Absorbent and method for producing the same, and method for separating and recovering acidic compounds

Abstract

The absorbent of the present invention comprises water, an amine compound and an organic solvent, wherein the value obtained by subtracting the solubility parameter of the organic solvent from the solubility parameter of the amine compound is 1.1 ( ca l / c m3)1 / 2 or more and 4.2( ca l / c m3) 1 / 2 or less. The method for separating and recovering acidic compounds of the present invention comprises: a step of contacting a mixed gas containing the acidic compounds with the absorbent, thereby absorbing the acidic compounds in the absorbent; a step of separating the absorbent that has absorbed the acidic compounds into a first phase having a high acidic compound content and a second phase having a low acidic compound content; and a step of releasing the acidic compounds from the first phase by heating the first phase.

Description

Technical Field

[0001] The present invention relates to an absorbent and a method for preparing the same, as well as a method for separating and recovering acidic compounds. Background Art

[0002] Thermal power plants, boilers in steel mills, kilns in cement plants, and the like discharge mixed gases containing acidic compounds. Due to environmental issues such as global warming, there is a demand for technologies that can separate and recover only the acidic compounds from mixed gases containing acidic compounds. Here, an acidic compound refers to a compound that generates an acid when dissolved in water. Specific examples of acidic compounds include carbon dioxide, hydrogen sulfide, and sulfur disulfide. One method for recovering acidic compounds from mixed gases containing acidic compounds involves using an alkaline absorbent. In this method, the mixed gas is first brought into contact with the absorbent, causing the acidic compounds to be absorbed by the absorbent. The absorbent that has absorbed the acidic compounds is then heated, causing the acidic compounds to be released from the absorbent. Furthermore, the acidic compounds released from the absorbent are recovered.

[0003] As an example of such an absorbent, Patent Document 1 below proposes an absorbent comprising water, a tertiary amine, and an organic solvent. The absorbent described in Patent Document 1 is suitable for separating and recovering carbon dioxide contained at a relatively high partial pressure in a mixed gas. However, if the absorbent described in Patent Document 1 is applied to a mixed gas with a low carbon dioxide partial pressure, the energy required to heat the carbon dioxide to separate from the absorbent becomes relatively high. In recent years, due to growing concern for the global environment, there has been a demand for absorbents that can separate acidic compounds using less energy.

[0004] In order to reduce the energy required to separate the acidic compound from the absorbent, Patent Document 2, for example, proposes an absorbent that phase-separates into a first phase containing a small amount of the acidic compound and a second phase containing a high amount of the acidic compound.

[0005] In the gas deoxygenation method described in Patent Document 2, acidic compounds are removed from the second phase by heating only the second phase, which contains a high concentration of acidic compounds. This separation of the absorbent into two phases reduces the absolute amount of absorbent required for heating. This also reduces the energy required for regenerating the absorbent.

[0006] Patent Document 2 discloses various materials, such as water, alcoholic solvents, and alkaline salts, as components of the absorbent. The various components and their mixing ratios are determined from these materials so that the absorbent exhibits the property of absorbing acidic compounds and phase separation after absorbing the acidic compounds is extremely difficult. However, Patent Document 2 does not contain any guidance regarding the determination of the components and mixing ratios of the absorbent.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-36933

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2006-136885 Summary of the Invention

[0011] The object of the present invention is to provide an absorbent that absorbs acidic compounds contained in a mixed gas and performs phase separation after absorbing the acidic compounds, a method for producing the absorbent, and a method for separating and recovering the acidic compounds.

[0012] The absorbent of the present invention comprises water, an amine compound, and an organic solvent, wherein the value obtained by subtracting the solubility parameter of the organic solvent from the solubility parameter of the amine compound is 1.1 (cal / cm 3 ) 1 / 2 Above and 4.2 (cal / cm 3 ) 1 / 2 the following.

[0013] The method for producing an absorbent of the present invention comprises: a step of mixing water, an amine compound, and an organic solvent; and, before the mixing step, a step of subtracting the solubility parameter of the organic solvent from the solubility parameter of the amine compound to obtain a value of 1.1 (cal / cm 3 ) 1 / 2 Above and 4.2 (cal / cm 3 ) 1 / 2 The steps of selecting the amine compound and the organic solvent are as follows.

