Inorganic powder, inorganic powder water slurry, and inorganic powder-carrying porous material

Abstract

The present invention provides an inorganic powder capable of repeatedly adsorbing and desorbing carbon dioxide or radiating and storing heat and an inorganic powder water slurry which can be carried on a carrying base material such as a heat exchanger base material. Provided is an inorganic powder-carrying porous material in which an inorganic powder is carried on a porous material.　The present invention provides: an inorganic powder which has a specific surface area of 3-120 m2 / g as measured by the BET method, which has calcium carbonate, calcium hydroxide, or a mixture of the same as the main component, and in which the calcium carbonate, the calcium hydroxide, or the mixture of the same contains, with respect to the total mass of the inorganic powder, 0.1-15% of an element selected from the group consisting of strontium, barium, radium, beryllium, and magnesium; an inorganic powder water slurry in which the inorganic powder is dispersed in water; and a porous material on which the inorganic powder is carried.

Description

Inorganic powders, inorganic powder aqueous slurries, and inorganic powder-supported porous materials

[0001] The present invention relates mainly to inorganic powders, inorganic powder aqueous slurries, and inorganic powder-supported porous materials used as carbon dioxide adsorption / desorption materials or chemical heat storage materials.

[0002] Various efforts are being made in countries around the world to achieve zero-emission targets. Among these, the use of renewable energy is being actively pursued, with proposals for power generation using solar energy, solar thermal energy, wind power, geothermal energy, and tidal power, for example. However, such naturally occurring energies are susceptible to fluctuations in load due to changes in factors such as sunshine hours and wind speed, making it difficult to ensure a stable supply. Therefore, the development of systems that can store renewable energy on a large scale in some form is desired.

[0003] On the other hand, chemical heat storage materials that utilize the reversible reaction of chemical substances are known. For example, calcium oxide (CaO) releases heat when it hydrates and changes to calcium hydroxide, and conversely, absorbs heat when calcium hydroxide dehydrates and changes back to calcium oxide, so it can be used as a chemical heat storage material that can repeatedly release and store heat. Chemical heat storage materials are filled inside heat exchangers and the like to exchange heat. However, when inorganic powders such as calcium oxide are used as chemical heat storage materials, the low thermal conductivity of inorganic powders makes it difficult to recover heat at locations far from the heat exchanger, resulting in a problem of low heat recovery efficiency. In addition, calcium oxide powder in particular increases in volume when hydrated and decreases in volume when dehydrated, but there was also the problem that the calcium oxide powder would become finer as heat release and storage were repeated. Furthermore, powdered chemical heat storage materials have gaps when filled, so there was also the problem that sufficient filling could not be achieved.

[0004] Various studies are being conducted to solve these problems. For example, calcium acetate (Ca(CH) ３ COO) ２A system has been proposed to obtain thermal energy by a direct carbonation reaction of a CaO-MgO mixture prepared by physically mixing CaO with small magnesium oxide (MgO) particles and then calcining it at high temperature (Non-Patent Literature 1). A CaO-MgO mixture with an MgO content of 26% by weight showed a high carbon dioxide absorption rate of 53% by weight after calcination at 50°C (Non-Patent Literature 1).

[0005] Furthermore, it has been confirmed that CaO-MgO porous monoliths synthesized by the rapid, self-sustaining combustion reaction of molded pellets consisting of a mixture of calcium and magnesium nitrates, urea, and starch can capture carbon dioxide at high temperatures (650°C) under atmospheric pressure (Non-Patent Literature 2). These porous monoliths were able to undergo repeated carbonation-decarboxylation.

[0006] LIYU LI, DAVID L. KING, ZIMIN NIE and CHRIS HOWARD, Magnesia-Stabilized Calcium Oxide Absorbents with Improved Durability for High Temperature CO2 Capture, Ind. Eng. Chem. Res. 2009, 48, 10604-10613, ACS Publications, Washington, DCRALPH RAJAMATHI, BHOJARAJ, and C. NETHRAVATHI, Porus CaO-MgO Nanostructures for CO2 Capture, ACS Appl. Nano Mater. 2021, 4, 10969-10975, ACS Publications, Washington, DC

[0007] As described in Non-Patent Documents 1 and 2, systems have been proposed that utilize the adsorption and desorption of carbon dioxide by calcium oxide to perform heat dissipation and heat storage. However, these systems tend to become less efficient in the adsorption and desorption reactions as heat dissipation and storage are repeated.

[0008] Therefore, the present invention aims to provide an inorganic powder capable of repeatedly adsorbing and desorbing carbon dioxide, or releasing and storing heat. Furthermore, the present invention aims to provide an inorganic powder aqueous slurry that can be supported on a support substrate such as a heat exchanger substrate. Furthermore, the present invention aims to provide an inorganic powder-supported porous material in which inorganic powder is supported on a porous material.

