Methane production reactor

Abstract

Provided is a methane production reactor with which methane yield can be improved and methane can be efficiently produced. A methane production reactor according to one embodiment has a gas flow path. The gas flow path supplies a raw material gas containing carbon oxide and hydrogen. This methane production device comprises a ceramic substrate and a catalyst layer.This methane production device comprises a ceramic substrate and a catalyst layer. The catalyst layer is disposed on the surface of the ceramic substrate so as to face the gas flow path. The catalyst layer contains a methanation reaction catalyst capable of promoting a reaction for generating methane. The thermal conductivity of the ceramic substrate is at least 8 W / m∙K. The thickness of the catalyst layer is at most 600 μm.

Description

methane production reactor

[0001] This invention relates to a methane production reactor.

[0002] In recent years, from the perspective of reducing environmental impact, the recovery of carbon dioxide and its reuse as a raw material for carbon compounds has been considered. For example, a method has been proposed for producing methane 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 the methanation reaction is started and continued by the heat, including the reaction heat from the catalytic combustion of 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 yield. In particular, when attempting to increase the amount of catalyst to improve the methane yield, the catalyst layer becomes thicker, reducing thermal conductivity and causing a significant decrease in methane yield due to heat accumulation. The main objective of the present invention is to provide a methane production reactor that can improve methane yield and efficiently produce methane.

[0005] [1] A methane production reactor according to one embodiment of the present invention has a gas channel. A raw material gas containing carbon oxide and hydrogen is supplied to the gas channel. The methane production apparatus comprises a ceramic substrate and a catalyst layer. The catalyst layer is arranged on the surface of the ceramic substrate so as to face the gas channel. The catalyst layer contains a methanation reaction catalyst capable of promoting the reaction that produces methane. The thermal conductivity of the ceramic substrate is 8 W / m·K or more. The thickness of the catalyst layer is 600 μm or less. [2] In the methane production reactor described in [1] above, the thickness of the catalyst layer may be 5 μm or more. [3] In the methane production reactor described in [1] or [2] above, the thickness of the catalyst layer may be 300 μm or more. [4] In the methane production reactor described in any of [1] to [3] above, the porosity of the catalyst layer may be 0.01% or more and less than 20%. [5] In the methane production reactor described in any of [1] to [4] above, the porosity of the catalyst layer may be 15% or less. [6] In the methane production reactor described in any of [1] to [5] above, the thermal conductivity of the ceramic substrate may be 100 W / m·K or more. [7] In the methane production reactor described in any of [1] to [6] above, the porosity of the ceramic substrate may be 65% or less. The average pore size of the ceramic substrate may be 50 μm or less. [8] In the methane production reactor described in any of [1] to [7] above, the ceramic substrate may be a honeycomb-shaped substrate having partitions that constitute a plurality of cells. At least a portion of the plurality of cells includes the gas flow path. [9] In the methane production reactor described in any of [1] to [8] above, the raw material gas may contain carbon dioxide and hydrogen.

[10] In the methane production reactor described in any of [1] to [9] above, the raw material gas may further contain oxygen.

[11] In the methane production reactor described in any of [1] to

[10] above, the ceramic substrate may contain Si and SiC.

[12] In the methane production reactor described in any of [1] to

[11] above, the methanation catalyst may contain a transition metal as an active ingredient.

[13] In the methane production reactor described in

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

[14] In the methane production reactor described in

[12] or

[13] above, the methanation catalyst may further include a carrier supporting the transition metal. The carrier may include cerium oxide, silicon oxide, zirconium oxide, yttrium oxide, aluminum oxide, or a composite oxide thereof.

[0006] According to embodiments of the present invention, methane yield can be improved and methane can be produced efficiently.

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

[0008] Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. Furthermore, in order to clarify the explanation, the drawings may schematically represent the width, thickness, shape, etc., of each part compared to the embodiments; however, these are merely examples and do not limit the interpretation of the present invention.

[0009] A. Schematic diagram 1 of the methane production reactor is a schematic perspective view of a methane production reactor according to one embodiment of the present invention; Figure 2 is a schematic cross-sectional view of the methane production reactor of Figure 1. The methane production reactor 100 typically has a gas channel 15. The methane production reactor 100 comprises a ceramic substrate 1 and a catalyst layer 2. The catalyst layer 2 contains a methanation reaction catalyst capable of promoting the reaction that produces methane (hereinafter referred to as the methanation reaction). The catalyst layer 2 is arranged on the surface of the ceramic substrate 1 so as to face the gas channel 15. A raw material gas containing carbon oxide (typically carbon dioxide and / or carbon monoxide) and hydrogen is supplied to the gas channel 15 of the methane production reactor 100. When the raw material gas is supplied to the gas channel 15, the methanation reaction shown in the following formulas (I) and / or (II) typically proceeds in the methane production reactor 100. Since these methanation reactions are exothermic reactions, heat of reaction is generated as the methanation reaction progresses.

