Gas separation method, hollow-fiber membrane module, and gas separation device

Abstract

This gas separation method comprises the following steps. A gas absorption liquid is caused to absorb a to-be-separated gas by bringing a mixed gas, which contains to-be-separated gas, into gas-liquid contact with the gas absorption liquid. The gas absorption liquid in which the to-be-separated gas has been absorbed is caused to flow to the outside of a plurality of first hollow-fiber membranes formed using a porous body, and the partial pressure of the to-be separated gas inside each of the plurality of first hollow-fiber membranes is made lower than the partial pressure of the to-be-separated gas on the outside of the plurality of first hollow-fiber membranes, whereby the to-be-separated gas is desorbed from the gas absorption liquid in which the to-be-absorbed gas has been absorbed. The minimum intrusion pressure of the gas absorption liquid, which has absorbed the to-be-separated gas, into the plurality of first hollow-fiber membranes is 100 kPa or higher.

Description

Gas separation method, hollow fiber membrane module, and gas separation apparatus

[0001] This disclosure relates to a gas separation method, a hollow fiber membrane module, and a gas separation apparatus. This application claims priority under Japanese application No. 2024-192817, filed on November 1, 2024, and incorporates all the provisions of the said Japanese application.

[0002] Japanese Patent Publication No. 2007-297605 (Patent Document 1) describes a methane separation method for separating methane from biogas containing methane and carbon dioxide. This method involves separating methane from biogas containing methane and carbon dioxide and CO2 ２ The absorbent liquid is mixed in a mixer. Next, the mixture is introduced into a gas-liquid separator to separate the methane and the CO2 that has absorbed carbon dioxide. ２ The absorbent liquid is separated. Then, CO2 is released into the inside of the hollow fiber permeable membrane. ２ The absorbent solution is supplied, and CO2 enters the permeable membrane. ２ By allowing the absorbent liquid to permeate, CO ２ The carbon dioxide absorbed by the absorbent solution is released to the outside of the permeable membrane, thus separating the carbon dioxide.

[0003] Japanese Patent Publication No. 2007-297605

[0004] The gas separation method according to this disclosure comprises the following steps: The gas to be separated is absorbed into the gas absorbent by bringing a mixed gas containing the gas to be separated into gas-liquid contact with the gas absorbent. The gas absorbent containing the absorbed gas to be separated is flowed outside a plurality of first hollow fiber membranes formed of a porous body, and the partial pressure of the gas to be separated inside each of the plurality of first hollow fiber membranes is made lower than the partial pressure of the gas to be separated outside the plurality of first hollow fiber membranes, thereby desorbing the gas to be separated from the gas absorbent containing the absorbed gas to be separated. The minimum intrusion pressure of the gas absorbent containing the absorbed gas to be separated into the plurality of first hollow fiber membranes is 100 kPa or more.

[0005] Figure 1 is a schematic cross-sectional view showing the configuration of a hollow fiber membrane module according to the first embodiment. Figure 2 is a schematic plan view showing the configuration of a hollow fiber membrane. Figure 3 is a schematic diagram showing the configuration of a gas separation device according to the first embodiment. Figure 4 is a schematic cross-sectional view showing the configuration of a first hollow fiber membrane module. Figure 5 is a schematic cross-sectional view showing the configuration of a second hollow fiber membrane module. Figure 6 is a flowchart schematically showing the gas separation method according to the first embodiment. Figure 7 is a schematic diagram illustrating the gas separation method according to the first embodiment. Figure 8 is a schematic cross-sectional view illustrating the step of absorbing the gas to be separated into a gas absorption liquid. Figure 9 is a schematic cross-sectional view illustrating the step of desorbing the gas to be separated from the gas absorption liquid. Figure 10 is a schematic diagram showing the configuration of a gas separation device according to the second embodiment. Figure 11 is a schematic diagram showing the configuration of a gas separation device according to the third embodiment. Figure 12 is a schematic plan view showing the configuration of a hollow fiber membrane according to the fourth embodiment. Figure 13 is a diagram showing the evaluation results using the gas separation device according to the example.

[0006] According to the methane separation method of Patent Document 1, CO supplied to the inside of a hollow fiber permeable membrane ２ The absorbent liquid and the CO that permeated to the outside of the hollow fiber-like permeable membrane. ２ The absorbent liquid needs to be recovered. Therefore, CO ２ The equipment for recovering the absorbent solution has become more complex, and the methane separation equipment has become larger.

[0007] The purpose of this disclosure is to provide a gas separation method and a hollow fiber membrane module that enable miniaturization of gas separation equipment. Furthermore, it is also to provide a miniaturized gas separation equipment.

[0008] According to this disclosure, a gas separation method, a hollow fiber membrane module, and a gas separation apparatus that can be miniaturized can be provided.

[0009] The embodiments of this disclosure will now be listed and described.

[0010] (1) The gas separation method according to the present disclosure comprises the following steps: The gas to be separated is absorbed into the gas absorbent by bringing a mixed gas containing the gas to be separated into gas-liquid contact with the gas absorbent. The gas absorbent containing the absorbed gas to be separated is flowed outside a plurality of first hollow fiber membranes formed of a porous body, and the partial pressure of the gas to be separated inside each of the plurality of first hollow fiber membranes is made lower than the partial pressure of the gas to be separated outside the plurality of first hollow fiber membranes, thereby desorbing the gas to be separated from the gas absorbent containing the absorbed gas to be separated. The minimum intrusion pressure of the gas absorbent containing the absorbed gas to be separated into the plurality of first hollow fiber membranes is 100 kPa or more. This makes it possible to miniaturize the gas separation apparatus.

[0011] (2) The gas separation method according to (1) above may further include the following steps: The gas absorbent liquid from which the gas to be separated has been removed may be recovered. The gas to be separated may be absorbed into the recovered gas absorbent liquid. This reduces the amount of gas absorbent liquid consumed.

[0012] (3) In the gas separation method according to (1) or (2) above, in the step of absorbing the gas to be separated into the gas absorption liquid, the gas to be separated may be absorbed into the gas absorption liquid by bringing the mixed gas and the gas absorption liquid into gas-liquid contact using a plurality of second hollow fiber membranes formed of porous material. This makes it possible to effectively miniaturize the gas separation device.

[0013] (4) In the gas separation method according to any of (1) to (3) above, the gas absorbent liquid may be heated in the step of desorbing the gas to be separated from the gas absorbent liquid in which the gas to be separated has been absorbed. This makes it possible to effectively desorb the gas to be separated from the gas absorbent liquid in which the gas to be separated has been absorbed.

[0014] (5) According to the gas separation method described in any of (1) to (4) above, in the step of desorbing the gas to be separated from the gas absorption liquid in which the gas to be separated has been absorbed, the pressure inside each of the plurality of hollow fiber membranes may be made lower than atmospheric pressure so that the partial pressure of the gas to be separated inside each of the plurality of first hollow fiber membranes is lower than the partial pressure of the gas to be separated outside the plurality of first hollow fiber membranes.

[0015] (6) According to the gas separation method described in any of (1) to (4) above, in the step of desorbing the gas to be separated from the gas absorption liquid in which the gas to be separated has been absorbed, sweep gas may be passed inside each of the plurality of first hollow fiber membranes to make the partial pressure of the gas to be separated inside each of the plurality of first hollow fiber membranes lower than the partial pressure of the gas to be separated outside the plurality of first hollow fiber membranes.

[0016] (7) In the gas separation method according to any of (1) to (6) above, the gas absorbent liquid may be cooled in the step of absorbing the gas to be separated into the gas absorbent liquid. This makes it possible to effectively absorb the gas to be separated into the gas absorbent liquid.

[0017] (8) According to the gas separation method according to any of (1) to (7) above, the average pore size of the porous body forming the plurality of first hollow fiber membranes may be 0.3 nm or more and 50 nm or less. The porous body forming the plurality of first hollow fiber membranes may be made of fluororesin. This makes it possible to more reliably prevent the gas absorbent liquid from permeating through the plurality of first hollow fiber membranes.

[0018] (9) According to the gas separation method according to any of (1) to (8) above, the average outer diameter of each of the multiple first hollow fiber membranes may be 0.6 mm or less. The average inner diameter of each of the multiple first hollow fiber membranes may be 0.36 mm or less. This prevents deformation or buckling of each of the multiple first hollow fiber membranes 1a.

