Hollow fiber-like porous body, hollow fiber membrane, and method for manufacturing hollow fiber-like porous body

Abstract

This hollow fiber-like porous body 10 has an outer surface 10a and an inner surface 10b, and each of the outer surface 10a and the inner surface 10b has a plurality of pores. A ratio R2 / R1 of an opening rate R2 (%) on the inner surface 10b to an opening rate R1 (%) on the outer surface 10a is 200 or more. In the hollow fiber-like porous body 10, for example, the average pore diameter D1 on the outer surface 10a is smaller than the average pore diameter D2 on the inner surface 10b.

Description

Hollow fiber porous body, hollow fiber membrane, and method for manufacturing a hollow fiber porous body

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

[0002] Membrane separation is a method developed to separate acidic gases, such as carbon dioxide, from gas mixtures containing them. Compared to absorption methods, which separate acidic gases by having an absorbent absorb them, membrane separation can efficiently separate acidic gases while keeping operating costs down.

[0003] Examples of separation membranes used in membrane separation methods include hollow fiber membranes having a straw shape (for example, Patent Document 1). Hollow fiber membranes have the advantage of a larger membrane area per unit volume compared to flat membrane separation membranes. Hollow fiber membranes are equipped with hollow fiber-shaped porous bodies and, if necessary, further equipped with a separation functional layer supported by the porous bodies.

[0004] Hollow fiber-like porous materials are manufactured, for example, by phase separation methods. Examples of phase separation methods include non-solvent-induced phase separation (NIPS) and drying-induced phase separation (DIPS). In the NIPS method, for example, a polymer solution is discharged from the outside of a double-tube nozzle while a core liquid containing a poor solvent is discharged from the inside of the nozzle, and the discharged polymer solution and core liquid are immersed in a solidifying solution containing a poor solvent. This promotes phase separation and porosity, resulting in a hollow fiber-like porous material.

[0005] Japanese Patent Publication No. 2014-184424

[0006] The separation function layer is formed, for example, by immersing a hollow fiber-like porous material in a coating solution containing the material for the separation function layer (coating process), and then drying the coating solution (drying process). Generally, in the coating process, the hollow fiber-like porous material is immersed in the coating solution while being conveyed by a roll. Therefore, the hollow fiber-like porous material is required to have sufficient strength to prevent cracking or breakage during conveyance by the roll. However, if the pore size of the porous material is reduced to improve its strength, the permeation rate of the fluid passing through the porous material decreases. Since there is a trade-off relationship between the strength of the hollow fiber-like porous material and the permeation rate of the fluid, it has been difficult to realize a hollow fiber-like porous material that achieves both.

[0007] The inventors of the present invention diligently studied how to realize a hollow fiber porous material suitable for achieving both strength and permeation rate of the permeating fluid. As a result, they focused on making the porosity of the outer surface and the inner surface of the porous material different, and thus completed the present invention. The present invention aims to provide a hollow fiber porous material for use in hollow fiber membranes that is suitable for achieving both strength and permeation rate of the permeating fluid.

[0008] The present invention provides a porous body in the form of a hollow fiber having an outer surface and an inner surface, wherein each of the outer surface and the inner surface has a plurality of pores, and the ratio R2 / R1 of the porosity ratio R2 (%) of the inner surface to the porosity ratio R1 (%) of the outer surface is 200 or more.

[0009] Furthermore, the present invention provides a hollow fiber membrane equipped with the above-described porous body.

[0010] Furthermore, the present invention provides a method for manufacturing a hollow fiber-like porous body, comprising the steps of: discharging a polymer solution containing a base polymer from the outside of a double-tube nozzle and discharging a core liquid containing a specific component from the inside of the nozzle; and immersing the discharged polymer solution and the core liquid in a coagulation solution, wherein the difference between the HSP value of the base polymer and the HSP value of the specific component is 6 MPa in absolute value. 0.5 Above 20 MPa 0.5 The following manufacturing methods are provided.

[0011] According to the present invention, it is possible to provide a hollow fiber porous body used in hollow fiber membranes that is suitable for achieving both strength and permeation rate of the permeating fluid, and a hollow fiber membrane equipped with said porous body.

[0012] Figure 1 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 2 is a diagram illustrating a method for manufacturing a hollow fiber porous body. 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. Figure 5A is an image (100,000x magnification) showing the result of observing the outer surface of the hollow fiber porous body of Example 1 with a scanning electron microscope (SEM). Figure 5B is an image (100,000x magnification) showing the result of observing the inner surface of the hollow fiber porous body of Example 1 with an SEM. Figure 6A is an image (100,000x magnification) showing the result of observing the outer surface of the hollow fiber porous body of Example 2 with an SEM. Figure 6B is an image (100,000x magnification) showing the result of observing the inner surface of the hollow fiber porous body of Example 2 with an SEM. Figure 7A is an image (100,000x magnification) showing the result of observing the outer surface of the hollow fiber porous body of Comparative Example 1 with an SEM. Figure 7B is an image (100,000x magnification) showing the result of SEM observation of the inner surface of the hollow fiber porous material of Comparative Example 1. Figure 8A is an image (100,000x magnification) showing the result of SEM observation of the outer surface of the hollow fiber porous material of Comparative Example 2. Figure 8B is an image (100,000x magnification) showing the result of SEM observation of the inner surface of the hollow fiber porous material of Comparative Example 2.

