Method for producing gas separation membrane

Abstract

[Problem] To provide a means capable of improving gas permeability in a gas separation membrane provided with a porous base material and a gas separation layer. [Solution] Provided is a method for producing a gas separation membrane provided with a gas separation layer containing a polymer having gas separation performance, and a porous base material, the method comprising: a dropping step for dropping a coating liquid containing the polymer and a solvent onto the porous base material; and a drying step for removing the solvent from the dropped coating liquid by drying and forming the gas separation layer containing the polymer on the surface of the porous base material, wherein the contact angle of the coating liquid with respect to the porous base material is 50° or more, and the droplet diameter when the coating liquid is dropped onto the porous base material is greater than the average pore diameter of the porous base material.

Description

Gas separation membrane manufacturing method

[0001] The present invention relates to a method for producing a gas separation membrane.

[0002] Gas separation membranes have been used to separate specific types of gas molecules from a gas containing a mixture of multiple types of gas molecules. JP 2023-125585 A reports that by including a crosslinked organic-inorganic hybrid resin having a specific structure in a gas separation layer located on a porous substrate, it is possible to achieve good gas permeability and gas separation selectivity, particularly under high-pressure conditions.

[0003] However, the inventors have conducted studies and found that the gas separation membranes described in this document may have insufficient gas permeability.

[0004] Therefore, an object of the present invention is to provide a means for improving the gas permeability of a gas separation membrane comprising a porous substrate and a gas separation layer.

[0005] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by forming a gas separation layer containing a polymer on a porous substrate by dropping a coating liquid containing a polymer and a solvent onto a porous substrate in the manufacturing process of the gas separation membrane, and further controlling the contact angle of the coating liquid and the droplet diameter during dropping, thereby completing the present invention.

[0006] One aspect of the present invention relates to a method for producing a gas separation membrane comprising a gas separation layer containing a polymer having gas separation properties and a porous substrate. The method includes a coating step of dripping a coating liquid containing the polymer and a solvent onto the porous substrate, and a drying step of removing the solvent from the dripped coating liquid by drying to form a gas separation layer containing the polymer on the surface of the porous substrate. The method is characterized in that the contact angle of the coating liquid with the porous substrate is 50° or more, and the droplet diameter when the coating liquid is dripped onto the porous substrate is larger than the average pore diameter of the porous substrate.

[0007] FIG. 1 is a perspective view schematically showing the overall structure of a gas separation membrane according to one embodiment of the present invention. FIG. 2 is a cross-sectional view of the gas separation membrane shown in FIG. 1 taken along line II-II. FIG. 3 is an explanatory diagram schematically showing a main part of a vehicle engine system equipped with a gas separation membrane according to one embodiment of the present invention. FIG. 4 is an explanatory diagram schematically showing a main part of a vehicle air conditioning system equipped with a gas separation membrane according to one embodiment of the present invention. FIG. 5 is an explanatory diagram schematically showing the appearance of a gas separation membrane module used to evaluate a gas separation membrane according to one embodiment of the present invention.

[0008] One aspect of the present invention is a method for producing a gas separation membrane comprising a gas separation layer containing a polymer having gas separation performance and a porous substrate, the method comprising: a coating step of dripping a coating liquid containing the polymer and a solvent onto the porous substrate; and a drying step of removing the solvent from the dripped coating liquid by drying to form a gas separation layer containing the polymer on the surface of the porous substrate, wherein the contact angle of the coating liquid with the porous substrate is 50° or more, and the droplet diameter when the coating liquid is dripped onto the porous substrate is larger than the average pore diameter of the porous substrate. This manufacturing method of the gas separation membrane according to this aspect can improve the gas permeability of the produced gas separation membrane.

[0009] Hereinafter, a gas separation membrane according to the present embodiment will be described with reference to the accompanying drawings. The technical scope of the present invention should be defined based on the claims and is not limited to the following embodiments. In the description of the drawings, the same elements are given the same reference numerals, and redundant explanations will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0010] [Gas Separation Membrane] Fig. 1 is a perspective view schematically showing the overall structure of a gas separation membrane according to one embodiment of the present invention. Fig. 2 is a cross-sectional view taken along line II-II of the gas separation membrane shown in Fig. 1. As shown in Figs. 1 and 2, the gas separation membrane 1 according to this embodiment includes a gas separation layer 10 and a porous substrate 20 that supports the gas separation layer 10.

