Preparation method and application of hollow fiber humidifying membrane

Abstract

The invention provides a preparation method and application of a hollow fiber humidification membrane, belongs to the technical field of separation membrane materials, and aims to solve the problems that in an existing method, mechanical performance is partially reduced due to acid treatment, and long-time use of a membrane tube is not facilitated. The invention relates to a preparation method of a hollow fiber humidifying membrane, which comprises the following steps: mixing a polysulfone high polymer material, a small molecule additive, a pore-foaming agent and an organic solvent, stirring and dissolving to form a uniform solution; enabling the uniform solution and the core liquid to pass through a spinning nozzle to obtain hollow fiber membrane filaments; performing multi-section temperature control heat treatment to obtain membrane filaments with a metastable-state pore channel structure; putting into a cross-linking liquid medium to keep constant temperature, then washing with water, and finally drying to obtain the hollow fiber humidifying membrane. The pore-foaming agent is polyvinylpyrrolidone. The hollow fiber membrane provided by the invention can be used as a humidifying membrane in a water management process of a fuel cell proton exchange membrane, and is particularly applied to a high-power fuel cell membrane humidifier.

Description

Technical Field

[0001] The present invention relates to the technical field of separation membrane materials, and particularly to a preparation method and application of a hollow fiber humidification membrane. Background Art

[0002] As one of the most mature fuel cells, proton exchange membrane fuel cells (PEMFCs) have the advantages of zero pollution, low operating temperature, high current density, and fast response speed, and have broad application prospects. When a PEMFC generates electricity, the hydrogen ions generated by the electrochemical reaction must combine with a certain number of water molecules before they can be transmitted between the membranes. When the number of water molecules bound to each sulfonate group in the membrane is less than four, the membrane cannot conduct hydrogen ions. When the water content in the membrane is moderate, not only its conductivity reaches the optimal value, but also its internal resistance is minimized. Therefore, the water content of the electrolyte membrane directly reflects the ohmic voltage loss of the battery and the water content of the diffusion layer, and greatly affects the performance of the battery. Therefore, it is necessary to humidify the reaction gases entering the fuel cell stack, and the membrane humidifier has become the mainstream solution adopted in the current hydrogen fuel cell system.

[0003] The humidification membrane is a key component of the membrane humidifier, and its water vapor permeability, water vapor / air selectivity, and application stability will directly affect the performance of the membrane humidifier. Traditional hollow fiber humidification membranes are usually produced under relatively mild conditions using conventional preparation processes. However, when applied to high-power fuel cell systems, such humidification membranes face many challenges. When a high-power fuel cell operates, it has a relatively high temperature. In a high-temperature environment, the polymer chain segments of ordinary humidification membranes are prone to increased thermal motion, resulting in deformation or even collapse of the membrane pore structure. This will not only reduce the water transmission efficiency of the humidification membrane, but also may cause a significant decrease in the mechanical strength of the membrane, affecting its service life, and thus severely restricting the performance and stability of the fuel cell system.

[0004] Currently, most of the humidification membranes applied to high-power systems use high-temperature cross-linking treatment and acid treatment to improve the performance and application stability of the membrane. However, the high-temperature cross-linking temperatures mentioned in the patents are all relatively high. On the one hand, the energy consumption is relatively high at this temperature, and the required equipment is all high-temperature and high-pressure, which is not conducive to batch production. On the other hand, acid treatment can improve the humidification performance of the humidification membrane, but at the same time, it also causes partial reduction of the mechanical properties, which is not conducive to the long-term use of the membrane tube. Under high-temperature and high-flow impact, the humidification membrane is prone to bursting or breaking, so that it cannot meet the requirements of the system working conditions. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the present invention provides a preparation method and application of a hollow fiber humidification membrane to solve the problems in the existing methods, where high-temperature cross-linking treatment and acid treatment are used to improve the performance and application stability of the membrane, but the acid treatment also causes partial reduction of mechanical properties, which is not conducive to the long-term use of the membrane tube.

[0006] The specific invention content is as follows: In a first aspect, the present invention provides a preparation method of a hollow fiber humidification membrane, including the following steps: S1: Mix a polysulfone-based polymer material, a small molecule additive, a pore-forming agent, and an organic solvent, and stir and dissolve to form a homogeneous solution; S2: After passing the homogeneous solution and the core liquid through a spinneret, enter a coagulation bath for solidification and molding to obtain semi-solution-state hollow fiber membrane filaments; S3: Perform multi-stage temperature-controlled heat treatment on the semi-solution-state hollow fiber membrane filaments to obtain membrane filaments with a metastable pore structure; S4: Place the membrane filaments with the metastable pore structure in a cross-linking liquid medium at 80-100 °C for 2-10 h, then transfer to a constant-temperature circulating water for washing, and finally dry to obtain a hollow fiber humidification membrane; The small molecule additive is at least one of polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, water, ethanol, and diethylene glycol monoethyl ether, and the pore-forming agent is polyvinylpyrrolidone.

