Carbon dioxide absorption liquid, and carbon dioxide separation and recovery method

Abstract

Provided are: a carbon dioxide absorption liquid which has high carbon dioxide absorption capacity and is unlikely to undergo a decrease in performance even if used repeatedly; and a carbon dioxide separation and recovery method having excellent long-term reliability.　The carbon dioxide absorption liquid contains a compound represented by formula (I) and one or more types of organic solvent selected from among formulae (II) to (IV), and does not undergo phase separation following carbon dioxide absorption. Symbols in the formulae are as described in the description.

Description

Carbon dioxide absorption liquid and carbon dioxide separation and recovery method

[0001] The present disclosure relates to a carbon dioxide absorbing liquid and a method for separating and recovering carbon dioxide.

[0002] In recent years, the rapid increase in greenhouse gas emissions such as carbon dioxide and methane associated with social activities has been cited as one of the causes of global warming. Carbon dioxide in particular is the most significant greenhouse gas, and in accordance with the Paris Agreement that came into effect in 2016, measures to reduce carbon dioxide emissions are urgently needed.

[0003] Carbon dioxide separation and capture has attracted attention as an effort to reduce carbon dioxide emissions, and the development of carbon dioxide absorbents has been actively pursued. For this reason, in recent years, the development of carbon dioxide separation and capture technology using a chemical absorption method, primarily an aqueous solution of an amine compound, has been actively promoted for carbon dioxide-containing gases emitted from power plants and steelworks.

[0004] For example, Patent Document 1 discloses an absorbent that absorbs acidic compounds contained in a mixed gas and undergoes phase separation after absorbing the acidic compounds, the absorbent containing water, an amine compound, and an organic solvent, wherein the difference between the solubility parameter of the amine compound and the solubility parameter of the organic solvent is within a specific range.

[0005] Patent Document 2 discloses a carbon dioxide absorbing liquid that contains a specific carbon dioxide chemically absorbing amine, a specific tertiary polydentate amine, and a specific diluent, as a carbon dioxide absorbing liquid that has excellent carbon dioxide separation and recovery ability.

[0006] Patent Document 3 discloses a specific absorption liquid containing a specific alkanolamine compound and a specific imidazole compound as an absorption liquid capable of separating and recovering carbon dioxide with high efficiency and low energy cost.

[0007] Furthermore, Patent Document 4 discloses a specific absorbent for selectively removing hydrogen sulfide from a fluid stream containing carbon dioxide and hydrogen sulfide, the specific absorbent comprising a specific secondary amine, a non-aqueous solvent having at least two functional groups selected from an ether group and a hydroxy group, and a co-solvent.

[0008] International Publication No. 2017 / 110569 Japanese Patent Application Laid-Open No. 2021-154237 International Publication No. 2021 / 193963 Special Publication No. 3018-531146

[0009] A carbon dioxide absorbing liquid absorbs carbon dioxide from a gas containing carbon dioxide, for example, by coming into contact with the gas. The absorbing liquid after absorbing carbon dioxide releases carbon dioxide by, for example, heating. It is desirable to reuse the absorbing liquid after releasing carbon dioxide. On the other hand, amines in the absorbing liquid that has absorbed carbon dioxide can decrease due to reactions when heated, which can lead to a decrease in the performance of the absorbing liquid. The present disclosure aims to provide a carbon dioxide absorbing liquid that has high carbon dioxide absorption capacity and is resistant to performance degradation even with repeated use, and a carbon dioxide separation and recovery method that has excellent long-term reliability.

[0010] The present disclosure includes the following aspects: [1] A carbon dioxide absorbing liquid containing a compound represented by the following formula (I) and one or more organic solvents selected from the following formulas (II) to (IV), which does not undergo phase separation after absorbing carbon dioxide. In the formula, R １ is a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent, a cyclic alkyl group which may have a substituent, or an alkyl(poly)oxyalkylene group which may have a substituent, ２ is a linear or branched alkylene group having 2 to 4 carbon atoms which may have a substituent, R ３ and R ４ are each independently an alkyl group having 1 to 4 carbon atoms which may have a substituent, and R ５ and R ６ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may have a substituent, and R ７ and R ８ are each independently a linear or branched alkylene group having 2 to 6 carbon atoms which may have a substituent, n is an integer of 0 to 2, and R ９ and R １０are each independently an alkyl group having 1 to 4 carbon atoms which may have a substituent. ２ is a 1,2-ethylene group, n is 1 or 2, and R ５ and R ６at least one of which is an alkyl group having 1 to 6 carbon atoms which may have a substituent. [2] The carbon dioxide absorbing liquid according to [1], wherein the content ratio of the compound represented by formula (1) is 40 to 80 mass %. [3] The carbon dioxide absorbing liquid according to [1] or [2], wherein the viscosity at 25°C after carbon dioxide absorption is 300 mPa·s or less. [4] The carbon dioxide absorbing liquid according to any of [1] to [3], further containing 0 to 30 mass % of water. [5] The carbon dioxide absorbing liquid according to any of [1] to [4], wherein the carbon dioxide absorbing liquid has an absorbable amount of carbon dioxide per 1 kg of carbon dioxide of 30 g or more. [6] The carbon dioxide absorbing liquid according to any of [1] to [5], wherein the compound represented by formula (I) contains 3-(alkylamino)propan-1-ol. [7] The carbon dioxide absorbing liquid according to any of [1] to [6], wherein the compound represented by formula (I) contains 4-(alkylamino)butan-1-ol. [8] The carbon dioxide absorbing liquid according to any one of [1] to [7], wherein the compound represented by formula (I) contains 2-(alkylamino)propan-1-ol. [9] The carbon dioxide absorbing liquid according to any one of [1] to [8], wherein the compound represented by formula (I) contains 1-(alkylamino)-2-methylpropan-2-ol.

