Method for manufacturing gas separation membranes

Abstract

The present invention provides a method for manufacturing a gas separation membrane that can separate carbon dioxide and nitrogen, achieving both gas selectivity (separability) and permeability. [Solution] A method for manufacturing a gas separation membrane having a porous substrate and a separation function membrane, wherein a gas separation membrane coating liquid containing a gas-permeable polymer material and inorganic fine particles is applied to one side of a porous substrate and dried to form a separation function membrane, and the application and drying process is repeated alternately four or more times, wherein the proportion of inorganic fine particles in the coating liquid used in the first application and drying process is 70% by mass or more, the proportion of inorganic fine particles in the coating liquid decreases as the layers become higher, and the mass percentage of inorganic fine particles in the coating liquid used in at least the last application and drying process is 30% by mass or less.

Description

[Technical Field]

[0001] This invention relates to a method for producing a gas separation membrane. [Background technology]

[0002] Gas separation membranes that selectively and efficiently permeate only the target gas molecules are known, and attempts are being made to apply them to CCS (Carbon Capture Storage) technology, which separates and recovers carbon dioxide, considered a major cause of global warming, and stores it underground or on the seabed.

[0003] The gas separation membrane described above requires both gas selectivity (separation ability) and permeability, and these are in a trade-off relationship, making it difficult to achieve both at a high level.

[0004] Patent Document 1 describes that separation performance and permeability can be improved by making the surface roughness of the separation layer, which is made of an inorganic material such as zeolite, 10 μm or less. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-167149 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, the gas separation membrane described in Patent Document 1 separates propane and propylene, and does not separate carbon dioxide (CO2) and nitrogen (N2).

[0007] This invention has been made in view of the problems of the prior art, and its objective is to provide a method for manufacturing a gas separation membrane that can separate carbon dioxide (CO2) and nitrogen (N2) and achieve both gas selectivity (separability) and permeability. [Means for solving the problem]

[0008] The inventors of the present invention have conducted extensive research to achieve the above objectives and have discovered that the objectives can be achieved by using multiple coating solutions with different concentrations of inorganic fine particles and forming a separation-functional membrane under predetermined coating conditions when fabricating an organic-inorganic hybrid membrane (MMM: Mixed Matrix Membrane) type gas separation membrane. This has led to the completion of the present invention.

[0009] In other words, the present invention provides a method for manufacturing a gas separation membrane, which comprises a porous substrate and a separation function membrane. The process includes a coating and drying step in which a gas separation membrane coating solution containing a gas-permeable polymer material and inorganic fine particles is applied to one side of a porous substrate and dried to form a separation function membrane. The above coating and drying process is repeated alternately for four or more times. The mass %(x) of inorganic fine particles in the coating solution, represented by the following formula (1), The mass % (x1) of inorganic fine particles in the coating liquid used in the first coating and drying process is 70% by mass or more. Mass % of inorganic fine particles of coating solution used in the i-th coating and drying process (x i ) and the mass %(x) of inorganic fine particles of the coating solution used in the i+1th coating and drying process. i+1 The relationship with x i ≥x i+1 Satisfying the conditions, At least the mass %(x) of inorganic fine particles of the coating solution used in the final coating and drying step n ) is 30% by mass or less, and, In the coating and drying process described above, the coating liquid used in the coating and drying process has a concentration of inorganic fine particles of 30% by mass or less, and the total solid content concentration (by mass) of the polymer material and inorganic fine particles combined in the coating liquid, accumulated over the number of times the coating and drying process is performed, is characterized in that the total solid content by mass %·times is 5%·times or more. x=m particle / (m polymer+m particle )×100 Formula (1) However, in Formula (1), m polymer represents the mass of the polymer, and m particle represents the mass of the particles.

Advantages of the Invention

[0010] According to the present invention, a plurality of coating liquids with different concentrations of inorganic fine particles are used to form a separation functional membrane under predetermined coating conditions to produce an organic-inorganic hybrid type gas separation membrane. Therefore, a thin and less defective separation functional membrane can be formed, and a method for manufacturing a gas separation membrane capable of producing a gas separation membrane that can achieve both gas permeability and selectivity can be provided.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic diagram of the gas separation membrane. [Figure 2] It is a cross-sectional SEM image of the separation functional membrane. [Figure 3] It is a surface SEM image of the separation functional membrane.

