Ionic liquid composition for carbon dioxide separation membrane, carbon dioxide separation membrane retaining said composition, and carbon dioxide concentrator equipped with said carbon dioxide separation membrane

Abstract

To provide an ion liquid composition for a carbon dioxide separation membrane usable for the carbon dioxide separation at high partial pressure to low partial pressure, especially 1 kPa or lower, the carbon dioxide separation membrane holding the composition and a carbon dioxide concentrator with the carbon dioxide separation membrane.SOLUTION: The CO2 permeability and CO2 selectivity of a carbon dioxide separation membrane can be improved by using an ion liquid composition where an ion liquid (I) in which cation is aminium having one or more primary or secondary amino groups and ethylene diamine or propylene diamine skeleton and anion is one or more selected from among methane sulfonate, trifluoromethane sulfonate, nitrate, chloride and acetate and an ion liquid (II) in which cation has no primary and secondary amino groups and anion is oxo acid anion, are combined and carbon dioxide having high partial pressure to low partial pressure of 1 kPa or lower can be selectively separated and recovered.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an ionic liquid composition for use in a carbon dioxide separation membrane, a carbon dioxide separation membrane holding the composition, and a carbon dioxide concentrating device equipped with the carbon dioxide separation membrane. [Background technology]

[0002] Technology to separate and capture carbon dioxide is necessary for the production of hydrogen and methane from natural gas, and for maintaining closed living environments such as outer space and underwater.From the perspective of reducing greenhouse gas emissions, research is being actively conducted on carbon dioxide separation and capture technology, targeting large emission sources such as thermal power plants and steelworks, and also for the application of carbon dioxide as fertilizer in the agricultural sector. Representative carbon dioxide gas separation technologies include: (1) chemical absorption, which separates carbon dioxide from a mixed gas containing carbon dioxide by selectively absorbing it into a solvent through a chemical reaction, and then recovers it by stripping it from the solvent through a reverse reaction; (2) physical absorption, which physically separates carbon dioxide from a mixed gas containing carbon dioxide by selectively absorbing it into a solvent without using a chemical reaction, and then strips it from the solvent by reducing the pressure to recover it; and (3) membrane separation, which utilizes the partial pressure difference of carbon dioxide across a membrane to supply a gas containing carbon dioxide to be separated from one side of the membrane and selectively transport and separate the carbon dioxide in the gas to be separated to the other side of the membrane.

[0003] Ionic liquids are generally liquid salts composed only of cations and anions, with melting points near or below room temperature. Ionic liquids have the following characteristics: they are liquid over a wide temperature range, have very low vapor pressure (non-volatile), are flame-retardant, have excellent heat resistance, chemical stability, a wide potential window, high ionic conductivity, and can dissolve a wide variety of chemical species. Therefore, ionic liquids have been the subject of extensive research, including as electrolytes for electrochemical devices, solvents in various processes such as separation and refinement and organic reactions, and functional materials for actuators and lubricants.

[0004] In carbon dioxide separation and recovery technology, ionic liquids have these properties, particularly the non-volatility and low specific heat required for carbon dioxide absorbents, and so their use as carbon dioxide absorbents is being considered. For example, in the chemical absorption method, it has been proposed to use a chemical absorption ionic liquid, such as an ionic liquid having an amino group in the cation, as an absorption liquid (Patent Documents 1, 2, and 3), or to use an ionic liquid as a solvent in a non-aqueous absorption liquid containing an amine compound (Patent Document 4, Non-Patent Document 1). In addition, in the physical absorption method, it has been proposed to use, as the absorption liquid, an ionic liquid with excellent physical absorption properties, such as an ionic liquid using an imidazolium-based cation that does not have an amino group in the cation (Patent Documents 5 to 8).

[0005] On the other hand, since membrane separation methods separate gases by utilizing differences in solubility in and diffusibility through a membrane, it is necessary to improve both the permeability and selectivity of carbon dioxide in order to improve the separation efficiency of carbon dioxide. However, with polymer membranes that have been used as conventional carbon dioxide separation membranes, it is known that increasing the selectivity results in a decrease in permeability, and there has been a limit to the improvement in the permeability and selectivity of carbon dioxide using polymer membranes.

[0006] Non-Patent Document 2 describes the performance limits of such conventional polymer membranes, and Figure 2(c) shows the upper limit of the selectivity of carbon dioxide (CO2) over nitrogen (N2) (hereinafter referred to as "CO2 selectivity") for polymer membranes exhibiting any CO2 permeability coefficient. To overcome this limit, it is considered effective to use a substance called a carrier, which selectively and reversibly reacts with and transports specific components in the gas to be separated.

[0007] When a liquid membrane containing the carrier is used as a carbon dioxide separation membrane, selective transport based on the chemical reaction between carbon dioxide and the carrier is utilized, which allows for higher selectivity of carbon dioxide separation than conventional polymer membranes, and the permeation rate of carbon dioxide through the membrane is often also fast. However, when a membrane is used with a volatile ordinary solvent, the gas separation function of the membrane is deactivated due to the volatilization loss of the solvent, and therefore it cannot be used for a long period of time. Therefore, it has been proposed to use a liquid membrane containing a nonvolatile ionic liquid as the carrier, instead of a volatile solvent.

[0008] For example, a liquid membrane containing an ionic liquid having an amino group in the cation has been proposed, and the above-mentioned Patent Document 1 describes the use of a porous liquid membrane impregnated with an absorption liquid whose main component is an ionic liquid having a primary amino group in the cation as a carbon dioxide separation membrane. Furthermore, Patent Document 9 discloses a liquid membrane in which an ionic liquid is held in the pores of a porous membrane for the purpose of separating and recovering carbon dioxide, and the ionic liquid is composed of a cation having an amino group, such as 1-(3-aminopropyl)-3-methylimidazolium.

[0009] Carbon dioxide separation membranes using ionic liquids containing imidazolium cations such as 1,3-dialkylimidazolium have also been proposed (Patent Documents 10 and 11, Non-Patent Documents 3 and 4).

[0010] Furthermore, Patent Document 12 proposes a separation membrane suitable for carbon dioxide fertilization in the agricultural field, which includes a porous layer with affinity for an ionic liquid, in which an ionic liquid-containing liquid is held in the pores. The document lists, as the ionic liquid to be used in the separation membrane, an ionic liquid containing a cation selected from ammoniums, imidazoliums, and phosphoniums, and an anion selected from fluorine-containing anions, cyano-group-containing anions, and anions derived from amino acids, and among these, tetrabutylphosphonium prolinate ([P 4444 [R3R'P], such as [Pro] +A combination of a phosphonium represented by the formula (wherein R is an alkyl group having 2 to 6 carbon atoms, and R' is an alkyl group having 4 to 16 carbon atoms) and an anion derived from proline is considered to be preferred. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-36950 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-55785 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-10760 [Patent Document 4] Japanese Patent Application Laid-Open No. 2017-104775 [Patent Document 5] Japanese Patent Application Laid-Open No. 2006-305544 [Patent Document 6] Japanese Patent Application Laid-Open No. 2009-106909 [Patent Document 7] Special Publication No. 2011-510811 [Patent Document 8] Japanese Patent Application Laid-Open No. 2016-77935 [Patent Document 9] US Patent Publication No. 2014 / 0283839 [Patent Document 10] Japanese Patent Application Laid-Open No. 2010-214324 [Patent Document 11] International Publication No. 2013 / 118776 [Patent Document 12] International Publication No. 2018 / 211945 [Patent Document 13] International Application No. JP2021 / 005629 [Non-patent literature]

[0012] JPEG0007752335000001.jpg41165 Summary of the Invention [Problem to be solved by the invention]

[0013] In order to effectively utilize unused carbon dioxide as a carbon source, technology for highly efficient separation and capture of carbon dioxide is required. Traditionally, development of technology for separating and capturing high-concentration (high partial pressure) carbon dioxide has been the main focus, but in recent years, in anticipation of separation and capture from various carbon dioxide emission sources, there is also a need to develop technology for separating and capturing low-concentration (low partial pressure) carbon dioxide, such as that found in the atmosphere. Therefore, membrane separation using a carrier, which has the potential to achieve high carbon dioxide permeability selectivity as mentioned above, is expected to be one of the promising separation and recovery technologies.

[0014] For example, Patent Document 11 discloses that a carbon dioxide permeable membrane comprising an amino acid ionic liquid and a porous membrane impregnated with the amino acid ionic liquid, wherein the amino acid liquid contains 3 to 50 mass % of water, maintains high carbon dioxide permeability and carbon dioxide / nitrogen selectivity even when the carbon dioxide partial pressure is low, and also discloses that the carbon dioxide partial pressure in the mixed gas may be 15 kPa. Furthermore, specifically, the invention relates to a carbon dioxide permeable membrane comprising an amino acid ionic liquid and a porous membrane impregnated with the amino acid ionic liquid, wherein the amino acid liquid contains 3 to 50 mass % of water, and maintains high carbon dioxide permeability and carbon dioxide / nitrogen selectivity even when the carbon dioxide partial pressure is low. 4444 The graph shows the results of measurements carried out using 1-ethyl-3-methylimidazolium glycinate ([emim][Gly]) or 1-ethyl-3-methylimidazolium glycinate ([emim][Gly]) while varying the partial pressure in the range of 2 to 30 kPa. However, no carbon dioxide separation membrane has yet been found that can efficiently separate carbon dioxide at partial pressures as low as 1 kPa or less.

