Acid gas-absorbing liquid and acid gas capturing method

Abstract

Provided is an acid gas-absorbing liquid that has sufficient carbon dioxide absorption capacity for gases such as an atmosphere having a low carbon dioxide concentration and has low hygroscopicity. Also provided is an acid gas capturing method using the same. This acid gas-absorbing liquid reversibly absorbs and desorbs carbon dioxide, and contains an oxygen-containing polymer and a primary amine. The oxygen-containing polymer has a solubility parameter of 15.0-26.0 (MPa)1 / 2 and the primary amine has a solubility parameter of 13.0-25.0 (MPa)1 / 2.

Description

Acid gas absorption solution and acid gas recovery method

[0001] This invention relates to an acidic gas absorption solution and an acidic gas recovery method useful for recovering acidic gases from gases.

[0002] A known method for recovering acidic gases, such as carbon dioxide, from a gas is to use an acidic gas absorbent (hereinafter simply referred to as "absorbent") containing an amine compound and an organic solvent to absorb and separate the acidic gas, and then recover 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, from the viewpoint of energy conservation. For example, Patent Document 1 describes a carbon dioxide absorbent containing a primary alkanolamine such as diglycolamine and a polyol such as triethylene glycol.

[0004] Japanese Patent Publication No. 2024-8922

[0005] However, carbon dioxide absorbents made from a combination of amines and polyols, as described in Patent Document 1, are prone to hygroscopicity, and in direct air recovery (DAC) technology, the water content in the absorbent after carbon dioxide absorption tends to be high. Therefore, when recovering carbon dioxide after absorption and removing water from the absorbent to obtain a regenerated carbon dioxide absorbent, a large amount of energy is required for heating.

[0006] This invention has been made in view of the above circumstances, and aims to provide an acidic gas absorbent liquid that has sufficient carbon dioxide absorption capacity for gases such as the atmosphere with low carbon dioxide concentration, and has low hygroscopicity, and an acidic gas recovery method using the same.

[0007] This invention is based on the discovery that an acidic gas absorbent solution, obtained by combining a predetermined organic solvent and a predetermined amine compound, has suppressed hygroscopicity and can effectively absorb carbon dioxide from gases with low carbon dioxide concentrations.

[0008] The present invention provides the following means: [1] An acidic gas absorbent that reversibly absorbs and desorbs carbon dioxide, comprising an oxygen-containing polymer and a primary amine, wherein the oxygen-containing polymer has a solubility parameter of 15.0 to 26.0 (MPa) １／２ The primary amine has a solubility parameter of 13.0 to 25.0 (MPa). １／２ An acidic gas absorbent, wherein [2] the primary amine is at least one selected from the group consisting of aliphatic amines, aromatic amines and etheramines, wherein [3] the oxygen-containing polymer has a group represented by -OR at its terminus, where R is a hydrogen atom or a bonding group having 1 to 8 carbon atoms, and the bonding group may be linear or branched, may have an unsaturated bond, and may contain at least one of a nitrogen atom and an oxygen atom, wherein [1] or [2], the acidic gas absorbent, wherein [4] the oxygen-containing polymer has repeating units having 3 or more carbon atoms, wherein [5] the oxygen-containing polymer is at least one selected from the group consisting of polyethers, polyesters, polycarbonates and polyether polycarbonates, wherein [6] the oxygen-containing polymer has a content of 50 to 99% by mass, wherein [1] to [5], the acidic gas absorbent, wherein [4] the oxygen-containing polymer is at least one selected from the group consisting of polyethers, polyesters, polycarbonates and polyether polycarbonates, the acidic gas absorbent, wherein [5] the oxygen-containing polymer has a content of 50 to 99% by mass, wherein [6] the oxygen-containing polymer has a content of 50 to 99% by mass, wherein [1] to [5], the acidic gas absorbent, wherein [1] [7] An acidic gas absorbent according to any of [1] to [6], wherein the primary amine content is 1 to 50% by mass.

[0009] [8] An acid gas recovery method comprising contacting an acid gas absorbent liquid of any of [1] to [7] with a gas containing an acid gas, and recovering the acid gas by desorbing it from the acid gas absorbent liquid obtained. [9] The acid gas recovery method of [8], wherein the desorption of the acid gas is performed under reduced pressure.

[10] The acid gas recovery method of [8] or [9], wherein the acid gas is carbon dioxide, and carbon dioxide from the atmosphere is recovered.

[0010] According to the present invention, an acidic gas absorbent is provided that has sufficient carbon dioxide absorption capacity for gases with low carbon dioxide concentrations and has low hygroscopicity. The acidic gas recovery method of the present invention using the acidic gas absorbent can effectively absorb carbon dioxide from gases with low carbon dioxide concentrations, and can reduce the energy required for carbon dioxide recovery and the regeneration of the acidic gas absorbent.

