Acid gas removal agent, acid gas removal method, acid gas absorption device, and cleaning device

Abstract

The invention provides an acid gas removing agent, an acid gas removing method, an absorption device provided with the acid gas removing agent, and an acid gas cleaning device, wherein the change of the carbon dioxide absorption amount is small even in the coexistence of water when the carbon dioxide in the gas is removed. The acidic gas remover is used that contains one or more compounds selected from the group consisting of hydroxyl group-containing compounds and derivatives of hydroxyl group-containing compounds, said hydroxyl group-containing compounds and derivatives of hydroxyl group-containing compounds containing constituent units having a number average molecular weight of less than 500, a carbon number of 3 or more and an oxygen number of 1 or more, and having a solubility parameter (LogS) value of-2.25 or less.

Description

Technical Field

[0001] The present invention relates to an acidic gas removing agent for removing acidic gases, particularly carbon dioxide, from gases by a physical absorption method. Background Art

[0002] The present invention can be applied to the case of recovering acidic gases, particularly carbon dioxide, from gases at pressures above atmospheric pressure. Such gases are typically synthesis gases produced by coal gasification or natural gas reforming.

[0003] Carbon dioxide constitutes a greenhouse gas that is considered to cause global warming. The entry into force of the Kyoto Protocol reflects the requirement for both industry and society to reduce carbon dioxide emissions into the atmosphere.

[0004] Capturing and storing carbon dioxide at large power plants, heavy industries, and other sites where large amounts of carbon dioxide are generated is one of the most promising methods for achieving global greenhouse gas emission reduction targets.

[0005] As industrial methods for capturing carbon dioxide, a physical absorption method and a chemical absorption method are known. The chemical absorption method is a method of absorbing and capturing carbon dioxide by using a chemical reaction, and an acidic gas removing agent is used under low pressure (atmospheric pressure). The physical absorption method is a method of absorbing and capturing carbon dioxide under high pressure, and an acidic gas removing agent is used under high pressure. As the acidic gas removing agent used in the physical absorption method, a liquid that can physically dissolve carbon dioxide is used. The higher the partial pressure of carbon dioxide, the easier it is to dissolve in the liquid, and since the carbon dioxide absorption amount of the liquid is increased, the physical absorption method is particularly suitable for high-pressure processes.

[0006] As an acidic gas removing agent, for example, polyethylene glycol dimethyl ether is described in Patent Document 1.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Laid-Open No. 59-216831 Summary of the Invention

[0010] However, as described in Patent Document 1, existing acidic gas removing agents tend to have a reduced carbon dioxide absorption amount in the presence of water. In actual industrial production, water vapor is sometimes contained, and there is a need for an acidic gas removing agent in which the variation in carbon dioxide absorption amount is small even in the presence of water.

[0011] The present invention has been completed to solve such problems, and provides an acidic gas removing agent, an acidic gas removing method, an acidic gas absorption device, and a cleaning device in which the variation in carbon dioxide absorption amount is small even in the presence of water when removing carbon dioxide from a gas.

[0012] In the research on an acidic gas removing agent that can absorb carbon dioxide well even in the presence of water, it was found that a specific parameter indicating solubility in water is closely related to the carbon dioxide absorption amount.

[0013] Specifically, the present invention is as follows [1] to

[13] .

[0014] [1] An acidic gas removing agent for removing carbon dioxide from a gas, containing one or more compounds selected from hydroxy-containing compounds and derivatives of the above hydroxy-containing compounds. The number-average molecular weight of the above hydroxy-containing compounds and derivatives of the above hydroxy-containing compounds is less than 500, and it includes a structural unit having 3 or more carbon atoms and 1 or more oxygen atoms, and the value of the solubility parameter (LogS) is -2.25 or less.

[0015] [2] The acidic gas removing agent according to [1], wherein the above structural unit is a structural unit derived from an alkylene oxide having 3 or more carbon atoms.

[0016] [3] The acidic gas removing agent according to [2], wherein the above alkylene oxide is propylene oxide.

[0017] [4] The acidic gas removing agent according to any one of [1] to [3], wherein the derivative of the above hydroxy-containing compound is a compound obtained by converting the hydroxy terminus of the above hydroxy-containing compound into the following formula (1).

[0018] -O-R(1)

[0019] In formula (1), R is a monovalent organic group having 1 to 4 carbon atoms, which may have a branched chain or an unsaturated bond. Additionally, it may contain a nitrogen atom and an oxygen atom.

[0020] [5] The acidic gas removing agent according to any one of [1] to [4], wherein when the carbon dioxide absorption amount per unit mass of the acidic gas removing agent is set as a (g / kg) at 30 °C and 3 MPa, and the carbon dioxide absorption amount per unit mass of a mixture of 90% by mass of the acidic gas removing agent and 10% by mass of water is set as b (g / kg), the following formulas (2) and (3) are satisfied.

[0021] a≥100 (2)

[0022] b / a≥0.80 (3)

[0023] [6] The acidic gas removing agent according to any one of [1] to [5], which does not contain an amine compound.

[0024] [7] The acidic gas removing agent according to any one of [1] to [6], which is used to remove carbon dioxide from a gas by a physical absorption method.

[0025] [8] The acid gas removing agent according to any one of [1] to [7], wherein the acid gas removing agent is a liquid at room temperature.

[0026] [9] An acid gas removing method, which comprises bringing the acid gas removing agent according to any one of [1] to [8] into contact with the gas to remove carbon dioxide in the gas.

[0027]

[10] The acid gas removing method according to [9], wherein the acid gas removing agent is brought into contact with the gas at a temperature in the range of 0 to 200°C.

[0028]

[11] The acid gas removing method according to [9] or

[10] , wherein the acid gas removing agent is brought into contact with the gas at a pressure in the range of 0.7 to 7.0 MPa.

[0029]

[12] An absorption device filled with the acid gas removing agent according to any one of [1] to [8].

[0030]

[13] A cleaning device comprising the absorption device according to

[12] .

[0031] According to the present invention, there are provided an acid gas removing agent and an acid gas removing method using the same, which have a small change in the carbon dioxide absorption amount even in the coexistence of water when removing carbon dioxide in a gas.

