Method and device for recovering carbon dioxide

Abstract

Provided is a method for recovering carbon dioxide which includes: a step in which carbon dioxide is brought into contact with an adsorbent capable of adsorbing carbon dioxide to cause the adsorbent to adsorb the carbon dioxide; and a step in which the adsorbent is immersed in a liquid and the carbon dioxide is desorbed from the adsorbent and recovered as a gas phase. The adsorbent has an adsorption of the liquid at 25°C and at a saturated vapor pressure of the liquid of 0.5 mmol / g or larger.

Description

Method and apparatus for capturing carbon dioxide

[0001] The present disclosure relates to methods and apparatus for capturing carbon dioxide.

[0002] From the perspective of curbing global warming, carbon dioxide (CO ２ There is active research and development into technologies to capture CO2 and separate it from mixed gases. ２ Through carbon recycling technology, it can also be used as a raw material for synthetic fuels (e-fuels).

[0003] CO ２ As a technique for recovering CO, for example, as described in Non-Patent Document 1, an adsorbent such as zeolite is used to recover the adsorbed CO ２ A method of desorbing and recovering the compounds by heating and reducing pressure is attracting attention.

[0004] Tadanori Nouchi et al., "Research on a CO2 Separation and Capture System for Engines Using Zeolite," Transactions of the Society of Automotive Engineers of Japan, Vol. 53, No. 3, May 2022

[0005] In the technology disclosed in Non-Patent Document 1, CO ２ To desorb the carbon dioxide, a heat source for heating and expensive pump power for decompression are required, which can increase costs.

[0006] The present disclosure has been made in light of the above circumstances, and one of its objectives is to provide a new method and apparatus for recovering carbon dioxide that can be achieved at lower cost.

[0007] A first aspect of the present invention is a method for recovering carbon dioxide, comprising: an adsorption step of bringing carbon dioxide into contact with an adsorbent capable of adsorbing carbon dioxide, thereby causing the carbon dioxide to be adsorbed onto the adsorbent; and a recovery step of immersing the adsorbent in a liquid, and desorbing the carbon dioxide adsorbed by the adsorbent in the adsorption step, and recovering the carbon dioxide in the form of a gas phase, wherein the adsorbent has an adsorption capacity for the liquid of 0.5 mmol / g or more at 25°C and under the saturated vapor pressure of the liquid.

[0008] A second aspect of the present invention is the method according to the first aspect, further comprising the step of contacting a second gas containing nitrogen as a main component with the adsorbent after the recovering step.

[0009] A third aspect of the present invention is the method according to the first or second aspect, wherein the adsorbent has an adsorption amount of carbon dioxide of 0.5 mmol / g or more at 25° C. under a carbon dioxide partial pressure of 100 kPa.

[0010] A fourth aspect of the present invention is the method according to any one of the first to third aspects, wherein a Henry's constant determined from a vapor adsorption isotherm of the liquid onto the adsorbent at 25°C is 100 mmol / (g kPa) or more.

[0011] Aspect 5 of the present invention is the method according to any one of Aspects 1 to 3, wherein the adsorbent has a Henry's law constant determined from a vapor adsorption isotherm of the liquid at 25°C of less than 100 mmol / (g kPa).

[0012] Aspect 6 of the present invention is the method according to any one of Aspects 1 to 3, wherein the ratio of the amount of carbon dioxide adsorbed by the adsorbent at 25°C and under the saturated vapor pressure of the liquid to the amount of carbon dioxide adsorbed at 25°C when the liquid does not exist as a vapor is 0.8 or more.

[0013] A seventh aspect of the present invention is the method according to any one of the first to sixth aspects, wherein the liquid is at least one selected from the group consisting of water and organic solvents.

[0014] Aspect 8 of the present invention is an apparatus for recovering carbon dioxide, comprising: an area for accommodating an adsorbent capable of adsorbing carbon dioxide; the area comprising one or more openings that allow the introduction of carbon dioxide and a liquid for immersing the adsorbent; and the adsorbent having an adsorption amount of the liquid of 0.5 mmol / g or more at 25°C and under the saturated vapor pressure of the liquid.

[0015] A ninth aspect of the present invention is the device according to the eighth aspect, wherein the device has two or more of the regions.

[0016] According to embodiments of the present invention, it is possible to provide a novel method and apparatus for capturing carbon dioxide that can reduce costs.

[0017] FIG. 1A is a schematic diagram of an example of an apparatus for capturing carbon dioxide according to an embodiment of the present invention. FIG. 1B is a schematic diagram illustrating an example of the operation of apparatus 1. FIG. 1C is a schematic diagram illustrating an example of the operation of apparatus 1. FIG. 2A is a schematic diagram of another example of an apparatus for capturing carbon dioxide according to an embodiment of the present invention. FIG. 2B is a schematic diagram illustrating an example of the operation of apparatus 100. FIG. 2C is a schematic diagram illustrating an example of the operation of apparatus 100. FIG. 2D is a schematic diagram illustrating an example of the operation of apparatus 100. FIG. 2E is a schematic diagram illustrating an example of the operation of apparatus 100. FIG. 2F is a schematic diagram illustrating an example of the operation of apparatus 100. FIG. 2G is a schematic diagram illustrating an example of the operation of apparatus 100. FIG. 2H is a schematic diagram illustrating an example of the operation of apparatus 100. FIG. 2I is a schematic diagram illustrating an example of the operation of apparatus 100. FIG. 3 is a schematic diagram of yet another example of an apparatus for capturing carbon dioxide according to an embodiment of the present invention. FIG. 4 is a graph showing the change in adsorption amount of ethanol (EtOH) on zeolite 4A at 25° C. versus vapor pressure.

