Methods for producing methane gas

Abstract

According to the present invention, a base material powder composition comprises a raw material containing an alkaline-earth metal compound, a raw material containing an aluminum compound, and a raw material containing silica. The raw material containing an alkaline-earth metal compound and / or the raw material containing an aluminum compound generates a pyrolysis gas when fired. First, the base material powder composition is compacted and fired to obtain a porous ceramic (step S2). Thereafter, the porous ceramic is impregnated with a solution containing a catalyst metal compound and dried (step S4). In step S4, heating / mixing in which the porous ceramic and the solution containing a catalyst metal compound are mixed while being heated is continued under conditions such that the solution containing the catalyst metal compound evaporates, until the porous ceramic dries up. Thereafter, the porous ceramic is fired (step S5) and subjected to a reduction treatment (step S6).

Description

Catalyst structure manufacturing method and methane gas manufacturing method

[0001] The present invention relates to a method for producing a catalyst structure that can be used as a catalyst for chemical reactions such as methanation reactions, and a method for producing methane gas that uses the catalyst structure.

[0002] In recent years, the methanation reaction represented by the following formula (1) has been attracting attention as a method for achieving carbon neutrality. As shown in formula (1), the methanation reaction uses carbon dioxide gas and hydrogen gas as raw materials to produce methane gas and water. ２ +4H ２ →CH ４ +2H ２ O... (1)

[0003] Hydrogen gas, which is a raw material for the methanation reaction, can be produced using renewable energy. Specifically, hydrogen gas can be obtained by electrolyzing water using electricity generated by solar cells, wind power, etc.

[0004] The methane gas produced by the methanation reaction can be used, for example, as the main component of city gas. Carbon neutrality can be achieved by balancing the amount of carbon dioxide gas emitted by using the methane gas produced by the methanation reaction with the amount of carbon dioxide gas used as a raw material for the methanation reaction.

[0005] The methanation reaction described above is typically carried out in the presence of a catalyst structure, which serves to facilitate efficient chemical reactions.

[0006] Patent Document 1 discloses a catalyst structure for use in a methanation reaction. This catalyst structure has a structure in which a group of catalytic metal particles (hereinafter referred to as catalytic metal) is supported on a substrate. The catalytic metal is nickel.

[0007] Japanese Patent Application Laid-Open No. 2022-94211

[0008] To further improve the efficiency of chemical reactions such as methanation reactions, a catalyst structure with a large specific surface area and a sufficient amount of catalytic metal dispersed uniformly is desired. Here, "specific surface area" refers to the surface area per unit mass.

[0009] An object of the present invention is to provide a method for producing a catalyst structure that can obtain a catalyst structure having a large specific surface area and in which a sufficient amount of catalytic metal is uniformly dispersed, and a method for producing methane gas that uses the catalyst structure obtained by this method.

[0010] The catalyst structure manufacturing method according to the present invention comprises: (A) a step of preparing a base powder composition comprising an alkaline earth metal compound-containing raw material containing an alkaline earth metal compound, an aluminum compound-containing raw material containing an aluminum compound, and a silica-containing raw material containing silica, wherein at least one of the alkaline earth metal compound-containing raw material and the aluminum compound-containing raw material generates a pyrolysis gas when fired; (B) a step of forming the base powder composition and firing the powder composition to obtain a porous ceramic having a porous structure; and (C) a step of supporting a group of catalyst metal particles on the porous ceramic, wherein the step (C) comprises: (C1) a step of impregnating the porous ceramic with a catalyst metal compound-containing solution containing a compound of the catalyst metal, and drying the porous ceramic impregnated with the catalyst metal compound-containing solution; (C2) a step of firing the dried porous ceramic; and (C3) a step of performing a reduction treatment on the fired porous ceramic, wherein the step (C1) The porous ceramic and the catalytic metal compound-containing solution are mixed under heating under conditions in which the catalytic metal compound-containing solution evaporates, and this heating and mixing is continued until the porous ceramic becomes dry.

[0011] In the catalyst structure production method according to the present invention, the alkaline earth metal compound-containing raw material may contain calcium carbonate and magnesium carbonate, the aluminum compound-containing raw material may contain aluminum hydroxide, and clay may be used as the silica-containing raw material.

[0012] The method for producing methane gas according to the present invention involves bringing the catalyst structure obtained by the above-described method for producing a catalyst structure according to the present invention into contact with a raw material gas containing carbon dioxide gas and hydrogen gas, and obtaining a synthesis gas containing methane gas by a methanation reaction.

[0013] In the method for producing methane gas according to the present invention, the catalytic metal may be nickel, and the porous ceramic supporting the nickel particle group may contain a basic oxide.

