Gas treatment method and gas treatment device

Abstract

To provide a gas treatment method and a gas treatment apparatus where the deterioration of a treatment liquid to be used is suppressed and an acidic compound can be separated and recovered for a long term.SOLUTION: A gas treatment apparatus 100 is used comprising: an absorber 11 where an acidic compound is absorbed in a treatment liquid by bringing a gas to be treated containing the acidic compound generating an acid when dissolved in water into contact with a treatment liquid that is phase-separated by the absorption of the acidic compound and the treatment liquid is phase-separated into a first phase part having a relatively high percentage content of the acidic compound and a second phase part having a relatively low percentage content of the acidic compound; a separator 12 to separate the treatment liquid into a first liquid mainly containing the first phase part and a second liquid mainly containing the second phase part; a deoxidation treatment part 13 to perform deoxidation treatment to the separated second liquid; and a releaser 14 to release the acidic compound from the first liquid and the second liquid by heating the first liquid with the deoxidation-treated second liquid.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas processing method and a gas processing device. [Background technology]

[0002] Various methods are known for recovering carbon dioxide (CO2) from large volumes of gas containing CO2 (CO2-containing gas), such as exhaust gas from power plants and by-product gas from blast furnaces. Examples of such methods include chemical absorption methods such as amine absorption. Chemical absorption methods involve using an alkaline aqueous solution, such as an amine aqueous solution, as an absorption liquid (treatment liquid), bringing a CO2-containing gas into contact with the absorption liquid to absorb the CO2, and then heating the absorption liquid that has absorbed the CO2 to release the CO2 from the absorption liquid, and recovering the released CO2.

[0003] In such chemical absorption methods, a large amount of thermal energy is required in the process of heating the absorption solution that has absorbed CO2 and releasing the CO2 from the absorption solution, which is called the absorption solution regeneration process. For this reason, the cost (running cost) for separating and capturing CO2 is high in methods of capturing CO2 using chemical absorption methods. In order to reduce these running costs, methods for reducing the energy required to separate and capture acidic compounds such as CO2 are being studied.

[0004] An example of a chemical absorption method that can reduce running costs is the method described in Patent Document 1. Patent Document 1 describes a gas treatment method that includes an absorption step in which a gas to be treated containing acidic compounds that generate acid when dissolved in water is brought into contact with a treatment liquid that undergoes phase separation due to absorption of the acidic compounds in an absorber, thereby absorbing the acidic compounds contained in the gas to be treated into the treatment liquid, a liquid delivery step in which the treatment liquid into which the acidic compounds contained in the gas to be treated have been absorbed is delivered from the absorber to a regenerator, and a regeneration step in which the treatment liquid is heated in the regenerator to separate the acidic compounds from the treatment liquid. In the absorption step, the treatment liquid that has come into contact with the acidic compounds in the gas to be treated phase-separates into a first phase portion having a high content of acidic compounds and a second phase portion having a low content of acidic compounds, and in the liquid delivery step, the treatment liquid in a state in which the separated first phase portion and the second phase portion are mixed is introduced into the regenerator. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-187553 Summary of the Invention [Problem to be solved by the invention]

[0006] The invention described in Patent Document 1, as described above, uses a treatment liquid that undergoes phase separation upon absorption of acidic compounds such as CO2. Examples of such treatment liquids include treatment liquids containing water, an amine compound capable of acting as a chemical absorbent, and an organic solvent (typically an ether compound) capable of acting as a physical absorbent. Such treatment liquids are homogeneous in one phase when no acidic compounds are absorbed, but undergo phase separation into two phases upon absorption of acidic compounds. Specifically, the treatment liquid separates into two phases: a first phase (amine phase) with a relatively high acidic compound content and a second phase (organic solvent phase, ether phase) with a relatively low acidic compound content. When a treatment liquid that undergoes phase separation upon absorption of acidic compounds, such as the treatment liquid described in Patent Document 1, is used, the regeneration temperature of the treatment liquid in the regeneration step (e.g., below 100°C) is lower than the regeneration temperature (e.g., 120°C or higher) when a typical treatment liquid that does not undergo phase separation upon absorption of acidic compounds is used. Furthermore, according to Patent Document 1, introducing the second phase fraction into a regenerator together with the first phase fraction can reduce the energy required to separate the acidic compounds, compared to removing the second phase fraction, which has a low content of acidic compounds. This is thought to be because, in the regeneration step, amine compounds that do not interact with (bond to) the acidic compounds migrate from the first phase fraction to the second phase fraction, making it easier for the acidic compounds to be released from the first phase fraction.

[0007] However, the treatment solution contains components that gradually change chemically over a long period of time when used to recover acidic compounds. These chemically changing components are the components that constitute the first phase after phase separation of the treatment solution (the components that are mainly contained in the first phase). Specifically, in the case of a treatment solution containing an amine compound and an organic solvent, these components are the amino compounds. This change reduces the performance of the treatment solution, so in order to maintain the performance of the treatment solution, it is necessary to replenish (or replace) the components that constitute the first phase, such as the amine compounds. In order to reduce the cost (running cost) of separating and recovering acidic compounds such as CO2, it is necessary to suppress the deterioration of the treatment solution, i.e., the deterioration of the components that constitute the first phase, such as the amine compounds.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide a gas treatment method and gas treatment device that can suppress deterioration of the treatment liquid used and separate and recover acidic compounds over a long period of time. [Means for solving the problem]

[0009] As a result of various investigations, the present inventors have found that the above object can be achieved by the present invention described below.

[0010] A gas treatment method according to one embodiment of the present invention includes the steps of: bringing a gas to be treated, which contains an acidic compound that generates an acid when dissolved in water, into contact with a treatment liquid that undergoes phase separation due to absorption of the acidic compound, thereby absorbing the acidic compound into the treatment liquid; separating the treatment liquid, which has been phase-separated into a first phase portion having a relatively high content of the acidic compound and a second phase portion having a relatively low content of the acidic compound by absorbing the acidic compound into a first liquid mainly containing the first phase portion and a second liquid mainly containing the second phase portion; deoxidizing the separated second liquid; and releasing the acidic compound from the first liquid and the second liquid by heating the first liquid together with the second liquid that has been deoxidized.

[0011] According to this configuration, deterioration of the treatment liquid used can be suppressed, and acidic compounds can be separated and recovered over a long period of time. This is believed to be due to the following reasons.

[0012] As mentioned above, deterioration of the treatment liquid due to the separation and recovery of acidic compounds over a long period of time is thought to be deterioration of the components that make up the first phase portion (the components that are mainly contained in the first phase portion).

[0013] One example of such deterioration is thermal deterioration, in which the components constituting the first phase (the components mainly contained in the first phase, such as amine compounds) change quality when heated. When a treatment liquid that undergoes phase separation into the first and second phases upon absorption of an acidic compound, such as the treatment liquid described above, is used as the treatment liquid, the regeneration temperature of the treatment liquid can be lowered compared to when a different treatment liquid (a treatment liquid that does not undergo phase separation) is used. In other words, even if the heating temperature of the treatment liquid that has absorbed the acidic compound is lowered, the acidic compound can be released from the treatment liquid. This suggests that thermal deterioration of the components constituting the first phase (the components mainly contained in the first phase) is suppressed. Therefore, it is thought that deterioration of the treatment liquid due to heating, i.e., thermal deterioration, is suppressed.

[0014] In addition to thermal degradation, the degradation can also include oxidative degradation, which is degradation in which components constituting the first phase (components mainly contained in the first phase) are oxidized by oxygen dissolved in the treatment liquid (dissolved oxygen). When a treatment liquid that undergoes phase separation into the first and second phases upon absorption of an acidic compound is used, thermal degradation is suppressed as described above, and therefore oxidative degradation is thought to have a significant impact on the degradation of the treatment liquid. To suppress this potentially significant oxidative degradation, the inventors focused on reducing the dissolved oxygen in the treatment liquid by subjecting the treatment liquid to a deoxidation treatment. In this regard, they also considered deoxidizing the entire treatment liquid and deoxidizing the first liquid, which mainly contains the first phase, which contains many components susceptible to oxidative degradation. After further investigation, the inventors have noticed that the second phase, which has a relatively low content of acidic compounds, has a lower polarity than the first phase, and therefore has a higher amount of dissolved oxygen (dissolved oxygen) than the first phase. Based on this, the inventors have found that applying the deoxidation treatment to the second liquid, which primarily contains the second phase, is effective in suppressing oxidative degradation of the components that make up the first phase (the components that are primarily contained in the first phase). In other words, the inventors have found that applying the deoxidation treatment to the second liquid, rather than to the first liquid, which primarily contains the first phase, which contains many components that are subject to oxidative degradation, is effective in suppressing oxidative degradation of the components that make up the first phase (the components that are primarily contained in the first phase).

