Methane production reactor

Abstract

Provided is a methane production reactor which can significantly improve the methane conversion rate and efficiently produce methane. A methane production reactor according to one embodiment of the present invention comprises a ceramic base material and a methanation reaction catalyst. The ceramic base material defines a gas flow path. A raw material gas containing carbon oxide and hydrogen is supplied to the gas flow path. The methanation reaction catalyst can facilitate a reaction for generating methane. The methanation reaction catalyst is disposed so as to be able to contact the raw material gas supplied to the gas flow path. The thermal conductivity of the ceramic base material is 8 W / m·K or more.

Description

Methane Production Reactor

[0001] The present invention relates to a methane production reactor.

[0002] In recent years, from the viewpoint of reducing environmental load, studies have been conducted on recovering carbon dioxide and reusing it as a raw material for carbon compounds. For example, a method for producing methane has been proposed in which a raw material gas containing hydrogen gas, oxygen gas, and carbon dioxide gas is supplied to a reactor equipped with a catalyst, and a methanation reaction is initiated and continued by heat including reaction heat from catalytic combustion of the hydrogen gas (see, for example, Patent Document 1).

[0003] International Publication No. 2021 / 045101

[0004] However, the method for producing methane described in Patent Document 1 may result in an insufficient methane conversion rate. A main object of the present invention is to provide a methane production reactor that can significantly improve the methane conversion rate and efficiently produce methane.

[0005] [1] A methane production reactor according to one embodiment of the present invention includes a ceramic substrate and a methanation catalyst. The ceramic substrate defines a gas flow path. A raw material gas containing carbon oxides and hydrogen is supplied to the gas flow path. The methanation catalyst is capable of promoting a reaction to produce methane. The methanation catalyst is arranged so as to be in contact with the raw material gas supplied to the gas flow path. The thermal conductivity of the ceramic substrate is 8 W / m·K or more. [2] In the methane production reactor described in [1] above, the thermal conductivity of the ceramic substrate may be 100 W / m·K or more. [3] In the methane production reactor described in [1] or [2] above, the raw material gas may further contain oxygen. [4] In the methane production reactor described in any one of [1] to [3] above, the ceramic substrate may be a honeycomb substrate having partition walls that define a plurality of cells. At least some of the plurality of cells include the gas flow path. [5] The methane production reactor according to [4] above may further include a catalyst layer provided on the surface of the partition wall. The catalyst layer may contain the methanation reaction catalyst. [6] In the methane production reactor according to [5] above, a weighted average of the thermal conductivity of the ceramic substrate and the thermal conductivity of the catalyst layer may be 5 W / m·K or more. [7] In the methane production reactor according to any one of [4] to [6] above, the porosity of the partition wall may be 65% or less. [8] In the methane production reactor according to any one of [4] to [7] above, the thickness of the partition wall may be 0.0635 mm or more and 1.27 mm or less. The cell density of the honeycomb substrate may be 50 cpsi or more and 900 cpsi or less. [9] In the methane production reactor according to any one of [1] to [8] above, the ceramic substrate may contain Si and SiC.

[10] In the reactor for producing methane according to any one of [1] to [9] above, the methanation catalyst may contain a transition metal as an active component.

[11] In the reactor for producing methane according to

[10] above, the transition metal may contain Co, Fe, Pt, Ru, Rh, Pd, Ni, Cu, Ag, Au, Ir, or a combination thereof.

[12] In the methane production reactor according to

[11] above, the transition metal may contain Ni.

[13] In the methane production reactor according to any one of

[10] to

[12] above, the methanation reaction catalyst may further contain a support that supports the transition metal. The support may contain cerium oxide, silicon oxide, zirconium oxide, yttrium oxide, aluminum oxide, or a composite oxide thereof.

[14] In the methane production reactor according to

[13] above, the support may contain cerium oxide.

[0006] According to an embodiment of the present invention, the methane conversion rate can be improved, and methane can be produced efficiently.

[0007] 1 is a schematic perspective view of a methane production reactor according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the methane production reactor of FIG.

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In addition, in order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part more schematically than in the embodiment, but these are merely examples and do not limit the interpretation of the present invention.

