JP7806977B2 - Carbon dioxide absorbent, carbon dioxide capture method, and carbon dioxide separation and capture device - Google Patents

Description

The present invention relates to a carbon dioxide absorbent, a carbon dioxide recovery method, and a carbon dioxide separation and recovery device.

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 (approximately 10 to 30% by volume) carbon dioxide from exhaust gases emitted from thermal power plants and stores the carbon dioxide by burying it underground or in the sea. Technologies related to carbon dioxide absorbents used in CCS include those described in Patent Documents 1 and 2, for example.
Patent Document 1 describes a method for recovering carbon dioxide using specific alkanolamines as a carbon dioxide absorbent. Patent Document 2 describes the use of a carbon dioxide absorbing solution containing a carbon dioxide chemically absorbing amine having a nitrogen-hydrogen bond and a tertiary amine solvent having no nitrogen-hydrogen bond as a carbon dioxide absorbent.

As described in Patent Documents 1 and 2, many techniques using alkanolamines as carbon dioxide absorbents for use in CCS are known.
In response to this, a technology called Direct Air Capture (DAC) that directly captures low-concentration carbon dioxide (approximately 0.04% by volume) in the air has recently been attracting 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.

Various techniques relating to DAC have also been investigated. For example, Patent Document 3 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 4 discloses a carbon dioxide absorbent containing a predetermined amount or more of a polyamine compound having an alicyclic hydrocarbon structure.
Patent Document 5 discloses a carbon dioxide absorbent containing a predetermined amount or more of an amine compound having a predetermined heterocyclic structure.
Furthermore, Patent Document 6 discloses a carbon dioxide absorbent containing a specific cyclic amine compound and a porous material.

Japanese Patent Application Laid-Open No. 2008-13400 JP 2017-104776 A JP 2017-031046 A International Publication No. 2022/138302 International Publication No. 2022/163209 International Publication No. 2023/013397

The carbon dioxide absorbent disclosed in Patent Document 6 is a solid absorbent in which an amine compound is supported on a porous material.
When reusing a solid absorbent, a method such as steam stripping is usually used to desorb carbon dioxide from the absorbent after absorbing carbon dioxide. However, when the amine compounds disclosed in Patent Documents 1 to 6 are used, there is a risk that the amine compound will elute from the porous material during steam stripping or that the amine compound will volatilize due to heating during steam stripping. As such, there is room for further improvement in the reusability of conventionally known carbon dioxide absorbents.
An object of the present invention is to provide a carbon dioxide absorbent that is excellent in carbon dioxide absorption properties and reusability, a carbon dioxide recovery method using the same, and a carbon dioxide separation and recovery apparatus.

The present inventors have found that the above problems can be solved by using a carbon dioxide absorbent containing a specific solid amine compound.
That is, the present invention relates to the following.
[1] A carbon dioxide absorbent comprising a non-azo solid amine compound (A) having two or more aromatic rings and two or more primary amino groups.
[2] The carbon dioxide absorbent according to [1], wherein the amine compound (A) is a non-polymer compound.
[3] The carbon dioxide absorbent according to [1] or [2], wherein the amine compound (A) is an amine compound represented by the following general formula (1):

In formula (1), X and Y each independently represent a single bond or an oxygen atom, n and m each independently represent a number from 1 to 6, and p represents a number from 0 to 2.
[4] The carbon dioxide absorbent according to [3], wherein the amine compound represented by the general formula (1) is any one of compounds represented by the following formulas (1-1) to (1-3):

[5] The carbon dioxide absorbent according to any one of [1] to [4], wherein the carbon dioxide absorbent comprises the amine compound (A) and a porous material (B), and at least a part of the amine compound (A) is supported on the porous material (B).
[6] The carbon dioxide absorbent according to [5], wherein the porous material (B) contains at least one selected from the group consisting of porous silica and porous alumina.
[7] A method for recovering carbon dioxide using the carbon dioxide absorbent according to any one of [1] to [6].
[8] The method according to [7], 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 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. [9] 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 [1] to [6] into contact with a gas containing carbon dioxide, thereby causing the carbon dioxide absorbent to absorb carbon dioxide; and a desorption device equipped with a mechanism for desorbing carbon dioxide from the carbon dioxide absorbent that has absorbed carbon dioxide.

The present invention provides a carbon dioxide absorbent that has excellent carbon dioxide absorption properties and reusability, a carbon dioxide recovery method using the same, and a carbon dioxide separation and recovery device.

1 is a schematic diagram showing one embodiment of a carbon dioxide separation and capture apparatus of the present invention. 1 is a graph showing the results of evaluating the carbon dioxide absorbency of the carbon dioxide absorbents of Examples 1 to 6.

[Definition]
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 preferred definitions can be adopted arbitrarily, and it can be said that a combination of preferred definitions is more preferred. In the present embodiment, the description "XX to YY" means "XX or more and YY or less."

In this specification, "good carbon dioxide absorbency" means that the carbon dioxide absorbent has a large carbon dioxide absorption amount. Also, "good carbon dioxide absorbency in air" means that the absorbent has a large absorption amount of carbon dioxide at a low concentration (about 0.04% by volume) in air.
In this specification, "excellent repetitive usability" means that when a carbon dioxide absorption-desorption cycle test is conducted, the mass retention rate of the carbon dioxide absorbent and the retention rate of the carbon dioxide absorption amount are both high.

[Carbon dioxide absorbent]
The carbon dioxide absorbent of the present invention contains a non-azo solid amine compound (A) (hereinafter, also simply referred to as "amine compound (A)") having two or more aromatic rings and two or more primary amino groups.
The carbon dioxide absorbent of the present invention has the above-mentioned configuration, and is therefore excellent in carbon dioxide absorption property and repeated usability. In particular, the carbon dioxide absorbent of the present invention is excellent in repeated usability even when a steam stripping method is used to desorb carbon dioxide from the absorbent after carbon dioxide absorption.
Furthermore, the carbon dioxide absorbent of the present invention exhibits good carbon dioxide absorption properties even in air with a low carbon dioxide concentration of about 0.04% by volume, and can therefore 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 recovering carbon dioxide from gas having a low carbon dioxide concentration of 0.01% by volume or more and 1% by volume or less.

