Carbon dioxide absorbent, method for carbon dioxide recovery, and device for carbon dioxide separation and recovery

Abstract

Provided are: a carbon dioxide absorbent containing an amine compound (A) represented by a general formula (1); a method for carbon dioxide recovery using the carbon dioxide absorbent; and a device for carbon dioxide separation and recovery.　General formula (1): H2N-(CH2)m-X-(CH)-NHR. (In formula (1), X is a phenylene group or a cyclohexene group, and R is a C3-6 aliphatic hydrocarbon group. m and n are each independently a number selected from among 1-6.)

Description

Carbon dioxide absorbent, carbon dioxide capture method, and carbon dioxide separation and capture device

[0001] The present invention relates to a carbon dioxide absorbent, a carbon dioxide recovery method, and a carbon dioxide separation and recovery apparatus.

[0002] From the perspective of global warming, there is a need to reduce carbon dioxide emissions. One method for reducing carbon dioxide emissions is carbon dioxide capture and storage (CCS), a technology that efficiently captures high-concentration carbon dioxide (approximately 10-30% by volume) from exhaust gases emitted by thermal power plants and stores it underground or in the sea. In contrast, direct air capture (DAC), a technology that directly captures low-concentration carbon dioxide (approximately 0.04% by volume) from the air, has recently attracted attention. The carbon dioxide absorbent used in DAC is required to have a higher carbon dioxide absorption capacity than the carbon dioxide absorbent used in CCS.

[0003] In recent years, various technologies related to DAC have been studied. For example, Patent Document 1 discloses an absorbent for absorbing carbon dioxide in air, which contains an alkylamine substituted with a hydroxy group or an optionally substituted amino group. Patent Document 2 also discloses a carbon dioxide absorbent that contains a predetermined amount or more of a polyamine compound having an alicyclic hydrocarbon structure, which improves the ability to absorb carbon dioxide in air, and which also has excellent reusability. Patent Document 3 discloses a carbon dioxide absorbent that contains a specific cyclic amine compound and a porous material, in which the cyclic amine compound has 35 mol% or more of primary amino groups relative to all amino groups, thereby improving reusability.

[0004] As a method for absorbing / desorbing carbon dioxide in these carbon dioxide absorbents, a method of adsorbing and desorbing carbon dioxide by changing the temperature is generally known, in which carbon dioxide is absorbed under non-heating conditions and desorbed under heating conditions.

[0005] JP 2017-031046 A International Publication No. 2022 / 138302 International Publication No. 2023 / 013397

[0006] However, the carbon dioxide absorbent containing an amine compound disclosed in Patent Document 1 must be heated to a high temperature of, for example, 120 to 140°C to desorb the carbon dioxide in order to desorb and recover the absorbed carbon dioxide. Therefore, heating to such a temperature requires a very large amount of thermal energy. Furthermore, there is a concern that the amine compound contained in the carbon dioxide absorbent may be thermally decomposed by this heating, making the thermal stability of the carbon dioxide absorbent an issue. Furthermore, the carbon dioxide absorbents containing an amine compound disclosed in Patent Documents 2 and 3 use specific amine compounds to improve the desorption properties of absorbed carbon dioxide and enhance reusability, but further improvement in these properties is required. An object of the present invention is to provide a carbon dioxide absorbent that improves the balance between carbon dioxide absorption and desorption properties of absorbed carbon dioxide, thereby exhibiting good carbon dioxide absorption and excellent carbon dioxide desorption properties. More specifically, the present invention aims to provide a carbon dioxide absorbent that can desorb absorbed carbon dioxide by heating at a low temperature of less than 100°C at atmospheric pressure (1 atm), and that exhibits little decrease in carbon dioxide absorption even when the carbon dioxide absorbent is regenerated by such a desorption treatment, resulting in excellent reusability.

[0007] The present inventors have found that the above-mentioned problems can be solved by a carbon dioxide absorbent containing a specific amine compound. That is, the present invention relates to the following: [1] A carbon dioxide absorbent containing an amine compound (A) represented by the following general formula (1): H ２ N-(CH ２ ) ｍ -X-(CH ２ ) ｎ -NHR １ (1) (In formula (1), X is a phenylene group or a cyclohexylene group, and R １is an aliphatic hydrocarbon group having 3 to 6 carbon atoms. m and n each independently represent a number from 1 to 6.) [2] The carbon dioxide absorbent according to [1], wherein the amine compound (A) is a compound that is liquid at 25°C. [3] The carbon dioxide absorbent according to [1] or [2], wherein X in the general formula (1) is a 1,3-phenylene group or a 1,3-cyclohexylene group. [4] The carbon dioxide absorbent according to any of [1] to [3], wherein the amine compound (A) is an amine compound represented by the following formula (1-1) or (1-2): [5] The carbon dioxide absorbent according to any one of [1] to [4], wherein the carbon dioxide absorbent further comprises a porous material (B). [6] The carbon dioxide absorbent according to [5], wherein the porous material (B) comprises at least one selected from the group consisting of silica and alumina. [7] A method for recovering carbon dioxide using the carbon dioxide absorbent according to any one of [1] to [6]. [8] The method according to [7], wherein the method comprises an absorption step of contacting the carbon dioxide absorbent with a gas containing carbon dioxide to cause the carbon dioxide absorbent to absorb carbon dioxide, and a desorption step of desorbing carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide in the absorption step, the desorption step comprising a step of subjecting the carbon dioxide absorbent that has absorbed carbon dioxide to low-temperature heating conditions of 45°C or higher and lower than 100°C at atmospheric pressure. [9] A carbon dioxide separation and capture system comprising: an absorption device equipped with a mechanism for contacting the carbon dioxide absorbent according to any one of [1] to [6] with a gas containing carbon dioxide to cause the carbon dioxide absorbent to absorb carbon dioxide; and a desorption device equipped with a mechanism for desorbing carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide.

[0008] According to the present invention, it is possible to provide a carbon dioxide absorbent that has an improved balance between carbon dioxide absorption and desorption of absorbed carbon dioxide, and that has good carbon dioxide absorption and also excellent carbon dioxide desorption.

[0009] 1 is a schematic diagram showing one embodiment of a carbon dioxide separation and capture apparatus of the present invention. １ 1 is a H-NMR chart of the amine compound obtained in Production Example 2. １ 1 H-NMR chart.

[0010] [Definitions] A mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The following present embodiment is an example for explaining the present invention, and does not limit the content of the present invention. The present invention can be carried out by appropriately modifying it within the scope of its gist. In the present embodiment, the definitions that are considered to be preferred can be adopted arbitrarily, and it can be said that a combination of preferred definitions is more preferable. In the present embodiment, the description "XX to YY" means "XX or more and YY or less."

