Method and system for capturing and removing atmospheric carbon dioxide

Abstract

Provided are a method and a system for capturing and removing atmospheric carbon dioxide, the method and the system being capable of efficiently and directly reducing low-concentration atmospheric carbon dioxide. A method for capturing and removing atmospheric carbon dioxide according to the present invention comprises steps for generating a carbonate of sodium by using a solution of NaOH generated through electrolysis or electrodialysis and bringing the same into contact with atmospheric carbon dioxide. The method comprises the following first to fourth steps. (1) A first step for spreading the solution of NaOH onto a hydrophilic and porous medium to wet the same. (2) A second step for generating sodium carbonate by causing atmospheric carbon dioxide to come into contact with the NaOH. (3) A third step for adding water to maintain a moist state in which water is present in a liquid phase and to thereby increase the CO2 / Na ratio in the carbonate of sodium. (4) A fourth step for draining out a solution of the carbonate of sodium from the medium and collecting the same in a storage tank.

Description

Method and system for capturing and removing carbon dioxide from the atmosphere

[0001] The present invention relates to a method and system for capturing and removing carbon dioxide from the atmosphere. This application claims priority to Japanese Patent Application No. 2023-218078, filed on December 25, 2023, the contents of which are incorporated herein by reference.

[0002] As a measure against climate change, several methods for direct air capture (DAC) of atmospheric carbon dioxide have been researched and developed. Among these, a technology that captures low concentrations (400 ppm) of carbon dioxide in the atmosphere by absorbing and reacting them with an alkaline aqueous solution such as sodium hydroxide or potassium hydroxide is progressing toward practical operation. Carbon dioxide can be captured by converting it into carbonates such as calcium carbonate, or separated as concentrated carbon dioxide (see Non-Patent Document 1).

[0003] Various methods have been adopted for supplying this alkaline aqueous solution. For example, a method has been devised in which a sodium hydroxide aqueous solution is produced by electrolyzing seawater present in large quantities, and the sodium hydroxide aqueous solution is supplied to concentrated seawater while carbon dioxide is supplied, and the carbon dioxide reacts with magnesium in the seawater to recover magnesium carbonate (see Patent Document 1).

[0004] Regarding the captured carbonates containing carbon dioxide, methods such as separating carbon dioxide by heat treatment or storing it underground are being considered. Furthermore, to efficiently capture low concentrations (400 ppm) of carbon dioxide in the atmosphere, an air contactor that brings an alkaline aqueous solution into contact with air is used. Conventional techniques, such as an absorption tower that draws air into the air contactor using a blower and brings the air into gas-liquid contact, are used in air contactors (Non-Patent Document 1). Other methods have also been devised, such as simply bubbling the drawn-in air through an alkaline aqueous solution or spraying the air onto a moving alkaline aqueous solution to bring the air into contact and absorb it (see Patent Document 1). Other methods have also been devised, such as simply spraying an alkaline aqueous solution into the drawn-in air to bring the air into contact and absorb it (see Patent Document 2).

[0005] Another method has been proposed in which the surface of a smooth or roughened plate covered with an alkaline aqueous solution is exposed to an air flow maintained in a laminar or near-laminar state (see Patent Document 3).

[0006] On the other hand, in electrochemical reaction devices such as electrolysis, salts containing Na (NaCl and Na ２ SO ４ ) to produce an acidic aqueous solution and a basic NaOH aqueous solution, and CO ２ There is a report on a carbon dioxide removal (CDR) technology in which a carbon dioxide reacts with a metal to generate carbonate, which is then recovered and fixed (Patent Document 4).

[0007] Japanese Patent Application Laid-Open No. 2023-25798 Japanese Patent Application Laid-Open No. 2022-105973 Special Publication No. 2008-510600 International Publication No. 2022 / 191095

[0008] Japan Science and Technology Agency, Center for Low Carbon Society Strategy, "Proposal for Innovation Policy Planning Based on Quantitative Scenarios of Technology, Economy, and Society Toward a Low Carbon Society: Cost and Evaluation of the Direct Air Capture (DAC) Method for Carbon Dioxide," [online], February 2020, [Retrieved September 20, 2023], Internet <URL: https: / / www. jst. go. jp / lcs / pdf / fy2019-pp-07.pdf>

[0009] When high-concentration carbon dioxide emitted by combustion reactions at thermal power plants, factories, and the like is captured and removed using a liquid such as an alkaline aqueous solution, an absorption tower or the like is used to absorb the gas into the liquid through gas-liquid contact. However, compared to such cases, the concentration of carbon dioxide in the atmosphere is low (400 ppm) and the absorption rate is significantly slower, making the absorption tower method unsuitable. Furthermore, methods such as bubbling air through an alkaline aqueous solution, spraying onto a moving alkaline aqueous solution, or spraying the alkaline aqueous solution in air to achieve gas-liquid contact, or exposing a surface covered with an alkaline aqueous solution to an air flow maintained in a laminar or near-laminar state, are inefficient due to the small area of ​​gas-liquid contact.

[0010] On the other hand, in addressing climate change, it is desirable to suppress the release of new carbon dioxide into the atmosphere due to the energy consumption required to install and operate atmospheric carbon dioxide capture systems. Furthermore, even if renewable energy is used as a power source for operation, the amount of energy consumed reduces the amount of energy available for other uses, indirectly impacting the environment. Therefore, reducing the amount of energy consumed is desirable. When capturing carbon dioxide using an alkaline aqueous solution in an absorption tower, the air conditioner's blower consumes a large amount of energy due to pressure loss caused by the packing used for gas-liquid contact. Furthermore, because the absorption tower requires the release of a large amount of alkaline aqueous solution, the air conditioner's liquid pump also consumes a relatively large amount of energy. Absorption towers are also expensive to install. Furthermore, when capturing low concentrations of carbon dioxide in the atmosphere, the blower and liquid pump consume a certain amount of energy, even when using gas-liquid contact methods such as blowing or bubbling air taken into the air conditioner or spraying alkaline aqueous solution.

[0011] In addition, in the technology disclosed in Patent Document 3, the alkaline aqueous solution exposed to the airflow maintained in a laminar or near-laminar state completely covers the surface of a smooth or roughened plate and moves by flowing over the surface of the plate. In this case, the airflow comes into gas-liquid contact with the liquid surface of the alkaline aqueous solution covering the entire surface of the plate, and the contact area is at most the apparent surface area of ​​the plate, which is inefficient. Furthermore, even if the surface area is increased by roughening the plate surface, the roughening causes the contacting airflow to transition from laminar to turbulent, resulting in increased pressure loss. Patent Document 4 uses NaOH produced by an electrochemical reaction device such as electrolysis, but does not disclose a method for efficiently capturing and removing carbon dioxide from dilute atmospheric air.

[0012] The objective of the present invention is to provide a method and system for recovering and removing carbon dioxide from the atmosphere, which is capable of efficiently and directly reducing dilute carbon dioxide in the atmosphere by using an aqueous NaOH solution produced by an electrochemical reaction with sodium salt, in relation to measures to prevent global warming using electricity such as renewable energy.

[0013] The inventors have studied various factors related to the capture of low concentrations of carbon dioxide in the atmosphere as a measure against climate change, and have invented a method and system for capturing and removing carbon dioxide from the atmosphere. To achieve the goal of efficiently capturing and removing carbon dioxide from the atmosphere and immobilizing it, the inventors have invented a method and system for capturing and removing carbon dioxide from the atmosphere. In this process, an acidic aqueous solution and an aqueous solution of NaOH are produced by electrolysis or electrodialysis, and carbon dioxide from the atmosphere is brought into contact with the aqueous solution of NaOH to produce carbonate. The process involves bringing the aqueous solution of NaOH into contact with a hydrophilic and porous medium so that the aqueous solution spreads over the medium, and evaporating the water from the aqueous solution to form a layer of NaOH, and then allowing the carbon dioxide from the atmosphere to come into contact with the layer of NaOH in an air-dried state, resulting in the formation of NaOH. ２ CO ３ (CO ２ / Na ratio = 0.5), and then adding water to the medium to keep the medium in a wet state with liquid water present, and ２ CO ３ NaHCO ３ ・2H ２ O.CO. ２ / Na = 0.67) or bicarbonate (NaHCO ３ .CO ２ The carbonate solid containing HCl (Na = 1) is grown as a crystal while CO ２ It has been found that the above-mentioned problems can be solved by a method characterized by a series of steps including a step of improving the Na / Na ratio, and a step of washing the medium with water by supplying water that dissolves carbonates attached to the medium, causing the carbonates to flow out of the medium and be collected in a storage tank, and reusing the washed medium.

[0014] Specifically, the present invention relates to the following carbon dioxide recovery system: [1] A method for recovering and removing carbon dioxide from the atmosphere, which includes a step of contacting carbon dioxide in the atmosphere with an aqueous solution of NaOH produced by electrolysis or electrodialysis to produce sodium carbonate, characterized in that the method for recovering and removing carbon dioxide from the atmosphere comprises the following first to fourth steps: (1) A first step of wetting and spreading the aqueous solution of NaOH on a hydrophilic and porous medium; (2) A deposition layer of NaOH is formed on the medium while evaporating the water content of the aqueous solution, and carbon dioxide in the atmosphere comes into contact with the deposition layer of NaOH to produce sodium carbonate (Na ２ CO ３ .CO ２ (3) Add water to the NaOH layer formed on the medium to maintain a wet state in which liquid water is present, and then add sodium sesquicarbonate (Na ２ CO ３ NaHCO ３ ・2H ２ O.CO. ２ / Na = 0.67) and sodium bicarbonate (NaHCO ３ .CO ２ / Na=1), while growing a crystal of the sodium carbonate containing at least one selected from the group consisting of CO ２ [2] The method for capturing and removing carbon dioxide from the atmosphere according to [1], further comprising a fifth step (5) of reusing the washed medium. [3] The method for capturing and removing carbon dioxide from the atmosphere according to [1] or [2], characterized in that in the fourth step, the sodium carbonate is extracted from the aqueous solution of sodium carbonate accumulated in the storage tank and stored on land in a place without inflow of water. [4] In the third step, the CO2 of the solid sodium carbonate or its aqueous solution is extracted. ２[5] The method for recovering and removing carbon dioxide from the atmosphere according to any one of [1] to [3], characterized in that the water content in the process is controlled by measuring the NaOH / Na ratio and the pH of the aqueous solution of sodium carbonate. [6] The method for recovering and removing carbon dioxide from the atmosphere according to any one of [1] to [4], characterized in that in the second process, the carbon dioxide in the atmosphere comes into contact with the NaOH deposit layer by natural wind. [7] The method for recovering and removing carbon dioxide from the atmosphere according to any one of [1] to [4], characterized in that in the fourth process, NaCl or NaOH is added to the aqueous solution of sodium carbonate collected in the storage tank. ２ SO ４ [7] In the fourth step, the aqueous solution of sodium carbonate collected in the storage tank is in a liquid-solid mixed state in which a solid salt containing sodium sesquicarbonate and a saturated aqueous solution are mixed, and the liquid phase is removed and returned to the medium, and the solid CO ２ [8] The method for capturing and removing carbon dioxide from the atmosphere according to any one of [1] to [5], further comprising a step of separating carbonates having a CO / Na ratio greater than that of sodium sesquicarbonate. ２ CO gas is introduced to the aqueous solution. ２ [9] The method for recovering and removing carbon dioxide from the atmosphere according to any one of [1] to [5], characterized in that the ratio of sodium carbonate and its aqueous solution in the first closed treatment tank is increased. ２

[10] The method for recovering and removing carbon dioxide from the atmosphere according to [8], characterized in that a gas is generated and introduced into a second closed treatment tank. ２

[11] The method for capturing and removing carbon dioxide from the atmosphere according to [8], wherein the gas is at least one selected from the group consisting of soil release gas, biomass decomposition gas, exhaust gas due to respiration of organisms, gas derived from gas and oil fields, and exhaust gas from auxiliary equipment that uses combustion. ２

[12] The method for recovering and removing carbon dioxide from the atmosphere according to any one of [1] to

[11] , further comprising the steps of: bringing the acidic aqueous solution produced by the electrolysis or electrodialysis into contact with a basic mineral to produce an aqueous solution containing alkaline earth metal ions; mixing the produced aqueous solution containing alkaline earth metal ions with the solid salt of sodium carbonate obtained in the fourth step or an aqueous solution containing same; precipitating the alkaline earth metal carbonate and storing it on land; producing an aqueous solution of sodium salt, which is reused for the electrolysis or electrodialysis;

