Method for producing hollow fiber-like porous body, hollow fiber-like porous body, and hollow fiber membrane

Abstract

This method for manufacturing a hollow fiber-like porous body includes: a discharge step for discharging a polymer solution containing a base polymer and a polar solvent from an outer discharge port of a nozzle having a double-pipe structure, and discharging a core liquid from an inner discharge port of the nozzle; a solidification step for immersing the discharged polymer solution and core liquid in a solidification liquid; a cleaning step for cleaning a molded body obtained by the solidification step; and a drying step for drying the molded body after the cleaning step. The base polymer includes at least one selected from the group consisting of polysulfone, polyether sulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate, and polyamide. The content of the polar solvent in the molded body after the drying step is 20,000 ppm by mass or less. The outer diameter of the molded body after the drying step is 500 μm or more.

Description

Method for producing hollow fiber-shaped porous body, hollow fiber-shaped porous body, and hollow fiber membrane

[0001] The present invention relates to a method for producing a hollow fiber-shaped porous body, a hollow fiber-shaped porous body, and a hollow fiber membrane.

[0002] As a method for separating acid gas from a mixed gas containing an acid gas such as carbon dioxide, a membrane separation method has been developed. The membrane separation method can efficiently separate the acid gas while suppressing operating costs, compared with an absorption method in which the acid gas contained in the mixed gas is absorbed into an absorbent for separation.

[0003] Examples of the separation membrane used in the membrane separation method include a hollow fiber membrane having a straw shape (for example, Patent Document 1). A hollow fiber membrane has an advantage of a larger membrane area per volume than a flat sheet-shaped separation membrane. A hollow fiber membrane includes a hollow fiber-shaped porous body, and further includes a separation functional layer supported by the porous body as necessary.

[0004] Japanese Unexamined Patent Application Publication No. 2014-184424

[0005] A hollow fiber-shaped porous body is produced, for example, according to a phase separation method. Examples of the phase separation method include a non-solvent induced phase separation method (NIPS method) and a dry induced phase separation method (DIPS method). In the NIPS method, for example, a polymer solution is discharged from a discharge port outside a nozzle having a double tube structure, and a core liquid is discharged from a discharge port inside the nozzle (discharging step), and the discharged polymer solution and core liquid are immersed in a coagulation liquid (coagulation step). Phase separation proceeds and pore formation is promoted by the coagulation step. The molded body obtained in the coagulation step is washed (washing step), and the washed molded body is dried (drying step). Thereby, a hollow fiber-shaped porous body is obtained.

[0006] The present inventors have found that in the method for producing a hollow fiber-shaped porous body by the NIPS method, part of the molded body may be dissolved during the drying step. When part of the molded bodies are dissolved, the molded bodies adhere to each other or aggregate, making it difficult to efficiently produce the hollow fiber-shaped porous body.

[0007] Accordingly, an object of the present invention is to provide a method for producing a hollow fiber-shaped porous body that enables efficient production of a hollow fiber-shaped porous body.

[0008] The present invention provides a method for producing a hollow fiber-like porous body, comprising: a discharge step of discharging a polymer solution containing a base polymer and a polar solvent from an outer discharge port of a double-tube nozzle and discharging a core liquid from an inner discharge port of the nozzle; a solidification step of immersing the discharged polymer solution and the core liquid in a solidification solution; a washing step of washing the molded body obtained by the solidification step; and a drying step of drying the molded body after the washing step, wherein the base polymer comprises at least one selected from the group consisting of polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate, and polyamide; the content of the polar solvent in the molded body after the drying step is 20,000 ppm by mass or less; and the outer diameter of the molded body after the drying step is 500 μm or more.

[0009] The present invention also provides a hollow fiber-like porous body containing a base polymer selected from the group consisting of polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate, and polyamide, having a polar solvent content of 20,000 ppm by mass or less, and an outer diameter of 500 μm or more.

[0010] Furthermore, the present invention provides a hollow fiber membrane equipped with the above-mentioned porous material.

[0011] According to the present invention, it is possible to provide a method for producing hollow fiber-like porous materials that can efficiently manufacture hollow fiber-like porous materials.

[0012] This figure illustrates a method for manufacturing a hollow fiber porous body according to one embodiment of the present invention. Figure 2 is a schematic cross-sectional perspective view showing a part of a hollow fiber porous body according to one embodiment of the present invention. Figure 3 is a schematic cross-sectional perspective view showing a part of a hollow fiber membrane according to one embodiment of the present invention. Figure 4 is a schematic cross-sectional perspective view showing an example of a hollow fiber membrane module equipped with a hollow fiber membrane.

[0013] A method for producing a hollow fiber-like porous body according to a first aspect of the present invention comprises: a discharge step of discharging a polymer solution containing a base polymer and a polar solvent from an outer discharge port of a double-tube nozzle and discharging a core liquid from an inner discharge port of the nozzle; a solidification step of immersing the discharged polymer solution and the core liquid in a solidification solution; a washing step of washing the molded body obtained by the solidification step; and a drying step of drying the molded body after the washing step, wherein the base polymer comprises at least one selected from the group consisting of polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate, and polyamide; the content of the polar solvent in the molded body after the drying step is 20,000 ppm by mass or less; and the outer diameter of the molded body after the drying step is 500 μm or more.

[0014] In a second embodiment of the present invention, for example, in the manufacturing method according to the first embodiment, the outer diameter of the molded article after the drying step is 1500 μm or less.

[0015] In a third embodiment of the present invention, for example, in the manufacturing method according to the first or second embodiment, the content of the polar solvent in the molded article after the washing step is in the range of 5,000 ppm by mass or more and 50,000 ppm by mass or less.

[0016] In a fourth embodiment of the present invention, for example, in a manufacturing method according to any one of the first to third embodiments, the base polymer includes at least one selected from the group consisting of polysulfone, polyethersulfone, and polyvinylidene fluoride.

[0017] In a fifth embodiment of the present invention, for example, in a manufacturing method according to any one of the first to fourth embodiments, the polar solvent includes at least one selected from the group consisting of amide compounds and lactone compounds.

[0018] In a sixth aspect of the present invention, for example, in a production method according to any one of the first to fifth aspects, the polar solvent includes at least one selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and γ-butyrolactone.

[0019] The hollow fiber-like porous body according to the seventh aspect of the present invention contains a base polymer comprising at least one selected from the group consisting of polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate, and polyamide, and has a polar solvent content of 20,000 ppm by mass or less, and an outer diameter of 500 μm or more.

[0020] In the eighth aspect of the present invention, for example, the porous body according to the seventh aspect has an outer diameter of 1500 μm or less.

[0021] In a ninth aspect of the present invention, for example, in a porous body according to the seventh or eighth aspect, the base polymer comprises at least one selected from the group consisting of polysulfone, polyethersulfone, and polyvinylidene fluoride.

[0022] In the tenth embodiment of the present invention, for example, in a porous body according to any one of the seventh to ninth embodiments, the polar solvent includes at least one selected from the group consisting of amide compounds and lactone compounds.

[0023] In the eleventh aspect of the present invention, for example, in a porous body according to any one of the seventh to tenth aspects, the polar solvent includes at least one selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and γ-butyrolactone.

[0024] In a twelfth aspect of the present invention, for example, in a porous body according to any one of the seventh to eleventh aspects, the porous body has an outer surface and an inner surface, and when nitrogen gas at 25°C is supplied to a space adjacent to the outer surface of the porous body, and the pressure in the space is adjusted to a value 20 kPa higher than the pressure in the space adjacent to the inner surface, the permeation rate of nitrogen gas permeating through the porous body is 10,000 GPU or more.

[0025] A hollow fiber membrane according to the thirteenth aspect of the present invention comprises a porous body according to any one of the seventh to twelfth aspects.

