WO2021193963A1

WO2021193963A1 - Absorption liquid for separating and recovering carbon dioxide from gas containing carbon dioxide, and carbon dioxide recovery method using same

Info

Publication number: WO2021193963A1
Application number: PCT/JP2021/013090
Authority: WO
Inventors: 洋市松崎; 上代　洋; フィロツアラムチョウドリ
Original assignee: 日本製鉄株式会社; 公益財団法人地球環境産業技術研究機構
Priority date: 2020-03-26
Filing date: 2021-03-26
Publication date: 2021-09-30
Also published as: JPWO2021193963A1; JP7394963B2

Abstract

Provided is an absorption liquid for separating and recovering carbon dioxide from gas containing carbon dioxide, the absorption liquid containing an alkanolamine compound represented by formula (1) and accounting for 30-70 mass% of the entire absorption liquid, an imidazole compound represented by formula (2), and water. R¹ is a hydrogen atom or an alkyl group of 1-4 carbon atoms, R² and R³ are each independently a hydrogen atom or an alkyl group of 1-3 carbon atoms, R¹, R², and R³ are not all hydrogen atoms, and n is 1 or 2. Im is an imidazole ring, the plurality of R are each independently a hydrogen atom or alkyl group of 1-10 carbon atoms bonded to the imidazole ring, and x is 1 or 2. If x is 1, L is a hydrogen atom or alkyl group of 1-10 carbon atoms bonded to the imidazole ring, and if x is 2, L is a single bond or a divalent linking group bonded to an imidazole ring and connecting two imidazole rings.

Description

Absorbent liquid for separating and recovering carbon dioxide from gas containing carbon dioxide and carbon dioxide recovery method using it

The present disclosure relates to an absorption liquid for separating and recovering carbon dioxide from a gas containing carbon dioxide (hereinafter, also referred to as an absorption liquid) and a method for recovering carbon dioxide using the absorption liquid.

In recent years, climate change and natural disasters, which are thought to be caused by global warming, have had a great impact on agricultural production, living environment, energy consumption, and so on. This global warming is thought to be caused by the increase in greenhouse gases such as carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons, which increase with the active social activity of humankind. .. Atmospheric carbon dioxide is cited as the most important greenhouse gas, and measures to reduce carbon dioxide emissions into the atmosphere have become a global issue.
The sources of carbon dioxide are thermal power plants that use coal, heavy oil, natural gas, etc. as fuel; blast furnaces at steel mills that reduce iron oxide with coke; Blast furnaces; boilers in various factories; kilns in cement factories; transportation equipment fueled by gasoline, heavy oil, light oil, etc. (for example, automobiles, ships, aircraft, etc.). Of these, equipment other than transportation equipment is stationary equipment, and it is easy to take measures to reduce the amount of carbon dioxide emitted into the atmosphere.

As a method for separating and recovering carbon dioxide from the gas emitted from the source exemplified above, several methods have been conventionally known.
For example, a method is known in which a gas containing carbon dioxide is brought into contact with an aqueous solution of alkanolamine in an absorption tower to absorb carbon dioxide. Here, as the alkanolamine, monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine, diglycolamine and the like are known, and among them, monoethanolamine is widely used.

However, when an aqueous solution of these alkanolamines is used as an absorbent for carbon dioxide, primary amines such as monoethanolamine are highly corrosive to the material of the device, so expensive corrosion-resistant steel should be used, and amines in the absorbent should be used. It is necessary to lower the concentration. Further, the emission and recovery of the absorbed carbon dioxide are generally carried out by heating the absorption liquid to about 120 ° C. in the regeneration tower, but in the above-mentioned alkanolamine, the amount of carbon dioxide absorbed in the absorption tower Since the amount of carbon dioxide emitted in the regeneration tower is not sufficient, a large amount of energy is required for recovery per unit mass of carbon dioxide as a result.

In an era where reduction of carbon dioxide generation, energy saving and resource saving are required, a large amount of energy consumption in carbon dioxide absorption and recovery is a major factor hindering the practical application of the technology, and carbon dioxide with less energy is required. Separation and recovery technology is required.
Therefore, as a conventional technique for separating and recovering carbon dioxide with less energy, for example, Patent Document 1 describes a combustion exhaust gas characterized by bringing a specific aqueous solution of hindered amine into contact with a combustion exhaust gas under atmospheric pressure. The method of removing carbon dioxide in it is described. In that example, N-methylaminoethanol and N-ethylaminoethanol are described as hindered amines, and as other hindered amines, amines such as 2-isopropylaminoethanol are described, although examples are not described.
Further, Patent Document 2 describes a method of absorbing a absorbing liquid and carbon dioxide that maximizes the performance while utilizing the characteristics of each amine by mixing a plurality of types of alkanolamines.

On the other hand, in Patent Document 3, a study using a non-aqueous organic compound such as alcohol as a solvent instead of an aqueous solution using water having a high specific heat as a solvent is also underway. When alcohols are used instead of water, for example, the specific heat is lowered, and carbon dioxide is separated and recovered via an unstable alkyl carbonate, so that improvement in low temperature dissipation is expected.

Patent Document 4 describes an absorption liquid that uses a mixed liquid of ethylene glycol or the like and water as a solvent.

Patent Document 5 describes an absorbing liquid and a recovery method for removing carbon dioxide from a high-pressure gas having a partial pressure of carbon dioxide of 0.4 to 5 MPa. It is described that the heat energy required in the dissipation step can be reduced by intentionally using an absorbent having low absorbency such as a morphophosphorus compound and an imidazole compound in the absorbent solution.

Further, Patent Document 6 describes a carbon dioxide absorbing aqueous solution containing 50% by mass of 2-amino-2-methyl-1-propanol (AMP) as an absorbent and 5% by mass of piperazine as an absorption accelerator. ..

Patent Document 7 describes a carbon dioxide absorbing aqueous solution containing 10% by mass of piperazine as an absorbent and 20% by mass of 2- (isopropylamino) ethanol (IPAE) as an absorption aid.

Patent Document 8 describes a carbon dioxide absorbing aqueous solution adjusted so that 1-methylimidazole is 0.6 mol / L, piperazine is 2.8 mol / L, and methylaminoethanol is 0.2 mol / L.

Patent Document 9 describes a carbon dioxide absorbing solution obtained by adding mercaptobenzimidazoles as an oxidation inhibitor of alkanolamine to an aqueous solution of alkanolamine.

