Gas separation membrane

Abstract

To provide a manufacturing method for a gas separation membrane which exhibits satisfactory carbon dioxide membrane permeation rate and carbon dioxide selectivity when separating carbon dioxide from a gas mixture containing water vapor and has robustness (repeated pressure load durability), and to provide the gas separation membrane.SOLUTION: Provided is a manufacturing method for a gas separation membrane, including steps of applying a resin composition on a support membrane, drying the applied resin composition, and thermally cross-linking the dried resin composition, wherein the step of thermally cross-linking is performed under a moist heat condition of a temperature of 60 to 95°C and a relative humidity of 40 to 90% RH. The gas separation membrane is also provided.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing a gas separation membrane for separating carbon dioxide from a mixed gas, and to the gas separation membrane.

Background Art

[0002] From the viewpoints of preventing global warming and efficiently recovering fossil resources, gas separation membranes have been intensively studied as one of the technologies for separating carbon dioxide from mixed gases.

[0003] In selectively separating carbon dioxide from a mixed gas, it is an issue to enhance its selectivity (carbon dioxide selectivity) and recover high-concentration carbon dioxide. In order to obtain a separation membrane excellent in carbon dioxide selectivity, it has been proposed to use a material having a high affinity for carbon dioxide. For example, a separation membrane used at room temperature (Non-Patent Documents 1 and 2) in which a porous support is impregnated with a polyamideamine dendrimer which is a liquid substance has been proposed.

[0004] The present inventors have previously proposed a gas separation membrane in which a layer containing a polymer material having an amino group and / or a hydroxyl group crosslinked with a crosslinking agent and a polyamideamine-based dendrimer is formed on the surface of a porous support membrane (Patent Document 1).

[0005] Also, the present inventors have previously proposed a gas separation membrane formed from a composition containing a crosslinkable vinyl alcohol-based polymer and a zinc complex in which an amine is coordinated (Patent Document 2).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0007] [Non-Patent Document 1] J.Am.Chem.Soc.122(2000)7594-7595 [Non-Patent Document 2] Ind.Eng.Chem.Res.40(2001)2502-2511 [Summary of the Invention] [Problems to be Solved by the Invention]

[0008] In recent years, in the gas separation membrane for integrated gasification combined cycle (IGCC) applications that has been under study, it has been required to efficiently and selectively separate carbon dioxide from a mixed gas containing steam under high pressure.

[0009] The carbon dioxide membrane permeation rate of the separation membranes described in Non-Patent Documents 1 and 2 is low. However, the carbon dioxide selectivity shown as the carbon dioxide membrane permeation rate relative to the nitrogen membrane permeation rate shows excellent values under the condition of supplying the mixed gas to the separation membrane without pressurization. However, when the mixed gas is pressurized and supplied to the separation membrane, there has been a problem that the polyamidoamine dendrimer flows out from the support over time and the carbon dioxide selectivity cannot be maintained.

[0010] The separation membrane described in Patent Document 1 shows a high carbon dioxide membrane permeation rate and excellent carbon dioxide selectivity. However, when it is used to separate carbon dioxide from a mixed gas containing steam under high pressure, the amine compound contained in the separation membrane flows out over time, and the carbon dioxide selectivity cannot be maintained, making it difficult to put into practical use.

[0011] The separation membrane described in Patent Document 2 has carbon dioxide selectivity even in an environment containing steam. However, when the pressure of the mixed gas is increased, there is a possibility that the carbon dioxide membrane permeation rate and the carbon dioxide selectivity may decrease.

[0012] From the perspective of providing a separation membrane for practical use, it is desirable to develop a separation membrane that exhibits good carbon dioxide membrane permeation rate and carbon dioxide selectivity even under higher pressures and in an environment containing water vapor, and has robustness (repeated pressure load durability) that can withstand long-term use.

[0013] The present invention solves the above-mentioned conventional problems, and its object is to separate carbon dioxide from a mixed gas containing water vapor under high pressure, showing good carbon dioxide membrane permeation rate and carbon dioxide selectivity, and to provide a manufacturing method of a gas separation membrane having robustness (repeated pressure load durability), and to provide the gas separation membrane.

Means for Solving the Problems

[0014] In a first aspect, the present invention provides a step of applying a resin composition on a support membrane; a step of drying the applied resin composition; and a step of thermally crosslinking the dried resin composition to provide a method for manufacturing a gas separation membrane, wherein the step of thermally crosslinking is carried out under wet heat conditions of a temperature of 60 to 95 °C and a relative humidity of 40 to 90% RH. The method for manufacturing a gas separation membrane is provided.

[0015] In one form, the resin composition contains a non-crosslinked vinyl alcohol copolymer (A) having a carboxyl group and a hydrophilic crosslinkable compound (B).

[0016] In one form, the non-crosslinked vinyl alcohol copolymer (A) having a carboxyl group contains acrylic acid or methacrylic acid monomer units and vinyl alcohol-based monomer units.

[0017] In one embodiment, the hydrophilic crosslinkable compound (B) has at least one structural unit selected from the group consisting of polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinyl pyrrolidone, polyacrylamide, polyamide amine dendrimer, polyethyleneimine, polyallylamine, and polyvinylamine.

[0018] In one embodiment, the resin composition further includes an alkali metal compound (C).

[0019] In one embodiment, the alkali metal compound (C) is selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal bicarbonates.