[0018] The present inventors have conducted research from various angles in order to realize a new method for capturing carbon dioxide that can reduce costs. They have found that carbon dioxide can be captured by adsorbing carbon dioxide onto an adsorbent that meets certain requirements and immersing the adsorbent in a liquid. This method does not necessarily require the use of a heat source or expensive pump power for decompression, and allows carbon dioxide to be captured at a lower cost. Details of each requirement specified in the embodiments of the present invention are given below. In this specification, unless otherwise specified, "capturing carbon dioxide" means capturing carbon dioxide in a gas phase, and does not intend, for example, to capture carbon dioxide in a state dissolved in a liquid.

[0019] A carbon dioxide recovery method according to an embodiment of the present invention (hereinafter also referred to as "carbon dioxide recovery method") includes: an adsorption step of bringing carbon dioxide into contact with an adsorbent capable of adsorbing carbon dioxide, thereby causing the carbon dioxide to be adsorbed onto the adsorbent; and a recovery step of immersing the adsorbent in a liquid, and desorbing the carbon dioxide adsorbed by the adsorbent in the adsorption step, and recovering it as a gas phase, wherein the adsorbent has an adsorption amount of the liquid of 0.5 mmol / g or more at 25°C and under the saturated vapor pressure of the liquid. The above method is a novel method for recovering carbon dioxide that can be reduced in cost. Furthermore, in conventional technologies, ２ In order to desorb CO, pump power is required to reduce the pressure, and when reducing the pressure with a pump, air may be drawn in, resulting in the generation of high-purity CO. ２ However, with the above method, air entrainment by the pump does not occur, and as a result, high purity CO ２ can be obtained in the gas phase.

[0020] Fig. 1A is a schematic diagram of an example of an apparatus that enables a carbon dioxide capture method according to an embodiment of the present invention. As shown in Fig. 1A, the carbon dioxide capture apparatus 1 includes an area 10 that accommodates a predetermined adsorbent 2 capable of adsorbing carbon dioxide. The area 10 includes a first opening 11 that allows carbon dioxide to be introduced, and a second opening 12 that allows a liquid to be introduced. The first opening 11 can be connected by piping to the outside (e.g., a carbon dioxide storage unit, etc., not shown) via a valve 11a. The second opening 12 can be connected by piping to the outside (e.g., a liquid storage unit, etc., not shown) via a valve 12a.

[0021] A method for recovering carbon dioxide according to an embodiment of the present invention can be carried out as follows using the above-described apparatus 1. As shown in Fig. 1B, valve 11a is opened, and gas 3 containing, for example, carbon dioxide is introduced into region 10 through first opening 11, and gas 3 is brought into contact with adsorbent 2. This allows carbon dioxide to be adsorbed onto adsorbent 2. Furthermore, by opening valve 12a as necessary, residual gas 3b, in which carbon dioxide has been reduced or removed from gas 3, can be recovered (discharged) through second opening 12.

[0022] After introducing the gas 3 containing carbon dioxide, the liquid 4 is introduced into the region 10 through the second opening 12, and the adsorbent 2 is immersed in the liquid 4 as shown in FIG. 1C . At this time, the adsorbent 2 has an adsorption capacity of 0.5 mmol / g or more of the liquid 4 at 25°C and under the saturated vapor pressure of the liquid 4. This allows exchange adsorption of carbon dioxide 3a and the liquid 4 to proceed in the adsorbent 2, enabling the carbon dioxide 3a to be desorbed from the adsorbent 2. The desorbed carbon dioxide 3a becomes bubbles, separates from the liquid 4, and can be recovered from the first opening 11. After recovering the carbon dioxide 3a, the valve 12a is opened to discharge the liquid 4. According to the above method, it is possible to separate and recover the carbon dioxide 3a (and the remaining gas 3b) from, for example, a mixed gas containing the carbon dioxide 3a.

[0023] When discharging the liquid 4 by gravity, for example, a gas 3 containing carbon dioxide 3a may be introduced into the region 10 to further push the liquid 4 out of the region 10 and allow the carbon dioxide 3a to be re-adsorbed by the adsorbent 2 (at this time, exchange adsorption between the liquid 4 and the carbon dioxide 3a may occur in the adsorbent 2). Alternatively, when discharging the liquid 4, a second gas (purge gas) 5 (not shown) mainly composed of nitrogen may be introduced into the region 10 to push the liquid 4 out of the region 10 and bring the second gas 5 into contact with the adsorbent 2. This allows the liquid 4 adsorbed by the adsorbent 2 to be desorbed and removed, making it easier to re-adsorb the carbon dioxide 3a to the adsorbent 2. Alternatively, when discharging the liquid 4, a third gas (level adjustment gas) 6 (not shown) for adjusting the water level may be introduced into the region 10 to push the liquid 4 out of the region 10. The third gas 6 may be cheaper than the second gas 5 and may be used mainly for the purpose of pushing the liquid 4 out of the region 10.

[0024] 1A to 1C show an example of the configuration and operation of the device 1, and the device 1 may have other configurations and operate in other ways so as to implement the carbon dioxide capture method according to an embodiment of the present invention. For example, the gas 3 and the liquid 4 (and the second gas 5 and the third gas 6) may be introduced (and discharged) using separate openings, or may be introduced (and discharged) using the same opening. Each of the components will be described in further detail below.