[0011] As used herein, "good carbon dioxide absorbency" means that the carbon dioxide absorbent has a large carbon dioxide absorption capacity. Furthermore, "good carbon dioxide absorbency in air" means that the carbon dioxide absorbent has a large absorption capacity for low-concentration (approximately 0.04% by volume) carbon dioxide in air. As used herein, "carbon dioxide desorption by low-temperature heating" refers to desorption of carbon dioxide once absorbed in a carbon dioxide absorbent when the absorbent is subjected to low-temperature heating conditions of atmospheric pressure (1 atm) and 45°C or higher but lower than 100°C. As used herein, "sufficiently regenerateable even when the carbon dioxide absorbent is regenerated by desorption of carbon dioxide by low-temperature heating" means that the carbon dioxide desorption by low-temperature heating is good, and that the carbon dioxide absorbent regains its carbon dioxide absorbency even under such low-temperature heating conditions. Furthermore, as used herein, "little decrease in carbon dioxide absorbency and excellent reusability" means that the carbon dioxide absorbent exhibits stable carbon dioxide absorbency and suppresses a decrease in the amount of carbon dioxide absorbed, even after repeated cycles of carbon dioxide absorption and desorption by low-temperature heating. The carbon dioxide absorbency and reusability can be specifically evaluated by the methods described in the examples.

[0012] [Carbon dioxide absorbent] The carbon dioxide absorbent of the present invention contains an amine compound (A) (hereinafter, also simply referred to as "amine compound (A)") represented by the following general formula (1): ２ N-(CH ２ ) ｍ -X-(CH ２ ) ｎ -NHR １(1) (In formula (1), X is a phenylene group or a cyclohexylene group, and R １ is an aliphatic hydrocarbon group having 3 to 6 carbon atoms. m and n each independently represent a number from 1 to 6.) The carbon dioxide absorbent of the present invention, having the above-described configuration, exhibits good carbon dioxide absorption properties. Even when the carbon dioxide absorbent is regenerated by absorbing carbon dioxide and then desorbing carbon dioxide by low-temperature heating, the carbon dioxide absorbent is sufficiently regenerated, with little deterioration in carbon dioxide absorption properties, and is excellent in reusability. Furthermore, the carbon dioxide absorbent of the present invention exhibits good carbon dioxide absorption properties even in air with a low carbon dioxide concentration of approximately 0.04% by volume. Therefore, it can be suitably used in a technology for directly capturing carbon dioxide from air (DAC). Furthermore, the carbon dioxide absorbent of the present invention can be suitably used, for example, when capturing carbon dioxide from a gas with a low carbon dioxide concentration of 0.01% by volume or more and 1% by volume or less.

[0013] The reason why the carbon dioxide absorbent of the present invention exhibits the above-mentioned effects is unclear, but is thought to be as follows. The amine compound (A) contained in the carbon dioxide absorbent has a cyclic structure and a primary amino group bonded to the cyclic structure via a (poly)methylene group. Therefore, it is thought that the amino group easily reacts with carbon dioxide to form a carbonate, thereby exhibiting excellent carbon dioxide absorption. Here, an amine compound in which a primary amino group is directly bonded to the cyclic structure is less likely to form a carbonate upon reaction with carbon dioxide, resulting in reduced carbon dioxide absorbability. However, the carbon dioxide absorbent of the present invention improves this drawback. Furthermore, an amine compound having two or more primary amino groups has excellent carbon dioxide absorbability, but the desorption property when carbon dioxide is desorbed by low-temperature heating after absorption of carbon dioxide is reduced. In other words, when regenerated by low-temperature heating, the carbon dioxide absorbency of the carbon dioxide absorbent cannot be fully restored and is reduced. In contrast, the amine compound (A) used in the present invention has one primary amino group and one secondary amino group, and therefore has excellent carbon dioxide desorption property upon low-temperature heating while maintaining good carbon dioxide absorbability, which is thought to improve repeated use. Furthermore, the hydrocarbon group (R in general formula (1)) bonded to the secondary amino group in the amine compound (A) １ ) is an aliphatic hydrocarbon group with a suitable bulkiness, which is thought to result in a good balance between carbon dioxide absorption and carbon dioxide desorption by low-temperature heating. In this specification, the term "primary amino group" refers to an amino group having two hydrogen atoms on the nitrogen atom, i.e., -NH ２ The term "secondary amino group" refers to an amino group having one hydrogen atom on the nitrogen atom.

[0014] <Amine Compound (A)> The amine compound (A) is an amine compound represented by the following general formula (1): ２ N-(CH ２ ) ｍ -X-(CH ２ ) ｎ -NHR １ (1) (In formula (1), X is a phenylene group or a cyclohexylene group, and R １is an aliphatic hydrocarbon group having 3 to 6 carbon atoms; m and n are each independently a number from 1 to 6.

[0015] The amine compound (A) may be a compound that is solid or liquid at 25° C., but from the viewpoint of improving the supportability on the porous material (B) described below and improving the ability to desorb carbon dioxide by low-temperature heating, it is preferably a compound that is liquid at 25° C. Here, a compound that is liquid at 25° C. means a compound having a melting point of 25° C. or lower.

[0016] In the general formula (1), X represents a phenylene group or a cyclohexylene group. From the viewpoint of improving carbon dioxide absorption ability and improving carbon dioxide desorption ability by low-temperature heating, X is preferably a 1,3-phenylene group, a 1,4-phenylene group, a 1,3-cyclohexylene group, or a 1,4-cyclohexylene group, more preferably a 1,3-phenylene group or a 1,3-cyclohexylene group, and even more preferably a 1,3-cyclohexylene group.

[0017] In the general formula (1), R １ is an aliphatic hydrocarbon group having 3 to 6 carbon atoms. Examples of the aliphatic hydrocarbon group include alkyl groups and alkenyl groups, and from the viewpoints of improving the ability to eliminate carbon dioxide by low-temperature heating, improving reusability, and ease of production, alkyl groups are preferred. １ is an unsubstituted group having no further substituents.

[0018] The alkyl group may be a linear alkyl group or a branched alkyl group, and is preferably a linear alkyl group from the viewpoint of improving the ability to eliminate carbon dioxide upon low-temperature heating and improving repeated use. Examples of linear alkyl groups include an n-propyl group, an n-butyl group, an n-pentyl group, and an n-hexyl group. Examples of branched alkyl groups include an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an isopentyl group, a neopentyl group, and an isohexyl group. The amine compound (A) can be used alone or in combination of two or more types.