[0032] The acid gas removing agent of the present invention is useful as an acid gas removing agent for removing carbon dioxide in a gas containing a large amount of carbon dioxide and water vapor discharged from a thermal power plant or the like. Detailed embodiments

[0033] The meanings and definitions of the terms in this specification are as follows.

[0034] "Removing carbon dioxide in a gas" is not limited to the case where carbon dioxide in the gas is removed to make the carbon dioxide concentration in the gas 0 vol%, but means that the carbon dioxide concentration in the gas is reduced.

[0035] For "pressure", the unit expression of MPa refers to absolute pressure, and the unit expression of MPaG refers to gauge pressure.

[0036] "Hydroxyl group-containing compound" refers to a general term for compounds having at least one hydroxyl group in one molecule.

[0037] "Derivative of hydroxyl group-containing compound" refers to a compound obtained by esterifying, etherifying or carbamate-esterifying a part or all of the hydroxyl groups of a hydroxyl group-containing compound.

[0038] The numerical range indicated by "~" means the numerical range with the numerical values before and after "~" as the lower limit value and the upper limit value, respectively.

[0039] "Carbon dioxide absorption ratio" refers to the ratio of the carbon dioxide absorption amount in the presence of water in the acidic gas removing agent to the carbon dioxide absorption amount in the absence of water. Specifically, it refers to b / a when the carbon dioxide absorption amount per unit mass of the acidic gas removing agent is set as a (g / kg) at 30 °C and 3 MPa, and the carbon dioxide absorption amount per unit mass of a mixture of 90% by mass of the acidic gas removing agent and 10% by mass of water is set as b (g / kg).

[0040] "Room temperature" refers to the temperature range of 15 to 25 °C.

[0041] [Acidic gas removing agent]

[0042] The acidic gas removing agent of the present invention is characterized in that it is an acidic gas removing agent for removing carbon dioxide from a gas, contains one or more compounds selected from hydroxy-containing compounds and derivatives of the above hydroxy-containing compounds, has a number average molecular weight of less than 500, contains structural units having 3 or more carbon atoms and 1 or more oxygen atoms, and has a value of solubility parameter (LogS) of -2.25 or less. Even in the presence of water in the gas, this acidic gas removing agent can reduce the variation in carbon dioxide absorption amount.

[0043] The "solubility parameter (LogS)" used in the present invention refers to a parameter indicating the limit amount of a compound dissolved in water. The LogS of a compound is calculated using a LogS prediction model. This LogS prediction model is constructed by the machine learning method described later.

[0044] The LogS of a compound is obtained through the following steps (1) to (3).

[0045] (1) Determine the terminal structure through the analysis of 1 H-NMR and 13 C-NMR of the compound. Divide the value obtained by subtracting the molecular weight of the terminal structure from the number average molecular weight by the molecular weight of the structural unit of the compound, and round the resulting integer value to obtain the number of repeating units. Based on the terminal structure and the number of repeating units, draw the chemical structure of the compound using ChemdrawPrime 17.1, which is chemical structure drawing program software.

[0046] (2) Represent the drawn chemical structure of the compound in SMILES notation to form a string using English numbers of ASCII characters (246 descriptors), and convert (numericalize) the information of the compound (molecule) into characteristic quantities using the molecular descriptor calculation software mordred 1.2.0.

[0047] (3) The characteristic quantity of the converted compound (molecule) is used to obtain the LogS value of the compound by the LogS prediction model constructed below.

[0048] The LogS prediction model is constructed by the following machine learning method. This machine learning method (algorithm) uses sklearn.ensemble.RandomForestRegressor of Scikit-learn 0.23.2, adopts the default independent variables, and uses the dataset obtained by using the sklearn.model_selection.train_test_split function (test_size = 0.20, random_state = 42) for the data of AqSolDB described in Sorkun, M.C., et al., Scientific Data vol.6, 143 (2019) as the training data.

[0049] It should be noted that the coefficient of determination in the data of AqSolDB that is not used for learning in the constructed LogS prediction model is 0.80 or more, and it is verified as a high-precision model.

[0050] As an index of the compatibility of a compound with water, for example, the Hansen solubility parameter (HSP value) and the octanol / water partition coefficient (LogP) have been known in the past. The HSP value does not fully consider the molecular size, and LogP is an index for measuring which of water and octanol dissolves more, and neither can be said to be an index representing pure solubility in water.

[0051] On the other hand, the solubility parameter (LogS) of the present invention is a parameter that purely represents the limit amount of a compound dissolved in water, and has a higher evaluation accuracy of compatibility with water than the HSP value and LogP.

[0052] When evaluating the carbon dioxide absorption ratio as an acidic gas remover, it is important to know the limit amount of the acidic gas remover dissolved in water. It is considered that the solubility parameter (LogS) of the hydroxy compound and its derivative is a more appropriate parameter than the previously known HSP value and partition coefficient LogP.

[0053] The number average molecular weight of the hydroxy compound is the molecular weight converted from the hydroxyl value. The molecular weight converted from the hydroxyl value is calculated based on JIS K1557-1:2007 to calculate the hydroxyl value of the hydroxy compound and according to the formula of 56100 / (hydroxyl value of the hydroxy compound)×(number of hydroxyl groups of the hydroxy compound).

[0054] The number average molecular weight of the derivative of the hydroxy compound is the molecular weight determined by gel permeation chromatography (GPC) using polystyrene as the standard substance.

[0055] The LogS of the acidic gas removing agent is preferably -2.25 or less, more preferably -6.00 to -2.25, further preferably -6.00 to -3.00, and particularly preferably -6.00 to -3.50. The larger the value of LogS, the higher the compatibility with water, and the smaller the value, the lower the compatibility with water. When the value of LogS is small, the compatibility with water decreases. When it is -2.25 or less, it is easily separated from water, and the carbon dioxide absorption amount in the coexistence of water is higher, so it is preferred.

[0056] Since the carbon dioxide absorption ratio is likely to be high, as a compound having a number average molecular weight of less than 500, a structural unit containing 3 or more carbon atoms and 1 or more oxygen atoms, and a LogS value of -2.25 or less, a structural unit derived from an alkylene oxide having 3 or more carbon atoms is preferably included. Since the carbon dioxide absorption ratio is likely to be even higher, as the above alkylene oxide, tetrahydrofuran, 1,2-epoxybutane, and propylene oxide are more preferred, and propylene oxide is further preferred.

