Inorganic oxide composite, carbon dioxide adsorbent, method for separating carbon dioxide, and method for producing sodium hydrogencarbonate

Abstract

To provide an inorganic oxide composite which has excellent carbon dioxide adsorptivity, can be used in a wide desired temperature range from ordinary temperature to a temperature exceeding 100 °C, can easily desorb adsorbed carbon dioxide, can be molded and processed, and can be used at a low cost.SOLUTION: An inorganic oxide composite comprising an inorganic oxide base material, 0.1% by mass or more of a nitrogen atom derived from an amine compound, and at least one metal atom selected from the group consisting of copper, vanadium, nickel, and iron.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inorganic oxide composite, a carbon dioxide adsorbent, a method for separating carbon dioxide, and a method for producing sodium hydrogencarbonate. [Background technology]

[0002] In recent years, the separation and recovery of carbon dioxide, a greenhouse gas, has attracted attention as a measure against global warming, and methods for separating carbon dioxide from exhaust gases emitted from automobiles and factories, the atmosphere, etc. have been developed.

[0003] Currently proposed technologies for separating and capturing carbon dioxide include solid adsorption, liquid absorption, and membrane separation, and are used depending on the concentration of carbon dioxide to be treated, etc. Solid adsorption is used to capture carbon dioxide directly from the atmosphere, a method known as Direct Air Capture (DAC), and to capture carbon dioxide contained in exhaust gases from thermal power plants and factories, by adsorbing carbon dioxide from the atmosphere onto a solid adsorbent to separate and capture it.

[0004] As the solid adsorbent, for example, a substance having carbon dioxide adsorption ability bound to the surface of a support is used, and amine compounds are known as substances having carbon dioxide adsorption ability. For example, Patent Document 1 proposes a carbon dioxide separating material containing polyamine, and the carbon dioxide separating material is made by supporting polyamine on a support such as silica. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2023 / 182173 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the carbon dioxide separating material described in Patent Document 1 is intended for use at temperatures of around 40°C or 60°C, and therefore requires heating before use. Furthermore, in order to desorb carbon dioxide from the carbon dioxide separating material described in Patent Document 1, it is necessary to reduce pressure; bring the material into contact with at least one of water vapor and an inert gas; and / or heat the material to, for example, around 60°C, resulting in high processing costs. Heating during carbon dioxide adsorption and / or desorption requires renewable energy, which increases costs and also generates carbon dioxide during the generation of renewable energy. Therefore, there is a need for a carbon dioxide adsorbent that has high carbon dioxide adsorption capacity even when used in a room temperature (15 to 25°C) environment and that also allows for easy carbon dioxide desorption.

[0007] Furthermore, when carbon dioxide is captured, if the carbon dioxide adsorbent is packed into a separation and capture device such as an adsorption tower, the carbon dioxide adsorbent must also be able to be molded and processed to increase its packing efficiency.

[0008] Therefore, an object of the present invention is to provide an inorganic oxide composite that is a material suitable for the adsorption and desorption of carbon dioxide, has excellent carbon dioxide adsorption ability, can be used over a wide range of desired temperatures from room temperature to over 100°C, can easily desorb adsorbed carbon dioxide, can be molded and processed, and is inexpensive to use, as well as to provide a carbon dioxide adsorbent that uses the inorganic oxide composite, a method for separating carbon dioxide, and a method for producing sodium hydrogencarbonate. [Means for solving the problem]

[0009] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by an inorganic oxide composite containing nitrogen atoms derived from an amine compound in a specific ratio and further containing a specific metal atom, thereby completing the present invention.

[0010] One aspect of the present invention relates to an inorganic oxide composite comprising an inorganic oxide base material, 0.1 mass % or more of nitrogen atoms derived from an amine compound, and at least one metal atom selected from the group consisting of copper, vanadium, nickel, and iron.

[0011] Another aspect of the present invention relates to a carbon dioxide adsorbent containing the above-mentioned inorganic oxide composite.

[0012] Another aspect of the present invention relates to a method for separating carbon dioxide, which comprises contacting the above-mentioned inorganic oxide composite with a gas to be treated that contains carbon dioxide.

[0013] Another aspect of the present invention relates to a method for producing sodium hydrogencarbonate, which comprises contacting the inorganic oxide composite with a gas to be treated containing carbon dioxide, and washing the inorganic oxide composite after contact with the gas to be treated with an aqueous solution containing at least one of sodium chloride and sodium hydroxide at 5°C or higher. [Effects of the Invention]

[0014] The present invention can provide an inorganic oxide composite that is a material suitable for the adsorption and desorption of carbon dioxide, has excellent carbon dioxide adsorption ability, can be used over a wide range of desired temperatures from room temperature to over 100°C, can easily desorb adsorbed carbon dioxide, can be molded and processed, and is inexpensive to use, as well as a carbon dioxide adsorbent that uses the inorganic oxide composite, a method for separating carbon dioxide, and a method for producing sodium hydrogencarbonate. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described below, but the present invention is not limited to the examples in the following description. In this specification, ratios, proportions, etc. based on mass are synonymous with ratios, proportions, etc. based on weight.

[0016] The inorganic oxide composite of the present invention comprises an inorganic oxide base material, 0.1 mass % or more of nitrogen atoms derived from an amine compound, and at least one metal atom selected from the group consisting of copper, vanadium, nickel, and iron.

[0017] In the present invention, it has been found that an inorganic oxide composite containing an inorganic oxide base material, nitrogen atoms derived from an amine compound, and at least one metal atom selected from the group consisting of copper, vanadium, nickel, and iron, selectively adsorbs carbon dioxide in a gas to be treated.

[0018] In the inorganic oxide composite of the present invention, it is preferable that an amine compound is supported on an inorganic oxide substrate, and the specific metal atom is coordinated to the nitrogen atom of the amino group of the amine compound. By adopting such a configuration, the inorganic oxide composite can exhibit superior carbon dioxide adsorption ability.

[0019] The term "supported" refers to a state in which the amine compound is attached to or bonded to the surface of the inorganic oxide substrate. When the inorganic oxide substrate is porous as described below, the term "supported" also refers to a state in which the amine compound is attached to or bonded to the inner surfaces of the pores of the inorganic oxide substrate. The amine compound is preferably supported by adhering or bonding to at least one of the surface of the inorganic oxide substrate and the inner surfaces of the pores, or by being filled into the pores of the inorganic oxide substrate and adhering to the inner surfaces of the pores.

[0020] When an amine compound is supported on an inorganic oxide substrate as described above and the metal atom is coordinated to the nitrogen atom of the amino group of the amine compound, the metal atom may be coordinated to some or all of the nitrogen atoms of the amino group of the amine compound. When some of the nitrogen atoms of the amino group are not coordinated with a metal atom, carbon dioxide adsorbed by the uncoordinated (free) amino group is difficult to desorb by a method using an aqueous solution containing at least one of sodium chloride and sodium hydroxide at 5°C or higher, as described below. Therefore, from the viewpoint of more suitably reusing the inorganic oxide composite of the present invention in carbon dioxide separation, it is more preferable that the metal atom be coordinated to all of the nitrogen atoms of the amino group of the amine compound. That is, it is more preferable that the inorganic oxide composite of the present invention does not contain any uncoordinated amino groups.

[0021] The presence or absence of the uncoordinated amino group can be confirmed, for example, by the ninhydrin coloring method. That is, the inorganic oxide composite of the present invention is added to a ninhydrin solution and heated at 90°C for 10 minutes. If the solution after the reaction exhibits a purple color due to the absorption peak at 570 nm, it can be determined that the uncoordinated amino group is present.

[0022] <Inorganic oxide base material> As described above, in the inorganic oxide composite of the present invention, it is preferred that an amine compound is supported on the inorganic oxide substrate and a specific metal atom is coordinated to the nitrogen atom of the amino group of the amine compound.

[0023] The form of the inorganic oxide substrate is not particularly limited, and may be, for example, primary particles consisting of fine particles, secondary particles (aggregates) formed by aggregation of primary particles, or a molded body formed from primary particles and / or secondary particles. That is, one preferred embodiment of the inorganic oxide substrate is inorganic oxide fine particles, and another preferred embodiment of the inorganic oxide substrate is an inorganic oxide molded body.

[0024] Examples of materials constituting the inorganic oxide substrate include silica, zeolite, alumina, silica alumina, titania, aluminum silicate, magnesium silicate, clay minerals, etc. The inorganic oxide substrate may contain at least one selected from the group consisting of these. Among these, from the viewpoint of further improving the heat resistance of the inorganic oxide composite and improving the moldability and processability, it is preferable that the inorganic oxide substrate contains silicon atoms, and the material constituting the inorganic oxide substrate is preferably silica, zeolite, alumina, or titania, and more preferably silica.