Patent Document 1: Japanese Patent No. 2871334 Patent Document 2: Japanese Patent No. 5452222 Patent Document 3: Japanese Patent Application Laid-Open No. 2012-236165 Patent Document 4: International Publication No. 2016/152782 Patent Document 5: International Publication No. 2009/066754 Patent Document 6: Japanese Patent Application Laid-Open No. 2015-24374 Patent Document 7: Japanese Patent Application Laid-Open No. 2013-158718 Patent Document 8: International Publication No. 2011-121633 Patent Document 9: Japanese Patent Application Laid-Open No. 2012-45518

As described above, Patent Documents 1 to 9 disclose a technique for separating and recovering carbon dioxide with less energy.
However, even with the absorbents exemplified in Patent Document 1 and Patent Document 2, the energy for separation and recovery cannot be sufficiently suppressed.
The absorption liquid having the composition described in Patent Document 3 has extremely low carbon dioxide absorption efficiency, and it is necessary to absorb carbon dioxide in a low temperature range of 20 ° C to 25 ° C, and the energy required for cooling during absorption is required. There is a problem that extra is required.
The absorption liquid having the composition described in Patent Document 4 has improved carbon dioxide emission performance under low temperature conditions as compared with the conventional aqueous solution, but its viscosity is relatively high, so that the carbon dioxide absorption efficiency is lowered. There is a tendency.
The absorbing liquid and the recovery method described in Patent Document 5 have low carbon dioxide absorption efficiency with respect to carbon dioxide having a relatively low partial pressure (generally about 0.02 MPa) generated from a thermal power plant or a steel mill blast furnace. Therefore, the energy per unit mass of carbon dioxide recovered is high.

Further, since the piperazine contained in the absorption liquids described in Patent Documents 6 to 8 has high reactivity with carbon dioxide, the heat energy required for the emission of carbon dioxide is large, and the energy cost is high.
Further, mercaptobenzimidazole contained in the absorption liquid described in Patent Document 9 has a problem such as an unpleasant odor.

Therefore, an object of the present disclosure is to provide an absorption liquid capable of separating and recovering carbon dioxide with high efficiency and low energy cost, and a method for recovering carbon dioxide using the absorption liquid.

As a result of intensive studies to achieve the above object, the inventors of the present disclosure contain at least one specific alkanolamine compound, a specific imidazole compound and water, and the content of the alkanolamine compound. By setting Was found to be able to be separated and recovered. The inventors of the present disclosure have made further studies based on these findings, and have completed the present disclosure.
That is, the present disclosure provides the following absorption liquid for separating and recovering carbon dioxide, and a method for separating and recovering carbon dioxide.
<1>
The content of the total absorption liquid is 30 to 70% by mass, and the alkanolamine compound represented by the following general formula (1) and
The imidazole compound represented by the following general formula (2) and
water and,
Contains,
An absorbent solution for separating and recovering carbon dioxide from a gas containing carbon dioxide.

(In the general formula (1), R ¹ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ² and R ³ are independently hydrogen atoms or an alkyl group having 1 to 3 carbon atoms. ¹ , R ² and R ³ are not all hydrogen atoms, and n is 1 or 2.)

(In the general formula (2), Im is an imidazole ring, a plurality of Rs are independently hydrogen atoms or alkyl groups having 1 to 10 carbon atoms, x is 1 or 2, and x is 1. , L is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and when x is 2, L is a single bond or a divalent linking group that connects two imidazole rings. However, it is contained in the imidazole ring. One of the two hydrogen atoms is bonded to R or L, and the other nitrogen atom is not bonded to either R or L.)
<2>
The alkanolamine compounds, in the general formula (1), ^{R 1} is a hydrogen atom, a methyl group, an ethyl group, n- propyl group, an isopropyl group or n- butyl group, ^{R 2} and ^{R 3,} respectively The absorption solution according to <1> above, which is an alkanolamine (I) independently having a hydrogen atom or a methyl group and n being 1 or 2.
<3>
In the alkanolamine compound, in the general formula (1), R ¹ is a methyl group, an ethyl group, an n-propyl group, an isopropyl group or an n-butyl group, and R ² and R ³ are hydrogen atoms. The absorption solution according to <1> or <2> above, wherein n is an alkanolamine (II) of 1 or 2.
<4>
In the alkanolamine compound, in the general formula (1), R ¹ is a methyl group, an ethyl group, an n-propyl group, an isopropyl group or an n-butyl group, and R ² and R ³ are hydrogen atoms. Alkanolamine (II) in which n is 1 or 2 and
In the general formula (1), ^{alkanolamine (III) in which R 1} is a hydrogen atom, R ² and R ³ are independently hydrogen atoms or methyl groups, and n is 1 or 2, respectively. The absorbing solution according to <1>, which is a mixed amine contained.
<5>
The absorption according to <3> or <4>, wherein the alkanolamine (II) is N-isopropylaminoethanol and the alkanolamine (III) is 2-amino-2-methyl-1-propanol. liquid.
<6>
The absorption liquid according to any one of <1> to <5>, wherein the content of the imidazole compound is 5 to 35% by mass with respect to the entire absorption liquid.
<7>
The absorption liquid according to any one of <1> to <6>, wherein the imidazole compound is an imidazole compound A represented by the following general formula (2A).

(In the general formula (2A), ^Ra is an alkyl group having 1 to 10 carbon atoms, the plurality of Rs are independently hydrogen atoms or alkyl groups having 1 to 10 carbon atoms, and x is 1 or 2. When x is 1, L is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and when x is 2, L is a single bond or a divalent linking group that connects two imidazole rings. )
<8>
The imidazole compound A is a compound represented by the following general formula (2D), <7>.
Absorbent solution described in.

(In the general formula (2D), R ⁴ is an alkyl group having 1 to 4 carbon atoms, and R ⁵ , R ⁶ and R ⁷ are independently hydrogen atoms or alkyl groups having 1 to 4 carbon atoms, respectively. .)
<9>
The imidazole compound is at least one selected from the group consisting of imidazole, 1-methylimidazole, 1-ethylimidazole, 1-butyl imidazole, 1-isopropyl imidazole, 2-methyl imidazole, and 1,2-dimethyl imidazole. The absorbing solution according to any one of <1> to <6>, which is a compound.
<10>
The absorption liquid according to any one of <1> to <9>, wherein the imidazole compound is 1-methylimidazole.
<11>
The absorption liquid according to any one of <1> to <10>, wherein the total content of the alkanolamine compound, the imidazole compound, and the water is 99% by mass or more with respect to the entire absorption liquid.

