Hollow fiber porous membranes and hollow fiber porous membrane modules

Abstract

The present invention provides hollow fiber membranes and hollow fiber membrane modules that possess gas barrier properties, excellent water vapor permeability, and are useful as humidity control devices, fuel cell systems, and the like. [Solution] In a cross-section perpendicular to the longitudinal direction of the hollow fiber porous membrane, the pore area on the inner surface of the hollow fiber porous membrane is 1260 nm. 2 The hollow fiber porous membrane has a dense layer having only the following voids, the average pore diameter of the outer surface of the hollow fiber porous membrane is greater than the average pore diameter of the inner surface, and satisfies at least one of the following conditions (1) or (2): (1) When X1 is the total of alkali metal ions in the region from the inner surface to a depth of 0 to 100 nm detected by time-of-flight secondary ion mass spectrometry, and X2 is the total of the peak intensities of the alkali metal ions in the region from the outer surface to a depth of 0 to 100 nm, X1 > X2. (2) This is the condition in condition (1) with alkali metal ions replaced by alkaline earth metal ions.

Description

[Technical Field]

[0001] This invention relates to hollow fiber porous membranes and hollow fiber porous membrane modules. More specifically, it relates to hollow fiber porous membranes and hollow fiber porous membrane modules suitably used in humidity control units used in air conditioners and fuel cell systems. [Background technology]

[0002] Hollow fiber membranes are widely used in medical applications such as blood purifiers for patients with renal failure, and in water treatment applications such as water purifiers. Furthermore, hollow fiber membranes with pores of a size that allows for gas separation exhibit superior gas separation properties compared to various inorganic membranes, and can be used in environments where chemical resistance and heat resistance are required. For this reason, in recent years, the use of hollow fiber membranes has been expanding to humidify fuel gas to keep electrolyte membranes in fuel cell systems moist, and to dehumidify moisture in compressed air in factories.

[0003] When using hollow fiber membranes for humidification in polymer electrolyte fuel cells, automotive applications require large amounts of air humidification, around 5,000 NL / min, while stationary applications often use hot water as the humidification power source. In either case, durability and heat resistance of the hollow fiber membrane are particularly important. Furthermore, it must also possess gas barrier properties to suppress air leakage from the hollow fiber membrane.

[0004] Several types of hollow fiber membranes that selectively permeate water vapor as described above are currently commercially available, but each has different materials and permeation principles. For example, a membrane that uses polyimide resin as the material and is operated by the dissolution diffusion method has excellent heat resistance and strength, but it has the disadvantage of a low water vapor permeability coefficient. Another example is a membrane that uses fluorine-based ion exchange membranes as the material and operates on the principle of ion hydration, which has a high water vapor permeability coefficient but poor heat resistance and the membrane itself is very expensive.

[0005] On the other hand, membranes made of polyetherimide resin that perform humidification and dehumidification by capillary condensation achieve both water vapor permeability and heat resistance and are used in many industrial fields. However, the absolute strength of the membrane is weak, and in particular it lacks flexibility, so problems such as the hollow fiber membrane breaking when humidifying or dehumidifying large amounts of gas are likely to occur.

[0006] Polysulfone resins, which are commonly used as ultrafiltration membranes and microfiltration membranes for humidification in fuel cells, are also used because they exhibit excellent strength stability under humid conditions.

[0007] A cross-sectional structure for hollow fiber membranes that achieves both water vapor permeability and membrane strength has been proposed by wet-dry spinning a spinning stock consisting of a water-soluble organic solvent solution of polysulfone resin and vinylpyrrolidone resin (Patent Document 1). However, in the above-mentioned conventional technology, pore formation on the outer surface of the hollow fiber membrane may be insufficient, and water vapor permeability may not be sufficiently achieved. Furthermore, a manufacturing method for hollow fiber membranes for water purifiers in which the outer surface of the hollow fiber membrane has high openings has also been disclosed (Patent Document 2). However, because it is an external pressure type hollow fiber membrane structure, the inner surface side has a low-density porous structure and does not have a dense layer with the pore size necessary for gas barrier properties and water vapor permeability. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] International Publication No. 2024 / 043095 [Patent Document 2] Patent No. 06973071 [Overview of the project] [Problems that the invention aims to solve]

[0009] The object of the present invention is to provide a hollow fiber membrane and a hollow fiber membrane module that have gas barrier properties, excellent water vapor permeability, and can be effectively used as a humidity control device, fuel cell system, etc. Means for Solving the Problems

[0010] In order to solve the above problems, the present invention has the following configuration.

[0011] In a cross-section perpendicular to the longitudinal direction of the hollow fiber porous membrane (hereinafter referred to as a vertical cross-section), the pore area on the inner surface of the hollow fiber porous membrane is 1260 nm 2 It has a dense layer having only the following voids, and the average pore diameter of the outer surface in the vertical cross-section is larger than the average pore diameter of the inner surface, It is a hollow fiber porous membrane that satisfies at least one of the following (1) or (2). (1) When the total peak intensity of alkali metal ions in the region from a depth of 0 to 100 nm from the inner surface, detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS), is X1, and the total peak intensity of the alkali metal ions in the region from a depth of 0 to 100 nm from the outer surface is X2, X1 > X2. (2) When the total peak intensity of alkaline earth metal ions in the region from a depth of 0 to 100 nm from the inner surface, detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS), is X3, and the total peak intensity of the alkaline earth metal ions in the region from a depth of 0 to 100 nm from the outer surface is X4, X3 > X4. Advantages of the Invention

[0012] The hollow fiber porous membrane obtained by the present invention and the hollow fiber membrane module thereof can be effectively used as a hollow fiber porous membrane and a membrane module excellent in water vapor permeability and gas barrier properties. Brief Description of the Drawings

[0013] [Figure 1] It is a figure which shows the cross-section perpendicular to the longitudinal direction of the hollow fiber porous membrane which concerns on embodiment of this invention. [Figure 2] It is a figure which shows the scanning electron micrograph near the inner surface in the cross-section perpendicular to the longitudinal direction of the hollow fiber porous membrane of this invention. [Figure 3]This is a diagram showing a scanning electron micrograph near the outer surface in a cross-section perpendicular to the longitudinal direction of the hollow fiber porous membrane of the present invention. [Figure 4] This is a schematic diagram of an air conditioner. [Figure 5] This is a block diagram regarding the power supply of a fuel cell vehicle. [Figure 6] This is a schematic diagram of a heat exchanger. [Figure 7] This is a schematic diagram explaining a method for measuring the air leakage amount. [Figure 8] This is a schematic diagram explaining a method for measuring the water vapor permeation amount. [Figure 9] This is a schematic diagram explaining a method for measuring the water vapor permeation amount.

