Carbon dioxide recovery system and carbon dioxide recovery method

Abstract

Provided are a carbon dioxide recovery system and a carbon dioxide recovery method that involve circulation in which an absorber, after absorbing carbon dioxide, is regenerated at room temperature and reused to absorb carbon dioxide and in which the absorber is not prone to loss of capacity as an absorber even after repeated regeneration. The present invention is provided with: a carbon dioxide absorption processing unit (10) that brings an aqueous solution containing a hydroxide into contact with a gas to obtain a post-absorption solution that has absorbed carbon dioxide; a carbon dioxide desorption processing unit (20) that, by adding an acid to the post-absorption solution, obtains a post-desorption solution from which the carbon dioxide has been desorbed, and that recovers the carbon dioxide; and an electrolysis unit (30) that performs electrolysis on the post-desorption solution to obtain an acid produced at a positive electrode and a hydroxide produced at a negative electrode. The hydroxide obtained at the electrolysis unit (30) is used by the carbon dioxide absorption processing unit (10), and the acid is used by the carbon dioxide desorption processing unit (20).

Description

Carbon dioxide capture system and capture method

[0001] The present disclosure relates to a system and method for recovering carbon dioxide contained in a gas.

[0002] Greenhouse gases are considered to be the main cause of global warming. In recent years, technological developments have been made to capture carbon dioxide, a major greenhouse gas, from the atmosphere and to utilize it effectively.

[0003] One method for recovering carbon dioxide contained in a gas is to bring the gas into contact with an absorbent that absorbs carbon dioxide, and amine-based absorbents are known as such absorbents. The amine-based absorbent that has absorbed carbon dioxide can be desorbed by heating it to about 120°C, and since its ability to absorb carbon dioxide is restored after desorption, it can be reused as an absorbent. For example, Patent Document 1 discloses a carbon dioxide capture module that includes an absorption section containing an amine-based absorbent, and is designed for use in the living space of an ordinary household.

[0004] International Publication No. 2023 / 199856

[0005] However, since amines have the property of reacting with oxygen and changing their properties, the amine-based absorbent has a problem that its ability to absorb carbon dioxide gradually decreases, and there is also a problem that a large amount of energy is required for heat treatment to desorb carbon dioxide from the amine-based absorbent after absorbing carbon dioxide.

[0006] Meanwhile, inorganic alkali salts are another type of absorbent that is different from amine-based absorbents. The use of inorganic alkali salts as absorbents has the advantage of being less likely to cause unwanted side reactions and less likely to cause the problem of gradual decline in absorbent capacity. However, to return the products (carbonates and / or hydrogen carbonates) generated by the reaction with carbon dioxide back to the inorganic alkali salts and regenerate them as absorbents, heat treatment at high temperatures of 800°C or higher is required, which also requires a large amount of energy. Furthermore, calcium carbonate, one example of such products, can be directly mixed into concrete and consumed as a material without being regenerated as an absorbent, but this method does not allow for the creation of a cycle in which the absorbent can be regenerated and reused to absorb carbon dioxide.

[0007] The contents of the present disclosure have been made in consideration of the above circumstances when an absorbent that absorbs carbon dioxide is brought into contact with a gas to recover the carbon dioxide contained in the gas, and its purpose is to provide a carbon dioxide recovery system and recovery method that has a cycle in which the absorbent after absorbing carbon dioxide is regenerated at room temperature and used again to absorb carbon dioxide, and in which the absorbent's ability as an absorbent is unlikely to deteriorate even if the absorbent is repeatedly regenerated.

[0008] In order to solve the above-mentioned problems, the carbon dioxide recovery system according to the present disclosure is a system for recovering carbon dioxide contained in a gas, comprising: a carbon dioxide absorption treatment section that brings the gas into contact with an aqueous solution containing a hydroxide of an alkali metal or alkaline earth metal to obtain a post-absorption solution in which carbon dioxide has been absorbed as carbonate and / or bicarbonate; a carbon dioxide desorption treatment section that adds an acid to the post-absorption solution to obtain a post-desorption solution in which carbon dioxide has been desorbed from the carbonate and / or bicarbonate, and recovers the carbon dioxide; and an electrolysis section that electrolyzes the post-desorption solution to obtain an acid produced at an anode and a hydroxide produced at a cathode, wherein the hydroxide produced in the electrolysis section is used in the carbon dioxide absorption treatment section, and the acid produced in the electrolysis section is used in the carbon dioxide desorption treatment section.

[0009] The carbon dioxide recovery system may be configured to include a transport means for transporting the hydroxide obtained in the electrolysis unit to the carbon dioxide absorption treatment unit, and a transport means for transporting the acid obtained in the electrolysis unit to the carbon dioxide desorption treatment unit.

[0010] The carbon dioxide recovery system may further include an immobilization treatment unit that immobilizes the carbon dioxide recovered in the carbon dioxide desorption treatment unit, and the immobilization of carbon dioxide in the immobilization treatment unit may be performed by using, as a raw material, hydrogen generated by electrolyzing the desorbed solution in the electrolysis unit.

[0011] The carbon dioxide recovery system may be configured such that the carbon dioxide absorption treatment section has a bubbling device that turns the gas into bubbles and introduces the bubbles into an aqueous solution containing a hydroxide of an alkali metal or alkaline earth metal.

[0012] Furthermore, the carbon dioxide recovery system recovers carbon dioxide contained in the gas discharged from the gas generation source device, and may be configured so that hydrogen generated by electrolyzing the desorbed solution in the electrolysis section is utilized in the gas generation source device.

[0013] Furthermore, in the carbon dioxide recovery system, at least one of the carbon dioxide absorption treatment unit, the carbon dioxide desorption treatment unit, and the electrolysis unit may be configured as a microchannel device including a substrate on which a flow path is formed, and a lid provided on the substrate so as to cover the flow path.

[0014] In order to solve the above-mentioned problems, the carbon dioxide recovery method according to the present disclosure is a method for recovering carbon dioxide contained in a gas, comprising: a carbon dioxide absorption step of contacting the gas with an aqueous solution containing a hydroxide of an alkali metal or alkaline earth metal to obtain a post-absorption solution in which carbon dioxide has been absorbed as carbonate and / or bicarbonate; a carbon dioxide desorption step of adding an acid to the post-absorption solution to obtain a post-desorption solution in which carbon dioxide has been desorbed from the carbonate and / or bicarbonate, and recovering the carbon dioxide; and an electrolysis step of electrolyzing the desorption solution to obtain an acid produced at an anode and a hydroxide produced at a cathode, wherein the hydroxide produced in the electrolysis step is used in the carbon dioxide absorption step, and the acid produced in the electrolysis step is used in the carbon dioxide desorption step.

[0015] The carbon dioxide recovery system and recovery method disclosed herein have excellent effects, such as the ability to create a cycle in which the absorbent material, after absorbing carbon dioxide, can be regenerated at room temperature and used again to absorb carbon dioxide, and the absorbent material's ability to function as an absorbent material is unlikely to decrease even if it is repeatedly regenerated.

[0016] 5 is a block diagram showing a first example of a schematic configuration of a carbon dioxide capture system according to an embodiment of the present disclosure. FIG. 6 is a block diagram showing a second example of a schematic configuration of a carbon dioxide capture system according to an embodiment of the present disclosure. FIG. 7 is a schematic diagram showing an example of the configuration of a moisture amount adjuster having a function of removing moisture. FIG. 8 is a schematic diagram illustrating a case where the carbon dioxide absorption treatment unit according to the first embodiment has a spray device. FIG. 9 is a schematic diagram of a bubbling device suitable as a gas absorption device according to the first embodiment. FIG. 10 is a diagram showing the state of the bubbling device of FIG. 5 during operation. FIG. 11 is a schematic diagram of a state where the container of the bubbling device of FIG. 5 is attached to a base. FIG. 12 is a schematic diagram showing an example of a carbon dioxide desorption treatment unit according to the first embodiment. FIG. 13 is a schematic diagram showing an example of an electrolysis unit according to the first embodiment. FIG. 14 is a flowchart showing the process flow in a carbon dioxide absorption treatment unit according to a second embodiment. FIG. 15 is a flowchart showing the process flow in a carbon dioxide desorption treatment unit according to the second embodiment. FIG. 16 is a flowchart showing the process flow in an immobilization treatment unit according to the second embodiment. FIG. 17 is a perspective view schematically showing a carbon dioxide absorption treatment unit according to the second embodiment. FIG. 18 is a perspective view schematically showing a carbon dioxide desorption treatment unit according to the second embodiment. FIG. 19 is a schematic diagram showing an example of a gas-liquid separation treatment unit.

[0017] 1. Carbon dioxide capture system and capture method according to the present disclosure The carbon dioxide capture system and capture method according to the present disclosure are described below. The carbon dioxide capture system according to the present disclosure may be in the form of a carbon dioxide capture device including a carbon dioxide absorption treatment unit, a carbon dioxide desorption treatment unit, and an electrolysis unit, or may be in the form of a system in which the carbon dioxide absorption treatment unit alone functions as a carbon dioxide absorption treatment device, the carbon dioxide desorption treatment unit alone functions as a carbon dioxide desorption treatment device, and the electrolysis unit alone functions as an electrolysis device, and these devices work together to capture carbon dioxide. This also applies when the carbon dioxide capture system according to the present disclosure further includes an immobilization treatment unit.