[0010] In one embodiment, the thermal conductivity of the ceramic substrate 1 is 8 W / m·K or higher, and the thickness of the catalyst layer 2 is 600 μm or less. The inventors discovered that if the amount of catalyst per unit volume in a methane production reactor is small, the contact between the raw material gas and the methanation reaction catalyst becomes insufficient, and the methane yield decreases. Therefore, the inventors confirmed that if the content of the methanation reaction catalyst in the catalyst layer (hereinafter sometimes referred to as catalyst content) is increased, the thickness of the catalyst layer increases, the thermal conductivity of the catalyst layer decreases, and the reaction heat generated by the methanation reaction is not dissipated from the catalyst layer, causing the catalyst layer to be partially excessively heated. As a result, when the temperature of the catalyst layer reaches a high temperature range, for example, above 600°C, the methane yield may decrease due to equilibrium limitation of the methanation reaction and / or deterioration (sintering) of the methanation reaction catalyst. Therefore, the inventors diligently studied the balance between catalyst content and thermal diffusivity in the catalyst layer and found that the methane yield can be stably improved by adjusting the thickness of the catalyst layer and the thermal conductivity of the ceramic substrate. More specifically, since the thickness of the catalyst layer facing the gas flow path is 600 μm or less, and the thermal conductivity of the ceramic substrate supporting the catalyst layer is 8 W / m·K or higher, even if the catalyst content in the catalyst layer is increased, the reaction heat generated by the methanation reaction is smoothly transferred from the catalyst layer to the ceramic substrate, uniformly heating the entire catalyst layer through the ceramic substrate. As a result, the catalyst layer can be stably controlled to a temperature suitable for the methanation reaction (for example, around 300°C). Consequently, the methane yield can be stably improved, and methane can be produced with energy savings. In other words, a methane production reactor according to one embodiment can achieve an excellent methane yield. Furthermore, since thermal degradation of the methane production reactor (ceramic substrate and / or methane reaction catalyst) can be suppressed, the lifespan of the methane production reactor can be extended and the maintainability of the methane production reactor can be improved.

[0011] The thermal conductivity of the ceramic substrate 1 is preferably 10 W / m·K or higher, more preferably 50 W / m·K or higher, even more preferably 100 W / m·K or higher, and particularly preferably 120 W / m·K or higher. When the thermal conductivity of the ceramic substrate is above this lower limit, the reaction heat generated by the methanation reaction is rapidly diffused from the catalyst layer to the ceramic substrate, improving the uniformity of the catalyst layer. As a result, the temperature can be appropriately controlled throughout the gas flow path, and the methanation reaction can proceed with an excellent methane yield. On the other hand, 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, for example, by preparing a sample of a predetermined size from the object, measuring the thermal diffusivity of the sample using an optical AC thermal diffusivity measuring device (typically 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, based on the following formula (1): Thermal conductivity = Thermal diffusivity × Specific heat × Bulk density ... (1)

[0012] The thermal diffusivity of the ceramic substrate 1 is, for example, 1.0 × 10⁻⁶ －５ I understand ２ / s ~ 10 x 10 －５ I understand ２ The temperature is / s. 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.

[0013] The porosity of the ceramic substrate 1 is appropriately set according to the purpose. For example, the porosity of the ceramic substrate 1 is 70% or less, preferably 65% ​​or less, and more preferably 50% or less. On the other hand, the porosity of the ceramic substrate 1 is, for example, 0% or more, and also, for example, 0.1% or more. When the porosity of the ceramic substrate is within such a range, the thermal conductivity of the ceramic substrate can be stably adjusted to the above range. The porosity is measured, for example, by the mercury intrusion method.

[0014] When the porosity of the ceramic substrate 1 exceeds 0%, the average pore diameter of the ceramic substrate 1 is, for example, 60 μm or less, preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. On the other hand, the average pore diameter of the ceramic substrate 1 is, for example, 1 μm or more, preferably 5 μm or more. When the average pore diameter of the ceramic substrate is within this range, the thermal conductivity of the ceramic substrate can be stably adjusted within the above range. The average pore diameter is measured, for example, by the mercury intrusion method.