[0014] The method for separating and recovering an acidic compound of the present invention comprises: contacting a mixed gas containing the acidic compound with an absorbent containing water, an amine compound, and an organic solvent, thereby absorbing the acidic compound in the absorbent; separating the absorbent having absorbed the acidic compound into a first phase having a high content of the acidic compound and a second phase having a low content of the acidic compound; and releasing the acidic compound from the first phase by heating the first phase, wherein the value obtained by subtracting the solubility parameter of the organic solvent from the solubility parameter of the amine compound is 1.1 (cal / cm 3 ) 1 / 2 Above and 4.2 (cal / cm 3 ) 1 / 2 the following.

[0015] The "solubility parameter" in this specification refers to the solubility parameter calculated by the Fedors method. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of an apparatus for separating and recovering acidic compounds using an absorbent according to one embodiment of the present invention. DETAILED DESCRIPTION

[0017] [Absorbent]

[0018] The absorbent of the present invention has the property of absorbing acidic compounds and releasing the absorbed acidic compounds, and contains water, an amine compound, and an organic solvent.

[0019] The value obtained by subtracting the solubility parameter of the organic solvent from the solubility parameter of the amine compound (hereinafter referred to as "solubility parameter difference") was 1.1 (cal / cm 3 ) 1 / 2 Above, preferably 1.2 (cal / cm 3 ) 1 / 2 On the other hand, the solubility parameter difference is 4.2 (cal / cm 3 ) 1 / 2 Below, preferably 4.0 (cal / cm 3 ) 1 / 2 By setting such a solubility parameter difference, the absorbent can be maintained in a single, unseparated liquid phase before absorbing the acidic compound. By forming the absorbent into a single liquid phase, the absorbent can be uniformly contacted with the mixed gas containing the acidic compound. This allows the absorbent to efficiently absorb the acidic compound in the mixed gas.

[0020] Furthermore, by creating the solubility parameter difference, the absorbent after absorbing the acidic compound separates into two phases: a phase with a high acidic compound content (first phase) and a phase with a low acidic compound content (second phase). The thus-separated first phase is then subjected to a treatment to remove the acidic compound, allowing the acidic compound absorbed in the absorbent to be recovered. In other words, the absorbent according to the present invention does not require the entire absorbent to be treated to remove the acidic compound, as with conventional absorbents. Instead, the treatment to remove the acidic compound only needs to be performed on the first phase of the absorbent. Therefore, the absorbent according to the present invention can remove the acidic compound using less energy than conventional methods.

[0021] By setting the solubility parameter difference to 1.1 (cal / cm 3 ) 1 / 2 The above can facilitate phase separation of the absorbent that has absorbed the acidic compound. On the other hand, by setting the solubility parameter difference to 4.2 (cal / cm 3 ) 1 / 2This prevents the absorbent from separating before absorbing the acidic compound. This allows the absorbent, which consists of a single phase, to uniformly contact the mixed gas, thereby improving the efficiency of the absorbent in absorbing the acidic compound.

[0022] (Amine compound)

[0023] As the amine compound, one or more selected from the group consisting of primary amines, secondary amines, and tertiary amines can be used, preferably alkanolamines. Since alkanolamines contain amino and hydroxyl groups within their molecules, they have a high affinity for water and can effectively absorb acidic compounds. If the absorbent contains multiple amine compounds, the solubility parameter of the amine compound is determined by taking the volume average of the solubility parameters of the individual amine compounds.

[0024] Examples of primary amines include 1,3-diaminopropane (DAP), 2-ethanolamine (MEA), DL-2-amino-1-propanol (AP), 2-(2-aminoethoxy)ethanol (AEE), and (R)-4-amino-2-methyl-1-butanol (AMB). Examples of secondary amines include 2-(methylamino)ethanol (MAE), 2-(ethylamino)ethanol (EAE), and 2-(butylamino)ethanol (BAE). Examples of tertiary amines include triethanolamine (TEA), N-methyldiethanolamine (MDEA), tetramethylethylenediamine (TEMED), pentamethyldiethylenetriamine (PMDETA), hexamethyltriethylenetetramine, and bis(2-dimethylaminoethyl)ether. Examples of the alkanolamine include 2-ethanolamine (MEA), DL-2-amino-1-propanol (AP), 2-(2-aminoethoxy)ethanol (AEE), (R)-4-amino-2-methyl-1-butanol (AMB), 2-(methylamino)ethanol (MAE), 2-(ethylamino)ethanol (EAE), and 2-(butylamino)ethanol (BAE).

