Humidifying membrane module for fuel cell, hollow fiber membrane for humidifying fuel cell, method for producing hollow fiber membrane for humidifying fuel cell, and method for humidifying fuel cell

Abstract

For example, provided is a humidifying membrane module for a fuel cell comprising a hollow fiber membrane with excellent durability. For example, a hollow fiber membrane (40) for humidifying a fuel cell comprising a tubular braid (41) and a porous membrane (42) provided at the outer periphery side of the braid (41); a humidifying membrane module for a fuel cell (1) comprising the hollow fiber membrane (40); and a method for humidifying a fuel cell using the hollow fiber membrane (40).

Description

Humidifying membrane module for fuel cells, hollow fiber membrane for humidifying fuel cells, method for manufacturing hollow fiber membrane for humidifying fuel cells, and method for humidifying fuel cells

[0001] The present invention relates to a humidifying membrane module for a fuel cell, a hollow fiber membrane for humidifying a fuel cell, a method for manufacturing a hollow fiber membrane for humidifying a fuel cell, and a method for humidifying a fuel cell.

[0002] A polymer electrolyte fuel cell includes an ion exchange membrane as an electrolyte. The ion exchange membrane transports protons generated at the fuel electrode to the air electrode. Because the ion exchange membrane exhibits high ionic conductivity in a wet state, a humidifier is required to humidify the membrane. Known examples of such humidifiers include those using hollow fiber membrane modules (see, for example, Patent Documents 1 and 2).

[0003] In recent years, the advancement of system performance has led to a demand for smaller fuel cells, which in turn has led to a strong demand for smaller humidifiers. Meanwhile, to humidify the ion-exchange membranes of high-power fuel cells used in large vehicles, etc., humidifiers with a higher air flow rate are required. To achieve a larger air flow rate while miniaturizing the humidifiers, it is necessary to increase the air flow rate per hollow fiber membrane. Since an increased air flow rate per membrane can make the hollow fiber membrane more susceptible to breakage, there is a demand for improving the durability of the hollow fiber membranes.

[0004] In the field of water treatment, hollow fiber membranes whose inner periphery is reinforced with a cylindrical braid are known (e.g., Patent Document 3). However, while hollow fiber membranes used for water treatment allow treated water to permeate the membrane, hollow fiber membranes used in fuel cell humidifiers must separate water vapor from air, which requires different properties for the hollow fiber membranes. Therefore, the use of such hollow fiber membranes in fuel cell humidifiers has not been considered until now.

[0005] International Publication No. 2018 / 190147 International Publication No. 2022 / 255039 Japanese Patent Application Laid-Open No. 2016-10792

[0006] The present invention provides, for example, a humidifying membrane module for a fuel cell, which includes a hollow fiber membrane having excellent durability.

[0007] Illustrative configurations of the present invention are listed below. [1] A humidifying membrane module for a fuel cell, comprising a hollow fiber membrane, the hollow fiber membrane comprising a tubular braid and a porous membrane provided on the outer periphery of the braid. [2] The humidifying membrane module for a fuel cell of [1], wherein the braid contains polyphenylene sulfide fibers. [3] The humidifying membrane module for a fuel cell of [1] or [2], wherein the porous membrane contains polyphenylsulfone. [4] The humidifying membrane module for a fuel cell of any of [1] to [3], wherein the porous membrane has a dense layer on the outer periphery with a smaller pore size than on the inner periphery. [5] The humidifying membrane module for a fuel cell of any of [1] to [4], wherein dry air flows on the outer side of the hollow fiber membrane and moist air flows on the inner side. [6] A hollow fiber membrane for humidifying a fuel cell, comprising a cylindrical braid and a porous membrane provided on the outer periphery of the braid. [7] A method for manufacturing a hollow fiber membrane for humidifying a fuel cell, the hollow fiber membrane comprising a cylindrical braid and a porous membrane provided on the outer periphery of the braid, the method comprising the steps of applying a membrane-forming solution to the outer surface of the braid, and coagulating the membrane-forming solution applied to the braid in a coagulation liquid at 20° C. to 50° C. to obtain the porous membrane. [8] A method for humidifying a fuel cell using a hollow fiber membrane comprising a cylindrical braid and a porous membrane provided on the outer periphery of the braid.