[0011] Here, the gas separation layer 10 is a layer that separates a gas containing one or more components from a mixed gas containing two or more components. ２ and N ２ from air containing O ２ and a layer for separating CO ２ and water vapor (H ２ O) from air containing CO ２ or water vapor (H ２ O) can be applied as a separate layer.

[0012] Furthermore, in the gas separation membrane according to this embodiment, the structure of the porous substrate 20 is not particularly limited as long as it can support the gas separation layer 10 and ensure the permeability of the gas separated by the gas separation layer 10. As shown in Figure 2, in the gas separation membrane 1 of this embodiment, the porous substrate 20 ensures the gas permeability of the porous substrate 20 by forming elongated holes in each of the plurality of pores 20A that directly connect the surface 20B on the gas separation layer 10 side to the back surface 20C on the opposite side.

[0013] Although not shown, in the gas separation membrane of the present invention, for example, in a porous substrate 20 having a plurality of pores 20A, the pores 20A can be connected to other pores 20A, have numerous branching and merging sections, or bend, forming communicating holes that connect the surface 20B and the back surface 20C, thereby ensuring the gas permeability of the porous substrate 20.

[0014] The main components of the gas separation membrane according to this embodiment will be described below.

[0015] [Gas Separation Layer] The material forming the gas separation layer 10, i.e., the polymer having gas separation performance, is not particularly limited, and conventionally known materials can be suitably employed. Examples of such materials include organic polymer materials such as polymers of intrinsic microporosity (PIM), polytrimethylsilylpropyne (PTMSP), polyimide, and silicone. These can be used alone or in combination of two or more. Among them, it is preferable to use polyimides such as aromatic polyimides and fluorine-containing polyimides, and intrinsic microporous polymers such as PIM-1, and it is more preferable to use PIM-1. PIM-1 has, for example, a structural unit represented by the following formula (I):

[0016]

[0017] In the above formula (I), R １ is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, and R ２ is a hydrogen atom, a linear or branched alkyl group having 1 to 4 carbon atoms, or a cyano group, and R ３ is a hydrogen atom, a linear or branched alkyl group having 1 to 4 carbon atoms, or a cyano group. １ , R ２ and R ３ may be the same or different.

[0018] As shown in formula (I), PIM-1 is a polymer that has a rigid ladder structure and a bent backbone, and is capable of forming micropores within the layer. Therefore, gas separation layer 10 containing PIM-1 has excellent gas permeability.

[0019] The material forming the gas separation layer 10 may be a composite material in which particles are further contained in the various polymers described above. Suitable examples of materials for forming such particles include inorganic materials, typically ceramic materials such as silica and zeolite. Various particles produced and commercially available by known manufacturing methods can be used. Examples of such particles include: (1) fumed silica nanoparticles synthesized by a gas-phase method (dry method) in which a silicon-containing raw material such as silicon tetrachloride is burned in an oxygen and hydrogen flame to hydrolyze the raw material; and (2) colloidal silica nanoparticles synthesized by a liquid-phase method (wet method) typified by a water glass method in which sodium silicate is ion-exchanged to remove sodium and then heated and aged, or an alkoxide hydrolysis method in which an alkoxide such as tetraethoxysilane is hydrolyzed and polycondensed in an alcohol solvent.

[0020] From the viewpoint of forming fine pores between the above-mentioned particles, or between the particles and the polymer, etc., and thereby forming a gas separation layer 10 with better gas permeability and gas selectivity, the average particle diameter (D50) of the particles is preferably 1 nm or more and 20 nm or less, more preferably 1 nm or more and 10 nm or less, and even more preferably 1 nm or more and 5 nm or less.