[0019] (10) The hollow fiber membrane module according to the present disclosure comprises a plurality of hollow fiber membranes and a housing. The plurality of hollow fiber membranes are formed of a porous material. The plurality of hollow fiber membranes are bundled together. The housing houses the plurality of hollow fiber membranes. The plurality of hollow fiber membranes partition the inside of the housing into a gas flow path and a liquid flow path. The gas flow path includes the space surrounded by each of the plurality of hollow fiber membranes. The average pore size of the porous material forming the plurality of hollow fiber membranes is 0.3 nm or more and 50 nm or less. The porous material forming the plurality of hollow fiber membranes is made of fluororesin. This makes it possible to miniaturize a gas separation device using the hollow fiber membrane module.

[0020] (11) The gas separation apparatus according to the present disclosure comprises the hollow fiber membrane module according to (10) above, a liquid transfer pump, and a gas recovery unit. The liquid transfer pump is connected to the liquid flow path. The gas recovery unit is connected to the gas flow path. This makes it possible to miniaturize the gas separation apparatus.

[0021] [Details of Embodiments of the Disclosure] Embodiments of the Disclosure will be described below with reference to the drawings. In the following drawings, the same or corresponding parts will be given the same reference numerals, and their descriptions will not be repeated.

[0022] (First Embodiment) <Hollow Fiber Membrane Module> First, the configuration of the hollow fiber membrane module 10 according to the first embodiment will be described.

[0023] As shown in Figure 1, the hollow fiber membrane module 10 according to the first embodiment has a plurality of hollow fiber membranes 1 and a housing 2. The hollow fiber membrane module 10 is used for the separation and recovery of gas using a liquid and the desorption of gas from a liquid.

[0024] Multiple hollow fiber membranes 1 are bundled together. The outer shape of each of the multiple hollow fiber membranes 1 is tubular. Each of the multiple hollow fiber membranes 1 is formed of a porous material. In other words, each of the multiple hollow fiber membranes 1 is provided with multiple pores (not shown). Each of the multiple hollow fiber membranes 1 has a first end 31 and a second end 32.

[0025] Each of the multiple hollow fiber membranes 1 has an opening at a first end 31. In each of the multiple hollow fiber membranes 1, the second end 32 is opposite the first end 31. The direction from the first end 31 to the second end 32 is the first direction 101. Each of the multiple hollow fiber membranes 1 extends along the first direction 101. Each of the multiple hollow fiber membranes 1 has an opening at a second end 32.

[0026] Each of the multiple hollow fiber membranes 1 is formed from a porous material made of fluororesin. Specifically, each of the multiple hollow fiber membranes 1 is formed from a material mainly composed of polytetrafluoroethylene (PTFE) or modified PTFE. Modified PTFE is PTFE copolymerized with hexafluoropropylene (HFP), alkyl vinyl ether (AVE), chlorotrifluoroethylene (CTFE), etc. In modified PTFE, the molar ratio of HFP, AVE, and CTFE to tetrafluoroethylene is 1 / 50 or less. "Main component" refers to the component with the largest mass content. For example, the content of PTFE or modified PTFE may be 50% by mass or more, or 70% by mass or more, or even 95% by mass or more.

[0027] The housing 2 contains a plurality of hollow fiber membranes 1. From another perspective, the housing 2 surrounds the plurality of hollow fiber membranes 1. The plurality of hollow fiber membranes 1 divide the interior of the housing 2 into a gas flow path 91 and a liquid flow path 92. The gas flow path 91 includes the space surrounded by each of the plurality of hollow fiber membranes 1. In other words, a portion of the gas flow path 91 is located inside the plurality of hollow fiber membranes 1. The liquid flow path 92 is located outside the plurality of hollow fiber membranes 1.

[0028] The housing 2 is provided with a liquid inlet 81, a liquid outlet 82, a gas inlet 83, and a gas outlet 84. The liquid inlet 81 is connected to a liquid flow path 92. The liquid inlet 81 opens in a direction perpendicular to, for example, the first direction 101. In the first direction 101, the liquid inlet 81 is located between the first end 31 and the second end 32 of each of the multiple hollow fiber membranes 1.

[0029] The liquid outlet 82 opens in a direction perpendicular to the first direction 101, for example. The liquid outlet 82 is spaced apart from the liquid inlet 81. The liquid outlet 82 is connected to the liquid flow path 92. The liquid outlet 82 and the liquid inlet 81 are connected via the liquid flow path 92. In the first direction 101, the liquid outlet 82 is located, for example, between the liquid inlet 81 and the first end 31 of the plurality of hollow fiber membranes 1.

[0030] The gas inlet 83 communicates with the gas flow path 91. The gas inlet 83 opens, for example, in a direction opposite to the first direction 101. The gas outlet 84 communicates with the gas flow path 91. The gas outlet 84 and the gas inlet 83 communicate with each other via the gas flow path 91. The gas outlet 84 opens, for example, in the first direction 101.

[0031] The housing 2 is formed of a fluororesin such as PTFE and perfluoroalkoxy alkane (PFA). From another perspective, the hollow fiber membrane module 10 is formed of a fluororesin. The minimum internal pressure at which the housing 2 ruptures is, for example, 1 MPa or more. Therefore, in the separation and recovery of gas using a liquid and the desorption of gas from a liquid, the pressures of the liquid and the gas can be made sufficiently high. Thereby, the efficiency in the separation and recovery of gas and the desorption of gas can be improved.

[0032] The housing 2 includes a first holding portion 28, a second holding portion 29, a first cylindrical portion 21, a second cylindrical portion 22, a third cylindrical portion 23, a fourth cylindrical portion 24, a first lid portion 26, and a second lid portion 27. The first holding portion 28 holds the first end portions 31 of each of the plurality of hollow fiber membranes 1. The first holding portion 28 seals the gaps between the plurality of hollow fiber membranes 1. The outer shape of the first holding portion 28 is, for example, disc-shaped.

[0033] The second holding portion 29 holds the second end portions 32 of each of the plurality of hollow fiber membranes 1. The second holding portion 29 seals the gaps between the plurality of hollow fiber membranes 1. The second holding portion 29 is separated from the first holding portion 28. The second holding portion 29 is located in the first direction 101 with respect to the first holding portion 28. The liquid flow path 92 is provided between the first holding portion 28 and the second holding portion. The outer shape of the second holding portion 29 is, for example, disc-shaped.

[0034] The first cylindrical portion 21 is annular. The first cylindrical portion 21 holds the first holding portion 28. Specifically, for example, the first holding portion 28 is fitted inside the first cylindrical portion 21. Note that the first cylindrical portion 21 and the first holding portion 28 may be integrally formed.

[0035] The second cylindrical portion 22 connects the first cylindrical portion 21 and the third cylindrical portion 23. The second cylindrical portion 22 surrounds a plurality of hollow fiber membranes 1. For example, a liquid outlet 82 is provided in the second cylindrical portion 22.

[0036] The third cylindrical portion 23 connects the second cylindrical portion 22 and the fourth cylindrical portion 24. The third cylindrical portion 23 is located in the first direction 101 with respect to the first cylindrical portion 21. The third cylindrical portion 23 is annular.

[0037] The fourth cylindrical portion 24 connects the third cylindrical portion 23 and the fifth cylindrical portion 25. The fourth cylindrical portion 24 is located in the first direction 101 with respect to the second cylindrical portion 22. For example, a liquid inlet 81 is provided in the fourth cylindrical portion 24.

[0038] The fifth cylindrical portion 25 is annular. The fifth cylindrical portion 25 holds the second holding portion 29. Specifically, for example, the second holding portion 29 is fitted inside the fifth cylindrical portion 25. Note that the fifth cylindrical portion 25 and the second holding portion 29 may be integrally formed.

[0039] The first lid portion 26 is connected to the first cylindrical portion 21. The first lid portion 26 is separated from the plurality of hollow fiber membranes 1. From another perspective, a space is provided between the first lid portion 26 and the plurality of hollow fiber membranes 1. The space is included in the gas flow path 91. For example, a gas inlet 83 is provided in the first lid portion 26.

[0040] The second lid portion 27 is connected to the fifth cylindrical portion 25. The second lid portion 27 is separated from the plurality of hollow fiber membranes 1. From another perspective, a space is provided between the second lid portion 27 and the plurality of hollow fiber membranes 1. The space is included in the gas flow path 91. A gas outlet 84 is provided in the second lid portion 27.

