Method for recovering carbon dioxide in ambient air and porous body for recovering carbon dioxide, and method for synthesizing sodium carbonate

Abstract

To provide: a method for recovering low concentration CO2 in ambient air (method for recovering CO2) by a low-energy and simple method, for example, by synthesizing particularly sodium carbonate (method for synthesizing sodium carbonate); and a porous body which recovers CO2 (porous body for recovering CO2.SOLUTION: A method for recovering CO2 comprises: a step of immersing at least a part of an alkali-resistant porous body having a pore and a part that can be wetted by alkaline water in an alkaline solution; and a step of recovering CO2 in ambient air as a salt generated by a reaction between the alkaline solution and CO2 from ambient air (atmosphere) by utilizing a capillary phenomenon of the pore and a contact between at least a part of a surface of the porous body and CO2 contained in ambient air.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for recovering carbon dioxide (CO2) in the atmosphere, a porous body for recovering carbon dioxide (CO2), and preferably a method for synthesizing sodium carbonate.

Background Art

[0002] Although various methods for fixing CO2 in the atmosphere have been proposed, since there is only 300 ppm in the atmosphere, there is no practical method considering the energy balance. On the other hand, for example, as a method for synthesizing sodium carbonate, the Solvay process (ammonia-soda process) is the main method, but heat utilization is required.

[0003] Patent Document 1 discloses a sheet for a total heat exchange element including a porous member and a film containing inorganic fibers provided on one surface of the porous member, wherein a part of the inorganic fibers contained in the film exists in the pores of the porous member from the interface with the porous member at a depth of 0.15 μm or more and 50 μm or less, and since pores are formed between the inorganic fibers in the film containing inorganic fibers, water vapor contained in outside air or the like is condensed by the Kelvin capillary condensation theory and filled in the pores to form a wet seal and discharge carbon dioxide or the like in the room. A sheet for a total heat exchange element is described.

[0004] Patent Document 2 discloses an electrodialysis cell in which a first bipolar membrane, an intermediate bipolar membrane, an anion exchange membrane, a cation exchange membrane, and a second bipolar membrane are arranged between negative electrodes, the electrodialysis cell receives a sodium nitrate solution to generate nitric acid and sodium hydroxide, supplies nitric acid to a dissolution tank to dissolve a material to be dissolved containing a Group 2 element to generate a nitrate solution of the Group 2 element, supplies sodium hydroxide to a gas absorption tower to absorb carbon dioxide to generate a sodium carbonate solution, supplies the nitrate solution of the Group 2 element and the sodium carbonate solution to a reaction tank to generate a carbonate of the Group 2 element, fixes carbon dioxide, and circulates the generated sodium nitrate solution to the electrodialysis cell. A carbon dioxide fixation device is described.

[0005] Non-Patent Document 1 describes an amine scrubbing method consisting of two steps: an absorption step and a stripping step. In the absorption step, CO2 is absorbed by contacting the amine at low temperature and high pressure. Stripping is a step of removing the CO2 captured by the amine, and increasing the temperature promotes the release of CO2. As amine aqueous solutions, diethanolamine (DEA), monoethanolamine (MEA), methyldiethanolamine (MDEA), etc. are used. As problems of amine scrubbing, solvent loss during the process, a large amount of energy associated with solvent regeneration, high toxicity, and energy for operating the system are described. Non-Patent Document 2 describes direct CO2 recovery using NaOH. Specifically, it is a method of recovering CO2 by spraying a NaOH spray onto CO2. Since it becomes a spray form, the surface area becomes large and the CO2 absorption efficiency is high. Although it is possible on a laboratory scale, the problem is that fairly large-scale equipment is required for practical use.