[0020] In one embodiment, the resin composition

[0021]

Chemical formula

[0022]

Chemical formula

[0023]

Chemical formula

[0024]

Chemical formula

[0025] Moreover, the present invention provides, in a second aspect, a gas separation membrane produced by the above method.

[0026] In one embodiment, in the water vapor adsorption test at a temperature of 60 ° C, the amount of water vapor adsorbed in the range of relative pressure of 0.5 to 0.9 is 150 to 900 cm 3 (STP) / g, and the tensile modulus of elasticity under the measurement conditions of a temperature of 25 ° C and a relative humidity of 60% RH is 5 to 7 N / mm 2 .

[0027] In one embodiment, the gas separation membrane is for separating carbon dioxide. [Effect of the Invention]

[0028] According to the present invention, there are provided a method for producing a gas separation membrane that exhibits good carbon dioxide membrane permeation rate and carbon dioxide selectivity and has robustness (repeated pressure load durability) when separating carbon dioxide from a mixed gas containing water vapor under high pressure, and the gas separation membrane. [Brief Description of the Drawings]

[0029]

Figure 1

Figure 2

[0030] The method for producing a gas separation membrane of the present invention includes a step of applying a resin composition onto a support membrane; a step of drying the applied resin composition; and a step of thermally crosslinking the dried resin composition . Hereinafter, it will be described in order.

[0031] (Steps 1 and 2) In the first and second steps of the method for producing a gas separation membrane of the present invention, a resin composition is applied onto a support membrane, and the applied resin composition is dried. The resin composition contains a non-crosslinked vinyl alcohol copolymer (A) having a carboxyl group and a hydrophilic crosslinkable compound (B).

[0032] <Non-crosslinked vinyl alcohol copolymer (A) having a carboxyl group> The non-crosslinked vinyl alcohol copolymer (A) having a carboxyl group (hereinafter sometimes simply referred to as "copolymer (A)") constitutes the polymer matrix of the gas separation membrane of the present invention.

[0033] Copolymer (A) is a non-crosslinked (not crosslinked) copolymer composed of a monomer unit having a carboxyl group and a vinyl alcohol-based monomer unit. Examples of the monomer unit having a carboxyl group include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, α-chloroacrylic acid, and cinnamic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid, and mesaconic acid; and metal salts thereof, such as alkali metal salts; esters, such as methyl ester or ethyl ester; and anhydrides, such as maleic anhydride, itaconic anhydride, and citraconic anhydride. The monomer unit having a carboxyl group constituting copolymer (A) may be selected from only one of the above-exemplified ones or two or more kinds may be selected. However, from the viewpoints of the affinity and water retention of the gas separation membrane for a mixed gas containing water vapor, as the monomer unit having a carboxyl group, acrylic acid, methacrylic acid, crotonic acid, and itaconic acid, and their alkali metal salts, methyl esters, or ethyl esters are preferable, and among them, acrylic acid, methacrylic acid, and their alkali metal salts, methyl esters, or ethyl esters are more preferable.

[0034] Examples of the vinyl alcohol-based monomer unit constituting copolymer (A) include vinyl alcohol; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl caproate. The vinyl alcohol-based monomer unit constituting copolymer (A) may be selected from only one of the above-exemplified ones or two or more kinds may be selected.

[0035] The copolymer (A) can be in the form of a random copolymer, block copolymer, or graft copolymer of monomer units having a carboxyl group and vinyl alcohol-based monomer units.

[0036] When the copolymer (A) is a random copolymer, the copolymer (A) can be produced by copolymerizing an unsaturated carboxylic acid having a carboxyl group, its salts, esters, or anhydrides with a vinyl ester and saponifying. When the copolymer (A) is a block copolymer, the copolymer (A) can be produced, for example, by polymerizing an unsaturated carboxylic acid having a carboxyl group such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, or maleic acid, or its acid anhydride in an aqueous solution of a vinyl alcohol-based polymer having a mercapto group at the terminal (see, for example, JP-A-59-187003 and JP-A-2001-233678). When the copolymer (A) is a graft copolymer, the copolymer (A) can be produced by adding 2,2'-azobisisobutyronitrile (AIBN) to a methanol solution of vinyl acetate and S-7-octen-1-yl thioacetate and polymerizing to obtain a copolymer of vinyl acetate and a thioester-based monomer, then saponifying this copolymer to produce a vinyl alcohol-based polymer having a mercapto group in the side chain, and polymerizing a monomer having a carboxyl group in the presence of a polymerization catalyst. In the gas separation membrane of the present invention, the copolymer (A) is preferably a block or graft copolymer from the viewpoint of obtaining a gas separation membrane showing good carbon dioxide membrane permeation rate and carbon dioxide selectivity under high pressure.

[0037] The content of the copolymer (A) contained in the resin composition constituting the gas separation membrane of the present invention is preferably 1 to 40 wt%, more preferably 2 to 30 wt%, and still more preferably 3 to 20 wt% based on the total weight of the resin composition. When the content of the copolymer (A) is less than 1 wt% based on the total weight of the resin composition, the affinity and water retention of the separation membrane for the mixed gas containing water vapor and the solubility of the alkali metal compound (C) described later decrease. When the content of the copolymer (A) exceeds 40 wt% based on the total weight of the resin composition, the film-forming property of the resin composition decreases.

