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

Abstract

Disclosed are: a carbon dioxide absorbent which contains an amine compound (A) represented by general formula (1) and a porous material (B); a method for recovering carbon dioxide using the carbon dioxide absorbent; and an apparatus for separating and recovering carbon dioxide. In formula (1), each R1 independently represents a hydroxy group or an organic group having 1 to 10 carbon atoms. n1 to n4 each independently represent a number of 1 to 8, and m represents a number of 0 to 10.

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 capture method, and a carbon dioxide separation and capture device.

[0002] In light of the issue of global warming, there is a need to reduce carbon dioxide emissions. One method for reducing carbon dioxide emissions is to capture carbon dioxide using a carbon dioxide absorbent. A typical carbon dioxide absorbent is an aqueous solution of an amine compound, such as monoethanolamine. Aqueous solutions of amine compounds have the characteristic of not releasing the absorbed carbon dioxide unless the temperature is elevated, for example, to 120°C or higher. Raising the carbon dioxide release temperature above the boiling point of water requires a large amount of energy to capture the carbon dioxide due to the high latent heat and specific heat of water. As described above, one challenge with conventional carbon dioxide absorbents is further energy conservation during carbon dioxide separation and capture. Furthermore, conventional carbon dioxide absorbents suffer from the problem of volatilization loss of a small amount of the amine compound when contacted with gas during the carbon dioxide absorption process. Therefore, reducing the volatility of the amine compound contained in the carbon dioxide absorbent is also an issue. Furthermore, conventional chemical absorption methods involve steam heating to temperatures of approximately 110°C to 130°C to boil the carbon dioxide absorbent and regenerate it. Therefore, this method requires a significant amount of thermal energy. Furthermore, there is a concern that the amine compound contained in the carbon dioxide absorbent may be thermally decomposed during this regeneration process, and therefore the thermal stability of the carbon dioxide absorbent is also an issue.

[0003] In recent years, carbon dioxide absorbents in which an amine compound is supported on a porous material have been studied. By supporting an amine compound on a porous material and solidifying it, it becomes possible to recover carbon dioxide with less energy than with an aqueous solution, which has problems with high latent heat and specific heat. Examples of technologies related to such solidified carbon dioxide absorbents include those described in Patent Documents 1 to 3.

[0004] Patent Document 1 describes a solid absorbent for separating and capturing carbon dioxide, which contains a specific alkanolamine and is supported on a support. Patent Document 2 describes a carbon dioxide absorbent in which an amine compound is supported on porous particles in which hydrophilic fibers and porous powder are combined with a hydrophilic binder. Patent Document 3 describes a carbon dioxide absorption composition containing polyethylene polyamine, phosphoric acid and / or a phosphate salt, and silica.

[0005] JP 2012-139622 A JP 2018-187574 A JP 2020-58966 A

[0006] However, according to studies by the present inventors, there is room for improvement in terms of repeated usability of carbon dioxide absorbents containing an amine compound and a porous material as described in Patent Documents 1 to 3. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a carbon dioxide absorbent that has good carbon dioxide absorption properties and is particularly excellent in repeated usability, a carbon dioxide recovery method using the carbon dioxide absorbent, and a carbon dioxide separation and recovery apparatus.

[0007] The present inventors have found that the above-mentioned problems can be solved by a carbon dioxide absorbent containing an amine compound having a specific structure and a porous material. 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), and a porous material (B): In formula (1), R 1are each independently a hydroxy group or an organic group having 1 to 10 carbon atoms. n1 to n4 are each independently a number from 1 to 8, and m is a number from 0 to 10. [2] The carbon dioxide absorbent according to [1], wherein in the general formula (1), n1 to n4 are each independently a number from 3 to 8, and m is a number from 1 to 10. [3] The carbon dioxide absorbent according to [1] or [2], wherein in the general formula (1), n1 to n4 are all 3. [4] The carbon dioxide absorbent according to any one of [1] to [3], wherein at least a part of the amine compound (A) is supported on the porous material (B). [5] The carbon dioxide absorbent according to any one of [1] to [4], wherein the porous material (B) contains at least one selected from the group consisting of porous silica and porous alumina. [6] The carbon dioxide absorbent according to any one of [1] to [5], wherein the porous material (B) is in a particulate form. [7] The volume median particle diameter (D ５０ [8] The carbon dioxide absorbent according to [6], wherein the specific surface area of ​​the porous material (B) measured by the BET method is 2 m or more and 500 m or less. ２ / g or more 3000m ２ [9] The carbon dioxide absorbent according to any one of [1] to [8], wherein the pore size of the porous material (B) is 5 nm or more.

[10] The carbon dioxide absorbent according to any one of [1] to [8], wherein the pore volume of the porous material (B) is 0.1 cm ３ / g or more 5.0cm ３ / g or less.

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

[10] , wherein the content of the amine compound (A) in the carbon dioxide absorbent is 0.1 parts by mass or more and 1,000 parts by mass or less relative to 100 parts by mass of the porous material (B).

[12] The carbon dioxide absorbent according to any one of [4] to

[11] , wherein a pore embedding ratio of the carbon dioxide absorbent calculated by the following formula is 90% or less: Pore embedding ratio (%) of carbon dioxide absorbent = {pore volume of porous material (B) (cm ３ / g) - pore volume of carbon dioxide absorbent (cm ３ / g)} / pore volume of porous material (B) (cm３ / g) × 100

[13] A method for recovering carbon dioxide using the carbon dioxide absorbent according to any one of [1] to

[12] .

[14] The method according to

[13] , wherein the method comprises 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, and the desorption step comprises at least one step selected from the group consisting of the following (I) to (III): (I) a step of subjecting the carbon dioxide absorbent that has absorbed carbon dioxide to reduced pressure conditions; (II) a step of bringing an inert gas that does not contain carbon dioxide into contact with the carbon dioxide absorbent that has absorbed carbon dioxide; and (III) a step of heating the carbon dioxide absorbent that has absorbed carbon dioxide.

[15] A carbon dioxide separation and capture system comprising: an absorption device equipped with a mechanism that brings the carbon dioxide absorbent according to any one of [1] to

[12] into contact with a gas that contains carbon dioxide, thereby causing the carbon dioxide absorbent to absorb carbon dioxide; and a desorption device equipped with a mechanism that desorbs 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 good carbon dioxide absorption properties and is particularly excellent in terms of reusability, a carbon dioxide recovery method using the carbon dioxide absorbent, and a carbon dioxide separation and recovery apparatus.

[0009] 1 is a schematic diagram showing one embodiment of a carbon dioxide separation and capture apparatus of the present invention.

[0010] [Definitions] In this specification, "good carbon dioxide absorbency" means that the amount of carbon dioxide absorbed when contacted with a gas containing carbon dioxide is large, and "good carbon dioxide absorbency from air" means that the amount of carbon dioxide absorbed is large for a low concentration (about 0.04% by volume) of carbon dioxide in the air. In this specification, "good reusability" of a carbon dioxide absorbent means that the retention rate of the carbon dioxide absorption rate is high when a cycle test of carbon dioxide absorption and desorption is conducted. The carbon dioxide absorption rate and its retention rate can be specifically evaluated by the method described in the Examples. A "primary amino group" is an amino group having two hydrogen atoms on a nitrogen atom, i.e., -NH ２ In this specification, the expression "XX to YY" means "XX or more and YY or less."