[0015] As described above, it is believed that by subjecting the second liquid containing mainly the second phase portion to the deoxidation treatment, it is possible to suppress oxidative deterioration of the components constituting the first phase portion (components mainly contained in the first phase portion). Therefore, it is believed that deterioration due to oxidation (oxidative deterioration) of the treatment liquid is suppressed. It is believed that by subjecting the second liquid containing mainly the second phase portion to the deoxidation treatment, without subjecting the entire treatment liquid to the deoxidation treatment, it is possible to efficiently suppress the oxidative deterioration.

[0016] Furthermore, when treating an oxidizing atmosphere gas such as exhaust gas, oxidation degradation is generally more of a problem than thermal degradation, and from this perspective, being able to efficiently suppress oxidation degradation is thought to favorably contribute to efficiently suppressing degradation of the treatment solution used.

[0017] Furthermore, in the gas treatment method, the second liquid is subjected to the deoxidation treatment before the first liquid and the second liquid are mixed. As a result, the second liquid, which is a part of the treatment liquid before the treatment liquid is heated to release the acidic compounds from the treatment liquid, is subjected to the deoxidation treatment. As a result, the treatment liquid becomes deoxidized when heated to release the acidic compounds from the treatment liquid. Since oxidation degradation is more likely to occur at higher temperatures, it is believed that by performing the deoxidation treatment on the second liquid, which is the treatment liquid before being mixed with the first liquid, the deoxidation treatment is performed before heating to release the acidic compounds from the treatment liquid, thereby effectively suppressing oxidation degradation.

[0018] From the above, it is believed that thermal deterioration of the treatment solution can be suppressed and oxidative deterioration of the treatment solution can also be efficiently suppressed. Therefore, it is believed that deterioration of the treatment solution used can be suppressed and acidic compounds can be separated and recovered continuously for a long period of time. In other words, it is believed that acidic compounds can be separated and recovered continuously for a long period of time without replenishing or replacing the treatment solution.

[0019] Furthermore, in the gas treatment method, it is preferable that the treatment liquid contains water, an amine compound, and an organic solvent, the first phase portion has a higher amine compound content than the second phase portion, and the second phase portion has a higher organic solvent content than the first phase portion.

[0020] According to this configuration, deterioration of the treatment liquid used can be further suppressed, and acidic compounds can be separated and recovered for a longer period of time.

[0021] Furthermore, in the gas treatment method, it is preferable that the deoxidation treatment is at least one selected from the group consisting of a treatment of heating the second liquid, a treatment of contacting the second liquid with an oxygen scavenger, a treatment of reducing the pressure of the second liquid, and a treatment of irradiating the second liquid with ultrasonic waves.

[0022] According to this configuration, the deoxidation treatment can effectively remove dissolved oxygen from the second liquid, and deterioration of the treatment liquid used can be further suppressed, thereby enabling separation and recovery of acidic compounds continuously for a longer period of time.

[0023] In the gas processing method, the deoxidation process is preferably a hydrogen supply process in which hydrogen is supplied to the second liquid.

[0024] According to this configuration, the deoxidation treatment can effectively remove dissolved oxygen from the second liquid. This is thought to be because supplying hydrogen to the second liquid reduces the oxygen partial pressure, and this reduction in oxygen partial pressure results in deoxidation. In this way, dissolved oxygen is effectively removed from the second liquid, and deterioration of the treatment liquid used can be further suppressed. Therefore, acidic compounds can be separated and recovered continuously for a longer period of time.

[0025] In the gas treatment method, the deoxidation treatment is more preferably a treatment in which the second liquid is brought into contact with a noble metal catalyst while hydrogen is being supplied to the second liquid in the hydrogen supply treatment.

[0026] According to this configuration, the deoxidation treatment can more effectively remove dissolved oxygen from the second liquid. This is thought to be due to the fact that, in addition to the deoxidation caused by the reduction of oxygen partial pressure as described above, the presence of a noble metal catalyst promotes the reaction of reducing oxygen with hydrogen (the reaction of producing water from hydrogen and oxygen). In this way, by deoxidizing the second liquid to which hydrogen has been supplied in contact with a noble metal catalyst in addition to the deoxidation caused by the hydrogen supply treatment, dissolved oxygen is more effectively removed from the second liquid, and deterioration of the treatment liquid used can be further suppressed. Therefore, acidic compounds can be separated and recovered continuously for a longer period of time.

[0027] In the gas treatment method, it is preferable that hydrogen be brought into contact with the first liquid and the second liquid when the acidic compounds are released from the first liquid and the second liquid.

[0028] According to this configuration, deterioration of the treatment solution used can be further suppressed, acidic compounds can be separated and recovered for a longer period of time, and the energy required for separating and recovering the acidic compounds can be reduced. This is believed to be due to the following reasons.

[0029] When releasing the acidic compounds from the first liquid and the second liquid, by bringing the first liquid and the second liquid into contact with hydrogen, it is possible to lower the temperature (regeneration temperature) of the treatment liquid (the first liquid and the second liquid) at which the acidic compounds can be released from the treatment liquid. Therefore, it is thought that not only can thermal deterioration of the treatment liquid be further suppressed, but also the energy required to separate and recover the acidic compounds can be reduced.

[0030] Furthermore, when a deoxidation treatment using hydrogen, such as the hydrogen supply treatment, is used as the deoxidation treatment, both the gas supplied during this treatment and the gas used to release the acidic compounds are hydrogen. This facilitates the supply of these gases. For example, the hydrogen used in the deoxidation treatment and the hydrogen used to release the acidic compounds can be supplied from the same hydrogen supply unit.

[0031] In addition, a gas treatment device according to another aspect of the present invention is a gas treatment device comprising: an absorber that brings a gas to be treated, which contains acidic compounds that produce acid when dissolved in water, into contact with a treatment liquid that undergoes phase separation due to absorption of the acidic compounds, thereby absorbing the acidic compounds into the treatment liquid; a separator that separates the treatment liquid, which has been phase-separated into a first phase portion having a relatively high content of the acidic compounds and a second phase portion having a relatively low content of the acidic compounds, into a first liquid mainly containing the first phase portion and a second liquid mainly containing the second phase portion; a deoxidation treatment unit that deoxidizes the separated second liquid; and a releaser that releases the acidic compounds from the first liquid and the second liquid by heating the first liquid together with the second liquid that has been deoxidized.

[0032] With this configuration, as described above, the regeneration temperature of the treatment liquid can be lowered, which is thought to suppress thermal degradation of the components that make up the first phase portion (components mainly contained in the first phase portion, such as amine compounds) in the emitter. Furthermore, as described above, it is thought that the deoxidation treatment by the deoxidation treatment unit can also efficiently suppress oxidative degradation of the components that make up the first phase portion. Therefore, with the gas treatment device, deterioration of the treatment liquid used can be suppressed, and acidic compounds can be separated and recovered over a long period of time.

[0033] Furthermore, in the gas treatment device, it is preferable that the treatment liquid contains water, an amine compound, and an organic solvent, the first phase portion has a higher content of the amine compound than the second phase portion, and the second phase portion has a higher content of the organic solvent than the first phase portion.

[0034] According to this configuration, deterioration of the treatment liquid used can be further suppressed, and acidic compounds can be separated and recovered for a longer period of time.

[0035] In addition, in the gas treatment device, it is preferable that the deoxidation treatment unit is at least one selected from the group consisting of a treatment unit that heats the second liquid, a treatment unit that brings the second liquid into contact with an oxygen scavenger, a treatment unit that reduces the pressure of the second liquid, and a treatment unit that irradiates the second liquid with ultrasonic waves.

[0036] According to this configuration, the deoxidation treatment by the deoxidation treatment unit can effectively remove dissolved oxygen from the second liquid, and deterioration of the treatment liquid used can be further suppressed, thereby enabling separation and recovery of acidic compounds continuously for a longer period of time.

[0037] In the gas treatment device, the deoxidation treatment unit preferably includes a hydrogen supply unit that supplies hydrogen to the second liquid.

[0038] According to this configuration, the deoxidation treatment by the deoxidation treatment unit can effectively remove dissolved oxygen from the second liquid, and deterioration of the treatment liquid used can be further suppressed, thereby enabling separation and recovery of acidic compounds continuously for a longer period of time.

[0039] In the gas treatment device, it is more preferable that the deoxidation treatment unit further includes a noble metal catalyst that is brought into contact with the second liquid while the hydrogen supply unit supplies hydrogen to the second liquid.