[0041] The packing rate of the multiple hollow fiber membranes 1 in the hollow fiber membrane module 10 is 10% or more and 80% or less. "Packing rate of the hollow fiber membrane" refers to the packing density of the hollow fiber membranes 1 packed in the housing 2. Specifically, it is the ratio (%) of the sum of the cross-sectional areas occupied by the multiple hollow fiber membranes 1 in a cross-section perpendicular to the longitudinal direction (first direction 101) of the hollow fiber membranes 1 housed in the housing 2 to the internal cross-sectional area of ​​the housing 2. The internal cross-sectional area of ​​the housing 2 is the cross-sectional area of ​​the liquid flow path 92 in a cross-section perpendicular to the first direction 101 and where the cross-sectional area of ​​the liquid flow path 92 is minimized. Specifically, the internal cross-sectional area of ​​the housing 2 is, for example, the area of ​​a circle whose diameter is the inner diameter of the third cylindrical portion 23. The cross-sectional area occupied by the hollow fiber membranes 1 is the area of ​​a circle whose diameter is the average outer diameter D1 of the hollow fiber membranes 1.

[0042] In the above description, a configuration was described in which a liquid outlet 82 is provided in the second cylindrical portion 22 and a liquid inlet 81 is provided in the fourth cylindrical portion 24. However, the configuration of the housing 2 is not limited to the above configuration. Specifically, the liquid outlet 82 may be provided in the fourth cylindrical portion 24. The liquid inlet 81 may be provided in the second cylindrical portion 22. From another point of view, in the first direction 101, the liquid inlet 81 may be located between the liquid outlet 82 and the first end 31 of the plurality of hollow fiber membranes 1. The housing 2 does not need to have a gas inlet 83.

[0043] <Hollow Fiber Membrane> Figure 2 shows the structure of the hollow fiber membrane 1 as viewed in the first direction 101. When viewed in the first direction 101, the outer shape of each of the multiple hollow fiber membranes 1 is annular. The average outer diameter D1 of each of the multiple hollow fiber membranes 1 is 0.6 mm or less. The average outer diameter D1 is the maximum distance between two points on the outer surface of the hollow fiber membrane 1 as viewed in the first direction 101. The average outer diameter D1 may be, for example, 0.5 mm or less, or 0.45 mm or less. The average outer diameter D1 may be, for example, 0.1 mm or more, or 0.2 mm or more. The average outer diameter D1 may be 0.1 mm or more and 0.6 mm or less, or 0.2 mm or more and 0.45 mm or less.

[0044] The average inner diameter D2 of each of the multiple hollow fiber membranes 1 is 0.36 mm or less. The average inner diameter D2 is the maximum distance between two points on the inner circumferential surface of the hollow fiber membrane 1 when viewed in the first direction 101. The average inner diameter D2 may be 0.3 mm or less, or 0.25 mm or less. The average inner diameter D2 may be, for example, 0.05 mm or more, or 0.1 mm or more. The average inner diameter D2 may be 0.05 mm or more and 0.36 mm or less, or 0.1 mm or more and 0.3 mm or less.

[0045] The "average outer diameter" mentioned above refers to the average value of the outer diameters at any two points when the cross-section of the hollow fiber membrane 1 is circular. When the cross-section of the hollow fiber membrane 1 is elliptical, the minor and major axes of the outer surface are measured and the average value is taken as the average outer diameter. Furthermore, when the cross-section of the hollow fiber membrane 1 is an irregular shape other than a circle or ellipse, edge information of the outer surface is extracted from the cross-section and approximated to a circle, and the average outer diameter is taken by dividing the resulting circumference by pi.

[0046] The average outer diameter can be measured by the following procedure. First, the hollow fiber membrane 1 is sliced ​​crosswise with a plane perpendicular to the length direction (first direction 101), and observed with an electron microscope so that the entire cross-section is in the field of view. The outer diameter is measured at two locations approximately diagonally opposite each other on the above cross-section (positions where the phase is shifted by approximately 90 degrees), and the average value is taken as the average outer diameter (D1).

[0047] The "average inner diameter" mentioned above refers to the average value of the inner diameters of any two points when the cross-section of the hollow fiber membrane 1 is circular. When the cross-section of the hollow fiber membrane 1 is elliptical, the minor and major axes of the inner surface are measured and the average value is taken as the average inner diameter. Furthermore, when the cross-section of the hollow fiber membrane 1 is an irregular shape other than a circle or ellipse, edge information of the inner surface is extracted from the cross-section and approximated as a circle, and the average inner diameter is obtained by dividing the resulting circumference by pi.

[0048] The average inner diameter can be measured by the following procedure. First, the hollow fiber membrane 1 is sliced ​​crosswise with a plane perpendicular to the length direction (first direction 101), and the entire cross-section is observed with an electron microscope so that it is within the field of view. The inner diameter is measured at two locations approximately diagonally opposite each other on the above cross-section (positions where the phase is shifted by approximately 90 degrees), and the average value is taken as the average inner diameter (D2).

[0049] The average thickness (first thickness T1) of each of the multiple hollow fiber membranes 1 is, for example, 0.05 mm or more and 0.19 mm or less. The first thickness T1 is half the value obtained by subtracting the average inner diameter D2 from the average outer diameter D1. By having a first thickness T1 of 0.05 mm or more, the pressure resistance strength of the hollow fiber membrane 1 can be sufficiently improved. Therefore, rupture of the hollow fiber membrane 1 due to internal pressure and buckling of the hollow fiber membrane 1 due to external pressure can be prevented. By having a first thickness T1 of 0.19 mm or less, it is possible to prevent an excessive decrease in the gas permeability of the hollow fiber membrane 1.

[0050] The average pore size of the porous body forming the multiple hollow fiber membranes 1 is 0.3 nm or more and 50 nm or less. The average pore size may also be, for example, 1 nm or more and 40 nm or less, or 5 nm or more and 30 nm or less.

[0051] The average pore size can be measured, for example, using a pore distribution measuring device. The palm porometer "CFP-1500A" manufactured by Porous Materials, Inc. can be used as such a device. Specifically, first, for a dry hollow fiber membrane 1, the relationship between the differential pressure applied to the hollow fiber membrane 1 and the airflow rate permeating through the membrane 1 is measured. Using the measured differential pressure and airflow rate, a graph is created with the differential pressure on the horizontal axis and the airflow rate on the vertical axis to obtain a drying curve.

[0052] Next, the relationship between the differential pressure applied to the hollow fiber membrane 1 and the airflow rate permeating through the hollow fiber membrane 1, which is wetted with a liquid, is measured. Specifically, the liquid used is GALWICK (propylene, 1,1,2,3,3,3-hexafluoride oxide) manufactured by Porous Materials, Inc. The hollow fiber membrane 1 is immersed in this liquid, and then removed from the liquid to obtain a hollow fiber membrane 1 wetted with this liquid. The measured differential pressure and airflow rate are used to create a graph with differential pressure on the horizontal axis and airflow rate on the vertical axis to obtain a wetting curve.

[0053] Using the differential pressure P at the intersection of the dry curve and the wet curve, the average flow hole diameter d is determined by the following equation 1. This average flow hole diameter d is the average hole diameter mentioned above.

[0054]

[0055] Here, the unit of d is μm. c is 2860 (constant). γ is the surface tension of the above liquid. The unit of γ is dyne / cm. Note that dyne / cm is the same as mN / m. The unit of differential pressure P is PaG. The "G" in "PaG" indicates gauge pressure.

[0056] Note that if the average pore size is less than 20 nm, the measurement pressure may become too high and measurement may not be possible using the above measurement method. In this case, the average pore size can be measured using a pore size distribution analyzer that uses a liquid such as IPA (isopropyl alcohol) instead of air as the fluid permeating through the hollow fiber membrane 1.

[0057] Other measurement methods include, for example, the pore distribution measurement method using gas adsorption based on capillary condensation, the mercury intrusion method, and the pure water intrusion method. In the mercury intrusion method and the pure water intrusion method, a liquid (such as mercury) repelled by the hollow fiber membrane 1 is injected into the pores under pressure. The pore distribution is measured using the applied pressure, the volume of liquid that has entered the pores, and Washburn's equation.

