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, even if the gas contains moisture, 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 250-20000, a boiling point of 200°C or higher, and a solubility parameter of 15.0 (MPa)1 / 2 or more and less than 19.5 (MPa)1 / 2. The amine compound has a solubility parameter of 13.0-25.5 (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 acidic gases using an acidic gas absorbing solution (hereinafter simply referred to as the absorbing solution) containing 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] Incidentally, exhaust gases from thermal power plants and various industrial processes often contain water vapor (moisture). Therefore, when recovering acidic gases from such exhaust gases, a process of removing the moisture in advance by heating or the like is required. In addition, when reusing the absorption liquid, the acidic gas is absorbed into the absorption liquid from the moisture-containing exhaust gas, and then the acidic gas is desorbed and the moisture is separated and removed by heating, thereby regenerating the absorption liquid.

[0006] In either case, when the exhaust gas or the absorption liquid is heated to evaporate the water in order to remove the water, a large amount of energy is required for heating. Even when the absorption liquid described in Patent Document 1 is used to heat only the phase with a high content of acid gases and perform the acid gas desorption treatment, it cannot be said that the energy required for heating can be sufficiently reduced due to the latent heat of water.

[0007] Furthermore, 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.

[0008] The present invention has been made to solve such problems, and aims to provide an acidic gas absorption liquid and an acidic gas reduction method that can reduce the energy required to recover acidic gas from gas, even if the gas contains moisture, and that has little effect on solvent loss.

[0009] The present invention is based on the finding that when carbon dioxide is absorbed into an acidic gas absorbing solution containing a combination of a predetermined hydrophobic oxygen-containing polymer and an aqueous amine compound having a predetermined solubility parameter, phase separation occurs into an aqueous phase and an organic phase that has absorbed carbon dioxide.

[0010] 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 250 to 20,000, a boiling point of 200°C or higher, and a solubility parameter of 15.0 (MPa). １／２ More than 19.5 (MPa) １／２ The amine compound has a solubility parameter of less than 13.0 (MPa) １／２ ~25.5 (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 acidic gas absorbing liquid according to [1] or [2], wherein the difference between the solubility parameter of the oxygen-containing polymer and the solubility parameter of the amine compound is 7.0 (MPa). １／２ The acidic gas absorbing liquid of any of [1] to [3], 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 %. [5] The acidic gas absorbing liquid of any of [1] to [4], 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 of any of [1] to [5], which is used in a process for recovering and separating acidic gases. [7] A method for reducing acidic gases, comprising contacting the acidic gas absorbing liquid of any of [1] to [6] with a gas containing carbon dioxide and moisture to reduce carbon dioxide in the gas. [8] The method for reducing acidic gases of [7], wherein an organic phase containing the oxygen-containing polymer and the amine compound is recovered from the acidic gas absorbing liquid that has undergone phase separation by contact with a gas containing carbon dioxide and moisture, and reused as an acidic gas absorbing liquid to be contacted with a gas containing carbon dioxide and moisture.

[0011] According to the present invention, an acidic gas absorption liquid and an acidic gas reduction method are provided which can reduce the energy required to recover acidic gases from gases, even when the gases contain moisture, and which have little effect on solvent loss.

[0012] 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 １３ The 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 result was then divided by the formula weight of the structural unit of the oxygen-containing polymer to obtain an integer (rounded off) to obtain the number of repeating units.

[0013] [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 250 to 20,000, a boiling point of 200°C or higher, and a solubility parameter of 15.0 (MPa). １／２ More than 19.5 (MPa) １／２ The amine compound has a solubility parameter of 13.0 to 25.5 (MPa) or less. １／２ is.

[0014] 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) can reversibly absorb and desorb, among acidic gases, particularly carbon dioxide, and can be regenerated and reused. Hereinafter, an example will be described in which the acidic gas absorbed by the acidic gas absorbing liquid is carbon dioxide.