[0025] <Adsorbent 2> The adsorbent 2 has an adsorption amount of the liquid 4 of 0.5 mmol / g or more at 25°C and under the saturated vapor pressure of the liquid 4. The adsorbent 2 may have a porous structure and may be capable of selectively adsorbing carbon dioxide 3a. Furthermore, the adsorbent 2 is capable of adsorbing the liquid 4, and the adsorption amount of the liquid 4 of 0.5 mmol / g or more at 25°C and under the saturated vapor pressure of the liquid 4 enables exchange adsorption of the carbon dioxide 3a with the liquid 4 when the adsorbent 2 having adsorbed carbon dioxide 3a is immersed in the liquid 4. The adsorption amount can be measured by a volumetric method. It is preferable that the adsorbent 2 does not undergo (or undergoes only small changes in) its material properties, such as reaction and decomposition, when coexisting with the liquid 4. The form of the adsorbent 2 is not particularly limited, but pellets, beads, or molded bodies (e.g., coated on a honeycomb support) on the order of several millimeters are preferred for reducing pressure loss.

[0026] The adsorbent 2 preferably has an adsorption amount of carbon dioxide 3a of 0.5 mmol / g or more, more preferably 1.5 mmol / g or more, and even more preferably 3.5 mmol / g or more at 25°C and under a carbon dioxide partial pressure of 100 kPa. This makes it possible to more selectively adsorb carbon dioxide 3a, making it easier to recover a sufficient amount of carbon dioxide. The adsorption amount can be measured by a volumetric method.

[0027] The adsorbent 2 may be porous and somewhat flexible. Therefore, the pores of the adsorbent 2 may change in size by, for example, about 1.1 times due to an external force. Liquid 4 may enter the pores, causing the adsorbent 2 to adsorb the liquid 4. Therefore, 1.1 times the window diameter of the adsorbent 2 is preferably equal to or greater than the kinetic diameter of the liquid 4. This facilitates exchange and adsorption of carbon dioxide 3a with the liquid 4 in the adsorbent 2 to which carbon dioxide 3a has been adsorbed. When the adsorbent 2 contains multiple adsorbents, it is preferable that 1.1 times the window diameter of any one of the adsorbents contained in the adsorbent 2 is equal to or greater than the kinetic diameter of the liquid 4, and it is more preferable that 1.1 times the window diameter of all of the adsorbents contained in the adsorbent 2 is equal to or greater than the kinetic diameter of the liquid 4. When the liquid 4 contains multiple liquid compounds, it is preferable that 1.1 times the window diameter of the adsorbent 2 is equal to or greater than the kinetic diameter of any one of the liquid compounds contained in the liquid 4, and it is more preferable that it is equal to or greater than the kinetic diameter of all of the liquid compounds contained in the liquid 4. When the adsorbent 2 contains multiple adsorbents and the liquid 4 contains multiple liquid compounds, it is preferable that 1.1 times the window diameter of any one of the adsorbents contained in the adsorbent 2 is equal to or greater than the kinetic diameter of any one of the liquid compounds contained in the liquid 4, and it is more preferable that 1.1 times the window diameter of all the adsorbents contained in the adsorbent 2 is equal to or greater than the kinetic diameter of all the liquid compounds contained in the liquid 4. The upper limit of the window diameter is not particularly limited, but may be, for example, 1.5 nm or less. In this specification, the window diameter of the adsorbent 2 is defined as the largest sphere diameter that can pass through the narrowest part of the path that a molecule must pass through when being incorporated into the adsorbent. If the adsorbent 2 is a crystalline material, the window diameter may be geometrically calculated from the crystal structure obtained by X-ray crystal structure analysis. Otherwise, it may be determined by a molecular probe method such as that disclosed in, for example, T.A. Braymer, et al., Carbon, Vol. 32, 445-452, 1994. In the molecular probe method, the presence or absence of adsorption is measured using several types of probe molecules with different kinetic diameters in an atmosphere of 25°C and 1 atmosphere, and the kinetic diameter of the smallest probe molecule that is adsorbed can be used as the window diameter.In this specification, the dynamic diameter of the liquid 4 is defined as the mean free path l (unit: m) and the number density n (unit: m. －３ ) to (√2πln) （－１／２） is defined as:

[0028] In one preferred embodiment of the present invention, the Henry's constant obtained from the adsorption isotherm of the liquid 4 to the adsorbent 2 at 25°C is 100 mmol / (g kPa) or more. This can increase the adsorption force of the liquid 4 to the adsorbent 2, making it easier to perform exchange adsorption between carbon dioxide 3a and the liquid 4. In this specification, the Henry's constant can be obtained from the slope of a linear approximation of three or more plots of the adsorption isotherm in a sufficiently low-pressure region where the adsorption amount is 0.5 mmol / g or less.

[0029] In one preferred embodiment of the present invention described above, the adsorption force of the liquid 4 on the adsorbent 2 is relatively high. Therefore, after the introduction and discharge of the liquid 4, when the second gas 5 is brought into contact with the adsorbent 2, the second gas 5 and / or the region 10 (i.e., the adsorbent 2) may be appropriately heated to facilitate desorption of the liquid 4. In addition to directly heating the second gas 5 and / or the adsorbent 2, a method of heating the adsorbent 2 using a heated liquid 4 can also be employed. The heating temperature is preferably 40° C. or higher. On the other hand, the heating temperature is preferably 200° C. or lower in order to suppress thermal changes in the adsorbent 2.

[0030] In another preferred embodiment of the present invention, the Henry's constant obtained from the adsorption isotherm of the liquid 4 to the adsorbent 2 at 25°C is less than 100 mmol / (g kPa). This can reduce the adsorption force of the liquid 4 to the adsorbent 2, making it easier to desorb the liquid 4 from the adsorbent 2 after introducing and discharging the liquid 4 without heating the second gas 5 and / or region 10. The Henry's constant is more preferably 50 mmol / (g kPa) or less, and even more preferably 20 mmol / (g kPa) or less. The lower limit of the Henry's constant is not particularly limited, but can be, for example, 0.01 mmol / (g kPa) or more.