[0058] The porosity of the porous material forming the multiple hollow fiber membranes 1 is, for example, 30% to 80%. The water pressure resistance of each of the multiple hollow fiber membranes 1 is, for example, 1 MPa or more. This makes it possible to more reliably prevent liquid from permeating each of the multiple hollow fiber membranes 1. The minimum internal pressure required for each of the multiple hollow fiber membranes 1 to rupture is, for example, 1 MPa or more. The minimum external pressure required for each of the multiple hollow fiber membranes 1 to buckle is, for example, 1 MPa or more. This makes it possible to prevent deformation and buckling of the multiple hollow fiber membranes 1 caused by internal and external pressure. Therefore, it is possible to prevent deterioration of the performance of the hollow fiber membrane module 10.

[0059] "Porosity" refers to the ratio of the total volume of voids to the total volume of the hollow fiber membrane 1. Porosity can be determined using the volume of the hollow fiber membrane 1, the weight of the hollow fiber membrane 1, and the true specific gravity of the material of the hollow fiber membrane 1 (for example, PTFE).

[0060] Specifically, first, the average outer diameter (D1) and the average inner diameter (D2) of the hollow fiber membrane 1 for which the porosity is to be measured are measured using SEM. Next, the length (L) of the hollow fiber membrane 1 for which the porosity is to be measured is measured in 1 mm units. Next, the weight (W) of the hollow fiber membrane 1 is measured in 0.0001 g units using an electronic balance.

[0061] The volume of only the resin in the hollow fiber membrane 1 is designated as V1. The volume of the entire hollow fiber membrane 1 is designated as V2. Note that the volume of the entire hollow fiber membrane 1 is the volume of the hollow fiber membrane 1 including pores. Using the above measurement values, Equation 2, and Equation 3, V1 and V2 are calculated.

[0062]

[0063]

[0064] Here, “ρ” represents the true specific gravity of the material of the hollow fiber membrane 1. When the hollow fiber membrane 1 is formed of PTFE, ρ is 2.17 [g / cm ３ .

[0065] Using V1, V2, and the following Equation 4, the porosity is measured.

[0066]

[0067] <Gas Separation Device> Next, the configuration of the gas separation device 100 according to the first embodiment will be described. The gas separation device 100 separates a target gas from a mixed gas. As shown in FIG. 3, the gas separation device 100 according to the first embodiment mainly includes a first hollow fiber membrane module 10a, a second hollow fiber membrane module 10b, a first flow path 71, and a second flow path 72.

[0068] As shown in FIG. 4, the configuration of the first hollow fiber membrane module 10a is the same as the configuration of the above-described hollow fiber membrane module 10 (see FIG. 1), except that the gas inlet is sealed. The first hollow fiber membrane module 10a includes a plurality of first hollow fiber membranes 1a and a first housing 2a. The plurality of first hollow fiber membranes 1a and the first housing 2a respectively correspond to the plurality of hollow fiber membranes 1 and the housing 2.

[0069] The first housing 2a is provided with a first gas flow path 91a, a first liquid flow path 92a, a first liquid inlet 81a, a first liquid outlet 82a, a first gas inlet 83a, and a first gas outlet 84a. The first gas flow path 91a, the first liquid flow path 92a, the first liquid inlet 81a, the first liquid outlet 82a, the first gas inlet 83a, and the first gas outlet 84a correspond to the gas flow path 91, the liquid flow path 92, the liquid inlet 81, the liquid outlet 82, the gas inlet 83, and the gas outlet 84, respectively.

[0070] As shown in Figure 5, the configuration of the second hollow fiber membrane module 10b is the same as that of the hollow fiber membrane module 10 (see Figure 1), except for the positions of the liquid outlet and liquid inlet. The second hollow fiber membrane module 10b has a plurality of second hollow fiber membranes 1b and a second housing 2b. The plurality of second hollow fiber membranes 1b and the second housing 2b correspond to a plurality of hollow fiber membranes 1 and housings 2, respectively.

[0071] The second housing 2b is provided with a second gas flow path 91b, a second liquid flow path 92b, a second liquid inlet 81b, a second liquid outlet 82b, a second gas inlet 83b, and a second gas outlet 84b. The second gas flow path 91b, the second liquid flow path 92b, the second liquid inlet 81b, the second liquid outlet 82b, the second gas inlet 83b, and the second gas outlet 84b correspond to the gas flow path 91, the liquid flow path 92, the liquid inlet 81, the liquid outlet 82, the gas inlet 83, and the gas outlet 84, respectively.

[0072] As shown in Figure 3, the first channel 71 connects the first hollow fiber membrane module 10a and the second hollow fiber membrane module 10b. Specifically, the first channel 71 connects the first liquid inlet 81a and the second liquid outlet 82b. The first channel 71 is made of fluororesin.

[0073] The second channel 72 connects the first hollow fiber membrane module 10a and the second hollow fiber membrane module 10b. Specifically, the second channel 72 connects the first liquid outlet 82a and the second liquid inlet 81b. The second channel 72 is made of fluororesin. The first channel 71, the first hollow fiber membrane module 10a, the second channel 72, and the second hollow fiber membrane module 10b form a channel through which the gas absorbent liquid 90, described later, circulates.

[0074] The gas separation device 100 further comprises a first liquid transfer pump 41, a second liquid transfer pump 42, a heating unit 58, and a cooling unit 59. The first liquid transfer pump 41 is located in the first flow path 71. From another perspective, the first liquid transfer pump 41 is connected to the first liquid flow path 92a (see Figure 4) and the second liquid flow path 92b (see Figure 5), respectively. The first liquid transfer pump 41 supplies the gas absorption liquid 90 to the first hollow fiber membrane module 10a.

[0075] The heating unit 58 is provided, for example, in the first flow path 71. In the first flow path 71, the heating unit 58 is provided, for example, between the first liquid transfer pump 41 and the first hollow fiber membrane module 10a. The heating unit 58 may also be attached to the first hollow fiber membrane module 10a. The heating unit 58 heats at least one of the gas absorbent liquid 90 flowing through the first flow path 71 and the gas absorbent liquid 90 flowing inside the first hollow fiber membrane module 10a.

[0076] The second liquid pump 42 is located in the second flow path 72. From another perspective, the second liquid pump 42 is connected to the first liquid flow path 92a (see Figure 4) and the second liquid flow path 92b, respectively. The second liquid pump 42 supplies the gas absorbent liquid 90 to the second hollow fiber membrane module 10b.

[0077] The cooling unit 59 is provided, for example, in the second flow path 72. In the second flow path 72, the cooling unit 59 is provided, for example, between the second liquid transfer pump 42 and the second hollow fiber membrane module 10b. The cooling unit 59 may also be attached to the second hollow fiber membrane module 10b. The cooling unit 59 cools at least one of the gas absorbent liquid 90 flowing through the second flow path 72 and the gas absorbent liquid 90 flowing inside the second hollow fiber membrane module 10b.

[0078] The gas separation device 100 further comprises a first gas recovery unit 61, a second gas recovery unit 62, and a mixed gas supply unit 63. The first gas recovery unit 61 is connected to the first hollow fiber membrane module 10a. Specifically, the first gas recovery unit 61 is connected to the first gas outlet 84a. From another perspective, the first gas recovery unit 61 is connected to the first gas flow path 91a (see Figure 4).

[0079] The first gas recovery unit 61 includes, for example, a third flow path 73, a first vacuum pump 51, and a first gas storage unit 53. The third flow path 73 connects the first hollow fiber membrane module 10a and the first gas storage unit 53. The first vacuum pump 51 is provided in the third flow path 73. The first vacuum pump 51 evacuates the first gas flow path 91a. The first gas storage unit 53 stores the gas to be separated, as described later.

[0080] The mixed gas supply unit 63 is connected to the second hollow fiber membrane module 10b. Specifically, the mixed gas supply unit 63 is connected to the second gas inlet 83b. The mixed gas supply unit 63 supplies the mixed gas to the second gas flow path 91b.

[0081] The second gas recovery unit 62 is connected to the second hollow fiber membrane module 10b. Specifically, the second gas recovery unit 62 is connected to the second gas outlet 84b. From another perspective, the second gas recovery unit 62 is connected to the second gas flow path 91b (see Figure 5).

[0082] The second gas recovery unit 62 includes, for example, a fourth flow path 74, a second vacuum pump 52, and a second gas storage unit 54. The fourth flow path 74 connects the second hollow fiber membrane module 10b and the second gas storage unit 54. The second vacuum pump 52 is provided in the fourth flow path 74. The second vacuum pump 52 evacuates the second gas flow path 91b. The second gas storage unit 54 stores a mixed gas from which at least a portion of the gas to be separated has been separated.