[0008] According to the present invention, for example, a humidifying membrane module for a fuel cell is provided, which includes a hollow fiber membrane having excellent durability.

[0009] 1 is a schematic diagram showing a cross section of a humidifying membrane module for a fuel cell according to an embodiment of the present invention; 2 is a schematic diagram showing a cross section of a hollow fiber membrane; 3 is a photograph showing a braid used in an example; and 4 is a photograph showing a cross section of a hollow fiber membrane obtained in an example.

[0010] [Humidifying Membrane Module for Fuel Cells] A humidifying membrane module 1 for fuel cells, which is one example of the present invention, will now be described with reference to the drawings. Fig. 1 is a schematic diagram showing a cross section of the humidifying membrane module 1 for fuel cells. The humidifying membrane module 1 for fuel cells comprises a cylindrical case 10 and a plurality of hollow fiber membranes 40 housed inside the case 10. An inlet 11 is provided at one end of the side of the case 10, and an outlet 12 is provided at the other end. Heads 20 and 30 are attached to both ends of the case 10, respectively.

[0011] The plurality of hollow fiber membranes 40 are bundled and fixed at both ends inside the case 10 by sealing parts 50, 60. The sealing parts 50, 60 are formed from a resin or the like, and fill the spaces between the plurality of hollow fiber membranes 40 and the space between the plurality of hollow fiber membranes 40 and the case 10. Both ends of the hollow fiber membranes 40 are not closed by the sealing parts 50, 60, allowing air to pass from one end to the other.

[0012] The fuel cell humidifying membrane module 1 is formed with an outer path (arrow X) that passes through the outside of the hollow fiber membrane 40 and an inner path (arrow Y) that passes through the inside of the hollow fiber membrane 40. The outer path is a path through which air that flows in from the inlet 11 flows outside the hollow fiber membrane 40 and flows out from the outlet 12. The inner path is a path through which air that flows in from the head 30 flows inside the hollow fiber membrane 40 and flows out from the head 20.

[0013] The fuel cell humidifying membrane module 1 may be configured so that dry air flows through the outer passage and wet air flows through the inner passage, or so that dry air flows through the inner passage and wet air flows through the outer passage. As will be described later, when the hollow fiber membrane 40 has a dense layer (skin layer) on the outer periphery, it is advantageous from the standpoint of humidifying performance to configure the module so that dry air flows through the outer passage and wet air flows through the inner passage, as opposed to conventional general humidifying membrane modules. The membrane separation action of the hollow fiber membrane 40 allows water vapor to be supplied from the wet air side to the dry air side, humidifying the dry air. Supplying humidified air to the ion exchange membrane of the fuel cell keeps the ion exchange membrane moist.

[0014] The fuel cell humidifying membrane module according to the present invention may have a configuration different from that described above, as long as it is capable of humidifying air using hollow fiber membranes. For example, the fuel cell humidifying membrane module may have a configuration including an inner pipe, as disclosed in WO 2022 / 255039.

[0015] [Hollow Fiber Membrane] A hollow fiber membrane 40 for humidifying a fuel cell will be described in detail below. FIG. 2 is a diagram showing a cross section of the hollow fiber membrane 40. FIG. 2 is a schematic diagram and does not necessarily correspond to the actual dimensions and shape of the hollow fiber membrane 40. The hollow fiber membrane 40 includes a tubular braided cord 41 and a porous membrane 42 provided on the outer periphery of the braided cord. The hollow fiber membrane 40 is typically cylindrical or approximately cylindrical, but may have other shapes such as an elliptical cylindrical shape or an approximately elliptical cylindrical shape.

[0016] (Braided Cord) The braided cord 41 is formed into a hollow cord shape by weaving or knitting yarns selected from the group consisting of monofilaments, multifilaments, and spun yarns. The braided cord 41 may be woven or knitted into a tubular shape from the beginning, or may be formed into a tubular shape by joining flat woven or knitted pieces together.

