Gas separation membrane and method for producing gas separation membrane

Abstract

The present invention provides a highly functional gas separation membrane capable of improving gas separation properties and also improving gas permeability, and a method for manufacturing the gas separation membrane. The gas separation membrane comprises: a porous substrate; a first gas separation membrane impregnated on one surface side of the porous substrate; and a second gas separation membrane disposed so as to overlap the first gas separation membrane, the first gas separation membrane having higher gas permeability and lower gas selectivity than the second gas separation membrane.

Description

[0001] Cross-references between related applications

[0002] This application claims priority based on Japanese Patent Application No. 2024-044764 filed on March 21, 2024, the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a gas separation membrane for separating an arbitrary gas from a plurality of types of mixed gases, and a method for producing the gas separation membrane. Background Art

[0004] A gas separation membrane that separates any gas from a plurality of mixed gases is, for example, a functional membrane that can selectively separate only carbon dioxide from combustion gas with a high carbon dioxide concentration discharged from factories, etc., or selectively separate only nitrogen oxides contained in exhaust gas from automobiles.

[0005] Such gas separation membranes are typically made of polymer materials that selectively allow only specific gases to permeate (see, for example, Japanese Patent Application Laid-Open No. 2018-167149). Conventional gas separation membranes require increased thickness to ensure adequate gas separation performance. However, increasing the thickness of the gas separation membrane decreases gas permeability, necessitating the supply of gas at high pressure to minimize separation efficiency degradation. Increasing the gas supply pressure relative to the gas separation membrane can easily damage the membrane.

[0006] Therefore, for example, Japanese Patent Application Laid-Open No. 2022-045753 discloses a gas separation membrane having improved gas permeability and separation properties by providing a structure in which clusters of multiple particles aggregated in pores of a porous substrate are provided in contact with a gas separation layer. Summary of the Invention

[0007] However, even the gas separation membrane disclosed in Japanese Patent Application Laid-Open No. 2022-045753 cannot achieve high gas separation performance unless the thickness of the separation layer formed on the porous substrate is sufficiently ensured. Therefore, even if particle clusters are formed within the pores of the porous substrate, sufficient gas permeability cannot be ensured.

[0008] The present invention provides a highly functional gas separation membrane capable of improving gas separation performance and also improving gas permeability, and a method for producing the gas separation membrane.

[0009] The present inventors have newly discovered that by forming a gas separation membrane with two layers and impregnating one layer of the gas separation membrane into the surface layer of a porous substrate, it is possible to achieve both high permeability and separation performance of the gas separation membrane.

[0010] (1) The gas separation membrane of claim 1 of the present invention is characterized by comprising: a porous substrate; a first gas separation layer impregnated on one side of the porous substrate; and a second gas separation layer arranged to overlap with the first gas separation layer, wherein the first gas separation layer has higher gas permeability and lower gas selectivity than the second gas separation layer.

[0011] (2) Aspect 2 of the present invention is the gas separation membrane of aspect 1, wherein the average pore diameter of the first gas separation layer is smaller than the average pore diameter of the porous substrate and is equal to or smaller than the thickness of the second gas separation layer.

[0012] (3) Scheme 3 of the present invention is a method for manufacturing a gas separation membrane, which is used to manufacture the gas separation membrane of Scheme 1 or 2, and the method for manufacturing the gas separation membrane is characterized in that the method for manufacturing the gas separation membrane includes: a first membrane-forming liquid coating step, wherein a first membrane-forming liquid in which a constituent material of the first gas separation layer is dissolved or dispersed by a first solvent is coated on one side of the porous substrate, and the first membrane-forming liquid is allowed to penetrate from one side of the porous substrate to a predetermined depth, thereby forming the first gas separation layer penetrated on one side of the porous substrate; and a second membrane-forming liquid coating step, wherein a second membrane-forming liquid in which a constituent material of the second gas separation layer is dissolved or dispersed by a second solvent is coated on the first gas separation layer formed by penetration on one side of the porous substrate by the first membrane-forming liquid coating step, thereby forming the second gas separation layer.

[0013] (4) Aspect 4 of the present invention is the method for producing a gas separation membrane according to aspect 3, wherein the first solvent is poorly soluble or insoluble in the second solvent.

[0014] (5) Aspect 5 of the present invention is the method for producing a gas separation membrane according to aspect 3 or 4, wherein the first solvent is a nonpolar solvent and the second solvent is a polar solvent.

