Carbon dioxide absorbent, method for recovering carbon dioxide, and apparatus for separating and recovering carbon dioxide

Abstract

Provided are: a carbon dioxide absorbent containing an amine compound (A) represented by general formula (1); a method for recovering carbon dioxide using the carbon dioxide absorbent; and an apparatus for separating and recovering carbon dioxide.　Formula (1): H2N-(CH2)m-X-(CH2)n-NHR1 (In formula (1), X is a phenylene group or a cyclohexylene group, and R1 is a 2-12 C hydrocarbon group which may have a hydroxy group, and m and n are each independently a number from 1 to 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] Various technologies related to DAC have been studied. For example, Patent Document 1 discloses an absorbent for absorbing carbon dioxide in the air, which contains an alkylamine substituted with a hydroxy group or an optionally substituted amino group. Patent Document 2 discloses a carbon dioxide absorbent containing a predetermined amount or more of a polyamine compound having an alicyclic hydrocarbon structure. Patent Document 3 discloses a carbon dioxide absorbent containing a predetermined amount or more of an amine compound having a predetermined heterocyclic structure. Furthermore, Patent Document 4 discloses a carbon dioxide absorbent containing a specific cyclic amine compound and a porous material.

[0004] Furthermore, methods for absorbing / desorbing carbon dioxide in a carbon dioxide absorbent include temperature swing and pressure swing. Temperature swing is a method of adsorbing and desorbing carbon dioxide by changing the temperature, whereby carbon dioxide is absorbed under low-temperature (non-heated) conditions and desorbed under high-temperature (heated) conditions. Pressure swing is a method of absorbing / desorbing carbon dioxide by changing the pressure, whereby carbon dioxide is absorbed under high-pressure (pressurized or atmospheric) conditions and desorbed under low-pressure (reduced) conditions. Among these, carbon dioxide absorption / desorption by pressure swing is advantageous in terms of energy because it does not require the step of heating the carbon dioxide absorbent containing the amine compound disclosed in Patent Documents 1 to 4. Furthermore, because the amine compound is less likely to deteriorate due to heat, it is possible to suppress a decrease in the reusability of the carbon dioxide absorbent.

[0005] Regarding the use of pressure swing in DAC technology, for example, US Pat. No. 5,629,663 discloses a method for converting CO ２ a step of removing CO ２ CO from the air by passing it through contact with the adsorbent ２ absorbing the CO ２ The adsorbent is passed through an ion exchange resin to ２ CO from the adsorbent ２ absorbing the ion exchange resin into a second CO ２ to remove CO from the ion exchange resin by contacting the resin with an adsorbent. ２ and absorbing said second CO via a temperature swing or pressure swing or by electrolysis. ２ and recovering the adsorbent.

[0006] Japanese Patent Application Laid-Open No. 2017-031046 International Publication No. 2022 / 138302 International Publication No. 2022 / 163209 International Publication No. 2023 / 013397 Special Publication No. 2009-502483

[0007] The carbon dioxide capture method described in Patent Document 5 requires the use of first and second adsorbents, making the process complicated. Furthermore, the carbon dioxide absorbents containing amine compounds disclosed in Patent Documents 1 to 4 have good carbon dioxide absorption properties, but there is room for improvement in carbon dioxide desorption properties when pressure swing is used after carbon dioxide absorption. If the carbon dioxide desorption properties are insufficient, there is a concern that the carbon dioxide absorbency will gradually decrease when carbon dioxide adsorption and desorption are repeated in the carbon dioxide absorbent. An object of the present invention is to provide a carbon dioxide absorbent that has excellent carbon dioxide absorption properties, and that exhibits little decrease in carbon dioxide absorbency even when carbon dioxide is absorbed and then desorbed by pressure swing to regenerate the carbon dioxide absorbent, and that is excellent in repeated use.

[0008] 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 １ is a hydrocarbon group having 2 to 12 carbon atoms which may have a hydroxy group. 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 which 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 one of [1] to [3], wherein the amine compound (A) is any one of the amine compounds represented by the following formulas (1-1) to (1-6): [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 capturing 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, wherein the desorption step comprises subjecting the carbon dioxide absorbent that has absorbed carbon dioxide to reduced pressure conditions. [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.