[0017] If the braid 41 is a woven fabric, it may be formed by, for example, plain weave, twill weave, or satin weave. If the braid 41 is a knitted fabric, it may be formed by, for example, circular knitting, weft knitting, or warp knitting.

[0018] The braid 41 is preferably made of organic fibers, and more preferably made of multifilament organic fibers. Examples of organic fibers that can be used include synthetic fibers, semi-synthetic fibers, recycled fibers, and natural fibers. One of these organic fibers may be used alone, or two or more may be used in combination.

[0019] Examples of synthetic fibers include polyphenylene sulfide fibers, polyester fibers, polyamide fibers, acrylic fibers, polyolefin fibers, polyvinyl alcohol fibers, polyvinylidene chloride fibers, polyvinyl chloride fibers, polyurethane fibers, phenolic resin fibers, fluororesin fibers, and polyalkylene paraoxybenzoate fibers. Examples of polyester fiber materials include polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polylactic acid, and polyglycolic acid. Examples of polyamide fiber materials include polyamide 6, polyamide 66, polyamide 610, polyamide 11, polyamide 12, polyamide 6T, polyamide 6I, and polyamide 9T. Examples of acrylic fiber materials include polyacrylonitrile. Examples of polyolefin fiber materials include polyethylene and polypropylene. Examples of fluororesin fiber materials include polyvinylidene fluoride and polytetrafluoroethylene. These synthetic fibers may be used alone or in combination.

[0020] Semi-synthetic fibers can be fibers made by chemically processing natural polymers as the main component. Semi-synthetic fibers may be fibers derived from cellulose or proteins. Examples of cellulose-derived fiber materials include acetyl cellulose and triacetyl cellulose. Examples of protein-derived fibers include promix fibers. Examples of regenerated fibers include rayon, cupra, polynosic, and lyocell. Examples of natural fibers include cotton, hemp, linen, and silk. One of these fibers may be used alone, or two or more may be used in combination.

[0021] The braided cord 41 is preferably formed from synthetic fibers. Furthermore, from the viewpoints of heat resistance, hydrolysis resistance, and moisture absorption resistance, the braided cord 41 preferably contains polyphenylene sulfide fibers. The braided cord 41 preferably contains 50% by mass or more of polyphenylene sulfide fibers, more preferably 70% by mass or more of polyphenylene sulfide fibers, even more preferably 90% by mass or more of polyphenylene sulfide fibers, particularly preferably 95% by mass or more of polyphenylene sulfide fibers, and most preferably 98% by mass or more of polyphenylene sulfide fibers. The braided cord 41 may contain 100% by mass of polyphenylene sulfide fibers.

[0022] When the braided cord 41 includes a multifilament, the fineness of the single fibers constituting the multifilament (single yarn fineness) is not particularly limited. The single yarn fineness may be, for example, in the range of 0.2 dtex to 10 dtex, 0.5 dtex to 9 dtex, 1 dtex to 8 dtex, 2 dtex to 7 dtex, 3 dtex to 6 dtex, or 4 dtex to 5 dtex.

[0023] When the braided cord 41 includes multifilaments, the number of filaments in the multifilaments is not particularly limited. The number of filaments may be, for example, in the range of 12 filaments to 384 filaments, in the range of 24 filaments to 192 filaments, or in the range of 48 filaments to 92 filaments.

[0024] When the braided cord 41 includes multifilaments, the fineness of the multifilaments is not particularly limited. The fineness of the multifilaments may be, for example, within a range of 20 dtex to 1000 dtex, 50 dtex to 800 dtex, 100 dtex to 700 dtex, 200 dtex to 600 dtex, or 300 dtex to 500 dtex.

[0025] There is no particular limitation on the number of stitches in the braid 41. For example, the number of stitches may be in the range of 4 to 96, 8 to 84, 12 to 64, 16 to 48, or 20 to 40.