[0015] (6) Aspect 6 of the present invention is the method for producing a gas separation membrane according to any one of aspects 3 to 5, wherein the first gas separation layer is formed of a rubber-like polymer material and the second gas separation layer is formed of a glass-like polymer material.

[0016] (7) Aspect 7 of the present invention is the method for producing a gas separation membrane according to any one of aspects 3 to 6, wherein the coating in the first membrane-forming liquid coating step and the second membrane-forming liquid coating step is spray coating.

[0017] According to the aspects of the present invention, it is possible to provide a highly functional gas separation membrane capable of improving gas separation performance and also improving gas permeability, and a method for producing the gas separation membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic cross-sectional view showing an example of the gas separation membrane according to this embodiment.

[0019] Figure 2 This is a flowchart showing a method for producing a gas separation membrane according to one embodiment of the present invention. DETAILED DESCRIPTION

[0020] The following describes a gas separation membrane and a method for manufacturing a gas separation membrane according to one embodiment of the present invention with reference to the accompanying drawings. It should be noted that the embodiments described below are described in detail to facilitate understanding of the main points of the invention and do not limit the present invention unless otherwise specified. In addition, the drawings used in the following description may show enlarged portions of essential components for ease of understanding of the features of the present invention, and the dimensional ratios of the components may not necessarily correspond to the actual dimensions.

[0021] [Gas separation membrane]

[0022] Figure 1 This is a schematic cross-sectional view showing a gas separation membrane according to one embodiment of the present invention.

[0023] The gas separation membrane 10 of the present embodiment is a functional membrane that separates a mixed gas of carbon dioxide, nitrogen, and oxygen into carbon dioxide, nitrogen, and oxygen by selectively allowing only carbon dioxide to permeate therethrough, for example.

[0024] The gas separation membrane 10 of this embodiment is composed of a substrate 11 , a first gas separation layer 12 , and a second gas separation layer 13 .

[0025] The substrate 11 is a support body composed of a porous material and supports the first gas separation layer 12 and the second gas separation layer 13. The substrate 11 has a plurality of pores P1 extending between one surface 11a and the other surface 11b.

[0026] Examples of the constituent material of the base material 11 include porous polyethylene (PE), porous polypropylene (PP), porous polyethylene terephthalate (PET), and porous polytetrafluoroethylene (PTFE).

[0027] The substrate 11 may be in the form of a sheet, for example. The thickness of the substrate 11 may be such that it is not damaged by the inflow pressure of the gas to be separated, and may be, for example, 10 μm to 100 μm. Furthermore, as a specific example of the size Δ1 of the pores P1 formed in the substrate 11, the average pore diameter may be, for example, 10 μm to 100 μm.

[0028] The first gas separation layer 12 is a layer impregnated from one side 11a of the substrate 11 in an arbitrary range along the thickness direction T, with one side (upper surface) being located at the same position as the one side 11a of the substrate 11. Specifically, the first gas separation layer 12 is formed so that its entirety is impregnated into the one side 11a of the substrate 11. More specifically, the constituent material of the first gas separation layer 12 is formed so that it partially penetrates the plurality of pores P1 present in the substrate 11 on the one side 11a of the substrate 11.

[0029] Examples of the constituent material of the first gas separation layer 12 include rubber-like polymer materials having a plurality of pores, such as porous silicone resin, porous polydimethylsiloxane (PDMS), and polyethyleneimine (PEI).

[0030] The first gas separation layer 12 may be formed by impregnation from one surface 11a of the substrate 11 to a depth of, for example, 1 μm to 10 μm in the thickness direction T. The first gas separation layer 12 is preferably formed so that its upper surface is not stacked above the one surface 11a of the substrate 11.

[0031] The average pore diameter of the plurality of pores P2 formed in the first gas separation layer 12 is smaller than the average pore diameter of the plurality of pores P1 in the substrate 11. Specifically, the plurality of pores P1 in the substrate 11 have their average pore diameter narrowed on one surface 11a due to the impregnation and formation of the first gas separation layer 12, thereby becoming the plurality of pores P2 formed in the first gas separation layer 12.

[0032] Furthermore, the average pore diameter of the plurality of pores P2 formed in the first gas separation layer 12 is equal to or less than the thickness Δt of the superimposed second gas separation layer 13. As a specific example of the size Δ2 of the pores P2 formed in the first gas separation layer 12, the average pore diameter may be, for example, 1 μm or less.

