Ionic liquid, ionic liquid for carbon dioxide absorbent, carbon dioxide absorbent, carbon dioxide isolation method, carbon dioxide isolation / recovery method, device using carbon dioxide absorbent, and method for producing ionic liquid

Abstract

Provided is a novel ionic liquid in which a cation has four amino groups. The present invention pertains to an ionic liquid characterized by being represented by general formula (1) (In the formula: R11, R2 and R3 are each independently a C2-10 straight-chain or branched-chain alkylene group; R4 is a C2-10 straight-chain or branched-chain alkylene group; and n is an integer of 1-3. A1n- represents an anion.)

Description

Ionic liquid, ionic liquid for carbon dioxide absorbent, carbon dioxide absorbent, carbon dioxide separation method, carbon dioxide separation and recovery method, apparatus using carbon dioxide absorbent, and method for producing ionic liquid.

[0001] The present invention relates to ionic liquids, ionic liquids for carbon dioxide absorbents, carbon dioxide absorbents, carbon dioxide separation methods, carbon dioxide separation and recovery methods, apparatus using carbon dioxide absorbents, and methods for producing ionic liquids.

[0002] In recent years, increased consumption of fossil fuels such as oil and coal due to industrial activities, as well as deforestation, has led to a continuous increase in the concentration of greenhouse gases such as carbon dioxide and methane in the atmosphere, resulting in global warming. If this warming continues at this rate, it is believed that serious consequences will appear in various aspects of life, including desertification of the Earth's surface, rising sea levels, and changes in ecosystems.

[0003] In this context, technologies for reducing carbon dioxide emissions and capturing carbon dioxide are attracting attention as a way to prevent global warming and reduce greenhouse gas emissions. Technologies for capturing carbon dioxide include chemical absorption, physical absorption, solid absorption, and membrane separation, but chemical absorption is mainly used because it can handle a wide range of concentrations. This chemical absorption method involves absorbing carbon dioxide into a liquid through a chemical reaction, and then releasing and capturing the carbon dioxide by heating the absorbent liquid.

[0004] As a liquid used to absorb carbon dioxide, for example, Patent Document 1 discloses an ionic liquid having one or more primary or secondary amino groups in the cation and an ethylenediamine or propylenediamine skeleton of amino acid.

[0005] Japanese Patent Publication No. 2016-10760 Japanese Patent Publication No. 2024-46408

[0006] However, although the carbon dioxide absorbent described in Patent Document 1 can absorb carbon dioxide at room temperature, there is room for further improvement in its carbon dioxide absorption performance. Furthermore, since it is necessary to recover the absorbed carbon dioxide after it has been absorbed by the carbon dioxide absorbent, good desorption properties of the absorbed carbon dioxide are also required.

[0007] Incidentally, the applicant has proposed various phosphonium-based ionic liquids having alkyl groups to which primary amino groups are bonded. For example, Patent Document 2 discloses a carbon dioxide absorbent containing tributyl(3-aminopropyl)phosphonium bromide.

[0008] Such phosphonium-based ionic liquids contain an amino group (-NH) within their molecule. ２ Because it has the properties of carbon dioxide, it can absorb carbon dioxide, but it is presumed that further improvement will require an ionic liquid with a larger number of amino groups.

[0009] Therefore, the object of the present invention is to solve at least one of the following problems. Specifically, the object of the present invention is to provide a novel ionic liquid having four amino groups in its cation. Another object of the present invention is to provide an ionic liquid for carbon dioxide absorbents and a carbon dioxide absorbent that have excellent carbon dioxide absorption performance. Furthermore, the object of the present invention is to provide a carbon dioxide absorbent that, in addition to the above carbon dioxide absorption performance, allows for easy removal of carbon dioxide when the absorbent is regenerated. Another object of the present invention is to provide a carbon dioxide separation method, a carbon dioxide separation and recovery method using the above carbon dioxide absorbent, and an apparatus using the carbon dioxide absorbent. Another object of the present invention is to provide a method for producing a novel ionic liquid having four amino groups in its cation.

[0010] In view of the above circumstances, the present inventors conducted extensive research and, as a result, discovered that a phosphonium-based ionic liquid in which the cation has four alkyl groups to which primary amino groups are bonded, that is, an ionic liquid represented by the following general formula (1), exhibits (1) superior carbon dioxide absorption performance compared to conventional liquids, or (2) good carbon dioxide desorption after absorption, and thus completed the present invention.

[0011] General formula (1):

[0012]

[0013] (In the formula, R１ , R ２ and R ３ each independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, and R ４ represents a linear or branched alkylene group having 2 to 10 carbon atoms, and n represents an integer of 1 to 3. A1 ｎ－ represents an anion.)

[0014] That is, the present invention (1) provides an ionic liquid represented by the following general formula (1):

[0015]

[0016] (In the formula, R １ , R ２ and R ３ each independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, and R ４ represents a linear or branched alkylene group having 2 to 10 carbon atoms, and n represents an integer of 1 to 3. A1 ｎ－ represents an anion.)

[0017] Further, the present invention (2) provides a carbon dioxide absorbent comprising the ionic liquid of the present invention (1).

[0018] Further, the present invention (3) provides a carbon dioxide separation method characterized by having a carbon dioxide separation step of bringing a mixed gas containing carbon dioxide into contact with the carbon dioxide absorbent of the present invention (2) to absorb carbon dioxide in the mixed gas by the carbon dioxide absorbent, thereby separating carbon dioxide from the mixed gas.

[0019] Furthermore, the present invention (4) provides a carbon dioxide separation and recovery method characterized by comprising: a carbon dioxide separation step of contacting the carbon dioxide absorbent of the present invention (2) with a mixed gas containing carbon dioxide, thereby separating carbon dioxide from the mixed gas by causing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas; and a carbon dioxide recovery step of heating the carbon dioxide absorbent that has absorbed carbon dioxide in the carbon dioxide separation step at a temperature of 60°C to 150°C, thereby desorbing carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide, thereby regenerating the carbon dioxide absorbent and recovering the desorbed carbon dioxide.

[0020] Furthermore, the present invention (5) provides an apparatus characterized in that the carbon dioxide absorbent of the present invention (2) is used.

[0021] Furthermore, the present invention (6) comprises: a first step of reacting phosphine with a linear or branched terminal olefin having 2 to 10 carbon atoms and a primary amino group to obtain a phosphine compound having three alkylamino groups; a second step of reacting the phosphine compound having three alkyl groups having a primary amino group hydrogen halide base with a hydrogen halide salt to obtain a phosphine compound having three alkyl groups having a primary amino group hydrogen halide base; a third step of reacting the phosphine compound having three alkyl groups having a primary amino group hydrogen halide salt with a hydrogen halide salt of a linear or branched alkylamine compound having 2 to 10 carbon atoms and a primary amino group to obtain a phosphonium halide compound having four alkyl groups having a primary amino group hydrogen halide base; and neutralizing the phosphonium halide compound having four alkyl groups having a primary amino group hydrogen halide base with an alkali compound to obtain the following general formula (2):

[0022]

[0023] (In the formula, R １ , R ２ and R ３ Each of these independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, and R ４X represents a linear or branched alkylene group with 2 to 10 carbon atoms. － The present invention provides a method for producing an ionic liquid, characterized by having a fourth step of obtaining an ionic liquid represented by (where represents a halogen ion), and a third step of

[0024] The present invention provides a novel ionic liquid having four amino groups in its cation. Furthermore, the present invention provides a compound for carbon dioxide absorbent and a carbon dioxide absorbent with excellent carbon dioxide absorption performance. In addition, the present invention provides a carbon dioxide absorbent that, in addition to the above-mentioned carbon dioxide absorption performance, allows for easy desorption of carbon dioxide during regeneration. Furthermore, the present invention provides a carbon dioxide separation method, a carbon dioxide separation and recovery method, and an apparatus using the carbon dioxide absorbent. Finally, the present invention provides a method for producing a novel ionic liquid having four amino groups in its cation.

[0025] The present invention will be described below based on preferred embodiments. The ionic liquid of the present invention is given by the following general formula (1):

[0026]

[0027] (In the formula, R １ , R ２ and R ３ Each of these independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, and R ４ A1 represents a linear or branched alkylene group with 2 to 10 carbon atoms, and n represents an integer between 1 and 3. ｎ－ represents an anion. ) It is an ionic liquid represented by .

[0028] In general formula (1), R １ , R ２ and R ３ Each of these independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, and R ４ R represents a linear or branched alkylene group with 2 to 10 carbon atoms. １ , R ２ , R３ and R ４ These elements may be identical or different, but from a synthesis standpoint, it is preferable that they be identical.

[0029] R in general formula (1) １ , R ２ , and R ３ Examples include linear alkylene groups having 2 to 10 carbon atoms, preferably linear alkylene groups having 2 to 4 carbon atoms, specifically including ethylene groups, propylene groups, butylene groups, etc. R in general formula (1) ４ Examples include linear alkylene groups having 2 to 10 carbon atoms, preferably linear alkylene groups having 2 to 8 carbon atoms. Specifically, examples include ethylene groups, propylene groups, butylene groups, pentylene groups, hexylene groups, heptylene groups, octylene groups, nonylene groups, desilene groups, and the like.

[0030] R in general formula (1) １ , R ２ , and R ３ Examples include branched alkylene groups having 2 to 10 carbon atoms, preferably branched alkylene groups having 2 to 4 carbon atoms, specifically, 2-methylpropylene groups, 2-methylbutylene groups, etc. R in general formula (1) ４ Examples include branched alkylene groups having 2 to 10 carbon atoms, preferably branched alkylene groups having 2 to 8 carbon atoms, specifically including 2-methylpropylene groups, 2-methylbutylene groups, and 2-methylpentylene groups.

[0031] In general formula (1), the group bonded to the P atom is a primary amino group (-NH ２ ) has "-R １ -NH ２ "-R ２ -NH ２ "-R ３ -NH ２ " is an alkylamino group having 2 to 10 carbon atoms, preferably 2 to 4 carbon atoms, and "-R ４ -NH ２" is an alkylamino group having 2 to 10 carbon atoms, preferably 2 to 8 carbon atoms. "-R １ -NH ２ "-R ２ -NH ２ "-R ３ -NH ２ Examples of alkylamino groups related to "" include ethylamino group, n-propylamino group, isopropylamino group, n-butylamino group, isobutylamino group, n-pentylamino group, n-hexylamino group, n-heptylamino group, n-octylamino group, isopropylamino group, isobutylamino group, s-butylamino group, t-butylamino group, isopentylamino group, s-pentylamino group, t-pentylamino group, isohexylamino group, s-hexylamino group, t-hexylamino group, ethylhexylamino group, and preferably ethylamino group, n-propylamino group, isopropylamino group, n-butylamino group, isobutylamino group, etc. Also, "-R ４ -NH ２ Examples of alkylamino groups related to "" include ethylamino group, n-propylamino group, isopropylamino group, n-butylamino group, isobutylamino group, n-pentylamino group, n-hexylamino group, n-heptylamino group, n-octylamino group, isopropylamino group, isobutylamino group, s-butylamino group, t-butylamino group, isopentylamino group, s-pentylamino group, t-pentylamino group, isohexylamino group, s-hexylamino group, t-hexylamino group, ethylhexylamino group, and the like, with ethylamino group, n-propylamino group, isopropylamino group, n-butylamino group, and the like being preferred.

