Carbon dioxide capture system and carbon dioxide capture method

Abstract

Provided are a carbon dioxide capture system and capture method enabling simple and efficient capture of low concentrations of carbon dioxide in the atmosphere at reduced energy consumption. This carbon dioxide capture system comprises: a liquid supply unit for an alkaline aqueous solution; and a medium which is made of an air-permeable fibrous substance or porous substance and into the interior of which the alkaline aqueous solution supplied from the liquid supply unit penetrates and diffuses. The medium is arranged so as to be in contact with a natural wind-powered airflow. Carbon dioxide in the air is captured as carbonate generated by a reaction between the carbon dioxide and the alkaline aqueous solution which make contact in the medium interior. This carbon dioxide capture method comprises: bringing the aforementioned medium into contact with the natural wind-powered airflow; and supplying the alkaline aqueous solution, causing the alkaline aqueous solution to penetrate and diffuse into the medium interior, and thereby capturing the carbon dioxide in the air as carbonate generated by the reaction between the carbon dioxide and the alkaline aqueous solution that make contact in the medium interior.

Description

Carbon dioxide recovery system and carbon dioxide recovery method

[0001] The present invention relates to a carbon dioxide recovery system and a carbon dioxide recovery method. This application claims priority based on Japanese Patent Application No. 2023-218066, 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 Documents 1 to 5).

[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 is used, which brings air into contact with an alkaline aqueous solution. Conventional techniques, such as an absorption tower, are used in air contactors, where air is drawn in by a blower and gas-liquid contact is achieved (see Non-Patent Documents 1 and 4). Other methods have also been devised, such as simply bubbling the drawn-in air in 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] JP 2023-25798 A JP 2022-105973 A JP 2008-510600 A

[0007] Low Carbon Society Strategy Center, Japan Science and Technology Agency, "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> Mahdi Fasihi et al. Journal of Cleaner Production, volume 224 (2019) pp. 957-980. David W. Keith et al. Joule, 2, August 15, 2018, pp. 1573-1594. Eloy S. Sanz-Perez et al. Chem. Rev. 116, 2016, pp. 11840-11876. Kenton Heidel et al. Energy Procedia, volume 4 (2011) pp. 2861-2868.

[0008] When high-concentration carbon dioxide emitted by combustion reactions at thermal power plants and factories is captured and removed using a liquid such as an aqueous alkali 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 aqueous alkali solution, spraying onto a moving aqueous alkali solution, or spraying the aqueous alkali solution into the air to achieve gas-liquid contact, as well as methods such as exposing a surface covered with an aqueous alkali solution to an air flow maintained in a laminar or near-laminar state, are inefficient due to the small area of ​​gas-liquid contact.

[0009] On the other hand, in addressing climate change, it is desirable to reduce the release of new carbon dioxide into the atmosphere due to the energy consumed in installing and operating atmospheric carbon dioxide capture systems. Furthermore, even if renewable energy is used as a power source for operation, the amount of energy consumed decreases 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. Furthermore, absorption towers are 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.

[0010] 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.

[0011] An object of the present invention is to provide a carbon dioxide recovery system and a carbon dioxide recovery method that can recover low concentrations of carbon dioxide in the atmosphere simply and efficiently while reducing energy consumption.

[0012] The inventors have considered the various factors involved in capturing carbon dioxide at low concentrations in the atmosphere as a measure against climate change, and have invented an efficient carbon dioxide capture system and method for capturing such carbon dioxide.

[0013] As a result of extensive research, the inventors have discovered that carbon dioxide can be efficiently captured by contacting an airflow caused by natural wind and an alkaline aqueous solution with a medium made of a material with an extremely large specific surface area, air permeability, and through which the alkaline aqueous solution can penetrate and diffuse, such as fibrous materials such as filter paper or nonwoven fabric, or porous materials such as sponge. Furthermore, by forming the medium into a shape that allows air to easily flow around it and supplying and allowing the alkaline aqueous solution to penetrate while contacting it with an airflow caused by natural wind, low concentrations of carbon dioxide in the atmosphere can be more efficiently absorbed by the alkaline aqueous solution. The alkaline aqueous solution that has penetrated the medium diffuses and moves within it, coming into contact with air that has permeated into the medium from the surroundings, absorbing carbon dioxide from the air and ultimately being extracted from the medium. By permeating a medium with a large specific surface area and diffusing within or on its surface, the area of ​​gas-liquid contact with the permeating air increases, thereby increasing the rate of carbon dioxide absorption from the air.

[0014] Specifically, the present invention relates to the following carbon dioxide recovery systems: [1] A carbon dioxide recovery system comprising a medium having an alkaline aqueous solution permeated therein, the medium being made of fibrous or porous material that allows air to pass through, the medium being arranged to be in contact with natural wind-driven airflow, and recovering carbon dioxide in the air as carbonate produced by a reaction between the carbon dioxide contacting the medium inside the medium and the alkali. [2] The carbon dioxide recovery system according to [1], wherein the medium is made of a hydrophilic material. [3] The carbon dioxide recovery system according to [1] or [2], wherein the medium is at least one selected from the group consisting of filter paper, nonwoven fabric, filter, sponge, and cloth. [4] The carbon dioxide recovery system according to any one of [1] to [3], further comprising a holder for suspending and holding the medium, wherein the medium is one selected from the group consisting of a curtain shape, a ribbon shape, and a flat plate shape. [5] The carbon dioxide recovery system according to [4], wherein the holder is provided with a movable mechanism that can change the vertical and / or horizontal position of the medium. [6] The carbon dioxide capture system according to [4] or [5], wherein the holding unit is provided with a mechanism that can change the medium between a deployed position and a stored position. [7] The carbon dioxide capture system according to any of [1] to [6], wherein the medium is formed of a flexible material that can be deformed by natural wind force. [8] The carbon dioxide capture system according to any of [1] to [7], wherein a plurality of the media are arranged in parallel at intervals. [9] The carbon dioxide capture system according to any of [1] to [8], wherein the alkali is sodium hydroxide or potassium hydroxide.

[10] The carbon dioxide capture system according to any of [1] to [9], further comprising a liquid supply unit and an extraction unit, wherein the liquid supply unit is configured to supply an aqueous solution of the alkali to the medium, and wherein a solution containing carbonate produced by a reaction with the alkali inside the medium is extracted from the medium in the extraction unit.

[11] The carbon dioxide recovery system according to

[10] , wherein the liquid supply unit is configured to supply the aqueous alkaline solution to an upper portion of the medium, and the aqueous carbonate solution flowing down from the medium is extracted below the medium in the extraction unit.

[12] The carbon dioxide capture system according to

[11] , wherein the medium has an inclined surface along which the liquid supplied from the liquid supply unit flows.

[13] The carbon dioxide capture system according to

[11] or

[12] , wherein the extraction unit is a storage tank provided below the medium and stores the aqueous solution containing the carbonate that flows down from the medium.

[14] The carbon dioxide capture system according to

[10] , wherein the liquid supply unit is a storage tank that stores the aqueous alkaline solution, wherein a lower part of the medium is arranged so as to be in contact with the aqueous alkaline solution, and wherein the liquid supply unit supplies the aqueous alkaline solution to the medium by utilizing surface tension or capillary action between the medium and the aqueous alkaline solution.

[15] The carbon dioxide capture system according to

[14] , wherein a lower part of the medium is fixed to the bottom of the storage tank, and a part above the liquid level of the aqueous alkaline solution in the storage tank is formed as a protrusion that is erected so as to be in contact with air.

[16] The carbon dioxide capture system according to

[14] , further comprising a flotation device that floats the medium in the aqueous alkaline solution in the storage tank.

[17] The carbon dioxide recovery system according to any one of [1] to

[16] , further comprising an additional liquid supply unit for supplying additional aqueous alkaline solution and / or water to the medium.

[18] A carbon dioxide recovery method comprising the steps of: allowing an aqueous alkaline solution to penetrate and diffuse into the medium; and exposing the medium to a natural wind-driven airflow, and recovering carbon dioxide in the air as carbonate produced by a reaction between the carbon dioxide and the alkali contacting the aqueous alkaline solution inside the medium, wherein the medium is made of a fibrous or porous material that is permeable to air.

[19] The carbon dioxide recovery method according to

[18] , wherein the medium is made of a hydrophilic material.

[20] The carbon dioxide recovery method according to

[18] or

[19] , wherein the medium is made of at least one material selected from the group consisting of filter paper, nonwoven fabric, filter, sponge, and fabric.

[21] The method for recovering carbon dioxide according to any one of

[18] to

[20] , wherein the medium is one selected from the group consisting of a curtain, a ribbon, and a flat plate, and is held in a suspended state and brought into contact with the air flow while an aqueous alkaline solution is supplied.

[22] The method for recovering carbon dioxide according to any one of

[18] to

[21] , wherein the medium is made of a flexible material that can be deformed by natural wind force.

[23] The method for recovering carbon dioxide according to any one of

[18] to

[22] , wherein the aqueous alkali solution is made of a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution.

[24] The method for recovering carbon dioxide according to any one of

[18] to

[23] , wherein the aqueous alkali solution is constantly supplied to the medium, and a solution containing carbonate produced by a reaction with the alkali inside the medium is constantly removed from the medium.

[25] The method for recovering carbon dioxide according to any one of

[18] to

[24] , wherein the aqueous alkali solution is supplied to an upper part of the medium, and the aqueous carbonate solution that flows down from the medium is removed and recovered as the carbonate.

[26] The method for recovering carbon dioxide according to any one of

[18] to

[24] , wherein the aqueous alkali solution is stored, and the lower part of the medium is brought into contact with the aqueous alkali solution, and the aqueous alkali solution is supplied to the medium by utilizing surface tension or capillary action.

[27] The method for recovering carbon dioxide according to any one of

[18] to

[26] , further comprising supplying an additional aqueous alkaline solution and / or water to the medium.

[0015] According to the present invention, it is possible to provide a carbon dioxide recovery system and a carbon dioxide recovery method that can recover low-concentration carbon dioxide in the atmosphere simply and efficiently while reducing energy consumption.

