Absorbent for capturing acid gases, and preparation method therefor and use thereof

Abstract

The present application relates to the field of the absorption and regeneration of acid gases, and specifically relates to an absorbent for capturing acid gases, and a preparation method therefor and the use thereof. A compound for capturing acid gases provided by the present application has a structure as represented by formula (I), wherein R1 is an alkyl group having five or more carbon atoms, M is at least one of a proton-bound organic amine group and a proton-bound heterocyclic group containing a nitrogen atom, and n is an integer from 1 to 4. The compound for capturing acid gases provided by the present application has a relatively weak alkalinity and a relatively small acting force towards acid gases; moreover, the generation of a solid can be avoided during the absorption of acid gases with the compound, and therefore difficulties in the regeneration of the acid gases are reduced, and the regeneration process is relatively easy. The compound provided by the present application has a higher absorption rate for acid gases in the case of a relatively high water content.

Description

A kind of absorbent for capturing acid gas and its preparation method and application

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on December 26, 2023, with application number 2023118110382 and invention name “A kind of absorbent for capturing acidic gas, preparation method and application thereof”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of acid gas absorption and regeneration, and in particular to an absorbent for capturing acid gas, and a preparation method and application thereof. Background Art

[0004] The large-scale emission of acidic gases such as sulfur dioxide and carbon dioxide not only impacts the ecological environment and human health but also wastes resources. Therefore, the absorption and regeneration of acidic gases has become an important method for resource recycling. Acidic gases can be captured using technologies such as chemical absorption, pressure swing adsorption, and membrane separation. Chemical absorption is the most widely used method, often using alcoholamine absorbents to absorb the acidic gases. However, alcoholamines react strongly with carbon dioxide, resulting in high heat of reaction and a regeneration temperature between 105 and 120°C. This results in high regeneration energy consumption, leading to high energy losses in acid gas regeneration. Currently, researchers have explored the use of carboxylates and carboxylate-based ionic liquids for acidic gas absorption. However, materials such as carboxylate-based ionic liquids have high viscosity. While increasing the water concentration can reduce the viscosity of the system, the increased water content reduces the acid gas absorption rate.

[0005] The prior art discloses the use of carboxylate compounds as absorbents for capturing carbon dioxide. By using quaternary ammonium ions or quaternary phosphonium ions as cations of the carboxylate, the absorption rate of carbon dioxide can be improved. However, the absorbent material easily produces solids when absorbing acidic gases such as carbon dioxide, which brings inconvenience to the separation process.

[0006] Summary of the Invention

[0007] Therefore, the technical problem to be solved by the present application is to overcome the defect of the carboxylate absorbent in the prior art that it is easy to produce solids when absorbing acidic gases, thereby providing an absorbent for capturing acidic gases and its preparation method and application, thereby improving the absorption rate of acidic gases and reducing the difficulty of regenerating acidic gases.

[0008] On the one hand, the present application provides a compound for capturing acidic gas, characterized in that it has a structure shown in formula (I),

[0009] Wherein, R1 is an alkyl group having 5 or more carbon atoms, M is at least one of a proton-bound organic amine group and a proton-bound nitrogen-containing heterocyclic group, and n is an integer of 1-4.

[0010] In one embodiment, the R1 is a branched alkyl group.

[0011] Optionally, the number of carbon atoms in R1 is 6-20.

[0012] In one embodiment, the organic amine is at least one of aliphatic amine and alcohol amine.

[0013] Optionally, the organic amine is at least one of monoamine, diamine, and polyamine.

[0014] In one embodiment, the nitrogen-containing heterocycle is At least one of the following, wherein R2, R3, R4, R5, and R6 are any one of an alkyl group, a substituted alkyl group, or a hydrogen atom.

[0015] In one embodiment, the compound for capturing acidic gas has any of the following structures:

[0016] The present application provides an absorbent for capturing acidic gas, comprising the above-mentioned compound for capturing acidic gas.

[0017] On the other hand, the present application provides a method for preparing an absorbent for capturing acidic gases, comprising the following steps: mixing a carboxylic acid and an organic weak base to obtain an absorbent, wherein the carboxylic acid has a molecular formula of R1COOH, wherein R1 is an alkyl group having 5 or more carbon atoms.

[0018] In one embodiment, the absorbent further comprises water.

[0019] In one embodiment, the carboxylic acid is a fatty acid. Alternatively, the carboxylic acid is at least one of 2,2-dimethylhexanoic acid, 2-ethylhexanoic acid, 2-ethylheptanoic acid, 2-propylpentanoic acid, 2-propylhexanoic acid, 2-propylnonanoic acid, 2-butyloctanoic acid, and 2-hexyldecanoic acid.