[0032] The ionic liquid represented by general formula (1) is composed of a cation and anion. The cation constituting the ionic liquid represented by general formula (1) is a phosphonium cation having four groups bonded to a P atom, and all of the groups bonded to the P atom are alkyl groups having primary amino groups. In other words, the ionic liquid represented by general formula (1) is a phosphonium-based ionic liquid having four alkyl groups bonded to primary amino groups in the cation.

[0033] In the general formula (1), n represents an integer of 1 or more and 3 or less.

[0034] In the general formula (1), A1 ｎ－ represents an anion, and A1 ｎ－ is not particularly limited as long as it forms an ionic liquid in pair with the phosphonium cation of the general formula (1). A1 ｎ－ Examples of A1 include fluoride ion (F － ), chloride ion (Cl － ), bromide ion (Br － ), iodide ion (I － ), and other halide ions, phosphate ion (H ２ PO ４ － , HPO ４ ２－ , PO ４ ３－ ), methanolamine phosphate ion (NH ２ CH ２ OPO ３ ２－ ), ethanolamine phosphate ion (NH ２ C ２ H ４ OPO ３ ２－ ), propanolamine phosphate ion (NH ２ C ３ H ６ OPO ３ ２－ ), butanolamine phosphate ion (NH ２ C ４ H ８ OPO ３ ２－ ), diethyldithiophosphate ion ((C ２ H ５ ) ２ O ２ PS ２ － ), dimethyl phosphate ion ((CH ３ ) ２ PO ４ － ), diethyl phosphate ion ((C ２ H ５ ) ２ PO ４－ Phosphate group-containing anions such as ) and methylsulfonic acid (CH ３ SO ３ － ), fluoromethylsulfonic acid (CF ３ SO ３ － ), benzenesulfonic acid (C ６ H ５ SO ３ － ) and other sulfonic acid group-containing anions, bis(trifluoromethanesulfonyl)imide ions ((CF ３ SO ２ ) ２ N － ), bis(fluorosulfonyl)imide ion ((FSO ２ ) ２ N － ) and other imide group-containing anions, imidazolate ions ((C) ３ H ３ N ２ ) － ), benzimidazolate ion ((C ７ H ５ N ２ ) － ), benzotriazolate ion ((C ６ H ４ N ３ ) － ) and other nitrogen heterocycle-containing anions, acetate ions (CH ３ COO － ), formate ion (HCOO － ), propionate ion (C ２ H ５ COO － ), oxalate ion ((COO) ２ ２－ ), maleate ion (C ２ H ２ (COO) ２ ２－ ), malonate ion (CH ２ (COO) ２ ２－ ) and other carboxylic acid group-containing anions, glycine ions ((NH ２ )CH ２ COO － ), alanine ion (((NH ２ ) C２ H ４ COO － ), β-alanine ion ((NH ２ ) C ２ H ４ COO － ), isoleucine ion (CH ３ CH ２ (CH ３ )CH(NH ２ ) CHCOO － ), leucine ion ((CH ３ ) ２ CHCH ２ (NH ２ ) CHCOO － ), methionine ion (CH ３ SC ２ H ４ (NH ２ ) CHCOO － ), valine ion ((CH ３ ) ２ CH(NH ２ ) CHCOO － ), phenylalanine ion (PhCH ２ (NH ２ ) CHCOO － ), tryptophan ion (INDOLE-CH ２ (NH ２ ) CHCOO － ), tyrosine ion (p-HO-PhCH ２ (NH ２ ) CHCOO － ), asparagine ion (H ２ NCOCH ２ (NH ２ ) CHCOO － ), cysteine ​​ion (HSCH ２ (NH ２ ) CHCOO － ), glutamine ion (H ２ NCOC ２ H ４ (NH ２ ) CHCOO － ), serine ions (HOCH ２ (NH ２ ) CHCOO － ), threonine ion (CH ３ (OH)CH(NH２ ) CHCOO － ), aspartate ion (HOCOCH ２ (NH ２ ) CHCOO － ), glutamate ion (HOCOC ２ H ４ (NH ２ ) CHCOO － ), arginine ion (H ２ N(HN)=CNHC ３ H ６ (NH ２ ) CHCOO － ), histidine ion (IMID-CH ２ (NH ２ ) CHCOO － ), L-(+)-lysine ion (H ２ NC ４ H ８ (NH ２ ) CHCOO － ), D-(-)-lysine ion (H ２ NC ４ H ８ (NH ２ ) CHCOO － ), DL-lysine ion (H ２ NC ４ H ８ (NH ２ ) CHCOO － ), proline ion (Pyl-COO － ) and other amino acid anions, tetrafluoroborate (BF ４ － ), hexafluorophosphate (PF ６ － ) are examples. Note that if these anions have a chiral center, they may be optical isomers or racemates. Among these, A1 ｎ－ fluoride ions (F － ), chloride ions (Cl － ), bromide ions (Br － ), iodide ion (I － ), phosphate ion (H ２ PO ４ － ), methanolamine phosphate ion (NH２ CH ２ OPO ３ ２－ ), ethanolamine phosphate ion (NH ２ C ２ H ４ OPO ３ ２－ ), propanolamine phosphate ion (NH ２ C ３ H ６ OPO ３ ２－ ), butanolamine phosphate ion (NH ２ C ４ H ８ OPO ３ ２－ ), bis(trifluoromethanesulfonyl)imide ion ((CF ３ SO ２ ) ２ N － ), bis(fluorosulfonyl)imide ion ((FSO ２ ) ２ N － ), benzotriazolate ion ((C ６ H ４ N ３ ) － ), alanine ion (((NH ２ ) C ２ H ４ COO － ), β-alanine ion (((NH ２ ) C ２ H ４ COO － ), glycine ion ((NH ２ )CH ２ COO － ), L-(+)-lysine ion (H ２ NC ４ H ８ (NH ２ ) CHCOO － ) is preferable.

[0035] When the ionic liquid of the present invention is used as a carbon dioxide absorbent, it can exhibit excellent carbon dioxide absorption performance. Furthermore, even when the absorbed carbon dioxide is expelled and the absorbent is regenerated, its ability to absorb carbon dioxide is restored, making it a regenerated carbon dioxide absorbent with excellent carbon dioxide absorption performance. Therefore, in the general formula (1), R １ , R ２ and R ３ R is a linear or branched alkylene group having 2 to 10 carbon atoms, preferably a linear or branched alkylene group having 2 to 4 carbon atoms, preferably a linear alkylene group having 2 to 4 carbon atoms, ４ is a linear or branched alkylene group having 2 to 10 carbon atoms, preferably a linear or branched alkylene group having 2 to 8 carbon atoms, and A1 ｎ－ Preferably, fluoride ions (F － ), chloride ions (Cl － ), bromide ions (Br － ), iodide ion (I － ), phosphate ion (H ２ PO ４ － ), methanolamine phosphate ion (NH ２ CH ２ OPO ３ ２－ ), ethanolamine phosphate ion (NH ２ C ２ H ４ OPO ３ ２－ ), propanolamine phosphate ion (NH ２ C ３ H ６ OPO ３ ２－ ), butanolamine phosphate ion (NH ２ C ４ H ８ OPO ３ ２－ ), bis(trifluoromethanesulfonyl)imide ion ((CF ３ SO ２ ) ２ N －), bis(fluorosulfonyl)imide ion ((FSO ２ ) ２ N － ), benzotriazolate ion ((C ６ H ４ N ３ ) － ), alanine ion (((NH ２ ) C ２ H ４ COO － ), β-alanine ion (((NH ２ ) C ２ H ４ COO － ), glycine ion ((NH ２ )CH ２ COO － ), L-(+)-lysine ion (H ２ NC ４ H ８ (NH ２ )CHCOO-)

[0036] Ionic liquids represented by general formula (1) include tetrakis(3-aminopropyl)phosphonium fluoride, tetrakis(3-aminopropyl)phosphonium chloride, tetrakis(3-aminopropyl)phosphonium bromide, tetrakis(3-aminopropyl)phosphonium iodide, tetrakis(3-aminopropyl)phosphonium phosphate, tetrakis(3-aminopropyl)phosphonium methanolamine phosphate, tetrakis(3-aminopropyl)phosphonium ethanolamine phosphate, tetrakis(3-aminopropyl)phosphonium propanolamine phosphate, tetrakis(3-aminopropyl)phosphonium butanolamine phosphate, tetrakis(3-aminopropyl)phosphonium bis(trifluoromethanesulfonyl)imide, tetrakis(3-aminopropyl)phosphonium bis(fluorosulfonyl)imide, tetrakis(3-aminopropyl)phosphonium alanine, tetrakis(3-aminopropyl)phosphonium β-alanine, tetrakis(3-aminopropyl)phosphonium glycine, and tetrakis(3-aminopropyl Tris(3-aminopropyl)2-aminoethylphosphonium L-(+)-lysine, Tris(3-aminopropyl)2-aminoethylphosphonium fluoride, Tris(3-aminopropyl)2-aminoethylphosphonium chloride, Tris(3-aminopropyl)2-aminoethylphosphonium bromide, Tris(3-aminopropyl)2-aminoethylphosphonium iodide, Tris(3-aminopropyl)2-aminoethylphosphonium phosphate, Tris(3-aminopropyl)2-aminoethylphosphonium methanolamine phosphate, Tris(3-aminopropyl Tris(3-aminopropyl)2-aminoethylphosphonium / ethanolamine phosphate, Tris(3-aminopropyl)2-aminoethylphosphonium / propanolamine phosphate, Tris(3-aminopropyl)2-aminoethylphosphonium / butanolamine phosphate, Tris(3-aminopropyl)2-aminoethylphosphonium / bis(trifluoromethanesulfonyl)imide, Tris(3-aminopropyl)2-aminoethylphosphonium / bis(fluorosulfonyl)imide, Tris(3-aminopropyl)2-aminoethylphosphonium / alanine,Examples include tris(3-aminopropyl)2-aminoethylphosphonium / β-alanine, tris(3-aminopropyl)2-aminoethylphosphonium / glycine, and tris(3-aminopropyl)2-aminoethylphosphonium / L-(+)-lysine.

[0037] The method for producing the ionic liquid of the present invention is not limited, and it may be produced by any method. The ionic liquid of the present invention is preferably produced by the method for producing the ionic liquid of the present invention described below.

[0038] The present invention provides a method for producing an ionic liquid, comprising: a first step of reacting phosphine (a) with a linear or branched terminal olefin (compound b) having a primary amino group and 2 to 10 carbon atoms to obtain a phosphine compound (compound c) having three alkylamino groups; a second step of reacting the phosphine compound (compound c) having three alkyl groups having a primary amino group hydrogen halide base with a hydrogen halide (d) to obtain a phosphine compound (compound e) having three alkyl groups having a primary amino group hydrogen halide base; a third step of reacting the phosphine compound (compound e) having three alkyl groups having a primary amino group hydrogen halide base with a hydrogen halide salt of a linear or branched alkylamine compound (compound f) having a primary amino group and 2 to 10 carbon atoms to obtain a phosphonium halide compound (compound g) having four alkyl groups having a primary amino group hydrogen halide base; A phosphonium halide compound (compound g) having four alkyl groups with a primary amino group hydrogen halide base reacts with an alkali compound (h) to neutralize the mixture, and the following general formula (2): (In the formula, R １ , R ２ and R ３ Each of these independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, and R ４ X represents a linear or branched alkylene group with 2 to 10 carbon atoms. － The method for producing an ionic liquid is characterized by having a fourth step of obtaining an ionic liquid represented by (where represents a halogen ion), and having

[0039] The first step in the method for producing an ionic liquid of the present invention is to react phosphine (a) with a linear or branched terminal olefin (compound b) having 2 to 10 carbon atoms and a primary amino group to obtain a phosphine compound (compound c) having three alkylamino groups.