[0021] The particle diameter of the above particles can be measured and calculated as follows. First, the gas separation membrane is cut in the thickness direction at an arbitrary position on the gas separation membrane. Next, the obtained cut surface is observed using an optical microscope, a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like, and if necessary, further observed using energy dispersive X-ray analysis (EDS) or X-ray photoelectron spectroscopy (XPS). The maximum distance between any two points on the contour lines of four particles is measured. Then, the average of the maximum distances of the four particles is calculated to be the particle diameter of the particle.

[0022] From the viewpoint of forming fine pores between the polymer and particles having modifying groups that cause steric hindrance, thereby forming a gas separation layer 10 with excellent gas permeability and gas selectivity, it is preferable that the particles have modifying groups on their surfaces. Particles having such modifying groups can be obtained, for example, by surface-modifying particles with a silane coupling agent.

[0023] From the viewpoint of improving gas permeability and gas selectivity, it is preferable that the gas separation layer 10 contains a polymer and the above-mentioned particles. From the viewpoint of improving gas permeability and gas selectivity, the content of the above-mentioned particles in the gas separation layer 10 is preferably 10% by mass or more and 80% by mass or less, and more preferably 20% by mass or more and 60% by mass or less.

[0024] In the present invention, the particle content in the gas separation layer can be measured and calculated as follows. First, a certain amount (1 g) of the gas separation layer is taken and its mass is measured. Next, the polymer is removed from the gas separation layer by combustion or the like, and the mass of the particles remaining is measured. After that, the ratio of the mass of the particles to the mass of the gas separation layer is calculated, and this is used as the particle content in the gas separation layer.

[0025] (Thickness) From the viewpoint of improving gas permeability, the thickness of the gas separation layer 10 is preferably 500 nm or less, more preferably 400 nm or less. Furthermore, from the viewpoint of the mechanical strength of the gas separation layer, the thickness of the gas separation layer 10 is preferably 5 nm or more, more preferably 10 nm or more. In one embodiment, the thickness of the gas separation layer 10 is preferably 5 nm or more and 500 nm or less, more preferably 10 nm or more and 400 nm or less. The thickness of the gas separation layer is the distance from the portion where the components of the gas separation layer permeate the porous substrate to the surface 10A of the gas separation layer 10 (see FIG. 2).

[0026] The thickness of the gas separation layer can be measured and calculated as follows. First, the gas separation membrane is cut along the thickness direction at any position on the gas separation membrane. Next, the obtained cut surface is observed using an optical microscope, SEM, TEM, etc., and if necessary, further observed using EDS, XPS, or FT-IR, and the distance from the portion where the components of the gas separation layer have permeated into the porous substrate to the surface of the gas separation layer is measured at four locations. Then, the average value of the distances at these four locations is calculated to determine the thickness of the gas separation layer. Whether the components of the gas separation layer have permeated into the porous substrate can be determined, for example, by the color and brightness of the gas separation layer and the porous substrate observed using an optical microscope.

[0027] [Porous substrate] The material forming the porous substrate 20 may be either an organic material or an inorganic material, but is preferably an organic material. Examples of organic materials include various resin materials such as polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). These can be used alone or in combination of two or more. When combining two or more types of various resin materials, they may be mixed to form a uniform material, or may have a structure of two or more layers, with one type of resin material being used as one layer. Suitable materials for forming the porous substrate 20 include PTFE and PP.

[0028] From the viewpoint of imparting mechanical strength and high gas permeability, the thickness of the porous substrate 20 is preferably 1 μm or more and 3000 μm or less, more preferably 5 μm or more and 500 μm or less, and even more preferably 5 μm or more and 150 μm or less.

[0029] In the present invention, the thickness of the porous substrate can be measured and calculated as follows. First, the gas separation membrane is cut along the thickness direction at an arbitrary position on the gas separation membrane. Next, the obtained cut surface is observed using an SEM, TEM, or the like, and, if necessary, further observed using EDS, XPS, or FT-IR, and the distance from the front surface 20B to the back surface 20C of the porous substrate 20 is measured at four locations. Then, the average value of the distances at the four locations is calculated to be the thickness of the porous substrate.

