Regeneration method for carbon dioxide adsorbent, method for adsorbing and separating carbon dioxide, and method for continuously adsorbing and separating carbon dioxide

Abstract

The present invention addresses the problem of providing a regeneration method for a carbon dioxide adsorbent, a method for continuously adsorbing and separating carbon dioxide that involves the regeneration method, and a method for adsorbing and separating carbon dioxide that allows for simple separation of carbon dioxide from a carbon dioxide adsorbent onto which carbon dioxide has been adsorbed.　The present invention relates to: a regeneration method for a carbon dioxide adsorbent that contains an alkali metal carbonate and a specific metal compound, wherein the carbon dioxide adsorbent is brought into contact with water and then brought into contact with an aqueous solution that contains the alkali metal carbonate; a continuous adsorption and separation method that involves repeating an adsorption step for bringing a carbon dioxide adsorbent into contact with a gas that includes carbon dioxide, a separation step for heating the carbon dioxide adsorbent onto which carbon dioxide has been adsorbed to a specific temperature, and the regeneration method for the carbon dioxide adsorbent; and a method for adsorbing and separating carbon dioxide that includes a separation step for heating a carbon dioxide adsorbent onto which carbon dioxide was adsorbed at an adsorption step to a specific temperature under an atmosphere of a gas that includes carbon dioxide.

Description

Method for regenerating carbon dioxide adsorbent, method for adsorbing and separating carbon dioxide, and method for continuous adsorption and separation of carbon dioxide

[0001] The present invention relates to a method for regenerating a carbon dioxide adsorbent, a method for adsorbing and separating carbon dioxide, and a method for continuous adsorption and separation of carbon dioxide.

[0002] In recent years, various studies have been conducted on methods for capturing carbon dioxide, which is considered a cause of global warming, and various capture methods have been proposed. For example, as one of the technologies for directly capturing carbon dioxide from gases such as the atmosphere (DAC), a method of adsorbing and separating carbon dioxide using a solid adsorbent has been proposed. As an example, Patent Document 1 describes "a method for adsorbing and separating carbon dioxide, comprising the steps of bringing a specific carbon dioxide adsorbent into contact with a gas containing carbon dioxide to adsorb carbon dioxide onto the carbon dioxide adsorbent, and heating the carbon dioxide adsorbent, on which carbon dioxide has been adsorbed, to 50°C to 900°C to separate the carbon dioxide from the carbon dioxide adsorbent."

[0003] International Publication No. 2022 / 145217

[0004] As described in Patent Document 1, carbon dioxide adsorption and separation methods that use alkali metal carbonates as adsorbent components are said to allow for repeated adsorption and separation of carbon dioxide multiple times because alkali metal carbonates have the characteristics and functions of causing and proceeding with reversible reactions in the adsorption and separation (desorption) of carbon dioxide. However, when carbon dioxide adsorption and separation methods are repeated, the carbon dioxide adsorption performance of the carbon dioxide adsorbent generally gradually decreases. In particular, the inventors have found that the decrease in adsorption performance (degradation of the carbon dioxide adsorbent) is accelerated depending on the gas that is brought into contact with the carbon dioxide adsorbent. However, conventional carbon dioxide adsorption and separation methods, including Patent Document 1, have not considered this aspect. Therefore, in conventional carbon dioxide adsorption and separation methods, carbon dioxide adsorbent materials with reduced adsorption performance must be discarded, and measures are needed to address environmental protection (environmental burden) and cost.

[0005] The present invention aims to provide a method for regenerating a carbon dioxide adsorbent and a method for continuous adsorption and separation of carbon dioxide including this regeneration method. Furthermore, the present invention aims to provide a method for adsorption and separation of carbon dioxide that can easily separate carbon dioxide from a carbon dioxide adsorbent that has adsorbed carbon dioxide.

[0006] The inventors of the present invention have diligently studied carbon dioxide adsorption and separation technology using alkali metal carbonates as adsorption components, and have found that when carbon dioxide is repeatedly adsorbed and separated (adsorbed and desorbed) onto a carbon dioxide adsorbent, components other than carbon dioxide in the gas that comes into contact with the carbon dioxide adsorbent, particularly nitrogen oxides and sulfur oxides, have a greater impact on the carbon dioxide adsorption performance of the carbon dioxide adsorbent (in this invention, this may simply be referred to as "adsorption performance of the carbon dioxide adsorbent" or "adsorption performance") than the degradation (decomposition) of the adsorbent component. Further investigation by the inventors has found that by-products, which are produced when components other than carbon dioxide react with the adsorbent component, are less likely to undergo a reverse reaction under the conditions of the separation process (desorption process), and thus gradually become mixed into the carbon dioxide adsorbent, which is one of the factors that reduces the adsorption performance of the carbon dioxide adsorbent. The inventors have also found that such by-products are water-soluble, and that the by-products can be removed by washing the carbon dioxide adsorbent with water when its adsorption performance has decreased. Furthermore, it was discovered that by heating the carbon dioxide adsorbent to 50-900°C in an atmosphere of carbon dioxide-containing gas during the separation process, the adsorbed carbon dioxide could be easily separated and desorbed from the carbon dioxide adsorbent. This invention was completed after further investigation based on these findings.

[0007] In other words, the object of the present invention has been achieved by the following means: <1> A method for regenerating a carbon dioxide adsorbent that adsorbs carbon dioxide in a gas, wherein the carbon dioxide adsorbent contains an alkali metal carbonate containing at least one alkali metal element and a metal compound containing at least one element selected from the group consisting of Group 3 and Group 4 elements of the periodic table, and the carbon dioxide adsorbent is brought into contact with water, and then brought into contact with an aqueous solution containing an alkali metal carbonate containing at least one alkali metal element. <2> The regeneration method according to <1>, wherein the metal compound contains at least one element selected from the group consisting of cerium, titanium, and zirconium. <3> The regeneration method according to <1> or <2>, wherein the metal compound contains the element zirconium. <4> The regeneration method according to any one of <1> to <3>, wherein the metal compound is zirconium oxide. <5> The regeneration method according to any one of <1> to <4>, wherein the gas is the atmosphere or factory exhaust gas. <6> The regeneration method according to any one of <1> to <4>, wherein the gas is exhaust gas from a power plant. <7> The regeneration method according to any one of <1> to <6>, wherein the gas contains at least one selected from the group consisting of nitrogen oxides and sulfur oxides. <8> The regeneration method according to any one of <1> to <7>, wherein the alkali metal carbonate contained in the aqueous solution is potassium carbonate. <9> A continuous adsorption and separation method for carbon dioxide, comprising repeatedly performing an adsorption step of bringing a carbon dioxide adsorbent into contact with a gas containing carbon dioxide, and a separation step of heating the carbon dioxide adsorbent that has adsorbed carbon dioxide in the adsorption step to 50 to 900°C, wherein the carbon dioxide adsorbent contains an alkali metal carbonate containing at least one alkali metal element and a metal compound containing at least one element selected from the group consisting of Group 3 and Group 4 elements of the periodic table, and after performing the adsorption step and the separation step at least once each, the carbon dioxide adsorbent after the separation step is regenerated by the regeneration method according to any one of <1> to <8>. <10> The continuous adsorption separation method for carbon dioxide according to <9>, wherein at least one of the multiple separation steps is heated in an atmosphere of carbon dioxide-containing gas.<11> A method for adsorbing and separating carbon dioxide, comprising an adsorption step of bringing a carbon dioxide adsorbent into contact with a gas containing carbon dioxide, and a separation step of heating the carbon dioxide adsorbent, which has adsorbed carbon dioxide in the adsorption step, to 50 to 900°C in an atmosphere of gas containing carbon dioxide.

[0008] The present invention can provide a method for regenerating a carbon dioxide adsorbent, and a continuous adsorption and separation method for carbon dioxide including this regeneration method. Furthermore, the present invention can provide a carbon dioxide adsorption and separation method that can easily separate carbon dioxide from a carbon dioxide adsorbent that has adsorbed carbon dioxide.

[0009] In the present invention and this specification, when describing content, physical properties, etc., by indicating numerical ranges, if the upper and lower limits of the numerical range are described separately, either upper or lower limit can be appropriately combined to form a specific numerical range. On the other hand, when multiple numerical ranges represented by "~" are set and described, the upper and lower limits forming the numerical range are not limited to a specific combination of the upper and lower limits described before and after "~" as a specific numerical range, but can be a numerical range formed by appropriately combining the upper and lower limits of each numerical range. In the present invention and this specification, a numerical range represented by "~" means a range that includes the numbers described before and after "~" as the lower and upper limits.

[0010] [Method for regenerating carbon dioxide adsorbent] The method for regenerating a carbon dioxide adsorbent of the present invention (hereinafter sometimes simply referred to as "the regeneration method of the present invention") is a method for adsorbing carbon dioxide in a gas and separating (desorbing) the adsorbed carbon dioxide, that is, a method for regenerating a used carbon dioxide adsorbent used in a method for adsorbing and separating carbon dioxide. The carbon dioxide adsorbent to be regenerated may be contaminated with by-products or have by-products accumulated or deposited on its surface, and further, the main product obtained by the reaction of an alkali metal carbonate and carbon dioxide may be contaminated or accumulated and deposited on the surface of the carbon dioxide adsorbent. Specifically, the regeneration method of the present invention is a method in which a (used) carbon dioxide adsorbent is brought into contact with water and then into contact with an aqueous solution containing an alkali metal carbonate containing at least one alkali metal element. Thereby, by-products mixed, accumulated, deposited, etc. on the carbon dioxide adsorbent are removed from the carbon dioxide adsorbent to recover a metal compound (a porous material if necessary), and the recovered metal compound and a new alkali metal carbonate are brought into contact and mixed to regenerate the carbon dioxide adsorbent. In the regeneration method of the present invention, the degree of regeneration of the carbon dioxide adsorbent cannot be uniquely determined by variations in the contact conditions with water and the contact conditions with the aqueous solution containing the alkali metal carbonate, but it is also possible to achieve an adsorption performance equivalent to that of the carbon dioxide adsorbent before use by selecting both contact conditions. Thus, the regeneration method of the present invention can also be said to be a method for producing a carbon dioxide adsorbent (regenerated carbon dioxide adsorbent) regenerated from a used carbon dioxide adsorbent. That is, the method for regenerating a carbon dioxide adsorbent is synonymous with the method for producing a regenerated carbon dioxide adsorbent, and is an invention of a method for producing a substance (regenerated carbon dioxide adsorbent).

