Acidic gas-absorbing liquid and acidic gas reduction method

Abstract

Provided are an acidic gas-absorbing liquid and an acidic gas reduction method that can reduce the energy required for recovering acidic gas from gas and that has little impact on solvent loss. The acidic gas-absorbing liquid according to the present invention reversibly absorbs and desorbs carbon dioxide, and contains an oxygen-containing polymer and an amine compound. 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 has a number average molecular weight of 300-4000, a boiling point of 200°C or higher, and a solubility parameter of 19.5-26.0 (MPa)1 / 2. The difference between the solubility parameter of the oxygen-containing polymer and the solubility parameter of the amine compound is 4.0-6.3 (MPa)1 / 2.

Description

Acid gas absorbing solution and acid gas reduction method

[0001] The present invention relates to an acid gas absorbing solution useful for reducing acid gases in gas, and a method for reducing acid gases.

[0002] A known method for recovering acidic gases, such as carbon dioxide, from gases involves absorbing and separating the gases using an acidic gas absorbing solution (hereinafter simply referred to as the absorbing solution) containing water, an amine compound, and an organic solvent, and then recovering the acidic gases by desorbing them from the absorbing solution through heating. Such an absorbing solution utilizes the reversible reaction of the amine compound to produce and regenerate an amine salt, and is also called a chemical absorbing solution.

[0003] In the above-described acidic gas recovery method, various methods have been proposed from the viewpoint of energy conservation for reducing the energy required for heating when desorbing acidic gases from an absorbing solution. For example, Patent Document 1 proposes a method using an absorbing solution containing an amine compound and an organic solvent whose solubility parameter differs from that of the amine compound within a predetermined range. This method utilizes the phase separation of the absorbing solution that has absorbed acidic gases into a phase with a high acidic gas content and a phase with a low acidic gas content, which is achieved by selecting a combination of the amine compound with an alcohol such as 1-butanol or 1-pentanol, or an ether such as diethylene glycol diethyl ether. Then, by selectively heating the phase with a high acidic gas content to desorb the acidic gases, the energy required for recovering acidic gases can be reduced compared to when the entire absorbing solution is desorbed.

[0004] Patent No. 6460974

[0005] However, when the absorbent described in Patent Document 1 is heated to desorb acidic gases and regenerate the absorbent, the organic solvent contained therein volatilizes, which increases the cost of recovering the volatilized solvent and replenishing the organic solvent.Furthermore, the regeneration efficiency for reusing the absorbent is poor.

[0006] The present invention has been made to solve such problems, and aims to provide an acid gas absorption liquid and an acid gas reduction method that can reduce the energy required to recover acid gases from gas and have little effect on solvent loss.

[0007] The present invention is based on the discovery that by absorbing carbon dioxide into an acidic gas absorbing solution containing a combination of a predetermined hydrophilic oxygen-containing polymer and a hydrophilic amine compound, it is possible to suppress the volatilization of the acidic gas absorbing solution and to reduce the energy required to recover acidic gas from gas.

[0008] The present invention provides the following means: [1] An acidic gas absorbing liquid that reversibly absorbs and desorbs carbon dioxide, comprising an oxygen-containing polymer and an amine compound, wherein 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, a number average molecular weight of 300 to 4000, a boiling point of 200°C or higher, and a solubility parameter of 19.5 to 26.0 (MPa). １／２ The difference between the solubility parameter of the oxygen-containing polymer and the solubility parameter of the amine compound is 4.0 to 6.3 (MPa). １／２ [2] The acidic gas absorbing liquid according to [1], wherein the oxygen-containing polymer has a group represented by -OR at an end, wherein the 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. [3] The acidic gas absorbing liquid according to [1] or [2], wherein the oxygen-containing polymer is at least one selected from the group consisting of polyether monool, polyether polyol, polyester polyol, polycarbonate polyol, and polyether polycarbonate polyol. [4] The amine compound has a solubility parameter of 23.5 to 30.0 (MPa). １／２[5] The acidic gas absorbing liquid of any of [1] to [3], wherein the content of the oxygen-containing polymer is 5 to 90% by mass and the content of the amine compound is 5 to 90% by mass. [6] The acidic gas absorbing liquid of [5], wherein the acidic gas absorbing liquid contains water, and the content of the water is 20% by mass or less. [7] The acidic gas absorbing liquid of any of [1] to [6], which is used in a process for recovering and separating acidic gases. [8] A method for reducing acidic gases, comprising contacting the acidic gas absorbing liquid of any of [1] to [7] with a gas containing carbon dioxide to reduce carbon dioxide in the gas. [9] The method for reducing acidic gases of [8], wherein the acidic gas absorbing liquid that has been phase-separated by contact with a gas containing carbon dioxide is heated to desorb carbon dioxide, and the obtained acidic gas absorbing liquid is recovered and reused as an acidic gas absorbing liquid to be contacted with a gas containing carbon dioxide.