[0014] According to the catalyst structure manufacturing method of the present invention, when the base powder composition is fired in step (B), at least one of the alkaline earth metal compound-containing raw material and the aluminum compound-containing raw material contained in the base powder composition generates a pyrolysis gas. Therefore, the generation of this pyrolysis gas allows the production of porous ceramics having a porous structure. The porous structure contributes to an increase in the specific surface area of ​​the catalyst structure.

[0015] In step (C1), the porous ceramics and the catalytic metal compound-containing solution are heated and mixed under conditions that evaporate the catalytic metal compound-containing solution, and the heating and mixing is continued until the porous ceramics are dried. This allows a sufficient amount of catalytic metal compound to be supported on the porous ceramics in a uniformly dispersed state.

[0016] Therefore, by carrying out the calcination treatment in step (C2) and the reduction treatment in step (C3) after step (C1), it is possible to obtain a catalyst structure having a large specific surface area and in which a sufficient amount of catalyst metal is uniformly dispersed.

[0017] 1. A flowchart of a catalyst structure manufacturing method according to an embodiment. 2. A graph illustrating the pore distribution of porous ceramics according to an embodiment. 3. A diagram showing the specific surface areas of a substrate, an unreduced catalyst structure, and a catalyst structure according to an embodiment. 4. A diagram showing the composition of components contained in a substrate and a catalyst structure according to an embodiment. 5. A graph showing an X-ray diffraction spectrum of an unreduced catalyst structure according to an embodiment. 6. A conceptual diagram showing the composition of a methane gas production device according to an embodiment. 7. A graph showing the relationship between the composition of a gas that has passed through a catalyst structure and the temperature of the catalyst structure when a catalyst structure according to an embodiment is applied to a methanation reaction. 8. A graph showing the relationship between the composition of a gas that has passed through a catalyst structure and the temperature of the catalyst structure when a catalyst structure according to another embodiment is applied to a methanation reaction. 9. A graph showing the relationship between the composition of a gas that has passed through a catalyst structure and the temperature of the catalyst structure when a catalyst structure according to yet another embodiment is applied to a methanation reaction. 10. A graph showing the relationship between the composition of a gas that has passed through a catalyst structure and the temperature of the catalyst structure when a catalyst structure according to yet another embodiment is applied to a methanation reaction. ２ Graph showing the relationship between conversion rate and reaction temperature. ４ Graph showing the relationship between selectivity and reaction temperature. ４ 1 is a graph showing the relationship between yield and reaction temperature, and FIG. 2 is a graph showing X-ray diffraction spectra of catalyst structures according to examples.

[0018] [Embodiment] A catalyst structure manufacturing method according to an embodiment will be described with reference to Fig. 1. The catalyst structure manufacturing method according to this embodiment includes a base material manufacturing process (steps S1 to S3) for manufacturing a base material that supports a catalyst metal, and a catalyst metal supporting process (steps S4 to S6) for supporting the catalyst metal on the manufactured base material.

[0019] In the base material manufacturing process, first, a powder composition for the base material, which is the material for the base material, is prepared (step S1). Note that this step S1 is an example of the above-mentioned step (A).

[0020] The base powder composition is prepared to contain an alkaline earth metal compound-containing raw material, an aluminum compound-containing raw material, and a silica-containing raw material.

[0021] At least one of the alkaline earth metal compound-containing raw material and the aluminum compound-containing raw material is one that generates a pyrolysis gas when fired. Here, "pyrolysis gas" refers to a gas generated by chemical decomposition accompanying heating during firing. The silica-containing raw material plays a role in imparting plasticity to the molded body described below. Specific examples of each raw material are described below.

[0022] The alkaline earth metal compound-containing raw material is a raw material that contains an alkaline earth metal element as a chemical composition, specifically, a raw material that contains an alkaline earth metal compound.

[0023] The alkaline earth metal compound-containing raw material can be, for example, a raw material containing an alkaline earth metal compound such as an alkaline earth metal carbonate, an alkaline earth metal basic carbonate, or an alkaline earth metal hydroxide. When fired, the raw material containing an alkaline earth metal carbonate, the raw material containing an alkaline earth metal basic carbonate, and the raw material containing an alkaline earth metal hydroxide generate pyrolysis gases such as carbon dioxide gas, carbon monoxide gas, and water vapor.

[0024] In this specification, alkaline earth metals also include magnesium, and thus alkaline earth metals refer to Group 2 elements other than beryllium.

[0025] As the alkaline earth metal, calcium and magnesium are preferred. Specifically, the alkaline earth metal compound-containing raw material is a compound represented by the chemical formula CaCO ３ Calcite, a mineral composed of calcium carbonate, has the chemical formula MgCO ３ Magnesite is a mineral composed of magnesium carbonate, with the chemical formula Mg ６ Al ２ CO ３ (OH) １６ ・4 (H ２ It is preferable to use hydrotalcite, which is a mineral composed of basic carbonate of magnesium represented by formula (I).