[0025] The inorganic oxide substrate is preferably porous, which allows the amine compound to be sufficiently supported, allowing carbon dioxide to easily enter the pores of the inorganic oxide substrate and improving its diffusibility, thereby improving the amount of carbon dioxide separated and recovered.

[0026] When the inorganic oxide substrate is porous, the specific surface area determined by the nitrogen adsorption method is 50 to 1000 m 2 / g. The specific surface area affects the density of the amine compound present per specific surface area and the diffusivity of carbon dioxide. 2 / g or less, the density per specific surface area of ​​the amine compound supported on the inorganic oxide substrate increases, so that the amino groups of the amine compounds come close to each other, and bond with carbon dioxide through each other's amino groups, thereby increasing the carbon dioxide adsorption capacity. Also, the number of very fine pores is reduced, and the pore space within the inorganic oxide substrate is of an appropriate size (width), improving the diffusion of carbon dioxide and facilitating carbon dioxide adsorption. Furthermore, the possibility of cracking occurring during the drying process for preparing the inorganic oxide substrate can be reduced. When the specific surface area is 50 m 2 When the SiO 2 content is 1 / g or more, the inorganic oxide composite can exhibit its ability to adsorb carbon dioxide. The specific surface area of ​​the inorganic oxide substrate is 50m 2 / g or more is preferable, and 70m 2 / g or more is more preferable, and 100m 2 / g or more is more preferable. 2 / g or less is preferable, and 950m 2 / g or less is more preferable, and 900m 2 / g or less is more preferable.

[0027] The specific surface area of ​​the inorganic oxide substrate can be calculated using the BET theory after obtaining an adsorption isotherm by the nitrogen adsorption method.

[0028] When the inorganic oxide substrate is porous, it is preferable that the average pore diameter determined by the nitrogen adsorption method is 1 to 100 nm. The average pore diameter affects the diffusibility of carbon dioxide and the strength of the inorganic oxide composite. The larger the average pore diameter, the more pore spaces of appropriate size (width) are present on the surface and inside of the inorganic oxide substrate, improving the diffusibility of carbon dioxide. An average pore diameter of 1 nm or more can increase the amount of carbon dioxide adsorption. Furthermore, if the average pore diameter is too large, it will be impossible to maintain the strength required for the inorganic oxide composite, so it is preferable that the average pore diameter of the inorganic oxide substrate be 100 nm or less. The average pore diameter of the inorganic oxide substrate is preferably 1 nm or more, more preferably 2 nm or more, and even more preferably 3 nm or more, and is preferably 100 nm or less, more preferably 70 nm or less, and even more preferably 60 nm or less.

[0029] The average pore diameter of the inorganic oxide substrate can be calculated from the specific surface area (S) of the sample obtained based on an adsorption isotherm obtained by a nitrogen adsorption method and the pore volume (V) of the sample using the formula: D = 4V / S (where D represents the average pore diameter (average pore diameter) of the sample, V represents the pore volume of the sample, and S represents the specific surface area of ​​the sample).

[0030] When the inorganic oxide substrate is porous, the pore volume is 1.0 to 5.0 cm 3 / g. The pore volume affects the amount of amine compound supported on the inorganic oxide substrate and the strength of the inorganic oxide composite. The larger the pore volume, the more amine compound can be supported.3 / g or more, the amount of carbon dioxide adsorption can be increased. In addition, if the pore volume is too large, the inorganic oxide composite cannot maintain the strength required. Therefore, the pore volume of the inorganic oxide substrate is set to 5.0 cm 3 / g or less is preferable. The pore volume of the inorganic oxide substrate is 1.0 cm 3 / g or more is preferable, and 1.3cm 3 / g or more is more preferable, and 1.5cm 3 / g or more is more preferable. The pore volume is 5.0 cm 3 / g or less is preferable, and 4.5cm 3 / g or less is more preferable, and 4.0 cm 3 / g or less is more preferable.

[0031] The pore volume of the inorganic oxide substrate can be measured by obtaining an adsorption isotherm by nitrogen adsorption, and then measuring the amount of nitrogen gas adsorbed (BET method) when the relative pressure (adsorption equilibrium pressure / saturated vapor pressure) becomes 0.95.

[0032] The inorganic oxide substrate preferably has a methanol hydrophobicity of 20% or less. The methanol hydrophobicity is an index showing the hydrophobicity of the particles. A methanol hydrophobicity of 0% indicates hydrophilicity. From the viewpoint of facilitating the loading of an amine compound, the degree of methanol hydrophobicity of the inorganic oxide substrate is preferably 20% or less, more preferably 10% or less, even more preferably 5% or less, and most preferably 0%.

[0033] The method for measuring the degree of methanol hydrophobicity is as follows: 50 cc of distilled water is placed in a 300 cc beaker, and 5 g of inorganic oxide substrate is added while stirring thoroughly. If the inorganic oxide substrate is uniformly dispersed, the inorganic oxide substrate is highly compatible with distilled water, and the degree of methanol hydrophobicity is 0%. If the inorganic oxide substrate is not uniformly dispersed, gradually add methanol dropwise until the inorganic oxide substrate is uniformly dispersed in the aqueous solution. The degree of methanol hydrophobicity D (unit: %) can be calculated using the following formula from the total amount of methanol added M (unit: cc) until the inorganic oxide substrate is uniformly dispersed. D=100M / (M+50) When the inorganic oxide substrate is an inorganic oxide molded body that settles when placed in distilled water, the inorganic oxide molded body may be pulverized into powder and then the above-mentioned measurement method may be applied.

[0034] When the inorganic oxide substrate is porous, it is preferable that the oil absorption is 100 ml / 100 g or more. The oil absorption affects the amount of amine compound supported. A high oil absorption allows a large amount of amine compound to be supported in the pores, thereby increasing the amount of carbon dioxide adsorbed. The oil absorption is preferably 100 ml / 100 g or more, more preferably 120 ml / 100 g or more, and even more preferably 150 ml / 100 g or more, and the upper limit is preferably 1000 ml / 100 g or less, more preferably 800 ml / 100 g or less, and even more preferably 600 ml / 100 g or less. That is, the oil absorption of the inorganic oxide substrate is preferably in the range of 100 ml / 100 g or more and 1000 ml / 100 g or less.

[0035] The oil absorption of the inorganic oxide substrate can be measured in accordance with JIS K 5101. Specifically, boiled linseed oil is added to the sample while kneading until the entire sample becomes a single mass. The oil absorption is expressed as the volume of boiled linseed oil per 100 g of sample when the entire sample becomes a single mass.

[0036] When the inorganic oxide base material is inorganic oxide fine particles, the inorganic oxide fine particles preferably have an average particle size (50% particle size, D50) of 1 μm to 1 mm in a cumulative particle size distribution based on volume. When the inorganic oxide fine particles have an average particle size of 1 μm or more, they are easy to handle and can suppress pressure loss when used as a carbon dioxide adsorbent, while when they are 1 mm or less, they can have high strength when processed. The inorganic oxide fine particles preferably have an average particle size (D50) of 1 μm or more, more preferably 10 μm or more, and preferably 1 mm or less, more preferably 500 μm or less, and even more preferably 100 μm or less.

[0037] The average particle size (D50) of the inorganic oxide fine particles can be measured by the electrical sensing zone method (Coulter counter method) in accordance with JIS Z 8832 (2010).

[0038] When the inorganic oxide substrate is inorganic oxide fine particles, the inorganic oxide fine particles are preferably spherical with a circularity of 0.8 or more. When the inorganic oxide fine particles have a circularity of 0.8 or more, the efficiency of packing into a separation and capture device when using the inorganic oxide composite for carbon dioxide adsorption and separation is increased, the amount of carbon dioxide adsorption can be increased, and pressure loss can be suppressed, thereby improving energy utilization efficiency. The circularity of the inorganic oxide fine particles is preferably 0.8 or more, more preferably 0.85 or more. There is no particular upper limit to the circularity, but it is most preferably 1.