[0026] In a fourteenth aspect of the present invention, for example, the hollow fiber membrane according to the thirteenth aspect further comprises a separation functional layer supported by the porous body.

[0027] In a 15th aspect of the present invention, for example, a hollow fiber membrane according to the 13th or 14th aspect is used to separate an acidic gas from a gas mixture containing an acidic gas.

[0028] The details of the present invention will be described below, but the following description is not intended to limit the present invention to any particular embodiment.

[0029] <Embodiment of Method for Manufacturing Hollow Fiber-Shaped Porous Body> The method for manufacturing a hollow fiber-shaped porous body according to this embodiment includes a discharge step of discharging a polymer solution containing a base polymer and a polar solvent from an outer discharge port of a double-tube nozzle and discharging a core liquid from an inner discharge port of the nozzle; a solidification step of immersing the discharged polymer solution and core liquid in a solidification solution; a washing step of washing the molded body obtained by the solidification step; and a drying step of drying the molded body after the washing step. The manufacturing method according to this embodiment is typically a non-solvent-induced phase separation method (NIPS method).

[0030] In this embodiment, the base polymer includes at least one selected from the group consisting of polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate, and polyamide. Furthermore, the content of polar solvent in the molded article after the drying process is 20,000 ppm by mass or less, and the outer diameter of the molded article after the drying process is 500 μm or more.

[0031] The base polymer having the above configuration can be dissolved in a polar solvent. The inventors have found that the polar solvent remaining in the molded article after the washing process can dissolve a portion of the base polymer during the drying process. Based on this finding, the inventors have found that in a method for producing a hollow fiber porous body, the dissolution of a portion of the molded article during the drying process can be suppressed by controlling the content of the polar solvent in the molded article after the drying process to 20,000 ppm by mass or less. According to the manufacturing method of this embodiment, a hollow fiber porous body can be efficiently produced.

[0032] The manufacturing method according to this embodiment can be carried out, for example, using the spinning apparatus 90 shown in Figure 1. Each step will be described in detail below with reference to Figure 1.

[0033] <Discharge Process> In the discharge process, a nozzle 91 with a double-tube structure is used. The nozzle 91 preferably has a coaxial double-tube structure. More specifically, the nozzle 91 has an outer tube and an inner tube surrounded by the outer tube and extending in the same direction as the outer tube. Both the outer tube and the inner tube are cylindrical (cylindrical, elliptical, rectangular, etc.), and are preferably cylindrical. The polymer solution L1 passes through the flow path between the outer tube and the inner tube and is discharged from the outer discharge port of the nozzle 91. The core liquid L2 passes through the flow path surrounded by the inner tube and is discharged from the inner discharge port of the nozzle 91. The shape and dimensions of the discharge port of the nozzle 91 can be appropriately adjusted according to the shape and dimensions of the target hollow fiber porous body. In addition, it is preferable that the outer discharge port and the inner discharge port of the nozzle 91 are located in the same virtual plane.

[0034] In the example shown in Figure 1, the nozzle 91 is configured to discharge both the polymer solution L1 and the core liquid L2 vertically downward. The polymer solution L1 discharged from the nozzle 91 moves vertically downward while in contact with the core liquid L2 and is sent to the solidification liquid L4, which will be described later. In this specification, the polymer solution L1 and core liquid L2 discharged from the nozzle 91 are sometimes collectively referred to as the discharged liquid L3.

[0035] [Polymer Solution] (Base Polymer) As described above, polymer solution L1 contains a base polymer. The base polymer includes at least one selected from the group consisting of polysulfone (PSF), polyethersulfone (PESU), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), cellulose acetate (CA), and polyamide (PA). A base polymer having such a composition is suitable for the NIPS method.

[0036] The base polymer may contain at least one selected from the group consisting of polysulfone, polyethersulfone, and polyvinylidene fluoride.

[0037] The base polymer may contain at least one selected from the group consisting of polysulfone and polyethersulfone. The base polymer may contain polysulfone. From the viewpoint of heat resistance, acid resistance and alkali resistance, it is preferable that the base polymer contains polysulfone.

[0038] The content of the base polymer in the polymer solution L1 is, for example, 10 wt% to 30 wt%.

[0039] (Polar Solvent) As described above, the polymer solution L1 contains a polar solvent. In this embodiment, the polar solvent is a good solvent that can dissolve the base polymer.

[0040] The polar solvent preferably contains an organic compound. In other words, the polar solvent is preferably an organic solvent. The polar solvent preferably contains at least one selected from the group consisting of amide compounds and lactone compounds, and more preferably contains an amide compound.

[0041] An amide compound is a compound having at least one amide group. Examples of amide compounds include N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO). A lactone compound is a compound having at least one lactone ring. Examples of lactone compounds include γ-butyrolactone.

[0042] The polar solvent may contain at least one selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and γ-butyrolactone.

[0043] A polar solvent containing an amide compound as an organic compound is also called an aprotic polar solvent. The polar solvent may be an aprotic polar solvent. In other words, the polar solvent may contain at least one selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0044] The content of the polar solvent in the polymer solution L1 is, for example, 40 wt% to 90 wt%.

[0045] The polymer solution L1 may contain specific components other than the base polymer and the polar solvent. Examples of the specific components include diacetone alcohol, diethylene glycol, and diethylene glycol monobutyl ether. The content of the specific component in the polymer solution L1 is, for example, 10 wt% to 40 wt%.

[0046] (Polymer solution) In the discharging step, the temperature of the polymer solution L1 discharged from the nozzle 91 is preferably adjusted appropriately. The temperature of the polymer solution L1 is, for example, 30°C or higher. The upper limit of the temperature of the polymer solution L1 is, for example, 80°C. The upper limit of the temperature of the polymer solution L1 may be 70°C, 60°C, or even 50°C. The temperature of the polymer solution L1 may be the same as the set temperature of the double-tube structured nozzle. The discharge amount of the polymer solution L1 discharged from the nozzle 91 can be appropriately adjusted according to the dimensions of the target hollow fiber porous body and the like.

[0047] [Core solution] The core solution L2 typically induces phase separation in the polymer solution L1 by coming into contact with the polymer solution L1. The core solution L2 is preferably a poor solvent that hardly dissolves the base polymer contained in the polymer solution L1.

[0048] The core solution L2 preferably contains water. The core solution L2 may contain water as a main component, or may be substantially composed only of water. As used herein, "main component" means the component contained in the largest amount by weight ratio in the core solution L2. The core solution L2 may further contain other components other than water (for example, an organic solvent). When the content ratio of the specific component in the core solution is 50 wt% or more, the structure of the inner surface of the hollow fiber porous body is likely to be changed.

[0049] In the discharging step, the temperature of the core solution L2 discharged from the nozzle 91 is preferably adjusted appropriately. As the temperature of the core solution L2, those described above for the polymer solution L1 can be mentioned. The temperature of the core solution L2 may be the same as the temperature of the polymer solution L1. The temperature of the core solution L2 may be the same as the set temperature of the double-tube structured nozzle. The discharge amount of the core solution L2 discharged from the nozzle 91 can be appropriately adjusted according to the dimensions of the target hollow fiber porous body and the like.

[0050] <Solidification Process> The solidification process is carried out by immersing the polymer solution L1 and core liquid L2 (discharged liquid L3) discharged from the nozzle 91 in the discharge process into the solidification liquid L4. In the example shown in Figure 1, the solidification liquid L4 is located below the nozzle 91. More specifically, the spinning apparatus 90 is located below the nozzle 91 and includes a solidification tank 92 containing the solidification liquid L4. The discharged liquid L3 discharged vertically downward from the nozzle 91 passes through the solidification tank 92 and is immersed in the solidification liquid L4.