[0038] From the viewpoints of the solubility of the alkali metal compound (C) and the affinity and water retention of the separation membrane for the mixed gas containing water vapor, the content of the monomer unit having a carboxyl group in the copolymer (A) is preferably 0.1 to 90 mol%, more preferably 0.5 to 80 mol%, still more preferably 1 to 70 mol%, particularly preferably 5 to 60 mol%, and most preferably 10 to 50 mol% based on all the monomer units constituting the copolymer (A). When the content of the monomer unit having a carboxyl group is less than 0.1 mol%, the solubility of the alkali metal compound (C) and the affinity and water retention of the separation membrane for the mixed gas containing water vapor decrease. When the content of the monomer unit having a carboxyl group exceeds 90 mol%, the film-forming property of the resin composition decreases, which is not preferable. The content of the vinyl alcohol-based monomer unit in the copolymer (A) can be appropriately adjusted according to the content of the monomer unit having a carboxyl group.

[0039] The saponification degree of the vinyl alcohol-based monomer unit portion in the copolymer (A) is preferably 90 to 99.9 mol%, more preferably 92 to 99.9 mol%, and still more preferably 95 to 99.9 mol%. When the saponification degree of the vinyl alcohol-based monomer unit portion in the copolymer (A) is less than 90 mol%, the affinity and water retention of the separation membrane for the mixed gas containing water vapor and the solubility of the alkali metal compound (C) decrease, and the carbon dioxide membrane permeation rate decreases. When the saponification degree of the vinyl alcohol-based monomer unit portion exceeds 99.9 mol%, the viscosity stability of the resin composition becomes poor, and the processability and film-forming property are inferior. In this specification, the "saponification degree" refers to the ratio of the number of moles of the vinyl alcohol monomer unit to the total number of moles of all vinyl alcohol-based monomer units, that is, monomer units (typically vinyl ester units) that can be converted to vinyl alcohol units by saponification and vinyl alcohol units. The saponification degree can be measured in accordance with the description in JIS K6726-1994.

[0040] The viscosity average degree of polymerization of the vinyl alcohol-based monomer unit portion in the copolymer (A) (hereinafter sometimes simply referred to as "degree of polymerization (P)") is preferably 300 to 2500. When the degree of polymerization (P) is less than 300, the mechanical strength of the gas separation membrane decreases. When the degree of polymerization (P) exceeds 2500, the viscosity of the resin composition is too high, and the processability and film-forming property decrease. The degree of polymerization (P) is more preferably 330 to 2200, and still more preferably 360 to 2000. The degree of polymerization (P) can be measured in accordance with JIS-K6726. That is, after saponifying and purifying the vinyl alcohol-based monomer unit portion, it is obtained from the intrinsic viscosity [η] measured in water at a temperature of 30°C by the following formula.

[0041]

Number

[0042] The copolymer (A) may contain other monomer units in addition to the monomer units having a carboxyl group and vinyl alcohol-based monomer units described above, as long as the effects of the present invention are not impaired. Examples of the monomer that forms the other monomer units include ethylene; acrylamide derivatives such as acrylamide and N-ethylacrylamide; methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, and N-ethylmethacrylamide; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, and i-propyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; and allyl compounds such as allyl acetate and allyl chloride. The content of the other monomer units is preferably 1 to 10 mol%, more preferably 2 to 5 mol%, based on all the monomer units constituting the copolymer (A).

[0043] The copolymer (A) is non-crosslinked (not crosslinked) from the viewpoint of exhibiting good carbon dioxide film permeation rate and carbon dioxide selectivity. The carboxyl groups in the monomer unit portion having a carboxyl group in the copolymer (A) interact ionically with the alkali metal compound (C) that functions as a carbon dioxide carrier in the separation membrane. Therefore, when crosslinked, the diffusibility of the alkali metal compound (C) decreases and the carbon dioxide film permeation rate decreases. Here, the fact that the copolymer (A) is "non-crosslinked (not crosslinked)" means that the hydroxyl group and / or carboxyl group of the copolymer (A) does not substantially have a covalent bond with a crosslinking agent. Although details will be described later, for example, when a crosslinking agent having an epoxy group is used to crosslink the resin composition, and a group (e.g., amino group) more reactive than the hydroxyl group and carboxyl group of the copolymer (A) is present in the system, the crosslinking agent reacts preferentially with that group. Therefore, the hydroxyl group and / or carboxyl group of the copolymer (A) can react slightly, but is not substantially crosslinked.

[0044] <Hydrophilic crosslinkable compound (B)> The hydrophilic crosslinkable compound (B) contained in the resin composition constitutes the polymer matrix of the gas separation membrane together with the copolymer (A). By including the hydrophilic crosslinkable compound (B) in the separation membrane, the affinity and water retention of the separation membrane for the mixed gas containing water vapor are improved, and the diffusibility of the alkali metal compound (C) in the separation membrane is also improved. Therefore, the carbon dioxide membrane permeation rate can be improved.

[0045] The hydrophilic crosslinkable compound (B) is a compound having at least one structural unit selected from the group consisting of, for example, polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinyl pyrrolidone, polyacrylamide, polyamideamine dendrimer, polyethyleneimine, polyallylamine, and polyvinylamine. The hydrophilic crosslinkable compound (B) is not particularly limited as long as it can achieve the object of the present invention. However, among the above-exemplified ones, from the viewpoints of affinity for carbon dioxide, crosslinkability, and alkali metal compound resistance, a compound having at least one structural unit selected from polyamideamine dendrimer, polyethyleneimine, polyallylamine, and polyvinylamine is preferable. In particular, polyamine amide dendrimer is suitable because it exhibits a molecular gate function by forming a carbamate bond that is reversible and rearrangeable with carbon dioxide (CO 2 ), thereby improving the carbon dioxide membrane permeation rate and carbon dioxide selectivity.

