Acid gas removal method, acid gas absorbent, and acid gas removal apparatus

Abstract

To provide an acid gas absorbent producing less waste and having reduced environmental load, and an acid gas removal method and an acid gas removal apparatus using the acid gas absorbent.SOLUTION: The present invention provides an acid gas absorbent containing a mixture of a liquid amine compound and water, and an acid gas removal method and an acid gas removal apparatus using the acid gas absorbent. In the acid gas absorbent, a solubility in water of a salt formed from a liquid amine compound and the acid gas is higher than a solubility in water of the liquid amine compound. The amine compound and water are separated into two phases before absorption of the acid gas or after desorption thereof, and, in this state, water-soluble impurities can be easily removed for purification.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The embodiments relate to a method for removing acid gas, an acid gas absorbent, and an apparatus for removing acid gas. [Background technology]

[0002] In recent years, the greenhouse effect caused by rising carbon dioxide (CO2) concentrations has been pointed out as one of the causes of global warming, and international measures to protect the environment on a global scale are urgently needed. CO2 is generated largely through industrial activities, and there is growing momentum to curb its emissions into the environment. In particular, there is an urgent need to reduce CO2 emissions from coal-fired power plants and factories. In addition to CO2, there is also a desire to reduce emissions of acidic gases such as hydrogen sulfide (H2S).

[0003] Therefore, as a method for reducing the emission of acidic gases such as CO2, the recovery of carbon dioxide using chemical absorbents has attracted much attention, along with the reduction of emissions by increasing the efficiency of thermal power plants and the like. As a specific absorbent, absorption by amine compounds has been studied for a long time. However, in the CO2 absorption and release process using chemical absorbents, the absorbent may be heated to regenerate the chemical absorbent, which is known to cause the amine compounds contained in the absorbent to oxidize and deteriorate. It is also known that exhaust gas contains not only carbon dioxide but also SOx and NOx, and these compounds are known to accelerate the deterioration of amine compounds or form thermally stable salts with amine compounds (Patent Document 1). When an amine compound is oxidized and deteriorated or forms a thermally stable salt, the acidic gas absorption performance decreases, so it is necessary to maintain the acidic gas absorption performance by distilling the amine compound, regenerating it by electrodialysis, or completely replacing the absorption liquid. When the absorption liquid is completely replaced, a large amount of amine compound waste is generated, so it is also necessary to devise a way to reduce the burden on the environment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4913390 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the embodiments is to provide an acid gas absorbent that has a high acid gas absorption capacity and is easy to regenerate, and an acid gas removal method and an acid gas removal apparatus that use the acid gas absorbent. [Means for solving the problem]

[0006] The embodiments provided by the present invention are as follows. [1] 1. A method for removing an acid gas from a gas to be treated that contains an acid gas, comprising: a first step of contacting the gas to be treated with an acid gas absorbent to absorb the acid gas; and a second step of releasing a part of the acid gas from the acid gas absorbent that has absorbed the acid gas in the first step, thereby regenerating the acid gas absorbent; Including, the acid gas absorbent is a mixture containing a liquid amine compound having a secondary amine structure and water, The method for removing an acidic gas, wherein a dissolution amount of a salt formed from the liquid amine compound and the acidic gas in water is higher than a dissolution amount of the liquid amine compound in water. [2] The method for absorbing an acidic gas according to [1], wherein the acidic gas absorbent is in a phase-separated state into an organic phase and an aqueous phase after releasing a portion of the acidic gas in the second step. [3] The method for removing an acid gas according to [1] or [2], wherein the solubility of the liquid amine compound in water at 25° C. is 50,000 mg / L or less. [4] The liquid amine compound is represented by the following formula (a) or (b): [ka] (In the formula, R 1 , R 3 , R 4 , and R 8 each independently represents a linear alkyl group, a branched alkyl group, a cyclic alkyl group, a heterocyclic aliphatic group containing oxygen or sulfur, a substituted or unsubstituted aliphatic group consisting of the three elements carbon, nitrogen and hydrogen atoms, or a substituted or unsubstituted aromatic group, R 2 , R 5 , and R 7 are each independently a C1 to C7 linear alkylene chain or a C3 to C7 branched alkylene chain, R6 is a straight-chain alkyl group, a branched alkyl group, a substituted or unsubstituted aliphatic group consisting of the three elements carbon, nitrogen and hydrogen atoms, a substituted or unsubstituted aromatic group, or hydrogen. The method for removing an acidic gas according to any one of [1] to [3], [5] R 1 , R 3 , R 4 , and R 8 are each independently a linear or branched C3 to C6 alkyl group, R 2 , R 5 , and R 7 are each independently a C2 to C4 linear alkylene chain or a C3 to C4 branched alkylene chain; R 6 is a linear or branched C1-C3 alkyl group or hydrogen; [4] A method for removing acid gases, [6] R 1 and R 3 are identical to R 4 and R 8 are identical to The method for removing acid gases according to [4] or [5]. [7] The method for removing an acidic gas according to any one of [1] to [6], wherein in the second step, the released acidic gas is recovered. [8] The method for removing an acid gas according to any one of [1] to [7], wherein the acid gas absorbent regenerated in the second step is reused in the first step. [9] The method for removing an acid gas according to any one of [1] to [8], further comprising a step of stirring and mixing an acid gas absorbent in advance, prior to the first step.

[10] The method for removing an acidic gas according to any one of [1] to [9], wherein the gas to be treated from which the acidic gas has been removed in the first step is at least partially removed by the liquid amine compound and then released into the environment.

[11] The method for removing an acid gas according to any one of [1] to

[10] , wherein the second step involves regenerating the acid gas absorbent by heating and / or reducing pressure.

[12] The method for removing an acid gas according to any one of [1] to

[11] , wherein in the second step, the heat generated in the first step is used to heat the acid gas absorbent, thereby regenerating the acid gas absorbent.

[13] The method for removing an acidic gas according to any one of [1] to

[12] , wherein the acidic gas is carbon dioxide.