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 structure having an aromatic ring and two or more primary amino groups, and it is thought that the amino groups react with carbon dioxide to easily form a carbonate, thereby exhibiting excellent carbon dioxide absorbency.
When the amine compound (A) has two or more aromatic rings, the melting point of the amine compound (A) increases, making it more likely to become a solid amine, and its solubility in water decreases. This improves the reusability of the carbon dioxide absorbent, and in particular, even when a steam stripping method is used to desorb carbon dioxide after absorbing carbon dioxide, the amine compound (A) is less likely to elute, resulting in a carbon dioxide absorbent with excellent reusability. Furthermore, the amine compound (A) must be a non-azo compound in order to be applicable to a method using a heating means, such as a steam stripping method, when desorbing carbon dioxide, and to avoid denaturation due to photoreaction.

<Amine Compound (A)>
The amine compound (A) is a non-azo solid amine compound having two or more aromatic rings and two or more primary amino groups.
As used herein, the term "primary amino group" refers to an amino group having two hydrogen atoms on the nitrogen atom, ie, an _--NH.sub.2 group.
In this specification, the term "non-azo compound" refers to a compound that does not contain an azo bond (-N=N-) in the molecule.
As used herein, the term "solid amine compound" refers to an amine compound that has a melting point of more than 25°C and is solid at 25°C.

From the viewpoint of improving reusability, the melting point of the amine compound (A) is preferably 50° C. or higher, more preferably 80° C. or higher, even more preferably 100° C. or higher, still more preferably 110° C. or higher, and still more preferably 120° C. or higher. There is no particular upper limit, but from the viewpoint of improving carbon dioxide absorption ability and improving supportability on the porous material (B) described below, the melting point is preferably 300° C. or lower, more preferably 280° C. or lower, even more preferably 250° C. or lower, still more preferably 200° C. or lower, still more preferably 180° C. or lower, still more preferably 160° C. or lower, and still more preferably 150° C. or lower.
The melting point of the amine compound (A) can be measured specifically by the method described in the Examples.

From the viewpoints of improving carbon dioxide absorption and reusability, the amine compound (A) has two or more aromatic rings. From the viewpoints of improving carbon dioxide absorption and reusability, and of facilitating carbon dioxide desorption, the number of aromatic rings in the amine compound (A) is preferably 2 to 10, more preferably 2 to 6, even more preferably 2 to 4, still more preferably 2 to 3, and even more preferably 2.

The number of amino groups in the amine compound (A) is 2 or more from the viewpoint of improving carbon dioxide absorbency, and is preferably 8 or less, more preferably 6 or less, even more preferably 4 or less, and still more preferably 3 or less from the viewpoint of reducing water solubility and improving repeated useability.
The number of primary amino groups in the amine compound (A) is 2 or more from the viewpoint of improving carbon dioxide absorbency, and is preferably 8 or less, more preferably 6 or less, even more preferably 4 or less, and still more preferably 3 or less from the viewpoint of reducing water solubility and improving repeated useability.

From the viewpoint of improving carbon dioxide absorption, amine compound (A) preferably contains primary amino groups in an amount of 30 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, even more preferably 60 mol% or more, even more preferably 70 mol% or more, even more preferably 80 mol% or more, and even more preferably 90 mol% or more, but not more than 100 mol%, relative to the total amino groups contained in amine compound (A).

The amine compound (A) is preferably a non-polymer compound from the viewpoint of improving carbon dioxide absorption and reusability, and from the viewpoint of improving supportability on the porous material (B) described below.
As used herein, the term "non-polymer compound" refers to a low-molecular-weight compound, and specifically refers to a compound having a molecular weight of 1,000 or less. From the viewpoint of improving carbon dioxide absorption and supporting ability in the porous material (B), the molecular weight of the amine compound (A) is preferably 800 or less, more preferably 700 or less, even more preferably 600 or less, still more preferably 500 or less, still more preferably 400 or less, and still more preferably 350 or less, and from the viewpoint of improving reusability, it is preferably 212 or more.

From the viewpoint of improving the carbon dioxide desorption property and further improving the reusability, the maximum carbon dioxide dissociation temperature of the amine compound (A) is preferably 280° C. or lower, more preferably 250° C. or lower, even more preferably 200° C. or lower, still more preferably 180° C. or lower, and still more preferably 150° C. or lower. The lower limit of the maximum carbon dioxide dissociation temperature is not particularly limited, but is, for example, 40° C. or higher, preferably 80° C. or higher, and more preferably 100° C. or higher.
The maximum carbon dioxide dissociation temperature is a value measured by the following method.
The 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 desorption of carbon dioxide 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 the amine compound (A) to stand in air at 23°C and 50% RH for 24 hours.

From the viewpoint of improving carbon dioxide absorption and reusability, the amine compound (A) is preferably an amine compound represented by the following general formula (1):

In formula (1), X and Y each independently represent a single bond or an oxygen atom, n and m each independently represent a number from 1 to 6, and p represents a number from 0 to 2.

X and Y in formula (1) may be the same or different, but from the perspective of ease of production, they are preferably the same. That is, X and Y in formula (1) are preferably both single bonds or both oxygen atoms.

In formula (1), n and m may be the same or different, but are preferably the same from the viewpoint of ease of production. From the viewpoint of improving carbon dioxide absorption, n and m are preferably 1 to 4, more preferably 1 to 3, even more preferably 1 or 2, and still more preferably 1.
In formula (1), p is preferably 0 or 1, and more preferably 0, from the viewpoint of improving carbon dioxide absorption capacity and reusability.
When p is 2, X and Y in formula (1) are preferably oxygen atoms.

The amine compound represented by the general formula (1) is preferably any of the compounds represented by the following formulas (1-1) to (1-3) from the viewpoint of improving carbon dioxide absorbency and repeated use, and from the viewpoint of ease of production, and is more preferably a compound represented by the following formula (1-1) or (1-2), and even more preferably a compound represented by the following formula (1-2).