[0018] FIG. 1 is a schematic diagram of a carbon dioxide (CO ) ion exchanger according to an embodiment of the present disclosure. ２1 is a block diagram showing a first example of the schematic configuration of a carbon dioxide recovery system, which is an example of a recovery system in which hydrogen generated in an electrolysis unit is used in a gas generation source device. As shown in FIG. 1, the carbon dioxide recovery system according to an embodiment of the present disclosure includes a carbon dioxide absorption treatment unit (CO ２ absorption treatment unit) 10 and carbon dioxide desorption treatment unit (CO ２ The carbon dioxide capture system according to the embodiment of the present disclosure includes a desorption processing unit (desorption treatment unit) 20 and an electrolysis unit 30. As in the example of FIG. 1 , the carbon dioxide capture system according to the embodiment of the present disclosure may be configured so that hydrogen generated in the electrolysis unit 30 is utilized in the gas generation source device 60. In this case, the carbon dioxide-containing gas to be captured is the gas generated from the gas generation source device 60.

[0019] The gas generation source device 60 is not particularly limited as long as it is a device that generates a gas containing carbon dioxide, but specific examples include combustion devices such as boilers and blast furnaces in combustion facilities that generate large amounts of carbon dioxide, such as thermal power plants and steel mills. That is, the carbon dioxide-containing gas to be recovered is typically exhaust gas (flue gas) generated by combustion.

[0020] 2 is a block diagram showing a second example of a schematic configuration of a carbon dioxide capture system according to an embodiment of the present disclosure. As shown in FIG. 2, the carbon dioxide capture system according to an embodiment of the present disclosure may include an immobilization treatment unit 40 that immobilizes the captured carbon dioxide.

[0021] 1 and 2, potassium hydroxide (KOH) is used as the "hydroxide of an alkali metal" and potassium bicarbonate (KHCO ) is used as the "post-absorption solution that has absorbed carbon dioxide" in order to facilitate understanding of the flow of the process performed in the carbon dioxide capture system according to the embodiment of the present disclosure. ３ ) is obtained, and sulfuric acid (H ２ SO ４ ) is used, and in the immobilization treatment unit 40, carbon dioxide is converted to methane (CH ４ 1 and 2 show examples of the carbon dioxide recovery system of the present disclosure, but the compounds applicable to the carbon dioxide recovery system of the present disclosure are not limited to these. Note that "aq" in Figures 1 and 2 means an aqueous solution.

[0022] Furthermore, the carbon dioxide capture method according to the embodiment of the present disclosure includes a carbon dioxide absorption step, a carbon dioxide desorption step, and an electrolysis step. The carbon dioxide absorption step is carried out in the carbon dioxide absorption treatment unit 10, the carbon dioxide desorption step is carried out in the carbon dioxide desorption treatment unit 20, and the electrolysis step is carried out in the electrolysis unit 30. When the carbon dioxide capture system according to the embodiment of the present disclosure includes the immobilization treatment unit 40, the immobilization treatment unit 40 carries out the immobilization step.

[0023] In the carbon dioxide absorption treatment unit 10 in the carbon dioxide recovery system according to an embodiment of the present disclosure, a gas is brought into contact with an aqueous solution containing a hydroxide of an alkali metal or alkaline earth metal to obtain a post-absorption solution in which carbon dioxide has been absorbed as carbonate and / or bicarbonate.

[0024] Examples of gases containing carbon dioxide to be recovered include exhaust gases produced by combustion in boilers, blast furnaces, etc., but are not limited to this. For example, the carbon dioxide to be recovered can also be carbon dioxide contained in the air.

[0025] An aqueous solution containing an alkali metal or alkaline earth metal hydroxide as an absorbent functions as a carbon dioxide absorbing solution. Therefore, hereinafter, the "aqueous solution containing an alkali metal or alkaline earth metal hydroxide" may also be simply referred to as the "absorption solution."

[0026] Alkali metals are Group 1 elements excluding hydrogen, such as sodium, potassium, and rubidium. Alkaline earth metals are Group 2 elements, such as magnesium, calcium, and strontium. In the carbon dioxide recovery system according to the embodiment of the present disclosure, potassium hydroxide, sodium hydroxide, or calcium hydroxide is preferably used as the hydroxide of an alkali metal or alkaline earth metal, with potassium hydroxide being more preferred. The reasons for this include: (1) its high carbon dioxide absorption capacity; (2) the carbonates and / or bicarbonates (potassium carbonate and / or potassium bicarbonate) produced by absorbing carbon dioxide have higher water solubility than other salts (especially sodium salts), making precipitation less likely to occur; and (3) potassium has higher ionic conductivity than other alkali metals such as sodium, making it advantageous for electrolysis. In particular, when the carbon dioxide absorption treatment unit 10 is configured as a microchannel device (e.g., in the case of the second embodiment described below), potassium hydroxide is preferred to avoid stagnation of the flow in the microchannel due to insoluble carbonates and / or bicarbonates.

[0027] The post-absorption solution obtained in the carbon dioxide absorption treatment unit 10 is an aqueous solution containing carbonate and / or bicarbonate. For example, when a potassium hydroxide aqueous solution is used as the absorbing solution, two types of products are generated by absorbing carbon dioxide: potassium carbonate and potassium bicarbonate. Since potassium bicarbonate is produced when the carbon dioxide absorption reaction is carried out to completion, the post-absorption solution is ideally an aqueous potassium bicarbonate solution, but in reality it is an aqueous solution containing potassium bicarbonate, potassium carbonate, and potassium hydroxide.

[0028] As in the first embodiment described below, the carbon dioxide absorption treatment unit 10 can have a configuration including a gas absorption device (gas absorption device) that brings gas and liquid (gas and liquid) into contact with each other, thereby absorbing at least some components of the gas into the liquid. Such a gas absorption device will be described in detail in the first embodiment. Furthermore, as a method for bringing the gas and the absorbing liquid into contact with each other, as in the second embodiment described below, a method may be used in which the gas and the absorbing liquid are supplied to a flow path and circulated through the flow path while being in contact with each other.

[0029] In the carbon dioxide desorption treatment unit 20 in the carbon dioxide capture system according to the embodiment of the present disclosure, an acid is added to the post-absorption solution obtained in the carbon dioxide absorption treatment unit 10 to obtain a post-desorption solution in which carbon dioxide has been desorbed from carbonates and / or hydrogencarbonates, and the carbon dioxide is recovered. Note that the form of adding the acid to the post-absorption solution may be a form in which an aqueous solution in which an acidic chemical substance is dissolved (i.e., an acidic solution) is added, or a form in which the acidic chemical substance itself is added.

[0030] Because this reaction of desorbing carbon dioxide occurs at room temperature, the carbon dioxide desorption step performed in the carbon dioxide desorption treatment unit 20 can be carried out at room temperature. In other words, it can be carried out with less energy (with less energy loss) than heat treatment at high temperatures of 800°C or higher, which is a conventional method of desorbing carbon dioxide from carbonates.

[0031] For example, when an aqueous solution of potassium hydroxide is used as the absorption liquid, potassium bicarbonate is produced by absorbing carbon dioxide, and sulfuric acid is added as an acid to the produced potassium bicarbonate. As shown in the following reaction formula (1), the alkali metal ions and sulfate ions bond preferentially, and carbon dioxide (carbonate ions) are released. ３ +H ２ SO ４ → K ２ SO ４ +2CO ２ ↑+2H ２ O... (1)

[0032] That is, the acid to be added to the post-absorption solution can be one that can desorb carbon dioxide (carbonate ions) as shown in reaction formula (1), i.e., an acid stronger than carbon dioxide (an acid with a large acid dissociation constant Ka, i.e., an acid with a small negative common logarithm pKa) can be used. Specific examples include sulfuric acid, phosphoric acid, nitric acid, and acetic acid. Among these, sulfuric acid or phosphoric acid is preferably used, and phosphoric acid is more preferably used, from the viewpoints of low volatility of the acid and high water solubility of the salt generated by the addition of the acid. Sulfuric acid has the advantage of being inexpensive, but phosphoric acid has the advantage of causing less damage to the electrodes used in the electrolysis unit 30 than sulfuric acid, thereby extending the cycle for replacing the electrodes.

[0033] Furthermore, when phosphoric acid is used as the acid added to the post-absorption solution, the number of moles of hydrogen generated in the electrolysis unit 30 per mole of phosphoric acid (unit amount of substance) added in the carbon dioxide desorption treatment unit 20 is large, and the carbon dioxide desorption performance per weight unit of phosphoric acid is high, so it is possible to more efficiently recover carbon dioxide in the carbon dioxide desorption treatment unit 20 and more efficiently recover hydrogen in the electrolysis unit 30. Note that when phosphoric acid is used as the acid, carbon dioxide (carbonate ions) are desorbed as shown in the following reaction formula (2). However, reaction formula (2) is an ideal reaction, and the post-desorption solution contains K ３ P.O. ４ Not only that, but K ２ HPO ４ , K.H. ２ P.O. ４ Intermediate products such as 3KHCO may also be included. ３ +H ３ P.O. ４ → K ３ P.O. ４ +3CO ２ ↑+3H ２ O... (2)

[0034] When hydrochloric acid is used as the acid added to the post-absorption solution, a post-desorption solution containing chlorides (e.g., potassium chloride when potassium hydroxide aqueous solution is used as the absorption solution) is obtained. When this post-desorption solution is electrolyzed in the electrolysis unit 30, chloride ions are oxidized at the anode, resulting in the desorption of chlorine gas. The generated chlorine gas can accelerate corrosion and deterioration of the electrolysis device in the electrolysis unit 30, and adding chloride resistance to the device increases the cost of the device. Furthermore, when chlorine gas is regenerated into hydrochloric acid, an additional step of dissolving the chlorine gas in water is required, which may increase the processing time and reduce the reaction yield in the regeneration process. Therefore, in the circulation in which the acid obtained in the electrolysis unit 30 is used in the carbon dioxide desorption treatment unit 20, not only does time efficiency decrease, but the amount of acid lost increases, making it impossible to achieve an efficient circulation.