[0013] A porous body according to a first aspect of the present invention is a hollow fiber-like porous body having an outer surface and an inner surface, wherein each of the outer surface and the inner surface has a plurality of pores, and the ratio R2 / R1 of the porosity ratio R2 (%) of the inner surface to the porosity ratio R1 (%) of the outer surface is 200 or more.

[0014] In a second aspect of the present invention, for example, in the porous body according to the first aspect, the porosity R1 on the outer surface is less than 0.5%.

[0015] In the third aspect of the present invention, for example, in the porous body according to the first or second aspect, the opening ratio R2 on the inner surface is 20% or more.

[0016] In the fourth aspect of the present invention, for example, in the porous body according to any one of the first to third aspects, the average pore diameter D1 on the outer surface is smaller than the average pore diameter D2 on the inner surface.

[0017] In the fifth aspect of the present invention, for example, in the porous body according to the fourth aspect, the ratio D2 / D1 of the average pore diameter D2 on the inner surface to the average pore diameter D1 on the outer surface is 10 or more.

[0018] In the sixth aspect of the present invention, for example, in the porous body according to any one of the first to fifth aspects, when nitrogen gas at 25°C is supplied to a space adjacent to the outer surface of the porous body, and the pressure in said space is adjusted to a value 20 kPa higher than the pressure in a space adjacent to the inner surface, the permeation rate of nitrogen gas permeating through the porous body is 5000 GPU or more.

[0019] In the seventh aspect of the present invention, for example, in the porous body according to any one of the first to sixth aspects, the breaking stress is 10 MPa or more in a tensile test under an environment at a temperature of 25°C.

[0020] In the eighth aspect of the present invention, for example, the porous body according to any one of the first to seventh aspects comprises polysulfone.

[0021] The hollow fiber membrane according to the ninth aspect of the present invention comprises the porous body according to any one of the first to eighth aspects.

[0022] In the tenth aspect of the present invention, for example, the hollow fiber membrane according to the ninth aspect further comprises a separation functional layer supported by said porous body.

[0023] In the eleventh aspect of the present invention, for example, the hollow fiber membrane according to the ninth or tenth aspect is used for separating acidic gas from a mixed gas containing acidic gas.

[0024] A manufacturing method according to a twelfth aspect of the present invention is a method for manufacturing a hollow fiber-like porous body, comprising the steps of: discharging a polymer solution containing a base polymer from the outside of a double-tube nozzle and discharging a core liquid containing a specific component from the inside of the nozzle; and immersing the discharged polymer solution and the core liquid in a solidification solution, wherein the difference between the HSP value of the base polymer and the HSP value of the specific component is 6 MPa in absolute value. 0.5 Above 20 MPa 0.5 It is within the following range.

[0025] In a thirteenth embodiment of the present invention, for example, in the manufacturing method according to the twelfth embodiment, the specific component includes diacetone alcohol.

[0026] In a fourteenth embodiment of the present invention, for example, in the manufacturing method according to the twelfth or thirteenth embodiment, the base polymer includes a polysulfone.

[0027] 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.

[0028] <Embodiment of Hollow Fiber Porous Body> Figure 1 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 is hollow fiber-like and has an outer surface 10a and an inner surface 10b. More specifically, 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.

[0029] The porous body 10 has pores. Each of the outer surface 10a and inner surface 10b of the porous body 10 has a plurality of pores. In this embodiment, the ratio R2 / R1 of the porosity ratio R2 (%) on the inner surface 10b to the porosity ratio R1 (%) on the outer surface 10a is 200 or more. A ratio of R2 / R1 of 200 or more indicates that there is a large difference between the porosity ratio R1 on the outer surface 10a and the porosity ratio R2 on the inner surface 10b, and that the porosity ratio R1 on the outer surface 10a is kept low compared to the porosity ratio R2 on the inner surface 10b. Therefore, in the porous body 10 according to this embodiment, the permeation rate of the permeating fluid is ensured by the porous body 10 on the inner surface 10b side, while the strength is ensured by the porous body 10 on the outer surface 10a side, where the porosity ratio R1 is kept low. The porous body 10 is suitable for achieving both strength and the permeation rate of the permeating fluid.

[0030] Furthermore, in this embodiment, the porous body 10 has a low porosity R1 on its outer surface 10a. For example, when forming a coating film of the separation function layer on the outer surface 10a, the coating liquid containing the material for the separation function layer does not easily penetrate the outer surface 10a. In other words, the porous body 10 suppresses the occurrence of defects in the separation function layer caused by excessive penetration of the coating liquid into the outer surface 10a.