[0046] As the polyamideamine dendrimer, the formula (5):

[0047]

Chemical formula

[0048]

Chemical formula

[0049] The polyamide amine dendrimer forms a branched structure by an amidation reaction with ethylenediamine, and by increasing the number of branches, the number of primary amino groups in the dendrimer can be increased. In the present invention, any generation of polyamide amine dendrimer can be preferably used regardless of the number of branches. However, a polyamide amine dendrimer of the 0th generation selected from, for example, the following formulas, which has a high content of primary amino groups and is considered advantageous for the expression of the molecular gate mechanism by the formation of a carbamate bond with carbon dioxide, is particularly preferable.

[0050] [Chemical formula]

[0051] The content of the hydrophilic crosslinkable compound (B) contained in the resin composition constituting the gas separation membrane of the present invention is preferably 1 to 90 wt%, more preferably 1.5 to 80 wt%, still more preferably 2 to 70 wt%, particularly preferably 3 to 50 wt% based on the total weight of the resin composition. When the content of the hydrophilic crosslinkable compound (B) is less than 1 wt% based on the total weight of the resin composition, the affinity and water retention of the separation membrane for the mixed gas containing water vapor decrease, and the diffusibility of the alkali metal compound (C) in the separation membrane also decreases, so the carbon dioxide membrane permeation rate decreases. When the content of the hydrophilic crosslinkable compound (B) exceeds 90 wt% based on the total weight of the resin composition, the film-forming property deteriorates, such as a part of the hydrophilic crosslinkable compound (B) bleeding out during film formation.

[0052] The hydrophilic crosslinkable compound (B) may include, in addition to the above polyamidoamine dendrimer, another amine-based polymer or a polymer in which a part thereof is modified. Examples of the amine-based polymer include polyethyleneimine, polyallylamine, and polyvinylamine. Among them, polyallylamine is preferable from the viewpoint of the stability of the membrane structure in a water vapor atmosphere.

[0053] When the hydrophilic crosslinkable compound (B) contains a polyamidoamine dendrimer and another amine-based polymer, the ratio of the content of the polyamidoamine dendrimer to the amine-based polymer is preferably 40 / 60 to 95 / 5 by weight from the viewpoint of improving the film-forming property and the carbon dioxide membrane permeation rate.

[0054] Polyamidoamine dendrimer, polyethyleneimine, polyallylamine, and polyvinylamine have highly reactive amino groups in their polymer chains. Therefore, when the hydrophilic crosslinkable compound (B) is the above compound, as described above, even when reacted with a crosslinking agent, the copolymer (A) is not substantially crosslinked, and the hydrophilic crosslinkable compound (B) can be selectively crosslinked. As a result, the separation membrane can retain the carbon dioxide membrane permeation rate without impairing the affinity and water retention for a mixed gas containing water vapor. Also, when using polyamidoamine dendrimer, crosslinking between dendrimers can prevent it from flowing out from the support, so suppression of a decrease in carbon dioxide selectivity can also be expected.

[0055] <Alkali metal compound (C)> In addition to the copolymer (A) and the hydrophilic crosslinkable compound (B), the resin composition can further contain an alkali metal compound (C). The gas separation membrane can improve the carbon dioxide membrane permeation rate by containing the alkali metal compound (C).

[0056] The alkali metal compound (C) functions as a carbon dioxide carrier in the gas separation membrane of the present invention. The oxide ions (OH - ) formed by the reaction of the alkali metal compound (C) and / or the alkali metal compound (C) with water vapor in a mixed gas containing water vapor react with carbon dioxide (CO 2 ) in the gas separation membrane to form bicarbonate (HCO 3- ) and carbonate (CO 3 2- ). By these moving according to the concentration gradient generated in the membrane, carbon dioxide (CO 2 ) is transported. The transport rate varies depending on the type of carbon dioxide carrier and the type of polymer matrix constituting the separation membrane, etc.

[0057] The alkali metal compound (C) is not particularly limited as long as the object of the present invention can be achieved. However, lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, etc. are expected to have long-term durability of separation performance because they have low chemical stability and vapor pressure of the carrier and are less likely to be lost from the separation membrane. Alkali metal hydroxides; alkali metal carbonates such as lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, and cesium carbonate; and alkali metal bicarbonates such as lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, rubidium bicarbonate, and cesium bicarbonate are preferred.

[0058] From the viewpoint of increasing the amount of carbon dioxide absorbed by the separation membrane, the content of the alkali metal compound (C) contained in the gas separation membrane is preferably 5 to 50 wt%, more preferably 10 to 40 wt%, and still more preferably 15 to 30 wt% based on the total weight of the resin composition. If the content of the alkali metal compound (C) is less than 5 wt% based on the total weight of the resin composition, the desired effect cannot be expected, and if it exceeds 40 wt% based on the total weight of the resin composition, it is excessive supply.

[0059] As described above, the alkali metal compound (C) may be directly contained in the resin composition (membrane-forming stock solution) containing the copolymer (A) and the hydrophilic crosslinkable compound (B), or after forming a membrane from the membrane-forming stock solution containing the copolymer (A) and the hydrophilic crosslinkable compound (B), a solution containing the alkali metal compound (C) may be applied to one or both surfaces of the membrane to contain it.