[0011] [Carbon dioxide adsorbent] First, the carbon dioxide adsorbent (unused carbon dioxide adsorbent) used in the method for adsorbing and separating carbon dioxide will be described. The carbon dioxide adsorbent contains an alkali metal carbonate containing at least one alkali metal element and a metal compound containing at least one element selected from the group consisting of Group 3 elements and Group 4 elements of the periodic table. This carbon dioxide adsorbent may further contain a porous material.

[0012] The average pore diameter of the carbon dioxide adsorbent is not particularly limited, but from the perspective of the carbon dioxide adsorption performance, it is preferably 0.3 to 500 nm, and more preferably 1 to 100 nm. The average pore diameter (unit: nm) of the carbon dioxide adsorbent can be analyzed and measured by the nitrogen adsorption method using any conventionally known and suitable specific surface area and pore distribution measuring device. Specifically, the adsorption / desorption isotherm of nitrogen with respect to the carbon dioxide adsorbent is obtained, and from the obtained adsorption / desorption isotherm, the total pore volume (V) (unit: cm ３ / g) and the specific surface area (A) (unit: m ２ / g) are further obtained, and the average pore diameter (D) can be calculated based on the formula: D = 4V / A.

[0013] The carbon dioxide adsorbent may have a porous material (substrate) supporting an alkali metal carbonate and a metal compound. In other words, the carbon dioxide adsorbent may be one in which an alkali metal carbonate and a metal compound are supported on a porous material and integrally formed. The form of the carbon dioxide adsorbent having a porous material is not limited to this, and in the carbon dioxide adsorbent, especially the alkali metal carbonate may exist in a state of being free from the porous material. Also, in the carbon dioxide adsorbent, the porous material may be a metal compound. In other words, it may be a carbon dioxide adsorbent in which an alkali metal carbonate is supported on a porous material composed of a metal compound. In this case, since the metal compound is a porous material and forms a substrate, usually it is not supported on the porous material, but a metal compound other than the metal compound that becomes the porous material may be supported on the porous material.

[0014] <Alkali Metal Carbonates> The carbon dioxide adsorbent contains an alkali metal carbonate containing at least one alkali metal element. The alkali metal carbonate functions as a carbon dioxide adsorbent by reacting with carbon dioxide in the presence of water as needed. For example, if the alkali metal carbonate is potassium carbonate, it becomes potassium bicarbonate (potassium hydrogen carbonate), and the resulting potassium bicarbonate is regenerated (returned) to potassium carbonate by heating in the separation process described later. This method of adsorbing and separating carbon dioxide using alkali metal carbonates can be repeated by utilizing the reversible reaction of alkali metal carbonates during adsorption and separation. The carbon dioxide adsorbent may contain one or more alkali metal carbonates.

[0015] The alkali metal carbonate preferably contains at least one alkali metal element selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium. From the viewpoint of carbon dioxide adsorption performance, the alkali metal carbonate preferably contains sodium, potassium, or cesium, and more preferably contains potassium.

[0016] The alkali metal carbonate is not particularly limited, and examples include lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, rubidium carbonate, rubidium bicarbonate, cesium carbonate, and cesium bicarbonate. From the viewpoint of carbon dioxide adsorption performance, potassium carbonate and potassium bicarbonate are preferred, and potassium carbonate is more preferred.

[0017] The content of alkali metal elements in the carbon dioxide adsorbent is not particularly limited, but from the viewpoint of carbon dioxide adsorption performance, it is preferably 1.0 to 20.0 mmol per 1.0 g of metal compound, and more preferably 1.0 to 10.0 mmol.

[0018] <Metal Compounds> The metal compound contained in the carbon dioxide adsorbent is a metal compound containing at least one element selected from the group consisting of Group 3 and Group 4 elements of the periodic table. The carbon dioxide adsorbent may contain one or more metal compounds. From the viewpoint of carbon dioxide adsorption performance and availability, the element contained in the metal compound is preferably at least one element selected from the group consisting of cerium, titanium, and zirconium, and more preferably contains zirconium.

[0019] The metal compound contained in the carbon dioxide adsorbent is not particularly limited, and examples include cerium compounds such as cerium oxide, cerium carbonate, cerium nitrate, cerium(III) hydroxide, cerium(IV) hydroxide, cerium chloride, cerium acetate, and cerium(III) acetylacetonate; titanium compounds such as titanium oxide, titanium hydroxide, tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetrabutyl titanate, tetraisobutyl titanate, tetra(2-ethylhexyl) titanate, tetraoctadecyl titanate, titanium(IV) oxyacetylacetonate, and titanium(IV) disipropoxybisacetylacetonate; and zirconium compounds such as zirconium oxide, zirconium carbonate(IV), zirconium oxynitrate, zirconium hydroxide(IV), and zirconium chloride(IV). From the viewpoint of carbon dioxide adsorption performance, the metal compound contained in the carbon dioxide adsorbent preferably contains zirconium oxide, and more preferably zirconium oxide.

[0020] The above-mentioned metal compound may be included in the carbon dioxide adsorbent as the metal compound itself, or in the form of a composite with alkali metal carbonate, porous material described later, other metal compounds, and / or other components described later.

[0021] From the viewpoint of carbon dioxide adsorption performance, the content of the above elements in the metal compound is preferably 0.1 to 20.0 mmol / g, and more preferably 0.1 to 10.0 mmol / g.

[0022] <Porous Materials> The porous material that serves as the base for the carbon dioxide adsorbent is not particularly limited, and examples include oxides such as aluminum oxide and silicon oxide, composite oxides such as calcium silicate and silica alumina, and activated carbon. Among these, it is preferable to use at least one selected from the group consisting of silicon oxide, aluminum oxide, activated carbon, and calcium silicate, from the viewpoint of carbon dioxide adsorption performance.

[0023] Activated carbon is a flammable substance. Therefore, if the temperature (heating temperature) in the separation process described later is, for example, 250°C or higher, it is more preferable to use silicon dioxide as the porous material.

[0024] The porous material exemplified above can be manufactured by any suitable conventional manufacturing method. Furthermore, commercially available porous materials can also be used as the porous material exemplified above.

[0025] The type of aluminum oxide is not particularly limited; for example, any crystal system such as α-type, γ-type, or θ-type can be used. Furthermore, the method for producing aluminum oxide is not particularly limited. For example, aluminum oxide can be produced by washing bauxite, an aluminum-containing mineral, with a hot sodium hydroxide solution, cooling and precipitating the aluminum hydroxide dissolved in the sodium hydroxide solution, and then heating and dehydrating it.

[0026] When the porous material is silicon dioxide, examples of silicon dioxide include silica gel, mesoporous silica, and zeolites. Silicon dioxide can be produced by wet or dry methods. Examples of wet methods include precipitation and gel methods. Examples of dry methods include combustion.

[0027] When producing silica gel, a porous material, by a wet process, Na ２ O・nSiO ２By using a compound represented by the general formula and neutralizing it with sulfuric acid or hydrochloric acid, a hydrogel can be obtained via a silica sol having the composition of polysilicic acid, and silica gel can be obtained by further removing water from the hydrogel. The method for removing water from the hydrogel is not particularly limited. The water in the hydrogel may be evaporated directly, or the water may be replaced with a relatively low-boiling hydrophilic organic solvent such as an alcohol or ketone, followed by drying and heating. By replacing the water in the hydrogel with a low-boiling hydrophilic organic solvent such as an alcohol or ketone, drying, and heating, silicon oxide with a larger pore volume and pore diameter can be obtained.

[0028] Mesoporous silica is not particularly limited in type, as long as it has mesopores in its structure. The pore size of mesoporous silica is usually 1.5 to 50 nm. Furthermore, there are no particular limitations on the method of producing mesoporous silica. For example, mesoporous silica can be produced from a mixture of a sol-gel precursor and a structurally controlling amphiphilic substance by a self-assembly process. Specifically, first, liquid crystal micelles are formed in water using a surfactant such as cetyltrimethylammonium bromide, and hydrolysis and condensation occur by adding a ceramic sol-gel precursor such as tetraethyl orthosilicic acid, forming a silica network around the micelles. Next, mesoporous silica is obtained by removing the organic template by heat treatment or solvent extraction.

[0029] The type of zeolite is not particularly limited and includes, for example, synthetic zeolite, artificial zeolite, and natural zeolite. Furthermore, the method of producing zeolite is not particularly limited. For example, a mixture consisting of an alumina source, a silica source, an alkali source, an organic structure-regulating agent, and water can be subjected to a hydrothermal reaction, followed by drying and calcination to produce zeolite.

[0030] The type of calcium silicate is not particularly limited; for example, any crystalline form such as wollastonite, tobermorite, or xonotlite can be used. Furthermore, the method for producing calcium silicate is not particularly limited. For example, calcium silicate (secondary particles) can be produced by hydrothermally reacting a mixture consisting of a siliceous raw material, a calcareous raw material, and water while stirring.