[0015] The present invention has been made in view of the above circumstances, and aims to provide an ionic liquid composition for a carbon dioxide separation membrane that can be used to separate carbon dioxide at a range of partial pressures from high to low, particularly at 1 kPa or less; a carbon dioxide separation membrane that retains the composition in its pores; and a carbon dioxide concentrating device that includes the carbon dioxide separation membrane. [Means for solving the problem]

[0016] In order to efficiently separate and capture carbon dioxide from the atmosphere using a liquid membrane containing an ionic liquid, it is necessary to improve the carbon dioxide permeability as well as the selectivity of carbon dioxide (CO2) over nitrogen (N2) (CO2 selectivity) under low carbon dioxide partial pressure conditions. In membrane separation, gas permeability is expressed as the product of the gas solubility and the gas diffusion rate. To improve the CO2 permeability and CO2 selectivity in membrane solutions containing ionic liquids as carriers, it is important to increase the solubility of carbon dioxide in the ionic liquid carrier, suppress the solubility of nitrogen, and further increase the diffusion rate of the carrier that has chemically reacted with carbon dioxide.

[0017] The inventors have attempted to use an ionic liquid using an aminium having one or more primary or secondary amino groups and an ethylenediamine or propylenediamine skeleton, which is described in Patent Document 3 as an ionic liquid having excellent chemical absorption properties, and an ionic liquid used as a diluent described in the same document, but have found that it is not possible to improve the carbon dioxide permeation selectivity (see Patent Document 13

[0122] [Comparative Examples 1 to 8]). As a result of further investigation, the present inventors have found that by using an ionic liquid composition that combines ionic liquid (I), which is an aminium having one or more primary or secondary amino groups in the cation and an ethylenediamine or propylenediamine skeleton, with ionic liquid (II), which has an oxoacid anion in the cation without a primary or secondary amino group, the CO2 permeability and CO2 selectivity of a carbon dioxide separation membrane can be improved, and further that it is possible to selectively separate and recover carbon dioxide even at low partial pressures (Patent Document 13).

[0018] The inventors have investigated ways to further improve the CO selectivity while maintaining or improving the CO permeability of the carbon dioxide separation membrane, and have found that methanesulfonate (CHSO) is used as the anion of the ionic liquid (I) instead of bis(trifluoromethylsulfonyl)amide (abbreviated as [TfN]) used in Patent Document 13. -), trifluoromethanesulfonate (CF3SO3 - ), nitrate (NO3 - ), chloride (Cl - ) or acetate (CH3COO - ) can further improve CO2 selectivity.

[0019] The present invention has been completed based on the above findings, and employs the following means. [1] An ionic liquid composition for use in a carbon dioxide separation membrane, Contains an ionic liquid (I) and an ionic liquid (II), The ionic liquid (I) has a cation that is an aminium having one or more primary or secondary amino groups and an ethylenediamine or propylenediamine skeleton, and an anion that is one or more selected from methanesulfonate, trifluoromethanesulfonate, nitrate, chloride, and acetate; The ionic liquid (II) is an ionic liquid composition for a carbon dioxide separation membrane, in which the cation does not have a primary or secondary amino group and the anion is an oxo acid anion. [2] The ionic liquid composition for a carbon dioxide separation membrane according to [1], wherein the aminium is one or more selected from 2-aminoethylaminium, 2-(N-hydroxyethylamino)ethylaminium, 3-aminopropylaminium, 3-(N-methylamino)propylaminium, 2-(2-(aminoethyl)amino)ethylaminium, and 2-(2-(2-(aminoethyl)aminoethyl)amino)ethylaminium. [3] The ionic liquid composition for a carbon dioxide separation membrane according to [1] or [2], wherein the oxoacid anion is one or more selected from the group consisting of carboxylate, phosphate, and phosphonate. [4] The ionic liquid composition for a carbon dioxide separation membrane according to [3], wherein the oxoacid anion is one or more selected from acetate, 2-(1-methoxyethoxy)propionate, and methylphosphonate. [5] The ionic liquid composition for a carbon dioxide separation membrane according to [3] or [4], wherein the cation of the ionic liquid (II) is one or more selected from the group consisting of 1-ethyl-3-methimidazolium, N,N-diethyl-N-methyl-N-heptylammonium, and N,N-diethyl-N-methyl-N-(6-hydroxyhexyl)ammonium. [6] A carbon dioxide separation membrane characterized by retaining the ionic liquid composition for a carbon dioxide separation membrane according to any one of [1] to [5]. [7] The carbon dioxide separation membrane according to [6], comprising an ionic liquid-affinity porous layer having the ionic liquid composition for carbon dioxide separation membranes retained in its pores, and an ionic liquid-non-affinity porous layer. [8] The carbon dioxide separation membrane according to [7], wherein the porous layer with an affinity for an ionic liquid contains an inorganic material. [9] The carbon dioxide separation membrane according to [8], wherein the inorganic material contains metal oxide particles having an average particle size of 0.001 to 10 μm on a number basis.

[10] The carbon dioxide separation membrane according to any one of [7] to [9], wherein the porous layer with an affinity for the ionic liquid has an average thickness of 0.01 to 100 μm.

[11] The carbon dioxide separation membrane according to any one of [6] to

[10] , for separating and concentrating carbon dioxide having a partial pressure of 1 kPa or less.

[12] A carbon dioxide concentrator comprising the carbon dioxide separation membrane according to any one of [6] to

[11] . [Effects of the Invention]

[0020] The ionic liquid composition for a carbon dioxide separation membrane of the present invention can improve CO2 permeability and CO2 selectivity, and can efficiently separate and recover carbon dioxide at partial pressures ranging from high to low, such as 1 kPa or less, particularly at very dilute concentrations of 0.04 kPa. [Brief explanation of the drawings]

[0021] [Figure 1] A schematic diagram of the device used to measure the CO2 permeability coefficient and N2 permeability coefficient of the CO2 separation membrane. [Figure 2]A diagram plotting the CO2 permeability coefficient and CO2 selectivity of Examples 1 to 5 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention provides an ionic liquid composition for use in a carbon dioxide separation membrane, which comprises ionic liquid (I) and ionic liquid (II), wherein the cation of ionic liquid (I) is an aminium having one or more primary or secondary amino groups and an ethylenediamine or propylenediamine skeleton, and the anion is methanesulfonate, trifluoromethanesulfonate, nitrate, chloride, or acetate, and the cation of ionic liquid (II) does not have a primary or secondary amino group, and the anion is an oxoacid anion.

[0023] The ionic liquid composition for a carbon dioxide separation membrane of the present invention, the carbon dioxide separation membrane holding the composition, and the carbon dioxide concentrating device equipped with the carbon dioxide separation membrane will be described in detail below. However, these are for the purpose of explaining the present invention and do not limit the scope of the present invention. Note that the symbol "~" indicating a range of numerical values ​​includes the numerical values ​​before and after it as the lower and upper limits.

[0024] [Ionic liquid (I)] The ionic liquid (I) in the ionic liquid composition for a carbon dioxide separation membrane of the present invention is an ionic liquid in which the cation is an aminium having one or more primary or secondary amino groups and an ethylenediamine or propylenediamine skeleton, and the anion is one or more selected from methanesulfonate, trifluoromethanesulfonate, nitrate, chloride, and acetate.

[0025] (cation) The cation in the ionic liquid (I) of the present invention is an aminium having a primary amino group in which one carbon atom and two hydrogen atoms are bonded to one nitrogen atom, or a secondary amino group in which two carbon atoms and one hydrogen atom are bonded to one nitrogen atom.

[0026] The aminium has at least one ethylenediamine skeleton or propylenediamine skeleton, and when it is an aminium having one ethylenediamine skeleton, it is represented by the following general formula.

[0027] [ka]

[0028] In the formula, R1 and R2 both represent hydrogen atoms, or one represents a hydrogen atom and the other represents a saturated or unsaturated alkyl group which may have a substituent. The alkyl group of R1 or R2 is preferably one having a small number of carbon atoms, such as a methyl group, an ethyl group, or a 2-hydroxyethyl group. R3, R4, and R5 all represent hydrogen atoms, or two of them represent hydrogen atoms and the other represents an optionally substituted saturated or unsaturated alkyl group, or all represent optionally substituted saturated or unsaturated alkyl groups. The alkyl groups may be the same or different, and may be linear or cyclic, branched, or two groups may be bonded to form a ring. Examples of compounds having an ethylenediamine skeleton represented by the above formula 1 include the following 2-aminoethylaminium and 2-(N-hydroxyethylamino)ethylaminium.