[0031] In yet another preferred embodiment of the present invention, the ratio of the amount of carbon dioxide 3a adsorbed by the adsorbent 2 at 25°C and under the saturated vapor pressure of the liquid 4 to the amount of carbon dioxide 3a adsorbed at 25°C in the absence of the liquid 4 as vapor is 0.8 or more. This indicates that the adsorbent 2 has a property of particularly easily adsorbing carbon dioxide 3a compared to the liquid 4. This makes it possible to sufficiently recover carbon dioxide 3a from the gas 3 again without carrying out a step of contacting the second gas 5 with the adsorbent 2 after introducing the liquid 4. The upper limit of this ratio is not particularly limited, but may be, for example, 1.2 or less.

[0032] The adsorbent 2 may be a porous material, such as zeolite, MOF (Metal Organic Framework), activated carbon, a solid absorbent, silica, or activated alumina. Among these, zeolite, MOF, activated carbon, and a solid absorbent are preferred because of their high carbon dioxide adsorption capacity. For example, the carbon dioxide adsorption capacity at 25°C and a carbon dioxide partial pressure of 100 kPa may be approximately 3 mmol / g for zeolite 4A, approximately 5 mmol / g for zeolite 13X, approximately 2.5 mmol / g for MOFs such as squaric acid complexes, approximately 2 mmol / g for activated carbons such as molecular sieves, or approximately 4 mmol / g for solid absorbents.

[0033] Zeolites have the general formula: M ２／ｎ O.Al ２ O ３ xSiO ２ ・yH ２ The zeolite can be represented by a porous hydrous tectoaluminosilicate represented by the formula O (where M is a cation, n is the valence of the cation, x≧2, y≧0). Since carbon dioxide is known to strongly interact with cations in the zeolite pores, a zeolite having a window diameter equal to or larger than the kinetic diameter of carbon dioxide (0.33 nm) and a small Si / Al ratio is preferred. Zeolite 4A, zeolite 5A, and zeolite 13X, which have a proven track record in removing carbon dioxide, are particularly preferred.

[0034] MOFs (Metal Organic Frameworks) are materials that have a porous coordination network structure formed by the interaction of metals and organic ligands. Examples of MOFs suitable for the fifth aspect of the present invention include one or more selected from the group consisting of Ca squaric acid complex, CALF-20, MIL-101, Al-PyrMOF, and Al-PMOF.

[0035] The activated carbon may be a porous material containing carbon as a main component. As the activated carbon, a molecular sieve carbon capable of selectively adsorbing carbon dioxide is preferably used.

[0036] The solid absorbent may be a porous carrier carrying a substance capable of adsorbing (absorbing) carbon dioxide. Examples of the porous carrier include mesoporous silica such as SBA-15, MCM-41, MSU-H, and MSU-F. The substance capable of adsorbing carbon dioxide is preferably an amine compound, and examples of the amine compound include polyethyleneimine, tetraethylenepentamine, 3-aminopropyltrimethoxysilane, and aminoethylaminopropyltrimethoxysilane.

[0037] <Gas 3 containing carbon dioxide 3a> Gas 3 contains carbon dioxide 3a. Gas 3 may be only carbon dioxide 3a, or a mixture of two or more types of gases. Gas 3 may be, for example, a mixed gas of nitrogen and carbon dioxide 3a, or may be exhaust gas from an automobile or the like. The content of carbon dioxide 3a in gas 3 is not particularly limited, but a higher content is preferable because the effects of the embodiment of the present invention become more pronounced. For example, 0.1% by volume or more is preferred, and 1% by volume or more is more preferred. The upper limit of the content is not particularly limited, but may be, for example, 50% by volume or less, or 25% by volume or less.

[0038] <Liquid 4> Liquid 4 is not particularly limited as long as it satisfies the relationship with adsorbent 2 as described above, and may be one type of liquid compound or two or more types of liquid compounds. It is preferable that liquid 4 does not affect (or has only a small effect on) adsorbent 2. It is preferable that liquid 4 does not dissolve carbon dioxide, and for example, it is preferable that the solubility of carbon dioxide at 25°C and under a carbon dioxide partial pressure of 100 kPa is 0.01 g / cm ３ Preferably, the liquid 4 is at or below 200°C. From the viewpoints of cost and safety, the liquid 4 is preferably at least one selected from the group consisting of water and organic solvents, and more preferably water. Examples of organic solvents include at least one selected from the group consisting of acetone, acetonitrile, benzene, chloroform, cyclohexane, dichloromethane, N,N-dimethylformamide, 1,4-dioxane, ethanol, ethyl acetate, isopropyl ether, methanol, 2-propanol, propylene carbonate, pyridine, tetrahydrofuran, toluene, and xylene. Furthermore, the liquid 4 preferably has a high boiling point (e.g., 50°C or higher). This can suppress volatilization of the liquid 4, which is preferable from the viewpoints of cost and process efficiency. On the other hand, a boiling point of 200°C or lower is preferable because it makes it easier to remove the liquid 4, for example, by the second gas 5.