[0019] Among the above, from the viewpoints of improving carbon dioxide absorption, improving carbon dioxide desorption by low-temperature heating, improving reusability, and ease of production, R １ is preferably at least one selected from the group consisting of an n-propyl group, an n-butyl group, an n-pentyl group, and an n-hexyl group, more preferably at least one selected from the group consisting of an n-propyl group, an n-butyl group, and an n-pentyl group, even more preferably at least one selected from the group consisting of an n-butyl group and an n-pentyl group, and still more preferably an n-butyl group. In addition, in the general formula (1), m and n are each independently a number of preferably 1 to 4, more preferably 1 to 3, and even more preferably 1 to 2, from the viewpoint of improving carbon dioxide absorption ability and improving carbon dioxide desorption property by low-temperature heating.

[0020] From the viewpoints of improving carbon dioxide absorbency, improving carbon dioxide desorption by low-temperature heating, improving repeated use, and ease of production, the amine compound (A) preferably includes an amine compound represented by the following formula (1-1) or (1-2), more preferably is an amine compound represented by the following formula (1-1) or (1-2), and even more preferably is an amine compound represented by the following formula (1-2):

[0021] The content of the amine compound (A) in all amine compounds in the carbon dioxide absorbent of the present invention is, from the viewpoint of improving carbon dioxide absorbency, improving carbon dioxide desorption property by low-temperature heating, and improving repeated usability, preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 75% by mass or more, and still more preferably 80% by mass or more, but 100% by mass or less.

[0022] Moreover, from the viewpoint of improving carbon dioxide absorbency, the content of the amine compound (A) in the carbon dioxide absorbent of the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, still more preferably 38% by mass or more, and still more preferably 40% by mass or more, and is 100% by mass or less.

[0023] The method for producing the amine compound (A) may include, for example, a method comprising the following steps (1) and (2) in this order: Step (1): A step of reacting a diamine represented by the following general formula (1a) with an aldehyde compound represented by the following general formula (1b) to obtain an imine; Step (2): A step of reducing the imine obtained in the step (1) NH ２ - (CH ２ ) ｍ -X-(CH ２ ) ｎ -NH ２ (1a) (wherein X, m, and n are the same as above) HCO-R ２ (1b) (wherein, R ２ is an aliphatic hydrocarbon group having 2 to 5 carbon atoms.

[0024] <<Step (1)>> In step (1), a diamine represented by the general formula (1a) is reacted with an aldehyde compound represented by the general formula (1b) to obtain an imine. In the general formula (1a), X is a phenylene group or a cyclohexylene group, the phenylene group being any of a 1,2-phenylene group, a 1,3-phenylene group, and a 1,4-phenylene group, and the cyclohexylene group being any of a 1,2-cyclohexylene group, a 1,3-cyclohexylene group, and a 1,4-cyclohexylene group. From the viewpoint of improving carbon dioxide absorption, improving carbon dioxide desorption by low-temperature heating, and improving repeated use, X is preferably at least one selected from the group consisting of a 1,3-phenylene group, a 1,4-phenylene group, a 1,3-cyclohexylene group, and a 1,4-cyclohexylene group, more preferably at least one selected from the group consisting of a 1,3-phenylene group and a 1,3-cyclohexylene group, and even more preferably a 1,3-cyclohexylene group.

[0025] Specific examples of the diamine represented by the general formula (1a) include orthoxylylenediamine, metaxylylenediamine, paraxylylenediamine, 1,2-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, and 1,4-bis(aminomethyl)cyclohexane. From the viewpoint of improving carbon dioxide absorbency, improving carbon dioxide desorption by low-temperature heating, and improving reusability, the diamine is preferably at least one selected from the group consisting of metaxylylenediamine, paraxylylenediamine, 1,3-bis(aminomethyl)cyclohexane, and 1,4-bis(aminomethyl)cyclohexane, more preferably at least one selected from the group consisting of metaxylylenediamine and 1,3-bis(aminomethyl)cyclohexane, and even more preferably 1,3-bis(aminomethyl)cyclohexane.

[0026] R in the general formula (1b) ２ is an aliphatic hydrocarbon group having 2 to 5 carbon atoms. Here, the CHO group becomes a methylene group when the general formula (1b) reacts, so R ２ is the R １ R is a group having one less carbon atom than ２ is preferably at least one selected from the group consisting of an ethyl group, an n-propyl group, an n-butyl group, and an n-pentyl group, more preferably at least one selected from the group consisting of an ethyl group, an n-propyl group, and an n-butyl group, even more preferably at least one selected from the group consisting of an n-propyl group and an n-butyl group, and still more preferably an n-propyl group, from the viewpoints of improving carbon dioxide absorbency, improving carbon dioxide desorption by low-temperature heating, improving repeated usability, and ease of production.

[0027] Specific examples of the aldehyde compound represented by the general formula (1b) include propionaldehyde (propanal), butyraldehyde (butanal), valeraldehyde (pentanal), hexylaldehyde (hexanal), isobutyraldehyde (2-methylpropanal), 2-methylbutyraldehyde (2-methylbutanal), isovaleraldehyde (3-methylbutanal), 2-methylvaleraldehyde (2-methylpentanal), 3-methylvaleraldehyde (3-methylpentanal), and 4-methylvaleraldehyde (4-methylpentanal), and one or more of these can be used.

[0028] In the step (1), from the viewpoint of obtaining the amine compound (A) represented by the general formula (1) in high yield, 0.8 to 1.2 moles, preferably 0.9 to 1.1 moles, more preferably 1.0 moles of the aldehyde compound represented by the general formula (1b) is reacted with 1.0 mole of the diamine represented by the general formula (1a).

[0029] The reaction between the diamine represented by general formula (1a) and the aldehyde compound represented by general formula (1b) is preferably carried out under stirring conditions. The reaction temperature is preferably in the range of 15°C to 100°C, more preferably 20°C to 80°C, from the viewpoint of improving reaction efficiency and suppressing thermal degradation of the diamine and aldehyde compounds used as raw materials. The reaction time can be selected appropriately, but is typically in the range of 15 minutes to 6 hours. From the same viewpoint, the temperature during mixing of raw materials, such as dropping the aldehyde into the diamine solution, is preferably 10°C or less. The reaction may be carried out without a solvent or in a solvent, but is preferably carried out in a solvent. The reaction in step (1) produces an imine, which is a reaction product of the diamine represented by general formula (1a) and the aldehyde compound represented by general formula (1b). The reaction product obtained in step (1) may be purified, or it can be directly subjected to step (2) without purification.

[0030] <<Step (2)>> In step (2), the imine obtained in step (1) is reduced to convert it to an amine. The reduction of the imine is preferably carried out by hydrogenation (hydrogenation) in the presence of a catalyst under heated and pressurized conditions. Examples of the catalyst used in step (2) include known hydrogenation catalysts, such as supported heterogeneous hydrogenation catalysts in which a metal such as Ni, Pt, Pd, or Ru is supported on carbon, silica, alumina, or diatomaceous earth; so-called Ziegler-type hydrogenation catalysts that use a transition metal salt such as an organic acid salt or acetylacetonate of Ni, Co, Fe, or Cr, etc., and a reducing agent such as organoaluminum; and homogeneous hydrogenation catalysts such as so-called organometallic complexes of organometallic compounds such as Ti, Ru, Rh, or Zr.