[0083] <Gas Separation Method> Next, the gas separation method according to the first embodiment will be described.

[0084] As shown in Figure 6, the gas separation method according to the first embodiment includes the steps of: bringing a mixed gas containing the gas to be separated into a gas absorbent liquid and bringing the gas absorbent liquid into gas-liquid contact to allow the gas to be separated to be absorbed into the gas absorbent liquid (S10); desorbing the gas to be separated from the gas absorbent liquid in which the gas to be separated has been absorbed (S20); recovering the gas absorbent liquid from which the gas to be separated has been desorbed (S30); and absorbing the gas to be separated into the recovered gas absorbent liquid (S40).

[0085] In the following, as an example of a gas separation method, the mixed gas is biogas and the gas to be separated is carbon dioxide (CO2). ２ This section describes a gas separation method when the gas is CO2. In other words, it describes how to separate CO2 from biogas. ２ This section describes gas separation methods for separating gases. Biogas, for example, contains CO2 as a component. ２ It contains methane.

[0086] First, a step (S10) is performed in which the gas to be separated is absorbed into the gas absorption liquid. The gas absorption liquid 90 is supplied to the first flow path 71, the first liquid flow path 92a, the second flow path 72, and the second liquid flow path 92b.

[0087] The gas absorbent liquid 90 is a liquid capable of selectively absorbing the gas to be separated. The components of the gas absorbent liquid 90 are determined in accordance with the gas to be separated. ２ If the substance is a gas, for example, an amine solution is used as the gas absorbent 90. The amine solution is, for example, an alkanolamine solution such as monoethanolamine solution or diethanolamine solution. The gas absorbent 90 may be corrosive to plastics and rubber.

[0088] The minimum intrusion pressure of the gas absorbent liquid 90 into the multiple first hollow fiber membranes 1a is 100 kPa or more. The minimum intrusion pressure of the gas absorbent liquid 90 into the multiple first hollow fiber membranes 1a may be, for example, 300 kPa or more, 500 kPa or more, or 1 MPa or more. The minimum intrusion pressure of the gas absorbent liquid 90 into the multiple first hollow fiber membranes 1a may be, for example, 10 MPa or less.

[0089] The minimum intrusion pressure of the gas-absorbing liquid 90 into the multiple first hollow fiber membranes 1a is the pressure at which, when the outside of the hollow fiber membranes 1 are filled with the gas-absorbing liquid 90 and the gas-absorbing liquid 90 is pressurized, the gas-absorbing liquid 90 penetrates into the hollow fiber walls, causing the absorbent liquid to begin leaking from the outside to the inside of the hollow fiber membranes 1. The minimum intrusion pressure of the gas-absorbing liquid 90 into the multiple first hollow fiber membranes 1a can be easily measured using the hollow fiber membrane module 10 (see Figure 1). Specifically, for example, with the liquid inlet 81 sealed, the gas-absorbing liquid 90 is introduced into the liquid flow path 92 from the liquid outlet 82. Subsequently, the gas-absorbing liquid 90 is pressurized. The pressure of the gas-absorbing liquid 90 when it begins to leak into the gas flow path 91 is measured using a pressure gauge. This pressure is considered to be the minimum intrusion pressure of the gas-absorbing liquid 90 into the multiple first hollow fiber membranes 1a.

[0090] The first liquid transfer pump 41 and the second liquid transfer pump 42 circulate the gas absorbent liquid 90. As a result, the gas absorbent liquid 90 flows along arrow L1. The gas absorbent liquid 90 is cooled by the cooling unit 59.

[0091] As shown in Figure 8, the gas absorbent liquid 90 flows into the second liquid channel 92b through the second liquid inlet 81b. The gas absorbent liquid 90 flows outside the plurality of second hollow fiber membranes 1b. Specifically, the gas absorbent liquid 90 flows along the plurality of second hollow fiber membranes 1b, for example, in the first direction 101. The plurality of second hollow fiber membranes 1b block the gas absorbent liquid 90 from reaching the second gas channel 91b. It is preferable that the gas absorbent liquid 90 does not enter the pores of the plurality of second hollow fiber membranes 1b, but it may penetrate into the interior of the pores.

[0092] Mixed gas is supplied from the mixed gas supply unit 63 to the second hollow fiber membrane module 10b. The mixed gas flows into the second gas flow path 91b along arrow G1. The mixed gas flows through the second gas flow path 91b along the first direction 101. The second vacuum pump 52 evacuates the second gas flow path 91b. As a result, the pressure inside each of the multiple second hollow fiber membranes 1b becomes lower than the pressure outside the multiple second hollow fiber membranes 1b.

[0093] The mixed gas flows through the space surrounded by each of the multiple second hollow fiber membranes 1b. As a result, the mixed gas permeates through the multiple second hollow fiber membranes 1b from the second gas flow path 91b to the second liquid flow path 92b. The gas to be separated is absorbed into the gas absorbent liquid 90 by gas-liquid contact between the mixed gas and the gas absorbent liquid 90 via the multiple second hollow fiber membranes 1b. In other words, the gas to be separated dissolves in the gas absorbent liquid 90. As a result, at least a portion of the gas to be separated is separated from the mixed gas. The mixed gas from which the gas to be separated has been separated flows into the second gas containment section 54 (see Figure 7) along arrow G2. The mixed gas from which the gas to be separated has been separated is, for example, high-concentration methane gas.

[0094] The mixed gas and the gas absorbent 90 may be in gas-liquid contact inside the pores of the multiple second hollow fiber membranes 1b, or they may be in gas-liquid contact around the multiple second hollow fiber membranes 1b. When the average pore size of the hollow fiber membrane 1 is 0.3 nm, each of the multiple second hollow fiber membranes 1b selectively permeates the gas to be separated contained in the mixed gas. For example, if the mixed gas is biogas and the biogas permeates the multiple second hollow fiber membranes 1b, CO ２ The rate of gas permeation is greater than that of methane gas. This allows the gas to be efficiently absorbed into the gas absorption liquid 90.

[0095] Next, a step (S20) is performed to desorb the gas to be separated from the gas absorbent liquid in which the gas to be separated has been absorbed. As shown in Figure 7, the gas absorbent liquid 90 in which the gas to be separated has been absorbed flows along arrow L2. Specifically, the gas absorbent liquid 90 in which the gas to be separated has been absorbed flows into the interior of the first hollow fiber membrane module 10a through the second liquid outlet 82b, the first flow path 71, and the first liquid inlet 81a. The gas absorbent liquid 90 in which the gas to be separated has been absorbed is heated by the heating unit 58.

[0096] As shown in Figure 9, the gas absorbent liquid 90 in which the target gas has been absorbed flows into the first liquid channel 92a. The gas absorbent liquid 90 in which the target gas has been absorbed flows outside the plurality of first hollow fiber membranes 1a. The gas absorbent liquid 90 in which the target gas has been absorbed flows along the plurality of first hollow fiber membranes 1a, for example, in the direction opposite to the first direction 101. The plurality of first hollow fiber membranes 1a block the gas absorbent liquid 90 in which the target gas has been absorbed from reaching the first gas channel 91a. It is preferable that the gas absorbent liquid 90 in which the target gas has been absorbed does not enter the pores of the plurality of first hollow fiber membranes 1a, but it may penetrate into the interior of the pores.

[0097] The first vacuum pump 51 evacuates the first gas flow path 91a. As a result, the pressure inside each of the multiple first hollow fiber membranes 1a becomes lower than atmospheric pressure. Consequently, the partial pressure of the gas to be separated inside each of the multiple first hollow fiber membranes 1a becomes lower than the partial pressure of the gas to be separated outside the multiple first hollow fiber membranes 1a. Therefore, the gas to be separated that has been absorbed by the gas absorption liquid 90 is released from the gas absorption liquid 90. The released gas to be separated flows into the first gas containment section 53 (see Figure 7) along arrow G3.

[0098] The partial pressure of the gas to be separated outside the first hollow fiber membrane 1a is the same as the partial pressure of the gas to be separated in the gas absorbent liquid 90 located outside the first hollow fiber membrane 1a. Specifically, when the gas absorbent liquid 90 is in contact with a gas, the partial pressure of the gas to be separated in the gas that reaches equilibrium with the gas absorbent liquid 90 is considered to be the partial pressure of the gas to be separated in the gas absorbent liquid 90.

