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

Abstract

The present invention provides a porous body having an improved permeation rate of a permeating fluid. A porous body 1 according to the present invention is a hollow fiber-like porous body having an outer surface 1a and an inner surface 1b. Openings are formed in each of the outer surface 1a and the inner surface 1b. An opening ratio R1 of the outer surface 1a is 10% or more. A ratio R1 / R2 of the opening ratio R1 (%) to an opening ratio R2 (%) of the inner surface 1b is 0.60 or more. A hollow fiber membrane 10 according to the present invention includes the porous body 1.

Description

Hollow fiber porous body, hollow fiber membrane, and method for manufacturing 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 has been developed as a method for separating acidic gases such as carbon dioxide from mixed gases. Compared to absorption methods, which separate acidic gases contained in mixed gases by absorbing them into an absorbent, membrane separation methods can efficiently separate acidic gases while reducing operating costs.

[0003] Examples of separation membranes used in membrane separation methods include straw-shaped hollow fiber membranes (see, for example, Patent Document 1). Hollow fiber membranes have the advantage of having a larger membrane area per volume than flat membranes. Hollow fiber membranes include a hollow fiber-shaped porous body and, if necessary, further include a separation function layer supported by the porous body.

[0004] JP 2014-184424 A

[0005] Hollow fiber-shaped porous bodies can be produced, for example, by forming a hollow fiber by melt spinning or the like and then stretching the hollow fiber. In this method, for example, openings are formed on the surface of the hollow fiber by stretching the hollow fiber. Conventionally, linear bodies such as hollow fibers have been stretched by a roll stretching method that utilizes the difference in rotation speed between multiple rolls, from the standpoint of productivity, etc. For example, Figure 2 on page 115 and Figure 14 on page 126 of "Mechanism and Evaluation Method of Molecular Orientation and Crystallization by Stretching of Polymers" (Masayoshi Ito et al., R&D Support Center, 2020) describe stretching a linear body by a roll stretching method.

[0006] However, according to the investigations of the present inventors, there is room for improvement in the permeation rate of a permeating fluid that passes through a porous body produced by stretching a hollow fiber by a roll stretching method. Therefore, the present invention provides a porous body with an improved permeation rate of a permeating fluid.

[0007] As a result of extensive investigations, the present inventors have newly discovered that in hollow fiber porous bodies produced by roll stretching, the open area ratio of the outer surface is excessively low compared to the open area ratio of the inner surface, and that this causes a decrease in the permeation rate of the permeating fluid. Based on this finding, the present inventors have furthered their investigations and found that the open area ratio of the outer surface can be increased by performing tenter stretching using a tenter instead of roll stretching, thereby completing the present invention.

[0008] The present invention provides a hollow fiber-shaped porous body having an outer surface and an inner surface, wherein openings are formed in each of the outer surface and the inner surface, the opening ratio R1 of the outer surface is 10% or more, and the ratio R1 / R2 of the opening ratio R1 (%) to the opening ratio R2 (%) of the inner surface is 0.60 or more.

[0009] The present invention further provides a hollow fiber membrane comprising the above porous body.

[0010] The present invention further provides a method for producing a hollow fiber-shaped porous body, the method comprising stretching the hollow fiber-shaped body with a tenter.

[0011] According to the present invention, a porous body having an improved permeation rate of a permeating fluid can be provided.

[0012] Fig. 1 is a cross-sectional perspective view schematically showing a part of a porous body according to one embodiment of the present invention. Fig. 2 is a view for explaining a method for specifying the aperture ratio of the outer surface of a porous body. Fig. 3 is a view for explaining a method for specifying the aperture ratio of the outer surface of a porous body. Fig. 4 is a view for explaining a method for manufacturing a porous body. Fig. 5 is a cross-sectional perspective view schematically showing a part of a hollow fiber membrane according to one embodiment of the present invention. Fig. 6 is a cross-sectional perspective view schematically showing a hollow fiber membrane module provided with the hollow fiber membrane of the present invention.

[0013] A porous body according to a first aspect of the present invention is a hollow fiber-shaped porous body having an outer surface and an inner surface, wherein openings are formed on each of the outer surface and the inner surface, the opening ratio R1 of the outer surface is 10% or more, and the ratio R1 / R2 of the opening ratio R1 (%) to the opening ratio R2 (%) of the inner surface is 0.60 or more.

[0014] In a second aspect of the present invention, for example, in the porous body according to the first aspect, the opening ratio R2 is 20% or more.

[0015] In a third aspect of the present invention, for example, in the porous body according to the first or second aspect, the ratio R1 / R2 is 2.00 or less.

[0016] In a fourth aspect of the present invention, for example, the porous body according to any one of the first to third aspects contains polyolefin.

[0017] In a fifth aspect of the present invention, for example, in a porous body according to any one of the first to fourth aspects, when air 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 80 kPa higher than the pressure in the space adjacent to the inner surface, the permeation rate of air passing through the porous body is 10,000 GPU or more.

[0018] In a sixth aspect of the present invention, for example, the porous body according to any one of the first to fifth aspects has a tensile breaking strength of 4.5 N or more.

[0019] A hollow fiber membrane according to a seventh aspect of the present invention comprises a porous body according to any one of the first to sixth aspects.

[0020] In an eighth aspect of the present invention, for example, the hollow fiber membrane according to the seventh aspect further comprises a separation function layer supported by the porous body.

[0021] In a ninth aspect of the present invention, for example, the hollow fiber membrane according to the seventh or eighth aspect is used to separate an acidic gas from a mixed gas containing the acidic gas.

[0022] A method for producing a porous body according to a tenth aspect of the present invention is a method for producing a hollow fiber-shaped porous body, the method including stretching a hollow fiber-shaped body with a tenter.

[0023] In an eleventh aspect of the present invention, for example, in the manufacturing method according to the tenth aspect, the hollow fiber bodies are stretched so that openings are formed on both the outer surface and the inner surface of the hollow fiber bodies.

[0024] In a twelfth aspect of the present invention, for example, the production method according to the tenth or eleventh aspect further comprises melt-spinning a resin composition containing a polymer to obtain the hollow fiber-shaped body.

[0025] In a thirteenth aspect of the present invention, for example, in the production method according to any one of the tenth to twelfth aspects, the stretching in the tenter includes cold stretching performed at a temperature of 80°C or less and hot stretching performed at a temperature higher than 80°C after the cold stretching.

[0026] In a fourteenth aspect of the present invention, for example, in the manufacturing method according to the thirteenth aspect, the cold drawing is carried out at a strain rate of 50.0% / sec or less.

[0027] In a fifteenth aspect of the present invention, for example, in the manufacturing method according to the thirteenth or fourteenth aspect, the hot drawing is carried out at a strain rate of 20.0% / sec or less.

[0028] In a sixteenth aspect of the present invention, for example, in the manufacturing method according to any one of the thirteenth to fifteenth aspects, the hot drawing is carried out two or more times.