The amine compound (A) may be used alone or in combination of two or more.
The amine compound (A) can be produced by a known method, and commercially available products can also be used.

From the viewpoint of improving carbon dioxide absorption and repeated use, the content of amine compound (A) in all amine compounds in the carbon dioxide absorbent of the present invention 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, even more preferably 90% by mass or more, still more preferably 95% by mass or more, and even more preferably 98% by mass or more, but not more than 100% by mass.

From the viewpoint of improving carbon dioxide absorbency, the content of 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, even more preferably 45% by mass or more, and still more preferably 50% by mass or more, but not more than 100% by mass. Furthermore, when the carbon dioxide absorbent contains a porous material (B) described below, from the viewpoint of improving carbon dioxide absorbency, the content of amine compound (A) in the carbon dioxide absorbent is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

From the viewpoint of further improving carbon dioxide absorbency and enabling carbon dioxide desorption with lower energy after carbon dioxide absorption, the carbon dioxide absorbent of the present invention preferably contains an amine compound (A) and a porous material (B), and at least a part of the amine compound (A) is supported on the porous material (B).
The reason why the carbon dioxide absorbency is improved when the carbon dioxide absorbent contains an amine compound (A) and a porous material (B) and at least a portion of the amine compound (A) is supported on the porous material (B) is presumably because the surface area of the portion of the solid amine compound (A) that can come into contact with carbon dioxide is increased. Also, depending on the type of amine compound (A), the bonding state between the amine compound (A) and carbon dioxide changes, and the maximum carbon dioxide dissociation temperature of the carbon dioxide absorbent is lower than when the amine compound (A) is used alone. This is thought to enable carbon dioxide desorption under lower energy conditions.

<Porous material (B)>
The porous material (B) is preferably one that can support the amine compound (A) and can withstand the conditions for carbon dioxide recovery, 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 enabling carbon dioxide desorption with lower energy after carbon dioxide absorption, 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 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, from the viewpoint of further improving carbon dioxide absorbency and enabling carbon dioxide to be desorbed with less energy after carbon dioxide absorption.

The porous material (B) is preferably in a particulate form. This increases the specific surface area of the porous material (B) and improves the amount of amine compound (A) supported, thereby further improving the carbon dioxide absorption capacity of the carbon dioxide absorbent.

The volume median particle diameter (D ₅₀ ) of the porous material (B) as measured by laser diffraction/scattering particle size distribution measurement 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 further improving the amount of the amine compound (A) supported.

The specific surface area of the porous material (B) measured by the BET method is preferably 2 m ² /g or more, more preferably 10 m 2 /g or more, even more preferably 100 m ² /g or more, still more preferably 200 m ² /g or more, still more preferably 400 m ² /g or more, and still more preferably 600 m ² /g or more, from the viewpoint of further improving the amount of amine compound (A) supported, and is preferably 3000 ^{m 2} /g or less, more preferably 1500 m ² /g or less, still more preferably 1200 m ² /g or less, and still more preferably 1000 m ² /g or less, from the viewpoint of improving handleability.

The pore volume of the porous material (B) is preferably 0.1 cm ³ /g or more, more preferably 0.3 cm ³ /g or more, and even more preferably 0.5 cm 3 /g or more, from the viewpoint of further improving the amount of amine compound (A) supported, and is preferably 5.0 cm ³ /g or less, more preferably 3.0 cm ³ /g or less, even more preferably 2.5 cm ³ /g or less, still more preferably 2.0 cm ³ /g or less, still more preferably 1.5 cm ³ /g or less, and even more preferably 1.0 cm ³ /g or less, from the viewpoint of improving ^repeated usability.
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.

Porous material (B) may be obtained by granulating the particulate porous material using a known method to form pellets, tablets, or other granulated products. Examples of granulation methods include dry granulation using a compression molding machine and wet granulation using a binder. Granulating and using particulate porous material can impart vibration resistance and abrasion resistance, and improve physical stability.

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 further improving carbon dioxide absorbency and enabling carbon dioxide desorption with less energy after carbon dioxide absorption, preferably 10 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, even more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, per 100 parts by mass of the porous material (B); and is preferably 1,000 parts by mass or less, more preferably 500 parts by mass or less, even more preferably 250 parts by mass or less, even more preferably 200 parts by mass or less, even more preferably 150 parts by mass or less, and even more preferably 120 parts by mass or less.

When the carbon dioxide absorbent contains an amine compound (A) and a porous material (B), the total content of the amine compound (A) and the porous material (B) in the carbon dioxide absorbent is, from the viewpoint of further improving carbon dioxide absorbency and enabling carbon dioxide desorption with less energy after carbon dioxide absorption, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 98% by mass or more, but not more than 100% by mass, when the total amount of the carbon dioxide absorbent is taken as 100% by mass.

<Other ingredients>
The carbon dioxide absorbent may contain appropriate components other than the amine compound (A) and the porous material (B) within a range that does not impair the effects of the invention. 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.).

From the perspective of improving carbon dioxide absorption capacity 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, even more preferably 0.5% by mass or less, even 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 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 small amounts of water as an impurity.

When the carbon dioxide absorbent contains the amine compound (A) and the porous material (B), the melting point of the carbon dioxide absorbent is, from the viewpoint of improving repeated use, preferably 50° C. or higher, more preferably 80° C. or higher, even more preferably 100° C. or higher, still more preferably 110° C. or higher, and still more preferably 120° C. or higher. There is no particular upper limit, but, from the viewpoint of improving carbon dioxide absorbency, it is preferably 300° C. or lower, more preferably 280° C. or lower, even more preferably 250° C. or lower, still more preferably 200° C. or lower, still more preferably 180° C. or lower, still more preferably 160° C. or lower, and still more preferably 150° C. or lower.
The melting point of the carbon dioxide absorbent can be measured by the same method as above.