[13] The method for recovering and removing carbon dioxide from the atmosphere according to any one of [1] to

[11] , further comprising the steps of: ２

[14] A system for recovering and removing carbon dioxide in the atmosphere, which produces sodium carbonate by contacting carbon dioxide in the atmosphere with an aqueous solution of NaOH produced by electrolysis or electrodialysis, characterized in that the system for recovering and removing carbon dioxide in the atmosphere comprises the following NaOH aqueous solution diffusion treatment unit to cleaning treatment unit: (1) An aqueous NaOH solution diffusion treatment unit including a hydrophilic and porous medium and having a mechanism for wetting and spreading the aqueous NaOH solution on the hydrophilic and porous medium; (2) A method for recovering and removing carbon dioxide in the atmosphere according to

[12] , further comprising a step of recovering sodium carbonate (Na ２ CO ３ .CO ２ / Na ratio = 0.5) ２(3) Add water to the NaOH layer formed on the medium to maintain a wet state where liquid water is present, and then add sodium sesquicarbonate (Na ２ CO ３ NaHCO ３ ・2H ２ O.CO. ２ / Na = 0.67) and sodium bicarbonate (NaHCO ３ .CO ２ / Na=1), while growing a crystal of the sodium carbonate containing at least one selected from the group consisting of CO ２ (16) The system for capturing and removing carbon dioxide from the atmosphere according to

[14] or

[15] , further comprising: (1) a water-controlling treatment unit having a mechanism for improving the Na / Na ratio. (4) A cleaning treatment unit having a mechanism for washing the medium with water by supplying water that dissolves the sodium carbonate attached to the medium, causing the aqueous solution of sodium carbonate to flow out from the medium and collect in a storage tank.

[15] The system for capturing and removing carbon dioxide from the atmosphere according to

[14] , further comprising: (5) a medium recycling unit that reuses the washed medium.

[16] The system for capturing and removing carbon dioxide from the atmosphere according to

[14] or

[15] , further comprising: a sub-treatment unit that extracts the sodium carbonate from the aqueous solution of sodium carbonate collected in the storage tank in the cleaning treatment unit and stores it on land in a place where there is no inflow of water.

[17] The system for capturing and removing carbon dioxide from the atmosphere according to

[14] or

[15] , further comprising: a water-controlling treatment unit that extracts the sodium carbonate from the aqueous solution of sodium carbonate collected in the storage tank in the water-controlling treatment unit, and stores the sodium carbonate on land in a place where there is no inflow of water.

[17] The system for capturing and removing carbon dioxide from the atmosphere according to

[14] or

[15] , further comprising: a water-controlling treatment unit that extracts the sodium carbonate from the aqueous solution of sodium carbonate collected in the storage tank in the water-controlling treatment unit. ２ The system for recovering and removing carbon dioxide in the atmosphere according to any one of

[14] to

[16] , further comprising a sub-processing unit that measures the water content of the processing unit by measuring the water content of the aqueous solution of sodium carbonate and the ratio of CO 2 to Na 2 , and the pH of the aqueous solution of sodium carbonate. ２ The system for recovering and removing carbon dioxide in the atmosphere according to any one of

[14] to

[17] , wherein in the collection treatment unit, the carbon dioxide in the atmosphere comes into contact with the NaOH deposit layer by natural wind.

[19] In the cleaning treatment unit, NaCl or Na ２ SO ４

[20] The system for recovering and removing atmospheric carbon dioxide according to any one of

[14] to

[18] , further comprising a sub-processing unit that allows the aqueous solution of sodium carbonate collected in the storage tank to coexist with a saturated aqueous solution of sodium sesquicarbonate, and then precipitates and separates a second solid salt of carbonate. ２

[21] The system for recovering and removing carbon dioxide from the atmosphere according to any one of

[14] to

[19] , further comprising a sub-processing unit for separating carbonates having a CO / Na ratio greater than sodium sesquicarbonate.

[22] In the cleaning process unit, the aqueous solution of sodium carbonate collected in the storage tank is transferred to a closed treatment tank, and a CO concentration higher than that of the atmosphere is added to the closed treatment tank. ２ CO gas is introduced to the aqueous solution. ２

[22] The system for recovering and removing carbon dioxide from the atmosphere according to any one of

[14] to

[20] , further comprising a sub-treatment unit for increasing the sodium carbonate and its aqueous solution in a first closed treatment unit. ２

[23] The system for recovering and removing atmospheric carbon dioxide according to

[21] , wherein the gas is generated and introduced into the second closed treatment tank. ２

[24] The system for recovering and removing carbon dioxide from the atmosphere according to

[21] , wherein the gas is at least one selected from the group consisting of soil release gas, biomass decomposition gas, exhaust gas due to respiration of organisms, gas derived from a gas or oil field, and exhaust gas from auxiliary equipment that uses combustion. ２

[25] The system for recovering and removing carbon dioxide from the atmosphere according to any one of

[14] to

[23] , further comprising a sub-processing unit that separates and recovers gas.

[25] The system for recovering and removing carbon dioxide from the atmosphere according to any one of

[14] to

[24] , further comprising a sub-processing unit that brings the acidic aqueous solution produced by the electrolysis or electrodialysis into contact with a basic mineral to produce an aqueous solution containing alkaline earth metal ions, mixes the produced aqueous solution containing alkaline earth metal ions with the solid salt of sodium carbonate obtained in the cleaning process unit or an aqueous solution containing same, precipitates the alkaline earth metal carbonate and stores it on land, produces an aqueous solution of sodium salt, and reuses it in the electrolysis or electrodialysis.

[26] The system for recovering and removing carbon dioxide from the atmosphere according to any one of

[14] to

[24] , further comprising a sub-processing unit that separates and recovers gas. ２ The system for recovering and removing carbon dioxide from the atmosphere according to

[25] , further comprising a sub-processing unit for recovering the carbon dioxide.

[0015] The present invention provides a method and system for capturing and removing atmospheric carbon dioxide that can efficiently and directly reduce carbon dioxide in dilute atmospheric air. Gravity, capillary action, and other factors can be effectively utilized. Compared to conventional technologies such as DAC-CCS, this method is low-energy and low-cost, and will lead to the realization of large-scale, economical negative emissions.

[0016] FIG. 1 is a principle diagram showing a method or system for capturing and removing carbon dioxide in the atmosphere according to this embodiment; FIG. 2 is a schematic diagram (simplified side view) of a method or system for capturing carbon dioxide when the medium is an inclined surface; FIG. 3 is a schematic diagram of a method or system for capturing carbon dioxide when the medium is a curtain-shaped medium; FIG. 4 is a schematic diagram of a method or system for capturing carbon dioxide showing another example of the medium (protrusions); ２ / Na ratio calibration curve (electrical conductivity (Ec) vs. pH) and atmospheric CO ２ 1 shows the actual measured values ​​(A and B) of the carbonate aqueous solution from Na ＋ CO2 ion meter and pH meter ２ / Na ratio calibration curve (Na ＋ Ion meter reading concentration vs. pH) and atmospheric CO２ FIG. 1 shows the actual measured values ​​(points between A and B) of the aqueous carbonate solution from

[0017] (Method for recovering and removing atmospheric carbon dioxide) A method for recovering and removing atmospheric carbon dioxide according to one embodiment of the present invention (sometimes referred to as the "method for recovering and removing atmospheric carbon dioxide according to this embodiment" or the "method for recovering and removing carbon dioxide according to this embodiment") is a method for recovering and removing atmospheric carbon dioxide, comprising a step of producing sodium carbonate by contacting atmospheric carbon dioxide with an aqueous solution of NaOH produced by electrolysis or electrodialysis. The method for recovering and removing carbon dioxide according to this embodiment comprises the following first to fourth steps.

[0018] (1) A first step of wetting and spreading the aqueous solution of NaOH on a hydrophilic and porous medium. (2) A layer of NaOH is formed on the medium while evaporating the water content of the aqueous solution. Carbon dioxide in the atmosphere comes into contact with the layer of NaOH to form sodium carbonate (Na ２ CO ３ .CO ２ (3) Add water to the NaOH layer formed on the medium to maintain a wet state in which liquid water is present, and then add sodium sesquicarbonate (Na ２ CO ３ NaHCO ３ ・2H ２ O.CO. ２ / Na = 0.67) and sodium bicarbonate (NaHCO ３ .CO ２ / Na=1), while growing a crystal of the sodium carbonate containing at least one selected from the group consisting of CO ２ (4) a fourth step of washing the medium with water by supplying water that dissolves the sodium carbonate adhering to the medium, thereby causing the aqueous solution of sodium carbonate to flow out from the medium and collect in a storage tank.

[0019] In the carbon dioxide capture and removal method of this embodiment, the first step preferably further includes a substep of producing the NaOH aqueous solution using an electrolysis or electrodialysis device. That is, the first step preferably includes producing the NaOH aqueous solution using an electrolysis or electrodialysis device and spreading the produced NaOH aqueous solution on a hydrophilic and porous medium. As described above, when the first step includes a substep of producing the NaOH aqueous solution using an electrolysis or electrodialysis device, the electrolysis or electrodialysis device and a device containing the medium used in steps 2 to 4 can be installed nearby. The produced NaOH aqueous solution can be transported via pipeline, for example, even in its aqueous solution state. This significantly reduces transportation costs and energy. This is because, to reduce the energy (power consumption) required for electrolysis and dialysis, it is effective to use the medium-concentration acid-base aqueous solution, for example, approximately 0.2 M to 1 M, as it is, as it is, as it is, coming out of the electrochemical device, without concentration. As a result, the carbon dioxide capture and removal method of this embodiment is significantly significant in that it can be completed almost entirely in isolated areas such as remote islands and deserts.

[0020] Fig. 1 is a principle diagram showing an example of a method for recovering and removing atmospheric carbon dioxide according to this embodiment. As an example of the method for recovering and removing atmospheric carbon dioxide according to this embodiment, the process can be carried out in the order shown in Fig. 1. (S2) An aqueous solution of NaOH produced by electrolysis or dialysis is spread on a hydrophilic and porous medium. (S3) Atmospheric CO ２ (S0) is brought into contact with a hydrophilic porous medium coated with a film of NaOH aqueous solution. (S4) Then, it is air-dried on the medium, and Na ２ CO ３ Generation (CO ２ (S5) Wet CO on the medium. ２ / Na ratio improvement (sesquichloride and NaHCO ３ (S7) After the salt is washed and discharged (S6), the carbonate solution is collected in a storage tank.

[0021] <Electrolysis / Electrodialysis> The electrolysis or electrodialysis used in the method for recovering and removing carbon dioxide of this embodiment is not particularly limited as long as it is an apparatus that can produce an aqueous solution of NaOH from an aqueous solution containing a sodium salt such as sodium chloride using an electrolysis method or an electrodialysis method. An alkali salt such as potassium may be mixed with the sodium salt. Examples of such an apparatus include an electrolysis apparatus and an electrodialysis apparatus.

[0022] The electrolysis and electrodialysis preferably consume little power. For example, the power source unit for electrolysis in industrial chloralkali electrolysis synthesis is around 2.1 Wh / g-NaOH, and the figure becomes even larger when the energy consumption of peripheral auxiliary equipment is added. The electrolysis and electrodialysis used in the recovery and removal method of this embodiment preferably consumes energy at the same level or less than this figure. At least, the conditions for the purity and concentration of the NaOH produced are more relaxed than in industrial NaOH production, so the overall energy consumption can be reduced. NaOH aqueous solution production and CO ２ If absorption is performed in a nearby location, transportation energy can be reduced. Furthermore, compared to conventional DACs, fan and heat energy are almost unnecessary. As a result, the overall CO ２ The energy and cost of the process can be low.

[0023] The sodium salts are NaCl and Na ２ SO ４ Rock salt containing NaCl, seawater, salt water, underground brine, etc. can be used, but rock salt with a relatively high purity, especially rock salt containing NaCl, is preferred. ２ Electricity with as small an emission coefficient as possible should be used, preferably electricity from renewable energy sources. The concentration of the generated aqueous NaOH solution is preferably 0.01 M to 2 M, and considering power consumption and overall costs, 0.1 M to 0.5 M is preferred.