[0009] One embodiment of the present invention is a specific surface area of ​​3-120 m² obtained by the BET method. ２ An inorganic powder having a concentration of calcium carbonate, calcium hydroxide, or a mixture thereof as its main component, wherein the calcium carbonate, calcium hydroxide, or mixture thereof contains 0.1-15% of an element selected from the group consisting of strontium, barium, radium, beryllium, and magnesium, based on the total mass of the inorganic powder.

[0010] A second embodiment of the present invention is an inorganic powder aqueous slurry comprising an inorganic powder mainly composed of calcium carbonate, calcium hydroxide, or a mixture thereof, and water, wherein the inorganic powder is an inorganic powder containing 0.1-15% of an element selected from the group consisting of strontium, barium, radium, beryllium, and magnesium, based on the total mass of the inorganic powder, and the specific surface area of ​​the inorganic powder by the BET method when dry is 3-120 m². ２ It is an inorganic powder aqueous slurry with a concentration of / g.

[0011] The third embodiment of the present invention is a specific surface area of ​​3-120 m² obtained by the BET method. ２ An inorganic powder-supported porous material is provided, wherein an inorganic powder mainly composed of calcium carbonate, calcium hydroxide, or a mixture thereof, at a concentration of / g, is supported on a porous material made of metal or ceramic, and the inorganic powder is an inorganic powder containing 0.1-15% of an element selected from the group consisting of strontium, barium, radium, beryllium, and magnesium, based on the total mass of the inorganic powder.

[0012] The present invention can provide inorganic powders and inorganic powder aqueous slurries that can repeatedly dissipate and store heat. Furthermore, the present invention can provide an inorganic powder-supported porous material in which inorganic powder is supported on a porous material. The inorganic powder of the present invention has the function of storing and dissipating heat by adsorbing and desorbing carbon dioxide, and can therefore be used as a chemical heat pump (chemical heat storage material) and for reducing greenhouse gas emissions.

[0013] Figure 1 shows an example of an apparatus for measuring the carbonation-decarboxylation characteristics of inorganic powder supported on a porous material. Figure 2 is a magnified view of the portion of the apparatus in Figure 1 that contains the porous material supporting the inorganic powder. Figure 3 is an electron microscope image showing how the crystal shape of calcium carbonate changes when decarboxylation and carbonation reactions are repeatedly performed on calcium carbonate powder.

[0014] Embodiments of the present invention will be described in more detail below, but the present invention is not limited to the following embodiments.

[0015] One embodiment of the present invention is a specific surface area of ​​3-120 m² obtained by the BET method. ２ An inorganic powder having a concentration of calcium carbonate, calcium hydroxide, or a mixture thereof as its main component, wherein the calcium carbonate, calcium hydroxide, or mixture thereof contains 0.1-15% of an element selected from the group consisting of strontium, barium, radium, beryllium, and magnesium, based on the total mass of the inorganic powder.

[0016] One embodiment is an inorganic powder mainly composed of calcium carbonate, calcium hydroxide, or a mixture thereof. The inorganic powder is calcium carbonate (calcium carbonate: CaCO3). ３ ), calcium hydroxide (calcium hydroxide: Ca(OH) ２) or mixtures thereof. In this specification, inorganic powder mainly composed of calcium carbonate, calcium hydroxide, or mixtures thereof means that calcium carbonate, calcium hydroxide, or mixtures thereof constitute the majority of the mass of the inorganic powder. When referring to inorganic powder mainly composed of calcium carbonate, calcium hydroxide, or mixtures thereof, it means, for example, that calcium carbonate, calcium hydroxide, or mixtures thereof constitute 85% or more, preferably 90% or more, and more preferably 95% or more, of the mass of the inorganic powder.

[0017] Calcium carbonate is the main component of seashells, eggshells, limestone, and chalk. Calcium carbonate is classified into heavy calcium carbonate, obtained by crushing and classifying limestone, and light calcium carbonate (precipitated calcium carbonate), obtained by chemical reactions. The calcium carbonate produced in one embodiment may be either heavy or light calcium carbonate. Calcium carbonate exists in various crystalline polymorphs, including calcite crystals (trigonal rhombohedral crystals), aragonite crystals (orthorhombic crystals), and vaterite crystals (hexagonal crystals). The calcium carbonate used in one embodiment is calcite crystal, and may have any shape, such as cubes, spindles, or spheres. Spindle-shaped calcite calcium carbonate has particularly high thermal stability. When calcium carbonate is strongly heated to above 825°C, it absorbs and desorbs carbon dioxide (decarboxylation) to obtain calcium oxide (CaO, quicklime), and this reaction is endothermic. The endothermic reaction of carbon dioxide desorption of calcium carbonate and the exothermic reaction of carbon dioxide adsorption of calcium oxide occur reversibly. Such reversible chemical reactions can be utilized as chemical heat storage materials.