[0040] According to this configuration, in addition to deoxidizing the second liquid by supplying hydrogen, the second liquid to which hydrogen has been supplied is also deoxidized by contacting it with a precious metal catalyst, thereby more effectively removing dissolved oxygen from the second liquid. As a result, deterioration of the treatment liquid used can be further suppressed, and acidic compounds can be separated and recovered continuously for a longer period of time.

[0041] Preferably, the gas treatment device further comprises a hydrogen supply unit that supplies hydrogen to the releaser and brings the first liquid and the second liquid into contact with hydrogen.

[0042] According to this configuration, the temperature (regeneration temperature) of the treatment liquid (the first liquid and the second liquid) at which the acidic compounds can be released from the treatment liquid in the releaser can be lowered. Therefore, it is thought that not only can thermal deterioration of the treatment liquid be further suppressed, but also the energy required to separate and recover the acidic compounds can be reduced. Therefore, deterioration of the treatment liquid used can be further suppressed, acidic compounds can be separated and recovered for a longer period of time, and the energy required to separate and recover the acidic compounds can be reduced. Furthermore, when the hydrogen supply unit is used as the deoxidation treatment unit, the supply of these hydrogens can be facilitated. For example, the hydrogen used in the deoxidation treatment unit and the hydrogen used in the releaser can be supplied from the same hydrogen supply unit. [Effects of the Invention]

[0043] According to the present invention, it is possible to provide a gas treatment method and a gas treatment device that can suppress deterioration of the treatment liquid used and separate and recover acidic compounds over a long period of time. [Brief explanation of the drawings]

[0044] [Figure 1] FIG. 1 is a schematic diagram showing an example of a gas treatment device according to an embodiment of the present invention. [Figure 2]FIG. 2 is a schematic view showing another example of a gas treatment device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a schematic view showing another example of a gas treatment device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a schematic view showing another example of a gas treatment device according to an embodiment of the present invention. [Figure 5] FIG. 5 is a schematic view showing another example of a gas treatment device according to an embodiment of the present invention. [Figure 6] FIG. 6 is a schematic view showing another example of a gas treatment device according to an embodiment of the present invention. [Figure 7] FIG. 7 is a schematic view showing another example of a gas treatment device according to an embodiment of the present invention. [Figure 8] FIG. 8 is a schematic view showing another example of a gas treatment device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0045] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these.

[0046] A gas treatment method according to an embodiment of the present invention is a method for separating and recovering acidic compounds from a gas to be treated that contains the acidic compounds, using a treatment liquid that undergoes phase separation by absorbing acidic compounds that produce acids when dissolved in water.

[0047] In the gas treatment method, first, the gas to be treated containing the acidic compounds is brought into contact with the treatment liquid. By doing so, the acidic compounds are absorbed into the treatment liquid. The treatment liquid into which the acidic compounds have been absorbed undergoes phase separation into a first phase portion having a relatively high content of the acidic compounds and a second phase portion having a relatively low content of the acidic compounds. Note that, hereinafter, the process of bringing the gas to be treated into contact with the treatment liquid to absorb the acidic compounds is also referred to as the absorption process.

[0048] In the gas treatment method, after the absorption step, the gas is separated into a first liquid mainly containing the first phase portion and a second liquid mainly containing the second phase portion. This separation is preferably performed into a first liquid consisting of the first phase portion and a second liquid consisting of the second phase portion. However, the first liquid may also contain the second phase portion as long as it mainly contains the first phase portion. Furthermore, the second liquid may also contain the first phase portion as long as it mainly contains the second phase portion. "Mainly containing" means that the phase portion comprises, for example, 80% by mass or more, and preferably 100% by mass. Hereinafter, the step of separating the first liquid from the second liquid will also be referred to as a "separation step."

[0049] The gas treatment method performs a deoxidation treatment on the second liquid separated in the separation step. By performing this deoxidation treatment, the amount of oxygen dissolved in the second liquid (dissolved oxygen) can be reduced. Note that the step of performing the deoxidation treatment on the second liquid is also referred to as a deoxidation treatment step hereinafter.

[0050] In the gas treatment method, the first liquid is heated together with the second liquid that has been subjected to the deoxidation treatment. For example, the heating may involve heating a mixed liquid obtained by mixing the first liquid with the second liquid that has been subjected to the deoxidation treatment. When the mixed liquid (the first liquid and the second liquid) reaches a predetermined temperature or higher through such heating, the acidic compound can be released from the first liquid and the second liquid. Hereinafter, the step of heating the mixed liquid (the first liquid and the second liquid) is also referred to as a release step.

[0051] In the gas treatment method, components contained in the gas to be treated that are not absorbed by the treatment liquid are not absorbed by the treatment liquid in the absorption step and are not released from the treatment liquid in the release step. Furthermore, components that are less absorbed by the treatment liquid are less absorbed by the treatment liquid in the absorption step, and a smaller amount is released from the treatment liquid in the release step. Furthermore, components contained in the gas to be treated that are absorbed by the treatment liquid and are not released from the treatment liquid even when the treatment liquid is heated are also not released from the treatment liquid in the release step. For these reasons, the gas treatment method, as described above, can recover high concentrations of acidic compounds (concentrations higher than the concentrations of acidic compounds in the gas to be treated) by absorbing the acidic compounds into the treatment liquid and releasing them from the treatment liquid. Furthermore, the gas treatment method can effectively remove dissolved oxygen from the second liquid by subjecting the second liquid to deoxidation in the deoxidation step. For this reason, the gas treatment method can suitably suppress the occurrence of deterioration (oxidation deterioration) of the treatment liquid due to dissolved oxygen, and can separate and recover acidic compounds for a long period of time.

[0052] The gas to be treated may be any gas containing the acidic compounds, and may also contain gases other than the acidic compounds. Examples of gases other than the acidic compounds include gases that are difficult to absorb into the treatment liquid, such as nitrogen. Specific examples of the gas to be treated include exhaust gas from power plants and by-product gases from blast furnaces. As in the example of the gas to be treated, the gas to be treated generally contains not only the acidic compounds but also gases other than the acidic compounds. Furthermore, gases other than the acidic compounds are often more difficult to absorb into the treatment liquid than the acidic compounds. When gases other than the acidic compounds are less easily absorbed into the treatment liquid, the acidic compounds are absorbed into the treatment liquid during the absorption process, but components other than the acidic compounds are less easily absorbed into the treatment liquid. Therefore, the gas treatment method can recover high concentrations of acidic compounds (concentrations higher than the concentrations of acidic compounds in the gas to be treated).

[0053] The acidic compound is not particularly limited as long as it generates an acid when dissolved in water. Examples of the acidic compound include acidic compounds contained in exhaust gas from power plants and by-product gas from blast furnaces. More specific examples of the acidic compound include carbon dioxide and sulfur compounds such as sulfur oxides (SOx) and hydrogen sulfide.

[0054] As described above, the treatment liquid is a treatment liquid that undergoes phase separation upon absorption of the acidic compound into a first phase portion having a relatively high content of the acidic compound and a second phase portion having a relatively low content of the acidic compound. Examples of the treatment liquid include an aqueous solution of an amine compound. The aqueous solution of the amine compound may further contain an organic solvent. For example, a treatment liquid containing water, an amine compound, and an organic solvent is preferably used. That is, the treatment liquid is preferably a treatment liquid containing water, an amine compound, and an organic solvent, and that undergoes phase separation into the first phase portion and the second phase portion. Such a treatment liquid is preferable because it undergoes favorable phase separation upon absorption of the acidic compound and can favorably lower the temperature (regeneration temperature) of the treatment liquid at which the acidic compound can be released from the treatment liquid. The first phase portion is a phase in which the content of the amine compound is higher than that of the second phase portion, and is hereinafter also referred to as the amine phase. The second phase portion is a phase in which the content of the organic solvent is higher than that of the first phase portion. For this reason, the second phase portion will hereinafter also be referred to as an ether phase or an organic phase, since a typical component of the organic solvent is an ether compound.

[0055] The amine compound is not limited to primary amines, but also includes secondary amines and tertiary amines. Examples of the primary amine include 2-aminoethanol [MEA: solubility parameter = 14.3 (cal / cm 3 ) 1 / 2 ], and 2-(2-aminoethoxy)ethanol [AEE: solubility parameter = 12.7 (cal / cm 3 ) 1 / 2Examples of the secondary amine include 2-(methylamino)ethanol [MAE: solubility parameter = 12.5 (cal / cm 3 ) 1 / 2 ], and 2-(ethylamino)ethanol [EAE: solubility parameter = 12.0 (cal / cm 3 ) 1 / 2 Examples of the tertiary amine include triethanolamine (TEA), N-methyldiethanolamine (MDEA), tetramethylethylenediamine (TEMED), pentamethyldiethylenetriamine (PMDETA), hexamethyltriethylenetetramine, and bis(2-dimethylaminoethyl)ether. These amine compounds may be used alone or in combination of two or more.