[0020] In one embodiment, the organic weak base is at least one of an organic amine compound and a nitrogen-containing heterocyclic compound.

[0021] Optionally, the organic amine compound is at least one of triethylamine, tripropylamine, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, hydroxyethylethylenediamine, 2-amino-2-methyl-1-propanol, N-methyl-1,3-propylenediamine, 1,4-butanediamine, N,N,N',N'-tetramethylhexanediamine, diethylenetriamine, and triethylenetetramine.

[0022] Optionally, the nitrogen-containing heterocyclic compound is at least one of a pyridine ring-containing compound, an imidazole ring-containing compound, a pyrrole ring-containing compound, and piperazine.

[0023] In one embodiment, the molar ratio of the carboxylic acid, the organic weak base and water is 1:(0.25-1):(0-20).

[0024] The present application provides a compound for capturing acidic gas, an absorbent, or an absorbent prepared by a method for preparing an absorbent for capturing acidic gas, for use in absorbing and regenerating acidic gas, wherein the acidic gas is at least one of carbon dioxide, sulfur dioxide, or hydrogen sulfide.

[0025] The step of absorbing the acid gas comprises contacting the acid gas to be absorbed with an absorbent, and performing absorption at an acid gas partial pressure of 0.003 MPa-1.0 MPa and a temperature of 0-50°C.

[0026] The step of regenerating the acid gas comprises stirring the absorbent after absorbing the acid gas in an environment of 80-100° C. for 0.1-2 hours for desorption, or stirring the absorbent after absorbing the acid gas in a vacuum condition of 10-80° C. for 0.1-1 hour for desorption.

[0027] The technical solution of this application has the following advantages:

[0028] 1. The compound for capturing acidic gases provided in the present application has a structure shown in formula (I), wherein R1 is an alkyl group having 5 or more carbon atoms, M is at least one of an organic amine group bound to a proton and a heterocyclic group containing a nitrogen atom bound to a proton, and n is an integer from 1 to 4. On the one hand, the compound for capturing acidic gases provided in the present application has a weak alkalinity and a small interaction force with the acidic gas. At the same time, the compound can avoid the formation of solids during the absorption of the acidic gas, reducing the difficulty of acidic gas regeneration and making the regeneration process easier. On the other hand, the compound provided in the present application has a higher absorption rate for acidic gases at a higher water content.

[0029] 2. In the compound for capturing acidic gases provided herein, R1 is a branched alkyl group. Increasing the carbon chain length improves the compound's absorption rate of acidic gases. Branched alkyl groups also weaken the interaction between branched alkyl groups and water, resulting in more stable organic and aqueous phases after carbon dioxide absorption.

[0030] 3. The present application provides an absorbent for capturing acidic gases, comprising the aforementioned compound for capturing acidic gases. The absorbent provided herein is a salt of a weak acid and weak base. This absorbent absorbs large amounts of acidic gases at high water contents, does not produce solids during the acidic gas absorption process, and does not increase the difficulty of acidic gas regeneration, thereby improving the acidic gas regeneration rate.

[0031] 4. This application provides a method for preparing an absorbent for capturing acidic gases. The absorbent is obtained by mixing a carboxylic acid, a weak organic base, and water. The carboxylic acid has the molecular formula R1COOH, where R1 is an alkyl group with 5 or more carbon atoms. This method simplifies the synthesis by simply mixing the carboxylic acid and the weak organic base to form a weak acid and weak base salt.

[0032] 5. The compounds, absorbents, and absorbents prepared by the preparation methods provided herein are capable of absorbing and regenerating acid gases. The regeneration step comprises heating the absorbent to 100°C after absorbing acid gases or subjecting the absorbent to vacuum conditions and stirring for a predetermined period of time to complete regeneration. The absorbents prepared by the compounds, absorbents, and preparation methods provided herein can desorb absorbed acid gases at 100°C or at room temperature using negative pressure, significantly reducing the energy consumption for acid gas regeneration. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0034] FIG1 is a schematic diagram showing the results of carbon dioxide absorption by the absorbents prepared in Examples 1 and 28-32 of the present application. DETAILED DESCRIPTION

[0035] The following examples are provided to further better understand the present application, but are not limited to the best implementation mode described herein, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the scope of protection of the present application.