Mode for Carrying Out the Invention

[0014] Hereinafter, modes for carrying out the present invention will be described in detail. Note that the present invention is not limited by the following embodiments.

[0015] In a cross-section perpendicular to the longitudinal direction of the hollow fiber porous membrane (hereinafter referred to as a vertical cross-section), the hollow fiber porous membrane has a dense layer having only the following voids, and the average pore diameter of the outer surface is larger than the average pore diameter of the inner surface. 2 The hollow fiber porous membrane satisfies at least one of the following (1) or (2). The hollow fiber porous membrane satisfies at least one of the following (1) or (2). (1) When the total peak intensity of alkali metal ions in the region from a depth of 0 to 100 nm from the inner surface, detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS), is X1, and the total peak intensity of alkali metal ions in the region from a depth of 0 to 100 nm from the outer surface is X2, X1 > X2. (2) When the total peak intensity of alkaline earth metal ions in the region from a depth of 0 to 100 nm from the inner surface, detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS), is X3, and the total peak intensity of alkaline earth metal ions in the region from a depth of 0 to 100 nm from the outer surface is X4, X3 > X4.

[0016] <Hollow fiber porous membrane> Figure 1 is a cross-sectional view perpendicular to the longitudinal direction of a hollow fiber porous membrane according to an embodiment of the present invention, Figure 2 is a cross-sectional view near the inner surface, and Figure 3 is a cross-sectional view near the outer surface, both shown at the same magnification. The inner surface 11 of the hollow fiber porous membrane of the present invention has a pore area of ​​1260 nm. 2 It has a dense layer 12 that consists only of the following voids, and the average pore diameter of the outer surface 21 is larger than the average pore diameter of the inner surface 11.

[0017] Furthermore, the hollow fiber porous membrane of the present invention is a hollow fiber porous membrane that satisfies at least one of the following conditions (1) or (2). (1) When X1 is the sum of the peak intensities of alkali metal ions in the region from the inner surface to a depth of 0 to 100 nm, as detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS), and X2 is the sum of the peak intensities of alkali metal ions in the region from the outer surface to a depth of 0 to 100 nm, then X1 > X2. (2) When X3 is the sum of the peak intensities of alkaline earth metal ions in the region from the inner surface to a depth of 0 to 100 nm, as detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS), and X4 is the sum of the peak intensities of alkaline earth metal ions in the region from the outer surface to a depth of 0 to 100 nm, then X3 > X4.

[0018] The gas barrier properties are improved by having a dense layer on the inner surface and by the distribution of alkali metal ions or alkaline earth metal ions in the region from the inner surface to a depth of 0-100 nm. The details of the mechanism are unknown, but this is because the pore area of ​​the dense layer is 1260 nm. 2 By having only the following voids, air is less likely to pass through, and the distribution of alkali metal ions or alkaline earth metal ions makes it easier to absorb water vapor from the air. It is thought that the gas barrier properties are improved because water vapor in the voids is efficiently absorbed in the dense layer with a small pore area.

[0019] The pore area of ​​the present invention is 1260 nm 2A dense layer having only the following voids is defined as a hollow fiber porous membrane with a pore area of ​​1260 nm in the direction of film thickness from the inner surface within the vertical cross-section. 2 This refers to the region where the area ratio of voids exceeding a certain value is 1% or less. The pore area in the hollow fiber membrane of the present invention is determined by importing electron microscope images of the hollow fiber membrane into a computer, analyzing them with image analysis software, and quantifying the result. The thickness of the dense layer is preferably 100 nm or more and 500 nm or less.

[0020] By having a structure in which the average pore diameter of the outer surface 21 is larger than the average pore diameter of the inner surface 11, and by satisfying at least one of (1) or (2) above, water vapor permeability is improved. This is thought to be because having a structure in which the average pore diameter of the outer surface 21 is larger than the average pore diameter of the inner surface 11 makes it easier for water vapor to be taken in from the outer surface, and furthermore, by satisfying at least one of the relationships X1 > X2 or X3 > X4, water vapor permeability is made easier towards the inner surface. In addition, it is preferable to satisfy at least one of (3) or (4) below. By setting it within this range, water vapor permeability is further improved. (3) 1.5 ≤ X1 / X2 ≤ 3.0 (4) 1.5 ≤ X3 / X4 ≤ 3.0 In this invention, peak intensities X1 and X2 are the peak intensities when focusing on the same alkali metal. Peak intensities X3 and X4 are the peak intensities when focusing on the same alkaline earth metal ion.

[0021] There are no particular limitations on the alkali metal ions or alkaline earth metal ions, and examples include Li ions, Na ions, K ions, Cs ions, Be ions, Mg ions, Ca ions, Ba ions, etc., but Li ions or Ca ions are preferred from the viewpoint of water absorption. As a method for forming a hollow fiber porous membrane that satisfies at least one of the above (3) or (4), for example, a method in which the hollow fiber porous membrane is impregnated with an aqueous solution containing alkali metal ions or alkaline earth metal ions and then washed, or a method in which water is passed through an aqueous solution containing alkali metal ions or alkaline earth metal ions on a hollow fiber porous membrane.

[0022] The average pore diameter of the inner or outer surface in a vertical cross-section of the hollow fiber porous membrane of the present invention can be measured by the following method. First, five cross-sections are obtained from each of three hollow fiber porous membranes. If the hollow fiber porous membrane is extracted from a membrane module, any three membranes are selected. Images of the obtained membrane cross-sections are observed using a SEM at a magnification of 5,000x. The obtained images are imported into a computer and binarized using image processing and analysis software. The pore area of ​​any five voids in the region from the inner or outer surface of the obtained image up to a length of 5% of the film thickness is calculated. The diameter of the void, assuming it is circular, is calculated from the calculated pore area. The same calculation is performed for five images taken for each of the five cross-sections, and the same measurement is performed for five hollow fiber porous membranes. The arithmetic mean of the obtained diameters is taken as the average pore diameter of the inner or outer surface.