[0011] The definitions and meanings of terms and notations used herein are as follows: The notation "X to Y" (where X and Y are numerical values) means a numerical range with X as the lower limit and Y as the upper limit. For numerical ranges (e.g., ranges of content, etc.), the lower and upper limits described in steps may be combined independently. The lower and upper limits of the numerical range may be replaced with the numerical values ​​described in the examples. The boiling point is the boiling point at a pressure of 0.101 MPa (1 atmosphere). The solubility parameter (δ) is the value at 25°C calculated by the Fedors method. For oxygen-containing polymers, １ H-NMR and １３ The terminal structure was confirmed by C-NMR analysis, and the number of units was calculated based on a structural formula in which the integer value (rounded to the nearest whole number) obtained by subtracting the formula weight of the terminal structure from the number-average molecular weight and dividing by the formula weight of the constituent unit of the oxygen-containing polymer was repeatedly used. The number-average molecular weight (Mn) of the oxygen-containing polymer was determined by gel permeation chromatography (GPC) using polystyrene as the standard substance.

[0012] [Acid Gas Absorbent Solution] The acid gas absorbent solution of the present invention is an acid gas absorbent solution that reversibly absorbs and desorbs carbon dioxide, and comprises an oxygen-containing polymer and a primary amine, wherein the oxygen-containing polymer has a solubility parameter (δ) of 15.0 to 26.0 (MPa). １／２ The primary amine has a solubility parameter (δ) of 13.0 to 25.0 (MPa). １／２ That is the case.

[0013] An acid gas is a gas containing carbon dioxide, and may contain other acid gases such as hydrogen sulfide and sulfurous acid gas. The absorbent of an embodiment of the present invention (hereinafter referred to as "this embodiment") can reversibly absorb and desorb carbon dioxide among acid gases, and can be regenerated and reused. Hereinafter, an embodiment in which the acid gas absorbed by the absorbent is carbon dioxide will be described.

[0014] The absorbent of this embodiment contains a predetermined oxygen-containing polymer and a primary amine. An absorbent formed by combining such an oxygen-containing polymer and a primary amine has suppressed hygroscopicity, and can effectively absorb carbon dioxide in a gas with a low carbon dioxide concentration, and can reduce the energy required for the recovery of carbon dioxide and the regeneration of the acid gas absorbent.

[0015] (Oxygen-containing polymer) The oxygen-containing polymer contained in the absorbent of this embodiment has a solubility parameter (δ) of 15.0 to 26.0 (MPa) １／２ and preferably 15.0 to 22.0 (MPa) １／２ more preferably 15.0 to 19.5 (MPa). １／２ If the δ of the oxygen-containing polymer is 15.0 (MPa) or more, carbon dioxide is likely to be absorbed by the absorbent. Also, if the δ of the oxygen-containing polymer is 26.0 (MPa) or less, it is easy to suppress the moisture absorption of the absorbent. １／２ If the δ of the oxygen-containing polymer is 15.0 (MPa) or more, carbon dioxide is likely to be absorbed by the absorbent. Also, if the δ of the oxygen-containing polymer is 26.0 (MPa) or less, it is easy to suppress the moisture absorption of the absorbent. １／２ If the δ of the oxygen-containing polymer is 26.0 (MPa) or less, it is easy to suppress the moisture absorption of the absorbent.

[0016] The oxygen-containing polymer may be a single type or two or more types may be used in combination. When two or more types of oxygen-containing polymers are contained in the absorbent, δ is the volume average value of the solubility parameters of various oxygen-containing polymers.

[0017] The oxygen-containing polymer preferably has a terminal group represented by -OR. In -OR, R is preferably a hydrogen atom or a bonding group having 1 to 8 carbon atoms, and more preferably a hydrogen atom or a bonding group having 1 to 4 carbon atoms. The bonding group may be linear or branched, may have an unsaturated bond, and may contain at least one of a nitrogen atom and an oxygen atom. In -OR, R is preferably a hydrogen atom or an alkyl group. Examples of the alkyl group include a methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, octyl group, and 2-ethylhexyl group. Because the oxygen-containing polymer has a terminal group containing an oxygen atom, the thickening of the absorbent solution is easily suppressed, and carbon dioxide is more easily absorbed into the absorbent solution.

[0018] From the viewpoint of enabling the absorption solution to be used with good fluidity even in low temperature environments (e.g., below 10°C), the oxygen-containing polymer preferably has repeating units with 3 or more carbon atoms, and more preferably has an oxypropylene group.