[0035] In contrast, when sulfuric acid or phosphoric acid is used as the acid to be added to the post-absorption solution, sulfate ions or phosphate ions are not oxidized at the anode, and therefore these ions are not gasified and desorbed, and can be directly regenerated as sulfuric acid or phosphoric acid by a reaction at the anode of the electrolysis unit 30, which will be described later. In addition, sulfuric acid and phosphoric acid are non-volatile, making them suitable for forming a circulation system in which the acid obtained in the electrolysis unit 30 is utilized in the carbon dioxide desorption treatment unit 20.

[0036] The reason for performing the carbon dioxide desorption step (a step of adding acid to the post-absorption solution) in the carbon dioxide desorption treatment unit 20 is as follows: If an aqueous potassium hydroxide solution were used as the absorption solution and the post-absorption solution containing potassium bicarbonate and / or potassium carbonate were directly electrolyzed without performing the carbon dioxide desorption step, potassium hydroxide could be regenerated, but oxygen and carbon dioxide would simultaneously be generated at the anode during the electrolysis. In other words, there would be a problem in that a separate step of separating oxygen and carbon dioxide would be required.

[0037] In the electrolysis unit 30 in the carbon dioxide recovery system according to the embodiment of the present disclosure, the desorbed solution obtained in the carbon dioxide desorption treatment unit 20 is electrolyzed to obtain an acid produced at the anode and a hydroxide produced at the cathode. As will be described later, the system may also be configured to recover hydrogen produced at the cathode.

[0038] The post-desorption solution is an aqueous solution containing a salt of an alkali metal or alkaline earth metal derived from the absorption liquid and an acid added in the carbon dioxide desorption treatment unit 20. For example, when an aqueous potassium hydroxide solution is used as the absorption liquid and sulfuric acid is used as the acid, the post-desorption solution is an aqueous solution containing potassium sulfate, and when phosphoric acid is used as the acid, the post-desorption solution is an aqueous solution containing potassium phosphate. By providing an anode and a cathode in this post-desorption solution and applying a voltage, electrolysis of the post-desorption solution is performed. The reactions that occur at both electrodes when electrolyzing a post-desorption solution containing potassium sulfate or potassium phosphate are as shown in the following reaction formulas (3) and (4). Anode: H ２ O → 2H ＋ +1 / 2O ２ ↑+2e － ...(3) Cathode: 2H ２ O + 2e － → 2OH － +H ２ ↑ ... (4)

[0039] In this way, water is electrolyzed to generate hydrogen. Simultaneously, hydrogen ions are generated at the anode and hydroxide ions are generated at the cathode, resulting in an acid being obtained near the anode and a hydroxide being obtained near the cathode. That is, by performing electrolysis in the electrolysis unit 30, an acid and a hydroxide can be obtained from the desorption solution. For example, if the desorption solution is an aqueous solution containing potassium sulfate, potassium sulfate is converted into sulfuric acid and potassium hydroxide, and if the desorption solution is an aqueous solution containing potassium phosphate, potassium phosphate is converted into phosphoric acid and potassium hydroxide.

[0040] The carbon dioxide capture system according to an embodiment of the present disclosure includes a transport means for transporting the hydroxide obtained in the electrolysis unit 30 to the carbon dioxide absorption treatment unit 10, and a transport means for transporting the acid obtained in the electrolysis unit 30 to the carbon dioxide desorption treatment unit 20. These transport means may be a flow path connecting the source and destination of transport, or may be a transport means such as a vehicle or ship that can accommodate the transported item. The hydroxide transported to the carbon dioxide absorption treatment unit 10 is used as a carbon dioxide absorbent in the carbon dioxide absorption treatment unit 10. Furthermore, the acid transported to the carbon dioxide desorption treatment unit 20 is used as an acid to be added to the post-absorption solution in the carbon dioxide desorption treatment unit 20. In other words, the carbon dioxide capture system according to an embodiment of the present disclosure has a cycle in which the hydroxide used as a carbon dioxide absorbent in the carbon dioxide absorption treatment unit 10 and the acid used for carbon dioxide desorption treatment in the carbon dioxide desorption treatment unit 20 are regenerated in the electrolysis unit 30 and used again for carbon dioxide absorption and desorption.

[0041] Most of the electricity required for this circulation is electricity for producing hydrogen by electrolysis of water (electrolysis performed in the electrolysis unit 30). In other words, the carbon dioxide capture system according to an embodiment of the present disclosure simultaneously generates hydrogen and captures carbon dioxide, making it possible to capture carbon dioxide in gaseous form using almost only the electricity consumption required for hydrogen production. While much of the general technological development of water electrolysis for hydrogen production has focused on improving cost efficiency, and there has also been a trend toward establishing carbon dioxide capture as a standalone technology in the development of carbon dioxide capture technology, the present inventors have discovered a technical concept that combines carbon dioxide capture and hydrogen generation, and have completed the carbon dioxide capture system according to an embodiment of the present disclosure.

[0042] Incidentally, during this circulation, an increase or decrease in the amount of water, which is the solvent of the absorption solution, may cause the concentration of the absorbent (hydroxide of an alkali metal or alkaline earth metal) in the absorption solution to become higher or lower than expected. A decrease in the amount of water in the absorption solution occurs, for example, due to evaporation of water. Specifically, when the "gas containing carbon dioxide to be captured" is air, moisture migrates to the air side due to evaporation. An increase in the amount of water in the absorption solution occurs, for example, due to liquefaction of water vapor when the "gas containing carbon dioxide to be captured" is a gas containing a large amount of water vapor, such as exhaust gas from a boiler.

[0043] When the amount of water decreases and the concentration of carbonate and / or bicarbonate in the post-absorption solution reaches its solubility (concentration in a saturated solution), the carbonate and / or bicarbonate precipitate, resulting in a problem of a decrease in the carbon dioxide absorption efficiency in this circulation. Furthermore, when the amount of water increases, problems arise, such as overflow due to an increase in the liquid volumes of the absorption solution, post-absorption solution, and post-desorption solution, an increase in the size of the apparatus, and a decrease in the carbon dioxide absorption efficiency per volume of the apparatus (per volume of absorption solution).

[0044] Therefore, the carbon dioxide capture system according to the embodiment of the present disclosure may include a water content adjuster in addition to the carbon dioxide absorption treatment unit 10, the carbon dioxide desorption treatment unit 20, and the electrolysis unit 30. The water content adjuster is a means for increasing or decreasing the amount of water as a solvent in at least one of the circulating absorption liquid, the post-absorption solution, and the post-desorption solution. When increasing water, the water content adjuster is a means for adding water to compensate for the deficiency relative to the predetermined amount of absorption liquid. When decreasing water, the water content adjuster is a means for removing water in excess of the predetermined amount of absorption liquid from the absorption liquid (or the post-absorption solution or the post-desorption solution) by evaporating or introducing dry gas. The predetermined amount of absorption liquid here refers to, for example, a suitable amount of absorption liquid measured in advance. By including such a water content adjuster, the absorbent concentration in the absorption liquid can be maintained as expected even during long-term circulation. This ultimately enables a stable carbon dioxide capture system to be realized, capable of efficiently capturing carbon dioxide.

[0045] The water content adjusting unit may increase or decrease the amount of water as a solvent in at least one of the circulating absorption solution, the post-absorption solution, and the post-desorption solution, but it is preferable to adjust the water content of the post-absorption solution, among these. This prevents the concentration of carbonate and / or bicarbonate in the post-absorption solution from reaching its solubility, thereby suppressing the precipitation of carbonate and / or bicarbonate.

[0046] 1, the moisture amount adjusting unit is preferably provided between the gas generation source device 60 and the carbon dioxide absorption treatment unit 10. In this case, the moisture amount adjusting unit is provided mainly for the purpose of reducing the moisture contained in the gas generated from the gas generation source device 60.

[0047] 3 is a schematic diagram showing an example of the configuration of a moisture amount regulator having a moisture removal function, and shows an example configuration in which a moisture amount regulator 70 is provided between the gas generation source device 60 and the carbon dioxide absorption treatment unit 10. The gas generated from the gas generation source device 60 is typically exhaust gas (flue gas), and therefore contains a large amount of water vapor as well as fine particles such as sulfur oxides and nitrogen oxides, as described above.

[0048] 3, the moisture amount adjuster 70 includes a gas inlet channel 71 connected to the gas generation source device 60, a moisture collector 72 connected to the gas inlet channel 71 on the side opposite the gas generation source device 60, and a gas outlet channel 73 connecting the moisture collector 72 to the carbon dioxide absorption treatment unit 10. The moisture collector 72 is a container having an internal storage space 72c, and is provided with a gas inlet 72a and a gas outlet 72b, with the gas inlet 72a connected to the gas inlet channel 71 and the gas outlet channel 73 connected to the gas outlet 72b.

[0049] With this configuration, the gas generated from the gas generation source device 60 is cooled by the surrounding outside air as it passes through the gas inlet path 71, and moisture exceeding the saturated amount is trapped as condensed water 74 in the storage space 72c within the moisture collector 72. Then, the gas with the adjusted moisture content passes through the gas outlet path 73 and is supplied to the carbon dioxide absorption treatment unit 10.

[0050] Furthermore, in a configuration in which the exhaust gas discharged from the gas generation source device 60 flows into the gas inlet passage 71, the sulfur oxides and nitrogen oxides contained in the exhaust gas are contained in the condensed water 74. Since sulfur oxides and nitrogen oxides cause the electrodes of the electrolysis unit 30 to wear out more quickly, it is preferable to remove the sulfur oxides and nitrogen oxides contained in the exhaust gas, and by providing the moisture amount adjustment unit 70, it is possible to remove the sulfur oxides and nitrogen oxides contained in the exhaust gas.