[0060] <Zinc complex (D)> The resin composition can further contain a zinc complex (D) in which an amine is coordinated. By containing the zinc complex (D) in which an amine is coordinated, a catalytic effect of a hydration reaction for converting carbon dioxide (CO 2 ) to bicarbonate ion (HCO 3 - ) can be expected, and it can be expected that the carbon dioxide membrane permeation rate will be further improved.

[0061] The zinc complex (D) is not particularly limited as long as the central metal is zinc and the ligand is an amine. As the amine, a secondary amine and / or a tertiary amine is preferred. As specific examples of the zinc complex (D), for example, those represented by the following formulas (1) to (4), or carbonic anhydrase derived from natural products, etc. can be preferably used. These may be used alone or in combination of two or more.

[0062] [Chemical formula]

[0063] [Chemical formula]

[0064] [Chemical formula]

[0065] [Chemical formula]

[0066] From the viewpoints of both the desired effect and the maintenance of film-forming properties, the content of the zinc complex (D) coordinated with an amine is preferably 0.1 to 20 wt%, more preferably 0.15 to 10 wt%, and even more preferably 0.2 to 5 wt%. If the content of the zinc complex (D) coordinated with an amine is less than 0.1 wt%, the effect of improving the carbon dioxide film permeation rate may not be obtained. If the content of the zinc complex (D) exceeds 20 wt%, a part may not be completely included in the separation membrane, and the film-forming properties may be impaired.

[0067] [Others] (Crosslinking agent) The resin composition contains a crosslinking agent. By crosslinking the copolymer (A) and the hydrophilic crosslinkable compound (B), particularly the hydrophilic crosslinkable compound (B), contained in the resin composition, the durability of the separation membrane can be improved. The crosslinking agent used in the separation membrane of the present invention selectively reacts with the functional groups that can be contained in the copolymer (A) and the hydrophilic crosslinkable compound (B), particularly the amino group that can be contained in the hydrophilic crosslinkable compound (B). From this perspective, it is preferable to use a crosslinking agent having an epoxy group. Examples of the crosslinking agent having an epoxy group include epichlorohydrin; diepoxyalkane; diepoxyalkene; diglycidyl ether compounds such as (poly)ethylene glycol diglycidyl ether and (poly)glycerin diglycidyl ether. When a crosslinking agent having an aldehyde group such as glutaraldehyde is used as the crosslinking agent, the hydroxyl groups of the copolymer (A) and the hydrophilic crosslinkable compound (B) are crosslinked to form a fragile acetal bond. Therefore, defects such as pinholes are likely to occur after film formation, which is not preferable from the perspective of contributing to the durability of the separation membrane. The content of the crosslinking agent contained in the resin composition needs to be appropriately adjusted from the perspective of suppressing the progress of an unintended crosslinking reaction and a decrease in membrane performance during actual use after the formation of the separation membrane. (Additive) The resin composition may contain additives such as a plasticizer and a surfactant. Examples of the plasticizer include ethylene glycol, propylene glycol, glycerin, triacetyl glycerin, dioctyl phthalate, triethylene glycol dicaprylate, and ionic liquids. Examples of the surfactant include nonionic surfactants, cationic surfactants, and organic fluorine compounds. By using these, the film-forming property of the resin composition can be improved. (Solvent) The resin composition is mixed with a solvent and prepared as a membrane-forming stock solution. Examples of the solvent include water, organic solvents such as dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N,N-dimethylacetamide (DMAc), and mixtures thereof. The solvent is not particularly limited as long as the effects of the present invention are achieved, but water is particularly preferable.

[0068] The resin composition prepared as the film-forming stock solution is applied onto the support membrane in the first step of the method for producing a gas separation membrane of the present invention as described above. As the coating method, a known coating method such as slot die coating, knife coating, microgravure coating, bar coating, spin coating, etc. can be appropriately selected. Examples of the support membrane include porous membranes made of organic materials or inorganic materials. Among them, porous polymer membranes made of polysulfone, polyethersulfone, polyamide, polyimide, polyacrylonitrile, polystyrene, polyvinylidene fluoride, polyvinyl chloride, polymethyl methacrylate, etc., such as ultrafiltration membranes and microfiltration membranes, are preferable. The shape of the support membrane can be appropriately selected from various shapes such as film shape, hollow fiber shape, or cylindrical body. The pore size and film thickness of the support membrane are not particularly limited as long as they do not interfere with the object of the present invention.

[0069] The resin composition applied onto the support membrane is made into a dry coating film by removing the solvent in the second step of the method for producing a gas separation membrane of the present invention. Drying can be appropriately selected and carried out from natural drying methods, ventilation drying methods, and reduced-pressure drying methods under normal temperature and pressure. Further, drying can also be carried out using heating means as long as the copolymer (A) and / or the hydrophilic crosslinkable compound (B) contained in the resin composition do not crosslink and microcrystals of the copolymer (A) and / or the hydrophilic crosslinkable compound (B) do not precipitate on the membrane surface. If the drying rate of the coating film is too fast, microcrystals of the copolymer (A) and / or the hydrophilic crosslinkable compound (B) may precipitate on the membrane surface, leading to a decrease in the performance of the separation membrane.