<12>
A step A in which the absorption liquid according to any one of <1> to <11> is brought into contact with a gas containing carbon dioxide to obtain an absorption liquid that has absorbed carbon dioxide from the gas containing carbon dioxide.
Step B in which the absorption liquid is heated to desorb and dissipate carbon dioxide from the absorption liquid, and the released carbon dioxide is recovered.
A method of separating and recovering carbon dioxide from a gas containing carbon dioxide.
<13>
The method according to <12>, wherein in the step B, the absorption liquid is heated at 80 to 95 ° C. to desorb carbon dioxide.

According to the present disclosure, there is provided an absorption liquid capable of separating and recovering carbon dioxide with higher efficiency and lower energy cost than a conventional absorption liquid consisting of an aqueous solution having an amine composition, and a method for recovering carbon dioxide using the absorption liquid. ..

Hereinafter, an embodiment which is an example of the present disclosure will be described in detail.

The numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.
The numerical range when "greater than" or "less than" is added to the numerical values before and after "to" means a range in which these numerical values are not included as the lower limit value or the upper limit value.
The term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes.
In the numerical range described stepwise in the present disclosure, the upper limit value described in one numerical range is the upper limit value of the numerical range described in another stepwise description, or the lower limit value described in one numerical range. May be replaced with the lower limit of the numerical range described in other steps.
Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.
In the present disclosure, the combination of preferred embodiments is a more preferred embodiment.
In the present disclosure, the alkyl group having 3 or more carbon atoms may be a linear alkyl group or a branched alkyl group.

<Absorbent for separating and recovering carbon dioxide>
The absorption liquid for separating and recovering carbon dioxide of the present disclosure (sometimes referred to simply as "absorption liquid" in the present disclosure) has a content of 30 to 70% by mass with respect to the entire absorption liquid, and has the following general formula ( An alkanolamine compound represented by 1) (sometimes simply referred to as an "alkanolamine compound" in the present disclosure) and an imidazole compound represented by the following general formula (2) (simply "imidazole compound" in the present disclosure). It may be noted) and water.

In the general formula (1), R ¹ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ² and R ³ are independently hydrogen atoms or an alkyl group having 1 to 3 carbon atoms. Not all of R ¹ , R ² and R ³ are hydrogen atoms, and n is 1 or 2.

In the general formula (2), when Im is an imidazole ring, a plurality of Rs are independently hydrogen atoms or alkyl groups having 1 to 10 carbon atoms, x is 1 or 2, and x is 1, L is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and when x is 2, L is a single bond or a divalent linking group that connects two imidazole rings. However, one of the two nitrogen atoms contained in the imidazole ring is bonded to R or L, and the other nitrogen atom is not bonded to either R or L.

The absorbent liquid according to the present disclosure can separate and recover carbon dioxide with high efficiency and low energy cost due to the above configuration. The absorbent solution according to the present disclosure was found based on the following findings.

The absorption liquid for separating and recovering carbon dioxide recovers carbon dioxide by contacting it with a gas containing carbon dioxide. Carbon dioxide is recovered in the absorption liquid by chemically reacting with components such as amines in the absorption liquid, and the chemical reaction is an exothermic reaction. If the heat generated during carbon dioxide recovery is large, the temperature of the absorbing liquid may rise. The lower the temperature of the absorption liquid, the higher the recovery efficiency of carbon dioxide. Therefore, it is necessary to suppress the increase in the temperature of the absorption liquid. However, if the temperature of the absorption liquid is lowered by a chiller or the like, the energy cost is high. Become. Therefore, it is necessary to suppress the heat generated during carbon dioxide capture.
The heat generated during carbon dioxide recovery is due to the solvation of the salt and solvent generated when carbon dioxide is recovered in the absorption liquid. Since the magnitude of solvation is proportional to the dielectric constant of the solvent in the absorbing liquid, the use of a non-aqueous solvent having a small dielectric constant suppresses heat generation generated during carbon dioxide recovery.

Therefore, the inventor tried to study an absorption liquid using a non-aqueous solvent.
First, when an alkanolamine compound was used as the amine of the absorption liquid and only ethylene glycol was used as the non-aqueous solvent as the solvent, it was clarified that the effect of suppressing heat generation generated during carbon dioxide recovery was low. The reason is considered to be the structure of the salt generated when carbon dioxide is recovered in the absorption liquid. There are two types of salt structures generated when carbon dioxide is recovered in the absorption liquid, carbamionate anion and bicarbonate ion, and when the former salt structure is formed, heat generation is large. In order to form bicarbonate ions, it is necessary to contain water in the absorption liquid, and when ethylene glycol alone is used as the solvent, carbamionate anion, which generates a large amount of heat, is preferentially generated, so that carbon dioxide can be recovered. It was considered that the effect of suppressing the fever generated at that time was low.

Next, the inventor considered that it was appropriate to use a mixed solvent of water and a non-aqueous solvent as the solvent of the absorption liquid, and examined the solvent type.
When an alkanolamine compound was used as the amine of the absorption liquid and a mixed solvent of water and ethylene glycol was used as the non-aqueous solvent, the recovery rate of carbon dioxide was lowered. It is considered that the reason is that a large number of hydrogen bonds were formed between water and ethylene glycol, and the clay of the absorption liquid was improved, so that the efficiency of the gas-liquid reaction was lowered.

Then, when an alkanolamine compound was used as the amine of the absorption liquid and a mixed solvent of water and an imidazole compound was used as the solvent, and the content of the alkanolamine compound was within a specific range, the carbon dioxide was recovered. It was found that the effect of suppressing the heat generated in the solvent is high and the recovery rate of carbon dioxide is good.

From the above findings, it has been found that the absorption liquid according to the present disclosure can separate and recover carbon dioxide with high efficiency and low energy cost by the above configuration.
According to the absorption liquid according to the present disclosure, carbon dioxide can be dissipated under lower temperature conditions without impairing the excellent carbon dioxide absorption efficiency with respect to the conventional absorption liquid composed of an aqueous solution having an amine composition. Further, according to the absorption liquid according to the present disclosure, it is possible to recover carbon dioxide with a lower energy consumption. As a result, the energy required for the separation and recovery of carbon dioxide is reduced, and carbon dioxide can be recovered efficiently and with low energy consumption. In addition, by significantly improving the ability to dissipate carbon dioxide under low temperature conditions, it is possible to utilize the so-called low-grade waste heat that was conventionally discarded, and the energy required for separation and recovery of carbon dioxide is greatly reduced. It is possible to do.