When the carbon dioxide absorbent contains the amine compound (A) and the porous material (B), from the viewpoint of improving the carbon dioxide desorption property and further improving the reusability, the maximum carbon dioxide dissociation temperature of the carbon dioxide absorbent is preferably 200° C. or lower, more preferably 180° C. or lower, even more preferably 160° C. or lower, and still more preferably 150° C. or lower. The lower limit of the maximum carbon dioxide dissociation temperature is not particularly limited, but is, for example, 40° C. or higher, preferably 80° C. or higher, and more preferably 100° C. or higher.
The maximum carbon dioxide dissociation temperature can be measured by the same method as above.

From the viewpoint of enabling carbon dioxide desorption at a temperature lower than the melting point of the carbon dioxide absorbent, the melting point of the carbon dioxide absorbent is preferably a temperature higher than the maximum carbon dioxide dissociation temperature of the carbon dioxide absorbent.
Furthermore, it is preferable that the difference between the melting point of the carbon dioxide absorbent and the maximum carbon dioxide dissociation temperature of the carbon dioxide absorbent is large. If the difference between the melting point of the carbon dioxide absorbent and the maximum carbon dioxide dissociation temperature is small, the carbon dioxide absorbent may melt and aggregate simultaneously with desorption of carbon dioxide, reducing the surface area and decreasing the carbon dioxide absorbency. However, if the difference between the melting point of the carbon dioxide absorbent and the maximum carbon dioxide dissociation temperature is large, carbon dioxide desorption at a temperature lower than the melting point of the carbon dioxide absorbent is possible, and a decrease in carbon dioxide absorbency due to melting of the carbon dioxide absorbent can be avoided.
The difference between the melting point of the carbon dioxide absorbent and the maximum carbon dioxide dissociation temperature (melting point of the carbon dioxide absorbent - maximum carbon dioxide dissociation temperature of the carbon dioxide absorbent) is preferably 5°C or more, more preferably 10°C or more, and even more preferably 20°C or more, from the viewpoint of further improving carbon dioxide absorbability and enabling carbon dioxide to be desorbed with lower energy after carbon dioxide absorption.

When the carbon dioxide absorbent contains the amine compound (A) and the porous material (B), the method for preparing the carbon dioxide absorbent is not particularly limited, and a known method 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 part of the amine compound (A) is supported on the porous material (B), the carbon dioxide absorbent can be preferably prepared by the following method.
First, an amine compound (A) is dissolved in an organic solvent, and then a porous material (B) is added thereto, followed by stirring for 1 to 24 hours at a temperature preferably from 5 to 60° C. 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 a carbon dioxide absorbent.
As the organic solvent, from the viewpoint 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 preferable, and at least one selected from the group consisting of dichloromethane, methanol, ethanol, and isopropyl alcohol is more preferable.

[Method for capturing carbon dioxide]
The carbon dioxide recovery method 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 in a technology for directly capturing carbon dioxide from air (DAC).
In addition, it becomes possible to recover carbon dioxide with lower energy, and further, even when a steam stripping method is used to desorb carbon dioxide from the absorbent after absorbing carbon dioxide, the reusability of the carbon dioxide absorbent can be improved.

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.

<Absorption process>
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.

Gases containing carbon dioxide are not particularly limited, but examples include air, exhaust gas from thermal power plants, steel mills, cement factories, chemical plants, biofermentation gas, and natural gas. There is a particular need to recover carbon dioxide from these gases in an energy-saving manner, and the present invention is particularly effective for this purpose. The carbon dioxide concentration in the gas, the gas pressure, and the gas temperature 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 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 a known process for removing other acidic gases. Specifically, examples include an embodiment in which the carbon dioxide recovery method of the present invention is applied to a gas containing acidic gases other than carbon dioxide, or an embodiment in which the other acidic gases are removed from a gas containing acidic gases other than carbon dioxide by known means and then the carbon dioxide recovery method of the present invention is applied.
From the viewpoint of improving the efficiency of separating and recovering carbon dioxide, the relative humidity (RH) of the carbon dioxide-containing gas is preferably 30% RH or higher, more preferably 35% RH or higher, and even more preferably 40% RH or higher, and is preferably 70% RH or lower, more preferably 65% RH or lower, and even more preferably 60% RH or lower. In this specification, a gas with a RH of less than 30% is defined as a dry gas.

In the absorption process, the temperature at which 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 amount of carbon dioxide absorbed, it is preferably at least 0°C and less than 60°C, and more preferably at least 20°C and less than 60°C.

More preferably, the method of the present invention 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, wherein the desorption step comprises at least one step selected from the group consisting of the following (I) to (III): By this method, carbon dioxide can be easily separated and recovered from a gas containing carbon dioxide.
(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; and (III) a step of heating the carbon dioxide absorbent having absorbed carbon dioxide.

<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). Two or more of the steps (I) to (III) may be combined.
Furthermore, from the viewpoint of the effectiveness of using the carbon dioxide absorbent of the present invention, the desorption step preferably includes the step (III). Since the carbon dioxide absorbent of the present invention includes a solid amine compound (A), even when heating is performed in the desorption step, the mass retention rate and the retention rate of the carbon dioxide absorption amount of the carbon dioxide absorbent can be maintained within a high range.

(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 separation and recovery of carbon dioxide.
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 improving the efficiency of separating and recovering carbon dioxide, the temperature 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, the temperature is preferably lower than 50° C., more preferably 45° C. or lower.

(II) In the step of contacting a carbon dioxide absorbent having carbon dioxide absorbed therein 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 the group consisting of nitrogen and argon.
In the step (II), examples of the method for contacting the carbon dioxide absorbent with the inert gas not containing carbon dioxide include the same contact methods as those described in the absorption step.
In step (II), the temperature at which the carbon dioxide-free inert gas is brought into contact with the carbon dioxide absorbent is not particularly limited, and the heating specified in step (III) may be carried out simultaneously in step (II), or the temperature may be room temperature or lower. From the viewpoint of suppressing thermal degradation of the amine compound (A) in the carbon dioxide absorbent, the temperature is preferably less than 50°C, more preferably 45°C or lower. Furthermore, 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.

