Acidic gas-absorbing liquid and acidic gas reduction method

Abstract

This acidic gas-absorbing liquid reversibly absorbs and desorbs carbon dioxide, and contains a silicone compound and an amine compound. The viscosity of the silicone compound at 25°C is 0.1-15.0 mPa·s, the amine compound is a primary amine compound, and the solubility parameter of the amine compound is 8.0-9.5 (cal / cm3)1 / 2.

Description

Acid gas absorption solution and method for reducing acid gas

[0001] The present invention relates to an acidic gas absorbent and an acidic gas reduction method, and more particularly to an acidic gas absorbent that improves carbon dioxide absorption and prevents phase separation of the absorbent after carbon dioxide absorption, and to an acidic gas reduction method using the absorbent.

[0002] For example, in order to reduce greenhouse gases (such as carbon dioxide), a method is known for recovering acidic gases, such as carbon dioxide, from gases. This method involves using an acidic gas absorbent (hereinafter also simply called an absorbent) containing an amine compound and an organic solvent to absorb and separate the acidic gas, and then recovering the absorbed acidic gas by desorption from the absorbent by heating. Such an absorbent utilizes the reversible reaction of amine salt formation and regeneration by the amine compound, and is also called a chemical absorbent.

[0003] In the above-mentioned methods for recovering acidic gases, various methods have been proposed to reduce the energy required for heating when desorbing the acidic gas from the absorbent liquid, from the viewpoint of energy conservation. For example, Patent Document 1 proposes an acidic gas absorbent liquid containing an amine compound and a silicone compound.

[0004] International Publication No. 2024-122624

[0005] However, the absorbent liquid described in Patent Document 1 had the problem that its carbon dioxide absorption capacity was insufficient. In order to solve this problem, the present inventors attempted to improve the carbon dioxide absorption capacity by changing the amine compound described in Patent Document 1 to another amine compound, but it was found that the absorbent liquid underwent phase separation after carbon dioxide absorption. When the absorbent liquid underwent phase separation after carbon dioxide absorption, it became difficult to handle, such as becoming highly viscous and prone to solidification, when trying to remove the acidic gas from the absorbent liquid and reuse it.

[0006] This invention was made to solve these problems, and aims to provide an acidic gas absorbent that improves carbon dioxide absorption and prevents phase separation of the absorbent liquid even after carbon dioxide absorption, as well as a method for reducing acidic gases using the absorbent liquid.

[0007] This invention is based on the discovery that an acidic gas absorbent containing a silicone compound having a predetermined viscosity and a primary amine compound having predetermined solubility parameters improves carbon dioxide absorption and prevents phase separation of the absorbent even after carbon dioxide absorption.

[0008] The present invention provides the following means: [1] An acidic gas absorbent that reversibly absorbs and desorbs carbon dioxide, comprising a silicone compound and an amine compound, wherein the viscosity of the silicone compound at 25°C is 0.1 to 15.0 mPa·s, the amine compound is a primary amine compound, and the solubility parameter of the amine compound is 8.0 to 9.5 (cal / cm³). ３ ) １／２ [1] An acidic gas absorbent. [2] The acidic gas absorbent according to [1], wherein the content of the silicone compound relative to the total mass of the acidic gas absorbent is 10 to 97% by mass. [3] The acidic gas absorbent according to [1] or [2], wherein the content of the amine compound relative to the total mass of the acidic gas absorbent is 3 to 90% by mass. [4] The acidic gas absorbent according to any one of [1] to [3], wherein the mass ratio of the silicone compound to the amine compound is 10 / 90 to 97 / 3. [5] The acidic gas absorbent according to any one of [1] to [4], which is an acidic gas absorbent for a separation and recovery process for separating and recovering acidic gases. [6] The acidic gas absorbent according to any one of [1] to [5], wherein the silicone compound is a liquid at room temperature. [7] The acidic gas absorbent according to any one of [1] to [6], wherein the amine compound is linear or branched. [8] An acid gas reduction method comprising contacting an acid gas absorbent described in any of [1] to [7] above with a gas containing carbon dioxide to reduce the amount of carbon dioxide in the gas. [9] An acid gas reduction method according to [8] above, comprising heating the acid gas absorbent that has been in contact with a gas containing carbon dioxide to remove carbon dioxide from the acid gas absorbent, recovering the acid gas absorbent from which the carbon dioxide has been removed, and reusing it as an acid gas absorbent to be in contact with a gas containing carbon dioxide.

