Ionic liquid-containing gel membrane

Abstract

The present invention provides an ionic liquid-containing gel membrane that is a separation membrane that selectively permeates carbon dioxide, can be thinned, and achieves both gas permeability and selectivity. [Solution] The ionic liquid-containing gel membrane is a separation membrane that selectively allows carbon dioxide to permeate, and contains a gel having a three-dimensional network structure formed by a terminal cross-linking reaction between multiple hyperbranched polyethylene glycol compounds, and an ionic liquid, where the ionic liquid contains an anion and a cation that contain a cyano group.

Description

[Technical Field]

[0001] The present invention relates to an ionic liquid-containing gel film. [Background technology]

[0002] In recent years, there has been an increasing need for technologies to reduce the concentration of carbon dioxide in the air as a measure against global warming. Among these technologies, membrane separation, which uses a carbon dioxide separation membrane to selectively separate carbon dioxide, is attracting attention as a more energy-efficient process than chemical absorption, because it can separate carbon dioxide without additional energy by simply contacting the target gas with the membrane as long as there is a partial pressure difference on both sides of the membrane.

[0003] Membrane separation, an energy-saving process, is also used to separate and capture carbon dioxide from boiler exhaust gases, a heat source at chemical plants and other facilities. However, the carbon dioxide concentration in the exhaust gas is low, at approximately 10% by mass, and the gas pressure is equivalent to atmospheric pressure. Therefore, to take advantage of the energy-saving characteristics of membrane separation, which uses partial pressure difference as a driving force, carbon dioxide separation membranes must not only have high selectivity, which is the ability to selectively permeate carbon dioxide, but also gas permeability, which is the capacity to permeate large amounts of gas. However, as described in Non-Patent Document 1, high selectivity and high permeability are generally said to be in a trade-off relationship, and various methods have been attempted to achieve both.

[0004] Various liquid membranes, in which a porous structure is impregnated with a liquid component, are known as gas separation membranes used in membrane separation methods. Because the diffusion coefficient in liquids is higher than in polymers, liquid membranes tend to be highly permeable separation membranes. One type of liquid membrane proposed is one that uses an ionic liquid as the liquid component. Ionic liquids typically have extremely low volatility and remain liquid at room temperature, allowing for long-term storage in an atmospheric environment. However, liquids that are advantageous in terms of substance mobility are vulnerable to the pressure differences that are unavoidable in gas separation processes, and ionic liquids generally leak out of the porous structure. For this reason, as described in Non-Patent Document 2, a technology is known that employs a highly strong gel membrane as the porous structure and impregnates the gel membrane with an ionic liquid to form an ionic liquid-containing gel membrane, thereby stably trapping the ionic liquid within the membrane.

[0005] As an example, Patent Document 1 discloses a carbon dioxide separation membrane in which an ionic liquid is impregnated into a double network (DN) gel membrane containing a polymer network structure and an inorganic particle network structure formed from inorganic particles. Patent Document 2 also discloses a carbon dioxide separation membrane in which an ionic liquid is impregnated into an interpenetrating polymer network (IPN) gel membrane made of two different types of polymers. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-37688 [Patent Document 2] International Publication No. 2023-032744 [Non-patent literature]

[0007] [Non-Patent Document 1] Journal of Membrane Science 320(2008), pp. 390-400 [Non-patent document 2] Gel Technology Handbook NTS 2014 Volume 1 Chapter 8 Summary of the Invention [Problem to be solved by the invention]

[0008] According to the solution-diffusion mechanism, which is generally known as the permeation mechanism in gas separation membranes, it is self-evident and common technical knowledge that the thinner the membrane, the higher the permeability due to the diffusion resistance. It is expected that ionic liquid-containing gel membranes used as carbon dioxide separation membranes can also be made thinner to achieve both high permeability and high selectivity.

[0009] However, in reality, thinning an ionic liquid-containing gel membrane is not easy because defects such as pinholes are likely to occur. Through extensive research by the present inventors, it has been found that in order to achieve the desired processing capacity of a carbon dioxide separation membrane for carbon dioxide contained in exhaust gases and air, it is necessary to increase gas permeability by making the membrane thickness at least 1 μm or less.

[0010] In contrast, the ionic liquid-containing gel membranes specifically disclosed in the examples of Patent Documents 1 and 2 all have thicknesses exceeding 1 μm. As is clear from this, the thinning technology for ionic liquid-containing gel membranes used in carbon dioxide separation membranes is insufficient, and there is a need to develop a thinning technology that can meet the increasing demand for high permeability in recent years.

[0011] An object of the present invention is to provide an ionic liquid-containing gel membrane that is a separation membrane that selectively permeates carbon dioxide, can be thinned, and achieves both gas permeability and selectivity. [Means for solving the problem]

[0012] <1> According to one aspect of the present invention, there is provided an ionic liquid-containing gel membrane, which is a separation membrane that selectively permeates carbon dioxide, and which comprises a gel having a three-dimensional network structure formed by a terminal cross-linking reaction between a plurality of hyperbranched polyethylene glycol compounds, and an ionic liquid, wherein the ionic liquid contains an anion and a cation that contain a cyano group.

[0013] <2> According to another aspect of the present invention, the thickness is 1 μm or less. <1> The ionic liquid-containing gel film according to the present invention is provided.

[0014] <3> According to yet another aspect of the present invention, the plurality of multi-branched polyethylene glycol compounds are a first 4-branched polyethylene glycol compound having a thiol group at each end and a second 4-branched polyethylene glycol compound having a monovalent organic group containing a carbon-carbon double bond at each end, and the crosslinking is caused by a thiol-ene reaction between the thiol groups and the organic groups. <1> or <2> The ionic liquid-containing gel film according to the present invention is provided.

[0015] <4> According to yet another aspect of the present invention, the organic group at each end of the second 4-branched polyethylene glycol compound is a maleimidyl group represented by the following formula: <3> The ionic liquid-containing gel film according to the present invention is provided.

[0016] [ka] In the formula, * represents the bonding site to the remainder of the second 4-branched polyethylene glycol compound.

[0017] <5> According to yet another aspect of the present invention, the mass average molecular weight Mw1 of the first 4-branched polyethylene glycol compound and the mass average molecular weight Mw2 of the second 4-branched polyethylene glycol compound each fall within the range of 5,000 g / mol or more and 100,000 g / mol or less. <3> or <4> The ionic liquid-containing gel film according to the present invention is provided.