[0051] The polymer solution L1 sent to the solidification tank 92 solidifies upon contact with the solidification liquid L4. More specifically, phase separation occurs when the polymer solution L1 and the solidification liquid L4 come into contact. This forms a hollow fiber-like molded body 10p. The immersion time of the polymer solution L1 in the solidification liquid L4 can be appropriately adjusted depending on the composition of the polymer solution L1 and the solidification liquid L4, for example, from 1 second to 60 minutes.

[0052] (Coagulation Solution) The coagulation solution L4 typically induces phase separation in the polymer solution L1 upon contact with it. Preferably, the coagulation solution L4 is a poor solvent that hardly dissolves the base polymer contained in the polymer solution L1.

[0053] The coagulation solution L4 preferably contains water. The coagulation solution L4 may contain water as its main component, or it may be composed substantially of water alone. The coagulation solution L4 may further contain other components other than water (e.g., organic solvents). The composition of the coagulation solution L4 may be the same as or different from that of the core liquid L2.

[0054] The temperature of the coagulation solution L4 is adjusted to, for example, a range of 10°C to 90°C.

[0055] In this embodiment, the content of the polar solvent in the molded body 10p after the solidification process is, for example, in the range of 10,000 ppm by mass or more and 250,000 ppm by mass or less. The lower limit of the content of the polar solvent in the molded body 10p after the solidification process may be 20,000 ppm by mass.

[0056] The content of polar solvent in the molded body 10p after the solidification process can be determined, for example, by absolute calibration using gas chromatography, as follows: First, the molded body 10p after the solidification process is left to stand overnight. Then, a solution is obtained by adding 1 mL of chloroform to 10 mg of the molded body 10p and stirring. Next, a sample is obtained by filtering the solution through a 0.45 μm membrane filter. A chromatogram of the sample is obtained using a gas chromatograph-mass spectrometer (Shimadzu Corporation, GCMS-QP2050, column: Agilent, GC / MS column HP-5msUI). The content of polar solvent in the sample is calculated from the area of ​​the peak area of ​​the chromatogram. The content of polar solvent in the sample is considered to be the content of polar solvent in the molded body 10p after the solidification process.

[0057] Furthermore, pre-washing may be performed between the solidification process and the washing process. Pre-washing can be performed, for example, using water.

[0058] <Washing Process> The washing process is carried out by washing the molded body 10p obtained in the solidification process with a washing solution L5. The washing process may be carried out by continuously immersing the molded body 10p sent from the solidification tank 92 in the washing solution L5 (in-line washing), or by immersing the bobbin on which the molded body 10p has been wound in the washing solution L5 (batch washing). In-line washing is more preferable because it shortens the washing time. In the example in Figure 1, the molded body 10p is washed by in-line washing. In detail, the spinning apparatus 90 is equipped with a washing tank 93 containing the washing solution L5. The molded body 10p sent from the solidification tank 92 is immersed in the washing solution L5 by passing through the washing tank 93. The washing solution L5 is preferably water. After washing with the washing solution L5, surface treatment may be performed using isopropanol (IPA), ethanol, etc., as needed.

[0059] The temperature of the cleaning solution L5 is preferably appropriately adjusted. For in-line cleaning, the temperature of the cleaning solution L5 is, for example, 50°C or higher. The lower limit of the temperature of the cleaning solution L5 in in-line cleaning may be 60°C, or even 70°C. The upper limit of the temperature of the cleaning solution L5 in in-line cleaning is, for example, 90°C. For batch cleaning, the temperature of the cleaning solution L5 is, for example, 5°C or higher. The lower limit of the temperature of the cleaning solution L5 in batch cleaning may be 10°C. The upper limit of the temperature of the cleaning solution L5 in batch cleaning is, for example, 30°C.

[0060] The washing time is preferably appropriately adjusted. In inline washing, the immersion time in the washing solution L5 is set appropriately according to the washing speed, for example, in the range of 10 seconds to 10 minutes. In batch washing, the immersion time in the washing solution L5 is for example in the range of 5 minutes to 6 hours.

[0061] In this embodiment, the content of the polar solvent in the molded body 10p after the cleaning process is, for example, in the range of 5,000 ppm by mass or more and 50,000 ppm by mass or less. The lower limit of the content of the polar solvent in the molded body 10p after the cleaning process may be 5,500 ppm by mass, and more preferably 6,000 ppm by mass. The upper limit of the content of the polar solvent in the molded body 10p after the cleaning process may be 45,000 ppm by mass.

[0062] In in-line washing, the content of polar solvent in the molded body 10p after the washing process is, for example, in the range of 5,000 ppm by mass or more and 15,000 ppm by mass or less. In batch washing, the content of polar solvent in the molded body 10p after the washing process is, for example, in the range of 5,000 ppm by mass or more and 45,000 ppm by mass or less.

[0063] The content of polar solvent in the molded body 10p after the washing process can be determined by the same method as the method for determining the content of polar solvent in the molded body 10p after the solidification process described above.

[0064] <Drying Process> The drying process is carried out by drying the molded body 10p after the washing process. Known methods such as natural drying, hot air drying, reduced pressure drying, vacuum drying, drying by microwave irradiation, and drying using an IR (far-infrared) heater can be used to dry the molded body 10p. In the drying process, it is preferable to heat the molded body 10p by hot air drying or the like. In the drying process, the molded body 10p sent from the washing tank 93 may be continuously dried in a dryer, or the bobbin on which the molded body 10p has been wound may be set in a dryer and dried. In the example in Figure 1, the molded body 10p sent from the washing tank 93 is continuously dried in a dryer. In detail, the spinning apparatus 90 is equipped with a dryer 94. The molded body 10p sent from the washing tank 93 is dried by passing through the dryer 94. Through the drying process, a hollow fiber-like porous body 10 can be formed from the molded body 10p.

[0065] The heating temperature of the molded body 10p is preferably appropriately adjusted. The heating temperature of the molded body 10p is preferably above the boiling point of the solidification liquid L4, for example, 100°C or higher. The lower limit of the heating temperature of the molded body 10p may be 110°C. The upper limit of the heating temperature of the molded body 10p is preferably below the boiling point of the polar solvent contained in the polymer solution L1, for example, 200°C. The upper limit of the heating temperature of the molded body 10p may be 150°C. The heating temperature of the molded body 10p may be the same as the set temperature of the dryer 94.

[0066] The heating time of the molded body 10p is preferably appropriately adjusted. The heating time of the molded body 10p is, for example, in the range of 1 to 10 minutes.

[0067] As described above, in this embodiment, the content of the polar solvent in the molded article 10p after the drying process is 20,000 ppm by mass or less. The upper limit of the content of the polar solvent in the molded article 10p after the drying process may be 19,000 ppm by mass, 18,000 ppm by mass, 17,000 ppm by mass, or even 16,000 ppm by mass. The lower limit of the content of the polar solvent in the molded article 10p after the drying process is, for example, 0 ppm by mass.

[0068] The content of polar solvent in the molded body 10p after the drying process can be determined by the same method as the method for determining the content of polar solvent in the molded body 10p after the solidification process described above.

[0069] As described above, in this embodiment, the outer diameter of the molded body 10p after the drying process is 500 μm or more. The lower limit of the outer diameter of the molded body 10p after the drying process may be 600 μm, or even 700 μm. The upper limit of the outer diameter of the molded body 10p after the drying process is, for example, 1500 μm. The upper limit of the outer diameter of the molded body 10p after the drying process may be 1400 μm, 1300 μm, or even 1200 μm.

[0070] The outer diameter of the molded body 10p after the drying process can be determined, for example, by the following method. First, the molded body 10p is cut in a direction perpendicular to its central axis, and the cross-section is observed with a microscope. In the obtained image, the diameter of the smallest circle that can enclose the outer surface of the molded body 10p is identified. The above operation is repeated any number of times (at least 5 times), and the average value of the identified diameters is considered to be the outer diameter of the molded body 10p.