[0057] When the above compound is a hydroxyl group-containing compound, as the above hydroxyl group-containing compound, at least one selected from polyether monohydric alcohols, polyether polyhydric alcohols, polyester polyhydric alcohols, and polycarbonate diols is preferred. These hydroxyl group-containing compounds can be used alone or in combination of two or more.

[0058] As the above hydroxyl group-containing compound, from the viewpoint of easy availability, polyether monohydric alcohols, polyether polyhydric alcohols, polyester polyhydric alcohols, and polycarbonate diols are preferred, polyether monohydric alcohols and polyether polyhydric alcohols are more preferred, and polypropylene glycol and polyoxyethylene polyoxypropylene diol are further preferred.

[0059] The polyether monohydric alcohol is preferably a polyether monohydric alcohol obtained by subjecting a cyclic ether to ring-opening addition polymerization with an initiator having one group containing an active hydrogen atom in one molecule.

[0060] As the group containing an active hydrogen atom in the above initiator, a hydroxyl group is preferred. Specific examples of the above initiator include methanol, ethanol, 2-propanol, n-butanol, tert-butanol, allyl alcohol, isobutanol, 2-ethylhexanol, decanol, lauryl alcohol, tridecanol, cetyl alcohol, stearyl alcohol, oleyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol mono-isobutyl ether, ethylene glycol mono-tert-butyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monobenzyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monobutyl ether and other monohydric alcohols. From the viewpoint of maintaining a relatively high carbon dioxide absorption amount in the coexistence of water, methanol, ethanol, 2-propanol, n-butanol, tert-butanol, allyl alcohol, isobutanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol mono-isobutyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether are preferred. The above initiator can be used alone in one kind, or two or more kinds can be used in combination.

[0061] The polyether polyol is preferably a polyether polyol obtained by subjecting a cyclic ether and an initiator having at least two active hydrogen atoms in one molecule to a ring-opening addition polymerization reaction. Examples of the polyether polyol include polypropylene glycol, polyoxyethylene polyoxypropylene glycol, polyoxytetramethylene glycol, and an addition polymer of polyoxytetramethylene glycol and an alkylene oxide.

[0062] As the group containing an active hydrogen atom in the above initiator, a hydroxyl group is preferred. Specific examples of the above initiator include water; diols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, bisphenol S, resorcinol; and trihydric or higher alcohols such as glycerol, diglycerol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, glucose, sorbitol, dextrose, fructose, sucrose, methyl glucoside, trehalose, novolac, resol, castor oil. From the viewpoint of maintaining a relatively high carbon dioxide absorption amount in the coexistence of water, water, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, glycerol, trimethylolpropane, pentaerythritol, sorbitol are preferred. The above initiator can be used alone in one kind, or two or more kinds can be used in combination.

[0063] As the cyclic ether used in the production of polyether monoalcohols or polyether polyols, an organic compound having 3 to 20 carbon atoms with a cyclic ether structure is preferred. Examples of the organic compound having 3 to 20 carbon atoms with a cyclic ether structure include compounds having an epoxy group such as propylene oxide, 1,2-epoxybutane, 2,3-epoxybutane, α-alkylene oxide having 5 to 20 carbon atoms, styrene oxide, cyclopentene oxide, cyclohexene oxide, epichlorohydrin, glycidyl alkyl ether, glycidyl alkyl ester; oxetane, tetrahydrofuran. As the cyclic ether used in the production of polyether monoalcohols or polyether polyols, tetrahydrofuran, 1,2-epoxybutane, and propylene oxide are preferred, and propylene oxide is more preferred. The cyclic ether used in the production of polyether monoalcohols or polyether polyols may be used alone or in combination of two or more.

[0064] The ring-opening addition polymerization reaction of the cyclic ether is preferably carried out using a catalyst. Examples of the catalyst include composite metal cyanide complex catalysts; base catalysts such as sodium hydroxide, potassium hydroxide, cesium hydroxide; Ziegler-Natta catalysts composed of an organoaluminum compound and a transition metal compound; metal porphyrin catalysts obtained by reacting with porphyrin as a complex; phosphazene catalysts; phosphazene salts containing imino groups; tris(pentafluorophenyl)borane; catalysts composed of metal Salen complexes; catalysts composed of reduced Robson-type macrocyclic ligands. The catalysts may be used alone or in combination of two or more.

[0065] The production of polyether monoalcohols or polyether polyols by ring-opening addition polymerization using a catalyst can be carried out, for example, under the production conditions described in International Publication No. 2003 / 062301, International Publication No. 2004 / 067633, Japanese Patent Application Laid-Open No. 2004-269776, Japanese Patent Application Laid-Open No. 2005-15786, International Publication No. 2013 / 065802, Japanese Patent Application Laid-Open No. 2015-10162, etc.

[0066] The polyester polyol is preferably obtained by subjecting a dibasic acid component or a dialkyl ester of a dibasic acid component to an esterification reaction or a transesterification reaction with an alcohol. Examples of the polyester polyol include polyester polyols composed of condensates of dibasic acids and alcohols having two or more hydroxyl groups, and polycaprolactone polyols which are ring-opening polymers of cyclic ester compounds. The esterification reaction or transesterification reaction for producing the polyester polyol can be carried out by a known method.

[0067] As the dibasic acid component or dialkyl ester of the dibasic acid component used in the production of polyester polyol, for example, there may be mentioned aliphatic dibasic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, tridecanedioic acid, dimer acid, or dialkyl esters such as dimethyl esters, diethyl esters, dipropyl esters, dibutyl esters of these dibasic acids; alicyclic dibasic acids such as 1,4-cyclohexanedicarboxylic acid, or dialkyl esters such as dimethyl esters, diethyl esters, dipropyl esters, dibutyl esters of these dibasic acids; aromatic dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, or dialkyl esters such as dimethyl esters, diethyl esters, dipropyl esters, dibutyl esters of these dibasic acids, etc.