[10] The carbon dioxide absorbing liquid according to any one of [1] to [9], wherein the compound represented by formula (I) contains 2-(alkylamino)-2-methylpropan-1-ol.

[11] The carbon dioxide absorbing liquid according to any one of [1] to

[10] , wherein the compound represented by formula (I) contains 2-(alkylamino)ethan-1-ol.

[12] A method for separating and recovering carbon dioxide from a gas containing carbon dioxide, comprising the following steps A and B: step A: contacting a gas containing carbon dioxide with the absorption liquid according to any one of [1] to

[11] to obtain an absorption liquid that has absorbed carbon dioxide from the gas containing carbon dioxide; and step B: heating the absorption liquid that has absorbed carbon dioxide obtained in step A to desorb and release the carbon dioxide from the absorption liquid, and recovering the released carbon dioxide.

[0011] The present disclosure provides a carbon dioxide absorbing solution that has high carbon dioxide absorption capacity and whose performance is unlikely to deteriorate even with repeated use, and a carbon dioxide separation and recovery method that has excellent long-term reliability.

[0012] Hereinafter, the carbon dioxide absorbing solution and the method for separating and recovering carbon dioxide will be described. In this disclosure, unless otherwise specified, the "to" symbol indicating a numerical range includes the numerical values ​​before and after it as the lower and upper limits. When there are multiple identical symbols in a chemical formula, unless otherwise specified, the identical symbols are not limited to representing the same substituent, and may represent different substituents within the range specified by the symbol. In this specification, a "compound represented by formula (I)" may be referred to as "compound (I)." This also applies to compounds represented by other formulas. In this specification, a "(poly)oxyalkylene group" is a general term for an oxyalkylene group and a polyoxyalkylene group.

[0013] [Carbon dioxide absorbing liquid] The carbon dioxide absorbing liquid (hereinafter also simply referred to as absorbing liquid) of the present disclosure contains a compound represented by the following formula (I) and one or more organic solvents selected from the following formulae (II) to (IV), and is characterized in that it does not undergo phase separation after absorbing carbon dioxide.

[0014] The symbols in the formula will be explained later.

[0015] The absorbing liquid of the present disclosure has high absorption capacity when separating and recovering carbon dioxide from a gas containing carbon dioxide. Furthermore, the absorbing liquid of the present disclosure generates a low heat of reaction when absorbing carbon dioxide, thereby reducing the energy consumption when separating and recovering carbon dioxide. Furthermore, the absorbing liquid of the present disclosure does not undergo phase separation even after absorbing carbon dioxide, so that unevenness in the concentration of compound (I) in the liquid does not occur. Even when the absorption and release of carbon dioxide is repeated, deterioration of compound (I) is suppressed, and the liquid can be used repeatedly for a long period of time. Furthermore, because the absorbing liquid of the present disclosure does not undergo phase separation, for example, when the absorbing liquid is circulated by a pump, the load on the pump or the like can be reduced, and the load on the device can also be reduced.

[0016] The absorbing liquid of the present disclosure contains at least the compound (I) and an organic solvent, and may further contain other components as necessary. Hereinafter, each component that can be contained in the absorbing liquid will be described.

[0017] <Compound (I)> The present absorbing solution contains the following compound (I).

[0018] However, R １ is a hydrogen atom, a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms which may have a substituent, or an alkyl(poly)oxyalkylene group which may have a substituent, R ２ is a linear or branched alkylene group having 2 to 4 carbon atoms which may have a substituent.

[0019] R １ In the formula (I), examples of the linear, branched, or cyclic alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a cyclobutyl group, an n-pentyl group, a cyclopentyl group, an n-hexyl group, and a cyclohexyl group. Among these, preferred alkyl groups are linear alkyl groups, isobutyl groups, cyclobutyl groups, and cyclopentyl groups, more preferred are linear alkyl groups or isobutyl groups, and even more preferred are linear alkyl groups having 1 to 4 carbon atoms or isobutyl groups. Examples of substituents that the alkyl group may have include substituents consisting only of halogen, carbon, oxygen, and hydrogen, such as alkyl groups and alkoxy groups. Examples of the alkyl moiety in these substituents include the same groups as those for the linear, branched, and cyclic alkyl groups described above.