[0009] A. Overview of the Methane Production Reactor FIG. 1 is a schematic perspective view of a methane production reactor according to one embodiment of the present invention; FIG. 2 is a schematic cross-sectional view of the methane production reactor of FIG. 1. In one embodiment, the methane production reactor 100 includes a ceramic substrate 1 and a methanation reaction catalyst. The ceramic substrate 1 defines a gas flow path 15. A raw material gas containing carbon oxides and hydrogen is supplied to the gas flow path 15. The methanation reaction catalyst can promote a reaction that produces methane (hereinafter referred to as methanation reaction). The methanation reaction catalyst is arranged so as to be able to come into contact with the raw material gas supplied to the gas flow path 15. The ceramic substrate 1 has a thermal conductivity of 8 W / m·K or more.

[0010] When a raw material gas containing carbon oxides (typically, carbon dioxide and / or carbon monoxide) and hydrogen is supplied to a gas flow path of a methane production reactor, a methanation reaction typically proceeds as shown in the following formula (I) and / or formula (II): Since these methanation reactions are exothermic reactions, the internal temperature of the gas flow passage rises as the methanation reactions proceed.

[0011] The inventors discovered that when a methanation reaction proceeds while a raw material gas is passed through a gas flow path, the heat of the methanation reaction generates a temperature gradient in which the temperature decreases from the upstream side to the downstream side in the feed direction of the raw material gas. In this case, excessive heat may be generated in the upstream portion of the gas flow path in the feed direction of the raw material gas, resulting in a high temperature range exceeding, for example, 600°C. When the temperature of the gas flow path reaches this high temperature range, the chemical equilibrium of the methanation reaction shifts to the reactant side, resulting in a decrease in methane conversion rate and deterioration of the methanation reaction catalyst, resulting in a decrease in activity. Furthermore, the temperature may become insufficient in the downstream portion of the gas flow path in the feed direction of the raw material gas, resulting in a decrease in the reaction rate of the methanation reaction.

[0012] Therefore, the present inventors conducted extensive research into temperature control of the gas flow passages of a methane production reactor and found that the thermal uniformity of the gas flow passages can be improved by appropriately adjusting the thermal conductivity of the ceramic substrate defining the gas flow passages. More specifically, the thermal conductivity of the ceramic substrate 1 is 8 W / m·K or higher, preferably 10 W / m·K or higher, more preferably 50 W / m·K or higher, and even more preferably 100 W / m·K or higher. This allows the ceramic substrate 1 to rapidly diffuse the reaction heat generated by the methanation reaction when a raw material gas is supplied to the gas flow passages 15 to promote the methanation reaction, thereby improving the thermal uniformity of the gas flow passages 15. As a result, the temperature can be appropriately controlled throughout the gas flow passages 15, allowing the methanation reaction to proceed with an excellent methane conversion rate. This significantly improves the methane production efficiency. Meanwhile, the upper limit of the thermal conductivity of the ceramic substrate 1 is not limited, but is typically 1000 W / m·K. The thermal conductivity is calculated based on the following formula (1): thermal conductivity = thermal diffusivity × specific heat × bulk density (1) - for example, by preparing a sample of a predetermined size from the object, measuring the thermal diffusivity of the sample using an optical alternating current thermal diffusivity measuring device (typically a Laser-PIT), measuring the specific heat of the sample using differential scanning calorimetry (DSC), and measuring the bulk density of the sample using Archimedes density measurement.

[0013] The thermal diffusivity of the ceramic substrate 1 is, for example, 1.0×10 －５ m ２ / s ~ 10 x 10 －５ m ２ The specific heat of the ceramic substrate 1 is, for example, 600 J / (kg·K) to 750 J / (kg·K). The bulk density of the ceramic substrate 1 is, for example, 1.0 g / mL to 3.0 g / mL.

[0014] In one embodiment, the raw material gas supplied to the gas flow passage 15 further contains oxygen. In this case, a combustion reaction shown in the following formula (3) can proceed in the gas flow passage 15. Since the combustion reaction (3) is an exothermic reaction, the generated reaction heat can be effectively used to continue the methanation reaction described above. ２ +2H ２ →2H２ O...(3) Meanwhile, the combustion reaction (3) has a faster reaction rate than the methanation reaction and may proceed preferentially in the upstream portion of the gas flow path in the feed gas supply direction. This may result in the formation of a localized high-temperature area (hot spot) in the upstream portion of the gas flow path. The formation of a hot spot may result in a decrease in methane conversion rate and / or deterioration of the methanation reaction catalyst. In contrast, in one embodiment, the thermal conductivity of the ceramic substrate 1 is within the above range, so that the reaction heat generated by the combustion reaction (3) can also be rapidly diffused. As a result, the temperature of the gas flow path 15 can be appropriately controlled even if the feed gas further contains oxygen. This allows the methane production reactor 100 to stably perform automethanation, in which the methanation reaction continues even when external heating is stopped.