[0024] "Electrolysis Device" The electrolysis device may be either a hydrogen generation type or an oxygen reduction type. When infrastructure for consuming and selling hydrogen is in place, the hydrogen generation type is preferred. Furthermore, when hydrogen infrastructure is not in place, the oxygen reduction type is preferred from the viewpoint of low power consumption. The electrolysis device may include an electrolyte, a diaphragm, a cathode electrode, and an anode electrode. The electrolyte includes an anolyte and a catholyte. The diaphragm separates the anolyte and the catholyte in the electrolysis device. The diaphragm in this embodiment may be an ion exchange membrane or a porous membrane (a method known as a diaphragm method). Since it is preferable that the raw salt contains few Ca and Mg ions as impurities, it is recommended to remove them through pretreatment using a precipitant, an ion exchange agent, or the like, taking into consideration cost and energy consumption. When the raw salt contains a large amount of impurities, a porous membrane diaphragm method is preferred. A disadvantage of the conventional diaphragm method is poor NaOH concentration and purity, but this drawback is not a major problem in this patent. On the other hand, when the raw material salt contains few impurities, an ion exchange membrane is preferred for improving electrolysis efficiency and carbon dioxide neutralization efficiency. In particular, it is preferable to use a cation exchange membrane that allows alkali metal ions to pass between the cathode and the cathode, and a selective permeable membrane for monovalent cations. Unexpected electron or ion movement prevents the flowing current from being used for acid-base generation, resulting in a decrease in current efficiency. When using a porous membrane diaphragm, measures are required to prevent undesired ion flow, such as creating a one-way water flow to prevent mixing of a basic aqueous solution with an acidic aqueous solution. Furthermore, placing an ion exchange membrane on the anode side is also preferable for improving current efficiency. The current efficiency should be at least 70%, preferably 90% or higher, and more preferably closer to 100%.

[0025] Seawater or salt water can be used as the aqueous solution containing sodium chloride, which is the electrolyte of the electrolysis device. The same raw material purification technology as that used in conventional chloralkali electrolysis using seawater can be used. The electrolyte concentration is 0.1 M or more, preferably 0.5 M or more to reduce resistance, more preferably 1 M or more, or the saturated concentration of the salt. The concentration should be as high as possible within the soluble range, and 5 M or more is even more preferable. To prevent the generation of chlorine, MnO ２For example, an electrode using a catalyst for oxygen generation (chlorine suppression) such as the above, or a cation exchange resin modified electrode, or a method of adding an ion exchange membrane in addition to the diaphragm, is used.

[0026] "Electrodialysis Device" The electrodialysis device described above is constructed by stacking bipolar membranes and ion exchange membranes. It can be a two-compartment device consisting of a bipolar membrane and a cation exchange membrane, or a three-compartment device consisting of a bipolar membrane, a cation exchange membrane, and an anion exchange membrane. Tens to thousands of these membrane sets are typically stacked, with anode and cathode electrodes at both ends. In a three-compartment device, the raw salt, NaOH, and acid can be separated into separate chambers. A two-compartment device has the advantage of requiring less voltage (power) than a three-compartment device. Although the acid and raw material are mixed, this technology can be used. The power consumption can be reduced to a level equivalent to that of the oxygen reduction electrolysis device described above. While the current density is lower than that of an electrolysis device, this can be overcome by improving the membrane. While electrolysis devices face resource issues for electrode materials in future large-scale applications, electrodialysis devices have the advantage of requiring significantly fewer electrodes, eliminating resource issues. Hydrocarbon-based bipolar and ion exchange membranes are the mainstream, and mass production of membranes can significantly reduce costs. To reduce power consumption, the current density is set to 5 to 500 mA / cm ２ , preferably 10 to 50 mA / cm ２ is.

[0027] <First Step> As the first step of the carbon dioxide capture and removal method of this embodiment, a step of wetting and spreading the NaOH aqueous solution over a hydrophilic and porous medium will be described. The first step corresponds to S2 shown in FIG. 1. The method of wetting and spreading the NaOH aqueous solution over a hydrophilic and porous medium is not particularly limited, and examples thereof include supplying the NaOH aqueous solution from above the medium. For example, a method of placing the medium on an inclined substrate and supplying the NaOH aqueous solution upstream of the medium can be used. When the medium is placed at an angle, gravity allows the NaOH aqueous solution to spread downstream.

[0028] FIG. 2 shows a schematic diagram (simplified side view) of a carbon dioxide capture system in which the medium is an inclined surface. For example, a sloped structure is possible in which the medium 10 is placed on an inclined surface 50 formed like a hillside, and an NaOH aqueous solution is supplied from a nozzle 30-1 to the top of the medium 10, causing it to flow through the inclined medium 10 toward the storage tank 20 below. Alternatively, the medium itself may have a three-dimensional structure with an inclined surface, without providing an inclined surface 50. As the NaOH aqueous solution flows down the surface of the inclined surface or inside the medium, it can be circulated through the medium and the medium by carbon dioxide in the atmosphere, wetting and spreading the solution throughout the medium.

[0029] FIG. 3 shows a method of capturing carbon dioxide using a curtain-shaped medium 10. The medium is formed into a belt-like shape using fabric such as a curtain or ribbon and is hung down. A mechanism for supplying an aqueous NaOH solution is provided above the medium 10. For example, as shown in FIG. 3, a required amount of aqueous NaOH solution can be supplied through a nozzle 30-1 connected to an upper pipe 40-1. The middle pipe 40-2 shown in FIG. 3 may supply an aqueous NaOH solution through a nozzle 30-2, or may supply water as described below.

[0030] "Hydrophilic and porous medium" The hydrophilic and porous medium used in the method for capturing and removing carbon dioxide according to this embodiment (sometimes referred to as "the medium according to this embodiment") is hydrophilic and porous. Because the medium according to this embodiment is hydrophilic and porous, it can effectively bring NaOH into contact with dilute (approximately 400 ppm) atmospheric carbon dioxide. If the medium according to this embodiment is hydrophilic, the aqueous NaOH solution will spread evenly over the medium, and even after the water has evaporated, the NaOH will form a very thin layer of adhesion on the medium. This is because NaOH itself is hydrophilic. Fewer devices are required to uniformly supply the aqueous NaOH solution to the medium, making it much simpler and less costly. Without hydrophilicity, NaOH would become large particles, reducing the actual surface area and increasing the CO ２ The presence of large particles can be observed by observing their shape with a scanning electron microscope. If the thickness of the medium is increased within a range of 1 mm or less, the initial CO ２Since the absorption rate improved, it is clear that it is desirable for NaOH to be dispersed thinly and widely in the medium. If the medium is too thick, it will be costly, and if it is too thin, the water retention capacity will be low. The thickness is preferably 0.01 to 100.0 mm, more preferably 0.1 to 10.0 mm.

[0031] Furthermore, because the medium according to this embodiment is porous, when the NaOH aqueous solution spreads uniformly over the medium, the actual surface area (specific surface area of ​​the medium) becomes larger, the gas-liquid interface and the gas-solid interface become larger, and the aqueous NaOH solution can effectively come into contact with carbon dioxide in the atmosphere.

[0032] The porous material can be classified into micropores (<2 nm), mesopores (2 to 50 nm), and macropores (>50 nm) depending on their diameter. The pore size that can be wetted with the NaOH aqueous solution of the present invention is not particularly limited, as it also depends on the hydrophilicity of the medium. In addition, a large number of macropores is preferable, taking into account the film thickness.

[0033] In this embodiment, the medium is preferably a substrate such as a cloth, fiber, curtain, sponge, or plate, with minute micropores (<50 nm), macropores (>50 nm), or irregularities on the surface, making it porous so that water can seep in.

[0034] The medium according to this embodiment preferably has liquid permeability or air permeability. That is, the porous pores preferably have interconnected pores. It is preferable to have macropores that allow gas to pass through in two or more directions, rather than micropores that allow gas to stagnate or become blocked with NaOH. In this case, carbon dioxide in the atmosphere can efficiently come into contact with the surface of the medium.

[0035] The medium according to this embodiment preferably also has base resistance and durability. The base resistance preferably includes long-term durability against high concentrations of NaOH. Examples of such media include organic materials such as cellulose and rayon, which have hydroxyl groups (OH groups) or carboxyl groups on their surfaces, and hydrophilic polymers such as surface-treated polyalkanes. Other examples of such media include inorganic materials such as aluminum silicate, zirconia, alumina, silicates, titania, glass wool, asbestos materials, and basalt fiber. These materials have surface hydroxyl groups and are hydrophilic. Hydrophilicity can be determined by whether or not a drop of water penetrates and spreads, or whether the contact angle is 90 degrees or less.

[0036] To impart durability, the hydrophilic material may be composited with a stable resin such as nylon or PPS (polyphenylene sulfide). The medium according to this embodiment may be a composite containing at least one hydrophilic substance and another substance. In this case, for example, a hydrophilic porous substance may be coated on another substance, or a hydrophilic substance may be coated on another porous substance. When the medium according to this embodiment is a composite, specific examples include a composite in which a PPS mesh is coated with a mixture of zirconium oxide and a polymer, such as a membrane for water electrolysis, and a composite of nylon and an ion exchange membrane (an anion exchange membrane and a cation exchange membrane).

[0037] Furthermore, strong base resistance is required for the portion that comes into contact with NaOH, but strong base resistance is not required for the portion where carbonation progresses and the pH decreases.

[0038] <Second step> <Air drying of NaOH: NaOH → Na ２ CO ３ In the second step of the carbon dioxide recovery and removal method of this embodiment, a layer of NaOH is formed while evaporating the water content of the aqueous solution, and carbon dioxide in the atmosphere comes into contact with the layer of NaOH, resulting in the formation of NaOH. ２ CO ３ (CO ２The process for producing a NaOH solution (Na ratio = 0.5) is described below. The water evaporates, exposing solid NaOH, but by adjusting the medium, a thin NaOH layer can be easily formed. It is preferable that the NaOH layer is formed while evaporating the water from the aqueous solution, and that atmospheric carbon dioxide comes into contact with the NaOH layer. The NaOH layer that comes into contact with atmospheric carbon dioxide may be in a dry or semi-dry state, or in a wet state containing an aqueous NaOH solution. It is preferable that the NaOH layer be as dry or semi-dry as possible. It is preferable that the atmospheric carbon dioxide comes into contact with the NaOH layer by natural wind. Furthermore, when the atmospheric carbon dioxide comes into contact with the NaOH layer by natural wind, the NaOH layer that comes into contact with the atmospheric carbon dioxide by the natural wind may be in an air-dried state, or in a wet state containing an aqueous NaOH solution. It is preferable that the NaOH layer be as air-dried as possible.

[0039] The air-drying state refers to a state in which the moisture contained in a material evaporates due to the wind and the material dries.

[0040] NaOH gradually ２ CO ３ Salt (CO ２ / Na ratio = 0.5), this reaction occurs both in aqueous solution and in solid phase. Since the reaction proceeds more easily in solid than in aqueous solution, it is desirable to have less water. ２ CO ３ The salts of exist in anhydrous and hydrated forms. When carrying out outdoors where there is a lot of precipitation, it is advisable to install a roof to prevent rain from directly hitting the medium and storage tank. Also, if drying is promoted by sunlight, CO ２ If the media deteriorates due to sunlight, measures should be taken to improve the light resistance of the media or to block the light. ２ As the absorption reaction of NaOH progresses, the CO ２ The / Na ratio increases and the pH of the solution decreases. ２ CO ３ is stable even at high temperatures, and the higher the reaction temperature, the more Na ２ CO ３ The carbonation reaction is faster up to

[0041] <3rd step> <Na ２ CO ３ →Sodium sesquicarbonate: Wetting> In the third step of the method for recovering and removing carbon dioxide according to the present embodiment, water is then added onto the medium to maintain a wet state in which liquid water is present, and sodium sesquicarbonate (Na ２ CO ３ NaHCO ３ ・2H ２ O.CO. ２ While growing a crystal of sodium carbonate containing HCl (Na = 0.67), CO ２ The step of increasing the Na / Na ratio will now be described.

