CO2 capture system

Abstract

This system provides a CO2 recovery system that can achieve high purity of the target product. [Solution] A CO2 recovery system that recovers CO2 by contacting a reaction solution containing NaOH stored in a reaction vessel with a CO2-containing gas to produce a target product, wherein the target product extracted from the reaction solution is adjusted according to the maximum temperature of the reaction solution after the production of NaHCO3, the extraction temperature of the target product, and the initial concentration of NaOH in the reaction solution, the target product being an aqueous solution of sodium sesquicarbonate, the maximum temperature of the reaction solution after the production of NaHCO3 being less than 65°C, the extraction temperature being between 0°C and 40°C, and the initial concentration of NaOH being greater than 0% and less than or equal to the concentration of NaOH required to produce saturated solubility Na2CO3 at the extraction temperature, derived based on the relationship between the temperature of the reaction solution and the NaOH concentration required to produce saturated solubility Na2CO3.

Description

Technical Field

[0001] The present disclosure relates to a CO2 recovery system.

Background Art

[0002] In recent years, it has been required to suppress the emission of CO2 gas as a greenhouse gas, and various methods for recovering CO2 gas have been studied. As a method for recovering CO2, for example, there is a method in which CO2 is chemically absorbed into an amine solution and recovered. However, since the amine solution that has absorbed CO2 cannot be used as a resource, separation of CO2 is required. And for the separation of CO2, it is necessary to raise the temperature, which causes energy loss. In addition, there is a method in which CO2 is physically adsorbed onto zeolite and recovered. However, since it is necessary to apply pressure and heat during adsorption, energy loss is caused, and the zeolite on which CO2 is adsorbed cannot be used as a resource, and separation of CO2 is required.

[0003] Furthermore, as a method for recovering CO2, there is a method in which CO2 is chemically absorbed into an alkaline solution such as NaOH and recovered. For example, in the configuration disclosed in Patent Document 1, CO2 generated in L-glutamic acid fermentation is aerated into an aqueous NaOH solution to generate NaHCO3 or Na2CO3, thereby fixing and recovering CO2. Also, in the configuration disclosed in Patent Document 2, exhaust gas from a power plant, chemical plant, etc. is brought into contact with an aqueous NaOH solution to generate NaHCO3 or Na2CO3 and recover CO2 from the exhaust gas. All of these products are useful as resources, and the recovered CO2 can be effectively reused without separating CO2. Also, even when separating CO2, citric acid may be added to the product aqueous solution, and since it is not necessary to raise the temperature, energy loss can be reduced.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] To more effectively utilize NaHCO3 and Na2CO3 as resources, improved purity is required. However, in the configurations disclosed in Patent Documents 1 and 2, the proportion of products changes depending on the CO2 concentration in the CO2-containing gas and the reaction time, making it difficult to differentiate between products and resulting in a tendency for the purity of the obtained products to decrease. Therefore, there is room for improvement in order to differentiate between products and increase their purity.

[0006] This disclosure aims to provide a CO2 recovery system that can achieve high purity of the target product. [Means for solving the problem]

[0007] One aspect of the present disclosure is a CO2 recovery system that recovers CO2 by contacting a reaction solution containing NaOH stored in a reaction vessel with a CO2-containing gas to produce a target product, The target product removed from the reaction solution is adjusted according to the highest temperature of the reaction solution after the formation of NaHCO3, the removal temperature (the temperature of the reaction solution when the target product is removed from the reaction vessel), and the initial concentration of NaOH in the reaction solution. The target product described above is an aqueous solution of sodium sesquicarbonate. The maximum temperature of the reaction solution after the formation of NaHCO3 is less than 65°C. The above extraction temperature is between 0°C and 40°C. The initial concentration of NaOH described above is derived from the relationship between the temperature of the reaction solution and the NaOH concentration required to produce saturated Na2CO3, and is less than or equal to the NaOH concentration required to produce saturated Na2CO3 at the extraction temperature, and greater than 0% in the CO2 recovery system.

[0008] Another aspect of the present disclosure is a CO2 recovery system that recovers CO2 by contacting a reaction solution containing NaOH stored in a reaction vessel with a CO2-containing gas to produce a predetermined target product, The maximum temperature of the reaction solution after the formation of NaHCO3 is determined according to the target product to be removed from the reaction solution. The initial concentration of NaOH in the reaction solution is determined based on the target product removed from the reaction solution and the removal temperature, which is the temperature of the reaction solution when the target product is removed from the reaction vessel. The target product described above is an aqueous solution of sodium sesquicarbonate. The maximum temperature of the reaction solution after the formation of NaHCO3 is less than 65°C. The above extraction temperature is between 0°C and 40°C. The initial concentration of NaOH described above is derived from the relationship between the temperature of the reaction solution and the NaOH concentration required to produce saturated Na2CO3, and is less than or equal to the NaOH concentration required to produce saturated Na2CO3 at the extraction temperature, and greater than 0% in the CO2 recovery system. [Effects of the Invention]

[0009] According to the CO2 recovery system of the above embodiment, the target product extracted from the reaction solution can be adjusted by adjusting the maximum temperature of the reaction solution after the generation of NaHCO3 in the reaction solution, the extraction temperature which is the temperature of the reaction solution when the target product, an aqueous solution of sodium sesquicarbonate, is extracted from the reaction vessel, and the initial concentration of NaOH in the reaction solution. This makes it easy to differentiate between products and to extract the target product, an aqueous solution of sodium sesquicarbonate, in high purity.

[0010] Also, according to the CO2 recovery system of the above other embodiment, the maximum temperature of the reaction solution after the formation of NaHCO3 is defined according to the aqueous sodium sesquicarbonate solution which is the target product, and the initial concentration of NaOH in the reaction solution is defined based on the aqueous sodium sesquicarbonate solution which is the target product and the extraction temperature. Thereby, it is possible to obtain a CO2 recovery system suitable for obtaining an aqueous sodium sesquicarbonate solution which is a predetermined target product with high purity.

[0011] As described above, according to the above embodiment, it is possible to provide a CO2 recovery system capable of purifying the target product to a high purity.

[0012] Note that the reference numerals in parentheses described in the claims indicate the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of the present disclosure.

Brief Description of Drawings

[0013] [Figure 1] Conceptual diagram showing the configuration of the CO2 recovery system in Embodiment 1. [Figure 2] Diagram showing a linear approximation formula for temperature (liquid temperature) and the NaOH concentration required to generate the saturated solubility of NaHCO3. [Figure 3] Conceptual diagram showing the correspondence between the initial NaOH concentration and the target product in Embodiment 1. [Figure 4] Diagram showing a linear approximation formula for temperature (liquid temperature) and the NaOH concentration required to generate the saturated solubility of Na2CO3. [Figure 5] Conceptual diagram showing the correspondence between the initial NaOH concentration and the target product in Embodiment 2. [Figure 6] Conceptual diagram showing the correspondence between the initial NaOH concentration and the target product in Embodiment 3. [Figure 7] Conceptual diagram showing the correspondence between the initial NaOH concentration and the target product in Embodiment 4. [Figure 8] Conceptual diagram showing the correspondence between the initial NaOH concentration and the target product in Embodiment 5. [Figure 9]Conceptual diagram showing the configuration of the CO₂ recovery system in Embodiment 6. [Figure 10] Conceptual diagram showing the correspondence between the initial concentration of NaOH and the target product.