[0031] The temperature during the hydrogenation reaction is preferably 0°C or higher, more preferably 10°C or higher, and even more preferably 20°C or higher, from the viewpoint of improving reaction efficiency and suppressing side reactions, and is preferably 200°C or lower, more preferably 150°C or lower, and even more preferably 100°C or lower. The pressure during the hydrogenation reaction is preferably 0.01 MPaG or higher, more preferably 0.1 MPaG or higher, and even more preferably 0.3 MPaG or higher, and is preferably 10 MPaG or lower, and more preferably 3 MPaG or lower, from the viewpoint of improving reaction efficiency and suppressing side reactions. The reaction time is not particularly limited, but is preferably 3 minutes or higher, more preferably 10 minutes or higher, and even more preferably 30 minutes or higher, and is preferably 24 hours or lower, more preferably 12 hours or lower, and even more preferably 8 hours or lower.

[0032] The hydrogenation reaction may be carried out in the presence of a solvent. The solvent is not particularly limited as long as it does not inhibit the hydrogenation reaction, and examples include hydrocarbon solvents such as aliphatic hydrocarbons such as pentane, hexane, isopentane, heptane, octane, and isooctane; alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, and ethylcyclohexane; aromatic hydrocarbons such as toluene, ethylbenzene, and xylene; and cyclic ethers such as tetrahydrofuran and 1,4-dioxane. These solvents may be used alone or in combination of two or more.

[0033] After the hydrogenation reaction, the catalyst can be removed from the resulting reaction solution, and, if necessary, separation, distillation, or other purification can be performed to obtain the amine compound (A) of the present invention. The amine compound obtained by the production method is typically a 1-adduct (amine compound (A): target compound) formed by the reaction of one aldehyde compound represented by general formula (1b) with the diamine compound used as the raw material and hydrogenating it, and a 2-adduct (by-product) formed by the reaction of two aldehydes represented by general formula (1b) with the diamine compound used as the raw material and hydrogenating it. This reaction mixture may be used as is as a raw material for producing a carbon dioxide absorbent, or may be purified to increase the content of the 1-adduct (amine compound (A)) and then used as a raw material for producing a carbon dioxide absorbent.

[0034] The method for producing the amine compound (A) is not limited to the above method. For example, the amine compound (A) can also be produced by a method of subjecting a diamine represented by the general formula (1a) to an amine represented by the following general formula (1c) to deammoniating in the presence of a catalyst; a method of reacting a diamine represented by the general formula (1a) with an alcohol represented by the following general formula (1d) in the presence of a catalyst under a hydrogen atmosphere; or a method of reacting a diamine represented by the general formula (1a) with a chloride represented by the following general formula (1e). In this case, the compounds represented by the general formulas (1c) to (1e) are reacted in amounts of preferably 0.8 to 1.2 moles, more preferably 0.9 to 1.1 moles, and even more preferably 1.0 mole, respectively, per mole of the diamine represented by the general formula (1a). ２ N-R １ (1c) HO-R １ (1d) Cl-R １ (1e) (In formulas (1c) to (1e), R １ is the same as above.)

[0035] <Porous Material (B)> From the viewpoint of further improving carbon dioxide absorbency and improving the carbon dioxide desorption property by low-temperature heating, the carbon dioxide absorbent of the present invention preferably further contains a porous material (B), and it is more preferable that at least a part of the amine compound (A) is supported on the porous material (B).

[0036] The porous material (B) is preferably one that can support the amine compound (A) and can withstand the conditions for carbon dioxide desorption, and examples thereof include at least one selected from the group consisting of silica, alumina, silica-alumina, magnesia, zirconia, zeolite, zeolite-related compounds, clay minerals, natural minerals, activated carbon, carbon molecular sieves (porous carbon), porous resins (synthetic adsorbents), metal-organic frameworks, and solid waste. Among these, from the viewpoint of further improving carbon dioxide absorbability and improving carbon dioxide desorption properties by low-temperature heating, the porous material (B) preferably contains at least one selected from the group consisting of silica and alumina, more preferably contains silica, and even more preferably contains mesoporous silica. The content of silica and alumina, preferably silica, more preferably mesoporous silica, in the porous material (B) is, from the viewpoint of further improving carbon dioxide absorbency and improving carbon dioxide desorption by low-temperature heating, preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, still more preferably 90% by mass or more, still more preferably 95% by mass or more, and still more preferably 98% by mass or more, but 100% by mass or less.

[0037] From the viewpoint of increasing the amount of the amine compound (A) supported and improving the carbon dioxide absorption property, the shape of the porous material (B) is preferably particulate. When the porous material (B) is particulate, the volume median particle diameter (D ５０ ) is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more from the viewpoint of improving handleability, and is preferably 500 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, still more preferably 180 μm or less, and still more preferably 160 μm or less from the viewpoint of increasing the amount of amine compound (A) supported.

[0038] The specific surface area of ​​the porous material (B) measured by the BET method is preferably 2 m or more from the viewpoint of increasing the amount of the amine compound (A) supported.２ / g or more, more preferably 10m ２ / g or more, more preferably 100m ２ / g or more, and even more preferably 200m ２ / g or more, and even more preferably 400m ２ / g or more, and even more preferably 600m ２ / g or more, and from the viewpoint of improving the handling property, it is preferably 3000m ２ / g or less, more preferably 1500m ２ / g or less, more preferably 1200m ２ / g or less, and even more preferably 1000m ２ / g or less.

[0039] The pore volume of the porous material (B) is preferably 0.1 cm 3 from the viewpoint of increasing the amount of the amine compound (A) supported. ３ / g or more, more preferably 0.3 cm ３ / g or more, more preferably 0.5 cm ３ / g or more, and from the viewpoint of improving repetitive use, it is preferably 5.0 cm ３ / g or less, more preferably 3.0 cm ３ / g or less, more preferably 2.5 cm ３ / g or less, and even more preferably 2.0 cm ３ / g or less, and even more preferably 1.5 cm ３ / g or less, and even more preferably 1.0 cm ３ / g or less.

[0040] The specific surface area and pore volume can be measured, for example, using a constant volume method with a specific surface area / pore size distribution measuring device (e.g., "ASAP2020" manufactured by Shimadzu Corporation). A more specific gas adsorption measurement method using a specific surface area / pore size distribution measuring device involves, for example, pretreating the sample by heating and evacuating, and then placing 0.1 g of the measurement sample in a sample tube. The sample is then heated to 40°C and evacuated for 6 hours, after which it is cooled to room temperature and the sample mass is measured. The liquid nitrogen temperature is set and the pressure range is specified for measurement, and the specific surface area, pore volume, and pore size can be analyzed and calculated from the resulting nitrogen adsorption isotherm.