[0040] The phosphine (a) in the first step is PH ３ It is a compound represented by the chemical formula shown.

[0041] The linear or branched terminal olefin (compound b) having a primary amino group and having 2 to 10 carbon atoms in the first step is a linear or branched olefin having a double bond at one end, preferably an olefin having 2 to 4 carbon atoms, and having a primary amino group at the end opposite the double bond. Examples of compound b include vinylamine (CH4). ２ =CHNH ２ ), allylamine (CH ２ =CHCH ２ NH ２ ), 2-methylallylamine (CH ２ = C(CH ３ )CH ２ NH ２ ), 3-buten-1-amine (CH ２ =CHCH ２ CH ２ NH ２ Examples include:

[0042] In the first step, PH ３ When using one type of compound b to react with (a), R in general formula (2) １ , R ２ and R ３ All of these yield the same ionic liquid, and also pH ３ When two types of compound b are used as the compound to react with (a), R in general formula (2) １ , R ２ and R ３ All of them are the same ionic liquid, and R １ , R ２ and R ３ One of them yields a different ionic liquid, and also pH３ When three types of compound b are used as the compound to react with (a), R in general formula (2) １ , R ２ and R ３ All of them are the same ionic liquid, and R １ , R ２ and R ３ One of them is a different ionic liquid, and R １ , R ２ and R ３ Each of these yields a different ionic liquid.

[0043] In the first step, PH ３ The molar ratio of compound b to (a) is theoretically 3, but it can be 3 to 5, preferably 3 to 4.

[0044] In the first step, PH ３ The reaction between (a) and compound b is preferably carried out in the presence of a radical initiator such as an azo compound such as azobisisobutyronitrile, azobisvaleronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-propanecarbomidine), or an organic peroxide such as di-tert-butyl peroxide, tert-butyl hydroperoxide, or benzoyl peroxide. The amount of radical initiator used is determined by the pH. ３ (a) is 0.1 to 10 mol%, preferably 0.5 to 5 mol%.

[0045] In the first step, PH ３ The solvent used when reacting (a) with compound b is not particularly limited, but examples include toluene, methanol, ethanol, propanol, acetonitrile, n-hexane, etc.

[0046] In the first step, PH ３ The reaction temperature between (a) and compound b is preferably above the temperature at which the radical initiator becomes active, preferably 50 to 120°C, more preferably 60 to 100°C. The reaction pressure is not particularly limited, but pH ３ Considering the boiling point, the gauge pressure is preferably 0.1 to 10 MPa. The reaction time is selected as appropriate.

[0047] In the first step, PH ３ The reaction atmosphere between (a) and compound b is an inert gas atmosphere. Examples of inert gases include nitrogen gas, argon gas, and helium gas.

[0048] Then, by performing the first step, a phosphine compound (compound c) having three alkylamino groups is obtained. The alkyl group in compound c is an alkyl group having a primary amino group, and compound c has three of these alkyl groups having primary amino groups.

[0049] The second step in the method for producing the ionic liquid of the present invention is to react a phosphine compound having three alkylamino groups (compound c) obtained in the first step with a hydrogen halide (d) to obtain a phosphine compound having three alkyl groups having a primary amino group hydrogen halide base (compound e).

[0050] The hydrogen halide (d) in the second step can be hydrogen chloride, hydrogen bromide, hydrogen iodide, etc., with hydrogen bromide being preferred. The hydrogen halide (d) is preferably used as an aqueous solution.

[0051] In the second step, the molar ratio of hydrogen halide (d) to compound c is theoretically 3, but the amine valency of compound c is measured by neutralization titration, and then hydrogen halide is added. Any molar ratio that results in a neutral pH after the titration is complete is acceptable.

[0052] In the second step, the solvent used for the reaction between compound c and hydrogen halide (d) is water.

[0053] In the second step, the reaction temperature between compound c and hydrogen halide (d) is 0 to 80°C, preferably 30 to 60°C. The reaction pressure is not particularly limited, but is preferably atmospheric pressure. The reaction time is selected as appropriate.

[0054] In the second step, the reaction atmosphere between compound c and hydrogen halide (d) is an inert gas atmosphere. Examples of inert gases include nitrogen gas, argon gas, and helium gas.

[0055] Then, in the second step, by reacting compound c with hydrogen halide (d), the primary amino group of compound c reacts with hydrogen halide and is converted into a "hydrogen halide base of the primary amino group", which is a quaternary amino group, and a phosphine compound (compound e) having three alkyl groups with a hydrogen halide base of the primary amino group is obtained. The alkyl group of compound e is -NH ３ ＋ ·X － (X represents a halogen element.) It is an alkyl group having a quaternary ammonium group in which the counter anion represented by is a halogen ion, and compound e has three alkyl groups with a hydrogen halide base of the primary amino group.

[0056] The third step in the method for producing an ionic liquid according to the present invention is to react a phosphine compound (compound e) having three alkyl groups with a hydrogen halide base of the primary amino group obtained by performing the second step with a hydrogen halide salt (compound f) of a linear or branched alkylamine compound having 2 to 10 carbon atoms and having a primary amino group, to obtain a phosphonium halide compound (compound g) having four alkyl groups with a hydrogen halide base of the primary amino group.

[0057] The hydrogen halide salt (compound f) of a linear or branched alkylamine compound having 2 to 10 carbon atoms and having a primary amino group according to the third step is a quaternary ammonium salt obtained by reacting an alkylamine compound with hydrogen halide. The alkylamine compound used as a raw material for producing compound f is a linear or branched saturated hydrocarbon having 2 to 10 carbon atoms, preferably a linear or branched saturated hydrocarbon having 2 to 8 carbon atoms, and has a primary amino group at the end. That is, compound f is obtained by converting the primary amino group of the alkylamine compound used as a raw material for producing compound f into a "hydrogen halide base of the primary amino group", which is a quaternary amino group, and is -NH ３ ＋ ·X －An alkane having a quaternary ammonium group in which the counter anion represented by (X represents a halogen element) is a halogen ion. Examples of the compound f include 2-bromoethylamine hydrobromide, 2-chloroethylamine hydrochloride, 3-bromopropylamine hydrobromide, 3-chloropropylamine hydrochloride, 4-bromobutylamine hydrobromide, 4-chlorobutylamine hydrochloride, 5-bromopentylamine hydrobromide, 5-chloropentylamine hydrochloride, 6-bromohexylamine hydrobromide, 8-bromooctylamine hydrobromide, 10-bromodecylamine hydrobromic acid, 3-methyl-4-bromobutylamine hydrobromide, and the like.

[0058] In the third step, the molar ratio of the compound f to the compound e is theoretically 1, but it may be 1 to 1.2.

[0059] In the third step, the solvent for the reaction between the compound e and the compound f is water.

[0060] In the third step, the reaction temperature between the compound e and the compound f is preferably 30 to 100 °C. The reaction pressure is not particularly limited, but preferably normal pressure. The reaction time is appropriately selected.

[0061] In the third step, the reaction atmosphere between the compound e and the compound f is an inert gas atmosphere. Examples of the inert gas include nitrogen gas, argon gas, and helium gas.

[0062] In the third step, by reacting the compound e and the compound f, a phosphonium halide compound (compound g) having four alkyl groups having a hydrogen halide base of a primary amino group is obtained. The alkyl group of the compound g is -NH ３ ＋ ·X － An alkyl group having a quaternary ammonium group in which the counter anion represented by (X represents a halogen element) is a halogen ion, and the compound g has four alkyl groups having a hydrogen halide base of this primary amino group.

[0063] The fourth step in the method for producing the ionic liquid of the present invention involves reacting a phosphonium halide compound (compound g) having four alkyl groups with a primary amino group hydrogen halide base obtained in the third step with an alkali compound (h) to neutralize it, and then obtaining the following general formula (2):

[0064]

[0065] (In the formula, R １ , R ２ and R ３ Each of these independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, and R ４ X represents a linear or branched alkylene group with 2 to 10 carbon atoms. － This is a process to obtain an ionic liquid represented by (where represents a halogen ion).

[0066] The alkali compound (h) in the fourth step is not particularly limited as long as it can carry out a neutralization reaction, but is not particularly limited as long as it can convert the quaternary ammonium group of compound g to a primary amino group, and examples include sodium hydroxide, potassium hydroxide, and aqueous ammonia.

[0067] In the fourth step, the molar ratio of alkali compound (h) to compound g is theoretically 3, but it can be between 3 and 3.1.

[0068] In the fourth step, the solvent used for the reaction between compound g and alkali compound (h) is water.

[0069] In the fourth step, the reaction temperature between compound g and alkali compound (h) is 0 to 60°C, preferably 20 to 50°C. The reaction pressure is not particularly limited, but is preferably atmospheric pressure. The reaction time is selected as appropriate.

[0070] In the fourth step, the reaction atmosphere between compound g and alkali compound (h) is an inert gas atmosphere. Examples of inert gases include nitrogen gas, argon gas, and helium gas.

[0071] Then, in the fourth step, compound g is reacted with alkali compound (h) to obtain an ionic liquid represented by general formula (2).

[0072] In general formula (2), R １ , R ２ and R ３ Each independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, preferably 2 to 4 carbon atoms, R ４ R represents a linear or branched alkylene group having 2 to 10 carbon atoms, preferably 2 to 8 carbon atoms. １ , R ２ , R ３ and R ４ These elements may be identical or different, but from a synthesis standpoint, it is preferable that they be identical.

[0073] R related to general formula (2) １ , R ２ , R ３ and R ４ In general formula (1), the group bonded to the P atom is the R group related to general formula (1). １ , R ２ , R ３ and R ４ This is similar to the group bonded to the P atom in general formula (1).

[0074] The ionic liquid represented by general formula (2) is composed of a cation and a halogen ion. The cation constituting the ionic liquid represented by general formula (2) is a phosphonium cation having four groups bonded to a P atom, and all of the groups bonded to the P atom are alkyl groups having primary amino groups. In other words, the ionic liquid represented by general formula (2) is a phosphonium-based ionic liquid in which the cation is a phosphonium ion having four alkyl groups to which primary amino groups are bonded.

[0075] The present invention's method for producing an ionic liquid involves, after performing the fourth step, converting the halogen anion of the ionic liquid represented by general formula (2) to an anion other than a halogen anion, and then producing the following general formula (3):

[0076]

[0077] (In the formula, R １ , R ２ and R ３Each of these independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, and R ４ This represents a linear or branched alkylene group with 2 to 10 carbon atoms. A2 ｎ－ The fifth step may involve obtaining an ionic liquid represented by (where represents an anion other than a halogen ion).

[0078] The fifth step is to convert the halogen anions in the ionic liquid represented by general formula (2) obtained in the fourth step into anions other than halogen anions, thereby obtaining an ionic liquid represented by general formula (3).

[0079] In the fifth step, the method for converting the halogen anion of the ionic liquid represented by general formula (2) to an anion other than the halogen anion is not particularly limited. Examples include a method of converting the halogen anion to a hydroxide anion using an anion exchange resin and neutralizing it with an acid, or a method using a side decomposition reaction in which the sodium salt of the acid to be substituted is mixed in solution and extracted with an organic solvent.

