahydrofuran 2 wt %, and methanesulfonic acid 90 wt %;

[0235] The structural unit of the polybenzimidazole A7 is shown below:

[0236]

[0237] Wherein, the number average molecular weight of the polybenzimidazole A7 is 126,000;

[0238] (2) The mixed liquid is heated to 80° C. and extruded into a spinneret through a gear pump, using the spinneret shown in FIG1 ; the support is a polyethylene hydrophobic microporous membrane (prepared by melt spinning and stretching) with a porosity of 60%-80%; a concentric circle composite spinning technique is used to allow the casting liquid to contact the polyethylene hydrophobic microporous membrane in the spinneret (the spinneret cavity height is 10 cm), the contact time is 10 s, and the contact pressure is controlled at 0.1 MPa; the support is pulled from bottom to top through the interior of the spinneret, passes through an annular scraper and controls the thickness of the polybenzimidazole nascent membrane to be 80 μm, thereby obtaining a nascent polybenzimidazole membrane attached to the support; excess casting liquid flows out through the casting liquid outlet, and part of the casting liquid penetrates into the support;

[0239] (3) After the polybenzimidazole primary film is pulled for 100 cm in an air bath at 150° C., it is cut and placed in an air bath at 150° C. to dry for 100 minutes, to form a polybenzimidazole functional layer with a dense structure;

[0240] (4) introducing tetrahydrofuran into the support body through the central core tube to induce phase separation, thereby causing the portion of the casting liquid infiltrated into the support body to undergo non-solvent tetrahydrofuran-induced phase separation to form a connecting layer with a porous structure; subsequently, the solvent in the primary membrane is completely volatilized in an oven at 110° C.; and a finished membrane - a hollow fiber separation membrane is prepared.

[0241] The thickness of the functional layer of the prepared hollow fiber separation membrane is about 10 to 12 μm; the connecting layer is embedded in the support body and has a thickness of about 300 μm.

[0242] The prepared hollow fiber separation membrane has a breaking strength of 52 MPa; at 100°C and a test pressure of 0.5 MPa, the pure helium flux is 22.6 GPU, the pure hydrogen flux is 22.1 GPU, the nitrogen flux and the methane flux are 0.16 GPU and 0.13 GPU respectively; the separation coefficients of helium / nitrogen and helium / methane reach 141.4 and 173.8 respectively.

[0243] Comparative Example 1

[0244] (1) Polybenzimidazole A1 and methanesulfonic acid were mixed and stirred at 150° C. and 1.0 MPa for 24 h to obtain a mixed solution (casting solution); wherein the mass fraction composition was: polybenzimidazole 10 wt % and methanesulfonic acid 90 wt %;

[0245] The polybenzimidazole A1 comprises the following structural units:

[0246]

[0247] Wherein, the number average molecular weight of the polybenzimidazole A1 is 68,000;

[0248] (2) The mixed liquid is heated to 140° C. and extruded into a spinneret through a gear pump, using the spinneret shown in FIG1 ; a concentric circle composite spinning technique is used to make the casting liquid contact with a polyester fiber braided tube in the spinneret (the spinneret cavity height is 10 cm), and spinning is performed at 140° C. The casting liquid and the braided tube are in contact for 2 s, and the contact pressure is 0.05 MPa; the support is pulled from bottom to top through the interior of the spinneret, passes through an annular scraper, and controls the thickness of the polybenzimidazole primary film to be 100 μm, thereby obtaining a polybenzimidazole primary film attached to the support; excess casting liquid flows out through the casting liquid outlet, and part of the casting liquid penetrates into the support; when the polybenzimidazole primary film reaches a length of 200 cm, it is moved into an oven;

[0249] (3) The solvent in the polybenzimidazole primary membrane is completely volatilized directly in a 200°C oven, and then the residual solvent is removed through water washing and ethanol washing steps to form a finished membrane - a hollow fiber separation membrane.

