JP2023002341A - gas separation membrane - Google Patents

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

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

BACKGROUND ART From the viewpoint of preventing global warming and highly efficient recovery of fossil resources, gas separation membranes have been vigorously studied as one of the techniques for separating carbon dioxide from mixed gas.

In selectively separating carbon dioxide from a mixed gas, the problem is to increase the selectivity (carbon dioxide selectivity) and recover high-concentration carbon dioxide. In order to obtain a separation membrane with excellent carbon dioxide selectivity, it has been proposed to use a material with a high affinity for carbon dioxide. Separation membranes used at room temperature have been proposed (Non-Patent Documents 1 and 2).

The present inventors have previously reported that a layer containing a polyamidoamine-based dendrimer and a polymeric material having amino groups and/or hydroxyl groups crosslinked with a crosslinking agent is formed on the surface of a porous support membrane for gas separation. proposed a membrane (Patent Document 1).

In addition, the present inventors have previously proposed a gas separation membrane formed from a composition containing a crosslinkable vinyl alcohol-based polymer and an amine-coordinated zinc complex (Patent Document 2).

JP-A-2008-68238 WO2014/157012

J. Am. Chem. Soc. 122 (2000) 7594-7595 Ind. Eng. Chem. Res. 40 (2001) 2502-2511

Gas separation membranes for Integrated Gasification Combined Cycle (IGCC) applications, which have been studied in recent years, can efficiently and selectively separate carbon dioxide from mixed gases containing water vapor under high pressure. is required.

The carbon dioxide permeation rate of the separation membranes described in Non-Patent Documents 1 and 2 is low. However, the carbon dioxide selectivity, which is expressed as the membrane permeation rate of carbon dioxide relative to the membrane permeation rate of nitrogen, exhibits excellent values under the conditions in which the mixed gas is supplied to the separation membrane without pressurization. However, when the mixed gas is pressurized and supplied to the separation membrane, there is a problem that the polyamidoamine dendrimer flows out from the support over time, making it impossible to maintain carbon dioxide selectivity.

The separation membrane described in Patent Document 1 exhibits a high carbon dioxide membrane permeation rate and excellent carbon dioxide selectivity. However, when used to separate carbon dioxide from a mixed gas containing water vapor under high pressure, the amine compound contained in the separation membrane flows out over time, and the carbon dioxide selectivity can be maintained. Therefore, it was difficult to put it into practical use.

The separation membrane described in Patent Document 2 has carbon dioxide selectivity even in an environment containing water vapor. However, when the pressure of the mixed gas was increased, there was a possibility that the carbon dioxide membrane permeation rate and the carbon dioxide selectivity would decrease.

From the viewpoint of providing a separation membrane that can be used practically, it exhibits a good carbon dioxide membrane permeation rate and carbon dioxide selectivity even in a higher pressure environment containing water vapor, and can be used for a long time. Development of a separation membrane having robustness (repeated pressure load durability) capable of withstanding pressure is desired.

The present invention is intended to solve the above-mentioned conventional problems, and the object thereof is to provide a carbon dioxide membrane with a good carbon dioxide membrane permeation rate and carbon dioxide selectivity in separating carbon dioxide from a mixed gas containing water vapor under high pressure. and to provide a method for producing a gas separation membrane having robustness (repeated pressure load durability), and the gas separation membrane.

In a first aspect of the present invention,
A step of applying a resin composition onto the support film;
A method for producing a gas separation membrane, comprising a step of drying the applied resin composition; and a step of thermally crosslinking the dried resin composition,
The thermal cross-linking step is performed under wet heat conditions at a temperature of 60 to 95 ° C. and a relative humidity of 40 to 90% RH.
A method for manufacturing a gas separation membrane is provided.

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

In one certain form, the non-crosslinked vinyl alcohol-based copolymer (A) having a carboxyl group contains an acrylic acid or methacrylic acid monomer unit and a vinyl alcohol-based monomer unit.

In one embodiment, the hydrophilic crosslinkable compound (B) comprises polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinylpyrrolidone, polyacrylamide, polyamidoamine dendrimer, polyethyleneimine, polyallylamine and polyvinylamine. It has at least one structural unit selected from the group.

In one certain form, the said resin composition further contains an alkali metal compound (C).

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.