[0080] In general formula (3), R １ , R ２ and R ３ Each independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, preferably 2 to 4 carbon atoms, R ４ R represents a linear or branched alkylene group having 2 to 10 carbon atoms, preferably 2 to 8 carbon atoms. １ , R ２ , R ３ and R ４ These elements may be identical or different, but from a synthesis standpoint, it is preferable that they be identical.

[0081] R related to general formula (3) １ , R ２ , R ３ and R ４ In general formula (1), the group bonded to the P atom is the R group related to general formula (1). １ , R ２ , R ３ and R ４ This is similar to the group bonded to the P atom in general formula (1).

[0082] In the fifth step, an anion other than the halogen anion that replaces the halogen ion, namely A2 in general formula (3), ｎ－ For example, phosphate ions (H ２ PO ４ － HPO ４ ２－ , PO ４ ３－ ), methanolamine phosphate ion (NH ２ CH ２ OPO ３ ２－ ), ethanolamine phosphate ion (NH ２ C ２ H ４ OPO ３ ２－ ), propanolamine phosphate ion (NH ２ C ３ H ６ OPO ３ ２－ ), butanolamine phosphate ion (NH ２ C ４ H ８ OPO ３ ２－ ), diethyldithiophosphate ion ((C ２ H ５ ) ２ O ２ PS ２ － ), dimethyl phosphate ion ((CH ３ ) ２ PO ４ － ), diethyl phosphate ion ((C ２ H ５ ) ２ PO ４ － Phosphate group-containing anions such as ) and methylsulfonic acid (CH ３ SO ３ － ), fluoromethylsulfonic acid (CF ３ SO ３ － ), benzenesulfonic acid (C ６ H ５ SO ３ －) and other sulfonic acid group-containing anions, bis(trifluoromethanesulfonyl)imide ions ((CF ３ SO ２ ) ２ N － ), bis(fluorosulfonyl)imide ion ((FSO ２ ) ２ N － ) and other imide group-containing anions, imidazolate ions ((C) ３ H ３ N ２ ) － ), benzimidazolate ion ((C ７ H ５ N ２ ) － ), benzotriazolate ion ((C ６ H ４ N ３ ) － ) and other nitrogen heterocycle-containing anions, acetate ions (CH ３ COO － ), formate ion (HCOO － ), propionate ion (C ２ H ５ COO － ), oxalate ion ((COO) ２ ２－ ), maleate ion (C ２ H ２ (COO) ２ ２－ ), malonate ion (CH ２ (COO) ２ ２－ ) and other carboxylic acid group-containing anions, glycine ions ((NH ２ )CH ２ COO － ), alanine ion (((NH ２ ) C ２ H ４ COO － ), β-alanine ion ((NH ２ ) C ２ H ４ COO － ), isoleucine ion (CH ３ CH ２ (CH ３ )CH(NH ２ ) CHCOO－ ), leucine ion ((CH ３ ) ２ CHCH ２ (NH ２ ) CHCOO － ), methionine ion (CH ３ SC ２ H ４ (NH ２ ) CHCOO － ), valine ion ((CH ３ ) ２ CH(NH ２ ) CHCOO － ), phenylalanine ion (PhCH ２ (NH ２ ) CHCOO － ), tryptophan ion (INDOLE-CH ２ (NH ２ ) CHCOO － ), tyrosine ion (p-HO-PhCH ２ (NH ２ ) CHCOO － ), asparagine ion (H ２ NCOCH ２ (NH ２ ) CHCOO － ), cysteine ​​ion (HSCH ２ (NH ２ ) CHCOO － ), glutamine ion (H ２ NCOC ２ H ４ (NH ２ ) CHCOO － ), serine ions (HOCH ２ (NH ２ ) CHCOO － ), threonine ion (CH ３ (OH)CH(NH ２ ) CHCOO － ), aspartate ion (HOCOCH ２ (NH ２ ) CHCOO － ), glutamate ion (HOCOC ２ H ４ (NH ２ ) CHCOO － ), arginine ion (H２ N(HN)=CNHC ３ H ６ (NH ２ ) CHCOO － ), histidine ion (IMID-CH ２ (NH ２ ) CHCOO － ), L-(+)-lysine ion (H ２ NC ４ H ８ (NH ２ ) CHCOO － ), D-(-)-lysine ion (H ２ NC ４ H ８ (NH ２ ) CHCOO － ), DL-lysine ion (H ２ NC ４ H ８ (NH ２ ) CHCOO － ), proline ion (Pyl-COO － ) and other amino acid anions, tetrafluoroborate (BF ４ － ), hexafluorophosphate (PF ６ － ) are examples. Note that if these anions have a chiral center, they may be optical isomers or racemates. Among these, A1 ｎ－ fluoride ions (F － ), chloride ions (Cl － ), bromide ions (Br － ), iodide ion (I － ), phosphate ion (H ２ PO ４ － ), methanolamine phosphate ion (NH ２ CH ２ OPO ３ ２－ ), ethanolamine phosphate ion (NH ２ C ２ H ４ OPO ３ ２－ ), propanolamine phosphate ion (NH ２ C ３H ６ OPO ３ ２－ ), butanolamine phosphate ion (NH ２ C ４ H ８ OPO ３ ２－ ), bis(trifluoromethanesulfonyl)imide ion ((CF ３ SO ２ ) ２ N － ), bis(fluorosulfonyl)imide ion ((FSO ２ ) ２ N － ), benzotriazolate ion ((C ６ H ４ N ３ ) － ), alanine ion (((NH ２ ) C ２ H ４ COO － ), β-alanine ion (((NH ２ ) C ２ H ４ COO － ), glycine ion ((NH ２ )CH ２ COO － ), L-(+)-lysine ion (H ２ NC ４ H ８ (NH ２ ) CHCOO － ) is preferable.

[0083] Ionic liquids represented by general formula (3) include tetrakis(3-aminopropyl)phosphonium phosphate, tetrakis(3-aminopropyl)phosphonium methanolamine phosphate, tetrakis(3-aminopropyl)phosphonium ethanolamine phosphate, tetrakis(3-aminopropyl)phosphonium propanolamine phosphate, tetrakis(3-aminopropyl)phosphonium butanolamine phosphate, tetrakis(3-aminopropyl)phosphonium bis(trifluoromethanesulfonyl)imide, tetrakis(3-aminopropyl)phosphonium bis(fluorosulfonyl)imide, tetrakis(3-aminopropyl)phosphonium alanine, tetrakis(3-aminopropyl)phosphonium β-alanine, tetrakis(3-aminopropyl)phosphonium glycine, tetrakis(3-aminopropyl)phosphonium L-(+)-lysine, tris(3-aminopropyl)2-aminoethylphosphonium fluoride, tris(3-aminopropyl)2-aminoethylphosphonium chloride, and tris(3-aminopropyl)2-aminoethylphosphonium Tris(3-aminopropyl)2-aminoethylphosphonium iodide, Tris(3-aminopropyl)2-aminoethylphosphonium phosphate, Tris(3-aminopropyl)2-aminoethylphosphonium methanolamine phosphate, Tris(3-aminopropyl)2-aminoethylphosphonium ethanolamine phosphate, Tris(3-aminopropyl)2-aminoethylphosphonium propanolamine phosphate, Tris(3-aminopropyl)2-aminoethylphosphonium butanolamine phosphate, Tri Examples include tris(3-aminopropyl)2-aminoethylphosphonium / bis(trifluoromethanesulfonyl)imide, tris(3-aminopropyl)2-aminoethylphosphonium / bis(fluorosulfonyl)imide, tris(3-aminopropyl)2-aminoethylphosphonium / alanine, tris(3-aminopropyl)2-aminoethylphosphonium / β-alanine, tris(3-aminopropyl)2-aminoethylphosphonium / glycine, and tris(3-aminopropyl)2-aminoethylphosphonium / L-(+)-lysine.

[0084] In the general formula (3), n represents an integer of 1 or more and 3 or less.

[0085] The ionic liquid for a carbon dioxide absorbent of the present invention has the following general formula (1):

[0086]

[0087] (In the formula, R １ , R ２ and R ３ each independently represent a linear or branched alkylene group having 2 to 10 carbon atoms, R ４ represents a linear or branched alkylene group having 2 to 10 carbon atoms, and n represents an integer of 1 or more and 3 or less. A1 ｎ－ represents an anion.) The ionic liquid for a carbon dioxide absorbent is characterized in that it is an ionic liquid represented by the formula.

[0088] The ionic liquid for a carbon dioxide absorbent of the present invention can absorb carbon dioxide by the reaction of the ionic liquid represented by the general formula (1) with carbon dioxide. That is, the ionic liquid of the present invention is an ionic liquid for a carbon dioxide absorbent used as a substance for absorbing carbon dioxide in a carbon dioxide absorbent. The ionic liquid represented by the general formula (1) according to the ionic liquid for a carbon dioxide absorbent of the present invention is the same as the ionic liquid represented by the general formula (1) according to the ionic liquid of the present invention, except as described below.

[0089] The carbon dioxide absorbent of the present invention is a carbon dioxide absorbent characterized by containing the ionic liquid for a carbon dioxide absorbent of the present invention. That is, the carbon dioxide absorbent of the present invention is a carbon dioxide absorbent characterized by containing an ionic liquid represented by the general formula (1). In the carbon dioxide absorbent of the present invention, the ionic liquid represented by the general formula (1) absorbs carbon dioxide. The ionic liquid represented by the general formula (1) according to the carbon dioxide absorbent of the present invention is the same as the ionic liquid represented by the general formula (1) according to the compound of the present invention.

[0090] The ionic liquid represented by general formula (1) used in the carbon dioxide absorbent of the present invention has virtually no vapor pressure and, furthermore, possesses high heat resistance due to the presence of a phosphonium cation. Therefore, even in the heating temperature range during regeneration after carbon dioxide has been absorbed by the carbon dioxide absorbent of the present invention, for example, a heating temperature range of 60°C to 150°C, the ionic liquid represented by general formula (1) is not substantially discharged outside the system by volatilization or other means.

[0091] As for the ionic liquid represented by general formula (1) used in the carbon dioxide absorbent of the present invention, from the viewpoint of ease of synthesis and carbon dioxide absorption performance, tetrakis(3-aminopropyl)phosphonium fluoride, tetrakis(3-aminopropyl)phosphonium chloride, tetrakis(3-aminopropyl)phosphonium bromide, tetrakis(3-aminopropyl)phosphonium iodide, tetrakis(3-aminopropyl)phosphonium phosphate, tetrakis(3-aminopropyl)phosphonium methanolamine phosphate, tetrakis(3-aminopropyl)phosphonium ethanolamine phosphate, tetrakis(3-aminopropyl)phosphonium propanolamine phosphate, tetrakis(3-aminopropyl)phosphonium butanolamine phosphate, tetrakis(3-aminopropyl)phosphonium bis(trifluoromethanesulfonyl)imide, tetrakis(3-aminopropyl)phosphonium bis(fluorosulfonyl)imide, tetrakis(3-aminopropyl)phosphonium alanine, tetrakis(3-aminopropyl)phosphonium β-alanine, tetra Kiss(3-aminopropyl)phosphonium glycine, tetrakiss(3-aminopropyl)phosphonium L-(+)-lysine, tris(3-aminopropyl)2-aminoethylphosphonium fluoride, tris(3-aminopropyl)2-aminoethylphosphonium chloride, tris(3-aminopropyl)2-aminoethylphosphonium bromide, tris(3-aminopropyl)2-aminoethylphosphonium iodide, tris(3-aminopropyl)2-aminoethylphosphonium phosphate, tris(3-aminopropyl)2 - Aminoethylphosphonium methanolamine phosphate, Tris(3-aminopropyl)2-aminoethylphosphonium ethanolamine phosphate, Tris(3-aminopropyl)2-aminoethylphosphonium propanolamine phosphate, Tris(3-aminopropyl)2-aminoethylphosphonium butanolamine phosphate, Tris(3-aminopropyl)2-aminoethylphosphonium bis(trifluoromethanesulfonyl)imide, Tris(3-aminopropyl)2-aminoethylphosphonium bis(fluorosulfonyl)imide,It is preferable that the compounds are tris(3-aminopropyl)2-aminoethylphosphonium / alanine, tris(3-aminopropyl)2-aminoethylphosphonium / β-alanine, tris(3-aminopropyl)2-aminoethylphosphonium / glycine, or tris(3-aminopropyl)2-aminoethylphosphonium / L-(+)-lysine.