[0051] The gas inlet channel 71 is preferably formed in a spiral shape. With such a configuration, the gas that has flowed into the gas inlet channel 71 can be sufficiently cooled and can be supplied to the carbon dioxide absorption treatment unit 10 with an appropriate moisture content.

[0052] The carbon dioxide capture system according to an embodiment of the present disclosure may be configured so that hydrogen generated by electrolysis in the electrolysis unit 30 is utilized in the gas generation source device 60. In this configuration, the hydrogen generated in the electrolysis unit 30 is immediately utilized as fuel for a boiler serving as the gas generation source device 60 in a thermal power plant or as a reducing agent (blast furnace reducing agent) for a blast furnace serving as the gas generation source device 60 in a steelworks, which is advantageous in terms of cost and safety compared to storing the recovered hydrogen separately. Consequently, a carbon dioxide capture system and capture method that are suitable for a circular economy and suitable for large combustion facilities such as thermal power plants and steelworks can be realized. Note that, when configured in this manner, the carbon dioxide capture system according to an embodiment of the present disclosure may include a hydrogen storage unit that temporarily stores the hydrogen recovered in the electrolysis unit 30.

[0053] Furthermore, the carbon dioxide capture system according to the embodiment of the present disclosure may further include an immobilization treatment unit 40 in addition to the carbon dioxide absorption treatment unit 10, the carbon dioxide desorption treatment unit 20, and the electrolysis unit 30 described above. The immobilization treatment unit 40 uses, as a raw material, hydrogen generated by electrolyzing the desorbed solution in the electrolysis unit 30, to immobilize the carbon dioxide captured in the carbon dioxide desorption treatment unit 20. By including the immobilization treatment unit 40 in the carbon dioxide capture system according to the embodiment of the present disclosure, the hydrogen generated in the electrolysis unit 30 can be immediately used within the capture system, which is advantageous in terms of cost and safety compared to separately storing the captured hydrogen.

[0054] When the carbon dioxide capture system according to the embodiment of the present disclosure is configured to include the immobilization treatment unit 40 in this manner, in order to be able to adjust the amounts and blending ratios of carbon dioxide and hydrogen introduced into the immobilization treatment unit 40, it is preferable that the system include a carbon dioxide storage unit that temporarily stores the carbon dioxide captured by the carbon dioxide desorption treatment unit 20, and a hydrogen storage unit that temporarily stores the hydrogen captured by the electrolysis unit 30.

[0055] Immobilization of carbon dioxide means converting carbon dioxide into another carbon compound, and the destination of carbon dioxide conversion in the immobilization treatment unit 40 is not particularly limited as long as hydrogen is used as a raw material, but examples of destinations include C1 compounds (compounds with one carbon atom) such as methane, methanol, and formic acid. All three of these exemplified compounds are useful and valuable destinations. In the immobilization treatment unit 40, for example, a mixed gas of carbon dioxide recovered in the carbon dioxide desorption treatment unit 20 and hydrogen generated in the electrolysis unit 30 is circulated as a raw material gas through a flow path equipped with a catalyst layer to synthesize C1 compounds.

[0056] For example, the reaction for synthesizing methane (methanation reaction) is a reversible reaction as shown in the following reaction formula (5). Therefore, the yield of methane can be increased by removing water vapor from the reaction system in order to shift the equilibrium to the product side. However, since unreacted gas remains even after removing water vapor, it is preferable to provide the immobilization treatment unit 40 with a mechanism for separating the raw material gas from the generated methane. Furthermore, since the reaction for synthesizing methane proceeds rapidly, it is preferable to have a mechanism for continuously circulating the raw material gas through the flow path to cause the reaction. Nickel can be used as a catalyst in the reaction for synthesizing methane, and for example, if the porous catalyst contains about 5 mass % of nickel based on the total mass, it will function as a catalyst. 4H ２ +CO ２ ←→ CH ４ +2H ２ O... (5)

[0057] The reaction for synthesizing methanol is also a reversible reaction, as shown in the following reaction formula (6). The resulting product, methanol, can be liquefied by cooling to about room temperature and separated from the raw material gas. Examples of catalysts used in the reaction for synthesizing methanol include Cu-Zn catalysts. 3H ２ +CO ２ ←→ CH ３ OH+H ２ O... (6)

[0058] The reaction for synthesizing formic acid is also a reversible reaction, as shown in the following reaction formula (7). As shown in this reaction formula, formic acid can be synthesized using only one molecule of hydrogen per molecule of carbon dioxide, so the amount of hydrogen required for synthesis is small, which is advantageous in terms of cost as a carbon dioxide immobilization treatment performed in the immobilization treatment unit 40. ２ +CO ２ ←→ HCOOH...(7)

[0059] 2. First Embodiment As a first embodiment, a carbon dioxide capture system and capture method according to the present disclosure will be described in detail using as an example a carbon dioxide capture system in which the carbon dioxide absorption treatment unit 10, the carbon dioxide desorption treatment unit 20, and the electrolysis unit 30 are each configured with devices that are not microchannel devices. This configuration makes it easy to increase the size of each device, and is therefore suitable for capturing carbon dioxide from gas (specifically, exhaust gas) generated in a gas generation source device 60 such as a boiler or blast furnace in a combustion facility such as a thermal power plant or steelworks.

[0060] <Carbon dioxide absorption treatment unit (carbon dioxide absorption step)> The carbon dioxide absorption treatment unit 10 can be configured to have a gas absorption device (gas absorption device) that brings gas and liquid (gas and liquid) into contact with each other to absorb at least some of the components in the gas into the liquid. Examples of such gas absorption devices include a spray device (spray tower), a bubbling device (bubble tower), and a filling device (packed tower). The gas absorption device included in the carbon dioxide absorption treatment unit 10 is not limited to one type, and different types of gas absorption devices may be combined (for example, a spray device and a bubbling device may be combined). When the "gas containing carbon dioxide to be recovered" is exhaust gas from the gas generation source device 60, the positive pressure of the exhaust gas can be used to supply the exhaust gas into the gas absorption device.

[0061] When the carbon dioxide absorption treatment unit 10 is configured to have a spray device, the absorption liquid is sprayed and dispersed into a container (empty tower) filled with a gas containing the carbon dioxide to be recovered, and the gas and liquid are brought into contact with each other, causing the carbon dioxide to be absorbed by the absorption liquid.

[0062] When the carbon dioxide absorption treatment unit 10 is configured to have a bubbling device, a gas containing the carbon dioxide to be recovered is blown into the absorption liquid contained in the container through a bubble generation unit having a member (such as a porous member) that can turn the gas into bubbles, and the gas and liquid are brought into contact, causing the carbon dioxide to be absorbed into the absorption liquid.

[0063] When the carbon dioxide absorption treatment unit 10 is configured to have a filling device, a gas containing carbon dioxide to be recovered is introduced into a container (empty tower) filled with filler from the bottom of the container, and the absorption liquid is dripped almost uniformly onto the filler inside the container, causing the carbon dioxide to be absorbed by the absorption liquid.

[0064] Fig. 4 is a schematic diagram illustrating a case where the carbon dioxide absorption treatment unit 10 has a spray device as a gas absorption device. As shown in Fig. 4, a container (container) that is the main body of the carbon dioxide absorption treatment unit 10 is provided with a spray nozzle 101 that sprays the absorption liquid L1 into the container. In the embodiment of the present disclosure, at least a part of the supply source of the absorption liquid L1 is the electrolysis unit 30, and new absorption liquid L1 may be supplied as needed.

[0065] When the absorption liquid L1 is sprayed from the spray nozzle 101 inside the container of the carbon dioxide absorption treatment unit 10, which is filled with gas containing carbon dioxide to be recovered, it comes into contact with the gas inside the container and absorbs the carbon dioxide. The post-absorption solution L2 that has absorbed the carbon dioxide is stored at the bottom of the container. The post-absorption solution L2 is transported to the carbon dioxide desorption treatment unit 20, and the gas from which the carbon dioxide has been removed is released, for example, into the atmosphere.

[0066] The method of transporting the post-absorption solution L2 to the carbon dioxide desorption treatment unit 20 is not particularly limited, and for example, a flow path may be provided connecting the carbon dioxide absorption treatment unit 10 and the carbon dioxide desorption treatment unit 20, and the post-absorption solution L2 may be transported through this flow path, or the post-absorption solution L2 may be transported by a transportation means such as a vehicle or ship that can accommodate the post-absorption solution L2.

[0067] Next, a bubbling device suitable as a gas absorption device included in the carbon dioxide absorption treatment unit 10 will be described with reference to Figures 5 to 7. Figure 5 is a schematic diagram of a bubbling device that turns gas into bubbles and introduces them, Figure 6 is a diagram showing the state of the bubbling device during operation, and Figure 7 is a schematic diagram of the state in which the container 111 of the bubbling device is attached to the base part 115.

[0068] As shown in FIGS. 5 to 7 , the carbon dioxide absorption treatment unit 10 includes a substantially cylindrical container 111 that contains the absorption liquid L1. The container 111 is formed of a transparent material (e.g., polypropylene) that is alkali-resistant. The container 111 is configured to be detachable from a base 115. An exhaust port 111e is provided at the top of the container 111, and an exhaust flow path 111f is connected to the exhaust port 111e. Gas inside the container 111 can be exhausted to the outside (atmosphere) through the exhaust flow path 111f. The container 111 may be configured so that the upper side is open.