[0007] Preferably, in the step S1, based on the mass of the homogeneous solution being 100%, the amount of the polymer material is 15-30 wt%, the amount of the small molecule additive is 2%-20 wt%, the amount of the pore-forming agent is 2%-20 wt%, and the rest is an organic solvent; The organic solvent is at least one of dimethyl sulfoxide, N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, and triethyl phosphate.

[0008] Preferably, in the step S3, the multi-stage temperature-controlled heat treatment includes: First, place the hollow fiber membrane filaments in an environment with a temperature of 20-60 °C for no more than 10 min to quickly form the semi-solution-state membrane filaments; Then, wind up and concentrate the hollow fiber membrane filaments and transfer them to an environment with a temperature of 45-90 °C for continuous treatment for 2-6 h to cause the additives in the membrane to migrate to the surface and obtain membrane filaments with a metastable pore structure.

[0009] Preferably, the polysulfone-based polymer material is at least one of polysulfone, polyethersulfone, polyphenylsulfone, sulfonated polyphenylsulfone, sulfonated polyethersulfone, sulfonated polysulfone, polyimide, and polyetheretherketone.

[0010] Preferably, in the step S4, the cross-linking liquid medium is any one of glutaraldehyde, azobisisobutyronitrile aqueous solution and persulfide solution.

[0011] Preferably, in the step S4, the constant-temperature circulating water is deionized water, the temperature of the constant-temperature water washing is 20 - 60 °C, and the time of the constant-temperature water washing is 10 - 24 h.

[0012] Preferably, after the membrane filaments with the metastable pore structure are transferred to the constant-temperature circulating water for water washing in the step S4, the method further includes: Placing the washed membrane filaments with the metastable pore structure in a wetting liquid medium at 20 - 60 °C for constant temperature for 5 - 24 h, and then drying to obtain a hollow fiber humidifying membrane.

[0013] Preferably, the wetting liquid medium is at least one of sodium dodecylbenzenesulfonate, quaternary ammonium compound, acid glyceride, polysorbate, span, pyrrolidone carboxylic acid and betaine.

[0014] In a second aspect, the present invention provides a hollow fiber humidifying membrane prepared by the method for preparing a hollow fiber humidifying membrane described in the first aspect above. The cross-section of the hollow fiber humidifying membrane is a sponge pore structure, the outer surface is loose and porous, and the inner surface is dense.

[0015] Preferably, the maximum load of the hollow fiber membrane is greater than 6 N, the strength of the hollow fiber membrane is greater than 9 MPa, and the elongation at break of the hollow fiber membrane is greater than 50%.

[0016] Preferably, the hollow fiber membrane is kept at a constant temperature of 95 °C in a dry state for 200 h, the maximum load is still greater than 6 N, the strength of the hollow fiber membrane is still greater than 9 MPa, and the elongation at break of the hollow fiber membrane is still greater than 50%.

[0017] In a third aspect, an application of a hollow fiber humidifying membrane prepared by the method for preparing a hollow fiber humidifying membrane described in the first aspect above is proposed. The hollow fiber membrane is applied to a humidifier in a high-power hydrogen fuel cell system.