[0018] <6> According to yet another aspect of the present invention, the ionic liquid contains at least a tricyanomethanide ion, a tetracyanoborate ion, or a dicyanoamide ion as the cyano group-containing anion. <1> ~ <5> The ionic liquid-containing gel film according to any one of the above items is provided.

[0019] <7> According to yet another aspect of the present invention, the ionic liquid contains at least a tricyanomethanide ion or a tetracyanoborate ion as the cyano group-containing anion. <4> The ionic liquid-containing gel film according to the present invention is provided.

[0020] <8> According to yet another aspect of the present invention, the ionic liquid contains at least a 1-ethyl-3-methylimidazolium ion as the cation. <1> ~ <7> The ionic liquid-containing gel film according to any one of the above items is provided.

[0021] <9> According to yet another aspect of the present invention, the content of the ionic liquid is in the range of 70 parts by mass or more and 98 parts by mass or less per 100 parts by mass of the ionic liquid-containing gel film. <1> ~ <8> The ionic liquid-containing gel film according to any one of the above items is provided.

[0022] <10> According to yet another aspect of the present invention, there is provided a porous support and a <1> ~ <9> and a carbon dioxide separation membrane made of the ionic liquid-containing gel membrane according to any one of the above. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide an ionic liquid-containing gel membrane that is a separation membrane that selectively permeates carbon dioxide, can be made thin, and achieves both permeability and selectivity. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a cross-sectional view of a carbon dioxide separation membrane-containing laminate according to one embodiment of the present invention. [Figure 2] FIG. 2 is a microscopic image of a cross section of a carbon dioxide separation membrane-containing laminate according to one example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described below are more specific embodiments of any of the above aspects. The following items can be incorporated into each of the above aspects, either singly or in combination.

[0026] Furthermore, the embodiments shown below are merely examples of configurations for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention is not limited by the materials, shapes, structures, etc. of the components described below. Various modifications can be made to the technical idea of ​​the present invention within the technical scope defined by the claims.

[0027] In the drawings, elements having the same or similar functions are denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, the drawings are schematic, and the relationship between dimensions in one direction and dimensions in another direction, and the relationship between the dimensions of one member and the dimensions of another member, etc. may differ from the actual relationship.

[0028] <<Ionic liquid-containing gel membrane and carbon dioxide separation membrane-containing laminate>> Fig. 1 is a cross-sectional view of a carbon dioxide separation membrane-containing laminate according to one embodiment of the present invention. Fig. 2 is a microscope image of a cross-section of a carbon dioxide separation membrane-containing laminate according to one example of the present invention. The cross-sections shown in Figs. 1 and 2 are cross-sections along the thickness direction of the carbon dioxide separation membrane-containing laminate.

[0029] The carbon dioxide separation membrane-containing laminate 10 shown in Fig. 1 comprises a porous support 1 and a carbon dioxide separation membrane 2 provided on one surface thereof. The carbon dioxide separation membrane 2 is an ionic liquid-containing gel membrane containing a gel having a three-dimensional network structure in which multiple hyperbranched polyethylene glycol compounds (prepolymers) are crosslinked at their ends, and an ionic liquid. The ionic liquid contains an anion and a cation containing a cyano group.

[0030] The carbon dioxide separation membrane-containing laminate 10 is suitable for selectively removing carbon dioxide from a gas to be treated (gas to be separated), and the gas to be separated may be a mixed gas containing carbon dioxide. As described in detail below, the carbon dioxide separation membrane 2 included in the carbon dioxide separation membrane-containing laminate 10 can be thinned and has excellent gas permeability, and therefore can be suitably applied to, for example, separating and removing carbon dioxide from exhaust gas or air in a chemical plant or the like where the partial pressure of carbon dioxide in the mixed gas is low.

[0031] <Porous support> The porous support 1 supports a carbon dioxide separation membrane 2 made of an ionic liquid-containing gel membrane that can be thinned, thereby making it possible to provide a carbon dioxide separation membrane-containing laminate 10 that is particularly excellent in gas permeability. For this reason, the porous support 1 needs to be a porous substrate that can support a gel-like thin film that has been thinned to a thickness of, for example, 1 μm or less.

[0032] The material of the porous support 1 can be, for example, a permeable (porous) polymer containing at least one selected from polytetrafluoroethylene (PTFE), mixed cellulose esters, polyketones, etc. The shape of the porous support 1 may be any shape such as a flat membrane, a tube, or a hollow fiber.

[0033] The membrane thickness of the porous support 1 is preferably in the range of 10 μm to 1000 μm, more preferably in the range of 20 μm to 100 μm. If the membrane thickness is small, the support may not have sufficient mechanical strength to support the carbon dioxide separation membrane 2. On the other hand, if the membrane thickness is large, the flexibility of the membrane tends to be impaired, making it difficult to handle, and the resistance to gas permeation may increase, which is undesirable.

[0034] The average size of the pores in the porous support 1 (average pore diameter) is preferably in the range of 0.01 μm to 10 μm, more preferably in the range of 0.06 μm to 1 μm. If the pore diameter is small, the gas permeability of the resulting laminate 10 may be insufficient. On the other hand, if the pore diameter is large, for example, when a reaction solution for forming a carbon dioxide separation membrane is applied to the porous support 1 and formed into a thin film, problems may arise, such as the reaction solution penetrating into the pores and filling them, or pinholes being generated. Here, the pore diameter can be measured by a conventional method such as mercury intrusion porosimetry.

[0035] <Carbon dioxide separation membrane> The carbon dioxide separation membrane 2 is an ionic liquid-containing gel membrane obtained by impregnating a gel with an ionic liquid. The gel constituting this ionic liquid-containing gel membrane is a high-strength gel with a uniform, high-strength three-dimensional network structure obtained by a terminal cross-linking reaction between multiple hyperbranched compounds having a polyethylene glycol (PEG) skeleton.

[0036] Other high-strength gels with different structures include double network (DN) gel membranes (see Patent Document 1) consisting of the above-mentioned polymer network structure and inorganic particle network structure, and interpenetrating polymer network (IPN) gel membranes consisting of two types of polymers (see Patent Document 2). The present inventors have demonstrated that these gel membranes are prone to defects such as pinholes when attempting to thin them to, for example, 1 μm or less, making thinning difficult. The present inventors speculate that the reason for this is that DN gel membranes and IPN gel membranes essentially derive their strength from the entanglement of heterogeneous substances, and that these entanglement points become a hindrance when thinning to a thickness of 1 μm or less, causing defects.