[0030] The average pore size and porosity of the porous substrate 20 are not particularly limited as long as the porous substrate 20 has sufficient gas permeability. The average pore size (diameter) of the porous substrate may be, for example, 0.01 μm or more, 0.02 μm or more, 0.03 μm or more, or 0.05 μm or more, and may be 0.5 μm or less, 0.3 μm or less, or 0.1 μm or less. That is, the average pore size of the porous substrate is, for example, 0.01 to 0.3 μm, or even 0.02 to 0.1 μm. The porosity of the porous substrate 20 is preferably 40% or more and 80% or less.

[0031] The average pore diameter of a porous substrate can be measured and calculated as follows. Depending on whether the shape of the pores in the porous substrate is elongated or continuous, the surface or cross section of the porous substrate is observed using an SEM, TEM, or the like, and the maximum distance between any two points on the contour line of the pores (observation surface) of the porous substrate is measured. The average value of the pores observed in several to several tens of fields of view is then calculated to determine the average pore diameter.

[0032] The porosity of the porous substrate can be measured using a general immersion method.

[0033] The characteristics of the components of the gas separation membrane of this embodiment will be described below.

[0034] In the gas separation membrane of this embodiment, the O ２ The gas permeability is preferably 3000 GPU or more, more preferably 5000 GPU or more, even more preferably 6000 GPU or more, and even more preferably 6500 GPU or more. ２ Preferably, the permeability is 30,000 GPU or less, more preferably 10,000 GPU or less.

[0035] [Method for Producing Gas Separation Membrane] The method for producing a gas separation membrane of this embodiment includes the following coating step and drying step as steps for forming the gas separation membrane on one surface of a porous substrate.

[0036] (1) Coating Process The coating process is a process of applying a coating liquid to one surface 20B of the porous substrate 20. This coating process is characterized in that when applying the coating liquid to the porous substrate 20, the coating liquid is dripped onto the porous substrate 20. By using this method of dripping the coating liquid onto the porous substrate 20, a gas separation layer can be formed without pressurizing the coating liquid applied to the porous substrate 20.

[0037] (Coating Liquid) In the coating liquid, the above-mentioned polymer and, if necessary, the above-mentioned particles can be used as the gas separation layer material.

[0038] Furthermore, the solvent contained in the coating liquid is preferably an organic solvent. Examples of organic solvents that can be used include tetrahydrofuran (THF), 4-methyltetrahydropyran (MTHP), chloroform, dichloromethane, N-methyl-2-pyrrolidone, toluene, isopropyl alcohol, and tetralin. These can be used alone or in combination of two or more. For example, from the viewpoint of high solubility of PIM-1 and polyimide, the organic solvent used for PIM-1 and polyimide preferably contains tetrahydrofuran (THF), 4-methyltetrahydropyran (MTHP), or chloroform, more preferably tetrahydrofuran (THF) or 4-methyltetrahydropyran (MTHP), and even more preferably 4-methyltetrahydropyran (MTHP).

[0039] The content of the polymer in the coating liquid may be 0.1% by mass or more, or 0.3% by mass or more, based on 100% by mass of the total mass of the coating liquid. The upper limit of the content of the polymer is not particularly limited, but may be 20% by mass or less, or 10% by mass or less. That is, the content of the polymer in the coating liquid is, for example, 0.1 to 20% by mass, or even 0.3 to 10% by mass, based on 100% by mass of the total mass of the coating liquid. The content of the particles may be 1% by mass or more, or 10% by mass or more, based on 100% by mass of the total mass of the solid components of the coating liquid. The upper limit of the content of the particles may be 60% by mass or less, or 50% by mass or less. That is, the content of the particles in the coating liquid is, for example, 1 to 60% by mass, or even 10 to 50% by mass, based on 100% by mass of the total mass of the solid components of the coating liquid.

[0040] Further, the contact angle of the coating liquid with respect to the porous substrate is 50° or more. When the contact angle is in this range, the wettability of the coating liquid with respect to the porous substrate is suppressed, so that the coating liquid can be prevented from penetrating deeper into the porous substrate, and a decrease in the permeability of the gas separation membrane can be suppressed. Furthermore, the upper limit of the contact angle is not particularly limited, but is preferably 150° or less, more preferably 120° or less, and even more preferably 115° or less. In this specification, the contact angle is calculated by the θ / 2 method.