[0016] 1 is a conceptual diagram for explaining a carbon dioxide capture system. FIG. 1 is a schematic diagram of a carbon dioxide capture system when an alkaline aqueous solution is supplied from above the medium. FIG. 1 is a schematic diagram of a carbon dioxide capture system when an alkaline aqueous solution is supplied from below the medium. FIG. 1 is a schematic diagram of a carbon dioxide capture system when an alkaline aqueous solution is supplied from above and below the medium. FIG. 1 is a schematic diagram of a carbon dioxide capture system when an alkaline aqueous solution is supplied from above and below the medium. FIG. 2 is a schematic diagram of a carbon dioxide capture system when an alkaline aqueous solution is supplied from above and below the medium. FIG. 2 is an example of a retention structure for a carbon dioxide capture system in which the medium is curtain-shaped. FIG. 3 is a schematic diagram of a carbon dioxide capture system in which a plurality of curtain-shaped media are arranged in parallel. FIG. 3 is a schematic diagram of a carbon dioxide capture system showing another example of the medium (protrusions). FIG. 4 is a schematic diagram of a carbon dioxide capture system showing another example of the medium (floating body structure). FIG. 4 is a schematic diagram (simplified side view) of a carbon dioxide capture system in which the medium is an inclined surface. FIG. 5 is a schematic diagram of a carbon dioxide capture system in which an alkaline aqueous solution or water (moisture) is additionally supplied. FIG. 6 is a schematic diagram of a carbon dioxide capture system (ribbon-shaped medium) provided with a movable mechanism. FIG. 7 is a schematic diagram of a carbon dioxide capture system (curtain-shaped medium) provided with a movable mechanism. FIG. 1 is a schematic diagram of a carbon dioxide capture system (medium with a radiator core structure) equipped with a movable mechanism.

[0017] (Carbon dioxide recovery system) A carbon dioxide recovery system according to one embodiment of the present invention (sometimes referred to as "the carbon dioxide recovery system of this embodiment" or "the recovery system of this embodiment") comprises a medium into which an aqueous alkaline solution has permeated. The medium is made of fibrous or porous material that allows air to pass through. The medium is arranged so as to come into contact with airflow caused by natural wind, and is capable of recovering carbon dioxide in the air as carbonate produced by a reaction between the carbon dioxide and the alkali that come into contact inside the medium. The recovery system of this embodiment may further comprise a liquid supply unit that supplies the aqueous alkaline solution. Furthermore, the recovery system of this embodiment preferably comprises a medium into which the aqueous alkaline solution has permeated and diffused.

[0018] FIG. 1 is a conceptual diagram illustrating a carbon dioxide capture system according to this embodiment. FIG. 1 shows a carbon dioxide capture medium as an example of an embodiment to illustrate the carbon dioxide capture principle. In the following figures, identical reference numerals indicate identical or corresponding parts. First, FIG. 1(A) will be described. An alkaline aqueous solution 12 is supplied to the medium 10 from an alkaline aqueous solution supply line 30, which serves as an alkaline aqueous solution supply unit. The alkaline aqueous solution supply line 30 may be, for example, a pipe or tube, but any other device capable of supplying the alkaline aqueous solution may be used. The supply method is not limited, and simple equipment may also be used. The alkaline aqueous solution 12 diffuses through the fibrous or porous medium 10 and moves along the flow 14 of alkaline aqueous solution shown in the cross section of the medium. While FIG. 1(A) shows the alkaline aqueous solution 12 supplied at the top of the medium 10 flowing downwards due to gravity, the medium 10 may also be placed in a container or the like, allowing the supplied alkaline aqueous solution 12 to diffuse and permeate across the medium surface. Air permeation 18 occurs from the surface of the medium 10 that contacts the air, and the carbon dioxide contained in the permeated air is absorbed by the alkaline aqueous solution inside the medium. When the medium 10 is placed in a container or the like, air comes into contact with the air inside and around the container on one side (the upper side) of the medium 10, and carbon dioxide is absorbed and captured through the medium 10 that has been permeated with the alkaline aqueous solution. When the medium 10 is placed vertically as shown in FIG. 1(A), the alkaline aqueous solution that has absorbed and captured carbon dioxide is extracted by flowing down or accumulating from the bottom of the medium. Carbon dioxide can also be extracted by extracting the alkaline aqueous solution inside the medium 10. This alkaline aqueous solution 16 contains the produced carbonate.

[0019] Here, the medium 10 is positioned so that it comes into contact with the airflow, allowing it to be formed into a structure with low resistance and allowing air to easily flow around it. Therefore, by using natural wind to circulate air around the medium and allowing it to permeate the medium, energy consumption in the air conditioner can be significantly reduced. Even if a secondary fan is used to circulate air, low resistance eliminates the need for high pressure, reducing energy consumption due to pressure loss. To more effectively circulate air using natural wind, the medium 10 can be made flexible, suspended so that it can move with the airflow of natural wind, or, if multiple media 10 are used, gaps can be provided between each media. This allows the medium to autonomously respond to changes in wind direction and speed without consuming any energy, allowing it to be used continuously even in strong winds without being affected.

[0020] In the present invention, the medium 10 may be positioned so that it comes into contact with the airflow of natural wind. That is, when natural wind is introduced into the system from outside, the natural wind generates an airflow, and the medium 10 comes into contact with that airflow, thereby replacing the surrounding air. The air replacement rate around the medium 10 is preferably at least as fast as possible to prevent a decrease in the carbon dioxide concentration around the medium 10. Furthermore, the replacement rate is sufficient as long as the carbon dioxide concentration around the medium 10 does not decrease; a higher rate is not required. Even in completely windless conditions, if the area around the medium 10 is open to the outside air, carbon dioxide is replaced by diffusion from the air, so that a certain concentration of carbon dioxide around the medium 10 is maintained. Therefore, when using an auxiliary fan, it is sufficient to generate additional air replacement to the extent that the carbon dioxide concentration around the medium 10 does not decrease compared to the atmospheric concentration, and it is preferable that this be the upper limit of the energy consumption caused by using the auxiliary fan. Auxiliary fans can be used appropriately depending on changes in natural wind volume, but it is desirable to reduce energy consumption by auxiliary fans as much as possible by installing this system in a location where adequate natural wind force can be expected.

[0021] The alkaline aqueous solution 12 diffusing within the medium 10 comes into contact with the permeated air with a large gas-liquid contact area between supply and removal. This increases the surface area of ​​the medium 10 in contact with the surrounding air, increasing the amount of permeable air. Furthermore, the distance traveled by the alkaline aqueous solution within the medium increases, thereby increasing the gas-liquid contact time, thereby achieving efficient carbon dioxide absorption. It is also possible to steadily supply alkaline aqueous solution or water to the medium and steadily remove the same amount of alkaline aqueous solution with absorbed carbon dioxide. In the case of the absorption tower described above, the absorbing solution passes through the interior in a short time. Therefore, to increase the amount of gas contacted per unit amount of absorbing solution, a large amount of gas must be pressurized and passed through high-resistance packing, unavoidably consuming energy due to pressure loss. In contrast, according to the present embodiment, the gas-liquid contact time can be increased by increasing the travel distance within the medium 10, as described above. Furthermore, since the alkaline aqueous solution can be brought into contact with a sufficient amount of air simply by permeating the medium while the air around the medium is replaced by natural wind force, there is no need to pressurize and circulate air, thereby reducing energy consumption due to pressure loss. When processing carbon dioxide emitted from thermal power plants and factories, the gas must be treated according to the amount of emissions, but there are no such restrictions when capturing carbon dioxide from the atmosphere. Carbon dioxide can be captured very easily by simply bringing the medium into contact with air, allowing it to permeate, and then absorbing it into an alkaline aqueous solution that has been permeated.

[0022] Furthermore, when the carbon dioxide capture system of this embodiment includes a liquid supply unit that supplies the alkaline aqueous solution, the liquid supply unit may be a storage tank that stores the alkaline aqueous solution. In the carbon dioxide capture system of this embodiment, the lower part of the medium may be arranged so as to be in contact with the alkaline aqueous solution, and the liquid supply unit may be configured to supply the alkaline aqueous solution to the medium by utilizing surface tension or capillary action between the medium and the alkaline aqueous solution. In another installation form for supplying the alkaline aqueous solution, for example, as shown in FIG. 1(B), the medium 10 is in contact with the alkaline aqueous solution in a storage tank 20 that supplies the alkaline aqueous solution, and the alkaline aqueous solution can be permeated into the medium 10 by surface tension (or capillary action, the same applies below). In such a structure, the storage tank 20 also serves as the alkaline aqueous solution supply unit, and a system can be adopted in which the supply of the alkaline aqueous solution and the removal of carbon dioxide after absorption are performed using the same storage tank 20. The alkaline aqueous solution permeates from the storage tank 20 and diffuses throughout the medium 10 along the upward flow 14A of the alkaline aqueous solution, while carbonates produced by absorbing carbon dioxide also diffuse through the medium 10 and are discharged into the storage tank 20 along the downward flow 14B of the alkaline aqueous solution. In this case, water lost due to evaporation can be additionally replenished into the storage tank 20. Whenever a certain amount of carbonates accumulates in the storage tank 20, they can be recovered by removing them from the storage tank 20 as an alkaline aqueous solution containing carbonates using a pump, drain pipe, etc. (not shown), and the storage tank 20, drain pipe, etc. also function as an extraction section for the aqueous solution containing carbonates.

[0023] The medium 10 for supplying and penetrating an alkaline aqueous solution according to this embodiment is one into which the alkaline aqueous solution can penetrate. A variety of fibrous, porous, and air-permeable materials can be used. Materials typically used for gas or liquid permeability applications, such as filter paper, nonwoven fabric, fabric, sponges, and filters, are preferred. Materials with high wettability (hydrophilicity) are particularly preferred. Hydrophilic materials include polymers and inorganic materials containing components with hydroxyl or carboxyl groups. Examples include cellulose and rayon, which have hydroxyl (OH) or carboxyl groups on their surfaces, and hydrophilic polymers such as surface-treated polyalkanes. Inorganic materials include aluminum silicate, zirconia, glass wool, asbestos, and basalt fiber. The alkaline aqueous solution supplied to such a medium 10 spreads across its entire surface due to its wettability, increasing the contact area with the air permeating from the surrounding area. The wettability of a medium material can be determined by water penetration and water contact angle. Preferably, the water contact angle when the material has a smooth surface is 90° or less, more preferably 60° or less, and even more preferably 30° or less. To enhance durability, hydrophilic materials can be combined with stable resins such as nylon or PPS (polyphenylene sulfide). Examples of materials that can be used include PPS mesh coated with a mixture of zirconium oxide and polymer, as in water electrolysis membranes, and composites of nylon and ion exchange membranes. Because alkaline aqueous solutions tend to have a small contact area with air due to surface tension, spreading them over a medium with high wettability (hydrophilicity) and a large specific surface area increases the contact area with air, thereby improving the absorption rate of low concentrations (400 ppm) of carbon dioxide in air.