[0006] Non-Patent Document 3 shows a method of recovering CO2 by filling the air and dropping NaOH droplets. Although it is a simple method, it is less efficient compared to the spray type as in Non-Patent Document 2. Also, it is described that the equipment also becomes large-scale. Non-Patent Document 4 describes a method of blowing air into a NaOH solution. Although it is a simple method, it is necessary to collect and blow air. It is described that it is difficult to recover above the saturated dissolution concentration.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0008]

Non-Patent Document 1

[0009] As described above, there is no practical method for recovering CO2 from the atmosphere that satisfies the energy balance, and the Solvay process (ammonia - soda process), which is the main synthetic method of sodium carbonate, has a problem that heat utilization is required. Therefore, an object of the present invention is to provide a method for synthesizing, for example, preferably sodium carbonate (a method for synthesizing carbonate) by a low - energy and simple method, a method for recovering low - concentration CO2 from the atmosphere (a CO2 recovery method), and a porous body for recovering CO2 (a porous body for CO2 recovery). [Means for Solving the Problems]

[0010] The present invention for solving the above problems is as follows. [1] At least a part of an alkali-resistant porous body having pores and a part that can be wetted by alkaline water is immersed in an alkaline solution, and by utilizing the capillary action of the pores and the fact that at least a part of the surface of the porous body is in contact with CO2 contained in the atmosphere, CO2 in the atmosphere is recovered as a salt generated by the reaction of the alkaline solution and the CO2 from the atmosphere. This is a method for recovering CO2. Note that "contacting with CO2" can also be rephrased as "the step of contacting with CO2", and "recovering CO2" can also be rephrased as "the step of recovering CO2". [2] The method for recovering CO2 according to [1], wherein the salt contains carbonate. [3] The method for recovering CO2 according to [2], wherein the carbonate is a carbonate containing sodium. Carbonates containing sodium refer to salts in which Na and CO3 are related, such as Na2CO3·NaHCO3·2H2O and NaHCO3. [4] The method for recovering CO2 according to [3], wherein the carbonate containing sodium contains sodium carbonate. [5] The method for recovering CO2 according to any one of [1] to [4], which includes further dissolving CO2 gas in the alkaline solution. [6] An alkali-resistant porous body having pores and a part that can be wetted by alkaline water, wherein at least a part of the surface of the porous body is immersed in an alkaline solution, and by utilizing the capillary action of the pores and the fact that at least a part of the surface of the porous body is in contact with CO2 contained in the atmosphere, CO2 in the atmosphere is recovered as a salt generated by the reaction of the alkaline solution and the CO2 from the atmosphere. This is a porous body for a CO2 recovery method.

Advantages of the Invention

[0011] According to the method for recovering CO2 in the atmosphere according to the present invention, CO2 can be recovered with energy savings. For example, if CO2 is recovered as sodium carbonate, the problem of heat can be solved and sodium carbonate can be synthesized.

Brief Description of the Drawings

[0012]

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Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and can be modified, corrected, or improved without departing from the scope of the invention.

[0014] (Mechanism of precipitation) The mechanism by which salts of the solute of the alkaline solution and CO2 precipitate on the surface of the porous body by immersing at least a part of the porous body in an alkaline solution placed in the atmosphere is presumed as follows. As the alkaline solution, for example, an aqueous sodium hydroxide solution is preferable, and as the porous body, for example, a silica-based porous body having alkali resistance is preferable. In this case, since the salt (carbonate) that precipitates is preferably sodium carbonate, the following mainly describes them as examples.

[0015] CO2 dissolves in the NaOH aqueous solution. This liquid moves to the porous body surface by capillary rise and dries to form a saturated solution. CO2 gas in the atmosphere reacts with the wet surface of the porous body to precipitate Na2CO3 (Na3(CO3)(HCO3)). The balance between the capillary rise rate and the drying rate is important. If the drying rate is fast, Na salts will precipitate inside the porous body, making it difficult to supply liquid by capillary rise. Conversely, if the drying rate is slow, the surface will be liquid-rich and precipitation will be difficult. CO2 dissolves at the interface between the porous body and the Na salt to form a new Na salt.

[0016] Therefore, as long as the pore diameter of the porous body, temperature, and humidity are adjusted to meet this condition, porous bodies of any material (inorganic, metal, polymer (sponge), etc.) can be used. The unfired ceramics described in the following examples are not essential. However, the porous body must have alkali resistance and be wettable with alkaline water.