[0015] B. Details of the Methane Production Reactor Next, details of the methane production reactor according to one embodiment will be described. A methanation reaction catalyst is typically disposed in the gas flow path 15 of the methane production reactor 100. The methanation reaction catalyst is typically capable of promoting the methanation reaction represented by the above-described formula (I) and / or formula (II).

[0016] The methanation catalyst contains any suitable metal element as an active component. The methanation catalyst may contain a metal element in a metallic state, a salt of the metal element, or an oxide of the metal element. The methanation catalyst preferably contains a metal element in a metallic state.

[0017] Examples of metal elements include alkali metals, alkaline earth metals, and transition metals, and preferably transition metals. Specific examples of transition metals include Co, Fe, Pt, Ru, Rh, Pd, Ni, Cu, Ag, Au, and Ir. These transition metals may be used alone or in combination. In one embodiment, the methanation catalyst contains Ni. When the methanation catalyst contains Ni, the methanation reaction and / or the combustion reaction described above can be further promoted.

[0018] The methanation catalyst may further contain a support in addition to the above-described active component. The support is capable of supporting the active component (typically a transition metal). The support is composed of any appropriate inorganic material depending on the application. Examples of inorganic materials include oxides, carbides, nitrides, sulfides, halides, hydrides, and hydroxides. The inorganic materials may be used alone or in combination.

[0019] Among such inorganic materials, oxides are preferred. Specific examples of oxides include cerium oxide, silicon oxide, zirconium oxide, yttrium oxide, aluminum oxide, and composite oxides thereof. In one embodiment, the support contains cerium oxide. When the above-mentioned active component (particularly Ni) is supported on a support containing such an oxide, the activity of the methanation reaction catalyst can be stably improved.

[0020] When the methanation catalyst contains an active component and a support, the content of the active component is, for example, 0.01 to 80 parts by mass, preferably 1 to 50 parts by mass, and more preferably 1 to 20 parts by mass, relative to 100 parts by mass of the support. When the content of the active component is within this range, the activity of the methanation catalyst can be improved more stably.

[0021] The mass of the methanation catalyst per unit volume of the gas flow passage is, for example, 30 g / L or more, preferably 50 g / L or more, while the upper limit of the mass of the methanation catalyst per unit volume of the gas flow passage is typically 1000 g / L or less.

[0022] 1 and 2, in one embodiment, the methane production reactor 100 has a flow-through structure. The ceramic substrate 1 has any suitable configuration that defines a gas flow path 15.

[0023] Examples of ceramic materials that can be used to form the ceramic substrate 1 include zirconia-based materials, alumina-titanium carbide-based composite materials, Si-SiC-based composite materials, aluminum nitride, aluminum oxide, silicon nitride, silicon carbide, zirconia, cordierite, and mullite. These ceramic materials can be used alone or in combination. Of these ceramic materials, cordierite and Si-SiC-based composite materials are preferred.

[0024] In one embodiment, the ceramic substrate 1 is made of a Si-SiC composite material. In other words, the ceramic substrate 1 contains Si and SiC. When the ceramic substrate contains Si and SiC, the thermal conductivity of the ceramic substrate can be stably adjusted to fall within the above-mentioned range.

[0025] The Si-SiC composite material may be a porous body or a dense body. Porous Si-SiC composite materials are described in detail, for example, in JP 2002-201082 A. Dense Si-SiC composite materials are described in detail, for example, in JP 11-035376 A. The entire disclosures of these publications are incorporated herein by reference. Of the Si-SiC composite materials, dense bodies are preferred.

[0026] Examples of such ceramic substrates 1 include cylindrical substrates and honeycomb substrates. In one embodiment, the methane production reactor 100 includes a honeycomb substrate 1a and a catalyst layer 2. The honeycomb substrate 1a includes partition walls 13 that define a plurality of cells 14. At least some of the cells 14 include gas flow channels 15. In the illustrated example, all of the cells 14 include the gas flow channels 15. The catalyst layer 2 is provided on the surface of the partition walls 13. The catalyst layer 2 includes the methanation reaction catalyst described above. With this configuration, when the raw material gas is supplied to the gas flow channels, the raw material gas can be efficiently brought into contact with the methanation reaction catalyst in the catalyst layer. This allows the methanation reaction to proceed smoothly, further improving the methane conversion rate.