[0036] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0037] During the research and development process, it was discovered that the water-to-salt ratio of existing acid gas carboxylate absorbents significantly affects the acid gas absorption rate. The higher the water-to-salt ratio, the less acid gas the absorbent absorbs. Furthermore, as the amount of acid gas absorbed increases, solids are generated in the absorption system. These solids not only cause inconvenience in subsequent operations, such as easily clogging pipelines and damaging equipment, but also increase the number of solid removal steps. Furthermore, they make acid gas regeneration difficult, reducing the acid gas regeneration rate.

[0038] Therefore, the inventors reacted carboxylic acid with an organic weak base to generate a weak acid and weak base salt. Taking the reaction of 2-butyloctanoic acid and ethanolamine as an example, the reaction equation is shown in Formula (II). The obtained weak acid and weak base salt can solve the above problem.

[0039] The carboxylate onium salts in Comparative Examples 5-9 of the present application were synthesized by mature technology, and the synthesis method was referenced from the literature Suarez, PAZ; Dullius, JEL; Einloft, S.; DE Souza RF and Dupont, J., Polyhedron, 1996, 15, 1217-1219.

[0040] Examples 1-27

[0041] Example 1-27 provides a method for preparing an absorbent for capturing acidic gases. The specific steps and parameters are as follows:

[0042] According to the names and amounts of carboxylic acid, organic weak base and water in Table 1, the raw materials were mixed and stirred to obtain an absorbent.

[0043] Table 1 Absorbent preparation information and structural formula

[0044] Examples 28-32

[0045] Examples 28-32 provide a method for preparing an absorbent for capturing acidic gases. The specific steps and parameters are as follows:

[0046] 2-Butyloctanoic acid, ethanolamine and deionized water were mixed and stirred uniformly according to the molar ratios of carboxylic acid, organic weak base and water of 1:1:0, 1:1:1, 1:1:2.8, 1:1:5.6 and 1:1:20 respectively to obtain an absorbent.

[0047] Example 33

[0048] This embodiment provides a method for preparing an absorbent for capturing acidic gases. The specific steps and parameters are as follows:

[0049] 2-Butyloctanoic acid, triethylenetetramine and deionized water were mixed and stirred uniformly according to the molar ratio of carboxylic acid, organic weak base and water of 1:0.25:10 to obtain an absorbent.

[0050] Comparative Example 1

[0051] This comparative example provides a preparation method for an absorbent for capturing acidic gases, and the specific steps and parameters are as follows:

[0052] 0.1 mol of 2-butyloctanoic acid and 1.33 mol of water are directly mixed and stirred.

[0053] Comparative Example 2

[0054] This comparative example provides a preparation method for an absorbent for capturing acidic gases, and the specific steps and parameters are as follows:

[0055] 0.1 mol of ethanolamine (MEA) and 1.33 mol of water are directly mixed and stirred.

[0056] Comparative Example 3

[0057] This comparative example provides a preparation method for an absorbent for capturing acidic gases, and the specific steps and parameters are as follows:

[0058] Mix 0.1 mol of potassium acetate and 1.33 mol of water to obtain an absorbent.

[0059] Comparative Example 4

[0060] This comparative example provides a preparation method for an absorbent for capturing acidic gases, and the specific steps and parameters are as follows:

[0061] 0.1 mol of acetic acid, 0.1 mol of MEA and 1.33 mol of water were mixed to obtain an absorbent.

[0062] Comparative Example 5

[0063] This comparative example provides a preparation method for an absorbent for capturing acidic gases, and the specific steps and parameters are as follows:

[0064] 0.1 mol of triethylbutylammonium isobutyrate and 1.33 mol of water were mixed to obtain an absorbent.

[0065] Comparative Example 6

[0066] This comparative example provides a preparation method for an absorbent for capturing acidic gases, and the specific steps and parameters are as follows:

[0067] 0.1 mol of tributylhexylphosphonium acetate and 1.33 mol of water were mixed to obtain an absorbent.

[0068] Comparative Example 7

[0069] This comparative example provides a preparation method for an absorbent for capturing acidic gases, and the specific steps and parameters are as follows:

[0070] An absorbent was obtained by mixing 0.1 mol of tributylhexylphosphonium 2-ethylhexanoate and 10 g of water.

[0071] Comparative Example 8

[0072] This comparative example provides a preparation method for an absorbent for capturing acidic gases, and the specific steps and parameters are as follows:

[0073] An absorbent was obtained by mixing 0.1 mol of trimethylbutylammonium 2-butyloctanoate and 10 g of water.