Examples

[0017] (Preparation of Porous Body) The porous bodies shown in Tables 1 and 2 were prepared. (Table 1) JPEG2025102103000002.jpg89144 Note that since No. 5´ can be treated as equivalent to No. 5 under the same production conditions, it was omitted from Table 1. For the raw materials of the silica-based porous body and the reaction solution, an unfired ceramic production experience kit (manufactured by F-Plan, model number: FN1S) was used. (Table 2) JPEG2025102103000003.jpg40145 Note that the measurement of porosity %, water absorption %, bulk density g / cm 3 , apparent density g / cm 3 is as follows. Apparent density ρ a , bulk density ρ b , true density ρt, as shown in Fig. 15, when considering a sample of weight W as consisting of the original solid (its volume Vs), pores open towards the surface (its volume Vo), and pores closed towards the surface (its volume Vc), the following relationships in formulas (1) to (3) hold. (Formulas 1 - 3) JPEG2025102103000004.jpg4373 Also, let P represent the porosity (open porosity) in the volume of the solid, and the following equation (4) is obtained. o It becomes Equation (4). (Equation 4) JPEG2025102103000005.jpg1561 Specifically, in accordance with JIS R1634, the weight in water, saturated weight, and dry weight were measured by the Archimedes method, and the bulk density, apparent density, porosity, and water absorption were calculated.

[0018] The No. 1 to No. 10 silica-based porous bodies in Table 1 were produced by the production method shown in Fig. 8(a). That is, 32 g, 40 g, or 50 g of a solidifying liquid mainly composed of NaOH was added to the unfired porous body raw material (silica-based raw material) and mixed, cured (60 °C, 1 day), and dried (60 °C, 1 day). Here, as the silica-based porous body raw material, for example, those with 70% or more silica can be used. Also, as the solidifying liquid mainly composed of NaOH, an alkaline solution mainly composed of NaOH or KOH can be used.

[0019] The No. 1 and No. 5 silica-based porous bodies were in a substantially disc shape with a diameter of 8 cm and a thickness of 30 mm, and the circular bottom and top surfaces had edge portions that became thicker along the circumference. The No. 4 silica-based porous body was in a substantially disc shape with a diameter of 8 cm and a thickness of 30 mm without an edge. Also, the No. 3 silica-based porous body was a rectangular parallelepiped with a thickness of 30 mm, where one side of the bottom and top surfaces was a 9 cm square with slightly rounded corners.

[0020] The No. 11 to No. 15 porous bodies used alumina instead of unfired ceramic mainly composed of silica as the raw unfired porous body raw material, and were in a substantially disc shape with a diameter of 3 cm and a thickness of 30 mm.

[0021] (Generation of precipitate using silica-based porous body) As shown in Fig. 1(a), in the atmosphere, a part including the bottom surface 1a (not shown) of the silica-based porous body 1 No. 1 was immersed in the NaOH aqueous solution 31 with a NaOH concentration of 3 mol / L placed in the container 41 and left standing (the day of standing was the first day). As shown in Fig. 1(b), on the 16th day after standing, almost entirely white precipitates 11a were formed on the edge portion 1c of the upper surface 1b, and scattered almost white precipitates 11b were generated and deposited on the inner upper surface 1b from the edge portion 1c. The bottom surface 1a is an example of at least a part of the silica-based porous body 1 selected when the silica-based porous body 1 is immersed in the NaOH aqueous solution placed in the container 41. Therefore, depending on the mode of immersing the silica-based porous body in the NaOH aqueous solution or the like, a part thereof can be appropriately selected.

[0022] On the 22nd day after standing, as shown in Fig. 1(c), the precipitate 11a' moved outward of the circle at the edge portion 1c, and the precipitate 11b' laminated in the thickness (upper side) direction over the entire inner side, increasing the amount of generation, that is, the amount of the precipitate (precipitated substance).