[0056] The organic solvent is, for example, 1-butanol [solubility parameter = 11.3 (cal / cm 3 ) 1 / 2 ], 1-pentanol [solubility parameter = 11.0 (cal / cm 3 ) 1 / 2 ], octanol, diethylene glycol diethyl ether [DEGDEE: solubility parameter = 8.2 (cal / cm 3 ) 1 / 2 and diethylene glycol dimethyl ether (DEGDME).The organic solvents may be used alone or in combination of two or more.

[0057] When the treatment liquid contains the amine compound, the organic solvent, and water, the content of the amine compound is preferably 20% by mass or more and less than 40% by mass. The content of the organic solvent is preferably 40% by mass or more and 60% by mass or less. The balance of the treatment liquid is water, and the content of water is preferably, for example, more than 0% by mass and 20% by mass or less. Examples of the treatment liquid include a treatment liquid containing 30% by mass of the amine compound, 60% by mass of the organic solvent, and 10% by mass of water. The treatment liquid may contain other components, such as an ionic liquid, in addition to the amine compound, the organic solvent, and water.

[0058] When the treatment liquid contains the amine compound, the organic solvent, and water, the difference between the solubility parameter of the amine compound and the parameter of the organic solvent (solubility parameter difference) is 1.1 (cal / cm 3 ) 1 / 2 More than 4.2(cal / cm 3 ) 1 / 2 It is preferable that the solubility parameter is equal to or less than the above. The solubility parameter can be calculated by the following formula (1).

[0059] δ=[(ΔH-RT) / V] 1 / 2 (1) In formula (1), δ represents the solubility parameter, ΔH represents the molar latent heat of vaporization, R represents the gas constant, T represents the absolute temperature, and V represents the molar volume.

[0060] The state of the treatment liquid after absorbing carbon dioxide when the treatment liquid contains an amine compound, an organic solvent, and water will be described. A treatment liquid containing 30% by mass of an amine compound, 60% by mass of an organic solvent, and 10% by mass of water was used as the treatment liquid. The combination of the amine compound and the organic solvent was varied, and the state of the treatment liquid for each combination was observed. The results are shown in Table 1. Table 1 also shows the solubility parameter of the amine compound, the solubility parameter of the organic solvent, the value obtained by subtracting the solubility parameter of the organic solvent from the solubility parameter of the amine compound (solubility parameter difference), and the state of the treatment liquid after absorbing carbon dioxide. "Good" in Table 1 indicates that the treatment liquid was in a single liquid phase before absorbing carbon dioxide and separated into two liquid phases upon carbon dioxide absorption. "Not miscible" in Table 1 indicates that the two-liquid state did not form a single liquid phase before absorbing carbon dioxide. "Not separated" in Table 1 indicates that the treatment liquid remained in a single liquid phase even after absorbing carbon dioxide. Furthermore, "-" in Table 1 indicates that the treatment solution for this combination was not observed and no results are available. Note that the solubility parameters of the amine compound and the organic solvent shown in Table 1 are reported to one decimal place only due to significant digits, and therefore the value obtained by subtracting the solubility parameter of the organic solvent from the solubility parameter of the amine compound may contain a rounding error and may not reflect the difference in solubility parameters shown in Table 1.

[0061] [Table 1]

[0062] When the treatment liquid contains an amine compound, an organic solvent, and water, it is preferable that the value obtained by subtracting the solubility parameter of the organic solvent from the solubility parameter of the amine compound (solubility parameter difference) be within a predetermined range. Specifically, the solubility parameter difference is 1.1 (cal / cm 3 ) 1 / 2 More than 4.2(cal / cm 3 ) 1 / 2It is preferable that the calorie content is 1.2 (cal / cm 3 ) 1 / 2 More than 3.8(cal / cm 3 ) 1 / 2 It can be seen that it is more preferable that the solubility parameter difference is less than 0.05. By selecting the amine compound and the organic solvent so that this solubility parameter difference is within the above range, the treatment liquid can absorb carbon dioxide, and what was in a single phase before absorbing carbon dioxide becomes a two-phase state after absorbing carbon dioxide. That is, the treatment liquid undergoes phase separation upon absorption of carbon dioxide. If the solubility parameter difference is too small, phase separation tends not to occur even when the resulting liquid is allowed to absorb carbon dioxide. On the other hand, if the solubility parameter difference is too large, the resulting liquid tends to be in a two-phase state even before absorbing carbon dioxide. In this two-phase state, the organic solvent and water are insufficiently miscible, and the amine compound is contained in a larger amount in one of the phases, for example, the aqueous phase. Even if the gas to be treated is contacted with a liquid in such a state, the contact state between the liquid and the gas to be treated becomes uneven, which may reduce the absorption efficiency.

[0063] The treatment solution gradually deteriorates when used for a long period of time to recover the acidic compounds. That is, the treatment solution contains components that gradually deteriorate chemically when used for a long period of time to recover the acidic compounds. A typical component that deteriorates is a component that constitutes the first phase, and in the case of a treatment solution containing an amine compound, an organic solvent, and water, it is the amine compound.

[0064] The deterioration of amine compounds can be primarily attributed to thermal degradation, i.e., deterioration caused by changes in properties due to heating. The gas treatment method uses a treatment liquid that undergoes phase separation upon absorption of acidic compounds, and therefore the regeneration temperature can be lowered compared to when other treatment liquids (treatment liquids that do not undergo phase separation) are used. Therefore, it is believed that the deterioration of amine compounds can be sufficiently suppressed.

[0065] In addition to thermal degradation, the deterioration can also be oxidative degradation, which is degradation in which the amine compound is oxidized by oxygen dissolved in the treatment liquid (dissolved oxygen). Since the gas treatment method suppresses thermal degradation, the influence of oxidative degradation is considered to be significant. To suppress this oxidative degradation, which is considered to have a significant impact, the present inventors focused on reducing the dissolved oxygen from the treatment liquid by subjecting the treatment liquid to a deoxidation treatment. In this regard, the present inventors also considered the location of the deoxidation treatment. As a result, they found that the compositions of the first phase and the second phase are as follows: The amine phase, which is the first phase, has a relatively high content of the amine compound (the organic solvent:the ether compound content is relatively low), and therefore has a relatively high polarity. Therefore, the amine phase, which is the first phase, has a relatively high content of water and a relatively low content of dissolved oxygen. On the other hand, the ether phase, which is the second phase, has a relatively high content of the ether compounds (a relatively low content of the amine compounds), resulting in a relatively low polarity. Therefore, the ether phase, which is the second phase, has a relatively low content of water and a relatively high content of dissolved oxygen. When deoxidizing the treatment liquid, it is conceivable to deoxidize the entire treatment liquid in order to minimize the amount of dissolved oxygen in the treatment liquid. It is also conceivable to deoxidize the first liquid, which is primarily composed of the amine phase, which is the first phase that contains a large amount of amine compounds that are subject to oxidative degradation. The present inventors have discovered that, instead of or in addition to deoxidizing the entire treatment liquid or the first liquid, using a second liquid primarily composed of the second phase is effective in suppressing oxidative degradation of the amine compounds. In other words, it was found that subjecting the second liquid, which mainly contains the second phase portion, to the deoxidation treatment is effective in suppressing oxidative deterioration of the components that make up the first phase portion (the components mainly contained in the first phase portion: amine compounds).Based on the above, the inventors have discovered that applying the deoxidation treatment to the second liquid, rather than to the first liquid, which mainly contains the first phase, which contains many components that are subject to oxidative degradation, is effective in suppressing oxidative degradation of the components that make up the first phase (the components mainly contained in the first phase). Furthermore, when treating oxidative atmospheric gases such as exhaust gases, oxidative degradation is generally more of a problem than thermal degradation. From this perspective, it is believed that being able to efficiently suppress oxidative degradation will contribute favorably to efficiently suppressing degradation of the treatment liquid used.

[0066] Furthermore, in the gas treatment method, the second liquid is subjected to the deoxidation treatment before the first liquid and the second liquid are mixed. As a result, the second liquid, which is a part of the treatment liquid before the treatment liquid is heated to release the acidic compounds from the treatment liquid, is subjected to the deoxidation treatment. As a result, the treatment liquid becomes deoxidized when heated to release the acidic compounds from the treatment liquid. Since oxidation degradation is more likely to occur at higher temperatures, it is believed that by performing the deoxidation treatment on the second liquid, which is the treatment liquid before being mixed with the first liquid, the deoxidation treatment is performed before heating to release the acidic compounds from the treatment liquid, thereby effectively suppressing oxidation degradation.