Embodiments for Carrying Out the Invention

[0012] The method for manufacturing the gas separation membrane of the present invention will be described in detail. This method for manufacturing the gas separation membrane is a method for manufacturing an organic-inorganic hybrid membrane (MMM) type gas separation membrane that combines a polymer material and inorganic fine particles. The above gas separation membrane ensures the strength to withstand the pressure difference between its upstream side and downstream side by supporting a separation functional membrane containing the above polymer material and the above inorganic fine particles on a porous substrate having pores communicating in the thickness direction.

[0013] The polymer material used in the above separation functional membrane has a rigid ladder-type structure or a bent skeleton, and has a large free volume in which fine pores are formed inside, and is a material having gas permeability and gas separation property.

[0014] By combining this polymer material with inorganic fine particles, it is possible to improve gas permeability not only because of the gas permeability of the polymer material itself, but also because gas permeates through the interface between the polymer material and the inorganic fine particles, and between the aggregated inorganic fine particles.

[0015] However, while the aggregated inorganic microparticles described above have high gas permeability, they may have low gas separation properties. In addition, when aggregated particles are exposed to the membrane surface, the inorganic microparticles that are not enclosed in the polymer material cannot maintain their aggregated state, and cracks may form between the particles. Due to these effects, if the aggregated inorganic microparticles are connected throughout the entire thickness, the gas separation properties will decrease.

[0016] Furthermore, because the porous substrate has large surface irregularities due to its pores, it is difficult to form a thin separation-functional membrane using polymer materials alone, resulting in defects where the membrane is interrupted and reducing gas separation performance.

[0017] The present invention provides a method for producing a gas separation membrane, comprising a step of forming a separation membrane by stacking multiple coating layers, which involves applying a gas separation membrane coating solution containing a gas-permeable polymer material and inorganic fine particles to a porous substrate and drying it to form a thin coating layer.

[0018] In the above separation function membrane formation process, first, a gas separation membrane coating solution with a high concentration of inorganic fine particles is pressed onto a porous substrate and dried. The aggregated inorganic fine particles in the resulting coating film fill the pores of the porous substrate, forming a base layer with reduced surface irregularities. This makes it possible to laminate a uniform coating layer in the in-plane direction on top of the base layer.

[0019] Then, a coating solution with a high concentration of polymer material and a low concentration of inorganic fine particles is applied and dried onto the formed base layer to form a coating layer, and this coating layer with a high concentration of polymer material forms the surface layer of the separation function membrane.

[0020] According to the gas separation membrane manufacturing method of the present invention, as shown in Figure 1, aggregated inorganic fine particles and defects do not connect throughout the entire thickness direction, and polymer material is always present at some point in the thickness direction.

[0021] Therefore, it is possible to form a thin, defect-free gas separation membrane, achieving both gas separation and permeability.

[0022] Specifically, the process involves applying a gas separation membrane coating solution containing a gas-permeable polymer material and inorganic fine particles to one side of a porous substrate, drying the solution, and forming a separation function membrane. The application and drying process is repeated alternately for four or more times. As a result, it is not necessary to form a separation function film of sufficient thickness in a single coating, allowing the use of a coating solution with a low solid content concentration and low viscosity, making it possible to form a homogeneous separation function film and suppressing in-plane directional variations.

[0023] Furthermore, even if a defect occurs in a certain layer of the laminated coating layer formed by performing the above coating and drying process multiple times, that defect will be covered by the coating layer above or below it, thus preventing the defect from spreading in the thickness direction.

[0024] The coating solution used in the first coating and drying process has a concentration of inorganic fine particles of 70% by mass or more. In a coating solution containing inorganic fine particles at a concentration of 70% by mass or more, the inorganic fine particles tend to aggregate and become coarser, making it difficult for them to penetrate deep into the pores of the porous substrate. The coating layer formed with this solution can fill the pores of the porous substrate, form a base layer, and smooth the surface of the porous substrate.

[0025] And the mass %(x) of inorganic fine particles of the coating liquid used in the i-th coating and drying step. i ) and the mass %(x) of inorganic fine particles of the coating solution used in the subsequent i+1th coating and drying step. i+1 The relationship with x i ≥x i+1 It satisfies the condition.

[0026] The polymer material described above not only separates gases but also acts as a binder. Coating layers formed with coating solutions that have a high concentration of inorganic fine particles are prone to large defects due to the polymer material being interrupted.

[0027] As described above, by forming a base layer with a high concentration of inorganic fine particles on the lower side and a coating layer with a high concentration of polymer material on the surface side, the aggregated inorganic fine particles fill the pores of the porous substrate, forming a base layer and smoothing it. At the same time, a coating layer with a large proportion of polymer material suppressing the occurrence of defects can be laminated to form a separation function membrane, thereby preventing the occurrence of defects in the separation function membrane as a whole.