[0026] The alkaline earth metal compound-containing raw material may be a combination of two or more minerals selected from calcite, magnesite, hydrotalcite, etc. This allows for the production of a large amount of pyrolysis gas. Furthermore, the amount of pyrolysis gas produced can be adjusted by adjusting the amount of hydrotalcite added.

[0027] The aluminum compound-containing raw material is a raw material that contains aluminum element as a chemical composition, specifically, a raw material that contains an aluminum compound.

[0028] The aluminum compound-containing raw material may be, for example, a raw material containing an aluminum compound such as aluminum carbonate, aluminum basic carbonate, or aluminum hydrate. When fired, the raw material containing aluminum carbonate, the raw material containing aluminum basic carbonate, and the raw material containing aluminum hydrate generate pyrolysis gases such as carbon dioxide gas, carbon monoxide gas, and water vapor.

[0029] Specifically, the aluminum compound-containing raw material is a compound represented by the chemical formula Al(OH) ３ It is preferable to use a raw material containing aluminum hydroxide represented by the chemical formula or alumina monohydrate represented by the chemical formula AlOOH. More specifically, the aluminum compound-containing raw material is preferably a raw material containing aluminum hydroxide represented by the chemical formula NH ４ AlO(OH)HCO ３ It is preferable to use ammonium dawsonite, which is a raw material represented by the formula: Since ammonium dawsonite is an aluminum carbonate and also an ammonium compound, when fired, ammonia gas may also be generated as the pyrolysis gas described above.

[0030] As the aluminum compound-containing raw material, for example, a raw material containing aluminum hydroxide and ammonium dawsonite may be used in combination. This combination enables the generation of a large amount of pyrolysis gas. Furthermore, the amount of pyrolysis gas generated can be adjusted by the amount of ammonium dawsonite added.

[0031] The silica-containing raw material is a raw material containing silica. As the silica-containing raw material, for example, kaolinite clay, specifically silicate, more specifically clay such as elutriated clay or artificial clay is preferably used. Among the silica-containing raw materials, clay is particularly effective in imparting plasticity to the molded body described below.

[0032] The silica-containing raw material may also generate a pyrolysis gas when fired, similar to the alkaline earth metal compound-containing raw material and the aluminum compound-containing raw material.

[0033] The powder composition for the base material can be obtained by mixing the alkaline earth metal compound-containing raw material, aluminum compound-containing raw material, and silica-containing raw material that have been pulverized into powder form as described above. For example, the powder composition for the base material can be obtained by pulverizing the alkaline earth metal compound-containing raw material, aluminum compound-containing raw material, and silica-containing raw material in a ball mill and mixing them.

[0034] The base powder composition preferably contains a total of 90% by mass or more, and more preferably 95% by mass or more, of the alkaline earth metal compound-containing raw material, the aluminum compound-containing raw material, and the silica-containing raw material. The proportions of the alkaline earth metal compound-containing raw material, the aluminum compound-containing raw material, and the silica-containing raw material in the base powder composition are each preferably 20% by mass or more, and more preferably 30% by mass or more.

[0035] Next, the powder composition for the base material is molded, and the molded body (hereinafter referred to as a molded body) is fired to obtain a porous ceramic (step S2). Note that this step S2 is an example of the above-mentioned step (B).

[0036] An example of a method for molding the powder composition for a base material is pressure molding. Examples of pressure molding include uniaxial molding and biaxial molding. Alternatively, the molded body may be formed by forming a slurry of the powder composition for a base material (hereinafter referred to as a slurry) and drying it. The slurry of the powder composition for a base material is formed by adding water to the powder composition for a base material and kneading it. The water may be industrial water. The slurry is molded, for example, by casting it into a mold.

[0037] The temperature for firing the molded body is preferably 500° C. or higher and 1200° C. or lower. The firing time is preferably 30 minutes or longer, and more preferably 1 hour or longer.

[0038] The main reason why porous ceramics are formed by firing is due to the foaming of pyrolysis gases described above. Specifically, as described above, the alkaline earth metal compound-containing raw material, aluminum compound-containing raw material, and silica-containing raw material contained in the base powder composition generate pyrolysis gases such as carbon dioxide gas, carbon monoxide gas, and water vapor when fired. The generation of these pyrolysis gases forms fine bubbles within the structure, which remain as pores in the structure. This results in porous ceramics with a porous structure containing countless fine pores within.