[0020] The alkyl group in the alkyl(poly)oxyalkylene group includes the same as the linear, branched, or cyclic alkyl group described above. The alkylene group in the alkyl(poly)oxyalkylene group includes an ethylene group (—CH ２ CH ２ -), propylene group (-CH ２ CH ２ CH ２ -, -CH(CH ３ ) CH ２ -), butylene group (-CH２ CH ２ CH ２ CH ２ -, -CH(CH ３ ) CH ２ CH ２ -, -CH(CH ２ CH ３ ) CH ２ -, -C(CH ３ ) ２ CH ２ -), etc., with an ethylene group or a propylene group being preferred. Substituents that the alkyl(poly)oxyalkylene group may have include those consisting only of halogen, carbon, oxygen, or hydrogen, such as alkyl groups and alkoxy groups. The alkyl moiety in these substituents includes the same groups as the linear, branched, and cyclic alkyl groups described above. As the alkyl(poly)oxyalkylene group, a group represented by formula (a) is preferred. R １１ (O(CH ２ ) ｐ ) ｑ -(O) ｒ -* ... (a) where R １１ represents a linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent, or a cyclic alkyl group which may have a substituent, p is 2 or 3, q ​​is an integer of 1 to 3, r is 0 or 1, and * represents the bonding position to the carbon atom in formula (I).

[0021] R ２ The alkylene group in the above group may be the same as the alkylene group in the alkyl(poly)oxyalkylene group. Substituents that the alkylene group may have include substituents consisting only of halogen, carbon, oxygen, and hydrogen, such as alkyl groups and alkoxy groups. The alkyl moiety in these substituents may be the same as the linear, branched, and cyclic alkyl groups described above.

[0022] Examples of Compound (I) include the compounds shown in Tables 1-1 to 1-5 below.

[0023]

[0024]

[0025]

[0026]

[0027]

[0028] Among these, compound (I) is preferably a compound containing a methylamino group, an ethylamino group, a propylamino group, an isobutylamino group, or a butylamino group, and more preferably an alkyl monoaminoethanol such as 2-(methylamino)ethanol, 2-(ethylamino)ethanol, 2-(propylamino)ethanol, 2-(isobutylamino)ethanol, or 2-(butylamino)ethanol. From the viewpoint of the amount and rate of absorption of carbon dioxide, compound (I) in the absorbing solution preferably has a ratio of (number of nitrogen atoms + number of oxygen atoms) / (total number of atoms other than hydrogen) of 0.35 or more, in order to increase the polarity of the molecule and promote the generation of a carbon dioxide absorber. From the viewpoint of long-term heat resistance, compound (I) in the absorbing solution preferably has a ratio of R １ In order to suppress the decomposition caused by the above oxidation reaction, R １ The number of carbon atoms in the compound (I) is preferably 2 or more. Compound (I) may be used singly or in combination of two or more, and from the viewpoints of absorption amount, absorption rate, and heat resistance, it is preferable to use a combination of two or more.

[0029] <Organic Solvent> The present absorption liquid contains one or more organic solvents selected from the following formulae (II) to (IV). The compound (I) can absorb carbon dioxide and release the carbon dioxide when heated, but separation of the carbon dioxide requires a high amount of energy. By using the specific organic solvent, the separation efficiency of the compound (I) and carbon dioxide is improved, the carbon dioxide release temperature can be lowered, and the carbon dioxide release efficiency is increased. Furthermore, by using the specific organic solvent, phase separation from the compound (I) after carbon dioxide absorption is suppressed. The organic solvent may be used alone or as a mixed solvent of two or more types.

[0030] However, R ３ and R ４are each independently an alkyl group having 1 to 4 carbon atoms which may have a substituent, and R ５ and R ６ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may have a substituent, and R ７ and R ８ are each independently a linear or branched alkylene group having 2 to 6 carbon atoms which may have a substituent, n is an integer of 0 to 2, and R ９ and R １０ are each independently an alkyl group having 1 to 4 carbon atoms which may have a substituent.

[0031] In compound (II), R ３ and R ４ Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group. Examples of the substituent that the alkyl group may have include a substituent consisting only of halogen, carbon, oxygen, and hydrogen, such as an alkyl group and an alkoxy group. Examples of the alkyl moiety in these substituents include the same groups as the linear, branched, and cyclic alkyl groups described above.

[0032] Specific examples of compound (II) include dimethyl sulfoxide, ethyl methyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, diisopropyl sulfoxide, dibutyl sulfoxide, etc., with dimethyl sulfoxide being preferred.

[0033] In compound (III), R ５ and R ６Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, a neopentyl group, an isopentyl group, an n-hexyl group, a 2-methylpentyl group, a 3-methylpentyl group, and a 2,2-dimethylbutyl group. Examples of the substituent that the alkyl group may have include a substituent consisting only of halogen, carbon, oxygen, and hydrogen, such as an alkyl group and an alkoxy group. Examples of the alkyl moiety in these substituents include the same groups as the linear, branched, and cyclic alkyl groups described above. R ７ and R ８ The alkylene group of the above R ２ In addition to the same groups as those mentioned above, examples of the alkylene group include a pentylene group and a hexylene group. Examples of the substituent that the alkylene group may have include a substituent consisting only of halogen, carbon, oxygen, and hydrogen, such as an alkyl group and an alkoxy group. Examples of the alkyl moiety in these substituents include the same groups as the linear, branched, and cyclic alkyl groups mentioned above. Furthermore, n is an integer of 0 to 2. However, in the compound (I), R ２ is a 1,2-ethylene group, n in compound (III) is 1 or 2, and R ５ and R ６ At least one of the groups is an alkyl group having 1 to 6 carbon atoms which may have a substituent.