[0018] Compared with the prior art, the present invention has the following advantages: A high-temperature resistant hollow fiber membrane provided by the present invention is prepared through multi-stage heat treatment, which strengthens the stability of polymer chain segments while eliminating or reducing internal stress during the processing of the membrane tube, ensures the stability of the membrane pore structure, enhances the strength and high-temperature resistance of the membrane tube. At 95 °C, the maximum load is still greater than 6 N, the tensile strength is still greater than 9 MPa, and the elongation at break is still greater than 50% after 200 h of dry-state constant temperature. Meanwhile, the high-temperature treatment temperature is 80-100 °C, which ensures the cross-linking reaction inside the membrane while reducing energy consumption and is easy for batch production. After high-temperature treatment of this membrane tube, hydrophilic substances are not easily dissolved out from the membrane tube, endowing the membrane with high hydrophilicity, and further endowing it with high water vapor permeability and permeation stability. Therefore, the high-temperature resistant hollow fiber membrane provided by the present invention can be used as a humidifying membrane in the water management process of fuel cell proton exchange membranes, especially applied to the membrane humidifier of high-power fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0020] Figure 1 Shows the flow chart of the preparation method of the hollow fiber membrane provided by the embodiment of the present invention; Figure 2 Shows the SEM image of the cross-section of the hollow fiber membrane provided by the embodiment of the present invention; Figure 3 Shows the partially enlarged SEM image of the cross-section of the hollow fiber membrane provided by the embodiment of the present invention; Figure 4 Shows the SEM image of the inner surface of the hollow fiber membrane provided by the embodiment of the present invention; Figure 5 Shows the SEM image of the outer surface of the hollow fiber membrane provided by the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually illustrative only and in no way limits the present invention and its application or use. Based on the embodiments of the present invention, any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with the features of other existing technologies falls within the protection scope of the present invention. In addition, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

[0022] Where the specific experimental steps or conditions are not specified in the embodiments, the operations or conditions of the conventional experimental steps described in the prior art in this field can be followed. The reagents and other instruments not indicating the manufacturer can be obtained as conventional reagent products through commercial purchase. In addition, the accompanying drawings are only schematic illustrations of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings represent the same or similar parts, and thus the repeated description thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0023] The technologies, methods, and devices known to those of ordinary skill in the relevant fields may not be discussed in detail, but where appropriate, the said technologies, methods, and devices should be regarded as part of the description of the present invention.

[0024] In the description of the present invention, it should be understood that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Without further statement, the above terms have no special meaning and thus should not be construed as limiting the protection scope of the present invention.

[0025] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] Before elaborating on a method for preparing a hollow fiber humidifying membrane and its application provided by the present invention, it is necessary to make the following description of the related technologies: As one of the most mature fuel cells, the proton exchange membrane fuel cell (PEMFC) has the advantages of zero pollution, low operating temperature, high current density, and fast response speed, and has broad application prospects. When the PEMFC generates electricity, the hydrogen ions generated by the electrochemical reaction must combine with a certain number of water molecules before they can be transferred between the membranes. When the number of water molecules bound to each sulfonate group in the membrane is less than four, the membrane cannot conduct hydrogen ions. When the water content in the membrane is moderate, not only its conductivity reaches the optimal value, but also its internal resistance will be reduced to the minimum. Therefore, the water content of the electrolyte membrane directly reflects the Ohmic voltage loss of the battery and the water content of the diffusion layer, and greatly affects the performance of the battery. Therefore, it is necessary to humidify the reaction gases entering the fuel cell stack, and the membrane humidifier has become the mainstream solution adopted by the current hydrogen fuel cell system.

[0027] The humidifying membrane is a key component of the membrane humidifier, and its water vapor permeability, water vapor / air selectivity, and application stability will directly affect the performance of the membrane humidifier. Traditional hollow fiber humidifying membranes are usually produced by conventional preparation processes under relatively mild conditions. However, when applied to high-power fuel cell systems, such humidifying membranes face many challenges. When a high-power fuel cell operates, it has a relatively high temperature. In a high-temperature environment, the polymer chain segments of ordinary humidifying membranes are prone to increased thermal motion, resulting in deformation or even collapse of the membrane pore structure. This will not only reduce the water transmission efficiency of the humidifying membrane, but also may cause a significant decrease in the mechanical strength of the membrane, affecting its service life, and thus severely restricting the performance and stability of the fuel cell system.

[0028] At present, most of the humidifying membranes applied to high-power systems use high-temperature cross-linking treatment and acid treatment to improve the performance and application stability of the membrane. However, the high-temperature cross-linking temperatures mentioned in the patents are relatively high. On the one hand, the energy consumption is relatively high at this temperature, and the required equipment is high-temperature and high-pressure, which is not conducive to mass production. On the other hand, acid treatment can improve the humidifying performance of the humidifying membrane, but at the same time it also causes some reduction in mechanical properties, which is not conducive to the long-term use of the membrane tube. Under the impact of high temperature and high flow rate, the humidifying membrane is prone to bursting or breaking, so that it cannot meet the requirements of the system working conditions.

[0029] To enable those skilled in the art to understand the present invention more clearly, the following examples are now used to describe in detail a method for preparing a hollow fiber humidifying membrane according to the present invention.