[0031] When the porous material is activated carbon, the activated carbon can be produced by heating a carbonaceous raw material to carbonize it into a carbonized product, and then activating it. The carbonaceous material used as the raw material for activated carbon is not particularly limited. Examples of carbonaceous materials include wood, sawdust, coconut shells, pulp wastewater, coal, petroleum products, and synthetic resins.

[0032] The method for activating (revitalizing) carbides after carbonization of carbonaceous materials is not particularly limited. Examples of activation methods include gas activation and chemical activation.

[0033] Methods of gas activation include, for example, high-temperature treatment with water vapor, carbon dioxide, or air. Gas activation is thought to proceed in two stages. In the first stage, the heating process, the unorganized parts of the carbide are selectively decomposed and consumed, releasing fine pores within the carbon structure and rapidly increasing the internal surface area. In the second stage, the gasification reaction process, the carbon crystals constituting the carbide, or the carbon constituting the fine pore areas, are reacted and consumed, forming large pores in a complex and organized manner. In this pore formation process, if the carbon reaction consumption rate is 50% or less, the activated carbon will be mainly composed of micropores, and if the carbon reaction consumption rate exceeds 75%, the activated carbon will have increased macropores. At intermediate carbon reaction consumption rates, activated carbon with both micropores and macropores can be obtained.

[0034] Methods for chemical activation include, for example, the use of zinc chloride, phosphoric acid, calcium chloride, and potassium sulfide. It is generally known that chemical activation increases the pore volume and average pore diameter of activated carbon. Furthermore, activated carbon can take on a variety of forms depending on the raw materials and manufacturing method, such as powder, granules, crushed, fibrous, and honeycomb, but the form of activated carbon that can be applied to the carbon dioxide adsorbent of the present invention is not particularly limited.

[0035] As the porous material, the aforementioned metal compounds can also be used.

[0036] <Other Components> In addition to the components listed above, the carbon dioxide adsorbent may further contain other components. These other components may be any components that do not fall under any of the alkali metal carbonates, metal compounds, or porous materials listed above. Examples include alkali metal compounds such as cesium nitrate, cesium oxide, cesium hydroxide, and cesium acetate (excluding the alkali metal carbonates mentioned above), and alkaline earth metal compounds such as magnesium carbonate, magnesium oxide, calcium carbonate, and calcium oxide.

[0037] Other components may be present in the carbon dioxide adsorbent as themselves, or in the form of alkali metal carbonates, metal compounds, composites with porous materials, or oxides derived therefrom. The total content of other components in the carbon dioxide adsorbent is not particularly limited and can be determined as appropriate.

[0038] <Shape of carbon dioxide adsorbent> The shape of the carbon dioxide adsorbent is not particularly limited. Carbon dioxide adsorbent is usually in powder or molded form. As a molded form, it can be a molded form (porous material) formed into granules (spherical), pellets (columnar), rings, honeycomb shapes, etc., or a powdered carbon dioxide adsorbent can be molded into a predetermined shape by any suitable conventional method. As a carbon dioxide adsorbent, for example, it can be molded into granules (spherical), pellets (columnar), extruded shapes, ring shapes, honeycomb shapes, and furthermore, after being molded into a predetermined shape, it can be crushed and classified to obtain granules of any suitable size.

[0039] For example, the diameter of granular (spherical) carbon dioxide adsorbent is usually preferably 10 mm or less, and more preferably 5 mm or less, from the viewpoint of improving handling and maximizing carbon dioxide adsorption performance. There is no particular lower limit to the diameter of the carbon dioxide adsorbent. Here, the diameter of the carbon dioxide adsorbent refers to the diameter of the sphere if it is spherical, the diameter if it is pellet-shaped (columnar) and the cross-section when cut in a direction perpendicular to the direction of extension is circular, and the maximum width (maximum diameter) of the cross-section if it is any other shape.

[0040] <Method for Manufacturing Carbon Dioxide Adsorbent> The method for manufacturing the carbon dioxide adsorbent is not particularly limited, and any method can be applied as appropriate. For example, one method may include contacting a metal compound with a solution containing an alkali metal carbonate (alkali metal carbonate solution), heating it, and obtaining a carbon dioxide adsorbent. Here, "heating" includes a drying step and / or a calcination step.

[0041] The alkali metal carbonate solution used in the above manufacturing method (the step of obtaining the carbon dioxide adsorbent) is not particularly limited as long as it is a solution containing the alkali metal carbonate described above. The solvent that can be used in the alkali metal carbonate solution is not particularly limited and includes, for example, water (ion-exchanged water, (ultra)pure water), alcohols such as methanol, ethanol, and isopropyl alcohol, polar organic solvents such as acetone, acetonitrile, and tetrahydrofuran, and mixed solvents containing two or more of these solvents. In the present invention, "solution" may also include dispersions, suspensions, etc.

[0042] The concentration of alkali metal carbonate in the alkali metal carbonate solution is not particularly limited, but is preferably 1 to 53% by mass, more preferably 5 to 50% by mass, and even more preferably 10 to 50% by mass, from the viewpoint of the efficiency of manufacturing the carbon dioxide adsorbent. If the carbon dioxide adsorbent contains the other materials mentioned above, a mixed alkali metal carbonate solution (e.g., a mixed aqueous solution) containing the other materials can be used. The content of the other materials in this mixed solution is not particularly limited, but is preferably 0.01 to 90% by mass, more preferably 0.1 to 90% by mass, and even more preferably 1 to 90% by mass, from the viewpoint of the efficiency of manufacturing the carbon dioxide adsorbent.

[0043] The method of contact between the metal compound and the alkali metal carbonate solution is not particularly limited. For example, any conditions that allow the alkali metal carbonate solution to come into even contact with the metal compound are acceptable. If the metal compound is porous, any conditions that allow the alkali metal carbonate solution to penetrate into its pores and be uniformly absorbed are also acceptable. As contact methods, any conventionally known and suitable methods can be applied, such as dropping droplets of alkali metal carbonate solution onto the metal compound, spraying the alkali metal carbonate solution onto the metal compound, or immersing the metal compound in the alkali metal carbonate solution. The contact conditions are not particularly limited and can be, for example, at a temperature around room temperature (20-30°C), under an air atmosphere (atmospheric atmosphere) or an inert gas atmosphere.

[0044] The drying process is carried out by drying the metal compound in contact with the alkali metal carbonate solution until there is no change in mass. Specifically, for example, it can be carried out by drying at room temperature for about one hour, and then further heating using a conventionally known and suitable drying apparatus (e.g., an oven) at a temperature of preferably 30 to 120°C until there is no change in mass.

[0045] In the above manufacturing method, a firing process may be carried out following the drying process. Specifically, the firing process can be carried out by heating at a temperature of 30 to 500°C, more preferably 30 to 300°C, using a conventionally known and suitable heat treatment apparatus (e.g., an oven, a muffle furnace), until the mass change ceases.

[0046] The atmosphere in which the heating process (drying process and firing process) is carried out is not particularly limited, and examples include an air atmosphere (atmospheric atmosphere), as well as an inert gas atmosphere such as nitrogen gas, argon gas, or helium gas.

[0047] By the above manufacturing method, a carbon dioxide adsorbent can be obtained in which alkali metal carbonate is attached to the surface of the metal compound, and if the metal compound is porous, also to the pores.

[0048] A method for producing a carbon dioxide adsorbent having a porous material is not particularly limited, and for example, a method can be cited that includes the steps of (1) bringing a porous material into contact with a solution containing a metal compound (metal compound solution) and heating to obtain a carbon dioxide adsorbent precursor, and (2) bringing the obtained carbon dioxide adsorbent precursor into contact with an alkali metal carbonate solution and heating to obtain a carbon dioxide adsorbent. Here, "heating" includes a drying step and / or a calcination step.

[0049] The metal compound solution used in step (1) is not particularly limited as long as it contains the metal compound described above. The solvent that can be used in the metal compound solution is not particularly limited and includes, for example, water (ion-exchanged water, (ultra)pure water), alcohols such as methanol, ethanol, and isopropyl alcohol, polar organic solvents such as acetone, acetonitrile, and tetrahydrofuran, and mixed solvents containing two or more of these solvents.

[0050] The concentration of the metal compound in the metal compound solution is not particularly limited, but is preferably 0.01 to 100% by mass, more preferably 0.1 to 100% by mass, and even more preferably 1 to 100% by mass, from the viewpoint of the production efficiency of the carbon dioxide adsorbent precursor. If the carbon dioxide adsorbent contains the other materials mentioned above, a mixed solution of the metal compound containing the other materials (e.g., a mixed aqueous solution) can be used. The content of the other materials in this mixed solution is not particularly limited, but is preferably 0.01 to 90% by mass, more preferably 0.1 to 90% by mass, and even more preferably 1 to 90% by mass, from the viewpoint of the production efficiency of the carbon dioxide adsorbent precursor.

[0051] The method of contact between the porous material and the metal compound solution is not particularly limited. For example, any condition that allows the metal compound solution to come into even contact with the porous material so that the solution can penetrate into the pores of the porous material and be uniformly absorbed is acceptable. As contact methods, any conventionally known and suitable method can be applied, such as dropping droplets of the metal compound solution onto the porous material, spraying the metal compound solution onto the porous material, or immersing the porous material in the metal compound solution. The contact conditions are not particularly limited and can be, for example, at a temperature near room temperature, under an air atmosphere or an inert gas atmosphere.

[0052] The drying process is carried out by drying the porous material in contact with the metal compound solution until there is no change in mass. Specifically, for example, it can be carried out by drying at room temperature for about one hour, and then further heating it using a conventionally known and suitable drying apparatus (e.g., an oven) at a temperature of preferably 30 to 120°C until there is no change in mass.