[0034] Specific examples of compound (III) include 3-(2-methoxyethoxy)-1-propanol, dipropylene glycol methyl ether, 3-(3-methoxypropoxy)-1-propanol, 4-(4-methoxybutoxy)butanol, 2-[2-(2-methoxyethoxy)ethoxy]ethanol, 3-[2-(2-methoxyethoxy)ethoxy]propanol, 2-[2-(2-methoxypropoxy)propoxy]propanol, 3-[3-(3-methoxypropoxy)propoxy]propanol, 4 -[4-(4-methoxybutoxy)butoxy]butanol, 2-(2-ethoxyethoxy)ethanol, 2-(2-isopropoxyethoxy)ethanol, 2-(2-propoxyethoxy)ethanol, 2-(2-butoxyethoxy)ethanol, 1-methoxy-2-(2-methoxyethoxy)ethane, 1-methoxy-3-(2-methoxyethoxy)propane, 2-methoxy-1-[(1-methoxypropanol)oxy]propane, 1-methoxy-3-(3-methoxypropoxy)propane, 1-methoxy ethoxy-4-(4-methoxybutoxy)butane, 2,5,8,11-tetraoxadodecane, 2,5,8,12-tetraoxatridecane, 3,6,9-trimethyl-2,5,8,11-tetraoxadodecane, 2,6,10,14-tetraoxapentadecane, 2,7,12,17-tetraoxaoctadecane, 1-ethoxy-2-(2-methoxyethoxy)ethane, 1-(2-isopropoxyethoxy)-2-methoxyethane, 1-methoxy-2-(2-propoxyethoxy)ethane, 1-(2- butoxyethoxy)-2-methoxyethane, 1-ethoxy-2-(2-ethoxyethoxy)ethane, 2-[2-(2-isopropoxyethoxy)ethoxy]propane, 1-[2-[2-(propoxy)ethoxy]ethoxy]propane, 1-[2-(2-butoxyethoxy)ethoxy]butane, 2-[2-(2-butoxyethoxy)ethoxy]propane, 1-{2-[2-(pentyloxy)ethoxy]ethoxy}pentane, 1-{2-[2-(2,2-dimethylpropoxy)ethoxy]ethoxy}-2,2-Dimethylpropane, 3-methyl-1-{2-[2-(3-methylbutoxy)ethoxy]ethoxy}butane, 1-{2-[2-(hexyloxy)ethoxy]ethoxy}hexane, 2-methyl-1-(2-{2-[(2-methylpentyl)oxy]ethoxy}ethoxy)pentane, 3-methyl-1-(2-{2-[(3-methylpentyl)oxy]ethoxy}ethoxy)pentane, 1-{2-[2-(2,2-dimethylbutoxy)ethoxy]ethoxy}-2,2-dimethyl methylbutane, pentyldiglycol, 2-[2-(2,2-dimethylpropoxy)ethoxy]ethan-1-ol, 2-[2-(3-methylbutoxy)ethoxy]ethan-1-ol, 2-[2-(hexyloxy)ethoxy]ethan-1-ol, 2-{2-[(2-methylpentyl)oxy]ethoxy}ethan-1-ol, 2-{2-[(3-methylpentyl)oxy]ethoxy}ethan-1-ol, 2-[2-(2,2-dimethylbutoxy)ethoxy]ethan- 1-ol, ethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,4-butanediol, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-(2-butoxyethoxy)butane, 1-[2-(hexyloxy)ethoxy]hexane, 1,3-dimethoxypropane, 1,2-dimethoxypropane, 2-methoxyethan-1-ol, 2-ethoxyethan-1-ol, 2-butoxyethan-1-ol, 2-(hexyloxy)ethoxy Examples of the ethoxypropan-1-ol include 3-methoxypropan-1-ol, 2-methoxypropan-1-ol, 3-butoxypropan-1-ol, and 2-hexyloxypropan-1-ol. Of these, 2-(2-ethoxyethoxy)ethanol, 1-ethoxy-2-(2-ethoxyethoxy)ethane, and 1-methoxy-2-(2-methoxyethoxy)ethane are preferred, and 2-(2-ethoxyethoxy)ethanol and 1-ethoxy-2-(2-ethoxyethoxy)ethane are more preferred.

[0035] In compound (IV), R ９ and R １０Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group. Examples of the substituent that the alkyl group may have include a substituent consisting only of halogen, carbon, oxygen, and hydrogen, such as an alkyl group and an alkoxy group. Examples of the alkyl moiety in these substituents include the same groups as the linear, branched, and cyclic alkyl groups described above.

[0036] Specific examples of compound (IV) include 1,3-dimethyl-2-imidazolidone, 1-ethyl-3-methyl-2-imidazolidone, 1,3-diethyl-2-imidazolidone, 1,3-dipropyl-2-imidazolidone, 1,3-diisopropyl-2-imidazolidone, and 1,3-dibutyl-2-imidazolidone.

[0037] In the absorbing liquid of the present disclosure, the content of compound (I) in the absorbing liquid is preferably 40 to 80 mass%, more preferably 45 to 75 mass%, and even more preferably 50 to 70 mass%, based on the total amount of the absorbing liquid, from the viewpoint of carbon dioxide absorption efficiency. The content of the organic solvent in the absorbing liquid is preferably 10 to 60 mass%, more preferably 15 to 55 mass%, and even more preferably 20 to 50 mass%.