[0027] The honeycomb substrate 1a may have any suitable shape (overall shape). Examples of the shape of the honeycomb substrate 1a include a cylindrical shape with a circular bottom, an elliptical cylindrical shape with an elliptical bottom, a rectangular prism with a polygonal bottom, and a cylindrical shape with an irregular bottom. In one embodiment, the honeycomb substrate 1a has a cylindrical shape. The outer diameter and length of the honeycomb substrate 1a can be appropriately set depending on the purpose.

[0028] In the illustrated example, the honeycomb substrate 1a includes outer walls 16 and partition walls 13 located inside the outer walls 16. The outer walls 16 and the partition walls 13 may be formed integrally or separately. In the illustrated example, the outer walls 16 and the partition walls 13 are formed integrally. Note that the honeycomb substrate 1a does not necessarily have to include the outer walls 16. In this case, the honeycomb substrate 1a is composed of the partition walls 13.

[0029] The outer wall 16 has a cylindrical shape. The thickness of the outer wall 16 is set arbitrarily and appropriately. The thickness of the outer wall 16 is, for example, 1 mm to 10 mm, or, for example, 2 mm to 8 mm.

[0030] As described above, the partition walls 13 define a plurality of cells 14. The cells 14 extend in the longitudinal direction (axial direction) of the honeycomb substrate 1a from the first end face E1 (inlet end face) to the second end face E2 (outlet end face) of the honeycomb substrate 1a (see FIG. 2). The cells 14 have any appropriate shape in a cross section perpendicular to the longitudinal direction of the honeycomb substrate 1a. Examples of the cross-sectional shape of the cells include a triangle, a rectangle, a pentagon, a polygon with hexagons or more, a circle, and an ellipse. The cross-sectional shapes and sizes of the cells may all be the same, or at least some may be different. Among such cross-sectional shapes of the cells, a rectangle is preferred, and a square or rectangle is more preferred.

[0031] The cell density of the honeycomb substrate 1a is, for example, 40 cpsi or more, preferably 50 cpsi or more, more preferably 100 cpsi or more, even more preferably 200 cpsi or more, particularly preferably 400 cpsi or more, and particularly preferably 500 cpsi or more. On the other hand, the cell density of the honeycomb substrate 1a is, for example, 1000 cpsi or less, preferably 900 cpsi or less. When the cell density is in this range, the raw material gas can be brought into contact with the catalyst layer more efficiently. In this specification, the "cell density of the honeycomb substrate" means the cell density of the cross section in the length direction (direction in which the cells extend) of the honeycomb substrate, and "cpsi" refers to the cell density of 6.4516 cm of the cross section. ２ This refers to the number of cells per square inch.

[0032] In the illustrated example, the partition walls 13 have first partition walls 13a and second partition walls 13b that are perpendicular to each other, and the first partition walls 13a and the second partition walls 13b define a plurality of cells 14. The cross-sectional shape of the cells 14 is quadrangular except for the portions where the first partition walls 13a and the second partition walls 13b contact the outer wall 16. The configuration of the partition walls is not limited to the above-described partition walls 13. The partition walls may have first partition walls extending in the radial direction and second partition walls extending in the circumferential direction, which define a plurality of cells.

[0033] The thickness of the partition walls 13 can be set arbitrarily and appropriately. The thickness of the partition walls 13 is typically thinner than the thickness of the outer walls 16. The thickness of the partition walls 13 is, for example, 0.0508 mm or more, preferably 0.0635 mm or more. On the other hand, the thickness of the partition walls 13 is, for example, 1.52 mm or less, preferably 1.27 mm or less, more preferably 1.00 mm or less, even more preferably 0.50 mm or less, particularly preferably 0.20 mm or less, and particularly preferably 0.15 mm or less. When the thickness of the partition walls is in this range, the mechanical strength of the honeycomb substrate can be sufficient, and the cell density can be adjusted to the above-mentioned range. The thickness of the partition walls is measured, for example, by cross-sectional observation using a scanning electron microscope (SEM).

[0034] The partition walls 13 may or may not have pores. The porosity of the partition walls 13 can be appropriately set depending on the purpose. The porosity of the partition walls 13 is, for example, 70% or less, preferably 65% ​​or less, and more preferably 50% or less. On the other hand, the porosity of the partition walls 13 is, for example, 0% or more, or, for example, 0.1% or more. The porosity is measured by, for example, mercury intrusion porosimetry.

[0035] The bulk density of the partition walls 13 can be appropriately set depending on the purpose. The bulk density of the partition walls 13 is, for example, 1.0 g / cm ３ ~3.0 g / cm ３ and preferably 2.0 g / cm ３ ~3.0 g / cm ３ The bulk density is measured by, for example, the Archimedes method.