[0026] The outer diameter of the braided cord 41 is not particularly limited. Here, the outer diameter of the outer peripheral surface of the braided cord 41 is calculated as (major axis + minor axis) / 2. The outer diameter of the braided cord 41 may be, for example, within a range of 0.5 mm to 3 mm, 0.8 mm to 2.5 mm, 1 mm to 2 mm, 1.5 mm to 1.95 mm, 1.6 mm to 1.9 mm, or 1.7 mm to 1.85 mm.

[0027] There are no particular limitations on the inner diameter of the braided cord 41. Here, the inner diameter of the braided cord 41 is calculated as (major axis + minor axis) / 2 for the inner circumferential surface. The inner diameter of the braided cord 41 may be, for example, within a range of 0.2 mm to 2 mm, 0.4 mm to 1.8 mm, 0.5 mm to 1.5 mm, 0.7 mm to 1.3 mm, or 0.9 mm to 1.1 mm.

[0028] There are no particular limitations on the thickness of the braided cord 41. The thickness of the braided cord 41 is calculated as (outer diameter - inner diameter) / 2. The thickness of the braided cord 41 may be, for example, within a range of 0.1 mm to 1.5 mm, a range of 0.2 mm to 1 mm, or a range of 0.3 mm to 0.5 mm.

[0029] (Porous Membrane) As shown schematically in FIG. 2 , the porous membrane 42 has a porous layer 421 on the inner circumferential side and a dense layer (skin layer) 422 on the outer circumferential side. This configuration makes it easier to ensure the humidifying performance of the porous membrane 42 while improving durability with the braided cord 41. However, in one embodiment, the porous membrane may have a dense layer on the inner circumferential side and a porous layer on the outer circumferential side. The dense layer 422 has a smaller pore size than the porous layer 421. Although the porous layer 421 and the dense layer 422 are shown clearly separated in FIG. 2 , the boundary between the porous layer 421 and the dense layer 422 does not need to be clear.

[0030] The porous membrane 42 is preferably formed of a polymer. The porous membrane 42 may contain at least one polymer selected from the group consisting of polyphenylsulfone, polyethersulfone, polysulfone, polyvinylidene fluoride, polyacrylonitrile, polyethylene, and polypropylene. The porous membrane 42 may also contain a hydrophilizing agent such as polyvinylpyrrolidone, polyethylene glycol, ethylene glycol, or triethylene glycol.

[0031] From the viewpoint of ease of preparing a membrane with a pore size appropriate for humidification applications, the porous membrane 42 preferably contains polyphenylsulfone or polysulfone, and more preferably contains polyphenylsulfone. Polyphenylsulfone is also preferred from the viewpoint of affinity when the braided cord 41 contains polyphenylene sulfide fibers, i.e., from the viewpoint of the peel strength of the porous membrane 42. That is, the hollow fiber membrane 40 is most preferably a combination of a braided cord 41 containing polyphenylene sulfide fibers and a porous membrane 42 containing polyphenylsulfone. The porous membrane 42 preferably contains 30% by mass or more of polyphenylsulfone, more preferably 40% by mass or more, and even more preferably 50% by mass or more. Polyphenylsulfone typically has the repeating unit shown below and does not contain an isopropylidene group.

[0032]

[0033] The porous membrane 42 preferably contains polyphenylsulfone and polyvinylpyrrolidone. For example, polyvinylpyrrolidone having a K value in the range of 25 to 35 may be used. The polyvinylpyrrolidone may be used in an amount of, for example, 0.5 to 1.5 parts by mass, or 0.5 to 1 part by mass, per 1 part by mass of polyphenylsulfone.

[0034] In the porous membrane 42, the total content of polyphenylsulfone and polyvinylpyrrolidone relative to the total content of the polymer component and the hydrophilizing agent is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 95% by mass or more. In the porous membrane 42, the total content of polyphenylsulfone and polyvinylpyrrolidone relative to the total content of the polymer component and the hydrophilizing agent may be 100% by mass.