[0069] A bubble generation unit is disposed at the bottom 111a of the container 111 for introducing gas containing carbon dioxide into the absorbing liquid L1 as fine bubbles. The bubble generation unit is composed of a gas inlet 111b provided at the bottom 111a of the container 111, a retention space 111d for the gas introduced from the gas inlet 111b, and a porous member 112 formed in a substantially circular plate shape. An introduction flow path 111c is connected to the gas inlet 111b. In this embodiment, gas can be introduced into the retention space 111d at the bottom 111a of the container 111 by an air pump 116 connected to the introduction flow path 111c.

[0070] The porous member 112 has a large number of small holes 112a formed therethrough in the vertical direction. Gas introduced into the retention space 111d in the bottom 111a of the container 111 passes through the small holes 112a, turning into fine bubbles 113b and being supplied to the absorption liquid L1. The small holes 112a are formed over substantially the entire surface of the porous member 112, and the fine bubbles 113b are generated substantially uniformly over substantially the entire surface (upper surface) of the porous member 112 that comes into contact with the absorption liquid L1. The porous member 112 can be made of a porous ceramic material.

[0071] The bubbles 113b generated on the surface of the porous member 112 separate from the surface of the porous member 112 and rise toward the liquid level 113a of the absorption liquid L1. As the bubbles 113b rise, they come into contact with the absorption liquid L1, and the carbon dioxide contained in the bubbles 113b (the introduced gas) is absorbed into the absorption liquid L1. The bubbles 113b that have reached the liquid level 113a remain at the liquid level 113a with the gas covered by a thin film of the absorption liquid L1. The size of the container 111 and the height of the liquid level 113a of the absorption liquid L1 may be set so that substantially all of the carbon dioxide contained in the bubbles 113b is absorbed into the absorption liquid L1 by the time the bubbles 113b move from the surface of the porous member 112 to the liquid level 113a.

[0072] The outer diameter of the porous member 112 is formed slightly smaller than the inner diameter of the container 111, and a seal member 112b is interposed between the outer peripheral surface of the porous member 112 and the inner peripheral surface of the bottom 111a of the container 111. This prevents gas from leaking from the retention space 111d between the outer peripheral surface of the porous member 112 and the inner peripheral surface of the bottom 111a of the container 111, thereby suppressing convection of air bubbles 113b in the absorption liquid L1.

[0073] It is preferable that the porous member 112 has a hydrophilic surface (upper surface) that comes into contact with the absorbing liquid L1 and a hydrophobic surface (lower surface) that faces the gas retention space 111d. As a result, the hydrophilic surface that comes into contact with the absorbing liquid L1 can contribute to the refinement of the gas bubbles 113b, and the hydrophobic surface that faces the gas retention space 111d can prevent the absorbing liquid L1 from leaking into the retention space 111d.

[0074] A defoamer 114, which is a solid (solid), is provided on the liquid surface 113a of the absorbing liquid L1 and in the vicinity of the liquid surface 113a. The defoamer 114 is either floating on the liquid surface 113a of the absorbing liquid L1 or dispersed in the liquid near the liquid surface 113a. The defoamer 114 forcibly bursts and defoams the air bubbles 113b on the liquid surface 113a of the absorbing liquid L1 and in the vicinity of the liquid surface 113a. By defoaming the air bubbles 113b with the defoamer 114, new air bubbles 113b can be sequentially sent toward the liquid surface 113a of the absorbing liquid L1. The surface of the defoamer 114 that comes into contact with the absorbing liquid L1 is hydrophobic. For example, hydrophobic PTFE (polytetrafluoroethylene) powder can be used as the defoamer 114.

[0075] The container 111 is detachably mounted on a base 115. The base 115 holds the container 111 containing the absorption liquid L1, and also introduces and exhausts gas into and from the container 111. A mounting portion 115a on which the container 111 is mounted is formed at the bottom of the base 115. The container 111 can be mounted on the mounting portion 115a in such a manner that, for example, a vertical portion 115b rising upward is integrally formed at one end of the mounting portion 115a, and a protrusion 111h extending in the vertical direction and formed on the side of the container 111 engages with a recess 115e formed in the vertical portion 115b.

[0076] An inlet flow path 115c and an outlet flow path 115d for gas are formed in the base part 115. The inlet flow path 115c includes an air pump 116 for sucking gas from the outside and a CO 2 detector for detecting the carbon dioxide concentration in the gas introduced into the housing 111. ２ The inlet flow path 115c is connected to an inlet flow path 111c formed in the protrusion 111h of the container 111, and a valve 118a capable of opening and closing the inlet flow paths 111c and 115c is provided midway between the inlet flow paths 111c and 115c. The exhaust flow path 115d is provided with a CO ２The discharge flow path 115d is connected to a discharge flow path 111f formed in the cover 111g of the container 111, and a valve 118b capable of opening and closing the discharge flow paths 111f and 115d is provided midway between the discharge flow paths 111f and 115d. ２ The sensors 117a and 117b may be, for example, NDIR sensors.

[0077] 7 shows an example of a small (tabletop) bubbling device, but by changing the size of the container 111 depending on the amount of carbon dioxide to be absorbed, it is possible to make a bubbling device suitable for the scale of the carbon dioxide capture system according to the present disclosure. Therefore, by making the container 111 larger, it is possible to make a bubbling device suitable for absorbing carbon dioxide contained in exhaust gas from gas generation source devices 60 such as boilers and blast furnaces in combustion facilities such as thermal power plants and steel mills.

[0078] In the example of Fig. 7, the capacity of the container 111 is 500 to 1000 mL, and the discharge rate of the air pump 116 is set to 5 to 15 L / min. By operating an on / off switch (not shown) provided on the base 115, the air pump 116 is activated to introduce air bubbles 113b into the absorbing liquid L1 in the container 111, and carbon dioxide is absorbed by the absorbing liquid L1. ２ By providing a display unit that displays the carbon dioxide concentration in the gas measured by the sensors 117a and 117b, it is possible to know that carbon dioxide has been absorbed by the absorbing liquid L1. Furthermore, by operating the on / off switch again, the air pump 116 is stopped, the introduction of air bubbles 113b into the absorbing liquid L1 in the container 111 is stopped, and the absorption of carbon dioxide by the absorbing liquid L1 is stopped.

[0079] When the gas bubbles 113b introduced into the absorbing liquid L1 by the bubble generating unit rise from the bottom 111a of the container 111, they come into contact with the absorbing liquid L1, causing the carbon dioxide contained in the gas bubbles 113b to be absorbed into the absorbing liquid L1. The gas bubbles 113b that have risen to the liquid surface 113a of the absorbing liquid L1 and / or near the liquid surface 113a are defoamed by the defoamer 114, so that new gas bubbles 113b can be sent one after another toward the liquid surface 113a of the absorbing liquid L1 by the bubble generating unit. This allows gas to be efficiently introduced into the absorbing liquid L1, and carbon dioxide to be efficiently absorbed by the absorbing liquid L1.

[0080] <Carbon dioxide desorption treatment unit (carbon dioxide desorption step)> The configuration of the device that the carbon dioxide desorption treatment unit 20 has is not particularly limited, and for example, it may be configured to separate carbon dioxide from the desorbed solution by applying a known gas-liquid separation device to the solution after acid is added to the post-absorption solution.

[0081] FIG. 8 is a schematic diagram showing an example of the carbon dioxide desorption treatment unit 20. In this example, a container 211, which is the main body of the carbon dioxide desorption treatment unit 20, is provided with an acid inlet 212, a carbon dioxide outlet 213, and a desorbed solution outlet 214. The container 211 contains the post-absorption solution L2 transported from the carbon dioxide absorption treatment unit 10. By adding acid to the post-absorption solution L2 through the acid inlet 212, carbon dioxide is desorbed from the post-absorption solution L2. The desorbed carbon dioxide is located in the upper part of the container 211 and can be extracted and recovered through the carbon dioxide outlet 213 provided at the top of the container 211. The desorbed solution can also be extracted from the desorbed solution outlet 214 provided at the bottom of the container 211. The extracted desorbed solution is transported to the electrolysis unit 30.

[0082] The method for transporting the desorbed solution to the electrolysis unit 30 is not particularly limited. For example, a flow path may be provided connecting the carbon dioxide desorption treatment unit 20 and the electrolysis unit 30, and the desorbed solution may be transported through this flow path, or the desorbed solution may be transported by a transportation means such as a vehicle or ship that can accommodate the desorbed solution.

[0083] <Electrolysis Unit (Electrolysis Step)> The configuration of the device included in the electrolysis unit 30 is not particularly limited, and any known electrolysis device may be used to perform electrolysis on the desorbed solution. Fig. 9 is a schematic diagram showing an example of the electrolysis unit 30, and in this example, the electrolysis unit 30 includes a container 311 that contains a solution. The solution contained in this container 311 may be the desorbed solution itself that has been transferred from the carbon dioxide desorption treatment unit 20, or may be the desorbed solution to which new water or other optional components have been added.