[0018] On the other hand, calcium hydroxide is generally called slaked lime, its aqueous solution is called limewater, and its suspension is called lime milk. Calcium hydroxide reacts with carbon dioxide to form calcium carbonate, releasing heat during this reaction. Calcium hydroxide also reacts with water or steam to form calcium oxide (CaO, generally called quicklime), releasing heat during this reaction. Conversely, calcium oxide releases heat when it comes into contact with water or steam to form calcium hydroxide. It also releases heat when it reacts with carbon dioxide to form calcium carbonate. Thus, the endothermic dehydration reaction of calcium hydroxide and the exothermic hydration reaction of calcium oxide occur reversibly. Furthermore, as mentioned above, the endothermic desorption reaction of calcium carbonate to carbon dioxide and the exothermic adsorption reaction of calcium oxide to carbon dioxide occur reversibly. Such reversible chemical reactions can be used as chemical heat storage materials (chemical heat pumps).

[0019] As described above, the inorganic powder of one embodiment can be used as a chemical heat storage material. Here, the chemical heat storage material refers to a member that can chemically release and store heat. As chemical heat storage materials, for example, those using isopropanol (a combination of an endothermic reaction in which isopropanol is heated and decomposed into acetone and hydrogen, and an exothermic reaction in which acetone and hydrogen react to produce isopropanol), or those using magnesium hydroxide (a combination of an endothermic reaction in which magnesium hydroxide dehydrates to produce magnesium oxide, and a hydration exothermic reaction of magnesium oxide) are known. In this specification, a chemical heat storage material using the dehydration endothermic reaction (heat storage) and hydration exothermic reaction (heat release) of calcium hydroxide and calcium oxide, or the carbon dioxide adsorption and desorption of calcium carbonate and calcium oxide is proposed. In this specification, a substance itself in which an endothermic reaction and an exothermic reaction occur reversibly, and a mixture containing the substance as a main component are referred to as substances for chemical heat storage materials (for example, "calcium hydroxide for chemical heat storage materials", "calcium hydroxide slurry for chemical heat storage materials"), or substances used for chemical heat storage materials (for example, "calcium hydroxide used for chemical heat storage materials", "calcium hydroxide slurry used for chemical heat storage materials"), etc. Note that in this specification, when it is said "used for chemical heat storage materials", it is intended to include the meaning of "used for the production of chemical heat storage materials". In addition, a member in which a substance in which an endothermic reaction and an exothermic reaction occur reversibly is supported on a support substrate or the like, or filled in a housing or the like so that the heat stored by the substance can be utilized is widely referred to as a "chemical heat storage material".

[0020] The inorganic powder of one embodiment preferably has a specific surface area measured by the BET method of 3 - 120 m ２ / g. The BET specific surface area of the inorganic powder can be measured in accordance with Japanese Industrial Standard JIS Z 8830 "Method for Measuring Specific Surface Area of Powder (Solid) by Gas Adsorption". In order to use the inorganic powder as a chemical heat storage material, the BET specific surface area is preferably 9 - 30 m ２ / g, more preferably 10 - 20 m ２ / g.

[0021] Also, the volume-based average particle diameter (D５０ ) is preferably 0.2-10 μm. Laser diffraction particle size measurement is also called laser diffraction particle size distribution measurement and can be measured using a laser diffraction particle size distribution analyzer. In order to use the inorganic powder of one embodiment as a chemical heat storage material, D ５０ The value is preferably 0.5–8.0 μm, more preferably 1.0–7.0 μm. BET specific surface area and D ５０ The values ​​shown are all approximate particle sizes for inorganic powders. By dispersing inorganic powders with particle sizes that meet the above ranges in water, it is possible to obtain a high-concentration, low-viscosity inorganic powder aqueous slurry.

[0022] In one embodiment, the inorganic powder contains 0.1–15% of an element selected from the group consisting of strontium, barium, radium, beryllium, and magnesium, based on the total mass of the inorganic powder. If the main component of the inorganic powder is calcium carbonate, it is preferable that it contains a carbonate of a metal selected from the group consisting of strontium, barium, radium, beryllium, and magnesium, but it may also contain hydroxide salts of these metals. If the main component of the inorganic powder is calcium hydroxide, it is preferable that it contains a hydroxide salt of a metal selected from the group consisting of strontium, barium, radium, beryllium, and magnesium, but it may also contain carbonates of these metals. If the main component of the inorganic powder is a mixture of calcium carbonate and calcium hydroxide, it is preferable that it contains a mixture of carbonate and hydroxide salts of a metal selected from the group consisting of strontium, barium, radium, beryllium, and magnesium. In any case of the inorganic powder, it is important that the inorganic powder contains a predetermined amount of metal elements. The amount of metallic elements contained in inorganic powder can be measured using known methods, such as inductively coupled plasma (ICP) emission spectroscopy.

[0023] The second embodiment of the present invention is an inorganic powder aqueous slurry comprising an inorganic powder mainly composed of calcium carbonate, calcium hydroxide or a mixture thereof, and water, wherein the inorganic powder is calcium carbonate, calcium hydroxide or a mixture thereof, and contains 0.1-15% of an element selected from the group consisting of strontium, barium, radium, beryllium and magnesium based on the total mass of the inorganic powder, and the specific surface area of the inorganic powder by the BET method when dried is 3-120 m ２ / g, which is an inorganic powder aqueous slurry.