[0009] The present invention provides an acidic gas absorbent that improves carbon dioxide absorption and prevents phase separation of the absorbent liquid even after carbon dioxide absorption, as well as a method for reducing acidic gases using the absorbent liquid.

[0010] The definitions and meanings of terms and notations used herein are given below. In this specification, preferred forms of embodiments are shown, but combinations of two or more individual preferred forms are also preferred forms. When there are several numerical ranges for matters indicated by numerical ranges, a preferred form can be created by selectively combining their lower and upper limits. For example, from a statement like "preferably 10 to 90, more preferably 30 to 60," the "preferred lower limit (10)" and the "more preferred upper limit (60)" can be combined to become "10 to 60." Also, in numerical ranges described herein, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples. Numerical ranges expressed using "~" mean that the numbers before and after "~" are the lower and upper limits. For the structural formulas of chemical substances, known structural formulas are applied to silicone compounds and amine compounds, and in cases where the structural formula is not known, １ H-NMR and １３ Identified by 13C-NMR analysis. In this specification, the "solubility parameter" is the value at 25°C calculated by the Fedors method. For amine compounds, known structural formulas were used in the calculation using the Fedors method. In this specification, "room temperature" means 25°C.

[0011] [Acid Gas Absorbent Liquid] The acid gas absorbent liquid of the present invention absorbs carbon dioxide (hereinafter referred to as "CO2") ２ It is an acidic gas absorbent that reversibly absorbs and desorbs (sometimes described as "). It contains a silicone compound and an amine compound. The silicone compound has a viscosity of 0.1 to 15.0 mPa·s at 25°C. The amine compound is a primary amine compound with a solubility parameter of 8.0 to 9.5 (cal / cm³). ３ ) １／２. The acidic gas absorbent may or may not contain water, but preferably does not contain water. The acidic gas absorbent may or may not contain silicone compounds other than the above silicone compound (for example, silicone compounds having a viscosity at 25°C of less than 0.1 mPa·s, silicone compounds having a viscosity at 25°C of more than 15.0 mPa·s, etc.). The acidic gas absorbent may or may not contain amine compounds other than the above amine compound (for example, secondary amine compounds, tertiary amine compounds, solubility parameter of 8.0 (cal / cm ３ ) １／２ amine compounds less than , solubility parameter of 9.5 (cal / cm ３ ) １／２ amine compounds more than , etc.).

[0012] The acidic gas is a gas containing carbon dioxide, and may further contain other acidic gases such as hydrogen sulfide, sulfurous acid gas, for example. The acidic gas absorbent according to an embodiment of the present invention (hereinafter referred to as the present embodiment) can reversibly absorb and desorb carbon dioxide among acidic gases in particular, and can be regenerated and reused. Hereinafter, a case where the acidic gas absorbed by the acidic gas absorbent is carbon dioxide will be described as an example.

[0013] The acidic gas absorbent of the present embodiment includes a silicone compound having a predetermined viscosity and a primary amine compound having a predetermined solubility parameter, and may further include other components as necessary.

[0014] (Silicone Compounds) There are no particular restrictions on the type of silicone compound, and examples include silicone oils, silicone resins, silicone rubbers, and other silicone compounds that are liquid at room temperature. Examples of silicone oils include hydrophilic oil-type silicone oils, solvent-type silicone oils obtained by adding a solvent to silicone, emulsion-type silicone oils, and self-emulsifying silicone oils. Among these, emulsion-type silicone oils, hydrophilic oil-type silicone oils, and self-emulsifying silicone oils are preferred from the viewpoint of having low hygroscopicity and being able to easily improve carbon dioxide absorption. These may be used individually or in combination of two or more. Among these, silicone compounds that are liquid at room temperature are preferred in terms of their ability to absorb carbon dioxide, and silicone oils are more preferred.

[0015] <Viscosity of Silicone Compounds> The viscosity of silicone compounds at 25°C is not particularly limited as long as it is between 0.1 and 15.0 mPa·s. However, it is preferably between 1.0 and 10.0 mPa·s, more preferably between 2.0 and 5.0 mPa·s, and especially preferably between 3.0 and 5.0 mPa·s, as it exhibits excellent low volatility and makes it less likely to separate into two layers as an acidic gas absorbent. The viscosity of silicone compounds at 25°C is measured as described in the examples. When two or more silicone compounds are used in combination, the viscosity of each silicone compound at 25°C is between 0.1 and 15.0 mPa·s, and the viscosity of the entire silicone compound used in combination at 25°C is also between 0.1 and 15.0 mPa·s.