[0030] To obtain a high-temperature resistant hollow fiber humidification membrane, the design idea proposed by the present invention is as follows: Through multi-stage heat treatment, while strengthening the stability of polymer chain segments, internal stress during the membrane tube processing is eliminated or reduced, ensuring the stability of the membrane pore structure, enhancing the strength and high-temperature resistance of the membrane tube; at the same time, the high-temperature treatment temperature is 80-100 °C, which ensures the cross-linking reaction inside the membrane while reducing energy consumption and facilitating batch production. In addition, after the cross-linking reaction of the high-temperature treated membrane tube, polyvinylpyrrolidone is not easily dissolved out from the membrane tube, endowing the membrane with high hydrophilicity, and then endowing it with high water vapor permeability and permeation stability. Therefore, the high-temperature resistant hollow fiber membrane provided by the present invention can be used as a humidification membrane in the water management process of fuel cell proton exchange membranes, especially applied to the humidifier of high-power fuel cell membranes, and has strong competitiveness.

[0031] In a first aspect, an embodiment of the present invention provides a method for preparing a hollow fiber humidification membrane, Figure 1 which shows a flowchart of the method for preparing the hollow fiber membrane provided by the embodiment of the present invention, as Figure 1 shown, including the following steps: S1: Mix a polysulfone-based polymer material, a small molecule additive, a pore-forming agent, and an organic solvent, and stir and dissolve to form a homogeneous solution; In some embodiments, the polysulfone-based polymer material is at least one of polysulfone, polyethersulfone, polyphenylsulfone, sulfonated polyphenylsulfone, sulfonated polyethersulfone, sulfonated polysulfone, polyimide, and polyetheretherketone; the small molecule additive is at least one of polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, water, ethanol, and diethylene glycol; the pore-forming agent is polyvinylpyrrolidone; the organic solvent is at least one of dimethyl sulfoxide, N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, and triethyl phosphate; In some embodiments, in step S1, based on the mass of the homogeneous solution being 100%, the amount of the polymer material is 15-30 wt%, the amount of the small molecule additive is 2%-20 wt%, the amount of the pore-forming agent is 2%-20 wt%, and the rest is the organic solvent.

[0032] S2: After passing the homogeneous solution and the core liquid through a spinneret, enter a coagulation bath for solidification and molding to obtain a semi-solution state hollow fiber membrane filament; In specific implementation, the homogeneous solution is introduced into the outer channel of the spinneret through a metering pump, and the core liquid is introduced into the inner channel of the spinneret through a metering pump. The homogeneous solution is extruded through the spinneret, and under the action of the core liquid and the air bath, a primary coagulation solution film is formed. The primary coagulation solution film is introduced into the coagulation bath for solidification and molding to obtain a semi-solution state hollow fiber membrane filament; In some embodiments, a constant nitrogen gas is added to the extrusion of the homogeneous solution and the core liquid in the kettle to reduce the influence caused by the liquid level difference; S3: Perform multi-stage temperature-controlled heat treatment on the semi-solution-state hollow fiber membrane filaments; In some embodiments, first place a single semi-solution-state hollow fiber membrane filament in an environment with a temperature of 20 - 60 °C and treat it for no more than 10 minutes to quickly form the membrane filament; Through low-temperature treatment of a single membrane filament, the membrane filament that is still not fully solidified and formed inside quickly forms from the semi-solution state; Then wind up and concentrate multiple low-temperature-treated hollow fiber membrane filaments and transfer them to an environment with a temperature of 45 - 90 °C and continue to treat for 2 - 6 hours to allow the additives inside the membrane to migrate to the surface and obtain membrane filaments with a metastable pore structure; Through medium-temperature treatment, the additives including the solvent inside the membrane filament migrate to the surface, further evaporating the residual solvent and allowing the additives to migrate to the surface to form a pore structure, without causing the loss of additives and ensuring the effect of subsequent high-temperature cross-linking.

[0033] S4: Place the membrane filaments with the metastable pore structure in a cross-linking liquid medium at 80 - 100 °C and keep it at a constant temperature for 2 - 10 hours, then transfer it to wash in a constant-temperature circulating water, place the washed membrane filaments with the metastable pore structure in a wetting liquid medium at 20 - 60 °C and keep it at a constant temperature for 5 - 24 hours, and then dry to obtain hollow fiber humidifying membranes; In some embodiments, in step S4, the cross-linking liquid medium is one of glutaraldehyde, azobisisobutyronitrile aqueous solution, and persulfide solution.