[0009] According to the present invention, an acid gas absorbing solution and an acid gas reduction method are provided which can reduce the energy required for recovering acid gases from gas and have little effect on solvent loss.

[0010] The definitions and meanings of terms and notations used in this specification are shown below. A numerical range expressed using "to" means that the numerical values ​​before and after "to" are the lower and upper limits. The number average molecular weight (Mn) of the oxygen-containing polymer is the molecular weight determined by gel permeation chromatography (GPC) using polystyrene as the standard substance. The hydroxyl value-based molecular weight of the oxygen-containing polymer (hydroxyl-terminated) was calculated from the hydroxyl value determined based on JIS K 1557-1:2007 using the formula 56100 / (hydroxyl value) x (number of terminal hydroxyl groups per molecule). The boiling point of the oxygen-containing polymer is a value calculated using chemical structure drawing software "ChemDraw v17.1" (CambridgeSoft). The solubility parameter is a value at 25°C calculated by the Fedors method. When calculating using the Fedors method, known structural formulas were applied to amine compounds, and the following structural formulas were applied to oxygen-containing polymers: １ H-NMR and １３The terminal structure was identified by C-NMR analysis, and the formula weight of the terminal structure was subtracted from the number average molecular weight. The obtained value was then divided by the formula weight of the structural unit of the oxygen-containing polymer to obtain an integer value (rounded off) to obtain the number of repeating units.

[0011] [Acidic Gas Absorbent] The acidic gas absorbent of the present invention is an acidic gas absorbent that reversibly absorbs and desorbs carbon dioxide, and contains an oxygen-containing polymer and an amine compound. 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, a number-average molecular weight of 300 to 4000, a boiling point of 200°C or higher, and a solubility parameter of 19.5 to 26.0 (MPa). １／２ The difference between the solubility parameter of the oxygen-containing polymer and the solubility parameter of the amine compound is 4.0 to 6.3 (MPa). １／２ is.

[0012] The acidic gas is a gas containing carbon dioxide, and may also contain other acidic gases such as hydrogen sulfide and sulfur dioxide. The acidic gas absorbing liquid of an embodiment of the present invention (hereinafter referred to as the present embodiment) is capable of reversibly absorbing and desorbing, among acidic gases, particularly carbon dioxide. Hereinafter, a case where the acidic gas absorbed by the acidic gas absorbing liquid is carbon dioxide will be described as an example.

[0013] The acidic gas absorbent of this embodiment contains a hydrophilic oxygen-containing polymer having a predetermined solubility parameter and a hydrophilic amine compound whose solubility parameter difference is within a predetermined range. In this acidic gas absorbent, the oxygen-containing polymer and the amine compound are compatible and miscible with each other. Upon absorbing carbon dioxide, the acidic gas absorbent undergoes phase separation into a lower layer containing an amine salt formed by absorbing carbon dioxide and an upper layer containing the oxygen-containing polymer. When carbon dioxide is desorbed from this phase-separated acidic gas absorbent by heating, the amine compound regenerated by desorbing the acidic gas from the amine salt is extracted into the oxygen-containing polymer in the upper layer, and the oxygen-containing polymer and the amine compound are again mixed. That is, the acidic gas absorbent that has absorbed carbon dioxide can be regenerated by heating to desorb carbon dioxide and return to a mixed state. It is presumed that the oxygen-containing polymer in the upper layer, which is phase-separated by absorbing carbon dioxide into the acidic gas absorbent, promotes carbon dioxide desorption. This is thought to reduce the energy required to recover carbon dioxide from gas. In addition, oxygen-containing polymers have a higher boiling point and are less likely to volatilize than conventional organic solvents used in combination with amine compounds, which reduces the impact on solvent loss and improves the regeneration efficiency of acid gas absorption solutions.