[0250] The functional layer of the prepared hollow fiber separation membrane is very thick; there is no porous connecting layer, and the functional layer is directly attached to the support outside the support. Due to the lack of a connecting layer, the functional layer has poor adhesion to the support, easily detaching from the support, and thus shortening the membrane's lifespan. When the internal pressure exceeds 0.04 MPa, the functional layer is damaged. When external pressure is applied, the membrane's lifespan is reduced to only 2,000-5,000 hours after repeated pressure changes.

[0251] The prepared hollow fiber separation membrane has a breaking 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, the nitrogen flux and the methane flux are 0.11 GPU and 0.10 GPU respectively, and the separation coefficients of hydrogen / nitrogen and hydrogen / methane reach 105 and 116 respectively.

[0252] Figure 10 shows an electron microscope image of the hollow fiber separation membrane prepared in Comparative Example 1; from left to right and from top to bottom are images of the overall cross-section, functional layer, magnified functional layer, outer surface, inner surface and support cross-section.

[0253] Comparative Example 2

[0254] (1) Polybenzimidazole A7 and methanesulfonic acid were mixed and stirred at 150° C. and 1.0 MPa for 24 h to obtain a mixed solution (casting solution); wherein the mass fraction composition was: polybenzimidazole 10 wt % and methanesulfonic acid 90 wt %;

[0255] The structural units of the polybenzimidazole A7 are as follows:

[0256]

[0257] Wherein, the number average molecular weight of the polybenzimidazole A7 is 126,000;

[0258] (2) The mixed liquid was extruded through a gear pump, and a spinneret as shown in FIG1 was used. The concentric circle composite spinning technology was adopted to make the casting liquid contact with the nylon braided tube in the spinneret (the spinneret cavity height was 10 cm). The spinning was carried out at 140° C. The contact time between the casting liquid and the braided tube was 2 s, and the contact pressure was 0.1 MPa. The thickness of the primary polybenzimidazole membrane was controlled to be 30 μm by an annular scraper. The membrane was passed through a 200 cm length and entered into a pure water coagulation bath and was wound at a winding speed of 5 cm / min.

[0259] (3) The solvent in the primary membrane is then transferred to water in pure water, and the residual solvent is removed through water washing and ethanol washing steps to form a finished membrane - a hollow fiber separation membrane.

[0260] The average thickness of the prepared hollow fiber separation membrane was approximately 600 μm; the thickness of the functional layer was approximately 500 nm; and the outer diameter of the support was 1400 μm. The membrane's functional layer exhibited poor adhesion to the support, which resulted in the membrane's easy detachment and reduced lifespan. The functional layer was damaged when the internal pressure exceeded 0.05 MPa.

[0261] In addition, the prepared hollow fiber separation membrane has a breaking 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, the nitrogen flux and the methane flux are 0.33 GPU and 0.27 GPU respectively. The separation coefficients of hydrogen / nitrogen and hydrogen / methane reach 83.7 and 102.2 respectively.

[0262] Comparative Example 3

[0263] (1) Polybenzimidazole A7 and N-methylpyrrolidone (NMP) were mixed and stirred at 50° C. and normal pressure for 24 hours to obtain a mixed solution (casting solution); wherein the mass fraction composition was: polybenzimidazole 10 wt %, NMP 90 wt %;

[0264] The structural units of the polybenzimidazole A7 are as follows:

[0265]

[0266] Wherein, the number average molecular weight of the polybenzimidazole A7 is 126,000;

[0267] (2) The mixed liquid was extruded through a gear pump, and a spinneret as shown in FIG1 was used. The concentric circle composite spinning technology was adopted to make the casting liquid contact with the nylon braided tube in the spinneret (the spinneret cavity height was 10 cm). The spinning was carried out at 60° C. The contact time between the casting liquid and the braided tube was 2 s, and the contact pressure was 0.05 MPa. The thickness of the primary polybenzimidazole membrane was controlled to be 30 μm by an annular scraper. The membrane was passed through a 200 cm length and entered a pure water coagulation bath and was wound at a winding speed of 5 cm / min.