[0092] In the carbon dioxide absorbent of the present invention, the form in which the ionic liquid represented by general formula (1) exists is not particularly limited, and for example, it may exist in a form supported on a carrier.

[0093] The first embodiment of the carbon dioxide absorbent of the present invention is a carbon dioxide absorbent characterized by comprising a porous carrier and an ionic liquid for carbon dioxide absorbent of the present invention supported on the porous carrier. In other words, the first embodiment of the carbon dioxide absorbent of the present invention is a carbon dioxide absorbent characterized by comprising a porous carrier and an ionic liquid represented by general formula (1) supported on the porous carrier. In the first embodiment of the carbon dioxide absorbent of the present invention, the ionic liquid represented by general formula (1), which is a liquid, is taken into the pores of the porous carrier and physically adsorbed, so that the ionic liquid represented by general formula (1) is supported on the porous carrier.

[0094] The porous carrier according to the first embodiment of the carbon dioxide absorbent of the present invention is not particularly limited as long as it has a porous structure having many pores inside and can take in an ionic liquid represented by general formula (1) into its internal pores and physically adsorb and retain the ionic liquid represented by general formula (1) within the pores. Examples of porous carriers include activated carbon, silica gel, layered silicates, mesoporous silica, zeolites, vermiculite, molecular sieves, porous silica, diatomaceous earth, porous resins, porous fibers, porous metal-organic structures, porous alumina, porous ceramics, porous concrete, activated clay, or clay minerals. Activated carbon, silica gel, zeolites, and molecular sieves are preferred because they can carry a large amount of the ionic liquid represented by general formula (1). Furthermore, if the porous carrier is a porous material capable of retaining water within its pores, such as activated carbon, silica gel, zeolite, or molecular sieve, then when the gas to be treated containing carbon dioxide contains moisture, the moisture in the gas is adsorbed into the pores of the porous material. This prevents the carbon dioxide absorbent compound from leaching out of the porous material alone, thus improving the carbon dioxide absorption performance of the carbon dioxide absorbent. The porous material capable of retaining water within its pores is not particularly limited as long as it can retain water within its pores, but examples include materials that can contain water at a water content of 5 to 30% by mass, preferably 10 to 25% by mass.

[0095] The BET specific surface area of ​​the porous carrier is preferably 1.0 × 10⁻⁶. １ ~5.0 x 10 ３ I understand ２ / g, preferably 1.0 × 10 ２ ~2.0 x 10 ３ I understand ２ The value is / g. Furthermore, the pore volume of the porous carrier obtained by the gas adsorption method is preferably 0.1 to 2.0 mL / g, and more preferably 0.3 to 1.5 mL / g.

[0096] The shape of the porous carrier can be, for example, granular, powdery, fibrous, plate-like, cylindrical, or honeycomb-like. Of these, granular or powdery forms are preferred from the viewpoint of contact with mixed gases containing carbon dioxide and packing into packing equipment such as columns and towers. The porous carrier may also be a molded body. Among porous carriers, activated carbon, silica gel, zeolite, and molecular sieves are preferred from the viewpoint of ease of handling and the ability to easily support ionic liquids represented by the general formula (1), and activated carbon and silica gel are particularly preferred.

[0097] Various types of activated carbon can be used as the activated carbon in the present invention, for example, activated carbon made from wood, coconut shells, coal, petroleum pitch, coke, coal tar, etc. The activated carbon may also be a molded body. In addition to the characteristics of the porous carrier described above, the activated carbon preferably has physical properties measured according to JIS K1474 (Activated Carbon Test Method) such as a loss on drying of 0.1 to 5.0%, a residue on ignition of 0.1 to 5.0%, a packing density of 0.25 to 0.85 g / ml, an acetone adsorption performance of 14.0 to 41.0%, an iodine adsorption performance of 600 to 2600 mg / g, and a hardness of 90.0 to 100.0%.

[0098] Various types of silica gel can be used in the present invention, and for example, those containing 99.0% by mass or more, and particularly 99.9% by mass or more, of silicon dioxide are preferred. The silica gel may be a molded body. In addition to the porous carrier properties described above, the silica gel preferably has an average particle size of 0.01 to 10 mm as measured by a scanning electron microscope, and preferably has a drying loss of 10% or less.

[0099] Various types of zeolites can be used in the present invention, including LTA-type zeolite, FER-type zeolite, MWW-type zeolite, MFI-type zeolite, MOR-type zeolite, LTL-type zeolite, FAU-type zeolite, BEA-type zeolite, and the like. The zeolite may also be a molded body. In addition to the porous carrier properties described above, it is preferable that the zeolite has an average particle size of 0.01 to 15 mm as measured by a scanning electron microscope.

[0100] In the first embodiment of the carbon dioxide absorbent of the present invention, when two or more ionic liquids represented by general formula (1) are supported on a porous carrier, the two or more ionic liquids represented by general formula (1) may be supported as a mixed solution, or each of the two or more ionic liquids represented by general formula (1) may be supported on a different part of the porous carrier. That is, for example, when supporting two ionic liquids represented by general formula (1) on a porous carrier, the two ionic liquids represented by general formula (1) may be mixed first, and the resulting mixed solution may be incorporated into the pores of the porous carrier and supported, or one of the two compounds represented by general formula (1) may be incorporated into the pores of the porous carrier first, and then the other ionic liquid represented by general formula (1) may be incorporated into the pores of the porous carrier to support the two ionic liquids represented by general formula (1). The same applies when supporting three or more ionic liquids represented by general formula (1) on a porous carrier.

[0101] The impregnation rate (content) of the ionic liquid represented by general formula (1) in the carbon dioxide absorbent of the first embodiment of the present invention is not particularly limited, but is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, relative to the total carbon dioxide absorbent. By having the amount of compound represented by general formula (1) impregnated in the carbon dioxide absorbent within the above range, it can be uniformly present on the inner surface of the pores of the porous carrier, thereby enabling efficient absorption of carbon dioxide.

[0102] The carbon dioxide absorbent of the first embodiment of the present invention is an ionic liquid represented by general formula (1) that is capable of chemical adsorption of carbon dioxide, supported on a porous carrier. As a result, carbon dioxide can be absorbed more efficiently when the temperature of the carbon dioxide absorbent is between -20°C and 50°C, and the carbon dioxide is easily desorbed, making it easy to regenerate the carbon dioxide absorbent.

[0103] The carbon dioxide absorbent of the first embodiment of the present invention is spread out on the surface of a porous carrier with a large surface area, thereby increasing the contact area between the ionic liquid represented by general formula (1) and carbon dioxide. Therefore, the carbon dioxide absorbent of the first embodiment of the present invention can achieve high carbon dioxide absorption efficiency.

[0104] The first embodiment of the carbon dioxide absorbent of the present invention is supported on a solid carrier and can be used by packing it into columns or reaction towers. Furthermore, compared to liquid carbon dioxide absorbents, the first embodiment of the present invention allows for more efficient contact with carbon dioxide or carbon dioxide-containing gases because appropriate gaps are formed when it is packed into columns or reaction towers.

[0105] A porous carrier relating to the first embodiment of the carbon dioxide absorbent of the present invention, and anion A1 of the ionic liquid for the carbon dioxide absorbent of the present invention supported on the porous carrier. ｎ－ The combinations are not particularly limited. When the ionic liquid represented by general formula (1) contains a hydrophilic anion, silica gel with good affinity for water can be used as the porous support. For example, by supporting the ionic liquid for carbon dioxide absorption of the first embodiment of the carbon dioxide absorbent on silica gel, a carbon dioxide absorbent with excellent absorption performance can be obtained. Furthermore, when the ionic liquid represented by general formula (1) contains a lipophilic anion, activated carbon with good compatibility with it can be used as the porous support. By supporting the ionic liquid for carbon dioxide absorption of the first embodiment of the carbon dioxide absorbent on activated carbon, a carbon dioxide absorbent with excellent absorption performance can be obtained.

[0106] The carbon dioxide absorbent of the present invention can separate and recover carbon dioxide from a mixed gas containing carbon dioxide. The other components of the mixed gas are not particularly limited, as long as the gas contains carbon dioxide. Examples of the other components include oxygen, nitrogen, carbon monoxide, nitric oxide, nitrogen dioxide, dinitrogen monoxide, dinitrogen trioxide, dinitrogen tetroxide, dinitrogen pentoxide, sulfur monoxide, sulfur dioxide, sulfur trioxide, phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid, water, etc. The concentration of carbon dioxide in the mixed gas is not particularly limited and may be a high concentration with a purity of about 100%, or it may be a concentration similar to that found in the atmosphere.

[0107] The carbon dioxide absorbent of the present invention is useful as an absorbent for separating and recovering carbon dioxide from mixed gases containing carbon dioxide emitted from sources such as power plants (coal-fired and natural gas-fired), factories (chemical plants, waste treatment plants, steel mills, etc.), and transportation equipment (automobiles, aircraft, ships, etc.). It is also useful as an absorbent used in DAC (Direct Air Capture) devices that directly separate and recover carbon dioxide from the atmosphere. In other words, the carbon dioxide absorbent of the present invention is suitable as a carbon dioxide absorbent used in various devices such as equipment used in power plants, factories, and transportation equipment, as well as DAC devices.

[0108] Next, a method for separating carbon dioxide and a method for separating and recovering carbon dioxide using the carbon dioxide absorbent of the present invention will be described.

[0109] The present invention provides a carbon dioxide separation method characterized by having a carbon dioxide separation step (A) in which carbon dioxide is separated from a mixed gas by contacting a carbon dioxide absorbent of the present invention with a mixed gas containing carbon dioxide, thereby allowing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas.

[0110] The present invention provides a carbon dioxide separation and recovery method comprising: a carbon dioxide separation step (A) in which a carbon dioxide absorbent of the present invention is brought into contact with a mixed gas containing carbon dioxide, thereby allowing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas and separating the carbon dioxide from the mixed gas; and a carbon dioxide recovery step (B) in which the carbon dioxide absorbent that has absorbed carbon dioxide in the carbon dioxide separation step is heated at a temperature of 60°C to 150°C to desorb the carbon dioxide from the carbon dioxide absorbent, thereby regenerating the carbon dioxide absorbent and recovering the desorbed carbon dioxide.