In one embodiment, the resin composition is

からなる群から選択される、アミンが配位されている亜鉛錯体（Ｄ）を更に含む。

and an amine-coordinated zinc complex (D) selected from the group consisting of

Moreover, this invention provides the gas separation membrane manufactured by the said method in a 2nd aspect.

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

In one embodiment, the gas separation membrane is for separating carbon dioxide.

According to the present invention, when separating carbon dioxide from a mixed gas containing water vapor under high pressure, a gas that exhibits a good carbon dioxide membrane permeation rate and carbon dioxide selectivity and has robustness (durability against repeated pressure loads). A method for producing a separation membrane and the gas separation membrane are provided.

FIG. 1 is a process diagram of the method for producing a gas separation membrane of the present invention. FIG. 2 is a diagram showing the results of a robustness (repeated pressure load durability) test of the gas separation membrane of the present invention.

The method for producing a gas separation membrane of the present invention comprises:
A step of applying a resin composition onto the support film;
drying the applied resin composition; and thermally crosslinking the dried resin composition. They will be described in order below.

(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).

<Non-Crosslinked Vinyl Alcohol Copolymer (A) Having Carboxyl Group>
The non-crosslinked vinyl alcohol copolymer (A) having carboxyl groups (hereinafter sometimes simply referred to as "copolymer (A)") constitutes the polymer matrix of the gas separation membrane of the present invention.

The copolymer (A) is a non-crosslinked (non-crosslinked) copolymer composed of a monomer unit having a carboxyl group and a vinyl alcohol-based monomer unit. Examples of monomer units having a carboxyl group include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, α-chloroacrylic acid and cinnamic acid; maleic acid, fumaric acid, itaconic acid, citraconic acid and unsaturated dicarboxylic acids such as mesaconic acid; and metal salts thereof such as alkali metal salts; esters such as methyl esters or ethyl esters; anhydrides such as maleic anhydride, itaconic anhydride and citraconic anhydride . As for the monomer unit having a carboxyl group that constitutes the copolymer (A), only one type may be selected from the above-exemplified ones, or two or more types may be selected. However, from the viewpoint of the affinity and water retention of gas separation membranes for mixed gases containing water vapor, monomer units having a carboxyl group include acrylic acid, methacrylic acid, crotonic acid and itaconic acid, and alkali metal salts thereof. , methyl ester or ethyl ester are preferred, and acrylic acid, methacrylic acid and their alkali metal salts, methyl esters or ethyl esters are more preferred.

Examples of vinyl alcohol-based monomer units constituting the copolymer (A) include vinyl alcohol; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, and the like. As for the vinyl alcohol-based monomer units constituting the copolymer (A), only one type may be selected from among the above-exemplified ones, or two or more types may be selected.

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

When the copolymer (A) is a random copolymer, the copolymer (A) is obtained by copolymerizing an unsaturated carboxylic acid having a carboxyl group, a salt, ester, or anhydride thereof with a vinyl ester, followed by saponification. It can be manufactured by When the copolymer (A) is a block copolymer, the copolymer (A) may be reacted with acrylic acid, methacrylic acid, crotonic acid, itaconic acid, etc. in an aqueous solution of a vinyl alcohol polymer having a mercapto group at its terminal. It can be produced by polymerizing an acid or an unsaturated carboxylic acid having a carboxyl group such as maleic acid, or an acid anhydride thereof (see, for example, JP-A-59-187003 and JP-A-2001-233678). . When the copolymer (A) is a graft copolymer, the copolymer (A) is added, for example, to a methanol solution of vinyl acetate and S-7-octen-1-yl thioacetate with 2,2′-azobis After adding isobutyronitrile (AIBN) and polymerizing to obtain a copolymer of vinyl acetate and a thioester monomer, this copolymer is saponified to produce a vinyl alcohol polymer having a mercapto group in the side chain. It can be produced by producing a coalescence 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 a block or graft copolymer from the viewpoint of obtaining a gas separation membrane exhibiting a good carbon dioxide membrane permeation rate and carbon dioxide selectivity under high pressure. is preferred.

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%, relative to the total weight of the resin composition. and more preferably 3 to 20 wt%. When the content of the copolymer (A) is less than 1 wt% with respect to the total weight of the resin composition, the affinity and water retention of the separation membrane for a mixed gas containing water vapor, and the alkali metal compound (C) described later. Solubility decreases. If the content of the copolymer (A) exceeds 40 wt% with respect to the total weight of the resin composition, the film formability of the resin composition is deteriorated.