[0071] The molded body 10p after the drying process, i.e., the hollow fiber-like porous body 10, is preferably wound up using a winding machine 95. The spinning apparatus 90 may further include free rollers for feeding the molded body 10p from the coagulation tank 92 to the winding machine 95.

[0072] <Embodiment of Hollow Fiber Porous Body> Figure 2 is a schematic cross-sectional perspective view showing a part of a hollow fiber porous body 10 according to one embodiment of the present invention. The porous body 10 can be obtained by the method for manufacturing a hollow fiber porous body described above. The porous body 10 is hollow fiber-like and has an outer surface 10a and an inner surface 10b. In particular, the porous body 10 has a shape such as cylindrical, elliptical, or rectangular, and is preferably cylindrical. The porous body 10 can be used as a porous support for a hollow fiber membrane, which will be described later.

[0073] In this embodiment, the porous body 10 contains a base polymer, has a polar solvent content of 20,000 ppm by mass or less, and has an outer diameter of 500 μm or more. The base polymer includes at least one selected from the group consisting of polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate, and polyamide. The porous body 10 enables excellent permeation rate of the permeable fluid.

[0074] The content of the polar solvent in the porous body 10 can be determined by the same method as the content of the polar solvent in the molded body 10p after the drying process described above.

[0075] As described above, in this embodiment, the outer diameter of the porous body 10 is 500 μm or more. The lower limit of the outer diameter of the porous body 10 may be 600 μm, and further 700 μm. The upper limit of the outer diameter of the porous body 10 is, for example, 1500 μm. The upper limit of the outer diameter of the porous body 10 may be 1400 μm, 1300 μm, and further 1200 μm.

[0076] The inner diameter of the porous body 10 is not particularly limited. For example, the inner diameter of the porous body 10 is 1000 μm or less. For example, the lower limit of the inner diameter of the porous body 10 is 300 μm.

[0077] The outer diameter of the porous body 10 can be determined in the same way as the outer diameter of the molded body 10p after the drying process described above. Specifically, first, the porous body 10 is cut in a direction perpendicular to the central axis Ax of the porous body 10, and the cross-section is observed with a microscope. In the obtained image, the diameter of the smallest circle that can surround the outer surface 10a of the porous body 10 is identified. The above operation is repeated any number of times (at least 5 times), and the average value of the identified diameters is considered to be the outer diameter of the porous body 10. The inner diameter of the porous body 10 can also be determined in the same way. However, in the obtained image, the diameter of the smallest circle that can surround the inner surface 10b of the porous body 10 is identified, and the average value of the identified diameters is considered to be the inner diameter of the porous body 10.

[0078] The thickness of the porous body 10 is not particularly limited. For example, the thickness of the porous body 10 may be 0.5 mm or less, 0.3 mm or less, 0.1 mm or less, 0.08 mm or less, or even 0.05 mm or less. The lower limit of the thickness of the porous body 1 is, for example, 0.01 mm.

[0079] The thickness of the porous body 10 can be determined by the following method. First, the porous body 10 is cut in a direction perpendicular to its central axis Ax, and the cross-section is observed with a microscope. In the obtained image, the distance between the outer surface 10a and the inner surface 10b of the porous body 10 is determined at arbitrary locations (at least 5 locations). The average value of the determined distances is considered to be the thickness of the porous body 10.

[0080] The length of the porous body 1 parallel to the central axis Ax is not particularly limited. For example, the length of the porous body 1 is in the range of 0.1 m to 10 m.

[0081] The porous body 10 has a porous structure. From the viewpoint of improving the permeation rate of acidic gases that permeate the porous body 10, it is preferable that the porous body 10 has continuous pores formed in a three-dimensional manner. However, the porous body 10 may have independent pores, or it may have both continuous pores and independent pores. The porous body 10 may also have through-holes that penetrate through the porous body 10.

[0082] As described above, the porous body 10 contains a base polymer. For example, the porous body 10 may have a three-dimensional network-like skeleton containing the base polymer.

[0083] The base polymer may contain at least one selected from the group consisting of polysulfone, polyethersulfone, and polyvinylidene fluoride.

[0084] The base polymer may contain at least one selected from the group consisting of polysulfone and polyethersulfone. The base polymer may contain polysulfone. From the viewpoint of heat resistance, acid resistance and alkali resistance, it is preferable that the base polymer contains polysulfone.

[0085] The porous body 10 may contain a base polymer as its main component, or it may be composed substantially of only a base polymer. In this specification, "main component" means the component that is present in the most abundant amount by weight in the porous body 10. The porous body 10 may further contain other components besides the base polymer.

[0086] The polar solvent preferably contains an organic compound. In other words, the polar solvent is preferably an organic solvent. The polar solvent preferably contains at least one selected from the group consisting of amide compounds and lactone compounds, and more preferably contains an amide compound.

[0087] Amide compounds are compounds having at least one amide group. Examples of amide compounds include N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO). Lactone compounds are compounds having at least one lactone ring. Examples of lactone compounds include γ-butyrolactone.

[0088] The polar solvent may include at least one selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and γ-butyrolactone.

[0089] A polar solvent containing an amide compound as an organic compound is also called an aprotic polar solvent. The polar solvent may be an aprotic polar solvent. In other words, the polar solvent may contain at least one selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0090] As described above, the porous body 10 enables excellent permeation rates of the permeating fluid. For example, when nitrogen gas at 25°C is supplied to a space adjacent to the outer surface 10a of the porous body 10, and the pressure in that space is adjusted to a value 20 kPa higher than the pressure in the space adjacent to the inner surface 10b, the permeation rate of nitrogen gas permeating through the porous body 10 is 10,000 GPU or more. In this specification, unless otherwise specified, "pressure" means absolute pressure. Note that GPU is 10 -6 ·cm 3 (STP) / (sec・cm 2 This means cmHg. 3 (STP) refers to the volume of nitrogen gas at 1 atmosphere and 0°C.

[0091] The nitrogen gas permeation rate (GPU) through the porous body 10 can be determined by the following method. First, nitrogen gas at 25°C is supplied to a space adjacent to the outer surface 10a of the porous body 10, and the pressure in this space is adjusted to a value 20 kPa higher than the pressure in the space adjacent to the inner surface 10b. This causes the nitrogen gas to permeate the porous body 10 in the direction from the outer surface 10a to the inner surface 10b. The above permeation rate can be calculated based on the flow rate of nitrogen gas that has permeated through the porous body 10.

[0092] The lower limit of the nitrogen gas permeation rate through the porous material 10 may be 20,000 GPU. The upper limit of the nitrogen gas permeation rate through the porous material 10 may be, for example, 100,000 GPU. The upper limit of the nitrogen gas permeation rate through the porous material 10 may be 90,000 GPU, 80,000 GPU, or even 70,000 GPU or less.

[0093] <Embodiment of Hollow Fiber Membrane> Figure 3 is a schematic cross-sectional perspective view showing a part of a hollow fiber membrane 30 according to one embodiment of the present invention. The hollow fiber membrane 30 of this embodiment comprises the hollow fiber-like porous body 10 described above.

[0094] The hollow fiber membrane 30 may further comprise a separation function layer 20 supported by a porous body 10. In this case, the porous body 10 functions as a porous support for the separation function layer 20. In the hollow fiber membrane 30, it is preferable that the separation function layer 20 is in contact with and covers the outer surface 10a of the porous body 10. However, the separation function layer 20 may also be in contact with and cover the inner surface 10b of the porous body 10.

[0095] (Separation Functional Layer) The separation functional layer 20 is preferably a layer that preferentially allows acidic gases contained in the mixed gas to permeate.