[0031] The porosity R1 on the outer surface 10a and the porosity R2 on the inner surface 10b can be determined by the following method. First, the porous body 10 is cut in a direction parallel to the central axis Ax of the porous body 10 to prepare a test specimen. The shape of the test specimen is typically semi-cylindrical. Next, the surface of the test specimen corresponding to the outer surface 10a is observed with a scanning electron microscope (SEM). The magnification at this time is, for example, 100,000 times. This yields an SEM image (for example, Figure 5A) showing an area of ​​1.1 μm vertically × 1.6 μm horizontally. Next, the obtained SEM image is binarized to create a binarized image. The pores present in the binarized image are identified, and the total area of ​​the pores is calculated by image processing. The surface area of ​​the test specimen in the binarized image (μm 2 The total pore area (μm²) relative to the total pore area (μm²) 2 The ratio of ) is considered to be the porosity R1. The porosity R2 on the inner surface 10b can be determined by the same method.

[0032] The ratio R2 / R1 may be 210 or higher, 220 or higher, 230 or higher, 240 or higher, or even 250 or higher. The ratio R2 / R1 may be 260 or higher, 270 or higher, 280 or higher, 290 or higher, or even 300 or higher.

[0033] The upper limit of the ratio R2 / R1 is, for example, 1000. The ratio R2 / R1 may be 950 or less, 900 or less, 850 or less, 800 or less, 750 or less, 700 or less, 650 or less, 600 or less, 550 or less, and even 500 or less.

[0034] The ratio R2 / R1 may be between 250 and 550, or between 300 and 500.

[0035] The porosity R1 on the outer surface 10a may be less than 0.5%. When the porosity R1 on the outer surface 10a is less than 0.5%, it is easier to realize a porous body 10 that balances strength and the permeation rate of the permeating fluid.

[0036] The porosity R1 on the outer surface 10a may be 0.4% or less, 0.3% or less, or even 0.2% or less.

[0037] The lower limit of the porosity R1 on the outer surface 10a is, for example, 0.03%. The porosity R1 on the outer surface 10a may be 0.05% or more, 0.095% or more, or even 0.1% or more.

[0038] The porosity R2 on the inner surface 10b may be 20% or more. When the porosity R2 on the inner surface 10b is 20% or more, it is easier to realize a porous body 10 that balances strength and the permeation rate of the permeating fluid.

[0039] The porosity R2 on the inner surface 10b may be 21% or more, 22% or more, 23% or more, 24% or more, 25% or more, 26% or more, 27% or more, 28% or more, 29% or more, 30% or more, 31% or more, 32% or more, 33% or more, 34% or more, or even 35% or more.

[0040] The upper limit of the porosity R2 on the inner surface 10b is, for example, 98%. The porosity R2 on the inner surface 10b may be 95% or less, 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55% or less, or even 50% or less.

[0041] In this embodiment, the average pore diameter D1 on the outer surface 10a is smaller than the average pore diameter D2 on the inner surface 10b. When the average pore diameter D1 on the outer surface 10a is smaller than the average pore diameter D2 on the inner surface 10b, it is easier to improve the strength of the porous body 10 on the outer surface 10a side, while at the same time, it is easier to improve the permeation rate of the permeating fluid in the porous body 10 on the inner surface 10b side. Therefore, a porous body 10 in which the average pore diameter D1 is smaller than the average pore diameter D2 is suitable because it balances strength and the permeation rate of the permeating fluid.

[0042] The average pore diameter D1 on the outer surface 10a and the average pore diameter D2 on the inner surface 10b can be determined by the following method. First, a test specimen is prepared for the open area ratio R1 using the method described above. Next, the surface of the test specimen corresponding to the outer surface 10a is observed with a scanning electron microscope (SEM). The magnification at this time is, for example, 100,000 times. This yields an SEM image showing an area of ​​1.1 μm vertically and 1.6 μm horizontally. Next, the obtained SEM image is binarized to create a binarized image. The area of ​​a specific pore present in the binarized image is calculated by image processing. The radius of a circle with the same area as the calculated area (circular equivalent radius) is considered to be the radius of that specific pore. The radii of any number of pores (at least 20) are calculated, and the average of the calculated values ​​is considered to be the average pore diameter D1. The average pore diameter D2 on the inner surface 10b can be determined by the same method.

[0043] The average pore size D1 on the outer surface 10a may be 10.0 nm or less. When the average pore size D1 on the outer surface 10a is 10.0 nm or less, it is easier to realize a porous body 10 that balances strength and gas permeability.

[0044] The average pore size D1 on the outer surface 10a may be 9.5 nm or less, 9.0 nm or less, 8.5 nm or less, 8.0 nm or less, 7.5 nm or less, 7.0 nm or less, or even 6.5 nm or less.