Hereinafter, the absorption liquid according to the present disclosure will be described in detail.
(Alkanolamine compound)
The absorption liquid according to the present disclosure contains an alkanolamine compound represented by the following general formula (1) in a proportion of 30 to 70% by mass with respect to the entire absorption liquid. The alkanolamine compound contained in the absorption liquid according to the present disclosure may be one kind or two or more kinds, and when two or more kinds of alkanolamine compounds are contained, the total amount thereof is 30 to 70 with respect to the entire absorption liquid. It is mass%.

In the general formula (1), R ¹ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ² and R ³ are independently hydrogen atoms or an alkyl group having 1 to 3 carbon atoms, respectively, and R ¹ , R ² and R ³ are not all hydrogen atoms, and n is 1 or 2.

^{R 1} in the general formula (1) is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.
^{Specific examples of R 1} in the general formula (1) include a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group and the like.
Among these, hydrogen atom, methyl group, ethyl group, n-propyl group, isopropyl group or n-butyl group are preferable, and methyl group and ethyl group are preferable from the viewpoint of separating and recovering carbon dioxide with high efficiency and low energy cost. A group, an n-propyl group, an isopropyl group or an n-butyl group is more preferable, and an isopropyl group is further preferable.

N in the general formula (1) is 1 or 2, and 1 is more preferable.

^{R 2} and R ³ in the general formula (1) are independently hydrogen atoms or alkyl groups having 1 to 3 carbon atoms, and specifically, hydrogen atoms, methyl groups, ethyl groups, and n-propyl groups. Alternatively, an isopropyl group can be mentioned. Among these, a hydrogen atom or a methyl group is preferable.

Specific alkanolamine compounds represented by the general formula (1) include N-ethylaminoethanol, Nn-propylaminoethanol, N-isopropylaminoethanol, Nn-butylaminoethanol, and 2-amino. -1-propanol, N-isobutylaminoethanol, 2-amino-2-methyl-1-propanol, 3-ethylamino-1-propanol, 3-n-propylamino-1-propanol, 3-isopropylamino-1- Examples thereof include propanol, 3-n-butylamino-1-propanol, 3-isobutylamino-1-propanol and the like, which can also be used industrially.

The absorption liquid according to the present disclosure may contain at least one alkanolamine compound represented by the general formula (1), and may contain a mixed amine composed of a plurality of types of alkanolamine compounds.

The alkanolamine compounds, in the general formula (1), ^{R 1} is a hydrogen atom, a methyl group, an ethyl group, n- propyl group, an isopropyl group or n- butyl group, ^{R 2} and ^{R 3,} respectively It is preferably an alkanolamine (I) that is independently a hydrogen atom or a methyl group and has n of 1 or 2.

The alkanolamine compounds, in the general formula (1), R ¹ is methyl group, ethyl group, n- propyl group, an isopropyl group or n- butyl group, R ² and R ³ are hydrogen atom, More preferably, it is an alkanolamine (II) in which n is 1 or 2.

As the mixed amine, for example, in the general formula (1), R ¹ is a methyl group, an ethyl group, an n-propyl group, an isopropyl group or an n-butyl group, and R ² and R ³ are hydrogen atoms. during alkanolamine n is 1 or 2 (II), and the general formula (1), ^{R 1} is hydrogen atom, ^{R 2} and ^{R 3} are each independently a hydrogen atom or a methyl group, A mixed amine of alkanolamine (III) in which n is 1 or 2 can be mentioned.
Among them, a mixed amine of N-isopropylaminoethanol as the alkanolamine (II) and 2-amino-2-methyl-1-propanol as the alkanolamine (III) is preferable.

Hereinafter, the total amount of the alkanolamine compound in the absorption liquid according to the present disclosure will be described.
Generally, the higher the concentration of the amine component, the larger the absorption amount, absorption rate, desorption amount and desorption rate of carbon dioxide per unit liquid volume, which is desirable from the viewpoint of energy consumption, size and efficiency of plant equipment. If the concentration of the amine component exceeds 70% of the total absorption liquid, the effect of water as an activator may decrease, the amount of carbon dioxide absorbed may decrease, the mixture of the amine component may decrease, and the viscosity may increase. Etc. occur.
The content of the alkanolamine compound in the absorption liquid according to the present disclosure is 70% by mass or less with respect to the entire absorption liquid due to problems such as a decrease in the mixing property of the alkanolamine compound and an increase in viscosity. On the other hand, according to the experiments by the inventors of the present disclosure, when the content of the alkanolamine compound is less than 30% by mass with respect to the entire absorption liquid, not only the absorption performance is low, but also the emission rate and the emission amount (= recovered amount). ) Will also drop significantly. Therefore, the content of the alkanolamine compound is 30% by mass or more from the viewpoint of practical absorption performance and desorption performance. That is, the content of the alkanolamine compound is 30 to 70% by mass, preferably 40 to 70% by mass, based on the entire absorption liquid.

(Imidazole compound)
The absorption liquid according to the present disclosure contains an imidazole compound represented by the following general formula (2) as an imidazole compound. The imidazole compound contained in the absorption liquid according to the present disclosure may be one kind or two or more kinds.

In the general formula (2), Im is an imidazole ring, and a plurality of Rs are hydrogen atoms or alkyl groups having 1 to 10 carbon atoms that are independently bonded to the imidazole ring. When x is 1 or 2, L is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms bonded to the imidazole ring, and when x is 2, L connects two imidazole rings. It is a single bond or a divalent linking group. However, one of the two nitrogen atoms contained in the imidazole ring is bonded to R or L, and the other nitrogen atom is not bonded to either R or L. Here, the "imidazole ring" means a ring of imidazole having the following structure, excluding each hydrogen atom bonded to N at the 1-position and C at the 2-position, 4-position, and 5-position. Examples of the divalent linking group represented by L include a thiocarbonyl group and a carbonyl group.

For example, piperazine disclosed in Patent Documents 6 to 8 is generally used as an absorption promoter, but since it has high reactivity with carbon dioxide, it requires a large amount of heat energy to dissipate carbon dioxide, and the energy cost is high. Will be higher.
On the other hand, the imidazole compound represented by the general formula (2) _{has a much lower basicity (reactivity with CO 2} ) than piperazine, and is advantageous in suppressing energy costs.

The imidazole compound represented by the general formula (2) has three types depending on the binding form of N at the 1-position of imidazole, that is, the imidazole compound A represented by the following general formula (2A) and the following general formula (2B). Examples thereof include the imidazole compound B represented by the imidazole compound and the imidazole compound C represented by the following general formula (2C).