[0039] An example of the pore size distribution of porous ceramics is shown in Figure 2. The average diameter of the pores inside the porous ceramics is preferably 2 nm or more and 50 nm or less, and more preferably 2 nm or more and 30 nm or less. In this specification, the average diameter of the pores in the porous ceramics is defined as the value obtained by analyzing the pore size distribution of the measurement results obtained by the nitrogen adsorption method using the BJH (Barrett-Joyner-Halenda) method.

[0040] The structure defining the pores inside the porous ceramics is a crystal phase of MO (where M is an alkaline earth metal), Al ２ O ３ crystalline phase of aluminosilicate, and SiO ２The crystal phase of MO is mainly derived from the raw material containing alkaline earth metal compounds. ２ O ３ The crystalline phase of aluminosilicate is mainly derived from raw materials containing an aluminum compound. The crystalline phase of aluminosilicate is mainly derived from raw materials containing silica and raw materials containing an aluminum compound. SiO ２ The crystalline phase is mainly derived from the silica-containing raw material. By having such a crystalline phase, sufficient strength, heat resistance, and thermal shock resistance are obtained.

[0041] Next, the porous ceramic obtained by firing is pulverized (step S3). The pulverized material obtained by pulverization is then classified to obtain particles of the desired particle size. The pulverized material obtained by this pulverization and classification is the substrate for supporting the catalytic metal.

[0042] The porous structure caused by the foaming of the pyrolysis gas increases the specific surface area of ​​the substrate. The specific surface area of ​​the pulverized substrate is 30 [m ２ / g] or more, and 35 [m ２ / g] or more. In this specification, the specific surface area is a value measured in accordance with the specific surface area measurement method by gas adsorption specified in JIS Z8830.

[0043] The substrate manufacturing process has been described above. The catalytic metal supporting process for supporting catalytic metal on the substrate will now be described.

[0044] In the catalytic metal supporting step, first, a catalytic metal compound-containing solution is prepared. The catalytic metal compound-containing solution is a solution containing catalytic metal elements as a chemical composition, specifically, a solution containing a compound of the catalytic metal (hereinafter referred to as the catalytic metal compound).

[0045] The pulverized material as a base material is then impregnated with a solution containing a catalytic metal compound, and the pulverized material impregnated with the solution containing a catalytic metal compound is dried. Specifically, after adding the solution containing a catalytic metal compound to the pulverized material, the pulverized material and the solution containing a catalytic metal compound are mixed while being heated under conditions in which the solution containing a catalytic metal compound evaporates, and this heating and mixing is continued until the pulverized material becomes dry (step S4).

[0046] The catalytic metal compound-containing solution has a catalytic metal compound as a solute and a liquid component as a solvent. In this specification, the phrase "the catalytic metal compound-containing solution evaporates" means that the solvent constituting the catalytic metal compound-containing solution evaporates.

[0047] By continuing the heating and mixing until the pulverized material is dried, the porous structure of the pulverized material can be impregnated with the catalyst metal compound-containing solution to every corner of the pulverized material. That is, the catalyst metal compound can be sufficiently distributed to the inside of each pore distributed in the pulverized material's structure. Impregnation can be promoted by applying pressure or vacuum. Note that this step S4 is an example of the above-mentioned step (C1).

[0048] Examples of catalytic metal compounds include salts of catalytic metals. Examples of catalytic metals that can be used include nickel, rhodium, ruthenium, iron, and cobalt. Examples of catalytic metal compound-containing solutions include aqueous solutions of catalytic metal salts. As a specific example, when the catalytic metal is nickel, an aqueous solution of nickel nitrate can be used as the catalytic metal compound-containing solution.

[0049] The amount of catalyst metal supported on the catalyst structure can be adjusted by adjusting the amount of catalyst metal compound-containing solution added to the pulverized material as the substrate and the concentration of the catalyst metal compound in the catalyst metal compound-containing solution. The concentration of the catalyst metal compound in the catalyst metal compound-containing solution is, for example, 0.01 mol / L or more and 1.0 mol / L or less.

[0050] Next, the pulverized material impregnated with the catalytic metal compound-containing solution is dried and then calcined (step S5). This step S5 is an example of the above-mentioned step (C2). By this calcination, the catalytic metal compound contained as a solute in the catalytic metal compound-containing solution is fixed in the pores of the porous ceramic pulverized material in the form of particle groups.

[0051] However, the calcination oxidizes the catalytic metal. That is, the particle group after calcination is mainly composed of an oxide of the catalytic metal. Therefore, the calcined pulverized material is then subjected to a reduction treatment (step S6). This results in a catalytic structure in which the particle group is reduced to the catalytic metal. Note that this step S6 is an example of the above-mentioned step (C3).