[0045] The lower limit of the average pore size D1 on the outer surface 10a is, for example, 1.0 nm. The average pore size D1 on the outer surface 10a may be 1.5 nm or more, 2.0 nm or more, 2.5 nm or more, 3.0 nm or more, 3.5 nm or more, 4.0 nm or more, 4.5 nm or more, and even 5.0 nm or more.

[0046] The average pore diameter D2 on the inner surface 10b may be 50 nm or more. If the average pore diameter D1 on the outer surface 10a is 10.0 nm or less, and the average pore diameter D2 on the inner surface 10b is 50 nm or more, it is easier to realize a porous body 10 that balances strength and the permeation rate of the permeating fluid.

[0047] The average pore size D2 on the inner surface 10b may be 60 nm or more.

[0048] The upper limit of the average pore diameter D2 on the inner surface 10b is, for example, 600 nm. The average pore diameter D2 on the inner surface 10b may be 590 nm or less, 580 nm or less, 570 nm or less, 560 nm or less, 550 nm or less, 540 nm or less, 530 nm or less, 520 nm or less, 510 nm or less, and even 500 nm or less.

[0049] The ratio of the average pore diameter D2 to the average pore diameter D1, D2 / D1, may be 10 or more. When the ratio of the average pore diameter D2 to the average pore diameter D1, D2 / D1, is 10 or more, it is easier to realize a porous body 10 that balances strength and the permeation rate of the permeating fluid.

[0050] The ratio D2 / D1 may be 11 or greater, 12 or greater, 13 or greater, 14 or greater, 15 or greater, 16 or greater, 17 or greater, 18 or greater, 19 or greater, or even 20 or greater.

[0051] The upper limit of the ratio D2 / D1 is, for example, 100. The ratio D2 / D1 may also be 90 or less, 80 or less, 70 or less, 60 or less, 50 or less, 40 or less, or even 30 or less.

[0052] The outer diameter of the porous body 10 is not particularly limited. For example, the outer diameter of the porous body 10 may be 1.5 mm or less, 1.0 mm or less, 0.8 mm or less, 0.5 mm or less, and even 0.4 mm or less. The lower limit of the outer diameter of the porous body 10 is, for example, 0.1 mm. The outer diameter of the porous body 10 may be 0.3 mm or more.

[0053] The inner diameter of the porous body 10 is not particularly limited. For example, the inner diameter of the porous body 10 may be 1.0 mm or less, 0.8 mm or less, 0.5 mm or less, 0.4 mm or less, and even 0.3 mm or less. The lower limit of the inner diameter of the porous body 10 is, for example, 0.1 mm. The inner diameter of the porous body 10 may be 0.2 mm or more.

[0054] The outer diameter and inner diameter 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 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 by the same method. 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.

[0055] 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 10 is, for example, 0.01 mm.

[0056] 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.

[0057] The length of the porous body 10 parallel to the central axis Ax is not particularly limited. For example, the length of the porous body 10 is in the range of 0.1 m to 10 m.

[0058] The porous body 10 has a porous structure. The pores contained in this porous structure may be continuous pores formed in a three-dimensional manner. The porous body 10 does not have to have holes (through holes) that connect to both the pores on the outer surface 10a and the pores on the inner surface 10b. In other words, the porous body 10 does not have to have through holes that penetrate the outer surface 10a and the inner surface 10b. Such a porous structure makes it easier to realize a porous body 10 that is suitable for achieving both strength and the permeation rate of the permeable fluid. However, the porous body 10 may have through holes that penetrate the outer surface 10a and the inner surface 10b.

[0059] In this embodiment, the porous body 10 includes a base polymer. For example, the porous body 10 may have a three-dimensional network-like skeleton that includes the base polymer.

[0060] Examples of base polymers include polysulfone (PSF), polyethersulfone (PESU), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), cellulose acetate (CA), and polyamide (PA). The base polymer may contain at least one selected from these. From the viewpoint of heat resistance, acid resistance, and alkali resistance, it is preferable that the base polymer contains PSF.

[0061] 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.

[0062] As described above, the porous body 10 is suitable for achieving both strength and permeation rate of a permeated fluid. Regarding the permeation rate of the permeated 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 this space is adjusted to a value that is 20 kPa higher than the pressure in a space adjacent to the inner surface 10b, the permeation rate of nitrogen gas permeating through the porous body 10 is 5000 GPU or higher. In this specification, unless otherwise stated, "pressure" means absolute pressure. In addition, GPU means 10 -6 ・cm 3 (STP) / (sec・cm 2 ・cmHg). cm 3 (STP) means the volume of nitrogen gas at 1 atm and 0° C.

[0063] The permeation rate (GPU) of nitrogen gas permeating through the porous body 10 can be specified 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 said space is adjusted to a value that is 20 kPa higher than the pressure in the space adjacent to the inner surface 10b. Thereby, the nitrogen gas permeates through the porous body 10 in the direction from the outer surface 10a toward the inner surface 10b. The aforementioned permeation rate can be calculated based on the flow rate or the like of the nitrogen gas that has permeated through the porous body 10.