[0016] <Specific Examples of Silicone Compounds> There are no particular restrictions on specific silicone compound products. Examples include the KF-96 series, KS604, KS537, and KS538 manufactured by Shin-Etsu Chemical Co., Ltd., and FS544 manufactured by Dow Toray Industries, Inc.

[0017] (Primary amine compounds) The solubility parameter for primary amine compounds is 8.0 to 9.5 (cal / cm³). ３ ) １／２ As long as it is within this range, there are no particular restrictions, but preferably 8.2 to 9.2 (cal / cm³). ３ ) １／２, more preferably 8.4 to 8.9 (cal / cm³) ３ ) １／２ Particularly preferably 8.5 to 8.7 (cal / cm³) ３ ) １／２ Within the above range, phase separation is unlikely, either before or after carbon dioxide absorption. Furthermore, when two or more primary amine compounds are used in combination, the solubility parameters of each primary amine compound should be between 8.0 and 9.5 (cal / cm³). ３ ) １／２ Furthermore, the solubility parameter for the entire primary amine compound when two or more types are used in combination is 8.0 to 9.5 (cal / cm³). ３ ) １／２ That is the case.

[0018] While there are no particular restrictions on the primary amine compound, linear or branched primary amine compounds are preferred because they offer an excellent balance between carbon dioxide absorption and desorption properties in acidic gas absorbents and solubility in silicone compounds.

[0019] <Specific Examples of Primary Amine Compounds> Specific examples of primary amine compounds include, for example, (2-ethylhexyl)amine (2EHA), 3-(dibutylamino)propylamine (DBAPA), 3-(2-ethylhexyloxy)propylamine, benzylmethylamine, benzylethylamine, benzylpropylamine, benzylbutylamine, methylaniline, ethylaniline, propylaniline, and butylaniline. These may be used individually or in combination of two or more. Among these, (2-ethylhexyl)amine (2EHA) and 3-(dibutylamino)propylamine (DBAPA) are preferred.

[0020] There are no particular restrictions on the content of the silicone compound relative to the total mass of the acidic gas absorbent liquid, but from the viewpoint of fully exhibiting its carbon dioxide absorption capacity, it is preferably 10 to 97% by mass, more preferably 20 to 92% by mass, and particularly preferably 30 to 80% by mass.

[0021] There are no particular restrictions on the content of the primary amine compound relative to the total mass of the acidic gas absorbent solution, but from the viewpoint of fully exhibiting its carbon dioxide absorption capacity, it is preferably 3 to 90% by mass, more preferably 8 to 80% by mass, and particularly preferably 20 to 70% by mass.

[0022] There are no particular restrictions on the mass ratio of the silicone compound to the primary amine compound in the acidic gas absorbent solution, but from the viewpoint of compatibility between the amine compound and the silicone compound, it is preferably 10 / 90 to 97 / 3, more preferably 15 / 85 to 90 / 10, and particularly preferably 20 / 80 to 80 / 20. There are no particular restrictions on the total content of the silicone compound and the primary amine compound in the acidic gas absorbent solution, but it is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, particularly preferably 99% by mass or more, and may also be 100% by mass.

[0023] (Other components (additives)) The acidic gas absorbent may, if necessary, contain other components (additives) such as other silicone compounds, other amine compounds, antioxidants, corrosion inhibitors, viscosity modifiers, and surfactants, to the extent that they do not hinder the effects of the present invention, or may not contain them. There are no particular restrictions on the total content of other components (additives) in the acidic gas absorbent, but it is preferably 20% by mass or less, more preferably 10% by mass or less, particularly preferably 5% by mass or less, and may be 0% by mass. There are no particular restrictions on the water content in the acidic gas absorbent, but it is preferably 5% by mass or less, more preferably 3% by mass or less, particularly preferably 2% by mass or less, and may be 0% by mass.

[0024] The acidic gas absorbent of this embodiment can be produced by mixing the above-mentioned silicone compound and primary amine compound. Alternatively, the above-mentioned additives and water may be added and mixed as needed.