[0034] In some embodiments, in step S4, the constant-temperature circulating water is deionized water, the constant-temperature washing temperature is 20 - 60 °C, and the constant-temperature washing time is 10 - 24 hours.

[0035] In some embodiments, the wetting liquid medium is at least one of sodium dodecylbenzenesulfonate, quaternary ammonium compound, acid glyceride, polysorbate, span, pyrrolidone carboxylic acid, and betaine.

[0036] In some embodiments, for the low-temperature treatment and medium-temperature treatment, in addition to using a water bath as the way to control the temperature and water as the heat transfer medium, air, inert gas, oil, salt, etc. can also be used as the medium, and oven heating, oil bath heating, and salt bath / sand bath heating can be used as the ways to control the temperature to control the temperatures of the low-temperature treatment and medium-temperature treatment.

[0037] Adopting this technical solution, using the spinning head extrusion technology combined with the method of solidifying and forming in a coagulation bath can precisely control the diameter and wall thickness of the fiber, thereby affecting the air permeability and moisture permeability of the final product.

[0038] With this technical solution, through multi-stage temperature-controlled heat treatment steps, the additives in the membrane migrate to the surface, forming a metastable pore structure. This method helps to optimize the microporous structure of the membrane and improve its moisture absorption and desorption performance.

[0039] With this technical solution, through the low-temperature treatment of a single membrane filament and the medium-temperature treatment of multiple membrane filaments after low-temperature treatment, it is convenient for the rapid shaping of a single membrane filament. At the same time, the medium-temperature treatment of multiple filaments improves the treatment efficiency.

[0040] With this technical solution, through low-temperature heat treatment, medium-temperature heat treatment and constant-temperature treatment in a cross-linking liquid medium at 80 - 100 °C followed by water washing, the stability of the membrane can be further enhanced. At the same time, unreacted solvents and other impurities are removed, ensuring the purity and safety of the product.

[0041] With this technical solution, after drying after treatment with a wetting liquid medium, the hydrophilicity of the membrane can be increased, making it more suitable for use as an efficient humidification membrane.

[0042] In addition, the present invention also provides a hollow fiber humidification membrane prepared by the preparation method of the hollow fiber humidification membrane. The cross-section of the hollow fiber humidification membrane is a sponge pore structure, with a porous outer surface and a dense inner surface; the maximum load of the hollow fiber membrane is greater than 6 N, the strength of the hollow fiber membrane is greater than 9 MPa, and the elongation at break of the hollow fiber membrane is greater than 50%; the hollow fiber membrane is kept at a constant temperature of 95 °C in the dry state for 200 h, and the maximum load is still greater than 6 N, the strength of the hollow fiber membrane is still greater than 9 MPa, and the elongation at break of the hollow fiber membrane is still greater than 50%.

[0043] In addition, the present invention also proposes an application of a hollow fiber humidification membrane prepared by the preparation method of the hollow fiber humidification membrane. The hollow fiber membrane is applied to a humidifier in a high-power hydrogen fuel cell system.

[0044] With this technical solution, due to the good air permeability and moisture permeability of the hollow fiber humidification membrane, and the characteristics of a porous outer surface and a dense inner surface, it is very suitable for use in the humidifier of a hydrogen fuel cell system to maintain an appropriate humidity level and improve the battery efficiency and life.

[0045] With this technical solution, by effectively controlling the air humidity entering the fuel cell, the problem of electrolyte membrane damage caused by drying can be significantly reduced, thereby improving the overall performance and reliability of the fuel cell.

[0046] With this technical solution, the hollow fiber humidification membrane prepared by this method can not only meet the needs of industrial applications, but also reduce the use of harmful substances in the production process, playing a positive role in environmental protection.

[0047] The present invention is the first attempt to apply the prepared hollow fiber membrane to the membrane humidifier of high-power fuel cells. The prepared high-temperature resistant hollow fiber membrane has strong competitiveness in the humidification application scenario during the water management process of the proton exchange membrane of high-power fuel cells. The decay rate of the water vapor transmission rate after 400 hours of its application is less than 10%.

[0048] Example 1 Select polyethersulfone as the polysulfone-based polymer material, polyethylene glycol 400 as the small molecule additive, polyvinylpyrrolidone as the pore-forming agent, and N,N-dimethylformamide as the organic solvent. According to the mass ratio, weigh 24% of polyethersulfone, 5% of polyethylene glycol 400, 10% of polyvinylpyrrolidone, and the remaining 61% is N,N-dimethylformamide.