[0015] The catalyst layer 2 is typically supported by the ceramic substrate 1. In the illustrated example, the catalyst layer 2 is laminated on the surface of the ceramic substrate 1. The thickness of the catalyst layer 2 is 600 μm or less, preferably 550 μm or less, as described above. When the thickness of the catalyst layer is below this upper limit, the thermal conductivity of the catalyst layer can be stably improved. On the other hand, the thickness of the catalyst layer 2 is, for example, 100 μm or more, preferably 290 μm or more, more preferably 300 μm or more, and even more preferably 350 μm or more. When the thickness of the catalyst layer is above this lower limit, a sufficient catalyst content in the catalyst layer can be ensured.

[0016] The porosity of the catalyst layer 2 is, for example, 45% or less, preferably less than 20%, more preferably 18% or less, and even more preferably 15% or less. When the porosity of the catalyst layer is below such an upper limit, the thermal conductivity of the catalyst layer can be improved more stably, and the catalyst content in the catalyst layer can be improved stably. On the other hand, the porosity of the catalyst layer 2 is, for example, 0% or more, preferably 0.01% or more, more preferably 1% or more, and even more preferably 5% or more. When the porosity of the catalyst layer is above such a lower limit, the gas diffusivity in the catalyst layer can be improved, and the raw material gas and the methanation reaction catalyst can be brought into contact efficiently.

[0017] The thermal conductivity of the catalyst layer 2 is, for example, 0.05 W / m·K or higher, preferably 0.08 W / m·K or higher. On the other hand, the thermal conductivity of the catalyst layer 2 is, for example, 200 W / m·K or lower. The thermal conductivity of the catalyst layer is measured, for example, by the hot-wire method.

[0018] As described above, catalyst layer 2 contains a methanation catalyst. The methanation catalyst can typically promote the methanation reaction shown in formula (I) and / or formula (II) above.

[0019] The methanation catalyst contains any suitable metal element as an active ingredient. The methanation catalyst may contain a metal element in its metallic state, a salt of a metal element, or an oxide of a metal element. Preferably, the methanation catalyst contains a metal element in its metallic state.

[0020] Examples of metallic elements include alkali metals, alkaline earth metals, and transition metals, with transition metals being preferred. Specific examples of transition metals include Co, Fe, Pt, Ru, Rh, Pd, Ni, Cu, Ag, Au, and Ir. These transition metals can be used individually or in combination. In one embodiment, the methanation catalyst contains Ni. The presence of Ni in the methanation catalyst can further accelerate the methanation reaction described above.

[0021] The methanation catalyst may further contain a support in addition to the active component described above. The support can support the active component (typically a transition metal). The support is composed of any suitable inorganic material depending on the application. Examples of inorganic materials include oxides, carbides, nitrides, sulfides, halides, hydrides, and hydroxides. The inorganic materials can be used alone or in combination.

[0022] 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 such an oxide-containing support bears the above-mentioned active component (especially Ni), the activity of the methanation reaction catalyst can be stably improved.

[0023] When the methanation catalyst contains an active component and a support, the content ratio 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, per 100 parts by mass of the support. If the content ratio of the active component is within this range, the activity of the methanation catalyst can be improved more stably.

[0024] The methanation catalyst contained in catalyst layer 2 has any suitable shape. The methanation catalyst is typically particulate. Hereinafter, particulate methanation catalyst may be referred to as catalyst particles. In one embodiment, catalyst layer 2 contains aggregates formed by the aggregation of multiple catalyst particles. The aggregates of multiple catalyst particles can form mesopores in catalyst layer 2. The average secondary particle diameter of the multiple catalyst particles is, for example, 0.01 μm to 50 μm, preferably 0.1 μm to 20 μm. The standard deviation of the average secondary particle diameter of the multiple catalyst particles is, for example, 0.1 μm to 40 μm, preferably 0.5 μm to 30 μm. Here, secondary particle diameter means D50 in the volume-based cumulative particle size distribution of the particle group containing the aggregate. When the average secondary particle diameter and / or standard deviation of the catalyst particles are within this range, the porosity and thickness of the catalyst layer can be stably adjusted within the above range. The secondary particle size of the catalyst particles is measured, for example, using a laser diffraction / scattering particle size distribution analyzer.