[0029] [ka]

[0030] The propylene diamine skeleton is obtained by substituting a propylene group for the ethylene group in the ethylene diamine skeleton described above. Specifically, the ethylene group in the formula 1 described above is substituting a propylene group. The carbon atom of the propylene group in the propylene diamine skeleton may have a substituent such as an alkyl group or heteroalkyl group having a small carbon number. Examples of compounds having a propylenediamine skeleton include the following 3-aminopropylaminium and 3-(N-methylamino)propylaminium.

[0031] [ka]

[0032] The aminium according to the present invention also includes those having two or more ethylenediamine skeletons or propylenediamine skeletons. For example, in the formula 1, when either R1 or R2 is an aminoethyl group, the aminium is diethylenetriaminium, and when either R1 or R2 is a 2-(aminoethyl)aminoethyl group, the aminium is triethylenetetraaminium. Specific examples include the following 2-(2-(aminoethyl)amino)ethylaminium and 2-(2-(2-(aminoethyl)aminoethyl)amino)ethylaminium.

[0033] [ka]

[0034] (anion) The anion in ionic liquid (I) is methanesulfonate (CH3SO3 - ), trifluoromethanesulfonate (CF3SO3 - ), nitrate (NO3 - ), chloride (Cl - ), and acetate (CH3COO - ) is used.

[0035] Preferred examples of the ionic liquid (I) include the following, and among these, [HDAH]Cl or [HDAH]CH3COO (hereinafter abbreviated as [AcO]) is preferably used.

[0036] [ka]

[0037] [Ionic liquid (II)] The ionic liquid (II) in the ionic liquid composition for a carbon dioxide separation membrane of the present invention is an ionic liquid in which the cation does not have a primary or secondary amino group and the anion is an oxo acid anion.

[0038] (oxoacid anion) Examples of oxoacid anions include carboxylates such as acetate, propionate, butanoate, and lactate, phosphates such as dimethyl phosphate, diethyl phosphate, and dibutyl phosphate, phosphonates such as methyl phosphonate, ethyl phosphonate, and butyl phosphonate, sulfates such as methyl sulfate, ethyl sulfate, and octyl sulfate, and sulfonates such as methyl sulfonate and tosylate. Preferred are the carboxylates shown below.

[0039] [ka]

[0040] In the formula, R1 and R2 represent unsubstituted or saturated or unsaturated alkyl groups substituted with a hydroxyl group or a heteroatom.

[0041] Particularly preferably, the carboxylate used is acetate ([AcO]), 2-(1-methoxyethoxy)propionate (abbreviated as [1O2OPrO]), or the like.

[0042] (cation) The cation in the ionic liquid (II) of the present invention is not particularly limited as long as it does not have a primary or secondary amino group. Examples thereof include imidazoliums such as 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, and 1-octyl-3-methylimidazolium; N-butyl-N,N,N-trimethylammonium; N,N,N,N,N-tetrabutylammonium; N-(2-hydroxyethyl)-N,N,N-trimethylammonium; N,N-diethyl-N-methyl-N-heptylammonium; and N,N-diethyl-N-methyl-N-(6 ammoniums such as N-methylpyridinium, N-ethylpyridinium, and N-butylpyridinium; pyrrolidiniums such as N,N-dimethylpyrrolidinium, N-methyl-N-ethylpyrrolidinium, and N-methyl-N-butylpyrrolidinium; phosphoniums such as tetrabutylphosphonium, triethyloctylphosphonium, tributyloctylphosphonium, and trihexyltetradecylphosphonium; and particularly, imidazoliums having an alkyl group on the side chain, such as 1,3-dialkylimidazolium, are preferably used. In dialkylimidazoliums having alkyl groups on their side chains, shortening the alkyl groups on the side chains reduces the gas solubility due to physical absorption, thereby improving the selectivity for nitrogen and the like (see Comparative Examples 3 and 4 described below). Therefore, 1-ethyl-3-methylimidazolium (abbreviated as [emim]) is particularly preferably used. Representative examples of the ionic liquid (II) include the following ionic liquids:

[0043] [ka]

[0044] [Ratio of both ionic liquids] The preferred mixing ratio of the two ionic liquids for improving the carbon dioxide permselectivity varies depending on the combination of the two ionic liquids. For example, when the ionic liquid (I) is [HDAH][AcO] and the ionic liquid (II) is [emim][AcO], the permselectivity can be improved by using 1 to 99 mol % of the ionic liquid (I), preferably 5 to 95 mol %, and more preferably 10 to 90 mol %, of the total amount of the two ionic liquids.

[0045] [Carbon dioxide separation membrane] The carbon dioxide separation membrane of the present invention is not particularly limited as long as it can retain the ionic liquid composition for carbon dioxide separation of the present invention (hereinafter simply referred to as "ionic liquid composition"). For example, when the carbon dioxide separation membrane has a porous layer, the ionic liquid composition is retained in the pores of the porous layer by, for example, impregnating the membrane with the ionic liquid composition. Furthermore, when the carbon dioxide separation membrane has a porous layer containing inorganic material particles, the ionic liquid composition is similarly retained in the pores of the porous layer by, for example, impregnating the membrane with the ionic liquid composition.

[0046] A preferred carbon dioxide separation membrane includes an ionic liquid-affinity porous layer (C) that holds an ionic liquid composition (A) in its pores, and an ionic liquid-non-affinity porous layer (B). The porous layer (C) having an affinity for an ionic liquid may contain an inorganic material, for example, metal oxide particles having an average particle size of 0.001 to 10 μm on a number basis. The average thickness of the porous layer (C) having an affinity for the ionic liquid is preferably 0.01 to 100 μm. Each layer will be described below.

[0047] [Porous layer with no affinity for ionic liquid (B)] The porous layer with no affinity for ionic liquids (B) has a large number of pores (micropores or voids) inside, and its surface (which may include the surfaces (or wall surfaces) of the internal voids) is usually hydrophobic (relatively hydrophobic to the porous layer with an affinity for ionic liquids (C)). The voids may or may not include closed pores, but at least include interconnected pores (or through-pores) that are interconnected in the thickness direction. The porous layer with no affinity for ionic liquids (B) (the material that constitutes the porous layer with no affinity for ionic liquids (B) or the components that form the porous layer with no affinity for ionic liquids) may contain a resin (e.g., a thermoplastic resin) as the main component (for example, 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more (substantially 100% by weight) of the entire porous layer with no affinity for ionic liquids (B)). Because of its excellent formability, the ionic liquid non-affinity porous layer (B) is usually a porous film (porous film, microporous film or microporous film) formed from a thermoplastic resin.

[0048] Examples of thermoplastic resins include polyolefin resins, polyester resins (e.g., polyalkylene arylate resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate), polycarbonate resins (e.g., bisphenol polycarbonate resins such as bisphenol A polycarbonate resin, bisphenol F polycarbonate resin, and bisphenol S polycarbonate resin), polyamide resins (e.g., aliphatic polyamide resins such as polyamide 6 and polyamide 66), polysulfone resins (e.g., polysulfone and polyethersulfone), fluororesins, and cellulose derivatives. These thermoplastic resins may be used alone or in combination of two or more.

[0049] Among these thermoplastic resins, polyolefin resins, fluororesins, and cellulose derivatives (particularly polyolefin resins, fluororesins, and polyolefin resins from the viewpoint of easy availability) are preferred, and among these, poly α-C resins such as polyethylene resins and polypropylene resins are preferred. 2-3Olefin-based resins (particularly polyethylene-based resins), fluororesins such as PTFE and PVDF (particularly PVDF) are preferred.

[0050] These thermoplastic resins may contain conventional additives. Examples of conventional additives include stabilizers such as heat stabilizers, antioxidants, and ultraviolet absorbers, as well as preservatives, disinfectants, plasticizers, lubricants, colorants, viscosity modifiers, leveling agents, surfactants, and antistatic agents. These additives may be used alone or in combination of two or more. The proportion of the additives may be, for example, 50 parts by weight or less, preferably 30 parts by weight or less (e.g., 0.01 to 30 parts by weight), and more preferably 10 parts by weight or less (e.g., 0.1 to 10 parts by weight) per 100 parts by weight of the resin.

[0051] The method for preparing such a porous membrane of a thermoplastic resin is not particularly limited, and it may be prepared by a conventional method, for example, a method utilizing phase separation of a resin solution, a method of stretching a resin film, or a method of irradiating a resin film with high-energy rays such as alpha rays.

[0052] Furthermore, the ionic liquid non-affinity porous layer (B) may be subjected to a conventional surface treatment (for example, the treatment described in JP-A-6-9810, i.e., a treatment of adhering a crosslinked product derived from an ethylenically unsaturated monomer having a fluorinated alkyl group) in order to adjust the wettability (or contact angle) with the ionic liquid composition (A).