Mode for Carrying Out the Invention

[0014] (Embodiment 1) Embodiment 1 of the CO₂ recovery system will be described using FIGS. 1 to 3.

[0015] 1-1. Target Product In the CO₂ recovery system 1, the target product produced by bringing a CO₂-containing gas into contact with a reaction solution containing NaOH can be an aqueous solution or solid of NaHCO₃, an aqueous solution or solid of Na₂CO₃, or an aqueous solution or solid of sesquicarbonate of soda, which is a mixture of NaHCO₃ and Na₂CO₃. In this Embodiment 1, the target product is an aqueous solution of NaHCO₃.

[0016] 1-2. CO₂-Containing Gas As shown in FIG. 1, the CO₂ recovery system 1 of this embodiment is configured to recover CO₂ from the exhaust gas, which is a CO₂-containing gas discharged from the CO₂ emission facility 100. In this specification, the "CO₂-containing gas" refers to a gas containing CO₂ as a constituent component. The CO₂-containing gas may be a gas containing only CO₂ as a constituent component, or may be a gas containing inevitable impurities. Further, the CO₂-containing gas may be a mixed gas in which CO₂ and other substances are mixed. The ratio of CO₂ in the mixed gas is not limited, and the main component having the largest ratio in the mixed gas may be CO₂ or a substance other than CO₂.

[0017] 1-3. CO₂ Emission Facility 100 The CO2 emission equipment 100 shown in Figure 1 is not particularly limited as long as it is equipment that emits CO2-containing gas, and examples include equipment with a boiler, fuel cell, incinerator, and heat treatment equipment. An exhaust duct 20 is connected to the CO2 emission equipment 100, and exhaust gas G0, which is CO2-containing gas, is discharged through the exhaust duct 20. The temperature of the exhaust gas G0 discharged from the CO2 emission equipment 100 is not particularly limited, but it is preferably high, for example, it can have a temperature in the range of 100°C to 300°C, and in this embodiment, the exhaust gas G0 discharged from the CO2 emission equipment 100 has a temperature of 140°C.

[0018] 1-4. CO2 Capture System 1 The CO2 recovery system 1 of this embodiment mainly comprises a CO2 recovery device 10, a gas flow path 21, a moisture removal filter 30, an air pump 40, a liquid temperature control device 50, and a filter 60. Each component will be described below.

[0019] 1-5. Gas flow path 21 The gas passage 21 carries CO2-containing gas. In this embodiment 1, the gas passage 21 is formed by piping connected to an exhaust duct 20 that is connected to a CO2 emission facility 100. A portion of the exhaust gas G0, which is CO2-containing gas flowing through the exhaust duct 20, flows through the gas passage 21.

[0020] In this embodiment 1, considering that if the amount of CO2-containing gas bubbling in the reaction vessel 11, which will be described later, is too large, it will be difficult to form fine bubbles in the reaction liquid, the system is configured such that only a portion of the exhaust gas G0 discharged from the CO2 emission equipment 100 is circulated through the gas flow path 21, and the remaining exhaust gas that is not circulated through the gas flow path 21 is released to the outside via the exhaust duct 20.

[0021] 1-6. Moisture removal filter 30 The moisture removal filter 30 is installed in the gas passage 21 and removes moisture from the CO2-containing gas flowing through the gas passage 21. The moisture removal filter 30, although not shown, is composed of a water separator comprising a moisture separation section that separates water vapor contained in the CO2-containing gas as a liquid, and a gas passage section through which the CO2-containing gas, from which the water vapor has been separated and removed, passes. The separated moisture is stored in a tank (not shown) and discharged as needed. The exhaust gas that has passed through the gas passage section is discharged into a pipe 31 that communicates with the air pump 40, which will be described later. By removing water with the moisture removal filter 30, water is prevented from accumulating in the downstream air pump 40.

[0022] 1-7. Air pump 40 The air pump 40 is connected to the moisture removal filter 30 via piping 31 and is configured to draw in CO2-containing gas. The suction from the air pump 40 causes a portion of the exhaust gas from the exhaust duct 20 to flow into the gas flow path 21. The drawn-in CO2-containing gas is supplied to the reaction vessel 11, described later, via piping 41. While the configuration of the air pump 40 is not limited, it is preferable to use a diaphragm-type pump where the gas does not directly contact the drive unit of the air pump 40.

[0023] The drive control of the air pump 40 is performed by the pump control unit 45. The pump control unit 45 changes the on / off status of the suction operation of the air pump 40 based on the detection result from the pH sensor 13, which detects the pH of the reaction solution in the reaction vessel 11, which will be described later. When the suction operation of the air pump 40 is turned on, bubbling of the CO2-containing gas in the reaction vessel 11, which will be described later, begins, and when the suction operation of the air pump 40 is turned off, the bubbling stops.

[0024] Furthermore, the flow rate of the CO2-containing gas supplied by the air pump 40 can be controlled by the pump control unit 45 based on the detection result of the temperature sensor 12, which detects the temperature (liquid temperature) of the reaction liquid P in the reaction vessel 11, as described later. By adjusting the amount of CO2-containing gas supplied to the reaction vessel 11, as described later, the reaction heat generated in the reaction vessel 11 can be controlled to bring the temperature of the reaction liquid P to a predetermined temperature. Moreover, in this embodiment 1, the temperature of the reaction liquid P is adjusted by the liquid temperature adjustment device 50, as described later, along with the flow rate control of the air pump 40. In order to minimize the energy required to adjust the temperature of the reaction liquid P, the length of the piping forming the gas flow path 21 and the heat dissipation properties of the piping can be adjusted in advance according to the target temperature of the reaction liquid P.

[0025] 1-8. CO2 recovery device 10 The CO2 recovery device 10 recovers CO2 from the CO2-containing gas by contacting the reaction solution stored in the reaction vessel 11 with the CO2-containing gas. The reaction solution is an aqueous NaOH solution containing NaOH. The concentration of NaOH in the reaction solution will be described later.

[0026] CO2-containing gas is supplied to the reaction vessel 11 via piping 41. The tip of piping 41 is located near the inside bottom of the reaction vessel 11 and is configured to discharge the CO2-containing gas into the reaction liquid for bubbling. The reaction vessel 11 is also equipped with a temperature sensor 12 for detecting the temperature (liquid temperature) of the reaction liquid P and a pH sensor 13 for detecting the pH of the reaction liquid P.