[0015] The acidic gas absorbent of this embodiment contains a hydrophobic oxygen-containing polymer having a predetermined solubility parameter and an amine compound having a predetermined solubility parameter. Such an acidic gas absorbent is resistant to moisture absorption, and upon absorbing carbon dioxide, undergoes phase separation into an aqueous phase and an organic phase that has absorbed carbon dioxide. Therefore, there is no need to heat and evaporate the acidic gas absorbent to separate and remove moisture. Therefore, even in gases containing moisture, the energy required to recover carbon dioxide from the gas can be reduced. 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, resulting in less impact on solvent loss.

[0016] (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 250 to 20000. With such an oxygen-containing polymer, the amine salt produced when the acidic gas absorbing liquid absorbs carbon dioxide is easily dissolved in the acidic gas absorbing liquid, and phase separation into an aqueous phase and an organic phase containing the oxygen-containing polymer that has absorbed carbon dioxide is easily achieved.

[0017] 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 acidic gas absorbing solution.

[0018] 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.

[0019] <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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] <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.

[0024] 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.

[0025] 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.

[0026] Specific examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, polyoxytetramethylene glycol, and addition polymers of polyoxytetramethylene glycol and alkylene oxide.

[0027] <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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] <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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] <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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 viewpoints of ease of alkoxylation and separability from water, 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 aryl 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, and polyoxyalkylene dimethyl ether, polyoxyalkylene butyl methyl ether, and polyoxyalkylene 2-ethylhexyl methyl ether are more preferred.

[0040] <Number Average Molecular Weight> The number average molecular weight (Mn) of the oxygen-containing polymer is 250 to 20,000, preferably 350 or more, more preferably 500 or more, and preferably 10,000 or less, more preferably 5,000 or less. When Mn is 250 or more, the boiling point of the oxygen-containing polymer is likely to be 200° C. or more. Furthermore, from the viewpoint of achieving a viscosity that allows easy uniform mixing with the amine compound during preparation of the absorbing liquid, Mn is set to 20,000 or less.

[0041] <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.

[0042] <Solubility parameter> The solubility parameter (δ ａ ) is 15.0 (MPa) １／２ More than 19.5 (MPa) １／２ is less than δ ａ is 15.0 (MPa) １／２ If the temperature is above δ, carbon dioxide is easily absorbed by the acidic gas absorbing solution. ａ is 19.5 (MPa) １／２ If the solubility parameter (δ) of the oxygen-containing polymer is less than 100%, the oxygen-containing polymer is said to be hydrophobic and is prone to phase separation into an aqueous phase and an organic phase containing the oxygen-containing polymer that has absorbed carbon dioxide. ａ ) is preferably 16.0 (MPa) from the viewpoint of ease of absorption of carbon dioxide by the acidic gas absorbing solution. １／２ More preferably, 17.0 (MPa) １／２ From the viewpoint of easiness of phase separation between the aqueous phase and the organic phase containing the oxygen-containing polymer that has absorbed carbon dioxide, the pressure is preferably 19.4 (MPa) or more. １／２ Less than 19.3 (MPa), more preferably 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.

[0043] (Amine Compound) Solubility parameter of amine compound (δ ｂ ) is 13.0 (MPa) １／２ ~25.5 (MPa) １／２ δ ｂ is 13.0 (MPa) １／２ If the temperature is above δ, carbon dioxide is easily absorbed by the acidic gas absorbing solution. ａ is 25.5 (MPa) １／２If the solubility parameter (δ) of the amine compound is less than 100%, the amine compound is easily separated into an aqueous phase and an organic phase containing the amine compound that has absorbed carbon dioxide. ｂ ) is preferably 14.0 (MPa) from the viewpoint of ease of absorption of carbon dioxide by the acidic gas absorbing solution. １／２ From the viewpoint of facilitating phase separation between the aqueous phase and the organic phase containing the amine compound that has absorbed carbon dioxide, the pressure is preferably 25.3 (MPa) or more. １／２ More preferably, 25.0 (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.

[0044] The amine compound is preferably high in boiling point from the viewpoints of being resistant to volatilization even when heated for desorbing carbon dioxide from the acidic gas absorbing solution, suppressing the effect on solvent loss, and efficiently reusing the acidic gas absorbing solution. The boiling point of the amine compound is preferably 130° C. or higher, more preferably 140° C. or higher, and even more preferably 150° C. or higher. From the viewpoints of efficiently absorbing and desorbing acidic gases, the amine compound preferably contains a secondary amine.