[0041] (Coating means) The coating means is a method of dropping a coating liquid onto the surface of a porous substrate. By adopting this method, the pressure applied to the coating liquid on the porous substrate can be reduced, and the coating liquid can be prevented from penetrating deeper into the porous substrate. The method of dropping the coating liquid to apply it is not particularly limited, but it is preferable to adopt an inkjet method.

[0042] In this specification, the inkjet method refers to a method in which fine droplets are ejected from the nozzles of an inkjet head to apply a coating to an object.

[0043] Furthermore, in the manufacturing method of this embodiment, the droplet diameter of the coating liquid when dropped is larger than the average pore diameter of the porous substrate. By setting the droplet diameter of the coating liquid to such a size, it is possible to prevent a large amount of the coating liquid from penetrating into the porous substrate. For example, the ratio of the droplet diameter to the average pore diameter of the porous substrate (droplet diameter:pore diameter) is preferably 1.1:1 to 500:1, more preferably 1.5:1 to 300:1. The droplet diameter is not particularly limited as long as it is larger than the average pore diameter of the porous substrate, but may be, for example, 1 μm to 1000 μm, 5 μm to 500 μm, 10 μm to 100 μm, or 15 μm to 50 μm.

[0044] (2) Drying Step The drying step is a step of removing the organic solvent from the coating liquid applied to the porous substrate 20 by drying, and forming the gas separation layer 10 on the surface 20B of the porous substrate 20 to obtain a gas separation membrane. In this drying step, the gas separation layer 10 (deposition portion) is formed on the surface 20B of the porous substrate 20. In this drying step, for example, drying may be performed in the air at 10°C or higher and 40°C or lower for 1 hour to 8 hours.

[0045] According to the method for producing a gas separation membrane of this embodiment, a coating liquid containing a polymer having gas separation properties and a solvent is dropped onto the surface of the porous substrate, thereby coating the components of the gas separation layer on the porous substrate. Unlike other coating methods, such as bar coating (a method using a bar coater) and gravure coating (a method using a gravure coater), this coating method allows the coating liquid to be applied to the surface of the porous substrate without applying excessive pressure, thereby suppressing penetration of the coating liquid into the porous substrate. In addition to the above, by controlling the wettability by setting the contact angle of the coating liquid with the porous substrate to 50° or more, and by making the droplet diameter when the coating liquid is dropped onto the porous substrate larger than the average pore diameter of the porous substrate, penetration of the coating liquid into the porous substrate can be further suppressed. In this way, by suppressing penetration of the components of the gas separation layer into the porous substrate, the film thickness of the gas separation layer is substantially suppressed from increasing, thereby improving gas permeability.

[0046] Furthermore, it is possible to prevent the coating liquid from penetrating into the porous substrate and causing defects in the gas separation layer deposited on the porous substrate, thereby ensuring good gas selectivity.

[0047] A gas separation membrane module using the above-described gas separation membrane can separate specific gas molecules from a gas mixture and increase or decrease the concentration of the specific gas molecules. Furthermore, the above-described gas separation membrane has good vehicle mountability, gas selectivity, and excellent gas permeability. Therefore, such a gas separation membrane module can be suitably used in, for example, a vehicle engine system or a vehicle air conditioning system.

[0048] [Vehicle Engine System] Nitrogen oxides (NOx) in the exhaust are generated by mixing nitrogen dioxide (N2) in the combustion air with the fuel.２ and O ２ and react at high temperatures to form O ２ By applying a gas separation membrane module to the intake system of a vehicle engine system, O ２ Reduce the concentration and ２ The fuel can be combusted using nitrogen-enriched air, which results in a reduction in O2 in the combustion zone. ２ The concentration is reduced, and NOx in the exhaust gas can be reduced.

[0049] 3 is an explanatory diagram schematically illustrating a main portion of a vehicle engine system equipped with a gas separation membrane according to one embodiment of the present invention. The vehicle engine system 50 includes a gas separation membrane module 52 provided in an intake flow path of an engine 51. The gas separation membrane module 52 includes the above-described gas separation membrane 1. As shown in FIG. 3, when air is supplied to the gas separation membrane module 52, the air is separated into nitrogen-enriched air and an oxygen-containing gas by the gas separation membrane 1. When this nitrogen-enriched air is supplied to the engine 51, it is possible to perform lean combustion of fuel (not shown) in the engine 51, thereby reducing NOx in the exhaust gas from the engine 51.