[0027] The reaction vessel 11 is equipped with a liquid temperature control device 50 capable of heating or cooling the reaction solution inside the reaction vessel 11. A liquid temperature control device control unit 55 is connected to the liquid temperature control device 50 to control its operation. The liquid temperature control device control unit 55 is configured to control the heating or cooling operation of the liquid temperature control device 50 based on the liquid temperature, which is the temperature of the reaction solution P detected by a temperature sensor 12 installed in the reaction vessel 11. In addition to the pump control 45 controlling the operation of the air pump 40 as described above, based on the liquid temperature detected by the temperature sensor 12, the liquid temperature control device control unit 55 controls the operation of the liquid temperature control device 50, thereby maintaining the temperature of the reaction solution or aqueous product solution inside the reaction vessel 11 at a predetermined temperature.

[0028] 1-9. CO2 fixation reaction In the reaction vessel 11, a CO2-containing gas is brought into contact with a reaction solution containing NaOH (an aqueous NaOH solution). This brings the reaction shown in Equation 1 to the reaction shown in Equation 2. In this specification, Equations 1 and 2 are also referred to as the CO2 immobilization reaction. 2NaOH+CO2→ Na2CO3+H2O (Formula 1) Na2CO3+CO2+H2O → 2NaHCO3 (formula 2)

[0029] In the reaction vessel 11 shown in Figure 1, NaHCO3 and Na2CO3 are not present before the start of the above reaction. However, depending on the progress of the reaction, one of the following states occurs: Na2CO3 is produced and NaHCO3 is absent; some Na2CO3 further reacts with CO2 to produce NaHCO3 and both are present; or all Na2CO3 is converted to NaHCO3 and there is no Na2CO3 but NaHCO3 is present. Both NaHCO3 and Na2CO3 produced by the above reaction dissolve in the water in the reaction vessel 11 and become aqueous solutions. In this specification, NaHCO3, Na2CO3, and mixtures of both are collectively referred to as "products," and their aqueous solutions are collectively referred to as "aqueous product solutions." The product that is to be obtained in high purity is referred to as the "target product."

[0030] In this embodiment 1, the above reaction can be initiated by bubbling the CO2-containing gas supplied from the pipe 41 into the NaOH aqueous solution in the reaction vessel 11. In order to improve the frequency of contact between the CO2-containing gas and the NaOH aqueous solution, it is preferable to discharge the CO2-containing gas in the form of fine bubbles. Fine bubbles can be formed by a microbubble former (not shown) provided at the end of the pipe 41.

[0031] If the exhaust gas discharged from the CO2 emission equipment 100 contains a substance that inhibits the reaction in the reaction vessel 11, it is preferable to install a filter (not shown) upstream of the reaction vessel 11, for example, on the gas flow path 21, or between the moisture removal filter 30 and the air pump 40, or between the air pump 40 and the reaction vessel 11, to remove the substance that inhibits the reaction. However, if the exhaust gas discharged from the CO2 emission equipment 100 does not contain any components other than CO2, or if it is clear that it does not contain a substance that inhibits the reaction in the reaction vessel 11, then it is not necessary to install such a filter.

[0032] The exhaust section 14 shown in Figure 1 discharges the CO2-removed gas, from the reaction vessel 11 to the filter 60. The filter 60 collects harmful components in the CO2-removed gas. The configuration of the filter 60 is not limited, but in this embodiment 1, the CO2-removed gas is passed through the water W stored in the filter 60 by bubbling, thereby removing water-soluble substances (for example, NaOH from the reaction solution that reaches the exhaust section 14 as droplets due to bubbling in the reaction vessel 11, and nitrogen oxides NO contained in the exhaust gas). x It is configured to remove (etc.). The CO2 removal gas that has passed through the filter 60 is released to the outside of the CO2 recovery system 1 via the external discharge unit 61.

[0033] The target product can be recovered as follows: If the target product generated by the reactions of formulas 1 and 2 is in the form of an aqueous solution, the aqueous solution of the target product is discharged to the outside via an openable and closable drain cock 70 provided in the reaction vessel 11 and recovered in the recovery container 75. If the target product is in the form of a solid, the solid target product is discharged to the outside along with the aqueous solution in the reaction vessel 11 via the drain cock 70 provided in the reaction vessel 11 and recovered in the recovery container 75. After that, the solid target product is separated and recovered by filtration or centrifugation. The recovered target product can be used as a resource, for example, as a detergent, preservative, herbicide, etc.

[0034] After recovering the target product from the reaction vessel 11, the drain cock 70 is closed, and an aqueous NaOH solution, which is the reaction solution to be used in the next reaction, is supplied into the reaction vessel 11 from a reaction solution supply unit (not shown). The drain cock 70 is normally closed when no target product is being recovered.

[0035] 1-10. Initial concentration of NaOH, maximum temperature of the reaction solution, and extraction temperature. The concentration of NaOH in the reaction solution stored in the reaction vessel 11 before the start of the CO2 fixation reaction described above is referred to as the "initial NaOH concentration." In this embodiment 1, the initial NaOH concentration is determined based on the target product removed from the reaction solution, the highest temperature of the reaction solution after the formation of NaHCO3 in the reaction solution, and the removal temperature, which is the liquid temperature when the target product is removed from the reaction vessel 11.

[0036] In this embodiment 1, the target product extracted from the reaction solution is, as described above, an aqueous solution of NaHCO3 (sodium bicarbonate). The initial concentration of NaOH is set to a value greater than 0%, but less than or equal to the NaOH concentration required to produce saturated NaHCO3 at the extraction temperature, based on the relationship between the temperature of the reaction solution and the NaOH concentration required to produce saturated NaHCO3.

[0037] Regarding the relationship between the reaction solution temperature and the NaOH concentration required to produce saturated NaHCO3, first, the saturated solubility of NaHCO3 at 10°C intervals from 0°C to 40°C is shown in the upper part of Table 1 below. Then, the NaOH concentration required to produce saturated NaHCO3 at each temperature is calculated and shown in the lower part of Table 1 below.

[0038] [Table 1]

[0039] The first-order approximation equation for the temperature (liquid temperature) and the NaOH concentration required to produce saturated NaHCO3, as shown in the lower part of Table 1, can be calculated as shown in Equation 3 below and illustrated as shown in Figure 2. y = 0.144x + 6.82 (R 2 =0.996) (Equation 3) (where y: NaOH concentration required to produce saturated NaHCO3, x: liquid temperature)

[0040] In this embodiment 1, the approximation shown in Equation 3 above is used to represent the correspondence between the temperature of the reaction solution and the NaOH concentration required to produce saturated NaHCO3. The initial NaOH concentration is set to the first concentration range shown in Figure 3, which is less than or equal to the NaOH concentration A required to produce saturated NaHCO3 at the extraction temperature calculated based on the approximation in Equation 3, and greater than 0%. The form of the correspondence between the temperature of the reaction solution and the NaOH concentration required to produce saturated NaHCO3 is not limited, and a higher-order approximation may be used instead of the first-order approximation in this embodiment 1, or it may be defined by a map or logical formula.

[0041] Furthermore, the maximum temperature of the reaction solution after the formation of NaHCO3 is set to less than 65°C. Since the CO2 fixation reaction described above is an exothermic reaction, the temperature of the reaction solution rises during CO2 fixation. However, the temperature of the reaction solution (liquid temperature) is adjusted to less than 65°C by the air pump 40 and the liquid temperature control device 50 described above.