[0011] [Carbon Dioxide Absorbent] The carbon dioxide absorbent of the present invention contains an amine compound (A) represented by the following general formula (1) and a porous material (B). In formula (1), R 1 are each independently a hydroxy group or an organic group having 1 to 10 carbon atoms. n1 to n4 are each independently a number from 1 to 8, and m is a number from 0 to 10. By having the above-mentioned constitution, the carbon dioxide absorbent of the present invention has good carbon dioxide absorption properties and is particularly excellent in repeated use properties.

[0012] The reason why the carbon dioxide absorbent of the present invention exhibits the above-mentioned effects is not clear, but it is thought to be as follows. The amine compound (A) used in the carbon dioxide absorbent of the present invention has a primary amino group with a high carbon dioxide absorption rate, and is therefore thought to be able to exhibit high carbon dioxide absorption. Furthermore, the amine compound (A) has a tertiary amino group in the molecule, and the proportion of tertiary amino groups among all amino groups is high. The tertiary amino group does not form a carbamate with strong bonding strength when absorbing carbon dioxide, and is likely to act as a carbon dioxide mediator, which is thought to reduce the energy required to desorb carbon dioxide. This makes it possible to further improve the repeated use of the carbon dioxide absorbent.

[0013] By containing the porous material (B) in the carbon dioxide absorbent, at least a portion of the amine compound (A) is supported on the porous material (B). This increases the contact area between the amine compound (A) having carbon dioxide absorbency and a gas containing carbon dioxide, making it possible to perform desorption (separation and recovery) of carbon dioxide after absorption under lower energy conditions. Furthermore, the use of the porous material (B) is thought to suppress volatilization of the amine compound (A), improving the reusability of the carbon dioxide absorbent.

[0014] <Amine Compound (A)> The amine compound (A) is represented by the following general formula (1). In formula (1), R 1 are each independently a hydroxy group or an organic group having 1 to 10 carbon atoms, n1 to n4 are each independently a number from 1 to 8, and m is a number from 0 to 10.

[0015] In formula (1), preferably, n1 to n4 are each independently a number from 3 to 8, and m is a number from 1 to 10. In formula (1), an amine compound in which the number of methylene groups in the divalent group adjacent to the nitrogen atom (n1 to n4 in general formula (1)) is 2 is prone to undergo an intramolecular cyclization reaction when subjected to oxidation, heating, or the like. Therefore, for example, if the amine compound is allowed to absorb carbon dioxide and then subjected to heat treatment to desorb the carbon dioxide, an intramolecular cyclization reaction may occur, resulting in conversion to a different compound, and the reusability may be reduced. In contrast, if the number of methylene groups in the divalent group adjacent to the nitrogen atom (n1 to n4 in general formula (1)) is all 3 or more, the cyclization reaction is unlikely to occur, and the reusability is thought to be better. Furthermore, in formula (1), when m is a number from 1 to 10, the molecular weight of amine compound (A) is relatively high, and therefore volatilization is unlikely even when heat treatment is performed to desorb carbon dioxide after absorbing carbon dioxide. This is also thought to contribute to improved reusability.

[0016] In formula (1), R 1are each independently a hydroxy group or an organic group having 1 to 10 carbon atoms, preferably a hydroxy group or a hydrocarbon group having 1 to 10 carbon atoms which may have a hydroxy group, an amino group, a halogen atom, a thiol group, a nitro group, a cyano group, or a carboxy group. Preferred examples of the hydrocarbon group include an alkyl group, an aryl group, and an aralkyl group, and more preferably an alkyl group. From the viewpoint of improving carbon dioxide absorption by increasing the amino group concentration, R 1 is preferably a hydroxy group, or a hydrocarbon group having 1 to 6 carbon atoms which may have a hydroxy group, an amino group, or a cyano group, more preferably a hydroxy group, or an alkyl group having 1 to 4 carbon atoms which may have a hydroxy group, an amino group, or a cyano group, even more preferably an alkyl group having 1 to 2 carbon atoms which may have a hydroxy group, an amino group, or a cyano group, and even more preferably a methyl group. 1 may be the same or different, but from the viewpoint of ease of production, it is preferable that they are the same.

[0017] In formula (1), n1 to n4 each independently represent a number from 1 to 8, and from the viewpoint of increasing the amino group concentration and improving carbon dioxide absorbency, and from the viewpoint of improving repeated use, n1 to n4 are preferably 3 to 8, more preferably 3 to 6, even more preferably 3 to 4, and still more preferably all 3. n1 to n4 may be the same or different, but from the viewpoint of ease of production, it is preferable that they are all the same.

[0018] In formula (1), m is a number from 0 to 10. From the viewpoint of increasing the molecular weight of the amine compound (A) and suppressing volatilization to further improve repeated useability, m is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more, and from the viewpoint of preventing an excessive increase in viscosity and loss of fluidity, m is preferably 8 or less, more preferably 6 or less. In formula (1), m is an average value, and the amine compound (A) may contain two or more compounds having different m values.

[0019] The total amine value of the amine compound (A) is preferably 600 mgKOH / g or more, more preferably 800 mgKOH / g or more, even more preferably 1,000 mgKOH / g or more, and preferably 1,200 mgKOH / g or less, from the viewpoint of improving carbon dioxide absorption. The tertiary amine value of the amine compound (A) is preferably 100 mgKOH / g or more, more preferably 200 mgKOH / g or more, and preferably 500 mgKOH / g or less, from the viewpoint of further improving carbon dioxide desorption and repeated use. The total amine value indicates the amount of all amino groups in the compound and refers to the number of milligrams of potassium hydroxide (KOH) equivalent to the amount of acid required to neutralize 1 g of the compound. The tertiary amine value indicates the amount of tertiary amino groups in the compound and refers to the number of milligrams of potassium hydroxide (KOH) equivalent to the amount of acid required to neutralize the tertiary amino groups in 1 g of the compound. The total amine value and tertiary amine value can be specifically determined by the methods described in the Examples.

[0020] From the viewpoint of improving repetitive use, the proportion of tertiary amino groups in all amino groups in the amine compound (A) is preferably 40 mol % or more, and from the viewpoint of improving carbon dioxide absorption, it is preferably 48 mol % or less, more preferably 46 mol % or less. The proportion of tertiary amino groups in all amino groups is the value obtained by dividing the tertiary amine value of the amine compound (A) by the total amine value (tertiary amine value / total amine value).

[0021] From the viewpoint of improving carbon dioxide absorption, the amine compound (A) preferably has a proportion of primary amino groups in all amino groups of 9.0 mol% or more, more preferably 10 mol% or more, and even more preferably 15 mol% or more, and from the viewpoint of improving repeated use, it is preferably 40 mol% or less, more preferably 30 mol% or less, and even more preferably 20 mol% or less. The proportion of primary amino groups in all amino groups is the value obtained by dividing the primary amine value of the amine compound (A) by the total amine value (primary amine value / total amine value).

[0022] Specific preferred examples of the amine compound (A) are shown below, but are not limited to these.

[0023] From the viewpoints of improving carbon dioxide absorption capacity and repeated use, and ease of production, the amine compound (A) is preferably a compound represented by any one of the above structural formulas (1-1) to (1-4), and more preferably a compound represented by the above structural formula (1-1).