(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)") can be selected appropriately depending on the melting point and maximum carbon dioxide dissociation temperature of the carbon dioxide absorbent, but from the viewpoint of improving the efficiency of carbon dioxide separation and recovery, it is preferably 50°C or higher, more preferably 55°C or higher, even more preferably 60°C or higher, still more preferably 70°C or higher, and even more preferably 80°C or higher. Furthermore, from the viewpoint of improving the reusability of the carbon dioxide absorbent, it is preferably 250°C or lower, more preferably 230°C or lower, even more preferably 220°C or lower, still more preferably 200°C or lower, and even more preferably 180°C or lower.

The heating in step (III) can be carried out by a known method using an apparatus equipped with a heating means. Examples of heating methods include heating with steam or a heat medium, hot air heating, electromagnetic wave heating, ultrasonic heating, and induction heating.

In the method of the present invention, a carbon dioxide absorbent containing a solid, low-water-soluble amine compound (A) is used, and therefore a steam stripping method is preferably used in step (III). The steam stripping method can be carried out by heating the carbon dioxide absorbent that has absorbed carbon dioxide in a steam atmosphere. The heating temperature in the steam stripping method is preferably 80°C or higher, more preferably 90°C or higher. From the viewpoint of improving the reusability of the carbon dioxide absorbent, the heating temperature is preferably 250°C or lower, more preferably 230°C or lower, even more preferably 220°C or lower, still more preferably 200°C or lower, and even more preferably 180°C or lower.

The carbon dioxide absorbent and carbon dioxide separated in the desorption process can be recovered separately and reused.

[Carbon dioxide capture equipment]
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 device equipped with a mechanism for bringing the carbon dioxide absorbent into contact with a gas containing carbon dioxide, 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.

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

<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.

The absorption device 1 is not particularly limited as long as it has a configuration that allows contact between the carbon dioxide absorbent and 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 may include an absorbent holding unit 12 that holds carbon dioxide absorbent 12a inside a reaction tower 11, and a gas supply unit 13 that supplies a gas containing carbon dioxide to the absorbent holding unit 12. Furthermore, from the perspective 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 may also include 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.

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. It 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.

The carbon dioxide separation and capture system 100 may have a connection section 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 unit 12 of the absorption device 1 to the desorption device 2 using the connection unit 3.

<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 the desorption device 2 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.

1 , the desorption device 2 can include, inside the reaction tower 21, an absorbent holding section 22 that holds a carbon dioxide absorbent 22a that has absorbed carbon dioxide, and can further include a gas discharge section 23 that discharges the carbon dioxide desorbed from the carbon dioxide absorbent. The desorption device 2 also includes at least one mechanism (not shown) selected from a decompression mechanism for creating a decompression 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.
The desorption device 2 may be equipped with a carbon dioxide concentration measurement mechanism and the like, similar to the absorption device 1, in addition to the pressure reduction mechanism, inert gas supply mechanism, and heating mechanism.

The carbon dioxide absorbent after desorption of 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 desorption of carbon dioxide to the absorption device 1, and can be reused.

The carbon dioxide 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 applications, 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.

The present invention will be described below using examples, but the present invention is not limited to the scope of the examples. In these examples, various measurements and evaluations were performed using the following methods.

(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).

(Volume Median Particle Diameter ( _D50 ) of Porous Material)
The particle size distribution of the porous material was measured using a laser diffraction/scattering particle size distribution analyzer ("LMS-200e" manufactured by Malvern Instruments).
The particle size corresponding to a cumulative volume frequency of 50%, calculated from the smaller particle size in the particle distribution, was taken as the volume median particle size (D ₅₀ ) of the porous material.

(Carbon dioxide (CO ₂ ) absorption ability of carbon dioxide absorbent)
A carbon dioxide concentration meter and a petri dish were placed in an openable desiccator (inner dimensions: 370 mm × 260 mm × 272 mm) in an air environment of 23°C and 50% RH. Thereafter, a carbon dioxide absorbent was added to the petri dish in the desiccator in an amount such that the number of amino groups in the amine compound contained in the carbon dioxide absorbent was 10 mmol (5 mmol of the amine compound in this example), and the door was immediately closed, and the carbon dioxide absorbent was left to stand in the desiccator.
The carbon dioxide concentration (ppm) in the desiccator after a certain time had elapsed was measured using a _CO2 concentration meter ("CO2/Temperature/Humidity Data Logger TR-76Ui" manufactured by T&D Corporation), and the carbon dioxide absorption ability of the carbon dioxide absorbent was evaluated based on this concentration. Figure 2 shows a graph plotting the carbon dioxide concentration (ppm) in the desiccator on the vertical axis and the elapsed time (min) on the horizontal axis. The greater the decrease in carbon dioxide concentration, the higher the carbon dioxide absorption ability of the carbon dioxide absorbent.

(Maximum carbon dioxide (CO ₂ ) dissociation temperature of carbon dioxide absorbent)
A carbon dioxide concentration meter and a petri dish were placed in an openable desiccator (internal dimensions: 370 mm x 260 mm x 272 mm) under an air environment of 23°C and 50% RH. Then, a carbon dioxide absorbent was added to the petri dish in an amount such that the number of amino groups in the amine compound contained in the carbon dioxide absorbent was 10 mmol (5 mmol of amine compound in this example). The door was immediately closed, and the carbon dioxide absorbent was left to stand in the desiccator for 24 hours. The initial carbon dioxide concentration was adjusted to approximately 400 ppm.
Next, the carbon dioxide absorbent was taken out from the desiccator to obtain a carbon dioxide absorbent having absorbed carbon dioxide. The carbon dioxide absorbent having absorbed carbon dioxide was subjected to DSC measurement as follows to measure the maximum carbon dioxide dissociation temperature of the carbon dioxide absorbent.
First, differential scanning calorimetry was performed on the carbon dioxide absorbent using a differential thermogravimeter ("DTG-60" manufactured by Shimadzu Corporation) under conditions of a measurement temperature range of 23 to 250°C, a temperature rise rate of 10°C/min, and a nitrogen atmosphere. From the DSC curve obtained, the temperature at which the endothermic heat associated with carbon dioxide desorption was maximized was determined to be the maximum carbon dioxide dissociation temperature of the carbon dioxide absorbent.