[0039] <Second Gas 5> The second gas 5 is a gas containing nitrogen as a main component. For example, the second gas 5 may contain 50 vol% or more of nitrogen, preferably 75 vol% or more, and more preferably 100 vol% (i.e., pure nitrogen). The lower the content of vapor from the liquid 4 in the second gas 5, the more preferable it is. For example, the content of vapor from the liquid 4 is preferably 5 vol% or less, 3 vol% or less, 1 vol% or less, 0.1 vol% or less, and 0.01 vol% or less, in that order. From the viewpoints of cost and safety, the second gas 5 is preferably air (atmospheric air). Furthermore, from the viewpoint of minimizing the adsorbable components of the adsorbent 2, the second gas 5 is more preferably dry air from which water vapor and the like that may be adsorbed by the adsorbent 2 has been removed. The amount of water vapor in the dry air is preferably 0.1 vol% or less, and more preferably 0.01 vol% or less. Furthermore, the second gas 5 is preferably heated air whose water vapor content has been reduced by heating, and the heating temperature is preferably 40°C or higher and 200°C or lower.

[0040] <Third Gas 6> The third gas 6 is a gas for low-cost discharge of the liquid 4. The third gas 6 is preferably, for example, air, and more preferably air that has not been subjected to a drying treatment or a heating treatment, and the amount of water vapor in the third gas 6 may be, for example, more than 0.1 vol % and not more than 5 vol %.

[0041] The carbon dioxide capture device and the method using the same according to the embodiment of the present invention will be described in further detail below. According to the embodiment of the present invention, it is possible to provide a carbon dioxide capture device that can reduce costs, and the device can also separate and capture carbon dioxide 3a (and residual gas 3b) from a mixed gas containing carbon dioxide 3a, for example.

[0042] As illustrated in FIG. 1A , an apparatus 1 for recovering carbon dioxide 3a according to an embodiment of the present invention includes an area 10 containing an adsorbent 2 capable of adsorbing carbon dioxide 3a, and the area 10 includes one or more openings (a first opening 11 and a second opening 12 in FIG. 1A ) that allow the introduction of carbon dioxide 3a and a liquid 4 for immersing the adsorbent 2, and the adsorbent 2 has an adsorption amount of liquid 4 of 0.5 mmol / g or more at 25°C and under the saturated vapor pressure of the liquid 4. The above-described apparatus 1 is an apparatus for recovering carbon dioxide that can be further reduced in cost. Each component will be described in detail below. Components already described in detail (adsorbent 2, gas 3, liquid 4, second gas 5, third gas 6, etc.) will be omitted.

[0043] <Region 10> The region 10 includes a region 10 containing an adsorbent 2 capable of adsorbing carbon dioxide 3a. The region 10 includes one or more openings (first opening 11 and second opening 12 in FIG. 1A ) that allow the introduction of carbon dioxide 3a and a liquid 4 for immersing the adsorbent 2. The one or more openings (first opening 11 and second opening 11 in FIG. 1A ) may be provided at any position in the region 10. In one embodiment of the present invention, the first opening 11 is preferably provided above the region 10 in FIG. 1A , and more preferably on the upper surface of the region 10. This facilitates the collection of carbon dioxide 3a. In one embodiment of the present invention, the second opening 12 is preferably provided below the region 10 in FIG. 1A , and more preferably on the lower surface of the region 10. This facilitates the introduction and discharge of the liquid 4. The material of the region 10 is not particularly limited and may be, for example, stainless steel, acrylic, glass, or the like. The region 10 may be provided with a heater (not shown) for heating as needed.

[0044] Valves (valves 11a and 12a in FIG. 1A ) may be provided at or near one or more openings so that the one or more openings can be opened or closed. One or more openings may be connected to other regions (e.g., a storage section for carbon dioxide-containing gas 3, a storage section for carbon dioxide 3a, a storage section for residual gas 3b, a storage section for liquid 4, a storage section for second gas 5, a storage section for third gas 6, etc., not shown) by piping, and a valve may be provided between each of the openings and other regions.

[0045] It is preferable to provide two or more regions 10. This allows the step of bringing carbon dioxide 3a into contact with the adsorbent 2 to adsorb the carbon dioxide 3a onto the adsorbent 2 and the step of immersing the adsorbent 2 in the liquid 4 to desorb and recover the carbon dioxide 3a from the adsorbent 2 to be carried out in parallel, thereby improving treatment efficiency. An example of an apparatus provided with two or more regions 10 will be described below.

[0046] Figure 2A is a schematic diagram of an example of an apparatus that enables a method for capturing carbon dioxide according to an embodiment of the present invention, in which two regions 10 are provided. The carbon dioxide capture apparatus 100 includes a region 10 that accommodates an adsorbent 2, and the region 10 has one or more openings (a first opening 11 and a second opening 12 in Figure 2A) that allow carbon dioxide 3a and a liquid 4 to be introduced. Furthermore, a region 20 that has a similar configuration to the region 10 is included separately from the region 10, and the region 20 has a third opening 21 that corresponds to the first opening 11 and a fourth opening 22 that corresponds to the second opening 12. The first opening 11, the second opening 12, the third opening 21, and the fourth opening 22 can be connected to the outside (for example, a storage section for the gas 3 containing carbon dioxide 3a, a storage section for the carbon dioxide 3a, a storage section for the residual gas 3b, a storage section for the liquid 4, a storage section for the second gas 5, a storage section for the third gas 6, etc. (not shown)) via valves (valves 11a, 11b, 12a, 21a, 21b, and 22a). The second opening 12 is connected to the fourth opening 22 via valve 12b.

[0047] A method for capturing carbon dioxide according to an embodiment of the present invention can be carried out using the above-described apparatus 100 as follows.

[0048] In FIG. 2B , region 10 shows the state in which the adsorbent 2 is capable of adsorbing carbon dioxide 3 a, and region 20 shows the state after the adsorbent 2 is immersed in the liquid 4, the valve 21 b is opened, and the carbon dioxide 3 a is recovered from the third opening 21.