[14] An agent for removing acidic gases, comprising a mixture of a liquid amine compound having a secondary amine structure and water, The acid gas removing agent, wherein a solubility of a salt formed from the liquid amine compound and the acid gas in water is higher than a solubility of the liquid amine compound in water.

[15] The acid gas removing agent according to

[14] , which is in a phase-separated state into an organic phase and an aqueous phase before contact with an acid gas.

[16] an absorber for removing the acid gas from the gas to be treated by contacting the gas to be treated containing the acid gas with the acid gas absorbent according to

[14] or

[15] , thereby causing the acid gas to be absorbed by the acid gas absorbent; a regenerator for desorbing the acid gas from the acid gas absorbent that has absorbed the acid gas, thereby regenerating the acid gas absorbent; An acid gas removal device comprising: [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic diagram of an acid gas removal apparatus according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The embodiments will be described in detail below.

[0009] <Acid gas absorbent> The following embodiments will be described mainly with reference to the case where the acidic gas is carbon dioxide, but the acidic gas absorbent according to the embodiment can achieve the same effect with respect to other acidic gases such as hydrogen sulfide. The acidic gas absorbent according to the embodiment is suitable for absorbing oxidizing gases such as carbon dioxide and hydrogen sulfide. Among these, it is particularly suitable for absorbing carbon dioxide, and is suitable for removing and recovering carbon dioxide from gases to be treated such as factory exhaust gases.

[0010] The acidic gas absorbent according to the embodiment contains an amine compound and water as a main agent for absorbing acidic gas. The amine compound used here is a liquid amine compound having a secondary amine structure, and is an acidic gas remover containing a mixture of a liquid amine compound and water, and the amount of salt formed from the liquid amine compound and the acidic gas dissolved in water is higher than the amount of the liquid amine compound itself dissolved in water. Here, the liquid amine compound is an amine compound that is liquid at 25°C and atmospheric pressure. This liquid amine compound generally has a low solubility at room temperature, for example, a solubility in water at 25°C of 50,000 mg / L or less. When the liquid amine compound comes into contact with an acidic gas, it forms a salt, and when water coexists, it ionizes and the amount of dissolution increases. The amount of dissolution of such a salt is, for example, 2 times or more, preferably 5 times or more, more preferably 10 times or more, at 25°C, compared to the amount of dissolution of the original liquid amine. In this embodiment, the dissolved amount (mg / L) is the mass (mg) of the liquid amine based on the total volume (L) of water and the liquid amine compound.

[0011] The liquid amine compound contained in the acidic gas absorbent according to the embodiment increases in dissolution amount in water when it comes into contact with acidic gas, but since it is not compatible with water before coming into contact with acidic gas, it is in a state in which an organic phase (a layer containing a liquid amine compound) and an aqueous phase are separated, typically in a two-phase state. Then, when the acidic gas absorbent comes into contact with acidic gas, the liquid amine compound is charged and becomes easily soluble in water, so that the two layers become compatible, and the acidic gas absorbent typically becomes one phase. Then, the acidic gas absorbent after absorbing acidic gas can release the acidic gas by heating or decompression, and has the property of forming two phases of the liquid amine compound and water again after the release. Therefore, the acidic gas absorbent according to the embodiment can be regenerated by treatment such as heating or decompression. Even in general acidic gas absorbents, regeneration may be performed by heating, etc., but the heating temperature in such a case needs to be 120 ° C. or more. In contrast, in the acidic gas absorbent according to the embodiment, when regeneration is performed by heating, regeneration is possible at a heating temperature of, for example, 80 ° C. or less, preferably 70 ° C. or less.

[0012] Although acid gas absorbents are generally used repeatedly to remove and recover acid gas from the gas to be treated, they gradually deteriorate due to impurities such as water-soluble amine degradants, metal ions, heat-stable salts, and organic acids as they are used. When the acid gas absorbent according to the embodiment is contaminated with impurities, the acid gas is released from the acid gas absorbent and separated into an amine compound phase and an aqueous phase, and the contaminants are dissolved in the aqueous phase, so that the liquid amine compound and the contaminants can be separated. The acid gas absorbent can be regenerated by adding new water to the liquid amine compound after separation, and the water content is low when purifying the liquid amine compound, so that the energy required for purifying the liquid amine compound can be reduced, which is advantageous in terms of energy.

[0013] Here, in this embodiment, "a state in which the organic phase and the aqueous phase are phase-separated" means, for example, that the state in which the mixture of water and liquid amine is phase-separated into the organic phase and the aqueous phase, in other words, that the boundary between the organic phase and the aqueous phase can be visually confirmed. Here, in this embodiment, the organic phase is a phase mainly composed of a liquid amine compound in a phase-separated state, and is a phase containing a high concentration of the liquid amine compound in a state separated from the acidic gas. The aqueous phase is a phase mainly composed of water in a phase-separated state. When the carbon dioxide concentration of the acidic gas absorbent is high, the amount of the liquid amine compound dissolved in water increases, and the liquid amine compound dissolves in the aqueous solution. In this state, the organic phase and the aqueous phase are not phase-separated in the acidic gas absorbent (the acidic gas absorbent is one phase). When the acidic gas concentration is low, the solubility of the liquid amine compound in water decreases, and the acidic gas absorbent is phase-separated into an aqueous phase and an organic phase containing a high concentration of the liquid amine compound. In the case of phase separation, typically, an organic phase and an aqueous phase form a complete two-phase system. In the present embodiment, even if complete phase separation does not occur, the system is referred to as "two-phase" if the phase boundary can be confirmed.

[0014] The liquid amine compound used in the embodiment has a secondary amine structure, and as described above, the amount of the amine compound that dissolves in water changes upon contact with an acidic gas.

[0015] When the liquid amine compound used in the present embodiment has a secondary amine structure and a tertiary amine structure, it is preferable that the number of secondary amine structures is more than that of tertiary amine structures. It is preferable that the liquid amine compound of the present embodiment contains one or more secondary amine structures and one or less tertiary amine structures.