[0042] Here, a "wet state" refers to a state in which both solid salt and liquid aqueous solution exist. This solid-liquid reaction causes sodium sesquicarbonate to grow crystals. In the liquid phase, ions move more freely than in the solid phase. Crystal growth refers to the growth of solid salt crystals or an increase in total amount. This can be determined by the intensity of peak patterns in XRD (X-ray diffraction). If the aqueous solution is dilute, the crystals will dissolve, so it is desirable for the aqueous solution to be saturated or close to saturated. Adding water dilutes the solution in parts, but as the water spreads widely throughout the medium, crystal dissolution is minimized. Furthermore, by repeating dissolution and reprecipitation, small crystals dissolve preferentially and grow into larger crystals.

[0043] In the third step, it is preferable that liquid water is present in the porous pores of the medium according to this embodiment and in the grain boundaries of the carbonate crystals. That is, the water is not present enough to flow off, but is wet enough that, for example, water transfers to filter paper when pressed against it. A truly wet state is desirable.

[0044] The reaction proceeds and CO ２ / Na ratio = 0.5 Na ２ CO ３ Above this state, the carbonation reaction proceeds more easily in a wet state than in a dry state. The location and timing of adding water for wetting is determined by the amount of NaOH on the medium. ２ CO ３However, if too much water is supplied, carbonate will flow out of the medium into the reservoir tank due to insufficient carbonation. To prevent this, it is desirable to add an appropriate amount of water to maintain a wet state where liquid water is present. For example, since the medium and carbonate are hydrophilic, they can be wetted and spread to some extent even if they are supplied partially with water droplets or a shower.

[0045] As a specific example, pipes may be installed around the medium, with holes, mist showers, and automatic on-off valves installed in the pipes. Water for wetting can be supplied from upstream to downstream by gravity, but it can also be supplied by capillary action. The presence of the medium contributes to its water retention due to its hydrophilicity and porosity, and to an increase in the actual surface area of ​​the salt particles due to the large porous area. Carbonates, like NaOH, are hydrophilic. If they were hydrophobic, they would likely form large clumps rather than spreading throughout the medium.

[0046] For example, Figure 4 shows an example in which the wetting water is supplied by capillary action. As a form in which the medium 10 comes into contact with the water in the medium storage tank 20, the lower part of the medium 10 may be fixed to the bottom of the storage tank 20, and the part above the liquid level in the storage tank 20 may be formed as a protrusion that stands upright so that it comes into contact with the air. It is also possible to form the medium 10 in a cylindrical shape (cylinder, square tube, etc.) and fix the lower part to the bottom of the storage tank 20, protruding into the air like a pile from the liquid level, so that it comes into contact with the water below the liquid level and with the air above the liquid level.

[0047] Excessive water supply causes the carbonates to turn into a slurry and gradually migrate downstream on the media, but if the media area is large enough, most of the carbonates will remain on the media. Porosity prevents excessive carbonate migration.

[0048] Na in wet condition ２ CO ３ From a state where there is a lot of salt and its hydrated salts, sodium sesquicarbonate (Na ２ CO ３ NaHCO ３ ・2H ２O) crystal growth progresses, resulting in a state where sodium sesquicarbonate is abundant, and the CO ２ The average value of the / Na ratio can be increased from around 0.5 to around 0.67. It is preferable that the crystal growth of this sodium sesquicarbonate is carried out by contacting with water in a liquid phase and growing the crystals while accompanying dissolution and reprecipitation, rather than by supplying water only in the gas phase of water vapor.

[0049] "Sodium sesquicarbonate" Sodium sesquicarbonate is Na ２ CO ３ and NaHCO ３ CO between ２ In fact, it is not necessary for the salt composition to be pure, and Na ２ CO ３ and NaHCO ３ The state of the aqueous carbonate solution may be a mixed salt of CO ２ The / Na ratio is preferably as large as 0.67 or NaHCO ３ It is preferable to have the solution be mostly aqueous, as close to 1 as possible. However, if this takes too long, it will affect costs.

[0050] "Processing temperature conditions" In the atmosphere at around room temperature of about 25°C, CO ２ It is desirable to proceed to the next step when the absorption is stable, around 0.67. In the case of air, CO ２ When the temperature is low, the rate of absorption of CO in the aqueous solution after a long period of time at temperatures below 20°C suddenly slows down. ２ The / Na ratio tends to be higher than 0.67, so to some extent CO ２It is also possible to wait until the / Na ratio increases before proceeding to the next step. Regarding the high-temperature side, solid sodium sesquicarbonate decomposes at 70°C, so it is necessary to keep it below that temperature by avoiding direct sunlight, etc. Preferably it is 50°C or lower, more preferably 10°C or lower. It is effective to provide a temperature sensor, and if the temperature is too high, add more water to lower the temperature by the heat dissipation effect of evaporation. Considering the effect of improving the carbonation reaction rate due to high temperature and the negative effects of decomposition and equilibrium, there is an optimal temperature value. Carbonation should be promoted as much as possible when the temperature is high during the day, and CO should be slowly released at low temperatures such as at night. ２ It is preferable to increase the Na / Na ratio.

[0051] In the third step, when water is added to the medium, the water does not have to be pure water. A portion of the carbonate aqueous solution in the reservoir can be returned to the medium to maintain a moist state. The wetting switch point can be changed by changing the flow rate or flow rate of the aqueous solution.

[0052] "CO ２ Measurement of CO / Na ratio ２ Various measurement methods can be used to check the timing of switching between air-drying and wetting at a / Na ratio of 0.5 and to control the addition of water. ２ The results differ depending on the / Na ratio, so if the reaction is quick in wet conditions, water should be added actively, and if drying such as air drying is preferable, water should not be added and evaporation should be accelerated. ２ Measurements are made at a portion where the Na / Na ratio is around 0.5 and at multiple portions where it is expected to be around 0.67. Measurements can be made by sampling in batches or online. In particular, the measurement data is used to provide equipment for managing the wetness in the third process.

[0053] In the case of solids, the composition of the salt is analyzed by Raman spectroscopy or XRD analysis. ２ The CO / Na ratio can also be measured by solid TOC analysis. ２It can be calculated from the content. It can be measured online using Raman spectroscopy. It is desirable to be able to monitor and measure the solid state, but by sampling a portion of the carbonate and adding water to dissolve it, various measurements can be made using the resulting aqueous solution.

[0054] In the case of aqueous solutions, it can be measured using a pH meter, a Na+ ion meter, electrical conductivity, liquid TOC, gas chromatograph, ion chromatograph, ICP analysis, titrator, etc. Online measurement is possible using a pH meter, a sodium ion meter, electrical conductivity, etc. ２ The / Na ratio can be monitored by creating a calibration curve by combining multiple solutions that use different principles to measure the state of the solution. pH measurement is particularly important. For example, if you create a calibration curve by combining a pH meter (with temperature compensation) and a Na+ ion meter, you can measure the CO2 content of a small amount of salt water solution with these two measuring instruments. ２ By combining these two instruments with a device for adding a small amount of water to the sensor, online measurement is possible even with small amounts of solid samples.

[0055] The amount of moisture can be measured and controlled using a Na+ ion meter or electrical conductivity. It is recommended to measure at several locations and control the amount using the average value. ２ At a / Na ratio of 0.5 or more, temperature measurement of the wet sodium sesquicarbonate is important, and it is preferable to control the temperature by adding water.

[0056] <Fourth Step> "Collecting in a storage tank" As the fourth step of the carbon dioxide capture and removal method of this embodiment, a step of washing with water by supplying water that dissolves the sodium carbonate attached to the medium, causing it to flow out of the medium and be collected in a storage tank will be described. In the water washing, a larger amount of water than that used for wetting is supplied to wash the carbonate out of the medium. This water washing makes the medium reusable. The NaOH aqueous solution is again spread over the medium to wet it and collect the CO ２ Absorption is carried out using sodium sesquicarbonate or NaHCO ３When water is supplied to carbonate containing sodium, the carbonate downstream dissolves from the medium and accumulates in the storage tank. When water is supplied gradually, it is initially discharged into the storage tank at a concentration close to that of a saturated aqueous solution. If too much water is supplied, the carbonate concentration in the storage tank will become low, which may make the process of extracting carbonate solids from there difficult, so the amount of water is adjusted so that the concentration is close to that of a saturated aqueous solution and the water is discharged into the storage tank, stopping at a low concentration. The salt concentration can be measured with a sodium ion meter or electrical conductivity meter.

[0057] The storage tank according to this embodiment may be an open storage tank or a closed treatment tank. ２ Absorption can continue therein. ２ When the / Na ratio is 0.5 to 0.67, a high temperature is preferable, and when it is 0.67 or more, a low temperature is preferable. ２ It can be applied to gas recovery, etc. By sloping the storage tank, treatment tank, or piping, it is also possible to collect aqueous solutions by gravity.

[0058] In the fourth step, the water used for washing does not need to be pure water. Impurities such as NaCl may be present. It is not necessary to wash away all salts. An aqueous carbonate solution in a reservoir may be used and circulated to be discharged.

[0059] The reservoir tank in the fourth step may be, for example, each reservoir tank 20 in the examples shown in FIGS.

[0060] <Storage of Carbonate on Land> In the fourth step, it is preferable that the sodium carbonate is extracted from the aqueous solution of sodium carbonate accumulated in the storage tank and ultimately stored on land in a place where there is no inflow of water. ２ Carbonate solids with a CO / Na ratio of around 0.67 or higher can be produced. ２ / Na ratio = 0.67 or more, NaHCO ３ It can be produced by mixing with a high salt content. ２Unlike conventional CCS, which stores gas deep underground, the produced carbonate is solid and can be stored on land. Storage conditions vary depending on the type of carbonate, but it is generally best to store it in a place where there is no water inflow. ３ It is relatively stable when humidity is low, but when it comes into contact with water, it gradually decomposes in the air, so it must be stored in an environment that does not come into contact with water. ２ It can be stored stably in a high concentration environment. ３ It is more stable than NaHCO and is stable in contact with water for short periods of time, but becomes unstable over long periods of time and at high temperatures. ３ It is best to store sodium sesquicarbonate in a warehouse, tent, or cave where rainwater and groundwater cannot get in. In the case of sodium sesquicarbonate, it is sufficient to bury the carbonate in an open-cut hole and cover it with soil. Even if it comes into contact with water and decomposes, the CO produced will ２ If the gas is allowed to remain inside, it becomes quite stable. ２ CO ３ and MgCO ３ , CaCO ３ Basic magnesium carbonate is quite stable even when in contact with water. It is advisable to avoid contact with running water. Regarding storage temperature, sodium sesquicarbonate and NaHCO ３ Since it decomposes significantly at 70°C, it should be kept at a temperature below that, preferably 50°C or less, and more preferably 10°C or less.

[0061] <Removal of solid salt> Methods for removing solid salt from the carbonate aqueous solution accumulated in the water tank include natural air drying and heat drying. It is preferable to evaporate the aqueous solution slowly, avoiding high temperatures. The medium is CO 2 in the removal and drying steps. ２ However, if the subsequent separation process of the medium and the carbonate becomes complicated, it may not be necessary. ２To separate only the water without letting CO escape, methods such as low-temperature distillation using a temperature difference in a sealed container, desiccant dehydration using a dehydrating agent, and reverse osmosis membrane separation using pressure can be used. Silica gel dehydrating agents can be dehydrated at relatively low temperatures and can be regenerated by drying in the sun, etc. In membrane separation of carbonate solutions, CO ２ passes through the membrane, so CO ２ / Na ratio temporarily decreases, but ２ Gas is obtained, and after dehydration, high concentration CO ２ Using CO ２ It can be used to produce solid salts with a high Na / Na ratio.

[0062] <Precipitation Step> "Crystallization by Salting Out" In the fourth step, the aqueous solution of sodium carbonate collected in the storage tank is cooled, NaCl or Na ２ SO ４ The aqueous solution may be cooled, and a salting-out step may be performed in which a solid salt of the second carbonate is precipitated and separated by adding NaCl or Na ２ SO ４ By utilizing the salting-out effect of adding rock salt containing CO ２ In the method for removing carbon dioxide from the atmosphere according to this embodiment, the carbonate obtained in the fourth step may contain impurities, so there is a great advantage in that salts derived from natural rock salt or brine can be effectively used. ２ SO ４ When mixed, CO ２ This allows for the preferential precipitation of solid salts with a high Na / Na ratio. The higher the concentration and the lower the temperature, the greater the effect.