[0023] In the hollow fiber porous membrane of the present invention, it is more preferable that the porosity of the entire hollow fiber porous membrane is 60% or more and 85% or less. By having a porosity of 60% or more and 85% or less of the entire hollow fiber porous membrane, the density of the polymer skeleton of the main component in the hollow fiber porous membrane increases, making it possible to improve durability. If the porosity of the entire hollow fiber porous membrane is less than 60%, the amount of structural parts where the main component of the hollow fiber porous membrane is aggregated increases, which may reduce water vapor permeability. Also, if it exceeds 85%, the polymer aggregation of the main component of the porous membrane weakens, which may reduce durability.

[0024] The porosity can be determined by the following method. First, hollow fiber porous membranes, all cut to a uniform length, are dried in a dryer set to 50°C for 24 hours. Next, the number of hollow fiber porous membranes is adjusted so that the weight after drying is between 1g and 5g. The volume of the hollow fiber porous membrane is calculated from the number and length of the membranes used, as well as the outer and inner diameters of the membranes. The porosity is then calculated using the dry weight and the polymer density, which is the main component of the hollow fiber porous membrane.

[0025] The outer diameter of the hollow fiber porous membrane is preferably between 500 μm and 1200 μm. If the outer diameter is less than 500 μm, when high-flow air is passed through the hollow portion of the hollow fiber porous membrane, the pressure from the inlet to the outlet of the hollow portion increases, which may cause the fibers of the hollow fiber porous membrane to break. On the other hand, if it exceeds 1200 μm, the airflow outside the hollow fiber porous membrane may become uneven in a module equipped with the hollow fiber porous membrane, which may prevent the hollow fiber porous membrane from being effectively utilized. Furthermore, if the hollow fiber porous membrane becomes too thick, the size of the module tends to increase, making it unsuitable for space saving.

[0026] Furthermore, the thickness of the hollow fiber porous membrane is preferably between 50 μm and 300 μm. If the thickness is less than 50 μm, the rupture strength of the hollow fiber porous membrane decreases, and fiber breakage may occur when high-flow air is applied. If the thickness exceeds 300 μm, the structural control stability during film formation of the hollow fiber porous membrane is lacking, and the reproducibility of film formation in the void portions of the porous membrane may be poor.

[0027] The materials constituting the hollow fiber porous membrane of the present invention are not particularly limited, but examples include polysulfone polymers, polystyrene, polyurethane, polyethylene, polypropylene, polycarbonate, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl chloride, and polyester. Among these, it is preferable that the hollow fiber porous membrane contains a polysulfone polymer from the viewpoint of excellent heat resistance and ease of forming the hollow fiber porous membrane. Furthermore, although the content of the polysulfone polymer is not particularly limited, it is preferable that the polysulfone polymer is the main component of the hollow fiber porous membrane. The main component means that the material is contained in an amount of 90% by mass or more and 100% by mass or less based on 100% by mass of the entire hollow fiber porous membrane.

[0028] Here, polysulfone polymers are polymers having aromatic rings, sulfonyl groups, and ether groups in their main chain, and include polysulfone, polyphenylsulfone, polyethersulfone, and polyarylethersulfone. For example, polysulfone polymers represented by the following chemical formulas (I) and / or (II) are preferably used. In the formula, n is an integer of 1 or more, preferably 50 to 80. If n has a distribution, the average value of n is taken as n.

[0029] The polymer may be copolymerized with other monomers or be a modified polymer, as long as it does not hinder the effects of the present invention. When copolymerized with other monomers, the copolymerization ratio of the other monomers is preferably 10% by mass or less of the total polysulfone polymer.

[0030] [ka]

[0031] Specific examples of polysulfone polymers include "Udel Polysulfone" P-1700, P-3500 (manufactured by Solvay), "Ultrasson" S3010, P3010, S6010 (manufactured by BASF), "Victrex" (manufactured by Sumitomo Chemical Co., Ltd.), "Radel" Polyphenylsulfone R-5000NT (manufactured by Solvay), "Belladel" Polyethersulfone 3000MP (manufactured by Solvay), and "Ultrasson" E (manufactured by BASF).

[0032] When a polysulfone polymer is used as the main component of the hollow fiber porous membrane of the present invention, it is preferable that a hydrophilic polymer is included. Examples of hydrophilic polymers include polyalkylene oxide, polyvinyl alcohol, polyethylene glycol, and polyvinylpyrrolidone. Among these, hydrophilic polymers with a glass transition temperature higher than 150°C are preferred because they can provide a hollow fiber porous membrane with excellent heat resistance. Polyvinylpyrrolidone is preferred for humidification applications in fuel cell systems because of its excellent compatibility with polysulfone polymers and its high glass transition temperature of 180°C. In other words, it is particularly preferable that the hollow fiber porous membrane of the present invention contains both a polysulfone polymer and polyvinylpyrrolidone. The polyvinylpyrrolidone content in 100% by mass of the hollow fiber porous membrane is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 4% by mass or less. When the polyvinylpyrrolidone content in a hollow fiber porous membrane is 5% by mass or more, maintaining water vapor permeability may become difficult as the hydrophilicity or swelling properties of polyvinylpyrrolidone decrease in high temperature and / or low humidity environments. Furthermore, the polyvinylpyrrolidone content in 100% by mass of the hollow fiber porous membrane is preferably 1% by mass or more, and more preferably 2% by mass or more. When the polyvinylpyrrolidone content in the hollow fiber porous membrane is less than 1% by mass, the hydrophilicity of the hollow fiber porous membrane decreases, making it difficult to absorb water vapor when it comes into contact with it. The polyvinylpyrrolidone content in a hollow fiber porous membrane can be measured using an NC analyzer after weighing the hollow fiber porous membrane dried in a dryer, provided the polymer composition of the hollow fiber porous membrane is known.