[0029] In a seventeenth aspect of the present invention, for example, in the production method according to the sixteenth aspect, the hollow fiber body that has been subjected to the first thermal stretching is placed in an atmosphere of 80°C or less to cool, and then the hollow fiber body is subjected to the second thermal stretching.

[0030] The present invention will be described in detail below, but the following description is not intended to limit the present invention to a specific embodiment.

[0031] <Embodiment of Porous Body> As shown in Fig. 1, the porous body 1 of this embodiment is a hollow fiber-shaped porous body having an outer surface 1a and an inner surface 1b. Specifically, the hollow fiber-shaped porous body 1 has a shape such as a cylindrical, elliptical cylindrical, or rectangular cylindrical shape, and is preferably a cylindrical shape. The porous body 1 can be used as a porous support for a hollow fiber membrane, which will be described later.

[0032] In the porous body 1, openings (more specifically, a plurality of openings) are formed in each of the outer surface 1a and the inner surface 1b. In this embodiment, the opening rate R1 of the outer surface 1a is 10% or more, and the ratio R1 / R2 of the opening rate R1 (%) to the opening rate R2 (%) of the inner surface 1b is 0.60 or more. When the opening rate R1 and the ratio R1 / R2 satisfy the above ranges, the permeation rate of the permeating fluid passing through the porous body 1 tends to be improved.

[0033] The aperture ratio R1 of the outer surface 1a can be determined by the following method. First, the porous body 1 is cut along the central axis of the porous body 1 to prepare a test piece. The test piece is typically semi-cylindrical in shape. Next, the surface of the test piece corresponding to the outer surface 1a is observed with a scanning electron microscope (SEM). The magnification at this time is, for example, 50,000 times. This results in an electron microscope image (e.g., Figure 2A) displaying an area of ​​1.8 μm vertical x 2.5 μm horizontal. Next, the obtained electron microscope image is binarized to create a binarized image (e.g., Figure 2B). The apertures present in the binarized image are identified, and their total area is calculated by image processing. The area (μm) of the surface of the test piece in the binarized image is calculated. 2 ) to the total area of ​​the openings (μm 2 ) can be regarded as the aperture ratio R1.

[0034] The opening ratio R1 of the outer surface 1a of the porous body 1 is 10% or more as described above, and may be 11% or more, 12% or more, 13% or more, 14% or more, 15% or more, 16% or more, 17% or more, or even 18% or more. From the viewpoint of the strength of the porous body 1, the upper limit of the opening ratio R1 is, for example, 40% or less, 30% or less, or even 25% or less.

[0035] The aperture ratio R2 of the inner surface 1b of the porous body 1 is not particularly limited as long as the ratio R1 / R2 is 0.60 or greater, and may be, for example, 10% or greater, 15% or greater, 18% or greater, 20% or greater, 22% or greater, 23% or greater, 24% or greater, 25% or greater, or even 26% or greater. From the viewpoint of the strength of the porous body 1, the upper limit of the aperture ratio R2 may be, for example, 40% or less, or even 30% or less. The aperture ratio R2 of the inner surface 1b can be determined by the method described above for the aperture ratio R1, except that the surface of the test piece corresponding to the inner surface 1b is observed by SEM.

[0036] As described above, the ratio R1 / R2 of the opening ratio R1 (%) to the opening ratio R2 (%) is 0.60 or more, and may be 0.63 or more, 0.65 or more, 0.68 or more, 0.70 or more, 0.73 or more, 0.75 or more, 0.78 or more, or even 0.80 or more. The upper limit of the ratio R1 / R2 is, for example, 2.00 or less, 1.50 or less, 1.30 or less, 1.00 or less, or even 0.90 or less. According to the inventor's studies, in conventional porous bodies having the ratio R1 / R2 lower than 0.60, when stress (e.g., tensile stress) is applied to the porous body, the stress tends to concentrate near the openings on the outer surface of the porous body, making the porous body more susceptible to fracture. In contrast, in the porous body 1 of this embodiment, the ratio R1 / R2 is 0.60 or more, which makes it easier to distribute stress throughout the porous body 1, and makes the porous body 1 less susceptible to fracture. In particular, when the ratio R1 / R2 is close to 1.00, the porous body 1 tends to have good mechanical strength such as tensile strength at break and tensile elasticity. A porous body 1 having good mechanical strength tends to be less prone to defects during assembly of a hollow fiber membrane module (described later) or during operation of the module.

[0037] The average diameter D1 of the openings present on the outer surface 1a of the porous body 1 is not particularly limited and may be, for example, 10 nm or more, 20 nm or more, 30 nm or more, or even 40 nm or more. The upper limit of the average diameter D1 is, for example, 1 μm or less, and may be 500 nm or less, 300 nm or less, 100 nm or less, or even 50 nm or less.

[0038] The average diameter D1 of the openings present in the outer surface 1a can be determined by the following method. First, a test piece is prepared using the method described above for the opening ratio R1. Next, the surface of the test piece corresponding to the outer surface 1a is observed using an SEM. The magnification at this time is, for example, 50,000 times. This results in an electron microscope image displaying an area of ​​1.8 μm vertically and 2.5 μm horizontally. Next, the obtained electron microscope image is binarized to create a binarized image. The area of ​​a specific opening present in the binarized image is calculated by image processing. The radius of a circle having the same area as the calculated area is regarded as the radius of that specific opening. The radii of an arbitrary number of openings (at least 20) are calculated, and the average of the calculated values ​​is regarded as the average diameter D1 of the openings.

[0039] The average diameter D2 of the openings present on the inner surface 1b of the porous body 1 is not particularly limited and may be, for example, 10 nm or more, 20 nm or more, 30 nm or more, 40 nm or more, or even 50 nm or more. The upper limit of the average diameter D2 may be, for example, 1 μm or less, 500 nm or less, 300 nm or less, 100 nm or less, or even 80 nm or less. The average diameter D2 can be determined by the method described above for the average diameter D1, except that the surface of the test piece corresponding to the inner surface 1b is observed by SEM.

[0040] The ratio D1 / D2 of the average diameter D1 (nm) of the openings present on the outer surface 1a to the average diameter D2 (nm) of the openings present on the inner surface 1b is, for example, 0.60 or more, and may be 0.63 or more, 0.65 or more, 0.68 or more, 0.70 or more, 0.73 or more, 0.75 or more, 0.78 or more, or even 0.80 or more. The upper limit of the ratio D1 / D2 is, for example, 2.00 or less, and may be 1.50 or less, 1.30 or less, 1.00 or less, or even 0.90 or less.

[0041] The outer diameter of the porous body 1 is not particularly limited and may be, for example, 1.0 mm or less, 0.8 mm or less, 0.5 mm or less, or even 0.4 mm or less. The lower limit of the outer diameter of the porous body 1 is, for example, 0.1 mm or more, and may be 0.3 mm or more.