[0039] The circularity of inorganic oxide microparticles can be calculated by determining the particle area and perimeter of an image obtained by a particle image analyzer (for example, Sysmex Corporation's "FPIA-3000S" (trade name)) using the image analysis software attached to the device, and applying the results to the following formula. Circularity = perimeter of a circle with the same projected area / perimeter of the particle Perimeter of a circle with the same projected area: When a particle is observed from directly above, the area of ​​the particle's shadow projected onto the plane below is calculated, and the length of the outline of that circle is calculated. Particle perimeter: The length of the outline of the particle's shadow projected onto a plane below when the particle is observed from directly above

[0040] The inorganic oxide fine particles used in the present invention may be obtained by synthesis or may be commercially available. When the inorganic oxide fine particles are silica, examples of commercially available silica include "Sunsphere L-123" (trade name) manufactured by AGC Si-Tech Co., Ltd. When synthesized, the inorganic oxide fine particles can be synthesized, for example, according to the method described in Japanese Patent No. 6241252.

[0041] When the inorganic oxide substrate is an inorganic oxide molded body, its size is preferably 1 mm to 50 mm. Here, the "size" of the molded body refers to the most frequent particle size (sieve opening) in the particle size distribution determined by the dry sieving method specified in JIS Z 8815-1994. Specifically, the dry sieving method is a method in which an inorganic oxide substrate sample and multiple sieves with different openings are used to sieve the sample until the mass of the sample on each sieve stops changing, i.e., the mass becomes constant. The mass of the sample fractionated on each sieve is measured, and the volume of each fraction is calculated in mass percent to determine the mass-based particle size distribution. If the size of the inorganic oxide molded body is 1 mm or more, the pressure loss when the gas to be treated is passed through can be reduced, and if it is 50 mm or less, the mechanical strength of the inorganic oxide molded body can be maintained sufficiently high. The size of the inorganic oxide molded body is preferably 1 mm or more, more preferably 1.5 mm or more, and even more preferably 2 mm or more, and is preferably 50 mm or less, more preferably 30 mm or less, and even more preferably 10 mm or less.

[0042] Examples of the shape of the inorganic oxide molded body include general regular or irregular shapes such as spheres, ellipses, cylinders, polygonal pillars, rods, cones, polygonal pyramids, and irregular shapes combining these shapes, honeycomb shapes, and special shapes such as Raschig rings, Berl saddles, and Pall rings. To achieve variable packing efficiency, it is preferable to use molded bodies of general shapes. To improve the mixing efficiency of the gas to be treated when used for carbon dioxide separation, it is preferable to use molded bodies of special shapes. Molded bodies of special shapes disrupt the gas flow, intensify mixing, increase the gas diffusion rate into the molded body, and allow the molded body to be uniformly placed within the space, even if the molded body storage space in the separation and recovery device is large. Molded bodies into special shapes are not limited to the shapes described above, as long as they can be made into a shape that increases porosity.

[0043] The preferred range of mechanical strength of the inorganic oxide molded body is 3 kgf / cm in compressive strength. 2 More than 10kgf / cm is preferable. 2More preferably, the compressive strength is 3kgf / cm 2 If the thickness is more than this, it is possible to prevent the material from breaking into powder during handling.

[0044] One method for producing an inorganic oxide molded body is to granulate powdered inorganic oxide fine particles. Granulation methods include dry molding such as tableting and briquetting, as well as wet granulation such as spray granulation, rolling granulation, stirring granulation, and extrusion. Molded bodies can also be produced by injection molding.

[0045] In tableting or briquetting, small amounts of lubricants, excipients, etc. are added to powdered inorganic oxide microparticles and then molded using a tableting or briquetting machine to obtain molded bodies with a diameter of approximately 1 mm to 70 mm and a thickness of approximately 1 mm to 40 mm.

[0046] Wet granulation is a method of granulating powdered inorganic oxide fine particles by adding a binder and a solvent such as water or alcohol. Binders include organic binders and inorganic binders, but it is preferable to select a binder that can increase the mechanical strength of the molded body even when added in small amounts. Organic and inorganic binders may be used in combination. Examples of organic binders include polyvinyl alcohol, butyral resin, and acrylic resin. Examples of inorganic binders include flaky silica, silica sol, alumina sol, and montmorillonite clay minerals. When molding is performed using an inorganic binder, the solvent, such as water or alcohol, may be removed by drying, and then the product may be fired at a high temperature. This is because firing at a high temperature strengthens the chemical bond between the powdered inorganic oxide fine particles and the inorganic binder, resulting in a molded body with high mechanical strength.

[0047] Spray granulation is a method in which a solvent is added to powdered inorganic oxide particles and a binder to form a slurry, which is then sprayed from a spray nozzle while the solvent is dried. Relatively small spherical molded bodies with a diameter of approximately 1 mm to 10 mm are obtained.

[0048] Rolling granulation is a method in which powdered inorganic oxide particles and a binder are placed in the pan of a pan granulator, and a solvent is added while the pan is rotating at a speed of several tens of revolutions per minute to granulate the particles. The surface tension of the solvent causes the powdered inorganic oxide particles and binder to aggregate and form into spheres, which are then dried to obtain spherical molded bodies with diameters of 1 mm to 50 mm. If too little solvent is added, only small molded bodies are obtained, while if too much solvent is added, the entire mixture becomes a clay-like mass and may not be able to be molded into a sphere.

[0049] Agitation granulation is a method in which powdered inorganic oxide particles and a binder are placed in the container of an agitation granulator, and a solvent is added while the agitator blades rotate at a speed of several thousand revolutions per minute to granulate the particles. The surface tension of the solvent causes the powdered inorganic oxide particles and binder to aggregate and form into spheres, and the solvent is then dried to obtain relatively small spherical bodies with diameters of 1 mm to 10 mm. If too little solvent is added, only small bodies are obtained, while if too much solvent is added, the entire mixture becomes a clay-like mass and may not be able to be formed into spheres.

[0050] Extrusion molding is a method in which powdered inorganic oxide particles and a binder are mixed with a small amount of solvent to form a clay-like mixture, which is then extruded and molded using an extruder. This method allows the inorganic oxide particles to be molded into pellets or cylinders, for example, with a diameter of 1 to 10 mm and a length of 1 to 30 mm. The solvent is then dried to obtain a molded product. The extruded particles can also be placed in a granulator, sized, and then the solvent is dried to obtain a spherical molded product.

[0051] Injection molding is a molding method in which a mixture of powdered inorganic oxide particles, a binder, and a solvent is injected (injected) into a cavity of the same shape as the target object, and then dried to obtain a molded product.

[0052] Another method for producing inorganic oxide molded bodies, specific to silica as a constituent material, is as follows: Sodium silicate and a mineral acid such as sulfuric acid are mixed to produce primary silica particles ranging in size from a few nanometers to a few tens of nanometers, and a gel is produced in which these primary silica particles are three-dimensionally aggregated. This gel is then washed with water, dried, and crushed to produce granules ranging in size from 1 mm to 50 mm, or the gel is sprayed or dissolved in an organic solvent to form droplets, forming a spherical gel of 1 mm to 50 mm in size, which is then washed with water and dried to produce a silica molded body.

[0053] <Inorganic oxide composite> The inorganic oxide composite of the present invention is a composite containing the above-mentioned inorganic oxide base material, nitrogen atoms derived from an amine compound, and specific metal atoms.

[0054] The inorganic oxide composite of the present invention contains 0.1 mass% or more of nitrogen atoms derived from an amine compound. The amine compound has amino groups in its structure, and metal atoms (described below) coordinate to the nitrogen atoms of the amino groups, thereby contributing to the selective adsorption of carbon dioxide in the gas to be treated. Furthermore, when an uncoordinated amino group not coordinated with a metal atom is included as described above, the uncoordinated amino group itself also reacts with carbon dioxide, thereby selectively adsorbing carbon dioxide in the gas to be treated. When the inorganic oxide composite of the present invention contains 0.1% by mass or more of nitrogen atoms derived from an amine compound, it exhibits excellent carbon dioxide adsorption ability. The content of nitrogen atoms derived from the amine compound is preferably 20% by mass or less. When the content is 20% by mass or less, the inorganic oxide composite does not become sticky due to the influence of excess amine compound, making it easy to handle. The content is preferably, for example, 0.1 to 20% by mass. The content of nitrogen atoms derived from the amine compound is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more, and is preferably 20% by mass or less, more preferably 19% by mass or less, and even more preferably 18% by mass or less.

[0055] The content of nitrogen atoms derived from the amine compound in the inorganic oxide composite can be calculated from the mass ratio of nitrogen atoms to the total atomic mass of each atom constituting the inorganic oxide base material, each atom constituting the amine compound, and metal atoms.