[0068] As the alcohol used in the production of polyester polyol, for example, there may be mentioned diols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol; polyhydric alcohols having three or more hydroxyl groups such as glycerol, trimethylolpropane, trimethylolethane, pentaerythritol, sorbitol, sucrose.

[0069] The esterification reaction or transesterification reaction for producing polyester polyol is preferably carried out in the presence of a catalyst. As the catalyst, for example, there may be mentioned titanium compounds such as tetrabutyl titanate, tetraisopropyl titanate, tetra-2-ethylhexyl titanate, titanium acetylacetonate; tin compounds such as dibutyltin oxide, methylphenyltin oxide, hexaethyltin oxide; magnesium compounds such as magnesium carbonate, magnesium oxide, magnesium alkoxide. Among them, titanium compounds are preferred, and tetrabutyl titanate and titanium acetylacetonate are more preferred. The catalyst may be used singly or in combination of two or more.

[0070] As the polycarbonate diol, for example, there may be mentioned the condensation product of an alcohol and a carbonate compound, and the reaction product of an alcohol, a cyclic ester and a carbonate compound.

[0071] As the alcohol used in the production of polycarbonate diol, for example, diols can be cited. Specific examples of diols include acyclic aliphatic diols without side chains such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,16-hexadecanediol, 1,18-octadecanediol, 1,20-eicosanediol; acyclic aliphatic diols with side chains such as 2-methyl-1,8-octanediol, 2,2-dimethyl-1,3-propanediol, 2-ethyl-1,3-hexanediol, 2-ethyl-1,6-hexanediol, 2-methyl-1,4-butanediol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,4-dimethyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol; cyclic aliphatic diols such as 1,3-cyclohexanediol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, isosorbide, 2-bis(4-hydroxycyclohexyl)-propane, 2,7-norbornanediol, 2,3-norbornanediol, tetrahydrofuran-2,2-dimethanol, 2,5-bis(hydroxymethyl)-1,4-dioxane; aromatic diols such as 5,5-bis(hydroxymethyl)-2-phenyl-1,3-dioxane, p-xylene glycol, p-tetrachloroxylene glycol, 1,4-bis(hydroxyethoxy)benzene, 2,2-bis[(4-hydroxyethoxy)phenyl]propane. The alcohol can be used alone or in combination of two or more.

[0072] As the carbonate compound used in the production of polycarbonate diol, for example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, diphenyl carbonate, ethylene carbonate, trimethylene carbonate, propylene carbonate, 1,2-butene carbonate, neopentene carbonate can be cited. Among them, from the viewpoint of easy reaction with alcohol and cyclic ester, dimethyl carbonate, diethyl carbonate, diphenyl carbonate, and ethylene carbonate are preferred. The carbonate compound can be used alone or in combination of two or more.

[0073] As the cyclic ester used in the production of polycarbonate diol, for example, ε-caprolactone, β-propiolactone, β-methyl-β-propiolactone, δ-valerolactone, glycolide, lactide, etc. can be cited. Among them, ε-caprolactone is preferred. The cyclic ester can be used alone or in combination of two or more.

[0074] The production of polycarbonate diol can be carried out by using the methods described in, for example, JP-A-2012-77280, JP-A-2014-080590, JP-A-2015-91937, JP-A-2001-270938, JP-A-2010-126591, JP-B-2-289616, JP-B-4-239023, etc.

[0075] The number-average molecular weight of the hydroxy compound used in the acidic gas removing agent of the present invention is less than 500, preferably 100 to 499, more preferably 150 to 499, and particularly preferably 300 to 499. When the number-average molecular weight is less than 500, the viscosity decreases and the operation of the acidic gas removing agent becomes easier.

[0076] When the above compound is a derivative of a hydroxy compound, examples of the derivative of the hydroxy compound include derivatives of polyether monohydric alcohol, polyether polyhydric alcohol, polyester polyhydric alcohol, and polycarbonate diol. Particularly, derivatives obtained by esterifying, etherifying, or carbamoylating a part or all of the hydroxy groups of polyether monohydric alcohol, polyether polyhydric alcohol, polyester polyhydric alcohol, and polycarbonate diol can be mentioned. The derivative of the hydroxy compound is preferably a compound obtained by converting the hydroxy terminal of the above hydroxy compound into the following formula (1).

[0077] -O-R(1)

[0078] In formula (1), R is a monovalent organic group having 1 to 4 carbon atoms, which may have a branched chain or an unsaturated bond. In addition, it may contain at least one of a nitrogen atom and an oxygen atom. R is further preferably a hydrocarbon group having 1 to 4 carbon atoms.

[0079] R is particularly preferably at least one selected from linear or branched alkyl groups having 1 to 4 carbon atoms and allyl groups.

[0080] Examples of the derivative of the hydroxy compound include derivatives obtained by esterifying, etherifying, or carbamoylating a part or all of the hydroxy groups of the hydroxy compound. For example, derivatives obtained by adding sodium hydroxide and methanol to polyether monohydric alcohol to form an alcoholate at the terminal and then reacting with chloromethane to convert the hydroxy group into a methoxy group can be mentioned.

[0081] The method of esterifying, etherifying, or carbamoylating a part or all of the hydroxy groups of the hydroxy compound can be a method generally used for esterification reaction, etherification reaction, or carbamoylation reaction.

[0082] The number-average molecular weight of the derivative of the above hydroxy compound is less than 500, preferably 100 to 499, more preferably 150 to 498, and particularly preferably 300 to 497. When the number-average molecular weight is less than 500, the viscosity decreases and the operation of the acid gas removing agent becomes easy to perform.

[0083] Examples of the compound that reacts with the above hydroxy group when a part or all of the hydroxy groups of the hydroxy compound are esterified, etherified or carbamoylated include monohydric alcohols, carboxylic acids, monoisocyanate compounds, and haloalkanes.