[0049] Mix the above materials and stir to dissolve at 60°C until a homogeneous solution is formed.

[0050] Introduce the homogeneous solution into the outer channel of the spinneret through a metering pump, and introduce the core liquid into the inner channel of the spinneret through a metering pump. The homogeneous solution is extruded from the spinneret and forms a primary coagulation solution film under the action of the core liquid and the air bath. Then, introduce the primary coagulation solution film into the coagulation bath for solidification and molding. Subsequently, introduce the solidified and semi-solution-state hollow fiber membrane filaments into a water washing tank at 25°C, perform low-temperature treatment for 8 minutes and then wind up. Then, place the wound hollow fiber membrane filaments in a water washing tank at 60°C for medium-temperature treatment for 4 hours.

[0051] Put the metastable pore structure membrane filaments after medium-temperature treatment into a glutaraldehyde cross-linking liquid medium at 90°C and perform constant-temperature treatment for 6 hours. Then, perform water washing, set the water washing temperature at 40°C, the water washing time at 6 hours, and use circulating water for water washing. After the water washing is completed, put the membrane filaments into a sodium dodecylbenzenesulfonate wetting liquid medium at 40°C and keep it at a constant temperature for 12 hours. Finally, perform constant-temperature drying at 60°C in an oven for 4 hours to obtain the hollow fiber humidification membrane.

[0052] See Figures 2 - 5 , Figure 2 shows the SEM image of the cross-section of the hollow fiber membrane provided in this embodiment; Figure 3 shows the partially enlarged SEM image of the cross-section of the hollow fiber membrane provided in this embodiment; Figure 4 shows the SEM image of the inner surface of the hollow fiber membrane provided in this embodiment; Figure 5 shows the SEM image of the outer surface of the hollow fiber membrane provided in this embodiment. It can be seen that the hollow fiber humidification membrane prepared in this embodiment mainly includes an ultrathin and dense inner surface cortex and a porous outer surface. The thickness of the inner surface cortex is 1.429 μm, and the cross-section is a sponge-like and uniform porous structure.

[0053] Referring to the mechanical property data of the high-temperature resistant hollow fiber humidifying membrane shown in Table 1, the maximum load of the covalent organic framework hollow fiber membrane for humidification prepared in Example 1 is 7.2 N, the tensile strength reaches 10.1 MPa, and the elongation at break is 55%. After the membrane is kept at a constant temperature of 95 °C in the dry state for 200 h, the maximum load is still greater than 7 N, the tensile strength is greater than 10 MPa, and the elongation at break > 50% when detected again, showing no difference from the performance of the original membrane filament.

[0054] Referring to the simulation data of the application in a high-power fuel cell membrane humidifier shown in Table 2, the water vapor transmission efficiency of the high-temperature resistant hollow fiber humidifying membrane prepared in this example decays by 8% after 400 hours, showing good stability.

[0055] Example 2: A mixed material of polysulfone and sulfonated polyethersulfone is selected as the polysulfone-based polymer material (mass ratio 1:1), the small molecule additives are ethanol and polyethylene glycol 600 (mass ratio 1:1), the pore-forming agent remains polyvinylpyrrolidone, and the organic solvent is N-methylpyrrolidone. By mass ratio, 22% of the mixed polysulfone-based polymer material, 6% of the mixed small molecule additives, and 12% of polyvinylpyrrolidone are weighed, and the remaining 60% is N-methylpyrrolidone.

[0056] The materials are stirred and dissolved at 80 °C to form a homogeneous solution.

[0057] The homogeneous solution is introduced into the outer channel of the spinneret through a metering pump, and the core liquid is introduced into the inner channel of the spinneret through a metering pump. The homogeneous solution is extruded from the spinneret and forms a primary coagulation solution film under the action of the core liquid and the air bath. Then the primary coagulation solution film is introduced into a coagulation bath for solidification and molding. Subsequently, the solidified and semi-solution state hollow fiber membrane filaments are introduced into a water washing tank at 25 °C, and the membrane filaments are wound up after being treated at low temperature in the water washing tank for 5 min. Then the wound-up hollow fiber membrane filaments are placed in a water washing tank at 70 °C for medium-temperature treatment for 3 h.

[0058] The metastable pore structure membrane filaments after medium-temperature treatment are put into an aqueous solution cross-linking liquid medium of azobisisobutyronitrile at 85 °C for constant-temperature treatment for 8 h. Then water washing is carried out, the water washing temperature is set at 30 °C, the water washing time is 8 h, and circulating water washing is carried out. After the water washing is completed, the membrane filaments are then put into a quaternary ammonium compound wetting liquid medium at 30 °C for constant temperature for 18 h, and finally dried in an oven at 60 °C for 4 h to obtain a hollow fiber humidifying membrane.