In the general formula (2A), ^Ra is an alkyl group having 1 to 10 carbon atoms, and the plurality of Rs are independently hydrogen atoms or alkyl groups having 1 to 10 carbon atoms. When x is 1 or 2, L is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and when x is 2, L is a single bond or divalent linking two imidazole rings. It is a linking group of. Examples of the divalent linking group include a thiocarbonyl group and a carbonyl group.
From the viewpoint of absorption and dissipation properties, it is preferred that x is 1, R ^a is preferably an alkyl group having 1 to 4 carbon atoms, L and R is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms It is preferable that all of them are hydrogen atoms.

In the general formula (2B), a plurality of Rs are independently hydrogen atoms or alkyl groups having 1 to 10 carbon atoms, x is 1 or 2, and when x is 1, L is a hydrogen atom or carbon atoms. It is an alkyl group of 1 to 10, and when x is 2, L is a single bond or a divalent linking group that links two imidazole rings. Examples of the divalent linking group include a thiocarbonyl group and a carbonyl group.
From the viewpoint of absorption characteristics and emission characteristics, x is preferably 1 in the general formula (2B), and L and R are preferably hydrogen atoms or alkyl groups having 1 to 4 carbon atoms, both of which are hydrogen atoms. More preferably.

In the general formula (2C), a plurality of Rs in each imidazole ring are independently hydrogen atoms or alkyl groups having 1 to 10 carbon atoms, and L is a single bond or a divalent linking group that connects two imidazole rings. Is. Examples of the divalent linking group include a thiocarbonyl group and a carbonyl group.
From the viewpoint of absorption characteristics and emission characteristics, R is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms in the general formula (2C), and more preferably both are hydrogen atoms.

Among the imidazole compounds A to C, the imidazole compounds A and B having x of 1 in the general formulas (2A) and (2B) are more preferable, and the imidazole compound A is further preferable, from the viewpoint of absorption characteristics and emission characteristics.
Examples of the imidazole compound in which x is 1 in the general formulas (2A) and (2B) include the imidazole compound represented by the following general formula (2D).

In the general formula (2D), R ⁴ , R ⁵ , R ⁶ and R ⁷ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Preferably, R ⁴ represents an alkyl group having 1 to 4 carbon atoms, and R ⁵ , R ⁶ and R ⁷ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

The imidazole compound represented by the general formula (2D) is preferably imidazole, 1-methylimidazole, 1-ethylimidazole, 1-propylimidazole, 1-isopropylimidazole, 1-butylimidazole, 2-methylimidazole, 2-. Ethylimidazole, 2-propylimidazole, 2-isopropylimidazole, 2-butylimidazole, 1,2-dimethylimidazole, 1,4-dimethylimidazole, 1,5-dimethylimidazole, 2,4-dimethylimidazole, 4,5- Examples thereof include dimethylimidazole. More preferably, 1-methylimidazole, 1-ethylimidazole, 1-propyl imidazole, 1-isopropyl imidazole and 1-butyl imidazole are mentioned, and 1-methyl imidazole is particularly preferable.

In the absorption liquid according to the present disclosure, one type of imidazole compound or a combination of a plurality of types of imidazole compounds can be used.
From the viewpoint of improving the absorption efficiency of carbon dioxide, the content of the imidazole compound (total content when two or more kinds of imidazole compounds are contained) is preferably 5 to 35% by mass, preferably 10 to 35% by mass, based on the entire absorption liquid. It is more preferably 20% by mass.

(water)
The absorbing liquid according to the present disclosure contains water.
The content of water is not particularly limited, and the balance can be water, but it is preferably 5 to 60% by mass, more preferably 10 to 45% by mass, and 15 to 15 to 40% by mass with respect to the entire absorption liquid. 40% by mass is more preferable.
The water is not particularly limited, and distilled water, ion-exchanged water, tap water, groundwater and the like can be appropriately used.

(Other ingredients)
In addition, the absorption liquid according to the present disclosure may contain, if necessary, other components other than the alkanolamine compound, the imidazole compound and water, as long as the effects of the present disclosure are not impaired. Other components include stabilizers to ensure the chemical or physical stability of the liquid (eg, side reaction inhibitors such as antioxidants); deterioration of the material of equipment or equipment using the solutions of the present disclosure. Preventive agents (eg, corrosion inhibitors); antifoaming agents (eg, surfactants); and the like. The content of these other components is not particularly limited as long as it does not impair the effects of the present disclosure.

If piperazine is contained as another component, the heat energy required to dissipate carbon dioxide increases, and the energy cost increases. Therefore, the absorption liquid according to the present disclosure does not contain piperazine, or even if it contains piperazine, the content of piperazine is preferably 1% by mass or less with respect to the entire absorption liquid, and more preferably does not contain piperazine.
The absorption liquid according to the present disclosure may have a total content of the alkanolamine compound, the imidazole compound and water of 95% by mass or more, 98% by mass or more, or 99% by mass or more with respect to the entire absorption liquid.

(Method of measuring the content of each component in the absorption liquid)
The content of each component in the absorption liquid according to the present disclosure reflects the addition amount (mass%) of each component when preparing the absorption liquid, but the content of each component in the absorption liquid is GC-FID ( It can be quantified by gas chromatograph-hydrogen flame ionization detector).

(Manufacturing method of absorbent liquid)
The method for producing the absorbent liquid according to the present disclosure is not particularly limited. For example, an alkanolamine compound, an imidazole compound, and water, and if necessary, other components are prepared, and the content of the alkanolamine compound is 30 to 70% by mass with respect to the entire absorption liquid, and the content of the imidazole compound is high. The absorbent solution according to the present disclosure can be prepared by mixing so that the content is preferably 5 to 35% and the water content is preferably 5 to 60% by mass.

<Method of separating and recovering carbon dioxide from gas containing carbon dioxide>
The method for separating and recovering carbon dioxide from the carbon dioxide-containing gas according to the present disclosure is a step A in which the absorption liquid is brought into contact with the carbon dioxide-containing gas to obtain an absorption liquid that has absorbed carbon dioxide from the carbon dioxide-containing gas. A step B of heating the absorption liquid to desorb and dissipate carbon dioxide from the absorption liquid, and recovering the released carbon dioxide.

(Step A: Step of obtaining an absorbent liquid that has absorbed carbon dioxide)
By contacting the absorption liquid with a gas containing carbon dioxide, carbon dioxide can be absorbed by the absorption liquid.

Gases containing carbon dioxide include, for example, exhaust gas from thermal power plants that use heavy oil, natural gas, etc. as fuel; exhaust gas from boilers in factories; exhaust gas from kilns in cement factories; Exhaust gas from a blast furnace at a steelworks; exhaust gas from a converter at a steelworks that burns carbon in iron iron to make steel; etc.