[0024] Air permeates the medium through diffusion from the surrounding area. For example, by holding the medium and forming it into a structure that allows airflow around the medium by natural wind force and installing it in an appropriate location, such as outdoors, the air around the medium is replaced, and carbon dioxide is constantly supplied from the atmosphere by diffusion into the medium and absorbed into the alkaline aqueous solution. Alternatively, outside air can be taken in by natural wind force using an induction pipe or the like and circulated from an appropriate direction around the medium structure. In this way, atmospheric carbon dioxide can be efficiently absorbed without using an air conditioner that draws in air using a blower, which consumes a lot of energy. A fan can also be used as an auxiliary fan for air circulation, but the pressure loss is small, reducing energy consumption. Here, it is sufficient that the air around the medium structure is replaced at a rate sufficient to correspond to the absorption of carbon dioxide by the alkaline aqueous solution in the medium.

[0025] The system of this embodiment primarily utilizes natural wind force, making it suitable for outdoor installation. Because wind direction and speed fluctuate under natural conditions, the structure of the medium 10 should be able to accommodate these changes. Specifically, as described below, the medium 10 can be formed from a flexible material that can be deformed by natural wind force, or the medium 10 can be suspended and supported with a mechanism (sometimes referred to as a movable mechanism) that can move due to the airflow of natural wind force. This allows the medium 10 and its structure to adapt to changes in shape and position to accommodate changes in wind direction and speed. This allows the medium 10 to always adopt a shape and position appropriate for the wind direction, even when the wind direction changes. Furthermore, when the wind speed increases and high wind pressure is applied, these changes in shape and other factors can deflect the pressure and prevent any impact on the medium 10 or the entire structure. The movable mechanism is preferably installed so that it can automatically change position due to the wind force as the wind direction and speed change. For example, a mechanism similar to that used in aircraft for directional stabilization (weather vane stabilization) can be incorporated. Furthermore, by providing gaps such as slits or holes in the medium, excess airflow can be released through the gaps to accommodate increased wind speeds.

[0026] Furthermore, if the system of this embodiment is installed outdoors, it will need to be able to withstand strong winds such as typhoons. The movable mechanism and material selection described above can provide a certain degree of resistance to strong winds. Furthermore, by designing a mechanism that allows the medium 10, made of a flexible material, to be foldable and compactly stored, it can be temporarily stored and evacuated when an extreme storm is predicted, preventing the effects of the storm.

[0027] Regarding the supply of the alkaline aqueous solution and the withdrawal of the carbonate-containing aqueous solution, the supply position, movement path, withdrawal position, etc. can be appropriately set according to the structure of the medium 10. For example, as shown in FIG. 1(A), if the alkaline aqueous solution is supplied from the top of the medium 10, it can flow downward by gravity and be withdrawn from the bottom. Specifically, a receiving tank (see, for example, FIG. 2) can be installed below the medium 10 to store the carbonate-containing alkaline aqueous solution 16 extracted by dripping. Alternatively, instead of storing the alkaline aqueous solution in a tank, a channel like a gutter can be provided for the alkaline aqueous solution 16 dripping from the medium 10, so that it can be transferred directly to the carbonate treatment process. Alternatively, as shown in FIG. 1(B), the medium 10 can be installed in a storage tank 20, which supplies the alkaline aqueous solution to the medium 10 and stores the alkaline aqueous solution discharged and extracted from the medium 10, including carbonate produced by absorbing carbon dioxide. The accumulated carbonate-containing alkaline aqueous solution is sequentially transferred from the storage tank 20 to the carbonate treatment process.

[0028] As a specific example of a carbon dioxide capture system according to this embodiment, FIG. 2 shows a schematic diagram of a carbon dioxide capture system in which an alkaline aqueous solution is supplied from above the medium. A flat (or sheet-like) medium 10 is suspended from its upper portion by a holder 40 to form a structure. The holder 40 includes left and right support columns 42, 42, a connecting member 44 suspended between the left and right columns 42, 42, and a plurality of attachments 41 (e.g., pins, hooks, clips, pinches, strings, wires, and other thread-like members) for attaching the medium 10 to the connecting member 44. For example, by hooking the medium 10 to a rod-shaped or cylindrical connecting member 44 using an S-shaped or ring-shaped hook, the medium 10 can be made into a movable mechanism that can swing left and right, front and back, etc., due to natural wind airflow.

[0029] An alkaline aqueous solution supply line 30 is disposed above the medium 10, and the alkaline aqueous solution 12 is supplied from a supply port 32. The alkaline aqueous solution 12 passes through the supply port 32 and flows through a supply pipe 34 connected to the supply port 32, and is sprayed onto the top of the medium 10 from multiple nozzles 36 attached to the supply pipe 34. The supply port 32 or the supply pipe 34 can be provided with an on-off valve (not shown) to adjust the amount of alkaline aqueous solution supplied. The alkaline aqueous solution 12 diffuses through the fibrous or porous medium 10 and flows downward by gravity. During this flow, it comes into contact with the air permeating the medium 10, and the alkali reacts with carbon dioxide in the air to produce carbonate. This carbonate-containing alkaline aqueous solution 16 is stored in a storage tank 20 installed below the medium 10.

[0030] As a specific example of FIG. 1(B), FIG. 3 shows a schematic diagram of a carbon dioxide capture system in which an alkaline aqueous solution is supplied from the bottom of the medium. In this system, the storage tank 20 also serves as an alkaline aqueous solution supply unit. The bottom of the medium 10 is in contact with the alkaline aqueous solution in the storage tank 20, allowing the alkaline aqueous solution to penetrate the medium 10 by surface tension. The alkaline aqueous solution penetrates the medium 10 from the storage tank 20 and diffuses throughout the medium 10 along the upward flow of the alkaline aqueous solution. Carbonates produced by absorbing carbon dioxide also diffuse through the medium 10 and are discharged into the storage tank 20 along the downward flow of the alkaline aqueous solution. In this case, the alkaline aqueous solution containing carbonates is stored in the storage tank 20 installed below the medium 10. In this system, since the bottom of the medium 10 is in contact with the alkaline aqueous solution in the storage tank 20, the range of movement of the medium 10 due to natural wind force is limited compared to the system in FIG. 2, but similar effects can be achieved.

[0031] Furthermore, Figure 4 shows a schematic diagram of a carbon dioxide capture system in which an up-and-down moving mechanism 60 is provided to selectively supply the alkaline aqueous solution from above the medium, below the medium, or both. As shown in Figure 4, the up-and-down moving mechanism 60 may be, for example, a mechanism in which a thin tubular member is inserted into a support 42 and moved up and down. When the up-and-down moving mechanism 60 is provided, the up-and-down position (vertical position) of the medium 10 can be changed by extending or contracting the support 42. In Figure 4(A), the medium 10 is located above and away from the storage tank 20, and the alkaline aqueous solution is supplied only from above, while the carbonate-containing alkaline aqueous solution 16 is dripped and stored in the storage tank 20 installed below the medium 10. In Figure 4(B), the medium 10 is positioned below and in contact with the reservoir tank 20. The alkaline solution is supplied to the medium 10 by permeation from the reservoir tank 20 due to surface tension, and the carbonate-containing alkaline solution is also discharged into the reservoir tank 20. However, the alkaline solution can also be simultaneously supplied from above using a nozzle 36. This example combines the systems shown in Figures 2 and 3, allowing the alkaline solution to be supplied not only from the bottom of the medium 10 but also from the top of the medium 10. This allows the entire surface of the medium 10 to be evenly wetted with the alkaline solution, increasing the contact area between the medium 10 and the alkaline solution. This also improves the absorption rate of low-concentration carbon dioxide in the air. Furthermore, the water lost due to evaporation and the alkaline solution can be additionally replenished to the medium 10 and the reservoir tank 20. Furthermore, by changing the mounting height of the medium 10 using the vertically movable mechanism, various usage methods are possible, such as supplying only from the bottom of the medium 10, supplying only from the top of the medium 10, or supplying from both the bottom and top of the medium 10. The evaporation rate of water from the medium 10 is affected by factors such as temperature, humidity, wind speed, and the type of medium. When the evaporation rate of water is low, the system can be operated by supplying the alkaline aqueous solution from above, allowing the alkaline aqueous solution to easily flow to the bottom of the medium 10. When the evaporation rate of water is high, this can be addressed by reducing the concentration of the alkaline aqueous solution supplied to the medium 10 and increasing the supply amount, but it can also be adjusted by supplying the alkaline aqueous solution from both the top and bottom of the medium 10 so that the alkaline aqueous solution is sufficiently dispersed throughout the medium 10.Supplying the alkaline solution from above alone will make it difficult for it to reach the bottom if the water evaporates quickly. Furthermore, supplying the alkaline solution from below alone will limit the height it can reach. Therefore, combining these supply modes allows for more precise control tailored to the situation. In another embodiment, as shown in FIGS. 5A and 5B, one end of a wire 43 is connected to both ends of a connecting member 44, and the other end is hung on a pulley 46 attached to the top of a support 42. By adjusting the length of the wire 43, the connecting member 44 can be moved up and down independently of the upper and lower alkaline solution supply sections. Therefore, the vertical position of the medium 10 relative to the alkaline solution supply sections can be changed.

[0032] FIG. 6 shows an example of a carbon dioxide capture system support structure using a curtain-shaped medium. The medium 10 may be formed into a strip of fabric, such as a curtain or ribbon, and hung to allow air to flow around it. By using a curtain-shaped (with pleats on the left and right) or ribbon-shaped (with pleats on the top and bottom) medium 10A, it can flutter or sway with natural wind force. A curtain / ribbon structure may be a rail-type curtain with a curtain rail or a retractable roll curtain. In this case, a movable mechanism can be configured by attaching a curtain rail or retracting mechanism to the connecting member 44 at the hanging position. Furthermore, by providing the curtain / ribbon itself with a certain degree of flexibility, it can deflect wind pressure. For example, as shown in FIG. 6(A), a movable mechanism can be achieved by connecting one end of a wire 43 to both ends of the connecting member 44 and hanging the other end over a pulley 46 installed at the top of the support 42. The length of the wire 43 can be adjusted to allow the connecting member 44 to move up and down. Therefore, the vertical position (vertical position) of the medium 10A can be changed. In addition, excess airflow can be released by configuring the curtain ribbon structure from multiple narrow curtain ribbons or by providing gaps (e.g., slits, air holes, etc.) within the curtain ribbon structure to allow air to escape. Furthermore, the curtain-shaped medium 10A can be moved between an unfolded position ( FIG. 6(A) ) and a stored position ( FIG. 6(B) ) as needed. For example, if a strong wind is predicted, the medium 10A can be slid to one side to change its horizontal position and moved to be stored together for evacuation, as shown in FIG. 6(B) . In the case of a roll curtain, the medium 10A can be evacuated by changing its vertical position and rolling it up.