[0037] In contrast, the gel that constitutes the ionic liquid-containing gel membrane, which is the carbon dioxide separation membrane 2, has a uniform, high-strength three-dimensional network structure constructed by crosslinking multiple hyperbranched polyethylene glycol compounds at their ends, as described above. This gel is a high-strength gel consisting of a "single three-dimensional network structure" that does not have entanglement points with heterogeneous substances, as in DN gel membranes and IPN gel membranes, and is therefore less likely to develop defects when made thin.

[0038] The multiple multi-branched polyethylene glycol compounds may each be a multi-branched polyethylene glycol compound having three or more polyethylene glycol branches and having three or more polyethylene glycol branches. In particular, when the multiple multi-branched polyethylene glycol compounds are tetra-branched polyethylene glycol compounds, the gel formed by their terminal cross-linking reaction is called Tetra-PEG, which can have an ideal uniform three-dimensional network structure and is therefore preferable from the viewpoint of thin film formation. When the gel has a uniform three-dimensional network structure, it is presumed that the occurrence of structurally weak parts in the gel is suppressed, making it less likely for defects to occur when the gel is thinned.

[0039] In a preferred embodiment, the gel contained in the ionic liquid-containing gel membrane, which is the carbon dioxide separation membrane 2, has a three-dimensional network structure derived from a first 4-branched polyethylene glycol compound having a thiol group (—SH) at each end and a second 4-branched polyethylene glycol compound having a monovalent organic group containing a carbon-carbon double bond at each end (hereinafter, sometimes referred to as a “C═C-containing group”). In this case, the terminal functional groups contained in the first 4-branched polyethylene glycol compound and the second 4-branched polyethylene glycol compound do not react with each other intramolecularly, and no intramolecular reaction occurs. Furthermore, one thiol group in the first 4-branched polyethylene glycol compound is crosslinked with a carbon-carbon double bond (C═C) in the second 4-branched polyethylene glycol compound by a thiol-ene reaction, resulting in a uniform and high-strength three-dimensional network structure.

[0040] The first 4-branched polyethylene glycol compound having a thiol group (-SH) at each end (hereinafter, may be referred to as "Tetra-PEG-SH") is, for example, a compound represented by the following formula (I):

[0041] [ka]

[0042] In formula (I), n1 is an integer of 15 to 250, Y1 is a hydrocarbon group having 1 to 15 carbon atoms, *—CO—R 11 -**, *-CO-NH-R 11 -**, *-R 12 -OR 13 -**, *-R 12 -NH-R 13 -**, *-R 12 -CO-R 13 -**, *-R 12 -COO-R 13 -**, *-R 12 -CO-NH-R 13 -** or *-R 12 -O-CO-NH-R 13 -** and R 11 , R12 and R 13 are each independently a hydrocarbon group having 1 to 10 carbon atoms. Here, * and ** represent a bonding site with a thiol group (-SH) or an oxygen atom in formula (I). Each of the multiple n1s is independent and may be the same or different, and each of the multiple Y1s is independent and may be the same or different.

[0043] In formula (I), n1 is an integer of 15 or more and 250 or less, preferably an integer of 35 or more and 180 or less, more preferably an integer of 50 or more and 110 or less, and particularly preferably an integer of 50 or more and 60 or less. Multiple n1s are independent of each other and may be the same or different from each other. From the viewpoint of thinning and strength of the gel membrane, it is preferable that n1s are the same. When multiple n1s are the same, the polymer after polymerization tends to have a uniform three-dimensional network structure, and a gel membrane that is high in strength and can be thinned tends to be obtained. A high-strength gel membrane is preferred because it has excellent pressure resistance and permeability when used as a carbon dioxide separation membrane.

[0044] In formula (I), specific examples of the hydrocarbon group having 1 to 15 carbon atoms in Y1 include a methylene group, an ethylene group, a propylene group, a butylene group, a hexylene group, an octylene group, a cyclopentylene group, and a cyclohexylene group. From the viewpoint of ease of synthesis of raw materials, Y1 is preferably an ethylene group. 11 , R 12 and R 13Specific examples of the hydrocarbon group having 1 to 10 carbon atoms in the formula (I) include a methylene group, an ethylene group, a propylene group, a butylene group, a hexylene group, an octylene group, a cyclopentylene group, a cyclohexylene group, a phenylene group, and a tolylene group. Multiple Y1s are independent of each other and may be the same or different. From the viewpoint of thinning and strength of the gel membrane, it is preferable that Y1s are the same. When multiple Y1s are the same, the polymer after polymerization tends to have a uniform three-dimensional network structure, and a gel membrane that is high in strength and can be thinned tends to be obtained. A high-strength gel membrane is preferred because it has excellent pressure resistance and permeability when used as a carbon dioxide separation membrane.

[0045] The second 4-branched polyethylene glycol compound having a C═C-containing group at each end (hereinafter, may be referred to as "Tetra-PEG-C═C") is, for example, a compound represented by the following formula (II):

[0046] [ka]

[0047] In formula (II), n2 is an integer of 15 to 250, Y2 is a hydrocarbon group having 1 to 15 carbon atoms, -CO-, *-CO-NH-**, *-CO-R 21 -**, *-CO-NH-R 21 -**, *-R 22 -OR 23 -**, *-R 22 -NH-R 23 -**, *-R 22 -CO-R 23 -**, *-R 22 -COO-R 23 -**, *-R 22 -CO-NH-R 23 -** or *-R 22 -O-CO-NH-R 23 -** and R 21 , R 22 and R 23are each independently a hydrocarbon group having 1 to 10 carbon atoms, and R2 is a monovalent organic group having a carbon-carbon double bond (a C=C-containing group). Here, * and ** represent the bonding site with R2 or an oxygen atom in formula (II). Multiple n2s are each independent and may be the same or different from one another, multiple Y2s are each independent and may be the same or different from one another, and multiple R2s are each independent and may be the same or different from one another.

[0048] In formula (II), n2 is an integer of 15 or more and 250 or less, preferably an integer of 35 or more and 180 or less, more preferably an integer of 50 or more and 110 or less, and particularly preferably an integer of 50 or more and 60 or less. Multiple n2's are independent of each other and may be the same or different from one another. From the viewpoint of thinning and strength of the gel membrane, it is preferable that n2's are the same. When multiple n2's are the same, the polymer after polymerization tends to have a uniform three-dimensional network structure, and a gel membrane that is high in strength and can be thinned tends to be obtained. A high-strength gel membrane is preferred because it has excellent pressure resistance and permeability when used as a carbon dioxide separation membrane.