[0099] Next, a step (S30) is performed to recover the gas absorbent liquid from which the target gas has been removed. As shown in Figure 7, the gas absorbent liquid 90 from which the target gas has been removed flows along arrow L3. Specifically, the gas absorbent liquid 90 from which the target gas has been removed flows into the second hollow fiber membrane module 10b through the first liquid outlet 82a and the second flow path 72. In other words, the gas absorbent liquid 90 from which the target gas has been removed is recovered in the second hollow fiber membrane module 10b.

[0100] Next, a step (S40) is performed in which the gas to be separated is absorbed into the recovered gas absorbent. Step S40 is the same as step S10, except that the gas absorbent 90 recovered in step S30 is used. After step S40, steps S20 to S40 may be repeated.

[0101] Next, the effects of the gas separation method, hollow fiber membrane module 10, and gas separation apparatus 100 according to the first embodiment will be described.

[0102] According to the gas separation method of the first embodiment, a gas absorbent liquid 90 is flowed outside a plurality of first hollow fiber membranes 1a, and the pressure inside each of the plurality of first hollow fiber membranes 1a is made lower than the pressure outside the plurality of first hollow fiber membranes 1a, thereby desorbing the gas to be separated from the gas absorbent liquid 90 into which the gas to be separated has been absorbed. The minimum intrusion pressure of the gas absorbent liquid 90 into the plurality of first hollow fiber membranes 1a is 100 kPa or more. Therefore, it is possible to prevent the gas absorbent liquid 90 from permeating the plurality of first hollow fiber membranes 1a. As a result, when recovering the gas absorbent liquid 90, it is only necessary to recover the gas absorbent liquid 90 from the outside of the plurality of first hollow fiber membranes 1a, and it is not necessary to recover the gas absorbent liquid 90 from the inside of the plurality of first hollow fiber membranes 1a. Accordingly, the gas absorbent liquid 90 can be recovered using a simpler apparatus compared to the case in which the gas absorbent liquid 90 is recovered from both the outside and inside of the plurality of first hollow fiber membranes 1a. As a result, the gas separation device 100 can be made smaller.

[0103] Normally, when desorbing the target gas from the gas absorbent liquid 90 in which the target gas has been absorbed, the gas absorbent liquid 90 may be sprayed out in a mist by allowing it to permeate through a plurality of first hollow fiber membranes 1a. In this case, it is necessary to use a gas absorbent liquid 90 that can permeate through a plurality of first hollow fiber membranes 1a. In other words, in gas separation, the average pore size of the gas separation membrane used and the type of gas absorbent liquid 90 are limited. According to the gas separation method of the first embodiment, the target gas can be desorbed from the gas absorbent liquid 90 without the gas absorbent liquid 90 permeating through a plurality of first hollow fiber membranes 1a. For this reason, liquids that are difficult to permeate through the first hollow fiber membranes 1a, such as liquids with relatively high viscosity and liquids containing gas adsorbents as a slurry, can be used as the gas absorbent liquid 90.

[0104] Furthermore, when the gas absorbent liquid 90 is sprayed in a mist form, it may not be possible to recover all of the sprayed gas absorbent liquid 90. Consequently, the consumption of the gas absorbent liquid 90 may increase. According to the gas separation method of the first embodiment, it is possible to prevent an increase in the consumption of the gas absorbent liquid 90.

[0105] Compared to the case where the gas absorbent liquid 90 flows through the space inside the multiple first hollow fiber membranes 1a, the pressure loss of the gas absorbent liquid 90 is smaller when the gas absorbent liquid 90 flows through the space outside the multiple first hollow fiber membranes 1a. Therefore, compared to the case where the gas absorbent liquid 90 flows through the inside of the multiple first hollow fiber membranes 1a, the power required to flow the gas absorbent liquid 90 can be reduced by flowing it through the outside of the multiple first hollow fiber membranes 1a. As a result, the gas absorbent liquid 90 can be flowed using a relatively simple device. Consequently, the gas separation device 100 can be effectively miniaturized.

[0106] The gas separation method according to the first embodiment includes a step (S30) of recovering the gas absorbent liquid from which the gas to be separated has been removed, and a step (S40) of allowing the gas to be separated to be absorbed into the recovered gas absorbent liquid. This reduces the amount of gas absorbent liquid 90 consumed.

[0107] Normally, when absorbing a gas to be separated into a gas absorbent liquid 90, the mixed gas and the gas absorbent liquid 90 are brought into gas-liquid contact by supplying the mixed gas towards the sprayed gas absorbent liquid 90. In this case, a relatively large space is required for the mixed gas and the gas absorbent liquid 90 to come into gas-liquid contact. Consequently, the apparatus becomes large. According to the gas separation method of the first embodiment, the gas to be separated is absorbed into the gas absorbent liquid 90 by bringing the mixed gas and the gas absorbent liquid 90 into gas-liquid contact using a plurality of second hollow fiber membranes 1b. Each of the plurality of second hollow fiber membranes 1b is formed of a porous material. Therefore, the contact area between the mixed gas and the gas absorbent liquid 90 can be effectively increased. Consequently, the gas to be separated can be absorbed into the gas absorbent liquid 90 using a relatively small apparatus. As a result, the gas separation apparatus 100 can be effectively miniaturized.

[0108] According to the gas separation method of the first embodiment, in the step (S20) of desorbing the gas to be separated from the gas absorbent liquid, the gas absorbent liquid 90 is heated. This makes it possible to effectively desorb the gas to be separated from the gas absorbent liquid 90.

[0109] In the gas separation method according to the first embodiment, in the step (S10) of absorbing the gas to be separated into the gas absorption liquid, the gas absorption liquid 90 is cooled. This allows the gas absorption liquid 90 to effectively absorb the gas to be separated.

[0110] According to the gas separation method of the first embodiment, the average pore size of the porous body forming the plurality of first hollow fiber membranes 1a is 0.3 nm or more and 50 nm or less. The porous body forming the plurality of first hollow fiber membranes 1a is made of fluororesin. Thus, the plurality of first hollow fiber membranes 1a are hydrophobic and have sufficiently small pores. This makes it possible to more reliably prevent the gas absorption liquid 90 from permeating through the plurality of first hollow fiber membranes 1a.

[0111] Because the porous body forming the multiple first hollow fiber membranes 1a is made of fluororesin, the multiple first hollow fiber membranes 1a have corrosion resistance. Therefore, even when the gas absorbent liquid 90 is corrosive, corrosion of the multiple first hollow fiber membranes 1a can be prevented.

[0112] When the average thickness of the first hollow fiber membrane 1a is the same, the larger the average outer diameter D1 of the first hollow fiber membrane 1a, the more easily the first hollow fiber membrane 1a is deformed or buckled. According to the gas separation method of the first embodiment, the average outer diameter D1 of each of the multiple first hollow fiber membranes 1a is 0.6 mm or less. Therefore, deformation or buckling of each of the multiple first hollow fiber membranes 1a can be prevented.

[0113] If the average outer diameter D1 of each of the multiple first hollow fiber membranes 1a is excessively small, the pressure loss of the gas flowing inside each of the multiple first hollow fiber membranes 1a will increase excessively. According to the gas separation method of the first embodiment, the average outer diameter D1 of each of the multiple first hollow fiber membranes 1a is 0.1 mm or more. Therefore, it is possible to prevent an increase in the pressure loss of the gas flowing inside each of the multiple first hollow fiber membranes 1a.

[0114] If the average inner diameter D2 of the first hollow fiber membrane 1a is excessively large, the first hollow fiber membrane 1a is prone to deformation or buckling. In the gas separation method according to the first embodiment, the average inner diameter D2 of each of the multiple first hollow fiber membranes 1a is 0.36 mm or less. Therefore, deformation or buckling of each of the multiple first hollow fiber membranes 1a can be prevented.

[0115] If the average inner diameter D2 of each of the multiple first hollow fiber membranes 1a is excessively small, the pressure loss of the gas flowing inside each of the multiple first hollow fiber membranes 1a will increase excessively. According to the gas separation method of the first embodiment, the average inner diameter D2 of each of the multiple first hollow fiber membranes 1a is 0.05 mm or more. Therefore, it is possible to prevent an increase in the pressure loss of the gas flowing inside each of the multiple first hollow fiber membranes 1a.