[0053] As the ionic liquid non-affinity porous layer (B), commercially available products may be used, such as "Seapore (registered trademark)" and "Eupore (registered trademark)" manufactured by Ube Maxell Co., Ltd., and "Durapel" manufactured by Merck Millipore.

[0054] The average thickness of the porous layer (B) having no affinity for an ionic liquid may be, for example, 1 to 200 μm, preferably 5 to 150 μm, and more preferably 6 to 130 μm.

[0055] The pore size (average pore size or average pore size) of the ionic liquid non-affinity porous layer (B) may be selected from a wide range, for example, from 0.001 to 10 μm (e.g., 0.01 to 5 μm), and may be, for example, 0.001 to 1 μm (e.g., 0.005 to 0.5 μm), preferably 0.01 to 0.4 μm (e.g., 0.03 to 0.35 μm), and more preferably 0.05 to 0.3 μm (e.g., 0.07 to 0.25 μm). If the pore size is too small, gas permeability may decrease. If the pore size is too large, the ionic liquid composition (A) may permeate and may not be retained in the carbon dioxide separation membrane (ionic liquid-containing laminate). The pore size (average pore size or average pore size) can be measured by a conventional method such as mercury intrusion porosimetry.

[0056] The porosity (porosity or porosity) of the ionic liquid-incompatible porous layer (B) may be selected from a wide range, for example, from 1 to 90% (e.g., 10 to 80%), depending on the manufacturing method of the porous layer, and may be, for example, from 20 to 85%, preferably from 30 to 80%, and more preferably from 40 to 75%. If the porosity is too small, gas permeability may decrease. If the porosity is too large, the ionic liquid composition (A) may permeate and may not be retained in the carbon dioxide separation membrane (ionic liquid-containing laminate). The porosity (porosity or porosity) refers to the volume ratio of voids in one of the porous layers relative to the entire porous layer (the entire porous layer without an affinity for ionic liquid (B) or the entire porous layer with an affinity for ionic liquid (C)).

[0057] The interconnected pore ratio of the ionic liquid non-affinity porous layer (B) may be, for example, 50% or more, preferably 70% or more, and more preferably 90% or more (e.g., substantially 100%). The interconnected pore ratio represents the volume ratio of interconnected pores to voids in the porous layer, and may be calculated from a cross-sectional image observed with a scanning electron microscope (SEM) or the like.

[0058] The contact angle of the ionic liquid non-affinity porous layer (B) with the ionic liquid composition (A) may be, for example, 90° or more (e.g., 90 to 150°), preferably 95° or more (e.g., 95 to 148°), and more preferably 100° or more (e.g., 100 to 145°). If the contact angle is too small, the ionic liquid-containing liquid (A) may pass through and may not be retained.

[0059] [Porous layer (C) with affinity for ionic liquid (or second porous layer (C))] The ionic liquid-affinitive porous layer (C) has a large number of pores (pores or voids) inside, and its surface (which may include the surfaces (or wall surfaces) of the internal voids) is usually hydrophilic (relatively hydrophilic to the ionic liquid-non-affinitive porous layer (B)). The voids may or may not include closed pores, but at least include interconnected pores (or through pores) that interconnect in the thickness direction. The porous layer (C) with an affinity for ionic liquid (materials constituting the porous layer (C) with an affinity for ionic liquid, or components forming the porous layer (C) with an affinity for ionic liquid) may contain, as a main component, an organic material such as the resin described in the section on the porous layer (B) without an affinity for ionic liquid. However, in terms of excellent formability and mechanical properties, it is preferable that the porous layer (C) with an affinity for ionic liquid contains, as a main component, an inorganic material in a proportion of, for example, 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more (substantially 100% by weight) of the entire porous layer (C) with an affinity for ionic liquid. Therefore, the porous layer (C) with an affinity for ionic liquid is preferably made of an inorganic material, as a main component, in a proportion of, for example, 50% by weight or more, preferably 70% by weight or more, and even more preferably 90% by weight or more (substantially 100% by weight) of the porous layer (C) without an affinity for ionic liquid. Although the resin described in Section B) may be hydrophilized (e.g., a hydrophilized PTFE porous membrane, a hydrophilized PVDF porous membrane, etc.), it is usually a porous membrane (porous membrane, porous membrane, or microporous membrane) formed from an inorganic material. When the ionic liquid-affinity porous layer (C) is formed from an inorganic material, the ionic liquid-containing laminate is endowed with the rigidity inherent in inorganic materials, making the carbon dioxide separation membrane (ionic liquid-containing laminate) easy to handle even if it is thin, and effectively improving its handleability. In particular, this is preferred because it not only effectively suppresses swelling or gelation, which can cause a decrease in gas permeability, but also improves dimensional stability.

[0060] Examples of inorganic materials include metal oxides such as Group 4A metal oxides (e.g., titanium oxide, zirconium oxide, etc.), Group 5A metal oxides (vanadium oxide, etc.), Group 6A metal oxides (molybdenum oxide, tungsten oxide, etc.), Group 7A metal oxides (manganese oxide, etc.), Group 8 metal oxides (nickel oxide, iron oxide, etc.), Group 1B metal oxides (copper oxide, etc.), Group 2B metal oxides (zinc oxide, etc.), Group 3B metal oxides (aluminum oxide, indium oxide, etc.), Group 4B metal oxides (silicon oxide, tin oxide, etc.), and Group 5B metal oxides (antimony oxide, etc.).

[0061] These metal oxides can be used alone or in combination of two or more. Among these metal oxides, from the viewpoints of affinity (or hydrophilicity) with the ionic liquid composition (A), ease of preparation of a dispersion (or slurry) due to specific gravity, etc., and ease of availability, Group 3B metal oxides such as aluminum oxide and Group 4B metal oxides such as silicon oxide are preferred, and Group 3B metal oxides such as aluminum oxide are particularly preferred.

[0062] The inorganic material (or metal oxide) may be in the form of particles. The average particle size of the inorganic material (or metal oxide) may be, for example, 0.001 to 10 μm (e.g., 0.01 to 5 μm), preferably 0.1 to 3 μm (e.g., 0.3 to 2 μm), and more preferably 0.5 to 1.5 μm (e.g., 0.8 to 1.2 μm), based on the number of particles. In this specification and claims, the average particle size can be measured by the method described in the Examples below.

[0063] The shape of the particles is not particularly limited, and examples thereof include spherical (or nearly spherical), ellipsoidal, polygonal (such as polygonal pyramidal, cuboidal, or rectangular parallelepiped), plate-like, rod-like, and irregular shapes, but the particles are usually irregular in many cases. Furthermore, the inorganic material may or may not be surface-treated to improve dispersibility.

[0064] When the porous layer (C) with an affinity for an ionic liquid is prepared using a particulate inorganic material (or metal oxide), the gaps (voids) between the particles allow the gas permeability of the porous layer (C) with an affinity for an ionic liquid to be adjusted to a high level, effectively preventing a decrease in gas permeability even in the laminate structure. Furthermore, perhaps due to the rigidity of the porous layer (C) with an affinity for an ionic liquid, the encapsulated ionic liquid-containing liquid (A) is unlikely to ooze out even when it comes into contact with the surface of the carbon dioxide separation membrane (for example, the side of the porous layer (C) with an affinity for the ionic liquid in the carbon dioxide separation membrane). This makes it easier to stably maintain the ionic liquid composition (A) in a liquid state and effectively prevents the surface of the carbon dioxide separation membrane (ionic liquid-containing laminate) from becoming sticky.

[0065] The porous layer (C) having affinity for an ionic liquid may be subjected to a conventional surface treatment (e.g., treatment with a silane coupling agent) in order to adjust the wettability (or contact angle) with the ionic liquid composition (A).

[0066] The average thickness of the porous layer (C) having an affinity for an ionic liquid can be selected, for example, from the range of 0.01 to 100 μm (e.g., 0.03 to 70 μm), and may be, for example, 0.05 to 50 μm (e.g., 0.1 to 30 μm), preferably 0.5 to 20 μm (e.g., 1 to 15 μm), and more preferably 1 to 10 μm (e.g., 2 to 7 μm). If the average thickness is too large, the weight of the carbon dioxide separation membrane (ionic liquid-containing laminate) may increase.

[0067] The pore size (average pore size or average pore diameter) of the porous layer (C) with an affinity for an ionic liquid may be, for example, 0.001 to 10 μm (e.g., 0.01 to 5 μm). If the pore size is too small, not only will the amount of ionic liquid composition (A) that can be retained decrease, but gas permeability may also decrease. If the porous layer (C) with an affinity for an ionic liquid is formed from an inorganic material (e.g., metal oxide particles), it appears that gas permeability can be easily adjusted to a high level.