[0049] In formula (II), specific examples of the hydrocarbon group having 1 to 15 carbon atoms in Y2 include a methylene group, an ethylene group, a propylene group, a butylene group, a hexylene group, an octylene group, a cyclopentylene group, a cyclohexylene group, a phenylene group, and a tolylene group. 21 , R 22 and R 23 Specific examples of the hydrocarbon group having 1 to 10 carbon atoms include a methylene group, an ethylene group, a propylene group, a butylene group, a hexylene group, an octylene group, a cyclopentylene group, a cyclohexylene group, a phenylene group, and a tolylene group.

[0050] Y2 is preferably -CO-R from the viewpoint of ease of synthesis of raw materials. 21 -, and more preferably R 21is a methylene group, that is, Y2 is -CO-CH2-. Multiple Y2s are independent and may be the same or different from one another. From the viewpoint of thinning and strength of the gel membrane, it is preferable that Y2s are the same from the viewpoint of thinning and strength of the gel membrane. When multiple Y2s are the same, the polymer after polymerization tends to have a uniform three-dimensional network structure, and a gel membrane that is high in strength and can be thinned tends to be obtained. A high-strength gel membrane is preferred because it has excellent pressure resistance and permeability when used as a carbon dioxide separation membrane.

[0051] In formula (II), specific examples of the monovalent C═C-containing group represented by R2 include organic groups represented by the following formula: In the following formula, * represents the bonding site to the remainder of the second 4-branched polyethylene glycol compound.

[0052] [ka]

[0053] In this embodiment, in formula (II), it is preferable that four R2 are maleimidyl groups. That is, it is preferable that the compound is represented by the following formula (IIa). In formula (IIa), the definitions of n2 and Y2 are the same as those of n2 and Y2 in formula (II).

[0054] [ka]

[0055] It is preferable that all four ends of the second 4-branched polyethylene glycol compound are maleimidyl groups, for example, from the viewpoint of thin film formation, one of the reasons for which is an appropriate gelation rate.

[0056] Specifically, in forming a thin ionic liquid-containing gel film having a thickness of 1 μm or less, a gel precursor solution is prepared by mixing multiple hyperbranched polyethylene glycol compounds and an ionic liquid in a solvent. This gel precursor solution is then applied to a substrate, such as a porous support or a sacrificial film, to form a gel precursor film. This gel precursor film is then gelled by a terminal crosslinking reaction between the hyperbranched polyethylene glycol compounds, resulting in the formation of a three-dimensional network structure. In this case, it is preferable that the crosslinking reaction in the gel precursor solution prior to application to the substrate be sufficiently suppressed so as to prevent significant gelation. On the other hand, it is preferable that the gelation proceeds sufficiently after the gel precursor film is formed, resulting in a thin gel film with excellent gel strength. Although the reason for this is not entirely clear, it is believed that the combination of a thiol group and a maleimidyl group as the terminal functional groups in the hyperbranched polyethylene glycol compound provides the required moderate gelling rate both while the gel precursor solution is in solution before being applied to the substrate and after it has been formed into a thin gel precursor film, in order to obtain a high-strength gel film having a thickness of 1 μm or less.

[0057] In this embodiment, the mass average molecular weight Mw1 of the first 4-branched polyethylene glycol compound (Tetra-PEG-SH) and the mass average molecular weight Mw2 of the second 4-branched polyethylene glycol compound (Tetra-PEG-C=C) are each preferably in the range of 5,000 g / mol or more and 100,000 g / mol or less, and more preferably in the range of 5,000 g / mol or more and 50,000 g / mol or less. It is more preferable that the mass average molecular weight of the first and second 4-branched polyethylene glycol compounds is within this range. If the mass average molecular weights of the first and second 4-branched polyethylene glycol compounds are small, it tends to be difficult to obtain sufficient gel strength. Furthermore, if the mass average molecular weights of the first and second 4-branched polyethylene glycol compounds are large, the viscosity of the gel precursor solution becomes too high, making it difficult to apply the gel precursor solution in the form of a thin film. Here, the mass average molecular weight of the polyethylene glycol compound is determined from the polystyrene-equivalent molecular weight measured by gel permeation chromatography (GPC).

[0058] The blending ratio of the first 4-branched polyethylene glycol compound (Tetra-PEG-SH) and the second 4-branched polyethylene glycol compound (Tetra-PEG-C=C) that constitute the three-dimensional network structure of the carbon dioxide separation membrane 2 is preferably such that the ratio m1 / m2, where m1 is the number of moles of thiol groups in the first 4-branched PEG compound and m2 is the number of moles of carbon-carbon double bonds in the second 4-branched PEG compound, is within the range of 0.8 to 1.2, and more preferably within the range of 0.95 to 1.05. When m1 and m2 are the numbers of moles of terminal functional groups in the first and second 4-branched polyethylene compounds that fall within the above ranges, the polymerization reaction proceeds uniformly, making it possible to obtain a more uniform and stronger gel.

[0059] The first 4-branched polyethylene glycol compound represented by formula (I) and the second 4-branched polyethylene glycol compound represented by formula (II) may be produced by known methods or may be obtained as a commercially available product, for example, from NOF Corporation.

[0060] <Ionic liquid> The carbon dioxide separation membrane 2 contains an ionic liquid within its three-dimensional network structure. Ionic liquids have low volatility and are liquid at room temperature, so they are suitable for use as a liquid component in liquid membranes used as gas separation membranes. Here, from the viewpoint of selective permeability to carbon dioxide, an ionic liquid containing a cyano group as the anion is used. Among these, an ionic liquid containing any one of a tricyanomethanide ion, a tetracyanoborate ion, and a dicyanoamide ion as the anion is preferred, and an ionic liquid containing any one of a tricyanomethanide ion or a tetracyanoborate ion as the anion is more preferred.

[0061] Specific examples of cations constituting the ionic liquid include imidazolium cations, pyridinium cations, pyrrolidinium cations, piperidinium, ammonium, phosphonium cations, etc. Among these, imidazolium cations are preferred from the viewpoints of ease of preparation of the gel precursor solution prepared in the manufacturing process of the ionic liquid-containing gel film, uniformity of the resulting gel, etc.