[0035] In the porous membrane 42, the pore size of the dense layer 422 is not particularly limited as long as it can separate water vapor. The pore size of the porous layer 421 is not particularly limited as long as it is larger than the pore size of the dense layer 422. The pore sizes of the porous layer 421 and the dense layer 422 may be smaller toward the outer periphery.

[0036] The outer diameter of the porous membrane 42 is not particularly limited. Here, the outer diameter of the porous membrane 42 is calculated as (major axis + minor axis) / 2 for the outer peripheral surface. The outer diameter of the porous membrane 42 may be, for example, within a range of 0.6 mm to 4 mm, a range of 0.8 mm to 3.5 mm, a range of 1 mm to 3 mm, a range of 1.5 mm to 2.5 mm, a range of 1.7 mm to 2.3 mm, or a range of 1.8 mm to 2.2 mm.

[0037] There are no particular limitations on the thickness of the porous membrane 42. The thickness of the porous membrane 42 is calculated as (outer diameter of the porous membrane 42 - outer diameter of the braid 41) / 2. The thickness of the porous membrane 42 may be, for example, within a range of 0.02 mm to 0.5 mm, a range of 0.05 mm to 0.4 mm, a range of 0.07 mm to 0.3 mm, a range of 0.08 mm to 0.2 mm, or a range of 0.09 mm to 0.15 mm.

[0038] (Method for manufacturing hollow fiber membrane) The hollow fiber membrane 40 can be manufactured, for example, by passing the braid 41 through the inner nozzle of a double annular spinning nozzle, applying a membrane-forming solution ejected from the outer nozzle of the double annular spinning nozzle to its outer surface, impregnating it, coagulating it in a coagulation liquid, and then washing it in a washing tank.

[0039] The membrane-forming solution can be prepared by mixing at least one polymer selected from the group consisting of polyphenylsulfone, polyethersulfone, polysulfone, polyvinylidene fluoride, polyacrylonitrile, polyethylene, and polypropylene, a solvent, and a hydrophilizing agent such as polyvinylpyrrolidone, polyethylene glycol, ethylene glycol, or triethylene glycol.

[0040] Examples of the solvent that can be used include N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide (DEAc), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), and triethyl phosphate.

[0041] When producing a porous membrane 42 containing polyphenylsulfone, the membrane-forming solution may contain, for example, polyphenylsulfone, polyvinylpyrrolidone, and a solvent. In this case, the blending ratio of polyphenylsulfone may be, for example, within a range of 15% to 25% by mass, 17% to 23% by mass, 18% to 22% by mass, or 19% to 21% by mass, based on the total membrane-forming solution. Furthermore, the blending ratio of polyvinylpyrrolidone may be, for example, within a range of 8% to 22% by mass, 10% to 20% by mass, 12% to 18% by mass, or 13% to 17% by mass, based on the total membrane-forming solution. By including polyvinylpyrrolidone in an appropriate blending ratio, the balance between viscosity, hydrophilicity, and pore-forming ability is improved, thereby achieving both water vapor permeability and ease of spinning.

[0042] The temperature of the membrane-forming solution may be, for example, in the range of 10°C to 100°C, in the range of 15°C to 80°C, in the range of 20°C to 60°C, or in the range of 22°C to 30°C.

[0043] The inner diameter of the inner nozzle of the double annular spinning nozzle may be slightly larger than the outer diameter of the braided cord 41. The inner diameter of the inner nozzle of the double annular spinning nozzle may be, for example, 0.05 mm to 0.5 mm larger, 0.1 mm to 0.3 mm larger, or 0.15 mm to 0.25 mm larger than the outer diameter of the braided cord 41.

[0044] The speed at which the braid 41 is passed through the inner nozzle of the double annular spinning nozzle can be appropriately set in consideration of the composition of the membrane-forming solution, the desired membrane thickness, etc. The speed may be, for example, in the range of 10 m / min to 30 m / min, or in the range of 15 m / min to 25 m / min.