[0024] The molecular weight of the amine compound (A) is preferably 270 or more, more preferably 400 or more, and even more preferably 500 or more, from the viewpoint of suppressing weight loss due to heating during carbon dioxide desorption and further improving reusability, and from the viewpoint of improving carbon dioxide absorbency, it is preferably 1500 or less, more preferably 1200 or less, even more preferably 1000 or less, and still more preferably 800 or less. The molecular weight of the amine compound (A) is the weight average molecular weight (Mw) determined by tosylation GPC measurement using a gel permeation chromatography (GPC) apparatus described in the Examples.

[0025] <Physical Properties of Amine Compound (A)> From the viewpoint of further improving the carbon dioxide desorption property and reusability, the maximum carbon dioxide dissociation temperature of the amine compound (A), measured by the following method, is preferably 140°C or less, more preferably 130°C or less, even more preferably 120°C or less, even more preferably 110°C or less, and even more preferably 100°C or less. The lower limit of the maximum carbon dioxide dissociation temperature is not particularly limited, but is, for example, 40°C or more. (Method) Amine compound (A) having absorbed carbon dioxide is heated from 23°C to 250°C at a temperature increase rate of 10°C / min, and the temperature at which the amount of heat absorbed due to carbon dioxide desorption becomes maximum is measured, and this temperature is defined as the maximum carbon dioxide dissociation temperature. Here, the amine compound (A) having absorbed carbon dioxide can be prepared, for example, by leaving 5 mmol of amine compound (A) in air at 23°C and 50% RH for 24 hours.

[0026] The maximum endothermic temperature of amine compound (A), measured by the following method, is preferably 150° C. or higher, more preferably 180° C. or higher, even more preferably 200° C. or higher, and still more preferably 250° C. or higher, from the viewpoints of suppressing weight loss due to heating when carbon dioxide is desorbed and further improving reusability. (Method) Amine compound (A) is heated from 23° C. to 350° C. at a temperature increase rate of 10° C. / min, and the temperature at which the amount of heat absorbed due to the volatilization of amine compound (A) becomes maximum is measured, and this temperature is defined as the maximum endothermic temperature of amine compound (A).

[0027] <Method for producing amine compound (A)> The amine compound (A) can be obtained, for example, by subjecting a raw material amine represented by the following general formula (2) to a polycondensation reaction accompanied by deammoniating, preferably under heated and pressurized conditions. In formula (2), R 1 In the production of the amine compound represented by the structural formula (1-1), methyliminobis(propylamine) [N,N-bis(3-aminopropyl)methylamine] can be used as the raw material amine represented by the general formula (2).

[0028] The polycondensation reaction of the raw material amine is preferably carried out in the presence of a catalyst. Known hydrogenation catalysts can be used as the catalyst. Examples of the catalyst include supported heterogeneous hydrogenation catalysts in which metals such as Ni, Co, Pt, Pd, and Ru are supported on carbon, silica, alumina, and diatomaceous earth; so-called Ziegler-type hydrogenation catalysts that use organic acid salts or transition metal salts such as acetylacetone salts of Ni, Co, Fe, and Cr, 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, and Zr.

[0029] The temperature during the polycondensation reaction of the raw material amine is preferably 0 to 200°C, more preferably 10 to 180°C, and even more preferably 20 to 150°C, from the viewpoint of improving reaction efficiency and suppressing side reactions. The pressure during the polycondensation reaction of the raw material amine is preferably 0.01 MPaG or more, more preferably 0.1 MPaG or more, and even more preferably 0.3 MPaG or more, from the viewpoint of improving reaction efficiency and suppressing side reactions, and is preferably 10 MPaG or less, and even more preferably 3 MPaG or less. Pressurization during the polycondensation reaction is preferably carried out using an inert gas such as nitrogen. The polycondensation reaction time is not particularly limited, but is preferably 30 minutes or more, more preferably 1 hour or more, from the viewpoint of improving molecular weight, and is preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 8 hours or less, from the viewpoint of production efficiency.

[0030] The polycondensation reaction is preferably carried out in a solvent. The solvent is not particularly limited as long as it does not inhibit the polycondensation reaction, and examples thereof 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; and aromatic hydrocarbons such as toluene, ethylbenzene, and xylene. These may be used alone or in combination of two or more.

[0031] After the reaction, the catalyst is removed from the resulting reaction mixture, and the mixture is purified by distillation or the like as necessary to obtain the amine compound (A).

[0032] <Porous material (B)> The carbon dioxide absorbent of the present invention contains a porous material (B). From the viewpoint of enabling separation and recovery of carbon dioxide with lower energy, it is preferable that at least a part of the amine compound (A) is supported on the porous material (B) in the carbon dioxide absorbent, and it is more preferable that the amine compound (A) is supported on the porous material (B) and solidified.

[0033] The porous material (B) is preferably one that can support the amine compound (A) and can withstand the conditions for separating and recovering carbon dioxide, and examples thereof include porous silica, porous alumina, porous silica-alumina, porous magnesia, porous zirconia, zeolite, zeolite-related compounds, clay minerals, natural minerals, activated carbon, carbon molecular sieves (porous carbon), porous resins (synthetic adsorbents), porous metal-organic frameworks, and porous solid waste, and one or more of these can be used. Among these, from the viewpoints of improving carbon dioxide absorption capacity and reusability, the porous material (B) preferably contains at least one selected from the group consisting of porous silica and porous alumina, more preferably contains porous silica, and even more preferably contains mesoporous silica.

[0034] The shape of the porous material (B) is not particularly limited, but is preferably particulate, more preferably spherical. When the porous material (B) is particulate, the specific surface area of ​​the porous material (B) is increased, and the amount of the amine compound (A) supported can be increased. This can further increase the carbon dioxide absorption amount.

[0035] When the porous material (B) is particulate, the volume median particle diameter (D ５０ From the viewpoint of improving handleability, the thickness is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, still more preferably 20 μm or more, still more preferably 30 μm or more, still more preferably 40 μm or more, still more preferably 50 μm or more, still more preferably 70 μm or more, still more preferably 80 μm or more, and still more preferably 90 μm or more. From the viewpoint of further improving the amount of amine compound (A) supported, the thickness is preferably 500 μm or less, more preferably 300 μm or less, still more preferably 200 μm or less, still more preferably 180 μm or less, and still more preferably 160 μm or less.

[0036] The specific surface area of ​​the porous material (B) measured by the BET method is preferably 2 m or more from the viewpoint of further increasing the amount of the amine compound (A) supported. ２ / g or more, more preferably 10m ２ / g or more, more preferably 30m ２ / g or more, and even more preferably 50m ２ / g or more, and even more preferably 70m 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 From the viewpoint of further improving the carbon dioxide absorption property and carbon dioxide absorption rate of the carbon dioxide absorbent obtained, the specific surface area of ​​the porous material (B) measured by the BET method is even more preferably 800 m ２ / g or less, and even more preferably 700m ２ / g or less, and even more preferably 600m ２ / g or less, and even more preferably 500m ２ / g or less, and even more preferably 400m ２ / g or less.