[0042] Furthermore, the removal temperature, which is the liquid temperature when the target product is removed from the reaction vessel 11, can be within the range of general ambient temperature, and in this embodiment 1, it is set to 0°C or higher and 40°C or lower.

[0043] Furthermore, the upper limit A of the first concentration range shown in Figure 3 can be set to 3.86 to 4.57% when the extraction temperature is 10°C or higher and less than 20°C, preferably 3.86%, based on the values ​​in the lower row of Table 1 above. Also, the upper limit A of the first concentration range can be set to 4.57 to 5.29% when the extraction temperature is 20°C or higher and less than 30°C, preferably 4.57%, and also to 5.29 to 5.38% when the extraction temperature is 30°C or higher and less than 40°C, preferably 5.29%. In Figure 3, the symbol B indicates the NaOH concentration required to produce Na2CO3 with saturated solubility at the extraction temperature, calculated based on the approximate formula of Equation 4 described later.

[0044] 1-11. Initiation and Termination of Reactions In the CO2 recovery system 1 of this embodiment 1, the CO2 immobilization reaction is started by turning on the suction operation of the air pump 40 to begin bubbling of CO2-containing gas in the reaction vessel 11, thereby bringing the CO2-containing gas into contact with the reaction solution having an initial concentration of NaOH. Subsequently, when the pH sensor 13 detects that the pH of the reaction solution in the reaction vessel 11 has reached a value equivalent to the pH when all of the NaOH has been converted to NaHCO3, the CO2 immobilization reaction is stopped by turning off the suction operation of the air pump 40 and stopping the bubbling of the CO2-containing gas. Then, the target product is removed from the reaction vessel 11 via the drain cock 70 and recovered in the recovery container 75.

[0045] 1-12. Effects According to the CO2 recovery system 1 of this embodiment 1, the maximum temperature of the reaction solution after the generation of NaHCO3 is kept below 65°C, and the initial concentration of NaOH is within the first concentration range described above. Therefore, the NaHCO3 generated in the reaction vessel 11 is not thermally decomposed, does not become supersaturated, and does not precipitate. As a result, a highly pure aqueous solution of NaHCO3 can be obtained as the target product, and the production of different target products can be easily performed. Furthermore, since NaHCO3 does not precipitate, clogging of the microbubble former (not shown) installed at the end of the piping 41 can be prevented.

[0046] In this embodiment 1, the initial concentration of NaOH is defined based on the approximation formula 3 above, but instead, it can be done as shown in the modified forms 1-1, 1-2, and 1-3 below.

[0047] In modified form 1-1, instead of using the approximate formula 3 above, the extraction temperature is set to 10°C or higher and less than 20°C based on the NaOH concentration values ​​required to produce saturated solubility NaHCO3 shown in the lower part of Table 1 above, and the initial concentration of NaOH is in the first concentration range shown in Figure 3, greater than 0%, with an upper limit A of 3.86 to 4.57%, preferably the initial concentration of NaOH is greater than 0% and 3.86% or lower.

[0048] Furthermore, in modified form 1-2, instead of using the approximate formula 3 above, the extraction temperature is set to 20°C or higher and less than 30°C based on the NaOH concentration values ​​required to produce saturated solubility NaHCO3 shown in the lower part of Table 1 above, the initial concentration of NaOH is in the first concentration range shown in Figure 3, greater than 0%, and the upper limit A can be 4.57 to 5.29%, preferably the initial concentration of NaOH is greater than 0% and 4.57% or lower.

[0049] Furthermore, in modified forms 1-3, instead of using the approximate formula 3 above, the extraction temperature is set to 30°C or higher and less than 40°C based on the NaOH concentration values ​​required to produce saturated solubility NaHCO3 shown in the lower part of Table 1 above, the initial concentration of NaOH is in the first concentration range shown in Figure 3, greater than 0%, and the upper limit A can be 5.29 to 5.38%, preferably the initial concentration of NaOH is greater than 0% and 5.29% or lower.

[0050] In all of the above modified forms 1-1, 1-2, and 1-3, the precipitation of NaHCO3 is suppressed at the extraction temperature, thus achieving the same effects as in Embodiment 1.

[0051] (Embodiment 2) In this second embodiment, the configuration of the device is the same as in the first embodiment shown in Figure 1.

[0052] 2-1. Target product In Embodiment 1 described above, the target product was an aqueous solution of NaHCO3, but in Embodiment 2, the target product is an aqueous solution of sodium sesquicarbonate in which NaHCO3 and Na2CO3 are dissolved in water.

[0053] 2-2. Initial concentration of NaOH, maximum temperature of the reaction solution, and extraction temperature. In this second embodiment, the initial concentration of NaOH is set to a value greater than 0% but less than or equal to the NaOH concentration required to produce saturated Na2CO3 at the extraction temperature, based on the relationship between the temperature of the reaction solution and the NaOH concentration required to produce saturated Na2CO3.

[0054] Regarding the relationship between the reaction solution temperature and the NaOH concentration required to produce saturated Na2CO3, first, the saturated solubility of Na2CO3 at 10°C intervals from 0°C to 40°C is shown in the upper part of Table 2 below. Then, the NaOH concentration required to produce saturated Na2CO3 at each temperature is calculated and shown in the lower part of Table 2 below.

[0055] [Table 2]

[0056] The first-order approximation equation for the temperature (liquid temperature) and the NaOH concentration required to produce saturated NaHCO3, as shown in the lower part of Table 2, can be calculated as shown in Equation 4 below and illustrated as shown in Figure 4. y = 1.112x + 3.70 (R 2 =0.966) (Equation 4) (where y: NaOH concentration required to produce saturated Na2CO3, x: liquid temperature)

[0057] In this second embodiment, the approximation shown in Equation 4 above is used to represent the correspondence between the temperature of the reaction solution and the NaOH concentration required to produce saturated Na2CO3. The initial NaOH concentration is set to the second concentration range shown in Figure 5, which is less than or equal to the NaOH concentration B required to produce saturated Na2CO3 at the extraction temperature calculated based on the approximation in Equation 4, and greater than 0%. The form of the correspondence between the temperature of the reaction solution and the NaOH concentration required to produce saturated Na2CO3 is not limited; a higher-order approximation may be used instead of the first-order approximation in this first embodiment, or it can be defined by a map or a logical formula.

[0058] Furthermore, the maximum temperature of the reaction solution after the formation of NaHCO3 is set to less than 65°C, as in Embodiment 1. Also, the removal temperature, which is the liquid temperature when the target product is removed from the reaction vessel 11, is set to 0°C or higher and 40°C or lower, as in Embodiment 1. The other configurations are also the same as in Embodiment 1.