[0049] 2B , in FIG. 2C , valves 11a and 12a are opened to introduce gas 3 containing carbon dioxide 3a into region 10 through first opening 11, and the gas 3 is brought into contact with adsorbent 2. This allows carbon dioxide 3a to be adsorbed by adsorbent 2. Furthermore, remaining gas 3b other than carbon dioxide 3a can be recovered (discharged) through second opening 12 as necessary.

[0050] After the state of FIG. 2C, in FIG. 2D, the valves 11a, 12a and 21a are closed and the valve 12b is opened to move the liquid 4 from the region 20 to the region 10.

[0051] 2D , in FIG. 2E , valves 21 a and 11 b are opened to introduce gas 3 into region 20 through third opening 21, causing carbon dioxide 3 a to be adsorbed by adsorbent 2 in region 20, and pushing liquid 4 from region 20 into region 10. Region 10 is immersed in liquid 4, and carbon dioxide 3 a is desorbed from adsorbent 2 in region 10, and carbon dioxide 3 a is recovered through first opening 11. Note that the differential pressure required to raise the water level of liquid 4 in region 10 at this time is approximately 10 kPa / m, which can be achieved with much lower power (i.e., lower cost) than the pump power required for, for example, decompression.

[0052] After the state of FIG. 2E, in FIG. 2F, valve 12b is closed and valve 22a is opened to further introduce gas 3 into region 20, and carbon dioxide 3a is adsorbed by adsorbent 2, and residual gas 3b is recovered (discharged) from fourth opening 22 as necessary.

[0053] After the state of FIG. 2F, in FIG. 2G, the valves 21a, 22a and 11b are closed and the valve 12b is opened to move the liquid 4 from the region 10 to the region 20.

[0054] 2G , in FIG. 2H , valves 11 a and 21 b are opened to introduce gas 3 into region 10 from first opening 11, causing carbon dioxide 3 a to be adsorbed by adsorbent 2 in region 10, and pushing liquid 4 from region 10 to region 20. Region 20 is immersed in liquid 4, and carbon dioxide 3 a is desorbed from adsorbent 2 in region 20, and carbon dioxide 3 a is collected from third opening 21.

[0055] 2H, in FIG. 2I, valve 12b is closed and valve 12a is opened to further introduce gas 3 into region 10, and carbon dioxide 3a is adsorbed by adsorbent 2. Furthermore, if necessary, remaining gas 3b is recovered (discharged) from second opening 12 (i.e., returning to the state of FIG. 2C).

[0056] As shown in Figures 2C to 2H, by using the device 100, carbon dioxide 3a can be repeatedly recovered from the gas 3 without including a step of desorbing and removing the liquid 4 adsorbed on the adsorbent 2 by introducing and discharging a second gas 5. The device 100 preferably uses an adsorbent according to yet another preferred embodiment of the present invention (i.e., an adsorbent in which the ratio of the amount of carbon dioxide 3a adsorbed at 25°C and under the saturated vapor pressure of the liquid 4 to the amount of carbon dioxide 3a adsorbed at 25°C when the liquid 4 is not present as a vapor is 0.8 or greater). Note that Figures 2A to 2H show an example of the configuration and operation of the device 100, and the device 100 may have other configurations and operate in other ways so as to implement the carbon dioxide recovery method according to an embodiment of the present invention.

[0057] FIG. 3 is a schematic diagram of an example of an apparatus for implementing a method for capturing carbon dioxide according to an embodiment of the present invention, in which four regions 10 are provided. The carbon dioxide capture device 200 includes a region 10 containing an adsorbent 2, and the region 10 has one or more openings (first opening 11 and second opening 12 in FIG. 3 ) through which carbon dioxide or the like can be introduced. In addition to the region 10, the apparatus also includes a region 20 (including a third opening 21 and a fourth opening 22), a region 30 (including a fifth opening 31 and a sixth opening 32), and a region 40 (including a seventh opening 41 and an eighth opening 42) having a configuration similar to that of the region 10. Each region is connected to a pipe for introducing the gas 3, the second gas 5, and the level-adjusting gas 6, a pipe for recovering (discharging) the carbon dioxide 3a, the residual gas 3b, the second gas 5, and the level-adjusting gas 6, and a liquid storage unit 50, each via a valve. A liquid level sensor 60 is also connected to the liquid storage unit 50 and the pipe for recovering the carbon dioxide 3a.

[0058] By using the apparatus 200 of FIG. 3 , the following steps can be simultaneously performed: A. A step of contacting the adsorbent 2 with a gas 3 containing carbon dioxide 3a to adsorb the carbon dioxide 3a onto the adsorbent 2; B. A step of immersing the adsorbent 2 in a liquid 4 to desorb and recover the carbon dioxide 3a from the adsorbent 2; C. A step of introducing a level-adjusting gas 6 into the region to discharge (push) the liquid 4 from the region containing the adsorbent 2; and D. A step of introducing a second gas 5 to bring the second gas 5 into contact with the adsorbent 2. For example, FIG. 3 shows a state in which step A is performed in region 10, step B is performed in region 20, step C is performed in region 30, and step D is performed in region 40. Note that in step B, the level of the liquid 4 in region 20 can be adjusted using a liquid level sensor 60. By appropriately opening and closing valves, the apparatus 200 can switch between steps A, B, C, and D in each region, and can simultaneously perform steps A to D. Note that FIG. 3 shows an example of the configuration and operation of the device 200, and the device 200 may have a different configuration and may perform a different operation so as to implement the carbon dioxide capture method according to an embodiment of the present invention.