[0053] In the above manufacturing method, it is preferable to carry out a firing process following the drying process. Specifically, the firing process can be carried out by firing at 200 to 800°C for 1 to 12 hours using a conventionally known and suitable heat treatment apparatus (for example, a muffle furnace).

[0054] The atmosphere in which the heating process (drying process and firing process) is carried out is not particularly limited and can be, for example, an air atmosphere, or an inert gas atmosphere such as nitrogen gas, argon gas, or helium gas.

[0055] By the above step (1), a carbon dioxide adsorbent precursor can be obtained in which a metal compound or a metal element derived from a metal compound, or a compound thereof, is attached to or solid-solved in the surface and / or pores of a porous material.

[0056] Next, step (2) is performed to obtain a carbon dioxide adsorbent by bringing the carbon dioxide adsorbent precursor obtained in this way into contact with an alkali metal carbonate solution and heating (drying step, calcination step as appropriate). The alkali metal carbonate solution used in step (2) is not particularly limited as long as it is a solution containing the alkali metal carbonate described above, and for example, the alkali metal carbonate solution that is brought into contact with the metal compound in the above manufacturing method can be used.

[0057] The method of contacting the carbon dioxide adsorbent precursor with the alkali metal carbonate solution is not particularly limited. For example, any condition that allows the alkali metal carbonate solution to be evenly contacted with the carbon dioxide adsorbent precursor so that it can penetrate into the pores of the carbon dioxide adsorbent precursor and be uniformly absorbed is acceptable. The contact method is not particularly limited and is, for example, the same as the contact method between the metal compound and the alkali metal carbonate solution in the manufacturing method described above. The contact conditions are not particularly limited and can be, for example, at a temperature near room temperature, under an air atmosphere or an inert gas atmosphere.

[0058] The drying process is carried out by drying the carbon dioxide adsorbent precursor, which has been in contact with the alkali metal carbonate solution, until there is no change in mass. Specifically, for example, it can be carried out by drying at room temperature for about one hour, and then further heating it using a conventionally known and suitable drying apparatus (e.g., an oven) at a temperature of preferably 30 to 120°C until there is no change in mass.

[0059] In this manufacturing method, a firing process may be carried out following the drying process. Specifically, the firing process can be carried out by heating at a temperature of 30 to 500°C, more preferably 30 to 300°C, using a conventionally known and suitable heat treatment apparatus (e.g., an oven, a muffle furnace), until the mass changes no longer occur.

[0060] The atmosphere in which the heating process (drying process and firing process) is carried out is not particularly limited, and is, for example, the same as the atmosphere in process (1) above.

[0061] By step (2) described above, a carbon dioxide adsorbent can be obtained in which an alkali metal carbonate is attached to the surface and / or inside the pores of the porous material, in addition to a metal compound or a metal element derived from the metal compound or the same compound.

[0062] The carbon dioxide adsorbent used in the present invention and its manufacturing method have been described above. Regarding these, the contents of Patent Document 1 can be appropriately referenced, and those contents are incorporated directly as part of this specification.

[0063] [Regeneration Method] The regeneration method of the present invention involves contacting used carbon dioxide adsorbent with water, and then contacting it with an aqueous solution containing an alkali metal carbonate containing at least one alkali metal element. The regeneration method of the present invention will be described below in two parts: a step of contacting the used carbon dioxide adsorbent with water (also called the removal step), and a step of contacting the used carbon dioxide adsorbent obtained in the removal step with an aqueous solution containing an alkali metal carbonate containing at least one alkali metal element (alkali metal carbonate solution) (also called the re-adhesion step).

[0064] <Process of contact with water (removal process)> The carbon dioxide adsorbent used in the removal process is a used carbon dioxide adsorbent, for example, a carbon dioxide adsorbent that has been subjected to the carbon dioxide adsorption process and separation process described later using a carbon dioxide adsorbent. As described above, this carbon dioxide adsorbent contains (mixed with), adsorbed or attached by-products produced by the reaction of carbon dioxide in the gas with the adsorbent component (alkali metal carbonate), in addition to the main product produced by the reaction of components other than carbon dioxide with the adsorbent component. In the present invention, the amount of by-products contained in the carbon dioxide adsorbent is not particularly limited and is determined according to the decrease in the adsorption performance of the carbon dioxide adsorbent.

[0065] The water used in the removal process is not particularly limited, but pure water, ultrapure water, ion-exchanged water, etc., can be used. In addition, water mixed with alcohol, etc., can be used as long as it can remove the main product and by-products. The amount of water used is not particularly limited, but for example, it can be 1 to 500 parts by mass per 1 part by mass of carbon dioxide adsorbent, and is preferably 5 to 500 parts by mass, and more preferably 10 to 500 parts by mass, in terms of the removal efficiency of the main product and by-products.

[0066] The method of contact between the carbon dioxide adsorbent and water is not particularly limited, and any conventionally known and suitable method can be applied, such as dropping, spraying, or atomizing water onto the carbon dioxide adsorbent, or immersing the carbon dioxide adsorbent in water and mixing it by stirring as appropriate. The contact temperature between the carbon dioxide adsorbent and water is not particularly limited, and can be, for example, 5 to 50°C, but is preferably 5 to 30°C in terms of the removal efficiency of the main product and by-products, as well as workability. The contact time can be appropriately determined considering the removal efficiency, etc., and can be, for example, 10 minutes to 24 hours.

[0067] In the removal process, after bringing the carbon dioxide adsorbent into contact with water as described above, the carbon dioxide adsorbent is separated from the water and dried as needed. The method for separating the carbon dioxide adsorbent from water is not particularly limited, but examples include filtration, removal from water, and wiping. Various conventional drying methods can be applied to dry the carbon dioxide adsorbent after contact with water. For example, a method of heating at a temperature of preferably 100 to 250°C for 1 to 12 hours using any suitable drying apparatus (e.g., oven, muffle furnace) can be used. Note that in the regeneration method of the present invention, since the carbon dioxide adsorbent is brought into contact with an alkali metal carbonate solution after the removal process, it is not necessary to dry the carbon dioxide adsorbent until its mass changes.

[0068] The atmosphere in which the carbon dioxide adsorbent is brought into contact with water, and the atmosphere in which it is separated or dried, are not particularly limited, and examples include an air atmosphere and an inert gas atmosphere.

[0069] In the removal process, the main and by-products contained in, adsorbed, or attached to the used carbon dioxide adsorbent are removed and washed, and the aforementioned metal compounds, or porous materials to which the metal compounds are attached (sometimes referred to as "recovered adsorbent" for convenience), are recovered from the used carbon dioxide adsorbent.

[0070] <Step of contact with alkali metal carbonate solution (re-adhesion step)> In the regeneration method of the present invention, the next step is to contact the recovered adsorbent obtained in the removal step with an alkali metal carbonate solution (re-adhesion step). The alkali metal carbonate solution used in the re-adhesion step is not particularly limited as long as it is a solution containing the alkali metal carbonate described above. The alkali metal carbonate contained in the alkali metal carbonate solution used in the re-adhesion step may be the same as or different from the alkali metal carbonate that was attached to the used carbon dioxide adsorbent. The alkali metal carbonate solution used in the re-adhesion step can be the same alkali metal carbonate solution used in the method for producing the carbon dioxide adsorbent. The contact method and contact conditions in the re-adhesion step are not particularly limited, and the contact method and contact conditions between the metal compound and the alkali metal carbonate solution in the method for producing the carbon dioxide adsorbent, or the contact method and contact conditions between the carbon dioxide adsorbent precursor and the alkali metal carbonate solution in the method for producing the carbon dioxide adsorbent, can be applied.

[0071] In the re-adhesion step, it is preferable to heat the recovered adsorbent that has been in contact with the alkali metal carbonate solution (drying step), and the heated recovered adsorbent can also be calcined as appropriate. The heating step and calcination step of the recovered adsorbent are not particularly limited, and the heating step and calcination step in the method for manufacturing carbon dioxide adsorbent, or the heating step and calcination step in the method for contacting the carbon dioxide adsorbent precursor with the alkali metal carbonate solution in the method for manufacturing carbon dioxide adsorbent, can be applied.

[0072] The re-adhesion process allows alkali metal carbonates to be attached to the surface of the recovered adsorbent, and even to the pores of the recovered adsorbent, thereby regenerating the carbon dioxide adsorbent.

[0073] The characteristics and physical properties of the carbon dioxide adsorbent regenerated by the regeneration method of the present invention, such as the average pore diameter, alkali metal element content, and element content in the metal compound, are not particularly limited and can be set as appropriate. Preferably, the characteristics and physical properties of the regenerated carbon dioxide adsorbent are the same as (within the above range) as those of the carbon dioxide adsorbent used in the carbon dioxide adsorption separation method (unused carbon dioxide adsorbent), in terms of carbon dioxide adsorption performance.

[0074] [Applications of Regenerated Carbon Dioxide Adsorbent] Since the carbon dioxide adsorbent regenerated by the regeneration method of the present invention has recovered its carbon dioxide adsorption performance, it can be suitably used for carbon dioxide adsorption. Preferably, it can be used in a carbon dioxide adsorption and separation method, and can also be used in combination with a carbon dioxide adsorption step and a separation step in a continuous carbon dioxide adsorption and separation method. Specific applications in the industrial sector include the recovery of carbon dioxide from exhaust gases emitted from chemical plants, coal and natural gas power plants, steel mills (e.g., blast furnaces and converters), cement plants (e.g., kilns), waste treatment plants, paint plants, natural gas refineries, LNG plants, and semiconductor manufacturing plants (e.g., semiconductor manufacturing processes). In the transportation and logistics sector, it can be used for the recovery of carbon dioxide from exhaust gases emitted from automobiles, buses, trains, ships, aircraft, etc. Furthermore, in the field of air purification and environmental control, examples include air purifiers, air conditioners, the interiors of automobiles, spacecraft and space stations, submarines and ships, buses and trains, aircraft, air conditioners and water heaters for offices, buildings, schools, restaurants and kitchens, and agricultural greenhouses, as well as the capture of carbon dioxide emissions from the atmosphere.