[0042] The outer diameter of the porous body 1 can be determined by the following method. First, the porous body 1 is cut in a direction perpendicular to the longitudinal direction of the porous body 1, and the cross section is observed under a microscope. In the obtained image, the diameter of the smallest circle that can enclose the outer surface 1a of the porous body 1 is determined. The above procedure is repeated any number of times (at least five times), and the average of the obtained diameters is regarded as the outer diameter of the porous body 1.

[0043] The inner diameter of the porous body 1 is not particularly limited and may be, for example, 1.0 mm or less, 0.8 mm or less, 0.5 mm or less, 0.4 mm or less, or even 0.3 mm or less. The lower limit of the inner diameter of the porous body 1 is, for example, 0.1 mm or more, and may be 0.2 mm or more. The inner diameter of the porous body 1 can be determined by the method described above for the outer diameter of the porous body 1, except that the diameter of the smallest circle that can surround the inner surface 1b of the porous body 1 in the image is determined.

[0044] The thickness of the porous body 1 is not particularly limited, and may be, for example, 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 or more.

[0045] The thickness of the porous body 1 can be determined by the following method. First, the porous body 1 is cut in a direction perpendicular to the longitudinal direction of the porous body 1, and the cross section is observed under a microscope. In the obtained image, the distance between the outer surface 1a and the inner surface 1b of the porous body 1 is determined at any points (at least five points). The average value of the obtained distances is regarded as the thickness of the porous body 1.

[0046] The length of the porous body 1 in the longitudinal direction is not particularly limited, and is, for example, 0.1 m to 10 m.

[0047] The porous body 1 has a porous structure. The pores contained in this porous structure may be continuous pores formed in a three-dimensional manner. The porous body 1 preferably includes pores (through pores) that are connected to both the openings formed on the outer surface 1 a and the openings formed on the inner surface 1 b. However, the porous body 1 may also have independent pores.

[0048] The porous body 1 preferably contains a polymer P. As an example, the porous body 1 may have a three-dimensional network skeleton containing the polymer P. From the viewpoint of solvent resistance, the porous body 1 preferably contains a polyolefin as the polymer P. Specific examples of polyolefins include polyethylene (PE), polypropylene (PP), polybutylene (PB), and poly-4-methylpentene-1 (PMP), with PP being preferred. The polymer P may also be a polyolefin other than PE.

[0049] The porous body 1 may contain the polymer P as a main component, or may be composed essentially of only the polymer P. In this specification, the term "main component" refers to the component that is contained in the porous body 1 in the largest amount by weight. The porous body 1 may further contain components other than the polymer P.

[0050] (Method for manufacturing porous body) Next, a method for manufacturing the porous body 1 of this embodiment will be described with reference to Figures 3A and 3B. As shown in Figure 3B, the manufacturing method of this embodiment includes stretching the hollow fiber body 6 with a tenter 30 (stretching step).

[0051] The hollow fiber body 6 preferably has no openings on either its outer or inner surface, and preferably has substantially no pores between its outer and inner surfaces (i.e., has no porous structure). Specifically, it is preferable that no openings are visible on the outer or inner surfaces of the hollow fiber body 6 when observed at a magnification of 5000 times using an SEM. The hollow fiber body 6 preferably has the same configuration as the porous body 1, except for the dimensions, the presence or absence of openings, and the presence or absence of holes. In particular, the shape and material of the hollow fiber body 6 are preferably the same as those of the porous body 1. Note that the hollow fiber body 6 may have openings on its outer or inner surface, or may have a porous structure, depending on the circumstances.

[0052] The hollow fiber body 6 can be produced, for example, by a melt spinning method ( FIG. 3A ). That is, the production method of this embodiment may further include melt spinning a resin composition 5 containing the above-mentioned polymer P to obtain the hollow fiber body 6 (melt spinning step). In the melt spinning step, the resin composition 5 may contain the polymer P as a main component, or may be composed essentially of the polymer P alone. It is preferable that the resin composition 5 does not contain a solvent or the like. The composition of the resin composition 5 is typically the same as that of the porous body 1.

[0053] The melt spinning of the resin composition 5 can be carried out using, for example, a spinning apparatus 20 shown in Fig. 3A. The spinning apparatus 20 preferably includes a hopper 21, an extrusion section 22, and a nozzle 23. The hopper 21 is connected to the inlet of the extrusion section 22 and can supply the resin composition 5 to the extrusion section 22. The resin composition 5 charged into the hopper 21 is typically in the form of pellets.

[0054] The extrusion section 22 may have, for example, a screw disposed therein, and may extrude the resin composition 5 to the nozzle 23. The extrusion section 22 may have a heater disposed therein for heating the resin composition 5. For example, the pellet-shaped resin composition 5 supplied to the extrusion section 22 is softened by being heated by the heater and kneaded by the screw. The softened resin composition 5 is extruded from the extrusion section 22 and supplied to the nozzle 23. The heating temperature of the resin composition 5 can be adjusted appropriately depending on the melting point of the polymer P. For example, the heating temperature of the resin composition 5 is a temperature that is 10°C or more higher than the melting point of the polymer P, for example, 100°C to 300°C. The melt flow rate (MFR) of the resin composition 5 is not particularly limited and is, for example, 1.0 to 5.0 g / 10 min. In this specification, MFR is a value measured at a temperature of 230°C and a load of 2.16 kgf in accordance with Method A of Japanese Industrial Standards (formerly Japanese Industrial Standards; JIS) K7210-1:2014.

[0055] The nozzle 23 has a discharge port for discharging the softened resin composition 5. The nozzle 23 is preferably configured to discharge the resin composition 5 vertically downward from the discharge port. The shape and dimensions of the discharge port can be adjusted appropriately depending on the shape and dimensions of the desired hollow fiber body 6. The discharge port is typically double-annular. The hollow fiber body 6 can be formed by discharging the softened resin composition 5 from the double-annular discharge port and solidifying the resin composition 5. As an example, the solidification of the resin composition 5 progresses as the high-temperature resin composition 5 discharged from the nozzle 23 is cooled in the air.

[0056] 3A, the spinning apparatus 20 may further include a guide roll 25 and a take-up roll 26 for transporting and winding the hollow fiber 6. The hollow fiber 6 passes through the guide roll 25 and is then taken up by the take-up roll 26. The spinning apparatus 20 may include two or more guide rolls 25. The speed at which the hollow fiber 6 is taken up by the take-up roll 26 is not particularly limited and is, for example, 1 m / min to 100 m / min.