[0025] The solubility parameter of the amine compound is preferably 10 (cal / cm 3 ) 1 / 2 More than 12 (cal / cm 3 ) 1 / 2 On the other hand, the solubility parameter of the amine compound is preferably 20 (cal / cm 3 ) 1 / 2 Below, more preferably 15 (cal / cm 3 ) 1 / 2 By setting the solubility parameter of the amine compound to 10 (cal / cm 3 ) 1 / 2As described above, the absorbent before absorbing the acidic compound can be prevented from phase separation, so the acidic compound can be absorbed efficiently by the absorbent. 3 ) 1 / 2 Next, the absorbent after absorbing the acidic compound can be phase-separated. Therefore, by heating only the first phase containing a large amount of the acidic compound after the phase separation, the acidic compound can be recovered efficiently.

[0026] The absorbent preferably comprises a secondary amine. Secondary amines are more likely to undergo a bicarbonate reaction, in which one amine molecule absorbs one carbon dioxide molecule, than a carbamate reaction, in which two amine molecules absorb one carbon dioxide molecule. Therefore, secondary amines absorb more carbon dioxide per mol than primary amines. Furthermore, bicarbonate reactions have a lower heat of reaction than carbamate reactions. Therefore, the use of secondary amines can suppress the energy required for the absorption and removal of acidic compounds. Furthermore, by including a secondary amine in the absorbent, the acidic compounds can be easily absorbed even when the partial pressure of the acidic compounds in the mixed gas is low.

[0027] As the amine compound, a primary amine can be added to the secondary amine at a rate of 3% to 10% by mass. Using such an amine compound can increase the absorption rate of the acidic compound by the secondary amine. Alternatively, a tertiary amine can be added to the secondary amine at a rate of 3% to 10% by mass. The absorbent preferably comprises an alkanolamine. Using an amine compound having both an amino group and a hydroxyl group, such as an alkanolamine, can produce an absorbent with excellent affinity for water and high absorption performance for acidic compounds.

[0028] Tertiary amines react only with bicarbonates, so they can absorb more carbon dioxide per unit volume. However, tertiary amines have low carbon dioxide absorption efficiency due to their low pressure, making it difficult for the absorbent to absorb carbon dioxide when the carbon dioxide partial pressure is relatively low.

[0029] The absorbent preferably contains 20% or more of the amine compound, more preferably 25% or more of the amine compound. On the other hand, the absorbent preferably contains 40% or less of the amine compound, more preferably 35% or less of the amine compound. By setting the amine compound content to 20% or more, the absorption capacity of the acidic compound can be increased. Furthermore, by setting the amine compound content to 40% or less, the volume ratio of the first phase after phase separation can be reduced, thereby reducing the amount of absorbent required for heating. Consequently, the energy required to release the acidic compound from the absorbent can be reduced.

[0030] (Organic Solvent)

[0031] The organic solvent is selected such that the solubility parameter difference with the amine compound is within the above range. The organic solvent preferably comprises an alcohol having 2 to 15 carbon atoms and an ether having 4 to 20 carbon atoms, and more preferably comprises an alcohol having 3 to 10 carbon atoms and an ether having 4 to 12 carbon atoms.

[0032] The organic solvent is preferably an alcohol in which the hydrogen atoms of a linear hydrocarbon with 3 to 8 carbon atoms are replaced by hydroxyl groups. Such an alcohol can provide hydrophilicity due to the hydroxyl groups, while providing lipophilicity due to the linear hydrocarbon with 3 to 8 carbon atoms. The interaction between these hydrophilic and lipophilic groups can produce an absorbent that does not phase separate before absorbing the acidic compound but phase separates after absorbing the acidic compound. Specific examples of such alcohols include 1-butanol, 1-pentanol, and octanol.