[0045] The membrane-forming solution applied to the braid 41 is preferably coagulated by a dry-wet spinning method or a wet spinning method using a coagulation liquid, and then optionally subjected to post-processing steps such as washing, drying, and crosslinking to form the porous membrane 42. The coagulation liquid may be, for example, an aqueous liquid such as water. Washing may be performed, for example, in pressurized water at 110°C to 130°C for 0.3 to 5 hours, preferably 0.5 to 2 hours. Drying may be performed, for example, using a dryer at a temperature of 30°C to 100°C, preferably 40°C to 80°C, and more preferably 50°C to 70°C, for 6 to 48 hours, preferably 12 to 36 hours, and more preferably 18 to 30 hours. Washing and / or drying may be performed multiple times.

[0046] During spinning, a liquid prepared by blending water with a solvent such as N,N-dimethylformamide (DMF) at an appropriate concentration is applied to the inside or outside of the porous membrane 42 being formed, thereby forming a dense layer 422 on the porous membrane 42. From the viewpoint of achieving both improved durability due to the braid 41 and ensuring the humidifying performance of the porous membrane 42, it is preferable to form the dense layer 422 on the outer periphery of the porous membrane 42. If the above method is difficult, the dense layer 422 can be formed on the outer periphery of the porous membrane 42, for example, by adjusting the temperature of the coagulation liquid and / or the nozzle gap. In this case, the temperature of the coagulation liquid is, for example, within a range of 20°C to 50°C, more preferably within a range of 25°C to 45°C, and even more preferably within a range of 30°C to 40°C.

[0047] The above describes the embodiments of the present invention by way of example, but the present invention is not limited to the above-described embodiments, and includes all aspects encompassed by the concept of the present invention and the scope of the claims, and can be modified in various ways within the scope of the present invention.

[0048] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0049] Example 20 parts by weight of polyphenylsulfone (RADEL R-5000 manufactured by Solvay) and 15 parts by weight of polyvinylpyrrolidone K-30 (PVP K30G manufactured by Ashland) were dissolved in 65 parts by weight of N,N-dimethylformamide (manufactured by Luxi Chemical Co.) with stirring at room temperature to obtain a membrane-forming solution. Next, a tubular braided polyphenylene sulfide braid (manufactured by KB Seiren Co., Ltd.) shown in FIG. 3 was passed through the inside of a double-annular spinning nozzle with an inner diameter of 2.0 mm at a speed of 20 m / min. The outer surface of the braided polyphenylene sulfide braid was impregnated with the membrane-forming solution pumped and discharged from the outer nozzle of the double-annular spinning nozzle using a gear pump. After idling for 30 cm, the membrane was extruded into a coagulation solution of water at 35 °C and coagulated. The resulting membrane was passed through a 35 °C washing tank and then wound onto a bobbin. The resulting membrane was first washed in an autoclave at 121°C for 1 hour, and then the container filled with ion-exchanged water was placed in a dryer and first dried at 55°C for 24 hours. The membrane was then dry-heated at 170°C for 9 hours to crosslink the polyvinylpyrrolidone, followed by a second wash under the same conditions as the first wash and a second dry under the same conditions as the first dry. In this way, a hollow fiber membrane was obtained with an overall outer diameter of 2.0 mm, a braided outer diameter of 1.8 mm, an overall inner diameter of 1.0 mm, an overall thickness of 0.5 mm, a porous membrane thickness of 0.1 mm, and a braided thickness of 0.4 mm. The resulting hollow fiber membrane had a dense layer formed on the outer periphery. A photograph of the cross section of the resulting hollow fiber membrane is shown in Figure 4.

[0050] The details of the braid used were as follows: Material: Multifilament made of polyphenylene sulfide fiber Weaving method: Plain weave Outer diameter: 1.8 mm Inner diameter: 1.0 mm Multifilament fineness: 440 dtex Number of filaments: 96 f Single yarn fineness: 4.6 dtex Number of strands: 24

[0051] The obtained hollow fiber membrane was incorporated into a module, and wet air was passed through the inside of the hollow fiber membrane and dry air through the outside. It was confirmed that the dry air could be humidified. The tensile strength of the obtained hollow fiber membrane was measured using a small benchtop testing machine (EZ Test) manufactured by Shimadzu Corporation. The hollow fiber membrane was dried at 100°C for 1 hour, chucked at an effective length of 50 mm, and pulled at 20 mm / min to determine the breaking stress. The tensile strength of the hollow fiber membrane obtained in the examples exceeded the measurement limit, but was at least 197 N (21 N / mm ２ ) was.