[0111] In the carbon dioxide separation method and the carbon dioxide separation and recovery method of the present invention, the step of separating carbon dioxide from a mixed gas containing carbon dioxide is the carbon dioxide separation step (A) in both cases and is the same.

[0112] The carbon dioxide separation step (A) is a step in which the carbon dioxide absorbent of the present invention is brought into contact with a mixed gas containing carbon dioxide, thereby causing the carbon dioxide absorbent of the present invention to absorb the carbon dioxide in the mixed gas.

[0113] One example of the carbon dioxide separation process (A) is to supply a mixed gas containing carbon dioxide to an absorbent-packed column or absorbent-packed tower filled with the carbon dioxide absorbent of the present invention, bring the mixed gas into contact with the carbon dioxide absorbent, and separate the carbon dioxide from the mixed gas by allowing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas. In this form of carbon dioxide separation process (A), the mixed gas is brought into contact with the carbon dioxide absorbent by supplying the mixed gas to the absorbent-packed column or absorbent-packed tower, and the mixed gas that has been in contact with the carbon dioxide absorbent within the absorbent-packed column or absorbent-packed tower is discharged from the absorbent-packed column or absorbent-packed tower. Furthermore, the method of packing the carbon dioxide absorbent of the present invention into the absorbent-packed column or absorbent-packed tower is not particularly limited and can be carried out under atmospheric pressure or reduced pressure.

[0114] The temperature of the carbon dioxide absorbent in the carbon dioxide separation step (A) is not limited as long as the carbon dioxide absorbent can perform its function, but from the viewpoint of more efficiently absorbing carbon dioxide, it is preferable that the temperature be between -20°C and 50°C, preferably between 0°C and 50°C, and more preferably around room temperature of 25°C.

[0115] The pressure (absolute pressure) in the carbon dioxide separation process (A) is not particularly limited and can be carried out under atmospheric pressure.

[0116] In the carbon dioxide separation step (A), the carbon dioxide absorbent comes into contact with a mixed gas containing carbon dioxide, causing the carbon dioxide in the mixed gas to be absorbed by the carbon dioxide absorbent of the present invention, thereby separating the carbon dioxide from the mixed gas. In addition, the carbon dioxide separation step (A) yields a carbon dioxide absorbent that has absorbed carbon dioxide.

[0117] The carbon dioxide separation and recovery method of the present invention includes a carbon dioxide recovery step (B) in which a carbon dioxide absorbent that has absorbed carbon dioxide in a carbon dioxide separation step is regenerated and carbon dioxide is recovered. The carbon dioxide recovery step (B) is a step in which carbon dioxide is removed from the carbon dioxide absorbent that has absorbed carbon dioxide in a carbon dioxide separation step (A) by heating the carbon dioxide absorbent that has absorbed carbon dioxide in a carbon dioxide separation step (A).

[0118] The carbon dioxide recovery process (B) may include, for example, a method in which, after performing the carbon dioxide separation process (A), the carbon dioxide absorbent packed in the absorbent-packed column or absorbent-packed tower is heated to regenerate the carbon dioxide absorbent and recover the desorbed carbon dioxide.

[0119] In the carbon dioxide recovery step (B), the heating temperature of the carbon dioxide absorbent is 60°C to 150°C, preferably 80°C to 140°C. Generally, the higher the heating temperature, the easier it is for carbon dioxide to be released from the carbon dioxide absorbent that has absorbed carbon dioxide. In the carbon dioxide absorbent of the present invention, carbon dioxide can be released at a temperature of 60°C to 150°C, preferably 80°C to 140°C, and at a temperature equivalent to or higher than the temperature of the carbon dioxide separation step (A). For example, if the carbon dioxide absorbent is the carbon dioxide absorbent of the first embodiment of the present invention, the heating temperature is preferably 60 to 90°C.

[0120] In the carbon dioxide recovery process (B), the pressure (absolute pressure) is not particularly limited and may be carried out under atmospheric pressure or under reduced pressure. However, from the viewpoint of preventing oxidation of the carbon dioxide absorbent, it is preferable to carry it out under reduced pressure. When carried out under reduced pressure, the pressure (absolute pressure) is preferably 190 kPa or less, more preferably 160 kPa or less, and from the viewpoint of efficiently desorbing carbon dioxide from the carbon dioxide absorbent, it is preferably 150 kPa or less, particularly 110 kPa or less.

[0121] In the carbon dioxide separation and recovery method of the present invention, by using the recycled carbon dioxide absorbent obtained in the carbon dioxide recovery step (B) as a carbon dioxide absorbent to which a mixed gas containing carbon dioxide is contacted in the carbon dioxide separation step (A), the carbon dioxide separation step (A) and the carbon dioxide recovery step (B) can be repeated two or more times. For example, when repeating the carbon dioxide separation step (A) and the carbon dioxide recovery step (B) twice, the process is carried out as follows: "carbon dioxide separation step (A) → carbon dioxide recovery step (B) → carbon dioxide separation step (A) → carbon dioxide recovery step (B)". The carbon dioxide separation step (A) and the carbon dioxide recovery step (B) can be repeated as long as the carbon dioxide absorption performance is sustained.

[0122] In the carbon dioxide separation method and carbon dioxide separation and recovery method of the present invention, the carbon dioxide absorbent of the present invention, which contains a compound represented by general formula (1) that has excellent chemical absorption properties, is used for carbon dioxide absorption, thereby increasing the efficiency of carbon dioxide removal from the mixed gas.

[0123] The carbon dioxide separation method and carbon dioxide separation and recovery method of the present invention are suitably used when separating or recovering carbon dioxide from mixed gases containing carbon dioxide emitted from, for example, power plants such as coal-fired power plants and natural gas-fired power plants, factories such as chemical plants, waste treatment facilities and steel mills, and transportation equipment such as automobiles, aircraft and ships. They are also suitably used when separating or recovering carbon dioxide directly from the atmosphere.

[0124] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0125] (Synthesis Example 1: Tributyl(3-aminopropyl)phosphonium / β-alanine) A 1 L four-necked flask equipped with a reflux condenser, thermometer, and stirrer was purged with nitrogen, and 80.9 g (0.4 mol) of tributylphosphine was charged. 87.6 g (0.4 mol) of a slurry of 3-bromopropylamine hydrobromide suspended in 500 ml of 2-butanol was added under a nitrogen atmosphere. This was heated to a temperature of approximately 97-108°C, near the reflux temperature of 2-butanol, and the reaction was carried out for 8 hours to obtain the reaction solution. After cooling to room temperature, a color test using carbon disulfide confirmed that no tributylphosphine remained. 136.1 g (0.4 mol) of 20% sodium ethylate was added to this reaction solution, and the precipitated sodium bromide was filtered off by Celite filtration using a Hyfloo Supercell (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The resulting yellow filtrate was concentrated using an evaporator, and then washed with 300 ml of pure water and 200 ml of dichloromethane for extraction. The aqueous phase was then separated, concentrated using an evaporator, and 300 ml of ethanol was added to form an ethanol solution. Anhydrous magnesium sulfate was added, and the mixture was dehydrated overnight. After dehydration, the ethanol solution, filtered using a Hyfloo Supercell (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), was concentrated using an evaporator to obtain 125.9 g of a colorless, transparent viscous liquid with a viscosity (25°C) of 1722 cP (crude yield 92.5%). The NMR identification data of the obtained colorless, transparent liquid is as follows: (Identification Data) ３１ P-NMR; 34.10ppm １H-NMR; 0.98ppm (t, 9H, -CH3), 1.51-1.89ppm (m, 14H, -CH ２ -), 1.54 to 1.59 ppm (m, 2H, -CH2-) 2.37 to 2.65 ppm (m, 8H, P-CH ２ -), 2.92 ppm (t, 2H, -CH ２ -NH ２ ), 7.35ppm (s, 2H, -NH ２ As a result, it was confirmed to be tributyl(3-aminopropyl)phosphonium bromide.

[0126] 1500 ml of ion exchange resin (Organo, Amberlite IRA400J Cl, exchange capacity 1.4 equivalents / resin volume L) was packed into a glass column (inner diameter 65 mmφ × length 500 mm). 1000 ml of an aqueous solution containing 80 g (2.0 mol) of sodium hydroxide was passed through the column from above at a rate of SV = 1.0 using a tube pump, and then pure water was passed through until the effluent became neutral. Next, 140.0 g (0.41 mol) of the obtained tributyl(3-aminopropyl)phosphonium bromide was dissolved in 500 ml of pure water, and this aqueous solution was passed through the column from above at a rate of SV = 1.0, followed by the passing of another 1000 ml of pure water to obtain 1550 g of an aqueous solution of tributyl(3-aminopropyl)phosphonium hydroxide. Neutralization titration was performed with 1 / 10 N hydrochloric acid titration solution, resulting in a concentration of 6.5% and a yield of 89.0%. 500 g (0.12 mol) of the obtained aqueous solution of tributyl(3-aminopropyl)phosphonium hydroxide was dissolved in 10.7 g (0.12 mol) of β-alanine at room temperature. The resulting mixed aqueous solution was concentrated under reduced pressure using an evaporator. The concentrated solution was then mixed with methanol, and the methanol solution was dehydrated overnight with anhydrous magnesium sulfate. The dehydrated methanol solution was then concentrated under reduced pressure using an evaporator to obtain 41.4 g (crude yield 99.0%) of a colorless, transparent viscous liquid with a viscosity (25°C) of 288 cP. The NMR identification data of the obtained colorless, transparent viscous liquid is as follows: (Identification Data) ３１ P-NMR; 34.34ppm １ H-NMR; 0.80 ppm (t,9H,-CH ３ ), 1.31 to 1.45 ppm (m, 12H, -CH ２-), 1.54 to 1.59 ppm (m, 2H, -CH ２ -) 2.03 to 2.08 ppm (m, 8H, P-CH ２ -), 2.19ppm (t,2H,-CH ２ -COO),2.58,2.69ppm(t,2H,-CH ２ -NH ２ ), 3.20, 3.21 ppm (s, -NH ２ As a result, it was confirmed to be tributyl(3-aminopropyl)phosphonium β-alanine.

[0127] (Example 1) Synthesis of tetrakis(3-aminopropyl)phosphonium bromide: 150 ml of toluene and 133 g (2.33 mol) of allylamine were charged into a 1 L stainless steel autoclave equipped with a stirrer, thermometer, injection pump, safety valve, and gas inlet tube. The autoclave was purged three times with nitrogen gas and vacuum, and 22 g (0.65 mol) of phosphine gas manufactured by Nippon Chemical Industrial Co., Ltd. with a purity of 99.9% was charged. At this time, the temperature was raised to 80°C using a water bath, and the gauge pressure was 0.93 MPa (absolute pressure 1.03 MPa). Next, 1.06 g (0.006 mol) of azobisisobutyronitrile was dissolved in 150 ml of toluene and injected in stages over 6 hours, and the mixture was aged overnight at 80°C. At this time, the gauge pressure was 0.01 MPa (absolute pressure 0.11 MPa). After overnight maturation, the mixture was cooled to room temperature, the remaining gas was evacuated into a removal system, and the system was further purged with nitrogen gas and vacuum. The mixture was then extracted into a reduced-pressure round-bottom flask to obtain 585 g of a colorless, transparent liquid. Next, the obtained colorless, transparent liquid was heated under reduced pressure (gauge pressure 4 kPa (absolute pressure 105.3 kPa), 80°C) to remove excess allylamine and toluene. The vacuum and temperature were then increased and the mixture heated further (gauge pressure 0.2 kPa (absolute pressure 101.5 kPa), 160°C). Heating was stopped when the initial distillate began to appear, and the residue was used as the product. After cooling the obtained product to room temperature, it was purged with nitrogen gas to obtain 120 g of a colorless, transparent liquid. The NMR identification data for the obtained colorless, transparent liquid is as follows: (Identification Data) ３１ P-NMR (D ２ O); -29.73ppm １ H-NMR (D ２O); 1.40 to 1.46 ppm (m, 6H, -CH ２ -), 1.52 to 1.61 ppm (m, 6H, P-CH ２ -), 2.63 to 2.71 ppm (t, 6H, -CH ２ -NH ２ ), 4.67 ppm (s, 6H, -NH ２ As a result, it was confirmed to be tris(3-aminopropyl)phosphine.