[0014] (Oxygen-Containing Polymer) The oxygen-containing polymer contained in the acidic gas absorbing liquid is a polymer having at least one group selected from the group consisting of an oxyalkylene group, a carbonate group, and an ester group, and having a number average molecular weight (Mn) of 300 to 3000. With such an oxygen-containing polymer, the acidic gas absorbing liquid easily absorbs carbon dioxide and undergoes phase separation into a lower layer containing an amine salt produced by absorbing carbon dioxide, and an upper layer containing the oxygen-containing polymer.

[0015] The oxygen-containing polymer preferably has a group represented by -OR at its terminal. R in -OR is preferably a hydrogen atom or a linking group having 1 to 8 carbon atoms, more preferably a hydrogen atom or a linking group having 1 to 4 carbon atoms. The linking 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, and is preferably a hydrogen atom or an alkyl group. Examples of the alkyl group of the linking group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, an octyl group, and a 2-ethylhexyl group. When the oxygen-containing polymer has a terminal group containing an oxygen atom, carbon dioxide is more easily absorbed by the absorbing liquid.

[0016] Examples of oxygen-containing polymers include polyethers, polycarbonates, and polyesters, and among these, polyether monools, polyether polyols, polyester polyols, polycarbonate polyols, and polyether polycarbonate polyols are preferred. The oxygen-containing polymers may be used alone or in combination of two or more.

[0017] <Polyether Monool> The polyether monool is preferably obtained by addition polymerization of an alkylene oxide with an initiator having one active hydrogen atom per molecule. The addition polymerization can be carried out by a known method in the presence of a catalyst.

[0018] The initiator is preferably a compound having one hydroxyl group per molecule, and examples thereof include monohydric alcohols such as 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. One type of initiator may be used alone, or two or more types may be used in combination.

[0019] 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 the alkylene oxide 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 oxides may be used alone or in combination of two or more.

[0020] As the catalyst, known catalysts can be used, and examples thereof include alkali catalysts such as potassium hydroxide, transition metal compound-porphyrin complex catalysts such as complexes obtained by reacting organoaluminum compounds with porphyrins, composite metal cyanide complex catalysts such as zinc hexacyanocobaltate complexes having tert-butanol as a ligand, and catalysts made of phosphazene compounds. The catalysts may be used alone or in combination of two or more.

[0021] <Polyether Polyol> The polyether polyol is preferably one obtained by addition polymerization of an alkylene oxide with an initiator having two or more active hydrogen atoms in one molecule.

[0022] The initiator is preferably a compound having two or more hydroxyl groups in one molecule, and examples thereof include dihydric alcohols 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, and resorcinol; and trihydric or higher alcohols such as glycerin, diglycerin, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, glucose, sorbitol, dextrose, fructose, sucrose, methyl glucoside, trehalose, novolak, resol, and castor oil. Water can also be used as the initiator. Among these, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, glycerin, trimethylolpropane, pentaerythritol, and sorbitol are preferred. The initiators may be used alone or in combination of two or more.

[0023] Specific examples of the alkylene oxide include the same alkylene oxides as those used as raw materials for synthesizing the polyether monool. The addition polymerization can also be carried out by the same method as in the synthesis of the polyether monool.

[0024] Specific examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, polyoxytetramethylene glycol, and addition polymers of polyoxytetramethylene glycol and alkylene oxide.

[0025] <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 dibasic acid dialkyl 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.

