Acidic gas-absorbing liquid and method for reducing acidic gas

Abstract

Provided is an acidic gas-absorbing liquid that can suppress the latent heat of evaporation during recovery of absorbed acidic gas, suppress heating energy, and suppress blockage of a recovery line. Also provided is a method for reducing acidic gas using the same. This acidic gas-absorbing liquid reversibly absorbs and desorbs carbon dioxide, and comprises an oxygen-containing polymer, an amine compound, and a liquid having a boiling point of 50°C to 110°C. The oxygen-containing polymer has at least one group selected from the group consisting of an oxyalkylene group, a carbonate group, and an ester group, and the proportion of the liquid in the acidic gas-absorbing liquid is 0.01 to 5.0 mass%.

Description

Acid gas absorption solution and method for reducing acid gas

[0001] The present invention relates to an acidic gas absorbent and an acidic gas reduction method applicable to reducing acidic gases in a gas.

[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] When the absorbent solution is an aqueous solution, there is a problem in that the energy required to heat the solution to release the acidic gas absorbed by the absorbent solution becomes large due to the latent heat of vaporization of water.

[0004] To address this, for example, it is conceivable to apply an absorbent solution using a non-aqueous solvent such as silicone and fluoroether, as described in Patent Document 1.

[0005] International Publication No. 2024 / 122624

[0006] If an absorption solution using a non-aqueous solvent as described above is used, the non-aqueous solvent has a high boiling point and does not easily contain water. Therefore, the energy required for heating to remove acidic gases due to the latent heat of vaporization of water is suppressed, and energy conservation can be achieved.

[0007] However, such non-aqueous solvents have low volatility, and for example, in the process of recovering acidic gases by thermal swing, only the amine compounds among the absorbent components may volatilize and react with the acidic gas in the gas phase, causing carbonate to precipitate and potentially leading to blockage in the recovery pipeline for the detached acidic gas.

[0008] This invention has been made in view of the above circumstances, and aims to provide an acidic gas absorption liquid that can suppress the latent heat of vaporization when recovering absorbed acidic gases, suppress heating energy, and prevent blockage of the recovery pipeline, as well as a method for reducing acidic gases using the same.

[0009] This invention is based on the discovery that an acidic gas absorption liquid containing a predetermined amount of a liquid having a predetermined boiling point suppresses the latent heat of vaporization when recovering the absorbed acidic gas and facilitates the dissolution of carbonates of amine compounds.

[0010] The present invention provides the following means: [1] An acidic gas absorbent that reversibly absorbs and desorbs carbon dioxide, comprising an oxygen-containing polymer, an amine compound, and a liquid having a boiling point of 50 to 110°C, wherein the oxygen-containing polymer has at least one group selected from the group consisting of oxyalkylene groups, carbonate groups, and ester groups, and the content of the liquid in the acidic gas absorbent is 0.01 to 5.0% by mass. [2] The acidic gas absorbent according to [1], wherein the liquid is at least one selected from the group consisting of water, methanol, and ethanol. [3] The acidic gas absorbent according to [1] or [2], wherein the oxygen-containing polymer has a number average molecular weight of 250 to 20000. [4] The acidic gas absorbent according to any one of [1] to [3], wherein the oxygen-containing polymer has a boiling point of 200°C or higher. [5] The oxygen-containing polymer has a solubility parameter of 15.0 (MPa) １／２ The above is 19.5 (MPa). １／２ An acidic gas absorbent of any of [1] to [4], which is less than [6] the amine compound having a solubility parameter of 13.0 to 25.5 (MPa) １／２ An acidic gas absorbent according to any of [1] to [5]. [7] An acidic gas absorbent according to any of [1] to [6], 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. [8] An acidic gas absorbent according to any of [1] to [7], wherein the oxygen-containing polymer content is 5 to 99% by mass. [9] An acidic gas absorbent according to any of [1] to [8], wherein the amine compound content is 1 to 90% by mass.

[10] An acidic gas absorbent according to any of [1] to [9], for use in an acidic gas recovery and separation process.

[0011]

[11] A method for reducing acidic gases, comprising contacting an acidic gas absorbent liquid from any of [1] to

[10] with a gas containing carbon dioxide to reduce the amount of carbon dioxide in the gas.