[0036] The range of the thermal conductivity of the partition walls 13 is, for example, the same as the range of the thermal conductivity of the ceramic base 1 described above.

[0037] The catalyst layer 2 is formed on the surface of the partition wall 13. When the catalyst layer is formed on the surface of the partition wall, the reaction heat of the methanation reaction and / or the combustion reaction can be smoothly transferred from the catalyst layer to the partition wall. Therefore, the heat uniformity in the gas flow passage can be stably achieved. In the methane production reactor 100, the gas flow passage 15 is formed in a portion (typically the center portion) of the cross section of the cell 14 where the catalyst layer 2 is not formed. The catalyst layer 2 may be formed on the entire inner surface of the partition wall 13 (i.e., so as to surround the gas flow passage 15) as in the illustrated example, or may be formed on a part of the surface of the partition wall. When the catalyst layer 2 is formed on the entire inner surface of the partition wall 13, the methane conversion rate can be more stably improved.

[0038] The gas flow channels 15 are spaces formed inside the cells 14, and extend from a first end face E1 (inlet end face) to a second end face E2 (outlet end face) similarly to the cells 14 (see FIG. 2). The cross-sectional shape of the gas flow channels 15 may be the same as that of the cells 14, preferably a quadrangle, and more preferably a square or rectangle. The cross-sectional shapes and sizes of the gas flow channels 15 may all be the same, or at least some may be different.

[0039] As described above, the catalyst layer 2 contains a methanation catalyst. The methanation catalyst contained in the catalyst layer 2 may have any appropriate shape. The methanation catalyst is typically in a particulate form. Hereinafter, particulate methanation catalysts may be referred to as catalyst particles. In one embodiment, the catalyst layer 2 contains aggregates formed by aggregating a plurality of catalyst particles. The aggregates of the plurality of catalyst particles may form mesopores in the catalyst layer 2.

[0040] The content of the methanation catalyst in the catalyst layer 2 is, for example, 10% by mass to 100% by mass, and preferably 50% by mass to 100% by mass. The catalyst loading in the catalyst layer 2 is, for example, 0.007 mg / mm ２ ~1.869mg / mm ２ When the methanation reaction catalyst content and / or catalyst loading are within these ranges, the methanation reaction can proceed stably in the methane production reactor.

[0041] The catalyst layer 2 may contain an additive in addition to the methanation catalyst. Examples of the additive include a filler, a binder, a heat conductive material, and a heat transfer material. The additives may be used alone or in combination. The additive is added in an amount of, for example, 0.1 to 90 parts by mass, and preferably 0.1 to 50 parts by mass, per 100 parts by mass of the methanation catalyst.

[0042] The thermal conductivity of the catalyst layer 2 is, for example, 0.5 W / m·K to 1000 W / m·K, preferably 1.0 W / m·K to 1000 W / m·K. The thermal conductivity of the catalyst layer is measured, for example, by a hot wire method. The weighted average of the thermal conductivity of the catalyst layer 2 and the thermal conductivity of the ceramic substrate 1 is, for example, 0.5 W / m·K or more, preferably 5 W / m·K or more, more preferably 10 W / m·K or more, even more preferably 50 W / m·K or more, and particularly preferably 100 W / m·K or more. On the other hand, the upper limit of the weighted average of the thermal conductivity of the catalyst layer 2 and the thermal conductivity of the ceramic substrate 1 is typically 1000 W / m·K. When the weighted average of the thermal conductivity of the catalyst layer and the thermal conductivity of the ceramic substrate is within this range, the temperature can be appropriately controlled throughout the catalyst layer, resulting in a further improvement in the methane conversion rate.

[0043] The thickness of the catalyst layer 2 is, for example, 0.1 μm to 3000 μm, and preferably 20 μm to 300 μm. The average pore diameter in the catalyst layer 2 is, for example, 0.01 μm to 30 μm, and preferably 1 μm to 20 μm. The porosity in the catalyst layer 2 is, for example, 1% to 80%, and preferably 2% to 50%.

[0044] C. Methane Production Method Next, a methane production method according to one embodiment will be described with reference to Figure 2. In the methane production method, a methane production reactor is typically heated to a reaction initiation temperature before the feed gas is supplied. The reaction initiation temperature is, for example, 100°C or higher, preferably 150°C or higher. On the other hand, the upper limit of the reaction initiation temperature is typically 600°C.