[0009] According to the present invention, it is possible to provide a carbon dioxide absorbent that is excellent in carbon dioxide absorbency, and that exhibits little deterioration in carbon dioxide absorbency even when the carbon dioxide absorbent is regenerated by desorbing carbon dioxide through a pressure swing after absorbing carbon dioxide, and that is excellent in repeated use.

[0010] 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 is a H-NMR chart of the amine compound obtained in Production Example 4. １ 1 H-NMR chart.

[0011] [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."

[0012] In this specification, "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 at a low concentration (about 0.04% by volume) of carbon dioxide in air. In this specification, "excellent repeated usability even when the carbon dioxide absorbent is regenerated by desorption of carbon dioxide through pressure swing" means that the carbon dioxide absorbent has a large carbon dioxide absorption capacity and exhibits stable carbon dioxide absorbency even after repeated cycles of carbon dioxide absorption-carbon dioxide desorption under reduced pressure conditions. The carbon dioxide absorbency and repeated usability can be specifically evaluated by the methods described in the examples.

[0013] [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 １is a hydrocarbon group having 2 to 12 carbon atoms, which may have a hydroxy group. m and n each independently represent a number from 1 to 6.) The carbon dioxide absorbent of the present invention has the above-described configuration, and even when the carbon dioxide absorbent is regenerated by desorbing carbon dioxide using a pressure swing after absorbing carbon dioxide, the carbon dioxide absorbency is not significantly reduced, resulting in excellent reusability. Furthermore, the carbon dioxide absorbent of the present invention exhibits good carbon dioxide absorption 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.

[0014] The reason why the carbon dioxide absorbent of the present invention exhibits the above-mentioned effects is not clear, 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 absorbency. Here, an amine compound in which a primary amino group is directly bonded to the cyclic structure is less likely to form a carbonate by reaction with carbon dioxide, resulting in reduced carbon dioxide absorbency. Furthermore, an amine compound having two or more primary amino groups has excellent carbon dioxide absorbency, but the desorption property when desorbing carbon dioxide by pressure swing after carbon dioxide absorption is reduced. Therefore, the carbon dioxide absorbency of the carbon dioxide absorbent after regeneration by pressure swing is reduced. In contrast, the amine compound (A) used in the present invention has only one primary amino group, and therefore is thought to have excellent carbon dioxide desorption property by pressure swing and improved reusability. Furthermore, the hydrocarbon group (R in general formula (1)) bonded to the secondary amino group in the amine compound (A) １ It is believed that when the -NH 2 -NH 3 -NH 4 -NH 5 -NH 6 -NH 7 -NH 8 -NH 9 -NH 10 -NH 11 -NH 12 -NH 13 -NH 14 -NH 15 -NH 16 -NH 17 -NH 18 -NH 19 -NH 20 -NH 21 -NH 22 -NH 23 -NH 24 -NH 25 -NH 26 -NH 27 -NH 28 -NH 29 -NH 30 -NH 31 -NH 32 -NH 33 -NH 34 -NH 35 -NH 36 -NH 37 -NH 38 -NH 39 -NH 40 -NH 41 -NH 42 -NH 43 -NH 44 -NH 45 -NH 46 -NH 47 -NH 48 -NH 49 -NH 50 -NH 51 -NH 52 -NH ２A "secondary amino group" refers to an amino group having one hydrogen atom on the nitrogen atom.

[0015] <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 １ is a hydrocarbon group having 2 to 12 carbon atoms which may have a hydroxy group; m and n each independently represent a number from 1 to 6.

[0016] The amine compound (A) may be a compound that is solid or liquid at 25° C., but from the viewpoint of the ability to be supported on the porous material (B) described below and from the viewpoint of improving the ability to desorb carbon dioxide by pressure swing, it is preferably a compound that is liquid at 25° C. Here, a compound that is liquid at 25° C. means a compound whose melting point is lower than 25° C.

[0017] 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 due to pressure swing, 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-phenylene group.

[0018] In the general formula (1), R １ is a hydrocarbon group having 2 to 12 carbon atoms which may have a hydroxy group. Examples of the hydrocarbon include an alkyl group, an alkenyl group, an aryl group, and an aralkyl group. From the viewpoints of improving the ability to release carbon dioxide by pressure swing, improving reusability, and ease of production, an alkyl group, an aryl group, or an aralkyl group is preferred, and an alkyl group or an aralkyl group is more preferred.