[0064] The permeation rate of nitrogen gas permeating through the porous body 10 may be 6000 GPU or higher, 7000 GPU or higher, and further 8000 GPU or higher. The upper limit of the permeation rate of nitrogen gas permeating through the porous body 10 is, for example, 100000 GPU. The permeation rate of nitrogen gas permeating through the porous body 10 may be 50000 GPU or lower, 35000 GPU or lower, and further 20000 GPU or lower.

[0065] Regarding strength, for example, in a tensile test under an environment at a temperature of 25° C., the breaking stress of the porous body 10 is 10 MPa or higher.

[0066] The fracture stress (MPa) of the porous body 10 can be measured by the following method. First, the porous body 10 is cut in half perpendicular to its central axis Ax to prepare a 100 mm long test specimen. At 25°C in air, a tensile test is performed on the test specimen using a tensile testing machine (for example, Shimadzu Corporation's Autograph AGX-V desktop precision universal testing machine) with an initial chuck distance of 100 mm and a tensile speed of 200 mm / min, and the stress-strain curve (S-S curve) is determined. From the S-S curve, the maximum stress, which is the stress at which the test specimen fractures, can be determined. The maximum stress is considered to be the fracture stress of the porous body 10.

[0067] The upper limit of the fracture stress of the porous body 10 is, for example, 30 MPa. The fracture stress of the porous body 10 may be 25 MPa or less, 20 MPa or less, or even 15 MPa or less.

[0068] <Embodiment of Method for Manufacturing Hollow Fiber-Shaped Porous Body> Next, a method for manufacturing the hollow fiber-shaped porous body 10 according to this embodiment will be described. The method for manufacturing the porous body 10 is not limited to a specific method. The porous body 10 can be manufactured, for example, according to a phase separation method. As mentioned above, examples of phase separation methods are non-solvent-induced phase separation (NIPS method) and drying-induced phase separation (DIPS method). The porous body 10 according to this embodiment is particularly well-suited to achieving a balance between strength and permeation rate of the permeating fluid when manufactured using the NIPS method.

[0069] The following describes an example of a method for manufacturing a porous body 10 using the NIPS method, with reference to Figure 2. The method for manufacturing the porous body 10 includes, for example, a step of discharging a polymer solution 92 containing a base polymer from the outside of a double-tube nozzle 91 and discharging a core liquid 93 containing a specific component from the inside of the nozzle 91 (discharging step), and a step of immersing the discharged polymer solution 92 and core liquid 93 in a solidification liquid 94 (immersion step). The difference between the HSP value of the base polymer and the HSP value of the specific component is 6 MPa in absolute value. 0.5 Above 20 MPa 0.5 The following ranges apply. The core liquid 93 and the coagulation solution 94 are poor solvents. In this embodiment, the coagulation solution 94 does not contain any specific components.

[0070] The present inventors have found that in the discharge step of the NIPS method, the difference between the core liquid 93 and the HSP value of the base polymer contained in the polymer solution 92 is 6 MPa in absolute value. 0.5 Above 20 MPa 0.5 We have found that by including specific components within the following range, it is possible to manufacture a hollow fiber-like porous body 10 with an porosity ratio R2 / R1 greater than 200. This is because the phase separation process between the inside and outside of the polymer solution 92 changes when the specific components are included only in the core solution 93 of the poor solvent. According to this manufacturing method, it is possible to manufacture a porous body 10 that is suitable for achieving both strength and permeation rate of the permeating fluid.

[0071] In this specification, "HSP value" refers to the Hansen solubility parameter (δ). The Hansen solubility parameter (δ) is defined by a three-dimensional parameter (δD, δP, δH) and is expressed by the following equation (1). δ 2 = (δD) 2 + (δP) 2 + (δH) 2 ... (1) In equation (1), δD represents the London dispersion term, δP represents the polarity term, and δH represents the hydrogen bonding term. The HSP values ​​of the base polymer and specific components can be determined, for example, by the Hansen solubility sphere method or the molecular group contribution method. In the Hansen solubility sphere method, affinity evaluation is performed between the target substance and several solvents with known HSP values, and the solvents are divided into good solvents and poor solvents. Next, the HSP values ​​of these solvents are plotted on a three-dimensional graph with δD, δP, and δH as axes. A sphere with the smallest radius (Hansen sphere) is created where the HSP values ​​of the good solvents are inside the sphere and the HSP values ​​of the poor solvents are outside the sphere, and the center of this sphere is calculated as the HSP value of the target substance. In the molecular group contribution method, the structure of each constituent unit in the target substance is input using smiles (simplified molecular input line entry system) notation, and the HSP value for each unit is calculated. In either method, the Hansen Solubility Parameter in Practice (HSPiP) software can be used to calculate the HSP value.