[0038] In terms of absorption rate, compound (II) or (III) is preferred, and (III) is more preferred. Examples of compounds (II) II to (IV) include the compounds listed in Tables 2-1 to 2-10 below.

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049] <Optional Components> The absorbing liquid of the present disclosure may further contain other components as long as the effects of the present invention are achieved. Examples of other components include at least one amine compound selected from the group consisting of amino alcohols, cyclic polyamines, and chain polyamines; stabilizers (side reaction inhibitors such as antioxidants) for ensuring the chemical or physical stability of the absorbing liquid; and inhibitors (corrosion inhibitors, etc.) for preventing deterioration of the materials of devices and equipment that use the absorbing liquid. The total content of these other components in the absorbing liquid is preferably 5% by mass or less. Among the amine compounds listed here, compounds that can also fall under the above-mentioned compound (I) are treated as amine compound (I). That is, the amino alcohols in the amine compounds refer to amino alcohols that do not fall under the general formula (I).

[0050] The absorbing liquid of the present disclosure may also contain water. However, the absorbing liquid has high carbon dioxide absorption and desorption capacities even with a low water content. The water content in the absorbing liquid is preferably 0 to 30% by mass, more preferably 0 to 20% by mass, even more preferably 0 to 15% by mass, and particularly preferably 0 to 10% by mass. During use, the water content in the absorbing liquid may vary depending on the gas composition; however, the water content here is the initial value (at the start of use), and does not prevent the water content from exceeding 30% by mass due to such variation.

[0051] (Amine Compound) By using an amine compound other than Compound (I) in combination, it is possible to improve or enhance, for example, the amount of absorption, amount of release, absorption rate, and release rate of the absorbing liquid.

[0052] Suitable amino alcohols include, for example, monoethanolamine, 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1,3-dipropanol, 2-aminobutanol, 4-aminobutanol, diethanolamine, bis(2-hydroxy-1-methylethyl)amine, methyldiethanolamine, dimethylethanolamine, diethylethanolamine, triethanolamine, dimethylamino-1-methylethanol, etc. One of these compounds can be used alone, or two or more can be used in combination.

[0053] Among these, 2-aminobutanol or 2-amino-2-methyl-1-propanol is preferred as the amino alcohol from the viewpoint of further improving the ability of the compound (I) to react with or release carbon dioxide.

[0054] Suitable cyclic polyamines include compounds in which two or more nitrogen atoms are substituted in a cycloalkyl group, and specific examples include piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2,6-dimethylpiperazine, N-(2-aminoethyl)piperazine, 1,4-bis(3-aminopropyl)piperazine, 1-hydroxyethylpiperazine, diazabicycloundecene, and diazabicyclononene. One of these compounds can be used alone, or two or more can be used in combination.

[0055] Among these, piperazine, N-(2-aminoethyl)piperazine, or diazabicycloundecene is preferred as the cyclic polyamine from the viewpoint of further improving the ability of the compound (I) to react with or release carbon dioxide.

[0056] Suitable linear polyamines include compounds having two or more nitrogen atoms substituted thereon and having a linear or branched alkyl group having 2 to 6 carbon atoms between them, and specific examples thereof include ethylenediamine, N-isopropylethylenediamine, N-methylethylenediamine, N-ethylethylenediamine, N,N'-dimethylethylenediamine, N,N'-diethylethylenediamine, diethylenetriamine, 2,2-diamino-N-methyldiethylamine, N,N'-diisopropylethylenediamine, N,N'-di-tert-butylethylenediamine, N,N',N''-trimethylethylenediamine, triethylenetetramine, triethylenepentamine, N,N,N',N'-tetramethylethylenediamine, N,N-diethyl-N',N'-dimethylethylenediamine, N,N-diethyl-N',N'- Examples of such compounds include dimethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, tetraethylenepentamine, 1,3-diaminopropane, 3-(methylamino)propylamine, N-methyl-1,3-propanediaminopropane, N,N-dimethyl-1,3-propanediamine, N,N-diethyl-1,3-propanediamine, N,N-dibutyl-1,3-propanediamine, 3,3-diaminodipropylamine, tris(3-aminopropyl)amine, 3,3-diamino-N-methyldipropylamine, N,N'-bis(3-aminopropyl)ethylenediamine, N,N,N',N'-tetramethyl-1,3-propanediamine, N,N,N',N'-tetraethyl-1,3-propanediamine, 1,4-diaminobutane, aminoethylaminoethanol, and guanidine derivatives. These compounds can be used alone or in combination of two or more.

[0057] Among these, from the viewpoint of further improving the reactivity or release ability of compound (I) with carbon dioxide, 1,4-diaminobutane, 1,3-diaminopropane, 3,3-diaminodipropylamine, 3,3-diamino-N-methyldipropylamine, N,N'-bis(3-aminopropyl)ethylenediamine, or N,N-dibutyl-1,3-propanediamine is preferred as the chain polyamine.

[0058] (Antioxidant) Examples of the antioxidant include dibutylhydroxytoluene, butylhydroxyanisole, sodium erythorbate, sodium sulfite, and sulfur dioxide.