[0019] Examples of the alkyl group include a linear alkyl group, a branched alkyl group, and a cycloalkyl group. From the viewpoint of improving the ability to desorb carbon dioxide due to pressure swing and improving repeated use, a linear alkyl group or a branched alkyl group is preferred, and a branched alkyl group is more preferred. Examples of the linear alkyl group include linear alkyl groups having 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, and more preferably 2 to 4 carbon atoms, such as an ethyl group, an n-propyl group, and an n-butyl group. Examples of the branched alkyl group include branched alkyl groups having 3 to 12 carbon atoms, more preferably 3 to 8 carbon atoms, such as an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an isopentyl group, a neopentyl group, an isohexyl group, an isoheptyl group, an isooctyl group, and an ethylhexyl group.

[0020] The aryl group includes aryl groups having 6 to 12 carbon atoms, such as a phenyl group, a toluyl group, a mesityl group, a biphenyl group, and a naphthyl group.

[0021] The aralkyl group includes aralkyl groups having 7 to 12 carbon atoms, such as benzyl and phenethyl groups.

[0022] Among the above, from the viewpoints of improving the desorption of carbon dioxide by pressure swing, improving reusability, and ease of manufacture, R １ is preferably an alkyl group having 2 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, each of which may have a hydroxy group; more preferably a linear alkyl group having 2 to 4 carbon atoms, a branched alkyl group having 3 to 8 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms, each of which may have a hydroxy group; even more preferably a hydroxyethyl group, an ethylhexyl group, a benzyl group, or a phenethyl group; still more preferably an ethylhexyl group, a benzyl group, or a phenethyl group; and still more preferably an ethylhexyl group or a phenethyl group.

[0023] From the viewpoints of carbon dioxide absorbency, improvement in carbon dioxide desorption property due to pressure swing, improvement in repeated use, and ease of production, the amine compound (A) is any of the amine compounds represented by the following formulas (1-1) to (1-6), more preferably any of the amine compounds represented by the following formulas (1-2) to (1-6), even more preferably any of the amine compounds represented by the following formulas (1-2) to (1-4), and still more preferably an amine compound represented by the following formula (1-3):

[0024] The amine compound (A) can be used alone or in combination of two or more. A preferred embodiment of the method for producing the amine compound (A) is as follows. For example, the amine compound represented by formula (1-1) can be produced by stirring meta-xylylenediamine under heating conditions, preferably at 60 to 150°C, and then blowing ethylene oxide into the mixture to cause a reaction. The amine compounds represented by formula (1-2), (1-4), or (1-6) can be produced by reacting meta-xylylenediamine or 1,3-bis(aminomethyl)cyclohexane with an aldehyde compound, preferably under heating conditions, at 60 to 150°C to obtain an imine, and then reducing the imine with hydrogen. In the production of the amine compounds represented by formulas (1-2) and (1-4), benzaldehyde is used as the aldehyde compound, and in the production of the amine compound represented by formula (1-6), 2-ethylhexanal is used as the aldehyde compound. The amine compound represented by formula (1-3) or (1-5) can be produced according to the method described in JP-A-2002-161076. Specifically, it can be produced by reacting metaxylylenediamine or 1,3-bis(aminomethyl)cyclohexane with styrene in the presence of a basic catalyst such as lithium amide, usually at 25 to 150°C. After completion of the reaction, the catalyst can be removed, the reaction solvent can be distilled off, and / or the reaction mixture can be purified by distillation to obtain a more highly pure amine compound (A). A commercially available product may be used as the amine compound (A). For example, a commercially available product of the amine compound represented by formula (1-3) is "Gaskamine 240" manufactured by Mitsubishi Gas Chemical Company, Inc.

[0025] 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 carbon dioxide absorbency, improvement of carbon dioxide desorption property by pressure swing, and improvement of 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 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.

[0026] 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 40% by mass or more, still more preferably 45% by mass or more, and still more preferably 50% by mass or more, and is 100% by mass or less.

[0027] <Porous Material (B)> From the viewpoint of further improving carbon dioxide absorbency and improving carbon dioxide desorption property by pressure swing, 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).

[0028] The porous material (B) is preferably one that can support the amine compound (A) and can withstand the carbon dioxide desorption conditions, 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 absorbency and improving carbon dioxide desorption by pressure swing, 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 pressure swing, 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.

[0029] 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.