[0074] Comparative Example 9

[0075] This comparative example provides a preparation method for an absorbent for capturing acidic gases, and the specific steps and parameters are as follows:

[0076] An absorbent was obtained by mixing 0.1 mol of potassium 2-butyloctanoate and 10 g of water.

[0077] Application Example 1

[0078] 50 g of each of the absorbents prepared in Examples 1-33 and Comparative Examples 1-6 were injected into glass bottles. Each glass bottle was connected to a carbon dioxide balloon so that the solution was exposed to carbon dioxide at one atmosphere of pressure. The solution was stirred at 20°C for 3 hours. The weight of the glass bottle before and after carbon dioxide absorption was recorded, and the carbon dioxide absorption amount was obtained based on the weight gain of the system. The results of the carbon dioxide absorption amount of the absorbents prepared in Examples 1-33 and Comparative Examples 1-6 are shown in Table 2.

[0079] Table 2 Results of carbon dioxide absorption and absorption rate of absorbent

[0080] Among them, carbon dioxide absorption rate = carbon dioxide absorption amount / mass of absorbent.

[0081] As shown in Table 2, the absorbent prepared by the present application using a mixture of carboxylic acid and an organic weak base can effectively absorb carbon dioxide, with a carbon dioxide absorption rate of 2.3%-5.2%. Comparative Example 1 using only carboxylic acid has a low carbon dioxide absorption rate, while Comparative Example 3 using a carboxylate formed from a lower fatty alkyl carboxylic acid and a strong base, Comparative Example 4 using a lower fatty alkyl carboxylic acid and an organic weak base to prepare the absorbent, Comparative Example 5 using a quaternary ammonium salt of a lower fatty alkyl carboxylic acid, and Comparative Example 6 using a quaternary phosphonium salt of a lower fatty alkyl carboxylic acid, all have carbon dioxide absorption rates of only 0.8%-1.1%.

[0082] Referring to Figure 1, the water-salt molar ratios of Example 28, Example 29, Example 30, Example 31, Example 1 and Example 32 are 0, 1:1, 2.8:1, 5.6:1, 13.3:1 and 20:1, respectively. As shown in Figure 1, increasing the water-salt molar ratio in the absorbent can increase the absorption of carbon dioxide by the absorbent.

[0083] Application Example 2

[0084] In Application Example 1, the glass bottles containing absorbents for absorbing carbon dioxide prepared in Example 1 and Comparative Example 2 were stirred in an oil bath at 100°C, and the glass bottles containing absorbents for absorbing carbon dioxide prepared in Example 14 were stirred in an oil bath at 80°C. The outlets of the glass bottles were connected to spiral stainless steel tubes placed in ice water to intercept moisture in the gas. After regeneration for different periods of time, the desorption amount of carbon dioxide was obtained based on the change in the total weight of the glass bottles and the stainless steel tubes. The results are shown in Table 3.

[0085] Table 3 Comparison of absorbent thermal regeneration performance

[0086] According to Table 3, the absorbent prepared in the present application has a good desorption effect on the absorbed carbon dioxide, and the desorption rate can reach 80% at 80°C and 95% at 100°C. In Comparative Example 2, an organic weak base is used as the absorbent. Although the absorption amount of carbon dioxide is large, the desorption rate of thermally regenerated carbon dioxide is only 8%.

[0087] According to Tables 2 and 3, Comparative Example 1 uses carboxylic acid as the absorbent and only exhibits a small amount of physical absorption of carbon dioxide. Comparative Example 2 uses an organic weak base as the absorbent and exhibits an extremely low desorption rate of carbon dioxide at 100°C. This indicates that the absorption and regeneration of carbon dioxide by the carboxylic acid weak base salt absorbent prepared in the present application is achieved under the action of the product of the reaction between the carboxylic acid and the weak base, rather than the action of the carboxylic acid or the weak base alone.

[0088] Under normal temperature conditions, the glass bottle obtained in Example 1 in Application Example 1 after the absorbent absorbs carbon dioxide is connected to a water pump, the glass bottle is evacuated to maintain a negative pressure state, and the glass bottle is placed on a stirrer and stirred for 1 hour. A large amount of bubbles emerge, and the system changes from two phases to a homogeneous phase.

[0089] Under normal temperature conditions, the glass bottle in which the absorbent obtained in Example 14 obtained in Application Example 1 has absorbed carbon dioxide is connected to a water pump, the glass bottle is evacuated to maintain a negative pressure state, and the glass bottle is placed on a stirrer and stirred for 0.1h. A large amount of bubbles emerge, and the system changes from two phases to a homogeneous phase.