[12] The method for reducing acidic gases according to

[11] , wherein the acidic gas absorbent liquid that has been in contact with a gas containing carbon dioxide is heated to remove the carbon dioxide, and the resulting acidic gas absorbent liquid is recovered and reused.

[0012] By using the acidic gas absorbent liquid of the present invention, the latent heat of vaporization when recovering the absorbed acidic gas can be suppressed, reducing heating energy and preventing blockage of the recovery pipeline.

[0013] 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 boiling point of the synthesized oxygen-containing polymer is a value calculated using the chemical structure drawing software "ChemDraw v17.1" (Cambridge Software). The solubility parameter (δ) is a 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.

[0014] [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, an amine compound, and a liquid having a boiling point of 50 to 110°C. The oxygen-containing polymer has at least one group selected from the group consisting of oxyalkylene groups, carbonate groups, and ester groups, and the content of the liquid in the acid gas absorbent solution is 0.01 to 5.0% by mass.

[0015] The acidic gas is a gas containing carbon dioxide, and may also contain other acidic gases such as hydrogen sulfide or sulfur dioxide. The absorbent liquid of this embodiment (hereinafter referred to as "this embodiment") can reversibly absorb and desorb carbon dioxide, in particular, from among the acidic gases. The following explanation will use the case where the acidic gas absorbed by the absorbent liquid is carbon dioxide as an example.

[0016] The absorbent solution of this embodiment contains a predetermined oxygen-containing polymer, an amine compound, and a predetermined amount of liquid having a predetermined boiling point. In such an absorbent solution containing the predetermined liquid, the carbonate of the amine compound becomes more easily soluble as the liquid volatilizes, and the latent heat of vaporization is suppressed. Therefore, the heating energy required when recovering carbon dioxide absorbed by the absorbent solution can be suppressed, and blockage of the recovery pipeline can be suppressed.

[0017] (Oxygen-containing polymer) The oxygen-containing polymer contained in the absorbent solution of this embodiment has at least one group selected from the group consisting of oxyalkylene groups, carbonate groups, and ester groups. With such an oxygen-containing polymer, the carbonate produced when the amine compound in the absorbent solution absorbs carbon dioxide is easily soluble in the absorbent solution.

[0018] Examples of oxygen-containing polymers include polyethers, polycarbonates, and polyesters, of which polyether monools, polyether polyols, polyester polyols, polycarbonate polyols, and polyether polycarbonate polyols are preferred. The oxygen-containing polymer may be used alone or in combination of two or more types.

[0019] The oxygen-containing polymer preferably has a terminal group represented by -OR. The R in -OR 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. The R in -OR is preferably a hydrogen atom or an alkyl group. Examples of the alkyl group include methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, and 2-ethylhexyl groups. The presence of an oxygen-containing terminal group in the oxygen-containing polymer allows carbon dioxide to be more easily absorbed by the absorbent solution.

[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 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 polyether polyols include polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, polyoxytetramethylene glycol, and addition polymers of polyoxytetramethylene glycol and alkylene oxide. From the viewpoint of ease of handling of the absorbent liquid, polypropylene glycol is preferred as the polyether polyol.

[0028] <Polyester Polyols> Polyester polyols are preferably reaction products of esterification reactions between dibasic acids and polyhydric alcohols, or transesterification reactions between dialkyl dibasic acid esters and polyhydric alcohols. The esterification or transesterification reaction can be carried out by known methods in the presence of a catalyst.

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

[0030] Examples of polyhydric alcohols include diols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, neopentyl glycol, 1,4-butanediol, and 1,6-hexanediol; and trihydric or higher alcohols such as glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, sorbitol, and sucrose. Polyhydric alcohols may be used individually or in combination of two or more.

[0031] As the catalyst, for example, 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 can be mentioned. The catalyst may be used alone or in combination of two or more.

[0032] <Polycarbonate polyol> As the polycarbonate polyol, polycondensates of polyhydric alcohols and carbonate compounds, and polycondensates of polyhydric alcohols, cyclic esters and carbonate compounds can be mentioned. The synthesis of the polycarbonate polyol can be carried out by a known method.