[0059] Furthermore, the upper limit B of the second concentration range shown in Figure 5 can be set to 9.43 to 16.22% when the extraction temperature is 10°C or higher and less than 20°C, preferably 9.43%, based on the values ​​in the lower row of Table 2 above. Also, the upper limit B of the second concentration range can be set to 16.22 to 29.96% when the extraction temperature is 20°C or higher and less than 30°C, preferably 16.22%, and also to 29.96 to 36.98% when the extraction temperature is 30°C or higher and less than 40°C, preferably 29.96%. In Figure 5, the symbol A indicates the NaOH concentration required to produce NaHCO3 with saturated solubility at the extraction temperature calculated based on the approximate formula of Equation 3 described above.

[0060] 2-3. Initiation and Termination of the Reaction In the CO2 recovery system 1 of this second embodiment, the CO2 fixation reaction is started by turning on the suction operation of the air pump 40 to begin bubbling of the CO2-containing gas in the reaction vessel 11, thereby bringing the CO2-containing gas into contact with the reaction solution having an initial concentration of NaOH. Subsequently, when the pH sensor 13 detects that the pH of the reaction solution in the reaction vessel 11 has reached a value corresponding to the pH when all of the NaOH has been consumed and the ratio of Na2CO3 to NaHCO3 is the desired 50:50, the CO2 fixation reaction is stopped by turning off the suction operation of the air pump 40 to stop bubbling of the CO2-containing gas.

[0061] 2-4. Effects According to the CO2 recovery system 1 of this embodiment 2, the maximum temperature of the reaction solution after the generation of NaHCO3 is kept below 65°C, so the NaHCO3 generated in the reaction vessel 11 is not thermally decomposed. Furthermore, since the initial concentration of NaOH is within the second concentration range described above, Na2CO3 does not become supersaturated and does not precipitate. As a result, high-purity NaHCO3 as the target product and an aqueous solution of sodium sesquicarbonate in which Na2CO3 is dissolved in water can be obtained, making it easy to differentiate between target products. In addition, since Na2CO3 does not precipitate, the reactivity of the reaction between Na2CO3 and CO2 to generate NaHCO3 shown in equation 2 above is prevented, and the CO2 recovery rate is improved.

[0062] In this embodiment 2, the initial concentration of NaOH is defined based on the approximation formula 4 above, but instead, it can be done as shown in the modified forms 2-1, 2-2, and 2-3 below.

[0063] In modified form 2-1, instead of using the approximate formula 4 above, the extraction temperature is set to 10°C or higher and less than 20°C based on the NaOH concentration values ​​required to produce saturated solubility Na2CO3 shown in the lower part of Table 2 above, the initial concentration of NaOH is in the second concentration range shown in Figure 5, greater than 0%, and the upper limit B can be 9.43 to 16.22%, preferably the initial concentration of NaOH is greater than 0% and 9.43% or lower.

[0064] Furthermore, in modified form 2-2, instead of using the approximation formula 4 above, the extraction temperature is set to 20°C or higher and less than 30°C based on the NaOH concentration values ​​required to produce saturated solubility Na2CO3 shown in the lower part of Table 2 above, the initial concentration of NaOH is in the second concentration range shown in Figure 5, greater than 0%, and the upper limit B can be 16.22 to 29.96%, preferably the initial concentration of NaOH is greater than 0% and 16.22% or lower.

[0065] Furthermore, in modified form 2-3, instead of using the approximate formula 4 above, the extraction temperature is set to 30°C or higher and less than 40°C based on the NaOH concentration values ​​required to produce saturated solubility Na2CO3 shown in the lower part of Table 2 above, the initial concentration of NaOH is in the second concentration range shown in Figure 5, greater than 0%, and the upper limit B can be 29.96 to 36.98%, preferably the initial concentration of NaOH is greater than 0% and 29.96% or lower.

[0066] In all of the above modified forms 2-1, 2-2, and 2-3, the precipitation of Na2CO3 can be suppressed at the extraction temperature, and the same effects as in Embodiment 2 are achieved.

[0067] (Embodiment 3) In this third embodiment, the configuration of the device is the same as in the first embodiment shown in Figure 1.

[0068] 3-1. Target product In this third embodiment, the target product is solid NaHCO3.

[0069] 3-2. Initial concentration of NaOH, maximum temperature of the reaction solution, and removal temperature. In this third embodiment, the initial concentration of NaOH is set to be greater than or equal to the concentration of NaOH required to produce saturated solubility NaHCO3 at the extraction temperature, which is derived based on the relationship between the temperature of the reaction solution and the NaOH concentration required to produce saturated solubility NaHCO3, and less than or equal to the concentration of NaOH required to produce saturated solubility Na2CO3 at the extraction temperature, which is derived based on the relationship between the temperature of the reaction solution and the NaOH concentration required to produce saturated solubility Na2CO3.

[0070] In this third embodiment, the "NaOH concentration required to produce saturated solubility NaHCO3 at the extraction temperature, derived based on the relationship between the temperature of the reaction solution and the NaOH concentration required to produce saturated solubility NaHCO3" is the NaOH concentration A calculated based on the approximate formula of Equation 3 in Embodiment 1.

[0071] Furthermore, in this third embodiment, the "NaOH concentration required to produce saturated solubility Na2CO3 at the extraction temperature, derived based on the relationship between the temperature of the reaction solution and the NaOH concentration required to produce saturated solubility Na2CO3" is the NaOH concentration B calculated based on the approximate formula of Equation 4 in Embodiment 2.

[0072] Therefore, in this third embodiment, the initial NaOH concentration is set to a third concentration range shown in Figure 6, which is a range where the NaOH concentration A is greater than or equal to the NaOH concentration B required to produce NaHCO3 with saturated solubility at the extraction temperature calculated based on the approximate formula of Equation 3, and less than or equal to the NaOH concentration B required to produce Na2CO3 with saturated solubility at the extraction temperature calculated based on the approximate formula of Equation 4.

[0073] In this third embodiment, the maximum temperature of the reaction solution after the formation of NaHCO3 is set to less than 65°C, as in the first embodiment. The removal temperature, which is the liquid temperature when the target product is removed from the reaction vessel 11, is also set to 0°C or higher and 40°C or lower, as in the first embodiment. Other configurations are the same as in the first embodiment.

[0074] Furthermore, in the third concentration range shown in Figure 6, when the extraction temperature is 10°C or higher and less than 20°C, the lower limit A can be set to 3.86 to 4.57%, preferably 3.86%, based on the values ​​in the lower row of Table 1 above. On the other hand, the upper limit B can be set to 9.43 to 16.22%, preferably 9.43%, based on the values ​​in the lower row of Table 2 above.

[0075] Furthermore, for the third concentration range, when the extraction temperature is 20°C or higher and less than 30°C, the lower limit A can be set to 4.57 to 5.29%, preferably 4.57%, based on the values ​​in the lower row of Table 1 above. On the other hand, the upper limit B can be set to 16.22 to 29.96%, preferably 16.22%, based on the values ​​in the lower row of Table 2 above.

[0076] Furthermore, for the third concentration range, when the extraction temperature is 30°C or higher and less than 40°C, the lower limit A can be set to 5.29 to 5.38%, preferably 5.29%, based on the values ​​in the lower row of Table 1 above. On the other hand, the upper limit B can be set to 29.96 to 36.98%, preferably 29.96%, based on the values ​​in the lower row of Table 2 above.