[0268] (3) The solvent in the primary membrane is then transferred to water in pure water to form a finished membrane; the residual solvent is then removed through water washing and ethanol washing steps.

[0269] The thickness of the functional layer of the prepared hollow fiber separation membrane is about 200 nm, the structure of the membrane is not dense, and the selectivity is low; when the internal pressure exceeds 0.1 MPa, the functional layer is damaged.

[0270] In addition, the prepared hollow fiber separation membrane has a breaking strength of 165 MPa. At 100°C and a test pressure of 0.5 MPa, the pure helium flux is 107 GPU, the pure hydrogen flux is 89.5 GPU, the nitrogen flux and the methane flux are 12.9 GPU and 11.4 GPU respectively. The separation coefficients of hydrogen / nitrogen and hydrogen / methane reach 6.94 and 7.85 respectively.

[0271] Example of Purifying Helium

[0272] The raw helium-rich gas includes: 20% by volume of helium, 17% by volume of methane, 60% by volume of nitrogen, 1% by volume of hydrogen, 0.5% by volume of carbon dioxide, and 1.5% by volume of oxygen.

[0273] The helium-rich gas is refined as shown in FIG11 :

[0274] (1) Raw gas 1# first enters the cryogenic unit, where the temperature is -180°C and the pressure is 4 MPa;

[0275] (2) The top gas 2# obtained in step (1) enters the catalytic dehydrogenation unit, and a small amount of pure oxygen is introduced as a combustion-supporting gas during the combustion process to ensure the smooth operation of the catalytic reaction. The catalyst is Pt and the temperature is 98°C;

[0276] (3) The combusted gas is dried and then enters the membrane unit 3#, and is passed through the membrane assembly prepared by the hollow fiber membrane of Example 4 of the present application to perform primary and secondary membrane separation operations. The operating pressures on the positive pressure side of the membrane separation are 3 MPa and 3 MPa respectively;

[0277] (4) The helium-poor gas on the retentate side is refluxed to the cryogenic unit, and the crude helium product 4# on the permeate side enters the adsorption and impurity removal unit for pressure swing adsorption operation, wherein a composite adsorbent of 5A molecular sieve, coconut shell activated carbon, and activated alumina is used, with an adsorption pressure of 10 MPa, to obtain refined helium 5#.

[0278] The gas composition of each stage of the helium purification method is shown in Table 1.

[0279] Table 1

[0280] No.\Composition% Helium Nitrogen Methane Oxygen Hydrogen CO2 Water Raw gas 1#2060171.510.50 Cryogenic separation 2#73.3522.960.010.023.6600 Catalytic dehydrogenation 3#75.3223.570.011.070.0200.01 Primary membrane 95.8653.9310.0010.1790.02300.001 Secondary membrane 4#99.750.21700.010.02300 Product 5#99.9950.00500000

[0281] As can be clearly seen from the table above, the present invention can significantly increase the helium concentration through the cryogenic process, and effectively remove hydrogen in the mixed gas that is difficult to separate from the helium through the catalytic oxidation stage. Then, membrane separation is used for deep purification, and the resulting crude helium gas concentration is 99.75%. Then, through pressure swing adsorption, the resulting product helium concentration can reach 99.995%, meeting the 4N grade standard.

[0282] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A hollow fiber separation membrane, characterized in that The hollow fiber separation membrane includes a support, a functional layer, and a connecting layer located between the support and the functional layer, wherein at least a portion of the connecting layer is embedded in the support.