(Melting point of carbon dioxide absorbent)
DSC measurement was carried out using a thermogravimetric differential scanning calorimeter ("STA200RV" manufactured by Hitachi, Ltd.). The measurement conditions were set as follows: nitrogen flow rate 50 mL/min, temperature rise rate 10°C/min, measurement temperature range 40-350°C, and measurement was carried out by weighing out approximately 16 mg of carbon dioxide absorbent. The maximum endothermic peak temperature in the obtained DSC chart was taken as the melting point.

(Moisture content of carbon dioxide absorbent after carbon dioxide absorption)
Measurement was performed using an autosampler moisture meter ("CA-310" manufactured by Nitto Seiko Analytech Co., Ltd.) The sample weight was 0.1 g, and the measurement conditions were a vaporization temperature of 105°C and a heating time of 20 minutes. The moisture content was calculated by dividing the sample weight by the sample weight before measurement × 100 (%).

(Solubility of amine compounds in water)
An aqueous solution was prepared so that the concentration of the amine compound was 0.1% by mass, and whether or not the amine compound was dissolved was visually observed at 25° C. A solution in which no residual amine compound was found was judged to be soluble, and a solution in which residual amine compound was found was judged to be soluble. These results are shown in Table 2 for Examples 1 to 3.

(Cycle test)
Using a TG-DTA device ("STA200RV" manufactured by Hitachi, Ltd.), a _CO2 absorption-desorption cycle test of the carbon dioxide absorbent was conducted using the temperature program shown in Table 1. Approximately 16 mg of carbon dioxide absorbent was placed in a deep aluminum pan, which was then set in the TG-DTA device. The temperature history of temperature programs No. 1 to 11 shown in Table 1 was applied, and a _CO2 absorption-desorption cycle test was conducted. The measurement atmosphere during each program run is shown in the "Gas" column in Table 1, and the flow rate of the gas is shown in the "Gas Flow Rate" column. "Moisture-absorbing Air" in Table 1 refers to air (30-70% RH) that has been subjected to a drying process and then immersed in water to adjust the humidity.
In Table 1, X (°C) corresponds to the regeneration temperature (°C) in the cycle test described below.

[ _CO2 absorption amount in the second cycle (mg/g)]
The _CO2 absorption amount (mg/g) in the second cycle was determined by dividing the weight increase (mg) of the absorbent at the end of Program No. 6 in Table 1 by the weight (g) of the absorbent at the start of Program No. 6. A larger value indicates better carbon dioxide absorption.

[Regeneration rate (%) of the second cycle of _CO2 absorption-desorption]
The weight (g) of the absorbent at the start of Program No. 6 in Table 1 divided by the weight (g) of the absorbent at the end of Program No. 8 was multiplied by 100 to obtain the regeneration rate (%) of the second _CO2 absorption-desorption cycle. A higher regeneration rate indicates better reusability.

[Mass retention rate (2nd cycle/3rd cycle) (%)]
The mass retention rate (second cycle/third cycle) (%) was calculated by dividing the weight (g) of the absorbent at the end of Program No. 11 in Table 1 by the weight (g) of the absorbent at the end of Program No. 8 x 100. A higher mass retention rate indicates better reusability.

[ _CO2 absorption retention rate (2nd cycle/3rd cycle) (%)]
The weight increase (mg) of the absorbent at the end of Program No. 6 in Table 1 divided by the weight (g) of the absorbent at the start of Program No. 6 was used as the _CO2 absorption amount Y (mg/g) in the second cycle. The weight increase (mg) of the absorbent at the end of Program No. 9 in Table 1 divided by the weight (g) of the absorbent at the start of Program No. 9 was used as the _CO2 absorption amount Z (mg/g) in the third cycle. Z/Y x 100 was used as the _CO2 absorption amount retention rate (second cycle/third cycle) (%). A higher retention rate indicates better reusability.

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

(amine compounds)
HQ-BA: A compound represented by the following formula (1-1) (C ₂₀ H ₂₀ N ₂ O ₂ , Mw: 320.4) Produced by the method described in Production Example 1 below.

DAMB: A compound represented by the following formula (1-2) (C ₁₄ H ₁₆ N ₂ , Mw: 212.3) Produced by the method described in Production Example 2 below.

TP-DMA: A compound represented by the following formula (1-3) (C ₂₀ H ₂₀ N ₂ , Mw: 288.4). It was synthesized according to the method described in J. Am. Chem. Soc., No. 136, Vol. 22, pp. 7899-7906 (2014).

Production Example 1 (Production of HQ-BA)
According to the method described in Polymer Degradation and Stability, Vol. 95, pp. 2445-2452 (2010), hydroquinone and 4-chlorobenzonitrile (4CBN) were reacted to synthesize a dinitrile compound (HQ-BEN) represented by the following structural formula. HQ-BEN was then hydrogenated by the following method to produce HQ-BA.

2.99 g of granular Raney cobalt catalyst was weighed in water and transferred to a 200 cc autoclave, where it was purged with isopropyl alcohol three times. After the substituted isopropyl alcohol was removed, 15 g of meta-xylene (solvent) and 6 g of HQ-BEN were added. After the autoclave was airtight, the pressure inside the autoclave was purged with nitrogen (1 MPaG) and hydrogen (5 MPaG) three times each.
Furthermore, 15 g of liquid ammonia was charged, and hydrogen was sealed in at 5 MPaG (including the self-pressure of the liquid ammonia). Heating was started while stirring at about 750 rpm, and the reaction was carried out at 80°C. The reaction time was set to 3 hours from the start of heating. After completion of the reaction, the mixture was cooled with ice water, and the hydrogen and ammonia were purged to reduce the pressure inside the system, and the autoclave was opened. The reaction liquid was washed with methanol to remove the catalyst, and then the solvent was distilled off using an evaporator to obtain the target product, HQ-BA.