[0023] A part including the bottom surface 3a (not shown) of the silica-based porous body 3 No. 3 was immersed in the NaOH aqueous solution 33 with a NaOH concentration of 3 mol / L placed in the container 43 and left standing at room temperature (the day of standing was the first day). As shown in Fig. 2(a), on the 16th day after standing, slightly uneven white precipitates 13b faintly occurred on the upper surface 3b. On the 29th day after standing, as shown in Fig. 2(b), the precipitate 13b' covering the entire upper surface 3b laminated in the thickness (upper side) direction, increasing the amount of generation, that is, the amount of the precipitate.

[0024] A part including the bottom surface 2a (not shown) of the silica-based porous body 2 No. 2 was immersed in the NaOH aqueous solution 32 with a NaOH concentration of 0.1 mol / L placed in the container 42 and left standing at room temperature (the day of standing was the first day). As shown in Fig. 2(c), on the 27th day after standing, almost white precipitates 12a were generated, deposited, and laminated to some extent over about half of the circumference of the edge portion 2c.

[0025] The silica-based porous body 4 of No. 4 was immersed with its bottom surface 4a (not shown) in an aqueous Na2CO3 solution with a NaOH concentration of 1 mol / L and left standing at room temperature (the day of standing was the first day). As shown in Fig. 2(d), on the 27th day after standing, along the circumference of the upper surface 4b, a substantially white precipitate 14a occurred and precipitated over approximately 3 / 4 of the circumference, and was laminated to some extent in the thickness (upper side) direction.

[0026] The silica-based porous body 5 (5´) of No. 5 (5´) was placed in a container 45 (45´), and the portion including the bottom surface 5a ((5´a), not shown) of the silica-based porous body 5 (5´) was immersed in an aqueous NaOH solution 35 (35´) with a NaOH concentration of 3 mol / L and left standing at room temperature (the day of standing was the first day). As shown in Figs. 3(a) and (b), after standing for about one week, a substantially white precipitate 15a (15´a) occurred and precipitated over the entire edge portion 5c (5´c), and a substantially white precipitate 15b (15´b) occurred and precipitated continuously or scattered from the edge portion 5c (5´c) to the inner upper surface 5b (5´b).

[0027] (Identification of the precipitate) In Fig. 4, spectrum C shows the XRD of the precipitate in the silica-based porous body of No. 3, and spectrum D shows the XRD of the silica-based porous body of No. 5. Spectrum B shows the XRD of the precipitate of No. 4, and spectrum A shows the XRD of the precipitate in the silica-based porous body of No. 2. In spectra B, C, and D, the peak of the substance Na2(CO3)·H2O, which is the ▲ substance, was not detected, but the peak of the substance Na3(CO3)(HO3)·2H2O3, which is the ● substance, was observed under any conditions. Since Na3(CO3)(HCO3)·2H2O3 is a double salt of Na2CO3·H2O, precipitation of sodium carbonate was confirmed under any conditions. The measurement conditions of XRD, etc. are as follows. Using a copper tube target, characteristic X-rays of CuKα (wavelength (λ) = 0.15418 nm) emitted at a tube voltage of 30 kV and a tube current of 15 mA were used.

[0028] Figure 5(a) shows the XRD at positions E and F of the silica-based porous body (No. 1) shown in Fig. 5(b). The peak of Na3(CO3)·H2O, which is the substance indicated by ▲ in both, was detected. That is, the precipitation of sodium carbonate was confirmed. The measurement conditions of XRD were the same as those in Fig. 4.

[0029] (Prevention of evaporation of NaOH solution) As shown in Figs. 6(a) and 6(b), by preventing water from evaporating from the NaOH solution in which the portion including the bottom surface of the porous body 21 was immersed, a change in the NaOH concentration was prevented. The NaOH solution 36 was put into the plastic container 50, and the cylindrical plastic tube 51 containing the porous body 21 was fitted into the hole opened in the central portion of the lid 50a of the plastic container, and the plastic container 50 was covered with the lid 50a. The height of the plastic container 50 was 45 mm, and the height of the cylindrical plastic tube 51 was 50 mm. In some cases, tape was wound to maintain the sealing property between the hole opened in the central portion and the plastic tube 51.