[0057] The dimensions (outer diameter, inner diameter, thickness, etc.) of the hollow fiber 6 can be adjusted appropriately by adjusting the discharge speed of the resin composition 5 from the nozzle 23 and the winding speed of the hollow fiber 6 around the winding roll 26. The outer diameter of the hollow fiber 6 wound around the winding roll 26 is not particularly limited and is, for example, 0.1 mm to 1.0 mm. The inner diameter of the hollow fiber 6 is not particularly limited and is, for example, 0.1 mm to 1.0 mm. The thickness of the hollow fiber 6 is not particularly limited and is, for example, 0.01 mm to 0.5 mm. The outer diameter, inner diameter, and thickness of the hollow fiber 6 can be determined by the method described above for the porous body 1.

[0058] The method for producing the hollow fiber 6 is not limited to the melt spinning method described above. The hollow fiber 6 can also be produced by a non-solvent induced phase separation (NIPS) method or the like. In the NIPS method, for example, a solution containing a polymer P is discharged from the nozzle 23 and brought into contact with a coagulation liquid to produce the hollow fiber 6. However, in the NIPS method, it is necessary to select a polymer P that is soluble in a solvent, and it is difficult to use a polyolefin with excellent solvent resistance as the polymer P. On the other hand, the melt spinning method tends to make it easier to produce the hollow fiber 6 even when a polyolefin is used as the polymer P.

[0059] The manufacturing method of this embodiment may further include a heating step in which the hollow fiber 6 is subjected to a heat treatment (annealing treatment). The heat treatment tends to grow lamellar crystals of the polymer P present in the hollow fiber 6, improving the orientation order of the crystals. The heat treatment may be performed on the hollow fiber 6 in a state in which it is wound around the winding roll 26, or on the hollow fiber 6 removed from the winding roll 26.

[0060] The temperature for the heat treatment is preferably a temperature equal to or lower than the melting point of the polymer P, for example, 100° C. to 150° C. The time for the heat treatment is not particularly limited, and is, for example, 10 minutes to 10 hours.

[0061] The manufacturing method of this embodiment may further include cutting the hollow fiber bodies 6 (cutting step). In the cutting step, for example, the hollow fiber bodies 6 are cut in a direction perpendicular to the longitudinal direction of the hollow fiber bodies 6. The cutting step allows the hollow fiber bodies 6 to be adjusted to a length suitable for setting in the tenter 30. The cutting step may be performed before or after the heating step.

[0062] As described above, in the manufacturing method of this embodiment, the hollow fiber 6 is stretched in the tenter 30 ( FIG. 3B ). Specifically, the hollow fiber 6 is stretched in the longitudinal direction of the hollow fiber 6 while both ends of the hollow fiber 6 are held by clips provided on the tenter 30. In the stretching step, the hollow fiber 6 is preferably stretched so that openings are formed on both the outer and inner surfaces of the hollow fiber 6. A hollow fiber-shaped porous body 1 is obtained by the stretching step. Note that in FIG. 3B , multiple hollow fiber 6 are set in the tenter 30. However, in the manufacturing method of this embodiment, only one hollow fiber 6 may be stretched in the tenter 30.

[0063] According to the inventors' investigations, when a hollow fiber is stretched by a roll stretching method that utilizes differences in the rotation speeds of multiple rolls, stress resulting from the rotation of the subsequent rolls is applied to the hollow fiber the moment the hollow fiber passes through the previous roll. As a result, the hollow fiber is stretched to the set stretch ratio immediately upon passing through the previous roll. Therefore, in the roll stretching method, the hollow fiber tends to be stretched near the previous roll at a strain rate that is excessively higher than the set strain rate. An excessively high strain rate easily causes stress to concentrate locally in the hollow fiber. Due to the localized stress concentration, the resulting hollow fiber porous body tends to have an excessively low open area ratio on the outer surface compared to the open area ratio on the inner surface.

[0064] In contrast, in the manufacturing method of the present embodiment, the hollow fiber bodies 6 are stretched using a tenter 30. When the tenter 30 is used, the hollow fiber bodies 6 are stretched at a set strain rate, so that a relatively uniform stress is applied to the hollow fiber bodies 6. According to the inventors' investigations, the relatively uniform application of stress to the hollow fiber bodies 6 tends to prevent the opening ratio R1 of the outer surface 1a of the porous body 1 from decreasing excessively.

[0065] The stretching in the tenter 30 preferably includes cold stretching performed at a temperature of 80°C or less and hot stretching performed at a temperature higher than 80°C after the cold stretching. Cold stretching, for example, can cleave multiple lamellar crystals of the polymer P present in the hollow fiber 6, thereby forming minute voids. Hot stretching, for example, can enlarge the voids formed by cold stretching and form thin fibrous fibrils between the multiple lamellar crystals. Cold stretching and hot stretching make it easy to adjust the size of the openings formed in the outer and inner surfaces of the hollow fiber 6 to appropriate values.

[0066] The number of cold stretchings is typically one. The cold stretching temperature is 80°C or lower, as described above, and may be 50°C or lower. The cold stretching temperature is preferably 50°C or lower than the melting point of polymer P. The lower limit of the cold stretching temperature is not particularly limited, and may be, for example, 0°C or higher, or 10°C or higher. Cold stretching may be performed at a temperature around room temperature (25°C).

[0067] The draw ratio of the hollow fiber 6 by cold drawing is, for example, 1.1 times or more, and may be 1.2 times or more. The upper limit of the draw ratio of the hollow fiber 6 by cold drawing is not particularly limited, and is, for example, 2.0 times or less.

[0068] In the manufacturing method of this embodiment, cold stretching is preferably performed at a strain rate of 50.0% / sec or less. The strain rate in cold stretching may be 45.0% / sec or less, or may be 40.0% / sec or less. The lower the strain rate in cold stretching, the easier it is to adjust the ratio R1 / R2 of the open area ratio R1 (%) of the outer surface 1a to the open area ratio R2 (%) of the inner surface 1b of the porous body 1 to a value closer to 1.00. From the viewpoint of productivity, the lower limit of the strain rate in cold stretching is, for example, 10.0% / sec or more, 20.0% / sec or more, or even 30.0% / sec or more. In this specification, the strain rate refers to the ratio of the deformation amount (m) of the hollow fiber body 6 per second to the length (m) of the hollow fiber body 6 before stretching.

[0069] The number of times of hot stretching is not particularly limited and may be, for example, one or more times, two or more times, three or more times, four or more times, five or more times, or even six or more times. In the production method of this embodiment, it is preferable to perform hot stretching two or more times. The upper limit of the number of times of hot stretching is not particularly limited and may be, for example, 20 times or less, or 10 times or less.

[0070] As described above, the hot stretching temperature is higher than 80°C, and may be 90°C or higher, 100°C or higher, 110°C or higher, or even 120°C or higher. The hot stretching temperature is preferably lower than the melting point of the polymer P, and may be, for example, 150°C or lower, or 125°C or lower. When hot stretching is performed two or more times, the hot stretching temperatures may be the same or different for each time.