[0067] As a result, thermal deterioration of the treatment solution can be suppressed, and oxidative deterioration of the treatment solution can also be efficiently suppressed. Therefore, deterioration of the treatment solution used can be suppressed, and acidic compounds can be separated and recovered continuously for a long period of time. In other words, acidic compounds can be separated and recovered continuously for a long period of time without replenishing or replacing the treatment solution.

[0068] In order to confirm that the gas treatment method is effective in suppressing deterioration of the treatment liquid used and enabling acidic compounds to be separated and recovered continuously over a long period of time, the following was investigated.

[0069] The dissolved oxygen concentration of a representative treatment solution containing 30% by mass of EAE as an amine compound, 60% by mass of DEGDEE as an organic solvent, and 10% by mass of water was calculated. The dissolved oxygen concentration was calculated by multiplying the dissolved oxygen concentration calculated from the Henry's constants by the sum of the molar fractions of each component, assuming that each component (EAE, DEGDEE, and water) is a pure substance. The Henry's constant was also calculated by fitting the dissolved oxygen concentration predicted by the PSRK model. The calculation conditions used were a temperature of 50°C, a carbon dioxide partial pressure of 15 kPa, an oxygen partial pressure of 5 kPa, a Henry's constant for EAE of 66,690 kPa, a Henry's constant for DEGDEE of 63,406 kPa, and a Henry's constant for water of 5,314,267 kPa. The calculation results are shown in Table 2.

[0070] [Table 2]

[0071] The average EAE concentration in the first phase (amine phase) and the second phase (ether phase) (i.e., the mixed phase of the amine and ether phases) was calculated to be 26.7 mol % and 44 ppm, respectively. Meanwhile, the EAE concentration in the ether phase was calculated to be 5.9 mol % and 64 ppm, respectively. Although the reaction mechanism for EAE oxidative degradation is unknown, assuming the reaction rate is linearly proportional to the EAE and dissolved oxygen concentrations, the mixed phase was calculated to oxidize approximately 3.1 times faster (=(26.7 × 44) / (5.9 × 64)) than the second phase at the same temperature. These results also confirm that oxygen degradation can be suppressed by heating only the ether phase to degas it and then mixing it with the amine phase and then heating it to the specified temperature, rather than by mixing the amine and ether phases and then heating them to the specified temperature.

[0072] The deoxidation treatment is not particularly limited as long as it can remove dissolved oxygen from the second liquid when applied to the second liquid. Examples of the deoxidation treatment include a treatment of heating the second liquid (heating treatment), a treatment of contacting the second liquid with a deoxidizer (deoxidizer contact treatment), a treatment of reducing the pressure of the second liquid (decompression treatment), a treatment of irradiating the second liquid with ultrasonic waves (ultrasonic irradiation treatment), a treatment of supplying hydrogen to the second liquid (hydrogen supply treatment), and a treatment of contacting the second liquid with a noble metal catalyst while supplying hydrogen to the second liquid (catalyst contact treatment). These treatments may be used alone or in combination as the deoxidation treatment.

[0073] The heat treatment is not particularly limited as long as it can remove dissolved oxygen from the second liquid by heating the second liquid. The heat treatment is not particularly limited as long as the temperature (heating temperature) of the second liquid is a temperature at which dissolved oxygen can be removed from the second liquid. The conditions for the heat treatment can be determined appropriately, and the following conditions are preferred, for example. More specifically, the heat treatment is preferably a heat treatment in which the temperature (heating temperature) of the second liquid is equal to or higher than the temperature at which dissolved oxygen can be removed from the second liquid and lower than the temperature (regeneration temperature) of the treatment liquid at which the acidic compound can be released from the treatment liquid. If the heating temperature is too low, the second dissolved oxygen tends to be insufficiently removed. If the heating temperature is too high, the treatment agent (or its components) tends to evaporate.

[0074] The deoxidizing agent contact treatment is not particularly limited as long as it is a treatment that can remove dissolved oxygen from the second liquid by bringing the second liquid into contact with the deoxidizing agent. The deoxidizing agent is not particularly limited as long as it can remove dissolved oxygen from the second liquid by bringing a liquid containing dissolved oxygen into contact with the deoxidizing agent.

[0075] The decompression treatment is not particularly limited as long as it can remove dissolved oxygen from the second liquid by reducing the pressure of the second liquid. The conditions for the decompression treatment can be determined as appropriate, and are not particularly limited as long as the pressure (degree of decompression) during the decompression treatment is lower than the pressure (absorption pressure) at which oxygen is absorbed into the second liquid. The decompression treatment is preferably performed at a pressure at which the second liquid does not boil. That is, the decompression treatment is preferably performed at a pressure equal to or higher than the vapor pressure of water, which is the component of the treatment liquid that is most likely to boil. If the degree of decompression is too low, the second dissolved oxygen tends to be insufficiently removed. If the degree of decompression is too high, the treatment liquid (or its components) tends to evaporate (boil).

[0076] The ultrasonic irradiation treatment is not particularly limited as long as it can remove dissolved oxygen from the second liquid by irradiating the second liquid with ultrasonic waves. The ultrasonic irradiation conditions can be appropriately determined, and for example, the ultrasonic irradiation time is preferably 30 minutes or less. If the ultrasonic irradiation time is too short, the second dissolved oxygen tends to be insufficient to be removed. If the ultrasonic irradiation time is too long, the effect of ultrasonic irradiation tends to be saturated.

[0077] The hydrogen supply treatment is not particularly limited as long as it is a treatment that can remove dissolved oxygen from the second liquid by supplying hydrogen to the second liquid, and the catalyst contact treatment is not particularly limited as long as it is a treatment that can remove dissolved oxygen from the second liquid by contacting the second liquid with a noble metal catalyst while supplying hydrogen to the second liquid.

[0078] In the hydrogen supply treatment and the catalytic contact treatment, examples of the method for supplying hydrogen to the second liquid include a method for supplying hydrogen to the second liquid through a gas-permeable membrane and a method for supplying hydrogen to the second liquid using a gas nozzle, etc. By supplying hydrogen through a gas-permeable membrane or using a gas nozzle, hydrogen can be dissolved in the second liquid.

[0079] The gas-permeable membrane is a membrane that is more permeable to gases such as hydrogen than to liquids such as water. Specific examples include membranes that allow gases to pass through but not liquids. Examples of the gas-permeable membrane include membranes made of fluororesins such as polytetrafluoroethylene, copolymers of tetrafluoroethylene and perfluoroalkoxyethylene (PFA), and polytetrafluoroethylene (PTFE). The shape of the gas-permeable membrane is not limited, and it may be, for example, a flat membrane or a hollow fiber membrane, with a hollow fiber membrane being preferred. The gas nozzle is not particularly limited as long as it can supply hydrogen to the second liquid.

[0080] The method for contacting the second liquid with a noble metal catalyst is not particularly limited, as long as it can remove dissolved oxygen from the second liquid by contacting the second liquid, to which hydrogen has been supplied, with the noble metal catalyst. Specifically, this method removes dissolved oxygen from the second liquid by reacting the dissolved oxygen contained in the second liquid with hydrogen supplied to the second liquid in the presence of the noble metal catalyst. The noble metal catalyst is not particularly limited, as long as it can promote the reaction between the dissolved oxygen contained in the second liquid and the hydrogen supplied to the second liquid. Examples of the noble metal catalyst include palladium catalysts, and more specifically, metal palladium supported on various supports is preferred. Examples of such supports include ion exchange resins, activated carbon, synthetic adsorbents, and inorganic exchangers. A specific method for contacting the second liquid with a noble metal catalyst includes, for example, continuously passing the second liquid, to which hydrogen has been supplied, through a column packed with a noble metal catalyst such as the palladium catalyst.

[0081] The releasing step is not particularly limited as long as the acidic compound can be released from the first liquid and the second liquid by heating the first liquid together with the second liquid that has been subjected to the deoxidation treatment. The acidic compound released here is preferably carbon dioxide. For this reason, the temperatures of the first liquid and the second liquid in the releasing step are preferably equal to or higher than the temperature at which the carbon dioxide absorbed in the first liquid and the second liquid is released from the first liquid and the second liquid (the treatment liquid). Specifically, this temperature (heating temperature) is preferably equal to or higher than 80°C and less than 100°C.