[0063] "Separation step utilizing difference in saturated solubility" In the fourth step, the aqueous solution of sodium carbonate collected in the storage tank is in a liquid-solid mixed state in which a solid salt containing sodium sesquicarbonate and a saturated aqueous solution are mixed, and the liquid phase is removed and returned to the medium, and the CO ２The aqueous solution of sodium carbonate collected in the storage tank may be evaporated or concentrated to a certain extent to form a liquid-solid mixture in which a solid salt containing sodium sesquicarbonate and a saturated aqueous solution are mixed, and then the aqueous solution of sodium carbonate is separated from the saturated aqueous solution of sodium sesquicarbonate by a process of separating the carbonate having a ratio of 1 / Na greater than that of sodium sesquicarbonate. ２ CO ３ and NaHCO ３ By utilizing the difference in solubility of ２ Carbonates with a / Na ratio greater than sodium sesquicarbonate, i.e., NaHCO ３ A large proportion of carbonates (which may also contain some sesquisalts) can be separated.

[0064] Na ２ CO ３ and NaHCO ３ Since the solubility of sodium carbonate varies with temperature, the operation varies depending on the temperature of the aqueous solution of sodium carbonate accumulated in the reservoir. The temperature of the aqueous solution is preferably 5°C or higher, and more preferably in the range of room temperature, 20°C or higher and 40°C or lower.

[0065] When the temperature of the aqueous solution is 5°C or higher, the molar solubility of Na ２ CO ３ NaHCO ３ This difference is used to calculate NaHCO ３ A large proportion of carbonate can be extracted.

[0066] Na ２ CO ３ and NaHCO ３ The molar solubility of the two differs greatly at room temperature between 20°C and 40°C, with the difference being greatest at around 40°C. It is preferable to carry out this liquid-solid separation operation when the air temperature or water temperature is closest to 40°C, such as under sunlight during the day. At room temperature (20°C to 40°C), if a liquid-solid mixed state in which a solid salt containing sodium sesquicarbonate and a saturated aqueous solution are mixed is maintained, the liquid phase will contain Na. ２ CO ３ The concentration of NaHCO increases in the solid phase. ３ The ratio of CO2 to CO2 increases, so by removing the solid phase precipitate, ２For example, the liquid phase Na / Na ratio can be improved by pumping out the supernatant and separating it from the precipitate. ２ CO ３ The aqueous solution is separated from the solid phase and returned to the medium or separated into another reservoir, and the liquid phase is then separated from the atmosphere or other CO ２ and react it again to make sodium sesquicarbonate, etc. ２ By repeating the process of returning the supernatant liquid phase from the liquid-solid mixed state, the ratio of NaHCO3 to NaHCO3 can be improved. ３ The ratio of Na can be increased. ２ CO ３ It is effective to return the medium to the third step in a moist state, where a large amount of HCl is produced.

[0067] At temperatures below 5°C, the molar solubility is NaHCO ３ Na ２ CO ３ Since it is larger, the operation is reversed.

[0068] Therefore, it is preferable that the separation process utilizing the difference in saturated solubility has a process of measuring the air temperature and water temperature, and a control process of managing each process using the measurement results.

[0069] <Use of a Closed Treatment Tank, etc.> In the fourth step, the aqueous solution of sodium carbonate collected in the storage tank is transferred to a closed treatment tank, and CO 2 with a concentration higher than that of the atmosphere is introduced into the closed treatment tank. ２ CO gas is introduced to the aqueous solution. ２ When the closed treatment tank is used, the high concentration CO ２ The CO gas can be easily recovered. ２ The gas may be introduced from the inside or from the outside, for example.

[0070] "Method of introducing from inside" In the method of introducing from inside, there are a plurality of the sealed treatment tanks, and the sodium carbonate and its aqueous solution in the first sealed treatment tank are decomposed to introduce CO ２A method in which a gas is generated and introduced into a second closed treatment tank is also possible. ２ Separate the aqueous solution with a large Na / Na ratio, and extract Na from one of the solutions. ２ CO ３ It is partially decomposed to produce CO ２ By generating gas and introducing it into the other ２ By increasing the concentration of CO ２ Therefore, solid salts with a large Na / Na ratio can be preferentially precipitated.

[0071] The CO ２ Examples of methods for generating gas include a method of thermally decomposing the carbonate aqueous solution, a method of adding an acidic aqueous solution produced by electrolysis or electrodialysis to the carbonate aqueous solution, and a method of adding an acidic substance such as waste to the carbonate aqueous solution. Among the above methods, the method of adding an acidic aqueous solution produced by electrolysis or electrodialysis to the carbonate aqueous solution is preferred. This method produces high-concentration CO ２ Furthermore, if conventional underground isolation CCS systems are put to practical use in the future, the high concentration CO2 generated in this way will be ２ Gas can also be used.

[0072] "Method of introducing from outside" Examples of the method of introducing from outside include a method of introducing at least one gas selected from the group consisting of gas released from soil, biomass decomposition gas, exhaust gas due to respiration of organisms, gas derived from gas or oil fields, and exhaust gas from auxiliary equipment that utilizes combustion. ２ The most reliable method for producing aqueous solutions or solid salts with a high Na / Na ratio is to use a closed treatment tank and extract CO from sources other than the atmosphere. ２ Most of the carbon dioxide is taken from the atmosphere using the method of the present invention, but ultimately, CO ２ to form a solid salt.

[0073] Introduced CO ２ The concentration is 1000 ppm or more, preferably a higher concentration (3000 ppm or more). ２The / Na ratio can be improved to 0.9 or more. The same concentration can be used for storage. It is not necessary to have such a high concentration, so for example, CO ２ CO2 from selectively permeable membranes and amines ２ Concentrated CO using DAC (Direct Air Capture) technology that uses adsorbents, etc. ２ CO such as amine may be introduced. ２ The adsorbent reduces CO from a dilute state of 400 ppm to above 1% level. ２ It is difficult to concentrate CO2, but the energy required to concentrate it to 1000 ppm is small. ２ Sources include soil and biomass decomposition, agricultural emissions, respiration from livestock and other organisms, emissions from gas and oil fields, and emissions from surrounding combustion-based equipment. ２ The concentration is set at a standard that is acceptable even in indoor environments where people are present, and CO ２ The introduction of CO is also effective. ２ The advantage of this technology is that impurities other than the above can be present.

[0074] <MgCO ３ and CaCO ３ etc.> Preferably, the method further comprises a step of mixing the solid salt of sodium carbonate obtained in the fourth step or an aqueous solution containing the solid salt with an aqueous solution containing alkaline earth metal ions, precipitating the alkaline earth metal carbonate and storing it on land, generating an aqueous solution of sodium salt, and reusing the aqueous solution for the electrolysis or electrodialysis. The aqueous solution containing alkaline earth metal ions is a solution generated by contacting the acidic aqueous solution generated by the electrolysis or electrodialysis with basic minerals or waste (waste concrete, steel slag, etc.). The CO generated in the fourth step is preferably further mixed with the solid salt of sodium carbonate or an aqueous solution containing the solid salt, precipitating the alkaline earth metal carbonate and storing it on land, generating an aqueous solution of sodium salt, and reusing the aqueous solution for the electrolysis or electrodialysis. The aqueous solution containing alkaline earth metal ions is a solution generated by contacting the acidic aqueous solution generated by the electrolysis or electrodialysis with basic minerals or waste (waste concrete, steel slag, etc.). ２An aqueous solution with a large Na / Na ratio can be used to produce stable magnesium or calcium carbonates using basic minerals. In the electrolysis or electrodialysis for producing the NaOH aqueous solution, the acidic water produced as a pair with NaOH is used to neutralize various basic minerals (basalt, olivine, calcium silicate, etc., containing large amounts of alkali metals or alkaline earth metals such as K, Na, Ca, Mg, etc.), to produce aqueous solutions of chlorides or sulfates of magnesium or calcium. The CO produced in the fourth step is then added to these chlorides or sulfates. ２ When an aqueous solution with a high ratio of magnesium to magnesium is mixed, the poorly soluble magnesium (MgCO ３ and its hydrates. Precipitation of basic magnesium carbonate and calcium carbonate occurs. This hardly soluble carbonate solid is easier to store and manage than soluble sodium carbonate as land CCS (Carbon dioxide Capture & Storage). However, the CO immobilized as CCS is ２ of electric energy is CO ２ On the other hand, when precipitation of hardly soluble magnesium and calcium carbonates occurs, high concentration of CO ２ This has the advantage that it can be effectively used in CCU (Carbon dioxide capture & utilization) and conventional CCS, so the overall cost benefits are quite large. ２ can be collected in a closed treatment tank. ３ Not only that, but also basic magnesium carbonate (MgCO ３ A mixture of Mg(OH)2 and water of hydration is also a stable compound, but CO ２ A fixed amount of MgCO ３ It will be less than that, but CO ２ Gas is generated during neutralization, and can be collected and used. The neutralized salt solution can be reused for electrolysis or electrodialysis, so NaCl, which is less abundant than NaCl, can be used. ２ SO ４ This is the best way to recycle salt.

[0075] <Step 5> The method for capturing and removing atmospheric carbon dioxide of this embodiment may further include step (5) of reusing the washed medium. The term "reuse" refers to the step 5, in which the washed medium in step 4 is subjected to steps 1 to 4 at least once more to capture and remove atmospheric carbon dioxide. Depending on the material of the medium, the amount and concentration of the NaOH aqueous solution used in step 1, and the climate, steps 1 to 4 of the method for capturing and removing atmospheric carbon dioxide of this embodiment may be repeated 100 or more times, or even 1,000 or more times. When the method for capturing and removing atmospheric carbon dioxide of this embodiment includes step 5, steps 1 to 4 can be repeated while the medium remains installed, eliminating the need to reinstall the medium, which is preferable from the perspective of low cost and energy conservation.

[0076] (System for recovering and removing atmospheric carbon dioxide) A system for recovering and removing atmospheric carbon dioxide according to one embodiment of the present invention (sometimes referred to as "system for recovering and removing atmospheric carbon dioxide according to this embodiment" or "recovery and removal system according to this embodiment") produces sodium carbonate by contacting atmospheric carbon dioxide with an aqueous solution of NaOH produced by electrolysis or electrodialysis. It comprises the following NaOH aqueous solution diffusion treatment unit to cleaning treatment unit. (1) An aqueous NaOH solution diffusion treatment unit including a hydrophilic and porous medium and having a mechanism for wetting and spreading the aqueous NaOH solution on the hydrophilic and porous medium. (2) A layer of NaOH is formed on the medium while evaporating the water content of the aqueous solution, and carbon dioxide in the atmosphere comes into contact with the NaOH layer to produce sodium carbonate (Na ２ CO ３ .CO ２ / Na ratio = 0.5) ２ (3) Add water to the NaOH layer formed on the medium to maintain a wet state where liquid water is present, and then add sodium sesquicarbonate (Na ２ CO ３ NaHCO ３ ・2H ２ O.CO. ２ / Na = 0.67) and sodium bicarbonate (NaHCO ３ .CO ２ / Na=1), while growing a crystal of the sodium carbonate containing at least one selected from the group consisting of CO ２ (4) A cleaning treatment unit having a mechanism for supplying water that dissolves the sodium carbonate adhering to the medium, thereby washing the medium with water, and causing the aqueous solution of sodium carbonate to flow out from the medium and collect in a storage tank.

[0077] The NaOH aqueous solution diffusion treatment unit preferably includes a spray and a dripping device. The spray is installed to wet and spread the NaOH aqueous solution over the medium. ２ The collection treatment unit preferably includes the medium and a device for holding the medium. The moisture control treatment unit preferably includes a spray and a dripping device. The spray is installed to add the moisture. The amount of moisture added may be small. The added moisture may be pure water, and the Na returned from the storage tank of the cleaning treatment unit may be added. ２ CO ３ In the moisture control treatment unit, it is preferable to use an aqueous solution of sodium carbonate or sesquisodium carbonate. ２ The method may further include a sub-processing unit that measures the NaOH / Na ratio and the pH of the aqueous solution of sodium carbonate to control the moisture content of the processing unit. In addition, in the second step, the carbon dioxide in the atmosphere may come into contact with the NaOH deposit layer by natural wind.