[0016] Such liquid amine compounds are preferably represented by the following formula (a) or (b): [ka] (In the formula, R 1 , R 3 , R 4 , and R 8 each independently represents a linear alkyl group, a branched alkyl group, a cyclic alkyl group, a heterocyclic aliphatic group containing oxygen or sulfur, a substituted or unsubstituted aliphatic group consisting of the three elements carbon, nitrogen and hydrogen atoms, or a substituted or unsubstituted aromatic group, R 2 , R 5 , and R 7 are each independently a C1 to C7 linear alkylene chain or a C3 to C7 branched alkylene chain, R 6 is a straight-chain alkyl group, a branched alkyl group, a substituted or unsubstituted aliphatic group consisting of the three elements carbon, nitrogen and hydrogen atoms, a substituted or unsubstituted aromatic group, or hydrogen. This is shown by:

[0017] where R 1 , R 3 , R 4 , and R 8 are each independently a linear or branched C3 to C6 alkyl group, R 2 , R 5 , and R 7 are each independently a C2 to C4 linear alkylene chain or a C3 to C4 branched alkylene chain; R 6is hydrogen, a linear or branched C1-C3 alkyl group, It is more preferable that

[0018] R 1 and R 3 It is more preferable that R 4 and R 8 It is more preferable that are the same. R 5 and R 7 It is more preferable that are the same. The liquid amine compound represented by formula (a) is R 2 It is more preferable that the liquid amine compound represented by formula (b) has a symmetric structure with respect to NR 6 It is more preferable that the structure is symmetrical about the center.

[0019] From the viewpoint of the responsiveness to phase separation in response to carbon dioxide, the carbon number relative to the nitrogen number (C / N) contained in the liquid amine compound represented by formula (a) and / or formula (b) is preferably 4 to 12, more preferably 4 to 10, and even more preferably 5 to 8. If the carbon number relative to the nitrogen number is small, it tends to be easily dissolved in water and difficult to phase separate, so care must be taken. Also, if the carbon number relative to the nitrogen number is large, the viscosity may increase and it may become difficult to handle, so care must be taken. From the above viewpoint, the carbon number relative to the nitrogen number (C / N) contained in the secondary amine compound represented by formula (a) is more preferably 5 to 7, and even more preferably more than 5 and 7 or less.

[0020] R 6 is more preferably a methyl group or hydrogen.

[0021] R 2 More preferably, R is a linear propylene chain. 6 More preferably, R is a linear propylene chain. 7 is more preferably a linear propylene chain.

[0022] Specific examples of such liquid amine compounds include the following compounds. Et2CH-NH(CH2)2NH-CHEt2 Et2CH-NH(CH2)3NH-CHEt2 Et2CH-NH(CH2)4NH-CHEt2 Et2CH-NH(CH2)5NH-CHEt2 Et2CH-NH(CH2)6NH-CHEt2 Cyclopentyl-NH(CH2)2NH-Cyclopentyl Cyclopentyl-NH(CH2)3NH-Cyclopentyl Cyclohexyl-NH(CH2)3NH-Cyclohexyl Me3C-NH(CH2)3NH-CMe3 Me2CHCH2MeCH-NH(CH2)3NH-CHM e CH2CHMe2 Me2CHCH2MeCH-NH(CH2)4NH-CHM e CH2CHMe2 Me2CHCH2MeCH-NH(CH2)2NH-CHM e CH2CHMe2 EtMeCH-NH(CH2)2NH-CHMeCH2CHMe Cyclopentyl-NH(CH2)2NH-CHEt2 Cyclohexyl-NH(CH2)3NH-CHEtMe EtMeCH-NH(CH2)2NH-CHMeCH2CHMe2 (Me2CH)2CH-NH(CH2)2NH-CHMe2 EtMeCH-NH(CH2)2NH-CH(CHMe2)2 Me2CHCH2MeCH-NH(CH2)2NH(CH2)2NH-CHMeCH2CHMe2 Me2CHCH2MeCH-NH(CH2)3NH(CH2)3NH-CHMeCH2CHMe2 Me2CHCH2MeCH-NH(CH2)4NH(CH2)4NH-CHMeCH2CHMe2 <h2 style=";text-align:left;direction:ltr">Et2CH-NH(CH2)3NH(CH2)3NH-CHEt2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Et2CH-NH(CH2)2NMe(CH2)2NH-CHEt2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Et2CH-NH(CH2)3NMe(CH2)3NH-CHEt2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Et2CH-NH(CH2)4NMe(CH2)4NH-CHEt2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> EtMeCH-NH(CH2)3NMe(CH2)3NH-CHEtMe<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> (Me2CH)2CH-NH(CH2)3NMe(CH2)3NH-CH(CHMe2)2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Me2CHCH2MeCH-NH(CH2)2NMe(CH2)2NH-CHMeCH2CHMe2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Me2CHCH2MeCH-NH(CH2)3NMe(CH2)3NH-CHMeCH2CHMe2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Me2CHCH2MeCH-NH(CH2)4NMe(CH2)4NH-CHMeCH2CHMe2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Me3C-NH(CH2)2N(CMe3)(CH2)2NH-CMe3<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Me3C-NH(CH2)3NCMe(CH2)3NH-CMe3<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Et2CH-NH(CH2)3NEt(CH2)3NH-CHEt2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Et2CH-NH(CH2)3N(CHMe2)(CH2)3NH-CHEt2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Et2CH-NH(CH2)2NH(CH2)2NH-CHEt2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Et2CH-NH(CH2)4NH(CH2)4NH-CHEt2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Et2CH-NH(CH2)3NH(CH2)3NH-CHMeCH2CHMe2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> EtMeCH-NH(CH2)3NH(CH2)3NH-CHMeCH2CHMe2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> EtMeCH-NH(CH2)3NMe(CH2)3NH-CHMeCH2CHMe2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> Et2CH-NH(CH2)2NH(CH2)2NH-CHMeCH2CHMe2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> EtMeCH-NH(CH2)2NH(CH2)2NH-CHMeCH2CHMe2<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0023] <h2 style=";text-align:left;direction:ltr"> Of these, the following compounds are preferred: Et2CH-NH(CH2)2NH-CHEt2 Et2CH-NH(CH2)3NH-CHEt2 Et2CH-NH(CH2)4NH-CHEt2 Me2CHCH2MeCH-NH(CH2)2NH(CH2)2NH-CHMeCH2CHMe2 Me2CHCH2MeCH-NH(CH2)3NH(CH2)3NH-CHMeCH2CHMe2 Me2CHCH2MeCH-NH(CH2)4NH(CH2)4NH-CHMeCH2CHMe2 Et2CH-NH(CH2)2NMe(CH2)2NH-CHEt2 Et2CH-NH(CH2)3NMe(CH2)3NH-CHEt2 Et2CH-NH(CH2)4NMe(CH2)4NH-CHEt2 Me2CHCH2MeCH-NH(CH2)2NMe(CH2)2NH-CHMeCH2CHMe2 Me2CHCH2MeCH-NH(CH2)3NMe(CH2)3NH-CHMeCH2CHMe2 Me2CHCH2MeCH-NH(CH2)4NMe(CH2)4NH-CHMeCH2CHMe2