[0056] Examples of amine compounds having an amino group include 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-methyl-3-aminopropyltriethoxysilane, N-methyl-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, (3-trimethoxysilylpropyl)diethylenetriamine, ammonia, alkanolamines (methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, tert-butylamine, etc.), monoethanolamine, diethanolamine, N-methyldiethanolamine, isopropylaminoethanol, 2-amino-2-methyl-1-propanol, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, polyethyleneimine (PEI), 1,11-bis(isopropylamino)-3,6,9-triazaundecane, tetraisopropylated N,N,N',N'-tetrakis(3-aminopropyl)-1,4-butanediamine, 1,14-bis(isopropylamino)-3,6,9,12-tetraazatetradecane, 1,17-bis(isopropylamino)-3,6,9,12,15-pentaazaheptadecane, N,N'-bis(3-(isopropylamino)propyl)-1,4-butanediamine, piperazine, N-(2-aminoethyl)piperazine, melamine, imidazole, guanidine, amino acids (alanine, glycine, arginine, glutamine, lysine, etc.), and the like. These amine compounds may be used alone or in combination of two or more. Among these, from the viewpoints of raw material availability, boiling point, and viscosity, it is preferable to use an amine compound containing silicon in the molecule or a polyamine compound containing three or more amino groups in the molecule. Specifically, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, (3-trimethoxysilylpropyl)diethylenetriamine, diethylenetriamine, polyethyleneimine, and arginine are preferred.

[0057] The inorganic oxide composite of the present invention contains at least one metal atom selected from the group consisting of copper, vanadium, nickel, and iron. The metal atom reacts with bicarbonate ions generated from carbon dioxide, thereby selectively adsorbing carbon dioxide in the gas to be treated. From the viewpoint of obtaining a better carbon dioxide adsorption ability, the metal atom is preferably at least one of copper and vanadium, and more preferably copper. When the metal atom is copper, it is preferably a divalent copper ion. When the metal atom is vanadium, it is preferably a divalent vanadium ion. When the metal atom is nickel, it is preferably a divalent nickel ion. When the metal atom is iron, it is preferably a divalent iron ion.

[0058] It can be confirmed by ICP-MS or SEM-EDX that the inorganic oxide composite contains at least one metal atom selected from the group consisting of copper, vanadium, nickel, and iron.

[0059] When the metal atom is at least one selected from the group consisting of a divalent copper ion, a divalent vanadium ion, a divalent nickel ion, and a divalent iron ion, the inorganic oxide composite of the present invention has an absorption peak in a wavelength band of 400 to 1000 nm. Therefore, the inorganic oxide composite of the present invention preferably has an absorption peak in a wavelength band of 400 to 1000 nm. When the metal atom is a divalent copper ion, the inorganic oxide composite of the present invention has an absorption peak in the wavelength band of 400 to 1000 nm. Therefore, the inorganic oxide composite of the present invention preferably has an absorption peak in the wavelength band of 400 to 1000 nm.

[0060] In the inorganic oxide composite of the present invention, the content of the metal atoms is preferably 0.1% by mass or more. When the content is 0.1% by mass or more, better carbon dioxide adsorption ability can be obtained. The upper limit of the content is not particularly limited, but it is practical to set it to 20% by mass or less. The content may be, for example, 0.1 to 20% by mass. The content is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more.

[0061] The content of the metal atoms in the inorganic oxide composite can be calculated from the mass ratio of the metal atoms to the total atomic mass of the atoms constituting the inorganic oxide base material, the atoms constituting the amine compound, and the metal atoms.

[0062] In the inorganic oxide composite of the present invention, the density of the metal atoms per surface area of ​​the inorganic oxide composite is 1.0 × 10 -6 mol / m 2 It is preferable that the density is 1.0×10 or more. -6 mol / m 2 The density of 1.0×10 or more means that a large number of metal atoms are present on the surface of the inorganic oxide composite, and a superior carbon dioxide adsorption ability can be obtained. The upper limit of the density is not particularly limited, but is preferably 1.0×10 -4 mol / m 2 The density is, for example, 1.0×10 -6 ~1.0×10 -4 mol / m 2 It may be. The density above is 1.0 x 10 -6 mol / m 2 More than 1.1 × 10 is preferable. -6 mol / m 2 More preferably, 1.2 × 10-6 mol / m 2 The above is even more preferable.

[0063] The density of metal atoms per surface area of ​​the inorganic oxide composite can be determined as follows. Density of metal atoms per surface area of ​​inorganic oxide composite (mol / m 2 ) = Metal atom content (mass%) / (specific surface area of ​​inorganic oxide composite (m 2 / g) × atomic weight of metal atom × 100)

[0064] The inorganic oxide composite of the present invention preferably contains silicon atoms. The inclusion of silicon atoms improves the heat resistance of the inorganic oxide composite. The content of silicon atoms in the inorganic oxide composite is preferably 10 to 46% by mass. When the content is 10% by mass or more, the heat resistance of the inorganic oxide composite is further improved. When the content is 46% by mass or less, carbon dioxide adsorption ability is obtained. The silicon atom content is preferably 10% by mass or more, more preferably 11% by mass or more, and even more preferably 12% by mass or more, and is preferably 46% by mass or less, more preferably 45% by mass or less, and even more preferably 44% by mass or less. As mentioned above, it is more preferred that the inorganic oxide substrate contains silicon atoms.

[0065] The content of silicon atoms in the inorganic oxide composite can be calculated from the mass ratio of silicon atoms to the total atomic mass of each atom constituting the inorganic oxide base material, each atom constituting the amine compound, and each metal atom.

[0066] When the inorganic oxide substrate is a porous body as described above, the inorganic oxide composite of the present invention has a specific surface area of ​​50 to 1000 m2 as determined by the nitrogen adsorption method. 2 The specific surface area is preferably 1 / g. The meaning of the specific surface area is as described above in the section on inorganic oxide substrates. The specific surface area of ​​the inorganic oxide composite is 50m 2 / g or more is preferable, and 70m 2 / g or more is more preferable, and 100m2 / g or more is more preferable. 2 / g or less is preferable, and 950m 2 / g or less is more preferable, and 900m 2 / g or less is more preferable.

[0067] The specific surface area of ​​the inorganic oxide composite can be calculated by the same method as described above in the <Inorganic oxide substrate>.

[0068] When the inorganic oxide substrate of the inorganic oxide composite of the present invention is a porous body as described above, the average pore diameter determined by the nitrogen adsorption method is preferably 1 to 100 nm. The meaning of the average pore diameter is as described above in <Inorganic oxide substrate>. The average pore diameter of the inorganic oxide composite is preferably 1 nm or more, more preferably 2 nm or more, and even more preferably 3 nm or more, and is preferably 100 nm or less, more preferably 70 nm or less, and even more preferably 60 nm or less.

[0069] The average pore diameter of the inorganic oxide composite can be calculated by the same method as described above in the <Inorganic oxide substrate>.

[0070] When the inorganic oxide substrate of the present invention is a porous body as described above, the inorganic oxide composite has a pore volume of 0.1 to 5.0 cm 3 The meaning of the pore volume is as described above in the section on inorganic oxide substrates. The pore volume of the inorganic oxide composite is 0.1 cm 3 / g or more is preferable, and 0.15cm 3 / g or more is more preferable, and 0.2cm 3 / g or more is more preferable. The pore volume is 5.0 cm 3 / g or less is preferable, and 4.5cm 3 / g or less is more preferable, and 4.0 cm 3 / g or less is more preferable.

[0071] The pore volume of the inorganic oxide composite can be measured by the same method as described above in the <Inorganic oxide substrate>.

[0072] The inorganic oxide composite of the present invention preferably has a methanol hydrophobicity of 20% or less. The methanol hydrophobicity is an index showing the hydrophobicity of particles. A methanol hydrophobicity of 0% indicates hydrophilicity. The degree of methanol hydrophobicity of the inorganic oxide composite is preferably 20% or less, more preferably 10% or less, even more preferably 5% or less, and most preferably 0%, from the viewpoint of facilitating desorption of carbon dioxide by a method using an aqueous solution containing at least one of sodium chloride and sodium hydroxide at 5°C or higher, as described below.

[0073] The degree of methanol hydrophobicity can be measured by the same method as described above in the section on inorganic oxide substrates.

[0074] When the inorganic oxide substrate is a porous body, the preferred range of the oil absorption of the inorganic oxide composite is the same as the range described above in <Inorganic Oxide Substrate>. When the inorganic oxide substrate is inorganic oxide fine particles, the preferred ranges of the average particle diameter (50% particle diameter, D50) and circularity in the cumulative particle size distribution on a volume basis of the inorganic oxide composite are the same as the ranges described above in <Inorganic Oxide Substrate>.