The content of the monomer unit having a carboxyl group in the copolymer (A) is determined from the viewpoint of the solubility of the alkali metal compound (C) and the affinity and water retention of the separation membrane for a mixed gas containing water vapor. 0.1 to 90 mol% is preferable, 0.5 to 80 mol% is more preferable, 1 to 70 mol% is still more preferable, and 5 to 60 mol% is based on the total monomer units constituting the coalescence (A). is particularly preferred, and 10 to 50 mol % is most preferred. 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 a mixed gas containing water vapor are lowered. If the content of the monomer unit having a carboxyl group exceeds 90 mol %, the film formability of the resin composition is lowered, which is not preferable. The content of the vinyl alcohol-based monomer units in the copolymer (A) can be appropriately adjusted according to the content of the monomer units having a carboxyl group.

The degree of saponification 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%, more preferably 95 to 99 0.9 mol % is more preferred. When the degree of saponification 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 a mixed gas containing water vapor and the dissolution of the alkali metal compound (C) and the carbon dioxide membrane permeation rate decreases. When the degree of saponification of the vinyl alcohol-based monomer unit portion exceeds 99.9 mol %, the viscosity stability of the resin composition becomes poor, resulting in poor workability and film formability. As used herein, the term “saponification degree” refers to 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. refers to the ratio of the number of moles of the vinyl alcohol monomer unit to the total number of moles of Incidentally, the degree of saponification can be measured according to the description of JISK6726-1994.

The viscosity-average polymerization degree of the vinyl alcohol-based monomer unit portion in the copolymer (A) (hereinafter sometimes simply referred to as “polymerization degree (P)”) is preferably 300-2,500. If the degree of polymerization (P) is less than 300, the mechanical strength of the gas separation membrane is lowered. When the degree of polymerization (P) exceeds 2500, the viscosity of the resin composition is too high, resulting in poor workability and film formability. The degree of polymerization (P) is more preferably 330-2200, still more preferably 360-2000. The degree of polymerization (P) can be measured according to JIS-K6726. That is, it is determined by the following formula from the intrinsic viscosity [η] measured in water at a temperature of 30° C. after resaponification and purification of the vinyl alcohol monomer unit portion.

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

The copolymer (A) is non-crosslinked (not crosslinked) from the viewpoint of exhibiting a good carbon dioxide membrane permeation rate and carbon dioxide selectivity. The carboxyl group of the monomer unit portion having a carboxyl group in the copolymer (A) ionically interacts with the alkali metal compound (C), which functions as a carbon dioxide carrier, in the separation membrane, resulting in cross-linking. In this case, the diffusibility of the alkali metal compound (C) is lowered and the carbon dioxide membrane permeation rate is lowered. Here, the copolymer (A) is "non-crosslinked (not crosslinked)" means that the hydroxyl group and / or carboxyl group of the copolymer (A) has a covalent bond with the crosslinking agent. It means not having substantially. Although details will be described later, for example, in the case of cross-linking the resin composition using a cross-linking agent having an epoxide group, a group ( For example, amino groups), if present, the cross-linking agent preferentially reacts therewith, so that the hydroxyl and/or carboxyl groups of copolymer (A) may react slightly but are not substantially cross-linked.

<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 a mixed gas containing water vapor are improved, and the diffusibility of the alkali metal compound (C) in the separation membrane is improved. Therefore, the carbon dioxide membrane permeation rate can be improved.

Hydrophilic crosslinkable compound (B) is selected from the group consisting of, for example, polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinylpyrrolidone, polyacrylamide, polyamidoamine dendrimer, polyethyleneimine, polyallylamine and polyvinylamine. It is a compound having at least one type of structural unit. The hydrophilic crosslinkable compound (B) is not particularly limited as long as the object of the present invention can be achieved. However, among the above examples, at least one structural unit selected from polyamidoamine dendrimers, polyethyleneimine, polyallylamine and polyvinylamine is used from the viewpoint of affinity for carbon dioxide, crosslinkability and resistance to alkali metal compounds. Preferred are compounds having In particular, polyamineamide dendrimers exhibit a molecular gating function by forming reversible and rearrangeable carbamate bonds with carbon dioxide (CO ₂ ) at the terminal amino groups, thus improving carbon dioxide membrane permeation rate and carbon dioxide selectivity. is improved, which is preferable.