[0033] The alkaline aqueous solution can be supplied to the curtain ribbon structure by supplying the alkaline aqueous solution near the connecting member 44, where it is suspended (see FIG. 2 ), allowing it to flow downward through the interior of the medium 10A by gravity and dripping from the lower end of the curtain ribbon structure into the storage tank 20 provided below. Furthermore, a storage tank 20 for the alkaline aqueous solution is provided below the medium 10A as a supply unit for the alkaline aqueous solution. By positioning the medium 10A so that the lower end of the curtain ribbon structure is in contact with the alkaline aqueous solution in the storage tank 20, the alkaline aqueous solution can be permeated into the medium 10A by surface tension, and carbonates formed by absorbing carbon dioxide can be diffused within the medium 10A and discharged into the storage tank 20. By changing the vertical position of the medium 10A, it can be used in a position that is in contact with the alkaline aqueous solution and a position that is not, and its height can also be adjusted depending on the amount of alkaline aqueous solution.

[0034] FIG. 7 shows a schematic diagram of a carbon dioxide capture system in which multiple media are arranged in parallel at intervals. Multiple curtain- or ribbon-shaped media 10A can also be arranged in parallel at intervals to form a suspended structure. The alkaline aqueous solution supply unit can be composed of an alkaline aqueous solution supply line 30, an alkaline aqueous solution storage pipe 31 that stores the alkaline aqueous solution supplied from the alkaline aqueous solution supply line 30, a supply pipe 34 connected to the alkaline aqueous solution storage pipe 31, multiple branch pipes 37 connected to the supply pipe 34, and multiple nozzles 36 attached to the branch pipe 37. The alkaline aqueous solution supplied from the alkaline aqueous solution supply line 30 is supplied and stored in the alkaline aqueous solution storage pipe 31, flows through the supply pipe 34, passes through the branch pipe 37, and is sprayed from the nozzles 36 onto the top of the media 10. The media 10A is attached to the branch pipe 37 by a fixture 41 and is suspended. By providing each branch pipe 37 with an on-off valve (not shown), it is possible to select the medium to which the alkaline aqueous solution is supplied and to adjust the amount of alkaline aqueous solution supplied to each medium. In this way, in this carbon dioxide capture system, the supply pipe 34 and the branch pipe 37 form a structure that not only serves as a supply unit for the alkaline aqueous solution but also as a holding unit for the medium 10A. By using the same structure for the alkaline aqueous solution supply unit and the medium holding unit rather than separate structures, the system itself has a simple configuration and the number of components is reduced. Furthermore, by installing multiple curtain-shaped or ribbon-shaped media 10A in parallel with a gap between them, air can be allowed to flow between them, allowing for efficient carbon dioxide capture.

[0035] Another form of medium structure is a radiator core structure (fin structure) of a heat exchanger (see Figure 14 described below). Heat exchangers used for air cooling dissipate heat into the circulating air, so a radiator core structure is adopted to allow a large area of ​​contact with the air. When a radiator in an automobile engine or the like air-cools a coolant, plates such as corrugated fins or flat plate fins are attached to the radiator core to increase the contact area between the pipe through which the coolant circulates and the circulating air. Forming a medium 10 in such a radiator core structure and supplying an alkaline aqueous solution while circulating air can absorb carbon dioxide from the air. By adopting a radiator core structure with low air resistance, air can be easily circulated using natural wind force.

[0036] The situations differ between removing relatively high concentrations of carbon dioxide from exhaust gases from thermal power plants and factories and capturing low concentrations (400 ppm) of carbon dioxide from the atmosphere. In the case of exhaust gases, the goal is to treat only a certain amount of generated exhaust gas and remove as much carbon dioxide as possible until it is almost carbon dioxide-free (a level significantly lower than the carbon dioxide content of the atmosphere) before releasing it to the outside. On the other hand, when capturing low concentrations (400 ppm) of carbon dioxide from the atmosphere, the air to be treated is ubiquitous on Earth, and as long as a certain amount of carbon dioxide can be captured from the air, it is not necessary to completely remove the carbon dioxide. In other words, it is appropriate to quickly discharge the air from which the amount of carbon dioxide that can be efficiently removed has been removed, and then take in and process new air, thereby maximizing the carbon dioxide capture rate. In this respect, it is similar to air-cooled heat exchangers. In air-cooled systems, air at a lower temperature than the object to be cooled is taken in from the outside and circulated through the radiator. However, since the goal is not to raise the temperature of the air itself, it is more efficient to quickly exhaust the air that has risen in temperature due to heat radiation and take in new, cooler air from the outside. In this embodiment, a radiator core structure can be adopted as the structure of the medium to take advantage of such similarities, because this is different from the situation in which conventional technologies such as an absorption tower suited to the purpose of removing carbon dioxide from the above-mentioned exhaust gas are used.

[0037] As with the case of supplying an alkaline aqueous solution to a curtain / ribbon structure, the alkaline aqueous solution can be supplied from the upper end of the radiator core structure, allowed to flow downward through the medium by gravity, and then removed by dripping from the lower end of the radiator core structure into a reservoir 20 (see FIG. 2) provided below. Alternatively, a reservoir 20 (see FIG. 3) for the alkaline aqueous solution can be provided below, and the lower end of the radiator core structure can be brought into contact with the alkaline aqueous solution in the reservoir, causing the alkaline aqueous solution to permeate the medium by surface tension, and carbonates formed by absorbing carbon dioxide can also be diffused through the medium and discharged into the reservoir.

[0038] FIG. 8 also shows a carbon dioxide capture system with another example of a medium. As a form in which the medium comes into contact with the alkaline aqueous solution in the storage tank 20, the medium may be formed as a protrusion whose lower portion is fixed to the bottom of the storage tank 20 and whose upper portion above the liquid level of the alkaline aqueous solution in the storage tank 20 comes into contact with the air. For example, as shown in FIG. 8(A), a medium 10B may be formed into a cylindrical shape (cylinder, square tube, etc.) and its lower portion fixed 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 alkaline aqueous solution below the liquid level and comes into contact with the air above the liquid level. In the illustrated example, multiple such media 10B are provided, but a single medium may also be provided, and their size is not limited as long as they can be installed in the storage tank. Incidentally, providing multiple media allows for more efficient carbon dioxide capture. The media may be fixed to the bottom of the storage tank 20 using a fastener 40A such as a band, metal fittings, or tape, or by adhesive. Furthermore, the connection between the fixing device 40A and the medium 10B can be threaded, and the height (vertical position) of the medium 10B from the bottom can be changed by adjusting the degree of threading (the amount of threading). As shown in FIG. 8B, the alkaline aqueous solution can be supplied not only from the bottom of the storage tank 20 but also from the top of the medium 10B. For example, an alkaline aqueous solution supply unit consisting of an alkaline aqueous solution supply line 30, a supply port 32, a supply pipe 34, a nozzle 36, etc. can be provided at the top of the medium 10B, and the alkaline aqueous solution can be sprayed from the nozzle 36 into the cylindrical interior of the medium 10B. FIG. 9 also shows a carbon dioxide capture system with another example of a medium. In this example, a structure of the medium 10C floats on the liquid surface of the storage tank 20, with its upper surface in contact with the air and its lower surface in contact with the alkaline aqueous solution. A plurality of media 10C are stored in a mesh bag 40B, and the bag 40B is then fitted into a float (an example of a flotation device) 40C to form a float structure. For example, a hollow structure filled with air or a material that floats on water, such as polystyrene foam, may be used, and various shapes are possible, not limited to a ring shape like a float. In the illustrated example, a plurality of such media 10C are provided, but a single medium may also be used. Incidentally, providing a plurality of media 10C allows for efficient capture of carbon dioxide.

[0039] Furthermore, the medium is not limited to being in contact with the alkaline aqueous solution; the medium 10 may have an inclined surface along which the supplied alkaline aqueous solution flows. Figure 10 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 a platform 50 shaped like a hillside, and the alkaline aqueous solution is supplied from a nozzle 36 to the top of the medium 10 and flows downward through the inclined medium. Alternatively, the medium itself may have a three-dimensional structure with an inclined surface, without the platform 50. As the alkaline aqueous solution flows downward through the medium, it absorbs carbon dioxide from the air within the medium through air permeation 18. The carbonate-containing aqueous solution flowing down from the medium 10 is extracted from a storage tank 20 below the medium and sequentially transferred to a carbonate treatment process. The air around the medium 10 is replaced by an air flow 19.

[0040] In this way, the alkaline aqueous solution supplied to the medium 10 absorbs carbon dioxide from the air it comes into contact with as it moves, producing carbonate. If we consider the case where the alkaline aqueous solution moves through the medium at a constant speed, the amount of carbon dioxide absorbed and the amount of carbonate produced will be a function of the distance traveled. However, because the aqueous solution moves through the medium while coming into contact with air over a large area, a decrease in moisture content due to evaporation into the air occurs as the solution moves.

[0041] The alkaline aqueous solution may be supplied to the medium 10 steadily or intermittently. When the alkaline aqueous solution is supplied intermittently, the water in the alkaline aqueous solution may evaporate partially or entirely from the medium 10 into which the alkaline aqueous solution has permeated during the period when the supply is interrupted. Even in this case, a carbonate can be produced by reaction between the alkali inside the medium and carbon dioxide in contact with the alkali, and carbon dioxide in the air can be recovered.

[0042] FIG. 11 shows a schematic diagram of the carbon dioxide capture system shown in FIG. 7 , in which an alkaline aqueous solution or water (moisture) is additionally supplied. By supplying additional moisture or alkaline aqueous solution at an appropriate position on the medium 10, the concentration of the alkaline aqueous solution and the concentrations of carbon dioxide and carbonate contained therein can be controlled to maximize the carbon dioxide capture rate, and this can be optimized depending on the material, shape, temperature, etc. of the medium. Moisture reduction can also be controlled to some extent by controlling the ambient humidity, for example, by spraying a small amount of moisture around the medium. For example, as shown in FIG. 7 , multiple alkaline supply units consisting of a supply pipe 34, a branch pipe 37, a nozzle 36, etc. can be provided above and below the medium 10. As an example, FIG. 11 shows an example in which an additional alkaline supply unit is provided near the vertical center of the medium 10. Furthermore, the vertical positions of the additional nozzles 36 may be different for each nozzle by providing additional branch pipes from the branch pipe 37. The stored liquid 22 in the storage tank 20, sprayed from the nozzle 36 and flowing down from the medium 10A, is transferred to the carbonate treatment process and treated.