[0028] Furthermore, a coating solution containing inorganic fine particles at a mass percentage of 30% or less is used at least in the final coating and drying step.

[0029] Furthermore, for coating processes among multiple coating and drying steps, where a coating solution with a high concentration of polymer material and a concentration of inorganic fine particles is 30% by mass or less is used, the sum of the solid content concentrations (S) of coating solutions with a high concentration of polymer material, calculated by accumulating the combined solid content (mass%) of the polymer material and inorganic fine particles in the coating solution used in those coating processes for each coating step, is 5% by mass·times or more.

[0030] Since both the coating solution used for the first application and the coating solution used for the second application contain a solvent that dissolves polymer materials, the solvent in the second application redissolves the first application layer, causing inorganic particles to migrate from the lower coating layer, which has a larger proportion of inorganic particles, to the upper coating layer, which has a smaller proportion of inorganic particles.

[0031] Therefore, even if the surface of the separation function membrane is formed with a coating layer that has a high proportion of polymer material to improve gas separation performance, aggregates of inorganic fine particles may be exposed on the surface of the separation function membrane, which can reduce gas separation performance.

[0032] In the multiple coating and drying processes, if the sum of the solid content concentrations (S) of the coating solutions with a high concentration of the polymer material is 5% by mass or more, it is possible to prevent the exposure of aggregates of inorganic fine particles on the surface of the separation function membrane and the occurrence of defects such as interruptions in the coating layer on the surface side of the separation function membrane.

[0033] Furthermore, the sum of the solid content concentrations (S) for the coating and drying process using a coating solution in which the mass % of inorganic fine particles is 30% by mass or less is 7% by mass· times or more, and the mass % of inorganic fine particles in the coating solution used in the final coating and drying process is x n By having a concentration of 15% by mass or more and 25% by mass or less, gas selectivity can be improved without impairing gas permeability.

[0034] In other words, since aggregated inorganic fine particles have low gas selectivity, if the mass percentage of inorganic fine particles in the coating solution used in the final coating and drying step is 25% by mass or less, the outermost layer will be formed with a coating solution that has a high concentration of polymer material, and the gas that permeates the gas separation membrane will permeate more frequently through the parts with high gas selectivity.

[0035] Furthermore, by ensuring that the mass percentage of inorganic fine particles in the coating solution used in the final coating and drying step is 15% by mass or more, the inorganic fine particles do not shrink. This reduces the risk of defects occurring due to the shrinkage of polymer materials during drying, which can cause the coating layer to break and become gas-inselective, thus improving gas selectivity.

[0036] In this invention, the particle mass %(x) of the coating solution is the proportion of inorganic fine particles to the solid content of the coating solution, and is expressed by the following formula (1). x=m particle / (m polymer +m particle )×100 Formula (1) However, in equation (1), m polymer m is the mass of the polymer. particle This represents the mass of the particle.

[0037] The above-mentioned polymer materials can be those with a molecular structure that has micropores and a large free volume that allows gas to permeate. Examples include polymers of intrinsic microporosity (PIM), polydimethylsiloxane (PDMS), and polyimide (PI). Among these, "PIM" is preferred, and in particular, "PIM-1" obtained by reacting 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindan with tetrafluoroterephthalonitrile is preferred.

[0038] As the inorganic fine particles mentioned above, particles of metal oxides such as silica and alumina with an average primary particle size of 5 to 20 nm can be used. In particular, inorganic fine particles whose surfaces are modified with a silane coupling agent form gas permeability pathways at the interface with the polymer material, improving gas permeability and dispersibility in the solvent and the polymer material. As a result, even in environments with high concentrations of inorganic fine particles, aggregated secondary particles do not coarseen, and defects in the coating film can be suppressed.

[0039] The silane coupling agent used, depending on the polymer material, is represented by the following structural formula (1). This allows for the formation of carbon dioxide permeation pathways at the particle interface and the interface with the polymer material, thereby improving the separation of carbon dioxide (CO2) and nitrogen (N2). In addition, the silane coupling agent represented by the following structural formula (1) has the effect of reducing the surface energy of metal oxide fine particles. This can suppress excessive aggregation of particles in the coating solution and the separation function film.

[0040] [ka] However, in structural formula (1), R represents a methyl group or an ethyl group.