[0059] The following examples are provided to more specifically describe the embodiments of the present invention. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the above-described and below-described aims, and all such modifications are within the technical scope of the embodiments of the present invention.

[0060] As the adsorbent, in Test Examples 1 to 4, zeolite 4A (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., spherical, size: 1.4 to 2.3 mm, window diameter: 0.42 nm) was prepared, and in Test Example 5, zeolite 13X (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., pellet-shaped, size: 1.4 to 2.0 mm, window diameter: 0.74 nm) was prepared. In Test Example 6, activated carbon (molecular sieve carbon SHIRASAGI MSC 3K-172, manufactured by Osaka Gas Chemicals Co., Ltd., pellet-shaped, size: 1.4 to 2.0 mm, window diameter: 0.38 nm) was prepared. The window diameters of zeolite 4A and zeolite 13X were geometrically calculated from the crystal structure obtained by X-ray crystal structure analysis, and the window diameter of the molecular sieve carbon was a value determined by the molecular probe method. The liquids used were water (dynamic diameter: 0.35 nm) for Test Examples 1 and 6, ethanol (dynamic diameter: 0.43 nm) for Test Examples 2 and 5, ethyl butyrate (dynamic diameter ≧0.52 nm) for Test Example 3, and N,N-dimethylformamide (DMF) (dynamic diameter: 0.55 nm) for Test Example 4. For the adsorbents of Test Examples 1 to 6, vapor adsorption isotherms of the liquids at 25°C were obtained by volumetric sorption. From the obtained data, the adsorption amounts and Henry's constants of the liquids at 25°C and under the saturated vapor pressure of the liquids were calculated. The results are shown in Table 1 below. As an example, the adsorption isotherm of ethanol on zeolite 4A at 25°C for Test Example 2 is shown in Figure 4.

[0061] In Test Example No. 7, MOF (Ca squaric acid complex, window diameter: 0.34 nm) was prepared as an adsorbent as follows: Solution A was prepared by adding 0.1 mmol of 3,4-dihydroxy-3-cyclobutene-1,2-dione and 0.2 mmol of NaOH per 1 mL of water; ２ 0.2 mmol, CH ３ 0.4 mmol of COOH and CH ３ Solution B was prepared by adding 0.8 mmol of COONa, and solution A was added dropwise onto solution B without disrupting the interface. The solution was allowed to stand for 7 days, and the resulting crystals of the Ca squaric acid complex were filtered and washed. Pure water was used for washing. The window diameter of the MOF was calculated geometrically from the crystal structure obtained by X-ray crystal structure analysis. In Test Example No. 7, water (dynamic diameter: 0.35 nm) was used as the liquid. The water adsorption isotherm at 25°C for the MOF was obtained by volumetric method. From the obtained data, the adsorption amount and Henry's law constant at 25°C and under the saturated vapor pressure of water were calculated. The results are shown in Table 1 below.

[0062] For the above MOFs, the ratio of the amount of carbon dioxide adsorbed at 25°C and under the saturated vapor pressure of water to the amount of carbon dioxide adsorbed at 25°C in the absence of water vapor was calculated from values ​​in a publicly known literature (Tu et al., Energy & Fuels, August 18, 2021, Fig. 8). The results are shown in Table 1 below.

[0063] The following carbon dioxide recovery test was conducted using the apparatus 1 shown in FIG. 1A. The combinations of adsorbent 2 and liquid 4 were as shown in Table 1 below. First, dry air was used to thoroughly dry region 10 (and adsorbent 2), which was a glass tube (approximately 30 mmφ × approximately 20 mm). After drying, carbon dioxide 3a was circulated through region 10 at 10 mL / min for 10 minutes. Liquid 4 was introduced into region 10, and adsorbent 2 was immersed in liquid 4 to observe the desorption of carbon dioxide 3a (hereinafter also referred to as "first observation"). After liquid 4 was discharged from region 10, dry air was circulated as second gas 5 at 100 mL / min for one hour (when liquid 4 was an organic solvent) or half a day (when liquid 4 was water). Then, carbon dioxide 3a was circulated through region 10 at 10 mL / min for 10 minutes. Liquid 4 was introduced into region 10, and the adsorbent 2 was immersed in liquid 4. The desorption of carbon dioxide 3a was observed again (hereinafter also referred to as "second observation"). The results are shown in Table 1. In Table 1, "liquid adsorption amount" refers to the amount of liquid 4 adsorbed by the adsorbent 2 at 25°C and under the saturated vapor pressure of liquid 4, "Henry's constant" refers to the Henry's constant obtained from the adsorption isotherm of liquid 4 to the adsorbent 2 at 25°C, and "carbon dioxide adsorption amount ratio" refers to the ratio of the amount of carbon dioxide adsorbed by the adsorbent 2 at 25°C and under the saturated vapor pressure of water to the amount of carbon dioxide adsorbed by the adsorbent 2 in the absence of water vapor at 25°C. The "first observation" and "second observation" were evaluated as follows, with AA to C being considered acceptable and D being considered unacceptable. AA: The more violently the liquid surface of the liquid 4 shook, the more carbon dioxide 3a was desorbed from the entire adsorbent 2 contained in region 10, and a considerable amount of carbon dioxide 3a was recovered. A: Carbon dioxide 3a was desorbed from the entire adsorbent 2 contained in region 10 to the extent that the liquid surface of liquid 4 shook slightly, and a large amount of carbon dioxide 3a was recovered. B: The liquid surface of liquid 4 did not shook, and carbon dioxide 3a was desorbed from the entire adsorbent 2 contained in region 10, and a somewhat large amount of carbon dioxide 3a was recovered. C: The liquid surface of liquid 4 did not shook, and carbon dioxide 3a was desorbed from multiple locations on the adsorbent 2 contained in region 10, and a sufficient amount of carbon dioxide 3a was recovered.D: The surface of the liquid 4 did not fluctuate, and there were fewer locations where the carbon dioxide 3a was desorbed from the adsorbent 2 contained in the region 10 than in C above, and a sufficient amount of carbon dioxide 3a was not recovered.