[0043] The chemical reaction in which an aqueous solution of alkali absorbs carbon dioxide and produces carbonate occurs sequentially as follows in the case of an aqueous solution of sodium hydroxide, for example:

[0044] 2NaOH + CO ２ → Na ２ CO ３ + H ２ O (1) Na ２ CO ３ + CO ２ + H ２ O → 2NaHCO ３ (2)

[0045] The initial reaction represented by formula (1) releases water, which tends to accelerate in environments with a high sodium hydroxide concentration and low water content. However, the subsequent reaction represented by formula (2) consumes water, which tends to accelerate in environments with high water content. Therefore, additional water supply is desirable when the reaction represented by formula (1) has progressed to a certain extent. It is preferable to supply additional water at a position where the alkaline aqueous solution has already moved through the medium and the reaction represented by formula (1) has already progressed. For example, when the alkaline aqueous solution is supplied from above the medium, the reaction represented by formula (1) progresses at the upper side near the supply section, and as the alkaline aqueous solution moves downward, a water shortage occurs. Therefore, it is preferable to supply additional water to the lower side of the medium where water is insufficient. For example, as shown in FIG. 11, additional water may be supplied approximately halfway or 1 / 3-2 / 3 of the way through the medium. In other words, in this embodiment, the position for supplying additional water can be determined by converting the temporal change due to the chemical reaction into a spatial change (change due to the distance traveled) due to the steady movement of the alkaline aqueous solution through the medium. The supply of additional water or an aqueous alkaline solution can be controlled not only in terms of time but also in accordance with the spatial progress of the reaction.

[0046] Furthermore, sensors can be attached along the movement of the alkaline aqueous solution in the medium 10 to monitor the amount of carbonate produced, and the supply of additional water or alkaline aqueous solution can be controlled in response to the situation. Specifically, since the pH decreases as carbonate is produced, the progress of the reaction at that position can be monitored using a pH sensor attached to the medium 10. Furthermore, the progress of the reaction can be monitored by sampling the alkaline aqueous solution stored in the storage tank 20 or the like and quantifying the carbon dioxide, carbonate, and bicarbonate contained therein. It is desirable to maximize the carbon dioxide capture rate by using such control in response to fluctuations in conditions such as wind speed and temperature. The additional alkaline supply unit can also be applied to the carbon dioxide capture systems shown in other figures.

[0047] Furthermore, if a movable mechanism is installed on these curtain-shaped, ribbon-shaped, or radiator core structure media so that the hanging parts can easily rotate horizontally, so that the structures themselves act like vertical tails, the wide surface of the media will be oriented parallel to the wind direction due to directional stability (weather vane stability), and the wind pressure can be deflected, allowing the air around the media to be replaced.

[0048] For example, Figures 12-14 show schematic diagrams of carbon dioxide capture systems equipped with such a rotatable mechanism 33 in the holding section for suspending the media and the supply section for the alkaline aqueous solution. Figure 12 shows an example in which multiple ribbon-shaped media 10D are arranged in series, Figure 13 shows an example of a curtain-shaped media 10A, and Figure 14 shows an example of a media with a radiator core structure. In these examples, the alkaline aqueous solution 12 supplied from the alkaline aqueous solution supply line 30 flows from the supply port 32 through the supply pipe 34 and is sprayed onto the top of the media 10 from multiple nozzles 36 (some not shown) provided on the supply pipe 34. Each media 10 is attached to the supply pipe 34 by a fixture 41 and held in a suspended state. The supply pipe 34 is rotatably connected to the cylindrical supply port 32 and can move (rotate) horizontally around the supply port 32 as a central axis. In the case of the radiator core structure (FIG. 14), the center of a flat supply tank 35 is connected to the supply port 32, and the alkaline aqueous solution in the supply tank 35 is sprayed from a plurality of nozzles (not shown) provided at the bottom.

[0049] The natural wind force stabilizes the orientation of the medium 10 structure, aligning it with the wind direction by moving the supply pipe 34 and supply tank 35 using the aircraft's directional stabilization (weather vane stabilization) mechanism. For example, the structure is always positioned appropriately relative to the wind direction, such that the wide surface of the medium 10 is parallel to the wind direction. Furthermore, the connections between the supply port 32 and the supply pipe 34 or supply tank 35 can be threaded to adjust the degree of threading or looseness, or fixed in position using a fastener (not shown). This carbon dioxide capture system can also be configured to be movable (by natural wind force or manually) or immovable, as shown in Figure 12. An additional nozzle 36 or the like may be provided to configure an additional alkali supply unit. A storage tank 20 may be installed below the medium, and the stored liquid 22 in the storage tank 20 may be continuously removed from the drain pipe 24.

[0050] As the alkali, sodium hydroxide and potassium hydroxide can be preferably selected. In the case of a sodium (potassium) hydroxide aqueous solution, carbon dioxide that comes into contact with the solution reacts to form sodium (potassium) carbonate or sodium (potassium) bicarbonate, which is dissolved in the aqueous alkali solution and absorbed. Sodium hydroxide, in particular, can be produced by electrolysis or electrodialysis of sodium chloride or sodium sulfate obtained from seawater or lake water, and is preferably used.

[0051] Furthermore, when the medium is exposed to sunlight, its absorption increases its temperature, promoting the evaporation of water and affecting the solubility of carbon dioxide. Rainfall also affects the concentration of alkaline solutions during rainy weather. Therefore, providing a movable shielding structure (e.g., roof or cover) above and / or around the medium can control the absorption of sunlight and the intrusion of rainwater. Furthermore, in cold weather, the medium can be heated to an appropriate temperature by absorbing sunlight. These structures can be manually opened and closed, or automatically opened and closed using sensors that measure the surrounding environment, such as temperature and illuminance. While sunlight absorption can be promoted by partially or entirely using materials that absorb visible or infrared sunlight, combining them with a movable (either manual or automatic) solar shielding structure enables temperature control through sunlight absorption. Solar panels can be combined with the solar shielding structure to provide the power consumed by the system.

[0052] In this embodiment, the aqueous alkali solution and carbonate that have absorbed carbon dioxide are transferred via the storage tank 20 or directly to a carbon dioxide separation tank without using the storage tank 20, and acid is added to make them acidic, thereby releasing carbon dioxide and recovering the carbon dioxide as a gas. Furthermore, the salt newly generated by adding acid to the aqueous alkali solution and carbonate that have absorbed carbon dioxide can be transferred to an electrolytic cell or electrodialysis cell and regenerated into the alkali and acid by electrolysis or electrodialysis. The alkali and acid can be recycled and reused: the alkali for absorbing carbon dioxide, and the acid for recovering carbon dioxide from the aqueous alkali solution that has absorbed carbon dioxide. It is desirable to operate the electrolysis or electrodialysis using renewable energy such as wind power or solar power. It goes without saying that the above-described embodiments may be combined as appropriate.

[0053] (Method for Recovering Carbon Dioxide) One embodiment of the method for recovering carbon dioxide includes the steps of: penetrating and diffusing an aqueous alkali solution into a medium; and exposing the medium to a natural wind-driven airflow, recovering carbon dioxide in the air as carbonate produced by a reaction between the carbon dioxide and the alkali within the medium. The medium is made of a fibrous or porous material that allows air to pass through. The medium is preferably made of a hydrophilic material. At least one material selected from the group consisting of filter paper, nonwoven fabric, filter, sponge, and fabric can be used as the medium. The medium can be one selected from the group consisting of a curtain, ribbon, and flat plate, which can be suspended and exposed to the airflow while the aqueous alkali solution is supplied. The medium may also be made of a flexible material that can be deformed by natural wind. The aqueous alkali solution is preferably a sodium hydroxide solution or a potassium hydroxide solution. The aqueous alkali solution may be constantly supplied to the medium, and a solution containing carbonate produced by the reaction with the alkali within the medium may be constantly extracted from the medium. The alkaline aqueous solution may be supplied to an upper portion of the medium, and the aqueous solution containing the carbonate that flows down from the medium may be extracted and recovered as the carbonate. The alkaline aqueous solution may be stored, and the lower portion of the medium may be brought into contact with the alkaline aqueous solution, thereby utilizing surface tension or capillary action to supply the alkaline aqueous solution to the medium. The carbon dioxide recovery method of this embodiment may further include supplying an additional alkaline aqueous solution and / or water to the medium.

[0054] Specific examples of the carbon dioxide capture method of the present embodiment include, for example, specific examples in which the carbon dioxide capture systems described with reference to Figures 1 to 14 are used in the carbon dioxide capture system of the present embodiment. However, the carbon dioxide capture method of the present embodiment is not limited to the above specific examples.

[0055] 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.

[0056] 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.

[0057] (Preparation of Aqueous Sodium Hydroxide Solution) The aqueous sodium hydroxide solution used in the examples was prepared directly or by diluting 1 M aqueous sodium hydroxide solution (for volumetric analysis) or 8 M aqueous sodium hydroxide solution manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0058] [Example 1] The bottom surface is 260 cm ２ A nonwoven fabric (manufactured by Monotaro, 60% rayon, 40% polyester) serving as an example of a medium was placed in a polystyrene resin container measuring 20 cm x 13 cm and 7.5 cm in height. 10 mL of 1 M aqueous sodium hydroxide solution was sprayed onto the nonwoven fabric using a pipette to penetrate the nonwoven fabric, and the nonwoven fabric was then exposed to air for 1 hour, resulting in Example 1. In this Example 1, the nonwoven fabric impregnated with the aqueous sodium hydroxide solution was brought into contact with the air in the container on one side (the upper side), and carbon dioxide was captured via the medium impregnated with the aqueous alkaline solution. After 1 hour of exposure to air, 1.5 g of water lost by evaporation was added to replenish the nonwoven fabric, and the nonwoven fabric was removed from the container. 90 mL of water (ion-exchanged water) was added to extract the aqueous sodium hydroxide solution, and the pH was measured (Horiba, Ltd. pH meter, F-72). The pH was 12.743. The pH measurement method and conditions were the same for the subsequent examples and comparative examples unless otherwise noted. In the following examples and comparative examples, the same reagents and methods as those in Example 1 were used.

[0059] [Example 2] The same nonwoven fabric as in Example 1 was suspended by clipping its top to a rod placed horizontally above the same container. 10 mL of 1 M aqueous sodium hydroxide solution was sprayed and impregnated over the entire nonwoven fabric using a pipette, and then exposed to air for 1 hour to prepare Example 2. In Example 2, both sides of the nonwoven fabric impregnated with the aqueous sodium hydroxide solution were in contact with the ambient air, and an aqueous alkaline solution was supplied to the suspended medium and impregnated to capture carbon dioxide. After 1 hour of exposure to air, 1.5 g of water lost due to evaporation was added to replenish the water. Then, 90 mL of water was added as in Example 1 to extract the aqueous sodium hydroxide solution, and the pH was measured, resulting in a pH of 12.543. In the following examples and comparative examples, the suspension method and the spraying of the aqueous alkaline solution when the medium was suspended were performed using the same methods.