[0024] These amine compounds can also be used in combination of two or more kinds.

[0025] The structure of the amine compound is 1 H-NMR, 13 It is measured by C-NMR analysis.

[0026] In the acidic gas absorbent according to the embodiment, the ratio of the liquid amine compound to water is preferably 1 part of the liquid amine compound to 0.3 to 10 parts of water on a mass basis.

[0027] In general, an acid gas absorbent having a high amine compound content has a large amount of acid gas absorbed and desorbed per unit volume, and also has a high acid gas absorption rate and desorption rate, and is therefore preferable in terms of energy consumption, plant equipment size, and treatment efficiency.

[0028] An acidic gas absorbent having an amine compound content within the above range, when used for recovering acidic gases, has an appropriate viscosity and not only has a high acidic gas absorption amount and acidic gas absorption rate, but also has a large acidic gas desorption amount and a high acidic gas desorption rate, and is therefore advantageous in that it can efficiently recover acidic gases.

[0029] The acidic gas absorbent according to the embodiment may contain a surfactant or an antifoaming agent. The content of each of these is preferably 0.1 to 1000 ppm, more preferably 0.1 to 100 ppm, based on the total mass of the amine compound. It is even more preferably 2 to 20 ppm. The higher the content of the surfactant, the greater the effect of improving the dissipation of the amine compound, but if it is too high, the foaming property of the acidic gas absorbent becomes excessive, which may result in poor handling. Preferable specific examples of the antifoaming agent include silicone-based antifoaming agents and organic antifoaming agents. The antifoaming agent prevents foaming of the acidic gas absorbent, suppresses a decrease in the absorption efficiency and desorption efficiency of the acidic gas, and can prevent a decrease in the fluidity or circulation efficiency of the acidic gas absorbent.

[0030] The viscosity when the amine compound and water absorb the acidic gas and form a homogeneous phase is not particularly limited, but is preferably 1 to 200 mPa·s, more preferably 10 to 100 mPa·s, and even more preferably 40 to 60 mPa·s at 25° C.

[0031] Here, the viscosity of the acidic gas absorbent can be measured by a VISCOMETER DV-II+Pro (trade name) manufactured by BROOKFIELD Corporation.

[0032] The acid gas absorbent according to the embodiment may contain a surfactant or an antifoaming agent as described above in addition to the liquid amine compound and water, and may contain other optional components as necessary.

[0033] Optional ingredients include, for example, antioxidants, pH adjusters, and corrosion inhibitors.

[0034] Preferable specific examples of the antioxidant include dibutylhydroxytoluene (BHT), butylhydroxyanisole (BHA), sodium erythorbate, sodium nitrite, sulfur dioxide, 2-mercaptoimidazole, 2-mercaptobenzimidazole, etc. When an antioxidant is used, the content thereof is preferably 0.01 to 1 mass%, particularly preferably 0.1 to 0.5 mass%, based on the total mass of the acidic gas absorbent. The antioxidant can prevent deterioration of the acidic gas absorbent and improve its life.

[0035] Preferable specific examples of the anticorrosive agent include phosphate esters, tolyltriazoles, and benzotriazoles. When the anticorrosive agent is used, the content thereof is preferably 0.00003 to 0.0008 mass%, particularly preferably 0.00005 to 0.005 mass%, based on the total mass of the acidic gas absorbent. Such an anticorrosive agent can prevent corrosion of plant equipment and extend its life.

[0036] In addition, the acidic gas absorbent according to the embodiment preferably does not contain an organic compound having a boiling point of 100° C. or less. Such an organic compound may volatilize during the acidic gas absorption process, causing damage to the device or causing environmental pollution. For this reason, even when an organic compound such as an organic solvent is used for the purpose of improving solubility, the content thereof is preferably 1 mass % or less based on the total mass of the acidic gas absorbent.

[0037] In addition, it is preferable that the acid gas absorbent according to the embodiment does not contain metal. This is because metals may cause damage such as corrosion to the equipment with which the acid gas absorbent comes into contact. For this reason, it is preferable that the acid gas absorbent has a metal content of zero. However, the acid gas absorbent may come into contact with the equipment during use, and metals may be eluted from the equipment. Therefore, it is acceptable for the acid gas absorbent to contain a very small amount of metal. However, even in such a case, it is preferable that the metal content is 1 mass% or less based on the total mass of the acid gas absorbent.

[0038] As described above, the acid gas absorbent of the present embodiment can absorb and recover acid gases such as carbon dioxide from the gas to be treated with excellent efficiency. Furthermore, the regeneration treatment of the acid gas absorbent is also facilitated, and the energy required for recovering the acid gas is small.