[0075] <Method for adsorption and separation of carbon dioxide> The method for adsorption and separation of carbon dioxide using carbon dioxide adsorbent regenerated by the regeneration method of the present invention is not particularly limited, and includes, for example, an adsorption and separation method comprising an adsorption step of bringing the regenerated carbon dioxide adsorbent into contact with a gas containing carbon dioxide, and a separation step of heating the carbon dioxide adsorbent, which has adsorbed carbon dioxide in this adsorption step, to 50 to 900°C. The adsorption step is an example of the adsorption step using regenerated carbon dioxide adsorbent in the continuous adsorption and separation method of carbon dioxide of the present invention, which will be described later. The separation step is an example of the separation step in the continuous adsorption and separation method of carbon dioxide of the present invention, which will be described later (including the separation step in the carbon dioxide adsorption and separation method of the present invention, which will be described later).

[0076] [[Continuous Adsorption and Separation Method for Carbon Dioxide of the Present Invention]] The continuous adsorption and separation method for carbon dioxide of the present invention (hereinafter sometimes referred to as "the continuous adsorption and separation method of the present invention") is a method for continuous adsorption and separation of carbon dioxide, in which an adsorption step of bringing a carbon dioxide adsorbent into contact with a gas containing carbon dioxide and a separation step of heating the carbon dioxide adsorbent that has adsorbed carbon dioxide in the adsorption step to 50 to 900°C are repeated in this order, wherein after performing at least one adsorption step and one separation step, the carbon dioxide adsorbent after the separation step is regenerated by the regeneration method of the present invention, and then at least one adsorption step of bringing the regenerated carbon dioxide adsorbent into contact with a gas containing carbon dioxide and a separation step of heating the carbon dioxide adsorbent that has adsorbed carbon dioxide in the adsorption step to 50 to 900°C are performed. In the continuous adsorption and separation method of the present invention, the number of cycles of the adsorption and separation steps performed before the regeneration method of the present invention is carried out, and the number of cycles of the adsorption and separation steps performed after the regeneration method of the present invention are not particularly limited and can be appropriately determined according to the amount of decrease in the adsorption performance of the carbon dioxide adsorbent, etc.

[0077] The continuous adsorption and separation method of the present invention allows the adsorption and separation processes to be carried out continuously over multiple cycles because the regeneration method of the present invention is performed between the adsorption and separation cycles. In the present invention, "continuous" and "repeatedly" mean performing predetermined processes one after another (repeatedly), and do not mean performing them continuously in time, or not performing other processes between predetermined processes. Therefore, in the continuous adsorption and separation method of the present invention, a series of processes of the adsorption and separation processes, and further a series of processes of the separation process, regeneration method, and adsorption process, can be performed with time intervals, for example, with stops or pauses, or with other processes in between, as long as the effects of the present invention are not impaired.

[0078] The carbon dioxide adsorbent used in the continuous adsorption separation method of the present invention is a carbon dioxide adsorbent containing an alkali metal carbonate containing at least one alkali metal element and a metal compound containing at least one element selected from the group consisting of Group 3 and Group 4 elements of the periodic table. The carbon dioxide adsorbent used in the continuous adsorption separation method of the present invention may be the unused carbon dioxide adsorbent described above, or it may be a carbon dioxide adsorbent regenerated by the regeneration method of the present invention. The regenerated carbon dioxide adsorbent used in the continuous adsorption separation method of the present invention is the same as the regenerated carbon dioxide adsorbent used in the carbon dioxide adsorption separation method described above. It is preferable that the carbon dioxide adsorbent used in the first adsorption step is the same as the unused carbon dioxide adsorbent described above.

[0079] (Adsorption Step) The adsorption step in the continuous adsorption separation method of the present invention is a step of bringing a carbon dioxide adsorbent into contact with a gas containing carbon dioxide, thereby adsorbing the carbon dioxide in the gas onto the carbon dioxide adsorbent. The carbon dioxide adsorbent used in the adsorption step is determined according to, for example, the number of times of implementation in the continuous adsorption separation method of the present invention. For example, the carbon dioxide adsorbent used in the first adsorption step in the continuous adsorption separation method of the present invention is usually an unused carbon dioxide adsorbent or a regenerated carbon dioxide adsorbent, and the carbon dioxide adsorbent used in the adsorption step performed after the separation step described below is a carbon dioxide adsorbent that has adsorbed carbon dioxide or a regenerated carbon dioxide adsorbent, and the carbon dioxide adsorbent used in the adsorption step performed after the regeneration method of the present invention is a regenerated carbon dioxide adsorbent. Note that an unused carbon dioxide adsorbent can also be used instead of a regenerated carbon dioxide adsorbent in one or several of the adsorption steps performed multiple times.

[0080] In the adsorption step, the gas brought into contact with the carbon dioxide adsorbent only needs to contain carbon dioxide and may also contain other components. Examples of the gas containing carbon dioxide include, for example, air and a gas having a higher carbon dioxide concentration (partial pressure) than air. Further, since the regeneration method of the present invention and the continuous adsorption separation method of the present invention can regenerate the used carbon dioxide adsorbent, a gas containing nitrogen oxides (NOx) and / or sulfur oxides (SOx) at a higher concentration than air can be used. Examples of such a gas include gases discharged from various uses described in the above-mentioned uses of the regenerated carbon dioxide adsorbent, such as factory exhaust gas and power plant exhaust gas. The concentration (partial pressure) of carbon dioxide in the gas is not particularly limited and can be about 4.0×10 ２ ppm in the atmosphere, or can be a higher concentration. For example, the concentration of carbon dioxide in the gas can be 4.0×10 ２ to 2.0×10 ５ ppm, and is preferably 4.0×10 ２ to 1.0×10 ５ ppm, and more preferably 4.0×10 ２ to 5.0×10 ４ ppm.

[0081] The components other than carbon dioxide in a gas containing carbon dioxide are not particularly limited, but examples include water vapor, nitrogen, hydrogen, carbon monoxide, hydrocarbons such as methane, and various gases such as nitrogen oxides (NOx) and sulfur oxides (SOx). As a gas containing components other than carbon dioxide, a gas containing water vapor is one preferred embodiment, a gas containing at least one selected from the group consisting of nitrogen oxides and sulfur oxides is also a preferred embodiment in that it allows effective use of the regeneration method of the present invention, and a gas containing water vapor and at least one selected from the group consisting of nitrogen oxides and sulfur oxides is a more preferred embodiment. Examples of nitrogen oxides (NOx) include nitric oxide (NO) and nitrogen dioxide (NOx). ２ ), nitrogen trioxide (NO ３ ), nitrous oxide (dinitrogen monoxide, N ２ O), dinitrogen trioxide (N ２ O ３ ), dinitrogen tetroxide (N ２ O ４ ), dinitrogen pentoxide (N ２ O ５ Examples include sulfur oxides (SOx), such as sulfur monoxide (SO) and sulfur dioxide (sulfurous acid gas, SO). ２ ), sulfur trioxide (SO ３ Examples include the following. The concentrations (partial pressures) of other components in the gas are not particularly limited. For example, the concentration of nitrogen oxides (NOx) in the gas is 0 to 1.2 × 10⁻⁶. ３ It can be expressed in ppm, and ranges from 0 to 5.0 × 10⁻¹⁰. ２ It is preferably ppm, and 0 to 1.5 × 10 ２ It is preferable that the concentration be ppm. The concentration of sulfur oxides (SOx) in the gas is 0 to 1.2 × 10⁻¹⁰. ４ It can be expressed in ppm, and ranges from 0 to 5.0 × 10⁻¹⁰. ３ It is preferable that the concentration be ppm. The concentration of water vapor in the gas is not particularly limited and can be the concentration that results in the humidity in the adsorption process described later, for example, 4.0 × 10 ２ ~2.0 x 10 ５ It can be expressed as ppm, 4.0 × 10 ２ ~1.0 x 10 ５It is preferable that the concentration be ppm. The gas may contain one or more components other than carbon dioxide.

[0082] In the adsorption process, examples of gases to be brought into contact with the carbon dioxide adsorbent include air, various exhaust gases as described in the section on the applications of the recycled carbon dioxide adsorbent, and air, various factory exhaust gases, power plant exhaust gases, etc., can be suitably used.

[0083] The temperature in the adsorption process (the temperature at which the carbon dioxide adsorbent is used) is not particularly limited, but is preferably 0 to 100°C, and more preferably 5 to 80°C. In the adsorption process, it is preferable to bring the carbon dioxide adsorbent into contact with a gas containing carbon dioxide at a temperature of 100°C or lower (e.g., room temperature) as described above, but it can also be brought into contact with the gas at a temperature higher than 100°C. The temperature in the adsorption process can be adjusted by heating or cooling the carbon dioxide adsorbent and / or the gas using a heater or cooler. When heating or cooling the carbon dioxide adsorbent or the gas, it is preferable to make effective use of the heat, such as by exchanging heat with the gas discharged from the separation process. The humidity in the adsorption process (the humidity at which the carbon dioxide adsorbent is used) is not particularly limited, but since water may be necessary for carbon dioxide adsorption, it is preferably 1 to 100% RH, and more preferably 5 to 90% RH. The humidity in the adsorption process can be adjusted by being in the presence of moisture (water or water vapor), or by adding moisture to the gas by bubbling, etc. Furthermore, if the gas contains water vapor, the water vapor in the gas can be used to adjust the humidity.