[0033] Examples of polyhydric alcohols include 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, and 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 Examples include aliphatic diols such as ,4-dimethyl-1,5-pentanediol and 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, and 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-tetrachlorooxylendiol, 1,4-bis(hydroxyethoxy)benzene, and 2,2-bis[(4-hydroxyethoxy)phenyl]propane. Polyhydric alcohols may be used alone or in combination of two or more.

[0034] Examples of carbonate compounds include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, diphenyl carbonate, ethylene carbonate, trimethylene carbonate, propylene carbonate, 1,2-butylene carbonate, and neopentylene carbonate. A single carbonate compound may be used, or two or more may be used in combination.

[0035] Examples of the cyclic ester include, for example, ε-caprolactone, β-propiolactone, β-methyl-β-propiolactone, δ-valerolactone, glycolide, and lactide. The cyclic ester may be used alone or in combination of two or more.

[0036] <Polyether polycarbonate polyol> Examples of the polyether polycarbonate polyol include, for example, polycondensates of a polyether polyol and a carbonate compound. It may be a copolymerized product with a diol compound different from the polyether polyol. The synthesis of the polyether polycarbonate polyol can be carried out by a known method.

[0037] Specific examples of the polyether polyol used as a synthesis raw material of the polyether polycarbonate polyol include the above polyether polyol, and specific examples of the carbonate compound include the same ones as the carbonate compound that is a synthesis raw material of the above polycarbonate polyol.

[0038] When converting the hydroxyl group at the end of the oxygen-containing polymer as described above to an oxygen-containing polymer in which a group other than the hydroxyl group, represented by -OR, is introduced, the conversion of the hydroxyl group can be carried out by alkoxylation, esterification, urethanization, etc. by a known method. From the viewpoint of improving hydrophobicity, it is preferable to alkoxylate the end.

[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, polyoxyalkylene Examples include 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 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, polyoxyalkylene butyl methyl ether, and polyoxyalkylene 2-ethylhexyl methyl ether are more preferred, and polypropylene glycol dimethyl ether, polypropylene glycol butyl methyl ether, and polypropylene glycol 2-ethylhexyl methyl ether are even more preferred.

[0041] The oxygen-containing polymer has a number-average molecular weight (Mn) of preferably 250 to 20,000, more preferably 350 to 10,000, and even more preferably 500 to 5,000. A Mn of 250 or higher makes the oxygen-containing polymer more likely to have a boiling point of 200°C or higher. Furthermore, a Mn of 20,000 or lower makes it easier for the absorbent liquid to have a viscosity that allows for uniform mixing of each component.

[0042] The oxygen-containing polymer preferably has a boiling point of 200 °C or higher, more preferably 220 °C or higher, and even more preferably 250 °C or higher. If the boiling point is 200 °C or higher, the oxygen-containing polymer is difficult to volatilize during heating when recovering the carbon dioxide absorbed in the absorption liquid, the loss of the absorption liquid can be suppressed, and the absorption liquid can be efficiently reused.

[0043] The oxygen-containing polymer preferably has a solubility parameter (δ) of 15.0 (MPa) １／２ or more and less than 19.5 (MPa), more preferably 16.0 to 19.4 (MPa) １／２ and even more preferably 17.0 to 19.3 (MPa). １／２ When δ is within the above numerical range, carbon dioxide is easily absorbed by the absorption liquid and easily desorbed from the absorption liquid by heating when recovered. When two or more oxygen-containing polymers are contained in the absorption liquid, δ is the volume average value of the solubility parameters of the various oxygen-containing polymers. １／２

[0044] (Amine compound) The amine compound preferably has a solubility parameter (δ) of 13.0 to 25.5 (MPa), １／２ more preferably 14.0 to 25.3 (MPa), １／２ and even more preferably 15.0 to 25.0 (MPa). １／２ When δ is within the above numerical range, carbon dioxide is easily absorbed by the absorption liquid and easily desorbed from the absorption liquid by heating when recovered. When two or more amine compounds are contained in the absorption liquid, δ is the volume average value of the solubility parameters of the various oxygen-containing polymers.

[0045] The amine compound preferably has a boiling point of 120 °C or higher, more preferably 130 °C or higher, and even more preferably 140 °C or higher. If the boiling point is 120 °C or higher, carbon dioxide is easily absorbed by the absorption liquid, and the amine compound is also difficult to volatilize during heating when recovering the absorbed carbon dioxide, and the absorption liquid can be efficiently reused.