[0059] (Corrosion Inhibitor) Examples of the corrosion inhibitor include 1-hydroxyethane-1,1-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, 1-phosphonopropane-2-dicarboxylic acid, phosphonosuccinic acid, 2-hydroxyphosphonoacetic acid, and maleic acid-based polymers (e.g., copolymers of maleic acid and amylene, or terpolymers of maleic acid, acrylic acid, and styrene).

[0060] (Antifoaming Agent) Examples of antifoaming agents include silicone-based, polyether-based, acetylene diol-based, metal soap-based, phosphate ester-based, and fatty acid ester-based agents.

[0061] (pH Adjusting Agent) Examples of the pH adjusting agent include inorganic acids (hydrochloric acid, sulfuric acid, phosphoric acid, boric acid, etc.), organic acids (citric acid, formic acid, acetic acid, oxalic acid, p-toluenesulfonic acid, etc.), inorganic bases (sodium bicarbonate, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, ammonia, etc.), and organic bases (methylamine, dimethylamine, trimethylamine, diazabicycloundecene, piperazine, ethanolamine, triethanolamine, etc.).

[0062] (Viscosity Adjuster) Examples of viscosity adjusters include polyimine, polyvinyl alcohol, and polyethylene oxide.

[0063] <Physical Properties of Carbon Dioxide Absorbing Solution> The present absorbing solution can maintain a low viscosity even after absorbing carbon dioxide. For example, the present absorbing solution can have a viscosity of 300 mPa·s or less, preferably 280 mPa·s or less at 25°C after absorbing carbon dioxide. ２ When the absorbent liquid after absorption is subjected to an aging test at 120°C, the ratio of the viscosity c after the aging test to the viscosity c0 before the aging test (c / c0) can be 1.5 or less.

[0064] Furthermore, the present absorbing solution has excellent carbon dioxide absorption capacity, and for example, the amount of carbon dioxide that can be absorbed per 1 kg of the present absorbing solution can reach 30 g or more.

[0065] (Other Embodiments) The present absorbing liquid may be prepared by combining compound (I), an organic solvent, and further, optional components, to cause phase separation after absorbing carbon dioxide. The carbon dioxide absorbing liquid that causes phase separation can reduce the energy cost during carbon dioxide recovery.

[0066] <Gas Containing Carbon Dioxide> The present absorbent can be suitably used for separating and capturing carbon dioxide from a gas containing carbon dioxide. Examples of the carbon dioxide-containing gas include exhaust gas from thermal power plants fueled by coal, heavy oil, natural gas, etc., boilers in manufacturing plants, kilns in cement plants, steelmaking blast furnaces that reduce iron oxide with coke, steelmaking converters that burn carbon in pig iron to produce steel, integrated coal gasification combined cycle power generation facilities, natural gas produced during mining, and reformed gas. The carbon dioxide concentration in the gas is typically about 5 to 50%, particularly about 10 to 40%, by volume. Within this carbon dioxide concentration range, the effects of the present absorbent are optimally exhibited. Note that the carbon dioxide-containing gas may contain gases other than carbon dioxide, such as nitrogen, water vapor, carbon monoxide, hydrogen sulfide, carbonyl sulfide, sulfur dioxide, nitrogen dioxide, methane, and hydrogen. The absorbent of the present disclosure is also excellent at absorbing hydrogen sulfide in addition to carbon dioxide.

[0067] [Method for separating and recovering carbon dioxide] The method for separating and recovering carbon dioxide disclosed herein is a method for separating and recovering carbon dioxide from a gas containing carbon dioxide, and includes: step A of bringing the absorption liquid disclosed herein into contact with a gas containing carbon dioxide to obtain an absorption liquid that has absorbed carbon dioxide from the gas containing carbon dioxide; and step B of heating the absorption liquid that has absorbed carbon dioxide obtained in step A to desorb and release the carbon dioxide from the absorption liquid, and recovering the released carbon dioxide.

[0068] (Step A) In step A, the absorbing liquid is brought into contact with a gas containing carbon dioxide, so that the carbon dioxide in the gas containing carbon dioxide is absorbed into the absorbing liquid and separated.

[0069] In step A, the method for contacting the absorbing liquid with the gas containing carbon dioxide is not particularly limited. Examples include a method of bubbling the gas containing carbon dioxide into the absorbing liquid, a method of dropping the absorbing liquid in the form of a mist into the gas containing carbon dioxide (atomization or spraying method), and a method of countercurrently contacting the high-pressure gas containing carbon dioxide with the absorbing liquid in an absorption tower containing a porcelain or metal mesh filler.

[0070] (Step B) In step B, the absorption liquid obtained in step A that has absorbed carbon dioxide is heated to desorb and release carbon dioxide from the absorption liquid, and the released carbon dioxide is recovered.

[0071] The absorption liquid after carbon dioxide release in step B can be recycled and reused by returning it to step A. In this recycling process, the heat added in step B is used to raise the temperature of the absorption liquid by heat exchange with the absorption liquid that has absorbed carbon dioxide. This heat exchange reduces the energy consumption of the entire carbon dioxide separation and capture process.

[0072] The carbon dioxide separated and recovered by the carbon dioxide separation and recovery method using the absorption liquid of the present disclosure typically has a volume concentration of 95 to 100%, and can be pure or of very high concentration. The separated and recovered carbon dioxide can be used for carbon capture and storage (CCS) underground or on the seabed, or for enhanced oil recovery (EOR), technologies for which are currently being developed. Other uses of the separated and recovered carbon dioxide are not particularly limited. Examples include a synthetic raw material for chemical products, or a refrigerant for freezing food.