[0052] The obtained catalyst structure is used as a catalyst for chemical reactions such as methanation reactions. The specific surface area of ​​the catalyst structure before application to chemical reactions is 25 [m ２ / g] or more, and 30 [m ２ / g] or more is more preferable.

[0053] As described above, according to this embodiment, when the base powder composition is fired in step S2, the alkaline earth metal compound-containing raw material and the aluminum compound-containing raw material contained in the base powder composition generate pyrolysis gas. Specifically, the pyrolysis gas generates bubbles. Therefore, the generation of this pyrolysis gas results in a porous ceramic having a porous structure. The porous structure also contributes to an increase in the specific surface area of ​​the base material.

[0054] In step S4, the pulverized porous ceramic material is heated and mixed with the catalytic metal compound-containing solution, and this heating and mixing is continued until the pulverized material is dried under conditions that evaporate the catalytic metal compound-containing solution. This allows a sufficient amount of components containing catalytic metal elements to be supported uniformly on the pulverized material as a substrate. In addition, the firing in step S5 contributes to increasing the strength and heat resistance of the substrate.

[0055] As a result of the above, a catalyst structure can be obtained which has a large specific surface area, a sufficient amount of catalyst metal uniformly dispersed in the form of particle groups, and sufficient strength and heat resistance (specifically, heat resistance of 400°C or higher).

[0056] The chemical reaction to which the catalyst structure according to this embodiment is applied as a catalyst is not particularly limited. As an example, the catalyst structure according to this embodiment can be used as a catalyst for a methanation reaction. That is, by contacting the catalyst structure according to this embodiment with a raw material gas containing carbon dioxide gas and hydrogen gas, a synthesis gas containing methane gas and water as a by-product can be obtained.

[0057] When the catalyst structure according to this embodiment is used as a catalyst for a methanation reaction, nickel is preferably used as the catalyst metal, and the porous ceramics supporting the nickel particles preferably contain a basic oxide at least in the surface layer. Hydrogen is adsorbed onto the nickel, and carbon dioxide is adsorbed onto the basic oxide, thereby further promoting the methanation reaction.

[0058] The basic oxide is composed of an oxide of an alkaline earth metal derived from the alkaline earth metal compound-containing raw material. Specific examples of the basic oxide include CaO and MgO. During the methanation reaction, part of the basic oxide in the surface layer of the porous ceramics is converted into a carbonate (e.g., CaCO ) as carbon dioxide is adsorbed. ３ , MgCO ３ ), and carbon dioxide is released from the carbonate, which can then return to the basic oxide.

[0059] [Example] A powder composition for a base material containing a total of 98 mass% or more of an alkaline earth metal compound-containing raw material containing calcium carbonate and magnesium carbonate, an aluminum compound-containing raw material containing aluminum hydroxide, and a silica-containing raw material containing elutriated clay, and adjusted to a particle size of 20 mesh or less (particle size of 840 μm or less), was prepared. The powder composition for a base material was then uniaxially compacted at a pressure of 100 MPa for 1 minute.

[0060] Next, the compact obtained by uniaxial compaction was fired at a temperature of 800°C for 2 hours. This resulted in a porous ceramic that was made porous by foaming of the pyrolysis gas. The obtained porous ceramic was then crushed and classified to obtain a base material with a particle size of 9 to 20 mesh (particle size of 840 μm or more and 2040 μm or less). As shown in Figure 3, the specific surface area of ​​the obtained base material was 37.5 m ２ / g.

[0061] Figure 4 shows the composition of the components contained in the obtained substrate. The measurement results shown in Figure 4 were all obtained by fluorescent X-ray analysis, and the components were quantified as oxides. Among the components contained in the substrate, Al ２ O ３ is derived from an aluminum compound-containing raw material, and SiO ２ , TiO ２ , and Fe ２ O ３ is derived from the elutriated clay used as the silica-containing raw material, and the basic oxides MgO and CaO are derived from the alkaline earth metal compound-containing raw material.

[0062] In Fig. 4, the detection result of the MgO content also includes the content of magnesium carbonate, etc. The detection result of the CaO content also includes the content of calcium carbonate, etc. When focusing on basic oxides, the substrate according to the embodiment contains more CaO than MgO. In other words, in the substrate according to the example, the content of the component containing Ca is greater than the content of the component containing Mg.

[0063] Next, the substrate was treated with a compound having the chemical formula Ni(NO ３ ) ２ In a state where the substrate was immersed in an aqueous solution of nickel (II) nitrate represented by the formula (II) (hereinafter referred to as "aqueous nickel nitrate solution"), the substrate and the aqueous nickel nitrate solution were mixed while being heated under conditions where the water in the aqueous nickel nitrate solution evaporated, and this heating and mixing was continued until the substrate became dry.