[0033] The second gas separation layer 13 is formed on one surface 11a of the substrate 11 so as to overlap with the region where the first gas separation layer 12 is formed. Examples of materials constituting the second gas separation layer 13 include glassy polymer materials such as polyimide (PI), polysulfone (PSU), and polyamide (PA).

[0034] The second gas separation layer 13 may be formed by laminating, for example, within a range of 1 μm to 10 μm from one side 11a of the substrate 11. Furthermore, the second gas separation layer 13 is laminated such that its thickness Δt is greater than the average pore diameter Δ2 of the plurality of pores P2 formed in the underlying first gas separation layer 12.

[0035] According to the gas separation membrane 10 of this embodiment having the above-described structure, the first gas separation layer 12 having a gas separation function and the first gas separation layer 12 in the second gas separation layer 13 are formed by impregnating the first gas separation layer 12 within the thickness range of the substrate 11, thereby narrowing the pores P1 of the substrate 11 and forming the pores P2 of the first gas separation layer 12 on one side 11a of the substrate 11.

[0036] As a result, the thickness of the first gas separation layer 12 is limited to the thickness of the substrate 11, resulting in excellent gas permeability due to the thin membrane thickness. Furthermore, the membrane, which has two gas separation functions, consisting of the first gas separation layer 12 and the second gas separation layer 13, can achieve high gas separation performance. Therefore, according to this embodiment, a gas separation membrane 10 can be realized that achieves both gas permeability and gas separation performance.

[0037] Furthermore, the pores P1 of the substrate 11 can be narrowed to any desired average pore diameter on one side 11a depending on the impregnation material and impregnation time of the first gas separation layer 12. Therefore, sufficient gas separation performance can be achieved without using expensive materials, particularly those with minimal variation in average pore diameter, for the substrate 11. Consequently, a low-cost gas separation membrane 10 can be realized using an inexpensive substrate.

[0038] It should be noted that, while a single type of substrate 11 is used in this embodiment, multiple substrates having different average pore diameters may also be used. Furthermore, another gas separation layer may be formed overlapping the second gas separation layer 13, so that a membrane having a gas separation function may be constructed from three or more functional membrane layers.

[0039] [Method for producing gas separation membrane]

[0040] Figure 2 1 is a flow chart showing a method for producing a gas separation membrane according to one embodiment of the present invention. In this embodiment, a method for producing the gas separation membrane 10 according to the above-described embodiment will be described.

[0041] The method for producing a gas separation membrane of the present embodiment includes a substrate preparation step S1 , a first membrane-forming liquid coating step S2 , a first drying step S3 , a second membrane-forming liquid coating step S4 , and a second drying step S5 .

[0042] First, a substrate 11 serving as a support for the first gas separation layer 12 and the second gas separation layer 13 to be formed in subsequent steps is prepared (substrate preparation step S1 ). In this embodiment, a sheet made of porous polyethylene (PE) is used as the substrate 11 .

[0043] Next, a first film-forming liquid in which the constituent materials of the first gas separation layer 12 are dissolved or dispersed in a first solvent is applied to one side 11 a of the substrate 11 (first film-forming liquid application step S2 ).

[0044] In this embodiment, a first membrane-forming liquid is used in which a rubbery polymer material, such as a silicone resin, is dispersed in a first solvent. The first solvent is a solvent that is poorly soluble or insoluble in the second solvent used to form the second gas separation layer 13, described later. Specific examples of the first solvent include various non-polar liquid oils and fats, benzene, hexane, toluene, and the like. In this embodiment, benzene is used as the first solvent. Specifically, in this embodiment, a silicone resin dissolved in benzene is used as the first membrane-forming liquid.

[0045] The first film-forming liquid can be applied to one side 11a of the substrate 11 by spraying or using a roll coater. In this embodiment, the first film-forming liquid is sprayed onto one side 11a of the substrate 11 using a spray device. Spraying reduces the size of the droplets during application, which can shorten the drying time in the subsequent first drying step S3.

[0046] In the first film-forming liquid coating step S2, the first film-forming liquid is coated on one side 11a of the substrate 11, thereby allowing the first film-forming liquid to penetrate from the one side 11a of the substrate 11 to a predetermined depth along the thickness direction T. The first film-forming liquid penetrates into a portion of the plurality of pores P1 present in the substrate 11.