[0045] Next, the feed gas is supplied at any appropriate space velocity (SV) to the gas flow passage of the methane production reactor heated to the reaction initiation temperature, whereby the feed gas flows into the gas flow passage and comes into contact with the methanation reaction catalyst heated to the reaction initiation temperature.

[0046] The carbon oxide content in the feed gas is, for example, 0.1 mol % to 20 mol %, and preferably 1.0 mol % to 15 mol %. The hydrogen content in the feed gas is, for example, 0.4 mol % to 80 mol %, and preferably 4.0 mol % to 80 mol %. In one embodiment, the feed gas contains oxygen in addition to carbon dioxide and hydrogen. The oxygen content in the feed gas is, for example, 0.5 mol % to 10 mol %, and preferably 1.0 mol % to 5.0 mol %. Furthermore, the feed gas may contain nitrogen as the balance.

[0047] The space velocity (SV) of the raw gas is, for example, 100 h －１ More than 3000h, preferably －１ On the other hand, the space velocity (SV) of the raw material gas is, for example, 100,000 h －１ The following is the result.

[0048] When the feed gas contains oxygen in addition to carbon dioxide and hydrogen, the hydrogen combustion reaction shown in the above formula (3) typically proceeds preferentially over the methanation reaction shown in the above formulas (I) and (II). At this time, the reaction heat generated by the hydrogen combustion reaction is utilized to continue the hydrogen combustion reaction and to initiate the methanation reaction. Once the methanation reaction is initiated, the methanation reaction also generates reaction heat. This reaction heat is uniformly diffused by the ceramic substrate, allowing the temperature to be suitably controlled throughout the methane production reactor. As a result, the combustion reaction and methanation reaction continue stably, and even after the combustion reaction is completed, the methanation reaction continues stably. Therefore, in one embodiment, external heating of the methane production reactor is stopped.

[0049] With external heating of the methane production reactor stopped, the temperature (reaction temperature) within the gas flow path of the methane production reactor is maintained throughout the reactor at, for example, 100° C. to 600° C., preferably 250° C. to 450° C. When the reaction temperature is within this range, the methanation reaction can be continued more stably.

[0050] As a result, carbon oxides and hydrogen react in the gas flow path of the methane production reactor to produce methane gas. Thereafter, a methane-containing gas is continuously discharged from the gas flow path of the methane production reactor. The methane-containing gas contains methane gas and water vapor. In addition to methane gas and water vapor, the methane-containing gas may also contain unreacted remaining raw material gas (oxygen, hydrogen, and / or carbon oxides).

[0051] The methane conversion is the percentage of methane relative to the total of methane and unreacted carbon oxides contained in the methane-containing gas, and is, for example, 65% or more, preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more. On the other hand, the methane conversion is, for example, 100% or less, or, for example, 95% or less.

[0052] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0053] Example 1 Preparation of Honeycomb Substrate A clay containing 80 parts by mass of SiC raw material powder and 20 parts by mass of metal Si powder was extruded, dried, and calcined at 550°C for 3 hours in an oxidizing atmosphere, and then fired at 1450°C for 2 hours in a non-oxidizing atmosphere. This resulted in the preparation of the honeycomb substrate shown in FIG. 1. The honeycomb substrate had a cylindrical shape with a diameter of 20 mm and a length of 50 mm. The honeycomb substrate was made of a Si-SiC composite material. The honeycomb substrate included partition walls defining a plurality of cells and an outer wall surrounding the partition walls. The cross-sectional shape of the cells was rectangular. The cell density of the honeycomb substrate was 300 cpsi, the partition wall thickness was 0.254 mm, the partition wall average pore diameter was 11 μm, and the partition wall porosity was 55%. The thermal conductivity of the honeycomb substrate, the thickness of the partition walls, and the cell density of the honeycomb substrate are shown in Table 1. <<Preparation of Methanation Catalyst>> Cerium (IV) oxide particles (manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.) were introduced into distilled water and stirred under reduced pressure at room temperature (23°C) for 12 hours. This resulted in a dispersion of metal oxide particles. Nickel (II) nitrate hexahydrate was also dissolved in distilled water to obtain a nickel nitrate aqueous solution. Next, the nickel nitrate aqueous solution was added to the dispersion of metal oxide particles and stirred at room temperature (23°C) for 2 hours. Thereafter, the mixture of the dispersion and the aqueous solution was heated to 80°C while stirring to evaporate the water. Next, the remaining solid was heated at 500°C for 3 hours. This resulted in methanation catalyst particles (hereinafter referred to as catalyst particles). The catalyst particles contained nickel oxide (NiO) and cerium (IV) oxide supporting nickel oxide (NiO). The methanation reaction catalyst particles contained 10 parts by mass of Ni relative to 100 parts by mass of cerium oxide. <<Preparation of Catalyst Layer>> The obtained catalyst particles were dispersed in distilled water to prepare a catalyst slurry. The catalyst particle content in the catalyst slurry was 10% by mass. Next, the honeycomb substrate prepared above was immersed in the catalyst slurry for 5 seconds under normal pressure (0.1 MPa) and room temperature (23°C). Thereafter, the honeycomb substrate was pulled out of the catalyst slurry. In this way, the catalyst slurry was applied to the surfaces of the partition walls.The catalyst slurry applied to the partition wall surfaces was then heated and dried at 100°C for 120 minutes. The above-mentioned immersion and drying were repeated to form a catalyst layer on the partition wall surfaces. The catalyst layer contained aggregates of catalyst particles. The thickness of the catalyst layer was 10 µm. The amount of catalyst particles supported per unit area of ​​the partition wall was 1.9 g / cm. ２ In this way, a methane production reactor including a honeycomb substrate and a catalyst layer was manufactured.