[0033] <Method for manufacturing hollow fiber porous membranes> One embodiment of the present invention as a method for producing a hollow fiber porous membrane is as follows: A film-forming stock solution (the concentration of the polysulfone polymer is preferably 18% to 35% by mass, and more preferably 23% to 30% by mass) is prepared by dissolving a polysulfone polymer and a vinylpyrrolidone polymer in a mixed solution of a good solvent for polysulfone (N,N-dimethylacetamide, dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone, dioxane, etc.) and a poor solvent, and a core liquid is flowed inside when the stock solution is discharged from a double annular nozzle. After running the stock solution through a dry zone humidified by cold air, it is allowed to solidify in a solidification solution. In this case, because the humidity of the dry zone has an effect, it is possible to accelerate the phase separation behavior near the outer surface by supplying moisture from the outer surface of the membrane while running through the dry zone, thereby expanding the pore size and consequently reducing the permeation resistance during humidification. However, if the wind speed or relative humidity of the cold air is too high, solidification of the raw material at the outer surface becomes dominant, which conversely reduces the pore size and tends to increase the permeation resistance during humidification. Therefore, a wind speed of 0.1 to 1.0 m / s is preferable for the cold air. Furthermore, a relative humidity of 50 to 90% is preferable for the cold air. In addition, for process suitability, it is preferable to use a core solution composition based on the solvent used in the film-forming raw material. As for the core solution concentration, for example, when N,N-dimethylacetamide is used, an aqueous solution of 10 to 60% by mass, and more preferably 20 to 50% by mass, is used.

[0034] The solidified hollow fiber porous membrane is washed with warm water between 40°C and 90°C and then wound up. If the washing temperature is below 40°C, the cleaning of organic solvents and other substances may be insufficient, and substances leached from the hollow fiber porous membrane may affect its use. If the washing temperature exceeds 90°C, the hydrophilic polymer may be washed excessively, which may reduce the hydrophilicity of the hollow fiber porous membrane.

[0035] Next, a dry hollow fiber porous membrane is obtained by heat treatment to fix the desired void size. Heat treatment involves drying the wet hollow fiber porous membrane, thereby reducing the size of the voids. After this treatment, moisturizing the hollow fiber membrane (by adding glycerin or filling with water) becomes unnecessary.

[0036] As a heat treatment method for hollow fiber porous membranes, it is preferable to divide the hollow fiber porous membrane into several hundred to several thousand strands and dry it in a dry heat dryer at 40°C to 170°C for 30 minutes or more. More preferably, the temperature is 50°C to 170°C, and even more preferably 50°C to 150°C.

[0037] If the drying temperature is lower than 40°C, drying will take longer, and depending on the external atmosphere, temperature control may be difficult, making it impossible to control the size of the voids. If the drying temperature is higher than 170°C, when using polysulfone polymers, it will approach the glass transition temperature, which may damage the hollow fiber porous membrane. A drying time of 30 minutes or more is preferable. More preferably, it is 5 hours or more. There is no particular upper limit for the drying time, but considering work efficiency, it is preferable to keep it within 72 hours. If the drying time is shorter than 30 minutes, it may not be possible to completely remove the moisture from the hollow fiber membrane, and there may be areas that have not been heat-treated. In this case, areas where the voids in the hollow fiber membrane have shrunk and areas where they have not shrunk may coexist, resulting in insufficient separation of moisture in the water vapor and air, which may lead to air leakage. In addition, when heat is applied during use, the size of the voids in areas where the voids have not shrunk may change, which may cause fluctuations in the initial performance.

[0038] Next, the hollow fiber porous membranes are bundled together, and both ends are fixed with a resin such as a potting agent so as not to seal the hollow portion of the hollow fiber porous membrane. The ends of the hollow fiber membrane bundle fixed with resin are connected to a hose, and an aqueous solution containing alkali metal ions or alkaline earth metal ions is passed through the hollow fiber porous membrane bundle. The concentration of alkali metal ions or alkaline earth metal ions depends on the temperature of the aqueous solution used and the solubility of the salt dissolved to include the ion species, but it is preferable to pass an aqueous solution with a salt concentration in the range of 10% to 45% by mass at a water temperature of 20°C to 30°C. The water flow time is preferably 30 minutes or more, more preferably 2 hours or more. There is no particular upper limit on the water flow time, but considering work efficiency, it is preferable to keep it within 5 hours. After that, the aqueous solution is removed from the hollow fiber porous membrane bundle, distilled water is passed through for 30 minutes or more for washing, the distilled water is removed, and the hollow fiber porous membrane of the present invention can be manufactured by drying in a dry heat dryer at 50°C.

[0039] <Membrane Module> The membrane module of the present invention is a membrane module containing the hollow fiber porous membrane of the present invention. More specifically, the hollow fiber porous membrane of the present invention is filled into a cylindrical case, and both ends of the hollow fiber porous membrane are fixed with a potting material. The shape of the cylindrical case is not particularly limited; for example, it may be cylindrical, elliptical, rectangular, or polygonal prism. Furthermore, both ends of the hollow fiber porous membrane may be fixed to both ends of the cylindrical case, or both ends of the hollow fiber porous membrane may be fixed to different cylindrical cases. As the potting material, polyurethane, epoxy, silicone, nylon, etc., can be appropriately selected and used. An example of a method for manufacturing the membrane module of the present invention is as follows: First, the hollow fiber porous membrane is cut to the required length, the required number of strands are bundled together, and then placed in a cylindrical case. Then, temporary caps are placed on both ends, and potting material is placed in both ends of the hollow fiber porous membrane. Methods for adding the potting material include the centrifugal method, in which the adhesive is added while the cylindrical case is rotated in a centrifuge, and the static method, in which the area to be bonded is immersed in a container of potting material. However, there are no particular limitations as long as the hollow fiber porous membrane and the cylindrical case can be stably fixed. After the potting material has solidified, the ends of the hollow fiber porous membrane can be cut so that both ends are open, thereby obtaining a membrane module.