[0068] The porosity (porosity or porosity) of the ionic liquid-affinity porous layer (C) may be selected from a wide range of, for example, 1 to 90% (e.g., 10 to 80%), and may be, for example, 5 to 70% (e.g., 10 to 60%), preferably 15 to 50% (e.g., 20 to 45%), and more preferably 25 to 40% (e.g., 30 to 35%). If the porosity is too small, not only will the amount of ionic liquid composition (A) that can be retained decrease, but gas permeability may also decrease. If the porosity is too large, the ionic liquid-containing liquid (A) may not be stably retained.

[0069] The interconnected pore ratio of the porous layer (C) having an affinity for an ionic liquid may be, for example, 50% or more, preferably 70% or more, and more preferably 90% or more (for example, substantially 100%).

[0070] The contact angle of the porous layer (C) with the ionic liquid composition (A) may be, for example, less than 90° (e.g., 0° or more and less than 90°), preferably 85° or less (e.g., 15 to 85°), and more preferably 80° or less (e.g., 30 to 80°). If the contact angle is too large, it may become difficult to retain the ionic liquid composition (A).

[0071] The difference in contact angle with the ionic liquid composition (A) between the porous layer without affinity for ionic liquid (B) and the porous layer with affinity for ionic liquid (C) may be, for example, 10° or more (e.g., 15 to 55°), preferably 20° or more (e.g., 25 to 50°), and more preferably 30° or more (e.g., 30 to 45°). If the difference in contact angles is too small, it may be difficult to stably retain the ionic liquid composition (A). On the other hand, if the difference in contact angles is too large, when the basis weight of the ionic liquid composition (A) is low, it may not spread flat (or in the plane direction) inside the porous layer with affinity for ionic liquid.

[0072] [Carbon dioxide separation membrane (ionic liquid-containing laminate) and its manufacturing method] The carbon dioxide separation membrane (ionic liquid-containing laminate) of the present invention may comprise a laminate (ionic liquid-free laminate) comprising an ionic liquid-non-affinity porous layer (B) and an ionic liquid-affinity porous layer (C), and may further comprise a step (impregnation step) of impregnating the pores of the ionic liquid-affinity porous layer (C) with a liquid (or impregnation liquid) containing the ionic liquid composition (A).

[0073] The impregnation liquid may consist solely of the ionic liquid composition (A), or may be a mixed liquid (solution or dispersion) obtained by mixing the ionic liquid composition (A) with a solvent (or dispersion medium). From the viewpoint of facilitating the reduction of the equivalent membrane thickness of the ionic liquid composition (A), the impregnation liquid is preferably a mixed liquid. In this specification and claims, the term "equivalent membrane thickness" refers to the membrane thickness when a liquid membrane having the same area as the carbon dioxide separation membrane (ionic liquid-containing laminate) is formed using the ionic liquid composition (A) contained in the porous layer.

[0074] The solvent (or dispersion medium) is preferably a solvent with higher volatility than the ionic liquid composition (A), and examples thereof include water, alcohols (lower alcohols such as methanol, ethanol, isopropanol, butanol, and cyclohexanol), ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone), esters (methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl formate, and ethyl formate), ethers (diethyl ether, dioxane, and tetrahydrofuran), aliphatic hydrocarbons (hexane and the like), alicyclic hydrocarbons (cyclohexane and the like), aromatic hydrocarbons (benzene and the like), halogenated hydrocarbons (dichloromethane and dichloroethane), cellosolves (methyl cellosolve and ethyl cellosolve), cellosolve acetates, and amides (dimethylformamide and dimethylacetamide). These solvents can be used alone or in combination of two or more. Among these solvents, aqueous solvents (or water-soluble solvents) such as water and alcohols (e.g., C2-6 alkanols such as methanol) are commonly used. The concentration of the ionic liquid composition (A) in the impregnation liquid may be, for example, 0.001 to 100% by weight, preferably 0.01 to 50% by weight (e.g., 0.05 to 30% by weight), and more preferably 0.1 to 10% by weight (e.g., 0.1 to 8% by weight).

[0075] The method for impregnating with the impregnation liquid is not particularly limited, and may include, for example, a method of injecting the impregnation liquid under pressure. Specifically, in a laminate (a laminate not containing an ionic liquid) comprising a porous layer with no affinity for ionic liquid (B) and a porous layer with an affinity for ionic liquid (C), the surface of the laminate (or the outermost layer of the laminate) on the side of the porous layer with an affinity for ionic liquid (C) may be brought into contact with the impregnation liquid, and the opposite side (the side of the porous layer with no affinity for ionic liquid (B)) may be depressurized (or suctioned from the opposite side). This method allows the carbon dioxide separation membrane (an ionic liquid-containing laminate) of the present invention to be easily and efficiently formed. By appropriately adjusting the viscosity of the impregnation liquid, it is also possible to impregnate the porous layer with an affinity for ionic liquid (C) with the impregnation liquid simply by contacting the impregnation liquid with the impregnation liquid without depressurizing. Furthermore, when the above-mentioned mixed liquid is used as the impregnation liquid, the carbon dioxide separation membrane (ionic liquid-containing laminate) may be prepared by volatilizing the solvent (or dispersion medium) after the impregnation step. By removing the solvent (or dispersion medium), the equivalent membrane thickness of the ionic liquid-containing liquid (A) can be easily adjusted, and thinning is also easy. There are no particular restrictions on the method for volatilizing the solvent; volatilization can be achieved by heating and / or reducing the pressure as appropriate, depending on the boiling point and vapor pressure of the solvent.

[0076] In the carbon dioxide separation membrane (ionic liquid-containing laminate) of the present invention, the content of ionic liquid composition (A) preferably does not exceed 100 parts by volume per 100 parts by volume of voids inside the porous layer with an affinity for the ionic liquid (C). In other words, the carbon dioxide separation membrane (ionic liquid-containing laminate) preferably does not have a second ionic liquid-containing layer adjacent to the porous layer with an affinity for the ionic liquid (C) that contains (or retains) ionic liquid composition (A) and that contains ionic liquid composition (A) that does not fit into the voids. Therefore, from the viewpoint of improving the carbon dioxide permeation rate and handleability of the carbon dioxide separation membrane (ionic liquid-containing laminate), the porous layer (C) with affinity for an ionic liquid may contain 100 parts by volume or less of ionic liquid composition (A) relative to 100 parts by volume of the internal voids. This can be selected from the range of, for example, 0.1 to 99 parts by volume (e.g., 1 to 90 parts by volume), and may contain, for example, 3 to 80 parts by volume (e.g., 5 to 70 parts by volume), preferably 10 to 50 parts by volume (e.g., 15 to 45 parts by volume), and more preferably 20 to 40 parts by volume (e.g., 25 to 35 parts by volume). If the amount of ionic liquid composition (A) is too large, handleability may be reduced.

[0077] In the carbon dioxide separation membrane (ionic liquid-containing laminate) of the present invention, the equivalent membrane thickness of the ionic liquid composition (A) may be, for example, 0.01 to 5 μm (e.g., 0.05 to 3 μm), preferably 0.1 to 2 μm (e.g., 0.15 to 1.5 μm), and more preferably 0.2 to 1 μm (e.g., 0.2 to 0.7 μm). If the equivalent membrane thickness is too large, the permeation rate may decrease.

[0078] A laminate comprising a porous layer with no affinity for ionic liquid (B) and a porous layer with an affinity for ionic liquid (C) (an ionic liquid-free laminate) can be prepared, for example, by directly or indirectly laminating (or forming) the porous layer with an affinity for ionic liquid (C) on one surface of the porous layer with no affinity for ionic liquid (B). The method for laminating (or forming) the porous layer with an affinity for ionic liquid (C) is not particularly limited and may be, for example, pressure bonding, heat fusion, or adhesion with an adhesive or pressure-sensitive adhesive. When the porous layer with an affinity for ionic liquid (C) is formed from an inorganic material, it may be formed using a conventional method, such as sintering a powdered inorganic material. However, from the viewpoint of easy and efficient formation of the desired porous layer and improved handleability, it may also be formed by a method including a coating step of applying a dispersion (or slurry) of particulate (or powdered) inorganic material in a dispersion medium and drying the resulting coating.

[0079] Examples of the dispersion medium include the same solvents (or dispersion media) as exemplified in the section on the impregnation liquid. These dispersion media can be used alone or in combination of two or more. Of these dispersion media, water is usually used. When water is used as the dispersion medium, a small amount of alcohol such as isopropanol (for example, 0.01 to 10 parts by weight, preferably 0.1 to 2 parts by weight, per 100 parts by weight of the inorganic material) may be added as needed to improve the coatability of the ionic liquid-non-affinity porous layer (B).

[0080] If necessary, a small amount (for example, 0.01 to 10 parts by weight, preferably 0.1 to 2 parts by weight per 100 parts by weight of the inorganic material) of a binder (e.g., water-soluble resins such as carboxymethyl cellulose or its salts (e.g., sodium salts), hydroxyalkyl cellulose (e.g., hydroxyethyl cellulose, hydroxypropyl cellulose), and methyl cellulose; or a latex such as styrene-butadiene rubber latex) may be added. While a binder is not always necessary, it often makes it easier to prepare a porous layer (C) with a large thickness that has affinity for the ionic liquid.