The carbon dioxide concentration in the gas is not particularly limited, and may be usually 5 to 30% by volume, particularly 10 to 20% by volume. In such a carbon dioxide concentration range, the effects of the present disclosure are preferably exhibited.

The gas containing carbon dioxide may contain impurity gas derived from a source such as water vapor or CO in addition to carbon dioxide.

The method of bringing the gas containing carbon dioxide into contact with the absorption liquid is not particularly limited, and for example, a method of bubbling the gas containing carbon dioxide in the absorption liquid; a method of atomizing the absorption liquid in a gas stream containing carbon dioxide. (Spraying or spraying method); A method in which a gas containing carbon dioxide and an absorbing liquid are brought into countercurrent contact in an absorption tower containing a filler made of porcelain or metal mesh; and the like.

The temperature at which carbon dioxide in the gas containing carbon dioxide is absorbed by the absorbing liquid is usually 60 ° C. or lower, preferably 50 ° C. or lower, and more preferably 20 to 45 ° C.
The lower the temperature at which the carbon dioxide in the gas containing carbon dioxide is absorbed by the absorption liquid, the greater the amount of carbon dioxide absorbed, but how much the temperature should be lowered depends on the gas temperature of the gas containing carbon dioxide, the heat recovery target, etc. Determined by. Absorption of carbon dioxide by amine is an exothermic reaction, and if an attempt is made to increase the amount of carbon dioxide absorbed under low temperature conditions, energy is required to cool the absorption liquid. Is usually preferably carried out at around 40 ° C.

The carbon dioxide absorption process is usually performed under atmospheric pressure. Although it can be carried out under pressurization in order to enhance the carbon dioxide absorption performance, it is preferably carried out under atmospheric pressure from the viewpoint of suppressing energy consumption for pressurization.

(Process B: Carbon dioxide emission and recovery process)
By heating the absorption liquid that has absorbed the carbon dioxide obtained in the step A, the carbon dioxide is desorbed and released, and the released pure or high-concentration carbon dioxide can be recovered.

As a method of desorbing and dissipating carbon dioxide from the absorbing liquid that has absorbed carbon dioxide, for example, a method of heating the absorbing liquid and foaming it in a kettle to remove it; a shelf tower, a spray tower, a porcelain or a metal net A method of expanding the liquid interface and heating in a desorption tower containing the filler of the above;
By these methods, carbon dioxide existing as bicarbonate ions in the absorption liquid is desorbed as molecular carbon dioxide and released.

Here, when carbon dioxide is conventionally desorbed from the absorption liquid and dissipated, the absorption liquid is set to 100 to 120 ° C. when a conventional aqueous solution is used as the absorption liquid. The higher the temperature of the absorption liquid, the greater the amount of carbon dioxide emitted, but as the temperature rises, the energy required to heat the absorption liquid increases, so that temperature is the gas temperature and heat recovery in the process of discharging gas containing carbon dioxide. Determined by goals, etc.

On the other hand, according to the absorption liquid according to the present disclosure, when carbon dioxide is desorbed from the absorption liquid and dissipated, for example, the absorption liquid can be set to 70 to 120 ° C, and can be set to 70 to 95 ° C. can.
By optimizing the design of the emission tower, a sufficient amount of emission can be obtained in a low temperature range of 80 to 95 ° C. by utilizing so-called low-grade waste heat.

The absorbed liquid after desorbing and dissipating carbon dioxide in the step B can be sent to the step A again and recycled (recycled).

Hereinafter, examples will be described in more detail. However, the present disclosure is not limited to the examples.
In the following description, unless otherwise specified, all "%" are based on mass.

In the description of the examples, various alkanolamine compounds and imidazole compounds are used based on the following definitions.
Im: imidazole 1MIm: 1-methylimidazole 1EtIm: 1-ethylimidazole 1BuIm: 1-butylimidazole 1IPIm: 1-isopropylimidazole 2Mim: 2-methylimidazole 1,2DMIm: 1,2-dimethylimidazole Bm: bisimidazole 1,1 '-SIm: 1,1'-thiocarbonyldiimidazole EGL: ethylene glycol IPAE: N-isopropylaminoethanol AMP: 2-amino-2-methyl-1-propanol EAE: N-ethylaminoethanol NBAE: Nn- Butylaminoethanol 2A1P: 2-amino-1-propanol

<Example 1>
1 MIm, water and IPAE were mixed at a mass ratio of 5:40:55 to obtain an absorbent solution.
<Example 2>
1 MIm, water and IPAE were mixed at a mass ratio of 10:35:55 to obtain an absorbent solution.
<Example 3>
1 MIm, water and IPAE were mixed at a mass ratio of 15:30:55 to obtain an absorbent solution.
<Example 4>
1 MIm, water and IPAE were mixed at a mass ratio of 20:25:55 to obtain an absorbent solution.
<Example 5>
1 MIm, water and IPAE were mixed at a mass ratio of 25:20:55 to obtain an absorbent solution.

<Example 6>
1 MIm, water and IPAE were mixed at a mass ratio of 30:15:55 to obtain an absorbent solution.
<Example 7>
1 MIm, water and IPAE were mixed at a mass ratio of 10:45:45 to obtain an absorbent solution.
<Example 8>
1 MIm, water and IPAE were mixed at a mass ratio of 10:40:50 to obtain an absorbent solution.
<Example 9>
1 MIm, water and IPAE were mixed at a mass ratio of 10:30:60 to obtain an absorbent solution.
<Example 10>
1 MIm, water and IPAE were mixed at a mass ratio of 10:20:70 to obtain an absorbent solution.

<Example 11>
Im, water, IPAE and AMP were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Example 12>
2MIm, water, IPAE and AMP were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Example 13>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Example 14>
1EtIm, water, IPAE and AMP were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Example 15>
1 BuIm, water, IPAE and AMP were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.

<Example 16>
1 IPIm, water, IPAE and AMP were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Example 17>
1,2DMIM, water, IPAE and AMP were mixed at a mass ratio of 10:35:40:15 to obtain an absorbing solution.
<Example 18>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Example 19>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Example 20>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 5:40:40:15 to obtain an absorbent solution.

<Example 21>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 15:30:40:15 to obtain an absorbent solution.
<Example 22>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 20:25:40:15 to obtain an absorbent solution.
<Example 23>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 25:20:40:15 to obtain an absorbent solution.
<Example 24>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 35:10:40:15 to obtain an absorbent solution.
<Example 25>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 10:30:45:15 to obtain an absorbent solution.