[0128] Next, a 1 L four-necked flask equipped with a stirrer and thermometer was purged with nitrogen gas. 61.6 g (0.3 mol) of the obtained tris(3-aminopropyl)phosphine and 200 ml of pure water were charged, and 151.7 g (0.9 mol) of 48% hydrobromide solution was added dropwise from a dropping funnel over 15 minutes, causing the temperature to rise from 29°C to 51°C. The aqueous solution showed a pH of 7–8. Furthermore, 65.7 g (0.3 mol) of 3-bromopropylamine hydrobromide was added, and the mixture was heated and stirred at 70–75°C for 3 hours. After cooling, a sample was taken and P-NMR was measured, confirming the disappearance of tris(3-aminopropyl)phosphine (-29.7 ppm). The NMR identification data is as follows: (Identification Data) ３１ P-NMR (D ２ O); 36.34ppm １ H-NMR (D ２ O); 2.06 to 2.19 ppm (m, 8H, -CH ２ -), 2.60 to 2.69 ppm (m, 8H, P-CH ２ -), 3.27 to 3.30 ppm (t, 8H, -CH ２ -NH ２ ), 4.67ppm (s, 12H, HBr, -NH ２ As a result, it was confirmed that the substance was tetrakis(3-aminopropyl)phosphonium bromide 4-hydrobromide.

[0129] Next, 48 g (1.2 mol) of aqueous sodium hydroxide solution was added to an aqueous solution containing tetrakis(3-aminopropyl)phosphonium bromide and tetrahydrobromic acid to neutralize the hydrobromic acid. The water was removed under reduced pressure using an evaporator, 300 ml of isopropyl alcohol was added to the slurry, and dehydration was performed with anhydrous sodium sulfate. The precipitated sodium bromide was filtered using a Celite filtration aid. The isopropyl alcohol solution was concentrated under reduced pressure to obtain 99.1 g of a slightly yellowish liquid (crude yield 96.2%). The NMR identification data of the obtained slightly yellowish liquid is as follows: (Identification Data) ３１ P-NMR (D ２ O); 35.80ppm １ H-NMR (D ２ O); 1.60 to 1.68 ppm (m, 8H, -CH ２ -), 2.17 to 2.22 ppm (m, 8H, P-CH ２ -), 2.64 to 2.66 ppm (t, 8H, -CH ２ -NH ２ ), 4.69ppm (s, 8H, -NH ２ As a result, it was confirmed to be tetrakis(3-aminopropyl)phosphonium bromide.

[0130] (Example 2) A synthetic ion exchange resin of tetrakis(3-aminopropyl)phosphonium β-alanine (organo, Amberlite IRA400J Cl, exchange capacity 1.4 equivalents / resin volume L) was packed into a glass column (inner diameter 65 mmφ × length 500 mm) with 1500 ml of resin. 1000 ml of an aqueous solution containing 80 g (2.0 mol) of sodium hydroxide was flowed from above using a tube pump at a rate of SV = 1.0, and then pure water was flowed until the effluent became neutral. Next, an aqueous solution of 85.8 g (0.25 mol) of tetrakis(3-aminopropyl)phosphonium bromide obtained in Synthesis Example 1 was dissolved in 500 ml of pure water and flowed from the top of the column at a rate of SV = 1.0, and then 1000 ml of pure water was flowed to obtain 1590 g of an aqueous solution of tetrakis(3-aminopropyl)phosphonium hydroxide. The solution was titrated with 1 / 10 N hydrochloric acid titrator to confirm a concentration of 3.7% and a yield of 85.2%. 1200 g (0.158 mol) of the resulting aqueous solution of tetrakis(3-aminopropyl)phosphonium hydroxide was dissolved in 14.1 g (0.158 mol) of β-alanine at room temperature. The resulting mixed aqueous solution was concentrated under reduced pressure using an evaporator. The methanol solution, obtained by mixing the concentrate with methanol, was dehydrated overnight with anhydrous magnesium sulfate. The dehydrated methanol solution was then concentrated under reduced pressure using an evaporator to obtain 55.0 g (crude yield 99.0%) of a colorless, transparent, viscous liquid. The NMR identification data for the obtained colorless, transparent, viscous liquid is as follows: (Identification Data) ３１ P-NMR (D ２ O); 35.74ppm １ H-NMR (D ２ O); 1.53 to 1.62 ppm (m, 8H, -CH ２ -), 2.10 to 2.18 ppm (m, 8H, P-CH ２ -), 2.19 to 2.21 (t, 2H, -C(=O)-CH ２ -), 2.61 to 2.63 ppm (t, 8H, -CH ２ -NH ２ ), 2.68 to 2.70 ppm (t, 2H, -CH ２ ―NH ２ ), 4.68 ppm (s, 10H, -NH ２As a result, it was confirmed to be tetrakis(3-aminopropyl)phosphonium β-alanine.

[0131] (Example 3) Synthesis of Tetrakis(3-aminopropyl)phosphonium bis(trifluoromethanesulfonyl)imide 700 g (0.092 mol) of an aqueous solution of tetrakis(3-aminopropyl)phosphonium hydroxide used in Example 2 was mixed with 25.9 g (0.092 mol) of bis(trifluoromethanesulfonyl)imide at room temperature. The resulting mixed aqueous solution was concentrated under reduced pressure using an evaporator. The methanol solution, obtained by mixing the concentrate with methanol, was dehydrated overnight with anhydrous magnesium sulfate. The dehydrated methanol solution was then concentrated under reduced pressure using an evaporator to obtain 49.5 g (crude yield 99.0%) of a colorless, transparent, viscous liquid. The NMR identification data of the obtained colorless, transparent, viscous liquid is as follows: (Identification Data) ３１ P-NMR (D ２ O); 35.74ppm １ H-NMR (D ２ O); 1.56 to 1.64 ppm (m, 8H, -CH ２ -), 2.11 to 2.17 ppm (m, 8H, P-CH ２ -), 2.60 to 2.63 ppm (t, 8H, -CH ２ -NH ２ ), 4.68 ppm (s, 8H, -NH ２ As a result, it was confirmed to be tetrakis(3-aminopropyl)phosphonium bis(trifluoromethanesulfonyl)imide.

[0132] (Example 4) Synthesis of Tris(3-aminopropyl)2-aminoethylphosphonium bromide A 1 L four-necked flask equipped with a stirrer and thermometer was purged with nitrogen gas. 61.6 g (0.3 mol) of tris(3-aminopropyl)phosphine (used in Example 1) and 200 ml of pure water were charged, and 151.7 g (0.9 mol) of 48% hydrobromide solution was added dropwise from a dropping funnel over 15 minutes, causing the temperature to rise from 29°C to 51°C. The aqueous solution showed a pH of 7-8. Further, 61.5 g (0.3 mol) of 2-bromoethylamine hydrobromide was added, and the mixture was heated and stirred at 70-75°C for 3 hours. After cooling, a sample was taken and P-NMR was measured, confirming the disappearance of tris(3-aminopropyl)phosphine (-29.7 ppm). The NMR identification data is as follows. (Identification Data) ３１ P-NMR (D ２ O); 34.72ppm １ H-NMR (D ２ O); 1.95 to 2.00 ppm (m, 6H, -CH ２ -), 2.50 to 2.58 ppm (m, 6H, P-CH ２ -), 2.79 to 2.84 ppm (m, 2H, P-CH ２ -), 3.09 to 3.12 (m, 6H, -CH ２ -NH2), 3.30 to 3.38 (m, 2H, -CH ２ -NH ２ ), 4.65ppm (s, 12H, HBr, -NH ２ As a result, it was confirmed that the substance was tris(3-aminopropyl)2-aminoethylphosphonium bromide / 4-hydrobromide.

[0133] Next, 48 g (1.2 mol) of aqueous sodium hydroxide solution was added to an aqueous solution containing tris(3-aminopropyl)2-aminoethylphosphonium bromide and 4-hydrobromide to neutralize the hydrobromide. The water was removed under reduced pressure using an evaporator, 300 ml of isopropyl alcohol was added to the slurry, and the solution was dehydrated with anhydrous sodium sulfate. The precipitated sodium bromide was filtered using a Celite filtration aid. The isopropyl alcohol solution was concentrated under reduced pressure to obtain 87.7 g of a slightly yellowish liquid (crude yield 88.8%). The NMR identification data for the obtained slightly yellowish liquid is as follows: (Identification Data)３１ P-NMR (D ２ O); 33.00ppm １ H-NMR (D ２ O); 1.60 to 1.65 ppm (m, 6H, -CH ２ -), 2.17 to 2.23 ppm (m, 6H, P-CH ２ -), 2.32 to 2.38 ppm (m, 2H, P-CH ２ -), 2.64 to 2.68 (m, 6H, -CH ２ -NH ２ ), 2.84 to 2.89 (m, 2H, -CH ２ -NH ２ ), 4.68 ppm (s, 8H, -NH ２ As a result, it was confirmed to be tris(3-aminopropyl)2-aminoethylphosphonium bromide.

[0134] (Reference Example 1) Dissolve 30.2 g (0.086 mol) of tributyl(3-aminopropyl)phosphonium β-alanine obtained in Synthesis Example 1 in 300 ml of pure water, and add silica gel (CARiACT Q-30 manufactured by Fuji Silicia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 100 m²). ２ 55.9 g of (1 / g, average pore size 30 nm) was added and allowed to stand at room temperature until moisture permeated the silica gel. By concentrating under reduced pressure in an evaporator and completely removing the added water, 86.3 g of a carbon dioxide absorbent with tributyl(3-aminopropyl)phosphonium-β-alanine impregnated onto silica gel was obtained. The impregnation rate of tributyl(3-aminopropyl)phosphonium-β-alanine relative to the total mass of the carbon dioxide absorbent was 35.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 1 and carbon dioxide absorption test 2, which will be described later.

[0135] (Example 5) 42.4 g (0.1 mol) of tetrakis(3-aminopropyl)phosphonium bromide obtained in Example 1 was dissolved in 300 ml of pure water, and silica gel (CARiACT Q-30 manufactured by Fuji Silicia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 100 m²) was dissolved. ２78.7 g of (average pore size 30 nm) was added and allowed to stand at room temperature until moisture permeated the silica gel. By concentrating under reduced pressure in an evaporator and completely removing the added water, 121.9 g of a carbon dioxide absorbent with tetrakis(3-aminopropyl)phosphonium bromide impregnated onto silica gel was obtained. The impregnation rate of tetrakis(3-aminopropyl)phosphonium bromide relative to the total mass of the carbon dioxide absorbent was 35.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 1, carbon dioxide absorption test 2, and regeneration test described later.