[0054] Example 2 Except for changing the blending ratio of the SiC raw material powder and the metal Si powder, a methane production reactor was manufactured in the same manner as in Example 1. In the methane production reactor of Example 2, the average pore diameter of the partition walls was 13 µm, and the porosity of the partition walls was 48%.

[0055] Example 3 A methane production reactor was manufactured in the same manner as in Example 1, except that the honeycomb substrate composed of the Si-SiC composite material was changed to a honeycomb substrate prepared as follows. A clay containing SiC powder was extruded and then dried to prepare a dried honeycomb body. The dried honeycomb body had the same size and configuration as the honeycomb substrate of Example 1. A material powder containing Si powder was press-molded and then dried to obtain a Si supply body. Next, the Si supply body was heated at 1500°C for 4 hours under reduced pressure (200 Pa) while in contact with the dried honeycomb body, and the dried honeycomb body was impregnated with molten metal containing Si. In this way, a honeycomb substrate composed of a Si-SiC composite material was prepared. The partition walls of the honeycomb substrate did not have pores. In other words, the porosity of the partition walls of the honeycomb substrate was 0%.

[0056] Example 4 Except for changing the amount of molten metal Si, a honeycomb substrate made of a Si-SiC composite material was prepared in the same manner as in Example 3. In the partition walls of the honeycomb substrate, the average pore diameter was 10 μm and the porosity was 15%.

[0057] Example 5 A honeycomb substrate made of a Si-SiC composite material was prepared in the same manner as in Example 4, except that the cell density of the honeycomb substrate was changed to 50 cpsi and the partition wall thickness was changed to 1.27 mm. The partition walls of the honeycomb substrate had an average pore diameter of 10 μm and a porosity of 15%.

[0058] Example 6 A honeycomb substrate made of a Si-SiC composite material was prepared in the same manner as in Example 4, except that the cell density of the honeycomb substrate was changed to 600 cpsi and the partition wall thickness was changed to 0.102 mm. The partition walls of the honeycomb substrate had an average pore diameter of 13 μm and a porosity of 11%.

[0059] <Comparative Example 1> Except for changing the clay containing the SiC raw material powder and the metal Si powder to a clay containing a cordierite raw material, a methane production reactor was manufactured in the same manner as in Example 1. In the methane production reactor of Comparative Example 1, the average pore diameter of the partition walls was 11 µm, and the porosity of the partition walls was 52%.

[0060] <Comparative Example 2> Except for changing the blending ratio of the cordierite raw materials, a methane production reactor was manufactured in the same manner as in Comparative Example 1. In the methane production reactor of Comparative Example 2, the average pore diameter of the partition walls was 11 µm, and the porosity of the partition walls was 28%.