<Example 26>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 15:25:45:15 to obtain an absorbent solution.
<Example 27>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 10:35:45:10 to obtain an absorbent solution.
<Example 28>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 10:35:50: 5 to obtain an absorbent solution.
<Example 29>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 10:30:55: 5 to obtain an absorbent solution.
<Example 30>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 10:25:60: 5 to obtain an absorbent solution.

<Example 31>
1 MIm, water, IPAE and AMP were mixed at a mass ratio of 10:20:65: 5 to obtain an absorbent solution.
<Example 32>
1 MIm, water, IPAE and EAE were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Example 33>
1 MIm, water, IPAE and NBAE were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Example 34>
1 MIm, water, IPAE and 2A1P were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Example 35>
BIm, water, IPAE and AMP were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Example 36>
1,1'-SIm, water, IPAE and AMP were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Example 37>
1 MIm, water and IPAE were mixed at a mass ratio of 10:55:35 to obtain an absorbent solution.
<Example 38>
1 MIm, water and IPAE were mixed at a mass ratio of 10:60:30 to obtain an absorbent solution.

<Comparative example 1>
Water and IPAE were mixed at a mass ratio of 45:55 to obtain an absorbent solution.
<Comparative example 2>
Water, IPAE, and AMP were mixed in a mass ratio of 45:40:15 to obtain an absorbent.
<Comparative example 3>
Water, IPAE, and EAE were mixed at a mass ratio of 45:40:15 to obtain an absorbent solution.
<Comparative example 4>
Water, IPAE, and NBAE were mixed at a mass ratio of 45:40:15 to obtain an absorbent solution.
<Comparative example 5>
Water, IPAE, and 2A1P were mixed at a mass ratio of 45:40:15 to obtain an absorbent solution.

<Comparative Example 6>
EGL, water, and IPAE were mixed at a mass ratio of 10:35:55 to obtain an absorbent solution.
<Comparative Example 7>
EGL, water, IPAE, and AMP were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Comparative Example 8>
EGL, water, IPAE, and EAE were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Comparative Example 9>
EGL, water, IPAE, and NBAE were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.
<Comparative Example 10>
EGL, water, IPAE, and 2A1P were mixed at a mass ratio of 10:35:40:15 to obtain an absorbent solution.

<Comparative Example 11>
1 MIm, IPAE, and AMP were mixed at a mass ratio of 45:40:15 to obtain an absorbent solution.
<Comparative Example 12>
Water, IPAE, and AMP were mixed in a mass ratio of 45:40:15 to obtain an absorbent.

<Comparative Example 13>
1 MIm, water and IPAE were mixed at a mass ratio of 10:65:25 to obtain an absorbent solution.

The alkanolamine compound, imidazole compound and ethylene glycol used in the above Examples and Comparative Examples are reagent manufacturers such as Tokyo Chemical Industry Co., Ltd., and general purity products are used. IPAE is manufactured by Koei Chemical Industry Co., Ltd. and has a purity of 99% or more. As the water, ion-exchanged water was used.

<Evaluation>
For the absorbed liquids in Examples and Comparative Examples, the amount of carbon dioxide absorbed, the amount emitted, and the rate of emission were measured. Measurements were made on a carbon dioxide gas cylinder (purity 99.9%) and a nitrogen gas cylinder (purity 99.9%), a carbon dioxide gas flow controller and a nitrogen gas flow controller, a glass reaction vessel (0.5 L), a stirring blade and a temperature controller. This was performed using a carbon dioxide absorption / dissipation device in which a gas flow meter, a chiller, and a carbon dioxide concentration meter (IR100 manufactured by YOKOGAWA) were sequentially connected.
The circumference of the glass reaction vessel is covered with an electric heater, and the temperature of the absorption liquid in the glass reaction vessel is arbitrarily controlled by a temperature controller.
After adding 0.1 L of an absorbent solution into the glass reaction vessel, the gas in the upper part of the glass reaction vessel was replaced with nitrogen gas. The absorption liquid in the glass reaction vessel is kept at 40 ° C., and the carbon dioxide gas at a flow rate of 0.14 L / min and the nitrogen gas at a flow rate of 0.56 L / min are mixed with sufficient stirring at a rotation speed of 700 rpm in the glass reaction vessel. The step A was started by blowing into the absorption liquid inside, and continued for 2 hours.
After the step A was completed, the absorption liquid in the glass reaction vessel was heated to 80 ° C. to 90 ° C. to start the step B and continued for 2 hours.
In the steps A and B, the exhaust gas from the glass reaction vessel was analyzed by a carbon dioxide concentration meter. The amount of carbon dioxide dissolved in the absorption solution, that is, the amount of absorption was determined from the time course of the carbon dioxide concentration obtained from the carbon dioxide concentration meter. The amount of carbon dioxide emitted from the absorption liquid by heating was defined as a value obtained by subtracting the amount of carbon dioxide dissolved 2 hours after the start of the step B from the amount of carbon dioxide absorbed 2 hours after the start of the step A. The emission rate of carbon dioxide from the absorption liquid was defined as a change in the amount of carbon dioxide absorbed per unit time in 10 minutes after the start of emission of carbon dioxide in the step B. The percentage of the amount of carbon dioxide absorbed to the amount of carbon dioxide absorbed was defined as the emission rate.

Tables 1 to 3 show the compositions of the absorbents and the evaluation results in Examples and Comparative Examples.

From the comparison between Examples 1 to 38 and Comparative Examples 1 to 5, at least one of the alkanolamine compounds represented by the general formula (1) is represented by the general formula (2) in an amount of 30 to 70% by mass. It was confirmed that the absorption liquid for separating and recovering carbon dioxide from the carbon dioxide-containing gas containing the imidazole compound and water has an increase in the amount of carbon dioxide emission, the emission rate, and the emission rate as compared with the conventional absorption solution. Will be done.

Further, from the comparison between Examples 1 to 38 and Comparative Example 13, by containing 30% by mass or more of the alkanolamine compound represented by the general formula (1), not only the absorption characteristics are improved but also the emission characteristics are improved. Significant improvement is confirmed.

From the comparison between Examples 1 to 38 and Comparative Examples 6 to 10, at least one of the alkanolamine compounds represented by the general formula (1) is represented by the general formula (2) in an amount of 30 to 70% by mass. The absorbent solution for separating and recovering carbon dioxide from the carbon dioxide-containing gas containing the imidazole compound and water has higher emission performance while generally maintaining higher emission performance than the absorbent solution containing ethylene glycol instead of the imidazole compound. An increase in absorption rate is confirmed.

From the evaluation results of Examples 1 to 38, it is confirmed that the concentration of the imidazole compound with respect to the entire absorption liquid shows high performance in the range of 5 to 35%.