2. The hollow fiber separation membrane according to claim 1, wherein The connecting layer and the functional layer contain the same polymer; preferably, the connecting layer and the functional layer contain the same polymer and the connecting layer and the functional layer are formed from the same casting liquid; more preferably, the connecting layer and the functional layer contain the same polymer, the connecting layer and the functional layer are formed from the same casting liquid, and the connecting layer and the functional layer are formed by non-solvent-induced phase separation and thermally induced phase separation, respectively.

3. The hollow fiber separation membrane according to any one of claims 1 to 2, wherein The connecting layer and the functional layer both contain polybenzimidazole; preferably, the number average molecular weight of the polybenzimidazole is 50,000-300,000, more preferably the number average molecular weight of the polybenzimidazole is 56,000-287,000.

4. The hollow fiber separation membrane according to claim 3, wherein The polybenzimidazole comprises one or more structural units represented by formulas (A1) to (A8); Preferably, the polybenzimidazole comprises one or more structural units represented by formulae (A5) to (A8).

5. The hollow fiber separation membrane according to any one of claims 1 to 4, wherein The support is a fiber braided tube or a hollow fiber membrane, preferably a hollow fiber microporous membrane, more preferably one or more selected from a fiber braided tube, a polypropylene hollow microporous membrane, a polyethylene hollow microporous membrane and an inorganic hollow microporous membrane; and / or The connecting layer has a porous structure; and / or The connecting layer is obtained by non-solvent induced phase separation of the casting solution, and preferably the connecting layer is obtained by non-solvent induced phase separation of an acid solution containing polybenzimidazole.

6. The separation membrane according to any one of claims 1 to 5, wherein the average thickness of the hollow fiber separation membrane is 100-2000 μm; And / or, the average thickness of the tube wall of the support body is 50-2000 μm; And / or, the average thickness of the functional layer is 100-50000 nm; and / or, the average thickness of the connecting layer is 20-2000 μm; and / or, the separation membrane has a breaking strength of 10-500 MPa; and / or, at 100° C. and a test pressure of 0.5 MPa, a hydrogen / nitrogen separation factor of 110-300 and a hydrogen / methane separation factor of 125-360; and / or, at 100° C. and a test pressure of 0.5 MPa, a helium / nitrogen separation factor of 140-390 and a helium / methane separation factor of 170-500; and / or, at 25° C. and a test pressure of 0.5 MPa, a hydrogen / nitrogen separation factor of 200-550 and a hydrogen / methane separation factor of 200-860; And / or, at 25° C. and a test pressure of 0.5 MPa, the separation factor of helium / nitrogen is 240-900, and the separation factor of helium / methane is 200-2000.

7. A method for preparing a hollow fiber separation membrane, characterized in that: The method comprises: (1) preparing a casting solution containing a polymer; (2) coating the casting solution on a support, wherein a portion of the casting solution penetrates into the support to obtain a primary film coated on the support; (3) heating the primary film to form a functional layer; (4) injecting a core liquid into the support body to cause the casting liquid that has penetrated into the support body to undergo non-solvent induced phase separation to form a connecting layer; and (5) Optionally, heating is performed after forming the tie layer to remove substantially all of the solvent.

8. The method according to claim 7, wherein: Using a scraper, preferably an annular scraper, to coat the casting solution on the support; and / or The support is pulled through the casting liquid, preferably the support is pulled through the casting liquid from bottom to top; and / or The support is a fiber braided tube or a hollow fiber membrane, preferably a hollow fiber microporous membrane, and more preferably the support is one or more selected from a fiber braided tube, a polypropylene hollow microporous membrane, a polyethylene hollow microporous membrane and an inorganic hollow microporous membrane.

9. The method according to claim 7 or 8, wherein The casting solution is obtained by mixing the polymer, acid, optional volatile solvent and optional additives; preferably, the mixing conditions include: temperature of 25-160° C. and time of 2-72 hours.

10. The method according to any one of claims 7 to 9, wherein: The polymer is polybenzimidazole; preferably, the number average molecular weight of the polybenzimidazole is 50,000-300,000, and more preferably, the number average molecular weight of the polybenzimidazole is 56,000-287,000.