[0024] The second embodiment is an inorganic powder aqueous slurry comprising an inorganic powder mainly composed of calcium carbonate, calcium hydroxide or a mixture thereof, and water.

[0025] The inorganic powder used in the second embodiment is preferably the inorganic powder of the first embodiment. The main components of the inorganic powder are calcium carbonate, calcium hydroxide or a mixture thereof, and these components are contained at 85% or more, preferably 90% or more, and more preferably 95% or more based on the mass of the inorganic powder. The inorganic powder contains 0.1-15% of an element selected from the group consisting of strontium, barium, radium, beryllium and magnesium based on the total mass of the inorganic powder, calcium carbonate, calcium hydroxide or a mixture thereof.

[0026] Also, the specific surface area of the inorganic powder by the BET method when dried is 3-120 m ２ / g. Further, the volume-based average particle diameter (D ５０ ) by laser diffraction particle size measurement of the inorganic powder contained in the inorganic powder aqueous slurry of the second embodiment when dried is preferably 0.2-10 μm. In order to use the inorganic powder aqueous slurry of the second embodiment as a material for a chemical heat storage material, the value of D ５０ of the inorganic powder when dried is preferably 0.5-8.0 μm, more preferably 1.0-7.0 μm. By using an inorganic powder having a particle diameter within the above range, it is possible to obtain an inorganic powder aqueous slurry of the second embodiment with high concentration and low viscosity.

[0027] The second embodiment is an inorganic powder aqueous slurry composed of the inorganic powder of the first embodiment and water. The aqueous slurry of the second embodiment is particularly used for supporting the inorganic powder of the first embodiment on a porous material. The aqueous slurry is preferably mixed with water so that the solid content concentration of the inorganic powder is 50% by weight or more. In order to use the inorganic powder aqueous slurry of the second embodiment as a material for a chemical heat storage material, the solid content concentration of the inorganic powder is 50% by weight or more, preferably 55% by weight or more, and more preferably 60% by weight or more. In this specification, the "solid content concentration" refers to the concentration of the solute dissolved in water in the case of an aqueous solution, and refers to the concentration of the total weight of the solute dissolved in water and the solute suspended or dispersed in water in the case of a slurry such as a suspension or a dispersion.

[0028] Also, the viscosity of the inorganic powder aqueous slurry of the second embodiment is preferably 5,000 mPa·s or less. The viscosity of the inorganic powder aqueous slurry can be measured using a rotational viscometer in accordance with Japanese Industrial Standard JIS Z 8803:2011 "Method for Measuring Viscosity of Liquids". In order to use the inorganic powder aqueous slurry of the convenient embodiment as a material for a chemical heat storage material, the viscosity of the inorganic powder aqueous slurry is preferably 4,000 mPa·s or less, and more preferably 3,000 mPa·s or less.

[0029] The inorganic powder aqueous slurry of the second embodiment is characterized by having a relatively low viscosity while being highly concentrated. By utilizing such properties, it becomes possible to use the inorganic powder aqueous slurry of the second embodiment as a material for a chemical heat storage material.

[0030] The third embodiment of the present invention has a specific surface area by the BET method of 3 - 120 m ２An inorganic powder-supported porous material is provided, wherein an inorganic powder mainly composed of calcium carbonate, calcium hydroxide, or a mixture thereof, at a concentration of / g, is supported on a porous material made of metal or ceramic, and the inorganic powder is an inorganic powder containing 0.1-15% of an element selected from the group consisting of strontium, barium, radium, beryllium, and magnesium, based on the total mass of the inorganic powder.

[0031] The third embodiment is an inorganic powder-supported porous material, in which inorganic powder is supported on a porous material made of metal or ceramics.

[0032] The inorganic powder used in the third embodiment is preferably the inorganic powder of the first embodiment. The main components of the inorganic powder are calcium carbonate, calcium hydroxide, or a mixture thereof, and these components make up 85% or more, preferably 90% or more, and more preferably 95% or more, based on the mass of the inorganic powder. The inorganic powder contains calcium carbonate, calcium hydroxide, or a mixture thereof, with 0.1-15% of an element selected from the group consisting of strontium, barium, radium, beryllium, and magnesium, based on the total mass of the inorganic powder.

[0033] Furthermore, the specific surface area of ​​inorganic powders when dried using the BET method is 3-120 m². ２ It is / g. Furthermore, the volume-based average particle size (D) obtained by laser diffraction particle size measurement when the inorganic powder contained in the inorganic powder aqueous slurry of the second embodiment is dried. ５０ The particle size is preferably 0.2-10 μm. In order to use the inorganic powder aqueous slurry of the second embodiment, which uses the inorganic powder of the first embodiment, as the inorganic powder-supported porous material of the third embodiment, the drying time of the inorganic powder is D ５０ The value of is preferably 0.5–8.0 μm, and more preferably 1.0–7.0 μm. By using inorganic powder having a particle size that satisfies the above range, it is possible to obtain a high-concentration, low-viscosity inorganic powder aqueous slurry of the second embodiment, thereby making it easy to obtain the inorganic powder-supported porous material of the third embodiment.