[0084] The storage space within the storage body 311 is divided by a separator portion 314 into an anode-side storage space 311a in which the anode 312 is provided and a cathode-side storage space 311b in which the cathode 313 is provided. The separator portion 314 includes a separator body 314a that has ion conductivity and suppresses permeation of solution and gas between the anode-side storage space 311a and the cathode-side storage space 311b. The separator body 314a is, for example, a diaphragm. Examples of the base material of the diaphragm include fluorine-containing polymers such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), and polyolefins such as polypropylene (PP) and polyethylene (PE). These base materials may be used alone or in combination of two or more. A commercially available ion exchange membrane may also be used as the separator body 314a. FIG. 9 shows an example in which an aqueous potassium hydroxide solution is used as the absorption liquid (i.e., the post-desorption solution contained in the container 311 contains potassium ions) and a cation exchange membrane is used as the separator body 314a. In this example, potassium ions migrate from the post-desorption solution L31 on the anode 312 side toward the post-desorption solution L32 on the cathode 313 side. Note that both L31 and L32 may be post-desorption solutions, or L31 may be the post-desorption solution and L32 may be pure water or an aqueous potassium hydroxide solution containing a lower potassium ion content than the post-desorption solution. Even in such a case, the migration of potassium ions as described above occurs, resulting in an acid being obtained near the anode 312 and a hydroxide (potassium hydroxide) being obtained near the cathode 313.

[0085] The electrodes (anode 312 and cathode 313) may be made of a conductive substrate having a catalyst layer formed on its surface. The conductive substrate may be selected from, for example, titanium, nickel, stainless steel, graphite, etc., and the catalyst layer may be selected from, for example, metals such as platinum, ruthenium, iridium, etc., and oxides thereof. These materials may be used alone or in combination of two or more. The electrodes may be flat, or may be made into a perforated shape such as a wire mesh or punched metal, or may be surface-treated to provide microscopic irregularities to increase the current density.

[0086] When a voltage is applied to the anode 312 and the cathode 313, oxygen is generated from the post-desorption solution L31 on the anode 312 side, and hydrogen is generated from the post-desorption solution L32 on the cathode 313 side, as shown in the above reaction formulas (3) and (4). In order to release or collect the oxygen generated on the anode 312 side to the outside (atmosphere), an oxygen outlet 315 is provided in the lid 311c that closes the upper side of the anode-side accommodation space 311a in the accommodation body 311. In addition, in order to collect the hydrogen generated on the cathode 313 side, a hydrogen outlet 316 is provided in the lid 311d that closes the upper side of the cathode-side accommodation space 311b in the accommodation body 311.

[0087] In the carbon dioxide recovery system according to the present disclosure, the hydrogen recovered from the hydrogen outlet 316 may be used in any manner, including transport to the gas generation source device 60 as shown in FIG. 1 , or transport to the immobilization treatment device 40 as shown in FIG. 2 . The method of transporting hydrogen is not particularly limited. For example, hydrogen may be transported via a flow path connecting the electrolysis unit 30 and the gas generation source device 60 (or the immobilization treatment device 40), or may be transported by a transportation means such as a vehicle or ship capable of accommodating hydrogen. A hydrogen storage unit (not shown) for temporarily storing hydrogen recovered in the electrolysis unit 30 may also be provided. That is, hydrogen may be temporarily stored in the hydrogen storage unit (e.g., a gas storage device or facility such as a pressure-resistant container) before, during, or after transport from the electrolysis unit 30 to the gas generation source device 60 (or the immobilization treatment device 40).

[0088] Furthermore, as described above, an acid is obtained near the anode 312, and a hydroxide is obtained near the cathode 313. The obtained acid is transported to the carbon dioxide desorption treatment unit 20, and the obtained hydroxide is transported to the carbon dioxide absorption treatment unit 10.

[0089] The method for transporting the acid to the carbon dioxide desorption treatment unit 20 and the method for transporting the hydroxide to the carbon dioxide absorption treatment unit 10 are not particularly limited, and for example, a flow path connecting the electrolysis unit 30 and the carbon dioxide desorption treatment unit 20, and a flow path connecting the electrolysis unit 30 and the carbon dioxide absorption treatment unit 10 may be provided, and the acid and hydroxide may be transported through these flow paths, or they may be transported by a transportation means such as a vehicle or ship that can accommodate the acid and hydroxide.

[0090] When the "gas containing carbon dioxide to be recovered" in the carbon dioxide absorption treatment unit 10 is exhaust gas from a gas generation source device 60 such as a boiler or blast furnace in a thermal power plant, steelworks, or the like, it is possible to increase the liquid temperature of the solution contained in the container 311 in the electrolysis unit 30 without using a heater by utilizing the heat source of the gas generation source device 60. By performing electrolysis in the electrolysis unit 30 with the liquid temperature at a high level, the current efficiency is increased, and the power cost in the electrolysis unit 30 can be further reduced.

[0091] 3. Second Embodiment In the carbon dioxide capture system according to the present disclosure, at least one of the carbon dioxide absorption treatment unit 10, the carbon dioxide desorption treatment unit 20, and the electrolysis unit 30 may be configured with a microchannel device. From the viewpoint of miniaturizing the carbon dioxide capture system, it is preferable to configure two or more of these units with microchannel devices, and it is more preferable to configure all three of these units with microchannel devices. Such a miniaturized carbon dioxide capture system is suitable for capturing carbon dioxide from the air.

[0092] Furthermore, in the case of a carbon dioxide recovery system configured with microchannel devices, it is preferable that a plurality of microchannel devices constituting the carbon dioxide absorption treatment unit 10, the carbon dioxide desorption treatment unit 20, and the electrolysis unit 30 are provided. Such a configuration can further improve the efficiency of each process in the carbon dioxide absorption treatment unit 10, the carbon dioxide desorption treatment unit 20, and the electrolysis unit 30. By providing a plurality of microchannel devices in parallel, it is possible to perform processes simultaneously on a plurality of lines, and by providing a plurality of microchannel devices in series, it is possible to perform processes continuously. For example, by providing a plurality of microchannel devices constituting the carbon dioxide absorption treatment unit 10 in parallel, it is possible to simultaneously treat a large number of gases (processing in which carbon dioxide contained in the gas is absorbed by the absorption liquid), and by providing a plurality of microchannel devices constituting the carbon dioxide absorption treatment unit 10 in series, it is possible to absorb a larger amount of carbon dioxide into the absorption liquid in a series of processes.

[0093] Therefore, as a second embodiment, a recovery system for recovering carbon dioxide from air, in which the carbon dioxide absorption treatment unit 10, the carbon dioxide desorption treatment unit 20, and the electrolysis unit 30 are configured as microchannel devices (in this example, a carbon dioxide recovery device in which the carbon dioxide absorption treatment unit 10, the carbon dioxide desorption treatment unit 20, and the electrolysis unit 30 are configured as microchannel devices), will be exemplified, and the carbon dioxide recovery system and recovery method according to the present disclosure will be described in detail. Note that in this example, carbon dioxide from air is recovered, but in the second embodiment, the carbon dioxide-containing gas to be recovered is not limited to air; for example, carbon dioxide may be recovered from gas (specifically, exhaust gas) generated by the gas generation source device 60.

[0094] In the present disclosure, a microchannel device includes a substrate on which a channel is formed and a lid provided on the substrate to cover the channel. Examples of materials for the substrate and the lid include glass and resin. Examples of groove widths for the channel in the microchannel device include 1 mm or less. In the second embodiment, quartz is used as the material for the substrate, and silicone rubber is used as the material for the lid. Alternatively, a configuration may be adopted in which multiple substrates on which channels are formed are stacked to cover the channel in the lower substrate, and a lid is provided to cover the channel in the uppermost substrate.

[0095] Furthermore, a flow path on the lid side may be provided on the surface of the lid facing the substrate so as to face the flow path formed on the substrate. That is, a flow path on the lid side may be provided on the surface of the lid facing the substrate at a position corresponding to the flow path formed on the substrate, thereby providing a flow path in which both the flow paths are integrated.

[0096] <Carbon dioxide absorption treatment unit (carbon dioxide absorption process)> Figure 10 is a flowchart showing the processing flow in the carbon dioxide absorption treatment unit 10 related to the second embodiment, and Figure 14 is a perspective view showing a schematic view of the carbon dioxide absorption treatment unit 10 related to the second embodiment.

[0097] 14, in the carbon dioxide absorption treater 10 according to the second embodiment, a carbon dioxide absorption treater main body 10A is configured as a microchannel device. The carbon dioxide absorption treater main body 10A includes a substrate 11 on which microchannels 11a to 11c are formed, and a lid 12 provided on the substrate 11 so as to cover the microchannels 11a to 11c. An air supply port 13 is provided at the upstream end of the microchannel 11a, so that air can be supplied to the microchannel 11a. An absorption liquid supply port 14 is provided at the upstream end of the microchannel 11b, so that absorption liquid can be supplied to the microchannel 11b.

[0098] In the carbon dioxide absorption treatment unit main body 10A, air (atmospheric air) is supplied from the air supply port 13 to the microchannel 11a (step S11), and the absorbing liquid sent from the electrolysis unit 30 is supplied from the absorbing liquid supply port 14 to the microchannel 11b (step S12). Note that not only the absorbing liquid (hydroxide produced by electrolysis) sent from the electrolysis unit 30 but also new absorbing liquid (absorbing liquid obtained outside the circulation of the carbon dioxide recovery system according to the second embodiment) may be introduced into the absorbing liquid supply port 14 as needed.

[0099] The carbon dioxide absorption treatment unit 10 according to the second embodiment includes an absorption liquid storage tank 17. The absorption liquid storage tank 17 is a tank for temporarily storing the absorption liquid sent from the electrolysis unit 30 and the post-absorption solution (the absorption liquid after absorbing carbon dioxide) sent from the carbon dioxide absorption treatment unit main body 10A. The electrolysis unit 30 and the absorption liquid storage tank 17 are connected by a flow path P1, and the absorption liquid sent from the electrolysis unit 30 flows through the flow path P1 and is stored in the absorption liquid storage tank 17. The absorption liquid storage tank 17 and the absorption liquid supply port 14 are connected by a flow path P2, and the absorption liquid stored in the absorption liquid storage tank 17 flows through the flow path P2 and is supplied to the absorption liquid supply port 14.