[0062] The imidazolium cation preferably has one or more substituents selected from an alkyl group, an alkyl ether group, an alkylamine group, a 2-hydroxyethyl group, a 2-methoxyethyl group, a 2-(methylthio)ethyl group, etc. Specific examples of such imidazolium cations include 1-ethyl-3-methylimidazolium, 1-(2-hydroxyethyl)-3-methylimidazolium, 1-(2-methoxyethyl)-3-methylimidazolium, and 1-methyl-3-(2-(methylthio)ethyl)imidazolium.

[0063] The content of the ionic liquid in the carbon dioxide separation membrane 2 is preferably in the range of 70 parts by mass to 98 parts by mass, and more preferably in the range of 80 parts by mass to 95 parts by mass, per 100 parts by mass of the carbon dioxide separation membrane 2. An appropriate content of the ionic liquid is preferable from the viewpoint of achieving both gas permeability and selectivity. On the other hand, a high content of the ionic liquid tends to decrease the gel strength.

[0064] The thickness of the carbon dioxide separation membrane 2 is preferably 1 μm or less. A thickness of 1 μm or less is preferable because it improves permeability and enables both permeability and selectivity to be achieved. The thickness of the carbon dioxide separation membrane 2 is, for example, 100 nm or more, and in another example, 150 nm or more. The thickness of the carbon dioxide separation membrane 2 can be adjusted, for example, by adjusting the solids concentration (total concentration of the hyperbranched polyethylene glycol compound and the ionic liquid) contained in the gel precursor solution.

[0065] <<Method of manufacturing a carbon dioxide separation membrane-containing laminate>> The carbon dioxide separation membrane-containing laminate 10 is manufactured, for example, by the following method. Note that, although a manufacturing method using a sacrificial film and a transfer technique is described here, it can also be manufactured without using a sacrificial film or a transfer technique, as described later.

[0066] The manufacturing method using a sacrificial film and transfer technology includes a lamination step of laminating a sacrificial film and a gel precursor film on a substrate in this order, a step of causing a crosslinking reaction within the gel precursor film to form an ionic liquid-containing gel film, a lamination step of laminating a porous support onto the ionic liquid-containing gel film, and a transfer step of removing the substrate and the sacrificial film and transferring the ionic liquid-containing gel film onto the porous support. This manufacturing method is excellent as a technology for manufacturing thin ionic liquid-containing gel films without causing defects.

[0067] <Lamination process> The sacrificial film and the gel precursor film are laminated in this order on a substrate, which may be a commercially available glass plate or the like.

[0068] The sacrificial film is removed together with the substrate in the transfer process described below. The sacrificial film must be removable in the transfer process and must be difficult to dissolve in the solvent of the gel precursor solution described below. For example, when polystyrene is used as the material for forming the sacrificial film, a solvent that does not dissolve polystyrene (e.g., acetonitrile) is used as the solvent for the gel precursor solution.

[0069] A sacrificial film containing polystyrene is formed, for example, using a solution in which polystyrene is dissolved in a solvent such as toluene. A coating film made of the polystyrene solution is formed on one surface of a substrate such as a glass plate using a known coating method such as a spin coater, wire bar, roll coater, gravure coater, knife coater, or die coater. The coating film is dried to volatilize the solvent, thereby obtaining a sacrificial film.

[0070] The gel precursor film is formed by applying a gel precursor solution to a sacrificial film using a known coating method such as a spin coater, wire bar, roll coater, gravure coater, knife coater, or die coater. The gel precursor solution contains multiple hyperbranched polyethylene glycol compounds, an ionic liquid, and a solvent. The solvent is selected to dissolve the hyperbranched polyethylene glycol compounds and the ionic liquid but not the sacrificial film. Before applying the gel precursor solution to the sacrificial film, it is preferable to hydrophilize the surface of the sacrificial film by plasma treatment.

[0071] The gel precursor solution is prepared, for example, by mixing a first solution containing Tetra-PEG-SH, an ionic liquid, and a solvent with a second solution containing Tetra-PEG-C=C, an ionic liquid, and a solvent. The solvent selected is one that dissolves Tetra-PEG-SH, Tetra-PEG-C=C, and the ionic liquid but does not dissolve the sacrificial film. When polystyrene is used as the material for forming the sacrificial film as described above, acetonitrile, for example, is used as the solvent. At least one of the first and second solutions preferably contains a catalyst that promotes crosslinking by a thiol-ene reaction between -SH groups and C=C-containing groups. For example, the first solution may further contain 2-methylimidazole. 2-Methylimidazole converts thiolate ions (-S) of thiol groups (-SH) into thiolate ions (-S). - ) contributes to the deprotonation of

[0072] <Ionic liquid-containing gel film formation process> The ionic liquid-containing gel film is formed by inducing a terminal crosslinking reaction within the gel precursor film and promoting gelation. This reaction can be carried out, for example, by leaving the film at rest at 5 to 50°C for 1 minute to 24 hours.

[0073] A drying step may be carried out after this gelling step. In the drying step, the solvent component is removed using, for example, a thermostatic bath or a hot air dryer. The heating temperature and heating time may be any temperature that can remove the solvent. For example, they may be set within the range of 30 to 200°C and 1 minute to 24 hours. This results in a laminate in which a sacrificial film and a thinned ionic liquid-containing gel film are laminated in this order on the substrate.

[0074] <Lamination process> A porous support 1 is prepared. The laminate obtained above is laminated onto the porous support 1 so that the ionic liquid-containing gel membrane faces the porous support 1, thereby bonding the porous support 1 and the ionic liquid-containing gel membrane together.

[0075] <Transfer process> In the transfer step, the substrate and sacrificial film are removed, and the ionic liquid-containing gel film is transferred to the porous support 1. The transfer is performed by immersing the laminated body bonded in the bonding step in a solvent to dissolve the sacrificial film. By providing a sacrificial film, the thinned ionic liquid-containing gel film can be more easily peeled off than when peeled off from the substrate without providing a sacrificial film.

[0076] The solvent used here may be any solvent that can dissolve the sacrificial film. For example, when polystyrene is used as the sacrificial film, toluene can be used as the solvent.

[0077] In this way, the ionic liquid-containing gel membrane that constitutes the carbon dioxide separation membrane 2 is transferred from the substrate to the porous support 1 by dissolving the sacrificial membrane, and the carbon dioxide separation membrane-containing laminate 10 is obtained.