[0060] [Example 3] 10 mL of a 1 M aqueous sodium hydroxide solution was placed in the same container as in Example 1, and the same nonwoven fabric as in Example 1 was hung so that its lower part was brought into contact with the aqueous sodium hydroxide solution in the container, allowing it to penetrate by wicking up due to surface tension (capillary action), and then exposed to air for 1 hour to produce Example 3. In Example 3, the suspended medium was in contact with an aqueous alkaline solution in a reservoir, and carbon dioxide was captured by penetrating the medium due to surface tension. After 1 hour of exposure to air, 2.0 g of water lost due to evaporation was added to replenish the nonwoven fabric, and 90 mL of water was added as in Example 1 to extract the aqueous sodium hydroxide solution. The pH was measured and found to be 12.693.

[0061] Comparative Example 1: Comparative Example 1 was prepared by placing 10 mL of a 1 M aqueous sodium hydroxide solution in the same container as in Example 1, without using a nonwoven fabric or exposing the solution to air. This Comparative Example 1 was prepared using an aqueous sodium hydroxide solution before carbon dioxide absorption, and the pH of the aqueous sodium hydroxide solution in the container was simply measured. 90 mL of water was added immediately without exposing the solution to air, and the pH was measured, revealing a value of 12.902.

[0062] Comparative Example 2: 10 mL of a 1 M aqueous sodium hydroxide solution was placed in the same container as in Example 1, and the same nonwoven fabric as in Example 1 was placed thereon in the same manner, without exposure to air. Comparative Example 2 shows the aqueous sodium hydroxide solution that had permeated the nonwoven fabric of the medium before carbon dioxide absorption. The nonwoven fabric was immediately removed without exposure to air, and 90 mL of water was added to extract the aqueous sodium hydroxide solution. The pH was measured and found to be 12.899.

[0063] [Comparative Example 3] 10 mL of a 1 M aqueous solution of sodium hydroxide was placed in the same container as in Example 1 and exposed to air for 1 hour without using a nonwoven fabric to prepare Comparative Example 3. In Comparative Example 3, the sodium hydroxide solution was placed on the bottom of the container (260 cm) without using a medium. ２ ) of the aqueous sodium hydroxide solution comes into contact with the air in the container, i.e., no medium is used. In this case, the aqueous sodium hydroxide solution does not spread completely over the entire bottom surface due to surface tension, so the solution is concentrated at the bottom of the container (260 cm ２ After one hour of exposure to air, 0.5 g of water was added to replenish the water lost by evaporation, and then 90 mL of water was added. The pH of the aqueous sodium hydroxide solution in the container was measured and found to be 12.853.

[0064] The pH values ​​in Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1.

[0065] Comparative Example 1 and Comparative Example 2 showed almost the same pH, indicating that without exposure to air, the pH would not decrease simply because the sodium hydroxide aqueous solution had penetrated the medium. On the other hand, in Example 1-3, the pH was clearly lower than in Comparative Example 1-2, indicating that carbon dioxide was absorbed from the exposed air and carbonate was produced. Comparative Example 3 also showed a lower pH than Comparative Examples 1 and 2, indicating that carbon dioxide absorption occurred after 1 hour of exposure to air. However, the pH decrease in Example 1-3 was greater than in Comparative Example 3, indicating that carbon dioxide absorption was greatly promoted by this example.

[0066] The difference between Example 1 and Comparative Example 3, which were exposed to air for one hour, is simply the presence or absence of the nonwoven fabric medium. Example 1 showed a greater decrease in pH than Comparative Example 3, which further promoted carbon dioxide capture, demonstrating the effectiveness of the medium of this example; this difference is the effect of the medium. Furthermore, Examples 2 and 3 showed a greater decrease in pH than Example 1. Examples 2 and 3 used suspended media, which, when suspended, were exposed to air on both sides and facilitated the replacement of surrounding air, presumably further promoting carbon dioxide capture. This indicates that a structure that facilitates the replacement of surrounding air, such as the suspended structure of this example, is desirable for capturing carbon dioxide from the air. On the other hand, in Example 1, one side of the media was in contact with the air in the container at the bottom of the container, making it difficult for the air in the container to be replaced, which is presumably why the decrease in pH was smaller than when suspended.

[0067] [Example 4] Area 260 cm ２ An example of a medium, hard filter paper (manufactured by Advantec Toyo Co., Ltd., No. 4A), was sprayed with 10 mL of 1 M aqueous sodium hydroxide solution by pipette injection over the entire surface, and then hung and exposed to air for 1 hour, as in Example 2, to form Example 4. In this Example 4, the hard filter paper soaked in the aqueous sodium hydroxide solution was also in contact with the ambient air on both sides, and an aqueous alkaline solution was supplied to the suspended medium and soaked in it to capture carbon dioxide. After 1 hour of exposure to air, the moisture lost by evaporation was replenished, and 90 mL of water was added as in Example 1 to extract the aqueous sodium hydroxide solution, and the pH was measured, which was 12.7.

[0068] [Example 5] Area: 400 cm ２ The pH was measured in the same manner as in Example 4 under the same conditions and by the same method as in Example 4, except that hard filter paper of Example 4 was used, and the pH was found to be 12.6.

[0069] [Example 6] Area: 500 cm ２ The pH was measured in the same manner as in Example 4 under the same conditions and by the same method as in Example 4, except that hard filter paper of Example 4 was used, and the pH was found to be 12.5.

[0070] [Example 7] Area: 940 cm ２ The pH was measured in the same manner as in Example 4 under the same conditions and by the same method as in Example 4, except that hard filter paper of Example 4 was used, and the pH was found to be 11.8.

[0071] The pH values ​​of Examples 4 to 7 are shown in Table 2. The pH decreased as the area of ​​the hard filter paper used as the medium increased. This means that the larger the area of ​​the medium facing the air, the more efficiently it captures carbon dioxide in the air, and it is desirable to configure the medium so that the area facing the air is as large as possible.

[0072]

[0073] [Example 8] The hard filter paper used in Example 4 was 275 cm ２ The filter paper was cut into pieces of 100 mm in size, and 7 mL of 1 M sodium hydroxide solution was pipetted over the entire surface of the filter paper to allow it to soak in. The filter paper was then placed on the bottom of the same container as in Example 1 and exposed to air. To compensate for water loss due to natural drying, water was pipetted over the entire filter paper while monitoring the weight of the container containing the medium and sodium hydroxide solution, preventing weight loss due to water evaporation. Water was added to constantly maintain the initial moisture content, resulting in Example 8. This Example 8 promotes carbon dioxide capture by supplying additional alkaline aqueous solution or water to the alkaline aqueous solution permeating the medium. The change in pH over time was measured: the initial value was 13.46, the value after 3 hours was 11.81, and the value after 6 hours was 10.51. A decrease in pH due to exposure to air was observed. Note that the initial value refers to the pH immediately after the filter paper was soaked in the solution. The 3-hour value refers to the pH measured after 3 hours, when the sodium hydroxide aqueous solution was squeezed out of the filter paper. The "after 6 hours" refers to the value obtained by squeezing the aqueous sodium hydroxide solution from the filter paper after 6 hours and measuring the pH. The same applies to the following examples.

[0074] Example 9 was prepared under the same conditions as Example 8, except that instead of constantly maintaining the moisture content at the initial value by adding water, water was added every hour of natural drying to restore the moisture content to the initial value. When the pH of Example 9 was measured over time, the initial value was 13.46, the value after 3 hours (three water additions) was 11.42, and the value after 6 hours (six water additions) was 10.40. A decrease in pH due to exposure to air was observed.

[0075] Example 10 was prepared under the same conditions as Example 8, except that instead of constantly maintaining the moisture content at the initial value by adding water, the sample was allowed to air dry for three hours and then water was added to restore the moisture content to the initial value. The pH of Example 10 was measured over time, with the initial value being 13.28, the value after three hours (one water addition) being 10.89, and the value after six hours (two water additions) being 10.40. A decrease in pH due to exposure to air was observed.

[0076] The changes in pH over time for Examples 8-10 are shown in Table 3 below. Compared to Example 8, which maintained a constant moisture content, Example 9, which involved repeated 1-hour drying and water additions, and Example 10, which underwent a 3-hour drying process and no water additions between pH measurements, were exposed to air in a lower-moisture environment. The pH decreased more rapidly when exposed to air in a lower-moisture environment, demonstrating a clear difference in pH after 3 hours. However, after 6 hours, the difference in pH between the two samples narrowed. As mentioned above, when carbon dioxide reacts with an aqueous sodium hydroxide solution to produce carbonate, the preceding reaction (1) releases moisture, so a low-moisture environment is preferred. Furthermore, the subsequent reaction (2) absorbs moisture, so a high-moisture environment is preferred. This suggests that low moisture is preferred in the first half of the reaction, and therefore the pH decreased with exposure to air in a low-moisture environment after 3 hours. Conversely, high moisture is preferred in the second half of the reaction, resulting in a smaller pH difference after 6 hours.

[0077] As is clear from Examples 8-10, the carbon dioxide absorption rate can be increased by reducing the amount of additional water supplied during the stage where the reaction of formula (1) primarily proceeds, thereby creating a low-moisture environment, and by additionally supplying more water during the stage where the reaction of formula (2) continues to occur, thereby creating a high-moisture environment. In the present invention, carbon dioxide is absorbed as the aqueous alkaline solution moves through the medium. As described above, the reaction proceeds in accordance with the movement of the aqueous alkaline solution. Therefore, in the early stage, where the reaction of formula (1) primarily proceeds, additional water supply is limited, and in the later stage, where the reaction of formula (2) continues to occur, additional water supply is primarily carried out, thereby increasing the carbon dioxide capture rate.

[0078] [Comparative Example 4] In order to compare the capture of carbon dioxide by bubbling in an alkaline aqueous solution, in Comparative Example 4, 7 mL of the same 1 M sodium hydroxide aqueous solution as in Example 8 was placed in a polypropylene container with a diameter of 2.6 cm and air was bubbled into the sodium hydroxide aqueous solution at a flow rate of 200 mL / min. The initial pH value was 13.42, the value after 3 hours was 13.32, and the value after 6 hours was 13.27. Note that the initial value when no medium (filter paper) is used is the pH before the start of exposure to air (bubbling). "3 hours" refers to the value measured after 3 hours of the sodium hydroxide aqueous solution as it was in the container, and "6 hours" refers to the value measured after 6 hours of the sodium hydroxide aqueous solution as it was in the container as it was. The decrease was extremely slow compared to Examples 8-10. This result shows that when capturing low concentrations of carbon dioxide in the air in an alkaline aqueous solution, this example is preferable to the method of exposing the aqueous solution to air by absorbing and penetrating the aqueous solution into a medium such as filter paper and then exposing it to air, rather than bubbling air in the aqueous solution.