[0084] As the monohydric alcohol, a monohydric alcohol having 1 to 30 carbon atoms is preferred. Examples include linear alkyl alcohols such as methanol, ethanol, propanol, n-butanol, pentanol, hexanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nonadecanol, eicosanol, heneicosanol, docosanol, tricosanol, tetracosanol, pentacosanol, hexacosanol, heptacosanol, octacosanol, nonacosanol, triacontanol; branched alkyl alcohols such as isopropanol, isobutanol, isohexanol, 2-ethylhexanol, isononanol, isodecanol, isododecanol, isotridecanol, isotetradecanol, isotriacontanol, isohexadecanol, isoheptadecanol, isooctadecanol, isononadecanol, isoeicosanol, isheneicosanol, isodocosanol, isotricosanol, isotetracosanol, isopentacosanol, isohexacosanol, isoheptacosanol, isooctacosanol, isononacosanol, isopentadecanol; linear enols such as tetradecenol, hexadecenol, heptadecenol, octadecenol, nonadecenol; branched enols such as isohexadecenol, isooctadecenol; cyclic alkyl alcohols such as cyclopentanol, cyclohexanol; and phenols such as phenol, benzyl alcohol, monophenylated phenol, diphenylated phenol, triphenylated phenol.

[0085] Examples of the carboxylic acid include formic acid, acetic acid, propionic acid, isopropionic acid, butyric acid, isobutyric acid, pivalic acid, valeric acid, and isovaleric acid.

[0086] Examples of the monoisocyanate compound include methyl isocyanate, ethyl isocyanate, phenyl isocyanate, cyclohexyl isocyanate, and benzyl isocyanate.

[0087] As the halogenated alkane, for example, chloromethane, chloroethane, vinyl chloride, n-propyl chloride, isopropyl chloride, allyl chloride, n-butyl chloride, isobutyl chloride, sec-butyl chloride, tert-butyl chloride, 2-chloroethyl methyl ether, 2-chloroethyl ethyl ether, 2-chloroethyl propyl ether, 2-chloroethyl butyl ether and the like can be cited; bromomethane, bromoethane, vinyl bromide, n-propyl bromide, isopropyl bromide, allyl bromide, n-butyl bromide, isobutyl bromide, sec-butyl bromide, tert-butyl bromide, 2-bromoethyl methyl ether, 2-bromoethyl ethyl ether, 2-bromoethyl propyl ether, 2-bromoethyl butyl ether and the like can be cited; iodomethane, iodoethane, vinyl iodide, n-propyl iodide, isopropyl iodide, allyl iodide, n-butyl iodide, isobutyl iodide, sec-butyl iodide, tert-butyl iodide, 2-iodoethyl methyl ether and the like can be cited. From the viewpoint of efficient conversion of the hydroxyl end, chloromethane, allyl chloride, bromomethane, allyl bromide, iodomethane, allyl iodide are preferred.

[0088] Since the acidic gas removing agent of the present invention adsorbs acidic gas physically rather than chemically, it is preferably used for removing acidic gas by physical absorption method.

[0089] In addition, since it is difficult to apply when the acidic gas contains hydrogen sulfide or sulfur oxides (SOx), the acidic gas removing agent preferably does not contain an amine compound. It should be noted that whether an amine compound is present in the acidic gas removing agent can be confirmed by gas chromatography (GC analysis). When the amine compound is less than the detection lower limit value and not detected, it is considered that the acidic gas removing agent does not contain an amine compound.

[0090] In addition, in order to remove acidic gas by physical absorption method, the acidic gas removing agent is preferably a liquid at room temperature.

[0091] In the acidic gas removing agent of the present invention, the total content ratio of one or more compounds selected from hydroxyl group-containing compounds and derivatives of hydroxyl group-containing compounds can be appropriately set according to the usage mode, usually 1 to 100% by mass. From the viewpoint of cost performance, it is preferably 5 to 100% by mass, more preferably 5 to 95% by mass.

[0092] It should be noted that additives such as defoamers, dispersion stabilizers, surfactants, viscosity regulators, corrosion inhibitors and the like can also be added to the acidic gas removing agent.

[0093] When the carbon dioxide absorption amount per unit mass of the acidic gas removing agent is set to a (g / kg) at 30 °C and 3 MPa for the acidic gas removing agent of the present invention, and the carbon dioxide absorption amount per unit mass of a mixture of 90% by mass of the acidic gas removing agent and 10% by mass of water is set to b (g / kg), it is preferably to satisfy the following formulas (2) and (3).

[0094] a≥100 (2)

[0095] b / a ≥ 0.80 (3)

[0096] When the carbon dioxide absorption amount ratio (b / a) of the acid gas removing agent is 0.80 or more, it can be said that the change in the carbon dioxide absorption amount is small even in the coexistence of water. The carbon dioxide absorption amount ratio is more preferably 0.80 to 0.99, and further preferably 0.85 to 0.99.

[0097] When the carbon dioxide absorption amount a per unit mass of the acid gas removing agent is 100 g / kg or more, it can be said that carbon dioxide is well removed in the non - coexistence of water. The carbon dioxide absorption amount a is more preferably 100 to 300 g / kg, and further preferably 125 to 300 g / kg.

[0098] When the carbon dioxide absorption amount b per unit mass of a mixture of 90% by mass of the acid gas removing agent and 10% by mass of water is 100 g / kg or more, it can be said that carbon dioxide is well removed in the coexistence of water. The carbon dioxide absorption amount b is preferably 100 to 300 g / kg, and more preferably 110 to 300 g / kg.

[0099] Due to the small value of LogS and the low solubility of the acid gas removing agent of the present invention in water, the carbon dioxide absorption amount in the coexistence of water is less likely to decrease compared to that in the non - coexistence of water. Therefore, the change in the carbon dioxide absorption amount caused by the presence or absence of coexistent water of the acid gas removing agent of the present invention is small, and the carbon dioxide absorption amount ratio is high. The smaller the change in the carbon dioxide absorption amount ratio, the more capable of absorbing carbon dioxide in a certain amount without being affected by coexistent water, and thus the easier to control the carbon dioxide removal treatment.

[0100] On the other hand, in an acid gas removing agent with a large LogS value and easy solubility in water, it is speculated that the carbon dioxide adsorption sites of the acid gas removing agent are reduced due to hydration, and the carbon dioxide absorption amount decreases in the coexistence of water, so the carbon dioxide absorption amount ratio decreases. The acid gas removing agent that is easily soluble in water is likely to have a large change in the carbon dioxide absorption amount ratio due to the presence or absence of coexistent water.