[0078] The carbon dioxide separation membrane-containing laminate 10 may also be produced by other methods. For example, without using the above-mentioned sacrificial film or transfer technique, a gel precursor solution may be applied to one surface of the porous support 1 by a known coating method using a spin coater, wire bar, roll coater, gravure coater, knife coater, die coater, or the like to form a gel precursor membrane, and then the ionic liquid-containing membrane may be formed through the above-mentioned gelling and drying steps. [Example]

[0079] The following describes examples of the present invention. 1. Examples 1 to 6 1.1 Preparation of gel precursor solution Six types of gel precursor solution A with different dilution rates 0.4 , A 0.6 , A 0.8 , A 1.2 , A 1.4 and A 3.0 was prepared. Here, the dilution ratio of the gel precursor solution refers to the ratio expressed as [mass of acetonitrile] / [total mass of the multi-branched PEG compound and ionic liquid]. Note that the following catalysts, which are used in extremely small amounts, have little effect on the dilution ratio and are therefore not included in the above formula.

[0080] (Gel precursor solution A 3.0 ) Gel precursor solution A at a dilution ratio of 3.0 3.0 was prepared as follows: SUNBRIGHT (registered trademark) PTE-200SH (manufactured by NOF Corporation, Mw1=20,000) represented by the following structural formula was prepared as a 4-branched PEG compound having a thiol group at each end (Tetra-PEG-SH), and SUNBRIGHT PTE-200MA (manufactured by NOF Corporation, Mw2=20,000) represented by the following structural formula was prepared as a 4-branched PEG compound having a maleimidyl group at each end (Tetra-PEG-MA).

[0081] [ka]

[0082] Approximately 2 g of Tetra-PEG-SH solution was prepared by mixing 0.1 g of Tetra-PEG-SH, 0.4 g of 1-ethyl-3-methylimidazolium tricyanomethanide ([Emim][C(CN)3]) manufactured by Tokyo Chemical Industry Co., Ltd. as an ionic liquid, 1.5 g of acetonitrile (Fujifilm Wako Pure Chemical Industries, Ltd.) as a solvent, and 0.00075 g of 2-methylimidazole as a reaction catalyst. 2 g of Tetra-PEG-MA solution was also prepared by mixing 0.1 g of Tetra-PEG-MA, 0.4 g of the above [Emim][C(CN)3], and 1.5 g of the above acetonitrile. The Tetra-PEGSH solution and the Tetra-PEG-MA solution were mixed in equal amounts and stirred for approximately 20 seconds to obtain gel precursor solution A. 3.0 (dilution ratio 3.0) was prepared.

[0083] (Gel precursor solution A 0.4 , A 0.6 , A 0.8 , A 1.2 and A 1.4 ) Gel precursor solution A prepared above at a dilution ratio of 3.0 3.0 Gel precursor solution A was diluted to 0.4, 0.6, 0.8, 1.2, and 1.4. 0.4 , A 0.6 , A 0.8 , A 1.2 and A 1.4 was prepared.

[0084] 1.2 Production of carbon dioxide separation membrane-containing laminate (Example 1) The carbon dioxide separation membrane laminate 10 described with reference to FIG. 1 was produced by the following method. First, polystyrene (average molecular weight 192,000) was dissolved in toluene by shaking and stirring to prepare a 5% by mass toluene solution of polystyrene. This toluene solution of polystyrene was applied to a φ90 mm disk-shaped glass substrate using a spin coater, and the substrate was placed on a hot plate at 60°C to volatilize the solvent, thereby producing a sacrificial film.

[0085] Next, the sacrificial film was subjected to plasma treatment for 300 seconds to hydrophilize the surface. The water contact angle of the hydrophilized surface was approximately 70 degrees. The gel precursor solution A prepared above with a dilution ratio of 0.4 was applied to the hydrophilized sacrificial film surface. 0.4 A gel precursor film was formed by applying 2 ml of the solution using a spin coater.

[0086] The gel precursor film was left standing in a thermostatic chamber at 25°C for one day, and then left standing in a thermostatic chamber at 40°C for one day to complete the gelation and drying of the gel precursor film. This resulted in a laminate comprising a glass substrate, a sacrificial film, and an ionic liquid-containing gel membrane (carbon dioxide separation membrane) 2.

[0087] A cellulose mixed ester type membrane filter (manufactured by Advantec Toyo Co., Ltd., pore size 0.1 μm) was prepared as the porous support 1. The laminate obtained above was laminated on this porous support 1 so that the ionic liquid-containing gel membrane (carbon dioxide separation membrane) 2 faced the porous support 1, thereby bonding the porous support 1 and the ionic liquid-containing gel membrane (carbon dioxide separation membrane) 2. This was completely immersed in a toluene solvent while being shaken. The sacrificial membrane dissolved within 1 hour.

[0088] Dissolution of the sacrificial film removed the sacrificial film and the glass substrate from the laminate, thereby completing the transfer of the ionic liquid-containing gel membrane (carbon dioxide separation membrane) 2 onto the porous support 1. In this way, a carbon dioxide separation membrane-containing laminate 10 was obtained, comprising the porous support 1 and the carbon dioxide separation membrane 2 made of the ionic liquid-containing gel membrane.

[0089] (Example 2) Gel precursor solution A with a dilution ratio of 0.4 for Example 1 0.4 A gel precursor solution with a dilution ratio of 0.6 was added. 0.6 A carbon dioxide separation membrane-containing laminate 10 was obtained in the same manner as in Example 1, except for changing the above.

[0090] (Example 3) Gel precursor solution A with a dilution ratio of 0.4 for Example 1 0.4 A gel precursor solution with a dilution ratio of 0.8 was added. 0.8A carbon dioxide separation membrane-containing laminate 10 was obtained in the same manner as in Example 1, except for changing the above.

[0091] (Example 4) Gel precursor solution A with a dilution ratio of 0.4 for Example 1 0.4 A gel precursor solution with a dilution ratio of 1.2 was added. 1.2 A carbon dioxide separation membrane-containing laminate 10 was obtained in the same manner as in Example 1, except for changing the above.

[0092] (Example 5) Gel precursor solution A with a dilution ratio of 0.4 for Example 1 0.4 A gel precursor solution with a dilution ratio of 1.4 was added. 1.4 A carbon dioxide separation membrane-containing laminate 10 was obtained in the same manner as in Example 1, except for changing the above.

[0093] (Example 6) Gel precursor solution A with a dilution ratio of 0.4 for Example 1 0.4 A gel precursor solution with a dilution ratio of 3.0 was added. 3.0 A carbon dioxide separation membrane-containing laminate 10 was obtained in the same manner as in Example 1, except for changing the above.