[0078] The cleaning treatment unit preferably includes a spray and a dripping device. The amount of water may be greater than the added water of the moisture control treatment unit. The supernatant of the sesquioxide aqueous solution returned from the storage tank may be used. The cleaning treatment unit may further include a pipe for transporting the carbonate aqueous solution or the solid slurry to the storage tank. The cleaning treatment unit may have a sub-treatment unit for extracting the sodium carbonate from the sodium carbonate aqueous solution collected in the storage tank and storing it on land in a place where there is no inflow of water. In the cleaning treatment unit, NaCl or Na ２ SO ４ The storage temperature may be adjusted to, for example, sodium sesquicarbonate or NaHCO 3 . ３ Since CO2 significantly decomposes at 70°C, the temperature is preferably 50°C or lower, more preferably 10°C or lower, from the viewpoint of maintaining a temperature lower than this. In the cleaning treatment section, the aqueous solution of carbonate of sodium collected in the storage tank is in a liquid-solid mixed state in which a solid salt containing sodium sesquicarbonate and a saturated aqueous solution are mixed, and the liquid phase is removed and returned to the medium, and the CO2 in the solid phase is removed. ２ In the cleaning treatment unit, the aqueous solution of sodium carbonate collected in the storage tank is transferred to a closed treatment tank, and a CO 2 solution having a concentration higher than that of atmospheric CO 2 is introduced into the closed treatment tank. ２ CO gas is introduced to the aqueous solution. ２ The method may further include a sub-treatment section for increasing the ratio of sodium carbonate to sodium carbonate in the first closed treatment tank. ２ A gas may be generated and introduced into the second closed treatment vessel. ２The gas may be at least one selected from the group consisting of soil release gas, biomass decomposition gas, exhaust gas due to respiration of organisms, gas derived from gas and oil fields, and exhaust gas from auxiliary equipment that uses combustion. ２ The method may further include a sub-processing unit that separates and recovers gas. The method may further include a sub-processing unit that contacts the acidic aqueous solution produced by the electrolysis or electrodialysis with a basic mineral to produce an aqueous solution containing alkaline earth metal ions, mixes the produced aqueous solution containing alkaline earth metal ions with the solid salt of sodium carbonate obtained in the cleaning process unit or an aqueous solution containing the same, precipitates the alkaline earth metal carbonate and stores it on land, produces an aqueous solution of sodium salt, and reuses it in the electrolysis or electrodialysis. The aqueous solution containing alkaline earth metal ions and the solid salt of sodium carbonate or an aqueous solution containing the same are mixed inside the sealed treatment tank, and CO generated at the time is removed. ２ The apparatus may further include a sub-processing unit for recovering the

[0079] In the recovery and removal system of this embodiment, it is preferable that the NaOH aqueous solution diffusion treatment unit further includes an electrolysis or electrodialysis device and an aqueous NaOH solution generation unit that generates the NaOH aqueous solution using the electrolysis or electrodialysis device. That is, the NaOH aqueous solution diffusion treatment unit preferably includes the electrolysis or electrodialysis device, the aqueous NaOH solution generation unit that generates the NaOH aqueous solution using the electrolysis or electrodialysis device, and a diffusion treatment unit that wets and spreads the generated NaOH aqueous solution on a hydrophilic and porous medium. As described above, when the NaOH aqueous solution diffusion treatment unit includes the electrolysis or electrodialysis device and the aqueous NaOH solution generation unit, the electrolysis or electrodialysis device and the atmospheric CO ２The collection treatment unit and moisture control treatment unit can be installed nearby. The generated NaOH aqueous solution can be transported via pipeline, even in its aqueous solution state. This significantly reduces transportation costs and energy. This is because, in order to reduce the energy (power consumption) required for electrolysis and dialysis, it is effective to use the medium-concentration acid-base aqueous solution of approximately 0.2 M to 1 M as it is, as it is, coming out of the electrochemical device, without concentrating it. This is of great significance, for example, as it can be completed almost entirely in isolated areas such as remote islands and deserts.

[0080] The recovery and removal system of this embodiment may further include (5) a medium recycling unit that reuses the washed medium. The "reuse" of the recycling unit has the same meaning as the "reuse" described in the <5th step> of the recovery and removal method of this embodiment.

[0081] Regarding Energy and Cost: Compared to conventional DACs, the method for capturing and removing atmospheric carbon dioxide and the system for capturing and removing atmospheric carbon dioxide (hereinafter, the method and system may be collectively referred to as the "technology of the present disclosure") offer a significant advantage in that they virtually eliminate the need for large fans and thermal energy. Large fans are essential for continuous operation while maintaining the high operating temperatures of conventional DACs, and are a major factor in increasing costs. Conventional DACs are difficult to adapt to fluctuations, making them difficult to utilize renewable energy. The technology of the present disclosure makes it easier to utilize fluctuating renewable energy than conventional DACs, and can be left to operate at natural temperatures near room temperature. The cost of solar power generation in remote areas, such as the deserts of the Sunbelt, has dropped significantly in recent years. Renewable energy electricity faces land issues near demand areas, such as urban areas, and transmission issues in remote areas far from demand areas. DACs, when used in conjunction with underground CCS, can contribute to negative emissions, but the practical application of large-scale underground CCS remains unclear. The technology disclosed herein has the great advantage that it can be completed as a land-based CCS system using solid carbonates in remote areas as long as there is saltwater. The saltwater source can be seawater, salt lakes, underground brine water, etc. The technology disclosed herein has the following features: ２ Increased absorption rate and CO ２The former speed improvement contributes to cost reduction by efficient land use and downsizing of the system. The latter CO ２ Improving the NaOH / Na ratio contributes to reducing power energy and costs through the effective use of NaOH.

[0082] CO of conventional DAC ２ Processing cost is 50,000 yen / t-CO ２ In an example of oxygen reduction electrolysis or electrodialysis according to the technology of the present disclosure, when renewable energy power of 6 yen / kWh is used, the electricity cost of the electrochemical reaction portion is 8,000 yen / t-CO ２ Before and after, the total cost (mineral crushing, water treatment, etc.) was 12,000 yen / t-CO ２ It is possible to carry out the process before and after the electrolysis. ２ Processing cost is 50,000 yen / t-CO ２ It will be higher than.

[0083] Examples and specific examples of the system for recovering and removing carbon dioxide from the atmosphere of this embodiment include the examples and specific examples described above for the method for recovering and removing carbon dioxide from the atmosphere of this embodiment.

[0084] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0085] When carbon dioxide is absorbed into an alkaline aqueous solution and carbonate is produced, the pH decreases. Therefore, the carbon dioxide capture capacity can be estimated by exposing the alkaline aqueous solution to carbon dioxide for a certain period of time and measuring the pH. In the following examples and comparative examples, the lower the pH after the certain period of time, the better the carbon dioxide capture capacity.

[0086] (Apparatus) Electrolysis apparatus: Tsukuba Materials Information Laboratory (Minicell n-1-1) and sandwich cell. Hydrogen generation and oxygen generation electrodes are manufactured by Denora Permelec. Gas diffusion electrode for oxygen reduction is manufactured by Chemix. Electrodialysis apparatus: Astom (EX3B) (Preparation example) "Preparation of aqueous NaOH solution" An acid and base generation reaction was carried out using the above electrolysis apparatus. A Nafion membrane was used as the ion exchange membrane, and Pt electrodes were used as the anode and cathode. Various aqueous NaOH solutions were prepared for use in the following Experiments A to F and Examples.

[0087] 2.5M Na as the first electrolyte ２ SO ４ An aqueous solution was electrolyzed. 0.5M sulfuric acid and 1M NaOH could be produced as products up to that concentration. It was confirmed that hydrogen was generated at the anode. It was confirmed that introducing oxygen to the anode side could reduce the voltage while oxygen was being reduced. A 5M NaCl aqueous solution was electrolyzed as the second electrolytic solution. It was confirmed that 1M hydrochloric acid and 1M NaOH could be produced as products up to that concentration. Using various electrolytic solutions and controlling the preparation time, aqueous NaOH solutions of the following concentrations were prepared. 1M NaOH aqueous solution 0.2M NaOH aqueous solution

[0088] The acid-base generation reaction was carried out using the electrodialysis device. The ion exchange membrane used was a three-compartment cartridge consisting of a bipolar membrane, an anion exchange membrane, and a cation exchange membrane.

[0089] As the third electrolyte, a 2M NaCl aqueous solution was electrolyzed. 1M hydrochloric acid and 1M NaOH were produced up to that concentration. As the fourth electrolyte, 1M Na ２ SO ４ The aqueous solution was electrolyzed. 0.5M sulfuric acid and 1M NaOH were produced up to that concentration. It was confirmed that a similar reaction could be carried out in a two-chamber cartridge.

[0090] The lower the concentration of the acid and NaOH produced, the better the efficiency and power consumption. A concentration of 0.2M was primarily used in the following experiments. The power unit for NaOH production using hydrogen-generating electrolysis was 2.07 Wh / g-NaOH, a figure roughly equivalent to that of industrial chloralkali electrolysis (2.1 Wh / g-NaOH). On the other hand, oxygen-reduction electrolysis using gas diffusion electrodes yielded 0.9-1.9 Wh / g-NaOH, and electrodialysis yielded 1 Wh / g-NaOH, both figures lower than those for hydrogen-generating electrolysis. Hydrogen-generating electrolysis offers the advantage of replicating hydrogen for sale and use, and the superiority of each method depends on the overall situation.

[0091] "Experiments A to F" Experiments A to F relating to the various steps of the method for recovering and removing carbon dioxide according to this embodiment will be described below.

[0092] <Experiment A> "Comparison with and without a medium" A comparison was made between cases where a filter paper of the same area (hard filter paper No. 4A manufactured by ADVANTEC, mainly cellulose fiber, containing hydroxyl groups, film thickness 0.13 mm) was placed as a hydrophilic and porous medium in a polystyrene resin container (bottom surface 260 cm2) and cases where it was not placed. The polystyrene container was water-repellent, and the filter paper was hydrophilic. 0.2 M NaOH (10 ml) was dropped evenly onto the filter paper and spread. The initial pH of the aqueous solution was 13.15. When the pH was measured after leaving it in the atmosphere for 2 hours, it was 12.77 without the filter paper and decreased to 11.47 with the filter paper. The presence of the filter paper was found to have an effect of promoting the absorption of carbon dioxide from the atmosphere. It was confirmed that sodium ions and carbonate ions do not adsorb to the medium. For the same sodium ion concentration, the lower the pH, the greater the CO ２ The results are shown in Table 1. When comparing the rate of change in initial pH with NaOH, it was found that the rate was slow when no medium was used.

[0093]

[0094] <Experiment B> "Comparison of Media Types" Several types of hydrophilic, porous media (20 x 13 cm) were placed upright on the inside surface of a polypropylene resin container (7 cm diameter). 50 mL of 0.2 M NaOH was poured into the container and allowed to spread throughout the media. NaOH was supplied to the media via capillary action. The media was left in the open air, and the pH was measured (initial value: 13.12). The pH values ​​were 10.06, 10.10, 10.06, and 10.32 after 160 hours using nonwoven fabric (Monotaro, nonwoven wiper, 60% rayon, 40% polyester, 0.2 mm film thickness), Texwipe (Texwipe, nonwoven fabric), TX612, 0.25 mm film thickness), and kitchen towel (kitchen duster, 100% rayon, 0.3 mm film thickness). The pH values ​​without the media were 10.06, 10.10, 10.06, and 10.32, respectively, indicating that the pH values ​​with the media were lower than those without the media. All media were effective in lowering the pH. The results are shown in Table 2. Furthermore, when the relationship between the thickness of the medium and the rate of pH decrease in the first hour was examined, it was found that the thicker the medium, the faster the rate of pH decrease, and therefore it was found that it is desirable for NaOH to be dispersed thinly and widely in the medium.

[0095]

[0096] <Experiment C> "Comparison of dry and wet conditions, part 1" 10 mL of 1 M NaOH was used, and a nonwoven wiper was used as the medium. The area was 260 cm2. An experiment was conducted to determine whether the air-dried or wet condition absorbed more CO. ２ The efficiency of the absorbent was investigated. pH measurement was evaluated after 10-fold dilution. The medium was set on the bottom of a polystyrene container, and 10 mL of 1 M NaOH obtained in the above Preparation Example was added uniformly. When the medium was air-dried in the air without adding any more water, the pH dropped from an initial value of 12.81 to 11.32 after 3 hours. On the other hand, when 90 mL of water was added and the medium was wet, the pH only dropped to 12.27. In both pH ranges, NaOH was found to be a strong inhibitor of NaOH. ２ CO ３ The comparison was made under conditions where only the temperature had changed, but the air-dried condition was more efficient than the wet condition. ２ The results are shown in Table 3.