[0047] Then, in the subsequent first drying step S3, the solvent contained in the first membrane-forming solution, in this embodiment, benzene, which has been impregnated from one side 11a of the substrate 11 to a predetermined depth, evaporates, thereby impregnating the substrate 11 from one side 11a to a predetermined depth, forming the first gas separation layer 12 composed of the silicone resin. Various drying methods can be employed in this first drying step S3, such as natural drying, air drying, and drying using an infrared heater, within a temperature range where the substrate 11 and the silicone resin do not soften.

[0048] In the first drying step S3, benzene contained in the impregnated first membrane-forming solution evaporates, making the silicone resin porous and forming a plurality of pores P2. These pores P2 are formed by narrowing the pore width of the larger pore diameter pores P1 of the substrate 11 by impregnation.

[0049] In this manner, the upper surface of the first gas separation layer 12 impregnated and formed in the substrate 11 is flush with one side 11a of the substrate 11, and the entire first gas separation layer 12 is formed within the one side 11a of the substrate 11. Consequently, the combined thickness of the substrate 11 and the first gas separation layer 12 is equal to the thickness of the substrate 11, and the formation of the first gas separation layer 12 does not increase the thickness of the substrate 11. Thus, a portion of the gas separation function is imparted to the one side 11a of the substrate 11.

[0050] It should be noted that in this embodiment, a first membrane-forming liquid containing a silicone resin dissolved in benzene is used. However, this is not limiting. For example, a liquid containing polydimethylsiloxane (PDMS) dissolved in toluene can also be used as the first membrane-forming liquid. Thus, even with a first membrane-forming liquid containing a resin dissolved in a solvent, the solvent can be evaporated in the first drying step S3, thereby making the resin porous and forming pores P2.

[0051] Next, a second film-forming liquid in which the constituent materials of the second gas separation layer 13 are dissolved or dispersed in a second solvent is applied to the upper surface of the first gas separation layer 12 in the region where the first gas separation layer 12 is formed on one side 11 a of the substrate 11 (second film-forming liquid application step S4 ).

[0052] In this embodiment, a second membrane-forming liquid is used in which a glassy polymer material, such as polysulfone (PSU), is dispersed in a second solvent. The second solvent is a solvent that is poorly soluble or insoluble in the first solvent used to form the first gas separation layer 12. Specific examples of the second solvent include polar solvents such as water and ethanol. In this embodiment, ethanol is used as the second solvent. Specifically, in this embodiment, a second membrane-forming liquid in which polysulfone is dispersed in ethanol is used.

[0053] The second film-forming liquid can be applied to the upper surface of the first gas separation layer 12 by spraying or coating with a roll coater. In this embodiment, the second film-forming liquid is sprayed onto the upper surface of the first gas separation layer 12 using a spray device.

[0054] In the second film-forming liquid coating step S4, the second film-forming liquid is coated on the upper surface of the first gas separation layer 12, thereby forming a thin film of the second film-forming liquid overlapping the upper surface of the first gas separation layer 12. At this time, the solvent constituting the second film-forming liquid is poorly soluble or insoluble in the solvent constituting the first film-forming liquid. Therefore, the second film-forming liquid does not penetrate into the first gas separation layer 12, and the second film-forming liquid forms a film of a predetermined thickness on the first gas separation layer 12.

[0055] Then, in the subsequent second drying step S5, the solvent contained in the second membrane-forming liquid formed overlapping the upper surface of the first gas separation layer 12, that is, ethanol in this embodiment, evaporates, thereby forming a second gas separation layer 13 composed of polysulfone having a predetermined thickness, overlapping the upper surface of the first gas separation layer 12. Similar to the first drying step S3, various drying methods can be applied to the second drying step S5, such as natural drying, air drying, and drying with an infrared heater, within a temperature range within which the substrate 11, silicone resin, and polysulfone do not soften.

[0056] In this manner, the second gas separation layer 13 formed to overlap the first gas separation layer 12 may be formed so that the film thickness Δt is greater than the average pore diameter Δ2 of the pores P2 of the underlying first gas separation layer 12 .

[0057] Through the above steps, the gas separation membrane 10 of this embodiment can be obtained, in which a two-layer functional membrane having a gas separation function, namely, the first gas separation layer 12 and the second gas separation layer 13 supported on the substrate 11 .