[0030] 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 10m２ / 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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 carbon dioxide absorbency, of improving the carbon dioxide desorption property due to a pressure swing, and of 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 80 parts by mass or more, and is also 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, relative to 100 parts by mass of the porous material (B).

[0035] When the carbon dioxide absorbent comprises 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 90% by mass or more, still more preferably 95% by mass or more, and still more preferably 98% by mass or more, and is 100% by mass or less, from the viewpoint of carbon dioxide absorbency, improving carbon dioxide desorption property by pressure swing, and improving repeated usability.

[0036] <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.).

[0037] 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.

[0038] 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 to 60°C for 1 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. As the organic solvent, from the viewpoints of the solubility of the amine compound (A) and the ease of removal from the carbon dioxide absorbent, dichloromethane or a monohydric alcohol having 4 or less carbon atoms is preferred, a monohydric alcohol having 4 or less carbon atoms is more preferred, and at least one selected from the group consisting of methanol, ethanol, and isopropyl alcohol is even more preferred.

[0039] [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 pressure swing, and the reusability of the carbon dioxide absorbent can be improved.

[0040] The carbon dioxide recovery method according to the present invention includes 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 includes a step of subjecting the carbon dioxide absorbent that has absorbed carbon dioxide to reduced pressure conditions.

[0041] <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.

[0042] 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.

[0043] 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, and more preferably 20°C or higher and lower than 60°C.

[0044] In the absorption step, the pressure at which the carbon dioxide absorbent is brought into contact with the carbon dioxide-containing gas is preferably higher than the pressure in the desorption step described below, from the viewpoint of performing a pressure swing, and more preferably atmospheric pressure to pressurized conditions. The pressure is, for example, in the range of 0.1 to 10 MPa, preferably 0.1 to 1 MPa.

[0045] <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 includes a step of subjecting the carbon dioxide absorbent that has absorbed carbon dioxide to reduced pressure conditions. From the viewpoint of improving the carbon dioxide desorption property, the reduced pressure conditions are preferably 10 kPa or less, more preferably 5 kPa or less, and even more preferably 1 kPa or less. In the desorption step, the temperature when the carbon dioxide absorbent is subjected to reduced pressure conditions is not particularly limited, but from the viewpoint of improving the carbon dioxide desorption property, it is preferably 0°C or higher, more preferably 10°C or higher. Furthermore, from the viewpoint of suppressing thermal degradation of the amine compound (A) in the carbon dioxide absorbent, it is preferably less than 50°C, more preferably 45°C or lower.

[0046] The pressure reduction in the desorption step can be carried out by a known method using an apparatus equipped with a pressure reducing means such as a vacuum pump.

[0047] The carbon dioxide absorbent and carbon dioxide separated in the desorption step can be recovered separately and reused.

[0048] [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.

[0049] 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.

[0050] <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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] <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 a pressure swing, it is preferable to include at least a pressure reduction mechanism as the mechanism that desorbs carbon dioxide.

[0055] 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 pressure reduction mechanism (not shown) for creating a reduced pressure condition inside the reaction tower 21. In addition to the pressure reduction mechanism, the desorption device 2 may also include a heating / cooling mechanism, a carbon dioxide concentration measurement mechanism, and the like, similar to the absorption device 1.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] ( 1 H-NMR analysis) The structures of the amine compounds obtained in Production Examples 1, 2 and 4 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

[0060] (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).

[0061] (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 )