As a polyamidoamine dendrimer, formula (5):

［式中、Ａ^１は炭素数１～３の二価有機基を示し、ｎは０又は１の整数を示す。］
で示される基、及び／又は式（６）：

[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/or formula (6):

［式中、Ａ^２は炭素数１～３の二価有機基を示し、ｎは０又は１の整数を示す。］
で示される基を有するポリアミドアミンデンドリマーが好ましく、式（５）で示される基を有するポリアミドアミンデンドリマーがより好ましい。式（５）又は式（６）中、Ａ^１及びＡ^２で示される炭素数１～３の二価有機基としては、例えば直鎖状又は分枝状の炭素数１～３のアルキレン基、例えば－ＣＨ_２－、－ＣＨ_２－ＣＨ_２－、－ＣＨ_２－ＣＨ_２－ＣＨ_２－、－ＣＨ_２－ＣＨ（ＣＨ_３）－が挙げられる。中でも－ＣＨ_２－が好ましい。ｎは、分離膜の水蒸気を含む混合ガスに対する親和性及び保水性が増すことから、１であることが好ましい。

[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 polyamidoamine dendrimer having a group represented by is preferable, and a polyamidoamine dendrimer having a group represented by formula (5) is more preferable. In formula (5) or (6), the divalent organic group having 1 to 3 carbon atoms represented by A ¹ and A ² includes, for example, a linear or branched alkylene group having 1 to 3 carbon atoms, Examples include -CH ₂ -, -CH ₂ -CH ₂ -, -CH ₂ -CH ₂ -CH ₂ -, and -CH ₂ -CH(CH ₃ )-. Of these, -CH ₂ - is preferred. n is preferably 1 because the affinity and water retention of the separation membrane for the mixed gas containing water vapor are increased.

A polyamidoamine dendrimer forms a branched structure through 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, polyamidoamine dendrimers of any generation can be suitably used regardless of the number of branches. However, especially preferred are 0th generation polyamidoamine dendrimers selected from, for example, the following formulas, which have a high content of primary amino groups and are expected to be advantageous for the expression of a molecular gating mechanism through the formation of carbamate bonds with carbon dioxide. be.

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 wt%, based on the total weight of the resin composition. .5 to 80 wt%, more preferably 2 to 70 wt%, particularly preferably 3 to 50 wt%. If the content of the hydrophilic crosslinkable compound (B) is less than 1 wt% relative to the total weight of the resin composition, the affinity and water retention of the separation membrane for a mixed gas containing water vapor are reduced, and the alkali metal compound is used. Since the diffusibility in the separation membrane of (C) is also lowered, the carbon dioxide membrane permeation rate is lowered. If the content of the hydrophilic crosslinkable compound (B) exceeds 90% by weight with respect to the total weight of the resin composition, a portion of the hydrophilic crosslinkable compound (B) may bleed out during film formation. Decrease in film properties.

The hydrophilic crosslinkable compound (B) may contain other amine-based polymers or partially modified polymers in addition to the above polyamidoamine dendrimers. Examples of amine-based polymers include polyethyleneimine, polyallylamine and polyvinylamine. Among them, polyallylamine is preferable from the viewpoint of the stability of the film structure in a water vapor atmosphere.

When the hydrophilic crosslinkable compound (B) contains a polyamidoamine dendrimer and another amine polymer, the content ratio of the polyamidoamine dendrimer and the amine polymer is 40/60 to 95/5 by weight. is preferable from the viewpoint of improving the film formability and the carbon dioxide film permeation rate.

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

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

The alkali metal compound (C) functions as a carbon dioxide carrier in the gas separation membrane of the present invention. The alkali metal compound (C) and/or oxide ions (OH ⁻ ) produced by reaction of the alkali metal compound (C) and/or water vapor in the mixed gas containing water vapor are converted into carbon dioxide (CO ₂ ) to form bicarbonates (HCO ³⁻ ) and carbonates (CO ₃ ²⁻ ). Carbon dioxide (CO ₂ ) is transported as these move along the concentration gradient that occurs within the membrane. The transport rate varies depending on the type of carbon dioxide carrier, the type of polymer matrix forming the separation membrane, and the like.