[0077] 3-3. Initiation and Termination of the Reaction In the CO2 recovery system 1 of this embodiment 3, the CO2 fixation reaction is started by turning on the suction operation of the air pump 40 to begin bubbling of the CO2-containing gas in the reaction vessel 11, thereby bringing the CO2-containing gas into contact with the reaction solution having an initial concentration of NaOH. Subsequently, when the pH sensor 13 detects that the pH of the reaction solution in the reaction vessel 11 has reached a value corresponding to the pH when all of the NaOH has been consumed and the ratio of Na2CO3 to NaHCO3 is 50:50, the CO2 fixation reaction is stopped by turning off the suction operation of the air pump 40 to stop bubbling of the CO2-containing gas.

[0078] 3-4. Effects In the CO2 recovery system 1 of this embodiment 3, the maximum temperature of the reaction solution after the generation of NaHCO3 is kept below 65°C, so the NaHCO3 generated in the reaction vessel 11 is not thermally decomposed. Furthermore, since the initial concentration of NaOH is within the third concentration range described above, Na2CO3 does not become supersaturated and does not precipitate, but NaHCO3 becomes supersaturated and precipitates in the reaction vessel 11. As a result, since NaHCO3 is the only product that precipitates and becomes solid in the reaction vessel 11, solid NaHCO3 can be obtained with high purity as the target product, and the production of the target product can be easily differentiated. In addition, since Na2CO3 does not precipitate, the reactivity of the reaction between Na2CO3 and CO2 to produce NaHCO3 shown in the above formula 2 is prevented from decreasing, and the CO2 recovery rate is improved.

[0079] In this embodiment 3, the initial concentration of NaOH is defined based on the approximate formulas 3 and 4 above. However, this can be replaced with the modified forms 3-1, 3-2, and 3-3 described below.

[0080] In modified form 3-1, without using the approximate formulas of Equation 3 and Equation 4 above, the extraction temperature is set to 10°C or higher and less than 20°C, based on the value of NaOH concentration A required to produce saturated solubility NaHCO3 shown in the lower part of Table 1 and the value of NaOH concentration B required to produce saturated solubility Na2CO3 shown in the lower part of Table 2, and the initial concentration of NaOH is within the third concentration range shown in Figure 6, with the lower limit A being 3.86 to 4.57% and the upper limit B being 9.43 to 16.22%. The initial concentration of NaOH can be between 3.86% and 9.43%.

[0081] Furthermore, in modified form 3-2, without using the approximate formulas of Equation 3 and Equation 4 above, the extraction temperature is set to 20°C or higher and less than 30°C, based on the value of NaOH concentration A required to produce saturated solubility NaHCO3 shown in the lower part of Table 1 and the value of NaOH concentration B required to produce saturated solubility Na2CO3 shown in the lower part of Table 2, and the initial concentration of NaOH is in the third concentration range shown in Figure 6, with the lower limit A being 4.57 to 5.29% and the upper limit B being 16.22 to 29.96%. The initial concentration of NaOH can be 4.57% or higher and 16.22% or lower.

[0082] Furthermore, in modified form 3-3, without using the approximate formulas of Equation 3 and Equation 4 above, the extraction temperature is set to 30°C or higher and less than 40°C, based on the value of NaOH concentration A required to produce saturated solubility NaHCO3 shown in the lower part of Table 1 and the value of NaOH concentration B required to produce saturated solubility Na2CO3 shown in the lower part of Table 2, and the initial concentration of NaOH is within the third concentration range shown in Figure 6, with the lower limit A being 5.29 to 5.38% and the upper limit B being 29.96 to 36.98%. The initial concentration of NaOH can be set to 5.29% or higher and 29.96% or lower.

[0083] In all of the above modified forms 3-1, 3-2, and 3-3, at the extraction temperature, only NaHCO3 precipitates, allowing for the recovery of solid NaHCO3, thus achieving the same effects as in Embodiment 3.

[0084] (Embodiment 4) In this fourth embodiment, the configuration of the device is the same as in the first embodiment shown in Figure 1.

[0085] 4-1. Target product In this embodiment 4, the target product is either an aqueous solution of Na2CO3 or solid Na2CO3.

[0086] 4-2. Initial concentration of NaOH, maximum temperature of the reaction solution, and extraction temperature. In this fourth embodiment, the initial concentration of NaOH is greater than 0%, and falls within the fourth concentration range shown in Figure 7.

[0087] In this fourth embodiment, the maximum temperature of the reaction solution after the formation of NaHCO3 is set to 65°C or higher. Since the CO2 fixation reaction described above is an exothermic reaction, the temperature of the reaction solution rises during CO2 fixation. If the temperature of the reaction solution (liquid temperature) is below 65°C, the air pump 40 and liquid temperature control device 50 described above are used to heat it to 65°C or higher. The removal temperature, which is the liquid temperature when the target product is removed from the reaction vessel 11, is set to 0°C or higher and 40°C or lower, as in the first embodiment. The other configurations are the same as in the first embodiment.

[0088] 4-3. Initiation and Termination of the Reaction In the CO2 recovery system 1 of this embodiment 4, the CO2 fixation reaction is started by turning on the suction operation of the air pump 40 to begin bubbling of the CO2-containing gas in the reaction vessel 11, thereby bringing the CO2-containing gas into contact with the reaction solution having an initial concentration of NaOH. Subsequently, when the pH sensor 13 detects that the pH of the reaction solution in the reaction vessel 11 indicates that all of the NaOH has been consumed, the CO2 fixation reaction is stopped by turning off the suction operation of the air pump 40 to stop bubbling of the CO2-containing gas.

[0089] 4-4. Effects According to the CO2 recovery system 1 of this embodiment 4, the maximum temperature of the reaction solution after the generation of NaHCO3 is set to 65°C or higher, so the NaHCO3 generated in the reaction vessel 11 is thermally decomposed. Therefore, in the fourth concentration range described above, i.e., the entire range, the reaction vessel 11 contains either an aqueous Na2CO3 solution or solid Na2CO3 as a product, and no NaHCO3. As a result, high-purity Na2CO3 can be obtained as the target product, and the production of the target product can be easily differentiated. Furthermore, because NaHCO3 is not present, clogging of the microbubble former (not shown) installed at the end of the piping 41 due to NaHCO3 precipitation can be prevented.

[0090] (Embodiment 5) In this fifth embodiment, the configuration of the device is the same as in the first embodiment shown in Figure 1.

[0091] 5-1. Target product In this embodiment 5, the target product is solid Na2CO3.

[0092] 5-2. Initial concentration of NaOH, maximum temperature of the reaction solution, and extraction temperature. In this embodiment 5, the initial concentration of NaOH is set to be equal to or greater than the concentration of NaOH required to produce saturated solubility Na2CO3 at the extraction temperature, which is derived based on the relationship between the temperature of the reaction solution and the NaOH concentration required to produce saturated solubility Na2CO3.