[0040] <Potential applications of membrane modules> The membrane module of the present invention is applicable to air conditioners such as dehumidifiers, humidifiers, heat exchangers, and dehumidifying / humidifying units, as well as fuel cell systems and desiccant air conditioning systems.

[0041] <Dehumidifier> Next, a dehumidifier containing a membrane module including the hollow fiber porous membrane of the present invention will be described. This dehumidifier is a device that exchanges water vapor between two fluids via a hollow fiber membrane. For example, by supplying water or air containing water vapor to the inside of the hollow fiber membrane and supplying air to the outside of the hollow fiber membrane, water vapor permeates to the outside of the hollow fiber membrane, humidifying the air supplied to the outside of the hollow fiber membrane. Alternatively, for example, by supplying dry air to the inside of the hollow fiber membrane and air containing water vapor to the outside of the hollow fiber membrane, water vapor permeates through the hollow fiber membrane, thereby humidifying the air via the hollow fiber membrane. Furthermore, for example, by filling the inside of the hollow fiber membrane with an aqueous solution containing alkali metal ions and / or alkaline earth metal ions, and supplying moisture-containing air to the outside of the hollow fiber membrane, moisture permeation occurs through the hollow fiber membrane, humidifying the air. By adjusting the concentration of alkali metal ions and / or alkaline earth metal ions and the temperature of the aqueous solution, humidification through moisture exchange via the hollow fiber membrane becomes possible. Examples of aqueous solutions containing alkali metal ions and / or alkaline earth metal ions include aqueous lithium chloride solutions and aqueous calcium chloride solutions. By circulating the aqueous solution containing alkali metal ions and / or alkaline earth metal ions filling the inside of the hollow fiber membrane so that its concentration and temperature remain constant, stable humidity control becomes possible.

[0042] The dehumidifier and humidifier of the present invention can be suitably used in air conditioners, fuel cell systems, and total heat exchangers, but it can also be applied to other devices such as inkjet printers and composting equipment.

[0043] <Air conditioner> Next, the air conditioner including the dehumidifier / humidifier of the present invention will be described. This air conditioner is a device that controls humidity in general households, buildings, offices, factories, etc., such as an air conditioner or air handling unit.

[0044] The air conditioner of the present invention is a device that adjusts the humidity of the outside air taken in by the membrane module described above. An example of a schematic diagram of the air conditioner is shown in Figure 4. When outside air is taken into the air conditioner 40, it passes through the air filter 41, cooling coil 42, heating coil 43, dehumidifier / humidifier 44, and blower 45 in that order and is supplied to the room. The cooling coil 42 and heating coil 43 operate depending on whether the room is to be humidified or dehumidified.

[0045] <Fuel cell system> Next, a fuel cell system containing a membrane module including a hollow fiber porous membrane according to an embodiment of the present invention will be described. This fuel cell system can be applied, for example, to fuel cell vehicles and household fuel cells.

[0046] A fuel cell system comprises at least the membrane module 51 and a fuel cell 52 described above. While there are no particular limitations, an example of such a fuel cell system is one in which humidified air and / or hydrogen are supplied to the fuel cell using the membrane module while simultaneously providing power. In a fuel cell vehicle, for example, as shown in Figure 5, the power obtained is supplied to the motor 54 and battery 55 via the power control unit 53. Furthermore, the membrane module 51 functions as a humidifier and is housed in a metal or resin casing. The required specifications can be adjusted by freely changing the number of membrane modules installed depending on the application. <Heat exchanger> Next, a heat exchanger containing a membrane module including a hollow fiber porous membrane according to an embodiment of the present invention will be described. This heat exchanger is a device in which heat exchange occurs between a fluid inside the hollow fibers and a fluid outside the hollow fibers, via a hollow fiber porous membrane, from a higher temperature to a lower temperature. It can also function as a total heat exchanger by simultaneously exchanging water vapor. A schematic diagram of the heat exchanger is shown in Figure 6. The heat exchanger 60 is provided with a first fluid inlet 62 and a first fluid outlet 64, and a second fluid inlet 63 and a second fluid outlet 65. The membrane module 61 is connected such that one fluid, for example, the first fluid, flows inside the hollow fiber porous membrane within the membrane module 61, and the other fluid (the second fluid) flows outside the hollow fiber porous membrane.

[0047] By using the heat exchanger 60, heat is exchanged between the first fluid and the second fluid via the membrane module 61. [Examples]

[0048] The present invention will be described in more detail below based on examples. However, the present invention is not limited to the following examples. Each evaluation method in the examples is described in [1] to [8] below.

[0049] [1] Dimensional measurement of hollow fiber porous membranes Hollow fiber porous membranes were cut with a single blade in the direction of film thickness and set in a microwatcher (KEYENCE, VH-Z100). If the cross-section of the hollow fiber porous membrane was crushed during cutting, the cutting was repeated until it was nearly perfectly circular. The cross-section of the hollow fiber porous membrane was observed with a 1000x lens, and the film thickness width of the hollow fiber porous membrane was specified on the monitor screen projecting the cross-section, and the value displayed on the monitor screen was read. The outer diameter of the hollow fiber porous membrane was also displayed on the monitor screen by specifying the width of the hollow section. The same measurement was performed on 10 hollow fiber porous membranes, and the average value of the 10 measurement data was calculated to determine the outer diameter and film thickness of the hollow fiber porous membrane.

[0050] [2] Preparation of samples for SEM observation of porous membrane cross-sections The hollow fiber porous membrane obtained by film formation was moistened by immersing it in water for more than one hour, then frozen with liquid nitrogen and quickly folded to prepare a sample for cross-sectional observation of the porous membrane. If the voids in the hollow or film-thickened portions of the hollow fiber porous membrane were blocked, the sample preparation was repeated. Blockage of the hollow portions may occur when the hollow fiber porous membrane deforms in the direction of stress during the cutting process.

[0051] In each of the following methods, when using SEM images, the sample for observation was prepared and the image obtained using the method described herein.