[0075] <Production of inorganic oxide composite> The inorganic oxide composite of the present invention can be produced, for example, by a method including the following steps (I) and (II). (I) The inorganic oxide substrate is modified with an amine to obtain an amine-modified inorganic oxide substrate. (II) The above metal atom is coordinated to the amine-modified inorganic oxide substrate to obtain the inorganic oxide composite of the present invention.

[0076] The above step (I) may be carried out, for example, by the following method (1) or (2). (1) A method in which an amine compound is bound to and / or filled into the surface and / or pores of an inorganic oxide substrate. (2) A method in which a precursor of an amine compound is bound to and / or filled into the surface and / or pores of an inorganic oxide substrate, and then reacted on the surface and / or in the pores to bind and / or fill the target amine compound onto and / or into the surface and / or pores of the inorganic oxide substrate. The amine-modified inorganic oxide substrate may be obtained by either method (1) or method (2), or by a combination of both methods.

[0077] In the method (1), an amine compound is brought into contact with an inorganic oxide substrate, and if necessary, heated and maintained to obtain an amine-modified inorganic oxide substrate. As the amine compound, the above-mentioned amine compounds are used.

[0078] When the amine compound is brought into contact with the inorganic oxide substrate, the liquid amine compound may be brought into contact with the inorganic oxide substrate as it is, or a solution of the amine compound dissolved in a solvent may be brought into contact with the inorganic oxide substrate.

[0079] Examples of the solvent include water, alcohols, ethers, esters, amines, amides, etc. Among these, it is preferable to use alcohols from the viewpoints of availability and ease of removal after contact with the inorganic oxide substrate. From the viewpoint that a step of removing the solvent is not necessary, it is more preferable to contact the amine compound directly with the inorganic oxide substrate without using a solvent.

[0080] The concentration of the amine compound in the amine solution is preferably 10 to 100% by mass, more preferably 25% by mass or more, and even more preferably 50% by mass or more, from the viewpoint of increasing the contact efficiency with the inorganic oxide substrate and the supported amount.

[0081] The contact of the inorganic oxide substrate with the amine solution can be carried out by a conventionally known method, such as a method of immersing the inorganic oxide substrate in the amine solution, a method of dropping or spraying the amine solution onto the inorganic oxide substrate, a method of precipitating the inorganic oxide substrate in the amine solution, etc. Among these, the method of dropping or spraying the amine solution onto the inorganic oxide substrate is preferred from the viewpoint of ease of operation.

[0082] After contacting the amine solution with the inorganic oxide substrate, the mixture may be left at 20 to 80° C. for 1 to 48 hours, and if necessary, may be heated under reflux and stirred at 20 to 150° C. Alternatively, the mixture may be stirred in an autoclave at 20 to 150° C. for 1 to 48 hours. A reaction temperature of 20°C or higher reduces the viscosity of the amine compound, making it easier for the amine compound to fill the pores of the inorganic oxide substrate. A reaction temperature of 150°C or lower suppresses oxidation of the amine compound, preventing the amine compound from scattering before reaction. The reaction temperature is preferably 20°C or higher, and more preferably 25°C or higher. The temperature is preferably 150°C or lower, and more preferably 100°C or lower. When a low-molecular-weight compound is used as the amine compound, the reaction temperature is preferably 80°C or lower to suppress volatilization of the amine compound. A reaction time of 1 hour or longer allows the amine compound to be sufficiently filled into the pores of the inorganic oxide substrate, while a reaction time of 48 hours or shorter shortens the production process. The reaction time is preferably 1 hour or longer, more preferably 2 hours or longer. The reaction time is preferably 48 hours or shorter, more preferably 24 hours or shorter.

[0083] After the reaction, a drying step can be carried out if necessary. Drying can be carried out at 20 to 150° C. for about 1 to 24 hours. The drying step can be carried out under reduced pressure.

[0084] In the method (2), a precursor of an amine compound is used. The amine-modified inorganic oxide substrate can be obtained by contacting the precursor of the amine compound with the inorganic oxide substrate and allowing it to react for a period of time or by heating. The precursor of the amine compound can be dissolved in a solvent, or multiple amine compounds can be mixed.

[0085] Examples of the solvent include water, alcohols, ethers, esters, amines, amides, etc. Among these, it is preferable to use alcohols from the viewpoints of availability and ease of removal after contact with the inorganic oxide substrate. From the viewpoint of making the removal step unnecessary, it is more preferable to contact the precursor of the amine compound directly with the inorganic oxide substrate without using a solvent.

[0086] Examples of precursors of amine compounds include M- and D-aminosilane coupling agents and 2,4,6,8-tetramethylcyclotetrasiloxane. Because M-aminosilane coupling agents have one condensable alkoxy group, they produce linear dimeric aminosiloxane compounds through a condensation reaction. Because D-aminosilane coupling agents have two condensable alkoxy groups, they produce linear dimeric or higher aminosiloxane compounds and cyclic trimeric or higher aminosiloxane compounds through a condensation reaction. 2,4,6,8-tetramethylcyclotetrasiloxane can react with unsaturated amines in the presence of a catalyst, producing cyclic aminosiloxane compounds through the reaction.

[0087] The concentration of the amine compound precursor in the solution is preferably 20 to 100% by mass, more preferably 25% by mass or more, and even more preferably 50% by mass or more, from the viewpoint of increasing the contact efficiency with the inorganic oxide substrate and the supported amount.

[0088] The solution of the precursor of the amine compound may contain other components, such as platinum, ruthenium, and rhodium, as long as the effects of the present invention are not impaired.

[0089] The contact of the inorganic oxide substrate with the solution of the precursor of the amine compound can be carried out by a conventionally known method, such as a method of immersing the inorganic oxide substrate in the solution of the precursor of the amine compound, a method of adding dropwise or spraying the solution of the precursor of the amine compound to the inorganic oxide substrate, a method of precipitating the inorganic oxide substrate in the solution of the precursor of the amine compound, etc. Among these, from the viewpoint of ease of operation, the method of adding dropwise or spraying the solution of the precursor of the amine compound to the inorganic oxide substrate is preferred.

[0090] After contacting the solution of the precursor of the amine compound with the inorganic oxide substrate, the reaction is preferably carried out at 20 to 150° C. for 1 to 48 hours. When the reaction temperature is 20°C or higher, the reaction of the precursor of the amine compound proceeds quickly, and when the reaction temperature is 150°C or lower, oxidation of the amine compound is suppressed and scattering of the amine compound before the reaction can be prevented. The reaction temperature is preferably 20°C or higher, more preferably 40°C or higher. The temperature is preferably 150°C or lower, more preferably 100°C or lower. If the reaction time is 1 hour or more, the reaction of the precursor of the amine compound proceeds sufficiently, and if it is 48 hours or less, the production process can be shortened. The reaction time is preferably 1 hour or more, more preferably 2 hours or more. The reaction time is preferably 48 hours or less, more preferably 24 hours or less. When reactive functional groups are present on the surface of the inorganic oxide substrate, the reaction between the precursor of the amine compound and the reactive functional groups on the surface of the inorganic oxide substrate also proceeds.

[0091] After the reaction, a drying step can be carried out under reduced pressure, if necessary. Drying can be carried out at 20 to 150°C for about 1 to 24 hours.

[0092] The amine-modified inorganic oxide substrate obtained by the above step (I) preferably has a methanol hydrophobicity of 0 to 40%. The methanol hydrophobicity of the amine-modified inorganic oxide substrate is preferably 0% or more, and is preferably 40% or less, more preferably 30% or less, and even more preferably 20% or less.

[0093] The above step (II) is carried out, for example, as follows. An aqueous solution of metal chloride or metal sulfate is prepared, the amine-modified inorganic oxide substrate is added, and the mixture is stirred at room temperature, followed by filtration and washing. Alternatively, the amine-modified inorganic oxide substrate may be packed in an ion exchange column, and the prepared aqueous solution of metal chloride or metal sulfate may be passed through the column.

[0094] <Carbon dioxide adsorbent> The carbon dioxide adsorbent of the present invention contains the inorganic oxide composite of the present invention. The carbon dioxide adsorbent preferably contains 50% by mass or more of the inorganic oxide composite. When the content of the inorganic oxide composite is 50% by mass or more, better carbon dioxide adsorption ability is obtained. The content of the inorganic oxide composite is more preferably 60% by mass or more, and even more preferably 70% by mass or more. Furthermore, the content may be 100% by mass (i.e., the carbon dioxide adsorbent may be composed of the inorganic oxide composite of the present invention), or it may be less than 100% by mass, for example, 99% by mass or less, or 98% by mass or less.