[0019] Examples of oxygen-containing polymers include polyethers, polycarbonates, polyesters, and polyether polycarbonates. Polyethers are particularly preferred when absorbing carbon dioxide from the atmosphere using a pressure difference. The oxygen-containing polymer may also be a polyether monool, polyether polyol, polyester polyol, polycarbonate polyol, or polyether polycarbonate polyol, and it is preferable that the ends of these polymers have the group represented by -OR, or have been converted to the group represented by -OR.

[0020] <Polyether Monools> Polyether monools are preferably obtained by addition polymerization of an alkylene oxide to an initiator having one active hydrogen atom in one molecule. Addition polymerization can be carried out by known methods in the presence of a catalyst.

[0021] The initiator is preferably a compound having one hydroxyl group in one molecule, and examples of monohydric alcohols include methanol, ethanol, 2-propanol, n-butanol, tert-butanol, allyl alcohol, isobutanol, 2-ethylhexanol, decyl alcohol, 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 monoisobutyl 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, and tetraethylene glycol monobutyl ether. The initiator may be used alone or in combination of two or more.

[0022] The alkylene oxide preferably has 2 to 20 carbon atoms, more preferably 2 to 10 carbon atoms, and even more preferably 3 to 8 carbon atoms. Examples of alkylene oxides include propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, tetramethylene oxide (tetrahydrofuran), and α-olefin oxides having 5 to 20 carbon atoms. Of these, propylene oxide is preferred. The alkylene oxide may be used alone or in combination of two or more types.

[0023] Known catalysts can be used, including, for example, alkaline catalysts such as potassium hydroxide, transition metal compound-porphyrin complex catalysts such as complexes obtained by reacting organoaluminum compounds with porphyrin, complex metal cyanide complex catalysts such as zinc hexacyanocobaltate complexes with tert-butanol as a ligand, and catalysts consisting of phosphazene compounds. The catalyst may be used alone or in combination of two or more.

[0024] <Polyether Polyols> Polyether polyols are preferably obtained by addition polymerization of an alkylene oxide to an initiator having two or more active hydrogen atoms in one molecule.

[0025] The initiator is preferably a compound having two or more hydroxyl groups in one molecule, such as dihydric alcohols like ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, bisphenol S, and resorcinol; and trihydric or higher alcohols like glycerin, diglycerin, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol glucose, sorbitol, dextrose, fructose, sucrose, methyl glucoside, trehalose, novolac, resol, and castor oil. Water can also be used as an initiator. Of these, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, glycerin, trimethylolpropane, pentaerythritol, and sorbitol are preferred. The initiator may be used alone or in combination of two or more.

[0026] Specific examples of alkylene oxides include those similar to those used as raw materials for the synthesis of polyether monools described above. Addition polymerization can also be carried out using the same method as for the synthesis of polyether monools described above.

[0027] Specific examples of the polyether polyol include polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, polyoxytetramethylene glycol, and an addition product of polyoxytetramethylene glycol and an alkylene oxide. From the viewpoint of ease of handling of the absorption liquid and the like, polypropylene glycol is preferable as the polyether polyol.

[0028] <Polyester Polyol> The polyester polyol is preferably a reaction product of an esterification reaction between a dibasic acid and a polyhydric alcohol or a transesterification reaction between a dialkyl dibasic acid ester and a polyhydric alcohol. The esterification reaction or the transesterification reaction can be carried out by a known method in the presence of a catalyst.

[0029] Examples of the dibasic acid include aliphatic dibasic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, brassilic acid, dimer acid; alicyclic dicarboxylic acids such as 1,4 - cyclohexanedicarboxylic acid, and aromatic dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid. Examples of the dialkyl dibasic acid ester include dimethyl ester, diethyl ester, dipropyl ester, and dibutyl ester of the dibasic acid exemplified above. The dibasic acid may be used alone or in combination of two or more.

[0030] Examples of the polyhydric alcohol include diols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, neopentyl glycol, 1,4 - butanediol, 1,6 - hexanediol; and polyhydric alcohols having a valence of 3 or more such as glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, sorbitol, sucrose. The polyhydric alcohol may be used alone or in combination of two or more.

[0031] Examples of catalysts include titanium compounds such as tetrabutyl titanate, tetraisopropyl titanate, tetra-2-ethylhexyl titanate, and titanium acetylacetonate; tin compounds such as dibutyltin oxide, methylphenyltin oxide, and hexaethyltin oxide; and magnesium compounds such as magnesium carbonate, magnesium oxide, and magnesium alkoxide. The catalyst may be used alone or in combination of two or more types.

[0032] <Polycarbonate Polyols> Examples of polycarbonate polyols include polycondensates of polyhydric alcohols and carbonate compounds, and polycondensates of polyhydric alcohols and cyclic esters and carbonate compounds. Polycarbonate polyols can be synthesized by known methods.