[0037] The pore diameter of the porous material (B) is preferably 5 nm or more, more preferably 10 nm or more, from the viewpoint of further improving the carbon dioxide absorbency and carbon dioxide absorption rate. Furthermore, from the viewpoint of improving the mechanical strength and repeated use of the porous material (B), it is preferably 200 nm or less, more preferably 100 nm or less, even more preferably 80 nm or less, and even more preferably 70 nm or less. When the pore diameter of the porous material (B) used in the carbon dioxide absorbent is 5 nm or more, it is thought that the pores of the porous material (B) are less likely to be buried by the support of the amine compound (A), and the amine compound (A) is more likely to be adsorbed in a monolayer state on the surface of the porous material (B). This effect is thought to further improve the carbon dioxide absorbency and carbon dioxide absorption rate of the resulting carbon dioxide absorbent. Furthermore, from the viewpoint of further improving the carbon dioxide absorbency and carbon dioxide absorption rate of the resulting carbon dioxide absorbent, the pore diameter of the porous material (B) is more preferably 15 nm or more, even more preferably 20 nm or more.

[0038] The pore volume of the porous material (B) is preferably 0.1 cm 3 from the viewpoint of further improving the carbon dioxide absorption capacity and the carbon dioxide absorption rate. ３ / g or more, more preferably 0.3 cm ３ / g or more, more preferably 0.5 cm ３ / g or more, and even more preferably 0.7 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 In particular, the pore volume of the porous material (B) used in the carbon dioxide absorbent is 0.5 cm ３ / g or more, it is considered that the pores of the porous material (B) are less likely to be buried by the amine compound (A) being supported, and that the amine compound (A) is more likely to be adsorbed in a monolayer state on the surface of the porous material (B). This effect is considered to further improve the carbon dioxide absorbency and carbon dioxide absorption rate of the obtained carbon dioxide absorbent. Furthermore, from the viewpoint of further improving the carbon dioxide absorbency and carbon dioxide absorption rate of the obtained carbon dioxide absorbent, the pore volume of the porous material (B) is even more preferably 0.8 cm ３ / g or more, and even more preferably 1.0 cm ３ / g or more.

[0039] The specific surface area, pore size, and pore volume of the porous material (B) 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.

[0040] The volume median particle diameter (D ５０ ), specific surface area, pore diameter and pore volume are determined based on the volume median particle diameter (D ５０ ), specific surface area, pore diameter and pore volume.

[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] <Content> From the viewpoint of improving carbon dioxide absorbency and repeated useability, the content of the amine compound (A) in the carbon dioxide absorbent is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 10% by mass or more, still more preferably 20% by mass or more, still more preferably 25% by mass or more, still more preferably 30% by mass or more, still more preferably 35% by mass or more, and still more preferably 40% by mass or more. Also, from the viewpoint of improving repeated useability, the content is preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 70% by mass or less, and still more preferably 60% by mass or less.

[0043] From the viewpoint of further improving the carbon dioxide absorbency and the reusability, the content of the amine compound (A) in the carbon dioxide absorbent is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, even more preferably 10 parts by mass or more, still more preferably 25 parts by mass or more, and even more preferably 50 parts by mass or more, relative to 100 parts by mass of the porous material (B). Also, it is preferably 1000 parts by mass or less, more preferably 500 parts by mass or less, even more preferably 250 parts by mass or less, still more preferably 200 parts by mass or less, and even more preferably 150 parts by mass or less. From the viewpoint of further improving the carbon dioxide absorbency and the carbon dioxide absorption rate, the content of the amine compound (A) in the carbon dioxide absorbent is even more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, still more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less, relative to 100 parts by mass of the porous material (B).

[0044] From the viewpoint of further improving the carbon dioxide absorbency and the reusability, the total content of the amine compound (A) and the porous material (B) in the carbon dioxide absorbent is 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.

[0045] <Other Components> The carbon dioxide absorbent of the present invention 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 such components include amine compounds other than the component (A), deterioration inhibitors, antifoaming agents, antioxidants, desiccants for removing moisture (magnesium sulfate, molecular sieves, etc.), etc.

[0046] From the viewpoint of further improving the carbon dioxide absorbency and the repetitive usability, the content of the amine compound (A) in all the amine compounds contained in the carbon dioxide absorbent is 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 is 100% by mass or less.

[0047] From the viewpoint of further improving carbon dioxide absorbency and reusability, 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 even 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.

[0048] <Pore Burial Ratio> From the viewpoint of further improving the carbon dioxide absorbency and carbon dioxide absorption rate, the carbon dioxide absorbent of the present invention has a pore buried ratio of preferably 90% or less, more preferably 80% or less, even more preferably 70% or less, and even more preferably 65% ​​or less, calculated by the following formula. Furthermore, from the viewpoint of improving the carbon dioxide absorbency, the pore buried ratio of the carbon dioxide absorbent is preferably 10% or more, more preferably 15% or more. Pore buried ratio of carbon dioxide absorbent (%) = {pore volume of porous material (B) (cm ３ / g) - pore volume of carbon dioxide absorbent (cm ３ / g)} / pore volume of porous material (B) (cm ３ / g) × 100 When the pore embedding rate of the carbon dioxide absorbent is 90% or less, it is possible to avoid the phenomenon in which the supported amine compound (A) blocks the pores in the porous material (B) and interferes with the flow path of carbon dioxide, which is thought to result in further improvements in the carbon dioxide absorbency and carbon dioxide absorption rate. The pore volume of the carbon dioxide absorbent in the above formula can be measured in the same manner as for the pore volume of the porous material (B).

[0049] <Method for Preparing Carbon Dioxide Absorbent> 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. In 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), the porous material (B), and an organic solvent are blended and 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 content is dried under reduced pressure to obtain the carbon dioxide absorbent. From the viewpoint of the dispersibility of the amine compound (A) and the porous material (B) and the ease of removal from the carbon dioxide absorbent, the organic solvent is preferably a monohydric alcohol having 4 or less carbon atoms, more preferably at least one selected from the group consisting of methanol, ethanol, and isopropyl alcohol.

[0050] The carbon dioxide absorbent of the present invention has a good ability to absorb carbon dioxide from air, and therefore can be suitably used in a technology for directly absorbing carbon dioxide from air (DAC). Furthermore, the carbon dioxide absorbent of the present invention can be suitably used, for example, when recovering carbon dioxide at a low concentration of 0.01% by volume or more and 1% by volume or less.

[0051] The carbon dioxide absorbent of the present invention is particularly suitable for repeated use, and maintains a high rate of carbon dioxide absorption even after repeated cycles of carbon dioxide absorption and desorption. While it is preferable for a carbon dioxide absorbent to have a high initial carbon dioxide absorption rate, if the rate of carbon dioxide absorption is low after repeated use, the carbon dioxide absorbent will need to be replaced and discarded many times, which is industrially disadvantageous. Therefore, a carbon dioxide absorbent with good repeated use properties can be said to have high industrial applicability.

[0052] [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 improved. Furthermore, carbon dioxide can be recovered with less energy, and the carbon dioxide absorbent has good reusability.

[0053] The carbon dioxide recovery method of the present invention preferably includes a step (absorption step) of contacting the carbon dioxide absorbent with a gas containing carbon dioxide to allow the carbon dioxide absorbent to absorb carbon dioxide.

[0054] <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.

[0055] 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.