[0096] In one preferred embodiment, the separation functional layer 20 contains a resin. Examples of resins included in the separation functional layer 20 include polyether block amide resin, polyamide resin, polyether resin, polyimide resin, cellulose acetate resin, silicone resin, and fluororesin. In this embodiment, the separation functional layer 20 is preferably substantially made of resin.

[0097] In another preferred embodiment, the separation functional layer 20 contains an ionic liquid. The ionic liquid is a salt (ionic compound) that is liquid at 25°C. The separation functional layer 20 may have a double network gel containing the ionic liquid. The double network gel is a gel having two types of network structures that are independent of each other. The double network gel includes, for example, a first network structure composed mainly of an organic material, a second network structure composed mainly of an inorganic material, and an ionic liquid. The second network structure may be composed mainly of an organic material different from that of the first network structure. In this specification, "composed mainly of" means that 50 wt% or more, and more specifically 70 wt% or more, of the material is composed of the said material.

[0098] The organic material for constituting the first network structure includes, for example, polymers such as polyacrylamide (particularly polydialkylacrylamide such as polydimethylacrylamide). The polymer contained in the organic material has structural units derived from acrylamide derivatives and may further contain crosslinked structures. Polymers containing crosslinked structures can be prepared by known methods. For example, first, a prepolymer having structural units having N-hydroxysuccinimide ester groups is prepared. Structural units having N-hydroxysuccinimide ester groups are derived, for example, from N-acrylooxysuccinimide. Next, a polymer containing crosslinked structures can be obtained by reacting the prepolymer with an amine-based crosslinking agent. The amine-based crosslinking agent is a compound having two or more primary amino groups, for example, ethylene glycol bis(3-aminopropyl) ether.

[0099] The second network structure may include a network of multiple particles. This network of particles is formed, for example, by multiple particles being bonded to each other by hydrogen bonds. As an example, the particles included in the second network structure are silica particles.

[0100] In this embodiment, specific ionic liquids include, for example, ionic liquids having imidazolium, pyridinium, ammonium, or phosphonium and substituents having one or more carbon atoms.

[0101] In an ionic liquid having imidazolium and a substituent having one or more carbon atoms, examples of substituents having one or more carbon atoms include alkyl groups having one to 20 carbon atoms, cycloalkyl groups having three to 14 carbon atoms, and aryl groups having six to 20 carbon atoms. These may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, etc. (for example, hydroxyalkyl groups having one to 20 carbon atoms).

[0102] Examples of alkyl groups having 1 to 20 carbon atoms include methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, and n-eicosadecyl. Examples include i-propyl group, sec-butyl group, i-butyl group, 1-methylbutyl group, 1-ethylpropyl group, 2-methylbutyl group, i-pentyl group, neopentyl group, 1,2-dimethylpropyl group, 1,1-dimethylpropyl group, t-pentyl group, 2-ethylhexyl group, and 1,5-dimethylhexyl group, which may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, etc.

[0103] The alkyl groups described above may be substituted with cycloalkyl groups. The number of carbon atoms in the alkyl groups substituted with cycloalkyl groups is, for example, 1 to 20. Examples of alkyl groups substituted with cycloalkyl groups include cyclopropylmethyl group, cyclobutylmethyl group, cyclohexylmethyl group, and cyclohexylpropyl group, which may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, etc.

[0104] Examples of cycloalkyl groups having 3 to 14 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclododecyl, norbornyl, bornyl, and adamantyl groups, which may be further substituted with hydroxyl, cyano, amino, or monovalent ether groups.

[0105] Examples of aryl groups having 6 to 20 carbon atoms include phenyl, toluyl, xylyl, mesityl, anisyl, naphthyl, and benzyl groups, which may be further substituted with hydroxyl, cyano, amino, or monovalent ether groups.

[0106] Compounds having imidazolium and substituents with one or more carbon atoms may further have substituents such as alkyl groups and may form salts with counter anions. Examples of counter anions include alkyl sulfates, tosylates, methanesulfonates, acetates, bis(fluorosulfonyl)imides, bis(trifluoromethanesulfonyl)imides, thiocyanates, dicyanamides, tricyanomethanides, tetracyanoborates, hexafluorophosphates, tetrafluoroborates, and halides. From the viewpoint of gas separation performance, bis(fluorosulfonyl)imides, bis(trifluoromethanesulfonyl)imides, dicyanamides, tricyanomethanides, and tetracyanoborates are preferred.

[0107] Ionic liquids having imidazolium and substituents with one or more carbon atoms include, specifically, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium tetrachloroferate, 1-butyl-3-methylimidazolium iodide, 1-butyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate, 1 -Butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium trifluoro(trifluoromethyl)borate, 1-butyl-3-methylimidazolium tribromide, 1,3-dimethylimidazolium chloride, 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride, 1,3-diisopropylimidazolium tetrafluoroborate, 1,3-di-tert-butylimidazolium tetrafluoroborate, 1,3-dicyclohexylimidazolium tetrafluoroborate, 1,3-dicyclohexylimidazolium chloride, 1,2-dimethyl-3-propylimidazolium iodide, 1-hexyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium bromide, 1-methyl-3-propylimidazolium iodide, 1-methyl-3-n-octylimidazolium bromide, 1-methyl-3-n-octylimidazolium Examples include dazolium chloride, 1-methyl-3-n-octylimidazolium hexafluorophosphate, 1-methyl-3-[6-(methylsulfinyl)hexyl]imidazolium p-toluenesulfonate, 1-ethyl-3-methylimidazolium tricyanomethanide, 1-ethyl-3-methylimidazolium tetracyanoborate, and 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0108] In particular, from the viewpoint of gas separation performance, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([EMI][FSI]), 1-ethyl-3-methylimidazolium dicyanamide ([EMI][DCA]), 1-ethyl-3-methylimidazolium tricyanomethanide ([EMI][TCM]), 1-ethyl-3-methylimidazolium tetracyanoborate ([EMI][TCB]), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4m][TF2N]), and 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2OHim][TF2N]) are especially preferred.

[0109] The method for preparing the double network gel is not particularly limited, and for example, the method disclosed in E. Kamio et al., Adv. Mater, 29, 1704118 (2017) can be used.

[0110] The ionic liquid content in the double network gel is, for example, 50 wt% or more, preferably 60 wt% or more, more preferably 70 wt% or more, and even more preferably 80 wt% or more. The higher the ionic liquid content, the more preferentially the separation functional layer 20 can permeate carbon dioxide contained in the mixed gas. The upper limit of the ionic liquid content is not particularly limited, and is, for example, 95 wt%.

[0111] The content of the first network structure, which is mainly composed of organic material, in the double network gel is, for example, 1 wt% or more, preferably 5 wt% or more, and more preferably 10 wt% or more. The upper limit of the content of the first network structure is, for example, 15 wt%. The content of the second network structure, which is mainly composed of inorganic material, in the double network gel is, for example, 1 wt% or more, from the viewpoint of improving the strength of the double network gel. The upper limit of the content of the second network structure is, for example, 5 wt%. The ratio of the total weight of the first network structure and the second network structure to the weight of the double network gel is, for example, 2 wt% or more, preferably 5 wt% or more, and more preferably 10 wt% or more. This ratio is preferably 20 wt% or less. In this embodiment, the separation functional layer 20 preferably consists substantially of a double network gel.

[0112] The thickness of the separation functional layer 20 is, for example, 50 μm or less, preferably 25 μm or less, and more preferably 15 μm or less. The thickness of the separation functional layer 20 may, in some cases, be 10 μm or less, 5.0 μm or less, or 2.0 μm or less. The thickness of the separation functional layer 20 may be 0.05 μm or more, or 0.1 μm or more.