[0033] The organic solvent preferably comprises a linear ether having an ether bond and 4 to 20 carbon atoms, more preferably a linear ether having 2 to 4 ether bonds and 6 to 10 carbon atoms. Such linear ethers have high hydrophilicity and facilitate phase separation of the absorbent into two phases after absorbing the acidic compound. Specific examples of such ethers include diethylene glycol diethyl ether (DEGDEE) and diethylene glycol dimethyl ether (DEGDME).

[0034] The solubility parameter of the organic solvent is preferably 6 (cal / cm 3 ) 1 / 2 More than 8 (cal / cm 3 ) 1 / 2 On the other hand, the solubility parameter of the organic solvent is preferably 13 (cal / cm 3 ) 1 / 2 Below, more preferably 12 (cal / cm 3 ) 1 / 2 Below, more preferably 11 (cal / cm 3 ) 1 / 2 By setting the solubility parameter of the organic solvent to 6 (cal / cm 3 ) 1 / 2 The above can make it difficult for the absorbent to separate before absorbing the acidic compound, so the absorbent can be used to absorb the acidic compound efficiently. 3 ) 1 / 2 Then, the absorbent after absorbing the acidic compound can be easily phase-separated into two phases, and thus the acidic compound can be recovered efficiently.

[0035] As the organic solvent, a single compound or a mixture of multiple compounds may be used. When multiple organic solvents are used, the volume average of the solubility parameters of the organic solvents is defined as the solubility parameter of the organic solvent.

[0036] The organic solvent content is preferably 40% by mass or greater, more preferably 45% by mass or greater. On the other hand, the organic solvent content is preferably 60% by mass or less, more preferably 55% by mass or less. By setting the organic solvent content to 40% by mass or greater, phase separation due to absorption of the acidic compound can be promoted. On the other hand, by setting the organic solvent content in the absorbent to 60% by mass or less, the absorption capacity of the acidic compound can be increased.

[0037] The absorbent may appropriately contain additives such as absorption enhancers, antioxidants, preservatives, etc. As the absorption enhancer, for example, piperazine can be used.

[0038] <Method for producing absorbent>

[0039] The method for producing an absorbent of the present invention includes: a step of mixing water, an amine compound, and an organic solvent; and a step of selecting the amine compound and the organic solvent so that the mixed amine compound and the organic solvent satisfy the solubility parameter difference before the mixing step.

[0040] Thus, by selecting the amine compound and the organic solvent with attention paid to the difference in solubility parameters, it is possible to produce an absorbent that is a single liquid phase before absorbing the acidic compound and undergoes phase separation after absorbing the acidic compound.

[0041] [Method for separation and recovery of acidic compounds]

[0042] The separation and recovery method of the acidic compound of the present invention uses, for example Figure 1 The recovery method includes: a step of bringing a mixed gas containing an acidic compound into contact with the absorbent, thereby absorbing the acidic compound into the absorbent; a step of separating the absorbent having absorbed the acidic compound into a first phase having a high content of the acidic compound and a second phase having a low content of the acidic compound; and a step of releasing the acidic compound from the first phase by heating the first phase. Figure 1 The recovery device shown.

[0043] Figure 1The recovery device includes an absorber 1, a liquid separator 2, a regenerator 3, a reboiler 5, a condenser 6, a main heat exchanger 7, and a cooler 8. These components are connected by pipes L1 to L10. The absorbent in the absorber 1 is circulated to the absorber 1 via the liquid separator 2 and the regenerator 3 through pipes L2, L4, and L9 among these pipes L1 to L10.

[0044] Absorber 1 is where the acidic compounds in the mixed gas (the gas being treated) are absorbed by the absorbent. The mixed gas introduced into absorber 1 via pipe L1 comes into contact with the absorbent, whereupon the acidic compounds in the mixed gas are absorbed by the absorbent. The absorbent that has absorbed the acidic compounds in absorber 1 is transported via pipe L2 to liquid separator 2. The mixed gas, from which the acidic compounds have been removed, is discharged from the system via pipe L3. The absorption of the acidic compounds in absorber 1 is an exothermic reaction.