[0071] When hot stretching is performed two or more times, the hollow fiber 6 may be cooled between the hot stretches. As an example, the hollow fiber 6 that has been subjected to the first hot stretch may be placed in an atmosphere of 80°C or less to cool, and then the hollow fiber 6 may be hot stretched a second time. The temperature of the atmosphere may be 50°C or less, or may be 30°C or less. The lower limit of the temperature of the atmosphere may be, for example, 0°C or more, or may be 10°C or more. The atmosphere may have a temperature near room temperature (25°C). The cooling time of the hollow fiber 6 is not particularly limited and is, for example, 10 seconds to 1 hour. The hollow fiber 6 does not need to be cooled between the hot stretches.

[0072] The draw ratio of the hollow fiber 6 by hot drawing (the total draw ratio when hot drawing is performed two or more times) is, for example, 1.5 times or more, 2.0 times or more, or even 2.5 times or more. The upper limit of the draw ratio of the hollow fiber 6 by hot drawing is not particularly limited, and may be, for example, 10 times or less, 5.0 times or less, or even 3.0 times or less.

[0073] In the manufacturing method of this embodiment, it is preferable to perform hot stretching at a strain rate of 20.0% / sec or less. The strain rate in hot stretching may be 15.0% / sec or less, 10.0% / sec or less, or even 8.0% / sec or less. The lower the strain rate in hot stretching, the easier it is to adjust the ratio R1 / R2 of the open area ratio R1 (%) of the outer surface 1a to the open area ratio R2 (%) of the inner surface 1b of the porous body 1 to a value closer to 1.00. Furthermore, in the manufacturing method of this embodiment, it is preferable to set the strain rate in hot stretching to a value lower than the strain rate in cold stretching. From the viewpoint of productivity, the lower limit of the strain rate in hot stretching is, for example, 1.0% / sec or more, 3.0% / sec or more, or even 5.0% / sec or more. Note that when hot stretching is performed two or more times, the strain rates in hot stretching may be the same or different for each time.

[0074] The manufacturing method of this embodiment may further include heat-setting the porous body 1 obtained by the stretching step (heat-setting step). The heat-setting may be performed, for example, with the porous body 1 set in the tenter 30. The heat-setting temperature is preferably lower than the melting point of the polymer P, for example, 90°C to 160°C. The heat-setting time is not particularly limited, for example, 10 seconds to 1 hour. The heat-setting may be performed while shrinking the porous body 1. The heat-setting ratio at this time is, for example, 0.6 to 0.9. The heat-setting ratio refers to the ratio of the length (m) of the porous body 1 after the heat-setting treatment to the length (m) of the porous body 1 before the heat-setting treatment.

[0075] (Characteristics of the porous body) In the porous body 1 of this embodiment, the aperture ratio R1 of the outer surface 1a and the ratio R1 / R2 satisfy the above ranges, which tends to improve the permeation rate of the permeating fluid. As an example, the permeation rate of air passing through the porous body 1 may be, for example, 8000 GPU or more, 10000 GPU or more, 15000 GPU or more, 20000 GPU or more, 25000 GPU or more, or even 30000 GPU or more. The upper limit of the permeation rate is not particularly limited, and may be, for example, 100000 GPU or less, 50000 GPU or less, or even 35000 GPU or less. Note that the GPU is 10 -6 ·cm3 (STP) / (sec cm 2 cm 3 (STP) means the volume of air at 1 atmosphere and 0°C.

[0076] The permeation rate can be determined by the following method. First, air at 25°C is supplied to a space adjacent to the outer surface 1a of the porous body 1, and the pressure in this space is adjusted to a value 80 kPa higher than the pressure in the space adjacent to the inner surface 1b. This causes the air to permeate through the porous body 1 in the direction from the outer surface 1a to the inner surface 1b. The permeation rate can be calculated based on the flow rate of the air permeating the porous body 1, etc.

[0077] Furthermore, the porous body 1 of this embodiment tends to have good mechanical strength, such as tensile strength at break and tensile elasticity. For example, the tensile strength of the porous body 1 may be, for example, 4.0 N or more, and may be 4.4 N or more, 4.5 N or more, 4.6 N or more, 4.7 N or more, 4.8 N or more, or even 4.9 N or more. The upper limit of the tensile strength of the porous body 1 is not particularly limited, and may be, for example, 10 N or less. It should be noted that the porous body 1 of this embodiment tends to easily adjust the tensile strength to 4.0 N or more (particularly 4.5 N or more) even when the outer diameter is 1.0 mm or less. Such a porous body 1 makes it easy to mount a practically sufficient number of hollow fiber membranes in a hollow fiber membrane module, and to easily adjust the membrane area of ​​the hollow fiber membranes per volume to a practically sufficient value.

[0078] The tensile breaking strength of the porous body 1 can be measured by the following method. First, the porous body 1 is cut in a direction perpendicular to the longitudinal direction of the porous body 1 to prepare a test piece having a length of 40 mm. Next, the test piece is set in a commercially available tensile testing machine so that both ends of the test piece are held by chucks. A tensile test is performed on the test piece under conditions of an initial chuck distance of 20 mm and a tensile speed of 1000 mm / min. The strength (tensile breaking strength) at which the test piece breaks is measured.

[0079] The tensile elasticity of the porous body 1 is, for example, 0.08 N or more, and may be 0.10 N or more, 0.13 N or more, 0.15 N or more, 0.18 N or more, or even 0.20 N or more. There is no particular limitation on the upper limit of the tensile elasticity of the porous body 1, and it is, for example, 1.00 N or less. The tensile elasticity of the porous body 1 means the slope of the linear region that appears in the initial strain when the vertical axis is the test force (N) and the horizontal axis is the strain (-) based on the results of the tensile test.

[0080] <Embodiment of Hollow Fiber Membrane> As shown in Figure 4, the hollow fiber membrane 10 of this embodiment includes the porous body 1 described above. The hollow fiber membrane 10 may further include a separation function layer 2 supported by the porous body 1. In this case, the porous body 1 functions as a porous support that supports the separation function layer 2. In the hollow fiber membrane 10, the separation function layer 2 is preferably in contact with the outer surface 1a of the porous body 1 and covers the outer surface 1a. However, the separation function layer 2 may also be in contact with the inner surface 1b of the porous body 1 and cover the inner surface 1b.

[0081] (Separation functional layer) The separation functional layer 2 is preferably a layer that preferentially allows the acidic gas contained in the mixed gas to pass through, and is typically a dense layer (non-porous layer) in which no pores can be observed when observed at a magnification of 5000 times using a scanning electron microscope (SEM).

[0082] In a preferred embodiment, the separation functional layer 2 contains a resin. Examples of the resin contained in the separation functional layer 2 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 2 preferably consists essentially of resin.