[0050] [Vehicle Air Conditioning System] The presence of a driver and passengers in the vehicle cabin increases the amount of O2 in the air inside the vehicle. ２ The concentration gradually decreases, and CO ２ Concentration and water vapor (H ２ By applying a gas separation membrane module to a vehicle air conditioning system, the O ２ Increase the concentration and CO ２ Concentration and water vapor (H ２ As a result, the air composition in the vehicle cabin can be appropriately modified with a simple configuration.

[0051] 4 is an explanatory diagram showing a schematic diagram of a main part of a vehicle air conditioning system equipped with a gas separation membrane according to one embodiment of the present invention. The vehicle air conditioning system 60 includes gas separation membrane modules 62 provided in ducts in a vehicle compartment 61. These gas separation membrane modules 62 include the above-described gas separation membrane 1. Inside air in the vehicle compartment 61 is circulated to one side of the gas separation membrane module 62 through a duct in the vehicle compartment 61, and outside air is taken in and exhausted to the other side of the gas separation membrane module 62 through another duct. As shown in FIG. 4, when inside air and outside air are supplied to the gas separation membrane module 62, O 2 is converted from the outside air into O 2 through the gas separation membrane 1. ２ is separated from the internal air and CO ２ and water vapor (H ２ O) is separated and the inner air O ２ Increase the concentration and CO ２ Concentration and water vapor (H ２ O) concentration can be reduced, and the air composition in the vehicle cabin can be kept constant with a simple configuration.

[0052] The above describes one embodiment of the gas separation membrane of the present invention, but the present invention is not limited to the configuration described in the above embodiment and can be modified as appropriate based on the claims.

[0053] The following items are also included within the scope of the present invention: Item 1: A method for producing a gas separation membrane, comprising a gas separation layer containing a polymer having gas separation performance, and a porous substrate, the method comprising: a coating step of dripping a coating liquid containing the polymer and a solvent onto the porous substrate; and a drying step of drying to remove the solvent from the dripped coating liquid, thereby forming a gas separation layer containing the polymer on the surface of the porous substrate, wherein the contact angle of the coating liquid with the porous substrate is 50° or more, and the droplet size when the coating liquid is dripped onto the porous substrate is larger than the average pore size of the porous substrate; Item 2: A method for producing a gas separation membrane according to Item 1, wherein the average pore size of the porous substrate is 0.1 μm or less; Item 3: A method for producing a gas separation membrane according to Item 1 or 2, wherein the solvent includes at least one of THF, MTHP, and chloroform (preferably THF and MTHP); Item 4: The method for producing a gas separation membrane according to any one of Items 1 to 3, wherein the gas separation layer further contains particles (preferably silica particles); Item 5: The method for producing a gas separation membrane according to any one of Items 1 to 4, wherein the polymer is PIM-1.

[0054] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. Unless otherwise specified, each example and comparative example was carried out under atmospheric pressure, at room temperature (25°C), and at a relative humidity of 50% RH.

[0055] <Example of gas separation membrane production> In the following, PIM-1 is a compound represented by the above formula (I), and in formula (I), R １ is a methyl group, R ２ is a cyano group, R ３ is a hydrogen atom. The weight average molecular weight (Mw) of PIM-1 is 3.1 × 10 ５ The weight average molecular weight (Mw) / number average molecular weight (Mn) is 5.4. The silica particles have an average particle size of 5 nm, and the surface modifying group is a vinyl group.

[0056] [Example 1] (Coating process) First, a porous substrate consisting of a porous layer and a nonwoven fabric layer (porous layer (gas separation membrane layer side): material: PTFE, thickness: 50 µm, average pore diameter: ≦0.1 µm, nonwoven fabric layer: material: PET, thickness: 100 µm) was prepared.