[0033] Examples of the polyhydric alcohol include aliphatic diols 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, 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; alicyclic 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; and aromatic diols such as 5,5 - bis(hydroxymethyl) - 2 - phenyl - 1,3 - dioxane, p - xylene glycol, p - tetrachloroxylene diol, 1,4 - bis(hydroxyethoxy)benzene, 2,2 - bis[(4 - hydroxyethoxy)phenyl]propane. The polyhydric alcohol may be used alone or in combination of two or more kinds.

[0034] Examples of the carbonate compound include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, diphenyl carbonate, ethylene carbonate, trimethylene carbonate, propylene carbonate, 1,2 - butylene carbonate, neopentylene carbonate. The carbonate compound may be used alone or in combination of two or more kinds.

[0035] Examples of cyclic esters include ε-caprolactone, β-propiolactone, β-methyl-β-propiolactone, δ-valerolactone, glycolides, and lactides. Cyclic esters may be used individually or in combination of two or more.

[0036] <Polyether Polycarbonate Polyols> Examples of polyether polycarbonate polyols include polycondensates of polyether polyols and carbonate compounds. They may also be copolymers of diol compounds different from polyether polyols. Polyether polycarbonate polyols can be synthesized by known methods.

[0037] Specific examples of polyether polyols used as raw materials for the synthesis of polyether polycarbonate polyols include the polyether polyols mentioned above, and specific examples of carbonate compounds include those similar to the carbonate compounds used as raw materials for the synthesis of polycarbonate polyols mentioned above.

[0038] Furthermore, when converting the terminal hydroxyl groups of an oxygen-containing polymer having hydroxyl groups at its termini to an oxygen-containing polymer in which a group other than a hydroxyl group is introduced, represented by -OR, the conversion of the hydroxyl groups can be carried out by known methods such as alkoxylation, esterification, or urethane formation. From the viewpoint of obtaining an absorbent liquid with an easily handleable viscosity, alkoxylation of the termini is preferable.

[0039] Alkoxylation of the terminal hydroxyl groups of oxygen-containing polymers can be performed using, for example, organic halogen compounds such as alkyl halides. Examples of organic halogen compounds include organic chlorine compounds such as methyl chloride, ethyl chloride, vinyl chloride, n-propyl chloride, isopropyl chloride, allyl chloride, n-butyl chloride, isobutyl chloride, sec-butyl chloride, tert-butyl chloride, 2-chloroethylmethyl ether, 2-chloroethylethyl ether, 2-chloroethylpropyl ether, and 2-chloroethylbutyl ether; methyl bromide, ethyl bromide, vinyl bromide, n-propyl bromide, isopropyl bromide, allyl bromide, n-butyl bromide, and Examples of organic bromine compounds include isobutyl iodide, sec-butyl bromide, tert-butyl bromide, 2-bromoethylmethyl ether, 2-bromoethylethyl ether, 2-bromoethylpropyl ether, and 2-bromoethylbutyl ether; and organic iodine compounds such as methyl iodide, ethyl iodide, vinyl iodide, n-propyl iodide, isopropyl iodide, allyl iodide, n-butyl iodide, isobutyl iodide, sec-butyl iodide, tert-butyl iodide, and 2-iodoethylmethyl ether. Of these, methyl chloride, allyl chloride, methyl bromide, allyl bromide, methyl iodide, and allyl iodide are preferred from the viewpoint of efficiently converting hydroxyl groups.