[0045] The absorber 1 may be any absorber that allows the mixed gas and the absorbent to continuously contact each other. For example, the mixed gas and the absorbent may be brought into contact by spraying the absorbent into the mixed gas flow path, allowing the absorbent to flow down a packing material disposed in the mixed gas flow path, or introducing the mixed gas and the absorbent into a plurality of microscopic flow paths, respectively, and then merging the microscopic flow paths of the mixed gas and the absorbent.

[0046] The liquid separator 2 is a section for phase separation of the absorbent that has absorbed the acidic compounds. Liquid separator 2 separates the phases into a first phase with a high acidic compound content and a second phase with a low acidic compound content. Liquid separator 2 can be, for example, a container for gravity separation of the absorbent or a device for centrifugal separation of the absorbent. The first phase separated in liquid separator 2 is transported from pipe L4 to regenerator 3 via main heat exchanger 7. The second phase separated in liquid separator 2 is returned to absorber 1 from pipe L5 via cooler 8.

[0047] The regenerator 3 is a part that separates (releases) the acidic compounds from the first phase separated in the liquid separator 2. The first phase supplied to the regenerator 3 is heated in the reboiler 5, thereby separating the acidic compounds from the first phase. At the same time, the water contained in the first phase evaporates and becomes water vapor due to the heating of the reboiler 5. The separation of the acidic compounds from the first phase is an endothermic reaction. The heat of the reboiler 5 is supplied to the regenerator 3 via the pipe L10. The acidic compounds separated from the first phase are transported to the condenser 6 through the pipe L6 together with the water vapor. On the other hand, the first phase from which the acidic compounds have been separated is transported to the cooler 8 through the pipe L9.

[0048] The condenser 6 separates the acidic compounds and water vapor generated by the heating of the reboiler 5. The mixed gas of the acidic compounds and water vapor is cooled in the condenser 6, condensing the water vapor in the mixed gas into water. This water flows back to the regenerator 3 via the pipe L8. Meanwhile, the acidic compounds in the mixed gas are recovered outside the system via the blender L7.

[0049] The main heat exchanger 7 is a part that exchanges heat between the first phase transported from the liquid separator 2 to the regenerator 3 and the first phase returned from the regenerator 3 to the absorber 1. In the main heat exchanger 7, the first phase whose absorption performance is regenerated in the regenerator 3 is cooled, and the first phase separated in the liquid separator 2 is heated. Accordingly, the first phase flowing to the cooler 8 is cooled before being supplied to the cooler 8, thereby reducing the energy required for cooling in the cooler 8. In addition, the first phase supplied to the regenerator 3 is heated before being supplied to the regenerator 3, thereby reducing the energy required for heating in the reboiler 5. As the main heat exchanger 7, a heat exchanger of a known structure such as a plate heat exchanger can be used. The main heat exchanger 7 preferably uses a microchannel heat exchanger that can exchange heat between fluids with a relatively small temperature difference. By using a microchannel heat exchanger, energy efficiency can be improved.

[0050] Cooler 8 is a device that cools the absorbent before it is returned to absorber 1. Cooling the absorbent in cooler 8 maintains a low temperature within absorber 1. This improves the efficiency of the absorbent in absorbing acidic compounds. Cooler 8 can be a heat exchanger using inexpensive cooling water, such as river water.

[0051] As described above, in the recovery device, the absorbent arranged in the absorber 1 absorbs the acidic compound. And, in the liquid separator 2, the absorbent that has absorbed the acidic compound is separated into a first phase having a high content of the acidic compound and a second phase having a low content of the acidic compound. The first phase separated in the liquid separator 2 is heated in the regenerator 3 to restore the function of the absorbent. This heating is performed by the reboiler 5. The acidic compound absorbed in the absorbent is released by the heating of the reboiler 5. Here, by recovering the released acidic compound, the acidic compound contained in the mixed gas can be recovered. The first phase in which the absorption function of the absorbent is restored is returned to the absorber 1. According to the method for separating and recovering the acidic compound of the present invention, it is not necessary to heat the second phase in the absorbent in the reboiler 5. Therefore, the energy required for the reboiler 5 can be reduced compared to the case of heating the absorbent as a whole.