The alkali metal compound (C) is not particularly limited as long as the object of the present invention can be achieved. However, since the chemical stability and vapor pressure of the carrier are low and the possibility of loss from the separation membrane is low, long-term durability of separation performance can be expected. Lithium hydroxide, sodium hydroxide, potassium hydroxide, alkali metal hydroxides such as rubidium hydroxide and cesium hydroxide; alkali metal carbonates such as lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, and cesium carbonate; and lithium bicarbonate, sodium bicarbonate, potassium bicarbonate. , rubidium bicarbonate, and cesium bicarbonate are preferred.

The content of the alkali metal compound (C) contained in the gas separation membrane is preferably 5 to 50 wt% with respect to the total weight of the resin composition from the viewpoint of increasing the amount of carbon dioxide absorbed by the separation membrane. It is preferably 10 to 40 wt%, and even more preferably 15 to 30 wt%. If the content of the alkali metal compound (C) is less than 5 wt% relative to the total weight of the resin composition, the desired effect cannot be expected, and if it exceeds 40 wt% relative to the total weight of the resin composition, excessive supply will occur. be.

The alkali metal compound (C) may be directly contained in the resin composition (film-forming stock solution) containing the copolymer (A) and the hydrophilic crosslinkable compound (B), as described above, or the copolymer After forming a film from a film-forming stock solution containing (A) and a hydrophilic crosslinkable compound (B), one or both surfaces of the film are coated with a solution containing an alkali metal compound (C) to impregnate the film. may

<Zinc Complex (D)>
The resin composition can further contain a zinc complex (D) coordinated with an amine. By containing the zinc complex (D) to which the amine is coordinated, a catalytic effect for the hydration reaction that converts carbon dioxide (CO ₂ ) to bicarbonate ion (HCO ₃ ⁻ ) can be expected, and the carbon dioxide membrane Further improvement in permeation rate can be expected.

The zinc complex (D) is not particularly limited as long as the central metal is zinc and the ligand is an amine. Preferred amines are secondary amines and/or tertiary amines. As specific examples of the zinc complex (D), for example, those represented by the following formulas (1) to (4), carbonic anhydrases derived from natural products, and the like can be suitably used. These may be used alone or in combination of two or more.

The content of the amine-coordinated zinc complex (D) is preferably 0.1 to 20 wt%, more preferably 0.15 to 10 wt%, from the viewpoint of both the desired effect and the maintenance of film-forming properties. 0.2 to 5 wt% is more preferred. If the content of the amine-coordinated zinc complex (D) is less than 0.1 wt %, the effect of improving the carbon dioxide membrane permeation rate may not be obtained. If the content of the zinc complex (D) exceeds 20 wt%, part of it cannot be included in the separation membrane, possibly impairing the film formability.

<Others>
(crosslinking agent)
The resin composition contains a cross-linking agent. The durability of the separation membrane is improved by cross-linking the copolymer (A) and the hydrophilic cross-linkable compound (B), particularly the hydrophilic cross-linkable compound (B), contained in the resin composition with a cross-linking agent. be able to. The cross-linking agent used in the separation membrane of the present invention is a functional group that can be contained in the copolymer (A) and the hydrophilic cross-linkable compound (B), particularly a hydroxyl group, a carboxy group, or an amino group. From the viewpoint of selectively reacting amino groups that may be contained in the crosslinkable compound (B), it is preferable to use a crosslinker having an epoxy group. Examples of cross-linking agents having an epoxy group include epichlorohydrin; diepoxyalkanes; diepoxyalkenes; and diglycidyl ether compounds such as (poly)ethylene glycol diglycidyl ether and (poly)glycerin diglycidyl ether. When a cross-linking agent having an aldehyde group such as glutaraldehyde is used as the cross-linking agent, the hydroxyl groups of the copolymer (A) and the hydrophilic cross-linkable compound (B) are cross-linked to form a fragile acetal bond. Defects such as pinholes tend to occur after membrane formation, which is not preferable from the viewpoint of contributing to the durability of the separation membrane. The content of the cross-linking agent contained in the resin composition should be appropriately adjusted from the viewpoint of suppressing deterioration of membrane performance due to unintended cross-linking reaction during actual use after formation of the separation membrane. There is
(Additive)
The resin composition may contain additives such as plasticizers and surfactants. Examples of plasticizers include ethylene glycol, propylene glycol, glycerin, triacetylglycerin, dioctyl phthalate, triethylene glycol dicaprylate, and ionic liquids. Further, examples of surfactants include nonionic surfactants, cationic surfactants and organic fluoro compounds. By using these, the film formability of the resin composition can be improved.
(solvent)
The resin composition is mixed with a solvent to prepare a film-forming stock solution. Solvents include water, organic solvents such as dimethylformamide (DMF), dimethylsulfoxide (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 preferred.