[0057] On the other hand, Coating Solution A (PIM-1 as a polymer (PIM-1: 80% by mass relative to the total solid components of the coating solution), silica particles as particles (silica particles: 20% by mass relative to the total solid components of the coating solution), MTHP:tetralin=25:75 (polymer concentration: 0.5% by mass) as an organic solvent) was prepared.

[0058] Then, the coating liquid A prepared above was applied to the surface of the porous layer side of the porous substrate prepared above using an inkjet device (head: PrecisionCore print head manufactured by EPSON Corporation, droplet size: 20 μm, dot pitch: 300 DPI).

[0059] (Drying step) Next, the coating solution was dried in a draft at room temperature (25°C) for 4 hours to remove the organic solvent from the coating solution applied to the porous substrate, forming a gas separation layer and obtaining the gas separation membrane of this example.

[0060] Comparative Example 1 The same operations as in Example 1 were repeated except that Coating Solution A was changed to Coating Solution B (PIM-1 as the polymer and THF (polymer concentration: 4% by mass) as the organic solvent) and the coating means was changed from a method using an inkjet device to a method using a bar coater, thereby obtaining a gas separation membrane of this example.

[0061] [Comparative Example 2] The method using a bar coater was replaced with a gravure coater (plate / number of lines: 100 L / inch, cell period: 42 μm, cell width: 220 μm, bank width: 21 μm, cell presence rate: 84%, coating liquid amount: 25 cm ３ / m ２ The gas separation membrane of this example was obtained by repeating the same procedure as in Comparative Example 1, except that the coating means was changed to a method using a cellulose acetate copolymer.

[0062] Comparative Example 3 The coating solution B was changed to coating solution C (PIM-1 as the polymer, silica particles as the particles (silica particles relative to the total solid component of the coating solution: 40% by mass), and MTHP as the organic solvent (polymer concentration: 4% by mass)), and in addition, a gravure coater (plate / number of lines: 200 L / inch, cell period: 127 μm, cell width: 113 μm, bank width: 14 μm, cell presence ratio: 89%, coating solution volume: 7.5 cm) was used as the coating means. ３ / m ２ The same procedure as in Comparative Example 2 was repeated except that 1,2-dimethyl-2,4-trimethyl-1 ...

[0063] <Measurement of Contact Angle of Coating Liquid> In accordance with the Japanese Industrial Standards (JIS R 3257 (1999)) for testing wettability of glass substrate surfaces, a coating liquid was dropped onto the surface of the porous layer, and the contact angle of the coating liquid with the porous layer was measured by the θ / 2 method. The results are shown in Table 1 below.

[0064] <Measurement of Gas Separation Layer Thickness> The "gas separation layer thickness" was measured and calculated as follows. First, the gas separation membrane was cut at an arbitrary position along the thickness direction of the gas separation composite membrane. Next, the obtained cut surface was observed with an SEM, and the distance from the portion where the components of the gas separation layer had permeated into the porous substrate to the outer surface of the gas separation layer was measured at four points using a photograph of the cross section. Then, the average value of the distances at the four points was calculated and used as the thickness of the gas separation layer. The results are shown in Table 1 below.

[0065] <O ２ Transparency > “O ２ The "permeability" was measured and calculated as follows. Specifically, the gas separation membrane was evaluated using a stainless steel gas separation membrane module 71 shown in Figures 5(A) to 5(D). More specifically, as shown in Figure 5(A), a sample 73 cut out from the gas separation membrane produced in the Examples and Comparative Examples was fixed between the gas supply side 75 and the permeation side 77 of the gas separation membrane module 71. Thereafter, as shown in Figure 5(A), an inlet 75A of the gas supply side 75 was closed, and an outlet 77A of the permeation side 77 was connected to a vacuum device and evacuated to create a vacuum inside the gas separation membrane module 71. Thereafter, as shown in Figure 5(B), a (predetermined amount) of gas (O２ 5C), after the gas supply, the inlet 75A and the outlet 77A are closed, and the state shown in FIG. 5D is reached, that is, the pressure difference with the permeation side 77 is eliminated. ２ The gas permeation rate and permeability (permeability coefficient) were calculated. At this time, the gas permeability coefficient was calculated as permeability (unit (GPU): 1 GPU = 3.35 × 10 －１０ mol・m －２ ・s －１ ・Pa －１ The results are shown in Table 1 below.