[0041] The porous material (B) may be a granulated product such as pellets or tablets obtained by granulating the particulate porous material by a known method. Examples of the granulation method include a dry granulation method using a compression molding machine and a wet granulation method using a binder. By granulating and using the particulate porous material, vibration resistance and abrasion resistance can be imparted, and physical stability can be improved.

[0042] When the carbon dioxide absorbent comprises an amine compound (A) and a porous material (B), the content of the amine compound (A) in the carbon dioxide absorbent is, from the viewpoint of improving carbon dioxide absorbency, improving carbon dioxide desorption property by low-temperature heating, and improving repeated usability, preferably 10 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, still more preferably 40 parts by mass or more, still more preferably 50 parts by mass or more, still more preferably 70 parts by mass or more, still more preferably 75 parts by mass or more, and still more preferably 80 parts by mass or more, relative to 100 parts by mass of the porous material (B); and is preferably 1,000 parts by mass or less, more preferably 500 parts by mass or less, still more preferably 250 parts by mass or less, still more preferably 200 parts by mass or less, still more preferably 150 parts by mass or less, and still more preferably 120 parts by mass or less.

[0043] When the carbon dioxide absorbent contains the amine compound (A) and the porous material (B), the total content of the amine compound (A) and the porous material (B) in the carbon dioxide absorbent is, when the total amount of the carbon dioxide absorbent is taken as 100% by mass, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 88% by mass or more, and still more preferably 90% by mass or more, and is 100% by mass or less, from the viewpoint of improving carbon dioxide absorbency, improving carbon dioxide desorption property by low-temperature heating, and improving repeated usability.

[0044] <Other Components> The carbon dioxide absorbent can appropriately contain components other than the amine compound (A) and the porous material (B), as long as the effects of the invention are not impaired. Examples of the components other than the amine compound (A) and the porous material (B) include a deterioration inhibitor, an antifoaming agent, an antioxidant, and a desiccant for removing moisture (magnesium sulfate, molecular sieves, etc.).

[0045] From the viewpoint of improving carbon dioxide absorption ability and repeated use, the water content in the carbon dioxide absorbent is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, still more preferably 0.5% by mass or less, still more preferably 0.1% by mass or less, and still more preferably 0.01% by mass or less, and it is even more preferable that the carbon dioxide absorbent is substantially free of water. Here, "substantially free of water" means that water is not intentionally added, and does not exclude the presence of a small amount of water as an impurity.

[0046] When the carbon dioxide absorbent contains an amine compound (A) and a porous material (B), the method for preparing the carbon dioxide absorbent is not particularly limited, and known methods can be used. For example, the carbon dioxide absorbent can be prepared by blending the amine compound (A) and the porous material (B) and mixing them using a known device. When the carbon dioxide absorbent is an embodiment in which at least a portion of the amine compound (A) is supported on the porous material (B), the carbon dioxide absorbent can preferably be prepared by the following method. First, the amine compound (A) is dissolved in an organic solvent, and then the porous material (B) is added. The mixture is stirred, preferably at a temperature of 5°C to 60°C for 1 hour to 24 hours to prepare a mixture. Next, the organic solvent is removed from the resulting mixture by distillation or the like, and the remaining solid is dried under reduced pressure to obtain the carbon dioxide absorbent. The organic solvent is preferably one or more selected from the group consisting of dichloromethane or a monohydric alcohol having 4 or less carbon atoms, more preferably a monohydric alcohol having 4 or less carbon atoms, and even more preferably methanol, ethanol, and isopropyl alcohol, from the viewpoint of improving the solubility of the amine compound (A) and facilitating its removal from the carbon dioxide absorbent.

[0047] [Method for recovering carbon dioxide] The method for recovering carbon dioxide of the present invention (hereinafter also simply referred to as the "method of the present invention") is characterized by using the carbon dioxide absorbent. According to the method of the present invention, the amount of carbon dioxide absorbed from a gas containing carbon dioxide can be increased, and the method can be particularly suitably used for a technology for directly recovering carbon dioxide from air (DAC). Furthermore, carbon dioxide can be easily desorbed from the absorbent after absorbing carbon dioxide by low-temperature heating, and the reusability of the carbon dioxide absorbent can be improved.

[0048] The method for recovering carbon dioxide according to the present invention comprises an absorption step of bringing a carbon dioxide absorbent into contact with a gas containing carbon dioxide to cause the carbon dioxide absorbent to absorb carbon dioxide, and a desorption step of desorbing carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide in the absorption step, and it is preferable that the desorption step comprises a step of subjecting the carbon dioxide absorbent that has absorbed carbon dioxide to predetermined low-temperature heating conditions.

[0049] <Absorption Step> The absorption step is a step of bringing the carbon dioxide absorbent into contact with a gas containing carbon dioxide, thereby causing the carbon dioxide absorbent to absorb carbon dioxide. The method of bringing the carbon dioxide absorbent into contact with the gas can be selected appropriately depending on the form of the carbon dioxide absorbent, and is not particularly limited. For example, the carbon dioxide absorbent can be brought into contact with the gas containing carbon dioxide by passing the gas containing carbon dioxide through the carbon dioxide absorbent, spraying the carbon dioxide absorbent in the gas containing carbon dioxide, or placing the carbon dioxide absorbent in the gas containing carbon dioxide.

[0050] Examples of carbon dioxide-containing gases include, but are not limited to, air, thermal power plant exhaust gas, steel mill exhaust gas, cement factory exhaust gas, chemical plant exhaust gas, biofermentation gas, and natural gas. Energy-saving carbon dioxide recovery from these gases is particularly required, and the present invention is particularly effective for this purpose. The carbon dioxide concentration, gas pressure, and gas temperature in the gas are not particularly limited, and the method of the present invention can be applied to gases under a wide range of conditions. Furthermore, the carbon dioxide-containing gas may contain acidic gases other than carbon dioxide. Examples of such acidic gases include CO, NOx, and SOx in the exhaust gas, formaldehyde generated in methanol-fueled power generation, and hydrogen chloride and hydrogen sulfide. When the carbon dioxide-containing gas contains acidic gases other than carbon dioxide, it is preferable to combine the method with a known process for removing the other acidic gases. Specifically, the carbon dioxide recovery method of the present invention may be applied to a gas containing acidic gases other than carbon dioxide, or the method of the present invention may be applied after removing the other acidic gases from a gas containing acidic gases other than carbon dioxide by known means.