[0052] [3] Observation of the thickness of the dense layer An image of 30,000 times magnification of the inner surface side of the hollow fiber porous membrane was taken with a SEM and imported into a computer. Next, analysis processing was performed using image processing software. After adjusting the contrast and brightness of the SEM image to make it easier to recognize the pores in the mesh structure, the pore parts were made black and the membrane parts were made white, and then a threshold value was set to obtain a binary image. The threshold value was set so that the pores would not connect to form pores larger than the actual ones. When the structure part and the other parts could not be separated due to the difference in contrast within the image, the image was cut at the parts with the same contrast, each part was subjected to binary processing, and then they were joined together as before to return to a single image or the parts other than the structure part were filled with black for image analysis. When the pores were observed doubly in the depth direction, the shallower pores were measured.

[0053] Note that the pore area was obtained by analyzing, using image processing software, the area of the part displayed in black, that is, the area of the individual pore parts, by the binary processing of the above image. The number of pixels of the scale bar indicating a known length in the image was measured, and the length (μm) per pixel number was calculated. The size of the imported image was 4.21 μm in width × 3.16 μm in height.

[0054] The lower limit area of the pores detected during image analysis was set to 1260 nm 2 and the pores with a pore area exceeding 1260 nm 2 were filled with fluorescent color. The layer without pores with a pore area exceeding 1260 nm 2 was regarded as the dense layer, and the thickness of the dense layer was measured in the direction from one surface to the other surface.

[0055] In the thickness direction of the hollow fiber porous membrane, that is, a straight line perpendicular to the above surface was drawn in the direction from one surface to the other surface. The surface of the hollow fiber porous membrane where the dense layer exists (hereinafter referred to as the dense surface), and the distance between the end on the dense surface side of the pores with a pore area exceeding 1260 nm 2 closest to the dense surface on the above straight line was taken as the thickness of the dense layer.

[0056] The captured image (4.21 μm wide x 3.16 μm high) was divided vertically into three sections, obtaining three images with a field of view of 4.21 μm wide x 1.05 μm high. Next, the thickness from the pore closest to the dense surface to the dense surface was measured in each field of view, obtaining the thickness of three dense layers for each captured image. The same measurement was performed on five captured images, and the average value of the measurement data for a total of 15 dense layer thicknesses was calculated and used as the thickness of the dense layer.

[0057] [4] Measurement of the average pore size of the cross-section of a hollow fiber porous membrane A 5,000x magnification image of the inner surface cross-section of the hollow fiber porous membrane was captured using a SEM and imported into a computer. Next, the number of pixels of a scale bar indicating a known length in the image was measured using image processing software, and the length per pixel (μm) was calculated. The size of the imported image was 25.4 μm wide x 19.05 μm high. The image contrast and brightness were adjusted to make the pores of the mesh structure easier to recognize, with the pore areas made black and the membrane areas white. A threshold was then set, and the image was binarized for analysis. A straight line perpendicular to the surface was drawn in the thickness direction of the hollow fiber membrane, i.e., from the inner surface to the outer surface. Five arbitrary pores were selected in the region from the inner surface to a length of 5% of the film thickness, and their respective pore diameters were determined by analyzing and quantifying them using image analysis software.

[0058] For each hollow fiber porous membrane, five cross-sections were obtained, and the same treatment was performed on each cross-section. This process was carried out for three hollow fiber porous membranes, and the average of the calculated pore diameters was taken as the average pore diameter of the inner surface.

[0059] For calculating the average pore diameter of the outer surface, the same processing as for the inner surface was applied to a 5,000x magnified image of the cross-section of the outer surface of the hollow fiber porous membrane using SEM, and this was used to determine the average pore diameter.

[0060] [5] Measurement of porosity of porous membranes 100 hollow fiber porous membranes, each 30 cm long, were dried in a 50°C dryer until weight change ceased, and the dry weight (dw, in g) was determined. The volume (V, in cm³) of the hollow fiber porous membrane was calculated from the dimensions, number, and length of the hollow fiber porous membrane. 3The density (ρ, unit: g / cm³) of the polymer that is the main component of the hollow fiber porous membrane was calculated. 3 The porosity was calculated using the following formula. The density of the polymer, which is the main component of the hollow fiber porous membrane, can be measured with a densimeter, and the obtained value can be used.

[0061] Porosity (%) of the entire porous membrane = [1 - (dw / (V × ρ))] × 100 [6] Comparison of ionic strengths measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) TOF-SIMS measurements were performed on the cross-section of the hollow fiber membrane. Measurements were taken from the inner surface of the hollow fiber porous membrane in the depth direction, with primary ions set to Bi3++ and secondary ions set to positive polarity. The sum of the intensities of the observed ion species from the inner surface to a depth of 0-100 nm was compared with the sum of the intensities from the outer surface to a depth of 0-100 nm.

[0062] [7] Measurement of air leakage This will be explained using Figure 7. Air at 50 kPa was applied to one end of the hollow fiber inside the membrane module 70, and a plug 71 was placed on the other end. At this time, the amount of air leaking out to the outside of the hollow fiber was measured with a flow meter 72 and evaluated according to the following criteria. A (Good): Air leakage rate per unit area of ​​hollow fiber porous membrane (cc / min / cm²) 2 ) is less than 0.1. B (OK): Air leakage rate per unit area of ​​hollow fiber porous membrane (cc / min / cm²) 2 The value is 0.1 or greater, and less than 0.5. C (Not acceptable): Air leakage rate per unit area of ​​hollow fiber porous membrane (cc / min / cm²) 2 ) is 0.5 or higher.

[0063] [8] Measurement of moisture permeability into dry air The explanation will be given with reference to Figure 8. A membrane module 80 and a blower 86 were installed in a constant temperature and humidity chamber 81, and piping carrying the first fluid was airtightly connected to the first fluid inlet 84 and first fluid outlet 85 of the membrane module 80. Dry air was flowed as the first fluid 87 through the first fluid inlet 84 and first fluid outlet 85 of the membrane module 80 to the inside of the hollow fiber porous membrane, and humid air generated by the blower 86 in the constant temperature and humidity chamber 81 was flowed as the second fluid 88 through the opening of the membrane module 80 to the outside of the hollow fiber porous membrane. At that time, temperature and humidity sensors 82 and 83 were connected before the first fluid inlet 84 and after the first fluid outlet 85, respectively, and the amount of moisture permeation per unit time flowing out from the first fluid outlet 85 was calculated by measuring the relative humidity and temperature.