As described above, the resin composition prepared as the membrane-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. The coating method can be appropriately selected from known coating methods such as slot die coating, knife coating, microgravure coating, bar coating, and spin coating. Examples of the support film include porous films made of organic or inorganic materials. Among them, porous polymer membranes such as polysulfone, polyethersulfone, polyamide, polyimide, polyacrylonitrile, polystyrene, polyvinylidene fluoride, polyvinyl chloride, and polymethyl methacrylate, such as ultrafiltration membranes and microfiltration membranes, are preferred. be. The shape of the support membrane can be appropriately selected from various shapes such as film, hollow fiber, and cylindrical. The pore size and thickness of the supporting membrane are not particularly limited as long as they do not interfere with the object of the present invention.

In the second step of the method for producing a gas separation membrane of the present invention, the solvent is removed from the resin composition coated on the support membrane to form a dry coating. Drying can be carried out by appropriately selecting from a natural drying method under normal temperature and normal pressure, a ventilation drying method, a reduced pressure drying method, and the like. In addition, drying does not crosslink the copolymer (A) and/or the hydrophilic crosslinkable compound (B) contained in the resin composition, and the copolymer (A) and/or the hydrophilic crosslinkable compound (B) does not crosslink. A heating means can also be used as long as microcrystals of the compound (B) are not precipitated on the film 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 deterioration of the performance of the separation membrane.

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

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

In the method for producing a gas separation membrane of the present invention, thermal crosslinking is performed under moist heat conditions. Thermal crosslinking may vary depending on the types of the copolymer (A) and the hydrophilic crosslinkable compound (B) that constitute the separation membrane. It is preferably carried out under moist heat conditions of ~90% RH. By performing thermal crosslinking under the conditions within the above range, it is possible to prevent deterioration of robustness by suppressing deterioration of flexibility while imparting rigidity to the separation membrane. Therefore, a gas separation membrane having robustness can be obtained.

As used herein, the term “robustness” refers to the durability of a separation membrane against repeated pressure loads. On the other hand, in the separation membrane thermally crosslinked under the conditions within the above range, groups such as hydroxyl groups and amino groups remain in the separation membrane in an appropriate amount. It also retains its properties and affinity for carbon dioxide, and can exhibit a good carbon dioxide membrane permeation rate and carbon dioxide selectivity.

If the thermal crosslinking is performed at a temperature of less than 60° C., the crosslinking reaction does not proceed sufficiently, so that rigidity is not imparted and desired robustness cannot be obtained. If the thermal cross-linking temperature exceeds 95° C., the cross-linking reaction proceeds sufficiently, but the flexibility is lowered and the desired robustness cannot be obtained. If the thermal cross-linking is carried out at a relative humidity of less than 40% RH, the cross-linking reaction will proceed satisfactorily, but the flexibility will be reduced and the desired robustness will not be obtained. If the thermal crosslinking is carried out at a relative humidity exceeding 90% RH, the crosslinking reaction will not proceed sufficiently, so that rigidity will not be imparted and the desired robustness will not be obtained.

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

The affinity and water retention of the gas separation membrane for a mixed gas containing water vapor can be evaluated using, for example, the amount of water vapor adsorption. The water vapor adsorption amount of the gas separation membrane at a temperature of 60° C. and a relative pressure (p/p ₀ ) 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 diffusivity of the alkali metal compound (C), which is the carbon dioxide carrier in the separation membrane, decreases, so the carbon dioxide membrane permeation rate decreases. do. If the water vapor adsorption amount of the gas separation membrane exceeds 900 cm ³ (STP)/g, the cross-linking will be insufficient and the rigidity will be lacking, making it impossible to obtain the desired robustness.

Through the flow as described above, the gas separation membrane of the present invention can be produced.