[0073] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. Hereinafter, the carbon dioxide absorbing liquid may be simply referred to as the absorbing liquid.

[0074] [Evaluation method] <Phase separation> Phase separation of each absorbing solution was visually evaluated. Evaluation was performed twice, immediately after preparation and after carbon dioxide gas absorption as described below. ○ in the table indicates that phase separation did not occur immediately after preparation or after carbon dioxide absorption. *1 indicates that phase separation occurred immediately after preparation or after carbon dioxide absorption. *2 indicates that the solution was miscible immediately after preparation, but phase separation occurred after carbon dioxide absorption.

[0075] [Amount of carbon dioxide gas absorbed] 100 g of each of the above absorption solutions (contained in a gas absorption bottle with a capacity of 300 ml) was adjusted to 40°C in a water bath. A mixed gas (500 ml / min) of carbon dioxide gas at 100 ml / min and nitrogen gas at 400 ml / min was bubbled into the absorption solution for 1 hour. The amount of carbon dioxide gas absorbed at this time, Vabs (amount of carbon dioxide absorbed per hour (L), converted to standard conditions), was measured using a gas flow meter and a carbon dioxide concentration meter. Using this value, the amount of carbon dioxide absorbed per kg of absorption solution, Cabs (CO ２ The saturation energy (g / kg) was calculated as follows: Cabs = Vabs / 22.4 x 44 / 0.1. The evaluation criteria are as shown in Table 3, with A, S, and SS representing the ranges in which the gas can actually be used. The purities of the gases used are as follows: Carbon dioxide gas: 99.9% purity Nitrogen gas: 99.99% purity

[0076]

[0077] [Measurement of Viscosity of Absorbing Solution] The viscosity after the carbon dioxide gas absorption treatment was measured. The viscosity was measured using an E-type viscometer ("TV-22" manufactured by Toki Sangyo Co., Ltd.) at a sample cup temperature of 25°C, rotor number 1, range M, and rotation speed of 1-50 rpm. The evaluation criteria are as shown in Table 4, with A, S, and SS being the ranges that can actually be used.

[0078]

[0079] [Heat resistance test] The heat resistance of the absorbing solution was evaluated by the amine value. Carbon dioxide gas was blown into each absorbing solution as described above in [Amount of carbon dioxide gas absorbed] to form a carbon dioxide saturated solution. The amine value at this time was measured by the amine value measurement method described below. Thereafter, the carbon dioxide saturated solution was transferred to a separate container, sealed, and heated in an oven set at 130°C for one week or four weeks. After the heating test, the absorbing solution was again measured by the amine value measurement method.

[0080] <Method for measuring amine value> The amine value was measured by the following method. 0.05 g of the absorption solution was precisely weighed out, and ethanol was added to make the total amount 30 g. If the absorption solution was phase-separated, ethanol was added to make it 10 times the weight and homogenized, and then 5.0 g was precisely weighed out, and ethanol was added to make the total amount 30 g. Next, titration was carried out with a 0.2 M hydrogen chloride ethanol solution using a potentiometric titrator. The total amount of amine substance was calculated from the volume of the 0.2 M hydrogen chloride ethanol solution required for neutralization, and this was converted into the amount of potassium hydroxide (mg).

[0081] <Heat Resistance Test Evaluation> The amine value ratio before and after the heat resistance test (amine value after heat resistance test / amine value before heat resistance test) was calculated and evaluated. The evaluation criteria are as shown in Table 5, with A, S, and SS being practically usable ranges.

[0082]

[0083] [Preparation of Absorbing Solution] Each component was mixed so as to obtain the composition shown in Tables 6 to 17, thereby preparing 100 g of each of the carbon dioxide absorbing solutions of Examples 1 to 343 and Comparative Examples 1 to 20. In the tables, "%" indicates % by mass.

[0084]

[0085]

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096] As described in the above examples, the carbon dioxide absorbing solution of the present invention exhibits an effect of being superior in viscosity during carbon dioxide absorption compared to conventionally known carbon dioxide absorbing solutions. Furthermore, it has been found that the absorbing solution of the present disclosure can efficiently release carbon dioxide at a release temperature of 60°C, compared to 120°C, which is the release temperature of a commonly known aqueous ethanolamine (MEA) solution.

[0097] <Reference Examples> [Preparation of Absorbing Solution] 100 g of each of the carbon dioxide absorbing solutions of Reference Examples 1 to 20 was prepared by mixing the components so as to obtain the compositions shown in Table 18. As shown in Table 18, the absorbing solutions of Reference Examples 1 to 20 all underwent phase separation after absorbing carbon dioxide.

[0098] The absorption amounts of carbon dioxide gas, the viscosity after carbon dioxide absorption, and the heat resistance of the absorbing solutions of Reference Examples 1 to 20 were evaluated in the same manner as in the above Examples. The results are shown in Table 18.

[0099]

[0100] As shown in Table 18, it was shown that an absorption solution containing a compound represented by the following formula (I) and one or more organic solvents selected from the following formulas (II) to (IV) is excellent in terms of the amount of carbon dioxide absorbed and heat resistance, even if it undergoes phase separation after absorbing carbon dioxide.