Production Example 2 (Production of DAMB)
4,4'-Dicyanobiphenyl (DCB, reagent) was hydrogenated by the following method to produce 4,4-di(aminomethyl)biphenyl (DAMB).
3.0 g of granular Raney cobalt catalyst was weighed in water and transferred to a 100 mL autoclave, where it was reduced at atmospheric pressure under a hydrogen flow at 270°C for 2 hours. The catalyst was then transferred to a 200 mL autoclave whose atmosphere had been purged with argon, and a punched metal for catalyst fixation was installed. 10 g of meta-xylene (solvent) and 1.5 g of DCB (substrate) were added thereto, and the autoclave was airtight. The pressure inside the autoclave was then purged with nitrogen (1 MPaG) and hydrogen (10 MPaG) three times each.
Furthermore, 10 g of liquid ammonia was charged, and hydrogen was sealed in at 10 MPaG (including the liquid ammonia's own pressure). Heating was started while stirring at about 750 rpm, and the reaction was carried out for 1.5 hours after the internal temperature reached 80°C. After completion of the reaction, the autoclave was cooled with ice water, and hydrogen and ammonia were purged to reduce the pressure inside the system, and the autoclave was opened. The reaction liquid was washed with methanol to remove the catalyst, and the solvent was then distilled off using an evaporator to obtain the target product, DAMB.

MXDA: metaxylylenediamine (manufactured by Mitsubishi Gas Chemical Co., Inc.), a diamine represented by the following formula that is liquid at 25°C

Spirobisamine: 2,2'-(2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diyl)bis(2-methylpropan-1-amine) represented by the following formula, produced by the method described in Example 1 of WO 2022/255037.

(Porous material)
Mesoporous silica SBA15 (Merck)
BET specific surface area: 800 m ² /g, volume median particle diameter (D ₅₀ ): 100 μm, pore volume: 0.8 cm ³ /g
Pellet silica (pellets obtained by molding the raw silica below)
BET specific surface area: 253 m ² /g, average pellet diameter: 1.90 mm, average pellet length: 10.86 mm
Raw material silica ("CARIACT G-10" manufactured by Fuji Silysia Chemical Ltd., specific surface area: 300 m ² /g, particle size: 10 μm, pore volume: 1.3 mL/g, average pore size: 10 nm)

Examples 1 to 3 (Evaluation of carbon dioxide absorbents)
The amine compounds shown in Table 2 were used as carbon dioxide absorbents, and the carbon dioxide absorbency was evaluated by the above method. The results are shown in Figure 2. The maximum carbon dioxide dissociation temperature, melting point, and solubility in water were also evaluated by the above method.

Examples 4 to 6 (Preparation and Evaluation of Carbon Dioxide Absorbents)
(Preparation of carbon dioxide absorbent)
A nitrogen-purged glass container was charged with 1.5 g of the amine compound (A) shown in Table 2 and a large excess of methanol (dichloromethane in Examples 5 and 6), and the mixture was stirred with a stirrer at room temperature (23 ° C.) to dissolve the amine compound (A). Next, 1.5 g of the porous material was added, and the mixture was again purged with nitrogen, followed by stirring for 3 hours to achieve homogenization. Methanol or dichloromethane was distilled off from the resulting mixture at 40 ° C. under a reduced pressure of 50 hPa, and then the mixture was vacuum-dried at 80 ° C. for 3 hours to obtain a carbon dioxide absorbent in which the amine compound (A) was supported on the porous material (B).

(Evaluation of carbon dioxide absorbents)
The carbon dioxide (CO ₂ ) absorbency of the obtained carbon dioxide absorbent was evaluated by the above-mentioned method, and the results are shown in Figure 2. In addition, the carbon dioxide (CO ₂ ) maximum dissociation temperature, melting point, and moisture content after carbon dioxide absorption were measured by the above-mentioned method, and the results are shown in Table 2.

Comparative Example 1
In Example 1, MXDA (metaxylylenediamine) was used as the carbon dioxide absorbent instead of the amine compound (A), and the maximum carbon dioxide dissociation temperature, melting point, and solubility in water were evaluated using the above method. The maximum carbon dioxide dissociation temperature was 135°C, the melting point was 14°C, and the solubility in water was determined to be "yes." The carbon dioxide absorbent of Comparative Example 1 is a liquid at 25°C and dissolves in water, so if a steam stripping method is applied during regeneration of the absorbent, MXDA is likely to dissolve in steam, and it is thought that good repeated use is not possible.

Comparative Example 2
The carbon dioxide (CO ₂ ) absorption ability was evaluated by the above method using the spirobisamine as the carbon dioxide absorbent instead of the amine compound (A) in Example 1. However, the spirobisamine did not exhibit carbon dioxide absorption ability.

Comparative Example 3
An attempt was made to prepare a carbon dioxide absorbent in which the spirobisamine was supported on the porous material (B) in the same manner as in Example 4, except that the spirobisamine was used instead of the amine compound (A) in Example 4. However, since the spirobisamine had almost no solubility in solvents, it was not possible to support it on the porous material (B).

Figure 2 shows that the carbon dioxide absorbent of this example exhibited carbon dioxide absorption properties even in a system with a low carbon dioxide concentration (0.04 to 0.05% by mass). Furthermore, a comparison of Examples 1 to 3 with Examples 4 to 6 reveals that the carbon dioxide absorption properties of the amine compound (A) used in Examples 1 to 3 were further improved by supporting it on a porous material (B). This is presumably because the surface area of the portion of the amine compound (A) that can come into contact with carbon dioxide, which has carbon dioxide absorption properties, is increased.