[0113] One application of the hollow fiber membrane 30 according to this embodiment is the separation of acidic gases from a gas mixture containing acidic gases. Examples of acidic gases in the gas mixture include carbon dioxide, hydrogen sulfide, carbonyl sulfide, sulfur oxides (SOx), hydrogen cyanide, and nitrogen oxides (NOx), with carbon dioxide being preferred. The gas mixture contains other gases besides the acidic gas. Examples of other gases include nonpolar gases such as hydrogen and nitrogen, and inert gases such as helium, with nitrogen being preferred. In particular, the hollow fiber membrane 30 is suitable for separating carbon dioxide from a gas mixture containing carbon dioxide and nitrogen. However, the applications of the hollow fiber membrane 30 are not limited to the separation of acidic gases from the gas mixture described above.

[0114] <Embodiment of Method for Manufacturing Hollow Fiber Membrane> The hollow fiber membrane 30 can be manufactured, for example, by the following method. First, a porous body 10 is manufactured by the manufacturing method described above. Next, a coating solution containing the material for the separation functional layer 20 is applied to the outer surface 10a of the porous body 10 to form a coating film (coating step). As an example, the coating film can be formed by immersing the porous body 10 in the coating solution. Next, the separation functional layer 20 is formed by drying the coating film (drying step). In this way, the hollow fiber membrane 30 is obtained.

[0115] Drying of the coating film can be carried out, for example, under heating conditions. The heating temperature of the coating film is, for example, 50°C or higher. The heating time of the coating film is, for example, 3 seconds or more. The lower limit of the heating time of the coating film may be 5 seconds, 10 seconds, 30 seconds, 1 minute, or even 5 minutes. The upper limit of the heating time of the coating film is, for example, 10 minutes.

[0116] <Embodiment of Hollow Fiber Membrane Module> Figure 4 is a schematic cross-sectional perspective view showing an example of a hollow fiber membrane module 100 equipped with the hollow fiber membranes 30 described above. The hollow fiber membrane module 100 comprises a plurality of hollow fiber membranes 30. The hollow fiber membrane module 100 may further comprise a binding portion 40, a sealing portion 42, a cap 50, and a housing 60. In the hollow fiber membrane module 100, one end of the plurality of hollow fiber membranes 30 is bundled together by the binding portion 40. The other end of the plurality of hollow fiber membranes 30 is sealed by the sealing portion 42. The hollow fiber membranes 30 are housed in the housing 60. The cap 50 is integrated with the binding portion 40 and is placed over one end of the housing 60.

[0117] The hollow fiber membrane module 100 is preferably an external pressure type hollow fiber membrane module. In an external pressure type hollow fiber membrane module 100, for example, a mixed gas containing an acidic gas passes outside the hollow fiber membrane 30, and a permeate fluid with a higher acidic gas content than the mixed gas passes inside the hollow fiber membrane 30. However, the hollow fiber membrane module 100 may also be an internal pressure type hollow fiber membrane module.

[0118] Multiple hollow fiber membranes 30 are arranged parallel to each other and bundled together by a binding portion 40. The number of hollow fiber membranes 30 is not particularly limited and can be, for example, 1,000 to 20,000. The hollow fiber membranes 30 may also be bundled together by a net.

[0119] The binding portion 40 is the part that bundles one end of a plurality of hollow fiber membranes 30. The binding portion 40 has the shape of, for example, a cylinder or a truncated cone. The binding portion 40 is formed, for example, by casting. In this case, the binding portion 40 is also called the cast portion. The binding portion 40 may be made of resin filled between the hollow fiber membranes 30. Examples of resins that make up the binding portion 40 include epoxy and urethane.

[0120] The binding portion 40 separates the flow path for the mixed gas (the internal space of the housing 60) from the flow path for the permeable fluid (the internal space of the cap 50). The internal space of the housing 60 is isolated from the internal space of the cap 50 by the binding portion 40.

[0121] The sealing portion 42 is made of the same resin as the binding portion 40, for example. Alternatively, the binding portion 40 may be provided at the other end of the hollow fiber membrane 30 instead of the sealing portion 42. That is, both ends of the hollow fiber membrane 30 may be open.

[0122] The cap 50 is a funnel-shaped component integrated with the binding portion 40. The cap 50 has an internal space that communicates with each of the multiple hollow fiber membranes 30. Each of the multiple hollow fiber membranes 30 extends to the end face of the binding portion 40 and opens towards the internal space of the cap 50 at the end face of the binding portion 40. The permeating fluid is delivered from the hollow fiber membranes 30 to the outside of the hollow fiber membrane module 100 via the internal space of the cap 50. Components such as pipes and connectors may be connected to the tip of the cap 50. This tip may have a tubular shape, for example. The material of the cap 50 is not particularly limited. The cap 50 may be made of metal such as stainless steel (SUS); or resin such as polyvinyl chloride, polycarbonate, or polysulfone.

[0123] The housing 60 is a cylindrical component that houses a plurality of hollow fiber membranes 30 and binding portions 40. Both ends of the housing 60 are open. A cap 50 is attached to one end of the housing 60. The housing 60 has a nozzle-shaped outlet 60a for discharging the processed mixed gas (impermeable fluid) from its internal space. The outlet 60a protrudes perpendicular to the longitudinal direction of the housing 60 and communicates with the internal space of the housing 60.

[0124] The longitudinal direction of the housing 60 is parallel to the longitudinal direction of the hollow fiber membrane 30. The central axis O of the housing 60 is an axis that is parallel to the longitudinal direction of the housing 60 and passes through the center of the housing 60.

[0125] The material of the housing 60 is not particularly limited. The housing 60 may be made of metal such as stainless steel (SUS); or resin such as polyvinyl chloride, polycarbonate, or polysulfone. The material of the cap 50 may be the same as the material of the housing 60.

[0126] The hollow fiber membrane module 100 may further include a nut 80. The nut 80 is an example of a fastening member that secures the cap 50 and the housing 60 to each other. A threaded portion is provided on the outer circumferential surface of one end of the housing 60, and the nut 80 is screwed onto the threaded portion when the cap 50 is placed over the housing 60. The material of the nut 80 is not particularly limited. The nut 80 may be made of resin or metal.

[0127] The hollow fiber membrane module 100 may further include a cap 70 and a nut 82. The cap 70 is a funnel-shaped component attached to the other end of the housing 60. The nut 82 is an example of a fastening member that secures the cap 70 and the housing 60 to each other. The nut 82 is screwed onto a threaded portion provided on the outer circumferential surface of the other end of the housing 60. In this way, the cap 70 is fixed to the housing 60. A mixed gas is introduced from the outside of the hollow fiber membrane module 100 into the internal space of the housing 60 through the cap 70.

[0128] The cap 70 may be made of the same material as the cap 50. The nut 82 may be made of the same material as the nut 80. Instead of the cap 70 and the nut 82, the other end of the housing 60 may have a nozzle shape.

[0129] Membrane separation using the hollow fiber membrane module 100 is performed, for example, by the following method. First, a mixed gas is supplied to the internal space of the housing 60 through the cap 70. The concentration of acidic gas in the mixed gas is not particularly limited, and under standard conditions, is, for example, 0.01 vol% (100 volume ppm) or more, preferably 1 vol% or more, more preferably 10 vol% or more, even more preferably 30 vol% or more, and particularly preferably 50 vol% or more. The upper limit of the concentration of acidic gas in the mixed gas is not particularly limited, and under standard conditions, is, for example, 90 vol%. The pressure of the mixed gas supplied to the hollow fiber membrane module 100 is, for example, 0.1 MPa or more, preferably 0.3 MPa or more.

[0130] The gas mixture comes into contact with the outer surface of the hollow fiber membrane 30 within the internal space of the housing 60. This allows for the production of a permeate fluid with a higher acidic gas content than the gas mixture on the inner surface side of the hollow fiber membrane 30. In other words, the permeate fluid is supplied to the inside of the hollow fiber membrane 30. Preferably, the permeate fluid contains acidic gas as its main component. However, the permeate fluid may also contain small amounts of other gases besides acidic gas. The permeate fluid is sent from the hollow fiber membrane 30 to the outside of the hollow fiber membrane module 100 via the internal space of the cap 50.