[0052] [Other embodiments]

[0053] The above-described embodiments are not intended to limit the configuration of the present invention.

[0054] In the above recovery apparatus, the liquid separator 2 is described as being connected to the pipe L2 between the absorber 1 and the main heat exchanger 7. However, the liquid separator 2 is not limited to being connected in this location. For example, the liquid separator 2 may be connected to the pipe L4 between the main heat exchanger 7 and the regenerator 3. In this case, the absorbent that has absorbed the acidic compounds in the absorber 1 undergoes heat exchange in the main heat exchanger 7 with the absorbent from which the acidic compounds have been removed in the regenerator 3. After this, the absorbent is separated into a first phase and a second phase by the liquid separator 2. In this case, as in the recovery apparatus of the above embodiment, the first phase is supplied to the regenerator 3, and the second phase is refluxed to the absorber 1.

[0055] In the recovery device, another heat recovery device may be provided in the pipe L5 between the regenerator 3 and the main heat exchanger 7. Heat recovered by the heat recovery device is supplied to the reboiler 5, thereby reducing the energy required for the reboiler 5.

[0056] <Overview of Embodiments>

[0057] The absorbent of the embodiment comprises water, an amine compound, and an organic solvent, wherein the value of the solubility parameter of the organic solvent subtracted from the solubility parameter of the amine compound is 1.1 (cal / cm 3 ) 1 / 2 Above and 4.2 (cal / cm 3 ) 1 / 2 The amine compound is preferably a secondary amine, more preferably an alkanolamine. The organic solvent is preferably an alcohol having 2 to 15 carbon atoms or an ether having 4 to 20 carbon atoms, more preferably an alcohol having 3 to 8 carbon atoms in which the hydrogen atoms contained in the linear hydrocarbon are replaced by hydroxyl groups. The content of the amine compound is preferably 20% by mass or more and 40% by mass or less. The content of the organic solvent is preferably 40% by mass or more and 60% by mass or less.

[0058] Example

[0059] Hereinafter, the present invention will be described in detail based on Examples. However, the present invention should not be limitedly interpreted based on the description of these Examples.

[0060] One of each of the seven amine compounds shown in the left column of Table 1 below and the three organic solvents shown in the upper column of Table 1 was selected, and the amine compound, organic solvent, and water were mixed at a mass ratio of 30:60:10 to prepare a total of 21 absorbents.

[0061] The upper side of each column in Table 1 shows the value obtained by subtracting the solubility parameter of the organic solvent from the solubility parameter of the amine compound of each absorption liquid. The liquid phase of the absorbent before and after the absorption of carbon dioxide was confirmed for each absorbent produced. The evaluation results are shown at the lower side of each column. Here, "good" in Table 1 means that the absorbent before absorbing carbon dioxide is a single liquid phase, but the absorbent after absorbing carbon dioxide is phase-separated into two phases. "Not mixed" in Table 1 means that the absorbent before and after absorbing carbon dioxide is separated into two phases. "Not separated" in Table 1 means that the absorbent before and after absorbing carbon dioxide is a single phase.

[0062] Table 1

[0063]

[0064] The results shown in Table 1 confirmed that the absorbent was prepared by subtracting the solubility parameter of the organic solvent from the solubility parameter of the amine compound to obtain a value of 1.1 (cal / cm 3 ) 1 / 2 Above and 4.2 (cal / cm 3 ) 1 / 2 The combination of the amine compound and the organic solvent is selected in the following manner so that the absorbent forms a single liquid phase before absorbing the acidic compound, and phase-separates into two phases after absorbing the acidic compound. Thus, by using an absorbent that does not phase-separate before absorbing the acidic compound, the absorbent easily contacts the mixed gas, allowing the absorbent to absorb the acidic compound contained in the mixed gas. Furthermore, by using an absorbent that phase-separates after absorbing the acidic compound, the acidic compound can be recovered by heating only the first phase, which has a high acidic compound content. Consequently, the acidic compound contained in the mixed gas can be recovered using less energy.

[0065] This application is based on Japanese Patent Application No. 2015-249603 filed on December 22, 2015, the contents of which are incorporated herein by reference.