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

The gas separation membranes obtained in Examples and Comparative Examples were measured and evaluated for each item according to the following methods.

<Tensile modulus>
Using a tensile tester (“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 for: 2 mm width, 35 mm length, 15 mm distance between grips. From the obtained experimental data, the vertical axis: stress (MPa) and the horizontal axis: displacement (strain %) were plotted to calculate the tensile elastic modulus (N/mm ² ) (=stress/displacement). Table 1 shows the results.

<Robustness (repeated pressure load durability) test>
Robustness tests were conducted to investigate the effects of pressure fluctuations on membrane separation performance, assuming plant startup and shutdown. In the test, the following starting and stopping operations were repeated.
1. Start-up:
Supply side: temperature 85° C., supply gas composition CO ₂ /He=40/60 (400 mL (STP)/min), relative humidity 60% RH, normal pressure up to 2.4 MPa.
Permeate side: atmospheric pressure.
After returning to normal pressure, dry gas was flowed for 5 minutes, and the membrane cell was removed from the constant temperature bath at a temperature of 85°C.
2. Shutdown: Stored for a period of time (temperature 25°C, relative humidity 50-60% RH).
3. Start-up: Reset the membrane cell, and follow the steps in 1. above. The membrane separation performance was evaluated again under the conditions of

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

O: carbon dioxide selectivity α is stable ×: helium membrane permeation rate Q _He is increased, and carbon dioxide selectivity α is decreased. Table 1 shows the results.

<Water vapor adsorption amount>
The amount of water vapor adsorption was measured using an automatic vapor adsorption amount measuring device ("BELSORP-18" (trade name), manufactured by Microtrack Bell Co., Ltd.). The measurement conditions were a temperature of 60°C.
Table 1 shows the results.

<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 ) to obtain a measurement sample. The measurement was performed by a differential pressure method with a mixed gas set to a temperature of 85° C., a composition of CO ₂ /He=40/60 (400 mL/min), and a relative humidity of 60% RH, with a total pressure of 2.4 MPa on the supply side. . Subsequently, from the following equations, carbon dioxide membrane permeation rate Q _CO2 [m ³ (STP)/(m ² · s · Pa)], helium membrane permeation velocity Q _He [m ³ (STP) / (m ² · s · Pa)] and the carbon dioxide selectivity α were determined. Table 1 shows the results.

[Example 1]
1. Preparation of non-crosslinked vinyl alcohol copolymer (A) aqueous solution Polyvinyl alcohol (PVA-1) having terminal mercapto groups was synthesized by the method described in JP-A-59-187003. The content of vinyl alcohol units (degree of saponification) determined by ¹ H-NMR measurement was 98.5 mol %, and the viscosity average degree of polymerization measured according to JIS K6726 was 1,500. Next, 1269 g of water was added to 72.0 g of PVA-1, and dissolved by heating to a temperature of 95° C. in a 1 L four-necked separable flask equipped with a reflux condenser and a stirring blade. After cooling to room temperature, 1/2N 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 aqueous solution was heated to a temperature of 90° C. while nitrogen was bubbled through it, and then nitrogen was substituted by continuously bubbling nitrogen at a temperature of 90° C. for 30 minutes. After purging with nitrogen, 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 added to the aqueous solution. It was gradually added over 1.5 hours, and after the addition was completed, it was heated at a temperature of 90° C. for 2.5 hours to complete the polymerization. After cooling to room temperature, an aqueous solution of a non-crosslinked vinyl alcohol copolymer (A), which is a block copolymer of polyvinyl alcohol and polyacrylic acid having a solid concentration of 7.5 wt %, was obtained. A portion of the obtained aqueous solution was dried, dissolved in heavy water, and subjected to ¹ H-NMR measurement. The content of acrylic acid monomer units relative to the total number of monomer units was 30 mol %2. Preparation of film-forming stock solution (resin composition solution) Aqueous solution of the above non-crosslinked vinyl alcohol copolymer (A) (hereinafter “P-2”), Poval (“PVA124” (trade name), manufactured by Kuraray Co., Ltd.), poly Allylamine ("PAA-15C" (trade name), manufactured by Nitto Boseki Co., Ltd.), polyamidoamine dendrimer (20 wt% methanol solution, manufactured by Aldrich), cross-linking agent ("Epolite 400E" (trade name), manufactured by Kyoeisha Chemical Co., Ltd. ), and using glycerin, these are P-2 / NaOH (1 M aqueous solution) / “PVA124” / “PAA-15C” / polyamidoamine dendrimer / “Epolite 400E” (10 wt% aqueous solution) / glycerin = 19.5/2 They were mixed at a ratio of 5/9/16/14/12/27 wt%, and deionized water was added to prepare a film-forming stock solution (solid concentration: 8 wt%).
3. Membrane formation The membrane-forming undiluted solution is coated on an ultrafiltration membrane ("Biomax" (trade name), manufactured by Merck Ltd.) made of polyethersulfone with a molecular weight cut off of 300,000, and is continuously formed into a membrane by a slot die method. It was coated and dried at a temperature of 80° C. for 10 minutes to obtain a composite film in which a dry film (thickness of 2 to 3 μm) was formed.
4. Thermal cross-linking The composite film was placed in a thermo-hygrostat and held for 24 hours under wet heat conditions of 80°C and 40% RH to thermally cross-link the dry 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 on which the dry coating film of the composite membrane prepared above was formed, and gas A separation membrane was produced (carbonate loading: about 30 g/m ² ).