[0084] The conditions in the adsorption process can be appropriately determined, such as the concentration of carbon dioxide in the gas containing carbon dioxide, and the contact amounts of carbon dioxide and gas with the carbon dioxide adsorbent, within a range where the adsorption amount is less than or equal to the maximum (theoretical) adsorption amount of carbon dioxide by the carbon dioxide adsorbent.

[0085] The method of bringing the carbon dioxide adsorbent into contact with the gas containing carbon dioxide in the adsorption process is not particularly limited. For example, this could involve circulating the gas containing carbon dioxide through a container containing the carbon dioxide adsorbent, or placing the carbon dioxide adsorbent in the gas containing carbon dioxide to bring it into direct contact.

[0086] In a method of bringing a carbon dioxide adsorbent into contact with a gas containing carbon dioxide in a flow manner, the supply amount (space velocity SV) of the gas containing carbon dioxide at standard conditions (0°C, 0.1 MPa) is not particularly limited, but is preferably 10 to 1.0 × 10 ７ / h, more preferably 1.0 × 10 ２ ~5.0 x 10 ６ / h, and more preferably 1.0 × 10 ３ ~1.0 x 10 ６ / h. Let the spatial velocity SV be 10 or greater, then 1.0 × 10 ７ Setting the rate to less than / h can improve the carbon dioxide adsorption efficiency per unit time. Furthermore, while there are no particular restrictions on the supply rate (linear velocity LV) of the gas containing carbon dioxide under standard conditions (0°C, 0.1 MPa), it is preferably 1.0 × 10⁻¹⁶ to improve the contact efficiency between the carbon dioxide adsorbent and the gas containing carbon dioxide. －４ ~100 m / s, more preferably 1.0 × 10 －３ The pressure is approximately 10 m / s. The processing pressure on the carbon dioxide adsorbent is preferably 0.1 to 5 MPa, and more preferably 0.1 to 1 MPa. In the flow-through method, the gas containing carbon dioxide can be flowed together with the carrier gas. The carrier gas is preferably a gas that is not adsorbed by the carbon dioxide adsorbent, such as an inert gas, and specifically, noble gases such as nitrogen, helium, and argon. The supply amount (space velocity SV) and supply rate (linear velocity LV) of the carrier gas are not particularly limited and can be appropriately determined considering the above supply amount of gas containing carbon dioxide.

[0087] (Separation Step) The separation step in the continuous adsorption separation method of the present invention is performed on the carbon dioxide adsorbent that has adsorbed carbon dioxide in the adsorption step. The heating temperature in the separation step is set to a temperature that does not impair the function of the carbon dioxide adsorbent, the equipment containing the carbon dioxide adsorbent, etc. For example, it can be 50 to 900°C, preferably 50 to 600°C, more preferably 50 to 300°C, and even more preferably 120 to 300°C. The processing pressure is not particularly limited, but is preferably 0.001 to 5 MPa, and more preferably 0.01 to 1 MPa.

[0088] The gas (atmosphere) used during heating in the separation process is not particularly limited. For example, air (atmosphere) can be used as the heating atmosphere. From the viewpoint of more efficiently separating and removing carbon dioxide, an inert gas such as nitrogen gas may be used. Furthermore, the inventors have found that carbon dioxide adsorbed on the carbon dioxide adsorbent can be separated and desorbed by heating the carbon dioxide adsorbent to the above heating temperature, even in an atmosphere of carbon dioxide-containing gas. Therefore, the separation process can also be carried out by heating the carbon dioxide adsorbent to the above temperature in an atmosphere of carbon dioxide-containing gas. The concentration of carbon dioxide in the gas containing carbon dioxide used at this time can be appropriately determined within the same range as the concentration of carbon dioxide in the gas containing carbon dioxide used in the adsorption process, taking into consideration the amount of carbon dioxide to be separated, and it is preferable that the concentration be higher than the concentration of carbon dioxide in the atmosphere, for example, 4.0 × 10⁻⁶. ２ It is preferable to have a concentration of ppm to 100%, and 4.0 × 10 ２ ~2.0 x 10 ５ A ppm concentration is more preferable. Carbon dioxide gas can also be used as the gas containing carbon dioxide.

[0089] The humidity in the separation process (humidity at which the carbon dioxide adsorbent is used) is not particularly limited, and can be, for example, 1 to 100% RH, with 5 to 90% RH being preferred. The humidity in the adsorption process is adjusted as described above. The method of bringing the carbon dioxide adsorbent into contact with the gas in the separation process is not particularly limited. For example, this could be done by circulating the gas through a container containing the carbon dioxide adsorbent, or by placing the carbon dioxide adsorbent in the gas and bringing it into direct contact.

[0090] In a method of bringing a carbon dioxide adsorbent into contact with a gas in a flow manner, the amount of gas supplied (space velocity SV) under standard conditions (0°C, 0.1 MPa) is not particularly limited, but is preferably 10 to 1.0 × 10 ７ / h, more preferably 1.0 × 10 ２ ~5.0 x 10 ６ / h, and more preferably 1.0 × 10 ３ ~1.0 x 10 ６ / h. Let the spatial velocity SV be 10 or greater, then 1.0 × 10 ７ Setting it to less than / h can further improve the carbon dioxide separation efficiency per unit time. Furthermore, while there are no particular restrictions on the supply rate (linear velocity LV) of the gas containing carbon dioxide under standard conditions (0°C, 0.1 MPa), it is preferably 1.0 × 10⁻¹⁶ to improve the contact efficiency between the carbon dioxide adsorbent and the gas containing carbon dioxide. －４ ~100 m / s, more preferably 1.0 × 10 －３ The pressure is approximately 10 m / s. The processing pressure on the carbon dioxide adsorbent is preferably 0.001 to 5 MPa, and more preferably 0.01 to 1 MPa. In this invention, the lower limit of the processing pressure can also be 0.1 MPa. In the flow-through method, the gas can be flowed together with the carrier gas. The carrier gas and its supply amount are the same as the gas used in the adsorption process and its supply amount.

[0091] In the separation process, the carbon dioxide separated from the carbon dioxide adsorbent can be recovered by any suitable conventional method. Specifically, examples include recovering the separated carbon dioxide as dry ice by pressurizing, compressing, and cooling it; recovering it as a gas with an increased carbon dioxide concentration using a separation membrane; and recovering it as a gas with an increased carbon dioxide concentration by adsorbing and removing components other than carbon dioxide. The components other than carbon dioxide are those mentioned above.

[0092] (Regeneration Method of the Present Invention) As described above, when the adsorption performance of the carbon dioxide adsorbent decreases as a result of performing at least one adsorption step and one separation step, the carbon dioxide adsorbent regeneration method is performed before the adsorption step of the next cycle. The carbon dioxide adsorbent regeneration method is the same as the regeneration method of the present invention described above. In the continuous adsorption and separation method of the present invention, the timing of performing the carbon dioxide adsorbent regeneration method (number of adsorption and separation steps performed) can be appropriately determined according to the amount of decrease in the adsorption performance of the carbon dioxide adsorbent, the amount of carbon dioxide adsorbed, the work efficiency, etc. For example, it can be when the amount of carbon dioxide adsorbed by the initial carbon dioxide adsorbent (the carbon dioxide adsorbent used in the first adsorption step, or the carbon dioxide adsorbent used in the first adsorption step after regeneration) has decreased to, for example, 10%, and preferably to 50%.

[0093] (Adsorption and separation processes using recycled carbon dioxide adsorbent) After regenerating the carbon dioxide adsorbent whose carbon dioxide adsorption performance has deteriorated in this manner, at least one carbon dioxide adsorption process and one carbon dioxide separation process are performed using the recycled carbon dioxide adsorbent. The adsorption and separation processes using recycled carbon dioxide adsorbent are the same as the adsorption and separation processes performed before the regeneration of the carbon dioxide adsorbent, except that recycled carbon dioxide adsorbent is used.

[0094] In the continuous adsorption separation method of the present invention, the number of times the regeneration method of the present invention is performed is not particularly limited as long as it is at least once, and can be appropriately determined according to work efficiency and other factors. Since the regeneration method of the present invention can restore the adsorption performance of the carbon dioxide adsorbent to a level equivalent to the desired adsorption performance, the regeneration method of the present invention can be performed many times, and the continuous adsorption separation method of the carbon dioxide adsorbent, which includes multiple regeneration methods of the present invention, can be carried out semi-permanently.

[0095] [[The present invention's method for adsorbing and separating carbon dioxide]] The present invention's method for adsorbing and separating carbon dioxide (which may be referred to as "the present invention's method for adsorption and separation" in this specification) comprises an adsorption step of bringing a carbon dioxide adsorbent into contact with a gas containing carbon dioxide, and a separation step of heating the carbon dioxide adsorbent, which has adsorbed carbon dioxide in the adsorption step, to 50 to 900°C in an atmosphere of gas containing carbon dioxide.

[0096] The carbon dioxide adsorbent used in the adsorption separation method of the present invention is a carbon dioxide adsorbent containing an alkali metal carbonate containing at least one alkali metal element and a metal compound containing at least one element selected from the group consisting of Group 3 and Group 4 elements of the periodic table, and is the same as the carbon dioxide adsorbent used in the continuous adsorption separation method of carbon dioxide described above. This carbon dioxide adsorbent may be unused or may be regenerated by the regeneration method of the present invention.

[0097] (Adsorption step) The adsorption step in the adsorption separation method of the present invention is the same as the adsorption step in the continuous adsorption separation method of the present invention.

[0098] (Separation Process) The separation process in the adsorption separation method of the present invention is the same as the separation process in the continuous adsorption separation method of the present invention, except that a gas containing carbon dioxide is used as the gas used in the separation process instead of air or an inert gas, that is, the process is carried out under an atmosphere of a gas containing carbon dioxide. The gas containing carbon dioxide used is the same as the gas containing carbon dioxide used in the separation process of the continuous adsorption separation method of the present invention described above. The method for recovering the carbon dioxide separated from the carbon dioxide adsorbent is also the same as the recovery method in the separation process described above.