[0034] The porous material used in the third embodiment, which is composed of a metal or ceramic, is preferably a porous substrate containing a substance selected from the group consisting of, for example, silicon, iron, platinum, palladium, silicon carbide, aluminum nitride, silicon nitride, boron nitride, magnesium oxide, aluminum oxide, beryllium oxide, and mixtures thereof. Here, a porous substrate refers to a substrate material in which pores (micropores or holes) are present. Depending on the size of the pores, there are microporous substrates, mesoporous substrates, and macroporous substrates, and any of these substrates may be used in the third embodiment. The pores in the porous material may be independent pores or continuous pores.

[0035] Next, an example of a method for producing an inorganic powder according to one embodiment will be described. As an example of an inorganic powder according to one embodiment, an example of producing an inorganic powder mainly composed of calcium carbonate (calcium carbonate) will be described.

[0036] Limestone is calcined in an incinerator at approximately 900-1,100°C to decompose it and obtain calcium oxide. After the obtained calcium oxide is allowed to cool, it is reacted with water. The limestone used as a raw material is calcium carbonate (CaCO3). ３ This is the name (or trade name) of the ore. In other words, in this process, calcium carbonate may be used instead of limestone. When water is added to calcium oxide, heat is generated, and an aqueous slurry of calcium hydroxide (slaked lime) is obtained. In this process, heat is generated as the reaction between calcium oxide and water progresses, so the reaction proceeds sequentially without heating the reaction system. At this time, the reaction is carried out so that the pH of the reaction system is 9-14, preferably 10-13. The calcium oxide and water are reacted so that the solid content concentration of the aqueous slurry of calcium hydroxide obtained in this reaction is about 10-30% by mass, preferably about 12-20% by mass.

[0037] The obtained calcium hydroxide aqueous slurry is mixed with a separately prepared magnesium hydroxide aqueous slurry to obtain a calcium hydroxide / magnesium hydroxide mixed aqueous slurry. At this time, the magnesium hydroxide aqueous slurry can be mixed so that the amount of magnesium hydroxide is about 5-30%, preferably about 10-20%, relative to the solid content mass of calcium hydroxide. However, the amount of magnesium hydroxide is adjusted appropriately at this stage so that the final inorganic powder product contains the desired amount of magnesium element.

[0038] A gas containing carbon dioxide is introduced into the obtained calcium hydroxide / magnesium hydroxide aqueous slurry to carry out the carbonation reaction of calcium hydroxide and magnesium hydroxide. The carbonation reaction is carried out at room temperature to about 40°C (preferably around 30°C), and the carbon dioxide concentration in the introduced gas can be about 10-50% by volume, preferably about 20-30% by volume. In this way, a calcium carbonate / magnesium carbonate aqueous slurry is obtained.

[0039] The obtained calcium carbonate / magnesium carbonate aqueous slurry is dewatered using a suitable dewatering machine (such as a filter press) to obtain a dewatered cake with a solid content of approximately 50-70%. Next, the cake is dried using a suitable dryer (such as an air-flow dryer) to a moisture content of approximately 5% or less, preferably approximately 2% or less. Subsequently, the obtained solid is pulverized using a suitable grinding and classifying machine to obtain the inorganic powder of one embodiment, which is the target product.

[0040] An example of a method for producing an inorganic powder aqueous slurry according to the second embodiment will be described. As the inorganic powder aqueous slurry according to the second embodiment, an example of producing an inorganic powder aqueous slurry mainly composed of calcium carbonate (calcium carbonate) will be described.

[0041] Prepare water in which a suitable dispersant (such as a polycarboxylate-type surfactant, polyacrylate-type surfactant, alkyl sulfonic acid-type surfactant, quaternary ammonium-type surfactant, or polyphosphate-type surfactant) is dissolved. The amount of dispersant should be about 0.5-3 parts by weight, preferably 1.0-2.0 parts by weight, per 100 parts by weight of the solid content of the inorganic powder to be added later. Gradually add the inorganic powder obtained by the method described above to the obtained dispersant aqueous solution and stir to obtain an inorganic powder aqueous slurry. The solid content concentration of the inorganic powder aqueous slurry should be about 50% by weight or more, preferably about 55% by weight or more, more preferably about 65% by weight or more, and up to about 70% by weight. In this way, the inorganic powder aqueous slurry of the second embodiment, which is the target product, is obtained.

[0042] Another example of the method for producing the inorganic powder aqueous slurry of the second embodiment will be described. As the inorganic powder aqueous slurry of the second embodiment, an example of producing an inorganic powder aqueous slurry mainly composed of calcium hydroxide will be described.