Table 2 shows that, by comparing Examples 1 and 4 and Examples 3 and 6, the amine compound (A) used in Examples 1 and 3 significantly reduces the _CO2 maximum dissociation temperature and increases the difference between the _CO2 maximum dissociation temperature and the melting point when supported on the porous material (B). This facilitates desorption of carbon dioxide at a temperature lower than the melting point of the carbon dioxide absorbent, and also makes it possible to avoid a decrease in carbon dioxide absorbency due to melting of the carbon dioxide absorbent.
Furthermore, since the carbon dioxide absorbents of the present examples all have low solubility in water or low water absorption, the amine compound (A) is unlikely to elute into steam even when a steam stripping method is applied to regenerate the absorbent, and good repeated usability is expected.

Furthermore, a cycle test was conducted using the above method on the carbon dioxide absorbents of Examples 4 to 6, which contained the amine compounds (A) of Examples 1 to 3. The results are shown in Table 3.

Table 3 shows that the carbon dioxide absorbent of this embodiment has high mass retention and carbon dioxide absorption capacity retention, even after repeated cycles of carbon dioxide absorption and carbon dioxide desorption by heating.

Examples 7 and 8 (Preparation and Evaluation of Carbon Dioxide Absorbents)
(Preparation of carbon dioxide absorbent)
In a nitrogen-purged glass container, 8 g of HQ-BA as the amine compound (A) and 500 g of methanol were charged, and the mixture was stirred with a stirrer at room temperature (23 ° C.) to dissolve the amine compound (A). Next, 12 g of pelleted silica was added as the porous material (B), and the mixture was again purged with nitrogen, and the mixture was stirred for 3 hours to homogenize. From the resulting mixture, methanol was distilled off under a reduced pressure of 40 ° C. and 50 hPa, and then the mixture was vacuum dried at 80 ° C. for 3 hours to support the amine compound (A) on the porous material (B), and a carbon dioxide absorbent A having a content of 40% by mass of the amine compound (A) was obtained.

(Evaluation of carbon dioxide absorbents)
Using the obtained carbon dioxide absorbent A, a carbon dioxide absorption operation described below was performed, followed by a regeneration operation of the carbon dioxide absorbent A described below. This cycle was repeated three times in total to perform a _CO2 absorption-desorption cycle test of the carbon dioxide absorbent. The results of the obtained carbon dioxide absorption amounts are shown in Table 4.

[Carbon dioxide absorption operation]
In Example 7, dry simulated air (0% RH) with a _CO2 concentration of 400 ppm was first prepared using air cylinder gas and _CO2 / _N2 cylinder gas. This dry simulated air was passed through a column (diameter 30 mm, length 10 cm) packed with 10 g of carbon dioxide absorbent A at 5 L/min, and the carbon dioxide concentration (ppm) was measured at each of the inlet and outlet of the dry simulated air in the column using an NDIR (non-dispersive infrared) _CO2 concentration meter (manufactured by VAISARA). The carbon dioxide absorption amount of carbon dioxide absorbent A was calculated from the integrated amount of the difference in carbon dioxide concentration measured at the inlet and outlet of the column within a predetermined time (300 minutes) during which the dry simulated air was passed.
In Example 8, first, high-humidity gas with a humidity of 100% RH was prepared by passing air cylinder gas through water, and high- _CO2 gas was prepared by mixing _CO2 / _N2 cylinder gas and air cylinder gas to adjust the _CO2 concentration to 800 ppm. These gases were then mixed at a volume ratio of 1:1 to prepare humidity-conditioned simulated air (50% RH) with a _CO2 concentration of 400 ppm. This humidity-conditioned simulated air was passed through a column (diameter 30 mm, length 10 cm) packed with 10 g of carbon dioxide absorbent A at a rate of 5 L/min, and the carbon dioxide concentration (ppm) was measured at the inlet and outlet of the humidity-conditioned simulated air of this column using an NDIR (non-dispersive infrared) _CO2 concentration meter (manufactured by VAISARA). The carbon dioxide absorption amount of the carbon dioxide absorbent A was calculated from the integrated difference in carbon dioxide concentration measured at the inlet and outlet of the column during a predetermined time (300 minutes) during which the humidity-controlled simulated air was circulated.

[Regeneration operation of carbon dioxide absorbent]
After the absorption operation, the pressure in the entire column was reduced to 47.4 kPa, and water vapor at 80°C was passed through the column for 10 minutes to desorb the carbon dioxide adsorbed in the carbon dioxide absorbent A. Thereafter, dry nitrogen gas was passed through the column at 5 L/min for 30 minutes while the temperature inside the column was maintained at 80°C, to dry the carbon dioxide absorbent A.

Table 4 shows that the carbon dioxide absorbent of this embodiment absorbs a higher amount of carbon dioxide when the humidity is high than when the carbon dioxide-containing gas is dry.

The present invention provides a carbon dioxide absorbent that has excellent carbon dioxide absorption properties and reusability, a carbon dioxide recovery method using the same, and a carbon dioxide separation and recovery device.

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

Claims (7)

A carbon dioxide absorbent comprising a non-azo solid amine compound (A) having two or more aromatic rings and two or more primary amino groups,
The carbon dioxide absorbent, wherein the non-azo solid amine compound (A) is an amine compound represented by the following general formula (1):

In formula (1), X and Y each independently represent a single bond or an oxygen atom, n and m each independently represent a number from 1 to 6, and p represents a number from 0 to 2. The carbon dioxide absorbent according to claim 1 , wherein the amine compound represented by the general formula (1) is any one of compounds represented by the following formulas (1-1) to (1-3):
2. The carbon dioxide absorbent according to claim 1, wherein the carbon dioxide absorbent comprises the amine compound (A) and a porous material (B), and at least a part of the amine compound (A) is supported on the porous material (B). The carbon dioxide absorbent according to claim 3 , wherein the porous material (B) comprises at least one selected from the group consisting of porous silica and porous alumina. A method for recovering carbon dioxide, which uses the carbon dioxide absorbent according to any one of claims 1 to 4 . The method according to claim 5, 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; and (III) a step of heating the carbon dioxide absorbent having absorbed carbon dioxide. 5. A carbon dioxide separation and capture system comprising: an absorption device equipped with a mechanism for bringing the carbon dioxide absorbent according to claim 1 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.