[0081] The concentration of the inorganic material in the dispersion is, for example, 0.1 to 50% by weight, preferably 1 to 30% by weight, and more preferably 3 to 20% by weight (for example, 5 to 15% by weight) based on the total weight of the dispersion.

[0082] The coating method is not particularly limited, and includes conventional methods such as a roll coater method, an air knife coater method, a blade coater method, a rod coater method, a reverse coater method, a bar coater method, a comma coater method, a dip-squeeze coater method, a die coater method, a gravure coater method, a microgravure coater method, a silk screen coater method, a dip method, a spray method, and a spinner method. Of these methods, the bar coater method is widely used. If necessary, the dispersion (or coating liquid) may be applied multiple times.

[0083] In the coating step, after the dispersion is cast or coated, the dispersion medium is evaporated to dry the coating. The drying temperature can usually be selected depending on the boiling point of the dispersion medium, and may be, for example, 50 to 150°C, preferably 80 to 120°C, and more preferably 90 to 110°C.

[0084] The carbon dioxide separation membrane of the present invention (or an ionic liquid-free laminate comprising a porous layer with no affinity for ionic liquid (B) and a porous layer with an affinity for ionic liquid (C)) may have a two-layer structure consisting of the porous layer with no affinity for ionic liquid (B) and the porous layer with an affinity for ionic liquid (C), or may have a multilayer structure of three or more layers (e.g., a 3- to 5-layer structure) including another layer (or a third layer) such as the support layer. The third layer is not particularly limited as long as it is gas permeable, and examples thereof include the support layer [e.g., a net (or mesh) made of metal (stainless steel, etc.) or a resin], an adhesive or pressure-sensitive adhesive layer, etc. These third layers may be used alone or in combination of two or more. From the viewpoint of gas permeability, the carbon dioxide separation membrane (ionic liquid-containing laminate) of the present invention preferably has a two- to three-layer structure (particularly a two-layer structure). From the viewpoint of effective retention or immobilization of the ionic liquid composition (A), it is preferable that the porous layer with no affinity for ionic liquid (B) and the porous layer with an affinity for ionic liquid (C) are formed adjacent to each other.

[0085] The carbon dioxide separation membrane (ionic liquid-containing laminate) of the present invention obtained in this manner has excellent gas permeability and can be suitably used, for example, in the agricultural field as a carbon dioxide separation membrane (carbon dioxide concentration membrane) for fertilizing plants. The carbon dioxide separation membrane of the present invention is usually used with the ionic liquid-affinity porous layer (C) containing ionic liquid composition (A) on the gas supply side (supply side or upstream side) and the opposite side (the ionic liquid-non-affinity porous layer (B) side) on the permeation side (or downstream side).

[0086] The carbon dioxide permeability coefficient, nitrogen permeability coefficient and carbon dioxide selectivity can be measured by the method described in the examples below.

[0087] [Carbon dioxide concentrator equipped with a carbon dioxide separation membrane] The carbon dioxide concentrating apparatus of the present invention is equipped with the carbon dioxide separation membrane. The shape of the carbon dioxide separation membrane is not particularly limited, and may be, for example, a flat membrane, a spiral shape formed by winding a flat membrane, or a hollow fiber membrane. These shapes may be used alone or in combination of two or more. The carbon dioxide separation membrane is usually used to form a membrane module (concentration unit or separation unit) together with a support material for supporting or fixing the carbon dioxide separation membrane. The material and shape of the support material are not particularly limited as long as they do not inhibit gas permeation, and are selected appropriately depending on the shape of the carbon dioxide separation membrane. Furthermore, the concentration unit may include one carbon dioxide separation membrane, or may include two or more carbon dioxide separation membranes.

[0088] In addition to the concentration unit, the carbon dioxide concentrator of the present invention often further includes an intake unit for supplying a gas component containing carbon dioxide (e.g., atmospheric air) to the carbon dioxide separation membrane. The intake unit can supply a gas component containing carbon dioxide to the carbon dioxide separation membrane by generating a pressure difference between the upstream side (or gas supply side) and downstream side (permeation side) of the concentration unit. The intake unit is not particularly limited as long as it can generate the pressure difference, and may be disposed either upstream or downstream of the concentration unit. Specifically, it may be, for example, an air compressor disposed upstream of the concentration unit or a pump (e.g., a diaphragm pump) disposed downstream.

[0089] The carbon dioxide concentrator of the present invention can operate (or run) as long as it includes at least the concentration unit and the intake unit, so the device configuration (or design) can be simplified and it can be easily made smaller. Furthermore, the permeation rate (carbon dioxide permeation rate) of the carbon dioxide concentration membrane is high, so carbon dioxide can be effectively or efficiently concentrated (or enriched) even at a relatively low differential pressure. Therefore, even a small intake unit with low intake capacity can operate smoothly (without any problems). [Example]

[0090] The present invention will be specifically described below based on examples and comparative examples. Although the description will focus on the separation of low partial pressure carbon dioxide, the examples are intended to illustrate preferred examples of the present invention, and do not in any way limit the application of the present invention to the separation of high partial pressure carbon dioxide.

[0091] [Method for preparing carbon dioxide separation membrane] A carbon dioxide separation membrane (hereinafter referred to as "CO2 separation membrane") was prepared by the following method. (Separation membrane using a hydrophilized PTFE filter as the porous layer (C) with affinity for ionic liquid) The base material, a hydrophilized PTFE filter (Merck Millipore, average thickness: 30 μm), was washed with ethanol, acetone, and ultrapure water, and then the filter was dried under reduced pressure at 70°C for 12 hours using a vacuum dryer. A predetermined amount of ionic liquid was added dropwise to the filter, and while heating to 40°C, a vacuum was applied using a vacuum pump for 12 hours to impregnate the filter with the ionic liquid. Excess ionic liquid was wiped off from the filter so that the ionic liquid occupied 95-100% of the pore volume of the filter, and the resulting product was used as a CO2 separation membrane.

[0092] (Separation membrane using alumina particles as the porous layer (C) with affinity for ionic liquid) According to the method described in Patent Document 12 (e.g.,

[0124] and

[0127] ), an 8-10 wt% alumina particle (α-alumina, manufactured by Wako Pure Chemical Industries, Ltd.; average particle size (catalog value): approximately 1 μm; average particle size by number: 0.94 μm; amorphous) dispersion (alumina particle slurry) was prepared. The resulting alumina particle slurry was applied to a polyethylene porous membrane (average thickness: 20 μm) serving as the ionic liquid-incompatible porous layer (B) and dried at 100°C for 1 minute to form an alumina-coated filter (average thickness of the alumina layer after drying: 1 μm). The average particle size by number was determined by taking 10,000x magnification images using a scanning electron microscope (JEOL Ltd., "JSM-6700F"), measuring the long diameters of 20 randomly selected particles, and calculating the average of the long diameters. The obtained alumina-coated filter was used to prepare a CO2 separation membrane in the same manner as above.

[0093] (Separation membrane using silica particles as the porous layer (C) with affinity for ionic liquid) Silica-coated filters (average thickness of the silica layer after drying: 0.3 μm, 4.3 μm) were formed in the same manner as the alumina-coated filters, except that silica particles ("Aerosil 50" manufactured by Nippon Aerosil Co., Ltd., average particle size: 0.03 μm) were used instead of the alumina particles, and then CO separation membranes were formed in the same manner.

[0094] [Evaluation method for carbon dioxide separation membranes] The CO2 permeability coefficient and N2 permeability coefficient of the CO2 separation membrane were determined using the apparatus shown in FIG. In the figure, 1 is a CO2 / N2 standard gas cylinder, 2 is an N2 gas cylinder, 3 is a He gas cylinder, 4 to 6 are mass flow controllers, 7 is a CO2 separation membrane, 8 is a separation membrane holder, 9 is an oven, 10 and 11 are thermo-hygrometers, 12 and 14 are traps, 13 is a chiller, 15 and 16 are back pressure valves, 17 and 19 are soap film flow meters, and 18 is a gas chromatograph (TCD-GC).