[0058] With the thus-obtained gas separation membrane 10, for example, when air containing a high concentration of carbon dioxide is supplied at a predetermined pressure to one side of the gas separation membrane 10, the first gas separation layer 12 and the second gas separation layer 13 selectively allow only carbon dioxide to permeate, while nitrogen and oxygen, which are other air components, are not allowed to permeate. This gas separation function enables the removal of only carbon dioxide from combustion gas containing a high concentration of carbon dioxide, for example.

[0059] It should be noted that the gas separation membrane 10 is not limited to the selective permeation of carbon dioxide. Depending on the constituent materials and pore diameters of the first gas separation layer 12 and the second gas separation layer 13, for example, it can also selectively allow only nitrogen oxides to pass through from motor vehicle exhaust, or selectively allow various harmful gases to pass through, without limiting the gas composition of the separation object.

[0060] According to the manufacturing method of the gas separation membrane of the present embodiment as described above, by impregnating the first gas separation layer 12 inside the substrate 11, it is possible to prevent the concern that film formation defects will occur due to the inability to follow the shape of the substrate when the film overlaps with the substrate with a larger pore diameter to form a gas separation layer with a smaller pore diameter.

[0061] In addition, the obtained gas separation membrane has the first gas separation layer 12 with gas separation function and the first gas separation layer 12 in the second gas separation layer 13 being impregnated and formed within the thickness range of the substrate 11. Therefore, while reducing the overall thickness of the gas separation membrane and improving the permeability, it is possible to achieve higher gas separation performance by utilizing the two gas separation layers of the first gas separation layer 12 and the second gas separation layer 13.

[0062] In addition, in the first film-forming liquid coating step S2 and the second film-forming liquid coating step S4, if spraying is used, for example, the droplets of each film-forming liquid become smaller during coating, and the film thickness can also be reduced, thereby shortening the drying time in the drying step of each subsequent step and efficiently manufacturing the gas separation membrane 10.

[0063] The embodiments of the present invention have been described above, but such embodiments are provided as examples and are not intended to limit the scope of the invention. Such embodiments can be implemented in various other ways and can be omitted, replaced, or modified in various ways without departing from the scope of the invention. These embodiments and their variations are included in the scope and spirit of the invention and are also included in the invention described in the patent technical proposal and its equivalents.

[0064] The gas separation membrane and method for manufacturing the gas separation membrane according to the present invention enable efficient and low-cost recovery of carbon dioxide (CO2) from low-concentration emission sources, where the concentration is 10% or less. This contributes to the realization of a carbon-neutral society and therefore has industrial applicability.

Claims

1. A gas separation membrane, characterized in that: The gas separation membrane has: porous substrate; a first gas separation layer impregnated into one side of the porous substrate; and a second gas separation layer arranged to overlap with the first gas separation layer; The first gas separation layer has higher gas permeability and lower gas selectivity than the second gas separation layer.

2. The gas separation membrane according to claim 1, wherein The average pore diameter of the first gas separation layer is smaller than the average pore diameter of the porous substrate and is equal to or smaller than the thickness of the second gas separation layer.

3. A method for producing a gas separation membrane, which is used to produce the gas separation membrane according to claim 1 or 2, The method for producing a gas separation membrane is characterized in that: The method for manufacturing the gas separation membrane comprises: a first film-forming liquid coating step of coating a first film-forming liquid in which a constituent material of the first gas separation layer is dissolved or dispersed in a first solvent on one side of the porous substrate, and allowing the first film-forming liquid to penetrate from one side of the porous substrate to a predetermined depth, thereby forming the first gas separation layer impregnated on one side of the porous substrate; and The second film-forming liquid coating step is to coat a second film-forming liquid in which the constituent material of the second gas separation layer is dissolved or dispersed using a second solvent, overlapping the first gas separation layer formed by impregnation on one side of the porous substrate by the first film-forming liquid coating step, thereby forming the second gas separation layer.

4. The method for producing a gas separation membrane according to claim 3, wherein: The first solvent is poorly soluble or insoluble in the second solvent.

5. The method for producing a gas separation membrane according to claim 3, wherein: The first solvent is a non-polar solvent, and the second solvent is a polar solvent.

6. The method for producing a gas separation membrane according to claim 3, wherein: The first gas separation layer is formed of a rubber-like polymer material, and the second gas separation layer is formed of a glass-like polymer material.

7. The method for producing a gas separation membrane according to claim 3, wherein: The coating in the first film-forming liquid coating step and the second film-forming liquid coating step is spray coating.

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