[0093] In this embodiment 5, the "NaOH concentration required to produce saturated solubility Na2CO3 at the extraction temperature, derived based on the relationship between the temperature of the reaction solution and the NaOH concentration required to produce saturated solubility Na2CO3" is the NaOH concentration calculated based on the approximate formula of Equation 4 in Embodiment 2.

[0094] Therefore, in this embodiment 5, the initial NaOH concentration is set to a fifth concentration range shown in Figure 8, which is greater than or equal to the NaOH concentration required to produce Na2CO3 with saturated solubility at the extraction temperature calculated based on the approximate formula of Equation 4 above.

[0095] In this embodiment 5, the maximum temperature of the reaction solution after the formation of NaHCO3 is set to 65°C or higher, as in embodiment 4. The removal temperature, which is the liquid temperature when the target product is removed from the reaction vessel 11, is also set to 0°C or higher and 40°C or lower, as in embodiment 4. The other configurations are the same as in embodiment 1.

[0096] Furthermore, the lower limit B of the fifth concentration range shown in Figure 8 can be set to 9.43 to 16.22%, preferably 9.43%, based on the values ​​in the lower row of Table 2, when the extraction temperature is 10°C or higher and less than 20°C. Also, the lower limit B of the fifth concentration range can be set to 16.22 to 29.96%, preferably 16.22%, based on the values ​​in the lower row of Table 2, when the extraction temperature is 20°C or higher and less than 30°C. Also, the lower limit B of the fifth concentration range can be set to 29.96 to 36.98%, preferably 29.96%, based on the values ​​in the lower row of Table 2, when the extraction temperature is 30°C or higher and less than 40°C.

[0097] 5-3. Initiation and Termination of the Reaction In the CO2 recovery system 1 of this embodiment 5, the CO2 fixation reaction is started by turning on the suction operation of the air pump 40 to begin bubbling of the CO2-containing gas in the reaction vessel 11, thereby bringing the CO2-containing gas into contact with the reaction solution having an initial concentration of NaOH. Subsequently, when the pH sensor 13 detects that the pH of the reaction solution in the reaction vessel 11 indicates that all of the NaOH has been consumed, the CO2 fixation reaction is stopped by turning off the suction operation of the air pump 40 to stop bubbling of the CO2-containing gas.

[0098] 5-4. Effects According to the CO2 recovery system 1 of this embodiment 5, the maximum temperature of the reaction solution after the generation of NaHCO3 is set to 65°C or higher, so the NaHCO3 generated in the reaction vessel 11 is thermally decomposed. Furthermore, since the initial concentration of NaOH is within the fifth concentration range described above, Na2CO3 becomes supersaturated and precipitates in the reaction vessel 11. As a result, since the only product that precipitates and becomes solid in the reaction vessel 11 is Na2CO3, solid Na2CO3 can be obtained in high purity as the target product by filtering or centrifuging the recovered material in the recovery container 75, making it easy to selectively produce the target product.

[0099] In this embodiment 5, the initial concentration of NaOH is defined based on the approximation formula of Equation 4 above, but instead, it can be done as shown in the modified forms 5-1, 5-2, and 5-3 below.

[0100] In modified form 5-1, instead of using the approximate formula 4 above, the extraction temperature is set to 10°C or higher and less than 20°C based on the NaOH concentration values ​​required to produce saturated solubility Na2CO3 shown in the lower part of Table 2 above, and the initial concentration of NaOH is within the fifth concentration range shown in Figure 8, with the lower limit B being 9.43 to 16.22%, preferably the initial concentration of NaOH being 9.43% or higher.

[0101] Furthermore, in modified form 5-2, instead of using the approximate formula 4 above, the extraction temperature is set to 20°C or higher and less than 30°C based on the NaOH concentration values ​​required to produce saturated solubility Na2CO3 shown in the lower part of Table 2 above, and the initial concentration of NaOH is within the fifth concentration range shown in Figure 8, with the lower limit B being 16.22 to 29.96%, preferably the initial concentration of NaOH being 16.22% or higher.

[0102] Furthermore, in modified form 5-3, based on the NaOH concentration values ​​required to produce saturated solubility Na2CO3 shown in the lower part of Table 2 above, the extraction temperature is set to 30°C or higher and less than 40°C, the initial concentration of NaOH is within the fifth concentration range shown in Figure 8, and the lower limit B can be 29.96 to 36.98%, preferably the initial concentration of NaOH is 29.96% or higher.

[0103] In all of the above modified forms 5-1, 5-2, and 5-3, the only product obtained as a solid at the extraction temperature is Na2CO3. Therefore, the target product, solid Na2CO3, can be obtained with high purity, and the same effects as in Embodiment 5 are achieved.

[0104] (Embodiment 6) As shown in Figure 9, the CO2 recovery system 1 of this embodiment 6 includes an adjustment unit 80 and an initial NaOH concentration setting unit 81. The other components of this embodiment 6 are the same as those of embodiment 1 shown in Figure 1, and are denoted by the same reference numerals as in embodiment 1, and their descriptions are omitted.

[0105] 6-1. Adjustment section 80, NaOH initial concentration setting section 81 The adjustment unit 80 shown in Figure 9 adjusts the target product by adjusting the maximum temperature of the reaction solution after NaHCO3 generation, the extraction temperature, and the initial concentration of NaOH in the reaction solution. In this embodiment 6, the adjustment unit 80 adjusts the temperature (liquid temperature) of the reaction solution by adjusting the flow rate of the air pump 40 by the pump control 45 and by controlling the drive of the liquid temperature adjustment device 50 by the liquid temperature adjustment device control unit 55. It also adjusts the initial concentration of NaOH in the reaction solution introduced into the reaction vessel 11 via the NaOH initial concentration setting unit 81, which will be described later.

[0106] The NaOH initial concentration setting unit 81 shown in Figure 9 is configured to introduce a reaction solution having the initial NaOH concentration adjusted by the adjustment unit 80 into the reaction vessel 11 from the reaction solution input unit 15 provided in the reaction vessel 11.

[0107] In this embodiment 6, the adjustment unit 80 has a selection unit 82 for selecting a target product desired by the user, and sets the product selected by the user via the selection unit 82 as the target product. Then, it adjusts the initial concentration of NaOH in the reaction solution and the temperature of the reaction solution (liquid temperature) according to the set target product. The correspondence between the initial concentration of NaOH and the target product can be represented as shown in Figure 10.

[0108] 6-2. Preparation of the target product The preparation of the target product in this embodiment 6 will be described in detail below.

[0109] In this embodiment 6, if the user selects an aqueous NaHCO3 solution as the target product via the selection unit 82, the initial NaOH concentration is adjusted to the first concentration range via the initial NaOH concentration setting unit 81, similar to embodiment 1 described above. The maximum temperature and extraction temperature of the reaction solution are also adjusted via the air pump 40 and the liquid temperature adjustment device 50, similar to embodiment 1 described above. This allows the aqueous NaHCO3 solution to be obtained as the target product, similar to embodiment 1.