[0083] In another preferred embodiment, the separation functional layer 2 contains an ionic liquid. Ionic liquids are salts (ionic compounds) that are liquid at 25°C. The separation functional layer 2 may have a double-network gel containing an 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 mainly composed of an organic material, a second network structure mainly composed of an inorganic material, and an ionic liquid. The second network structure may be mainly composed of an organic material different from the first network structure. In this specification, "mainly composed" means that 50 wt% or more, or even 70 wt% or more, of the material in question is composed.

[0084] The organic material for forming the first network structure includes a polymer such as polyacrylamide (particularly, polydialkylacrylamide such as polydimethylacrylamide). The polymer contained in the organic material has structural units derived from an acrylamide derivative and may further include a crosslinked structure. A polymer including a crosslinked structure can be produced by a known method. For example, first, a prepolymer having a structural unit with an N-hydroxysuccinimide ester group is prepared. The structural unit with an N-hydroxysuccinimide ester group is derived from, for example, N-acryloxysuccinimide. Next, a polymer including a crosslinked structure 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, such as ethylene glycol bis(3-aminopropyl) ether.

[0085] The second network structure may include a network of particles, for example, formed by particles bonded to each other by hydrogen bonds. For example, the particles included in the second network structure are silica particles.

[0086] In this embodiment, specific examples of the ionic liquid include an ionic liquid having imidazolium, pyridinium, ammonium, or phosphonium and a substituent having one or more carbon atoms.

[0087] In the ionic liquid having an imidazolium and a substituent having one or more carbon atoms, examples of the substituent having one or more carbon atoms include an alkyl group having from 1 to 20 carbon atoms, a cycloalkyl group having from 3 to 14 carbon atoms, and an aryl group having from 6 to 20 carbon atoms, which may be further substituted with a hydroxy group, a cyano group, an amino group, a monovalent ether group, or the like (for example, a hydroxyalkyl group having from 1 to 20 carbon atoms).

[0088] Examples of the alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-nonadecyl group, an n-eicosadecyl group, an Examples of the alkyl group include an alkyl group, an i-propyl group, a sec-butyl group, an i-butyl group, a 1-methylbutyl group, a 1-ethylpropyl group, a 2-methylbutyl group, an i-pentyl group, a neopentyl group, a 1,2-dimethylpropyl group, a 1,1-dimethylpropyl group, a t-pentyl group, a 2-ethylhexyl group, and a 1,5-dimethylhexyl group, which may be further substituted with a hydroxy group, a cyano group, an amino group, a monovalent ether group, or the like.

[0089] The alkyl group may be substituted with a cycloalkyl group. The number of carbon atoms in the alkyl group substituted with a cycloalkyl group is, for example, 1 or more and 20 or less. Examples of the alkyl group substituted with a cycloalkyl group include a cyclopropylmethyl group, a cyclobutylmethyl group, a cyclohexylmethyl group, and a cyclohexylpropyl group, which may be further substituted with a hydroxy group, a cyano group, an amino group, a monovalent ether group, or the like.

[0090] Examples of the cycloalkyl group having from 3 to 14 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclododecyl group, a norbornyl group, a bornyl group, and an adamantyl group, which may be further substituted with a hydroxy group, a cyano group, an amino group, a monovalent ether group, or the like.

[0091] Examples of the aryl group having 6 to 20 carbon atoms include a phenyl group, a toluyl group, a xylyl group, a mesityl group, an anisyl group, a naphthyl group, and a benzyl group, which may be further substituted with a hydroxy group, a cyano group, an amino group, a monovalent ether group, or the like.

[0092] The imidazolium and the compound having a substituent having one or more carbon atoms may further have a substituent such as an alkyl group, and may form a salt with a counter anion. Examples of the counter anion include alkyl sulfate, tosylate, methanesulfonate, acetate, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, thiocyanate, dicyanamide, tricyanomethanide, tetracyanoborate, hexafluorophosphate, tetrafluoroborate, and halide. From the viewpoint of gas separation performance, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, dicyanamide, tricyanomethanide, and tetracyanoborate are preferred.

[0093] Specific examples of the ionic liquid having an imidazolium and a substituent having one or more carbon atoms include 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 tetrachloroferrate, 1-butyl-3-methylimidazolium iodide, 1-butyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate ...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 tetrachloroferrate, 1-butyl-3-methylimidazolium iodide, 1-butyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium 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-dimesitylimidazolium 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 of suitable imidazolium compounds include 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.

[0094] Among these, 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 ([C4mim][TF2N]), and 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2OHim][TF2N]) are particularly preferred.

[0095] The method for producing 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.

[0096] 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 carbon dioxide contained in the mixed gas can pass through the separation functional layer 2. The upper limit of the ionic liquid content is not particularly limited and is, for example, 95 wt%.

[0097] The content of the first network structure in the double-network gel, which is primarily made of organic material, 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 %. From the viewpoint of improving the strength of the double-network gel, the content of the second network structure in the double-network gel, which is primarily made of inorganic material, is, for example, 1 wt % or more. 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 2 preferably consists essentially of the double-network gel.

[0098] The thickness of the separation functional layer 2 is, for example, 50 μm or less, preferably 25 μm or less, and more preferably 15 μm or less. In some cases, the thickness of the separation functional layer 2 may be 10 μm or less, 5.0 μm or less, or 2.0 μm or less. The thickness of the separation functional layer 2 may be 0.05 μm or more, or 0.1 μm or more.

[0099] (Method for manufacturing hollow fiber membrane) The hollow fiber membrane 10 can be produced, for example, by the following method. First, a porous body 1 is produced by the method described above. Next, a coating liquid containing the material of the separation function layer 2 is applied to the outer surface 1a of the porous body 1 to form a coating film. As an example, the coating film can be formed by immersing the porous body 1 in the coating liquid. Next, the coating film is dried to form the separation function layer 2, and the hollow fiber membrane 10 is obtained. The coating film can be dried, 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, 1 minute or more, and may be 5 minutes or more.

[0100] (Uses of Hollow Fiber Membrane) Uses of the hollow fiber membrane 10 of this embodiment include separating 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 in addition to the acidic gas. Examples of other gases include non-polar gases such as hydrogen and nitrogen, and inert gases such as helium, with nitrogen being preferred. In particular, the hollow fiber membrane 10 of this embodiment is suitable for separating carbon dioxide from a gas mixture containing carbon dioxide and nitrogen. However, the use of the hollow fiber membrane 10 is not limited to separating acidic gases from the above-mentioned gas mixture.

[0101] <Embodiment of Hollow Fiber Membrane Module> As shown in Figure 5, the hollow fiber membrane module 100 of this embodiment includes a plurality of hollow fiber membranes 10. The hollow fiber membrane module 100 may further include a binding section 40, a sealing section 42, a cap 50, and a housing 60. In the hollow fiber membrane module 100, one ends of the plurality of hollow fiber membranes 10 are bundled by the binding section 40. The other ends of the plurality of hollow fiber membranes 10 are sealed by the sealing section 42. The hollow fiber membranes 10 are housed in the housing 60. The cap 50 is integrated with the binding section 40 and is placed on one end of the housing 60.