[0041] The average pore size of the porous substrate is preferably between 50 nm and 1 μm. Within this range, aggregates of inorganic fine particles can smooth the surface irregularities caused by the pores in the porous substrate, allowing for a thinner separation membrane and improved gas permeability.

[0042] Examples of resins that make up the porous substrate mentioned above include polytetrafluoroethylene (PTFE), polyethylene (PE), and polypropylene (PP).

[0043] The solvent used in the above coating solution can be an organic solvent that dissolves the polymer material, and examples include aromatic hydrocarbons such as toluene, xylene, mesitylene, cumene, and p-cymene; aliphatic hydrocarbons such as hexane and heptane; cyclic alkanes such as methylcyclohexane; cyclic ethers such as tetrahydrofuran, 4-methyltetrahydropyran, and 1,4-dioxane; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and 4-hydroxy-4-methyl-2-pentanone; esters such as methyl acetate, ethyl acetate, butyl acetate, methyl lactate, ethyl lactate, and γ-butyrolactone; carbonate esters such as ethylene carbonate and propylene carbonate; amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone (NMP); halogenated solvents such as chloroform, dichloromethane, chlorobenzene, dichlorobenzene, and tetrabromoethane.

[0044] The solid content concentration of the polymer material and particles combined in the above coating solution is preferably 1 to 10% by mass. A solid content concentration of 10% by mass or less suppresses the increase in viscosity of the coating solution, allowing for the formation of a uniform coating film with a low-viscosity coating solution.

[0045] The thickness of the above-mentioned separation membrane is preferably 1 to 3 μm. Having a thickness within this range suppresses the occurrence of defects and allows for a balance between gas separation and gas permeability.

[0046] Examples of known coating methods for coating liquids include bar coating, spray coating, roll coating, spin coating, gravure coating, die coating, knife coating, roll knife coating, blade coating, and kiss coating. [Examples]

[0047] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples.

[0048] Surface-modified silica nanoparticles, in which a modification group was provided on the surface of a silica nanoparticle nucleus with a particle size of 10 nm using a silane coupling agent (vinyltrimethoxysilane), and PIM-1 were added to THF solvent and stirred and mixed for 18 hours to prepare coating solution 1 and coating solution 2 shown in Tables 1 and 2 below.

[0049] Note that in Table 1, The mass percentage of PIM-1 is expressed as a mass percentage relative to the mass of the solvent. The particle mass percentage is the mass percentage of the particle relative to the total mass including PIM-1.

[0050] Next, a composite substrate (300mm x 300mm) made of a porous polytetrafluoroethylene (PTFE) substrate with a thickness of 50μm, a pore size of 100nm, and a void ratio of 50-60%, reinforced by bonding a PET nonwoven fabric to it, was placed on a multi-coater (Matsuo Sangyo Co., Ltd. "K404 (product number)"). 1.5mL of the above coating solution was measured out, and the coating pressure (pressure) was 0.19 Pa / m². 2 The coating film was formed by applying and drying the material onto a porous substrate at a coating speed of 3 m / min. Test specimens of gas separation membranes were prepared by repeatedly performing the above coating and drying process under the conditions shown in Table 1.

[0051] Figure 2 shows a cross-sectional SEM image of specimen 17. Figure 2 shows that there are few aggregated inorganic particles on the surface side, and that a smooth separation function membrane is formed.

[0052] Furthermore, Figure 3 shows a surface SEM image of a separation functional film in which a surface layer was formed using a coating solution with a different concentration of inorganic fine particles on a substrate layer formed with a coating solution with a concentration of 80% by mass of inorganic fine particles. Figure 3 shows that as the concentration of inorganic fine particles in the coating solution forming the surface layer increases, the aggregates of inorganic fine particles, which appear white in the image, increase on the surface of the separation function membrane.

[0053] <Rating> (Evaluation of gas permeability and gas separation properties) After creating a vacuum atmosphere on one side and the other side of the test specimen, the gas was allowed to permeate from one side to the other side of the specimen under a carbon dioxide or nitrogen atmosphere. The rate of pressure rise in the pressure vessel installed on the other side was measured to calculate the gas permeation rate (permeation amount), thereby determining the gas permeability (permeability). Additionally, the ratio of the carbon dioxide permeability to the nitrogen gas permeability was calculated to determine the gas selectivity, and the separation performance was evaluated according to the following criteria. The evaluation results are shown in Tables 1 and 2. (CO2 transmittance) ◎: ≥14000 GPU ○: 12000 GPU ≤ ○ < 14000 GPU △: 10000 GPU ≤ △ < 12000 GPU ×: <10000 GPU (CO2 / N2 selectivity) ◎:≧10 〇:7≦〇<10 △: 5.5 ≤ ○ < 7 ×:<5.5 (Separation performance evaluation) (Transmittance, Selectivity) ◎:(◎,◎) ○: If the rating is anything other than × and anything other than △, and at least one rating is ○. △: If any of the ratings are not ×, and at least one △ is given. ×: If even one × is marked