From the comparison between Examples 18 and 19 and Comparative Example 12, the absorption liquid according to the present disclosure is higher than the conventional aqueous solution even if the carbon dioxide emission step is carried out at a relatively low temperature of 80 to 85 ° C. It is confirmed that it shows performance.

From the comparison between Examples 11 to 17 and Examples 35 and 36, when imidazole, 1-methylimidazole, 1-ethylimidazole, 1-butylimidazole, 1-isopropylimidazole and 2-methylimidazole were used as the imidazole compounds. , It is confirmed that high performance is exhibited as compared with the case where bisimidazole and 1,1'-thiocarbonyldiimidazole are used as the imidazole compound.
Above all, it is confirmed that Example 13 using 1-methylimidazole exhibits high performance in both absorption characteristics and emission characteristics as compared with the case of using other imidazoles.
Furthermore, from the comparison between Example 2 and Example 13, only IPAE was used as compared with the case where AMP (corresponding to alkanolamine (I)) and IPAE (corresponding to alkanolamine (II)) were used in combination as alkanolamine. It is confirmed that the emission rate is higher.

According to the above examples, it is necessary to improve the amount of carbon dioxide emitted from the absorption liquid that has absorbed carbon dioxide under low temperature conditions while generally maintaining the amount of high carbon dioxide recovered from the gas containing carbon dioxide. Can be done. In particular, according to the absorption liquid according to the present disclosure, it is possible to obtain a sufficient emission amount even under extremely low temperature conditions of 80 to 95 ° C. as compared with the conventional case.
Furthermore, since the emission rate of carbon dioxide and the emission amount relative to the absorption amount of carbon dioxide can be increased, carbon dioxide can be recovered at a lower energy cost.
The carbon dioxide recovered in this way is usually 99% by volume or more and has an extremely high purity, and can be used in the chemical industry or the food industry. It can also be used for underground isolation in EOR (Enhanced Oil Recovery) and CCS (Carbon dioxide Capture and Storage), which are currently under consideration for practical use.

The entire disclosure of Japanese patent application 2020-056851 filed on March 26, 2020 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are referenced herein to the same extent as if individual documents, patent applications, and technical standards were specifically and individually stated. Is taken in by.

Claims

The content of the total absorption liquid is 30 to 70% by mass, and the alkanolamine compound represented by the following general formula (1) and
The imidazole compound represented by the following general formula (2) and
water and,
Contains,
An absorbent solution for separating and recovering carbon dioxide from a gas containing carbon dioxide.

(In the general formula (1), R 1 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R 2 and R 3 are independently hydrogen atoms or an alkyl group having 1 to 3 carbon atoms. Yes, not all of R 1 , R 2 and R 3 are hydrogen atoms, and n is 1 or 2).

(In the general formula (2), when Im is a midazole ring, a plurality of Rs are independently hydrogen atoms or alkyl groups having 1 to 10 carbon atoms, x is 1 or 2, and x is 1. , L is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and when x is 2, L is a single bond or a divalent linking group that connects two imidazole rings. However, it is contained in the imidazole ring. One of the two hydrogen atoms is bonded to R or L, and the other nitrogen atom is not bonded to either R or L.)
The alkanolamine compounds, in the general formula (1), R 1 is a hydrogen atom, a methyl group, an ethyl group, n- propyl group, an isopropyl group or n- butyl group, R 2 and R 3, respectively The absorption solution according to claim 1, which is an alkanolamine (I) which is independently a hydrogen atom or a methyl group and has n of 1 or 2.
In the alkanolamine compound, in the general formula (1), R 1 is a methyl group, an ethyl group, an n-propyl group, an isopropyl group or an n-butyl group, and R 2 and R 3 are hydrogen atoms. The absorption solution according to claim 1 or 2, wherein n is an alkanolamine (II) of 1 or 2.
In the alkanolamine compound, in the general formula (1), R 1 is a methyl group, an ethyl group, an n-propyl group, an isopropyl group or an n-butyl group, and R 2 and R 3 are hydrogen atoms. Alkanolamine (II) in which n is 1 or 2 and
In the general formula (1), alkanolamine (III) in which R 1 is a hydrogen atom, R 2 and R 3 are independently hydrogen atoms or methyl groups, and n is 1 or 2, respectively. The absorption solution according to claim 1, which is a mixed amine contained.
The absorption liquid according to claim 4, wherein the alkanolamine (II) is N-isopropylaminoethanol and the alkanolamine (III) is 2-amino-2-methyl-1-propanol.
The absorption liquid according to any one of claims 1 to 5, wherein the content of the imidazole compound is 5 to 35% by mass with respect to the entire absorption liquid.
The absorption liquid according to any one of claims 1 to 6, wherein the imidazole compound is an imidazole compound A represented by the following general formula (2A).

(In the general formula (2A), Ra is an alkyl group having 1 to 10 carbon atoms, the plurality of Rs are independently hydrogen atoms or alkyl groups having 1 to 10 carbon atoms, and x is 1 or 2. When x is 1, L is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and when x is 2, L is a single bond or a divalent linking group that connects two imidazole rings. )
The absorption liquid according to claim 7, wherein the imidazole compound A is a compound represented by the following general formula (2D).

(In the general formula (2D), R 4 is an alkyl group having 1 to 4 carbon atoms, and R 5 , R 6 and R 7 are independently hydrogen atoms or alkyl groups having 1 to 4 carbon atoms, respectively. .)
The imidazole compound is at least one selected from the group consisting of imidazole, 1-methylimidazole, 1-ethylimidazole, 1-butyl imidazole, 1-isopropyl imidazole, 2-methyl imidazole, and 1,2-dimethyl imidazole. The absorbing solution according to any one of claims 1 to 6, which is a compound.
The absorption liquid according to any one of claims 1 to 9, wherein the imidazole compound is 1-methylimidazole.
The absorption liquid according to any one of claims 1 to 10, wherein the total content of the alkanolamine compound, the imidazole compound, and the water is 99% by mass or more with respect to the entire absorption liquid.
A step A in which the absorption liquid according to any one of claims 1 to 11 is brought into contact with a gas containing carbon dioxide to obtain an absorption liquid that has absorbed carbon dioxide from the gas containing carbon dioxide.
Step B in which the absorption liquid is heated to desorb and dissipate carbon dioxide from the absorption liquid, and the released carbon dioxide is recovered.
A method of separating and recovering carbon dioxide from a gas containing carbon dioxide.
The method according to claim 12, wherein in the step B, the absorption liquid is heated at 80 to 95 ° C. to desorb carbon dioxide.