[0064] Using dry air at a temperature of 30°C as the first fluid and humid air at a temperature of 25°C and a relative humidity of 80%RH as the second fluid, the permeability of the membrane module per unit of time was measured and evaluated according to the following criteria. A (Good): Water vapor transmission rate per unit area of ​​hollow fiber porous membrane (g / hr / m 2 ) is 150 or more. B (OK): Water vapor transmission rate per unit area of ​​hollow fiber porous membrane (g / hr / m 2 ) is between 100 and 150. C (Not allowed): Water vapor transmission rate per unit area of ​​hollow fiber porous membrane (g / hr / m 2 ) is less than 100.

[0065] [9] Measurement of moisture permeability using dehumidifying liquid The following explanation is given with reference to Figure 9. A membrane module 90 and a blower 96 were installed in a constant temperature and humidity chamber 91, and piping carrying the first fluid was airtightly connected to the first fluid inlet 94 and first fluid outlet 95 of the membrane module 90. As the first fluid 97, a 25°C, 35% by mass lithium chloride aqueous solution flowed through the first fluid inlet 94 and first fluid outlet 95 of the membrane module 90 to the inside of the hollow fiber porous membrane, and as the second fluid 98, humid air from the constant temperature and humidity chamber 91 generated by the blower 96 flowed through the opening of the membrane module 90 to the outside of the hollow fiber porous membrane. A temperature and humidity sensor 92 was connected so that the second fluid 99 after flowing over the outside of the hollow fiber porous membrane could be directly measured, and the amount of moisture permeation per unit time flowing out from the second fluid 98 was calculated by measuring the relative humidity and temperature. Humid air at a temperature of 25°C and a relative humidity of 80% RH was used as the second fluid, and the amount of moisture permeation per unit time of the membrane module was measured and evaluated according to the following criteria. A (Good): Water vapor transmission rate per unit area of ​​hollow fiber porous membrane (g / hr / m 2 ) is 150 or more. B (OK): Water vapor transmission rate per unit area of ​​hollow fiber porous membrane (g / hr / m 2 ) is between 100 and 150. C (Not allowed): Water vapor transmission rate per unit area of ​​hollow fiber porous membrane (g / hr / m 2 ) is less than 100.

[0066] (Example 1) A film-forming stock solution was prepared by heating and dissolving 28% by mass of polysulfone (Solvay's "Udel" P-3500) and 5% by mass of polyvinylpyrrolidone (BASF's K30) in a total of 100% by mass of 66% by mass of N,N-dimethylacetamide and 1% by mass of water. A core solution was prepared by mixing 30% by mass of N,N-dimethylacetamide and 70% by mass of water, totaling 100% by mass.

[0067] The film-forming solution was sent to the spinneret section and discharged from the outer tube of the orifice-type double-tube spinneret, while the core solution was discharged from the inner tube. The discharged film-forming solution passed through a humidified dry zone atmosphere and was then led to a coagulation bath. Next, it was subjected to a water washing process at 80°C, and the resulting wet hollow fiber porous membrane was wound into a bundle. The bundle of wound hollow fiber porous membranes was dried in a dry heat dryer at 100°C for 24 hours to obtain a dry hollow fiber porous membrane X.

[0068] Fifty hollow fiber porous membranes X were bundled together, and both ends were sealed with potting resin. A portion of the ends was then cut to create openings on both sides of the hollow fiber porous membrane. Tubes were connected to both ends of the bundle of hollow fiber porous membranes, and a liquid transfer pump was used to circulate a 25°C, 40% by mass calcium chloride aqueous solution through the hollow fiber porous membrane for 2 hours. This was followed by circulating 25°C distilled water for 1 hour. After removing the distilled water remaining inside the hollow fibers, the membrane was dried in a dry heat dryer at 50°C for 12 hours to obtain hollow fiber porous membrane A.

[0069] The obtained hollow fiber porous membrane A was evaluated using the methods described in [1] to [6]. The results are shown in Table 1.

[0070] Next, 500 hollow fiber porous membranes A were packed into a 65 x 35 mm, 270 mm long rectangular prism module case made of polycarbonate. Both ends of the hollow fiber porous membranes were fixed to the ends of the module case with potting agent, and by cutting a portion of the ends of the potting agent, the ends of the hollow fiber membranes were opened, and headers were attached to both ends to form membrane module A. Here, both ends of the hollow fiber porous membranes were fixed in the longitudinal direction of the module case, and the effective length of the hollow fiber porous membranes in membrane module A that were not fixed with potting agent was 250 mm. The obtained membrane module A was evaluated using the methods described in [7] and [8]. The results are shown in Table 2.

[0071] (Example 2) Hollow fiber porous membrane B was obtained using the same experimental method as in Example 1, except that a 20% by mass lithium chloride aqueous solution was used at 25°C instead of a 40% by mass calcium chloride aqueous solution at 25°C. Similarly, membrane module B was obtained using the same experimental method as in Example 1, except that hollow fiber porous membrane B was used instead of hollow fiber porous membrane A. The results of the evaluations of hollow fiber porous membrane B and membrane module B, performed in the same manner as in Example 1, are shown in Tables 1 and 2.

[0072] (Example 3) Hollow fiber porous membrane C was obtained using the same experimental method as in Example 1, except that a 35% by mass lithium chloride aqueous solution was used at 25°C instead of a 40% by mass calcium chloride aqueous solution at 25°C. Similarly, membrane module C was obtained using the same experimental method as in Example 1, except that hollow fiber porous membrane C was used instead of hollow fiber porous membrane A. The results of the evaluations of hollow fiber porous membrane C and membrane module C, performed in the same manner as in Example 1, are shown in Tables 1 and 2.

[0073] (Example 4) Hollow fiber porous membrane D was obtained using the same experimental method as in Example 3, except that instead of hollow fiber porous membrane X, hollow fiber porous membrane Y was used, which was prepared by heating and dissolving a film-forming stock solution consisting of 18% by mass of polysulfone (Solvay "Udel" P-3500), 7.0% by mass of polyvinylpyrrolidone (BASF K30), 74% by mass of N,N-dimethylacetamide, and 1% by mass of water, totaling 100% by mass. Similarly, membrane module D was obtained using the same experimental method as in Example 3, except that hollow fiber porous membrane D was used instead of hollow fiber porous membrane C. The results of the evaluation of hollow fiber porous membrane D and membrane module D, which were performed in the same manner as in Example 3, are shown in Tables 1 and 2.