[0064] The nickel nitrate aqueous solution is an example of the catalytic metal compound-containing solution described above. By heating and mixing, nickel (II) nitrate contained as a solute in the nickel nitrate aqueous solution is fixed in the pores inside the porous ceramic substrate in the form of particle groups.

[0065] Next, the base material that had undergone the warm mixing was dried again in air at 100°C for 20 hours and then calcined in air at 600°C for 1 hour. The nickel (II) nitrate that had been fixed in the form of particles in the pores of the base material by the warm mixing was converted into nickel oxide (NiO) by this calcination. Hereinafter, the product resulting from this calcination is referred to as the "unreduced catalyst structure."

[0066] In the above manner, unreduced catalyst structures according to Examples A, B, and C, each having a different amount of supported nickel oxide, were prepared. The substrate supporting the nickel oxide was common to Examples A to C. The amount of supported nickel oxide was adjusted between Examples A to C by varying the ratio of the amount of nickel nitrate aqueous solution (concentration: 1 mol / L) added to the substrate during the heating and mixing described above.

[0067] 4 also shows the composition of the components contained in the unreduced catalyst structure according to Examples A to C. In Example A, 13 mL of a nickel nitrate aqueous solution was added to 1.9 g of the substrate and mixed with heating to obtain an unreduced catalyst structure containing 27.9 mass% NiO, calculated as Ni content. In Example B, 12 mL of a nickel nitrate aqueous solution was added to 1.18 g of the substrate and mixed with heating to obtain an unreduced catalyst structure containing 33.6 mass% NiO, calculated as Ni content. In Example C, 30 mL of a nickel nitrate aqueous solution was added to 3.0 g of the substrate and mixed with heating to obtain an unreduced catalyst structure containing 44.9 mass% NiO, calculated as Ni content.

[0068] The duration of the warming and mixing varied depending on the ratio of the amount of nickel nitrate aqueous solution (concentration: 1 mol / L) added, and was between 1 hour and 4 hours.

[0069] The "Before Methanation Reaction" column in Figure 3 also shows the specific surface area of ​​the unreduced catalyst structure for Examples A to C. The specific surface area decreased with the loading of nickel oxide, and increased with the loading of nickel oxide.

[0070] FIG. 5 shows the X-ray diffraction spectra of the unreduced catalyst structures of Examples A to C. The horizontal axis represents the diffraction angle 2θ in degrees, and the vertical axis represents the intensity of the diffracted beam. In all of the unreduced catalyst structures of Examples A to C, a peak indicating the presence of bunsenite composed of NiO is observed. Furthermore, the intensity of this peak increases as the amount of Ni increases. These results confirmed that nickel, as the catalytic metal, was indeed supported on the substrate.

[0071] Furthermore, in the unreduced catalyst structures of all of Examples A to C, the presence of quartz derived from the elutriated clay used as the silica-containing raw material and the presence of calcite derived from the alkaline earth metal compound-containing raw material were also observed.

[0072] As described above, the nickel-containing component supported on the unreduced catalyst structure was oxidized during the calcination process and exists in the form of nickel (II) oxide, represented by the chemical formula NiO. Therefore, prior to the production of methane gas by a methanation reaction, the unreduced catalyst structure was subjected to a reduction treatment. Following this reduction treatment, methane gas was produced. The configuration of the apparatus used for the reduction treatment and the production of methane gas is described below.

[0073] The configuration of a methane gas production apparatus according to an embodiment is shown in Figure 6. This methane gas production apparatus 10 includes a gas source 11, a gas pipe 12 connected at one end to the gas source 11, an unreduced catalyst structure 13a disposed within the gas pipe 12, an electric heater 14 that externally heats the portion of the gas pipe 12 where the unreduced catalyst structure 13a is disposed, and a gas analyzer 15 connected to the other end of the gas pipe 12.

[0074] First, the unreduced catalyst structure 13a was heated to 800°C by the electric heater 14, and hydrogen gas (3% by volume of H ２A reduction treatment was carried out by continuously supplying hydrogen gas (containing O) for 3 hours. The hydrogen gas reduced the individual nickel (II) oxide particles supported on the unreduced catalyst structure 13a to metallic nickel particles. As a result, the unreduced catalyst structure 13a became the catalyst structure 13b.

[0075] In this manner, the unreduced catalyst structures 13a according to Examples A, B, and C were converted into the catalyst structures 13b according to Examples A, B, and C, respectively, in the gas pipe 12 by the reduction treatment.

[0076] Thereafter, argon gas as an inert gas was continuously supplied from the gas source 11 for two hours to purge the hydrogen gas from the gas pipe 12. When a metal other than nickel is used as the catalytic metal, the oxide of that metal can be reduced in the same manner to obtain the catalytic metal.