[0070] The film thickness of the dry coating film is preferably from 0.1 to 100 μm, more preferably from 0.05 to 50 μm, and still more preferably from 0.1 to 25 μm, from the viewpoint of ensuring good carbon dioxide film permeation rate and carbon dioxide selectivity. When the film thickness of the dry coating film is less than 0.1 μm, defects such as pinholes may occur in the separation membrane or the separation membrane may be torn after film formation, and the desired robustness cannot be obtained. When the film thickness of the dry coating film exceeds 100 μm, the carbon dioxide selectivity increases but the carbon dioxide film permeation rate decreases. The film thickness of the dry coating film can be measured, for example, by observing the distribution of the alkali metal compound (C) using a scanning electron microscope (SEM) or time-of-flight secondary ion mass spectrometry (TOF-SIMS) of the cross-section of the gas separation membrane.

[0071] (Step 3) The dry coating film is thermally crosslinked in the third step of the method for producing the gas separation membrane of the present invention.

[0072] In the method for producing the gas separation membrane of the present invention, the thermal crosslinking is carried out under wet heat conditions. The thermal crosslinking may vary depending on the types of the copolymer (A) and the hydrophilic crosslinkable compound (B) constituting the separation membrane, but in the gas separation membrane of the present invention, it is preferably carried out under wet heat conditions of a temperature of 60 to 95 °C and a relative humidity of 40 to 90% RH. By performing the thermal crosslinking under the conditions within the above range, while imparting rigidity to the separation membrane, it is possible to avoid a decrease in robustness by suppressing a decrease in flexibility. Therefore, a gas separation membrane having robustness can be obtained.

[0073] In the present specification, "robustness" refers to the durability of the separation membrane against repeated pressure loads. On the other hand, since groups such as hydroxyl groups and amino groups remain appropriately in the separation membrane that has been thermally crosslinked under the conditions within the above range, the affinity and water retention of the separation membrane for a mixed gas containing water vapor and the affinity for carbon dioxide are also maintained, and good carbon dioxide film permeation rate and carbon dioxide selectivity can be exhibited.

[0074] When thermally crosslinked at a temperature below 60 °C, the crosslinking reaction does not proceed sufficiently, so rigidity is not imparted and the desired robustness cannot be obtained. When thermally crosslinked at a temperature exceeding 95 °C, the crosslinking reaction proceeds sufficiently, but the flexibility decreases and the desired robustness cannot be obtained. When thermally crosslinked at a relative humidity below 40%RH, the crosslinking reaction proceeds sufficiently, but the flexibility decreases and the desired robustness cannot be obtained. When thermally crosslinked at a relative humidity exceeding 90%RH, the crosslinking reaction does not proceed sufficiently, so rigidity is not imparted and the desired robustness cannot be obtained.

[0075] The rigidity of the gas separation membrane can be evaluated using, for example, the tensile elastic modulus. The tensile elastic modulus of the gas separation membrane is preferably 5 to 7 N / mm 2 under the conditions of a temperature of 25 °C and a relative humidity of 60%RH. When the tensile elastic modulus of the gas separation membrane is within the above range, the separation membrane has appropriate rigidity and flexibility and exhibits robustness. When the tensile elastic modulus of the gas separation membrane is less than 5 N / mm 2 , it lacks rigidity, so the desired robustness cannot be obtained. When the tensile elastic modulus of the gas separation membrane exceeds 7 N / mm 2 , the rigidity is sufficient, but it lacks flexibility, so the desired robustness may not be obtained.

[0076] The affinity and water retention of the gas separation membrane for a mixed gas containing water vapor can be evaluated using, for example, the water vapor adsorption amount. The water vapor adsorption amount of the gas separation membrane at a temperature of 60 °C and a relative pressure (p / p 0 ) in the range of 0.5 to 0.9 is preferably 150 to 900 cm 3 (STP) / g. When the water vapor adsorption amount of the gas separation membrane is within the above range, the separation membrane can exhibit a good carbon dioxide membrane permeation rate. When the water vapor adsorption amount of the gas separation membrane is less than 150 cm 3 (STP) / g, the diffusibility of the alkali metal compound (C) which is a carbon dioxide carrier in the separation membrane decreases, so the carbon dioxide membrane permeation rate decreases. When the water vapor adsorption amount of the gas separation membrane exceeds 900 cm 3 (STP) / g, the crosslinking is insufficient and it lacks rigidity, so the desired robustness cannot be obtained.

[0077] Through the above process, the gas separation membrane of the present invention can be manufactured.

[0078] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples only.

Examples

[0079] The gas separation membranes obtained in the examples and comparative examples were measured and evaluated for each item according to the following method.

[0080] <Tensile modulus> Using a tensile testing machine (“Autograph AGS-X” (trade name), manufactured by Shimadzu Corporation), measurement conditions: tensile test speed 10 mm / min, measurement environment: temperature 25°C, relative humidity 56%RH, tensile test sample size: width 2 mm, length 35 mm, grip distance 15 mm, a tensile test was conducted. From the obtained experimental data, the vertical axis: stress (MPa) and the horizontal axis: displacement (strain %) were plotted, and the tensile modulus (N / mm 2 )(= stress / displacement) was calculated. The results are shown in Table 1.