[0090] Under normal temperature conditions, the glass bottle in which the absorbent obtained in Example 14 obtained in Application Example 1 has absorbed carbon dioxide is connected to a water pump, the glass bottle is evacuated to maintain a negative pressure state, and the glass bottle is placed on a stirrer and stirred for 0.5 hours. A large amount of bubbles emerge, and the system changes from two phases to a homogeneous phase, indicating that the absorbent prepared in this application can desorb most of the carbon dioxide under negative pressure at normal temperature conditions, thereby achieving carbon dioxide regeneration.

[0091] Application Example 3

[0092] The absorbents obtained in Examples 1-33 and Comparative Examples 7-9 obtained in Application Example 1 were placed in a carbon dioxide atmosphere at 20° C. and stirred for 3 hours to observe the phase change.

[0093] As can be seen, while comparative examples 7-9, using carboxylic acid salts as absorbents, produced solids after absorbing carbon dioxide, the absorbents prepared in Examples 1-33 of the present application did not produce solids upon absorbing carbon dioxide. This is due to the poor symmetry and weak anionic and cationic interactions of the absorbents prepared in the present application, which make it difficult for carboxylic acid salts of weak acids and bases to produce solid products upon absorbing carbon dioxide.

[0094] Application Example 4

[0095] 50 g of the absorbent prepared in Example 1 was injected into a glass bottle, and the glass bottle was connected to a carbon dioxide balloon so that the solution was exposed to carbon dioxide at one atmosphere pressure. The solution was stirred at 0°C, 10°C, 40°C, and 50°C for 3 hours. The weight of the glass bottle before and after carbon dioxide absorption was recorded, and the carbon dioxide absorption amount was obtained based on the weight gain of the system. The results of the carbon dioxide absorption amount of the absorbent prepared in Example 1 at different temperatures are shown in Table 4.

[0096] Table 4 Results of carbon dioxide absorption by absorbent at different temperatures

[0097] It can be seen that the absorbent prepared in the present application can have a good absorption effect on carbon dioxide at a temperature of 0°C-50°C.

[0098] Application Example 5

[0099] For absorption at carbon dioxide partial pressures equal to and below 0.1 MPa, 50 g of the absorbent prepared in Example 1 was injected into a glass bottle. The glass bottle was placed in balloons containing a mixture of carbon dioxide and nitrogen at different concentrations and stirred at 20°C for 3 hours. The carbon dioxide absorption was obtained based on the weight gain of the system, and the carbon dioxide concentration in the balloon was measured.

[0100] For absorption with a carbon dioxide partial pressure higher than 0.1 MPa, taking an acid gas partial pressure of 0.5 MPa as an example, at 20°C, 10 g of the absorbent prepared in Example 1 was injected into a stainless steel pressure autoclave with a valve, with the magnet kept stationary. The air in the autoclave was pumped out with a water pump, and then filled with 0.5 MPa carbon dioxide gas. The valve was immediately closed, the pipeline was disconnected, and the autoclave was weighed to obtain the initial weight. The electromagnetic stirrer was started to allow the absorption liquid to fully contact with the carbon dioxide. The pipeline was reconnected and the valve was opened. Carbon dioxide was continuously filled to ensure that the carbon dioxide in the system was always maintained at 0.5 MPa. After maintaining for 3 hours, the valve was closed, the pipeline was disconnected, and the stainless steel autoclave was weighed. The absorption capacity of the absorbent at 0.5 MPa was obtained based on the difference between the two weights.

[0101] The results of the carbon dioxide absorption capacity of the absorbent prepared in Example 1 at different carbon dioxide partial pressures are shown in Table 5.

[0102] Table 5 Absorption of carbon dioxide by absorbent at different partial pressures

[0103] According to Table 5, the absorbent prepared in the present application can absorb carbon dioxide at a carbon dioxide concentration of 0.01 MPa-1.0 MPa, and has a better absorption capacity for high-concentration carbon dioxide.

[0104] Application Example 6

[0105] 10 g of the absorbent prepared in Example 1 was injected into a glass bottle, and a balloon containing a mixture of sulfur dioxide and nitrogen at a certain concentration was connected. The mixture was stirred at 20° C. for 3 hours, and the weight of the glass bottle after absorbing sulfur dioxide was recorded. The sulfur dioxide content in the balloon was 3% (partial pressure of 0.003 MPa). The amount of sulfur dioxide gas absorbed at this partial pressure was obtained based on the weight gain of the system.