[0066] Industrial applicability

[0067] The absorbent and acidic compound separation and recovery method of the present invention are used, for example, to remove acidic compounds from various mixed gases such as industrial waste gas, natural gas, and hydrogen gas, or to remove acidic compounds from mixed gases used for fuel, etc. In particular, they are suitable for separating carbon dioxide from mixed gases.

Claims

1. An absorbent, characterized in that The invention comprises water, an amine compound and an organic solvent, wherein the value of the solubility parameter of the organic solvent subtracted from the solubility parameter of the amine compound is 1.1 (cal / cm 3 ) 1 / 2 Above and 4.2 (cal / cm 3 ) 1 / 2 Hereinafter, the content of the amine compound is 20% by mass or more and 40% by mass or less, and the content of the organic solvent is 40% by mass or more and 60% by mass or less, After absorbing the acidic compound, the phase is separated into a first phase with a high content of the acidic compound and a second phase with a low content of the acidic compound. The combination of the amine compound and the organic solvent is any one of 2-ethanolamine and 1-butanol, 2-(2-aminoethoxy)ethanol and 1-butanol, 2-(methylamino)ethanol and 1-butanol, 2-ethanolamine and 1-pentanol, 2-(2-aminoethoxy)ethanol and 1-pentanol, 2-(methylamino)ethanol and 1-pentanol, and 2-(ethylamino)ethanol and diethylene glycol diethyl ether. The acidic compound is carbon dioxide; and the solubility parameter is a solubility parameter calculated by the Fedors method.

2. A method for producing an absorbent, characterized in that include: a step of mixing water, an amine compound, and an organic solvent; as well as Before the mixing step, the solubility parameter of the organic solvent is subtracted from the solubility parameter of the amine compound to obtain a value of 1.1 (cal / cm 3 ) 1 / 2 Above and 4.2 (cal / cm 3 ) 1 / 2 The step of selecting the amine compound and the organic solvent in the following manner, wherein the content of the amine compound is 20% by mass or more and 40% by mass or less, and the content of the organic solvent is 40% by mass or more and 60% by mass or less, After absorbing the acidic compound, the manufactured absorbent separates into a first phase with a high content of the acidic compound and a second phase with a low content of the acidic compound. The combination of the amine compound and the organic solvent is any one of 2-ethanolamine and 1-butanol, 2-(2-aminoethoxy)ethanol and 1-butanol, 2-(methylamino)ethanol and 1-butanol, 2-ethanolamine and 1-pentanol, 2-(2-aminoethoxy)ethanol and 1-pentanol, 2-(methylamino)ethanol and 1-pentanol, and 2-(ethylamino)ethanol and diethylene glycol diethyl ether. The acidic compound is carbon dioxide; and the solubility parameter is a solubility parameter calculated by the Fedors method.

3. A method for separating and recovering acidic compounds, characterized in that include: a step of bringing a mixed gas containing an acidic compound into contact with an absorbent containing water, an amine compound, and an organic solvent, thereby absorbing the acidic compound in the absorbent; a step of separating the absorbent having absorbed the acidic compound into a first phase having a high content of the acidic compound and a second phase having a low content of the acidic compound; as well as a step of releasing the acidic compound from the first phase by heating the first phase, wherein In the absorbent, the content of the amine compound is 20% by mass or more and 40% by mass or less, and the content of the organic solvent is 40% by mass or more and 60% by mass or less, The value of subtracting the solubility parameter of the organic solvent from the solubility parameter of the amine compound is 1.1 (cal / cm 3 ) 1 / 2 Above and 4.2 (cal / cm 3 ) 1 / 2 the following, The combination of the amine compound and the organic solvent is any one of 2-ethanolamine and 1-butanol, 2-(2-aminoethoxy)ethanol and 1-butanol, 2-(methylamino)ethanol and 1-butanol, 2-ethanolamine and 1-pentanol, 2-(2-aminoethoxy)ethanol and 1-pentanol, 2-(methylamino)ethanol and 1-pentanol, and 2-(ethylamino)ethanol and diethylene glycol diethyl ether. The acidic compound is carbon dioxide; and the solubility parameter is a solubility parameter calculated by the Fedors method.

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