[0062] (Carbon dioxide absorption-desorption cycle test under pressure swing conditions) A carbon dioxide concentration meter and a petri dish were placed in a desiccator (inner dimensions: 370 mm x 260 mm x 272 mm, capacity: approximately 26 L) in a constant temperature and humidity environment of 30°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 (carbon dioxide absorption step). The carbon dioxide concentration change in the desiccator was tracked for 23 hours using the carbon dioxide concentration meter. After 23 hours had passed, the carbon dioxide absorbent after carbon dioxide absorption was removed from the desiccator and placed in a vacuum dryer (oil rotary pump, vacuum degree specs: 6.7 x 10) with the internal temperature set to 30°C. －２Pa) for one hour (carbon dioxide desorption step). This carbon dioxide absorption-desorption cycle was performed three times. (1) Minimum carbon dioxide concentration in the carbon dioxide absorption step of the third cycle The minimum carbon dioxide concentration (ppm) in the desiccator in the carbon dioxide absorption step of the third cycle is shown in Table 1. The smaller this value, the higher the carbon dioxide absorption ability of the carbon dioxide absorbent, even after repeated carbon dioxide absorption-desorption cycles using the pressure swing method. (2) Carbon dioxide concentration difference in the carbon dioxide absorption step of the third cycle The difference (ppm) between the minimum and maximum carbon dioxide concentrations in the desiccator in the carbon dioxide absorption step of the third cycle was calculated and shown in Table 1. The larger this value, the higher the carbon dioxide absorption ability of the carbon dioxide absorbent, even after repeated carbon dioxide absorption-desorption cycles using the pressure swing method. (3) Minimum carbon dioxide concentration difference between cycles 2 and 3 The difference (ppm) between the minimum carbon dioxide concentration in the desiccator in the carbon dioxide absorption step of the second cycle and the minimum carbon dioxide concentration in the desiccator in the carbon dioxide absorption step of the third cycle was calculated and shown in Table 1. The smaller this absolute value, the less the fluctuation in the carbon dioxide absorption of the carbon dioxide absorbent is, even after repeated carbon dioxide absorption-desorption cycles by the pressure swing method, meaning that the carbon dioxide absorption is stable.

[0063] In the examples and comparative examples, the following amine compounds and porous materials were used.

[0064] (Amine Compounds) MXDA: metaxylylenediamine, manufactured by Mitsubishi Gas Chemical Company, Inc. MXDA-BAL1: amine compound represented by formula (1-2), produced by the method described in Production Example 1 below. G-240: amine compound represented by formula (1-3), a styrene (1 mol) adduct of metaxylylenediamine, manufactured by Mitsubishi Gas Chemical Company, Inc. "Gaskamine 240". BAC-BAL1: amine compound represented by formula (1-4), produced by the method described in Production Example 2 below. BAC-S: amine compound represented by formula (1-5), a styrene (1 mol) adduct of 1,3-bis(aminomethyl)cyclohexane, produced by the method described in Production Example 3 below. BAC-EH1: amine compound represented by formula (1-6), produced by the method described in Production Example 4 below. PEI600: polyethyleneimine (average molecular weight 600) having a structure represented by formula (1-7), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0065] (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

[0066] Production Example 1 (Production of an amine compound represented by formula (1-2)) 136 g (1 mol) of metaxylylenediamine (MXDA, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was charged into a reaction vessel, and 106 g (1 mol) of benzaldehyde (manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise over 15 minutes while stirring at room temperature under a nitrogen stream. After the dropwise addition was completed, the temperature was raised to 80°C, and after reaching 80°C, the reaction was carried out with stirring for 1.5 hours. The resulting reaction solution was dissolved in toluene and then concentrated to obtain an imine. Toluene was added to the obtained imine so that the imine concentration was 50 mass%. To the resulting imine, 5% supported Pd / C (manufactured by Tokyo Chemical Industry Co., Ltd.) was added as a catalyst in an amount of 3.5 mass% based on the imine, and a hydrogen reduction reaction was carried out under conditions of a hydrogen pressure of 5 MPa and a heating temperature of 100°C. The reaction was stopped when the amount of hydrogen flowing in reached 0, and the catalyst was removed by filtration, followed by distilling off the toluene to obtain the amine compound represented by formula (1-2).１ The H-NMR chart is shown in FIG. 1 H-NMR chemical shift: δ 7.1-7.9 ppm (m, 9H, -C ６ H ４ - and - C ６ H ５ ), δ3.8-3.85ppm (s, 6H, -CH ２ -C ６ H ４ -CH ２ - and -CH ２ -C ６ H ５ ), δ 1.9 ppm (s, -NH- and -NH ２ -, 3H)

[0067] Production Example 2 (Production of an amine compound represented by formula (1-4)) The reaction was carried out in the same manner as in Production Example 1, except that 142 g (1 mole) of 1,3-bis(aminomethyl)cyclohexane (1,3-BAC, manufactured by Mitsubishi Gas Chemical Co., Inc.) was used instead of MXDA, to obtain an amine compound represented by formula (1-4). １ The H-NMR chart is shown in FIG. 1 H-NMR chemical shift: δ 7.2-7.3 ppm (m, 5H, -C ６ H ５ ), δ3.8ppm (s, 2H, -CH ２ -C ６ H ５ ), δ2.4-2.6ppm (m, 4H, -CH ２ -C ６ H 10 -CH ２ -), δ0.5-1.9ppm (m, 10H, -C ６ H 10 -)