[0039] The acidic gas absorbent according to the embodiment, which contains a specific liquid amine compound and water, has an improved amount of acidic gas (particularly, carbon dioxide) absorbed per unit mole, and an improved amount and rate of acidic gas absorption per unit volume of the acidic gas absorbent.

[0040] <Method of removing acid gas> In the method for removing an acidic gas according to the embodiment, a gas to be treated containing an acidic gas is brought into contact with the above-described acidic gas absorbent, thereby removing the acidic gas from the gas to be treated.

[0041] The method for removing acidic gas according to the embodiment has a basic configuration including a step (first step) (absorption step) of absorbing acidic gas into an acidic gas absorbent according to the above-mentioned embodiment, and a step (second step) (regeneration step) of desorbing the acidic gas from the acidic gas absorbent according to the above-mentioned embodiment that has absorbed the acidic gas.

[0042] That is, the basic configuration of the method for removing acidic gas according to the embodiment includes a step (first step) of contacting a gas to be treated (e.g., exhaust gas, etc.) containing an acidic gas with an acidic gas absorbent to allow the acidic gas to be absorbed into the acidic gas absorbent, and a step (second step) of desorbing the acidic gas from the acidic gas absorbent with the acidic gas absorbed therein obtained in the above-mentioned acidic gas absorption step by, for example, heating, thereby regenerating the acidic gas absorbent.

[0043] In the step (first step), the method of contacting the gas to be treated containing the acid gas with the acid gas absorbent is not particularly limited, but can be, for example, a method of bubbling the gas to be treated in the acid gas absorbent, a method of dropping the acid gas absorbent in the form of mist into the gas flow to be treated (atomization or spray method), a method of countercurrently contacting the gas to be treated with the acid gas absorbent in an absorber containing a magnetic or metal mesh filler, a method of introducing the acid gas and the acid gas absorbent together into a static mixer, etc. In any of the methods, the acid gas absorbent that has not absorbed the acid gas tends to separate into two phases, so it is preferable to stir the acid gas absorbent before or during the contact.

[0044] The temperature of the first step (absorption step) is usually preferably from room temperature to 60°C. More preferably, it is 50°C or lower, and particularly preferably 20 to 45°C. In general, the amount of acidic gas absorbed increases as the temperature is lower, but the lower limit of the treatment temperature can be determined based on the gas temperature in the process, the heat recovery target, and the like. The pressure during the absorption of acidic gas is usually approximately atmospheric pressure. Although it is possible to increase the pressure to a higher level in order to improve the absorption performance, it is preferable to carry out the process under atmospheric pressure in order to reduce the energy consumption required for compression.

[0045] Methods for separating acid gases such as carbon dioxide from an acid gas absorbent that has absorbed the acid gas and recovering pure or high-concentration acid gases include a method in which the liquid interface is expanded and heated in a plate tower, spray tower, or regeneration tower containing a magnetic or metal mesh packing.

[0046] In the second step (regeneration step), the higher the temperature, the greater the amount of acidic gas desorbed. For this reason, it is generally heated to about 120°C. However, since increasing the temperature increases the energy required to heat the absorbent, it is preferable that the temperature during regeneration is low. The liquid amine compound used in the acidic gas absorbent according to the embodiment sufficiently releases acidic gas at a low temperature, so it can be regenerated at a lower temperature than general acidic gas absorbents. Specifically, it is generally possible to regenerate at 100°C or lower, preferably 80°C or lower, and more preferably 70°C or lower. In addition, the pressure during regeneration can usually be about 1 to 3 atm, but the acidic gas can be efficiently released by reducing the pressure. In the second step, either heating or reducing the pressure can be adopted, but they can also be combined to further improve the efficiency of regeneration.

[0047] After releasing the acid gas, the acid gas absorbent can be sent back to the first step (absorption step) for recycling. Since the acid gas is separated from the acid gas absorbent into two phases, an amine compound phase and a water phase, these are adjusted to a predetermined composition as necessary and sent to the first step (absorption step). If necessary, they can be stirred or mixed before the first step (absorption step). Since the contact efficiency of the amine compound with the water phase and the acid gas affects the acid gas absorption rate, it is necessary to contact them efficiently. In addition, in the first step (absorption step), the heat generated during the absorption of the acid gas is generally used in the process of recycling the acid gas absorbent, that is, to heat the acid gas absorption liquid injected into the regenerator in the second step.

[0048] The purity of the acid gas thus recovered is usually extremely high, about 95 to 99% by volume. This pure acid gas or high-concentration acid gas can be used as a raw material for synthesizing chemicals or polymeric substances, a refrigerant for freezing food, etc. In addition, the recovered acid gas can be isolated and stored underground, etc., a technology that is currently being developed.

[0049] Among the above-mentioned steps, the second step (regeneration step) consumes the most energy, and the second step (regeneration step) may consume about 50 to 80% of the energy of the entire process. Therefore, by reducing the energy consumption in the second step (regeneration step), the cost of the acid gas absorption and separation step can be reduced, and the acid gas removal from the exhaust gas can be carried out efficiently and economically.

[0050] According to this embodiment, by using the acidic gas absorbent of the above embodiment, in the second step (regeneration step), the acidic gas absorbent can be separated into an amine compound phase and an aqueous phase. In a general acidic gas removal method, a purification process is performed on the acidic gas absorbent that constitutes one phase after the acidic gas is desorbed. In contrast, in the acidic gas removal method according to the embodiment, it is possible to perform a purification process on the heterogeneous acidic gas absorbent that constitutes two phases all at once, but it is also possible to generate the amine compound phase and the aqueous phase independently.

[0051] When an acid gas absorbent is used, impurities are generated due to decomposition of the compounds. Since most of these impurities are water-soluble, when the acid gas absorbent separates into two phases, most of the impurities are dissolved in the aqueous phase. Therefore, the acid gas absorbent can be efficiently regenerated and purified by purifying the aqueous phase. It is also effective to replace the aqueous phase with pure water, etc., as necessary.