[0101] [Acid Gas Removal Method]

[0102] The acid gas removal method of the present invention can be, for example, a method of adding the acid gas removing agent of the present invention to an acid gas containing carbon dioxide. In addition, it can also be a method of continuously removing the acid gas by passing the acid gas containing carbon dioxide through a container filled with the acid gas removing agent of the present invention, or a method of removing the acid gas by batch treatment by filling the acid gas containing carbon dioxide into a container filled with the acid gas removing agent of the present invention.

[0103] In addition, in order to improve the contact efficiency between the acid gas removing agent of the present invention and the acid gas containing carbon dioxide, a perforated plate, a bubble cap tray, etc. can be used in a packed tower to bring the acid gas removing agent into contact with the acid gas containing carbon dioxide. In addition, the acid gas removing agent can be sprayed while the acid gas containing carbon dioxide is circulated for contact, or the acid gas containing carbon dioxide can be formed into minute bubbles for contact with the acid gas removing agent of the present invention.

[0104] In the method for removing carbon dioxide using the acid gas removing agent of the present invention, the total amount of one or more compounds selected from the hydroxy group-containing compounds and hydroxy group-containing compound derivatives contained in the acid gas removing agent of the present invention is preferably 0.1 to 100.0 moles, more preferably 0.1 to 10.0 moles, per 1 mole of carbon dioxide in the gas. In the method of treating a gas by circulating it in a container filled with the acid gas removing agent, the addition amount of the acid gas removing agent is adjusted so that the total amount of one or more compounds selected from the added hydroxy group-containing compounds and hydroxy group-containing compound derivatives is within the above range per 1 mole of carbon dioxide in the circulated gas.

[0105] The temperature at the time of bringing the acid gas removing agent into contact with the gas for treatment is preferably in the range of 0 to 200°C, more preferably 25 to 60°C. The pressure at the time of the above treatment is generally in the range of 0.7 to 7.0 MPa, preferably 2.0 to 5.0 MPa.

[0106] The gas to be treated is an acid gas containing carbon dioxide, and may contain hydrogen sulfide, etc. as other acid gases, as well as nitrogen, oxygen, hydrogen, water, etc. The acid gas removing agent of the present invention also exhibits a good carbon dioxide removing effect even when the gas to be treated contains water. When the gas to be treated contains water, from the viewpoint of a good carbon dioxide removing effect, the content of water in the liquid form is preferably 0.5 to 20.0 vol%, more preferably 1.0 to 15.0 vol%.

[0107] The acid gas removing method of the present invention can be implemented, for example, by passing a gas through an absorption device filled with the acid gas removing agent of the present invention. The absorption device used is generally provided in a cleaning device used in a gas cleaning process. As the objects to be removed in the cleaning process, not only acid gases such as carbon dioxide and hydrogen sulfide, but also dust and odors can be cited. As the cleaning device, for example, towers having irregular packings, regular packings, towers having trays, membrane contactors, radial flow scrubbers, spray scrubbers, venturi scrubbers, and rotary spray scrubbers can be cited.

[0108] Examples

[0109] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

[0110] [Evaluation method and measurement method]

[0111] <Number average molecular weight>

[0112] The number average molecular weight of the hydroxyl group-containing compound is the hydroxyl value conversion molecular weight calculated according to the hydroxyl value determined based on JIS K 1557-1:2007 and using the formula "56100 / (hydroxyl value of the hydroxyl group-containing compound)×(number of terminal groups of the hydroxyl group-containing compound)".

[0113] The number average molecular weight of the derivative of the hydroxyl group-containing compound is measured by gel permeation chromatography (GPC) under the following measurement conditions.

[0114] (Measurement conditions)

[0115] · Instrument used: "HLC-8320GPC", manufactured by Tosoh Corporation

[0116] · Chromatographic columns used: The following two types of chromatographic columns are connected in series and used in sequence.

[0117] "TSKgel (registered trademark) SuperHZ4000", manufactured by Tosoh Corporation, 2 pieces

[0118] "TSKgel (registered trademark) SuperHZ2500", manufactured by Tosoh Corporation, 2 pieces

[0119] · Column temperature: 40 °C

[0120] · Detector: Differential refractive index (RI) detector

[0121] · Eluent: Tetrahydrofuran

[0122] · Flow rate: 0.35 mL / minute

[0123] · Sample concentration: 0.5 mass%

[0124] · Sample injection volume: 20 μL

[0125] · Standard substance: Polystyrene

[0126] <Carbon dioxide absorption amount>

[0127] For the carbon dioxide absorption amount, a 300 mL pressure-resistant container (A) and a 150 mL pressure-resistant container (B) connected to a carbon dioxide gas cylinder by piping are prepared, and the value is obtained according to the following steps (i) to (iv). It should be noted that a regulator and a pressure gauge are connected between the carbon dioxide gas cylinder and the pressure-resistant container (A), and the pressure-resistant container (A) and the pressure-resistant container (B) are immersed in a water bath.

[0128] (i) Set the temperature of the water bath to 30 °C, and degas the pressure-resistant container (B) filled with 50 mL of the evaluation liquid under reduced pressure using a vacuum pump.

[0129] (ii) Fill the pressure-resistant container (A) with carbon dioxide reduced to 0.20 MPa using a regulator, and measure the pressure at this time. Then, connect the pressure-resistant container (A) to the pressure-resistant container (B), and measure the pressure after 1 hour. The carbon dioxide in the reduced pressure part is regarded as being absorbed by the evaluation liquid, and the amount of carbon dioxide absorbed per unit mass (mol / kg) is calculated.

[0130] (iii) Perform the same operation as (ii) at 0.35 MPa, 0.50 MPa, 0.60 MPa, and 0.80 MPa respectively, and calculate the Henry's constant Hb (MPa·kg / mol) indicating the pressure dependence of the amount of carbon dioxide absorbed per unit mass (mol / kg).

[0131] (iv) Calculate the amount of carbon dioxide absorbed per unit mass (g / kg) of the evaluation liquid according to the following formula.

[0132] Amount of carbon dioxide absorbed per unit mass of the evaluation liquid (g / kg)

[0133] = P (MPa) × n / Hb (MPa·kg / mol)

[0134] n: Molar mass of carbon dioxide = 44 (g / mol)

[0135] It should be noted that P (MPa) is calculated at 3.0 MPa, which is the representative use condition of the physical absorption liquid.