[0077] Hereinafter, as a method for producing methane gas according to the present invention, the results of applying the catalyst structure 13b according to Examples A to C as a catalyst for a methanation reaction will be described.

[0078] After removing the hydrogen gas from the gas pipe 12 as described above, the supply of raw material gas for the methanation reaction was started from the gas source 11 while the catalyst structure 13b was still heated to a temperature of 250°C or higher and 500°C or lower.

[0079] The raw material gas consisted of carbon dioxide gas and hydrogen gas. The volume ratio (≒ molar ratio) of carbon dioxide gas to hydrogen gas in the raw material gas was hydrogen gas / carbon dioxide gas = 4 / 1. The flow rate of the raw material gas to the catalyst structure 13b was 70 mL / min. The amount of unreduced catalyst structure 13a placed in the gas pipe 12 prior to the reduction treatment was 0.5 g, and the inner diameter of the gas pipe 12 was 6 mm.

[0080] The methanation reaction was carried out using each of three different catalyst structures 13b of Examples A, B, and C. In all cases, the methanation reaction proceeded smoothly without causing blockage in the gas pipe 12. The column "After methanation reaction" in Figure 3 also shows the specific surface areas of the catalyst structures of Examples A to C after application to the methanation reaction.

[0081] 7, 8, and 9 show the relationship between the composition of the gas (hereinafter referred to as outlet gas) that passed through the catalyst structure 13b and the temperature (hereinafter referred to as reaction temperature) of the catalyst structure 13b according to Examples A, B, and C. The composition of the outlet gas was measured by gas chromatography using the gas analyzer 15 shown in FIG.

[0082] As shown in Figures 7 to 9, in all of Examples A to C, methane (CH ４ ) and hydrogen (H ２ ) was confirmed. Furthermore, at a reaction temperature of 350°C, a decrease in methane (CH ４ ) production and the raw material hydrogen (H ２ ) and carbon dioxide (CO ２ ) was confirmed to have decreased.

[0083] Methane (CH ４ In all of Examples A to C, the production of methane gas peaked at a reaction temperature of 400° C. The peak value of the proportion of methane gas in the outlet gas was about 36 vol % in Example A, about 41 vol % in Example B, and about 42 vol % in Example C.

[0084] At a further increased reaction temperature of 450°C, methane (CH ４ ) production decreased. ２ ) and carbon dioxide (CO ２ ) was difficult to confirm.

[0085] As shown in the above-mentioned formula (1), the methanation reaction also produces water as a by-product. In all of Examples A to C, a cold trap confirmed that moisture was present in the outlet gas as a by-product. The cold trap was installed between the gas analyzer 15 shown in FIG. 6 and the other end of the gas pipe 12.

[0086] In FIG. ２ The relationship between the conversion rate and the reaction temperature is shown below. ２The conversion rate [%] is the ratio of the CO ２ The flow rate of CO in the outlet gas is a [mL / min]. ２ When the flow rate is b [mL / min], it is defined as (1-b / a) x 100.

[0087] In all of Examples A-C, CO ２ The conversion rate increased with increasing reaction temperature, reached a maximum at a reaction temperature of 400°C, and decreased at reaction temperatures above 450°C. ２ The maximum conversion was 86% in Example A, 88% in Example B, and 94% in Example C.

[0088] FIG. 11 shows the CH ４ The relationship between selectivity and reaction temperature is shown. ４ Selectivity [%] is the ratio of CO ２ The flow rate of CO in the outlet gas is a [mL / min]. ２ The flow rate of the gas is b [mL / min], and the CH ４ When the flow rate of the CH is c [mL / min], it is defined as c / (a-b) x 100. ４ The maximum selectivity [%] was 88% at a reaction temperature of 450°C in Example A, 75% at a reaction temperature of 350°C in Example B, and 80% at a reaction temperature of 400°C in Example C.

[0089] Figure 12 is CH ４ The relationship between the yield and the reaction temperature is shown below. ４ Yield [%] is the CO in the inlet gas ２ The flow rate of the gas is a [mL / min], and the CH ４ When the flow rate of CO is c [mL / min], c / a × 100 = CO ２ Conversion rate [%] × CH ４ It is defined as selectivity [%] / 100.

[0090] In any of Examples A-C, CH ４ The yield increased with increasing reaction temperature, reached a maximum at a reaction temperature of 400°C, and decreased at reaction temperatures above 450°C. ４The maximum yield was 75% in Example A, 56% in Example B, and 75% in Example C.