[0116] The hollow fiber membrane module 10 according to the first embodiment comprises a plurality of hollow fiber membranes 1 and a housing 2. The plurality of hollow fiber membranes 1 are formed of a porous material. The plurality of hollow fiber membranes 1 divide the inside of the housing 2 into a gas channel 91 and a liquid channel 92. The gas channel 91 includes a space surrounded by each of the plurality of hollow fiber membranes 1. The average pore size of the porous material forming the plurality of hollow fiber membranes 1 is 0.3 nm or more and 50 nm or less. The porous material forming the plurality of hollow fiber membranes 1 is made of fluororesin.

[0117] Therefore, when separating the target gas from the gas absorption liquid 90 using the hollow fiber membrane module 10 according to the first embodiment, it is possible to prevent the gas absorption liquid 90 from permeating through the multiple hollow fiber membranes 1. As a result, when recovering the gas absorption liquid 90, it is only necessary to recover the gas absorption liquid 90 from the liquid channel 92, and it is not necessary to recover the gas absorption liquid 90 from the gas channel 91. Consequently, the gas absorption liquid 90 can be recovered from the hollow fiber membrane module 10 using a simpler device compared to the case where the gas absorption liquid 90 is recovered from both the gas channel 91 and the liquid channel 92. As a result, the gas separation device 100 using the hollow fiber membrane module 10 can be miniaturized.

[0118] The gas separation device 100 according to the first embodiment includes a first hollow fiber membrane module 10a, a first liquid transfer pump 41, and a first gas recovery unit 61. The first liquid transfer pump 41 is connected to a first liquid flow path 92a. The first gas recovery unit 61 is connected to a first gas flow path 91a. Therefore, the gas absorption liquid 90 can be recovered from the hollow fiber membrane module 10 using a simple device. As a result, the gas separation device 100 can be miniaturized.

[0119] (Second Embodiment) Next, a gas separation device 100 according to the second embodiment will be described. The gas separation device 100 according to the second embodiment differs from the gas separation device 100 according to the first embodiment mainly in that it has a sweep gas supply unit 64, and is substantially the same as the gas separation device 100 according to the first embodiment in other respects. The following description will focus on the differences from the gas separation device 100 according to the first embodiment.

[0120] As shown in Figure 10, the gas separation device 100 may have a sweep gas supply unit 64. The sweep gas supply unit 64 is connected to the first gas inlet 83a of the first hollow fiber membrane module 10a. The sweep gas supply unit 64 supplies sweep gas to the first gas flow path 91a. The sweep gas is, for example, nitrogen (N ２ ) is a gas. The gas separation device 100 does not necessarily have a first vacuum pump 51 (see Figure 3).

[0121] According to the gas separation method of the second embodiment, in the step of desorbing the gas to be separated from the gas absorption liquid (S20), sweep gas is supplied to the first gas flow path 91a. The sweep gas passes inside each of the plurality of first hollow fiber membranes 1a along the first direction 101. As a result, the partial pressure of the gas to be separated inside each of the plurality of first hollow fiber membranes 1a becomes relatively lower than the partial pressure of the gas to be separated outside the plurality of first hollow fiber membranes 1a. Therefore, the gas to be separated that has been absorbed by the gas absorption liquid 90 is desorbed from the gas absorption liquid 90. The sweep gas and the gas to be separated that has been desorbed from the gas absorption liquid 90 flow into the first gas containment section 53.

[0122] (Third Embodiment) Next, a gas separation apparatus 100 according to the third embodiment will be described. The gas separation apparatus 100 according to the third embodiment differs from the gas separation apparatus 100 according to the second embodiment mainly in that it has a gas absorption section 55 and a heat exchanger 57, and is substantially the same as the gas separation apparatus 100 according to the second embodiment in other respects. The following description will focus on the differences from the gas separation apparatus 100 according to the second embodiment.

[0123] As shown in Figure 11, the gas separation device 100 may have a gas absorption section 55 and a heat exchanger 57. The gas absorption section 55 corresponds to the second hollow fiber membrane module 10b (see Figure 3).

[0124] The gas absorption unit 55 absorbs the gas to be separated into the gas absorption liquid 90 using a bubbling method. The gas absorption unit 55 holds the gas absorption liquid 90. The gas absorption unit 55 may cool the gas absorption liquid 90. In other words, the gas absorption unit 55 may have the same function as the cooling unit 59 described above. The gas absorption unit 55 is connected to the first flow path 71, the second flow path 72, and the mixed gas supply unit 63.

[0125] A heat exchanger 57 is provided in the first flow path 71 and the second flow path 72. In the first flow path 71, the heat exchanger 57 is provided between the gas absorption section 55 and the heating section 58. In the second flow path 72, the heat exchanger 57 is provided between the first hollow fiber membrane module 10a and the gas absorption section 55 (or cooling section 59).

[0126] The heat exchanger 57 facilitates heat exchange between the gas absorbent liquid 90 flowing through the first channel 71 and the gas absorbent liquid 90 flowing through the second channel 72. From another perspective, in the heat exchanger 57, the gas absorbent liquid 90 flowing through the first channel 71 is heated. In the heat exchanger 57, the gas absorbent liquid 90 flowing through the second channel 72 is cooled.

[0127] According to the gas separation method of the third embodiment, the gas absorbent liquid 90 circulates through the gas absorption section 55, the first flow path 71, the first hollow fiber membrane module 10a, and the second flow path 72. In the step of absorbing the gas to be separated into the gas absorbent liquid (S10), a mixed gas is supplied from the mixed gas supply section 63 to the gas absorption section 55. Bubbles of the mixed gas are generated inside the gas absorbent liquid 90 held by the mixed gas supply section 63. This increases the contact area between the gas to be separated and the gas absorbent liquid 90, resulting in more efficient absorption. The gas absorbent liquid 90 flows from the gas absorption section 55 to the first hollow fiber membrane module 10a through the second flow path 72.

[0128] (Fourth Embodiment) Next, the hollow fiber membrane module 10 according to the fourth embodiment will be described. The hollow fiber membrane module 10 according to the fourth embodiment differs from the hollow fiber membrane module 10 according to the first embodiment mainly in that the hollow fiber membrane 1 has a two-layer structure, and is substantially the same as the hollow fiber membrane module 10 according to the first embodiment in other respects. The following description will focus on the differences from the hollow fiber membrane module 10 according to the first embodiment.

[0129] As shown in Figure 12, each of the multiple hollow fiber membranes 1 may have a first layer 11 and a second layer 12. The first layer 11 forms the outer circumferential surface of the hollow fiber membrane 1. The second layer 12 forms the inner circumferential surface of the hollow fiber membrane 1. The second layer 12 is connected to the first layer 11. The second layer 12 is located inside the first layer 11. The second layer 12 is surrounded by the first layer 11.

[0130] The average pore size of the second layer 12 is smaller than the average pore size of the first layer 11. For example, the average pore size of the second layer 12 is 0.3 nm. The second layer 12 functions as a separation membrane. The average pore size of the first layer 11 is, for example, 10 nm. The first layer 11 functions as a support membrane. The average thickness of the second layer 12 (third thickness T3) is thinner than the average thickness of the first layer 11 (second thickness T2).

[0131] The second layer 12 may be located outside the first layer 11. From another perspective, the second layer 12 may form the outer surface of the hollow fiber membrane 1. The first layer 11 may form the inner surface of the hollow fiber membrane 1. The first layer 11 may be surrounded by the second layer 12. The average pore size of the second layer 12 may be greater than 0.3 nm and should be 10 nm or less.

[0132] In the above, we have described the case where the mixed gas is biogas, but the mixed gas is not particularly limited. For example, the mixed gas may be air. From another point of view, the gas separation device 100 may be used in direct air capture (DAC) technology. The sweep gas may be air. If both the mixed gas and the sweep gas are air, the mixed gas supply unit 63 and the sweep gas supply unit 64 may be a single device.

[0133] In the above description, the gas absorbent solution 90 was an amine solution, but the gas absorbent solution 90 is not limited to an amine solution. For example, the gas absorbent solution 90 may be a slurry solution containing a gas adsorption material such as zeolite.

[0134] Although the gas separation device 100 described above had two liquid transfer pumps, the number of liquid transfer pumps is not particularly limited. The gas separation device 100 may have only one liquid transfer pump. The gas separation device 100 does not need to have a second vacuum pump 52.

[0135] The positions of the first liquid inlet 81a and the first liquid outlet 82a in the first hollow fiber membrane module 10a are not particularly limited. In the first direction 101, the first liquid outlet 82a may be located between the first liquid inlet 81a and the second end 32 of each of the plurality of first hollow fiber membranes 1a. From another point of view, in the step of desorbing the gas to be separated from the gas absorption liquid (S20), the gas absorption liquid 90 may flow in the first direction 101 along the plurality of first hollow fiber membranes 1a.