[0026] Examples of dibasic acids include aliphatic dibasic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, brassylic 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 dibasic acid dialkyl esters include the dimethyl esters, diethyl esters, dipropyl esters, and dibutyl esters of the dibasic acids exemplified above. One type of dibasic acid may be used alone, or two or more types may be used in combination.

[0027] 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 tri- or higher hydric alcohols such as glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, sorbitol, and sucrose. One type of polyhydric alcohol may be used alone, or two or more types may be used in combination.

[0028] Examples of the catalyst 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. One type of catalyst may be used alone, or two or more types may be used in combination.

[0029] <Polycarbonate polyol> Examples of polycarbonate polyols include polycondensates of polyhydric alcohols and carbonate compounds, and polycondensates of polyhydric alcohols, cyclic esters, and carbonate compounds. Polycarbonate polyols can be synthesized by known methods.

[0030] 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 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, 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-tetrachloroxylenediol, 1,4-bis(hydroxyethoxy)benzene, and 2,2-bis[(4-hydroxyethoxy)phenyl]propane. The polyhydric alcohols may be used alone or in combination of two or more.

[0031] 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. The carbonate compounds may be used alone or in combination of two or more.

[0032] Examples of cyclic esters include ε-caprolactone, β-propiolactone, β-methyl-β-propiolactone, δ-valerolactone, glycolide, and lactide. The cyclic esters may be used alone or in combination of two or more.

[0033] <Polyether polycarbonate polyol> Examples of polyether polycarbonate polyols include polycondensates of polyether polyols and carbonate compounds. Polyether polyols may also be copolymerized with diol compounds different from the polyether polyol. Polyether polycarbonate polyols can be synthesized by known methods.

[0034] Specific examples of polyether polyols used as raw materials for synthesizing polyether polycarbonate polyols include the polyether polyols described above, and specific examples of carbonate compounds include the same carbonate compounds as the raw materials for synthesizing the polycarbonate polyols described above.

[0035] When the terminal hydroxyl group of the oxygen-containing polymer as described above is converted to an oxygen-containing polymer having a group other than a hydroxyl group introduced therein, represented by —OR, the conversion of the hydroxyl group can be carried out by a known method such as alkoxylation, esterification, urethanization, etc. From the viewpoint of improving hydrophobicity, it is preferable to alkoxylate the terminal.

[0036] The alkoxylation of the terminal hydroxyl groups of the oxygen-containing polymer can be carried out, for example, by a method using an organic halogen compound such as an alkyl halide. Examples of the organic halogen compound 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-chloroethyl methyl ether, 2-chloroethyl ethyl ether, 2-chloroethyl propyl ether, and 2-chloroethyl butyl ether; methyl bromide, ethyl bromide, vinyl bromide, n-propyl bromide, isopropyl bromide, allyl bromide, n-butyl bromide, and bromide. 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-iodoethyl methyl ether. Among these, from the viewpoint of efficient conversion of hydroxyl groups, methyl chloride, allyl chloride, methyl bromide, allyl bromide, methyl iodide, and allyl iodide are preferred.

[0037] Examples of oxygen-containing polymers having a group other than a hydroxyl group represented by -OR introduced at the end of the oxygen-containing polymer include polyoxyalkylene dimethyl ether, polyoxyalkylene diethyl ether, polyoxyalkylene dipropyl ether, polyoxyalkylene diisopropyl ether, polyoxyalkylene diaryl ether, polyoxyalkylene dibutyl ether, polyoxyalkylene disec-butyl ether, polyoxyalkylene ditert-butyl ether, polyoxyalkylene dipentyl ether, polyoxyalkylene dihexyl ether, polyoxyalkylene diheptyl ether, polyoxyalkylene dioctyl ether, polyoxyalkylene di(2-ethylhexyl) ether, polyoxyalkylene ethyl methyl ether, polyoxyalkylene propyl methyl ether, polyoxyalkylene isopropyl methyl ether, polyoxyalkylene butyl methyl ether, polyoxyalkylene Examples of the alkyl ether 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.Among these, from the viewpoint of ease of alkoxylation, 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

[0043] Preferred are 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, and polyoxyalkylene 2-ethylhexyl allyl ether, and more preferred is polyoxyalkylene dimethyl ether.