[0043] A suitable dispersant (such as a polycarboxylate-type surfactant) is added to the calcium hydroxide / magnesium hydroxide mixed aqueous slurry obtained during the process described above. At this time, the solid content concentration of the calcium hydroxide / magnesium hydroxide mixed aqueous slurry is adjusted to about 10-30% by mass, preferably about 12-20% by mass, and more preferably about 15-18% by mass, and the amount of dispersant added is about 0.5-3 parts by weight, preferably 1.0-2.0 parts by weight, per 100 parts by weight of solid content of calcium hydroxide / magnesium hydroxide. In this way, the target product, an inorganic powder (calcium hydroxide / magnesium hydroxide) aqueous slurry of the second embodiment, is obtained.

[0044] An example of a method for manufacturing an inorganic powder-supported porous material according to the third embodiment will be described. As the inorganic powder-supported porous material according to the third embodiment, an example of manufacturing a porous material on which an inorganic powder mainly composed of calcium carbonate is supported will be described.

[0045] The inorganic powder aqueous slurry of the second embodiment obtained above (an inorganic powder aqueous slurry mainly composed of calcium carbonate) is impregnated into a porous material. The porous material used here is, for example, a porous substrate containing a substance selected from the group consisting of silicon, silicon carbide, aluminum nitride, silicon nitride, boron nitride, magnesium oxide, aluminum oxide, beryllium oxide, and mixtures thereof. The impregnation of the porous material with the inorganic powder aqueous slurry is carried out under reduced pressure of about 10 kPa or less, preferably about 8 kPa or less, and more preferably 5 kPa or less, for a predetermined time (a time suitable for the size of the porous material). The porous material impregnated with the inorganic powder aqueous slurry is held in an environment of about 50-150°C, preferably about 80-120°C, and more preferably about 90-110°C for a predetermined time (a time suitable for the size of the porous material), and then dried in an environment slightly hotter than the holding temperature for half a day to several days to obtain the target product, the inorganic powder-supported porous material of the third embodiment.

[0046] The three embodiments of the use of the inorganic powder-supported porous material will be described.

[0047] Figure 1 shows an example of an apparatus for measuring the carbonation-decarboxylation characteristics of inorganic powder supported on a porous material according to the third embodiment.

[0048] In Figure 1, 1 is a porous material supporting inorganic powder, 2 is a reactor, 3 is a furnace, 4 is a mass flow controller, 5 is an evaporator, 6 is a microfeeder, 7 is a water storage tank, 8 is a gas chromatograph, 9 is a pressure gauge, 10 is a tube heater, and 11 is a vacuum pump. In Figure 1, the porous material supporting inorganic powder 1 is shown as a cylindrical porous material on which inorganic powder is supported. Although not shown in Figure 1, the apparatus is equipped with thermometers at appropriate locations. If the inorganic powder supported on the porous material is an inorganic powder mainly composed of calcium carbonate, then by operating the vacuum pump 10 to reduce the pressure in the apparatus system, including the reactor 2, and heating the furnace 3 (to approximately 900°C), a decarboxylation reaction of the inorganic powder occurs. The reaction conversion rate of the inorganic powder is calculated by analyzing the gas generated by the decarboxylation reaction using gas chromatography 8.

[0049] Figure 2 is an enlarged view of the portion of the porous material 1 supporting the inorganic powder in the apparatus shown in Figure 1. The endothermic reaction due to the decarboxylation of the inorganic powder is monitored by sequentially measuring the temperatures at four locations T1, T2, T3, and T4 in Figure 2.

[0050] (Mathematics 1) CaCO ３ + (heat) → CaO + CO ２ Thus, the inorganic powder supported on the inorganic powder-supported porous material 1 becomes an inorganic powder mainly composed of calcium oxide, which is produced by the decarboxylation of an inorganic powder mainly composed of calcium carbonate. Next, a carbonation reaction is carried out on the inorganic powder-supported porous material 1 that mainly consists of calcium oxide. Using a mass flow controller 4, a mixed gas of carbon dioxide and nitrogen is supplied to the reactor 2 surrounded by a furnace 3, and reacts with the inorganic powder supported on the inorganic powder-supported porous material 1 built into the reactor 2. By heating the temperature of the furnace 3 to approximately 900°C, the carbon dioxide in the mixed gas reacts with the inorganic powder (calcium oxide). The mixed gas that has passed through the inorganic powder-supported porous material 1 is analyzed by gas chromatography 8, and the reaction conversion rate of the inorganic powder is calculated.

[0051] The exothermic reaction caused by the carbonation of inorganic powders is monitored by sequentially measuring the temperatures at four locations, T1, T2, T3, and T4, in Figure 2.

[0052] (Math. 2) CaO + CO ２ → CaCO ３ + (Heat) By repeatedly performing the decarboxylation-carbonation reaction of the inorganic powder supported on the inorganic powder-supported porous material 1, the cycle characteristics of the inorganic powder supported on the inorganic powder-supported porous material 1 can be estimated.