[0081] <Robustness (repeated pressure load durability) test> As an examination of the influence of pressure fluctuation on the membrane separation performance assuming the startup and shutdown of the plant, a robustness test was conducted. In the test, the following startup and shutdown operations were repeated. 1. Startup: Supply side: temperature 85°C, supply gas composition CO 2 / He = 40 / 60 (400 mL (STP) / min), relative humidity 60%RH, pressurized from atmospheric pressure to 2.4 MPa. Permeate side: atmospheric pressure. After returning to atmospheric pressure, dry gas was passed for 5 minutes, and the membrane cell was taken out from the constant temperature bath at 85°C. 2. Shutdown: Stored for a certain period (temperature 25°C, relative humidity 50 - 60%RH). 3. Startup: The membrane cell was reset, and the membrane separation performance was evaluated again under the conditions of 1. above.

[0082] Robustness (repeated pressure load durability) was evaluated according to the following criteria.

[0083] 〇: The carbon dioxide selectivity α is stable ×: The helium membrane permeation rate Q He shows an increase, and the carbon dioxide selectivity α decreases The results are shown in Table 1.

[0084] <Water vapor adsorption amount> The water vapor adsorption amount was measured using an automatic vapor adsorption measurement device ("BELSORP-18" (trade name), manufactured by MicrotracBEL Corp.). The measurement condition was a temperature of 60°C. The results are shown in Table 1.

[0085] <Carbon dioxide membrane permeation rate and carbon dioxide selectivity> The prepared gas separation membrane was cut into a circular shape (diameter 47 mm, area 17.4 cm 2 ) and used as a measurement sample. The measurement was carried out by the differential pressure method with a mixed gas set at a temperature of 85°C, a composition of CO 2 / He = 40 / 60 (400 mL / min), and a relative humidity of 60%RH, with the total pressure on the supply side set to 2.4 MPa. Subsequently, from the following formula, the carbon dioxide membrane permeation rate Q CO2 [m 3 (STP) / (m 2 ·s·Pa)], the helium membrane permeation rate Q He [m 3 (STP) / (m 2 ·s·Pa)] and the carbon dioxide selectivity α were determined. The results are shown in Table 1.

[0086]

Number

[0087]

Number

[0088]

Number

[0089] [Example 1] 1. Preparation of Aqueous Solution of Non-Crosslinked Vinyl Alcohol-Based Copolymer (A) Using the method described in JP-A-59-187003, polyvinyl alcohol (PVA-1) having a mercapto group at the terminal was synthesized. 1 The content of vinyl alcohol units (saponification degree) determined by 1H-NMR measurement was 98.5 mol%, and the viscosity-average degree of polymerization measured in accordance with JIS K6726 was 1500. Next, 1269 g of water was added to 72.0 g of PVA-1, and the mixture was heated to 95 °C and dissolved in a 1 L four-neck separable flask equipped with a reflux condenser and a stirring blade. After cooling to room temperature, 1 / 2 N sulfuric acid was added to the aqueous solution to adjust the pH to 3.0. 50 g of acrylic acid was added thereto, and the temperature was raised to 90 °C while bubbling nitrogen into the aqueous solution, and nitrogen bubbling was continued at 90 °C for 30 minutes for nitrogen substitution. After nitrogen substitution, 197 mL of a 2% aqueous solution of 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] (AMHP, manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was gradually added to the aqueous solution over 1.5 hours. After the addition was completed, the mixture was heated at 90 °C for 2.5 hours to complete the polymerization. After cooling to room temperature, an aqueous solution of a non-crosslinked vinyl alcohol-based copolymer (A), which is a block copolymer of polyvinyl alcohol and polyacrylic acid with a solid content concentration of 7.5 wt%, was obtained. After drying a part of the obtained aqueous solution, it was dissolved in heavy water, 1 When 1H-NMR measurement was performed, the content of carboxyl groups in the block copolymer, that is, the content of acrylic acid monomer units relative to the total number of monomer units in the copolymer was 30 mol% 2. Preparation of Membrane-Forming Stock Solution (Resin Composition Solution) The above non-crosslinked vinyl alcohol copolymer (A) aqueous solution (hereinafter referred to as "P-2"), Poval ("PVA124" (trade name), manufactured by Kuraray Co., Ltd.), polyallylamine ("PAA-15C" (trade name), manufactured by Nitto Boseki Co., Ltd.), polyamidoamine dendrimer (20 wt% methanol solution, manufactured by Aldrich), crosslinking agent ("Epolite 400E" (trade name), manufactured by Kyoeisha Chemical Co., Ltd.), and glycerin were used, and these were mixed at a ratio of P-2 / NaOH (1M aqueous solution) / "PVA124" / "PAA-15C" / polyamidoamine dendrimer / "Epolite 400E" (10 wt% aqueous solution) / glycerin = 19.5 / 2.5 / 9 / 16 / 14 / 12 / 27 wt%. Ion-exchanged water was added to prepare a membrane-forming stock solution (solid content concentration: 8 wt%). 3. Membrane formation The above membrane-forming stock solution was formed into a membrane by continuous membrane formation using a slot die method on an ultrafiltration membrane ("Biomax" (trade name), manufactured by Merck) made of polyethersulfone with a molecular weight cut-off of 300,000, and dried at 80°C for 10 minutes to obtain a composite membrane with a dried coating film (film thickness: 2 - 3 μm). 4. Thermal crosslinking The composite membrane was placed in a thermostatic and humidistatic chamber and held for 24 hours under wet heat conditions of a temperature of 80°C and a relative humidity of 40%RH to thermally crosslink the dried coating film. 5. Preparation of gas separation membrane An aqueous solution of cesium carbonate (14.3 wt%) and Zn

[12] aneN4 (ZC) catalyst (0.2 wt%) was applied to the surface of the dried coating film of the above-prepared composite membrane to prepare a gas separation membrane (carbonate loading: approximately 30 g / m 2 ).