[0079] [Reference Example 1] On the other hand, carbon dioxide with a much higher concentration than that in the atmosphere, such as exhaust gas from a thermal power plant or factory, can also be easily captured by bubbling in an alkaline aqueous solution. In Reference Example 1, the change in pH over time of a sodium hydroxide aqueous solution was examined under the same conditions as in Comparative Example 4, except that 1% carbon dioxide, a higher concentration than in Comparative Example 4, was bubbled at a flow rate of 40 mL / min. The initial value was 13.30, and the value after 3 hours was 9.31. Even with a flow rate of 1 / 5 (40 / 200), the rate of pH decrease was rapid. Thus, the capture of low-concentration carbon dioxide in the atmosphere, which is the subject of this example, is in a significantly different situation from the capture of high-concentration carbon dioxide from exhaust gas.

[0080]

[0081] [Example 11] A cellulose-polyester blend wipe (Texwip, TX612), which is an example of a medium, was used in the same manner as in Example 1, with a length of 260 cm ２ The wipe was cut to a size of (20 cm x 13 cm) and placed on the bottom of the same container as in Example 1, and 10 mL of 1 M aqueous sodium hydroxide solution was poured into it to allow it to penetrate, and then exposed to air for 1 hour to produce Example 11. In Example 11, the wipe soaked in the aqueous sodium hydroxide solution was exposed to the air in the container on one side, similar to Example 1. After 1 hour of exposure to air, the wipe was removed and the pH was measured in the same manner as in Example 1, and was found to be 12.72.

[0082] Example 12: The same wipes as in Example 11 were hung over the same container, and 10 mL of 1 M aqueous sodium hydroxide solution was sprayed and soaked over the entire surface using a pipette. The wipes were then exposed to air for one hour to prepare Example 12. In Example 12, the wipes soaked in the aqueous sodium hydroxide solution were exposed to ambient air on both sides. After one hour of exposure to air, the pH was measured in the same manner as in Example 2, and found to be 12.46.

[0083] [Example 13] 10 mL of 1 M sodium hydroxide solution was placed in the same container as in Example 1, and the same wipe as in Example 11 was hung and its lower part was brought into contact with the sodium hydroxide solution in the container, allowing it to penetrate by wicking up due to surface tension, and exposed to air for 1 hour to produce Example 13. In Example 13, the suspended medium is in contact with an alkaline aqueous solution in a reservoir, and carbon dioxide penetrates the medium due to surface tension, capturing carbon dioxide. After 1 hour of exposure to air, the wipe was removed, and the pH was measured in the same manner as in Example 3, resulting in a pH of 12.61.

[0084] [Example 14] A polyester cloth (Tetoron), which is an example of a medium, was used in the same manner as in Example 1, with a length of 260 cm. ２ The polyester fabric was cut to a size of 20 cm x 13 cm, steamed to absorb water vapor, and then placed on the bottom of the same container as in Example 1. 10 mL of 1 M aqueous sodium hydroxide solution was poured into the cloth to allow it to permeate the fabric, and the cloth was exposed to air for 1 hour to produce Example 14. In Example 14, the polyester fabric permeated with the aqueous sodium hydroxide solution was exposed to the air in the container on one side, similar to Example 1. After 1 hour of exposure to air, the polyester fabric was removed, and 90 mL of water was added to extract the aqueous sodium hydroxide solution, similar to Example 1, and the pH was measured, which was 12.74.

[0085] [Example 15] The same polyester fabric as in Example 14 was steamed in the same manner to absorb water vapor, then hung over the same container. 10 mL of 1 M aqueous sodium hydroxide solution was sprayed and permeated over the entire surface using a pipette, and the fabric was then exposed to air for 1 hour to produce Example 15. In Example 15, the polyester fabric permeated with the aqueous sodium hydroxide solution was exposed to ambient air on both sides. After 1 hour of exposure to air, the pH was measured in the same manner as in Example 2, and found to be 12.69.

[0086] [Example 16] 10 mL of a 1 M aqueous sodium hydroxide solution was placed in the same container as in Example 1, and the same polyester cloth as in Example 14 was steamed to absorb water vapor. The cloth was then hung and its lower part was brought into contact with the aqueous sodium hydroxide solution in the container, allowing it to permeate by wicking up due to surface tension, and exposed to air for one hour to produce Example 16. In Example 16, the suspended medium was in contact with an aqueous alkaline solution in a reservoir, allowing carbon dioxide to permeate the medium due to surface tension and capture carbon dioxide. After one hour of exposure to air, the polyester cloth was removed, and the pH was measured in the same manner as in Example 3, resulting in a pH of 12.81.

[0087] The pH values ​​for Examples 11-16 are shown in Table 4. In addition to nonwoven fabrics and filter paper, cellulose-polyester blend wipes and polyester cloth that had been steamed to absorb water vapor were also selected as media. These wipes were placed on the bottom of a container, hung (permeation by spraying), and hung (wicking by surface tension) and exposed to air for one hour. The pH after one hour was lower due to the effect of the media than in Comparative Example 3, in which only aqueous sodium hydroxide solution was exposed to air in a container without a media. The hanging configuration, in which both sides were exposed to air, tended to result in a greater decrease in pH than the configuration in which the media was placed on the bottom of a container and exposed to air on one side. On the other hand, in the case of polyester cloth that had absorbed steam, wicking by surface tension was difficult due to the already contained moisture, and it is believed that Example 14, in which the media was placed on the bottom of a container and absorbed aqueous sodium hydroxide, had a lower pH than Example 16, which utilized wicking by surface tension. Thus, preferred conditions, such as the media and installation configuration, vary depending on the environment, such as humidity.

[0088]

[0089] [Example 17] A cylindrical wide-mouth bottle with a capacity of 500 mL (bottom 45 cm ２ , height 16cm, top opening 14cm ２50 mL of the 0.2 M sodium hydroxide aqueous solution obtained in the Preparation Example was placed in a wide-mouth bottle, and a 20 cm x 13 cm nonwoven fabric identical to that in Example 1, an example of a medium, was placed along the inside surface of the bottle to form a cylindrical shape. The bottom of the nonwoven fabric was contacted with the sodium hydroxide aqueous solution, which penetrated the medium by wicking due to surface tension, and exposed to air for 40 hours to produce Example 17. In Example 17, the cylindrical medium was in contact with the alkaline aqueous solution in the reservoir, which penetrated the medium by surface tension, and one side of the inside was in contact with the air in the container, capturing carbon dioxide. After 40 hours of exposure to air, the nonwoven fabric was removed from the container, weighed, and water was added to make up for the loss due to evaporation. The pH was measured, and the pH was found to be 10.63.

[0090] Example 18 was prepared under the same conditions as Example 17, except that the cellulose-polyester blend wipe (20 cm x 13 cm) was used instead of the nonwoven fabric as the medium. After 40 hours of exposure to air, the wipe was removed from the container, weighed, and the pH was measured by adding water to make up for the loss due to evaporation. The pH was found to be 10.73.

[0091] Comparative Example 5 was prepared by simply adding 50 mL of 0.2 M aqueous sodium hydroxide solution to the same container as in Example 17. After 40 hours of exposure to air, the weight was measured, and water was added to compensate for the loss due to evaporation, resulting in a pH measurement of 11.73.

[0092] The pH values ​​for Examples 17-18 and Comparative Example 5 are shown in Table 5. In Examples 17 and 18, the presence of a medium on the inner surface of the container reduced the pH by 1 or more after 40 hours compared to Comparative Example 5, where no medium was present. This result indicates that even when a medium is placed inside a cylindrical container (inner surface), where air exchange is thought to be slower than on the outer surface, the effect of the medium in capturing carbon dioxide is significant over time. Furthermore, because the pH reduction was greater in Example 17 (nonwoven fabric) than in Example 18 (wipe), a highly hydrophilic material is preferred for the medium.

[0093]

[0094] Example 19 To investigate the effect of the timing of supplying additional water to the medium, the same nonwoven fabric as in Example 1 was hung over the same container, and 10 mL of a 1 M aqueous solution of sodium hydroxide was sprayed and soaked over the entire surface using a pipette, followed immediately by an additional 10 mL of water being sprayed and soaked, to prepare Example 19. After soaking in the aqueous solution of sodium hydroxide, the fabric was exposed to air for 3 hours, and then an additional 90 mL of water was added to replace the water lost due to evaporation, and the aqueous solution of sodium hydroxide was extracted. The pH was measured and found to be 12.27.

[0095] Example 20 was prepared in the same manner as Example 19, except that 10 mL of water was additionally sprayed and infiltrated 1 hour after the aqueous sodium hydroxide solution was sprayed and infiltrated. After the aqueous sodium hydroxide solution was infiltrated and exposed to air for 3 hours, an additional 90 mL of water was added to compensate for the water loss due to evaporation, and the aqueous sodium hydroxide solution was extracted and the pH was measured, which was 12.08.

[0096] Example 21 was prepared in the same manner as Example 19, except that 1.5 hours after the aqueous sodium hydroxide solution was sprayed and infiltrated, an additional 10 mL of water was sprayed and infiltrated. After the aqueous sodium hydroxide solution was infiltrated, the mixture was exposed to air for 3 hours, and then 90 mL of water was added to compensate for the water loss due to evaporation, and the aqueous sodium hydroxide solution was extracted. The pH was measured and found to be 11.77.

[0097] Example 22 was prepared in the same manner as in Example 19, except that 10 mL of water was additionally sprayed and infiltrated 2 hours after the aqueous sodium hydroxide solution was sprayed and infiltrated. After the aqueous sodium hydroxide solution was infiltrated and exposed to air for 3 hours, an additional 90 mL of water was added to compensate for the water loss due to evaporation, and the aqueous sodium hydroxide solution was extracted and the pH was measured, which was 11.48.

[0098] The pH values ​​for Examples 19-22 are shown in Table 6. The longer the time between the infiltration of the sodium hydroxide aqueous solution and the supply of additional water, the lower the pH after 3 hours in the order of Example 19, Example 20, Example 21, and Example 22. Because the aqueous alkali solution in the medium loses water through evaporation, it is thought that additional water supply may be necessary to ensure fluidity. These results indicate that the carbon dioxide capture rate can be increased by limiting the supply of additional water when the reaction represented by formula (1) in the first stage is primarily proceeding, and then allowing a certain amount of time for additional water supply to occur when the reaction represented by formula (2) in the second stage is continuing.