[0046] Specific examples of amine compounds include butylamine, dibutylamine, 3-(dibutylamino)propylamine, 2-ethylhexylamine, methylbenzylamine, 3,3-iminobis(N,N-dimethylpropylamine), and monoethanolamine. Of these, butylamine, dibutylamine, 3-(dibutylamino)propylamine, 2-ethylhexylamine, methylbenzylamine, and 3,3-iminobis(N,N-dimethylpropylamine) are preferred.

[0047] (Liquid) In addition to the oxygen-containing polymer and amine compound, the absorbent liquid of this embodiment includes a liquid with a boiling point of 50 to 110°C. Liquids with such boiling points tend to volatilize when heated at relatively low temperatures when recovering carbon dioxide absorbed by the absorbent liquid. Therefore, precipitates of carbonate formed when some of the volatilized amine compound reacts with carbon dioxide are dissolved by the liquid re-condensed from the volatilized liquid, thereby preventing blockage of the carbon dioxide recovery pipeline.

[0048] The aforementioned liquid is preferably, for example, water, methanol, or ethanol. The aforementioned liquid may be used alone or in combination of two or more. Of these, water is preferred from the viewpoint of availability, ease of handling, and cost.

[0049] The content of the liquid in the absorbent solution is 0.01 to 5.0% by mass, preferably 0.02 to 5.0% by mass, more preferably 0.05 to 3.0% by mass, and even more preferably 1.0 to 3.0% by mass. If the content is 0.01% by mass or more, the formation of precipitates in the recovery pipeline of carbon dioxide absorbed by the absorbent solution can be suppressed. Furthermore, if the content is 5.0% by mass or less, the latent heat of vaporization of the absorbent solution can be suppressed, and the heating energy required when recovering carbon dioxide absorbed by the absorbent solution can be reduced.

[0050] From the viewpoint of sufficiently absorbing carbon dioxide and facilitating the recovery of absorbed carbon dioxide, the content of the oxygen-containing polymer in the absorbent liquid is preferably 1 to 99% by mass, more preferably 5 to 99% by mass, even more preferably 10 to 98% by mass, even more preferably 30 to 97% by mass, particularly preferably 40 to 90% by mass, and most preferably 45 to 75% by mass.

[0051] The content of the amine compound in the absorption solution is preferably 1 to 99% by mass, more preferably 1 to 90% by mass, even more preferably 2 to 80% by mass, even more preferably 3 to 70% by mass, particularly preferably 10 to 60% by mass, and most preferably 25 to 55% by mass, from the viewpoint of sufficiently absorbing carbon dioxide and facilitating the recovery of the absorbed carbon dioxide.

[0052] The mass ratio of the oxygen-containing polymer to the amine compound in the absorbent solution is preferably 1 / 99 to 99 / 1, more preferably 20 / 80 to 99 / 1, even more preferably 30 / 70 to 98 / 2, and particularly preferably 50 / 50 to 97 / 3, from the viewpoint of sufficiently absorbing carbon dioxide 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, amine compound, and liquid. The absorbent solution may optionally contain additives such as antioxidants, corrosion inhibitors, and viscosity modifiers.

[0054] The absorbent liquid of this embodiment is suitable for recovery and separation processes of acidic gases, and is particularly suitable for recovery and separation processes of carbon dioxide when the acidic gas is carbon dioxide. Examples of carbon dioxide recovery and separation processes include contacting a gas containing carbon dioxide with the absorbent liquid to selectively absorb carbon dioxide, then releasing and recovering the carbon dioxide by heating or depressurizing the absorbent liquid that has absorbed the carbon dioxide, and recovering the liquid after the release of carbon dioxide to regenerate it as an absorbent liquid.

[0055] The temperature at which carbon dioxide is absorbed into the absorbent liquid is preferably -10°C to less than 50°C, more preferably 0 to 40°C, taking into consideration the suppression of the cooling energy load on the target gas and sufficient separation of carbon dioxide. The pressure of the target gas at which carbon dioxide is absorbed into the absorbent liquid is not particularly limited.