[0038] <Number Average Molecular Weight> The number average molecular weight (Mn) of the oxygen-containing polymer is 300 to 4000, preferably 350 or more, more preferably 400 or more, and preferably 3500 or less, more preferably 3000 or less. When Mn is 300 or more, the boiling point of the oxygen-containing polymer tends to be 200° C. or more. Furthermore, from the viewpoint of keeping the difference in solubility parameter with the amine compound within a predetermined range, Mn is set to 4000 or less.

[0039] <Boiling Point> The boiling point of the oxygen-containing polymer is 200° C. or higher, preferably 220° C. or higher, and more preferably 250° C. or higher. When the boiling point is 200° C. or higher, the polymer is less likely to volatilize even when heated for desorbing carbon dioxide from the acidic gas absorbing solution, the effect on solvent loss is suppressed, and the acidic gas absorbing solution can be efficiently reused.

[0040] <Solubility parameter> The solubility parameter (δ ａ ) is 19.5 to 26.0 (MPa) １／２ δ ａ is 19.5 (MPa) １／２ If the above value is met, the oxygen-containing polymer can be said to be hydrophilic, and the acidic gas absorbing liquid mixed with the amine compound is likely to undergo phase separation into a lower layer containing the generated amine salt and an upper layer containing the oxygen-containing polymer by absorbing carbon dioxide. ａ is 26.0 (MPa) １／２ If the solubility parameter (δ) of the oxygen-containing polymer is less than 100%, carbon dioxide is easily absorbed by the acidic gas absorbing solution. ａ ) is preferably 19.6 (MPa) from the viewpoint of ease of phase separation. １／２ More preferably, 19.7 (MPa) １／２ From the viewpoint of ease of absorption of carbon dioxide by the acidic gas absorbing solution, it is preferably 25.0 (MPa) １／２ More preferably, 24.0 (MPa) or less １／２ In addition, when the acidic gas absorbing liquid contains two or more oxygen-containing polymers, δ ａ is the volume average value of the solubility parameters of various oxygen-containing polymers.

[0041] Solubility parameter (δ ａ ) and the solubility parameter of the amine compound (δ ｂ ) difference (|δ ａ -δ ｂ The smaller the δ |, the better the compatibility. ａ and δ ｂ Regardless of the magnitude relationship, |δ ａ -δ ｂ | is 4.0 to 6.3 (MPa) １／２ |δ ａ -δ ｂ | is 4.1 (MPa) １／２ If |δ is equal to or greater than this, the acidic gas absorbing liquid will easily separate into a lower layer containing the produced amine salt and an upper layer containing the oxygen-containing polymer as a result of absorbing carbon dioxide. ａ -δ ｂ| is 6.3 (MPa) １／２ If |δ is less than or equal to the above, the oxygen-containing polymer and the amine compound have good compatibility and are easily mixed, and the acidic gas absorbing liquid easily absorbs carbon dioxide. ａ -δ ｂ From the viewpoint of the ease of phase separation, | is preferably 4.1 (MPa) １／２ More preferably, 4.2 (MPa) １／２ From the viewpoint of ease of absorption of carbon dioxide by the acidic gas absorbing solution, it is preferably 6.2 (MPa) or more. １／２ The following is the result.

[0042] (Amine Compound) The amine compound is preferably hydrophilic so that the acidic gas absorbing liquid that has absorbed carbon dioxide can be easily phase-separated into a lower layer containing the generated amine salt and an upper layer containing the oxygen-containing polymer. The solubility parameter (δ ｂ ) is the solubility parameter (δ) of the oxygen-containing polymer. ａ ) and the difference (|δ ａ -δ ｂ In view of the range of |), preferably 23.5 to 30.0 (MPa) １／２ , more preferably 23.7 (MPa) １／２ More preferably, 24.0 (MPa) １／２ More preferably, 25.0 (MPa) １／２ More preferably, 25.5 (MPa) １／２ More preferably, 29.1 (MPa) １／２ More preferably, 28.2 (MPa) or less １／２ When the absorption liquid contains two or more kinds of amine compounds, δ ｂ is the volume average value of the solubility parameters of various amine compounds.