[0100] The microchannel 11c is a serpentine channel formed by the merging of the microchannels 11a and 11b. Therefore, in the microchannel 11c, the air supplied to the microchannel 11a and the absorbing liquid supplied to the microchannel 11b flow in a state of contact with each other (step S13), and carbon dioxide contained in the air is absorbed by the absorbing liquid.

[0101] An outlet 15 is provided at the downstream end of the microchannel 11c, and the outlet 15 is connected to the absorbent storage tank 17 via a channel P3. A pump 16 is provided in the middle of the channel P3, and the pump 16 applies back pressure to the microchannels 11a to 11c (reducing pressure from the outlet 15 side), causing the absorbent and air to flow in the flow direction F shown in FIG. 14 . By applying back pressure in this manner, a gas-liquid alternating flow (slug flow) is created in the microchannel 11c, allowing gas-liquid contact. Note that in this example, pressure is reduced from the outlet 15 side by the pump, but the absorbent and air may also be caused to flow in the flow direction F by applying pressure from the air supply port 13 and the absorbent supply port 14 side by a compressor or the like. Furthermore, the gas-liquid contact in the microchannel 11c may be contact by means other than the gas-liquid alternating flow, and may be contact by a flow of bubbles such as microbubbles.

[0102] When the absorbing liquid and air that have flowed through the microchannel 11c flow from the outlet 15 through the channel P3 and are sent to the absorbing liquid storage tank 17, the air and the absorbing liquid are separated in the tank (step S14), and the separated air is released into the atmosphere (step S15). The method for separating the air and the absorbing liquid is not limited to this, and for example, the air and the absorbing liquid may be separated by providing a gas-liquid separation treatment unit 50 (an apparatus exemplified in FIG. 16 ) midway along the channel P3 as in step S24 described below.

[0103] The absorbing liquid storage tank 17 sends the absorbing liquid again to the absorbing liquid supply port 14 until the absorbing liquid can sufficiently absorb carbon dioxide (step S16: No). Because the carbon dioxide concentration in the air is very low compared to the concentration of the absorbent (hydroxide of an alkali metal or alkaline earth metal) component in the absorbing liquid, the absorbing liquid cannot sufficiently absorb carbon dioxide by flowing through the microchannel 11c only once. Therefore, step S13 is repeated multiple times to obtain an absorbing liquid that has sufficiently absorbed carbon dioxide, i.e., a post-absorption solution. For example, the number of times that the absorbing liquid needs to flow through the microchannel 11c until it can sufficiently absorb carbon dioxide is measured in advance, a specified number of times to repeat step S13 is determined, and the post-absorption solution is obtained by repeating step S13 the specified number of times.

[0104] If the absorbing liquid has sufficiently absorbed carbon dioxide (step S16: Yes), the absorbing liquid storage tank 17 sends the post-absorption solution to the carbon dioxide desorption treatment unit 20 (step S17). The absorbing liquid storage tank 17 and the carbon dioxide desorption treatment unit 20 are connected by a flow path P4, and the post-absorption solution sent from the absorbing liquid storage tank 17 flows through the flow path P4 and reaches the carbon dioxide desorption treatment unit 20.

[0105] In the example of FIG. 14, the air supply port 13, the absorption liquid supply port 14, and the discharge port 15 are formed by passing stainless steel pipes through the cover body 12 made of silicone rubber, silicone tubes are used as the flow paths P1 to P4, and valves V are provided midway along the flow paths P1 and P4 to open and close the flow paths, but these configurations can be changed as appropriate.

[0106] <Carbon dioxide desorption treatment unit (carbon dioxide desorption step)> Fig. 11 is a flowchart showing the flow of treatment in the carbon dioxide desorption treatment unit 20 according to the second embodiment, and Fig. 15 is a perspective view schematically showing the carbon dioxide desorption treatment unit 20 according to the second embodiment. Fig. 16 is a schematic diagram showing an example of a gas-liquid separation treatment unit.

[0107] 15, in the carbon dioxide desorption processor 20 according to the second embodiment, a carbon dioxide desorption processor main body 20A is configured as a microchannel device. The carbon dioxide desorption processor main body 20A includes a substrate 21 on which microchannels 21a to 21c are formed, and a lid 22 provided on the substrate 21 so as to cover the microchannels 21a to 21c. A post-absorption solution supply port 23 is provided at the upstream end of the microchannel 21a, allowing post-absorption solution to be supplied to the microchannel 21a. An acidic solution supply port 24 is provided at the upstream end of the microchannel 21b, allowing an acidic solution (i.e., an aqueous solution containing acid) to be supplied to the microchannel 21b.

[0108] In the carbon dioxide desorption treatment unit main body 20A, the post-absorption solution sent from the carbon dioxide absorption treatment unit 10 is supplied from the post-absorption solution supply port 23 to the microchannel 21a (step S21), and the acidic liquid sent from the electrolysis unit 30 is supplied from the acidic liquid supply port 24 to the microchannel 21b (step S22). Note that not only the acidic liquid sent from the electrolysis unit 30 but also a new acidic liquid (an acidic liquid obtained outside the circulation of the carbon dioxide recovery system according to the second embodiment) may be introduced into the acidic liquid supply port 24 as needed.

[0109] The carbon dioxide desorption treatment unit 20 according to the second embodiment includes an acidic liquid storage tank 26. The acidic liquid storage tank 26 is a tank for temporarily storing the acidic liquid (acid produced by electrolysis) sent from the electrolysis unit 30. When the amount of acidic liquid stored in the acidic liquid storage tank 26 decreases, new acidic liquid may be added to the acidic liquid storage tank 26. The acidic liquid storage tank 26 and the acidic liquid supply port 24 are connected by a flow path P5, and the acidic liquid sent from the acidic liquid storage tank 26 flows through the flow path P5 and is supplied to the acidic liquid supply port 24.

[0110] The microchannel 21c is a serpentine channel where the microchannels 21a and 21b converge. Therefore, the post-absorption solution supplied to the microchannel 21a and the acidic solution supplied to the microchannel 21b converge and flow through the microchannel 21c, resulting in mixing of the post-absorption solution and the acidic solution (step S23). Mixing the post-absorption solution and the acidic solution results in a desorption solution in which carbon dioxide is desorbed from the carbonates and / or bicarbonates contained in the post-absorption solution, as described above. This desorption solution is an aqueous solution containing the acid contained in the acidic solution and a salt of an alkali metal or alkaline earth metal (see, for example, the above-described reaction formulas (1) and (2)). The desorption solution and carbon dioxide flow through the microchannel 21c and are discharged from an outlet 25 provided at the downstream end of the microchannel 21c.

[0111] The carbon dioxide desorption processor 20 according to the second embodiment includes a gas-liquid separation processor 50. The outlet 25 and the gas-liquid separation processor 50 are connected by a flow path P6, and the desorbed solution and carbon dioxide discharged from the outlet 25 flow through the flow path P6 and are supplied to the gas-liquid separation processor 50. The gas-liquid separation processor 50 separates the carbon dioxide generated in step S23 from the desorbed solution (step S24). The configuration of the gas-liquid separation processor 50 is not particularly limited, but gas-liquid separation can be performed, for example, using the configuration shown in FIG. 16. In the configuration shown in FIG. 16, the desorbed solution and carbon dioxide sent from the carbon dioxide desorption processor 20 pass through the flow path P6 and are stored in a container, which is the main body of the gas-liquid separation processor 50. Since the desorbed solution (L3 shown in FIG. 16) is located at the bottom of the container and the carbon dioxide is located at the top of the container, carbon dioxide is discharged from a flow path (gas discharge flow path) P7 provided at the top of the container, and the desorbed solution is discharged from a flow path (liquid discharge flow path) P8 provided at the bottom of the container. By recovering the carbon dioxide discharged from flow path P7, the system according to the second embodiment functions as a carbon dioxide recovery system. In this example, in order to immobilize the recovered carbon dioxide, the carbon dioxide discharged from flow path P7 is sent to the immobilization treatment unit 40 (step S25). In addition, the desorbed solution discharged from flow path P8 is sent to the electrolysis unit 30 (step S26).

[0112] In the example of Figure 15, the post-absorption solution supply port 23, acidic solution supply port 24, and discharge port 25 are formed by passing stainless steel pipes through a silicone rubber lid 22, and silicone tubes are used as flow paths P4 to P8, but these configurations can be changed as appropriate.

[0113] <Electrolysis Unit (Electrolysis Process)> FIG. 12 is a flowchart showing the flow of processing in the electrolysis unit 30 according to the second embodiment, and FIG. 17 is a perspective view showing a schematic view of the electrolysis unit 30 according to the second embodiment.

[0114] 17, the electrolysis unit 30 according to the second embodiment has an electrolysis unit main body 30A configured as a microchannel device. The electrolysis unit main body 30A includes a substrate 31 on which microchannels 31a to 31f are formed, and a lid 32 provided on the substrate 31 so as to cover the microchannels 31a to 31f. A post-desorption solution supply port 33 is provided at the upstream end of the microchannel 31a, enabling the post-desorption solution to be supplied to the microchannel 31a.

[0115] The microchannel 31a branches into microchannels 31b and 31c on the downstream side. An anode 34 is provided midway through the microchannel 31b, and a cathode 35 is provided midway through the microchannel 31c. The anode 34 has a structure in which a thin-film electrode is provided within the microchannel 31b, and the cathode 35 has a structure in which a thin-film electrode is provided within the microchannel 31c. By applying a voltage to these two thin-film electrodes, they function as an anode and a cathode, respectively. The voltage to be applied is not particularly limited, but is, for example, about 2V to 3V.