[0056] In the absorption step, the temperature at which the carbon dioxide absorbent is brought into contact with the gas containing carbon dioxide is, from the viewpoint of improving the amount of carbon dioxide absorbed, preferably 0°C or higher and lower than 60°C, more preferably 20°C or higher and lower than 60°C, and even more preferably 30°C or higher and lower than 60°C.

[0057] More preferably, the method of the present invention comprises an absorption step of contacting the carbon dioxide absorbent with a gas containing carbon dioxide to allow 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 at least one step selected from the group consisting of the following (I) to (III). This method makes it possible to separate and recover carbon dioxide from a gas containing carbon dioxide: (I) a step of subjecting the carbon dioxide absorbent that has absorbed carbon dioxide to reduced pressure conditions; (II) a step of contacting the carbon dioxide absorbent that has absorbed carbon dioxide with an inert gas that does not contain carbon dioxide; and (III) a step of heating the carbon dioxide absorbent that has absorbed carbon dioxide.

[0058] <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. A method for desorbing carbon dioxide from a carbon dioxide absorbent that has absorbed carbon dioxide is preferably a method including at least one step selected from the group consisting of the steps (I) to (III) above. Two or more of the steps (I) to (III) may be combined.

[0059] (I) In the step of subjecting the carbon dioxide absorbent that has absorbed carbon dioxide to reduced pressure conditions (hereinafter also referred to as "step (I)"), the reduced pressure conditions are preferably 10 kPa or less, more preferably 5 kPa or less, and even more preferably 1 kPa or less, from the viewpoint of improving the efficiency of carbon dioxide separation and recovery. Furthermore, from the viewpoint of suppressing volatilization of the amine compound (A) in the carbon dioxide absorbent, the reduced pressure conditions are preferably 0.1 kPa or more. In step (I), the temperature when the carbon dioxide absorbent is subjected to reduced pressure conditions is not particularly limited, but from the viewpoint of suppressing volatilization of the amine compound (A) in the carbon dioxide absorbent, the temperature is preferably less than 50°C, more preferably 45°C or less. Furthermore, from the viewpoint of improving the efficiency of carbon dioxide separation and recovery, the temperature is preferably 0°C or more, more preferably 10°C or more.

[0060] (II) In the step of contacting a carbon dioxide absorbent having absorbed carbon dioxide with an inert gas not containing carbon dioxide (hereinafter also referred to as "step (II)"), desorption of carbon dioxide can be promoted by lowering the partial pressure of carbon dioxide. Examples of the inert gas not containing carbon dioxide include nitrogen, helium, argon, etc., and one or more of these can be used. Among these, from the viewpoint of improving the efficiency of separation and recovery of carbon dioxide, the inert gas not containing carbon dioxide is preferably at least one selected from nitrogen and argon. In step (II), examples of a method for contacting the carbon dioxide absorbent with an inert gas not containing carbon dioxide include the same contact method as described in the absorption step. In step (II), the temperature when contacting the carbon dioxide absorbent with an inert gas not containing carbon dioxide is not particularly limited. In step (II), the heating specified in step (III) may be performed simultaneously, or the temperature may be room temperature or lower. From the viewpoint of suppressing volatilization of the amine compound (A) in the carbon dioxide absorbent, the temperature is preferably less than 50°C, more preferably 45°C or lower. From the viewpoint of improving the efficiency of separation and recovery of carbon dioxide, the temperature is preferably 0°C or higher, more preferably 10°C or higher.

[0061] (III) The heating temperature in the step of heating the carbon dioxide absorbent that has absorbed carbon dioxide (hereinafter also referred to as "step (III)") is preferably 50°C or higher and 120°C or lower, more preferably 55°C or higher and 110°C or lower, and even more preferably 60°C or higher and 100°C or lower, from the viewpoint of improving the efficiency of separating and recovering carbon dioxide. The heating in step (III) can be carried out by a known method using an apparatus equipped with a heating means. Examples of the heating method include heating with steam or a heat medium, hot air heating, electromagnetic wave heating, ultrasonic heating, and induction heating.

[0062] The carbon dioxide absorbent and carbon dioxide separated in the desorption step can be recovered separately and reused.

[0063] [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") has 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.

[0064] 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.

[0065] <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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] <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 is not particularly limited as long as it has a mechanism that desorbs carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide in the absorption device 1, but it is preferable that it is equipped with a mechanism for performing at least one of the steps (I) to (III) above. Examples of such a mechanism include a pressure reduction mechanism, an inert gas supply mechanism, and a heating mechanism.

[0070] 1 , the desorption apparatus 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 carbon dioxide desorbed from the carbon dioxide absorbent. The desorption apparatus 2 also includes at least one mechanism (not shown) selected from a pressure reduction mechanism for creating a reduced pressure condition inside the reaction tower 21, an inert gas supply mechanism for supplying an inert gas to the absorbent holding section 22, and a heating mechanism for heating the absorbent holding section 22. In addition to the pressure reduction mechanism, inert gas supply mechanism, and heating mechanism, the desorption apparatus 2 may also include a carbon dioxide concentration measurement mechanism, etc., similar to the absorption apparatus 1.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] (Total Amine Value of Amine Compound) The total amine value was measured in accordance with JIS K7237-1995 by the following method. (1) 0.1 g of an amine compound was dissolved in 20 mL of acetic acid. (2) The solution obtained in (1) above was titrated with a 0.1 N perchloric acid-acetic acid solution using an automatic potentiometric titrator ("AT-610" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) to determine the total amine value.

[0075] (Tertiary amine value of amine compound) The tertiary amine value was measured in accordance with ASTM D-2073 by the following method. (1) 0.5 g of an amine compound was precisely weighed into 110 mL of a screw tube, and 25 mL of acetic anhydride and 2 mL of acetic acid were added, and the opening of the screw tube was covered with parafilm. (2) The screw tube of (1) was heated on a hot plate at 130°C for 45 minutes. (3) The solution obtained in (2) above was titrated with a 0.1 N perchloric acid-acetic acid solution using the automatic potentiometric titrator to determine the tertiary amine value.

[0076] (Molecular Weight of Amine Compound) The molecular weight of the amine compound was determined by the following tosylation GPC measurement. 0.02 g of the amine compound was weighed into a vial for a block thermostatic bath, and trifluoroacetic anhydride was added to make 1 mL. The vial was sealed and heated for 1.1 hours in a block thermostatic bath set at 80°C. After cooling to room temperature, the stopper was opened and the mixture was heated again in the thermostatic bath at 80°C for 1.1 hours to volatilize excess trifluoroacetic anhydride. After cooling to room temperature, 1 mL of a chloroform / methanol = 85 / 15 (v / v) solution was added and allowed to stand for about 1 hour to dissolve. After visually confirming complete dissolution, the mixture was filtered through a non-aqueous filter with a pore size of 0.45 μm, and the filtrate was used as a measurement sample and subjected to GPC measurement under the following conditions to determine the weight-average molecular weight of the amine compound. [Measurement conditions] GPC apparatus: "Prominence" manufactured by Shimadzu Corporation Column: Connected column of "KF-403HQ" and "KF-404HQ" manufactured by Shodex Measurement temperature: 40°C Eluent: THF Detector: RI Standard sample: Polystyrene PS (Mp: 162-136000, manufactured by Agilent)

[0077] (Maximum endothermic temperature of amine compound) DSC measurement was performed on the amine compound as follows to measure the maximum endothermic temperature of the amine compound. First, differential scanning calorimetry was performed on the amine compound using a differential thermogravimeter ("DTG-60" manufactured by Shimadzu Corporation) under conditions of a measurement temperature range of 23 to 350°C, a heating rate of 10°C / min, and a nitrogen atmosphere. From the DSC curve obtained, the temperature at which the amount of endothermic heat associated with the volatilization of the amine compound was maximized was identified, and this temperature was defined as the maximum endothermic temperature of the amine compound.