[0090] [Example 2] A gas separation membrane (film thickness: 2 - 3 μm) was prepared in the same manner as in Example 1, except that the thermal crosslinking of the dried coating film was carried out under wet heat conditions of a temperature of 80°C and a relative humidity of 60%RH.

[0091] [Example 3] A gas separation membrane (film thickness: 2 - 3 μm) was prepared in the same manner as in Example 1, except that the thermal crosslinking of the dried coating film was carried out under wet heat conditions of a temperature of 80°C and a relative humidity of 80%RH.

[0092] [Example 4] A gas separation membrane (membrane thickness: 2 - 3 μm) was prepared in the same manner as in Example 1, except that the thermal cross-linking of the dry coating film was carried out under humid heat conditions of a temperature of 80°C and a relative humidity of 90%RH.

[0093] [Comparative Example 1] A gas separation membrane (membrane thickness: 2 - 3 μm) was prepared in the same manner as in Example 1, except that the thermal cross-linking of the dry coating film was carried out under dry conditions of a temperature of 80°C and a relative humidity of 0%RH with a process time of 30 minutes.

[0094] [Comparative Example 2] A gas separation membrane (membrane thickness: 2 - 3 μm) was prepared in the same manner as in Example 1, except that the thermal cross-linking of the dry coating film was carried out under dry conditions of a temperature of 80°C and a relative humidity of 0%RH.

[0095]

Table 1

[0096] The gas separation membrane of the present invention has good performance in selectively separating a specific gas species, particularly carbon dioxide, from a mixed gas, particularly a mixed gas containing water vapor, under high-pressure conditions, and has robustness (repeated pressure load durability). Therefore, it is useful in the separation of carbon dioxide from aqueous shift gas produced by coal gasification and natural gas.

Claims

1. A step of applying a resin composition onto a support membrane; A step of drying the applied resin composition; and A step of thermally crosslinking the dried resin composition A method for producing a gas separation membrane, comprising: The step of thermal crosslinking is carried out under wet heat conditions of a temperature of 60 to 95°C and a relative humidity of 40 to 90% RH, The resin composition contains a non-crosslinked vinyl alcohol copolymer (A) having a carboxyl group, a hydrophilic crosslinkable compound (B), and a crosslinking agent, The non-crosslinked vinyl alcohol copolymer (A) having a carboxyl group is in the form of a random copolymer, block copolymer, or graft copolymer of a monomer unit having a carboxyl group and a vinyl alcohol-based monomer unit, The hydrophilic crosslinkable compound (B) is represented by the formula (5): 【Chemical 1】 [In the formula, A １ represents a divalent organic group having 1 to 3 carbon atoms, and n represents an integer of 0 or 1.] A polyamidoamine dendrimer having a group represented by, and / or a group represented by the formula (6): [Chemical 2] [wherein, A ２ represents a divalent organic group having 1 to 3 carbon atoms, and n represents an integer of 0 or 1.] And the crosslinking agent is a crosslinking agent having an epoxy group, A method for producing a gas separation membrane.

2. The method according to claim 1, wherein the resin composition further contains an alkali metal compound (C).

3. The method according to claim 2, wherein the alkali metal compound (C) is selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, and alkali metal bicarbonates.

4. The resin composition The method according to any one of claims 1 to 3, further comprising a zinc complex (D) coordinated with an amine selected from the group consisting of. 【Chemical 1】 [Chemical Formula 2] 【Chemical Formula 3】 【Chemical Formula 4】

5. A gas separation membrane having a support membrane and a dried coating crosslinked product of a resin composition formed on the support membrane, The resin composition contains a non-crosslinked vinyl alcohol copolymer (A) having a carboxyl group, a hydrophilic crosslinkable compound (B), and a crosslinking agent, The non-crosslinked vinyl alcohol copolymer (A) having a carboxyl group is in the form of a random copolymer, block copolymer, or graft copolymer of a monomer unit having a carboxyl group and a vinyl alcohol-based monomer unit, The hydrophilic crosslinkable compound (B) is represented by the formula (5): A polyamidoamine dendrimer having a group represented by, and / or a group represented by the formula (6): 【Chemical Formula 3】 [In the formula, A １ represents a divalent organic group having 1 to 3 carbon atoms, and n represents an integer of 0 or 1.] And the crosslinking agent is a crosslinking agent having an epoxy group, 【Chemical 4】 [In the formula, A ２ represents a divalent organic group having 1 to 3 carbon atoms, and n represents an integer of 0 or 1.] A gas separation membrane in which the copolymer (A) is not crosslinked and the hydrophilic crosslinkable compound (B) is selectively crosslinked.

6.

7. The gas separation membrane according to claim 5 or 6 for separating carbon dioxide. In the water vapor adsorption test at a temperature of 60 °C, the water vapor adsorption amount in the range of relative pressure of 0.5 to 0.9 is in the range of 150 to 900 cm ３ (STP) / g, and The tensile elastic modulus under the measurement conditions of a temperature of 25°C and a relative humidity of 60% RH is 5 to 7 N / mm ２ The gas separation membrane according to claim 5, which is such. ​ ​

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