[0074] (Example 5) Hollow fiber porous membrane X was immersed in a 40% by mass calcium chloride aqueous solution at 25°C for 2 hours, and then immersed in distilled water at 25°C for 1 hour. Afterward, it was dried in a dry heat dryer at 50°C for 12 hours to obtain hollow fiber porous membrane E. Membrane module E was obtained using the same experimental method as in Example 1, except that hollow fiber porous membrane E was used instead of hollow fiber porous membrane A. The results of the evaluation of hollow fiber porous membrane E and membrane module E, performed in the same manner as in Example 1, are shown in Tables 1 and 2.

[0075] (Example 6) Hollow fiber porous membrane F was obtained using the same experimental method as in Example 3, except that instead of hollow fiber porous membrane X, hollow fiber porous membrane Z was used, which was prepared by heating and dissolving a film-forming stock solution consisting of 30% by mass of polysulfone (Solvay "Udel" P-3500), 2.0% by mass of polyvinylpyrrolidone (BASF K30), 67% by mass of N,N-dimethylacetamide, and 1% by mass of water, totaling 100% by mass. Similarly, membrane module F was obtained using the same experimental method as in Example 3, except that hollow fiber porous membrane F was used instead of hollow fiber porous membrane C. The results of the evaluation of hollow fiber porous membrane F and membrane module F, which were performed in the same manner as in Example 3, are shown in Tables 1 and 2.

[0076] (Comparative Example 1) Table 1 shows the results of the same evaluation performed using the hollow fiber porous membrane X as in Example 1. Furthermore, the membrane module X was obtained using the same experimental method as in Example 1, except that hollow fiber porous membrane X was used instead of hollow fiber porous membrane A, and the results of the evaluation performed in the same manner as in Example 1 are shown in Table 2.

[0077] (Comparative Example 2) Table 1 shows the results of the same evaluation performed using hollow fiber porous membrane Y as in Example 1. Furthermore, the membrane module Y was obtained using the same experimental method as in Example 1, except that hollow fiber porous membrane Y was used instead of hollow fiber porous membrane A, and the results of the evaluation performed in the same manner as in Example 1 are shown in Table 2.

[0078] (Example 7) Using membrane module C, the evaluation was performed using the method described in [9], and the moisture permeability was found to be 335 g / hr / m 2 As a result, the evaluation was A.

[0079] (Example 8) Using membrane module F, the following evaluation was performed using the method described in [9], and the moisture permeability was found to be 241 g / hr / m 2 As a result, the evaluation was A.

[0080] [Table 1]

[0081] [Table 2] [Explanation of Symbols]

[0082] 1: Hollow fiber porous membrane 11:Inner surface 12:Dense layer 21:Outer surface 40:Air conditioner 41: Air filter 42: Cooling coil 43: Heating coil 44: Dehumidifier 45: Blower 46: Outside air 47: Air supply 51: Membrane Module 52: Fuel cell 53: Power control unit 54: Motor 55: Battery 60: Heat exchanger 61: Membrane Module 62: First fluid inlet 63: Second fluid inlet 64: 1st fluid outlet 65:Second fluid outlet 70: Membrane Module 71: Stopper 72:Flow meter 80: Membrane Module 81: Constant temperature and humidity layer 82: Temperature and humidity sensor 83: Temperature and humidity sensor 84: 1st fluid inlet 85: 1st fluid outlet 86: Blower 87: 1st fluid 88:Second fluid 90: Membrane module 91: Constant temperature and humidity layer 92: Temperature and humidity sensor 94: 1st fluid inlet 95: 1st fluid outlet 96: Blower 97: 1st fluid 98:Second fluid 99:Second fluid

Claims

1. In a cross-section perpendicular to the longitudinal direction of the hollow fiber porous membrane, the pore area on the inner surface of the hollow fiber porous membrane is 1260 nm. ２ The dense layer has only the following voids, and the average pore diameter of the outer surface of the hollow fiber porous membrane is larger than the average pore diameter of the inner surface. A hollow fiber porous membrane that satisfies at least one of the following conditions (1) or (2). (1) When X1 is the sum of the peak intensities of alkali metal ions in the region from the inner surface to a depth of 0 to 100 nm, as detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS), and X2 is the sum of the peak intensities of alkali metal ions in the region from the outer surface to a depth of 0 to 100 nm, then X1 > X2. (2) When X3 is the sum of the peak intensities of alkaline earth metal ions detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS) in the region from the inner surface to a depth of 0 to 100 nm, and X4 is the sum of the peak intensities of alkaline earth metal ions in the region from the outer surface to a depth of 0 to 100 nm, then X3 > X4.

2. A hollow fiber porous membrane according to claim 1, satisfying at least one of the following conditions (3) or (4). (3) 1.5 ≤ X1 / X2 ≤ 3.0 (4) 1.5 ≤ X³ / X⁴ ≤ 3.0

3. The hollow fiber porous membrane according to claim 1, wherein the porosity of the entire hollow fiber porous membrane is 60% or more and 85% or less.

4. The hollow fiber porous membrane according to claim 1, wherein the outer diameter of the hollow fiber porous membrane is 500 μm or more and 1200 μm or less.

5. The hollow fiber porous membrane according to claim 1, wherein the hollow fiber porous membrane comprises a polysulfone polymer and polyvinylpyrrolidone.

6. A membrane module comprising a hollow fiber porous membrane according to claim 1 or 2.

7. A dehumidifier and humidifier comprising the membrane module described in claim 6.

8. The dehumidifier according to claim 7, wherein the hollow fiber porous membrane is filled with an aqueous solution containing alkali metal ions and / or alkaline earth metal ions.

9. An air conditioner including a dehumidifier / humidifier according to claim 7 or 8.

10. A heat exchanger comprising the membrane module described in claim 6.

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