[0043] The amine compound is unlikely to volatilize even when heated for desorption of carbon dioxide from the acidic gas absorbent, and the effect on solvent loss is suppressed. Furthermore, from the viewpoint of efficiently reusing the acidic gas absorbent, it is preferable that the amine compound has a high boiling point, preferably 130°C or higher, more preferably 140°C or higher, and even more preferably 150°C or higher.

[0044] Specific examples of the amine compound include 1,3-diaminopropane, 1-amino-2-propanol, 2-aminoethanol, DL-2-amino-1-propanol, 2-(2-aminoethoxy)ethanol, and 2-(methylamino)ethanol.

[0045] From the viewpoint of fully exhibiting the carbon dioxide absorption capacity and facilitating phase separation of the acidic gas absorbing liquid after absorbing carbon dioxide into a lower layer containing the generated amine salt and an upper layer containing the oxygen-containing polymer, the acidic gas absorbing liquid preferably has an oxygen-containing polymer content of 5 to 90 mass% and an amine compound content of 5 to 90 mass%. The oxygen-containing polymer content in the acidic gas absorbing liquid is more preferably 30 mass% or more, even more preferably 40 mass% or more, and more preferably 70 mass% or less, even more preferably 60 mass% or less. The amine compound content in the acidic gas absorbing liquid is more preferably 30 mass% or more, even more preferably 40 mass% or more, and more preferably 70 mass% or less, even more preferably 60 mass% or less.

[0046] It is preferable that the acidic gas absorbing liquid further contains water in addition to the oxygen-containing polymer and the amine compound. When the acidic gas absorbing liquid contains water, the water content is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. When the acidic gas absorbing liquid contains water, the amine salt produced by absorption of carbon dioxide is easily extracted into the lower layer containing water, facilitating phase separation. Furthermore, if the water content in the acidic gas absorbing liquid is 20% by mass or less, the influence of the latent heat of water on the energy required for heating can be suppressed when carbon dioxide absorbed in the acidic gas absorbing liquid is desorbed and recovered by heating.

[0047] The acidic gas absorbing liquid may contain additives such as antioxidants, corrosion inhibitors, viscosity modifiers, etc., as needed, within the range that does not impair the effects of the present invention.

[0048] The acidic gas absorbing liquid of the present embodiment can be produced by mixing the oxygen-containing polymer and the amine compound. If necessary, water and the above-mentioned additives may be added and mixed.

[0049] The acidic gas absorbent of this embodiment is suitable for use in a process for recovering and separating an acidic gas, and can be particularly suitable for use in a process for recovering and separating carbon dioxide when the acidic gas is carbon dioxide. Examples of the carbon dioxide recovery and separation process include a process in which a gas containing carbon dioxide is brought into contact with the acidic gas absorbent to selectively absorb and separate the carbon dioxide, and the carbon dioxide is stripped and recovered by heating or reducing the pressure of the liquid that has absorbed the carbon dioxide, and the liquid after the carbon dioxide stripping is recovered and regenerated as the acidic gas absorbent.

[0050] The temperature when carbon dioxide is absorbed into the acidic gas absorbing liquid is preferably −10° C. or higher, more preferably 0° C. or higher, from the viewpoint of suppressing the load of gas cooling energy, and is preferably 50° C. or lower, more preferably 40° C. or lower, for sufficient separation of carbon dioxide. The gas pressure when carbon dioxide is absorbed into the acidic gas absorbing liquid is not particularly limited.

[0051] The temperature at which carbon dioxide is stripped from the acidic gas absorbing solution is preferably 50°C or higher, more preferably 70°C or higher, in order to sufficiently desorb carbon dioxide from the acidic gas absorbing solution, and from the viewpoint of suppressing deterioration of the acidic gas absorbing solution, the temperature is preferably 120°C or lower, more preferably 100°C or lower, and even more preferably 90°C or lower.