[0131] The concentration of acidic gas in the gas mixture gradually decreases from the sealing portion 42 towards the binding portion 40. The gas mixture (impermeable fluid) processed in the internal space of the housing 60 is discharged to the outside of the housing 60 through the outlet 60a.

[0132] The hollow fiber membrane module 100 according to this embodiment is suitable for a continuous flow membrane separation method. However, the hollow fiber membrane module 100 according to this embodiment may also be used in a batch membrane separation method.

[0133] The above-described embodiments are mutually applicable, insofar as they do not conflict technically. The above embodiments may be combined with each other, insofar as they do not conflict technically.

[0134] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0135] [Preparation of Hollow Fiber-like Porous Material] (Example 1) A hollow fiber-like porous material of Example 1 was prepared using the method for producing a hollow fiber-like porous material described above. Polysulfone (PSF) was used as the base polymer. N-methyl-2-pyrrolidone (NMP) was used as the polar solvent. A mixture of 750 g of PSF and 3417 g of NMP was mixed under a nitrogen atmosphere and then stirred and dissolved at 100°C for 4 hours. In this way, the polymer solution of Example 1 (PSF concentration: 18 wt%) was prepared.

[0136] Next, using a double-tube nozzle maintained at 35°C, the polymer solution was discharged from the outer outlet and the core liquid from the inner outlet (discharge step). Ion-exchanged water was used as the core liquid. The discharge rate of the polymer solution was 15 mL / min. The discharge rate of the core liquid was 7 mL / min. Next, the polymer solution and core liquid discharged from the nozzle were immersed in a 50°C solidification solution for 5.4 seconds (solidification step). As a result, the polymer solution solidified, and a hollow fiber-like molded body was formed. Ion-exchanged water at 50°C was used as the solidification solution. After the solidification step, pre-washing was performed using 85°C ion-exchanged water for 0.37 minutes.

[0137] The molded body obtained in the solidification process was washed in-line using ion-exchanged water at 85°C for 1 minute (washing process). Next, the molded body after the washing process was dried in a dryer at 100°C for 5 minutes (drying process). This yielded the hollow fiber porous body of Example 1.

[0138] (Examples 2-10) Hollow fiber porous bodies of Examples 2-10 were prepared on the same day as Example 1. The temperature and time in the drying process were changed as shown in Table 1. Otherwise, the hollow fiber porous bodies of Examples 2-10 were prepared using the same method as in Example 1.

[0139] (Example 11) On a different day from Examples 1 to 10, the hollow fiber porous body of Example 11 was prepared. In Example 11, the washing step was performed by batch washing using ion-exchanged water at 23°C for 5 minutes. The drying step was performed at 120°C for 3 minutes. Except for these steps, the hollow fiber porous body of Example 11 was prepared by the same method as in Example 1. The solidification step in Example 11 was performed using the solidification solution used in Examples 1 to 10. Therefore, the concentration of polar solvent (NMP) in the solidification solution in Example 11 was higher than the concentration of polar solvent (NMP) in the solidification solution in Examples 1 to 10. As a result, the content of polar solvent (NMP) after the solidification step in Example 11 was higher than the content of polar solvent (NMP) after the solidification step in Examples 1 to 10.

[0140] (Examples 12-14) On the same day as Example 11, hollow fiber porous bodies of Examples 12-14 were prepared. The time for the washing process was changed as shown in Table 2. Except for this, the hollow fiber porous bodies of Examples 12-14 were prepared using the same method as in Example 11.

[0141] (Example 15) On a different day from Examples 11 to 14, the hollow fiber porous body of Example 15 was prepared. In Example 15, the core liquid discharge rate was 29 mL / min. The washing process was performed by batch washing using ion-exchanged water at 23°C for 60 minutes. Except for these conditions, the hollow fiber porous body of Example 15 was prepared by the same method as in Example 11. The solidification process in Example 15 was carried out using the same solidification solution as in Examples 1 to 10. That is, the polar solvent (NMP) concentration of the solidification solution in the solidification process of Example 15 was the same as the polar solvent (NMP) concentration of the solidification solution in the solidification process of Examples 1 to 10.

[0142] (Example 16) On the same day as Example 15, the hollow fiber porous body of Example 16 was prepared. In Example 16, the core liquid discharge rate was 40 mL / min. Except for this, the hollow fiber porous body of Example 16 was prepared by the same method as in Example 15.

[0143] (Example 17) On a different day from Examples 1 to 16, the hollow fiber porous material of Example 17 was manufactured. In Example 17, polysulfone (PSF) was used as the base polymer. N-methyl-2-pyrrolidone (NMP) was used as the polar solvent. Diethylene glycol (DEG) was used as the specific component. A mixture of 848 g of PSF, 2543 g of NMP, and 848 g of DEG was mixed under a nitrogen atmosphere, and then dissolved by stirring at 100°C for 4 hours. In this way, the polymer solution of Example 17 (PSF concentration: 20 wt%, DEG concentration: 20 wt%) was prepared.

[0144] Next, using a double-tube nozzle maintained at 35°C, the polymer solution was discharged from the outer outlet and the core liquid from the inner outlet (discharge step). Ion-exchanged water was used as the core liquid. The discharge rate of the polymer solution was 7.63 mL / min. The discharge rate of the core liquid was 5.14 mL / min. Next, the polymer solution and core liquid discharged from the nozzle were immersed in a 35°C solidification solution for 9 seconds (solidification step). This caused the polymer solution to solidify, forming a hollow fiber-like molded body. Ion-exchanged water at 35°C was used as the solidification solution. After the solidification step, a preliminary wash was performed using 55°C ion-exchanged water for 14 seconds.

[0145] The molded body obtained in the solidification process was washed in batches using ion-exchanged water at 23°C for 20 minutes x 2 times (total 40 minutes), and then washed again by changing the water (washing process). Next, the molded body after the washing process was dried in a dryer at 150°C for 10 minutes (drying process). This yielded the hollow fiber porous body of Example 17.

[0146] (Examples 18-20) On the same day as Example 17, hollow fiber porous bodies of Examples 18-20 were prepared. In the washing process, washing was performed in batches using ion-exchanged water at 23 degrees Celsius under the conditions of 20 minutes x 3 times (total 60 minutes), 20 minutes x 4 times (total 80 minutes), and 20 minutes x 5 times (total 100 minutes), respectively. The washing time was changed as shown in Table 2 by changing the number of times the water was changed to 2, 3, and 4 times, respectively. Except for this, the hollow fiber porous bodies of Examples 18-20 were prepared using the same method as in Example 17.

[0147] (Comparative Example 1) On a different day from Examples 11-14, a hollow fiber porous body of Comparative Example 1 was prepared. In Comparative Example 1, only a drying process was performed on the molded body obtained in the solidification process, without a washing process. The drying process was carried out at 120°C for 3 minutes. Except for these conditions, the hollow fiber porous body of Comparative Example 1 was prepared in the same manner as in Example 1. The solidification process of Comparative Example 1 was carried out using the solidification solution used in Examples 11-14. Therefore, the concentration of polar solvent (NMP) in the solidification solution in Comparative Example 1 was higher than the concentration of polar solvent (NMP) in the solidification solution in Examples 11-14. As a result, the content of polar solvent (NMP) after the solidification process of Comparative Example 1 was higher than the content of polar solvent (NMP) after the solidification process of Examples 11-14.

[0148] (Comparative Example 2) On the same day as Comparative Example 1, a hollow fiber porous body of Comparative Example 2 was prepared. In Comparative Example 2, a washing step was performed on the molded body obtained in the solidification step. The washing step was performed by in-line washing using ion-exchanged water at 50°C for 0.37 minutes. Except for this, the hollow fiber porous body of Comparative Example 2 was prepared by the same method as in Comparative Example 1.