[0082] In the releasing step, when releasing the acidic compounds from the mixed solution (the first and second solutions), it is preferable to contact the mixed solution with a gas that is substantially insoluble in the treatment solution. Hydrogen is preferable as the gas that is substantially insoluble in the treatment solution. That is, in the releasing step, when releasing the acidic compounds from the mixed solution, it is preferable to contact hydrogen with the mixed solution. By contacting hydrogen in this manner, the temperature at which carbon dioxide is released from the treatment solution is lowered, so that acidic compounds such as carbon dioxide can be separated and recovered from the gas to be treated with less energy. When hydrogen is supplied in this manner, the heating temperature in the releasing step is preferably 50°C or higher and 90°C or lower. Furthermore, when a deoxidation treatment using hydrogen, such as the hydrogen supply treatment or the catalytic contact treatment, is used as the deoxidation treatment, the hydrogen supplied in this releasing step can also be supplied from the supply unit that supplies hydrogen in the deoxidation treatment.

[0083] The apparatus (gas treatment apparatus) for performing the gas treatment method is not particularly limited as long as it can perform the absorption step, the separation step, the deoxidation step, and the release step. The gas treatment apparatus may include an absorber that brings the gas to be treated, which contains the acidic compounds, into contact with a treatment liquid that undergoes phase separation due to absorption of the acidic compounds, thereby absorbing the acidic compounds into the treatment liquid, a separator that causes the acidic compounds to be absorbed into the treatment liquid in the absorber and separates the treatment liquid, which has been phase-separated into the first and second phases, into a first liquid mainly containing the first phase and a second liquid mainly containing the second phase, a deoxidation treatment unit that deoxidizes the separated second liquid, and a releaser that releases the acidic compounds from the first liquid and the second liquid by heating the first liquid together with the deoxidized second liquid. Such a gas treatment device performs the absorption process in the absorber, the separation process in the separator, the deoxygenation process in the deoxygenation treatment unit, and the release process in the release unit, thereby suppressing deterioration of the treatment liquid used and enabling separation and recovery of acidic compounds over a long period of time.

[0084] The gas treatment device is used to recover high concentrations of acid compounds from a gas to be treated containing the acid compounds by using the treatment liquid. Specific examples of the gas treatment device 100 include a device including an absorber 11, a separator 12, a heater (deoxygenation treatment unit) 13, a releaser 14, a circulation path 15, and a heat exchanger 16, as shown in Fig. 1. Fig. 1 is a schematic diagram showing an example of the gas treatment device according to this embodiment.

[0085] The circulation path 15 includes a first flow path 21 through which the treated liquid is extracted from the absorber 11 and introduced into the releaser 14, and a second flow path 22 through which the treated liquid is extracted from the releaser 14 and returned to the absorber 11. The heat exchanger 16 can be omitted.

[0086] The absorber 11 is connected to a gas supply path 24 for supplying the gas to be treated, a gas discharge path 25 for discharging the gas after treatment in the absorber 11, a first flow path 21 for sending the treated liquid to the releaser 14, and a second flow path 22 for returning the treated liquid from the releaser 14 to the absorber 11. The gas supply path 24 can supply the gas to be treated into the absorber 11. The gas discharge path 25 can discharge gas that is not absorbed even when the gas to be treated is brought into contact with the treated liquid from inside the absorber 11. The first flow path 21 can extract the treated liquid that has accumulated in the absorber 11. The second flow path 22 can allow the treated liquid returned from the releaser 14 to flow down from above.

[0087] The absorber 11 brings the gas to be treated into contact with the treatment liquid, thereby absorbing acidic compounds such as carbon dioxide in the gas to be treated into the treatment liquid, and discharges the gas from which the acidic compounds have been removed. Such an absorber 11 may be any absorber that can continuously bring the gas to be treated into contact with the treatment liquid. Examples of absorbers that can be used include those that spray the treatment liquid into the flow path of the gas to be treated, those that allow the treatment liquid to flow down through packing materials placed in the flow path of the gas to be treated, and those that introduce the gas to be treated and the treatment liquid into multiple fine flow paths, respectively, and merge the fine flow paths of the gas to be treated and the fine flow paths of the treatment liquid. The absorption of acidic compounds into the treatment liquid is an exothermic reaction.

[0088] The releaser 14 is connected to the first flow path 21 and the second flow path 22. The first flow path 21 can introduce the treated liquid discharged from the absorber 11 into the releaser 14. The second flow path 22 can discharge the treated liquid stored in the releaser 14.

[0089] The releaser 14 stores the treatment liquid and releases the acidic compounds by heating the stored treatment liquid to a temperature at which the acidic compounds can be released or higher. The release of the acidic compounds from the treatment liquid, i.e., the desorption of the acidic compounds from the components contained in the treatment liquid, is an endothermic reaction. When the treatment liquid is heated in the releaser 14 as described above, not only are the acidic compounds released, but the water contained in the treatment liquid also evaporates. That is, in the releaser 14, the acidic compounds and water vapor are released from the treatment liquid.

[0090] The first flow path 21 is provided with the separator 12. The separator 12 is partitioned by a partition wall 31 into a first region 32 and a second region 33. The first region 32 stores the treated liquid discharged from the absorber 11. At this time, the treated liquid is phase-separated into the first phase and the second phase, and the second phase is located above the first phase. Therefore, when the amount of treated liquid stored in the first region 32 increases, the second phase preferentially flows over the partition wall 31 into the second region 33 and is stored in the second region 33. The treated liquid stored in the first region 32 is discharged from a first liquid flow path 35 connected to a lower portion of the first region 32. The treated liquid stored in the second region 33 is discharged from a second liquid flow path 36 connected to a lower portion of the second region 33. By discharging in this manner, a first liquid mainly composed of the first phase portion flows through the first liquid flow path 35, and a second liquid mainly composed of the second phase portion flows through the second liquid flow path 36. In this manner, the separator 12 separates the first liquid from the second liquid. The first liquid flow path 35 and the second liquid flow path 36 are provided with a pump 37 and a pump 38, respectively.

[0091] The heater 13 is connected to the second liquid flow path 36. The second liquid supplied from the second liquid flow path 36 is heated by the heater 13 to remove dissolved oxygen from the second liquid. That is, the heating treatment is performed on the second liquid as the deoxidation treatment. The heater 13 is a treatment section that heats the second liquid. As the heater 13, for example, a heater that directly or indirectly heats the treatment liquid using any heat source such as electricity, steam, or a burner can be used. The oxygen removed from the second liquid by the deoxidation treatment (oxygen derived from dissolved oxygen) flows into the release path 51 via the oxygen discharge path 41. Furthermore, the second liquid after the deoxidation treatment is mixed with the first liquid flowing through the first liquid flow path 35 via the second liquid supply path 42. A mixture of the first liquid and the second liquid after the deoxidation treatment is introduced into the emitter 14 via the first flow path 21.

[0092] The release device 14 is connected to a release path 51 and a heating path 52. The release path 51 is provided with an acid compound separator 53. The acid compound separator 53 condenses the water vapor by cooling a mixed gas of the acid compounds released from the treatment liquid and water vapor, and separates the condensed water from the acid compounds. The acid compound separator 53 is connected to a supply path 54 and a reflux path 55. The supply path 54 supplies the acid compounds separated in the acid compound separator 53 to a supply destination. The water separated in the acid compound separator 53 is refluxed to the release device 14 via the reflux path 55. The acid compound separator 53 and the reflux path 55 may be omitted.

[0093] The heating flow path 52 is provided with a first heating section 56. The first heating section 56 heats the treated liquid, returns a portion of the treated liquid to the emitter 14 via a return flow path 57, and returns the remainder of the treated liquid to the absorber 11 via the second flow path 22. A pump 59 is provided in the second flow path 22. The first heating section 56 may be arranged to heat the treated liquid inside the emitter 14, or, as shown in the figure, may be configured to heat the treated liquid extracted from the emitter 14 to the outside. The first heating section 56 may be configured to heat the treated liquid directly or indirectly using any heat source such as electricity, steam, or a burner.

[0094] The heat exchanger 16 is connected to the first flow path 21 and the second flow path 22, and exchanges heat between the treatment liquid flowing through the first flow path 21 and the treatment liquid flowing through the second flow path 22. The heat exchanger 16 is configured, for example, by a plate heat exchanger or the like, but may also be configured by a microchannel heat exchanger that is capable of exchanging heat between fluids with a relatively small temperature difference, thereby improving energy efficiency.

[0095] The gas treatment device 100 can recover a high concentration of acidic compounds from a gas to be treated that contains acidic compounds by performing the absorption process in the absorber 11, the separation process in the separator 12, the deoxidation process in the heater 13, and the release process in the release device 14. Furthermore, by performing the deoxidation process in the heater 13, the gas treatment device 100 can suppress deterioration of the treatment liquid used, allowing the treatment liquid to be used for a long period of time to recover the acidic compounds.