[0061] <Methanation Test> Four thermocouples were installed in the gas flow path of the methane production reactor obtained in the Examples and Comparative Examples. More specifically, thermocouples were installed in the gas flow path at positions 5 mm, 20 mm, 32 mm, and 45 mm from the inlet end face. Next, the methane production reactor was inserted into a reaction tube with an inner diameter of 21 mm. As a pretreatment for the reaction, the methane production reactor was heated to 500°C using an electric furnace installed around the reaction tube, and hydrogen gas was introduced into the reaction tube to reduce the methanation catalyst. Next, nitrogen gas was flowed through the reaction tube to lower the temperature of the electric furnace to 300°C, and then the feed gas under test condition A or B was introduced into the reaction tube. The feed gas under test condition A contained 10 mol% carbon dioxide, 3 mol% oxygen, 46 mol% hydrogen, and the balance nitrogen. The feed gas under test condition B contained 20 mol% carbon dioxide and 80 mol% hydrogen. That is, the raw material gas under test condition A contains oxygen, and the raw material gas under test condition B does not contain oxygen. In each of the examples and comparative examples, the space velocity SV of the raw material gas was set at three conditions (3000 h －１ , 10000h －１ , 30000h －１ ) was carried out. As a result, the raw material gas was supplied to the gas flow path provided in the methane production reactor, and a methane-containing gas flowed out of the reaction tube. At this time, the temperature at each position in the gas flow path was measured using the four thermocouples described above. The maximum temperature difference in the gas flow path is shown in Table 1. In addition, the concentrations of carbon dioxide and methane in the methane-containing gas flowing out of the reaction tube after heating of the electric furnace was stopped were measured using a gas chromatograph-thermal conductivity detector (GC-TCD). Based on the measurement results, the conversion rate (%) of carbon dioxide to methane was calculated using the following formula (A). Methane conversion rate (%) = (amount of methane contained in methane-containing gas (volume %) / sum of the amount of methane and the amount of carbon oxide contained in methane-containing gas (volume %)) × 100 (A). The methane conversion rate at each space velocity of the methane production reactor in Comparative Example 1 was set to 1, and the methanation rates in the methane production reactors in Examples 1 to 6 and Comparative Example 2 were normalized to obtain the methane conversion amount. The results are shown in Table 1.

[0062]

[0063] <Evaluation> As shown in Table 1, it is clear that when the thermal conductivity of the ceramic substrate is 8 W / m·K or more, the methane conversion rate (amount) can be significantly improved.

[0064] The methane production reactor according to the embodiment of the present invention can be used for producing methane, and is particularly suitable for continuous production of methane using exhaust gases emitted from various industrial products or industrial facilities as raw materials.

[0065] REFERENCE SIGNS LIST 100 Methane production reactor 1 Ceramic substrate 1a Honeycomb substrate 13 Partition wall 14 Cell 15 Gas flow path 2 Catalyst layer

Claims

1. A methane production reactor comprising: a ceramic substrate defining a gas flow path through which a raw material gas containing carbon oxides and hydrogen is supplied; and a methanation reaction catalyst capable of promoting a reaction to produce methane, the methanation reaction catalyst being arranged so as to be in contact with the raw material gas supplied to the gas flow path, wherein the thermal conductivity of the ceramic substrate is 8 W / m·K or more.

2. The reactor for producing methane according to claim 1, wherein the thermal conductivity of the ceramic substrate is 100 W / m·K or more.

3. The methane production reactor according to claim 1, wherein the feed gas further contains oxygen.

4. A methane production reactor according to any one of claims 1 to 3, wherein the ceramic substrate is a honeycomb substrate having partition walls that define a plurality of cells, and at least some of the plurality of cells include the gas flow path.

5. The reactor for producing methane according to claim 4, further comprising a catalyst layer provided on a surface of the partition wall, the catalyst layer containing the methanation reaction catalyst.

6. A reactor for producing methane according to claim 5, wherein the weighted average value of the thermal conductivity of the ceramic substrate and the thermal conductivity of the catalyst layer is 5 W / m·K or more.

7. The reactor for producing methane according to claim 4, wherein the porosity of the partition wall is 65% or less.

8. A reactor for producing methane according to claim 4, wherein the thickness of the partition walls is 0.0635 mm or more and 1.27 mm or less, and the cell density of the honeycomb substrate is 50 cpsi or more and 900 cpsi or less.

9. A methane production reactor according to any one of claims 1 to 3, wherein the ceramic substrate contains Si and SiC.

10. A methane production reactor according to any one of claims 1 to 3, wherein the methanation catalyst contains a transition metal as an active component.

11. The methane production reactor of claim 10, wherein the transition metal comprises Co, Fe, Pt, Ru, Rh, Pd, Ni, Cu, Ag, Au, Ir, or a combination thereof.

12. The methane production reactor of claim 11, wherein the transition metal comprises Ni.

13. The reactor for producing methane according to claim 10, wherein the methanation catalyst further comprises a support that supports the transition metal, and the support comprises cerium oxide, silicon oxide, zirconium oxide, yttrium oxide, aluminum oxide, or a composite oxide thereof.

14. The methane production reactor of claim 13, wherein the support comprises cerium oxide.

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