[0025] The acidic gas absorbent of the present embodiment is suitable for use in a separation and recovery process for separating and recovering acidic gas, and is particularly suitably used in a separation and recovery process for separating and recovering carbon dioxide when the acidic gas is carbon dioxide. Examples of the separation and recovery process for separating and recovering carbon dioxide include a process in which a gas containing carbon dioxide is brought into contact with an acidic gas absorbent to selectively absorb and separate carbon dioxide, carbon dioxide is desorbed and recovered by heating or depressurizing the liquid that has absorbed carbon dioxide, and the liquid after desorption of carbon dioxide is recovered and regenerated as an acidic gas absorbent.

[0026] There is no particular limitation on the absorbent temperature when causing carbon dioxide to be absorbed into the acidic gas absorbent, but from the viewpoint of suppressing the load of gas cooling energy, it is preferably -10 to 60°C, more preferably 0 to 50°C. When the temperature is equal to or higher than the lower limit of the above range, the load of gas cooling energy can be suppressed, and when the temperature is equal to or lower than the upper limit of the above range, carbon dioxide can be sufficiently absorbed. There is no particular limitation on the gas pressure when causing carbon dioxide to be absorbed into the acidic gas absorbent, but when it is assumed that the pressure is approximately the same as the partial pressure of carbon dioxide in the atmosphere, from the viewpoint of facilitating the separation and recovery of carbon dioxide by using the pressure difference from the atmosphere, it is preferably 20 to 100 Pa, more preferably 30 to 80 Pa, particularly preferably 32 to 65 Pa. Further, when it is assumed that the pressure is approximately the same as the partial pressure of carbon dioxide in combustion exhaust gas, from the viewpoint of easily reducing the amount of water absorbed and facilitating the separation and recovery of carbon dioxide, it is preferably 0.5 to 100 kPa, more preferably 1 to 50 kPa, particularly preferably 3 to 30 kPa.

[0027] There is no particular limitation on the temperature of the acidic gas absorbent when releasing carbon dioxide from the acidic gas absorbent, but it is preferably 50 to 120°C, more preferably 70 to 100°C, and particularly preferably 70 to 90°C. When the temperature is not lower than the lower limit of the above range, carbon dioxide can be sufficiently desorbed from the acidic gas absorbent; when the temperature is not higher than the upper limit of the above range, deterioration of the acidic gas absorbent can be suppressed. There is no particular limitation on the gas pressure when releasing carbon dioxide from the acidic gas absorbent, but from the viewpoint of facilitating separation and recovery of carbon dioxide using a pressure difference from the atmosphere, it is preferably 0.5 to 20 Pa, more preferably 2 to 20 Pa, and particularly preferably 2.5 to 15 Pa.

[0028] The temperature difference between the absorption of carbon dioxide into the acidic gas absorbent and the release of carbon dioxide from the acidic gas absorbent is set by weighing and balancing the thermal energy required for carbon dioxide release and the recovered amount, and is preferably 80°C or lower, more preferably 60°C or lower. By combining with processes such as hydrogen stripping and heat pumps, the temperature difference can be reduced, thereby reducing the required energy.

[0029] [Method for reducing acidic gas] In the method for reducing acidic gas of the present embodiment, the above-described acidic gas absorbent of the present embodiment is brought into contact with a gas containing carbon dioxide, so as to reduce carbon dioxide in the gas. The acidic gas absorbent of the present embodiment is not only effective for recovering carbon dioxide from a gas that does not contain moisture, but also when recovering carbon dioxide from a gas containing carbon dioxide and moisture, carbon dioxide can be separated and removed without heating to evaporate moisture, so the effect of reducing the energy required for recovering acidic gas from the gas can be further exhibited. There is no particular limitation on the method for reusing the acidic gas absorbent, and an example includes a method where: the acidic gas absorbent that has been contacted with the carbon dioxide-containing gas is heated to desorb carbon dioxide from the acidic gas absorbent; and the acidic gas absorbent from which carbon dioxide has been desorbed is recovered and reused as the acidic gas absorbent for contacting with the carbon dioxide-containing gas.