[0052] Although impurities may be dissolved in the amine compound phase, the volume of the amine compound phase to be refined is small relative to the total volume of the acidic gas absorbent, and therefore the amount of liquid to be refined is small, and the energy cost required for refinement can be reduced.

[0053] As described above, according to the embodiment of the method for removing acidic gas, the energy required for the second step (regeneration step) and the subsequent purification step can be reduced, and therefore, the removal and recovery of acidic gas can be efficiently performed under economically advantageous conditions.

[0054] <Acid gas removal equipment> The acid gas removal apparatus according to the embodiment includes an absorber that brings a gas to be treated containing an acid gas into contact with the acid gas absorbent described above, and removes the acid gas from the gas to be treated by having the acid gas absorbent absorb the acid gas; and a regenerator for desorbing the acid gas from the acid gas absorbent that has absorbed the acid gas, thereby regenerating the acid gas absorbent.

[0055] FIG. 1 is a schematic diagram of an acidic gas removal apparatus according to an embodiment. This acid gas removal device 1 includes an absorber 2 that brings a gas to be treated (e.g., exhaust gas) containing acid gas into contact with an acid gas absorbent, and absorbs and removes the acid gas from the gas containing acid gas, and a regenerator 3 that separates the acid gas from the acid gas absorbent that has absorbed the acid gas, and regenerates the acid gas absorbent. Hereinafter, an example will be described in which the acid gas is carbon dioxide.

[0056] As shown in Fig. 1, exhaust gas containing carbon dioxide, such as combustion exhaust gas discharged from a thermal power plant or the like, is introduced to the lower part of the absorber 2 through a gas supply port 4. This exhaust gas is forced into the absorber 2 and comes into contact with an acid gas absorbent supplied from an acid gas absorbent supply port 5 at the upper part of the absorber 2. As the acid gas absorbent, the acid gas absorbent according to the above-mentioned embodiment is used.

[0057] The acid gas absorbent uses the above-mentioned acid gas absorbing liquid. Since the acid gas absorbing liquid separates into two phases when left at rest, it is preferable to disperse the liquid by stirring or the like before contacting the liquid. In addition to the specific amine compound and water, the acid gas absorbent may contain other compounds such as nitrogen-containing compounds, antioxidants, and pH adjusters that improve the absorption performance of carbon dioxide, in any ratio.

[0058] In this way, when the exhaust gas comes into contact with the acid gas absorbent, the amine compound in the acid gas absorbing solution reacts with the carbon dioxide in the exhaust gas to form a salt, and the acid gas absorbent changes from a two-phase state to a homogeneous state. Meanwhile, the carbon dioxide in the exhaust gas is absorbed and removed by the acid gas absorbent. The exhaust gas from which the carbon dioxide has been removed is discharged from the gas outlet 6 to the outside of the absorber 2.

[0059] The acidic gas absorbent (rich liquid) that has absorbed carbon dioxide is pumped to the heat exchanger 7 by the rich liquid pump 8, and is further pumped to the regenerator 3. The acidic gas absorbent pumped into the regenerator 3 moves from the top to the bottom of the regenerator 3, during which the acidic gas in the acidic gas absorbent is desorbed, and the acidic gas absorbent is regenerated. During this acidic gas desorption process, an amine compound is produced from the salt of the amine compound in the acidic gas absorbent, and the amine compound phase and water phase are separated at the bottom of the regenerator 3.

[0060] The acidic gas absorbent (lean liquid) regenerated in the regenerator 3 is sent to the heat exchanger 7 and the absorbent cooler 10 by the lean liquid pump 9, and is returned to the absorber 2 from the acidic gas absorbent supply port 5. In FIG. 1, there is one liquid sending pipe for the lean liquid, but the amine compound phase and the water phase separated into two phases in the regenerator 3 can be sent independently. It is also possible to perform a purification process independently for each of them. When the amine compound phase and the water phase are sent independently from the regenerator 3, they are purified as necessary and then mixed at any stage before being supplied from the acidic gas absorbent 5 to the absorber 2. When mixing, it is also possible to improve the efficiency of acidic gas absorption by adjusting the blending ratio of the amine compound phase and the water phase. When adjusting the blending ratio, it is also possible to add a new amine compound or water. In addition, when reusing the regenerated acidic gas absorbent, it is preferable to disperse the acidic gas absorbent separated into two phases by stirring or the like before contacting it with the exhaust gas in the absorber 2.

[0061] On the other hand, the carbon dioxide separated from the acidic gas absorbent can be discharged from the upper part of the regenerator 3. At this time, for example, it can be brought into contact with reflux water supplied from the reflux drum 11 and discharged to the outside of the regenerator 3.

[0062] The reflux water with carbon dioxide dissolved therein is cooled in a reflux condenser 12, and then separated from a liquid component formed by condensing water vapor containing carbon dioxide in a reflux drum 11. This liquid component is led to an acid gas recovery step via a recovered acid gas line 13. Meanwhile, the reflux water from which carbon dioxide has been separated is sent to a regenerator 3.

[0063] According to the acidic gas removal device 1 of the present embodiment, it is possible to efficiently regenerate the acidic gas absorbing solution while reducing the energy required for regenerating the acidic gas absorbing solution.

[0064] A method for synthesizing the liquid compound having a secondary amine structure used in the embodiment will be briefly described below. The following synthesis methods are examples, and the synthesis method of the compound is not limited thereto.

[0065] The first synthetic method is the nucleophilic substitution reaction of an amine with a haloalkane. For compounds of formula (a), XR 2 -X (X is, for example, Br) and R 1 NH2(R 3 NH2) to give compounds of formula (b), 5 -NR 6 -R 7 -X and R 4 NH2(R 8 NH2) to give the desired compound.