[0068] Production Example 3 (Production of the Amine Compound Represented by Formula (1-5)) This compound was produced according to the method described in Example 3 of JP 2002-161076 A. 142 g (1 mol) of 1,3-bis(aminomethyl)cyclohexane (1,3-BAC, manufactured by Mitsubishi Gas Chemical Co., Inc.) and 2.8 g (2% by mass relative to 1,3-BAC) of lithium amide catalyst (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were charged into a reaction vessel and stirred at 100°C for 2 hours under a nitrogen stream. 104 g (1 mol) of styrene (manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise over 30 minutes, and after the dropwise addition, the mixture was stirred for another 2 hours at 100°C to carry out the reaction. After the reaction was completed, 10 g of water was added, the catalyst was removed by filtration, and then distillation under reduced pressure was performed to obtain an adduct of 1,3-bis(aminomethyl)cyclohexane with styrene (1 mol), which is the amine compound represented by formula (1-5).

[0069] Production Example 4 (Production of an amine compound represented by formula (1-6)) The reaction was carried out in the same manner as in Production Example 2, except that 36 g (1 mole) of 2-ethylhexanal (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of benzaldehyde, to obtain an amine compound represented by formula (1-6). １ The H-NMR chart is shown in FIG. 1 H-NMR chemical shift: δ 2.4-2.6 ppm (m, 6H, -CH ２ -N-), δ 1.6 ppm (m, 1H, CH in ethylhexyl group ３ -CH ２ -CH-), δ 1.2 ppm (m, 3H, -NH- and -NH ２ -), δ 0.8-1.8 ppm (m, 22H, -CH in the cyclohexane ring ２ -, CH in ethylhexyl group ３ - (CH ２ ) ３ - and CH ３ -CH ２ -CH-), δ 0.5 to 0.6 ppm (m, 2H, -CH- in the cyclohexane ring)

[0070] Examples 1 to 5 and Comparative Examples 1 and 2 (Preparation and Evaluation of Carbon Dioxide Absorbents) (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 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).

[0071] (Evaluation of Carbon Dioxide Absorbent) Using the obtained carbon dioxide absorbent, a carbon dioxide absorption-desorption cycle test was carried out under pressure swing conditions by the method described above. The results are shown in Table 1.

[0072]

[0073] From Table 1, it can be seen that the carbon dioxide absorbent of this example exhibits good and stable carbon dioxide absorption properties even after repeated carbon dioxide absorption-desorption cycles using the pressure swing method.

[0074] According to the present invention, it is possible to provide a carbon dioxide absorbent that is excellent in carbon dioxide absorbency, and that exhibits little deterioration in carbon dioxide absorbency even when the carbon dioxide absorbent is regenerated by desorbing carbon dioxide through a pressure swing after absorbing carbon dioxide, and that is excellent in repeated use.

[0075] REFERENCE SIGNS LIST 100 Carbon dioxide separation and capture apparatus 1 Absorption device 2 Desorption device 3 Connection section 11, 21 Reaction towers 12, 22 Absorbent holding section 12a Carbon dioxide absorbent 13 Gas supply section 21 Reaction tower 22a Carbon dioxide absorbent that has absorbed carbon dioxide 23 Gas discharge section 24 Absorbent discharge section

Claims

1. A carbon dioxide absorbent comprising an amine compound (A) represented by the following general formula (1): ２ N-(CH ２ ) ｍ -X-(CH ２ ) ｎ -N.H.R. １ (1) (In formula (1), X is a phenylene group or a cyclohexylene group, and R １ is a hydrocarbon group having 2 to 12 carbon atoms which may have a hydroxyl group; m and n each independently represent a number from 1 to 6.

2. 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 or 2, wherein X in said general formula (1) is a 1,3-phenylene group or a 1,3-cyclohexylene group.

4. The carbon dioxide absorbent according to any one of claims 1 to 3, wherein the amine compound (A) is any one of amine compounds represented by the following formulas (1-1) to (1-6):

5. The carbon dioxide absorbent according to any one of claims 1 to 4, further comprising a porous material (B).

6. 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.

7. 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 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, wherein the desorption step comprises a step of subjecting the carbon dioxide absorbent that has absorbed carbon dioxide to reduced pressure conditions.

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 claims 1 to 6 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 carbon dioxide.

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