[0030] There are no particular restrictions on the method of contact between the acidic gas absorbent and the gas. Examples include adding the acidic gas absorbent to the gas, continuously circulating the gas through a container filled with the acidic gas absorbent, or filling a container filled with the acidic gas absorbent with the gas. To improve the contact efficiency between the acidic gas absorbent and the gas, methods such as providing a packing material in the container, spraying the acidic gas absorbent onto the gas, or bubbling the gas into the acidic gas absorbent can also be used.

[0031] The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples, and various modifications are possible without departing from the spirit of the invention. Examples 1 to 11 and 31 to 35 are examples, and examples 12 to 30 are comparative examples.

[0032] [Preparation of Acidic Gas Absorbent Solution] (Examples 1-35) As shown in Tables 1-1 to 1-3, acidic gas absorbent solutions were prepared by mixing various silicone compounds and various amine compounds in predetermined mass ratios.

[0033] Tables 1-1 to 1-3 show the names of the silicone compounds, the mass ratio when two silicone compounds are used together (silicone compound 1 / silicone compound 2), the viscosity of the silicone compounds (unit: mPa·s), the names of the amine compounds, the mass ratio when two amine compounds are used together (amine compound 1 / amine compound 2), the class of the amine compounds, and the solubility parameters of the amine compounds (unit: (cal / cm³)). ３ ) １／２ ), mass ratio of silicone compound to amine compound (silicone compound / amine compound), acid gas absorbent (CO ２ Phase state (after absorption), CO of the acidic gas absorbent ２ Absorption amount (CO ２The evaluation results for amine compounds (molar ratio) and the moisture absorption amount of acidic gas absorbent liquid (unit: mass ppm) are shown. The abbreviations for amine compounds and silicone compounds in Tables 1-1 to 1-3 are as follows.・2EHA: (2-ethylhexyl)amine ・DBAPA: 3-(dibutylamino)propylamine ・MEA: monoethanolamine ・DAA: diallylamine ・DIAA: diisopropylethylamine ・KF-96L 1CS: Dimethyl silicone oil, manufactured by Shin-Etsu Chemical Co., Ltd. ・KF-96L 1.5CS: Dimethyl silicone oil, manufactured by Shin-Etsu Chemical Co., Ltd. ・KF-96L 2CS: Dimethyl silicone oil, manufactured by Shin-Etsu Chemical Co., Ltd. ・KF-96L 5CS: Dimethyl silicone oil, manufactured by Shin-Etsu Chemical Co., Ltd. ・KF-96 10CS: Dimethyl silicone oil, manufactured by Shin-Etsu Chemical Co., Ltd. ・KF-96 20CS: Dimethyl silicone oil, manufactured by Shin-Etsu Chemical Co., Ltd. ・KF-96 30CS: Dimethyl silicone oil, manufactured by Shin-Etsu Chemical Co., Ltd. ・KF-96 50CS: Dimethyl silicone oil, manufactured by Shin-Etsu Chemical Co., Ltd. ・KF-96 100CS: Dimethyl silicone oil, manufactured by Shin-Etsu Chemical Co., Ltd.

[0034] [Viscosity of Silicone Compounds (Unit: mPa·s)] The viscosity of silicone compounds was measured using a viscometer (manufactured by Toki Sangyo Co., Ltd., product name: VISCOMETER TV-25) at a measurement temperature of 25°C and rotor No. 1.

[0035] [Solubility Parameters of Amine Compounds] The solubility parameters for each amine compound are values ​​calculated at 25°C using the Fedors method.

[0036] [CO2 in acidic gas absorbent solution] ２[Phase State After Absorption] In Example 1, 3 g of KF-96L 1CS and 3 g of 2EHA were mixed and placed in a 10 mL glass vial to prepare an acidic gas absorbent. Carbon dioxide was absorbed into the acidic gas absorbent for 3 hours while stirring at 500 rpm under a carbon dioxide atmosphere of 800 mL / min. The phase state after carbon dioxide absorption was visually evaluated after standing for 12 hours after carbon dioxide absorption. When the phase state was visually confirmed, if the acidic gas absorbent was separated into two layers (phase separation), it was evaluated as "two-layer separation," and if it was a single layer, it was evaluated as "homogeneous." For Examples 2 to 35, as shown in Tables 1-1 to 1-3, the acidic gas absorbent was prepared by mixing various silicone compounds and various amine compounds in predetermined mass ratios, except that the CO2 in the acidic gas absorbent was the same as in Example 1. ２ The phase state after absorption was evaluated.