[0052] (Comparative Example) 20 parts by weight of polyphenylsulfone (RADEL R-5000 manufactured by Solvay) and 15 parts by weight of polyvinylpyrrolidone K-30 (PVP K30G manufactured by Ashland) were dissolved in 65 parts by weight of N,N-dimethylformamide (manufactured by Luxi Chemical Co.) with stirring at room temperature to obtain a membrane-forming solution. Next, while a mixture of N,N-dimethylformamide and water was flowing as a core liquid inside the double annular spinning nozzle, the membrane-forming solution was pumped and discharged using a gear pump from the outer nozzle of the double annular spinning nozzle. After idling for 60 cm, the membrane was extruded into a coagulation solution consisting of water at 60 ° C. and coagulated. The obtained membrane was passed through a washing tank at 45 ° C. and then wound onto a bobbin. The obtained membrane was primarily washed in an autoclave at 121 ° C. for 1 hour, and then the container filled with ion-exchanged water was placed in a dryer and primarily dried at 55 ° C. for 24 hours. Further, the membrane was dry heated at 170°C for 9 hours to crosslink the polyvinylpyrrolidone, then subjected to secondary washing under the same conditions as the primary washing, and secondary drying under the same conditions as the primary drying. In this way, a hollow fiber membrane having an overall outer diameter of 1.3 mm, an overall inner diameter of 0.9 mm, and a thickness of 0.2 mm was obtained. The tensile strength of the obtained hollow fiber membrane was measured in the same manner as in the examples, and was found to be 3.5 N (4.97 N / mm ２ ) was.

[0053] The humidifying membrane module for fuel cells, the hollow fiber membrane for humidifying fuel cells, the method for manufacturing the hollow fiber membrane for humidifying fuel cells, and the method for humidifying fuel cells of the present invention can be suitably used in the field of vehicular or stationary fuel cells.

[0054] DESCRIPTION OF SYMBOLS 1... Humidifying membrane module for fuel cell, 10... Case, 11... Inlet, 12... Outlet, 20, 30... Head, 40... Hollow fiber membrane, 41... Braided cord, 42... Porous membrane, 421... Porous layer, 422... Dense layer (skin layer), 50, 60... Sealing portion

Claims

1. A humidifying membrane module for a fuel cell, comprising a hollow fiber membrane, the hollow fiber membrane comprising a tubular braided cord and a porous membrane provided on the outer periphery of the braided cord.

2. The humidifying membrane module for a fuel cell according to claim 1, wherein the braided cord comprises polyphenylene sulfide fibers.

3. The humidifying membrane module for a fuel cell according to claim 1 or 2, wherein the porous membrane contains polyphenylsulfone.

4. A humidifying membrane module for a fuel cell according to claim 1 or 2, wherein the porous membrane has a dense layer on the outer periphery with a pore size smaller than that on the inner periphery.

5. A humidifying membrane module for a fuel cell according to claim 1 or 2, wherein dry air flows on the outside of said hollow fiber membrane and moist air flows on the inside.

6. A hollow fiber membrane for humidifying a fuel cell, comprising: a cylindrical braid; and a porous membrane provided on the outer periphery of the braid.

7. A method for manufacturing a hollow fiber membrane for humidifying a fuel cell, the hollow fiber membrane comprising a cylindrical braid and a porous membrane provided on the outer periphery of the braid, the method comprising the steps of: applying a membrane-forming solution to the outer surface of the braid; and solidifying the membrane-forming solution applied to the braid in a coagulation liquid at 20°C to 50°C to obtain the porous membrane.

8. A method for humidifying a fuel cell, comprising using a hollow fiber membrane comprising a cylindrical braid and a porous membrane provided on the outer periphery of the braid.