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

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

[Example 4]
A gas separation membrane (film thickness: 2 to 3 μm) was prepared in the same manner as in Example 1, except that the thermal crosslinking of the dried coating film was performed under wet heat conditions of 80° C. and 90% RH.

[Comparative Example 1]
A gas separation membrane (film thickness: 2 to 3 μm) was prepared in the same manner as in Example 1, except that the thermal crosslinking of the dried coating film was performed under the drying conditions of a temperature of 80° C. and a relative humidity of 0% RH for 30 minutes. made.

[Comparative Example 2]
A gas separation membrane (film thickness: 2 to 3 μm) was prepared in the same manner as in Example 1, except that the thermal crosslinking of the dried coating film was performed under the drying conditions of a temperature of 80° C. and a relative humidity of 0% RH.

The gas separation membrane of the present invention has good performance of selectively separating a specific gas species, especially carbon dioxide, from a mixed gas, especially a mixed gas containing water vapor, under high pressure conditions, and is robust (repeated pressure load durability), it is useful in such applications as the separation of carbon dioxide from aqueous shift gas and natural gas produced by coal gasification.

Claims (10)

A step of applying a resin composition onto the support film;
A method for producing a gas separation membrane, comprising a step of drying the applied resin composition; and a step of thermally crosslinking the dried resin composition,
The thermal cross-linking step is performed under wet heat conditions at a temperature of 60 to 95 ° C. and a relative humidity of 40 to 90% RH.
A method for producing a gas separation membrane. 2. The method according to claim 1, wherein the resin composition comprises a non-crosslinked vinyl alcohol copolymer (A) having a carboxyl group and a hydrophilic crosslinkable compound (B). 3. The method according to claim 2, wherein the non-crosslinked vinyl alcohol-based copolymer (A) having a carboxyl group contains acrylic acid or methacrylic acid monomer units and vinyl alcohol-based monomer units. The hydrophilic crosslinkable compound (B) is at least selected from the group consisting of polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinylpyrrolidone, polyacrylamide, polyamidoamine dendrimer, polyethyleneimine, polyallylamine and polyvinylamine. 4. A method according to claim 2 or 3, having one structural unit. The method according to any one of claims 2 to 4, wherein the resin composition further comprises an alkali metal compound (C). 6. The method of claim 5, wherein said alkali metal compound (C) is selected from the group consisting of alkali metal hydroxides, alkali metal carbonates and alkali metal bicarbonates. The resin composition is

7. The method of claim 5 or 6, further comprising an amine-coordinated zinc complex (D) selected from the group consisting of: A gas separation membrane produced by the method according to any one of claims 1 to 7. In a water vapor adsorption test at a temperature of 60° C., the water vapor adsorption amount is in the range of 150 to 900 cm ³ (STP)/g at a relative pressure range of 0.5 to 0.9,
9. The gas separation membrane according to claim 8, which has a tensile modulus of 5 to 7 N/mm ² under measurement conditions of a temperature of 25° C. and a relative humidity of 60% RH. 10. Gas separation membrane according to claim 8 or 9 for separating carbon dioxide.

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