[0059] The scanning electron microscope image of the high-temperature resistant hollow fiber humidifying membrane prepared in this example is basically the same as that prepared in Example 1, and will not be repeated here.

[0060] Referring to the mechanical property data of the high-temperature resistant hollow fiber humidifying membrane given in Table 1, the maximum load of the membrane prepared in Example 2 is 6.6 N, the tensile strength reaches 9.2 MPa, and the elongation at break is 60%. After the membrane is kept at a constant temperature in the dry state at 95 °C for 200 h, the maximum load is still greater than 6 N, the tensile strength is greater than 9 MPa, and the elongation at break > 50% when detected again, showing no difference from the performance of the original membrane filaments.

[0061] Referring to the simulation data of the application in a high-power fuel cell membrane humidifier in Table 2, the water vapor transmission efficiency of the high-temperature resistant hollow fiber humidifying membrane prepared in this example decays by 7% in 400 hours, showing good stability.

[0062] Comparative example: Polyethersulfone is selected as the polysulfone-based polymer material, polyethylene glycol 400 is used as the small molecule additive, polyvinylpyrrolidone is used as the pore-forming agent, and N,N-dimethylacetamide is used as the organic solvent. By mass ratio, 24% of polyethersulfone, 5% of polyethylene glycol 400, and 10% of polyvinylpyrrolidone are weighed, and the remaining 61% is N,N-dimethylacetamide.

[0063] The above materials are mixed and stirred and dissolved at 60 °C until a homogeneous solution is formed.

[0064] The homogeneous solution is introduced into the outer channel of the spinneret through a metering pump, and the core liquid is introduced into the inner channel of the spinneret through a metering pump, and is extruded from the spinneret. Under the action of the core liquid and the air bath, a primary coagulation solution film is formed, and then the primary solution film is introduced into a coagulation bath for curing and forming. Without low-temperature treatment, medium-temperature treatment and high-temperature cross-linking treatment, the subsequent steps are directly carried out.

[0065] The wound membrane filaments are washed with water. The washing temperature is set at 40 °C, the washing time is 6 h, and circulating water is used for washing. After the washing is completed, the membrane filaments are placed in a dodecylbenzenesulfonic acid sodium wetting liquid medium at 40 °C and kept at a constant temperature for 12 h, and finally dried at a constant temperature to obtain a hollow fiber membrane.

[0066] The difference in looseness and denseness between the outer surface and the inner surface of the hollow fiber membrane prepared in this comparative example is not obvious. Referring to Table 1, the maximum load is measured to be 5.6 N, the tensile strength is only 7 MPa, and the elongation at break is 40%. After the membrane is kept at a constant temperature in the dry state at 95 °C for 200 h, the maximum load drops to 4 N, the tensile strength is 5.5 MPa, and the elongation at break is 13%, showing a significant decline in performance.

[0067] Referring to the simulation data of the application in a high-power fuel cell membrane humidifier in Table 2, the water vapor transmission efficiency of the high-temperature resistant hollow fiber humidifying membrane prepared in this example decays by 25% in 400 hours, showing poor stability.

[0068] The performance tests were carried out on the hollow fiber membranes obtained from the above Examples 1 and 2 and the comparative example, and the relevant mechanical property data are shown in Table 1 below: Table 1. Performance Data of Hollow Fiber Membranes

[0069] The simulation tests of applying the hollow fiber membranes obtained from the above Examples 1 and 2 and the comparative example to a membrane humidifier for a high-power fuel cell were carried out, and the relevant performance parameters are shown in Table 2 below: Table 2. Performance Parameters of Simulation Tests of Hollow Fiber Membranes

[0070] As can be seen from the data in the above table, the attenuation coefficients (%) of the water vapor transmission rate of the high-temperature resistant hollow fiber humidification membranes prepared in Example 1 and Example 2 are significantly lower than those of the hollow fiber membranes in the comparative example; among them, the attenuation coefficient (%) of the water vapor transmission rate of the humidification membrane prepared in Example 2 is 4.9%, which is about 4.5 times that of the membrane in the comparative example, showing excellent durability performance.