[0102] The hollow fiber membrane module 100 is preferably an external pressure type hollow fiber membrane module. In the external pressure type hollow fiber membrane module 100, for example, a mixed gas containing an acidic gas passes through the outside of the hollow fiber membrane 10, and a permeated fluid having a higher acidic gas content than the mixed gas passes through the inside of the hollow fiber membrane 10. However, the hollow fiber membrane module 100 may also be an internal pressure type hollow fiber membrane module.

[0103] The hollow fiber membranes 10 are arranged in parallel to one another and bundled together by the bundling portion 40. The number of hollow fiber membranes 10 is not particularly limited and is, for example, 1,000 to 20,000. The hollow fiber membranes 10 may be bundled together by a net.

[0104] The binding portion 40 is a portion that bundles one end of a plurality of hollow fiber membranes 10. The binding portion 40 has, for example, a cylindrical or truncated conical shape. The binding portion 40 is formed, for example, by potting. In this case, the binding portion 40 is also called a potting portion. The binding portion 40 can be formed by a resin filled between the hollow fiber membranes 10. Examples of resins that form the binding portion 40 include epoxy and urethane.

[0105] The constraining portion 40 separates the flow path of the mixed gas (the internal space of the housing 60) from the flow path of the permeating 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 constraining portion 40.

[0106] The sealing part 42 is made of, for example, the same resin as the binding part 40. Instead of the sealing part 42, a binding part 40 may be provided at the other end of the hollow fiber membrane 10. That is, both ends of the hollow fiber membrane 10 may be open.

[0107] The cap 50 is a funnel-shaped part integrated with the binding section 40. The cap 50 has an internal space communicating with each of the hollow fiber membranes 10. Each of the hollow fiber membranes 10 extends to the end face of the binding section 40 and opens at the end face of the binding section 40 toward the internal space of the cap 50. The permeate fluid passes through the internal space of the cap 50 from the hollow fiber membranes 10 to the outside of the hollow fiber membrane module 100. Components such as piping and connectors can be connected to the tip of the cap 50. This tip has, for example, a tubular shape. The material of the cap 50 is not particularly limited. The cap 50 may be made of a metal such as stainless steel (SUS); a resin such as polyvinyl chloride, polycarbonate, or polysulfone; or the like.

[0108] The housing 60 is a cylindrical component that houses a plurality of hollow fiber membranes 10 and the binding portion 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 treated mixed gas (non-permeated fluid) from its internal space. The outlet 60a protrudes in a direction perpendicular to the longitudinal direction of the housing 60 and communicates with the internal space of the housing 60.

[0109] The longitudinal direction of the housing 60 is parallel to the longitudinal direction of the hollow fiber membranes 10. 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.

[0110] The material of the housing 60 is not particularly limited. The housing 60 may be made of a metal such as stainless steel (SUS), or a 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.

[0111] 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 peripheral surface of one end of the housing 60, and the nut 80 is screwed onto the threaded portion when the cap 50 is placed on the housing 60. The material of the nut 80 is not particularly limited. The nut 80 may be made of resin or metal.

[0112] The hollow fiber membrane module 100 may further include a cap 70 and a nut 82. The cap 70 is a funnel-shaped part attached to the other end of the housing 60. The nut 82 is an example of a fastening member that fastens the cap 70 and the housing 60 to each other. The nut 82 is threadedly engaged with a threaded portion provided on the outer peripheral surface of the other end of the housing 60. This fastens the cap 70 to the housing 60. A mixed gas is introduced from the outside of the hollow fiber membrane module 100 to the internal space of the housing 60 through the cap 70.

[0113] 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 the shape of a nozzle.

[0114] 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 the acidic gas in the mixed gas is not particularly limited, and 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 the acidic gas in the mixed gas is not particularly limited, and 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.

[0115] The mixed gas comes into contact with the outer surface of the hollow fiber membrane 10 in the internal space of the housing 60. This allows a permeated fluid having a higher acid gas content than the mixed gas to be obtained on the inner surface side of the hollow fiber membrane 10. In other words, the permeated fluid is supplied to the inside of the hollow fiber membrane 10. The permeated fluid preferably contains acid gas as a main component. However, the permeated fluid may also contain small amounts of gases other than acid gas. The permeated fluid passes through the internal space of the cap 50 and is sent from the hollow fiber membrane 10 to the outside of the hollow fiber membrane module 100.

[0116] The concentration of the acid gas in the mixed gas gradually decreases from the sealing portion 42 toward the confinement portion 40. The mixed gas (non-permeated fluid) treated in the internal space of the housing 60 is discharged to the outside of the housing 60 through the discharge port 60a.

[0117] The hollow fiber membrane module 100 of this embodiment is suitable for a continuous membrane separation method, but may also be used for a batchwise membrane separation method.

[0118] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0119] Example 1 [Preparation of hollow fiber body] First, a resin composition made of polypropylene was melt-spun to prepare a hollow fiber body. Specifically, the melt-spinning of the resin composition was carried out using a spinning apparatus 20 shown in FIG. 3A. In the extrusion section 22 of the spinning apparatus 20, pelletized resin composition was kneaded with a screw while being heated at 180°C, thereby softening the resin composition. The melt flow rate of the resin composition measured at a temperature of 230°C and a load of 2.16 kgf in accordance with Method A of JIS K7210-1:2014 was 1.9 g / 10 min.

[0120] The softened resin composition was discharged vertically downward from the double annular discharge port of the nozzle 23 and solidified to form a hollow fiber-shaped body. The hollow fiber-shaped body was taken up by the take-up roll 26 at a take-up speed of 40 m / min. The hollow fiber-shaped body taken up by the take-up roll 26 had an outer diameter of 0.38 mm and an inner diameter of 0.29 mm.

[0121] Next, the hollow fiber body was subjected to a heat treatment while wound on the winding roll 26. The heat treatment was carried out at 140° C. for 4 hours. Next, the hollow fiber body was cut into pieces having a length of 100 mm.

[0122] [Preparation of Porous Body] Next, the hollow fiber-shaped body was stretched using a tenter. Specifically, the hollow fiber-shaped body was first cold-stretched once at room temperature (25°C). In the cold stretching, the stretching ratio was set to 1.2 times and the strain rate was set to 36% / sec. Next, the hollow fiber-shaped body was hot-stretched once at 100°C. In the hot stretching, the stretching ratio was set to 2.56 times and the strain rate was set to 5.4% / sec. By stretching using the tenter, openings were formed on both the outer and inner surfaces of the hollow fiber-shaped body, and the porous body (hollow fiber-shaped porous body) of Example 1 was obtained. In Example 1, the obtained porous body was further subjected to heat setting treatment at 100°C for 1 minute. In the heat setting treatment, the heat setting ratio of the porous body was set to 0.8 times.