[0136] In the first direction 101, the second liquid inlet 81b may be located between the second liquid outlet 82b and the second end 32 of each of the plurality of second hollow fiber membranes 1b. From another point of view, in the step of allowing the gas to be separated to be absorbed by the gas absorption liquid (S10), the gas absorption liquid 90 may flow in the first direction 101 along the plurality of second hollow fiber membranes 1b.

[0137] The first to fourth embodiments and their variations described above can be combined as appropriate. Specifically, for example, the gas separation device 100 according to the first embodiment (see Figure 3) may have a heat exchanger 57. Similarly, the gas separation device 100 according to the second embodiment (see Figure 10) may have a heat exchanger 57. The gas separation device 100 according to the third embodiment (see Figure 11) may not have a sweep gas supply unit 64 and may have a first vacuum pump 51.

[0138] The performance of the gas separation apparatus 100 was evaluated using the gas separation apparatus 100 and gas separation method according to the third embodiment described above. Specifically, the performance of recovering carbon dioxide from air was evaluated.

[0139] Air was used as the mixed gas. Carbon dioxide was the gas to be separated. An amine solution was used as the gas absorbent 90. The concentration of the amine solution was 3 mol / L. Nitrogen gas was used as the sweep gas.

[0140] (Evaluation method) CO2 of the gas recovered in the first gas recovery unit 61 ２ The concentration was measured. The temperature of the gas absorbent liquid 90 flowing inside the first hollow fiber membrane module 10a changed between 40°C and 100°C. The flow rate of air supplied to the gas absorption section 55 was set to 50 mL / min. In this case, the amount of carbon dioxide supplied to the gas absorption section 55 is considered to be about 0.2 mL / min. The flow rate of the sweep gas was set to 20 mL / min. The flow rate of the gas absorbent liquid 90 was set to approximately 200 mL / min.

[0141] (Evaluation results) As shown in Figure 13, the CO gas recovered in the first gas recovery unit 61 ２ The concentration was 0.01% or higher. Furthermore, when only the sweep gas was supplied to the first hollow fiber membrane module 10a without circulating the gas absorption liquid 90, the CO2 in the gas recovered in the first gas recovery unit 61 was... ２ The concentration was 0%.

[0142] Based on the above results, according to the gas separation apparatus 100 and gas separation method described herein, CO2 can be separated from air. ２ The gas could be separated. Also, as shown in Figure 13, as the temperature of the gas absorbent liquid 90 flowing inside the first hollow fiber membrane module 10a increased, CO was desorbed from the gas absorbent liquid 90. ２ The amount of gas increased.

[0143] The embodiments and examples disclosed herein should be considered in all respects as illustrative and not restrictive. It should be understood that at least one configuration or feature described in each embodiment and example can be combined with other embodiments and examples, and can be modified in various ways. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and all modifications within the scope of the claims are intended to be included in the meaning of equivalents and within the scope.

[0144] 1 Hollow fiber membrane 1a First hollow fiber membrane 1b Second hollow fiber membrane 2 Housing 2a First housing 2b Second housing 10 Hollow fiber membrane module 10a First hollow fiber membrane module 10b Second hollow fiber membrane module 11 First layer 12 Second layer 21 First cylindrical section 22 Second cylindrical section 23 Third cylindrical section 24 Fourth cylindrical section 25 Fifth cylindrical section 26 First lid section 27 Second lid section 28 First holding section 29 Second holding section 31 First end section 32 Second end section 41 First liquid transfer pump 42 Second liquid transfer pump 51 First vacuum pump 52 Second vacuum pump 53 First gas storage section 54 Second gas storage section 55 Gas absorption section 57 Heat exchanger 58 Heating section 59 Cooling section 61 First gas recovery section 62 63 Second gas recovery section 64 Mixed gas supply section 71 First flow path 72 Second flow path 73 Third flow path 74 Fourth flow path 81 Liquid inlet 81a First liquid inlet 81b Second liquid inlet 82 Liquid outlet 82a First liquid outlet 82b Second liquid outlet 83 Gas inlet 83a First gas inlet 83b Second gas inlet 84 Gas outlet 84a First gas outlet 84b Second gas outlet 90 Gas absorbent liquid 91 Gas flow path 91a First gas flow path 91b Second gas flow path 92 Liquid flow path 92a First liquid flow path 92b Second liquid flow path 100 Gas separation device 101 First direction D1 Average outer diameter D2 Average inner diameter T1 First thickness T2 Second thickness T3 Third thickness

Claims

A step of bringing a gas-liquid contact between a gas-liquid mixture containing the gas to be separated and a gas absorbent liquid, thereby allowing the gas to be absorbed by the gas absorbent liquid, The method comprises the steps of: flowing a gas absorption liquid containing the gas to be separated outwards from a plurality of first hollow fiber membranes formed of a porous body, and lowering the partial pressure of the gas to be separated inside each of the plurality of first hollow fiber membranes to a lower partial pressure of the gas to be separated outside the plurality of first hollow fiber membranes, thereby desorbing the gas to be separated from the gas absorption liquid containing the gas to be separated. A gas separation method wherein the minimum intrusion pressure of the gas absorption liquid in which the gas to be separated has been absorbed into the plurality of first hollow fiber membranes is 100 kPa or more. 　 A step of recovering the gas absorbent liquid from which the gas to be separated has been removed, The gas separation method according to claim 1, further comprising the step of absorbing the gas to be separated into the recovered gas absorption liquid. 　 The gas separation method according to claim 1 or claim 2, wherein, in the step of absorbing the gas to be separated into the gas absorbent liquid, the gas to be separated is absorbed into the gas absorbent liquid by bringing the mixed gas and the gas absorbent liquid into gas-liquid contact using a plurality of second hollow fiber membranes formed of a porous body. 　 The gas separation method according to any one of claims 1 to 3, wherein in the step of desorbing the gas to be separated from the gas absorbent liquid in which the gas to be separated has been absorbed, the gas absorbent liquid in which the gas to be separated has been absorbed is heated. 　 The gas separation method according to any one of claims 1 to 4, wherein in the step of desorbing the gas to be separated from a gas absorption liquid in which the gas to be separated has been absorbed, the pressure inside each of the plurality of first hollow fiber membranes is made lower than atmospheric pressure so that the partial pressure of the gas to be separated inside each of the plurality of first hollow fiber membranes is lower than the partial pressure of the gas to be separated outside the plurality of first hollow fiber membranes. 　 A gas separation method according to any one of claims 1 to 4, wherein, in the step of desorbing the gas to be separated from a gas absorption liquid in which the gas to be separated has been absorbed, sweep gas is passed through the inside of each of the plurality of first hollow fiber membranes to make the partial pressure of the gas to be separated inside each of the plurality of first hollow fiber membranes lower than the partial pressure of the gas to be separated outside the plurality of first hollow fiber membranes. 　 The gas separation method according to any one of claims 1 to 6, wherein in the step of absorbing the gas to be separated into the gas absorption liquid, the gas absorption liquid is cooled. 　 The average pore size of the porous body forming the plurality of first hollow fiber membranes is 0.3 nm or more and 50 nm or less. The gas separation method according to any one of claims 1 to 7, wherein the porous body forming the plurality of first hollow fiber membranes is made of fluororesin. 　 The average outer diameter of each of the aforementioned plurality of first hollow fiber membranes is 0.6 mm or less. The gas separation method according to any one of claims 1 to 8, wherein the average inner diameter of each of the plurality of first hollow fiber membranes is 0.36 mm or less. 　 Multiple hollow fiber membranes formed from a porous material and bundled together, The system comprises a housing that contains the plurality of hollow fiber membranes, The aforementioned plurality of hollow fiber membranes divide the inside of the housing into a gas channel and a liquid channel. The gas flow path includes the space surrounded by each of the plurality of hollow fiber membranes, The average pore size of the porous body forming the plurality of hollow fiber membranes is 0.3 nm or more and 50 nm or less. The porous body forming the plurality of hollow fiber membranes is made of fluororesin, forming a hollow fiber membrane module. 　 A hollow fiber membrane module according to claim 10, A liquid transfer pump connected to the aforementioned liquid flow path, A gas separation apparatus comprising a gas recovery unit connected to the aforementioned gas flow path.

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