[0078] (Amine Compound Carbon Dioxide (CO ２) Maximum dissociation temperature) A carbon dioxide concentration meter and a petri dish were placed in a retractable desiccator (internal dimensions: 370 mm x 260 mm x 272 mm). An amine compound (5 mmol) was added to the petri dish in the desiccator, and the door was immediately closed. The amine compound was left in the desiccator for 24 hours in an air environment of 23°C and 50% RH. The initial carbon dioxide concentration was adjusted to approximately 400 ppm. Next, the amine compound was removed from the desiccator to obtain an amine compound that had absorbed carbon dioxide. The amine compound that had absorbed carbon dioxide was subjected to DSC measurement as follows to measure the maximum carbon dioxide dissociation temperature of the amine compound. First, differential scanning calorimetry was performed on the amine compound using a differential thermogravimetry analyzer ("DTG-60" manufactured by Shimadzu Corporation) under conditions of a measurement temperature range of 23 to 250°C, a heating rate of 10°C / min, and a nitrogen atmosphere. From the DSC curve thus obtained, the temperature at which the amount of endothermic heat accompanying the desorption of carbon dioxide becomes maximum was identified, and this temperature was taken as the maximum carbon dioxide dissociation temperature of the amine compound.

[0079] (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 )

[0080] (Specific surface area, pore diameter and pore volume of porous material and carbon dioxide absorbent) The specific surface area, pore diameter and pore volume of the porous material and carbon dioxide absorbent were measured using a specific surface area / pore diameter distribution measuring device ("ASAP2020" manufactured by Shimadzu Corporation).

[0081] (Pore Burial Ratio of Carbon Dioxide Absorbent) The pore burial ratio of the carbon dioxide absorbent was calculated from the following formula using the pore volume values ​​of the porous material and the carbon dioxide absorbent measured by the above-mentioned method: Pore Burial Ratio of Carbon Dioxide Absorbent (%) = {Pore Volume of Porous Material (B) (cm ３ / g) - pore volume of carbon dioxide absorbent (cm ３ / g)} / pore volume of porous material (B) (cm３ / g) × 100

[0082] (Evaluation 1 of Carbon Dioxide Absorption Capacity and Repeated Usability of Carbon Dioxide Absorbent) The carbon dioxide absorption capacity and repeated usability of the carbon dioxide absorbents listed in Table 1 were evaluated by the following method. 300 mg of an amine compound, 10 g of methanol, and 300 mg of a porous material were added to a nitrogen-purged glass container and stirred for 10 hours to homogenize. The resulting mixture was then placed in an environment of 40 ° C. and 100 hPa to distill off the methanol, and then vacuum-dried at room temperature (23 ° C.) for 24 hours to obtain a carbon dioxide absorbent. 15 mg of the resulting carbon dioxide absorbent was then placed in a differential thermogravimetry meter (Hitachi High-Tech Corporation "EXSTER TGD6200") and left to stand for 6 hours at 45 ° C. in a dry air environment, and the increase in mass of the solid carbon dioxide absorbent was measured. Here, the gas used during measurement was air (flow rate: 200 mL / min) during carbon dioxide absorption, and nitrogen (flow rate: 200 mL / min) during carbon dioxide desorption. The carbon dioxide absorption amount of the carbon dioxide absorbent was calculated from the increase in the mass of the carbon dioxide absorbent (first time). The unit of the carbon dioxide absorption amount in Table 1 is the carbon dioxide absorption amount (mg) per 1 g of the carbon dioxide absorbent.

[0083] After the first evaluation of carbon dioxide absorption capacity was completed, the carbon dioxide absorbent was removed from the apparatus, and the carbon dioxide absorbent that had absorbed carbon dioxide was heated at 120°C for 30 minutes to desorb the absorbed carbon dioxide, thereby regenerating the carbon dioxide absorbent. Next, the above-mentioned evaluation of carbon dioxide absorption capacity was performed again on the regenerated carbon dioxide absorbent, and the carbon dioxide absorption amount was measured (second time). Next, the carbon dioxide absorbent was removed from the apparatus, and the carbon dioxide absorbent that had absorbed carbon dioxide was heated at 120°C for 30 minutes to desorb the absorbed carbon dioxide, thereby regenerating the carbon dioxide absorbent again. Next, the above-mentioned evaluation of carbon dioxide absorption capacity was performed again on the regenerated carbon dioxide absorbent, and the carbon dioxide absorption amount was measured (third time). Here, the maintenance rate of carbon dioxide absorption amount was also calculated based on the first carbon dioxide absorption amount.

[0084] (Evaluation 2 of Carbon Dioxide Absorption Capacity and Repeated Usability of Carbon Dioxide Absorbents: Evaluation Under Practical Conditions) The carbon dioxide absorption capacity and repeated usability under practical conditions of the carbon dioxide absorbents shown in Tables 2 and 3 were evaluated by the following method. Carbon dioxide absorbents recover carbon dioxide from mixed gases that contain water vapor in addition to carbon dioxide, such as in air environments including outside air and indoor spaces, or combustion exhaust gas. Therefore, the amounts of carbon dioxide absorbed and desorbed under humidity-controlled conditions that take into account the influence of water vapor in the gas were measured by the following method using a catalyst analyzer ("BELCAT II" manufactured by MicrotrackBell Corporation), and the carbon dioxide absorption capacity and repeated usability of the carbon dioxide absorbents were evaluated.

[0085] (Evaluation 2-1: Heating Cycle Evaluation of Carbon Dioxide Absorbent) (1) 300 mg of an amine compound, 10 g of methanol, and 300 mg of a porous material were added to a nitrogen-purged glass container and stirred for 10 hours to achieve homogenization. The resulting mixture was then placed in an environment of 40°C and 100 hPa to distill off the methanol, and then vacuum dried at room temperature (23°C) for 24 hours to obtain a carbon dioxide absorbent. (2) Next, 200 mg of the resulting carbon dioxide absorbent was filled into the reaction tube of the catalyst analyzer and heated in a nitrogen stream (flow rate: 100 mL / min) at 100°C for 1 hour for drying and degassing pretreatment, after which the reaction tube was kept at 40°C. Next, the inlet gas was switched to a 400 ppm carbon dioxide / nitrogen mixed gas (total flow rate: 1000 mL / min) conditioned at 40 ° C and 40% RH (absorption step), and simultaneously, the change in the outlet gas composition of the catalyst analyzer over time was measured using a gas mass spectrometer (BELMASS; manufactured by MicrotrackBell) to obtain a breakthrough curve. After the amount of carbon dioxide absorbed reached saturation, the inlet gas was switched to nitrogen (flow rate: 500 mL / min) and heated to 80 ° C (desorption step). Subsequently, the change in the outlet gas composition of the catalyst analyzer over time was measured using a gas mass spectrometer. The amount of carbon dioxide absorbed by the carbon dioxide absorbent was calculated from the time from the start of absorption to saturation and the integrated change in the outlet concentration of carbon dioxide, and is shown in Table 2 (evaluation of the first carbon dioxide absorption capacity). In addition, the amount of carbon dioxide desorbed from the carbon dioxide absorbent was calculated from the time from the time the inlet gas was switched to nitrogen to the time when carbon dioxide was almost no longer detected from the outlet side and the integrated change in the outlet concentration of carbon dioxide. (3) After the first evaluation of the carbon dioxide absorption capacity was completed, the operation of (2) above was repeated nine more times for the carbon dioxide absorbent that had been regenerated by carrying out the desorption step, so that the carbon dioxide absorption step and desorption step were carried out a total of 10 times. The carbon dioxide absorption amount maintenance rates in the fifth and tenth evaluations were calculated based on the carbon dioxide absorption amount in the first evaluation.