[0040] Examples of oxygen-containing polymers in which a group other than a hydroxyl group, represented by -OR, is introduced at the end of the oxygen-containing polymer include polyoxyalkylene dimethyl ether, polyoxyalkylene ethyl ether, polyoxyalkylene propyl ether, polyoxyalkylene isopropyl ether, polyoxyalkylene allyl ether, polyoxyalkylene butyl ether, polyoxyalkylene sec-butyl ether, polyoxyalkylene tert-butyl ether, polyoxyalkylene pentyl ether, polyoxyalkylene hexyl ether, polyoxyalkylene heptyl ether, polyoxyalkylene octyl ether, polyoxyalkylene (2-ethylhexyl) ether, polyoxyalkylene ethyl methyl ether, polyoxyalkylene propyl methyl ether, polyoxyalkylene isopropyl methyl ether, polyoxyalkylene butyl methyl ether, and polyoxyalkylene methyl ether. Examples include polyoxyalkylene sec-butyl methyl ether, polyoxyalkylene tert-butyl methyl ether, polyoxyalkylene pentyl methyl ether, polyoxyalkylene hexyl methyl ether, polyoxyalkylene octyl methyl ether, polyoxyalkylene 2-ethylhexyl methyl ether, polyoxyalkylene methyl allyl ether, polyoxyalkylene ethyl allyl ether, polyoxyalkylene propyl allyl ether, polyoxyalkylene isopropyl allyl ether, polyoxyalkylene butyl allyl ether, polyoxyalkylene sec-butyl allyl ether, polyoxyalkylene tert-butyl allyl ether, polyoxyalkylene pentyl allyl ether, polyoxyalkylene hexyl allyl ether, polyoxyalkylene heptyl allyl ether, polyoxyalkylene octyl allyl ether, and polyoxyalkylene 2-ethylhexyl allyl ether.Of these, polyoxyalkylene dimethyl ether, polyoxyalkylene diallyl ether, polyoxyalkylene ethyl methyl ether, polyoxyalkylene propyl methyl ether, polyoxyalkylene isopropyl methyl ether, polyoxyalkylene butyl methyl ether, polyoxyalkylene sec-butyl methyl ether, polyoxyalkylene tert-butyl methyl ether, polyoxyalkylene pentyl methyl ether, polyoxyalkylene hexyl methyl ether, polyoxyalkylene heptyl methyl ether, polyoxyalkylene octyl methyl ether, polyoxyalkylene 2-ethylhexyl methyl ether, polyoxyalkylene methyl allyl ether, polyoxyalkylene Polyoxyalkylene ethyl allyl ether, polyoxyalkylene propyl allyl ether, polyoxyalkylene isopropyl allyl ether, polyoxyalkylene butyl allyl ether, polyoxyalkylene sec-butyl allyl ether, polyoxyalkylene tert-butyl allyl ether, polyoxyalkylene pentyl allyl ether, polyoxyalkylene hexyl allyl ether, polyoxyalkylene heptyl allyl ether, polyoxyalkylene octyl allyl ether, and polyoxyalkylene 2-ethylhexyl allyl ether are preferred, polyoxyalkylene dimethyl ether and polyoxyalkylene butyl methyl ether are more preferred, and polypropylene glycol dimethyl ether and polypropylene glycol butyl methyl ether are even more preferred.

[0041] The oxygen-containing polymer is preferably easy to handle and not easily volatile. From this viewpoint, the number-average molecular weight (Mn) is preferably 250 to 20,000, more preferably 350 to 10,000, even more preferably 500 to 5,000, and even more preferably 500 to 2,500.

[0042] When an oxygen-containing polymer absorbs carbon dioxide from the atmosphere using a pressure difference, from the viewpoint of suppressing volatilization, the vapor pressure at 25°C is preferably 1000 Pa or less, more preferably 0.01 to 100 Pa, and even more preferably 0.02 to 10 Pa.

[0043] (Primary amine) The amine compound used in the absorption solution of this embodiment is a primary amine with a solubility parameter (δ) of 13.0 to 25.0 (MPa). １／２ The pressure is preferably 13.0 to 23.0 (MPa). １／２ , more preferably 14.0 to 21.0 (MPa) １／２ The primary amine may be used alone or in combination of two or more. The δ of the primary amine is 13.0 (MPa). １／２ If the above is true, carbon dioxide is easily absorbed by the absorbent. Also, the δ of the primary amine is 25.0 (MPa). １／２ The following conditions make it easier to suppress the hygroscopicity of the absorbent liquid.

[0044] By using a primary amine as the amine compound, carbon dioxide can be effectively absorbed even from gases with low carbon dioxide concentrations. Primary amines have an amino group (-NH ２ Preferably, the nitrogen atom of the amine is bonded to a primary carbon. In this invention, a primary amine refers to a molecule containing at least one amino group (-NH₄). ２ This refers to substances that have ), and may also have a structure in the molecule corresponding to a secondary or tertiary amine.

[0045] Primary amines are considered to have a primary amine structure (amino group: -NH) from the viewpoint of suppressing the thickening of the absorbent solution when absorbing carbon dioxide. ２ ) or preferably there are few amine structures equivalent to secondary amines, -NH ２ It is more preferable to have one of these. The number of tertiary amine structures in the molecule is not limited because they contribute little to the reactivity with carbon dioxide.

[0046] From the viewpoint of enabling the absorption solution to absorb carbon dioxide well even in low-temperature environments (e.g., below 10°C), the primary amine is preferably liquid at 25°C, and its melting point is more preferably below 15°C, even more preferably below 0°C, and even more preferably below -10°C.

[0047] When primary amines absorb carbon dioxide from the atmosphere using a pressure difference, from the viewpoint of suppressing volatilization, the vapor pressure at 25°C is preferably 300 Pa or less, more preferably 250 Pa or less, even more preferably 200 Pa or less, and even more preferably 100 Pa or less.