[0052] The temperature difference between the absorption of carbon dioxide into the acidic gas absorbing solution and the release of carbon dioxide from the acidic gas absorbing solution is set by weighing the thermal energy for the release of carbon dioxide and the amount of recovery, and is preferably 80° C. or less, more preferably 60° C. or less. By combining with processes such as hydrogen stripping or a heat pump, the temperature difference can be reduced, and the required energy can be reduced (see Japanese Patent No. 6906766).

[0053] [Acid Gas Reduction Method] In the acid gas reduction method of this embodiment, the carbon dioxide in the gas is reduced by contacting the acid gas absorbing solution of this embodiment with a gas containing carbon dioxide. When the carbon dioxide absorbed in the acid gas absorbing solution of this embodiment is desorbed by heating, the acid gas absorbing solution that has absorbed carbon dioxide is in a phase-separated state, which facilitates desorption of the carbon dioxide. Therefore, according to the acid gas reduction method using the acid gas absorbing solution of this embodiment, it is possible to reduce the carbon dioxide in the gas and reduce the energy required to recover the carbon dioxide. Furthermore, the oxygen-containing polymer has a higher boiling point and is less likely to volatilize than conventional organic solvents used in combination with amine compounds, so it has less impact on solvent loss.

[0054] The contact between the acidic gas absorbing liquid and the gas may be, for example, by adding the acidic gas absorbing liquid to the gas, by continuously passing the gas through a container filled with the acidic gas absorbing liquid, or by filling a container filled with the acidic gas absorbing liquid with the gas. In order to increase the contact efficiency between the acidic gas absorbing liquid and the gas, methods such as providing a filler in the container, spraying the acidic gas absorbing liquid into the gas, or bubbling the gas into the acidic gas absorbing liquid can also be used.

[0055] In the acid gas reduction method of this embodiment, the acid gas absorbent that has been phase-separated by contact with a gas containing carbon dioxide is heated to desorb carbon dioxide, and the obtained acid gas absorbent can be recovered and reused as an acid gas absorbent to be contacted with a gas containing carbon dioxide. As described above, according to the acid gas absorbent of this embodiment, the acid gas absorbent that has been phase-separated by contacting with a gas containing carbon dioxide to absorb carbon dioxide can be returned to a mixed state and regenerated as an acid gas absorbent when heated to desorb carbon dioxide. This acid gas absorbent can be reused to reduce acid gases, and according to such an acid gas reduction method, the acid gas absorbent can be recycled.

[0056] The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples, and various modifications are possible within the scope of the present invention.

[0057] [Synthesis of Oxygen-Containing Polymer] (Synthesis Example 1) Using 1,000 g of propylene glycol as an initiator, 4,863 g of propylene oxide (PO) was polymerized in the presence of potassium hydroxide, followed by neutralization and removal of the neutralized salt to obtain PPG (1) (bifunctional polypropylene glycol (PPG) (number of terminal hydroxyl groups: 2); Mn: 550).

[0058] Synthesis Examples 2 and 3 PPG (2) (bifunctional PPG; Mn 880) or PPG (3) (bifunctional PPG; Mn 1300) was obtained in the same manner as in Synthesis Example 1, except that the amount of PO to be polymerized in Synthesis Example 1 was changed to 8,486 g (Synthesis Example 2) or 12,158 g (Synthesis Example 3).

[0059] [Preparation of Acidic Gas Absorbing Liquid] As the acidic gas absorbing liquid, a mixture of 60 mass % of an oxygen-containing compound (polymer), 30 mass % of an amine compound, and 10 mass % of water was prepared with each blending composition shown in Examples 1 to 11 in Table 1. The oxygen-containing polymers and amine compounds used in the acidic gas absorbing liquids of Examples 1 to 11 are shown below. <Oxygen-containing polymers> PPG (1) to (3): Each of the bifunctional PPGs produced in Synthesis Examples 1 to 3 PPG (4): Tripropylene glycol; Mn 330, manufactured by Tokyo Chemical Industry Co., Ltd. <Amine compounds> MAE: 2-(methylamino)ethanol AP: DL-2-amino-1-propanol MEA: 2-aminoethanol (also known as monoethanolamine) Table 1 shows the solubility parameters (δ) of the oxygen-containing compounds (polymers). ａ ), the solubility parameter of the amine compound (δ ｂ ), and δ ａ and δ ｂ The difference between (|δ ａ -δ ｂ |).