[0086] (Evaluation 2-2: Decompression Cycle Evaluation of Carbon Dioxide Absorbent) (1) 100 mg of the carbon dioxide absorbent produced in the same manner as above was weighed into the reaction tube of the catalyst analyzer, and the absorbent temperature was maintained at 60 ° C. for 1 hour, followed by pretreatment by decompression and evacuation. Next, the reaction tube was kept at 40 ° C., and the introduced gas was switched to a 400 ppm carbon dioxide / nitrogen mixed gas (total flow rate: 1000 mL / min) humidified to 40 ° C. and 40% RH (absorption step). At the same time, the change over time in the outlet gas composition of the catalyst analyzer was measured with a gas mass spectrometer ("BELMASS" manufactured by MicrotrackBell Corporation), thereby obtaining a breakthrough curve. The amount of carbon dioxide absorbed by the carbon dioxide absorbent was calculated from the time from the start of absorption until saturation was reached and the integrated change in the outlet concentration of carbon dioxide, and is shown in Table 3 (evaluation of the first carbon dioxide absorption capacity). (2) The amount of carbon dioxide desorbed by the carbon dioxide absorbent due to the decompression was determined as the amount of carbon dioxide absorbed when the carbon dioxide absorbent after desorption was used, because the amount of carbon dioxide equivalent to the carbon dioxide desorbed by the decompression was subsequently absorbed. Specifically, the absorbent that had absorbed carbon dioxide in (1) above was kept at 40°C and manually evacuated using a vacuum pump for 30 minutes (desorption step). Then, 400 ppm carbon dioxide / nitrogen mixed gas was introduced again in the same manner as in (1) above, and the change in the outlet gas composition over time was measured using a gas mass spectrometer (MicrotrackBell's "BELMASS"). The ultimate vacuum after 30 minutes of decompression was 0.5 kPa. (3) After the first evaluation of carbon dioxide absorption capacity was completed, the carbon dioxide absorbent regenerated by the desorption step described in (2) above was subjected to the steps (1) and desorption step nine more times, resulting in a total of 10 carbon dioxide absorption and desorption steps. The carbon dioxide absorption amount in the first evaluation was used as a reference, and the maintenance rates of the carbon dioxide absorption amount in the fifth and tenth evaluations were calculated. The unit of the carbon dioxide absorption amount in Tables 2 and 3 is the carbon dioxide absorption amount (mg) per 1 g of the carbon dioxide absorbent.

[0087] Synthesis Example 1: Production of direct condensation oligomer (P-MIBPA) of methyliminobis(propylamine)

[0043] An autoclave (volume 150 mL, material: SUS316L) equipped with a stirrer and a heater was charged with 0.80 g of Raney nickel catalyst (manufactured by W.R. Grace), 35 g of toluene solvent (manufactured by Kanto Chemical), and 8.0 g of methyliminobis(propylamine). Nitrogen substitution (1.0 MPa x 4) was performed, and nitrogen pressure was applied so that the internal pressure became 1.5 MPa, followed by stirring at a temperature of 140 ° C. for 4 hours. Next, the autoclave was cooled to room temperature, and the reaction solution was pressure filtered to obtain a mixed solution of the raw material methyliminobis(propylamine) and condensation oligomer. After the solvent was distilled off using an evaporator, further vacuum distillation was carried out at a boiling point of 130°C / 20 mmHg to remove unreacted methyliminobis(propylamine), yielding 4.6 g of P-MIBPA (Mw: 722) represented by the following structural formula. In the above formula, m calculated from the Mw of P-MIBPA is 4.5.

[0088] P-MIBPA has a total amine value of 1029 and a tertiary amine value of 413, that is, P-MIBPA has about 40 mol % of tertiary amino groups relative to the total amino groups.

[0089] Example 1 and Comparative Examples 1 and 2: Preparation and evaluation of carbon dioxide absorbents 1 Carbon dioxide absorbents were prepared and evaluated using the amine compounds and porous materials shown in Table 1 by the method described in "Evaluation of carbon dioxide absorption capacity and repeated usability of carbon dioxide absorbents 1" above. The results are shown in Table 1.

[0090]

[0091] Example 2 and Comparative Examples 3 to 4: Preparation of carbon dioxide absorbents and evaluation under practical conditions Carbon dioxide absorbents were prepared and evaluated using the amine compounds and porous materials shown in Table 2 by the method described in "Evaluation 2-1" in the above "Evaluation 2 of carbon dioxide absorption capacity and repeated usability of carbon dioxide absorbents." The results are shown in Table 2.

[0092] Example 3 and Comparative Examples 5 and 6: Preparation of Carbon Dioxide Absorbents and Evaluation Under Practical Conditions Carbon dioxide absorbents were prepared and evaluated using the amine compounds and porous materials shown in Table 3 by the method described in "Evaluation 2-2" in the above "Evaluation 2 of Carbon Dioxide Absorption Capacity and Repeated Usability of Carbon Dioxide Absorbents." The results are shown in Table 3.

[0093]

[0094]

[0095] In the examples and comparative examples shown in Tables 1 to 3, the following amine compounds and porous materials were used. (Amine compounds) P-MIBPA: the amine compound obtained in Synthesis Example 1 TEPA: tetraethylenepentamine (manufactured by Tokyo Chemical Industry Co., Ltd.) PEI: polyethyleneimine having the structure shown in Table 1 (average molecular weight 600; manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (Porous materials) 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 diameter: 10 nm, pore volume: 0.8 cm ３ / g

[0096] It can be seen from Table 1 that the carbon dioxide absorbent of the present invention has a high retention rate of carbon dioxide absorption capacity and is therefore excellent in repeated usability. Furthermore, it can be seen from Tables 2 and 3 that the carbon dioxide absorbent of the present invention has a high retention rate of carbon dioxide absorption capacity and is excellent in repeated usability even when used repeatedly using a mixed gas containing water vapor in addition to carbon dioxide.

[0097] Next, in Tables 5 to 7, the correlation between the pore size and pore volume of the porous material used and the carbon dioxide absorption rate and carbon dioxide absorption capacity of the carbon dioxide absorbent was evaluated.