[0048] Examples of primary amines include aliphatic amines, aromatic amines, and ether amines. Of these, aliphatic amines and ether amines are preferred, and alkyl amines are more preferred. As primary amines, those without hydroxyl groups are preferred from the viewpoint of suppressing the hygroscopicity of the absorbent solution. Alkanolamines tend to have a large δ and are undesirable from the viewpoint of suppressing the hygroscopicity of the absorbent solution. Here, an aliphatic amine refers to an amine whose substituents consist only of aliphatic hydrocarbons and which does not have an aromatic ring or hydroxyl group in the molecule. An aromatic amine refers to an amine whose substituents consist only of hydrocarbons containing an aromatic ring and which does not have a hydroxyl group in the molecule. An ether amine refers to an amine whose substituents contain an ether bond and which does not have a hydroxyl group in the molecule. An alkanol amine refers to an amine which has one or more hydroxyl groups in the molecule.

[0049] Specific examples of aliphatic amines include 2-hexylamine, n-octylamine, nonylamine, decylamine, 2-diethylaminoethylamine, 2-(di-N-propylamino)ethylamine, 2-diisopropylaminoethylamine, 2-(dibutylamino)ethylamine, 3-(diethylamino)propylamine, 3-(dibutylamino)propylamine, 3-(diisopropylamino)propylamine, 3-(diisobutylamino)propylamine, N-(3-aminopropyl)cyclohexylamine, etc. Specific examples of aromatic amines include benzylamine, 2-phenylethylamine, etc. Specific examples of etheramines include methoxypoly(oxyethylene)2-propylamine, polyoxypropylenediamine, 3-(2-ethylhexyloxy)propylamine, etc. Of these, 2-ethylhexylamine, 3-(dibutylamino)propylamine, and 3-(2-ethylhexyloxy)propylamine are preferred.

[0050] The absorbent liquid, even when applied to gases with low carbon dioxide concentrations such as DAC, effectively absorbs carbon dioxide from the gas and facilitates the recovery of the absorbed carbon dioxide. From this viewpoint, the oxygen-containing polymer content is preferably 50 to 99% by mass, more preferably 55 to 98% by mass, and even more preferably 60 to 97% by mass.

[0051] The content of primary amine in the absorption solution is preferably 1 to 50% by mass, more preferably 2 to 45% by mass, even more preferably 3 to 40% by mass, and even more preferably 5 to 30% by mass, from the viewpoint of effectively absorbing carbon dioxide from gases with low carbon dioxide concentrations and facilitating the recovery of absorbed carbon dioxide.

[0052] The mass ratio of the oxygen-containing polymer to the primary amine in the absorbent solution is preferably 50 / 50 to 99 / 1, more preferably 55 / 45 to 98 / 2, even more preferably 60 / 40 to 97 / 3, and even more preferably 70 / 30 to 90 / 10, from the viewpoint of effectively absorbing carbon dioxide from gases with low carbon dioxide concentrations and facilitating the recovery of the absorbed carbon dioxide.

[0053] The absorbent solution of this embodiment can be produced by mixing the above-mentioned oxygen-containing polymer and primary amine. The absorbent solution may optionally contain additives such as antioxidants, corrosion inhibitors, and viscosity modifiers. It is preferable that the absorbent solution does not contain water, from the viewpoint of reducing the energy derived from water among the energy required to recover acidic gases from the gas.

[0054] [Acid Gas Recovery Method] In the acid gas recovery method of this embodiment, the acid gas is recovered by desorbing it from the acid gas absorbent obtained by contacting the acid gas absorbent of this embodiment with a gas containing the acid gas. According to the method of this embodiment, the energy required for heating when recovering the acid gas from the absorbent that has absorbed the acid gas can be reduced. In addition, the absorbent obtained from which the acid gas has been desorbed along with the recovery of the acid gas can be reused for acid gas recovery, and according to the acid gas recovery method of this embodiment, the absorbent can be recycled.

[0055] Contact between the absorbent liquid and the gas may be achieved, for example, by adding the absorbent liquid to the gas, by continuously circulating the gas through a container filled with the absorbent liquid, or by filling a container filled with the absorbent liquid with the gas. To improve the contact efficiency between the absorbent liquid and the gas, methods such as providing a packing material in the container, spraying the absorbent liquid into the gas, or bubbling the gas into the absorbent liquid may also be used.

[0056] The desorption of acidic gases from an absorbent solution can be carried out, for example, by heating or reducing the pressure of the absorbent solution to release the acidic gases. From the viewpoint of suppressing the consumption of thermal energy, it is preferable to carry out the desorption of acidic gases under reduced pressure. Reduced pressure can be achieved, for example, by using a vacuum pump or a method that utilizes unused cold energy.