[0066] The pressure (or pressure difference) between the supply side and the permeation side was continuously measured by pressure gauges provided inside the supply side 75 and the permeation side 77. Furthermore, the internal pressure for determining a vacuum was set to 0.1 MPa (or less).

[0067] More specifically, using the following formulas (1) to (3), O ２ The permeation rate was calculated.

[0068] The pressure difference (dP / dt) on the permeation side over time is calculated by the following formula (1).

[0069]

[0070] Here, in equation (1), Pe represents the pressure (Pa) on the permeation side when the pressure difference between the supply side and the permeation side reaches 0 Pa, Ps represents the pressure (Pa) on the permeation side at the start of measurement, and t represents the time (s) required for the pressure difference between the supply side and the permeation side to reach 0 Pa after gas is supplied to the supply side.

[0071] The pressure difference over time (dP / dt (Pa·s)) calculated using the above formula (1) －１ )) to obtain the gas permeation rate (q (mol s －１ )) can be calculated by the following formula (2).

[0072]

[0073] Here, V in equation (2) is the permeation volume (L), and R is the molar gas constant (8.31 × 10 ３ Pa.L.K. －１ ・mol －１), and T indicates the absolute temperature (K) during the experiment. The temperature during the experiment was 25°C (298K).

[0074] The gas permeation rate (q (mol s)) obtained by the formula (2) －１ )) to obtain the permeability coefficient (P / δ(mol m －２ ・s －１ ・Pa －１ )) can be calculated by the following formula (3).

[0075]

[0076] Here, Ph in formula (3) represents the pressure (Pa) at the time of gas supply on the supply side, A represents the effective area of ​​the gas separation layer, and δ represents the thickness (μm) of the gas separation layer. ２ The permeability (unit: GPU) was calculated.

[0077]

[0078] As shown in Table 1, the gas separation membrane produced by the production method of the present invention is able to further improve gas permeability while maintaining good gas separation selectivity, since the components of the gas separation layer are prevented from permeating into the porous substrate. ２ More CO ２ In the gas separation membrane of JP 2023-125585 A, CO ２ The permeability of the gas separation membrane of the present invention is reported to be 69 GPU. ２ The permeability is the O 2 assumed for the gas separation membrane in the above publication. ２ It can be seen that the transmittance is improved by about 100 times.

[0079] DESCRIPTION OF SYMBOLS 1 Gas separation membrane, 10 Gas separation layer, 10A Surface, 20 Porous substrate, 20A Pore, 20B Surface, 20C Back surface, 50 Vehicle engine system, 51 Engine, 52 Gas separation membrane module, 60 Vehicle air conditioning system, 61 Vehicle compartment, 62 Gas separation membrane module, 71 Stainless steel gas separation membrane module, 73 Gas separation membrane sample, 75 Gas supply side, 75A Gas supply side inlet, 77 Gas permeation side, 77A Gas permeation side outlet

Claims

1. A method for producing a gas separation membrane comprising a gas separation layer containing a polymer having gas separation performance and a porous substrate, the method comprising: a coating step of dripping a coating liquid containing the polymer and a solvent onto the porous substrate; and a drying step of drying the solvent from the dripped coating liquid to form a gas separation layer containing the polymer on the surface of the porous substrate, wherein the contact angle of the coating liquid with the porous substrate is 50° or more, and the droplet size when the coating liquid is dripped onto the porous substrate is larger than the average pore size of the porous substrate.

2. The method for producing a gas separation membrane according to claim 1, wherein the average pore diameter of the porous substrate is 0.1 μm or less.

3. The method for producing a gas separation membrane according to claim 1 or 2, wherein the solvent comprises at least one of tetrahydrofuran, 4-methyltetrahydropyran, and chloroform.

4. The method for producing a gas separation membrane according to claim 1 or 2, wherein the gas separation layer further contains particles.

5. The method for producing a gas separation membrane according to claim 1 or 2, wherein the polymer comprises PIM-1.

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