[0051] In the absorption step, the temperature when the carbon dioxide absorbent is brought into contact with the gas containing carbon dioxide is not particularly limited, but from the viewpoint of improving the carbon dioxide absorption amount, the temperature is preferably 0°C or higher and lower than 60°C, more preferably 20°C or higher and lower than 60°C, even more preferably 20°C or higher and lower than 50°C, and still more preferably 20°C or higher and lower than 45°C.

[0052] In the absorption step, the pressure at which the carbon dioxide absorbent is brought into contact with the gas containing carbon dioxide can be any pressure, and from the viewpoint of favorable absorption of carbon dioxide, it is more preferable to carry out the contact under normal pressure to pressurized conditions. The pressure (absolute pressure) is, for example, in the range of 0.1 to 10 MPa, preferably 0.1 to 1 MPa.

[0053] <Desorption Step> The desorption step is a step of desorbing carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide in the absorption step. The desorption step in the present invention can be carried out using a conventionally known desorption method, but preferably includes a step of subjecting the carbon dioxide absorbent that has absorbed carbon dioxide to predetermined low-temperature heating conditions at atmospheric pressure. From the viewpoint of improving the carbon dioxide desorption property and reusability, the low-temperature heating conditions are preferably 45°C or higher, more preferably 50°C or higher, even more preferably 55°C or higher, and preferably lower than 100°C, more preferably 90°C or lower, even more preferably 80°C or lower, and still more preferably 70°C or lower. The amine compound (A) used in the carbon dioxide absorbent of the present invention can desorb and regenerate carbon dioxide even under such low-temperature heating conditions. Furthermore, since the temperature during desorption can be lowered in this way, volatilization and decomposition of the amine compound (A) itself due to heating can be suppressed, and a decrease in absorbency during the next carbon dioxide absorption can also be suppressed, thereby effectively improving reusability.

[0054] The low-temperature heating in the desorption step can be performed by a known method using an apparatus equipped with a heating means such as a heater. The carbon dioxide absorbent and carbon dioxide separated in the desorption step can be recovered separately and reused.

[0055] [Carbon dioxide separation and capture apparatus] The carbon dioxide separation and capture apparatus of the present invention (hereinafter also referred to as "the apparatus of the present invention") comprises an absorption apparatus equipped with a mechanism for bringing the carbon dioxide absorbent into contact with a gas containing carbon dioxide, and causing the carbon dioxide absorbent to absorb carbon dioxide, and a desorption apparatus equipped with a mechanism for desorbing carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide.

[0056] The apparatus of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing one embodiment of a carbon dioxide separation and capture apparatus 100 of the present invention, in which 1 is an absorption apparatus and 2 is a desorption apparatus.

[0057] <Absorption Device> The absorption device 1 in the carbon dioxide separation and capture system 100 is a mechanism that includes the carbon dioxide absorbent and brings the carbon dioxide absorbent into contact with a gas containing carbon dioxide, thereby causing the carbon dioxide absorbent to absorb carbon dioxide.

[0058] The absorption device 1 is not particularly limited as long as it has a configuration that brings the carbon dioxide absorbent into contact with a gas containing carbon dioxide, depending on the form of the carbon dioxide absorbent. For example, as shown in Fig. 1 , the absorption device 1 can be provided with an absorbent holding unit 12 that holds a carbon dioxide absorbent 12a inside a reaction tower 11, and further with a gas supply unit 13 that supplies a gas containing carbon dioxide to the absorbent holding unit 12. Furthermore, from the viewpoint of discharging the carbon dioxide absorbent that has absorbed carbon dioxide from the absorbent holding unit 12 and supplying new carbon dioxide absorbent, the absorption device 1 can also be provided with an absorbent discharge unit (not shown) that discharges the carbon dioxide absorbent 12a held in the absorbent holding unit 12, and an absorbent supply unit (not shown) that supplies new carbon dioxide absorbent to the absorbent holding unit 12.

[0059] The absorption device 1 may further include a heating / cooling mechanism to adjust the temperature when the carbon dioxide absorbent is brought into contact with the carbon dioxide-containing gas. The absorption device 1 may also include a carbon dioxide concentration measurement mechanism to measure the carbon dioxide concentration in the gas. Furthermore, the absorption device 1 may also include a pressurization / depressurization mechanism to adjust the pressure when the carbon dioxide absorbent is brought into contact with the carbon dioxide-containing gas.

[0060] The carbon dioxide separation and capture system 100 may have a connection part 3 for supplying the carbon dioxide absorbent that has absorbed carbon dioxide in the absorption device 1 to the desorption device 2. There are no particular limitations on the means for supplying the carbon dioxide absorbent that has absorbed carbon dioxide from the absorption device 1 to the desorption device 2, and the absorption device 1 may be stopped once after operating for a certain period of time, and the carbon dioxide absorbent in the reaction tower 11 provided in the absorption device 1 may be supplied all at once to the desorption device 2. Alternatively, the carbon dioxide absorbent may be supplied continuously or intermittently from the absorbent holding part 12 of the absorption device 1 to the desorption device 2 using the connection part 3.

[0061] <Desorption device> The desorption device 2 in the carbon dioxide separation and capture system 100 is a mechanism that desorbs carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide in the absorption device 1. The desorption device 2 has a mechanism that desorbs carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide in the absorption device 1. In the present invention, from the viewpoint of performing low-temperature heating, it is preferable to include at least a heating mechanism as a mechanism that desorbs carbon dioxide.

[0062] 1 , the desorption device 2 may include, inside the reaction tower 21, an absorbent holding section 22 that holds a carbon dioxide absorbent 22a that has absorbed carbon dioxide, and may further include a gas discharge section 23 that discharges the carbon dioxide desorbed from the carbon dioxide absorbent. The desorption device 2 also includes a heating mechanism (not shown) for creating a low-temperature heating condition inside the reaction tower 21. In addition to the heating mechanism, the desorption device 2 may also include a cooling mechanism, a carbon dioxide concentration measurement mechanism, and the like, similar to the absorption device 1.

[0063] The carbon dioxide absorbent after desorbing carbon dioxide in the desorption device 2 can be supplied again to the absorption device 1 from the absorbent discharge section 24, which is used to supply the carbon dioxide absorbent after desorbing carbon dioxide to the absorption device 1, and can be reused.

[0064] The carbon dioxide separation and capture system 100 may further include a capture device for capturing the desorbed carbon dioxide. The captured carbon dioxide can be used for agricultural purposes such as enhanced oil recovery and plant factories; industrial gas purposes such as beverages and welding; chemical synthesis; or carbon dioxide capture and storage (CCS). The captured carbon dioxide may also be concentrated before being used for these purposes.

[0065] The present invention will be described below with reference to examples, but the present invention is not limited to the scope of the examples. In the examples, various measurements and evaluations were carried out by the following methods.