[0056] The temperature at which carbon dioxide is released from the absorbent liquid is preferably 50 to 150°C, more preferably 60 to 130°C, and even more preferably 70 to 120°C, taking into consideration sufficient desorption of carbon dioxide from the absorbent liquid and suppression of blockage of the recovery pipeline.

[0057] The temperature difference of the absorbent during carbon dioxide absorption and release is set by comparing and balancing the thermal energy required for carbon dioxide release with the amount recovered, and is preferably 120°C or less, more preferably 100°C or less. By combining it with processes such as hydrogen stripping or a heat pump, the temperature difference can be reduced and the required energy can be decreased (see, for example, Japanese Patent No. 6906766).

[0058] [Method for Reducing Acidic Gases] In the acidic gas reduction method of this embodiment, the acidic gas absorbent liquid of this embodiment is brought into contact with a gas containing carbon dioxide to reduce the amount of carbon dioxide in the gas. The gas may be a gas containing carbon dioxide and water, or a gas that does not contain water. In either case, the method of this embodiment can sufficiently reduce the energy required for heating when recovering carbon dioxide from the absorbent liquid that has absorbed carbon dioxide.

[0059] 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.

[0060] In the acid gas reduction method of this embodiment, the absorbent solution is heated after being in contact with a gas containing carbon dioxide to remove the carbon dioxide, and the resulting absorbent solution can be recovered and reused. As described above, with the absorbent solution of this embodiment, carbon dioxide can be recovered by heating the absorbent solution that has absorbed carbon dioxide after being in contact with a gas containing carbon dioxide, thereby removing the carbon dioxide from the absorbent solution. Furthermore, the absorbent solution from which the carbon dioxide has been removed can be reused to reduce acid gases, and according to the acid gas reduction method of this embodiment, the absorbent solution can be recycled.

[0061] 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.

[0062] [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 PPG(1) (polypropylene glycol butyl methyl ether; Mn 1334).

[0063] (Synthesis Example 2) Using 1000 g of propylene glycol as an initiator, 1215 g of PO was polymerized in the presence of potassium hydroxide, followed by neutralization and removal of the neutralized salt to obtain PPG(2) (bifunctional PPG; Mn 2800).

[0064] [Preparation of Acid Gas Absorbent Solution] An acid gas absorbent solution was prepared by mixing an oxygen-containing polymer (A), an amine compound (B), and a liquid (C) according to the formulations shown in Table 1 for each example.

[0065] Details of the oxygen-containing polymer (A) and amine compound (B) in Table 1 are as follows: <Oxygen-containing polymer> ・PPG (1): Polypropylene glycol butyl methyl ether produced in Synthesis Example 1; δ = 17.5 (MPa) １／２ Boiling point 270°C or higher, PPG (2): Bifunctional PPG produced in Synthesis Example 2; δ = 19.3 (MPa) １／２ Boiling point 270°C or higher; TEG: Triethylene glycol; Mn 150; δ = 27.8 (MPa) １／２ Boiling point 285°C <Amine compound> DBA: Dibutylamine; δ = 16.8 (MPa) １／２ DBAPA: 3-(dibutylamino)propylamine; δ = 17.8 (MPa) １／２ • 2EHA: 2-ethylhexylamine; δ = 17.4 (MPa) １／２ MBA: Methylbenzylamine; δ = 19.9 (MPa) １／２ • IBDMPA: 3,3-Iminobis(N,N-dimethylpropylamine); δ = 17.3 (MPa) １／２ • MEA: Monoethanolamine; δ = 29.2 (MPa) １／２

[0066] [Evaluation of Acid Gas Absorbent Solution] The following items were evaluated for each absorbent solution in the example.

[0067] (Carbon dioxide absorption) 100 mL of absorption solution was placed in a 300 mL three-necked flask equipped with a reflux tubing and thermometer, and the temperature was raised to 40°C. A carbon dioxide-containing mixed gas (20 vol% carbon dioxide / 80 vol% nitrogen) was bubbled into the absorption solution through a needle with a diameter of 0.5 mm. The absorption solution was sampled after 90 minutes of bubbling. １３When the amount of carbon dioxide absorbed was determined by 13C-NMR measurement, it was confirmed that all absorption solutions absorbed 0.350 moles or more of carbon dioxide per mole of amine compound (B), indicating sufficient absorption.