[0110] In addition, similar to the modified forms 1-1, 1-2, and 1-3 described above, the target product, an aqueous NaHCO3 solution, may be obtained by adjusting the initial concentration of NaOH, the maximum temperature of the reaction solution, and the extraction temperature, in the same manner as in the modified forms 1-1, 1-2, and 1-3.

[0111] Furthermore, in this embodiment 6, if the user selects an aqueous solution of sodium sesquicarbonate as the target product via the selection unit 82, the initial NaOH concentration, the maximum temperature of the reaction solution, and the extraction temperature are adjusted via the initial NaOH concentration setting unit 81, the air pump 40, and the liquid temperature adjustment device 50, similar to the embodiment 2 described above. This makes it possible to obtain an aqueous solution of sodium sesquicarbonate as the target product, similar to the case of embodiment 2.

[0112] Furthermore, in this embodiment 6, if solid NaHCO3 is selected as the target product by the user via the selection unit 82, the initial NaOH concentration, the maximum temperature of the reaction solution, and the extraction temperature are adjusted via the initial NaOH concentration setting unit 81, the air pump 40, and the liquid temperature adjustment device 50, similar to the embodiment 3 described above. This makes it possible to obtain solid NaHCO3 as the target product, similar to the case of embodiment 3.

[0113] Furthermore, in this embodiment 6, if the user selects via the selection unit 82 that either an aqueous Na2CO3 solution or solid Na2CO3 may be used as the target product, the initial NaOH concentration, the maximum temperature of the reaction solution, and the extraction temperature are adjusted via the initial NaOH concentration setting unit 81, the air pump 40, and the liquid temperature adjustment device 50, similar to the embodiment 4 described above. This allows the user to obtain either an aqueous Na2CO3 solution or solid Na2CO3 as the target product, similar to the case of embodiment 4.

[0114] Furthermore, in this embodiment 6, if solid Na2CO3 is selected as the target product by the user via the selection unit 82, the initial NaOH concentration, the maximum temperature of the reaction solution, and the extraction temperature are adjusted via the initial NaOH concentration setting unit 81, the air pump 40, and the liquid temperature adjustment device 50, similar to the embodiment 5 described above. This makes it possible to obtain solid Na2CO3 as the target product, similar to the case of embodiment 3.

[0115] 6-3. Effects According to the CO2 recovery system of this embodiment 6, the target product extracted from the reaction solution can be adjusted by adjusting the maximum temperature of the reaction solution after NaHCO3 generation, the extraction temperature (the temperature of the reaction solution when the target product is extracted from the reaction vessel), and the initial concentration of NaOH in the reaction solution. This makes it easy to differentiate between products and extract the desired target product with high purity.

[0116] The present invention is not limited to the above embodiments and variations, and can be applied to various embodiments without departing from its spirit.

Claims

1. CO2 is added to the reaction solution containing NaOH stored in the reaction vessel (11). ２ CO ２ CO2 recovery ２ Recovery system (1), NaHCO3 in the above reaction solution ３ By adjusting the maximum temperature of the reaction solution after generation, the removal temperature (the temperature of the reaction solution when the target product is removed from the reaction vessel), and the initial concentration of NaOH in the reaction solution, the target product removed from the reaction solution can be adjusted. The target product described above is an aqueous solution of sodium sesquicarbonate. NaHCO3 in the above reaction solution ３ The maximum temperature of the reaction solution after generation is less than 65°C. The above extraction temperature is between 0°C and 40°C. The initial concentration of the NaOH is based on the correspondence relationship with the NaOH concentration required to generate Na ２ CO ３ , and is the saturated solubility of Na at the extraction temperature, which is derived based on the correspondence relationship with the NaOH concentration required to generate Na ２ CO ３ . It is greater than 0% and below the NaOH concentration required to generate Na ２ recovery system.

2. CO2 is added to the reaction solution containing NaOH stored in the reaction vessel (11). ２ CO ２ CO2 recovery ２ Recovery system (1), NaHCO3 in the above reaction solution ３ The maximum temperature of the reaction solution after generation is determined according to the target product to be extracted from the reaction solution. The initial concentration of NaOH in the reaction solution is determined based on the target product removed from the reaction solution and the removal temperature, which is the temperature of the reaction solution when the target product is removed from the reaction vessel. The target product described above is an aqueous solution of sodium sesquicarbonate. NaHCO3 in the above reaction solution ３ The maximum temperature of the reaction solution after generation is less than 65°C. The above extraction temperature is between 0°C and 40°C. The initial concentration of NaOH mentioned above is determined by the temperature of the reaction solution and the saturated solubility of Na. ２ CO ３ The saturation solubility of Na at the above extraction temperature was derived based on the correspondence with the NaOH concentration required to produce it. ２ CO ３ Below the NaOH concentration required to produce CO, and greater than 0%, ２ Collection system.

3. The above extraction temperature is 10°C or higher and less than 20°C. The initial concentration of NaOH is greater than 0%, and the upper limit is 9.43 to 16.22%, as described in claim 1 or 2. ２ Collection system.

4. The above extraction temperature is 20°C or higher and less than 30°C. The initial concentration of NaOH is greater than 0%, and the upper limit is 16.22 to 29.96%, as described in claim 1 or 2. ２ Collection system.

5. The above extraction temperature is 30°C or higher and less than 40°C. The initial concentration of NaOH is greater than 0%, and the upper limit is 29.96 to 36.98%, as described in claim 1 or 2. ２ Collection system.

6. CO2 is added to the reaction solution containing NaOH stored in the reaction vessel. ２ CO ２ CO2 recovery ２ It is a collection system, The target product described above is an aqueous solution of sodium sesquicarbonate. NaHCO3 in the above reaction solution ３ The maximum temperature of the reaction solution after generation is less than 65°C. The removal temperature, which is the temperature of the reaction solution when the target product is removed from the reaction vessel, is 10°C or higher and less than 20°C. The initial concentration of NaOH mentioned above is greater than 0%, with an upper limit of 9.43-16.22%. ２ Collection system.

7. CO2 is added to the reaction solution containing NaOH stored in the reaction vessel. ２ CO ２ CO2 recovery ２ It is a collection system, The target product described above is an aqueous solution of sodium sesquicarbonate. NaHCO3 in the above reaction solution ３ The maximum temperature of the reaction solution after generation is less than 65°C. The removal temperature, which is the temperature of the reaction solution when the target product is removed from the reaction vessel, is 20°C or higher and less than 30°C. The initial concentration of NaOH mentioned above is greater than 0%, with an upper limit of 16.22-29.96%. ２ Collection system.

8. CO2 is added to the reaction solution containing NaOH stored in the reaction vessel. ２ CO ２ CO2 recovery ２ It is a collection system, The target product described above is an aqueous solution of sodium sesquicarbonate. NaHCO3 in the above reaction solution ３ The maximum temperature of the reaction solution after generation is less than 65°C. The removal temperature, which is the temperature of the reaction solution when the target product is removed from the reaction vessel, is 30°C or higher and less than 40°C. The initial concentration of NaOH mentioned above is greater than 0%, with an upper limit of 29.96-36.98%. ２ Collection system.

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