[0066] ( 1 H-NMR analysis) The structures of the amine compounds obtained in Production Examples 1 and 2 were identified as follows: 1The measurement was carried out by H-NMR analysis. The measurement conditions were as follows: Nuclear magnetic resonance spectrometer: AVANCEIII-500 manufactured by Bruker Biospin Co., Ltd. Probe: 5 mmφ double resonance multinuclear probe (BBFO Plus Smart probe) Deuterated solvent: deuterated chloroform Measurement nucleus: 1H Measurement temperature: room temperature

[0067] (Specific Surface Area and Pore Volume of Porous Material) The specific surface area and pore volume of the porous material were measured using a specific surface area / pore size distribution measuring device ("ASAP2020" manufactured by Shimadzu Corporation).

[0068] (Volume median particle diameter of porous material (D ５０ The particle distribution of the porous material was measured using a laser diffraction / scattering particle size distribution analyzer (Malvern Instruments, "LMS-200e"). The particle size corresponding to a cumulative volume frequency of 50%, calculated from the smallest particle size in the particle distribution, was defined as the volume median particle size (D ５０ )

[0069] (Carbon dioxide absorption - carbon dioxide desorption cycle test by low-temperature heating) A carbon dioxide concentration meter ("CO2 / temperature / humidity data logger TR-76Ui" manufactured by T&D Corporation) and a petri dish were placed in a desiccator (internal dimensions: 370 mm x 260 mm x 272 mm, capacity: approximately 26 L) in a constant temperature and humidity environment of 23 ° C. and 50% RH. The carbon dioxide absorbent obtained in each example was weighed out so that the number of amino groups in the amine compound contained in the carbon dioxide absorbent was 10 mmol, and added to the petri dish in the desiccator. The door was immediately closed, and the carbon dioxide absorbent was left to stand in the desiccator. The carbon dioxide concentration change in the desiccator was tracked for 23 hours using the carbon dioxide concentration meter (carbon dioxide absorption step). After 23 hours, the carbon dioxide absorbent after carbon dioxide absorption was removed from the desiccator, and the carbon dioxide absorbent was heated to 60 ° C. under atmospheric pressure (1 atm), and this temperature was maintained for 1 hour to desorb carbon dioxide (carbon dioxide desorption step). This carbon dioxide absorption step and carbon dioxide desorption step were repeated three times (three cycles were performed). The initial carbon dioxide concentration in the desiccator (initial stage of the first run) was 300 to 700 ppm. (1) Mass Change of the Carbon Dioxide Absorbent: In each cycle, the mass of the carbon dioxide absorbent was measured after the carbon dioxide absorption step and the carbon dioxide desorption step, and the mass change during each step was calculated and shown in Table 1. Here, absorption amount 1 represents the mass change (mass increase) before and after the carbon dioxide absorption step in the first cycle, and desorption amount 1 represents the mass change (mass decrease) before and after the carbon dioxide desorption step in the first cycle. Similarly, absorption amount 2 and desorption amount 2 represent the mass change during the second cycle, and absorption amount 3 and desorption amount 3 represent the mass change during the third cycle. (2) Minimum Carbon Dioxide Concentration in the Carbon Dioxide Absorption Step: The minimum carbon dioxide concentration (ppm) in the desiccator during the carbon dioxide absorption step in each of the first to third cycles is summarized in Table 2. The smaller this value, the higher the carbon dioxide absorption ability of the carbon dioxide absorbent. Also, the smaller the change in this minimum carbon dioxide concentration compared to the minimum carbon dioxide concentration in the previous cycle, the more carbon dioxide absorption ability can be maintained even after repeated carbon dioxide absorption-desorption cycles by low-temperature heating.

[0070] (Gas Chromatography Analysis) Gas chromatography analysis was carried out under the following measurement conditions. [GC Measurement Conditions] Apparatus: "7890B GC" manufactured by Agilent Technologies, Inc. Column: "CP-Sil 8 CB for Amines" manufactured by Agilent Technologies, Inc. (length 30 m, film thickness 0.25 μm, inner diameter 0.25 mm) Column temperature: 40°C, 10 minutes → 20°C / minute temperature increase → 250°C, 10 minutes → 20°C / minute temperature increase → 300°C, 10 minutes Carrier gas: Helium carrier gas Flow rate: 2.2553 mL / min Inlet pressure: 22.474 psi (constant pressure mode) Detector: FID Inlet temperature: 250°C Detector temperature: 310°C

[0071] In the examples and comparative examples, the following amine compounds and porous materials were used.

[0072] (Amine compounds) MXDA: metaxylylenediamine, manufactured by Mitsubishi Gas Chemical Co., Inc. MXDA-Butanal: an amine compound represented by formula (1-1), produced by the method described in Production Example 1 below. BAC-Butanal: an amine compound represented by formula (1-2), produced by the method described in Production Example 2 below.

[0073]

[0074] (Porous material) Mesoporous silica: "SBA15" manufactured by Merck, volume median particle diameter (D ５０ ): 100 μm, specific surface area by BET method: 800 m ２ / g, pore volume: 0.8 cm ３ / g

[0075] Production Example 1 (Production of Amine Compound Represented by Formula (1-1)) 68 g (0.5 mol) of metaxylylenediamine (MXDA, manufactured by Mitsubishi Gas Chemical Co., Inc.) and 50 g of toluene (manufactured by Kanto Chemical Co., Inc.) were weighed and placed in a 300 mL three-neck flask, followed by stirring and mixing with a stirrer. While the three-neck flask was immersed in an ice bath to cool, 36 g (0.5 mol) of butyraldehyde (manufactured by Tokyo Chemical Industry Co., Ltd.) was slowly added dropwise so that the internal temperature did not exceed 10°C. After completion of the addition, the mixture was allowed to react with stirring at room temperature (23°C) for 1 hour. Toluene and water were then distilled off using an evaporator to obtain the reaction product (imine). 50 g of the resulting imine, 50 g of toluene, and 1 g of Pd / C (manufactured by N.E. Chemcat Corporation, PE type) were weighed and added to a 230 cc autoclave (material: SUS316L). The autoclave was purged with nitrogen three times, and then with hydrogen three times. A hydrogen reduction reaction was then carried out for two hours under conditions of a hydrogen pressure of 2 MPaG and a heating temperature of 80°C. Subsequently, a separation operation using toluene and water was carried out five times to remove free amine from the reaction solution, thereby obtaining an amine compound represented by formula (1-1). The resulting amine compound (a mixture of butyraldehyde mono-adduct and di-adduct) had a total amine equivalent of 105 g / eq and an active hydrogen equivalent of 69 g / eq. The amine compound obtained here was a mixture of butyraldehyde mono-adduct (MXDA-Butanal) and di-adduct. The area % (area %) of the chromatogram (GC) obtained by gas chromatography analysis was 85% / 15% for the mono-adduct / di-adduct, which, when converted to mass %, was 81% / 19% for the mono-adduct / di-adduct. Furthermore, the amine compound obtained in Production Example 1 １ The H-NMR chart is shown in FIG. 1 H-NMR chemical shift: δ 7.18-7.30 ppm (m, 4H, -C ６ H ４ -), δ3.77-3.87ppm (m, 4H, -CH ２ -C ６ H ４ -CH ２ -), δ2.62-2.66ppm (m, 2H, -NH-CH ２ -CH ２ -CH ２-), δ1.34-1.52ppm (m, 4H, -NH-CH ２ -CH ２ -CH ２ -), δ0.91-0.93ppm (t, -CH ３ , 3H), δ 0.91-1.52 ppm (m, 3H, -NH- and -NH ２ )