[0072] The lower limit of the difference between the HSP value of the base polymer and the HSP value of the specific component contained in polymer solution 92 is 6.5 MPa in absolute value. 0.5 7 MPa 0.5 7.5 MPa 0.5 , 8 MPa 0.5 8.5 MPa 0.5 Furthermore, 9 MPa 0.5 This may also be the case. The upper limit of the difference between the HSP value of the base polymer and the HSP value of the specific component is 19 MPa in absolute value. 0.5 , 18 MPa 0.5 , 17 MPa 0.5 , 16 MPa 0.5 , 15 MPa 0.5 , 14 MPa 0.5 , 13 MPa 0.5 , 12 MPa 0.5 , 11 MPa 0.5 Furthermore, 10 MPa 0.5 That is also acceptable.

[0073] The difference between the HSP value of the base polymer and the HSP value of the specific component is 7 MPa in absolute value. 0.5 Above 12 MPa 0.5 The following range may also apply: 8 MPa 0.5 Above 11 MPa 0.5 It may also be within the following range.

[0074] The core liquid 93 may contain components other than the specified component. The other component is typically water. The content of the specified component in the core liquid 93 is, for example, 50 wt% or more. When the content of the specified component in the core liquid 93 is 50 wt% or more, it is easy to change the structure of the inner surface 10b of the hollow fiber-like porous body 10.

[0075] The content of the specific component in the core liquid 93 may be 60 wt% or more, 70 wt% or more, or even 80 wt% or more. When the content of the specific component in the core liquid 93 is 80 wt% or more, phase separation is more likely to proceed inside the nozzle 91 during the subsequent immersion process.

[0076] The upper limit of the percentage of a specific component in the lead liquid 93 is, for example, 100%. In other words, the lead liquid 93 may consist only of the specific component.

[0077] The specific component has an absolute difference of 6 MPa from the HSP value of the base polymer contained in polymer solution 92. 0.5 Above 20 MPa 0.5 The following are examples of specific components, but they are not particularly limited. Specific components include diacetone alcohol, diethylene glycol, and diethylene glycol monobutyl ether. Specific components may contain diacetone alcohol as the main component, or they may consist substantially of diacetone alcohol alone.

[0078] The polymer solution 92 may contain a base polymer as its main component, or it may be composed substantially of only a base polymer.

[0079] From the viewpoint of heat resistance, acid resistance, and alkali resistance, the base polymer preferably contains polysulfone.

[0080] As described above, the coagulation solution 94 does not contain any specific components. The coagulation solution 94 may consist only of components other than the specific components. The coagulation solution 94 is typically water.

[0081] In the discharge process, a polymer solution 92 is discharged from the outside of a double-tube nozzle 91, and a core liquid 93 containing a specific component is discharged from the inside of the nozzle 91. In the immersion process, the film-forming solution 95 containing the discharged polymer solution 92 and core liquid 93 is immersed in a solidification liquid 94. As shown in Figure 2, the film-forming solution 95 may be immersed in the solidification liquid 94 while being transported by a roll. The film-forming solution 95 solidifies upon immersion in the solidification liquid 94. Phase separation occurs during the solidification process of the film-forming solution 95. At this time, the phase separation process changes between the inside and outside of the polymer solution 92. This results in a hollow fiber-like porous body 10. The obtained porous body 10 may be wound up using a winding machine 96.

[0082] The manufacturing method may further include a step (drying step) in which the solvent, such as the solidification liquid 94, is dried from the porous body 10 after the immersion step. Known methods such as natural drying, hot air drying, reduced pressure drying, and vacuum drying can be used for the drying step.

[0083] <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-shaped porous body 10 described above.

[0084] 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.

[0085] (Separation Functional Layer) The separation functional layer 20 is preferably a layer that preferentially allows acidic gases contained in the gas mixture to permeate. Typically, the separation functional layer 20 is a dense layer (non-porous layer) in which no pores can be observed when viewed with a SEM at a magnification of 5000x.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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).

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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%.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] <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 method described above. Next, a coating solution containing the material of 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. Generally, in the coating step, the porous body 10 is immersed in the coating solution while being transported by a roll. Therefore, the porous body 10 is subjected to stress as it is transported by the roll. As described above, the porous body 10 achieves a balance between strength and the permeation rate of the permeating fluid, so that cracks, fractures, etc., do not occur due to transport by the roll.

[0105] Next, the separation functional layer 20 is formed by drying the coated film (drying step). In this way, the hollow fiber film 30 is obtained. As described above, in the porous body 10, when forming the coated film of the separation functional layer 20 on the outer surface 10a, the coating liquid containing the material of the separation functional layer 20 does not easily penetrate the outer surface 10a. Therefore, the occurrence of defects in the separation functional layer 20 due to excessive penetration of the coating liquid into the outer surface 10a is suppressed.