[0136] For the case where the acid gas scavenger (100% by mass of the compound) is used as the evaluation liquid (when water is not coexistent), and for the case where a mixture of 90% by mass of the acid gas scavenger (compound) and 10% by mass of water is used as the evaluation liquid (when water is coexistent), the carbon dioxide absorption amounts of each evaluation liquid are obtained.

[0137] <Carbon dioxide absorption amount ratio>

[0138] The carbon dioxide absorption amount ratio is the ratio (b / a) of the amount of carbon dioxide absorbed per unit mass b (g / kg) of the mixture of 90% by mass of the acid gas scavenger and 10% by mass of water to the amount of carbon dioxide absorbed per unit mass a (g / kg) of the acid gas scavenger.

[0139] <Solubility parameter S (LogS)>

[0140] The solubility parameter (LogS) of each compound is obtained by the above method.

[0141] [Synthesis of Compound (Polymer)]

[0142] <Synthesis Example 1>

[0143] In a reactor equipped with a stirring blade, a distillate trap, and a pressure regulating device, 815 g of n-butanol was used as an initiator, and 2391 g of propylene oxide was polymerized in the presence of a potassium hydroxide (KOH) catalyst. After neutralization and removal of the neutralization salt, a polymer (A-1) as a polyoxyalkylene glycol was obtained (hydroxyl value 187 mg KOH / g, number average molecular weight 300, number of structural units from propylene oxide (PO unit number) 4).

[0144] <Synthesis Example 2>

[0145] 2000 g of the polymer (A-1) was charged into a reactor equipped with a stirring blade, a distillate trap, and a pressure regulating device.

[0146] Next, a 28 mass% sodium methoxide (NaOMe) methanol solution was added in such a way that the amount of NaOMe was 1.1 moles per 1 mole of the hydroxyl groups of the polymer (A-1). After heating to 70°C, nitrogen was introduced, and methanol was distilled off at atmospheric pressure. Then, the temperature was raised to 130°C, and the mixture was stirred and mixed under a reduced pressure of -0.1 MPaG for 4 hours to distill off methanol, converting the polymer (A-1) into a sodium alkoxide.

[0147] Next, after cooling to 100°C, chloromethane was gradually added at an input rate of 400 g / hr in an amount of 1.1 moles per 1 mole of the sodium in the sodium alkoxide, and the reaction was carried out at 100°C for 2 hours. Then, the mixture was stirred and mixed at 100°C and -0.1 MPaG for 0.5 hour, and unreacted chloromethane was distilled off under reduced pressure, thereby obtaining a crude product in which the hydroxyl groups of the polymer (A-1) were methoxylated.

[0148] Next, 2000 g of distilled water was added to the reactor, and the mixture was stirred and mixed for 15 minutes to perform oil-water separation of the neutralization salt. Only the oil layer was extracted, 4 mass parts of an adsorbent was added per 100 mass parts of the oil layer, and after heating to 120°C, the mixture was stirred and mixed under a reduced pressure of -0.1 MPaG for 1.5 hours. The adsorbent was filtered to obtain a polymer (B-1) as a terminal methylated derivative of the polymer (A-1) (number average molecular weight 476, PO unit number 7).

[0149] <Synthesis Example 3>

[0150] In a reactor equipped with a stirring blade, a distillate trap, and a pressure regulating device, 1340 g of ethylene glycol monobutyl ether (1 mol adduct of ethylene oxide with n-butanol) was used as an initiator, and 1926 g of propylene oxide was polymerized in the presence of a KOH catalyst. After neutralization and removal of the neutralization salt, a polymer (A-2) of polyoxyalkylene glycol was obtained (hydroxyl value: 188 mg KOH / g, number average molecular weight: 299, number of PO units: 3).

[0151] <Synthesis Example 4>

[0152] 2000 g of polymer (A-2) was charged instead of polymer (A-1), and otherwise, in the same manner as in Synthesis Example 2, a polymer (B-2) which is a terminal methylated derivative of polymer (A-2) was obtained (number average molecular weight: 437, number of PO units: 5).

[0153] <Synthesis Example 5>

[0154] In a reactor equipped with a stirring blade, a distillate trap, and a pressure regulating device, using diethylene glycol monobutyl ether (2 mol adduct of ethylene oxide with n-butanol) as an initiator, propylene oxide was polymerized in the presence of a KOH catalyst. After neutralization and removal of the neutralization salt, a polymer (A-3) of polyoxyalkylene monohydric alcohol was obtained (hydroxyl value: 175 mg KOH / g).

[0155] 2000 g of polymer (A-3) was charged instead of polymer (A-1), and otherwise, in the same manner as in Synthesis Example 2, a polymer (B-3) which is a terminal methylated derivative of polymer (A-3) was obtained (number average molecular weight: 476, number of PO units: 5).

[0156] <Synthesis Example 6>

[0157] In a reactor equipped with a stirring blade, a distillate trap, and a pressure regulating device, using ethylene glycol monoter-butyl ether (1 mol adduct of ethylene oxide with tert-butanol) as an initiator, propylene oxide was polymerized in the presence of a KOH catalyst. After neutralization and removal of the neutralization salt, a polymer (A-4) of polyoxyalkylene monohydric alcohol was obtained (hydroxyl value: 176 mg KOH / g).

[0158] 2000 g of polymer (A-4) was charged instead of polymer (A-1), and otherwise, in the same manner as in Synthesis Example 2, a polymer (B-4) which is a terminal methylated derivative of polymer (A-4) was obtained (number average molecular weight: 479, number of PO units: 6).

[0159] <Synthesis Example 7>

[0160] In a reactor equipped with a stirring blade, a distillate trap, and a pressure regulating device, using methanol as an initiator, in the presence of a NaOH catalyst, propylene oxide is subjected to ring-opening polymerization, followed by neutralization and removal of the neutralization salt to obtain a polymer (A-5) (hydroxyl value 171 mg KOH / g) which is a polyoxyalkylene monohydric alcohol.