[0066] The second synthetic method is the reductive amination of a ketone. For compounds of formula (a), NH2-R 2 The desired amine compound can be obtained by reacting -NH2 with R'R"C=O to obtain an imine derivative, which can be reduced. 1 or R 3 For compounds of formula (b), NH2-R2 -NH2-R instead of NH2 5 -NR 6 -R 7 -NH2 can be used. In this case, R 4 or R 8 becomes CHR'R”. EXAMPLES

[0067] Examples of the embodiment will be described below. In the following examples, the conditions before heating the acidic gas absorbent were 25° C. and atmospheric pressure. Example 1 In general formula (a), R 1 and R 3 is a 1-ethylpropyl group, and R 2 When a C3 linear alkyl compound (a-1) was mixed with water in a mass ratio of 50:50, two phases were formed, with the upper phase being an organic phase (amine compound phase) and the lower phase being an aqueous phase. When 20 g of this mixture of two phases was bubbled with CO2:N2 = 1:9 gas at 0.5 L / min, 12 NL / kg of carbon dioxide was absorbed in the first 10 minutes and 48 NL / kg in the first 100 minutes. The mixture that had absorbed carbon dioxide and formed one phase was dripped from the top of a glass column packed with molecular sieves 4A with a height of 36 cm and a diameter of 30 mm. The temperature inside the column was kept in the range of 60°C to 70°C, and an inert gas was passed through it at a rate of 50 ml / min. When the mixture that had passed through the column was separated, it was found to have formed two phases, and it was confirmed that carbon dioxide had been released and regenerated. Here, the saturated carbon dioxide absorption amount is the value measured by measuring the amount of inorganic carbon in the acid gas absorbent using an infrared gas concentration measuring device. The amount of dissolution of this compound was 18,000 mg / L at atmospheric pressure at 25° C. The amount of dissolution was determined by sampling the lower phase of the separated two phases, measuring the total organic carbon concentration with a Shimadzu Corporation total organic carbon meter TOC-L (product name), and converting it into the amount of amine dissolution from the chemical formula of compound (a-1).

[0068] Comparative Example 1 When diisopropylmethylamine and water were mixed at a ratio of 50:50, two phases were formed: the upper phase was an organic phase (amine compound phase) and the lower phase was an aqueous phase. When 20 g of this mixture was bubbled with CO2:N2 = 1:9 gas at 0.5 L / min, it absorbed 3.6 NL / kg of carbon dioxide in the first 10 minutes and 20.3 NL / kg in the first 100 minutes.

[0069] Example 2 In general formula (b), R 4 and R 8 is a 1-ethylpropyl group, and R 5 and R 7 is a C3 linear alkyl group, R 6 When compound (b-1) in which the aryl group is a methyl group was mixed with water in a mass ratio of 50:50, two phases were formed, with the upper phase being an organic phase and the lower phase being an aqueous phase. When 20 g of the mixture in which the two phases were formed was bubbled with CO2:N2=1:9 gas at 0.5 L / min, 7 NL / kg of carbon dioxide was absorbed in the first 10 minutes and 38 NL / kg in the first 100 minutes. The mixture in which carbon dioxide was absorbed and which formed one phase was dripped from the top of a glass column packed with molecular sieves 4A with a height of 36 cm and a diameter of 30 mm. The temperature inside the column was changed in the range of 60°C to 70°C, and an inert gas was passed through it at a rate of 50 ml / min. When the mixture that passed through the column was separated, it was found to have formed two phases, and it was confirmed that carbon dioxide had been released and regenerated. The amount of dissolution of this compound was 22,000 mg / L at 25°C and atmospheric pressure. The amount of dissolution was measured in the same manner as in Example 1.

[0070] Example 3 In general formula (b), R 4 and R 8 is a 1,3-dimethylbutyl group, and R 5 and R 7 is a C3 linear alkyl group, R 6When compound (b-2) in which the aryl group is a methyl group was mixed with water in a mass ratio of 50:50, two phases were formed, with the upper phase being an organic phase and the lower phase being an aqueous phase. When 20 g of the mixture in which two phases were formed was bubbled with CO2:N2=1:9 gas at 0.5 L / min, 7 NL / kg of carbon dioxide was absorbed in the first 10 minutes and 36 NL / kg in the first 100 minutes. The mixture in which carbon dioxide was absorbed and which formed one phase was dripped from the top of a glass column packed with molecular sieves 4A with a height of 36 cm and a diameter of 30 mm. The temperature inside the column was changed in the range of 60°C to 70°C, and an inert gas was passed through it at a rate of 50 ml / min. When the mixture that passed through the column was separated, it was found to have formed two phases, and it was confirmed that carbon dioxide had been released and regenerated. The amount of dissolution of this compound was 4,000 mg / L at 25°C and atmospheric pressure. The amount of dissolution was measured in the same manner as in Example 1.

[0071] Example 4 In general formula (b), R 4 and R 8 is a 1,3-dimethylbutyl group, and R 5 and R 7 is a C3 linear alkyl group, R 6 When compound (b-3) in which 1 is hydrogen was mixed with water in a mass ratio of 50:50, two phases were formed, with the upper phase being an organic phase and the lower phase being an aqueous phase. When 20 g of the mixture in which two phases were formed was bubbled with CO2:N2=1:9 gas at 0.5 L / min, 11 NL / kg of carbon dioxide was absorbed in the first 10 minutes and 56 NL / kg in the first 100 minutes. The mixture in which carbon dioxide was absorbed and which formed one phase was dripped from the top of a glass column packed with molecular sieves 4A with a height of 36 cm and a diameter of 30 mm. The temperature inside the column was changed in the range of 60°C to 70°C, and an inert gas was passed through it at a rate of 50 ml / min. When the mixture that passed through the column was separated, it was found to have formed two phases, and it was confirmed that carbon dioxide had been released and regenerated. The amount of dissolution of this compound was 11,000 mg / L at 25°C and atmospheric pressure. The amount of dissolution was measured in the same manner as in Example 1.