[0068] (Presence or absence of precipitate) 150 g of absorption solution and a stirring bar were placed in a 300 mL two-necked flask, and a 30 cm reflux tube was connected to one neck. Cooling water at 5°C was circulated through the reflux tube. 200 min －１ The mixture was stirred by rotating a stirring bar, and carbon dioxide was blown in from the other end at a rate of 200 mL / min. After 90 minutes, the presence or absence of precipitates in the reflux pipe was visually checked. The precipitates were evaluated according to the following criteria: <Evaluation Criteria> A: No precipitates B: Precipitates in less than 10% of the reflux pipe C: Precipitates in 10% to less than 50% of the reflux pipe D: Precipitates in 50% or more of the reflux pipe

[0069] (Latent heat of vaporization) Approximately 10 g of absorption solution was placed in a 20 mL vial. After measuring the mass of the absorption solution, it was left open and heated at 60°C for 1 hour, 500 min. －１ The mixture was stirred, and the mass of the absorbent solution was measured again. The amount of volatilization of the absorbent solution was determined from the difference in mass before and after stirring. Furthermore, regarding the absorbent solution before and after stirring, １ ¹H-NMR measurements were performed to determine the volatile components and their masses. The total amount of the latent heat of vaporization of each volatile component (reference values: water 2250 J / g, methanol 1101 J / g) was calculated as the latent heat of vaporization of the absorbent. The latent heat of vaporization was evaluated according to the following criteria: <Evaluation Criteria> A: Less than 500 J / g B: 500 J / g or more and less than 1000 J / g C: 1000 J / g or more and less than 2000 J / g D: 2000 J / g or more

[0070] The evaluation results for each are shown in Table 1. Examples 1-14 and 18-20 are examples, and examples 15-17 are comparative examples.

[0071]

[0072] As can be seen from Table 1, it was confirmed that the absorption solutions of Examples 1-14 and 18-20 suppressed the latent heat of vaporization and suppressed the formation of precipitates in the reflux pipe. Therefore, it can be said that the absorption solutions of Examples 1-14 and 18-20 suppress the latent heat of vaporization, reduce heating energy, and prevent blockage of the recovery pipeline when recovering absorbed carbon dioxide.

Claims

1. An acidic gas absorbent that reversibly absorbs and desorbs carbon dioxide, comprising an oxygen-containing polymer, an amine compound, and a liquid having a boiling point of 50 to 110°C, wherein the oxygen-containing polymer has at least one group selected from the group consisting of oxyalkylene groups, carbonate groups, and ester groups, and the content of the liquid in the acidic gas absorbent is 0.01 to 5.0% by mass.

2. The acidic gas absorbent according to claim 1, wherein the liquid is at least one selected from the group consisting of water, methanol, and ethanol.

3. The acidic gas absorbent liquid according to claim 1, wherein the oxygen-containing polymer has a number average molecular weight of 250 to 20,000.

4. The acidic gas absorbent according to claim 1, wherein the oxygen-containing polymer has a boiling point of 200°C or higher.

5. The oxygen-containing polymer has a solubility parameter of 15.0 (MPa). １／２ The above is 19.5 (MPa). １／２ The acidic gas absorbent according to claim 1, wherein the amount is less than [amount missing].

6. The amine compound has a solubility parameter of 13.0 to 25.5 (MPa). １／２ The acidic gas absorbent according to claim 1.

7. 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.

8. The acidic gas absorbent liquid according to claim 1, wherein the content of the oxygen-containing polymer is 5 to 99% by mass.

9. The acidic gas absorbent according to claim 1, wherein the content of the amine compound is 1 to 90% by mass.

10. The acid gas absorbent according to claim 1, for use in an acid gas recovery and separation process.

11. A method for reducing acidic gases, comprising contacting an acidic gas absorbent liquid according to any one of claims 1 to 10 with a gas containing carbon dioxide to reduce the amount of carbon dioxide in the gas.

12. The method for reducing acidic gas according to claim 11, comprising heating an acidic gas absorbent solution that has been brought into contact with a gas containing carbon dioxide to remove carbon dioxide, and recovering and reusing the obtained acidic gas absorbent solution.

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