[0054] [Table 1]

[0055] [Table 2]

[0056] From test specimens 36 and 37, it can be seen that the primer coating liquid that forms the base layer requires an inorganic fine particle concentration of 70% by mass or more. Furthermore, from test specimens 6, 7, 13, 15-17, 41, 42, and 44-47, it can be seen that the topcoat liquid forming the surface layer must have a concentration of inorganic fine particles of 30% by mass or less, and from test specimens 14 and 43, it can be seen that the sum of the solid content concentrations (S) of the coating liquid with a high concentration of polymer material must be 5% by mass or more.

[0057] Furthermore, from test specimens 15 and 17, it can be seen that both CO2 / N2 selectivity and CO2 permeability can be achieved when the sum of the solid content concentrations (S) of the coating solution with a high concentration of polymer material is 7% by mass or more, and the concentration of inorganic fine particles in the coating solution used in the final coating and drying step is 15% by mass or more and 25% by mass or less. [Explanation of symbols]

[0058] 1 Separation functional membrane 11. Primer 12 Surface layer 2 Polymer materials 3a Agglomerated inorganic fine particles (coarse) 3b Agglomerated inorganic fine particles (small diameter) 4. Defects 5 Porous base material

Claims

1. A method for manufacturing a gas separation membrane having a porous substrate and a separation function membrane, The process includes a coating and drying step in which a gas separation membrane coating solution containing a gas-permeable polymer material and inorganic fine particles is applied to one side of a porous substrate and dried to form a separation function membrane. The above coating and drying process is repeated alternately for four or more times. The mass % (x) of inorganic fine particles in the coating solution, represented by the following formula (1), Mass % of inorganic fine particles in the coating solution used in the first coating and drying process (x １ ) is 70% by mass or more, Mass % of inorganic fine particles in the coating solution used in the i-th coating and drying step (x ｉ ) and the mass % (x) of inorganic fine particles of the coating solution used in the i+1th coating and drying process. ｉ＋１ The relationship with x ｉ ≥ x ｉ＋１ Satisfying the conditions, At least the mass % (x) of inorganic fine particles of the coating solution used in the final coating and drying step. ｎ ) is 30% by mass or less, and, A method for producing a gas separation membrane, characterized in that, for the coating liquid used in the coating and drying step of the above-mentioned coating and drying step, in which the concentration of inorganic fine particles is 30% by mass or less, the sum of the solid content concentrations (S) of coating liquids with a high concentration of polymer material, calculated by accumulating the solid content concentration (by mass) of the polymer material and inorganic fine particles combined in the coating liquid for the number of times the above-mentioned coating and drying step is performed, is 5% by mass or more. x = m ｐａｒｔｉｃｌｅ / (m) ｐｏｌｙｍｅｒ +m ｐａｒｔｉｃｌｅ Formula (1) × 100 However, in formula (1), m ｐｏｌｙｍｅｒ m is the mass of the polymer. ｐａｒｔｉｃｌｅ This represents the mass of the particle.

2. Of the above coating and drying steps, the mass % (x) of inorganic fine particles in the coating liquid. ｉ The sum of the above solid content concentrations (S) for the coating and drying steps after the coating and drying step in which the amount is 30% by mass or less is 7% by mass or more. and Mass % (x) of inorganic fine particles in the coating solution used in the final coating and drying step ｎ The method for producing a gas separation membrane according to claim 1, characterized in that the amount of ) is 15% by mass or more and 25% by mass or less.

3. The method for producing a gas separation membrane according to claim 1, characterized in that the polymer material is at least one selected from the group consisting of intrinsically porous polymers (PIM), polydimethylsiloxane (PDMS), and polyimide (PI).

4. The method for producing a gas separation membrane according to claim 1, characterized in that the inorganic fine particles are silica particles whose surface is modified with a silane coupling agent represented by the following structural formula (1). 【Chemistry 2】 However, in structural formula (1), R represents a methyl group or an ethyl group.

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