[0106] 10 g of the absorbent prepared in Example 1 was injected into a glass bottle, connected to a balloon containing hydrogen sulfide, and stirred at 20° C. for 3 hours. The weight of the glass bottle after absorbing hydrogen sulfide was recorded, and the amount of hydrogen sulfide gas absorbed was obtained based on the weight gain of the system;

[0107] The results of the absorption of acidic gas by the absorbent prepared in Example 1 at 20°C are shown in Table 6.

[0108] Table 6 Amount of acid gas absorbed by absorbent

[0109] According to Table 6, the absorbent prepared in the present application can effectively absorb sulfur dioxide and hydrogen sulfide.

[0110] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A compound for capturing acidic gases, characterized in that, It has the structure shown in formula (Ⅰ). Among them, R1 is an alkyl group with at least 5 carbon atoms, M is at least one of an organic amine group combined with a proton and a heterocyclic group containing a nitrogen atom combined with a proton, and n is an integer from 1 to 4.

2. The compound for capturing acidic gas according to claim 1, characterized in that, The R1 is a branched-chain alkyl group; and / or, The organic amine is at least one of a fatty amine and an alkanolamine; and / or, The nitrogen atom-containing heterocycle is At least one of them, where R2, R3, R4, R5, and R6 are any one of an alkyl group, a substituted alkyl group, or a hydrogen atom.

3. The compound for capturing acid gas according to claim 2, characterized in that, The number of carbon atoms of the R1 is 6 - 20; and / or, The organic amine is at least one of a primary amine, a secondary amine, and a polyamine.

4. The compound for capturing acid gas according to claim 1, characterized in that, Has any one of the following structures:

5. An absorbent for capturing acid gas, characterized in that, It includes the compound for capturing acidic gas according to any one of claims 1 - 4.

6. The preparation method of the absorbent for capturing acid gas according to claim 5, characterized in that, It includes the following steps: Mix a carboxylic acid and an organic weak base to obtain an absorbent. The molecular formula of the carboxylic acid is R1COOH, where R1 is an alkyl group with at least 5 carbon atoms.

7. The preparation method according to claim 6, characterized in that, The absorbent further includes water; and / or, The carboxylic acid is a fatty acid; and / or, The organic weak base is at least one of an organic amine compound and a heterocyclic compound containing a nitrogen atom.

8. The preparation method according to claim 7, characterized in that, The carboxylic acid is at least one of 2,2 - dimethylhexanoic acid, 2 - ethylhexanoic acid, 2 - ethylheptanoic acid, 2 - propylpentanoic acid, 2 - propylhexanoic acid, 2 - propylnonanoic acid, 2 - butyloctanoic acid, and 2 - hexyldecanoic acid; and / or, The organic amine compound is at least one of triethylamine, tripropylamine, ethanolamine, diethanolamine, triethanolamine, N - methyldiethanolamine, N,N - dimethylethanolamine, N,N - diethylethanolamine, hydroxyethyl ethylenediamine, 2 - amino - 2 - methyl - 1 - propanol, N - methyl - 1,3 - Propanediamine, 1,4 - butanediamine, N,N,N’,N’ - tetramethylhexanediamine, diethylenetriamine, and triethylenetetramine; and / or, The heterocyclic compound containing a nitrogen atom is at least one of a pyridine ring - containing compound, an imidazole - containing compound, a pyrrole ring - containing compound, and piperazine; and / or, The molar ratio of the carboxylic acid, the organic weak base, and water is 1:(0.25 - 1):(0 - 20).

9. Use of the compound for capturing acidic gas according to any one of claims 1-4, the absorbent for capturing acidic gas according to claim 5, and the absorbent prepared by the method for preparing an absorbent for capturing acidic gas according to any one of claims 6-8 in absorbing and regenerating acidic gas, characterized in that The acidic gas is at least one of carbon dioxide, sulfur dioxide, and hydrogen sulfide.

10. The application according to claim 9, characterized in that The step of absorbing the acidic gas includes contacting the acidic gas to be absorbed with the absorbent and performing absorption at an acidic gas partial pressure of 0.003 MPa - 1.0 MPa and a temperature of 0 - 50°C; and / or, The step of regenerating the acidic gas includes stirring the absorbent after absorbing the acidic gas in an environment of 80 - 100°C for 0.1 - 2 h for desorption, or stirring the absorbent after absorbing the acidic gas under a vacuum condition of 10 - 80°C for 0.1 h - 1 h for desorption.

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