[0057] The aforementioned acidic gas recovery method is suitable when the acidic gas is carbon dioxide and carbon dioxide is being recovered from the atmosphere. The absorbent liquid of this embodiment has sufficient carbon dioxide absorption capacity even in the atmosphere with a low carbon dioxide concentration, and has low hygroscopicity. Therefore, according to the acidic gas recovery method of this embodiment, carbon dioxide can be effectively absorbed even from the atmosphere with a low carbon dioxide concentration. In addition, because the absorbent liquid contains little water, the energy required for heating during the recovery of carbon dioxide absorbed by the absorbent liquid and during the regeneration of the absorbent liquid can be reduced.

[0058] 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.

[0059] [Synthesis of Oxygen-Containing Polymers] (Synthesis Example 1) Using 552 g of n-butanol as an initiator, 7842 g of propylene oxide (PO) was polymerized in the presence of potassium hydroxide, then neutralized and the neutralized salt was removed to obtain monofunctional polypropylene glycol (PPG). Next, a methanol solution of 28% by mass sodium methoxide (NaOMe) was added (1.1 moles of NaOMe per mole of hydroxyl groups of monofunctional PPG), and after heating to 70°C, nitrogen was introduced and methanol was removed by distillation at atmospheric pressure. Then, the temperature was raised to 130°C and stirred and mixed under reduced pressure of -0.1 MPaG for 4 hours to remove methanol by distillation. Next, after cooling to 100°C, 1.1 moles of chloromethane per mole of NaOMe was added sequentially at an addition rate of 400 g / hr and the mixture was reacted at 100°C for 2 hours. Subsequently, the mixture was stirred and mixed at 100°C under reduced pressure of -0.1 MPaG for 0.5 hours, and unreacted chloromethane was removed by distillation under reduced pressure to obtain a crude product in which the hydroxyl groups of monofunctional PPG were methoxylated. Next, 2000 g of distilled water was added to the reactor and stirred and mixed for 15 minutes, and the neutralized salt was separated from the oil. 4 parts by mass of adsorbent were added to 100 parts by mass of the extracted oil layer, and after raising the temperature to 120°C, the mixture was stirred and mixed under reduced pressure of -0.1 MPaG for 1.5 hours. The adsorbent was filtered to obtain polypropylene glycol butyl methyl ether (PPG1) (Mn 1334).

[0060] (Synthesis Example 2) In Synthesis Example 1, the initiator was changed to 237 g of methanol and the PO to be polymerized to 7816 g, and otherwise the procedure was the same as in Synthesis Example 1 to obtain polypropylene glycol dimethyl ether (PPG2) (Mn 1849).

[0061] (Synthesis Example 3) Using 833 g of 2-ethylhexanol as an initiator, 2993 g of PO was polymerized in the presence of a complex cyanide to obtain polypropylene glycol (PPG3) (Mn 588).

[0062] [Preparation of Acidic Gas Absorbent Solution] Acidic gas absorbent solutions 1 to 8 were prepared by mixing oxygen-containing polymers and amine compounds according to the respective formulations shown in Tables 1 and 2.

[0063] Details of the oxygen-containing polymers and amine compounds in Table 1 are as follows: <Oxygen-containing polymers> ・PPG1: Polypropylene glycol butyl methyl ether produced in Synthesis Example 1 ・PPG2: Polypropylene glycol dimethyl ether produced in Synthesis Example 2 ・PPG3: Polypropylene glycol produced in Synthesis Example 3 ・TEG: Triethylene glycol, manufactured by Tokyo Chemical Industry Co., Ltd. <Amine compounds> ・2EHA: 2-Ethylhexylamine, manufactured by Tokyo Chemical Industry Co., Ltd. ・DBAPA: 3-(Dibutylamino)propylamine, manufactured by Tokyo Chemical Industry Co., Ltd. ・DGA: Diglycolamine, manufactured by Tokyo Chemical Industry Co., Ltd. ・DAA: Diamylamine, manufactured by Tokyo Chemical Industry Co., Ltd. ・2EHOPA: 3-(2-Ethylhexyloxy)propylamine, manufactured by Tokyo Chemical Industry Co., Ltd. Tables 1 and 2 show the solubility parameters (δ) of the oxygen-containing polymers and amine compounds.

[0064] [Gas Absorption Test] For each acidic gas absorbent, a test was conducted under two different conditions to evaluate its gas absorption capacity.

[0065] (Test 1) A glass absorption tower (inner diameter 30 mm, height 1.2 m) was filled with wire mesh packing ("Dixon Packing", size 3 mm, 100 mesh, manufactured by Toutoku Engineering Co., Ltd.; the same applies hereinafter). The air was adjusted to 25°C and 30% relative humidity to produce a test gas (carbon dioxide (CO2)). ２A solution (CO2) at a concentration of 500 ppm was introduced from the bottom of the column at a rate of 10 L / min using a compressor. The prepared acidic gas absorption solution was introduced from the top of the column at a rate of 4 mL / min using a pump while stirring, and the test gas and the acidic gas absorption solution were brought into contact (mass ratio of acidic gas absorption solution / test gas: 0.4). An infrared gas analyzer and a hygrometer installed at the bottom and top of the column respectively were used to measure the amount of CO2 in the introduced gas at the bottom of the column. ２ CO in exhaust gas from the top of the tower to the outside of the system at a concentration of 500 ppm and relative humidity of 30%. ２ The concentration and relative humidity were measured.