[0053] If the inorganic powder supported in the inorganic powder-supported porous material 1 is an inorganic powder mainly composed of calcium hydroxide (calcium hydroxide), it is preferable to first perform a carbonation reaction of calcium hydroxide to obtain calcium carbonate. By performing a carbonation reaction of calcium hydroxide, the inorganic powder supported in the inorganic powder-supported porous material can be converted into an inorganic powder mainly composed of calcium carbonate, making it possible to repeatedly perform the above decarboxylation-carbonation reaction.

[0054] (Math 3) Ca(OH) ２ + CO ２ → CaCO ３ + (heat)

[0055] The embodiments of the present invention will be described in detail below. The present invention is not limited to the following embodiments unless it exceeds the scope of its essence.

[0056] [Preparation of Calcium Carbonate Powder Containing Magnesium] In the process of producing calcium carbonate by hydrating calcium oxide and then reacting it with carbon dioxide, magnesium hydroxide was added to the calcium hydroxide aqueous slurry obtained midway through the process to carry out the final step of the carbonation reaction, and then dried to obtain an inorganic powder mainly composed of calcium carbonate containing magnesium (sample name: ES-55). The magnesium content of the obtained inorganic powder ES-55 was measured by ICP emission spectrometry and was found to be 6% by weight. Furthermore, the BET specific surface area of ​​the obtained inorganic powder ES-55 was measured according to JIS Z 8830 "Method for Measuring Specific Surface Area of ​​Powders (Solids) by Gas Adsorption" and was found to be 14 m². ２ It was / g.

[0057] BET specific surface area 12m ２ A solution was prepared by dry-mixing magnesium hydroxide with 2.5% by weight of magnesium element into calcium carbonate (control, sample name: ES-46) at a concentration of 1 / g (sample name: ES-63, BET specific surface area 12 m²). ２ / g).

[0058] Similarly, ES-46 was dry-mixed with magnesium hydroxide to a magnesium element content of 5% by weight (sample name: ES-64, BET specific surface area 12 m²).２ A solution was prepared ( / g). For comparison, a BET specific surface area of ​​6.6 m² was also prepared. ２ A sample of calcium carbonate (sample name: ES-72) was prepared at a concentration of 1 / g.

[0059] [Preparation of calcium hydroxide powder containing magnesium element] In the process of hydrating calcium oxide and then reacting it with carbon dioxide to produce calcium carbonate, the resulting calcium hydroxide aqueous slurry was dried to obtain calcium hydroxide (control, sample name: ES-57, BET specific surface area 10 m²). ２ / g).

[0060] ES-57 was dry-mixed with magnesium hydroxide to achieve a magnesium element content of 5% by weight (Sample name: ES-58, BET specific surface area 10 m²). ２ ( / g); ES-57 with magnesium hydroxide dry-mixed so that the magnesium element content is 15% by weight (Sample name: ES-59, BET specific surface area 9 m²) ２ A solution was prepared ( / g).

[0061] [Manufacturing of Inorganic Powder-Supported Porous Material] A dispersant (product name: Poise 520, manufacturer: Kao Corporation, polycarboxylate-type surfactant) was dissolved in water, and ES-55 was gradually added to obtain an ES-55 aqueous slurry. The concentration of the dispersant was adjusted to 1.0 part per 100 parts of solid weight of ES-55 in the ES-55 aqueous slurry, so that the solid content concentration of the aqueous slurry was approximately 50-65% by weight. The viscosity of the aqueous slurry was 330 mPas (measured with a rotational viscometer). Silicon-impregnated silicon carbide foam (NGK Insulators, Ltd., cylindrical shape with a diameter of 35 mm, a length of 60 mm, a central pore diameter of 7.5 mm, porosity of 92%, pore diameter of 0.4 mm) was placed in the aqueous slurry and maintained under reduced pressure of 5 kPa or less for 10 minutes to impregnate the silicon-impregnated silicon carbide foam with the ES-55 aqueous slurry. After leaving it at 90°C for 1 hour, the silicon-impregnated silicon carbide foam impregnated with ES-55 aqueous slurry was removed and dried in a 120°C dryer for more than 12 hours to obtain ES-55 supported silicon-impregnated silicon carbide foam (sample name: ES-55-SiSiC).

[0062] [Evaluation of porous materials supported by inorganic powder mainly composed of calcium carbonate] Using four types of inorganic powders (ES-63, ES-64, ES-46, ES-72) with different magnesium content, porous materials supported by inorganic powder were prepared using the same method as for ES-55-SiSiC. For each of the porous inorganic powder materials, the decarboxylation reaction and carbonation reaction were repeated 30 times using the apparatus shown in Figure 1. The decarboxylation reaction of the inorganic powder was carried out by heating to 900°C for 20 minutes under an argon gas atmosphere. On the other hand, the carbonation reaction of the inorganic powder was carried out by heating to 750°C for 20 minutes under a carbon dioxide gas atmosphere. After each decarboxylation reaction and carbonation reaction (one cycle), the reaction conversion rate was calculated and the cycle characteristics of each inorganic powder were evaluated.