[0037] [CO2 in acidic gas absorbent solution] ２ Absorption amount (unit: CO2) ２ [Amine compound (molar ratio)] In Example 1, 3 g of KF-96L 1CS and 3 g of 2EHA were mixed and placed in a 10 mL glass vial to prepare an acidic gas absorption solution. Carbon dioxide was absorbed into the acidic gas absorption solution while stirring at 500 rpm for 3 hours under a carbon dioxide atmosphere of 800 mL / min. The amount of carbon dioxide absorbed was calculated as follows. １３ The CO2 in the acidic gas absorbent was quantified from the integral value of the peaks derived from carbamates and / or bicarbonates, which are reaction products of carbon dioxide and amine compounds, using 13C NMR. Peaks in the range of 160 ppm to 163 ppm were considered to be the peaks derived from the carbamates and / or bicarbonates. Toluene was used as the internal standard. Manufacturer: Bruker Instrument name: Ascend400 For Examples 2 to 35, the CO2 in the acidic gas absorbent was prepared in the same manner as in Example 1, except that an acidic gas absorbent was prepared by mixing various silicone compounds and various amine compounds in predetermined mass ratios, as shown in Tables 1-1 to 1-3. ２ An evaluation of the amount of carbon dioxide absorbed was conducted. A carbon dioxide absorption rate of 0.30 or higher was considered to indicate good carbon dioxide absorption.

[0038] [Amount of moisture absorbed by acidic gas absorbent (unit: ppm by mass)] Acidic gas absorbent (CO) for each example ２ (Before absorption) 5 g was mixed with a stirrer tip in a 10 cc vial, and with the vial lid open, it was stirred at 500 rpm for 180 minutes in a fume hood. Afterwards, the acidic gas absorbent (CO2) was used. ２ The sample (before absorption) was extracted using a syringe with a needle, and the amount of moisture absorbed (unit: mass ppm) contained in the acidic gas absorption solution for each example was calculated using a Karl Fischer moisture analyzer (manufactured by Mitsubishi Chemical Analytec, trace moisture analyzer: model number CA-200).

[0039]

[0040]

[0041]

[0042] As can be seen from Tables 1-1 to 1-3, the silicone compounds have a viscosity of 0.1 to 15.0 mPa·s at 25°C, and the solubility parameter is 8.0 to 9.5 (cal / cm³). ３ ) １／２ Examples 1-11, 31-35, which contain a primary amine compound, have good carbon dioxide absorption capacity and CO ２ The acidic gas absorbent solution did not separate into two layers after absorption.

Claims

1. An acidic gas absorbent that reversibly absorbs and desorbs carbon dioxide, comprising a silicone compound and an amine compound, wherein the viscosity of the silicone compound at 25°C is 0.1 to 15.0 mPa·s, the amine compound is a primary amine compound, and the solubility parameter of the amine compound is 8.0 to 9.5 (cal / cm³). ３ ) １／２ It is an acidic gas absorbent.

2. The acidic gas absorbent according to claim 1, wherein the content of the silicone compound relative to the total mass of the acidic gas absorbent is 10 to 97% by mass.

3. The acidic gas absorbent according to claim 1 or 2, wherein the content of the amine compound relative to the total mass of the acidic gas absorbent is 3 to 90% by mass.

4. The acidic gas absorbent according to any one of claims 1 to 3, wherein the mass ratio of the silicone compound to the amine compound is 10 / 90 to 97 / 3.

5. An acidic gas absorbent liquid for a separation and recovery process for separating and recovering acidic gases, as described in any one of claims 1 to 4.

6. The acidic gas absorbent according to any one of claims 1 to 5, wherein the silicone compound is a liquid at room temperature.

7. The acidic gas absorbent according to any one of claims 1 to 6, wherein the amine compound is linear or branched.

8. A method for reducing acidic gases, comprising contacting an acidic gas absorbent liquid according to any one of claims 1 to 7 with a gas containing carbon dioxide to reduce the amount of carbon dioxide in the gas.

9. The method for reducing acidic gas according to claim 8, comprising heating an acidic gas absorbent solution that has been brought into contact with a gas containing carbon dioxide to remove carbon dioxide from the acidic gas absorbent solution, recovering the acidic gas absorbent solution from which the carbon dioxide has been removed, and reusing it as an acidic gas absorbent solution to be brought into contact with a gas containing carbon dioxide.

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