[0099] The adsorption separation method and the continuous adsorption separation method of the present invention can be carried out with or without attaching the carbon dioxide adsorbent to an appropriate device. The device to which the carbon dioxide adsorbent is attached is not particularly limited and is appropriately determined according to the application form of the adsorption separation method and the continuous adsorption separation method of the present invention. For example, devices to which the carbon dioxide adsorbent is attached include, for example, air purifiers, air conditioners, building materials, various containers (e.g., filters, cartridges), as well as factory exhaust gas equipment for discharged from chemical plants, exhaust gas equipment for discharged from power plants, and gas transfer equipment for carbon dioxide-containing gases. Various known devices (filters, cartridges) can be applied without particular limitation to the device (filter, cartridge) to which the carbon dioxide adsorbent is attached, and for example, the contents described in Patent Document 1 can be appropriately referred to, and the contents therein are incorporated as part of this specification.

[0100] Furthermore, when the carbon dioxide adsorbent is attached to the apparatus and the adsorption separation method and the continuous adsorption separation method of the present invention are performed, the separation process can be carried out with the adsorbent attached to the apparatus or with the adsorbent removed from the apparatus. Also, when the adsorption separation method and the continuous adsorption separation method of the present invention are carried out in a flow-through format, the gas flowing through the apparatus can be switched to the gas used in the separation process while the carbon dioxide adsorbent is attached to the apparatus.

[0101] The carbon dioxide adsorbent used in the present invention can be suitably applied, for example, to a method for recovering carbon dioxide from a gas containing carbon dioxide, and to a method for selectively removing and recovering carbon dioxide from a gas with a high concentration (partial pressure) of carbon dioxide. More preferably, it can be applied to the continuous adsorption separation method and the carbon dioxide adsorption separation method of the present invention. Furthermore, the carbon dioxide adsorbent used in the present invention can be suitably applied, for example, to a carbon dioxide recovery device for recovering carbon dioxide from a gas containing carbon dioxide or for selectively removing and recovering carbon dioxide from a gas with a particularly high concentration (partial pressure) of carbon dioxide.

[0102] The following are examples of the present invention, but the present invention is not limited thereto.

[0103] <Manufacturing of Carbon Dioxide Adsorbent (Base Material)> An aqueous solution was prepared by completely dissolving potassium carbonate (anhydrous) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in an amount of 2.5 mmol per gram of zirconium oxide in molded zirconium oxide pellets (Daiichi Rare Elements Chemical Industry, Z-3203 (product name)). The potassium carbonate aqueous solution was evenly dropped and brought into contact with the zirconium oxide pellets (contact step), and then dried at room temperature for 1 hour. Next, the material was dried in air at 40°C using a multi-oven (ETTAS, MOV300S (product name)) until there was no change in mass (drying step) to obtain (unused) carbon dioxide adsorbent (base material).

[0104] <Evaluation Method for Carbon Dioxide Adsorbent> The amount of carbon dioxide adsorbed by the carbon dioxide adsorbent in the examples was evaluated and quantified based on a calibration curve prepared as described below, using a catalyst analyzer (BELCAT II (product name) manufactured by Microtrac-Bell Co., Ltd.) and a micro GC (CP-4900 (product name) manufactured by Agilent) installed on the outlet gas line of this analyzer. The analytical conditions are as follows: - Analytical Conditions - Carrier gas: Helium Column: 10 m PPQ Unheated Column temperature: 100°C Pressure: 170 kPa

[0105] <Calibration Curve Creation> To quantify the amount of carbon dioxide adsorbed on the carbon dioxide adsorbent, a calibration curve was created using the following procedure. An empty measurement cell was set in the catalyst analyzer described above, and a mixture of 2 vol% carbon dioxide gas and helium was introduced using the gas flow meter built into the instrument from 0 to 25 cm. ３ (0°C, 0.1013 MPa (absolute)) / min, helium gas at 75-100 cm ３ (0°C, 0.1013 MPa (absolute)) / min, total 100 cm ３ The gas was circulated at a rate of [number] minutes, and gas analysis was performed. From the resulting GC chart, the peak position of carbon dioxide was identified, the area value was recorded, and a calibration curve was created for the volume percentage of carbon dioxide in the gas relative to the GC area value.

[0106] [Experimental Example 1: Regeneration of Carbon Dioxide Adsorbent] <Evaluation 1: Evaluation of Carbon Dioxide Adsorption Amount in Carbon Dioxide Adsorbent (Base Material)> 0.2 g of the carbon dioxide adsorbent (base material) powder, obtained by crushing the carbon dioxide adsorbent (base material) manufactured as described above and sieving it to 500 μm or less, was placed in the catalyst analyzer described above. Then, helium gas was introduced at 100 cm³. ３ The carbon dioxide adsorbent was pre-treated at 150°C for 1 hour while flowing (0°C, 0.1013 MPa (absolute)) / min at a heating rate of 10°C / min. Then, after cooling to 50°C, a mixture of 2 vol% carbon dioxide gas and helium was added in a 15 cm³ solution. ３ (0°C, 0.1013 MPa (absolute)) / min, helium gas at 85 cm ３ The adsorption process was carried out by flowing (0°C, 0.1013 MPa (absolute)) / min. Of the gases flowed, 50 cm³ of helium gas was used. ３ The amount per minute was supplied by bubbling water at 35°C and passing it through a condenser set to 25°C (space velocity (SV) was 2.2 × 10⁻¹⁶). ４ / h, linear velocity (LV) is 1.3 × 10⁻⁶ －２ (m / s). The outlet gas was analyzed with a microGC approximately every minute to calculate the carbon dioxide concentration in the outlet gas. The concentration difference obtained by subtracting the carbon dioxide concentration in the outlet gas from the carbon dioxide concentration in the inlet gas was used to calculate the amount of gas flowed per minute (here, 100 cm³). ３ The amount of carbon dioxide gas adsorbed onto the powdered carbon dioxide adsorbent (base material) was determined by multiplying by (0°C, 0.1013 MPa (absolute)). The values ​​of carbon dioxide gas amounts on the powdered carbon dioxide adsorbent (base material) obtained from a 60-minute measurement were accumulated to determine the total amount of carbon dioxide adsorbed per gram of carbon dioxide adsorbent (molecule) [total amount of carbon dioxide adsorbed (molecule) / g - carbon dioxide adsorbent]. This value is listed in Table 1 as "Evaluation 1 (base material)".

[0107] <Evaluation 2: Evaluation of carbon dioxide adsorption amount in nitrogen dioxide treated carbon dioxide adsorbent> (Nitrogen dioxide treatment) 4.2 g of the carbon dioxide adsorbent (base material) manufactured as described above was placed in the catalyst analyzer described above. The temperature was set to 50°C, and a mixed gas of nitrogen dioxide and helium at a volume of 225-275 ppm was introduced at 100 cm³. ３ The material was passed through a flow chamber at (0°C, 0.1013 MPa (absolute)) / min for 3 hours to produce carbon dioxide adsorbent pellets after nitrogen dioxide treatment.

[0108] (Evaluation of adsorption process and carbon dioxide adsorption amount) Next, 0.2 g of the prepared nitrogen dioxide treated carbon dioxide adsorbent was crushed and sieved to 500 μm or less, and placed in a catalyst analyzer. The adsorption process was carried out in the same manner as in <Evaluation 1> above, and the amount of carbon dioxide adsorbed at this time was determined. The total amount of carbon dioxide adsorbed per gram of carbon dioxide adsorbent (molecule) obtained from the 60-minute measurement [total amount of carbon dioxide adsorbed (molecule) / g - carbon dioxide adsorbent] was determined as the total amount of carbon dioxide adsorbed per gram of powdered nitrogen dioxide treated carbon dioxide adsorbent (molecule), and this value is listed in Table 1 as "Evaluation 2 (after nitrogen dioxide treatment)".

[0109] <Evaluation 3: Evaluation of carbon dioxide adsorption amount in the regenerated carbon dioxide adsorbent> (Regeneration treatment of carbon dioxide adsorbent) The carbon dioxide adsorbent (pellets) prepared in <Evaluation 2> above after nitrogen dioxide treatment was measured into a beaker, and 10 parts by mass of ultrapure water (Millipore water) were added to 1 part by mass of carbon dioxide adsorbent. A stirring bar was placed therein, and the mixture was stirred at 25°C for 1 hour using a stirrer. After stirring, the mixture was filtered using filter paper (size 5A), and the obtained carbon dioxide adsorbent was dried in a muffle furnace at 100°C for 2 hours (removal step of the regeneration method of the present invention). The re-adhesion step of the regeneration method of the present invention was performed on the dried carbon dioxide adsorbent (zirconium oxide) in the same manner as the contact step and drying step in <Manufacturing of carbon dioxide adsorbent (base material)> above to adsorb potassium carbonate, thereby obtaining the carbon dioxide adsorbent (regenerated material) after regeneration treatment.

[0110] (Evaluation of adsorption process and carbon dioxide adsorption amount) Next, 0.2 g of the powdered carbon dioxide adsorbent (recycled material) obtained by crushing the regenerated carbon dioxide adsorbent (recycled material) and sieving it to 500 μm or less was placed in a catalyst analyzer, and the adsorption process was carried out in the same manner as in <Evaluation 1> above, and the amount of carbon dioxide adsorbed at this time was determined. The total amount of carbon dioxide adsorbed per gram of regenerated carbon dioxide adsorbent (recycled material) obtained from the measurement over 60 minutes was calculated as the total amount of carbon dioxide adsorbed per gram of powdered carbon dioxide adsorbent (recycled material) [total amount of carbon dioxide adsorbed (molecule) / g - carbon dioxide adsorbent], and this value was listed in Table 1 as "Evaluation 3 (recycled material)".