[0063] Table 1 shows the conversion rate (%) at the end of one cycle, the conversion rate (%) at the end of 30 cycles, and the ratio (%) of the conversion rate (%) at the end of 30 cycles to the conversion rate (%) at the end of one cycle, as the cycle performance for each sample.

[0064]

[0065] An inorganic powder mainly composed of calcium carbonate containing magnesium element maintained a good reaction conversion rate even after repeating the decarboxylation and carbonation reaction cycle 30 times.

[0066] [Evaluation of porous materials supported by inorganic powder mainly composed of calcium hydroxide] Using three types of inorganic powders (ES-57, ES-58, ES-59) with different magnesium content, porous materials supported by inorganic powder were prepared using the same method as for ES-55-SiSiC described above. For each of the porous inorganic powder materials, the decarboxylation reaction and carbonation reaction were repeated 30 times using the apparatus shown in Figure 1. The decarboxylation reaction of the inorganic powder was carried out by heating to 900°C for 20 minutes under an argon gas atmosphere. On the other hand, the carbonation reaction of the inorganic powder was carried out by heating to 750°C for 20 minutes under a carbon dioxide gas atmosphere. After each decarboxylation reaction and carbonation reaction (one cycle), the reaction conversion rate was calculated and the cycle characteristics of each inorganic powder were evaluated.

[0067] Table 2 shows the conversion rate (%) at the end of one cycle, the conversion rate (%) at the end of 30 cycles, and the ratio (%) of the conversion rate (%) at the end of 30 cycles to the conversion rate (%) at the end of one cycle, as the cycle performance for each sample.

[0068]

[0069] Inorganic powders mainly composed of calcium hydroxide containing magnesium maintained a good reaction conversion rate even after 30 cycles of carbonation and decarboxylation reactions. On the other hand, as a control, inorganic powders without magnesium (ES-57, ES-46, and ES-72) showed a decrease in reaction conversion rate after 30 reaction cycles.

[0070] [Evaluation of Calcium Carbonate Crystal Shape] The crystalline shape of calcium carbonate was observed in ES-55-SiSiC, an inorganic powder-supported porous material prepared using ES-55, an inorganic powder mainly composed of calcium carbonate, by repeatedly performing decarboxylation and carbonation reactions. Electron microscope images of ES-55 before the decarboxylation reaction (Figure 3(a)) and electron microscope images of ES-55 after 10 cycles (parts T1 (Figure 3(b)), T2 (Figure 3(c)), and T3 (Figure 3(d)) in Figure 2 are shown in Figure 3. All electron microscope images in Figure 3 are at 10,000x magnification.

[0071] The inorganic powder ES-55 is spindle-shaped before the decarboxylation reaction (Figure 3(a)), but as the decarboxylation and carbonation reaction cycles are repeated, the proportion of spherical particles increases (Figures 3(b)-(d)). It can be seen that as the decarboxylation and carbonation reaction cycles are repeated, the sintering of the inorganic powder progresses and the specific surface area decreases. This is thought to reduce the reaction conversion rate as the reaction cycle is repeated. It is thought that the inclusion of a predetermined amount of magnesium element in the inorganic powder relatively suppresses the change in the crystal shape of the inorganic powder associated with the reaction cycle, thereby suppressing the decrease in the reaction conversion rate.

Claims

1. Specific surface area of ​​3-120 m² according to the BET method. ２ An inorganic powder having calcium carbonate, calcium hydroxide, or a mixture thereof as its main component, wherein the calcium carbonate, calcium hydroxide, or mixture thereof contains 0.1-15% of an element selected from the group consisting of strontium, barium, radium, beryllium, and magnesium, based on the total mass of the inorganic powder.

2. An inorganic powder aqueous slurry comprising an inorganic powder mainly composed of calcium carbonate, calcium hydroxide, or a mixture thereof, and water, wherein the inorganic powder is an inorganic powder containing 0.1-15% of elements selected from the group consisting of strontium, barium, radium, beryllium, and magnesium, based on the total mass of the inorganic powder, and the specific surface area of ​​the inorganic powder by the BET method when dry is 3-120 m². ２ An inorganic powder aqueous slurry with a concentration of / g.

3. Specific surface area of ​​3-120 m² according to the BET method. ２ An inorganic powder-supported porous material comprising an inorganic powder mainly composed of calcium carbonate, calcium hydroxide, or a mixture thereof, in a quantity of 1 / g, supported on a porous material made of metal or ceramic, wherein the inorganic powder is an inorganic powder containing 0.1-15% of an element selected from the group consisting of strontium, barium, radium, beryllium, and magnesium, based on the total mass of the inorganic powder.

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