[0106] 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 heating time of the coating film may be 5 seconds or more, 10 seconds or more, 30 seconds or more, 1 minute or more, or even 5 minutes or more.

[0107] <Embodiment of Hollow Fiber Membrane Module> Figure 4 is a schematic cross-sectional perspective view showing 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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, but is, for example, 0.01 vol% (100 ppm) or more under standard conditions, 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, but is, for example, 90 vol% under standard conditions. 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] The above-described embodiments are mutually applicable, insofar as they do not conflict with technical standards. The above embodiments and their variations may be combined with each other, insofar as they do not conflict with technical standards.

[0125] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0126] [Preparation of Hollow Fiber Porous Material] (Example 1) A hollow fiber porous material of Example 1 was prepared using the manufacturing method using the NIPS method described above. Polysulfone (PSF) (SOLVAY, UDEL® P-3500) was used as the base polymer. A mixture of 1800 g of PSF and 8200 g of N-methyl-2-pyrrolidone was mixed under a nitrogen atmosphere and then stirred and dissolved at 100°C for 5 hours. In this way, the polymer solution of Example 1 (PSF concentration: 18 wt%) was prepared. Diacetone alcohol was used as a specific component (difference from the HSP value of the base polymer: 9.22 MPa). 0.5 ) was used. Water and diacetone alcohol were mixed so that the concentration of diacetone alcohol was 80 wt%. In this way, the core solution of Example 1 was prepared. Water was used as the coagulation solution of Example 1. Using a metering pump, the polymer solution was discharged from the outside of a double-tube nozzle maintained at 35°C, and the core solution was discharged from the inside of the nozzle. The film-forming solution containing the discharged polymer solution and core solution was immersed in 10 L of coagulation solution for about 3 seconds. This obtained a hollow fiber-like porous body. The obtained porous body was washed by immersing it in water for 24 hours or more, followed by immersion in ethanol for 30 minutes. After that, it was dried at 120°C for 1 hour. The hollow fiber-like porous body thus produced was the porous body of Example 1. The porous body of Example 1 had an outer diameter of 0.85 mm and an inner diameter of 0.55 mm.

[0127] Figure 5A is an image (100,000x magnification) showing the result of SEM observation of the outer surface of the hollow fiber-like porous material of Example 1. Figure 5B is an image (100,000x magnification) showing the result of SEM observation of the inner surface of the hollow fiber-like porous material of Example 1.

[0128] (Example 2) Diethylene glycol as a specific component (difference from the HSP value of the base polymer: 17.25 MPa) 0.5 In Example 2, the film-forming solution containing the discharged polymer solution and core solution was immersed in 120 L of solidification solution for approximately 30 seconds. Except for this, the hollow fiber-like porous body of Example 2 was prepared by the same method as in Example 1. The porous body of Example 2 had an outer diameter of 0.85 mm and an inner diameter of 0.55 mm.

[0129] Figure 6A is an image (100,000x magnification) showing the result of SEM observation of the outer surface of the hollow fiber porous material of Example 2. Figure 6B is an image (100,000x magnification) showing the result of SEM observation of the inner surface of the hollow fiber porous material of Example 2.

[0130] (Comparative Example 1) N-methyl-2-pyrrolidone (NMP) as a specific component (difference from the HSP value of the base polymer: 5.58 MPa) 0.5 ) was used. Except for this, the hollow fiber porous body of Comparative Example 1 was prepared by the same method as in Example 1. The porous body of Comparative Example 1 had an outer diameter of 0.85 mm and an inner diameter of 0.55 mm.

[0131] Figure 7A is an image (100,000x magnification) showing the result of SEM observation of the outer surface of the hollow fiber-like porous material of Comparative Example 1. Figure 7B is an image (100,000x magnification) showing the result of SEM observation of the inner surface of the hollow fiber-like porous material of Comparative Example 1.

[0132] (Comparative Example 2) Ethylene glycol as a specific component (Difference from the HSP value of the base polymer: 23.87 MPa) 0.5 ) was used. Except for this, the hollow fiber porous body of Comparative Example 2 was prepared by the same method as in Example 1. The porous body of Comparative Example 2 had an outer diameter of 0.85 mm and an inner diameter of 0.55 mm.

[0133] Figure 8A is an image (100,000x magnification) showing the result of SEM observation of the outer surface of the hollow fiber-like porous material of Comparative Example 2. Figure 8B is an image (100,000x magnification) showing the result of SEM observation of the inner surface of the hollow fiber-like porous material of Comparative Example 2.

[0134] <Measurement of Open-Ratio and Average Pore Diameter> For the porous bodies of the Examples and Comparative Examples, the open-ratio R1 (%) on the outer surface, the open-ratio R2 (%) on the inner surface, the average pore diameter D1 (nm) on the outer surface, and the average pore diameter D2 (nm) on the inner surface were determined using the method described above. Based on the determined values, the ratios R2 / R1 and D2 / D1 were calculated. The results are shown in Table 1.