[0116] The anode 34 portion of the microchannel 31b and the cathode 35 portion of the microchannel 31c are connected by a microchannel 31d, so that the microchannels 31b to 31d function as electrolytic cells for electrolysis.

[0117] In the electrolysis unit 30, the desorption solution sent from the carbon dioxide desorption treatment unit 20 and new water to be used for electrolysis are supplied to the microchannel 31a from the desorption solution supply port 33 (steps S31 and S32). The desorption solution and new water supplied to the microchannel 31a are branched and flow into the microchannels 31b and 31c, and also flow into the microchannel 31d. In this state, electrolysis is performed by applying a voltage to the anode 34 and the cathode 35 (step S33). As a result, electrolysis of water occurs as shown in the above-mentioned reaction formulas (3) and (4), and oxygen (O ２ ) is generated at the cathode 35, and hydrogen (H ２At the same time, hydrogen ions are generated at the anode 34 and hydroxide ions are generated at the cathode 35, so that an acid is obtained near the anode 34 and a hydroxide is obtained near the cathode 35.

[0118] In the electrolysis unit main body 30A, a microchannel 31e is connected to the microchannel 31b on the downstream side of the anode 34, and an anode-side outlet 36 is provided at the downstream end of the microchannel 31e. Oxygen and acid generated near the anode 34 flow into the microchannel 31e, and the oxygen and acidic solution are discharged from the anode-side outlet 36.

[0119] The oxygen and acidic liquid discharged from the anode-side outlet 36 flow through a flow path P9 connected to the anode-side outlet 36 and are supplied to a gas-liquid separation processor 50A. This gas-liquid separation processor 50A can have the same configuration as the gas-liquid separation processor 50 described above. The gas-liquid separation processor 50A separates the oxygen from the acidic liquid (step S34). The separated oxygen flows through a flow path P11 connected to the gas-liquid separation processor 50A and is recovered or released into the atmosphere (step S36). The separated acidic liquid flows through a flow path P10 connected to the gas-liquid separation processor 50A and is supplied to the acidic liquid storage tank 26 of the carbon dioxide desorption processor 20 (step S37).

[0120] In the electrolysis unit main body 30A, a microchannel 31f is connected to the microchannel 31d downstream of the cathode 35, and a cathode-side outlet 37 is provided at the downstream end of the microchannel 31f. Hydrogen and hydroxide generated near the cathode 35 flow into the microchannel 31f, and hydrogen and an absorbing solution (aqueous solution containing hydroxide) are discharged from the cathode-side outlet 37.

[0121] The hydrogen and absorbing liquid discharged from the cathode-side outlet 37 flow through a flow path P12 connected to the cathode-side outlet 37 and are supplied to a gas-liquid separation treatment unit 50B. This gas-liquid separation treatment unit 50B can have the same configuration as the gas-liquid separation treatment unit 50 described above. The gas-liquid separation treatment unit 50B separates the hydrogen from the absorbing liquid (step S35). The separated absorbing liquid flows through a flow path P1 connected to the gas-liquid separation treatment unit 50B and is supplied to the absorbing liquid storage tank 17 of the carbon dioxide absorption treatment unit 10 (step S38). The separated hydrogen flows through a flow path P13 connected to the gas-liquid separation treatment unit 50B and is recovered, and in this example, is sent to the immobilization treatment unit 40 (step S39).

[0122] In the example of FIG. 17 , the post-desorption solution supply port 33, the anode-side discharge port 36, and the cathode-side discharge port 37 are formed by passing stainless steel pipes through the lid 32 made of silicone rubber, and silicone tubes are used as the flow paths P8 to P13, but these configurations can be changed as appropriate.

[0123] <Immobilization Processing Unit 40 (Immobilization Step)> In the second embodiment, methane synthesis is carried out in the immobilization processing unit 40. Fig. 13 is a flowchart showing the flow of processing in the immobilization processing unit 40 according to the second embodiment.

[0124] The immobilization unit 40 includes a catalyst layer and a catalyst layer heater. In this example, a porous catalyst containing approximately 5% by mass of nickel is used as the catalyst layer. In the immobilization unit 40, the catalyst layer heater is first turned on to heat the catalyst layer (step S41). A mixed gas containing carbon dioxide recovered in the carbon dioxide desorption unit 20 and hydrogen recovered in the electrolysis unit 30 is circulated as a raw material through the catalyst layer, and the methanation reaction shown in the aforementioned reaction formula (5) is carried out (step S42).

[0125] The carbon dioxide recovery system according to the second embodiment may further include an auxiliary electrolysis unit 90. If the proportion of hydrogen in the raw material in step S42 is low, the proportion of carbon dioxide and hydrogen in the raw material may be optimized by adding hydrogen generated by electrolysis in this auxiliary electrolysis unit 90 to the raw material in step S42.

[0126] Next, the immobilization treatment unit 40 separates the product methane from the unreacted raw material (step S43). The unreacted raw material is returned to the catalyst layer and used again as a reactant in the methanation reaction, and the product methane is recovered (step S44).

[0127] In other words, the carbon dioxide recovery system according to the second embodiment is equipped with an immobilization treatment unit 40, and is therefore able to use the hydrogen generated by electrolysis in the electrolysis unit 30 as a raw material to immobilize the carbon dioxide recovered in the carbon dioxide desorption treatment unit 20.

[0128] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be defined based on the claims. Furthermore, all modifications within the scope and meaning equivalent to the claims are included.

[0129] For example, in the carbon dioxide capture system according to the embodiment of the present disclosure, the carbon dioxide absorption treatment unit 10, the carbon dioxide desorption treatment unit 20, the electrolysis unit 30, and the immobilization treatment unit 40 may each have a plurality of corresponding devices. By providing the devices in parallel, processing can be performed simultaneously on a plurality of lines, and by providing the devices in series, processing can be performed continuously.

[0130] DESCRIPTION OF SYMBOLS 10 Carbon dioxide absorption treatment unit 11 Substrate 11a to 11c Microchannel 12 Lid 20 Carbon dioxide desorption treatment unit 21 Substrate 21a to 21c Microchannel 22 Lid 30 Electrolysis unit 31 Substrate 31a to 31f Microchannel 32 Lid 312 Anode (first embodiment) 313 Cathode (first embodiment) 34 Anode (second embodiment) 35 Cathode (second embodiment) 40 Immobilization treatment unit 60 Gas generation source device L1 Absorption liquid (aqueous solution containing hydroxide of alkali metal or alkaline earth metal) L2 Post-absorption solution L3 Post-desorption solution L31 Post-desorption solution on the anode side L32 Post-desorption solution on the cathode side

Claims

1. A system for recovering carbon dioxide contained in a gas, comprising: a carbon dioxide absorption treatment section that brings the gas into contact with an aqueous solution containing a hydroxide of an alkali metal or alkaline earth metal to obtain a post-absorption solution in which carbon dioxide has been absorbed as carbonate and / or bicarbonate; a carbon dioxide desorption treatment section that adds an acid to the post-absorption solution to obtain a post-desorption solution in which carbon dioxide has been desorbed from the carbonate and / or bicarbonate, and recovers the carbon dioxide; and an electrolysis section that electrolyzes the post-desorption solution to obtain an acid produced at an anode and a hydroxide produced at a cathode, wherein the hydroxide produced in the electrolysis section is used in the carbon dioxide absorption treatment section, and the acid produced in the electrolysis section is used in the carbon dioxide desorption treatment section.

2. A carbon dioxide recovery system as described in claim 1, characterized in that it comprises a transport means for transporting the hydroxide obtained in the electrolysis section to the carbon dioxide absorption treatment section, and a transport means for transporting the acid obtained in the electrolysis section to the carbon dioxide desorption treatment section.

3. A carbon dioxide recovery system as claimed in claim 1 or claim 2, further comprising an immobilization treatment unit that immobilizes the carbon dioxide recovered in the carbon dioxide desorption treatment unit, wherein the immobilization of carbon dioxide in the immobilization treatment unit is carried out using hydrogen generated by electrolyzing the desorbed solution in the electrolysis unit as a raw material.

4. A carbon dioxide recovery system as described in claim 1 or claim 2, characterized in that the carbon dioxide absorption treatment unit has a bubbling device that bubbles the gas and introduces it into an aqueous solution containing a hydroxide of an alkali metal or alkaline earth metal.

5. A carbon dioxide recovery system as claimed in claim 1 or claim 2, characterized in that the recovery system recovers carbon dioxide contained in gas discharged from a gas generation source device, and hydrogen generated by electrolyzing the desorbed solution in the electrolysis section is utilized in the gas generation source device.

6. A carbon dioxide recovery system as described in claim 1 or claim 2, characterized in that at least one of the carbon dioxide absorption processing unit, the carbon dioxide desorption processing unit and the electrolysis unit is composed of a microchannel device having a substrate on which a flow path is formed and a lid provided on the substrate so as to cover the flow path.

7. A method for recovering carbon dioxide contained in a gas, comprising: a carbon dioxide absorption step of contacting the gas with an aqueous solution containing a hydroxide of an alkali metal or alkaline earth metal to obtain a post-absorption solution in which carbon dioxide has been absorbed as carbonate and / or bicarbonate; a carbon dioxide desorption step of adding an acid to the post-absorption solution to obtain a post-desorption solution in which carbon dioxide has been desorbed from the carbonate and / or bicarbonate, and recovering the carbon dioxide; and an electrolysis step of electrolyzing the desorption solution to obtain an acid produced at an anode and a hydroxide produced at a cathode, wherein the hydroxide produced in the electrolysis step is used in the carbon dioxide absorption step, and the acid produced in the electrolysis step is used in the carbon dioxide desorption step.

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