[0098] Examples 4 to 9 (Evaluation of Carbon Dioxide Absorption Rate and Carbon Dioxide Absorption Capacity of Carbon Dioxide Absorbent) 15 mg of the amine compound (A) shown in Table 5, 10 g of methanol, and 1,350 mg of the porous material (B) shown in Table 5 were added to a nitrogen-purged glass container and stirred for 10 hours to homogenize. The resulting mixture was then placed in an environment of 40°C and 100 hPa to distill off the methanol, and then vacuum dried at room temperature (23°C) for 24 hours to obtain a carbon dioxide absorbent. (Measurement of Carbon Dioxide Absorption Rate) A 90 mm inner diameter Petri dish containing 500 mg of the resulting carbon dioxide absorbent and a carbon dioxide concentration meter ("TR-76UI" manufactured by T&D Corporation) were placed in a 25 L vacuum desiccator and held in a constant temperature and humidity chamber at 23°C and 50% RH for 1 hour. The change in carbon dioxide concentration (ppm) was calculated as the carbon dioxide absorption rate (ppm / h). The results are shown in Table 5. (Measurement of carbon dioxide absorption capacity) 15 mg of the obtained carbon dioxide absorbent was placed in a differential thermogravimetry meter ("EXSTER TGD6200" manufactured by Hitachi High-Tech Corporation) and allowed to stand for 6 hours at 45°C in a dry air environment, and the increase in mass of the solid carbon dioxide absorbent was measured. Here, air (flow rate: 200 mL / min) was used as the gas used during carbon dioxide absorption. The increase in mass of the carbon dioxide absorbent was taken as the carbon dioxide absorption capacity (mg), and the carbon dioxide absorption capacity per 1 g of carbon dioxide absorbent (mg / g) is shown in Table 5.

[0099] Examples 10 to 15 Carbon dioxide absorbents were prepared and evaluated in the same manner as in Examples 4 to 9, except that the amine compound (A) and porous material (B) shown in Table 6 were used and the amount of amine compound (A) used was changed to 330 mg and the amount of porous material (B) used was changed to 1,000 mg. The results are shown in Table 6.

[0100] Examples 16 to 21 Carbon dioxide absorbents were prepared and evaluated in the same manner as in Examples 4 to 9, except that the amine compound (A) and porous material (B) shown in Table 7 were used, and the amount of amine compound (A) used was changed to 600 mg and the amount of porous material (B) used was changed to 900 mg. The results are shown in Table 7. The grade of the porous material (B) used in Examples 4 to 21 is shown in Table 4.

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[0105] In Tables 5 to 7, the following amine compounds and porous materials were used. (Amine compounds) P-MIBPA: Amine compound obtained in Synthesis Example 1 (Porous materials) Q3: Porous silica particles "CARiACT Q3" (manufactured by Fuji Silysia Chemical Ltd.) Q6: Porous silica particles "CARiACT Q6" (manufactured by Fuji Silysia Chemical Ltd.) Q10: Porous silica particles "CARiACT Q10" (manufactured by Fuji Silysia Chemical Ltd.) Q15: Porous silica particles "CARiACT Q15" (manufactured by Fuji Silysia Chemical Ltd.) Q30: Porous silica particles "CARiACT Q30" (manufactured by Fuji Silysia Chemical Ltd.) Q50: Porous silica particles "CARiACT Q50" (manufactured by Fuji Silysia Chemical Ltd.)

[0106] Tables 5 to 7 show that when the pore diameter of the porous material (B) used is 5 nm or more, preferably 10 nm or more, the carbon dioxide absorption rate and carbon dioxide absorption capacity are better, regardless of the content of the amine compound (A). This is thought to be because when the pore diameter of the porous material (B) used is 5 nm or more, preferably 10 nm or more, it is possible to avoid the phenomenon in which the supported amine compound (A) blocks the pores in the porous material (B) and interferes with the flow path of carbon dioxide. From this perspective, it can be said that the pore embedding rate of the carbon dioxide absorbent is preferably 90% or less. Similarly, when the pore volume of the porous material (B) used is 0.5 cm３ / g or more, preferably 0.7 cm ３ / g or more, more preferably 0.8 cm ３ / g or more, more preferably 1.0 cm ３ / g or more, the carbon dioxide absorption rate and carbon dioxide absorption capacity are better.

[0107] According to the present invention, it is possible to provide a carbon dioxide absorbent that has good carbon dioxide absorption properties and is particularly excellent in terms of reusability, a carbon dioxide recovery method using the carbon dioxide absorbent, and a carbon dioxide separation and recovery apparatus.

[0108] 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) and a porous material (B): 【Chemistry 1】 In formula (1), R 1 are each independently a hydroxy group or an organic group having 1 to 10 carbon atoms, n1 to n4 are each independently a number from 1 to 8, and m is a number from 0 to 10.

2. 2. The carbon dioxide absorbent according to claim 1, wherein in the general formula (1), n1 to n4 each independently represent a number from 3 to 8, and m represents a number from 1 to 10.

3. The carbon dioxide absorbent according to claim 1, wherein n1 to n4 in the general formula (1) are all 3.

4. The carbon dioxide absorbent according to claim 1, wherein at least a portion of the amine compound (A) is supported on the porous material (B).

5. The carbon dioxide absorbent according to claim 1, wherein the porous material (B) comprises at least one selected from the group consisting of porous silica and porous alumina.

6. The carbon dioxide absorbent according to claim 1 , wherein the porous material (B) is in a particulate form.

7. The volume median particle diameter (D ５０ 7. The carbon dioxide absorbent according to claim 6, wherein the particle size is 1 μm or more and 500 μm or less.

8. The specific surface area of ​​the porous material (B) measured by the BET method is 2 m ２ / g or more 3000m ２ The carbon dioxide absorbent according to claim 1, wherein the carbon dioxide absorbent has a molecular weight of 1 / g or less.

9. The carbon dioxide absorbent according to claim 1, wherein the pore size of the porous material (B) is 5 nm or more.

10. The pore volume of the porous material (B) is 0.1 cm ３ / g or more 5.0cm ３ The carbon dioxide absorbent according to claim 1, wherein the carbon dioxide absorbent has a molecular weight of 1 / g or less.

11. 2. The carbon dioxide absorbent according to claim 1, wherein a content of the amine compound (A) in the carbon dioxide absorbent is 0.1 parts by mass or more and 1000 parts by mass or less relative to 100 parts by mass of the porous material (B).

12. The carbon dioxide absorbent according to claim 4, wherein the pore embedding rate of the carbon dioxide absorbent calculated by the following formula is 90% or less. Pore ​​embedding rate (%) of carbon dioxide absorbent = {pore volume (cm) of porous material (B)} ３ / g) - pore volume of carbon dioxide absorbent (cm ３ / g)} / pore volume of porous material (B) (cm ３ / g) × 100

13. A method for recovering carbon dioxide, which uses the carbon dioxide absorbent according to any one of claims 1 to 12.

14. The method according to claim 13, 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 at least one step selected from the group consisting of the following (I) to (III): (I) A step of subjecting the carbon dioxide absorbent having absorbed carbon dioxide to reduced pressure conditions (II) A step of contacting the carbon dioxide absorbent having absorbed carbon dioxide with an inert gas not containing carbon dioxide. (III) A step of heating the carbon dioxide absorbent having absorbed carbon dioxide.

15. 13. 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 12 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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