[0076] Production Example 2 (Production of Amine Compound Represented by Formula (1-2)) The same reaction as in Production Example 1 was carried out, except that 71 g (0.5 mol) of 1,3-bis(aminomethyl)cyclohexane (1,3-BAC, manufactured by Mitsubishi Gas Chemical Co., Inc.) was used instead of MXDA in Production Example 1, to obtain an amine compound represented by formula (1-2). The resulting amine compound (a mixture of butyraldehyde mono-adduct and di-adduct) had a total amine equivalent of 106 g / eq and an active hydrogen equivalent of 72 g / eq. The amine compound obtained here was a mixture of butyraldehyde mono-adduct (BAC-Butanal) and di-adduct, and the area % (area %) of the chromatogram (GC) obtained by gas chromatography analysis was 82% / 18% for the mono-adduct / di-adduct, which was converted to 78% / 22% by mass for the mono-adduct / di-adduct. The amine compound obtained in Production Example 2 １ The H-NMR chart is shown in FIG. 1 H-NMR chemical shift: δ 2.44-2.61 ppm (m, 6H, N-CH ２ -), δ1.25-1.78ppm (m, 4H, -NH-CH ２ -CH ２ -CH ２ -), δ0.90-0.93ppm (t, 3H, -CH ３ ), 0.55-0.86 ppm (m, 10H, -CH- and -CH ２ -), δ 0.55-1.78 ppm (m, 3H, -NH- and -NH ２ )

[0077] Examples 1-2, Comparative Example 1 (Preparation and Evaluation of Carbon Dioxide Absorbent) (Preparation of Carbon Dioxide Absorbent) 4 g of the amine compound shown in Table 1 and 25 g of methanol were placed in a nitrogen-purged glass container, and the mixture was stirred with a stirrer at room temperature (23°C) to dissolve the amine compound. Next, 4 g of porous material was added, and nitrogen substitution was performed again, followed by stirring for 3 hours to achieve homogenization. Methanol was distilled off from the resulting mixture using an evaporator, and the mixture was then dried in a reduced pressure dryer at 80°C for 3 hours to obtain a carbon dioxide absorbent in which the amine compound was supported on a porous material (amount of amine compound per 100 parts by mass of porous material: 100 parts by mass).

[0078] (Evaluation of Carbon Dioxide Absorbent) Using the obtained carbon dioxide absorbent, a carbon dioxide absorption-desorption cycle test under low-temperature heating conditions was carried out by the method described above, and the results are shown in Table 1. In addition, the minimum carbon dioxide concentration in the carbon dioxide absorption step was measured by the method described above, and the results are shown in Table 2.

[0079]

[0080]

[0081] It can be seen from Tables 1 and 2 that the carbon dioxide absorbents of the present examples have good carbon dioxide absorption properties, and that they exhibit good and stable carbon dioxide absorption properties even after repeated carbon dioxide absorption-desorption cycles by low-temperature heating. On the other hand, the carbon dioxide absorbent of Comparative Example 1 has excellent carbon dioxide absorption properties, but its carbon dioxide absorption properties are significantly reduced with repeated use. Therefore, it can be seen that the carbon dioxide absorbents of the present invention are superior in terms of the balance between carbon dioxide absorption properties and repeated usability.

[0082] According to the present invention, it is possible to provide a carbon dioxide absorbent which has excellent carbon dioxide absorbency, and which exhibits little deterioration in carbon dioxide absorbency even when the carbon dioxide absorbent is regenerated by absorbing carbon dioxide and then desorbing carbon dioxide by low-temperature heating, and which is excellent in repeated use.

[0083] REFERENCE SIGNS LIST 100 Carbon dioxide separation and capture device 1 Absorption device 2 Desorption device 3 Connection section 11, 21 Reaction tower 12, 22 Absorbent holding section 12a Carbon dioxide absorbent 13 Gas supply section 22a Carbon dioxide absorbent that has absorbed carbon dioxide 23 Gas discharge section 24 Absorbent discharge section

Claims

A carbon dioxide absorbent comprising an amine compound (A) represented by the following general formula (1): H ２ N-(CH) ２ ) ｍ -X-(CH) ２ ) ｎ -NHR １ (1) (In formula (1), X is a phenylene group or a cyclohexylene group, and R １ is an aliphatic hydrocarbon group having 3 to 6 carbon atoms; m and n are each independently a number from 1 to 6. 　 The carbon dioxide absorbent according to claim 1, wherein the amine compound (A) is a compound that is liquid at 25°C.

3. The carbon dioxide absorbent according to claim 1, wherein X in the general formula (1) is a 1,3-phenylene group or a 1,3-cyclohexylene group. 　 The carbon dioxide absorbent according to any one of claims 1 to 3, wherein the amine compound (A) is an amine compound represented by the following formula (1-1) or (1-2): The carbon dioxide absorbent according to any one of claims 1 to 4, further comprising a porous material (B). 　 The carbon dioxide absorbent according to claim 5, wherein the porous material (B) contains at least one selected from the group consisting of silica and alumina. 　 A method for recovering carbon dioxide, which uses the carbon dioxide absorbent according to any one of claims 1 to 6.

8. The method according to claim 7, comprising: an absorption step of bringing the carbon dioxide absorbent into contact with a gas containing carbon dioxide to cause the carbon dioxide absorbent to absorb carbon dioxide; and a desorption step of desorbing carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide in the absorption step, wherein the desorption step comprises a step of subjecting the carbon dioxide absorbent that has absorbed carbon dioxide to low-temperature heating conditions of 45°C or higher and lower than 100°C at atmospheric pressure.

7. A carbon dioxide separation and capture system comprising: an absorption device equipped with a mechanism for bringing the carbon dioxide absorbent according to any one of claims 1 to 6 into contact with a gas containing carbon dioxide, thereby causing the carbon dioxide absorbent to absorb carbon dioxide; and a desorption device equipped with a mechanism for desorbing carbon dioxide from the carbon dioxide absorbent that has absorbed the carbon dioxide.

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