[0095] First, the CO2 separation membrane 7 was sandwiched between two PTFE filters (manufactured by Advantec) and set in a separation membrane holder 8. After starting temperature control using an oven 9, a CO2 / N2 mixed gas at atmospheric pressure was supplied to the supply-side bypass at a predetermined flow rate, and high-purity He (99.99995 mol% or higher) at atmospheric pressure was supplied to the permeation-side bypass at a predetermined flow rate. The feed gas that passed through the bypass was analyzed by a gas chromatograph (Shimadzu Corporation, GC-8A) 18, and it was confirmed that the CO2 composition of the feed gas matched the target value (0.04 mol%). The permeate gas that passed through the bypass was analyzed by the same method, and it was confirmed that components other than He contained in the permeate gas were below the detection limit. Thereafter, the feed gas and permeate gas were supplied to the separation membrane holder 8, and a gas permeation test was started. The composition of the permeate gas was analyzed at regular intervals, and when the CO2 and N2 compositions remained constant for one hour or more, it was considered that a steady state had been reached. The feed gas and permeate gas were analyzed by a gas chromatograph 18, and the flow rates of the gases were measured by soap film flow meters 17 and 19 (Horiba, Ltd., SF-1U). From the CO2 composition, N2 composition, and flow rate, the flow rates of CO2 and N2 permeating the CO2 separation membrane 7 per unit time (cm 3 These values ​​were multiplied by the separation membrane thickness (cm) and then the separation membrane area (cm 2 ) by the gas partial pressure difference (cmHg) between the supply side and the permeation side to obtain the CO2 permeability coefficient and the N2 permeability coefficient. In the examples and comparative examples, unless otherwise specified, the unit of the permeability coefficient is Barrer (cm 3 cm / cm 2 ·s·cmHg×10 10) was used as the standard. The CO2 selectivity was defined as the ratio of the CO2 permeability coefficient to the N2 permeability coefficient.

[0096] [Synthesis of ionic liquids] (Synthesis Example 1: Synthesis of 2-(N-hydroxyethylamino)ethylaminium bis(trifluoromethylsulfonyl)amide ([HDAH][TfN])) A methanol solution of bis(trifluoromethylsulfonyl)imide (Kanto Chemical, hereafter referred to as HTf2N) (methanol was from Wako Pure Chemical Industries) was slowly added dropwise to a methanol solution of 2-(N-hydroxyethylamino)ethylamine (manufactured by Aldrich). After the addition was complete, the mixture was stirred overnight at room temperature to obtain a methanol solution containing [HDAH][Tf2N] shown in the following formula. The methanol was distilled off under reduced pressure, and the mixture was further dried in vacuo at 50°C for 30 hours to obtain [HDAH][Tf2N].

[0097] [ka]

[0098] (Synthesis Example 2: Synthesis of 2-(N-hydroxyethylamino)ethylaminium methanesulfonate ([HDAH]CH3SO3)) [HDAH]CH3SO3 shown in the following formula was obtained in the same manner as in Synthesis Example 1, except that methanesulfonic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of the HTf2N.

[0099] [ka]

[0100] (Synthesis Example 3: Synthesis of 2-(N-hydroxyethylamino)ethylaminium trifluoromethanesulfonate ([HDAH]CF3SO3)) [HDAH]CF3SO3 shown in the following formula was obtained in the same manner as in Synthesis Example 1, except that trifluoromethanesulfonic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of the HTf2N.

[0101] [ka]

[0102] (Synthesis Example 4: Synthesis of 2-(N-hydroxyethylamino)ethylaminium nitrate ([HDAH]NO3)) [HDAH]NO3 shown in the following formula was obtained in the same manner as in Synthesis Example 1, except that nitric acid (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of the HTf2N.

[0103] [ka]

[0104] (Synthesis Example 5: Synthesis of 2-(N-hydroxyethylamino)ethylaminium chloride ([HDAH]Cl)) [HDAH]Cl represented by the following formula was obtained in the same manner as in Synthesis Example 1, except that hydrochloric acid (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of the methanol solution of HTf2N.

[0105] [ka]

[0106] (Synthesis Example 6: Synthesis of 2-(N-hydroxyethylamino)ethylaminium acetate ([HDAH][AcO])) [HDAH][AcO] shown in the following formula was obtained in the same manner as in Synthesis Example 1, except that acetic acid (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a raw material instead of the methanol solution of HTf2N.

[0107] [ka]

[0108] (Synthesis Example 7: Synthesis of 1-ethyl-3-methylimidazolium 3-(2-methoxyethoxy)propionate ([emim][1O2OPrO])) N-Ethylimidazole (Sigma-Aldrich), dimethyl carbonate (Sigma-Aldrich), and methanol (Wako Pure Chemical Industries) were reacted at 120 °C for 1 day to obtain a methanol solution of 1-ethyl-3-methylimidazolium methyl carbonate ([emim]CHOCO2). The content of [emim]CHOCO2 in the methanol solution was determined by NMR (Bruker Avance 400). An equal amount of 3-(2-methoxyethoxy)propionate (Koei Chemical Industry) was slowly added dropwise to the [emim]CHOCO2 methanol solution, and the reaction was allowed to proceed at room temperature for 1 day. To remove unreacted materials, the mixture was evaporated under reduced pressure and extracted with toluene to obtain crude [emim][1O2OPrO]. The volatile components were then removed by drying under reduced pressure at 40 °C for 1 week to obtain [emim][1O2OPrO], as shown below.

[0109] [ka]

[0110] [Ionic liquids other than those mentioned above] In addition to the ionic liquids obtained in the above Synthesis Examples 1 to 7, the following commercially available ionic liquids were used. 1-Ethyl-3-methylimidazolium acetate ([emim][AcO], Iolitec)

[0111] [ka]

[0112] [Examples 1 to 5, Comparative Example 1] Based on the above-described method for preparing a CO2 separation membrane, a hydrophilized PTFE filter was impregnated with a mixture of the [HDAH]CH3SO3 obtained in Synthesis Example 2 and the [emim][AcO] in a ratio of 10 mol% to 90 mol%, to prepare a CO2 separation membrane, which was designated Example 1. Similarly, Examples 2, 3, 4, and 5, and Comparative Example 1 were prepared using the [HDAH]CF3SO3 obtained in Synthesis Example 3, the [HDAH]NO3 obtained in Synthesis Example 4, the [HDAH]Cl obtained in Synthesis Example 5, the [HDAH][AcO] obtained in Synthesis Example 6, and the [HDAH][Tf2N] obtained in Synthesis Example 1, instead of the [HDAH]CH3SO3. The gas permeability coefficients of Examples 1 to 5 and Comparative Example 1 were measured using a CO2 / N2 mixed gas (CO2 composition 0.04 mol%) at a temperature of 40°C, a feed gas flow rate of 400 ml / min, and a permeation gas flow rate of 100 to 150 ml / min. The obtained CO2 permeability coefficients, N2 permeability coefficients, and CO2 selectivities are shown in Table 1-1.

[0113] [Table 1-1]

[0114] Figure 2 plots the CO2 permeability coefficients and CO2 selectivities of Examples 1 to 5 and Comparative Example 1 in Table 1-1. In Figure 2, the upper performance limit of the polymer membrane shown in Figure 2(c) of Non-Patent Document 2 is shown by a solid line. When the CO2 selectivity is in a region above this solid line, it means that the CO2 separation performance is superior to that of conventional polymer membranes.

[0115] In addition, the gas permeability coefficients of Examples 1 to 4 and Comparative Example 1 were measured in the same manner, except that the permeation side gas was changed from He to Ar. The obtained CO2 permeability coefficients, N2 permeability coefficients, and CO2 selectivities are shown in Table 1-2.

[0116] [Table 1-2]

[0117] (summary) As shown in Table 1-1, it was found that all of the CO2 separation membranes of Examples 1 to 5 exhibited equivalent or higher CO2 permeability coefficients and higher CO2 selectivities compared to Comparative Example 1. By changing the anion of ionic liquid (I) from bis(trifluoromethylsulfonyl)amide to methanesulfonate, trifluoromethanesulfonate, nitrate, chloride, or acetate, the CO2 permeability coefficient and CO2 selectivity of the CO2 separation membrane could be improved. Furthermore, as shown in Table 1-2, this excellent effect can be obtained even when the permeation gas is changed from He to Ar. Furthermore, as shown in Figure 2, when compared to the upper performance limit of polymer membranes, the CO2 selectivity of the CO2 separation membrane of Comparative Example 1 is 187 times that of polymer membranes showing equivalent CO2 permeability coefficients. On the other hand, the CO2 selectivity of the CO2 separation membranes of Examples 1 to 5 is 267 to 447 times that of polymer membranes showing equivalent CO2 permeability coefficients. It can be seen that the CO2 separation membranes using the ionic liquid composition of the present invention exhibit superior CO2 permeation selectivity not only compared to conventional CO2 separation membranes but also compared to the CO2 separation membrane described in Patent Document 13.