[0072] (Reference Examples 1 and 2) When compound (a-1) and water were mixed at a volume ratio of 50:50, two phases were formed, with the upper phase being an organic phase and the lower phase being an aqueous phase. 1 ml of 1 mol / l sulfuric acid was added to 30 ml of the mixture, and after stirring, the sulfur concentration in the aqueous phase was measured by ICP and found to be 17.6 mg-S / L (Reference Example 1). When sulfuric acid was added to water not containing compound (a-1) as in Reference Example 1, the sulfur concentration was 9.8 mg-S / L. These results indicated that water-soluble impurities were present preferentially in the aqueous phase.

[0073] [ka]

[0074] From the results of each example, it was confirmed that a mixture containing a specific amine compound and water, which forms two phases before absorbing acidic gas, absorbs the acidic gas and becomes one phase. In addition, when sulfuric acid was added to the mixture which forms two phases, the sulfuric acid component was detected in the water phase. Therefore, an acidic gas absorbent which contains a specific amine compound and separates into two phases with water when carbon dioxide is not contained in the system is easy to separate from the water-soluble impurities contained in the system, and is easy to regenerate and purify, and therefore has a long life as an absorbent. Therefore, it is possible to reduce the amount of amine compound to be disposed of, and in the case of recycling, it can be regenerated with low energy by regenerating from a state separated from water.

[0075] According to at least one of the embodiments of the acid gas absorbent, the acid gas removal method, and the acid gas removal apparatus described above, it is possible to realize an acid gas absorption system that produces little waste and requires less energy for regeneration.

[0076] As described above, although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0077] Reference Signs List 1...Acid gas removal device, 2...Absorber, 3...Regenerator, 4...Gas supply port, 5...Acid gas absorbent supply port, 6...Gas outlet, 7...Heat exchanger, 8...Rich liquid pump, 9...Lean liquid pump, 10...Absorbent cooler, 11...Reflux drum, 12...Reflux cooler, 13...Acid gas carbon recovery line

Claims

1. 1. A method for removing an acid gas from a gas to be treated that contains an acid gas, comprising: a first step of contacting the gas to be treated with an acid gas absorbent to absorb the acid gas; and a second step of releasing a part of the acid gas from the acid gas absorbent that has absorbed the acid gas in the first step, thereby regenerating the acid gas absorbent; Including, the acid gas absorbent is a mixture containing a liquid amine compound having a secondary amine structure and water, The method for removing an acidic gas, wherein a dissolution amount of a salt formed from the liquid amine compound and the acidic gas in water is higher than a dissolution amount of the liquid amine compound in water.

2. 2. The method for absorbing an acidic gas according to claim 1, wherein the acidic gas absorbent is in a state of phase separation into an organic phase and an aqueous phase after releasing a part of the acidic gas in the second step.

3. 3. The method for removing acidic gases according to claim 1, wherein the liquid amine compound has a solubility in water at 25° C. of 50,000 mg / L or less.

4. The liquid amine compound is represented by the following formula (a) or (b): 【Chemistry 1】 (In the formula, R １ , R ３ , R ４ , and R ８ each independently represents a linear alkyl group, a branched alkyl group, a cyclic alkyl group, a heterocyclic aliphatic group containing oxygen or sulfur, a substituted or unsubstituted aliphatic group consisting of the three elements carbon, nitrogen and hydrogen atoms, or a substituted or unsubstituted aromatic group, R ２ , R ５ , and R ７ are each independently a C1 to C7 linear alkylene chain or a C3 to C7 branched alkylene chain, R ６ is a straight-chain alkyl group, a branched alkyl group, a substituted or unsubstituted aliphatic group consisting of the three elements carbon, nitrogen and hydrogen atoms, a substituted or unsubstituted aromatic group, or hydrogen.

3. The method for removing acidic gas according to claim 1 or 2, wherein

5. R １ , R ３ , R ４ , and R ８ are each independently a linear or branched C3 to C6 alkyl group; R ２ , R ５ , and R ７ are each independently a C2 to C4 linear alkylene chain or a C3 to C4 branched alkylene chain; R ６ is a linear or branched C1-C3 alkyl group or hydrogen; The method for removing acidic gases according to claim 4.

6. R １ and R ３ are identical to R ４ and R ８ are identical to The method for removing acidic gases according to claim 4.

7. 3. The method for removing acidic gas according to claim 1 or 2, wherein in the second step, the released acidic gas is recovered.

8. 3. The method for removing acidic gases according to claim 1, wherein the acidic gas absorbent regenerated in the second step is reused in the first step.

9. 3. The method for removing acid gas according to claim 1, further comprising a step of stirring and mixing the acid gas absorbent in advance before the first step.

10. 3. The method for removing acidic gases according to claim 1, wherein the gas to be treated from which acidic gases have been removed in the first step is at least partially removed by the liquid amine compound and then released into the environment.

11. 3. The method for removing acidic gases according to claim 1 or 2, wherein the second step involves regenerating the acidic gas absorbent by heating and / or reducing pressure.

12. 3. The method for removing acid gas according to claim 1, wherein in the second step, the heat generated in the first step is used to heat the acid gas absorbent, thereby regenerating the acid gas absorbent.

13. 3. The method for removing an acidic gas according to claim 1, wherein the acidic gas is carbon dioxide.

14. An agent for removing acidic gases, comprising a mixture of a liquid amine compound having a secondary amine structure and water, The acid gas removing agent, wherein a solubility of a salt formed from the liquid amine compound and the acid gas in water is higher than a solubility of the liquid amine compound in water.

15. The agent for removing acidic gases according to claim 14, which is in a phase-separated state into an organic phase and an aqueous phase before contact with an acidic gas.

16. an absorber for removing the acid gas from the gas to be treated by contacting the gas to be treated containing the acid gas with the acid gas absorbent according to claim 14 or 15, and causing the acid gas to be absorbed by the acid gas absorbent; a regenerator for desorbing the acid gas from the acid gas absorbent that has absorbed the acid gas, thereby regenerating the acid gas absorbent; An acid gas removal device comprising:

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