[0097]

[0098] <Experiment D> "Comparison of dry and wet conditions, part 2" 0.5M Na ２ CO ３ A nonwoven wiper was used as the medium, using 10 mL of the solution. The area was 260 cm2. An atmospheric carbon dioxide absorption experiment was conducted to determine whether the air-dried state or the wet state absorbed more CO2. ２ The pH was measured by diluting the solution 10 times. ２ CO ３ 10 mL of water was added uniformly. In the air-dried state without adding any more water, the pH was initially 11.40, but after 5 hours it was 10.80. On the other hand, in the wet state where 90 mL of water was added, the pH dropped to 10.59 after 5 hours, which was lower than the pH in the air-dried state. ２ CO ３ From the state of ２ As absorption progresses, CO ２ It was found that a large amount of water is preferable to improve the / Na ratio. ２ CO ３ This is the exact opposite of the change to 0.5M Na ２ CO ３ Even if 10 mL is added evenly and gradually dried, Na ２ CO ３ The medium also contains water, but the amount of water is not enough to ２ It can be said that absorption is slow. In this process, the presence of liquid water is important, and it can be inferred that it is desirable for Na+ and carbonate ions to be able to move freely. The results are shown in Table 4.

[0099]

[0100] <Experiment E> "Experiment using capillary action" A nonwoven wiper (20 x 13 cm) was placed against the inside surface of a polypropylene resin container (7 cm diameter) as a hydrophilic and porous medium. 50 mL of 0.2 M NaOH was placed in the container and spread over the medium. The lower part of the medium was moistened by the aqueous solution being absorbed by capillary action, while the upper part remained relatively dry. The sample was left in the atmosphere for a long time, and the CO2 was measured by pH and TOC analysis (Shimadzu TOC-L, SSM-5000A device). ２ The amount of CO calculated from the TOC analysis was measured. (Initial 13.12). After 376 hours, the pH was 9.91. The results are shown in Table 5. ２ / Na ratio = 0.66, which is almost sodium sesquicarbonate (CO ２ When this aqueous solution was slowly dried at room temperature in the air, it was found to have the same composition as when sodium sesquicarbonate (CO / Na ratio = 0.67) was dissolved. ２ It was confirmed by XRD that the solid salt with a ZnO / Na ratio of 0.67 could be extracted.

[0101]

[0102] <Experiment F> "Non-adsorption of the medium" "The fact that Na ions and carbonate ions do not adsorb to the medium is based on the amount of Na ions and the amount of CO2 by TOC analysis with or without the medium. ２ This was confirmed through experiments on the amount of water used. It was confirmed that when sufficient water exceeding the saturated solubility of carbonate was supplied to the medium as a cleaning operation, the aqueous solution could be discharged from the medium into another container (simulating a storage tank).

[0103] (Experimental Example 1) "Identification of sodium sesquicarbonate" Dry precipitation of carbonate solid salt from carbonate aqueous solution: NaHCO ３ : Na ２ CO ３ = 1:1 equivalent CO ２ An aqueous solution of sodium sesquicarbonate (Na 2 O 3 ) was used, and the solution was slowly air-dried in the presence of 4A filter paper as a hydrophilic and porous medium. A white solid salt precipitated out, which was taken out and analyzed by XRD. The crystals were found to be metastable salt crystals of sodium sesquicarbonate (Na 2 O 3 ). ２ CO ３ NaHCO３ ・2H ２ O.CO. ２ It was confirmed that sodium sesquicarbonate (NaHCO3 / Na = 0.67) was the main component. Simple quantification using XRD software revealed that sodium sesquicarbonate accounted for 73%. ３ 13%, Na ２ CO ３ ・H ２ From these figures, CO ２ It was found that / Na was approximately 0.67 (calculated value: 0.66).

[0104] (Experimental Example 2) "Drying experiment using dehydrating agent in a closed treatment tank" CO ２ When a carbonate aqueous solution with a Na / Na ratio of 0.67 was combined with dehydrated silica gel in a closed treatment tank, ２ A solid salt with a Na / Na ratio of 0.65 was precipitated. Using silica gel as a desiccant, dehydration was possible even at 60°C, confirming that it could be regenerated by drying in the sun, etc.

[0105] (Experimental Example 3) "Precipitation of solid carbonate salt from aqueous carbonate solution" CO ２ A saturated aqueous solution of carbonate with a NaCl / Na ratio of 0.67 was mixed with a saturated aqueous solution of NaCl and cooled to around 0°C. A solid salt precipitated. XRD of the precipitated solid salt was measured, and it was found to be sodium sesquicarbonate: Nahcolite (NaHCO ３ )=80:20(CO ２ The peak of NaCl was not observed. ２ It was confirmed that solid salts with high NaCl / Na ratios can be precipitated by adding NaCl.

[0106] (Comparative Experimental Example 1) "Na ２ CO ３ Precipitation of carbonate solid salts from aqueous solutions of CO ２ The same precipitation experiment as in Experimental Example 3 was carried out using a carbonate aqueous solution with a Na / Na ratio of 0.5. ２ CO ３ Only the hydrate was obtained.

[0107] (Experimental Example 4) "Precipitation due to solubility difference" Sodium sesquicarbonate (CO ２ A saturated aqueous solution of NaHCO3 (NaHCO3 / Na ratio = 0.67) was prepared at room temperature (approximately 21°C) to create a state in which a solid phase and a liquid phase coexisted. After leaving it in the air for one week, the precipitate was evaluated by XRD. ３ is 88%, and the rest is Na ２ CO ３ ・H ２ O and CO ２ The solid TOC analysis of the precipitate showed that the CO ２ The CO / Na ratio was 0.97. ２ It was found that the / Na ratio could be improved.

[0108] (Experimental Example 5) "CO in the atmosphere ２ Higher concentrations of CO ２ Introduction of CO ２ A carbonate aqueous solution (0.2 M in Na, 50 mL) with a CO / Na ratio of 0.67 was added at around room temperature (24°C) to 1000 ppm of CO. ２ Gas (the remainder was N2) was introduced. After 23 hours, the pH reached 8.28 and the CO2 in the aqueous solution ２ The / Na ratio was 0.99. ２ The gas mostly produces NaHCO ３ It was found that the CO concentration was in the form of an aqueous solution. Even at 1000 ppm, the CO concentration was very high compared to the atmosphere (approximately 400 ppm). ２ When the reaction temperature was raised from 24°C to 40°C, the pH reached 8.48 in 23 hours, and the CO ２ The pH / Na ratio was 0.964, which was sufficiently high. Even when the temperature was raised to 60°C, the pH reached 8.43 in 22 hours. ２ The / Na ratio was 0.962, which was a sufficiently high value. In other words, even at high temperatures, most of the ３ It was found to be in the form of an aqueous solution.

[0109] (Comparative Experimental Example 2) (Introduction of carbon dioxide from the atmosphere) In Experimental Example 5, 1000 ppm CO ２Instead of CO 2 , air (approximately 400 ppm, room temperature) was introduced. The other conditions were the same. Under these conditions, the pH was 9.89 even after 65 hours, and CO 2 . ２ The / Na ratio was 0.66.

[0110] (Experimental Example 6) "Two closed treatment vessels: heating of solid salt" Two closed treatment vessels were connected and CO ２ CO of solid salts with a high / Na ratio ２ An experiment was conducted to transfer CO to another container. ２ Carbonate solid (sodium sesquicarbonate) with a CO / Na ratio of 0.67 ２ 5 mmol of Na and 7.46 mmol of Na) were placed in a sealed container and heated to about 90°C on a hot plate. ２ The gas was collected (approximately 10 mL) in another sealed container (burette) via a tube. Sodium sesquicarbonate was thermally decomposed, and some of the sodium ２ CO ３ The carbon dioxide in the atmosphere was 400 ppm, but the high concentration CO ２ It was found that it is possible to efficiently convert the gas into HCl and then transfer it to another sealed container to achieve a high concentration.

[0111] (Comparative Experimental Example 3) "Two Closed Treatment Tanks: Heating of Solid Salt" CO ２ / Na ratio of 0.5 ２ CO ３ When heated to about 90°C, the carbonate solid ２ No. Heat decomposition requires temperatures of 400°C or higher.

[0112] (Experimental Example 7) CO from soil biomass ２ CO released from soil biomass ２ The effect of CO was tested by placing 2 L of leaf mold and 1 L of water in a 20 L plastic bag and leaving it at room temperature. The gas concentration was measured and found to be approximately 800-850 ppm. ２ A carbonate solution (0.2 M in Na, 50 mL, initial pH = 9.99) with a CO / Na ratio of 0.67 was added at 24°C. ２ After 24 hours, the pH reached 9.82 and CO ２The / Na ratio was 0.737. In addition, when the container of leaf mold was heated to 35°C, assuming a low latitude, the CO ２ The concentration was about 6000 ppm, and the pH and CO ２ / Na ratios of 8.8 and 1.0, respectively, and NaHCO ３ It became equivalent to an aqueous solution.

[0113] (Comparative Experimental Example 4) "CO from soil biomass ２ When compared under atmospheric conditions without soil, the pH reached 9.94 in 24 hours, and the pH was lower with soil, so CO2 from the soil was ２ It can be said that this has the effect of promoting the reaction.

[0114] (Experimental Example 8) "CO2 from aqueous carbonate solution and solid salt ２ Recovery DAC" CO ２ A carbonate aqueous solution (CO ２ 5 mmol of Na and 7.46 mmol of Na) were placed in a sealed container and sulfuric acid was added. ２ The gas was collected (approximately 112 mL) in a separate sealed container (burette and gas bag). ２ Addition of sulfuric acid in the amount corresponding to the stoichiometric ratio of CO ２ The recovery rate was nearly 100% within experimental error. ２ It was found that it is possible to convert and capture the carbon dioxide efficiently.

[0115] (Experimental Example 9) CO ２ Similarly, a solid carbonate with a Na / Na ratio of 0.67 was placed in a sealed container and sulfuric acid was added. ２ Addition of sulfuric acid in the amount corresponding to the stoichiometric ratio of CO ２ The recovery rate was nearly 100%. The neutralized aqueous solution was evaporated to dryness, and the precipitated salt was analyzed by XRD. ２ SO ４ (a mixture of Phases III and V).

[0116] (Experimental Example 10) Even if hydrochloric acid is used instead of sulfuric acid, CO ２ The recovery rate was almost 100%.２ CO from aqueous solutions of carbonates and solid salts with a / Na ratio of 0.5 ２ The results of this experiment can be compared to the situation of two connected closed treatment tanks.

[0117] (Comparative Experimental Example 5) "Na ２ CO ３ CO from aqueous solutions and solid salts of ２ Recovery DAC" CO ２ A carbonate aqueous solution (CO ２ 3.73 mmol of Na and 7.46 mmol of Na) were placed in a sealed container and sulfuric acid was added. ２ The gas was collected (approximately 84 mL). The number of moles of Na was the same as in Experimental Example 8. ２ Addition of sulfuric acid in the amount corresponding to the stoichiometric ratio of CO ２ The recovery rate was about 98%. ２ The amount of CO generated was three-quarters of that in the experimental example. ２ It can be said that the utilization rate is inferior to that of the experimental example.

[0118] (Experimental Example 11) "MgCO from aqueous solution and solid salt of sodium sesquicarbonate" ３ Production and CO ２ Recovery: CO ２ Carbonate solid (sodium sesquicarbonate) with a CO / Na ratio of 0.67 ２ A stoichiometric ratio of 0.5M MgSO4 (5 mmol of Na and 7.46 mmol of Na) was slowly added to the sesquisalt. When MgSO4 (MgSO4 is half the number of moles of Na in the sesquisalt) was added in a stoichiometric ratio, CO2 equivalent to half the number of moles of the sesquisalt (more than 98% of the theoretical amount) was released. ２ Gas was generated. When the precipitate was air-dried, MgCO ３ ・3H ２ It was O.