[0095] The carbon dioxide adsorbent of the present invention may contain components other than the inorganic oxide composite as long as the effects of the present invention are not impaired. For example, when the inorganic oxide base material is inorganic oxide fine particles, examples of other components include a binder compound, described below, used in granulating the inorganic oxide fine particles. The binder compound is commercially available or can be easily produced by a known method.

[0096] When the inorganic oxide substrate is inorganic oxide fine particles, the carbon dioxide adsorbent according to the present invention may be primary particles made of a powdery (particulate) inorganic oxide composite, or secondary particles (aggregates) formed by aggregation of the primary particles, or a molded body obtained by granulating the primary particles and / or secondary particles. Furthermore, when the inorganic oxide substrate is an inorganic oxide molded body, the carbon dioxide adsorbent according to the present invention may be a molded body made of an inorganic oxide composite, or a molded body obtained by further shaping and processing the molded body.

[0097] When the carbon dioxide adsorbent is in powder (particulate) form, the average particle size (50% particle size, D50) in the cumulative particle size distribution on a volume basis is preferably 1 μm to 1 mm. If the average particle size of the carbon dioxide adsorbent is 1 μm or more, pressure loss when the gas to be treated is passed through the carbon dioxide adsorbent can be suppressed, and if it is 1 mm or less, a carbon dioxide adsorbent with higher strength can be obtained. The powdered carbon dioxide adsorbent preferably has an average particle size (D50) of 1 μm or more, more preferably 10 μm or more, and preferably 1 mm or less, more preferably 500 μm or less, and even more preferably 100 μm or less.

[0098] The average particle size (D50) of the carbon dioxide adsorbent can be measured by the electrical sensing zone method (Coulter counter method) in accordance with JIS Z 8832 (2010).

[0099] When the carbon dioxide adsorbent is in powder form, it is preferable that the carbon dioxide adsorbent be spherical with a circularity of 0.8 or more. By using a carbon dioxide adsorbent with a spherical circularity of 0.8 or more, the efficiency of packing the carbon dioxide adsorbent into a separation and capture device can be increased, the amount of carbon dioxide adsorbed can be increased, and the pressure loss of the carbon dioxide adsorbent can be suppressed, thereby improving energy utilization efficiency. The powdered carbon dioxide adsorbent preferably has a circularity of 0.8 or more, more preferably 0.85 or more. There is no particular upper limit to the circularity, but it is most preferably 1.

[0100] The circularity of the carbon dioxide adsorbent can be calculated by determining the area and perimeter of particles from images obtained by a particle image analyzer (for example, "FPIA-3000S" (trade name) manufactured by Sysmex Corporation) using image analysis software attached to the device, and applying the results to the following formula: Circularity = perimeter of a circle with the same projected area / perimeter of the particle Perimeter of a circle with the same projected area: When a particle is observed from directly above, the area of ​​the particle's shadow projected onto the plane below is calculated, and the length of the outline of that circle is calculated. Particle perimeter: The length of the outline of the particle's shadow projected onto a plane below when the particle is observed from directly above

[0101] When the carbon dioxide adsorbent is a molded body obtained by molding an inorganic oxide composite or a molded body made of an inorganic oxide composite, the size thereof is preferably 1 mm to 50 mm. That is, the carbon dioxide adsorbent of the present invention is preferably a molded body having a size of 1 to 50 mm. Here, the "size" of the carbon dioxide adsorbent is the same as that described above in <Inorganic oxide substrate>. If the size of the carbon dioxide adsorbent molded body is 1 mm or more, the pressure loss when the gas to be treated is passed through can be reduced, and if it is 50 mm or less, the mechanical strength of the molded body can be maintained sufficiently high. The size of the molded body is preferably 1 mm or more, more preferably 1.5 mm or more, and even more preferably 2 mm or more, and is preferably 50 mm or less, more preferably 30 mm or less, and even more preferably 10 mm or less.

[0102] The shape of the molded body may be the same as that described above in the <Inorganic oxide substrate>.

[0103] The preferred range of the mechanical strength of the molded body is the same as the range described above in the <Inorganic oxide substrate>.

[0104] When the carbon dioxide adsorbent is a molded body, the method for producing the molded body may be the same as that described above in the <Inorganic oxide substrate>.

[0105] The carbon dioxide adsorbent may be used alone or in combination of two or more. When two or more types are used in combination, for example, two or more types of powdered carbon dioxide adsorbents with different particle sizes may be combined, two or more types of molded carbon dioxide adsorbents with different shapes (molded bodies of a general shape) may be combined, or a powdered carbon dioxide adsorbent may be combined with a molded carbon dioxide adsorbent (molded body of a general shape).

[0106] The carbon dioxide adsorbent of the present invention preferably has an adsorption amount of carbon dioxide of 0.01 mol or more per kg of the carbon dioxide adsorbent at 25° C. An adsorption amount of 0.01 mol or more indicates excellent carbon dioxide adsorption ability. The adsorption amount is more preferably 0.02 mol or more, even more preferably 0.05 mol or more, and particularly preferably 0.1 mol or more. There is no particular upper limit to the adsorption amount, but it can be, for example, 10 mol or less. The adsorption amount may be, for example, 0.01 to 10 mol.

[0107] As described above, in the carbon dioxide adsorbent of the present invention, the specific metal atoms react with bicarbonate ions generated from carbon dioxide, thereby selectively adsorbing carbon dioxide in the gas to be treated.

[0108] The carbon dioxide adsorption amount of the carbon dioxide adsorbent can be measured, for example, as follows. The column is filled with carbon dioxide adsorbent using a single cell evaluation device for solid oxide fuel cells manufactured by Microtrac-Bell Corp. Gas is passed through the column at a ratio of N2 / CO2 / H2O = 88.5 / 10 / 1.5 sccm, and the amount of carbon dioxide is measured by gas chromatography before and after filling with the carbon dioxide adsorbent.

[0109] The carbon dioxide adsorbent of the present invention preferably has a rate of change in the amount of carbon dioxide adsorbed (rate of change from the initial amount of carbon dioxide adsorbed before the heat resistance test) of within -50% when held at 80°C for 60 hours. If the rate of change from the initial amount of carbon dioxide adsorbed when held at 80°C for 60 hours is within -50%, it indicates excellent heat resistance. The rate of change in the amount of carbon dioxide adsorption when maintained at 80° C. for 60 hours is more preferably within −40%, and even more preferably within −20%.

[0110] Furthermore, since the carbon dioxide adsorbent of the present invention contains an inorganic oxide composite containing an inorganic oxide base material with excellent heat resistance, it is generally considered that it can be used even at temperatures exceeding 100°C.

[0111] <Carbon dioxide separation method> The inorganic oxide composite of the present invention is preferably used to adsorb gaseous carbon dioxide. That is, the method for separating carbon dioxide of the present invention comprises contacting the inorganic oxide composite of the present invention with a gas to be treated that contains carbon dioxide.

[0112] Examples of gases to be treated using the inorganic oxide composite of the present invention include the atmosphere, fuel exhaust gases from automobiles and factories, industrial gases such as helium gas and nitrogen gas, and gases emitted from enclosed spaces such as space stations due to human breathing or energy conversion by equipment.

[0113] The contact between the inorganic oxide composite of the present invention and the gas to be treated may be carried out at room temperature, at about 25 to 100°C, or at about 100 to 200°C. Because the inorganic oxide composite can selectively adsorb carbon dioxide due to the metal atoms contained in the inorganic oxide composite, the inorganic oxide composite of the present invention has a high carbon dioxide adsorption capacity and is suitable for use at room temperature. By carrying out the contact at room temperature, the consumption of regeneration energy associated with heating can be reduced. In this specification, "room temperature" means room temperature as defined in the 17th Edition of the Japanese Pharmacopoeia, specifically referring to a temperature range of 15 to 25°C. The contact can be carried out at room temperature by cooling or heating the gas to be treated to room temperature.

[0114] When treating a gas containing carbon dioxide using the inorganic oxide composite or carbon dioxide adsorbent of the present invention, the concentration of carbon dioxide in the gas to be treated is not particularly limited as long as it is a condition that the inorganic oxide composite or carbon dioxide adsorbent can withstand, but for example, it is preferably 100% by volume or less, more preferably 50% by volume or less, and even more preferably 20% by volume or less. There is no particular lower limit, but it is preferably 0.001% by volume or more, and more preferably 0.04% by volume or more. In particular, from the viewpoint of achieving high carbon dioxide adsorption capacity, the concentration of carbon dioxide in the gas to be treated is preferably in the range of 0.001 to 20% by volume, and more preferably 0.04 to 20% by volume. The gas to be treated may be at atmospheric pressure or may be pressurized.

[0115] The concentration of carbon dioxide in the gas to be treated can be measured by gas chromatography.