[0071] This is mainly because the humidification membranes prepared in Example 1 and Example 2 are subjected to multi-stage heat treatment during the preparation process, which strengthens the stability of the polymer chain segments while eliminating or reducing the internal stress during the membrane tube processing, making it have a regular and rigid channel structure, strengthening the stability of the membrane pore structure. At the same time, after the high-temperature treatment of the membrane tube cross-linking reaction, polyvinylpyrrolidone is not easily dissolved from the membrane tube, endowing the membrane with high hydrophilicity, and then endowing it with high water vapor permeability and permeation stability, strengthening the transmembrane transport of water vapor molecules.

[0072] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0073] For the method embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the present invention is not limited by the described action sequence, because according to the present invention, certain steps can be carried out in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0074] The above has introduced in detail a method for preparing a high-temperature resistant hollow fiber humidification membrane and its application provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for preparing a hollow fiber humidification membrane, characterized in that: The steps include: S1: mixing a polysulfone polymer material, a small molecule additive, a porogen and an organic solvent, and stirring and dissolving them to form a uniform solution; S2: After the uniform solution and the core liquid pass through the spinneret, they enter the coagulation bath for solidification and molding to obtain a semi-liquid hollow fiber membrane; S3: subjecting the semi-liquid hollow fiber membrane to a multi-stage temperature-controlled heat treatment to obtain a membrane with a metastable pore structure; S4: placing the membrane fiber of the metastable pore structure in a cross-linked liquid medium at 80-100° C. for 2-10 hours, then transferring it to constant temperature circulating water for washing, and finally drying it to obtain a hollow fiber humidification membrane; The small molecule additive is at least one of polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600, water, ethanol and diethylene glycol, and the porogen is polyvinyl pyrrolidone.

2. The method for preparing a hollow fiber humidification membrane according to claim 1, characterized in that: In the step S1, based on the mass of the uniform solution as 100%, the amount of the polymer material is 15-30wt%, the amount of the small molecule additive is 2%-20wt%, the amount of the porogen is 2%-20wt%, and the rest is organic solvent.

3. The method for preparing a hollow fiber humidification membrane according to claim 1, characterized in that: In step S3, the multi-stage temperature-controlled heat treatment includes: First, the semi-liquid hollow fiber membrane is placed in an environment with a temperature of 20-60° C. for no more than 10 minutes to allow the semi-liquid membrane to be quickly formed; The hollow fiber membrane filaments are then rolled up and concentrated and transferred to an environment with a temperature of 45-90° C. and treated for 2-6 hours to allow the additives in the membrane to migrate to the surface and obtain membrane filaments with a metastable pore structure.

4. The method for preparing a hollow fiber humidification membrane according to claim 1, characterized in that: In the step S2, the polysulfone polymer material is at least one of polysulfone, polyethersulfone, polyphenylsulfone, sulfonated polyphenylsulfone, sulfonated polyethersulfone, sulfonated polysulfone, polyimide and polyetheretherketone.

5. The method for preparing a hollow fiber humidification membrane according to claim 1, characterized in that: In the step S4, the cross-linking liquid medium is any one of glutaraldehyde, azobisisobutylcyanide aqueous solution and persulfide solution.

6. The method for preparing a hollow fiber humidification membrane according to claim 1, characterized in that: In step S4, the constant temperature circulating water is deionized water, the constant temperature water washing temperature is 20-60° C., and the constant temperature water washing time is 10-24 hours.

7. The method for preparing a hollow fiber humidification membrane according to claim 1, characterized in that: In step S4, after the membrane fibers of the metastable pore structure are transferred to constant temperature circulating water for washing, the method further comprises: The cleaned membrane fibers of the metastable pore structure are placed in a wetting liquid medium at 20-60° C. for 5-24 hours, and then dried to obtain a hollow fiber humidification membrane.

8. The method for preparing a hollow fiber humidification membrane according to claim 7, characterized in that: The wetting liquid medium is at least one of sodium dodecylbenzene sulfonate, quaternary ammonium compounds, acid glycerides, polysorbates, span, pyrrolidone carboxylic acid and trimethylammonium betaine.

9. A hollow fiber humidification membrane prepared by the method for preparing a hollow fiber humidification membrane according to any one of claims 1 to 8, characterized in that: The cross section of the hollow fiber humidification membrane is a sponge pore structure, the outer surface is loose and porous, and the inner surface is dense.

10. An application of a hollow fiber humidification membrane prepared by the method for preparing a hollow fiber humidification membrane according to any one of claims 1 to 8, characterized in that: The hollow fiber membrane is applied to a high-power hydrogen fuel cell system humidifier.

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