[0030] (Relationship between NaOH concentration and precipitation amount of sodium carbonate) Using a molded body (see Fig. 8(a)) formed by the raw material unfired porous body raw material (unfired ceramic mainly composed of silica): solidifying liquid (alkali solution mainly composed of NaOH or KOH) = 100:32 (weight ratio), the relationship between the NaOH concentration in the atmosphere and the precipitation amount of sodium carbonate was investigated. As a result, as shown in Fig. 7, as the NaOH concentration increased from 1 mol / L (Fig. 7(a)) to 3 mol / L (Fig. 7(b)) and further to 5 mol / L (Fig. 7(c)), the precipitation amount of sodium carbonate increased.

[0031] (CO2 injection method) The generation and precipitation of precipitates occurring in the porous body are greatly affected by the CO₂ concentration dissolved in the NaOH solution, as explained by the precipitation mechanism described above. And to promote the precipitation of precipitates, it is effective to increase the CO₂ concentration dissolved in the NaOH solution. That is, when the solution is a NaOH solution, it is preferable from the NaOH solution to a saturated sodium carbonate solution. Therefore, as shown in Fig. 8(b), CO₂ 62 was blown into the NaOH solution 37 using the hose 61 from the cylinder 60 filled with CO₂ gas. The conditions for CO₂ blowing were as follows. The CO₂ gas was circulated at a flow rate of 150 ml / min for 3 hours.

[0032] Ions constituting the porous body, such as silicate ions and aluminate ions, dissolved substances of the porous body are present in the solution. It is presumed that although the porous body dissolves to some extent, it does not fall apart because these dissolve and reach a dissolution equilibrium without significantly damaging the porous body. Furthermore, it is presumed that by dissolving these ions from the beginning, the dissolution of the porous body can be delayed.

[0033] Regarding the silica-based porous bodies in Fig. 8(a) where the solidifying liquid is 32 g (reaction liquid amount 32%, silica-based porous body of No. 7), 40 g (reaction liquid amount 40%, silica-based porous body of No. 8), and 50 g (reaction liquid amount 50%, silica-based porous body of No. 9) respectively, their porosity (%), three-point bending strength (MPa), and pore diameter (mm) were as shown in Fig. (c) of the same figure. The porosity (%) was measured by the Archimedes method in accordance with JIS R1634. Also, the three-point bending strength (MPa) was measured in accordance with JIS R1601. Furthermore, the pore diameter (nm) was measured by the mercury intrusion method in accordance with JIS R1655 measurement.

[0034] When CO2 was blown in and the NaOH concentration of the NaOH solution to be immersed was 3 mol / L, the state of the precipitate generated on the No. 7 silica-based porous body (32 wt%, Fig. 9(a)) in the atmosphere was as shown in Fig. 9(b) on the 7th day after standing and as shown in Fig. 9(c) on the 14th day. Also, for the No. 8 silica-based porous body (40 wt%, Fig. 9(a)), the state of the precipitated sodium carbonate was as shown in Fig. 9(e) on the 7th day after standing and as shown in Fig. 9(f) on the 14th day. For both silica-based porous bodies, as the standing period became longer, the amount of precipitate generated tended to increase.

[0035] (Identification by XRD) The precipitate (product substance) generated on the No. 7 silica-based porous body (32 wt%) and the No. 8 silica-based porous body (40 wt%) was identified by XRD. As a result, as shown in Fig. 10, peaks of both Na3(CO3)(HCO3)·2H2O and Na2CO3·H2O were observed for both. Therefore, it was confirmed that the precipitate (product substance) was sodium carbonate for both. Also, the ratios of Na3(CO3)(HCO3)·2H2O and Na2CO3·H2O in both were as shown in Table 3. The measurement conditions of XRD etc. were the same as those in Fig. 4. (Table 3) JPEG2025102103000006.jpg1896