[0045] Specific examples of the amine compound include diethylamine, N-ethylpropylamine, dipropylamine, diallylamine, diisopropylamine, di(2-methoxyethyl)amine, dibutylamine, disec-butylamine, diamylamine, dihexylamine, di-2-ethylhexylamine, 3,3-iminobis(N,N-dimethylpropylamine), 2-(ethylamino)ethanol, 2-(propylamino)ethanol, isopropylaminoethanol, 2-(butylamino)ethanol, methylpropylaminoethanol, 4-(ethylamino)butanol, 4-(butylamino)butanol, benzylmethylamine, benzylethylamine, benzylpropylamine, benzylbutylamine, methylaniline, ethylaniline, propylaniline, and butylaniline.

[0046] Solubility parameter (δａ ) and the solubility parameter of the amine compound (δ ｂ ) difference (|δ ａ -δ ｂ |) is preferably 7.0 (MPa) １／２ Less than 6.3 (MPa), more preferably １／２ More preferably, 6.0 (MPa) or less １／２ The compatibility is better when the oxygen-containing polymer is hydrophobic, the amine compound has a predetermined solubility parameter, and the smaller the difference between the solubility parameters of the two is, the better the compatibility is. ａ and δ ｂ Regardless of the magnitude relationship with |δ ａ -δ ｂ | is 7.0 (MPa) １／２ If the content is below this range, the compatibility between the two is good, a uniform absorbing solution is easily obtained, and the organic phase and aqueous phase of the acidic gas absorbing solution that has absorbed carbon dioxide are more easily separated.

[0047] From the viewpoints of fully exhibiting the carbon dioxide absorption capacity, phase separation into the organic phase and the aqueous phase of the acidic gas absorbent that has absorbed carbon dioxide, and facilitating a reduction in the energy required to recover carbon dioxide, the acidic gas absorbent 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 absorbent 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 absorbent 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.

[0048] The acidic gas absorbing liquid may contain additives such as antioxidants, corrosion inhibitors, viscosity modifiers, etc., as needed, within the scope that does not impair the effects of the present invention. The acidic gas absorbing liquid may also contain water. For example, even when the water content in the acidic gas absorbing liquid is about 50% by mass, the water contained in the acidic gas absorbing liquid that has absorbed carbon dioxide is separated as an aqueous phase, so that the water content in the organic phase can be reduced to less than 10% by mass.

[0049] The acidic gas absorbing liquid of the present embodiment can be produced by mixing the oxygen-containing polymer and the amine compound. If necessary, the additives and water may be added and mixed.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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).

[0054] [Acid gas reduction method] In the acid gas reduction method of this embodiment, the carbon dioxide in the gas containing carbon dioxide and moisture is reduced by contacting the acid gas absorbing solution of this embodiment with the gas. The acid gas absorbing solution of this embodiment is not only effective when recovering carbon dioxide from a gas containing no moisture, but also can separate and remove moisture without heating to evaporate it when recovering carbon dioxide from a gas containing carbon dioxide and moisture, and therefore can more effectively reduce the energy required to recover acid gas from the gas.

[0055] 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.

[0056] In the acidic gas reduction method of this embodiment, an organic phase containing an oxygen-containing polymer and an amine compound is recovered from an acidic gas absorbing liquid that has undergone phase separation upon contact with a gas containing carbon dioxide and moisture, and can be reused as an acidic gas absorbing liquid to be contacted with a gas containing carbon dioxide and moisture. As described above, according to the acidic gas absorbing liquid of this embodiment, the acidic gas absorbing liquid that has been contacted with a gas containing carbon dioxide and moisture to absorb carbon dioxide undergoes phase separation into an organic phase containing carbon dioxide, the oxygen-containing polymer, and the amine compound, and an aqueous phase. This organic phase can be easily separated and recovered from the aqueous phase. By heating the separated and recovered organic phase to desorb carbon dioxide, carbon dioxide can be recovered, and the organic phase can be regenerated as an acidic gas absorbing liquid. This acidic gas absorbing liquid can be reused for reducing acidic gases, and according to this acidic gas reduction method, the acidic gas absorbing liquid can be recycled.