[0064]

[0065] The following can be seen from Table 1. Test Examples Nos. 1, 2, and 5 to 7 are examples that satisfy all of the requirements according to an embodiment of the present invention, and were able to recover a sufficient amount of carbon dioxide in the first observation. Test Example No. 1 satisfied the requirement of one preferred embodiment of the present invention (i.e., the Henry's constant at 25°C in the adsorption isotherm of liquid 4 to adsorbent 2 is 100 mmol / (g kPa) or more), and a fairly large amount of carbon dioxide was recovered in the first observation. This is thought to be because the Henry's constant being 100 mmol / (g kPa) or more increased the adsorption force of liquid 4 to adsorbent 2, further promoting the exchange adsorption of carbon dioxide 3a with liquid 4. Test Examples Nos. 2, 5, and 6 satisfied the requirement of another preferred embodiment of the present invention (i.e., the Henry's constant at 25°C in the adsorption isotherm of liquid 4 to adsorbent 2 is less than 100 mmol / (g kPa)), and a somewhat large to fairly large amount of carbon dioxide was recovered in the second observation. This is thought to be because the Henry's constant was less than 100 mmol / (g kPa), which reduced the adsorption force of liquid 4 on adsorbent 2. Even when unheated dry air was used as second gas 5 after introducing and discharging liquid 4, a large amount of liquid 4 could be desorbed from adsorbent 2, and a large amount of carbon dioxide 3a could be adsorbed onto adsorbent 2 in the second adsorption step. Test Example No. 7 satisfied the requirement of yet another preferred embodiment of the present invention (i.e., the ratio of the amount of carbon dioxide adsorbed by adsorbent 2 at 25°C and under the saturated vapor pressure of water to the amount of carbon dioxide adsorbed at 25°C in the absence of water vapor is 0.8 or more), and a considerable amount of carbon dioxide was desorbed in the first and second observations. On the other hand, Test Examples Nos. 3 and 4 did not satisfy the requirement of an embodiment of the present invention, "the amount of carbon dioxide adsorbed at 25°C and under the saturated vapor pressure of liquid 4 is 0.5 mmol / g or more," and a sufficient amount of carbon dioxide was not recovered in the first observation. This is thought to be because the adsorption force of the liquid 4 on the adsorbent 2 was low, and exchange adsorption hardly occurred.

[0066] This application claims priority from Japanese Patent Application No. 2024-007514, filed on January 22, 2024. Japanese Patent Application No. 2024-007514 is incorporated herein by reference.

[0067] 1, 100, 200 Carbon dioxide recovery device 2 Adsorbent 3 Gas containing carbon dioxide 3a Carbon dioxide 3b Residual gas 4 Liquid 5 Second gas 6 Third gas 10, 20, 30, 40 Region 11 First opening 12 Second opening 21 Third opening 22 Fourth opening 31 Fifth opening 32 Sixth opening 31 Seventh opening 32 Eighth opening 50 Liquid storage section 60 Liquid level sensor 11a, 11b, 12a, 12b, 21a, 21b, 22a Valve

Claims

1. A method for recovering carbon dioxide, comprising: an adsorption step of bringing carbon dioxide into contact with an adsorbent capable of adsorbing carbon dioxide, thereby causing the carbon dioxide to be adsorbed onto the adsorbent; and a recovery step of immersing the adsorbent in a liquid and desorbing the carbon dioxide adsorbed by the adsorbent in the adsorption step, thereby recovering the carbon dioxide in the gas phase, wherein the adsorbent has an adsorption capacity of 0.5 mmol / g or more for the liquid at 25°C and under the saturated vapor pressure of the liquid.

2. The method of claim 1, further comprising the step of contacting a second gas primarily composed of nitrogen with the adsorbent after the recovering step.

3. The method according to claim 1 or 2, wherein the adsorbent has a carbon dioxide adsorption capacity of 0.5 mmol / g or more at 25°C and under a carbon dioxide partial pressure of 100 kPa.

4. The method according to any one of claims 1 to 3, wherein the Henry's constant determined from the vapor adsorption isotherm of the liquid onto the adsorbent at 25°C is 100 mmol / (g·kPa) or more.

5. The method according to any one of claims 1 to 3, wherein the Henry's constant determined from the vapor adsorption isotherm of the liquid onto the adsorbent at 25°C is less than 100 mmol / (g·kPa).

6. The method according to any one of claims 1 to 3, wherein the ratio of the amount of carbon dioxide adsorbed by the adsorbent at 25°C and under the saturated vapor pressure of the liquid to the amount of carbon dioxide adsorbed when the liquid does not exist as a vapor at 25°C is 0.8 or more.

7. The method according to any one of claims 1 to 6, wherein the liquid is at least one selected from the group consisting of water and organic solvents.

8. An apparatus for recovering carbon dioxide, comprising: an area for accommodating an adsorbent capable of adsorbing carbon dioxide; said area comprising one or more openings for allowing the introduction of carbon dioxide and a liquid for immersing said adsorbent; and said adsorbent having an adsorption capacity for said liquid of 0.5 mmol / g or more at 25°C and under the saturated vapor pressure of said liquid.

9. The device of claim 8, having two or more of said regions.

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