[0118] [Examples 6 to 8, Comparative Example 2] Based on the above-described CO2 separation membrane preparation method, a liquid mixture of the above-described [HDAH]CF3CO3 and the above-described [emim][AcO] in a ratio of 10 mol% to 90 mol% was impregnated into a silica-coated filter (average silica layer thickness: 4.3 μm) to prepare a CO2 separation membrane, which was designated Example 6. Similarly, a liquid mixture of [HDAH][Tf2N] instead of [HDAH]CF3CO3 was impregnated into the silica-coated filter to prepare Comparative Example 2. Furthermore, based on the above-mentioned CO2 separation membrane preparation method, a liquid obtained by mixing the above-mentioned [HDAH]Cl and the above-mentioned [emim][AcO] in a ratio of 10 mol% to 90 mol% was impregnated into a silica-coated filter (average thickness of the silica layer: 0.3 μm) and an alumina-coated filter (average thickness of the alumina layer: 1 μm) to prepare CO2 separation membranes, which were designated as Examples 7 and 8. The gas permeability coefficients of Examples 6 to 8 and Comparative Example 2 were measured using a CO2 / N2 mixed gas (0.04 mol%) at a temperature of 40°C, a feed gas flow rate of 400 ml / min, and a permeate gas flow rate of 100 to 150 ml / min. In Example 6 and Comparative Example 2, the permeate gas was Ar, and in Examples 7 and 8, the permeate gas was He. The obtained CO2 permeability, N2 permeability, and CO2 selectivity are shown in Table 2. In Table 2, the unit of gas permeability is GPU (cm 3 / cm 2 ·s·cmHg×10 6 ) is expressed as

[0119] [Table 2]

[0120] (summary) From Example 6 and Comparative Example 2 in Table 2, it was found that even when a silica-coated filter was used as the substrate instead of a hydrophilic PTFE filter, the same or higher CO2 permeability coefficient and high CO2 selectivity were exhibited. From Examples 7 and 8, it was revealed that even when other silica-coated filters or alumina-coated filters were used, they also functioned as CO2 separation membranes.

[0121] [Examples 9 to 12, Comparative Examples 3 and 4] Based on the above-described method for preparing a CO2 separation membrane, the [HDAH][AcO] and the [emim][AcO] were mixed so that the [HDAH][AcO] concentration was 30, 50, 70, or 90 mol%, and the mixture was impregnated into a hydrophilized PTFE filter to prepare CO2 separation membranes, which were designated as Examples 9, 10, 11, and 12. Similarly, CO2 separation membranes impregnated with only [emim][AcO] or only [HDAH][AcO] were designated as Comparative Examples 3 and 4, respectively. The gas permeability coefficients of Examples 9 to 12 and Comparative Examples 3 and 4 were measured using a CO2 / N2 mixed gas (0.04 mol%) at a temperature of 40°C, a feed gas flow rate of 400 ml / min, and a permeation gas flow rate of 40 to 150 ml / min. The obtained CO2 permeability coefficients, N2 permeability coefficients, and CO2 selectivities are shown in Table 3. Note that Example 5 ([HDAH][AcO] composition 10 mol%) was also included in this table.

[0122] [Table 3]

[0123] (summary) As can be seen from Table 3, the use of an ionic liquid mixture of [HDAH][AcO] and [emim][AcO] results in a separation membrane with a higher CO2 permeability coefficient than when each ionic liquid is used alone. The ionic liquid composition of the present invention exhibits a higher CO2 permeation selectivity than when each ionic liquid is used alone, and has a preferred composition range of 10 mol% to 90 mol%, which is wider than the composition range (5 mol% to 40 mol%) described in Patent Document 13.

[0124] [Example 13, Comparative Example 5] Based on the above-described method for preparing a CO2 separation membrane, a solution prepared by mixing the above-described [HDAH][AcO] and the [emim][1O2OPrO] obtained in Synthesis Example 9 so that the [HDAH][AcO] concentration was 10 mol % was impregnated into a hydrophilized PTFE filter to prepare a CO2 separation membrane, which was designated Example 13. Similarly, a CO2 separation membrane impregnated with [HDAH][Tf2N] instead of [HDAH][AcO] was prepared as Comparative Example 5. The gas permeability coefficients of Example 13 and Comparative Example 5 were measured using a CO2 / N2 mixed gas (0.04 mol%) at a temperature of 40°C, a feed gas flow rate of 400 ml / min, and a permeation gas flow rate of 100 ml / min. The obtained CO2 permeability coefficients, N2 permeability coefficients, and CO2 selectivities are shown in Table 4.

[0125] [Table 4]

[0126] (summary) As shown in Table 4, even when ionic liquid (II) is replaced by [emim][1O2OPrO] instead of [emim][AcO], high CO2 permeation selectivity is still observed. In other words, the carboxylate of ionic liquid (II) is not limited to acetate.

[0127] [Summary] Thus, by changing the anion of ionic liquid (I) from bis(trifluoromethylsulfonyl)amide to methanesulfonate, trifluoromethanesulfonate, nitrate, chloride, or acetate, separation membranes with equivalent or higher CO permeability and high CO selectivity can be obtained, even at extremely low CO concentrations of 0.04 mol%, equivalent to those in the atmosphere. When methanesulfonate, trifluoromethanesulfonate, nitrate, chloride, or acetate is used, these anions do not inhibit the chemical reaction between aminium and CO and maintain or enhance the thermodynamic stability of the chemical reactants. Therefore, even if the anion is changed, it is believed that the CO permeability of the separation membrane will remain equivalent or higher. Furthermore, the anion of ionic liquid (I) in the present invention has a smaller molecular size than bis(trifluoromethylsulfonyl)amide. Therefore, it is presumed that the physical dissolution of N is inhibited, resulting in a lower N permeability. As a result, CO separation membranes with high CO permeability and high CO selectivity can be obtained. [Industrial Applicability]

[0128] The present invention enables efficient separation and recovery of carbon dioxide at extremely low concentrations (0.04 kPa). This technology can be used not only in processes for separating and recovering high-partial-pressure carbon dioxide emitted from biogas production facilities, biomass power generation facilities, incinerators, chemical plants, steel plants, and power plants, but also for rapid and energy-efficient separation and recovery of low-partial-pressure carbon dioxide (1 kPa or less) contained in the atmosphere and in air in environments where normal ventilation is difficult, such as high-rise buildings and enclosed work spaces. This allows unused carbon dioxide to be utilized, for example, to promote the growth of plants and algae. Furthermore, since carbon dioxide can be removed from a space without ventilation, the heat energy of the space is not wasted outside the space, thereby reducing the energy required for air conditioning. [Explanation of symbols]

[0129] 1: CO2 / N2 standard gas cylinder 2: N2 gas cylinder 3: He gas cylinder 4~6: Mass flow controller 7:CO2 separation membrane 8: Separation membrane holder 9: Oven 10, 11: Thermohygrometer 12, 14: Trap 13: Chiller 15, 16: Back pressure valve 17, 19: Soap film flowmeter 18: Gas chromatograph (TCD-GC)

Claims

1. An ionic liquid composition for use in a carbon dioxide separation membrane, Contains an ionic liquid (I) and an ionic liquid (II), The ionic liquid (I) has a cation that is one or more aminiums selected from 2-aminoethylaminium, 2-(N-hydroxyethylamino)ethylaminium, 3-aminopropylaminium, 3-(N-methylamino)propylaminium, 2-(2-(aminoethyl)amino)ethylaminium, and 2-(2-(2-(aminoethyl)aminoethyl)amino)ethylaminium, and an anion that is one or more aminiums selected from methanesulfonate, trifluoromethanesulfonate, nitrate, chloride, and acetate, The ionic liquid (II) is an ionic liquid composition for a carbon dioxide separation membrane, in which the cation does not have a primary or secondary amino group and the anion is an oxo acid anion.

2. 2. The ionic liquid composition for a carbon dioxide separation membrane according to claim 1, wherein the oxoacid anion is one or more selected from the group consisting of carboxylate, phosphate, and phosphonate.

3. 3. The ionic liquid composition for a carbon dioxide separation membrane according to claim 2, wherein the oxoacid anion is one or more selected from acetate, 2-(1-methoxyethoxy)propionate, and methylphosphonate.

4. 4. The ionic liquid composition for a carbon dioxide separation membrane according to claim 2, wherein the cation of the ionic liquid (II) is one or more selected from the group consisting of 1-ethyl-3-methylimidazolium, N,N-diethyl-N-methyl-N-heptylammonium, and N,N-diethyl-N-methyl-N-(6-hydroxyhexyl)ammonium.

5. A carbon dioxide separation membrane characterized by retaining the ionic liquid composition for a carbon dioxide separation membrane according to any one of claims 1 to 4.

6. The carbon dioxide separation membrane according to claim 5, comprising an ionic liquid-affinity porous layer having the ionic liquid composition for carbon dioxide separation membranes retained in pores thereof, and an ionic liquid-non-affinity porous layer.

7. The carbon dioxide separation membrane according to claim 6 , wherein the porous layer with an affinity for an ionic liquid contains an inorganic material.

8. 8. The carbon dioxide separation membrane according to claim 7, wherein the inorganic material contains metal oxide particles having an average particle size of 0.001 to 10 μm on a number basis.

9. The carbon dioxide separation membrane according to any one of claims 6 to 8, wherein the porous layer with an affinity for an ionic liquid has an average thickness of 0.01 to 100 µm.

10. The carbon dioxide separation membrane according to any one of claims 5 to 9, for separating and concentrating carbon dioxide having a partial pressure of 1 kPa or less.

11. A carbon dioxide concentrating device comprising the carbon dioxide separation membrane according to any one of claims 5 to 10.

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