[0123] (Examples 2 to 5) Porous bodies of Examples 2 to 5 were obtained by the same method as Example 1, except that the stretching conditions of the hollow fiber body and the heat setting conditions were changed as shown in Table 1. In Example 2, the hollow fiber body was hot-stretched six times with a one-minute interval between each stretch. In Examples 3 to 5, the hollow fiber body was placed in a room temperature (25°C) atmosphere for one minute to cool between stretches. In Examples 2 to 5, the total stretch ratio of the hollow fiber body 6 by hot-stretching was set to 2.56 times.

[0124] Comparative Example 1 First, a hollow fiber was produced by the same method as in Example 1, except that the hollow fiber was not cut. Next, the hollow fiber was stretched by roll stretching. Specifically, the hollow fiber was first cold-stretched at room temperature (25°C) while being conveyed by rolls. In the cold stretching, the stretch ratio was set to 1.2 times and the strain rate was set to 36% / sec. Next, the hollow fiber was hot-stretched at 150°C while being conveyed by rolls. At this time, multiple rolls were arranged so that the number of hot stretches was 6. Furthermore, the hollow fiber was conveyed by rolls so that the hollow fiber was cooled in a room temperature (25°C) atmosphere for 1 minute between hot stretches. In the hot stretching, the total stretch ratio was set to 2.56 times and the strain rate was set to 5.4% / sec. By the roll stretching method, openings were formed on both the outer and inner surfaces of the hollow fiber-shaped body, thereby obtaining a porous body (hollow fiber-shaped porous body) of Comparative Example 1. In Comparative Example 1, the obtained porous body was further subjected to a heat setting treatment at 160°C for 0.1 minutes. In the heat setting treatment, the heat setting ratio of the porous body was set to 0.8 times.

[0125]

[0126] [Physical Properties of Porous Body] For the porous bodies of the Examples and Comparative Examples, the outer diameter, inner diameter, thickness, opening rate R1 of the outer surface, opening rate R2 of the inner surface, and the ratio R1 / R2 of the opening rate R1 (%) to the opening rate R2 (%) were determined by the method described above.

[0127] [Permeation Rate] The air permeation rate of the porous bodies of the Examples and Comparative Examples was measured using the following method. First, five porous bodies were placed inside a commercially available nylon tube, and both ends of the porous bodies were fixed with urethane resin. At this time, one end of the porous body was opened to the external space, and the other end was sealed with urethane resin. This resulted in an evaluation module. Next, air at 25°C was supplied to the space adjacent to the outer surface of the porous body inside the nylon tube, and the pressure in this space was adjusted to a value 80 kPa higher than the pressure in the space adjacent to the inner surface of the porous body. This caused the air to permeate the porous body in a direction from the outer surface to the inner surface. The air that permeated the porous body was discharged into the external space of the evaluation module through the open end of the porous body. The air permeation rate was calculated based on the flow rate of the air that permeated the porous body.

[0128] [Tensile Break Strength and Tensile Elasticity] The porous bodies of the Examples and Comparative Examples were subjected to tensile tests by the above-described method to determine the tensile break strength and tensile elasticity.

[0129]

[0130] As can be seen from Table 2, the porous bodies of the examples in which the opening rate R1 of the outer surface was 10% or more and the ratio R1 / R2 of the opening rate R1 (%) to the opening rate R2 (%) was 0.60 or more had improved permeation rates of air (permeating fluid) compared to the comparative examples.

[0131] As can be seen from Table 2, the porous body of Comparative Example 1 had an excessively low open area ratio R1 of the outer surface compared to the open area ratio R2 of the inner surface. This result is presumably due to the fact that the hollow fiber was stretched by roll stretching. Specifically, in Comparative Example 1, the moment the hollow fiber passed through the upstream roll, stress caused by the rotation of the downstream roll was applied to the hollow fiber, causing it to be immediately stretched to the set draw ratio. Therefore, in both cold stretching and hot stretching, it is thought that the hollow fiber was stretched near the upstream roll at a strain rate that was excessively higher than the set strain rate. It is presumed that the excessively high strain rate caused stress to be concentrated locally in the hollow fiber, resulting in an excessive decrease in the open area ratio R1 of the outer surface.

[0132] The porous bodies of the Examples had at least higher tensile strength at break than the Comparative Examples, and were excellent in mechanical strength.

[0133] The porous body of this embodiment is suitable as a porous support for a hollow fiber membrane. The hollow fiber membrane of this embodiment is suitable for separating an acidic gas from a gas mixture containing the acidic gas. In particular, the hollow fiber membrane of this embodiment is suitable for separating carbon dioxide from off-gas from a chemical plant or thermal power plant.

Claims

1. A hollow fiber-shaped porous body having an outer surface and an inner surface, wherein openings are formed on each of the outer surface and the inner surface, the opening rate R1 of the outer surface is 10% or more, and the ratio R1 / R2 of the opening rate R1 (%) to the opening rate R2 (%) of the inner surface is 0.60 or more.

2. The porous body according to claim 1, wherein the opening ratio R2 is 20% or more.

3. The porous body according to claim 1, wherein the ratio R1 / R2 is 2.00 or less.

4. The porous body according to claim 1, comprising a polyolefin.

5. The porous body according to claim 1, wherein when air 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 80 kPa higher than the pressure in the space adjacent to the inner surface, the permeation rate of air passing through the porous body is 10,000 GPU or more.

6. The porous body according to claim 1, having a tensile breaking strength of 4.5 N or more.

7. A hollow fiber membrane comprising the porous body according to any one of claims 1 to 6.

8. The hollow fiber membrane according to claim 7, further comprising a separation functional layer supported by the porous body.

9. The hollow fiber membrane according to claim 7, which is used to separate an acid gas from a gas mixture containing the acid gas.

10. A method for producing a hollow fiber-shaped porous body, the method comprising stretching a hollow fiber-shaped body with a tenter.

11. The method according to claim 10, wherein the hollow fiber is stretched so that openings are formed on both the outer and inner surfaces of the hollow fiber.

12. The method according to claim 10, further comprising melt-spinning a resin composition containing a polymer to obtain the hollow fiber.

13. The method of claim 10, wherein the stretching in the tenter includes cold stretching at a temperature of 80°C or less and hot stretching at a temperature higher than 80°C after the cold stretching.

14. The method according to claim 13, wherein the cold stretching is carried out at a strain rate of 50.0% / sec or less.

15. The method according to claim 13, wherein the hot stretching is carried out at a strain rate of 20.0% / sec or less.

16. The method of claim 13, wherein the hot stretching is carried out two or more times.

17. The method of claim 16, wherein the hollow fiber body that has been subjected to the first heat stretching is placed in an atmosphere of 80°C or less to cool, and then the hollow fiber body is subjected to the second heat stretching.

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