[0101] This application claims priority based on Japanese Patent Application No. 2024-153782, filed September 6, 2024, and Japanese Patent Application No. 2024-226611, filed December 23, 2024, the disclosures of which are incorporated herein in their entireties.

Claims

1. A carbon dioxide absorbing solution containing a compound represented by the following formula (I) and one or more organic solvents selected from the following formulas (II) to (IV), which does not undergo phase separation after absorbing carbon dioxide. Here, R １ is a hydrogen atom, a linear or branched alkyl group having 1 to 6 carbon atoms which may have a substituent, a cyclic alkyl group which may have a substituent, or an alkyl(poly)oxyalkylene group which may have a substituent, ２ is a linear or branched alkylene group having 2 to 4 carbon atoms which may have a substituent, R ３ and R ４ are each independently an alkyl group having 1 to 4 carbon atoms which may have a substituent, and R ５ and R ６ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may have a substituent, and R ７ and R ８ are each independently a linear or branched alkylene group having 2 to 6 carbon atoms which may have a substituent, n is an integer of 0 to 2, and R ９ and R １０ are each independently an alkyl group having 1 to 4 carbon atoms which may have a substituent, wherein the one or more organic solvents contain a compound represented by formula (III), and R ２ is a 1,2-ethylene group, n is 1 or 2, and R ５ and R ６ At least one of the groups is an alkyl group having 1 to 6 carbon atoms which may have a substituent.

2. The above R １ ~R １０ 2. The carbon dioxide absorbing solution according to claim 1, wherein at least one of the alkyl group, alkylene group, and alkyl(poly)oxyalkylene group has a substituent.

3. The carbon dioxide absorbing solution according to claim 1, wherein the content of the compound represented by formula (1) is 40 to 80 mass %.

4. The carbon dioxide absorbing solution according to claim 1, further comprising 0 to 30 mass % of water.

5. The carbon dioxide absorbing solution according to claim 1, wherein the content of the compound represented by formula (1) is 40 to 80 mass % and the content of water is 0 to 30 mass %.

6. The above R １ ~R １０ at least one of the alkyl group, the alkylene group, and the alkyl(poly)oxyalkylene group has a substituent; the content ratio of the compound represented by formula (1) is 40 to 80 mass %; and the carbon dioxide absorbing liquid contains 0 to 30 mass % of water.

7. The carbon dioxide absorbing solution according to claim 1, which has a viscosity of 300 mPa·s or less at 25°C after absorbing carbon dioxide.

8. The carbon dioxide absorbing solution according to claim 1, which can absorb 30 g or more of carbon dioxide per 1 kg.

9. The carbon dioxide absorbing solution according to claim 1, wherein the compound represented by formula (I) includes 3-(alkylamino)propan-1-ol.

10. The carbon dioxide absorbing solution according to claim 1, wherein the compound represented by formula (I) includes 4-(alkylamino)butan-1-ol.

11. The carbon dioxide absorbing solution according to claim 1, wherein the compound represented by formula (I) includes 2-(alkylamino)propan-1-ol.

12. The carbon dioxide absorbing solution according to claim 1, wherein the compound represented by formula (I) includes 1-(alkylamino)-2-methylpropan-2-ol.

13. The carbon dioxide absorbing solution according to claim 1, wherein the compound represented by formula (I) includes 2-(alkylamino)-2-methylpropan-1-ol.

14. The carbon dioxide absorbing solution according to claim 1, wherein the compound represented by formula (I) includes 2-(alkylamino)ethan-1-ol.

15. The carbon dioxide absorbing liquid according to claim 1, wherein the compound represented by formula (I) comprises one or more selected from 3-(alkylamino)propan-1-ol, 4-(alkylamino)butan-1-ol, 2-(alkylamino)propan-1-ol, 1-(alkylamino)-2-methylpropan-2-ol, 2-(alkylamino)-2-methylpropan-1-ol, and 2-(alkylamino)ethan-1-ol, the content ratio of the compound represented by formula (1) is 40 to 80% by mass, and the carbon dioxide absorbing liquid contains 0 to 30% by mass of water.

16. The compound represented by formula (I) contains one or more selected from 3-(alkylamino)propan-1-ol, 4-(alkylamino)butan-1-ol, 2-(alkylamino)propan-1-ol, 1-(alkylamino)-2-methylpropan-2-ol, 2-(alkylamino)-2-methylpropan-1-ol, and 2-(alkylamino)ethan-1-ol, and the R １ ~R １０ wherein at least one of the alkyl group and the alkylene group has a substituent, the content ratio of the compound represented by formula (1) is 40 to 80 mass%, and the carbon dioxide absorbing liquid contains 0 to 30 mass% of water.

17. A method for separating and recovering carbon dioxide from a gas containing carbon dioxide, comprising the following steps A and B: step A: bringing the absorbing liquid according to any one of claims 1 to 16 into contact with a gas containing carbon dioxide to obtain an absorbing liquid that has absorbed carbon dioxide from the gas containing carbon dioxide; and step B: heating the absorbing liquid that has absorbed carbon dioxide obtained in step A to desorb and release the carbon dioxide from the absorbing liquid, and recovering the released carbon dioxide.

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