[0094] 2. Comparative Examples 1 to 5 Here, instead of the gel membrane having a three-dimensional network structure formed by the terminal cross-linking reaction between the hyperbranched polyethylene glycol compounds according to this example, an IPN gel membrane was produced as the gel constituting the carbon dioxide separation membrane (ionic liquid-containing gel membrane). The IPN gel membrane was basically produced in accordance with the method disclosed in the above-mentioned Patent Document 2 (International Publication No. 2023-032744).

[0095] 2.1 Preparation of gel precursor solution Five types of gel precursor solution B with different dilution rates 1.6 , B4, B5, B 10 and B 20 was prepared. Here, the dilution ratio of the gel precursor solution refers to the ratio expressed as [mass of acetone] / [total mass of gel network precursor, ionic liquid, and crosslinking agent], which will be explained below.

[0096] (Gel precursor solution B 1.6 ) Gel precursor solution B 1.6 was prepared as follows. Although the amount of each material used is not specified in the following explanation, the dilution ratio represented by the above formula was 1.6.

[0097] Acetone solution 1 of a copolymer of vinylidene fluoride and hexafluoropropylene (PVDF-co-HFP) was prepared. In a separate vial, acetone solution 2 of a copolymer of ethyl acrylate and N-acryloyloxysuccinimide (poly(EA-co-NSA)) with diethylene glycol bis(3-aminopropyl) ether (DGBE) as a crosslinker was prepared.

[0098] A predetermined amount of poly(EA-co-NSA) was added to the above acetone solution 1 and stirred for 1 hour to dissolve the poly(EA-co-NSA), yielding a PVDF-co-HFP / poly(EA-co-NSA) solution.

[0099] Next, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Emim][Tf2N]) was added as an ionic liquid to the PVDF-co-HFP / poly(EA-co-NSA) solution, and the mixture was stirred for 30 minutes to dissolve [Emim][Tf2N], yielding a PVDF-co-HFP / poly(EA-co-NSA) / [Emim][Tf2N] solution.

[0100] Next, the acetone solution 2 was added to the PVDF-co-HFP / poly(EA-co-NSA) / [Emim][TfN] solution and stirred for 20 seconds. This mixed solution was then ultrasonicated for 20 seconds to obtain gel precursor solution B. 1.6 obtained.

[0101] (Gel precursor solutions B4, B5, B 10 and B 20 ) Gel precursor solution B prepared above at a dilution ratio of 1.6 1.6The dilution ratio was changed by changing the mass ratio of acetone to the total of the ionic liquid and gel network precursor. The dilution ratios were 4, 5, 10, and 20, respectively. 10 and B 20 was prepared.

[0102] 2.2 Production of carbon dioxide separation membrane-containing laminate (Comparative Example 1) A 15% by mass aqueous solution of polystyrene sulfonate sodium (PSS-Na) was prepared and filtered using a syringe filter (pore size 0.22 μm) to obtain an aqueous PSS-Na solution to be used for forming the sacrificial film.

[0103] A glass substrate was cleaned and subjected to plasma treatment for 5 minutes. The PSS-Na aqueous solution obtained above was applied to the plasma-treated surface of the glass substrate using a spin coater at a rotation speed of 3000 rpm for 1 minute to form a PSS-Na-containing layer. 30 seconds after application, the glass substrate with the PSS-Na-containing layer formed was placed on a hot plate at 120°C and dried for 5 minutes to form a sacrificial film.

[0104] The PSS-Na-containing sacrificial film was then subjected to air plasma treatment for 10 seconds to increase its wettability with the gel precursor solution. 1.6 The mixture was applied at 3000 rpm for 20 seconds using a spin coater to form a gel precursor film.

[0105] The gel precursor film was heated and dried in an oven at 50°C for 24 hours to complete the gelation and drying of the gel precursor film, thereby obtaining a laminate consisting of the glass substrate, the sacrificial film, and the ionic liquid-containing gel film.

[0106] A polytetrafluoroethylene (PTFE) layer was prepared as a porous support. The laminate obtained above was laminated onto this porous support so that the ionic liquid-containing gel membrane faced the porous support, thereby bonding the porous support and the ionic liquid-containing gel membrane. The porous support was then immersed in a saturated aqueous solution of [Emim][TfN] to dissolve the PSS-Na-containing sacrificial membrane.

[0107] The sacrificial film was dissolved, removing the sacrificial film and the glass substrate from the laminate, thereby completing the transfer of the ionic liquid-containing gel membrane onto the porous support. In this way, a carbon dioxide separation membrane-containing laminate comprising a porous support and a carbon dioxide separation membrane was obtained.

[0108] (Comparative Example 2) Gel precursor solution B with a dilution ratio of 1.6 compared to Comparative Example 1 1.6 A carbon dioxide separation membrane-containing laminate was obtained in the same manner as in Comparative Example 1, except that the solution was changed to gel precursor solution B4 with a dilution ratio of 4.

[0109] (Comparative Example 3) Gel precursor solution B with a dilution ratio of 1.6 compared to Comparative Example 1 1.6 A carbon dioxide separation membrane-containing laminate was obtained in the same manner as in Comparative Example 1, except that the solution was changed to gel precursor solution B5 with a dilution ratio of 5.

[0110] Comparative Example 4 Gel precursor solution B with a dilution ratio of 1.6 compared to Comparative Example 1 1.6 Gel precursor solution B at a dilution ratio of 10 10 A carbon dioxide separation membrane-containing laminate was obtained in the same manner as in Comparative Example 1, except for changing the above.

[0111] (Comparative Example 5) Gel precursor solution B with a dilution ratio of 1.6 compared to Comparative Example 1 1.6 Gel precursor solution B at a dilution ratio of 20 20 A carbon dioxide separation membrane-containing laminate was obtained in the same manner as in Comparative Example 1, except for changing the above.

[0112] <Evaluation> (Film-forming property evaluation) The carbon dioxide separation membrane-containing laminates of Examples 1 to 6 and Comparative Examples 1 to 5 were evaluated for their membrane formability. First, the samples were visually inspected to determine whether they had been formed without any abnormalities such as foreign matter. As a result, no abnormalities were visually observed in any of the samples.

[0113] The surface was then observed using a laser microscope (VK-X3000) manufactured by Keyence Corporation, and films that were formed without defects such as pinholes were rated as A, and films that had defects such as pinholes were rated as B. The results are shown in Tables 1 and 2.