[0111]

[0112] As shown in Table 1, although nitrogen dioxide treatment reduces the adsorption performance (adsorption amount) of the carbon dioxide adsorbent (Evaluation 2), the regeneration method of the present invention (water washing) removes components derived from potassium carbonate adsorbed on the nitrogen dioxide-treated carbon dioxide adsorbent, and then re-supports (adheres) potassium carbonate, thereby regenerating the adsorption performance of the carbon dioxide adsorbent (Evaluation 3). By using this regeneration method, it is possible to reuse zirconium dioxide, which accounts for the majority of the material composition forming the carbon dioxide adsorbent used in Experimental Example 1. Furthermore, since zirconium dioxide is generally more expensive than potassium carbonate, the amount of zirconium dioxide waste can be reduced, and a low-cost carbon dioxide adsorbent can be provided. In Experimental Example 1, nitrogen dioxide, one of the nitrogen oxides, was used as a component other than carbon dioxide in the gas that came into contact with the carbon dioxide adsorbent. However, it is presumed that even if nitrogen oxides other than nitrogen dioxide or various sulfur oxides are used as the component other than carbon dioxide, the adsorption performance of the carbon dioxide adsorbent can be regenerated by the regeneration method of the present invention, similar to the results for nitrogen dioxide.

[0113] [Experimental Example 2: Separation of Carbon Dioxide Using Carbon Dioxide] <Evaluation 4: Carbon Dioxide Desorption Treatment 1 Using a Gas Containing Carbon Dioxide> (Carbon Dioxide Separation Process) The carbon dioxide adsorbent (powder) obtained by the adsorption process in <Evaluation 3> of Experimental Example 1 above is heated to 150°C at a heating rate of 10°C / min using a catalyst analyzer, while a mixed gas of 2 volume% carbon dioxide gas and helium is added in 15 cm³. ３ (0°C, 0.1013 MPa (absolute)) / min, helium gas at 85 cm ３ The separation process was carried out by flowing (0°C, 0.1013 MPa (absolute)) / min for 1 hour. Of the gases flowed, helium gas was measured at 50 cm³. ３ The gas was bubbled into 35°C water and supplied through a condenser set to 25°C. In this way, a carbon dioxide separation process was carried out using a gas containing carbon dioxide, and a carbon dioxide adsorbent for carbon dioxide desorption treatment 1 was obtained.

[0114] (Evaluation of adsorption process and carbon dioxide adsorption amount) Next, 0.2 g of the carbon dioxide adsorbent obtained from carbon dioxide desorption treatment 1 was placed in a catalyst analyzer, the temperature of the carbon dioxide adsorbent was set to 50°C, and the adsorption process was carried out in the same manner as in <Evaluation 1> above, and the amount of carbon dioxide adsorbed at this time was determined. The total amount of carbon dioxide adsorbed per gram of carbon dioxide adsorbent (molecule) obtained from the measurement over 60 minutes [total amount of carbon dioxide adsorbed (molecule) / g - carbon dioxide adsorbent] was used to determine the total amount of carbon dioxide adsorbed per gram of carbon dioxide adsorbent (molecule) from carbon dioxide desorption treatment 1, and this value was recorded in Table 2 as "Evaluation 4 (Desorption study by carbon dioxide 1)".

[0115] <Evaluation 5: Carbon dioxide desorption treatment using a gas containing carbon dioxide 2> (Adsorption process) The carbon dioxide adsorbent (base material) produced in Experimental Example 1 as described above was crushed and sieved to 500 μm or less, and 0.2 g of the resulting powdered carbon dioxide adsorbent was placed in a catalyst analyzer. Next, helium gas was added at 100 cm³. ３The carbon dioxide adsorbent was pre-treated at 150°C for 1 hour while flowing (0°C, 0.1013 MPa (absolute)) / min at a heating rate of 10°C / min. Then, after cooling to 50°C, a mixture of 2 vol% carbon dioxide gas and helium was added in a 15 cm³ solution. ３ (0°C, 0.1013 MPa (absolute)) / min, helium gas at 85 cm ３ The adsorption process was carried out by flowing (0°C, 0.1013 MPa (absolute)) / min for 1 hour. Of the gases flowed, helium gas was used for 50 cm³. ３ The water was supplied by bubbling it in 35°C water and passing it through a condenser set to 25°C.

[0116] (Carbon dioxide separation process) Following the above adsorption process, the temperature of the carbon dioxide adsorbent is raised to 150°C while 100% carbon dioxide gas is separated into 100 cm³. ３ The separation process was carried out by flowing the mixture at (0°C, 0.1013 MPa (absolute)) / min for 1 hour. In this way, a carbon dioxide separation process was performed using a gas containing carbon dioxide, and a carbon dioxide adsorbent for carbon dioxide desorption treatment 2 was obtained.

[0117] (Evaluation of adsorption process and carbon dioxide adsorption amount) Next, the temperature of the carbon dioxide adsorbent in the catalyst analyzer was set to 50°C, and the adsorption process was performed in the same manner as in <Evaluation 1> above, and the amount of carbon dioxide adsorbed at this time was determined. The total amount of carbon dioxide adsorbed per gram of carbon dioxide adsorbent (molecule) obtained from the 60-minute measurement [total amount of carbon dioxide adsorbed (molecule) / g - carbon dioxide adsorbent] was used to determine the total amount of carbon dioxide adsorbed per gram of carbon dioxide adsorbent (molecule) for carbon dioxide desorption treatment 2, and this value was recorded in Table 2 as "Evaluation 5 (carbon dioxide desorption study 2)".

[0118]

[0119] The results shown in Table 2 indicate that by increasing the temperature of the carbon dioxide adsorbent, the carbon dioxide adsorbed on the adsorbent can be completely desorbed, even when using a gas with the same carbon dioxide concentration as the gas composition used in the adsorption process (Evaluation 4). Furthermore, even when using 100% carbon dioxide gas as the gas containing carbon dioxide, the adsorbent has the ability to adsorb and desorb carbon dioxide with an efficiency of approximately 50% (Evaluation 5). The results in Table 2 show that the carbon dioxide adsorption and separation method using the carbon dioxide adsorbent makes it possible to recover carbon dioxide from the atmosphere and exhaust gases and then adjust the carbon dioxide concentration when reusing the carbon dioxide, thus enabling the material to be provided to a wide range of fields.

[0120] As is clear from the results shown in Tables 1 and 2, the regeneration method of the present invention can regenerate used carbon dioxide adsorbent materials used in the carbon dioxide adsorption separation method to an adsorption performance preferably equivalent to the desired adsorption performance. Therefore, by incorporating the regeneration method of the present invention into the carbon dioxide adsorption separation method, it is possible to realize the continuous adsorption separation method of the present invention, which continuously performs the carbon dioxide adsorption separation method via the regeneration method of the present invention. Furthermore, it is clear that, in addition to a separation step using air or an inert gas, a separation step using a gas having the same carbon dioxide adsorption concentration as the gas composition used in the adsorption step, and even a separation step using 100% carbon dioxide gas can be applied as separation steps in the continuous adsorption separation method of the present invention. Moreover, the regeneration method of the present invention can be carried out using water, which has a low environmental impact, and can meet the increasing demands for environmental protection (environmental impact) and cost reduction in recent years.

Claims

1. A method for regenerating a carbon dioxide adsorbent that adsorbs carbon dioxide in a gas, wherein the carbon dioxide adsorbent contains an alkali metal carbonate containing at least one alkali metal element and a metal compound containing at least one element selected from the group consisting of Group 3 and Group 4 elements of the periodic table, and the carbon dioxide adsorbent is brought into contact with water, and then brought into contact with an aqueous solution containing an alkali metal carbonate containing at least one alkali metal element.

2. The regeneration method according to claim 1, wherein the metal compound comprises at least one element selected from the group consisting of cerium, titanium, and zirconium.

3. The regeneration method according to claim 2, wherein the metal compound contains the element zirconium.

4. The regeneration method according to claim 3, wherein the metal compound is zirconium oxide.

5. The regeneration method according to claim 1, wherein the gas is the atmosphere or factory exhaust gas.

6. The regeneration method according to claim 1, wherein the gas is exhaust gas from a power plant.

7. The regeneration method according to claim 1, wherein the gas comprises at least one selected from the group consisting of nitrogen oxides and sulfur oxides.

8. The regeneration method according to claim 1, wherein the alkali metal carbonate contained in the aqueous solution is potassium carbonate.

9. A method for continuous adsorption and separation of carbon dioxide, comprising repeatedly performing an adsorption step of bringing a carbon dioxide adsorbent into contact with a gas containing carbon dioxide, and a separation step of heating the carbon dioxide adsorbent, which has adsorbed carbon dioxide in the adsorption step, to 50 to 900°C, wherein the carbon dioxide adsorbent contains an alkali metal carbonate containing at least one alkali metal element and a metal compound containing at least one element selected from the group consisting of Group 3 and Group 4 elements of the periodic table, and after performing at least one of the adsorption step and the separation step, the carbon dioxide adsorbent after the separation step is regenerated by the regeneration method described in any one of claims 1 to 8.

10. The method for continuous adsorption separation of carbon dioxide according to claim 9, wherein at least one of the multiple separation steps is heated in an atmosphere of carbon dioxide-containing gas.

11. A method for adsorbing and separating carbon dioxide, comprising an adsorption step of bringing a carbon dioxide adsorbent into contact with a gas containing carbon dioxide, and a separation step of heating the carbon dioxide adsorbent, which has adsorbed carbon dioxide in the adsorption step, to 50 to 900°C in an atmosphere of gas containing carbon dioxide.

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