[0119] (Comparative Experimental Example 6) "Na ２ CO ３ MgCO from aqueous solutions and solid salts ３ Production and CO ２ Recovery" CO２ Instead of a carbonate solution with Na = 0.67, CO ２ A carbonate aqueous solution with a CO / Na ratio of 0.5 was used. To this carbonate aqueous solution, an MgSO4 aqueous solution (0.5 M, 5 mmol, stoichiometric ratio) was slowly added. ２ The error was close to zero, and almost no MgCO ３ ・3H ２ Compared with Experimental Example 11, CO ２ Without generating CO ２ It is clear that the amount of electricity is not being used effectively.

[0120] (Experimental Example 12) CO ２ To easily determine the NaOH-Na ratio, a pH meter (Horiba, F-2000) and an electrical conductivity meter (Horiba, LAQUAtwin, EC-33B) were used. ２ CO ３ -NaHCO ３ A two-dimensional calibration curve was created by changing the ratio and concentration of NaOH solution and atmospheric CO ２ A carbonate solution of unknown concentration was synthesized by reacting the two-dimensional calibration curve with the TOC measurement (total Na content known). The results were found to be consistent. Furthermore, the combination of a pH meter and a Na+ ion meter (HORIBA, LAQUAtwin, Na-11) also matched the TOC measurement results. ２ It was confirmed that the / Na ratio can be easily determined.

[0121] The present invention provides a method for capturing and removing carbon dioxide gas that can directly reduce carbon dioxide in the atmosphere on a large scale. Implementing a certain method described in the present invention can contribute to negative emissions. This technology suppresses global warming caused by carbon dioxide and promotes the realization of a low-carbon society.

[0122] 10: Medium 20: Storage tank 30-1, 30-2: Nozzle 40-1, 40-2: Pipe 50: Inclined surface 60: Pole

Claims

1. A method for recovering and removing carbon dioxide from the atmosphere, comprising a step of bringing carbon dioxide in the atmosphere into contact with an aqueous solution of NaOH generated by electrolysis or electrodialysis to produce a carbonate of sodium, the method for recovering and removing carbon dioxide from the atmosphere being characterized by having the following first to fourth steps. (1) A first step of spreading the aqueous solution of NaOH over a hydrophilic and porous medium. (2) While evaporating the water content of the aqueous solution, an adhering layer of NaOH is formed on the medium, and when carbon dioxide in the atmosphere comes into contact with the adhering layer of NaOH, sodium carbonate (Na ２ CO ３ .CO ２ / Na ratio = 0.5) is produced in a second step. (3) Adding water to the adhering layer of NaOH formed on the medium to maintain a wet state in which liquid water is present, and while growing crystals of the sodium carbonate containing at least one selected from the group consisting of sesquicarbonate (Na ２ CO ３ ·NaHCO ３ ·2H ２ O.CO ２ / Na = 0.67) and sodium bicarbonate (NaHCO ３ .CO ２ / Na = 1), improving the CO ２ / Na ratio of the sodium carbonate in a third step. (4) A fourth step of washing with water by supplying water for dissolving the sodium carbonate adhering to the medium, causing the aqueous solution of the sodium carbonate to flow out from the medium and collecting it in a storage tank.

2. Further, it has a fifth step of reusing the washed medium, and the method for recovering and removing carbon dioxide in the atmosphere according to claim 1.

3. In the fourth step, the sodium carbonate is taken out from the aqueous solution of the sodium carbonate aggregated in the storage tank and stored on land in a place where no water flows in, and the method for recovering and removing carbon dioxide in the atmosphere according to claim 1.

4. In the third step, the CO ２ / Na ratio of the solid of the sodium carbonate or its aqueous solution, and the pH of the aqueous solution of the sodium carbonate are measured to control the moisture in that step, and the method for recovering and removing carbon dioxide in the atmosphere according to claim 1 is characterized in that.

5. In the second step, the carbon dioxide in the atmosphere comes into contact with the adhesion layer of the NaOH by natural wind, and the method for recovering and removing carbon dioxide in the atmosphere according to claim 1.

6. In the fourth step, for the aqueous solution of the sodium carbonate aggregated in the storage tank, NaCl or Na ２ SO ４ is allowed to coexist to precipitate and separate a solid salt of a second carbonate. The method for recovering and removing carbon dioxide in the atmosphere according to any one of claims 1 to 5, comprising this step.

7. In the fourth step, with respect to the aqueous solution of sodium carbonate aggregated in the storage tank, from the liquid-solid mixed state in which a solid salt containing sodium sesquicarbonate and a saturated aqueous solution coexist, the liquid phase is removed and returned to the medium, and the solid phase has a CO ２ / Na ratio greater than that of sodium sesquicarbonate, and a step of separating a carbonate, according to any one of claims 1 to 5, for a method for recovering and removing carbon dioxide in the atmosphere.

8. In the fourth step, the aqueous solution of sodium carbonate aggregated in the storage tank is transferred to a closed treatment tank, and CO gas with a concentration higher than that of the atmosphere is introduced into the closed treatment tank to increase the CO / Na ratio of the aqueous solution. The method for recovering and removing carbon dioxide in the atmosphere according to any one of claims 1 to 5, characterized in that. ２ gas is introduced to increase the CO ２ / Na ratio.

9. There are a plurality of the closed treatment tanks, and the carbonate of sodium and its aqueous solution in the first closed treatment tank are decomposed to generate CO ２ gas, which is introduced into the second closed treatment tank. The method for recovering and removing carbon dioxide in the atmosphere according to claim 8, characterized in that.

10. CO with a higher concentration than the atmosphere described above ２ The gas is at least one selected from the group consisting of soil-emitted gas, biomass decomposition gas, exhaust gas from the respiration of organisms, gas derived from gas fields, and exhaust gas from auxiliary machines that utilize combustion. The method for recovering and removing carbon dioxide in the atmosphere according to claim 8.

11. Mix the aqueous solution of the sodium carbonate obtained in the fourth step with the acidic aqueous solution generated by the electrolysis or electrodialysis described above, and separate and recover CO ２ The method for recovering and removing carbon dioxide in the atmosphere according to any one of claims 1 to 5, further comprising a step of separating and recovering the gas.

12. The acidic aqueous solution generated by the electrolysis or electrodialysis is contacted with a basic mineral to generate an aqueous solution containing alkaline earth metal ions. The solid salt of the sodium carbonate obtained in the fourth step or an aqueous solution containing the same is mixed with the generated aqueous solution containing alkaline earth metal ions to precipitate alkaline earth metal carbonate and store it on land, and an aqueous solution of sodium salt is generated and reused in the electrolysis or electrodialysis. The method for recovering and removing carbon dioxide in the atmosphere according to claim 1 further includes a step.

13. Mixing the aqueous solution containing the alkaline earth metal ions and the solid salt of the sodium carbonate or the aqueous solution containing the same inside the sealed treatment tank, and recovering CO ２ generated at that time, the method for recovering and removing carbon dioxide in the atmosphere according to claim 12, further comprising a step of recovering.

14. A carbon dioxide recovery and removal system for the atmosphere that generates sodium carbonate by bringing carbon dioxide in the atmosphere into contact with an aqueous solution of NaOH produced by electrolysis or electrodialysis, the carbon dioxide recovery and removal system for the atmosphere being characterized by having the following treatment units (1) to (4). (1) A NaOH aqueous solution diffusion treatment unit that includes a hydrophilic and porous medium and has a mechanism for spreading the aqueous solution of NaOH over the hydrophilic and porous medium. (2) While evaporating the moisture of the aqueous solution, an adhesion layer of NaOH is formed on the medium, and when carbon dioxide in the atmosphere comes into contact with the adhesion layer of NaOH, sodium carbonate (Na ２ CO ３ .CO ２ / Na ratio = 0.5) is generated. An atmospheric CO ２ collection treatment unit. (3) Adding moisture to the adhesion layer of NaOH formed on the medium to maintain a wet state in which liquid water exists, and crystallizing at least one selected from the group consisting of sesquicarbonate (Na ２ CO ３ ·NaHCO ３ ·2H ２ O.CO ２ / Na = 0.67) and sodium bicarbonate (NaHCO ３ .CO ２ / Na = 1) while growing the sodium carbonate, and improving the CO ２ / Na ratio of the sodium carbonate. A moisture control treatment unit having a mechanism. (4) A cleaning treatment unit having a mechanism for washing with water by supplying moisture for dissolving the sodium carbonate adhering to the medium, flowing out the aqueous solution of the sodium carbonate from the medium, and aggregating it in a storage tank.

15. Further, it has a medium reuse unit for reusing the washed medium, and the system for recovering and removing carbon dioxide in the atmosphere according to claim 14.

16. In the washing treatment unit, it has a sub-treatment unit for taking out the sodium carbonate from the aqueous solution of the sodium carbonate aggregated in the storage tank and storing it on land in a place where no water flows in, and the system for recovering and removing carbon dioxide in the atmosphere according to claim 14.

17. In the moisture control processing unit, a sub-processing unit that measures the CO ２ / Na ratio of the solid of the carbonate of sodium or its aqueous solution, and the pH of the aqueous solution of the carbonate of sodium, and manages the moisture in the processing unit, the carbon dioxide recovery and removal system in the atmosphere according to claim 14.

18. The atmospheric CO ２ The carbon dioxide in the atmosphere contacts the adhesion layer of the NaOH by natural wind in the capture processing unit, and the carbon dioxide recovery and removal system in the atmosphere according to claim 14.

19. In the washing treatment unit, NaCl or Na ２ SO ４ is allowed to coexist in the aqueous solution of sodium carbonate aggregated in the storage tank to precipitate and separate a solid salt of a second carbonate. The carbon dioxide recovery and removal system in the atmosphere according to any one of claims 14 to 18, which has a sub-treatment unit for this purpose.

20. In the cleaning treatment unit, for the aqueous solution of sodium carbonate aggregated in the storage tank, from the liquid-solid mixed state in which a solid salt containing sesquicarbonate and a saturated aqueous solution are mixed, the liquid phase is removed and returned to the medium, and the CO ２ / Na ratio of the solid phase is separated from the carbonate having a larger CO / Na ratio than sesquicarbonate, and the carbon dioxide recovery and removal system in the atmosphere according to claim 14 having a sub-treatment unit.

21. In the washing treatment unit, an aqueous solution of sodium carbonate aggregated in the storage tank is transferred to a closed treatment tank, and a CO gas with a higher concentration than the atmosphere is introduced into the closed treatment tank to increase the CO / Na ratio of the aqueous solution. The carbon dioxide recovery and removal system in the atmosphere according to claim 14, comprising a sub-treatment unit for this purpose. ２ gas is introduced to increase the CO ２ / Na ratio of the aqueous solution.

22. Having a plurality of the closed treatment tanks, decomposing the sodium carbonate and its aqueous solution in the first closed treatment tank to generate CO ２ gas and introducing it into the second closed treatment tank, the carbon dioxide recovery and removal system in the atmosphere according to claim 21.

23. The CO with a higher concentration than the above-mentioned atmosphere ２ The gas is at least one selected from the group consisting of soil-emitted gas, biomass-decomposed gas, exhaust gas from the respiration of organisms, gas derived from gas fields, and exhaust gas from auxiliary machines using combustion. The carbon dioxide recovery and removal system in the atmosphere according to claim 21.

24. Mix an acidic aqueous solution generated by the electrolysis or electrodialysis with the aqueous solution of sodium carbonate obtained in the washing treatment unit to separate and recover CO ２ The carbon dioxide recovery and removal system in the atmosphere according to claim 14, further comprising a sub-treatment unit for separating and recovering gas.

25. The acidic aqueous solution generated by the electrolysis or electrodialysis is contacted with a basic mineral to generate an aqueous solution containing alkaline earth metal ions. The solid salt of the sodium carbonate obtained in the washing treatment unit or an aqueous solution containing the same is mixed with the generated aqueous solution containing alkaline earth metal ions to precipitate alkaline earth metal carbonate and store it on land, and an aqueous solution of sodium salt is generated and reused in the electrolysis or electrodialysis. The system for recovering and removing carbon dioxide in the atmosphere according to claim 14 further includes a sub-treatment unit.

26. Mixing the aqueous solution containing the alkaline earth metal ions and the solid salt of the sodium carbonate or the aqueous solution containing the same inside the sealed treatment tank, and recovering CO ２ The carbon dioxide recovery and removal system in the atmosphere according to claim 25, further including a sub-treatment unit for recovering the same.

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