[0096] Other apparatuses for carrying out the gas treatment method include, for example, gas treatment apparatuses such as the gas treatment apparatus 200 shown in FIG. 2 and the gas treatment apparatus 300 shown in FIG. 3, in which the separation step is carried out in a separator 12 provided in the absorber 11.

[0097] As shown in FIG. 2 , the gas treatment device 200 includes a separator 12 in the absorber 11. The separator 12 is provided in the lower part of the absorber 11 and is partitioned by a partition wall 31 into a first region 32 and a second region 33. The separator 12 also includes a partition wall 34 that covers the upper part of the second region. The treated liquid in the absorber 11 is stored in the first region 32. At this time, the treated liquid is phase-separated into the first phase portion and the second phase portion, and the second phase portion is located above the first phase portion. Therefore, when the amount of treated liquid stored in the first region 32 increases, the second phase portion preferentially flows over the partition wall 31 into the second region 33 and is stored in the second region 33. Note that, due to the presence of the partition wall 34, only the amount that flows over the partition wall 31 does not flow into the second region 33. The treatment liquid stored in the first region 32 is discharged from a first liquid flow path 35 connected to a lower portion of the first region 32. The treatment liquid stored in the second region 33 is discharged from a second liquid flow path 36 connected to a lower portion of the second region 33. By discharging the treatment liquid in this manner, a first liquid mainly composed of the first phase portion flows through the first liquid flow path 35, and a second liquid mainly composed of the second phase portion flows through the second liquid flow path 36. In this manner, the separator 12 separates the first liquid from the second liquid. The gas treatment device 200 is similar to the gas treatment device 100 shown in FIG. 1 except for including the separator 12.

[0098] As shown in FIG. 3 , in the gas treatment device 300, the treatment liquid stored in the absorber 11 is phase-separated into the first phase and the second phase due to the absorption of an acidic compound, with the second phase being located above the first phase. A first liquid flow path 35 is connected to the bottom of the absorber 11, and a second liquid flow path 36 is connected above the first liquid flow path 35. Specifically, the second liquid flow path 36 is connected so as to be below a liquid level 27 of the second phase and above an interface 28 between the first and second phases. The first liquid flow path 35 is also connected so as to be below the interface 28 between the first and second phases. By discharging the treatment liquid from the first liquid flow path 35 connected in this manner, a first liquid mainly composed of the first phase flows through the first liquid flow path 35. By discharging the treatment liquid from the second liquid flow path 36 connected as described above, a second liquid mainly composed of the second phase flows through the second liquid flow path 36. The separator 12 thus separates the first liquid from the second liquid. The gas treatment device 300 is similar to the gas treatment device 100 shown in FIG.

[0099] The gas treatment device 200 and the gas treatment device 300 can recover high concentrations of acidic compounds from a gas to be treated that contains acidic compounds, similar to the gas treatment device 100. Furthermore, deterioration of the treatment liquid used can be suppressed, and the treatment liquid can be used for recovering the acidic compounds for a long period of time.

[0100] As another apparatus for carrying out the gas treatment method, for example, as shown in FIGS. 4 to 8, there can be mentioned a gas treatment apparatus in which the deoxidation step is carried out in a place other than the heater 13.

[0101] As shown in FIG. 4, the gas treatment device 400 includes a pressure reducer 17. The pressure reducer 17 is connected to the second liquid flow path 36. A valve 45 is provided in the second liquid flow path 36 upstream of the pressure reducer 17. The pressure reducer 17 is connected to an oxygen discharge path 41 that discharges oxygen removed from the second liquid by the pressure reducer 17 (oxygen derived from dissolved oxygen). The oxygen discharge path 41 includes a compressor 46 downstream of the pressure reducer 17. The valve 45 is throttled and the pressure inside the pressure reducer 17 is reduced by the compressor 46, thereby removing dissolved oxygen from the second liquid supplied from the second liquid flow path 36. That is, the pressure reduction treatment is performed on the second liquid as the deoxygenation treatment. The pressure reducer 17 is a treatment section that reduces the pressure of the second liquid. The compressor 46 is not particularly limited, and a centrifugal compressor or the like can be used. The oxygen removed from the second liquid by the deoxidation treatment (oxygen derived from dissolved oxygen) flows into a discharge path 51 via an oxygen discharge path 41. The second liquid after the deoxidation treatment is mixed with the first liquid flowing through the first liquid flow path 35 via a second liquid supply path 42. A pump 43 is provided in the first liquid flow path 35. A mixed liquid obtained by mixing the first liquid and the second liquid after the deoxidation treatment is introduced into the discharger 14 via the first flow path 21. The gas treatment device 400 is similar to the gas treatment device 100 shown in FIG. 1 except that the deoxidation treatment is performed in the pressure reducer 17.

[0102] As shown in FIG. 5 , the gas treatment device 500 includes an ultrasonic irradiator 18. The ultrasonic irradiator 18 is connected to the second liquid flow path 36. The ultrasonic irradiator 18 irradiates the second liquid with ultrasonic waves to remove dissolved oxygen from the second liquid supplied from the second liquid flow path 36. That is, the ultrasonic irradiation treatment is performed on the second liquid as the deoxidation treatment. The ultrasonic irradiator 18 is a processing unit that irradiates the second liquid with ultrasonic waves. A general ultrasonic generator or the like can be used as the ultrasonic irradiator 18. The oxygen removed from the second liquid by the deoxidation treatment (oxygen derived from dissolved oxygen) flows into the release path 51 via the oxygen discharge path 41. The second liquid after the deoxidation treatment is mixed with the first liquid flowing through the first liquid flow path 35 via the second liquid supply path 42. The mixture of the first liquid and the second liquid after the deoxidation treatment is introduced into the emitter 14 via the first flow path 21. The gas treatment device 500 is similar to the gas treatment device 100 shown in FIG. 1, except that the deoxidation treatment is performed by the ultrasonic irradiator 18 .

[0103] As shown in FIG. 6 , the gas treatment device 600 includes a gas-liquid contactor 19. The gas-liquid contactor 19 is connected to the second liquid flow path 36. A functional material 61 is provided inside the gas-liquid contactor 19. The second liquid circulating through the gas-liquid contactor 19 comes into contact with the functional material 61. The gas-liquid contactor 19 also includes a first hydrogen supplying unit 62. The first hydrogen supplying unit 62 can supply hydrogen to the second liquid in the gas-liquid contactor 19 by supplying hydrogen to the gas-liquid contactor 19. Examples of the functional material 61 include a filler (such as a filler similar to the filler disposed in the absorber 11) and a precious metal catalyst. Note that the functional material 61 does not necessarily have to be provided. When a precious metal catalyst is used as the functional material 61, the second liquid is brought into contact with the precious metal catalyst while hydrogen is supplied to the second liquid by the first hydrogen supplying unit 62. That is, the second liquid is subjected to the catalytic contact treatment as the deoxidation treatment. By doing so, dissolved oxygen is removed from the second liquid supplied from the second liquid flow path 36. That is, the second liquid is subjected to the catalytic contact treatment as the deoxidation treatment. Furthermore, even when a material other than a precious metal catalyst (e.g., a filler) is used as the functional material 61 or when the functional material 61 is not provided (even when a precious metal catalyst is used as the functional material 61), hydrogen is supplied to the second liquid by the first hydrogen supply unit 62, thereby removing dissolved oxygen from the second liquid supplied from the second liquid flow path 36. That is, the hydrogen supply treatment is performed as the deoxidation treatment on the second liquid. The catalytic contact treatment can remove dissolved oxygen from the second liquid more preferably than the hydrogen supply treatment. The precious metal catalyst described above can be used as the precious metal catalyst. The first hydrogen supply unit 62 is not particularly limited as long as it can supply hydrogen.

[0104] The releaser 14 is also equipped with a second hydrogen supply unit 64 and a second heating unit 65. The second hydrogen supply unit 64 supplies hydrogen to the releaser 14, thereby supplying hydrogen to the treatment liquid in the releaser 14. The second heating unit 65 heats the treatment liquid in the releaser 14, thereby releasing acidic compounds from the treatment liquid. By supplying hydrogen to the treatment liquid in the releaser 14 using the second hydrogen supply unit 64, the temperature (regeneration temperature) of the treatment liquid at which the acidic compounds can be released from the treatment liquid (the first liquid and the second liquid) can be lowered. Since the regeneration temperature can be lowered in this way, the heating temperature of the treatment liquid by the second heating unit 65 can be lowered. Furthermore, when a treatment unit is used in which hydrogen is supplied to the second liquid while the second liquid is brought into contact with a noble metal catalyst, the hydrogen supplied to the releaser 14 can also be supplied from the first hydrogen supply unit 62 that supplies hydrogen in the hydrogen supply process or the catalytic contact process. That is, the first hydrogen supply unit 62 and the second hydrogen supply unit 64 may be the same unit.