[0135] <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 Table 1.

[0136] <Measurement of Fracture Stress> For the porous materials of the examples and comparative examples, the fracture stress (MPa) in a tensile test at a temperature of 25°C was determined using the method described above. A Shimadzu Autograph AGX-V benchtop precision universal testing machine was used as the tensile testing machine. The results are shown in Table 1.

[0137]

[0138] As shown in Table 1, the porous materials of Examples 1 and 2, which had an open-ratio R2 / R1 of 200 or more, showed a balanced relationship between nitrogen gas permeation rate and fracture stress in tensile tests compared to the porous materials of Comparative Examples 1 and 2, which had an open-ratio R2 / R1 of less than 200. This is thought to be because, in the porous materials of Examples 1 and 2, the open-ratio R2 / R1 of 200 or more ensured the nitrogen gas permeation rate by the porous material on the inner surface, while the strength was ensured by the porous material on the outer surface, where the open-ratio R1 was kept low. From these results, it was found that hollow fiber porous materials with an open-ratio R2 / R1 of 200 or more are suitable for achieving both strength and permeation rate of the permeating fluid. In the discharge process of the porous materials of Examples 1 and 2 using the NIPS method, the difference between the core liquid and the HSP value of the base polymer contained in the polymer solution was 6 MPa in absolute value. 0.5 Above 20 MPa 0.5 The following specific components were included in the manufacturing process. From these results, it was found that in the NIPS method, during the dispensing process, the core liquid contained an HSP value of 6 MPa in absolute terms from the HSP value of the base polymer contained in the polymer solution. 0.5 Above 20 MPa 0.5 It is believed that this can be manufactured by including specific components within the following range.

[0139] In the porous bodies of Examples 1 and 2, where the porosity ratio R2 / R1 is 200 or more, the porosity ratio R1 on the outer surface is kept low. For example, when forming a coating film of the separation functional layer on the outer surface, it is thought that the coating liquid containing the material for the separation functional layer does not easily penetrate to the outer surface. In other words, it is thought that using hollow fiber porous bodies with an porosity ratio R2 / R1 of 200 or more suppresses the occurrence of defects in the separation functional layer caused by excessive penetration of the coating liquid to the outer surface.

[0140] In Example 1, polysulfone was used as the base polymer of the polymer solution, and diacetone alcohol was used as the specific component of the core liquid. In Example 2, polysulfone was used as the base polymer of the polymer solution, and diethylene glycol was used as the specific component of the core liquid. However, the difference between the HSP value of the base polymer contained in the polymer solution and the HSP value of the specific component was 6 MPa in absolute value. 0.5 Above 20 MPa 0.5 As long as the following conditions are met, it is presumed that the same effects as in Examples 1 and 2 can be expected even when using base polymers other than polysulfone, diacetone alcohol, and specific components other than diethylene glycol.

[0141] 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 porous body in the form of a hollow fiber having an outer surface and an inner surface, wherein each of the outer surface and the inner surface has a plurality of pores, and the ratio R2 / R1 of the porosity ratio R2 (%) of the inner surface to the porosity ratio R1 (%) of the outer surface is 200 or more.

2. The porous body according to claim 1, wherein the porosity R1 on the outer surface is less than 0.5%.

3. The porous body according to claim 1, wherein the porosity R2 on the inner surface is 20% or more.

4. The porous body according to claim 1, wherein the average pore diameter D1 on the outer surface is smaller than the average pore diameter D2 on the inner surface.

5. The porous body according to claim 4, wherein the ratio D2 / D1 of the average pore diameter D2 on the inner surface to the average pore diameter D1 on the outer surface is 10 or more.

6. The porous body according to claim 1, wherein 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 5000 GPU or more.

7. The porous body according to claim 1, wherein the breaking stress in a tensile test conducted at a temperature of 25°C is 10 MPa or more.

8. The porous body according to claim 1, comprising a polysulfone.

9. A hollow fiber membrane comprising a porous body according to any one of claims 1 to 8.

10. The hollow fiber membrane according to claim 9, further comprising a separation functional layer supported by the porous body.

11. The hollow fiber membrane according to claim 9, used for separating an acidic gas from a gas mixture containing an acidic gas.

12. A method for manufacturing a hollow fiber-like porous body, comprising the steps of: discharging a polymer solution containing a base polymer from the outside of a double-tube nozzle and discharging a core liquid containing a specific component from the inside of the nozzle; and immersing the discharged polymer solution and the core liquid in a coagulation solution, wherein the difference between the HSP value of the base polymer and the HSP value of the specific component is 6 MPa in absolute value. 0.5 Above 20 MPa 0.5 Manufacturing methods within the following range.

13. The manufacturing method according to claim 12, wherein the specified component includes diacetone alcohol.

14. The manufacturing method according to claim 12, wherein the base polymer comprises a polysulfone.

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