[0161] Charge 2000 g of polymer (A-5) to replace polymer (A-1), and introduce 1.1 moles of allyl chloride per mole of hydroxyl groups of polymer (A-5) to replace methyl chloride. After heating to 85°C and reacting for 5 hours, raise the temperature to 100°C, and under a reduced pressure of -0.1 MPaG, stir and mix for 0.5 hour to distill off unreacted allyl chloride. Otherwise, obtain a polymer (B-5) (number average molecular weight 496, number of PO units 7) which is a terminal allylated derivative of polymer (A-5) in the same manner as in Synthesis Example 2.

[0162] <Synthesis Example 8>

[0163] In a reactor equipped with a stirring blade, a distillate trap, and a pressure regulating device, using propylene glycol as an initiator, in the presence of a KOH catalyst, propylene oxide is subjected to ring-opening polymerization, followed by neutralization and removal of the neutralization salt to obtain a polymer (A-6) which is a polyoxyalkylene diol.

[0164] Charge 2000 g of polymer (A-6) to replace polymer (A-1), and otherwise, obtain a polymer (B-6) (number average molecular weight 437, number of PO units 7) which is a terminal methylated derivative of polymer (A-6) in the same manner as in Synthesis Example 2.

[0165] <Synthesis Example 9>

[0166] In a reactor equipped with a stirring blade, a distillate trap, and a pressure regulating device, using ethylene glycol monoisopropyl ether as an initiator, in the presence of a KOH catalyst, propylene oxide is subjected to ring-opening polymerization, followed by neutralization and removal of the neutralization salt to obtain a polymer (A-7) which is a polyoxyalkylene diol.

[0167] Charge 2000 g of polymer (A-7) to replace polymer (A-1), and otherwise, obtain a polymer (B-7) (number average molecular weight 486, number of PO units 6) which is a terminal methylated derivative of polymer (A-7) in the same manner as in Synthesis Example 2.

[0168] <Synthesis Example 10>

[0169] In a reactor equipped with a stirring blade, a distillate trap, and a pressure regulating device, 765 g of propylene glycol was used as an initiator, and 3235 g of propylene oxide was polymerized in the presence of a KOH catalyst. After neutralization and removal of the neutralization salt, a polymer (A-8) as a polyoxyalkylene glycol was obtained (hydroxyl value: 282 mg KOH / g, number average molecular weight: 398, number of PO units: 7).

[0170] <Evaluation results>

[0171] Table 1 shows the theoretical structural formulas, number average molecular weights, LogS, and measurement results of carbon dioxide absorption amounts of the respective compounds (polymers) used as evaluation liquids.

[0172] Examples 1 to 8 are examples, and Examples 9 to 13 are comparative examples. It should be noted that the compound (C-1) in Example 11 is dimethyl polyethylene glycol ether (DMPEG) (manufactured by Tokyo Chemical Industry Co., Ltd.; number average molecular weight: 282, number of structural units derived from ethylene oxide: 5), the compound (C-2) in Example 12 is tripropylene glycol (TPG) (manufactured by AGC Inc.; number average molecular weight: 185, number of PO units: 3), and the compound (C-3) in Example 13 is PTMG250 (manufactured by Mitsubishi Chemical Corporation; number average molecular weight: 230, number of structural units derived from tetrahydrofuran: 3).

[0173] [Table 1]

[0174]

[0175] From Table 1, it can be seen that for a hydroxyl group-containing compound or a derivative of a hydroxyl group-containing compound having a number average molecular weight of less than 500 and containing a structural unit having 3 or more carbon atoms and 1 or more oxygen atoms, the carbon dioxide absorption amount in the coexistence of water is not easily reduced when LogS is -2.25 or less, and the carbon dioxide absorption amount ratio is high. That is, it is considered that the carbon dioxide absorption amount can be maintained even in the coexistence of water, and the change in the carbon dioxide absorption amount is small compared to the case of non-coexistence of water.

Claims

1. An acidic gas removing agent for removing carbon dioxide from a gas, comprising one or more compounds selected from hydroxy-containing compounds and derivatives of the hydroxy-containing compounds, wherein the number-average molecular weight of the hydroxy-containing compounds and the derivatives of the hydroxy-containing compounds is less than 500, the structural unit contains 3 or more carbon atoms and 1 or more oxygen atoms, and the value of the solubility parameter, LogS, is -2.25 or less.

2. The acid gas removing agent according to claim 1, wherein, The structural unit is a structural unit derived from an alkylene oxide having 3 or more carbon atoms.

3. The acid gas removing agent according to claim 2, wherein, The alkylene oxide is propylene oxide.

4. The acid gas removing agent according to claim 1 or 2, wherein The derivative of the hydroxy-containing compound is a compound obtained by converting the hydroxy end of the hydroxy-containing compound into the following formula (1), -O-R(1) In formula (1), R is a monovalent organic group having 1 to 4 carbon atoms, which may have a branched chain, may have an unsaturated bond, and may contain at least one of a nitrogen atom and an oxygen atom.

5. The acid gas removing agent according to claim 1 or 2, wherein, When the carbon dioxide absorption amount per unit mass of the acidic gas removing agent is a at 30 °C and 3 MPa, and the carbon dioxide absorption amount per unit mass of a mixture of 90% by mass of the acidic gas removing agent and 10% by mass of water is b, the following formulas (2) and (3) are satisfied, and the units of a and b are g / kg, a≥100 (2) b / a ≥ 0.80 (3).

6. The acid gas removing agent according to claim 1 or 2, wherein It does not contain an amine compound.

7. The acidic gas removing agent according to claim 1 or 2, for removing carbon dioxide from a gas by a physical absorption method.

8. The acid gas removing agent according to claim 1 or 2, wherein, The acidic gas removing agent is a liquid at room temperature.

9. An acidic gas removing method, wherein the acidic gas removing agent according to claim 1 or 2 is brought into contact with the gas to remove carbon dioxide from the gas.

10. The acid gas removal method according to claim 9, wherein, The acidic gas removing agent is brought into contact with the gas at a temperature in the range of 0 to 200 °C.

11. The acid gas removal method according to claim 10, wherein, The acidic gas removing agent is brought into contact with the gas at a pressure in the range of 0.7 to 7.0 MPa.

12. An absorption device filled with the acidic gas removing agent according to claim 1 or 2.

13. A cleaning device comprising the absorption device according to claim 12.

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