[0149] (Comparative Example 3) On the same day as Comparative Example 1, the hollow fiber porous material of Comparative Example 3 was prepared. In Comparative Example 3, the washing process was performed by in-line washing using ion-exchanged water at 50°C for 0.73 minutes. Except for this, the hollow fiber porous material of Comparative Example 3 was prepared by the same method as in Comparative Example 2.

[0150] (Comparative Example 4) On the same day as Comparative Example 1, the hollow fiber porous material of Comparative Example 4 was prepared. In Comparative Example 4, the washing process was performed by in-line washing using ion-exchanged water at 85°C for 0.37 minutes. Except for this, the hollow fiber porous material of Comparative Example 4 was prepared by the same method as in Comparative Example 2.

[0151] (Comparative Example 5) On the same day as Comparative Example 1, the hollow fiber porous material of Comparative Example 5 was prepared. In Comparative Example 5, the washing process was performed by in-line washing using ion-exchanged water at 85°C for 0.73 minutes. Except for this, the hollow fiber porous material of Comparative Example 5 was prepared by the same method as in Comparative Example 2.

[0152] (Comparative Example 6) On the same day as Examples 11 to 14, the hollow fiber porous body of Comparative Example 6 was prepared. In Comparative Example 6, the washing process was performed by in-line washing using ion-exchanged water at 85°C for 1 minute. Except for these steps, the hollow fiber porous body of Comparative Example 6 was prepared by the same method as in Example 11.

[0153] (Comparative Example 7) On the same day as Examples 17-20, the hollow fiber porous material of Comparative Example 7 was prepared. In Comparative Example 7, the washing process was performed by batch washing using ion-exchanged water at 23°C for 20 minutes. Except for these steps, the hollow fiber porous material of Comparative Example 7 was prepared by the same method as in Examples 17-20.

[0154] <Measurement of Polar Solvent Content> The polar solvent content was measured for the molded articles after the solidification process, after the washing process, and after the drying process using the method described above. The results are shown in Tables 1 to 4. However, in Comparative Examples 1 to 7, a portion of the molded articles dissolved during the drying process, and the molded articles melted together, so the polar solvent content in the molded articles after the drying process was not measured.

[0155] <Measurement of Outer Diameter> The outer diameter of the hollow fiber-like porous material was measured using the method described above. The results are shown in Tables 1 to 4. However, in Comparative Examples 1 to 7, the outer diameter of the porous material could not be measured for the reasons mentioned above.

[0156] <Measurement of Nitrogen Gas Permeation Rate> For the porous materials of the examples and comparative examples, the nitrogen gas permeation rate (GPU) was determined using the method described above. Specifically, the nitrogen gas permeation rate was measured using the following method. First, five porous materials were placed inside a commercially available nylon tube, and both ends of the porous materials were fixed with urethane resin. At this time, one end of the porous material was left open to the outside space, and the other end was sealed with urethane resin. This obtained an evaluation module. Next, nitrogen gas at 25°C was supplied to the space adjacent to the outer surface of the porous material inside the nylon tube, and the pressure in this space was adjusted to a value 20 kPa higher than the pressure in the space adjacent to the inner surface of the porous material. As a result, the nitrogen gas permeated through the porous material in the direction from the outer surface to the inner surface. The nitrogen gas that permeated through the porous material was discharged to the outside space of the evaluation module through the open end of the porous material. The nitrogen gas permeation rate was calculated based on the flow rate of nitrogen gas that permeated through the porous material. The results are shown in Tables 1 to 4. However, in Comparative Examples 1 to 7, the transmission velocity could not be measured for the reasons mentioned above.

[0157]

[0158]

[0159]

[0160]

[0161] As described above, in Comparative Examples 1 to 7, a portion of the molded articles dissolved during the drying process, and the molded articles melted together. In contrast, in Examples 1 to 20, no aggregation of the molded articles occurred, and hollow fiber-like porous bodies could be efficiently produced. From these results, it is considered that when the base polymer contains at least one selected from the group consisting of polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate, and polyamide, a hollow fiber-like porous body can be efficiently produced by controlling the washing and drying processes so that the content of polar solvent in the molded article after the drying process is 20,000 ppm by mass or less, and the outer diameter of the molded article after the drying process is 500 μm or more.

[0162] In Examples 1 to 16, polysulfone was used as the base polymer and N-methyl-2-pyrrolidone as the polar solvent. In Examples 17 to 20, polysulfone was used as the base polymer and N-methyl-2-pyrrolidone as the polar solvent, and diethylene glycol (DEG) was used as a specific component. However, it is presumed that similar effects to those in Examples 1 to 20 can be expected even if other base polymers, polar solvents, and specific components are used.

[0163] The porous material according to this embodiment is suitable as a porous support for a hollow fiber membrane. The hollow fiber membrane according to this embodiment is suitable for separating acidic gases from a gas mixture containing acidic gases. In particular, the hollow fiber membrane according to this embodiment is suitable for separating carbon dioxide from off-gas in chemical plants or thermal power plants.

Claims

1. A method for producing a hollow fiber porous body, comprising: a discharge step of discharging a polymer solution containing a base polymer and a polar solvent from an outer discharge port of a double-tube nozzle and discharging a core liquid from an inner discharge port of the nozzle; a solidification step of immersing the discharged polymer solution and the core liquid in a solidification solution; a washing step of washing the molded body obtained by the solidification step; and a drying step of drying the molded body after the washing step, wherein the base polymer comprises at least one selected from the group consisting of polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate, and polyamide; the content of the polar solvent in the molded body after the drying step is 20,000 ppm by mass or less; and the outer diameter of the molded body after the drying step is 500 μm or more.

2. The manufacturing method according to claim 1, wherein the outer diameter of the molded body after the drying step is 1500 μm or less.

3. The manufacturing method according to claim 1, wherein the content of the polar solvent in the molded article after the washing step is in the range of 5,000 ppm by mass or more and 50,000 ppm by mass or less.

4. The manufacturing method according to claim 1, wherein the base polymer comprises at least one selected from the group consisting of polysulfone, polyethersulfone, and polyvinylidene fluoride.

5. The production method according to claim 1, wherein the polar solvent comprises at least one selected from the group consisting of amide compounds and lactone compounds.

6. The production method according to claim 5, wherein the polar solvent comprises at least one selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and γ-butyrolactone.

7. A hollow fiber-like porous body containing a base polymer selected from the group consisting of polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose acetate, and polyamide, having a polar solvent content of 20,000 ppm by mass or less, and an outer diameter of 500 μm or more.

8. The porous body according to claim 7, wherein the outer diameter is 1500 μm or less.

9. The porous body according to claim 7, wherein the base polymer comprises at least one selected from the group consisting of polysulfone, polyethersulfone, and polyvinylidene fluoride.

10. The porous body according to claim 7, wherein the polar solvent comprises at least one selected from the group consisting of amide compounds and lactone compounds.

11. The porous body according to claim 10, wherein the polar solvent comprises at least one selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and γ-butyrolactone.

12. The porous body according to claim 10, wherein the porous body has an outer surface and an inner surface, and when nitrogen gas at 25°C is supplied to a space adjacent to the outer surface of the porous body and the pressure in the space is adjusted to a value 20 kPa higher than the pressure in the space adjacent to the inner surface, the permeation rate of nitrogen gas permeating through the porous body is 10,000 GPU or more.

13. A hollow fiber membrane comprising a porous body according to any one of claims 7 to 12.

14. The hollow fiber membrane according to claim 13, further comprising a separation functional layer supported by the porous body.

15. The hollow fiber membrane according to claim 13, used for separating an acidic gas from a gas mixture containing an acidic gas.

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