[0116] The humidity of the gas to be treated is preferably above 0% RH. If the humidity is above 0% RH, the moisture contained in the gas to be treated reacts with carbon dioxide to generate bicarbonate ions, and these bicarbonate ions react with metal atoms contained in the inorganic oxide composite and are easily adsorbed, which is preferable. The humidity of the gas to be treated is more preferably 20% RH or higher, and even more preferably 30% RH or higher. From the viewpoint of facilitating the above reaction, the humidity of the gas to be treated is preferably 80% RH or lower, more preferably 70% RH or lower, and even more preferably 60% RH or lower.

[0117] The inorganic oxide composite or carbon dioxide adsorbent can be reused for adsorption by desorbing carbon dioxide after adsorption. As a method for desorbing carbon dioxide, for example, washing with an aqueous solution containing at least one of sodium chloride and sodium hydroxide at 5°C or higher can be mentioned, as described below.

[0118] <Method of producing sodium bicarbonate> In the method for producing sodium bicarbonate of the present invention, the inorganic oxide composite of the present invention is brought into contact with a gas to be treated that contains carbon dioxide, and the inorganic oxide composite after contact with the gas to be treated is washed with an aqueous solution containing at least one of sodium chloride and sodium hydroxide at 5° C. or higher. This method allows carbon dioxide to be easily desorbed from the inorganic oxide composite, and can be recovered as harmless, stable, and industrially useful sodium bicarbonate.

[0119] Examples of the gas to be treated include the same gases as those mentioned above in the <Method for separating carbon dioxide>. The temperature during the contact may be the same as that mentioned above in the <Method for separating carbon dioxide>.

[0120] In the method for producing sodium hydrogen carbonate of the present invention, the inorganic oxide composite that has been brought into contact with the gas to be treated containing carbon dioxide is washed with an aqueous solution containing at least one of sodium chloride and sodium hydroxide, whereby the hydrogen carbonate ions adsorbed on the inorganic oxide composite are released as sodium hydrogen carbonate. From the viewpoint of reducing the environmental load, seawater may be used as the aqueous solution.

[0121] When the aqueous solution contains sodium chloride, the sodium chloride concentration in the aqueous solution is preferably in the range of 1 to 10% by mass from the viewpoint of utilizing seawater, and the concentration is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, and is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less.

[0122] When the aqueous solution contains sodium hydroxide, from the viewpoint of increasing the solubility of the inorganic oxide composite, the pH of the aqueous solution is preferably in the range of pH 7 to 12. The pH is preferably 7 or higher, more preferably 7.1 or higher, and is preferably 12 or lower, more preferably 11.9 or lower.

[0123] The temperature of the aqueous solution containing at least one of sodium chloride and sodium hydroxide used in the method for producing sodium bicarbonate of the present invention is 5°C or higher. A temperature of 5°C or higher allows the above-mentioned elimination reaction to proceed. The temperature is preferably 10°C or higher, more preferably 15°C or higher. From the viewpoint of energy conservation, the temperature is preferably 50°C or lower, more preferably 40°C or lower.

[0124] The amount of aqueous solution containing at least one of sodium chloride and sodium hydroxide used is preferably 0.001 to 1 L per 1 g of inorganic oxide composite after contact with the gas to be treated, from the viewpoints of carbon dioxide desorption, reuse of the inorganic oxide composite, and wastewater discharge. The amount used is preferably 0.002 L or more, more preferably 0.003 L or more, and even more preferably 0.005 L or more. The amount used is preferably 0.9 L or less, more preferably 0.8 L or less, and even more preferably 0.7 L or less.

[0125] Examples of the washing method include a method in which the aqueous solution is passed through an inorganic oxide composite packed in a column, or a method in which the inorganic oxide composite is added to the aqueous solution, stirred, and then filtered.

[0126] The sodium hydrogencarbonate obtained in the form of an aqueous solution by the method for producing sodium hydrogencarbonate of the present invention can be concentrated and recovered by electrodialysis using an ion exchange membrane, i.e., an electrodialysis membrane system using a cation exchange membrane and an anion exchange membrane in combination.

[0127] As described above, the present specification discloses the following configurations. <1> inorganic oxide base material, 0.1% by mass or more of nitrogen atoms derived from amine compounds, and An inorganic oxide composite comprising at least one metal atom selected from the group consisting of copper, vanadium, nickel, and iron. <2> The inorganic oxide composite contains silicon atoms. <1> The inorganic oxide composite according to claim 1. <3> an amine compound supported on the inorganic oxide substrate, and the metal atom is coordinated to a nitrogen atom of an amino group of the amine compound; <1> or <2> The inorganic oxide composite according to claim 1. <4> The inorganic oxide substrate is a porous body. <1> ~ <3> 10. The inorganic oxide composite according to any one of the above items. <5> The density of the metal atoms per surface area of ​​the inorganic oxide composite is 1.0 × 10 -6 mol / m 2The above <1> ~ <4> 10. The inorganic oxide composite according to any one of the above items. <6> The above has an absorption peak in a wavelength band of 400 to 1000 nm. <1> ~ <5> 10. The inorganic oxide composite according to any one of the above items. <7> The inorganic oxide base material is inorganic oxide fine particles. <1> ~ <6> 10. The inorganic oxide composite according to any one of the above items. <8> The inorganic oxide substrate is an inorganic oxide molded body. <1> ~ <6> 10. The inorganic oxide composite according to any one of the above items. <9> The method is used to adsorb gaseous carbon dioxide. <1> ~ <8> 10. The inorganic oxide composite according to any one of the above items. <10> The aforementioned <1> ~ <9> A carbon dioxide adsorbent comprising the inorganic oxide composite according to any one of the above items. <11> The molded body has a size of 1 to 50 mm. <10> The carbon dioxide adsorbent according to claim 1. <12> The aforementioned <1> ~ <9> 1. A method for separating carbon dioxide, comprising contacting a gas to be treated containing carbon dioxide with the inorganic oxide composite according to any one of the above items. <13> The contacting is carried out at room temperature. <12> The carbon dioxide separation method according to claim 1. <14> The concentration of the carbon dioxide contained in the gas to be treated is 0.001 to 20% by volume. <12> or <13> The carbon dioxide separation method according to claim 1. <15> The aforementioned <1> ~ <9> 1. A method for producing sodium hydrogencarbonate, comprising contacting the inorganic oxide composite according to any one of 1 to 3 with a gas to be treated containing carbon dioxide, and washing the inorganic oxide composite after contact with the gas to be treated with an aqueous solution containing at least one of sodium chloride and sodium hydroxide at 5°C or higher. [Example]

[0128] The present invention will be described in more detail below with reference to examples, but is not limited to these. Unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass," respectively. Example 3 is an example, and Examples 1, 2, 4, and 5 are comparative examples.

[0129] <Evaluation method> The carbon dioxide adsorbents of Examples 1 to 5 were evaluated as follows.

[0130] (nitrogen atom content) The content of nitrogen atoms derived from the amine compound in the carbon dioxide adsorbent was quantified using SEM-EDX (a scanning electron microscope "S-4800" (trade name) manufactured by Hitachi High-Technologies Corporation, and an energy dispersive X-ray analyzer (EDX) "X-MaxN80" manufactured by Horiba, Ltd., and its analysis software "EMAXevo software").

[0131] (Copper atom content) The content of copper atoms in the carbon dioxide adsorbent was determined by the above-mentioned SEM-EDX.

[0132] (Measurement of pore properties by nitrogen adsorption method) The specific surface area, average pore diameter, and pore volume of the carbon dioxide adsorbent were determined by nitrogen adsorption using a specific surface area and pore distribution measuring device "TriStar II 3020 type" (trade name, manufactured by Micromeritics). The average pore size is V (ml / g), which is the total pore volume of pores with diameters of 1.7 to 120 nm, and the specific surface area is S (m 2 / g), the average pore diameter (nm) can be calculated using the formula: average pore diameter (nm) = 4000V / S.