[0057] 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.

[0058] [Synthesis of Oxygen-Containing Polymer] (Synthesis Example 1) Using 1000 g of polypropylene glycol (bifunctional PPG (number of terminal hydroxyl groups: 2); Mn: 400) obtained by ring-opening polymerization of propylene glycol with propylene oxide (PO) as an initiator, 7000 g of PO was polymerized in the presence of potassium hydroxide, followed by neutralization and removal of the neutralized salt to obtain PPG (1) (bifunctional PPG; Mn: 5200).

[0059] Synthesis Example 2 PPG (2) (bifunctional PPG; Mn 2800) was obtained in the same manner as in Synthesis Example 1, except that the amount of PO to be polymerized was changed to 4000 g.

[0060] Synthesis Example 3 Using 1000 g of propylene glycol as an initiator, 12158 g of PO was polymerized in the presence of potassium hydroxide, followed by neutralization and removal of the neutralized salt to obtain PPG (3) (difunctional PPG; Mn 1300).

[0061] Synthesis Example 4 Using 74 g of butanol as an initiator, 326 g of PO was polymerized in the presence of a zinc hexacyanocobaltate complex having tert-butanol as a ligand to obtain PPG (4) (monofunctional PPG; Mn 540).

[0062] (Synthesis Example 5) Using 1,340 g of ethylene glycol monobutyl ether as an initiator, 1,926 g of PO was polymerized in the presence of potassium hydroxide, followed by neutralization and removal of the neutralized salt to obtain PPG (5') (monofunctional PPG: hydroxyl value 188 mg KOH / g). Next, to 2,000 g of PPG (5'), a 28 mass% methanol solution of sodium methoxide (NaOMe) was added so that 1.1 moles of NaOMe was added per mole of hydroxyl group in PPG (5'), and the mixture was heated to 70 ° C., followed by nitrogen flow, and the methanol was distilled off under atmospheric pressure. Thereafter, the mixture was heated to 130 ° C., stirred and mixed under a reduced pressure of -0.1 MPaG for 4 hours, and the methanol was distilled off. Next, the mixture was cooled to 100 ° C., and 1.1 moles of chloromethane per mole of NaOMe was added successively at a rate of 400 g / hr, and the mixture was allowed to react at 100 ° C. for 2 hours. The mixture was then stirred and mixed for 0.5 hours at 100°C under a reduced pressure of -0.1 MPaG, and the unreacted chloromethane was distilled off under reduced pressure to obtain a crude product in which the hydroxyl groups of PPG (5') were methoxylated. Next, 2000 g of distilled water was added to the reactor, and the mixture was stirred and mixed for 15 minutes to separate the neutralized salt into oil and water. Only the oil layer was extracted, and 4 parts by mass of adsorbent was added per 100 parts by mass of the oil layer. The mixture was heated to 120°C, and then stirred and mixed for 1.5 hours under a reduced pressure of -0.1 MPaG. The adsorbent was filtered to obtain PPG (5) (Mn 476), a terminally methylated derivative of PPG (5').

[0063] Synthesis Example 6 PPG (6) (monofunctional PPG: Mn 949) was obtained in the same manner as in Synthesis Example 3, except that the initiator in Synthesis Example 3 was changed to 743 g of 2-ethylhexanol and the amount of PO to be polymerized was changed to 3,457 g.

[0064] Synthesis Example 7 PPG (7) (terminally methylated derivative of monofunctional PPG: Mn 1334) was obtained in the same manner as in Synthesis Example 5, except that the initiator in Synthesis Example 5 was changed to 552 g of butanol and the amount of PO to be polymerized was changed to 7,842 g.

[0065] Synthesis Example 8 PPG (8) (terminally methylated derivative of monofunctional PPG: Mn 1849) was obtained in the same manner as in Synthesis Example 5, except that the initiator was changed to 171 g of methanol and the amount of PO to be polymerized was changed to 7,829 g.