[0136] (Example 6) 35.1 g (0.1 mol) of tetrakis(3-aminopropyl)phosphonium-β-alanine obtained in Example 2 was dissolved in 300 ml of pure water, and silica gel (CARiACT Q-30 manufactured by Fuji Silicia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 100 m²) was dissolved. ２ 65.3 g of (1 / g, average pore size 30 nm) was added and allowed to stand at room temperature until moisture permeated the silica gel. By concentrating under reduced pressure in an evaporator and completely removing the added water, 100.9 g of a carbon dioxide absorbent with tetrakis(3-aminopropyl)phosphonium-β-alanine impregnated onto silica gel was obtained. The impregnation rate of tetrakis(3-aminopropyl)phosphonium-β-alanine relative to the total mass of the carbon dioxide absorbent was 35.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 1 and carbon dioxide absorption test 2, which will be described later.

[0137] (Example 7) 54.3 g (0.1 mol) of tetrakis(3-aminopropyl)phosphonium bis(trifluoromethanesulfonyl)imide obtained in Example 3 was dissolved in 300 ml of pure water, and silica gel (CARiACT Q-30 manufactured by Fuji Silicia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 100 m²) was used. ２100.8 g of silica gel (average pore size 30 nm) was added and allowed to stand at room temperature until moisture permeated the silica gel. By concentrating under reduced pressure using an evaporator and completely removing the added water, 155.9 g of a carbon dioxide absorbent with tetrakis(3-aminopropyl)phosphonium-bis(trifluoromethanesulfonyl)imide impregnated onto silica gel was obtained. The impregnation rate of tetrakis(3-aminopropyl)phosphonium-bis(trifluoromethanesulfonyl)imide relative to the total mass of the carbon dioxide absorbent was 35.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 2 described later.

[0138] (Example 8) 65.3 g (0.1 mol) of tris(3-aminopropyl)2-aminoethylphosphonium bromide obtained in Example 4 was dissolved in 300 ml of pure water, and silica gel (CARiACT Q-30 manufactured by Fuji Silicia Chemical Co., Ltd., particle size 1.70-4.00 mm, BET specific surface area 100 m²) was dissolved. ２ 121.3 g (average pore size 30 nm) was added and allowed to stand at room temperature until moisture permeated the silica gel. By concentrating under reduced pressure in an evaporator and completely removing the added water, 187.0 g of a carbon dioxide absorbent with tris(3-aminopropyl)2-aminoethylphosphonium bromide impregnated onto the silica gel was obtained. The impregnation rate of tris(3-aminopropyl)2-aminoethylphosphonium bromide relative to the total mass of the carbon dioxide absorbent was 35.0% by mass. The obtained carbon dioxide absorbent was evaluated in carbon dioxide absorption test 2 described later.

[0139] (Evaluation) (Carbon Dioxide Absorption Test 1) 90 ml of the carbon dioxide absorbent obtained in Examples 5 and 6 and Reference Example 1 was packed into a glass column with an inner diameter of 20 mm and a length of 300 mm, and air (room temperature 25°C, average carbon dioxide concentration: 450 ppm) was passed through it at a flow rate of 100 ml / min using an air pump. The carbon dioxide concentration at the outlet of the glass column was measured and recorded using a data logger carbon dioxide meter (TR-76Ui-S, T&D Corporation), and the time until saturation occurred and the carbon dioxide concentration began to rise (breakthrough time) was determined. The number of moles of absorbed carbon dioxide was calculated by taking the difference between the average carbon dioxide concentration in the room and the average carbon dioxide concentration at the outlet as the amount of carbon dioxide absorbed. The absorption capacity was determined as the amount of carbon dioxide absorbed per gram of carbon dioxide absorbent. The results are shown in Table 1.

[0140]

[0141] The results shown in Table 1 indicate that the carbon dioxide absorbents of Examples 5 and 6 have superior carbon dioxide absorption performance compared to the carbon dioxide absorbent of Reference Example 1.

[0142] (Carbon Dioxide Absorption Test 2) The carbon dioxide absorbents obtained in Examples 5-8 and Reference Example 1 were placed in 35 ml Erlenmeyer flasks, and the volume was accurately measured to the nearest 0.1 mg. Carbon dioxide gas with a purity of 99.995% was blown in at a flow rate of 200 ml / min at room temperature (25°C), and the weight was accurately measured to the nearest 0.1 mg every 10 minutes. Gas blowing was stopped when the weight became constant. The increase in weight was used as the amount of carbon dioxide absorbed, and the number of moles was calculated. The absorption capacity was determined as the amount of carbon dioxide absorbed per gram of carbon dioxide absorbent. The results are shown in Table 2.

[0143]

[0144] The results shown in Table 2 indicate that the carbon dioxide absorbents of Examples 5 to 8 have superior carbon dioxide absorption performance compared to the carbon dioxide absorbent of Reference Example 1.

[0145] (Regeneration Test) The carbon dioxide absorbent obtained in Example 5 was placed in a 35 ml Erlenmeyer flask, and its weight was accurately measured to the nearest 0.1 mg. 99.995% pure carbon dioxide gas was blown in at a flow rate of 200 ml / min at room temperature (25°C), and the weight was accurately measured to the nearest 0.1 mg every 10 minutes. Gas blowing was stopped when the weight became constant. The increased weight was used as the amount of carbon dioxide absorbed, and the number of moles was calculated. The absorption capacity was determined as the amount of carbon dioxide absorbed per gram of carbon dioxide absorbent. The carbon dioxide absorbent from Example 5, which had absorbed carbon dioxide to saturation, was transferred to a 50 mm diameter Petri dish and regenerated by static heating in a vacuum dryer maintained at 80°C under full vacuum using a vacuum pump for 1 hour to expel the carbon dioxide. Next, the regenerated carbon dioxide absorbent was filled again into a 35 ml Erlenmeyer flask, and the carbon dioxide absorption and regeneration process was repeated 5 times. The regeneration rate was calculated based on the following formula. The results are shown in Table 3. Regeneration rate (%) = (Absorption capacity at regeneration / Initial absorption capacity) × 100

[0146]

[0147] The results shown in Table 3 indicate that when carbon dioxide absorbent is heated after the initial carbon dioxide absorption test to remove carbon dioxide, the recycled carbon dioxide absorbent regains its ability to absorb carbon dioxide. This demonstrates that recycled carbon dioxide absorbent exhibits excellent absorption performance and a high regeneration rate.

Claims

1. The following general formula (1): (In the formula, R １ , R ２ and R ３ Each of these independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, and R ４ A1 represents a linear or branched alkylene group with 2 to 10 carbon atoms, and n represents an integer between 1 and 3. ｎ－ An ionic liquid characterized by being represented by (where represents anion).

2. A1 in the general formula (1) ｎ－ The ionic liquid according to claim 1, characterized in that the ion is a fluoride ion, chloride ion, bromide ion, iodide ion, phosphate ion, methanolamine phosphate ion, ethanolamine phosphate ion, propanolamine phosphate ion, butanolamine phosphate ion, bis(trifluoromethanesulfonyl)imide ion, bis(fluorosulfonyl)imide ion, benzotriazolate ion, alanine ion, β-alanine ion, glycine ion, or L-(+)-lysine ion.

3. The following general formula (1) (wherein, R １ , R ２ and R ３ each independently represent a linear or branched alkylene group having 2 to 10 carbon atoms, R ４ represents a linear or branched alkylene group having 2 to 10 carbon atoms, n represents an integer of 1 or more and 3 or less. A1 ｎ－ represents an anion.). An ionic liquid for a carbon dioxide absorbent, characterized by being a compound represented by the formula.

4. A carbon dioxide absorbent characterized by containing the ionic liquid for carbon dioxide absorbent described in claim 3.

5. The carbon dioxide absorbent according to claim 4, characterized by comprising a porous carrier and an ionic liquid for carbon dioxide absorbent according to claim 3 supported on the porous carrier.

6. The carbon dioxide absorbent according to claim 5, characterized in that the porous carrier is activated carbon, silica gel, layered silicate, mesoporous silica, zeolite, vermiculite, molecular sieve, porous silica, diatomaceous earth, porous resin, porous fiber, porous metal-organic structure, porous alumina, porous ceramic, porous concrete, activated clay, or clay mineral.

7. A method for separating carbon dioxide, characterized by comprising a carbon dioxide separation step of contacting a carbon dioxide absorbent described in claim 5 with a mixed gas containing carbon dioxide, thereby allowing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas and separating the carbon dioxide from the mixed gas.

8. A method for separating and recovering carbon dioxide, comprising: a carbon dioxide separation step of contacting a carbon dioxide absorbent described in claim 5 with a mixed gas containing carbon dioxide, thereby separating carbon dioxide from the mixed gas by allowing the carbon dioxide absorbent to absorb the carbon dioxide in the mixed gas; and a carbon dioxide recovery step of heating the carbon dioxide absorbent that has absorbed carbon dioxide in the carbon dioxide separation step at a temperature of 60°C to 150°C to desorb carbon dioxide from the carbon dioxide absorbent, thereby regenerating the carbon dioxide absorbent and recovering the desorbed carbon dioxide.

9. The carbon dioxide separation and recovery method according to claim 8, characterized in that the recycled carbon dioxide absorbent obtained by the carbon dioxide recovery step is used as the carbon dioxide absorbent to which the mixed gas containing carbon dioxide is contacted in the carbon dioxide separation step, thereby repeating the carbon dioxide separation step and the carbon dioxide recovery step two or more times.

10. An apparatus characterized in that the carbon dioxide absorbent described in claim 4 is used.

11. The apparatus according to claim 10, characterized in that the apparatus is used in power plants, factories and transportation equipment.

12. The apparatus according to claim 10, characterized in that the apparatus is a DAC apparatus.

13. A first step involves reacting phosphine with a linear or branched terminal olefin having 2 to 10 carbon atoms and a primary amino group to obtain a phosphine compound having three alkylamino groups. A second step involves reacting the phosphine compound having three alkyl groups having a primary amino group hydrogen halide base with a hydrogen halide salt to obtain a phosphine compound having three alkyl groups having a primary amino group hydrogen halide base. A third step involves reacting the phosphine compound having three alkyl groups having a primary amino group hydrogen halide base with a hydrogen halide salt of a linear or branched alkylamine compound having 2 to 10 carbon atoms and a primary amino group to obtain a phosphonium halide compound having four alkyl groups having a primary amino group hydrogen halide base. The phosphonium halide compound having four alkyl groups having a primary amino group hydrogen halide base is reacted with an alkali compound and neutralized to obtain the following general formula (2): (In the formula, R １ , R ２ and R ３ Each of these independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, and R ４ X represents a linear or branched alkylene group with 2 to 10 carbon atoms. － A method for producing an ionic liquid, characterized by comprising a fourth step of obtaining an ionic liquid represented by (where represents a halogen ion), and 14. After performing the fourth step described above, the halogen anions of the ionic liquid represented by the general formula (2) are converted to anions other than halogen anions, and the following general formula (3): (In the formula, R １ , R ２ and R ３ Each of these independently represents a linear or branched alkylene group having 2 to 10 carbon atoms, and R ４ represents a linear or branched alkylene group with 2 to 10 carbon atoms, and n represents an integer between 1 and 3. A2 ｎ－ The method for producing an ionic liquid according to claim 13, characterized by having a fifth step of obtaining an ionic liquid represented by (where represents an anion other than a halogen ion).

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