[0105] Furthermore, since hydrogen is also supplied to the emitter 14, not only the gas-liquid contact section 19 may be provided with the precious metal catalyst, but also the emitter 14 may be provided with a precious metal catalyst 66, as in the gas treatment device 700 shown in Figure 7.

[0106] In the gas processing device 600 and the gas processing device 700, oxygen removed from the second liquid by the deoxidation treatment (oxygen derived from dissolved oxygen) flows to the release path 51 via the oxygen discharge path 41. The second liquid after the deoxidation treatment is mixed with the first liquid flowing through the first liquid flow path 35 via the second liquid supply path 42. A mixed liquid obtained by mixing the first liquid and the second liquid after the deoxidation treatment is introduced into the releaser 14 via the first flow path 21. The gas processing device 600 and the gas processing device 700 are similar to the gas processing device 100 shown in FIG. 1 except that the deoxidation treatment is performed in the gas-liquid contactor 19 and the releaser 14 has the above-mentioned configuration. The second hydrogen supply unit 64 may be provided in the releaser 14 in other gas processing devices, not just the gas processing device 600 shown in FIG. 6 and the gas processing device 700 shown in FIG. 7. By providing the second hydrogen supply unit 64, as described above, hydrogen can be supplied from the second hydrogen supply unit 64 to the treatment liquid in the releaser 14, thereby lowering the temperature (regeneration temperature) of the treatment liquid (the first liquid and the second liquid) at which the acidic compounds can be released from the treatment liquid.

[0107] As shown in FIG. 8, the gas treatment device 800 includes a deoxidizer contact unit 20. The deoxidizer contact unit 20 is connected to the second liquid flow path 36. By bringing the second liquid into contact with the deoxidizer contact unit 20, dissolved oxygen is removed from the second liquid supplied from the second liquid flow path 36. That is, the deoxidizer contact treatment is performed on the second liquid as the deoxidizer treatment. The deoxidizer contact unit 20 is a treatment unit that brings the second liquid into contact with a deoxidizer. After the deoxidizer treatment is performed on the second liquid, a mixed liquid obtained by mixing the first liquid and the second liquid after the deoxidizer treatment is introduced into the releaser 14. Note that, since the amount of oxygen removed from the second liquid (oxygen derived from dissolved oxygen) is small during the deoxidizer contact treatment, outflow to the release path via an oxygen discharge path is not necessary. The gas treatment device 800 may also include an oxygen discharge path, as in the gas treatment device 100 shown in FIG. 1. The gas treatment device 800 is similar to the gas treatment device 100 shown in FIG. 1, except that it does not include the oxygen discharge path and the deoxidation treatment is carried out in the deoxidizer contact section 20 .

[0108] Like the gas treatment device 100, each of the gas treatment devices 200, 300, 400, 500, 600, 700, and 800 can recover high concentrations of acidic compounds from a gas to be treated that contains acidic compounds. Furthermore, deterioration of the treatment liquid used can be suppressed, allowing the treatment liquid to be used for recovering the acidic compounds for a long period of time. [Explanation of symbols]

[0109] 11 Absorber 12 Separator 13 Heater (deoxidation treatment section) 14 Emitter 15 Circulation route 16 Heat exchanger 17 Pressure reducer 18 Ultrasonic irradiator 19 Catalyst contact area 20 Oxygen absorber contact area 21 First Channel 22 Second Channel 24 Gas supply line 25 Gas exhaust channel 27 Second phase liquid level 28 Interface between the first and second phases 31,34 Bulkhead 32 First area 33 Second area 35 1st liquid flow path 36 Second liquid flow path 37, 38, 43, 59 Pump 41 Oxygen exhaust channel 42 2nd liquid supply path 45 valve 46 Compressor 51 Release channel 52 Heating channel 53 Acidic compound separator 54 Supply route 55,57 Circulation path 56 1st heating section 61 Functional Materials 66 Precious metal catalysts 62 First Hydrogen Supply Unit 64 Second Hydrogen Supply Unit 65 2nd heating section 100,200,300,400,500,600,700,800 Gas treatment equipment

Claims

1. a step of bringing a gas to be treated, which contains an acidic compound that generates an acid when dissolved in water, into contact with a treatment liquid that undergoes phase separation upon absorption of the acidic compound, thereby absorbing the acidic compound into the treatment liquid; a step of absorbing the acidic compound into the treatment liquid, and separating the treatment liquid into a first phase portion having a relatively high content of the acidic compound and a second phase portion having a relatively low content of the acidic compound, into a first liquid mainly containing the first phase portion and a second liquid mainly containing the second phase portion; a step of deoxidizing the separated second liquid; and releasing the acidic compounds from the first liquid and the second liquid by heating the first liquid together with the second liquid that has been subjected to the deoxidation treatment.

2. the treatment liquid contains water, an amine compound, and an organic solvent; the first phase portion has a higher content of the amine compound than the second phase portion, 2. The gas processing method according to claim 1, wherein the second phase portion has a higher content of the organic solvent than the first phase portion.

3. 3. The gas treatment method according to claim 1, wherein the deoxidation treatment is at least one selected from the group consisting of a treatment of heating the second liquid, a treatment of contacting the second liquid with an oxygen scavenger, a treatment of reducing the pressure of the second liquid, and a treatment of irradiating the second liquid with ultrasonic waves.

4. 3. The gas processing method according to claim 1, wherein the deoxidation treatment is a hydrogen supply treatment in which hydrogen is supplied to the second liquid.

5. 5. The gas processing method according to claim 4, wherein the deoxidation treatment is a treatment in which the second liquid is brought into contact with a noble metal catalyst while hydrogen is being supplied to the second liquid in the hydrogen supply treatment.

6. 4. The gas treatment method according to claim 3, wherein hydrogen is brought into contact with the first liquid and the second liquid when the acidic compounds are released from the first liquid and the second liquid.

7. 5. The gas treatment method according to claim 4, wherein hydrogen is brought into contact with the first liquid and the second liquid when the acidic compounds are released from the first liquid and the second liquid.

8. 6. The gas treatment method according to claim 5, wherein hydrogen is brought into contact with the first liquid and the second liquid when the acidic compounds are released from the first liquid and the second liquid.

9. an absorber that brings a gas to be treated, which contains an acidic compound that generates an acid when dissolved in water, into contact with a treatment liquid that undergoes phase separation upon absorption of the acidic compound, thereby absorbing the acidic compound into the treatment liquid; a separator that separates the treated liquid, which has been phase-separated into a first phase portion having a relatively high content of the acidic compounds and a second phase portion having a relatively low content of the acidic compounds in the absorber by absorbing the acidic compounds into a first liquid mainly containing the first phase portion and a second liquid mainly containing the second phase portion; a deoxidation treatment unit that deoxidizes the separated second liquid; a releaser that releases the acidic compound from the first liquid and the second liquid by heating the first liquid together with the second liquid that has been subjected to the deoxidation treatment.

10. the treatment liquid contains water, an amine compound, and an organic solvent; the first phase portion has a higher content of the amine compound than the second phase portion, 10. The gas treatment device according to claim 9, wherein the second phase portion has a higher content of the organic solvent than the first phase portion.

11. 11. The gas treatment device according to claim 9 or 10, wherein the deoxidation treatment unit is at least one selected from the group consisting of a treatment unit that heats the second liquid, a treatment unit that brings the second liquid into contact with a deoxidizer, a treatment unit that reduces the pressure of the second liquid, and a treatment unit that irradiates the second liquid with ultrasonic waves.

12. The gas treatment device according to claim 9 or 10, wherein the deoxidation treatment unit includes a hydrogen supply unit that supplies hydrogen to the second liquid.

13. The gas treatment device according to claim 12 , wherein the deoxidation treatment unit further comprises a noble metal catalyst that contacts the second liquid while the hydrogen supply unit supplies hydrogen to the second liquid.

14. The gas treatment device according to claim 11 , further comprising a hydrogen supply unit that supplies hydrogen to the emitter to bring the first liquid and the second liquid into contact with hydrogen.

15. The gas treatment device according to claim 12 , further comprising a hydrogen supply unit that supplies hydrogen to the emitter to bring the first liquid and the second liquid into contact with hydrogen.

16. The gas treatment device according to claim 13 , further comprising a hydrogen supply unit that supplies hydrogen to the emitter to bring the first liquid and the second liquid into contact with hydrogen.

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