[0133] (density of copper atoms) From the copper atom content and specific surface area obtained above, the copper atom density per surface area of ​​the carbon dioxide adsorbent (powdered inorganic oxide composite) was calculated using the following formula. Density of metal atoms per surface area of ​​inorganic oxide composite (mol / m 2 ) = Metal atom content (mass%) / (specific surface area of ​​inorganic oxide composite (m 2 / g) × atomic weight of metal atom × 100)

[0134] (methanol hydrophobicity) 50 cc of distilled water was placed in a 300 cc beaker, and 5 g of carbon dioxide adsorbent was added while stirring thoroughly. If the carbon dioxide adsorbent was uniformly dispersed, the degree of methanol hydrophobicity was recorded as 0%. If the carbon dioxide adsorbent was not uniformly dispersed, methanol was gradually added dropwise until the carbon dioxide adsorbent was uniformly dispersed in the aqueous solution. The degree of methanol hydrophobicity D (unit: %) was calculated using the following formula from the total amount of methanol added M (unit: cc) until the adsorbent was uniformly dispersed. D=100M / (M+50)

[0135] (Absorption peak) The carbon dioxide adsorbent was added to a ninhydrin solution and heated at 90°C for 10 minutes to obtain a solution, and the solution was subjected to measurement of its ultraviolet-visible absorption spectrum using a UV-visible near-infrared spectrophotometer "V-670" (product name, manufactured by JASCO Corporation). The spectrum obtained was evaluated for the presence or absence of an absorption peak in the wavelength range of 400 to 1000 nm. The presence of an absorption peak was marked as +, and the absence of an absorption peak was marked as -.

[0136] (carbon dioxide adsorption amount) The amount of carbon dioxide adsorbed by the carbon dioxide adsorbent was determined by the method described in the description of the preferred embodiment of the present invention. The temperature of the gas to be treated used in the measurement was 25°C, and the humidity was 50% RH.

[0137] (Whether or not sodium bicarbonate is produced) After measuring the amount of carbon dioxide adsorption as described above, 10 ml of a 3 mass % aqueous sodium chloride solution was passed through the column packed with the carbon dioxide adsorbent at a rate of 10 ml per 1 g of the carbon dioxide adsorbent after contact with the gas to be treated. Sodium bicarbonate was recovered from the resulting solution by electrodialysis using an ion exchange membrane, and the amount of sodium bicarbonate produced was measured. The amount of sodium bicarbonate produced was 1 x 10 per 1 g of the carbon dioxide adsorbent before carbon dioxide adsorption. -3 g or more, it is marked as + (production), and the production amount is 1×10 -3 If it was less than g, it was recorded as - (no production).

[0138] (Moldability) The powdered (particulate) carbon dioxide adsorbent was molded into a cylindrical shape with a diameter of 5 mm and a height of 5 mm using a tablet molding machine. The obtained molded body was observed under an optical microscope, and the number of cracks was 100 / cm. 2 If the crack count is less than 100 / cm, it is graded as A (good). 2 If the result was above this, it was rated as B (bad).

[0139] (Heat resistance) 0.3 g of the carbon dioxide adsorbent was placed in a glass vial, covered with aluminum foil, and with several holes poked in it, placed in a heated oven and held in air at 80°C for 60 hours. The amount of carbon dioxide adsorbed after the heat resistance test was measured using the method described above, and the rate of change from the initial amount of carbon dioxide adsorbed before the heat resistance test was calculated.

[0140] <Test Example 1: Example 1 to Example 4> (Example 1) A porous silica powder having the following physical properties was used as the carbon dioxide adsorbent in Example 1. Specific surface area: 626.2m 2 / g Average pore size: 5.63nm Pore ​​volume: 1.742 cm 3 / g

[0141] (Example 2) The carbon dioxide adsorbent of Example 1 was modified with amine by the following method. 600 g of the carbon dioxide adsorbent of Example 1 (porous silica powder) was placed in a mixer FM10 manufactured by Nippon Coke Corporation, and then 600 g of aminopropyltriethoxysilane was added while stirring the silica, and the mixture was reacted at 80°C for 3 hours. After the reaction, the silica was washed with ethanol and filtered to obtain the carbon dioxide adsorbent of Example 2 (amine-modified porous silica powder). The carbon dioxide adsorbent of Example 2 contained 3 mass% of nitrogen atoms derived from the amine compound.

[0142] (Example 3) The carbon dioxide adsorbent of Example 2 was further subjected to copper complexation by the following method. 3 g of the carbon dioxide adsorbent of Example 2 (amine-modified porous silica powder) was weighed out and added to 200 g of a 0.1 g / L aqueous copper chloride solution, and the mixture was stirred at room temperature for 1 hour. After the reaction, the mixture was washed with water and filtered to obtain the carbon dioxide adsorbent of Example 3. The carbon dioxide adsorbent of Example 3 contained 1 mass % of nitrogen atoms derived from the amine compound and 4.1 mass % of copper atoms.

[0143] (Example 4) A carbon dioxide adsorbent (porous silica powder) was prepared by the same amine modification as in Example 2, except that MCM-41 manufactured by ACS MATERIAL was used as the carbon dioxide adsorbent (porous silica powder), to obtain a carbon dioxide adsorbent (amine-modified porous silica powder) of Example 4. The carbon dioxide adsorbent of Example 4 contained 3.2 mass% of nitrogen atoms derived from the amine compound.

[0144] The carbon dioxide adsorbents prepared in Examples 1 to 4 above were measured and evaluated for copper atom content, specific surface area, average pore diameter, pore volume, degree of methanol hydrophobicity, presence or absence of absorption peaks in the wavelength band of 400 to 1000 nm, carbon dioxide adsorption amount, and presence or absence of sodium bicarbonate formation. The results are shown in Table 1. A "+" indicates that the base material was amine-modified, and a "-" indicates that it was not. Furthermore, a "+" indicates that the amine-modified base material was further subjected to copper complexation, and a "-" indicates that it was not.

[0145] [Table 1]

[0146] <Test Example 2: Example 3 and Example 5> (Example 5) A carbon dioxide adsorbent (amine-modified ion exchange resin) of Example 5 was obtained in the same manner as in Example 3, except that an ion exchange resin (Purolite (registered trademark) A110, manufactured by Purolite) was used as the base material instead of the carbon dioxide adsorbent (porous silica powder). The carbon dioxide adsorbent of Example 5 contained 7.6 mass% of nitrogen atoms derived from the amine compound.

[0147] The carbon dioxide adsorbents prepared in Examples 3 and 5 were measured and evaluated for copper atom content, presence or absence of an absorption peak in the wavelength band of 400 to 1000 nm, carbon dioxide adsorption amount, moldability, and heat resistance (rate of change in carbon dioxide adsorption amount due to heat resistance test). The results are shown in Table 2.

[0148] [Table 2]

[0149] It was found that the carbon dioxide adsorbent of Example 3 has excellent carbon dioxide adsorption capacity at room temperature, can easily desorb adsorbed carbon dioxide, and has moldability and excellent heat resistance.

Claims

1. inorganic oxide base material, 0.1% by mass or more of nitrogen atoms derived from amine compounds, and An inorganic oxide composite comprising at least one metal atom selected from the group consisting of copper, vanadium, nickel, and iron.

2. The inorganic oxide composite according to claim 1 , wherein the inorganic oxide composite contains silicon atoms.

3. 2. The inorganic oxide composite according to claim 1, wherein an amine compound is supported on the inorganic oxide substrate, and the metal atom is coordinated to a nitrogen atom of an amino group of the amine compound.

4. The inorganic oxide composite according to claim 1 , wherein the inorganic oxide substrate is a porous body.

5. The density of the metal atoms per surface area of ​​the inorganic oxide composite is 1.0 × 10 －６ mol / m ２ The inorganic oxide composite according to claim 1 .

6. The inorganic oxide composite according to claim 1, which has an absorption peak in a wavelength band of 400 to 1000 nm.

7. The inorganic oxide composite according to claim 1 , wherein the inorganic oxide base material is inorganic oxide fine particles.

8. The inorganic oxide composite according to claim 1 , wherein the inorganic oxide substrate is an inorganic oxide molded body.

9. The inorganic oxide composite according to claim 1, which is used to adsorb gaseous carbon dioxide.

10. A carbon dioxide adsorbent comprising the inorganic oxide composite according to any one of claims 1 to 9.

11. The carbon dioxide adsorbent according to claim 10, which is a molded body having a size of 1 to 50 mm.

12. A method for separating carbon dioxide, comprising contacting the inorganic oxide composite according to any one of claims 1 to 9 with a gas to be treated that contains carbon dioxide.

13. The method for separating carbon dioxide according to claim 12, wherein the contact is carried out at room temperature.

14. 13. The carbon dioxide separation method according to claim 12, wherein the concentration of the carbon dioxide contained in the gas to be treated is 0.001 to 20% by volume.

15. A method for producing sodium hydrogencarbonate, comprising contacting the inorganic oxide composite according to any one of claims 1 to 9 with a gas to be treated containing carbon dioxide, and washing the inorganic oxide composite after contact with the gas to be treated with an aqueous solution containing at least one of sodium chloride and sodium hydroxide at a temperature of 5°C or higher.

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