[0060] [Evaluation of Acidic Gas Absorbing Liquid] The acidic gas absorbing liquid of each example was evaluated for the following items. The evaluation results are shown in Table 1. Examples 1 to 3 are working examples, and Examples 4 to 11 are comparative examples. <Evaluation of Phase Separation> Carbon dioxide was bubbled into 100 g of the acidic gas absorbing liquid at 40°C for 60 minutes at 1 L / min to absorb the carbon dioxide. This liquid was allowed to stand at 40°C for 10 minutes, and then visually observed for the presence or absence of phase separation. Cases where phase separation occurred after carbon dioxide absorption were evaluated as "A," cases where the liquid remained mixed without phase separation even after carbon dioxide absorption were evaluated as "B," and cases where phase separation occurred before carbon dioxide absorption were evaluated as "C."

[0061] <Evaluation of Volatility> The mass of the acidic gas absorbing solution was measured before and after heating at 120°C for 2 hours. A mass change (loss) of less than 1.0% by mass was evaluated as "A", and a mass change of 1.0% by mass or more was evaluated as "B". In the case of evaluation A, the acidic gas absorbing solution hardly volatilized during carbon dioxide desorption, which can be said to enable efficient recovery of carbon dioxide and regeneration of the acidic gas absorbing solution.

[0062]

[0063] As can be seen from Table 1, it was confirmed that the acidic gas absorbing liquids (Examples 1 to 3) containing a hydrophilic oxygen-containing polymer with a high boiling point and a predetermined solubility parameter and an amine compound whose solubility parameter difference from that of the oxygen-containing polymer is within a predetermined range undergo phase separation upon absorbing carbon dioxide. Furthermore, since the phase-separated liquid is less likely to volatilize when heated to desorb carbon dioxide, it can be said that there is little impact on solvent loss. Therefore, according to this embodiment, it can be said that the energy required to recover acidic gas from gas can be reduced and the acidic gas absorbing liquid can be efficiently regenerated.

Claims

1. An acidic gas absorbing liquid that reversibly absorbs and desorbs carbon dioxide, comprising an oxygen-containing polymer and an amine compound, the oxygen-containing polymer having at least one group selected from the group consisting of an oxyalkylene group, a carbonate group, and an ester group, a number average molecular weight of 300 to 4000, a boiling point of 200°C or higher, and a solubility parameter of 19.5 to 26.0 (MPa). １／２ The difference between the solubility parameter of the oxygen-containing polymer and the solubility parameter of the amine compound is 4.0 to 6.3 (MPa). １／２ This is an acid gas absorbing liquid.

2. The acidic gas absorbing liquid according to claim 1, wherein the oxygen-containing polymer has a group represented by -OR at an end, the R being 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.

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

4. The amine compound has a solubility parameter of 23.5 to 30.0 (MPa). １／２ The acidic gas absorbing solution according to claim 1, 5. The acidic gas absorbing liquid according to claim 1, wherein the content of the oxygen-containing polymer is 5 to 90 mass %, and the content of the amine compound is 5 to 90 mass %.

6. The acidic gas absorbing liquid according to claim 5, wherein the acidic gas absorbing liquid contains water, and the water content is 20 mass % or less.

7. The acid gas absorbing solution according to claim 1, which is used in an acid gas recovery and separation process.

8. A method for reducing an acid gas, comprising contacting a gas containing carbon dioxide with the acid gas absorbing solution according to any one of claims 1 to 7, thereby reducing the amount of carbon dioxide in the gas.

9. A method for reducing acid gases according to claim 8, in which the acid gas absorbing liquid that has been phase-separated by contact with a gas containing carbon dioxide is heated to desorb carbon dioxide, and the resulting acid gas absorbing liquid is recovered and reused as an acid gas absorbing liquid for contact with a gas containing carbon dioxide.

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