[0066] Synthesis Example 9 PPG (9) (terminally methylated derivative of monofunctional PPG: Mn 2586) was obtained in the same manner as in Synthesis Example 8, except that the initiator in Synthesis Example 8 was changed to 120 g of methanol and the amount of PO to be polymerized was changed to 7,880 g.

[0067] Synthesis Examples 10 and 11 PPG (10) (bifunctional PPG; Mn 880) or PPG (11) (bifunctional PPG; Mn 550) was obtained in the same manner as in Synthesis Example 3, except that the amount of PO to be polymerized in Synthesis Example 3 was changed to 8,486 g (Synthesis Example 10) or 4,863 g (Synthesis Example 11).

[0068] [Preparation of Acidic Gas Absorbing Liquid] (Examples 1 to 24) PPGs (1) to (11) obtained in Synthesis Examples 1 to 11 and tripropylene glycol (manufactured by Tokyo Chemical Industry Co., Ltd.; Mn 330; PPG (12)) were used as oxygen-containing polymers, and various amine compounds were mixed in the mass ratios shown in Table 1 to prepare acidic gas absorbing liquids.

[0069] Table 1 shows the solubility parameters (δ ａ ), the solubility parameter of the amine compound (δ ｂ ), and δ ａ and δ ｂ The difference between (|δ ａ -δ ｂ |) are shown. The abbreviations for the amine compounds in Table 1 are as follows: DAA: diamylamine DBA: dibutylamine BMA: benzylmethylamine IBDMAPA: 3,3-iminobis(N,N-dimethylpropylamine) EAE: 2-(ethylamino)ethanol MPAE: methylpropylaminoethanol MAE: 2-(methylamino)ethanol

[0070] [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 15 are working examples, and Examples 16 to 24 are comparative examples. <Water Content in Organic Phase> When an aqueous mixture obtained by stirring 10 g of acidic gas absorbing liquid and 10 g of water at 25°C (room temperature) for about 10 minutes was allowed to stand at 25°C (room temperature) for 24 hours, phase separation occurred into an organic phase (upper layer) mainly composed of the acidic gas absorbing liquid and an aqueous phase (lower layer) mainly composed of water. The water content in the organic phase was measured using a Karl Fischer moisture meter (coulometric titration method). Examples 16 to 24 had a water content exceeding 10% by mass, the upper limit of detection.

[0071]

[0072] As can be seen from Table 1, it was confirmed that the acidic gas absorbing liquid (Examples 1 to 15) containing a high-boiling point, hydrophobic oxygen-containing polymer having a predetermined solubility parameter and an amine compound having a predetermined solubility parameter undergoes phase separation by absorbing carbon dioxide, and the amount of water contained in the organic phase can be reduced. Therefore, according to this embodiment, it is not necessary to separate and remove water from the acidic gas absorbing liquid that has absorbed carbon dioxide by heating to evaporate it, and since the oxygen-containing polymer is not easily volatilized, it can be said that the organic phase can be efficiently separated and recovered, the energy required to recover acidic gas from the 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 250 to 20,000, a boiling point of 200°C or higher, and a solubility parameter of 15.0 (MPa). １／２ More than 19.5 (MPa) １／２ The amine compound has a solubility parameter of 13.0 to 25.5 (MPa) or less. 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 difference between the solubility parameter of the oxygen-containing polymer and the solubility parameter of the amine compound is 7.0 (MPa). １／２ The acidic gas absorbing solution according to claim 1, wherein:

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

7. A method for reducing an acidic gas, comprising contacting the acidic gas absorbing solution according to any one of claims 1 to 6 with a gas containing carbon dioxide and moisture, thereby reducing the amount of carbon dioxide in the gas.

8. A method for reducing acidic gases according to claim 7, in which an organic phase containing the oxygen-containing polymer and the amine compound is recovered from an acidic gas absorbing liquid that has been phase-separated by contact with a gas containing carbon dioxide and moisture, and reused as an acidic gas absorbing liquid for contacting with a gas containing carbon dioxide and moisture.

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