[0066] CO2 intake gas ２ CO in exhaust gas relative to concentration ２ The lower the concentration, the higher the carbon dioxide absorption capacity of the acidic gas absorbent. Furthermore, the smaller the fluctuation in relative humidity in the exhaust gas relative to the relative humidity of the inlet gas, the lower the hygroscopicity of the acidic gas absorbent.

[0067] CO in the measured exhaust gas ２ Table 1 shows the concentration and relative humidity (evaluation results). Examples 1 and 2 (acidic gas absorbent solutions 1 and 2) are examples, and Examples 3 and 4 (acidic gas absorbent solutions 3 and 4) are comparative examples.

[0068]

[0069] (Test 2) A glass absorption tower (inner diameter 30 mm, height 0.3 m) was filled with wire mesh packing. The test gas (carbon dioxide (CO2)) was prepared by adjusting the atmosphere to 25°C and 20% relative humidity. ２ A solution (CO2) at a concentration of 500 ppm was introduced from the bottom of the column at a rate of 5 L / min using a compressor. The prepared acidic gas absorption solution was introduced from the top of the column at a rate of 5 mL / min using a pump while stirring, and the test gas and the acidic gas absorption solution were brought into contact (mass ratio of acidic gas absorption solution / test gas: 1). An infrared gas analyzer and a hygrometer installed at the bottom and top of the column respectively were used to measure the introduced gas at the bottom of the column (CO2). ２ CO in exhaust gas from the top of the tower to the outside of the system at a concentration of 500 ppm and relative humidity of 20%. ２ The concentration and relative humidity were measured.

[0070] CO in the measured exhaust gas ２Table 2 shows the concentration and relative humidity (evaluation results). Examples 5 to 8 (acidic gas absorbents 2 and 5 to 7) are examples, and examples 9 and 10 (acidic gas absorbents 3 and 8) are comparative examples.

[0071]

[0072] Tables 1 and 2 show that when oxygen-containing polymers and amine compounds with δ values ​​within a predetermined range are combined, the carbon dioxide concentration can be sufficiently reduced, and the relative humidity of the test gas does not change significantly. The oxygen gas absorbent liquid of this embodiment, using a predetermined acidic gas polymer and amine compound, exhibits suppressed hygroscopicity and sufficient carbon dioxide absorption capacity in air with low carbon dioxide concentrations.

Claims

1. An acidic gas absorbent that reversibly absorbs and desorbs carbon dioxide, comprising an oxygen-containing polymer and a primary amine, wherein the oxygen-containing polymer has a solubility parameter of 15.0 to 26.0 (MPa). １／２ The primary amine has a solubility parameter of 13.0 to 25.0 (MPa). １／２ It is an acidic gas absorbent.

2. The acidic gas absorbent according to claim 1, wherein the primary amine is at least one selected from the group consisting of aliphatic amines, aromatic amines, and etheramines.

3. The acidic gas absorbent according to claim 1, wherein the oxygen-containing polymer has a group represented by -OR at its terminus, where R is a hydrogen atom or a bonding group having 1 to 8 carbon atoms, and the bonding group may be linear or branched, may have an unsaturated bond, and may contain at least one of a nitrogen atom and an oxygen atom.

4. The acidic gas absorbent according to claim 1, wherein the oxygen-containing polymer has repeating units with 3 or more carbon atoms.

5. The acidic gas absorbent liquid according to claim 1, wherein the oxygen-containing polymer is at least one selected from the group consisting of polyether, polyester, polycarbonate, and polyether polycarbonate.

6. The acidic gas absorbent liquid according to claim 1, wherein the content of the oxygen-containing polymer is 50 to 99% by mass.

7. The acidic gas absorbent according to claim 1, wherein the content of the primary amine is 1 to 50% by mass.

8. A method for recovering acidic gas, comprising contacting an acidic gas absorption liquid according to any one of claims 1 to 7 with a gas containing an acidic gas to obtain an acidic gas absorption liquid, from which the acidic gas is desorbed and recovered.

9. The method for recovering an acidic gas according to claim 8, wherein the desorption of the acidic gas is performed under reduced pressure.

10. The acid gas recovery method according to claim 8, wherein the acid gas is carbon dioxide and carbon dioxide is recovered from the atmosphere.

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