[0036] (Identification by XRF) Furthermore, the results of identification by XRF are shown in Table 4. Based on the results, for Na3(CO3)(HCO3)·2H2O, Na:C = 3:2, and for Na2CO3·H2O, Na:C = 2:1. Therefore, it should be Na:C = 64%:36%. Here, assuming that the precipitates are the same at 32 wt% and 40 wt%, since the precipitation weight ratio becomes the precipitation efficiency, it was found that 40 wt% is 7.65 times more efficient (= 1.392 g / 0.182 g × 100). The measurement conditions of XRF etc. were as follows. The Rh X-ray tube was adjusted between 4 and 50 kV and 1 and 1000 μA, and the measurement was carried out in the atmosphere. (Table 4) TIFF2025102103000007.tif21145

[0037] For the silica-based porous body of No. 7 (32 wt%), the pore diameter (nm), the porosity (%) by mercury porosimetry, and the porosity (%) by the Archimedes method were determined. Also, for the silica-based porous body of No. 8 (40 wt%) and the silica-based porous body of No. 9 (50 wt%), the pore diameter (nm), the porosity (%) by mercury porosimetry, and the porosity (%) by the Archimedes method were determined. Fig. 11 shows the results thereof.

[0038] The pore size distributions of the silica-based porous bodies of No. 7 to 9 and the fired alumina porous bodies of No. 11 to 15 were examined. As a result, it was found that the pore sizes increased in the order of the silica-based porous body of No. 8, the silica-based porous body of No. 9, and the fired alumina porous body of No. 15, for example.

[0039] (Comparison of the amount of deposits in the atmosphere (air atmosphere) and at 40 °C / 40 RH%) In the atmosphere, the portions including the respective bottom surfaces of the silica-based porous bodies of No. 7, No. 8, and No. 9 were immersed in an aqueous NaOH solution with a NaOH concentration of 3 mol / L and allowed to stand (the day of standing was the 1st day). At 20 h on the 7th day after standing, as shown in Figs. 13(a) to (c), almost white deposits occurred and precipitated on the respective upper surfaces (silica-based porous body of No. 7: Fig. (a) thereof, silica-based porous body of No. 8: Fig. (b) thereof, silica-based porous body of No. 9: Fig. (c) thereof. The amounts of deposits were 0.333 g, 0.542 g, and 0.475 g, respectively.

[0040] Instead of in the atmosphere (atmospheric environment), at a temperature of 40°C and a humidity of 40%, the parts including the bottom surfaces of the silica-based porous body No. 7, the silica-based porous body No. 8, and the silica-based porous body No. 9 were immersed in an aqueous NaOH solution with a NaOH concentration of 3 mol / L and allowed to stand (the day of standing was the first day). At 18 h on the fourth day after standing, as shown in FIGS. 14(a) to (c), almost white precipitates occurred and precipitated on the respective upper surfaces (silica-based porous body No. 7: FIG. (a) thereof, silica-based porous body No. 8: FIG. (b) thereof, silica-based porous body No. 9: FIG. (c) thereof). The amounts of the precipitates were 0.681 g, 0.635 g, and 0.910 g, respectively.

[0041] Regarding the comparison of the amounts of precipitates in the atmosphere and at 40°C / 40RH%, the amounts of precipitation (amounts of precipitates) for each silica-based porous body were compared and shown in Table 5. The precipitation efficiency numbers were calculated by dividing the amount of precipitation by the elapsed time. (The unit is [g / day]) (Table 5) TIFF2025102103000008.tif2797

[0042] From Table 5, when changing from the atmosphere (atmospheric environment) to 40°C / RH 40%, it became 3.36 times for the silica-based porous body No. 7, 1.94 times for the silica-based porous body No. 8, and 3.17 times for the silica-based porous body No. 9. Also, in the atmosphere, the silica-based porous body No. 8 showed the highest precipitation efficiency. On the other hand, in the 40°C / 40% environment, the silica-based No. 7 showed the lowest value (the lowest increase rate). And it can be seen that for all the porous bodies, the precipitation efficiency tended to increase with the increase in air temperature. Also, when the part including the bottom surface of the silica-based porous body No. 10 was immersed in an aqueous NaOH solution with a NaOH concentration of 3 mol / L at a temperature of 25°C and a humidity of 70% and allowed to stand, 0.72 g of Na2CO3 was precipitated in 10 days.