[0099]

[0100] [Example 23] Bottom surface is 136.62 cm ２ A sponge (MonotaRO chamois sponge, polyvinyl alcohol material, rectangular parallelepiped shape 7.3 cm x 3.0 cm x 17.5 cm), an example of a porous medium, was placed in the center of a styrene resin container measuring 19.8 cm x 6.9 cm and 5.8 cm in height. The 7.3 cm x 3.0 cm surface was set as the bottom (top) and cut to a height of 11.5 cm. 400 mL of 0.2 M sodium hydroxide solution was poured into the container and absorbed by the medium via capillary action. This was then exposed to air for 1 hour, resulting in Example 23. This example uses a porous sponge material as the medium, and is an example of a pile structure in which the medium, as shown in FIG. 8 (A), protrudes into the air like a pile from the surface of the alkaline aqueous solution and comes into contact with the alkaline aqueous solution below the liquid surface. The sponge medium protrudes approximately 9.4 cm above the surface of the sodium hydroxide aqueous solution and comes into contact with the air. After one hour of exposure to air, the aqueous sodium hydroxide solution was recovered and the pH was measured to be 13.001.

[0101] Example 24 Example 24 was prepared in the same manner as Example 23, except that the sample was exposed to air for 3 hours. The aqueous sodium hydroxide solution was recovered and the pH was measured, which was 12.985.

[0102] Example 25 Example 24 was prepared in the same manner as Example 23, except that the sample was exposed to air for 6 hours. The aqueous sodium hydroxide solution was recovered and the pH was measured, which was 12.962.

[0103] Example 26 Example 25 was prepared in the same manner as in Example 23, except that the aqueous sodium hydroxide solution was exposed to air for 24 hours. The pH of the recovered aqueous sodium hydroxide solution was measured and found to be 12.608.

[0104] Example 27 Example 25 was prepared in the same manner as in Example 23, except that the aqueous sodium hydroxide solution was exposed to air for 48 hours. The pH of the recovered aqueous sodium hydroxide solution was measured and found to be 11.531.

[0105] Comparative Example 6: In Comparative Example 6, 400 mL of a 0.2 M aqueous sodium hydroxide solution was poured into the same container as in Example 23 without using a medium and exposed to air for 1 hour. The liquid level of the aqueous sodium hydroxide solution at the opening of the container (136.62 cm ２ After one hour of exposure to air, the sodium hydroxide solution was recovered and the pH was measured, which was 13.340.

[0106] Comparative Example 7 Comparative Example 7 was prepared in the same manner as Comparative Example 6, except that the sample was exposed to air for 3 hours. The aqueous sodium hydroxide solution was recovered and the pH was measured, which was 13.340.

[0107] Comparative Example 8 Comparative Example 8 was prepared in the same manner as Comparative Example 6, except that the sample was exposed to air for 6 hours. The aqueous sodium hydroxide solution was recovered and the pH was measured, which was 13.323.

[0108] Comparative Example 9 Comparative Example 9 was prepared in the same manner as Comparative Example 6, except that the sample was exposed to air for 24 hours. The aqueous sodium hydroxide solution was recovered and the pH was measured, which was 13.144.

[0109] Comparative Example 10 Comparative Example 10 was prepared in the same manner as Comparative Example 6, except that the sample was exposed to air for 248 hours. The aqueous sodium hydroxide solution was recovered and the pH was measured, which was 12.810.

[0110] The pH values ​​in Examples 23-27 and Comparative Examples 6-10 are shown in Table 7.

[0111]

[0112] For the same air exposure time, the pH was lower in all Examples than in Comparative Examples, clearly demonstrating that the presence of a sponge (porous medium) facilitates the absorption of carbon dioxide from the air. The present invention makes it possible to significantly accelerate the absorption of carbon dioxide from the air, even with a simple method of simply placing a medium in an alkaline aqueous solution in a protruding form, allowing it to absorb by capillary action, and then exposing it to air. Furthermore, even if the medium is porous and has a certain thickness, it will adequately promote carbon dioxide absorption as long as it is air-permeable. Among Comparative Examples 6 to 10, only Comparative Examples 9 and 10, which were exposed to air for 24 hours or more, showed almost no decrease in pH. This demonstrates that the present invention is an excellent means for rapidly and effectively recovering low concentrations (400 ppm) of carbon dioxide from the atmosphere by using a medium.

[0113] The present invention is a carbon dioxide capture system for combating climate change. It can be used indoors or outdoors to capture carbon dioxide from the atmosphere while reducing installation costs and energy consumption that would otherwise lead to the release of new carbon dioxide.

[0114] 10 Medium 12, 16 Alkaline aqueous solution 14 Alkaline aqueous solution flow 18 Air permeability 19 Air flow 20 Storage tank 22 Stored liquid 24 Drain pipe 30 Alkaline aqueous solution supply line 31 Alkaline aqueous solution storage pipe 32 Supply port 33 Rotating and movable mechanism 34 Supply pipe 35 Supply tank 36 Nozzle 37 Branch pipe 40 Holding part 41 Mounting fixture 42 Support 43 Wire 44 Connecting member 46 Pulley 50 Unit 60 Up and down movable mechanism

Claims

1. A system for recovering carbon dioxide, comprising: a medium penetrated by an aqueous solution of an alkali, wherein the medium is made of a fibrous or porous material permeable to air, the medium is arranged to be in contact with an air flow of natural wind, and carbon dioxide in the air is recovered as a carbonate generated by a reaction of the carbon dioxide with the alkali in the medium.

2. The carbon dioxide recovery system according to claim 1, wherein the medium is formed of a hydrophilic material.

3. The carbon dioxide recovery system according to claim 1, wherein the medium is at least one selected from the group consisting of filter paper, non-woven fabric, filter, sponge, and fabric.

4. The carbon dioxide recovery system according to any one of claims 1 to 3, further comprising a holding part for suspending and holding the medium, and the medium is one selected from the group consisting of a curtain shape, a ribbon shape, and a flat plate shape.

5. The carbon dioxide recovery system according to claim 4, wherein the holding part is provided with a movable mechanism capable of changing the vertical position and / or the horizontal position of the medium.

6. The carbon dioxide recovery system according to claim 4, wherein the holding part is provided with a mechanism capable of changing the medium between a deployed position and a storage position.

7. The carbon dioxide recovery system according to any one of claims 1 to 3, wherein the medium is formed of a flexible material deformable by natural wind.

8. The carbon dioxide recovery system according to any one of claims 1 to 3, wherein the media are arranged in parallel at intervals.

9. The carbon dioxide recovery system according to any one of claims 1 to 3, wherein the alkali is sodium hydroxide or potassium hydroxide.

10. Further comprising a liquid supply part and a take-out part, wherein the liquid supply part is configured to supply an aqueous solution of the alkali to the medium, and in the take-out part, a solution containing a carbonate generated by a reaction of the aqueous solution of the alkali inside the medium is taken out from the medium.

11. The carbon dioxide recovery system according to claim 10, wherein the liquid supply part is configured to supply the aqueous solution of the alkali to the upper part of the medium, and in the take-out part, the aqueous solution containing the carbonate flowing down from the medium is taken out below the medium.

12. The carbon dioxide recovery system according to claim 11, wherein the medium has an inclined surface through which the liquid supplied from the liquid supply unit flows.

13. The carbon dioxide recovery system according to claim 11, wherein the extraction unit is a storage tank provided below the medium and stores the aqueous solution containing the carbonate flowing down from the medium.

14. The liquid supply unit is a storage tank that stores the aqueous solution of the alkali. The lower part of the medium is arranged so as to be in contact with the aqueous solution of the alkali. The liquid supply unit uses the surface tension or capillary phenomenon between the medium and the aqueous solution of the alkali to supply the aqueous solution of the alkali to the medium. The carbon dioxide recovery system according to claim 10.

15. The carbon dioxide recovery system according to claim 14, wherein the medium is fixed to the bottom of the storage tank at the lower part and is formed on a protrusion erected so that the upper part above the liquid level of the aqueous solution of the alkali in the storage tank is in contact with air.

16. The carbon dioxide recovery system according to claim 14, further comprising a floating device for floating the medium in the aqueous solution of the alkali.

17. Further, an additional liquid supply unit for supplying an additional aqueous solution of the alkali and / or water to the medium is provided. The carbon dioxide recovery system according to any one of claims 1 to 3.

18. A method for recovering carbon dioxide, comprising a step of infiltrating and diffusing an aqueous solution of an alkali into the medium, and a step of bringing the medium into contact with an air flow of natural wind power and recovering carbon dioxide in the air as a carbonate generated by reaction with the aqueous solution of the alkali inside the medium. The medium is made of a fibrous or porous material through which air is permeable.

19. The method for recovering carbon dioxide according to claim 18, wherein the medium is made of a hydrophilic material.

20. The method for recovering carbon dioxide according to claim 18, wherein at least one selected from the group consisting of filter paper, non-woven fabric, filter, sponge, and fabric is used as the medium.

21. Using one selected from the group consisting of a curtain shape, a ribbon shape, and a flat plate shape as the medium, suspending and holding these, bringing them into contact with the air flow, and supplying an aqueous solution of an alkali. The method for recovering carbon dioxide according to any one of claims 18 to 20.

22. The method for recovering carbon dioxide according to any one of claims 18 to 20, wherein a flexible material deformable by natural wind power is used as the medium.

23. The method for recovering carbon dioxide according to any one of claims 18 to 20, wherein an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide is used as the aqueous solution of the alkali.

24. The method for recovering carbon dioxide according to any one of claims 18 to 20, wherein the aqueous solution of the alkali is constantly supplied to the medium, and a solution containing carbonate generated by the reaction with the aqueous solution of the alkali inside the medium is constantly taken out from the medium.

25. The method for recovering carbon dioxide according to any one of claims 18 to 20, wherein the aqueous solution of the alkali is supplied to the upper part of the medium, and the aqueous solution containing the carbonate flowing down from the medium is taken out and recovered as the carbonate.

26. The method for recovering carbon dioxide according to any one of claims 18 to 20, wherein the aqueous solution of the alkali is stored, the lower part of the medium is brought into contact with the aqueous solution of the alkali, and the supply of the aqueous solution of the alkali to the medium is performed by utilizing surface tension or capillary action.

27. The method for recovering carbon dioxide according to any one of claims 18 to 20, further comprising supplying an additional aqueous solution of the alkali and / or water to the medium.

Images