[0091] 13 shows the X-ray diffraction spectrum of the catalyst structure 13b according to Examples A to C after the methanation reaction. In all of the catalyst structures 13b according to Examples A to C, a peak indicating the presence of metallic Ni as the catalytic metal is clearly observed. The intensity of this peak increases as the amount of Ni supported increases. This result indicates that NiO was indeed reduced to Ni in the previous reduction treatment.

[0092] The crystallite diameter of nickel was calculated using the Scherrer equation from the half-width of the spectrum indicating the presence of metallic nickel, and it was found that the larger the amount of Ni supported, the larger the crystallite diameter. The crystallite diameter of nickel in the catalyst structure 13b according to Example A was 33.4 nm. Furthermore, when the catalyst structure 13b according to Example A was observed using transmission electron microscopy (TEM), spherical nickel particles with a diameter of about 50 nm were confirmed.

[0093] As described above, by using the catalyst structure 13b according to Examples A to C as a catalyst for promoting a methanation reaction, methane gas could be produced using hydrogen gas and carbon dioxide gas as raw materials. The produced methane gas can be used, for example, as a main component of city gas.

[0094] In the catalyst structure 13b according to Examples A to C, nickel as the catalyst metal adsorbs hydrogen, and the basic oxide contained in the substrate supporting nickel adsorbs carbon dioxide, and the adsorbed hydrogen and carbon dioxide are converted to methane. This mechanism allows for efficient production of methane gas.

[0095] In the porous substrate, each pore containing nickel particles serves as a reaction site for the methanation reaction. The foaming of pyrolysis gas increases the porosity of the structure and the specific surface area, creating countless reaction sites within the substrate. This also contributes to the efficient production of methane gas.

[0096] 7 to 9 show the measurement results over a period of 340 minutes. When the durability of the catalyst structure 13b according to Example A was examined as a representative example, it was confirmed that the catalyst structure 13b according to Example A could withstand a methanation reaction at a reaction temperature of 400°C for 12 hours or more. In other words, the catalyst structure 13b according to this example has sufficient strength despite its porous structure, and therefore exhibits sufficient durability at temperatures at which the methanation reaction takes place (e.g., temperatures of 350°C or higher and 500°C or lower).

[0097] The present invention can be modified in various ways without departing from the broad spirit and scope of the present invention. The above-described embodiments and examples are intended to illustrate the present invention and do not limit the scope of the present invention. The scope of the present invention is defined by the claims, not by the embodiments and examples. Various modifications made within the scope of the claims and the meaning of the invention equivalent thereto are considered to be within the scope of the present invention.

[0098] This application is based on Japanese Patent Application No. 2024-031126, filed on March 1, 2024. The entire specification, claims, and drawings of Japanese Patent Application No. 2024-031126 are incorporated herein by reference.

[0099] 10... Methane gas production device, 11... Gas source, 12... Gas pipe, 13a... Unreduced catalyst structure, 13b... Catalyst structure, 14... Electric heater, 15... Gas analyzer.

Claims

1. (A) A step of preparing a powder composition for a base material comprising an alkaline earth metal compound-containing raw material containing an alkaline earth metal compound, an aluminum compound-containing raw material containing an aluminum compound, and a silica-containing raw material containing silica, wherein at least one of the alkaline earth metal compound-containing raw material and the aluminum compound-containing raw material generates a pyrolysis gas when fired, (B) A step of obtaining porous ceramics having a porous structure by molding and firing the powder composition for the base material, (C) A step of supporting a group of catalyst metal particles on the porous ceramic, A method for manufacturing a catalyst structure having, The step (C) is (C1) A step of impregnating the porous ceramic with a catalyst metal compound-containing solution containing the catalyst metal compound, and drying the porous ceramic impregnated with the catalyst metal compound-containing solution, (C2) A step of firing the dried porous ceramics, (C3) A step of subjecting the fired porous ceramics to a reduction treatment, Includes, In the above step (C1), A method for manufacturing a catalyst structure, comprising: heating and mixing the porous ceramics and the catalyst metal compound-containing solution under conditions in which the catalyst metal compound-containing solution evaporates, and continuing this heating and mixing until the porous ceramics become dry; The catalyst structure obtained is brought into contact with a source gas containing carbon dioxide and hydrogen gas, and a synthesis gas containing methane gas is obtained by a methanation reaction. Methods for producing methane gas.

2. The aforementioned alkaline earth metal compound-containing raw material contains calcium carbonate and magnesium carbonate, The aluminum compound-containing raw material contains aluminum hydroxide, As the silica-containing raw material, clay is used. The method for producing methane gas according to claim 1.

3. The catalyst metal is nickel, The porous ceramic supporting the nickel particle group contains a basic oxide, The method for producing methane gas according to claim 1 or 2.