11. The method according to claim 10, wherein: The polybenzimidazole comprises one or more structural units represented by formulas (A1) to (A8); Preferably, the polybenzimidazole comprises one or more structural units represented by formulae (A5) to (A8).

12. The method according to claim 10, wherein the acid is a monoprotic acid; preferably, the acid is selected from hydrochloric acid, hydrofluoric acid, methanesulfonic acid or a mixture thereof; and / or, the volatile solvent is selected from methanol, ethanol, tetrahydrofuran or a mixture thereof; and / or, the additive is selected from lithium nitrate, calcium chloride, sodium chloride, potassium chloride, polyethylene glycol, polyethylene oxide or a mixture thereof; and / or, the core liquid is selected from water, ethanol, methanol, isopropanol, acetone, tetrahydrofuran or a mixture thereof; And / or, based on the total weight of the casting solution, the amount of polybenzimidazole is 4-18wt%, the amount of the acid is 77-90wt%, the amount of the volatile solvent is 0-10wt%, and the amount of the additive is 0-5wt%.

13. The method according to claim 10, wherein the coating conditions include: Temperature is 20-240℃; And / or, the heating conditions in step (3) include: a temperature of 100-280°C; And / or, the contact time between the casting solution and the support is 1-15 seconds.

14. The method according to any one of claims 7 to 13, wherein: The coating in step (2) is implemented using a spinneret, which includes a support positioner, an annular scraper, and a core tube; The support body positioner forms a cavity around the support body; the cavity is used to store the casting liquid, and 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, and the diameter of the annular scraper is greater than the width of the support body positioner; The core tube is built into the supporting body. 15 . The method according to claim 7 , wherein the hollow fiber separation membrane is the hollow fiber separation membrane according to claim 1 .

16. A hollow fiber separation membrane prepared by the method according to any one of claims 7 to 14.

17. Use of the hollow fiber separation membrane according to any one of claims 1 to 6 and 16 for separation of helium / nitrogen, helium / methane, hydrogen / nitrogen or hydrogen / methane.

18. A method for purifying helium from a gas containing helium, characterized in that: The method comprises performing membrane separation using the hollow fiber separation membrane according to any one of claims 1 to 6 and 16.

19. The method according to claim 18, wherein The method comprises: subjecting the gas containing helium to condensation treatment, catalytic dehydrogenation treatment, membrane separation treatment and pressure swing adsorption impurity removal treatment through a cryogenic process to obtain purified helium.

20. The method according to claim 19, wherein The conditions for the condensation treatment include: temperature ≥ -220°C; preferably, the conditions for the condensation treatment include: temperature of -210°C to -150°C, pressure of 0.2-10 MPa; more preferably, the conditions for the condensation treatment include: temperature of -180°C to -150°C, pressure of 3-10 MPa; and / or Wherein, the conditions of the catalytic dehydrogenation treatment include: a temperature of 60-120°C, preferably 60-110°C; and / or wherein the catalytic dehydrogenation treatment is carried out in the presence of oxygen and a catalyst, wherein the catalyst is a noble metal catalyst; preferably, the catalyst is selected from Pt, Pb, Rh, Ru or Au; more preferably, the catalyst is selected from Pt, Pb or Au; and / or Wherein, the conditions of the membrane separation treatment include: membrane separation positive pressure side pressure > membrane separation permeate side pressure; preferably, the membrane separation positive pressure side pressure is 0.2-10MPa, more preferably, the membrane separation positive pressure side pressure is 0.5-10MPa; and / or The conditions for the pressure swing adsorption impurity removal treatment include: an adsorption pressure of 0.2-15 MPa, preferably 10-15 MPa; And / or, the adsorbent used in the adsorption and impurity removal treatment is selected from one or more of activated carbon, molecular sieve, metal organic framework material MOF, and activated alumina.

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