[0043] For example, sodium carbonate serves as a material for immobilizing CO2. Therefore, it can reduce CO2 from the atmosphere and has commercial value. And it can be the target of the CO2 trading price market. Normal carbon capture is to compress and place it under the underground rock formation. However, for example, sodium carbonate can be placed in a place without water and can be easily transported. Assuming that the use of oil decreases and dry ice becomes insufficient, it may be used as a Na2CO3 carbon source in the future. Also, for example, by producing methanol from CO2, etc., CO2 can be used worldwide. If these technologies are established, CO2 will become a valuable raw material. Therefore, if it can be stably stored until then, it can be assumed that the value of CO2, that is, for example, Na2CO3, will increase.

Industrial Applicability

[0044] CO2 concentration, fixation, and recovery are essential technologies for realizing the Paris Agreement. Even if the use of fossil fuels is reduced, using energy will increase CO2. Therefore, "negative emissions" are necessary. So far, in cases where the CO2 emission concentration is high, such as in power plants, ironmaking, chemicals, and cement, attempts at so-called CCS (Carbon dioxide Capture and Storage) such as separating, concentrating, and underground storage have been progressing on a large scale. However, it is difficult to use this system for DAC (Direct Air Capture) to collect CO2 once it is released into the atmosphere considering the energy balance. The present invention is in a very simple method and the system is also simple. Speaking specifically, DAC can be realized in the sense of individual households or decorating a flower on each desk, and there will surely be new markets and industries associated with this.

Explanation of Signs

[0045] 1, 2, 3, 4, 5, 5´: Silica-based porous body 1a, 2a, 3a, 4a, 5a, 5´a: Bottom surface 1b, 3b, 4b, 5b, 5´b: Upper surface 1c, 2c, 5c, 5´c: Edge part 11a, 11a´, 12a, 14a, 15a, 15´a: Deposits on the edge part 11b, 11b', 13b, 13b', 15b, 15'b: Deposits on the upper surface 21: Porous body 31, 32, 33, 35, 35', 36, 37: NaOH solution 41, 42, 43, 45, 45': Container 50: Plastic container 50a: Lid of the plastic container 51: Plastic cylinder 60: Gas cylinder 61: Hose 62: CO2 gas

Claims

Claim 1 At least a part of a porous body having pores and a portion wettable with alkaline water and being alkali-resistant is immersed in an alkaline solution, and by utilizing the capillary phenomenon of the pores and the fact that at least a part of the surface of the porous body is in contact with CO ２ contained in the atmosphere, CO ２ in the atmosphere is recovered as a salt generated by the reaction between the alkaline solution and the CO ２ in the atmosphere, the method for recovering CO ２ . Claim 2 The method for recovering CO according to claim 1, wherein the salt contains a carbonate. ２ ​ Claim 3 The method for recovering CO according to claim 2, wherein the carbonate is a carbonate containing sodium. ２ ​ Claim 4 The carbonate containing sodium includes sodium carbonate, and the method for recovering CO ２ according to claim 3. Claim 5 Further dissolving CO in the alkaline solution ２ The method for recovering CO according to any one of claims 1 to 4, which comprises ２ dissolving gas. Claim 6 A porous body having pores and a portion that can be wetted by alkaline water, which is alkali-resistant, wherein at least a part of the surface of the porous body is immersed in an alkaline solution, and by utilizing the capillary action of the pores and the fact that at least a part of the porous body is in contact with CO ２ contained in the atmosphere, salts generated by the reaction between the alkaline solution and the CO ２ in the atmosphere are recovered as salts generated by the reaction between the alkaline solution and the CO ２ in the atmosphere, and a porous body for a CO ２ recovery method.

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