[0114] (Film thickness measurement) The thickness of the carbon dioxide separation membranes provided in the stacks of Examples 1 to 6 and Comparative Examples 1 to 5 was measured by observing the cross section with a scanning electron microscope (FE-SEM JSM-7500F, JEOL Ltd., Japan).

[0115] (Measurement of ionic liquid content) The content of the ionic liquid in the ionic liquid-containing gel film provided in the laminates of Examples 1 to 6 was measured by the following method based on an experiment rather than a theoretical amount. First, the ionic liquid-containing gel film was cut into three pieces measuring 4.8 cm x 2.8 cm, and each test piece was vacuum-dried and then its mass (W1) was measured. Next, each test piece was immersed in a petri dish with a lid containing 30 cc of ethanol, shaken for 24 hours, removed, vacuum-dried again, and its mass (W2) was measured. The ionic liquid content in the ionic liquid-containing gel film was calculated using the following formula, and the average value of the three test pieces was taken as the ionic liquid content (experimental value). The results are shown in Table 1. Note that because ionic liquids readily absorb water, vacuum drying before mass measurement is essential. Ionic liquid content (mass%) = [(W1-W2) / W1] x 100

[0116] [Table 1]

[0117] [Table 2]

[0118] As the dilution rate of the gel precursor solution increases, the solid content decreases. Therefore, the thickness of the ionic liquid-containing gel film in each of the laminates in Examples 1 to 6 is the same as that of the gel precursor solution A with the highest dilution rate. 3.0 The thinnest film thickness was 0.85 μm in Example 6, in which a dilution ratio of 3.0 was used. FIG.

[0119] As shown in Table 1, the ionic liquid-containing gel film provided in the laminate of Example 6 was thin, with a thickness of 0.85 μm, but did not have defects such as pinholes and had good film formability, similar to the thicker films of Examples 1 to 5. Furthermore, the ionic liquid-containing gel films provided in the laminates of Examples 1 to 6 each had a high ionic liquid content (experimental value) of 80 mass%, which was in good agreement with the theoretical value.

[0120] Thus, by using a suitable combination of the gel and ionic liquid that constitute the ionic liquid-containing gel membrane, it was possible to obtain an ionic liquid-containing gel membrane with a thickness of 1 μm or less and a high ionic liquid content without generating defects. This suggests that the ionic liquid-containing gel membrane of this embodiment can achieve both high permeability and high selectivity, which are required for the carbon dioxide separation membrane 2.

[0121] The thickness of the ionic liquid-containing gel film provided in each of the laminates of Comparative Examples 1 to 5 was determined by the gel precursor solution B with the lowest dilution ratio. 1.6 The thickest was 9 μm in Comparative Example 1, where gel precursor solution B4 (dilution ratio 1.6) was used, and the thickest was 5 μm in Comparative Example 2, where gel precursor solution B4 (dilution ratio 4) was used. Thus, as in Examples 1 to 6, the thickness of the ionic liquid-containing gel film decreased as the dilution ratio of the gel precursor solution increased.

[0122] As shown in Table 2, the ionic liquid-containing gel films provided in the laminates of Comparative Examples 1 and 2 had good film-forming properties without defects such as pinholes. On the other hand, in Comparative Examples 3 to 5, which had thinner film thicknesses than Comparative Examples 1 and 2, defects such as pinholes were generated in the ionic liquid-containing gel films, resulting in poor film-forming properties. The film thickness of the ionic liquid-containing gel film of Comparative Example 3 was greater than 1 μm.

[0123] Thus, when an IPN gel membrane is used as the gel structure that makes up the ionic liquid-containing gel membrane, it is difficult to reduce the membrane thickness to 1 μm or less due to the occurrence of defects. This suggests that it is difficult to achieve both high permeability and high selectivity as a carbon dioxide separation membrane using technology that uses IPN gel membranes. [Explanation of symbols]

[0124] 1...porous support, 2...carbon dioxide separation membrane (ionic liquid-containing gel membrane), 10...carbon dioxide separation membrane-containing laminate.

Claims

1. The present invention provides an ionic liquid-containing gel membrane, which is a separation membrane that selectively allows carbon dioxide to permeate, and which comprises a gel having a three-dimensional network structure formed by a terminal cross-linking reaction between a plurality of hyperbranched polyethylene glycol compounds, and an ionic liquid, wherein the ionic liquid contains an anion and a cation that contain a cyano group.

2. 2. The ionic liquid-containing gel film according to claim 1, having a thickness of 1 μm or less.

3. 2. The ionic liquid-containing gel film according to claim 1, wherein the plurality of multi-branched polyethylene glycol compounds are a first 4-branched polyethylene glycol compound having a thiol group at each end and a second 4-branched polyethylene glycol compound having a monovalent organic group containing a carbon-carbon double bond at each end, and the crosslinking is caused by a thiol-ene reaction between the thiol groups and the organic groups.

4. 4. The ionic liquid-containing gel membrane according to claim 3, wherein the organic group at each end of the second 4-branched polyethylene glycol compound is a maleimidyl group represented by the following formula: 【Chemistry 1】 In the formula, * represents the bonding site to the remainder of the second 4-branched polyethylene glycol compound.

5. 4. The ionic liquid-containing gel film according to claim 3, wherein the mass average molecular weight of the first 4-branched polyethylene glycol compound and the mass average molecular weight of the second 4-branched polyethylene glycol compound are each within the range of 5,000 g / mol to 100,000 g / mol.

6. 2. The ionic liquid-containing gel film according to claim 1, wherein the ionic liquid contains at least a tricyanomethanide ion, a tetracyanoborate ion, or a dicyanoamide ion as the anion containing a cyano group.

7. 5. The ionic liquid-containing gel film according to claim 4, wherein the ionic liquid contains at least a tricyanomethanide ion or a tetracyanoborate ion as the anion containing a cyano group.

8. 2. The ionic liquid-containing gel film according to claim 1, wherein the ionic liquid contains at least a 1-ethyl-3-methylimidazolium ion as the cation.

9. 2. The ionic liquid-containing gel film according to claim 1, wherein the content of the ionic liquid is in the range of 70 parts by mass to 98 parts by mass relative to 100 parts by mass of the ionic liquid-containing gel film.

10. A carbon dioxide separation membrane-containing laminate comprising a porous support and a carbon dioxide separation membrane comprising the ionic liquid-containing gel membrane according to any one of claims 1 to 9 provided on one surface of the porous support.

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