[0025] The content ratio of the methanation reaction catalyst in the catalyst layer 2 is, for example, 10% by mass or more, preferably 50% by mass or more, and more preferably 80% by mass or more. On the other hand, the upper limit of the content ratio of the methanation reaction catalyst in the catalyst layer 2 is typically 100% by mass. The catalyst loading amount in the catalyst layer 2 is, for example, 0.007 mg / mm ２ to 1.869 mg / mm ２ , preferably 0.015 mg / mm ２ to 0.500 mg / mm ２ . When the content ratio of the methanation reaction catalyst and / or the catalyst loading amount falls within such a range, the aforementioned methanation reaction can proceed stably in the methane production reactor.

[0026] The mass of the methanation reaction catalyst per unit volume of the honeycomb-shaped substrate including the gas flow path 15 is, for example, 30 g / L or more, preferably 50 g / L or more. On the other hand, the upper limit of the mass of the methanation reaction catalyst per unit volume of the honeycomb-shaped substrate including the gas flow path 15 is typically 1000 g / L or less.

[0027] The catalyst layer 2 may contain additives in addition to the methanation reaction catalyst. Examples of the additives include fillers, binders, heat conductive materials, heat transfer materials, and pore-forming agents. The additives may be used alone or in combination. The addition ratio of the additives is, for example, 0.1 part by mass to 90 parts by mass, preferably 0.1 part by mass to 50 parts by mass, relative to 100 parts by mass of the methanation reaction catalyst.

[0028] In one embodiment, the raw material gas supplied to the gas flow path 15 further contains oxygen. In this case, a combustion reaction represented by the following formula (III) can proceed in the gas flow path 15. Since the combustion reaction (III) is an exothermic reaction, the generated reaction heat can be effectively used for continuing the methanation reactions of the aforementioned formula (I) and formula (II). O ２ +2H ２ →2H ２O ··· (III) On the other hand, the above combustion reaction (III) has a faster reaction rate than the above methanation reaction, and can proceed preferentially in the upstream portion of the gas flow path in the supply direction of the raw material gas. As a result, a local high-temperature portion (hot spot) may be formed in the upstream portion of the gas flow path. When a hot spot is formed, there is a risk that a decrease in methane yield and / or deterioration of the methanation reaction catalyst may occur. In contrast, in one embodiment, since the thermal conductivity of the ceramic substrate is within the above range, the reaction heat generated by the combustion reaction (III) can also be rapidly diffused from the catalyst layer to the ceramic substrate. As a result, even if the raw material gas further contains oxygen, the temperature of the catalyst layer can be appropriately controlled. Accordingly, the methane production reactor 100 can stably perform methanation in which the methanation reaction is continued while external heating is stopped.

[0029] B. Details of Methane Production Reactor Next, details of a methane production reactor according to one embodiment will be described. As shown in FIG. 1 and FIG. 2, in one embodiment, the methane production reactor 100 has a flow-through structure.

[0030] B-1. Ceramic Substrate The ceramic substrate 1 is made of any appropriate ceramic material. Examples of ceramic materials 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. Among these ceramic materials, cordierite and Si-SiC-based composite materials are preferably mentioned.

[0031] In one embodiment, the ceramic substrate 1 is composed of a Si-SiC-based 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 the above range.

[0032] The Si—SiC-based composite material may be a porous body or a dense body. The porous body of the Si—SiC-based composite material is described in detail, for example, in Japanese Patent Application Laid-Open No. 2002-201082. The dense body of the Si—SiC-based composite material is described in detail, for example, in Japanese Patent Application Laid-Open No. 11-035376. The entire descriptions of these publications are incorporated herein by reference. Among Si—SiC-based composite materials, dense bodies are preferably mentioned.

[0033] Such a ceramic substrate 1 has a shape capable of supporting the catalyst layer 2. The ceramic substrate 1 preferably has any appropriate configuration that defines the gas flow path 15. Examples of the shape of the ceramic substrate 1 include a cylindrical shape and a honeycomb shape. In one embodiment, the methane production reactor 100 includes a honeycomb-shaped substrate 1a and a catalyst layer 2. The honeycomb-shaped substrate 1a includes partition walls 13 that define a plurality of cells 14. At least a part of the plurality of cells 14 includes the gas flow path 15. In the illustrated example, all of the plurality of cells 14 include the gas flow path 15. The catalyst layer 2 is provided inside the cells 14. If the methane production reactor has such a configuration, when the raw material gas is supplied to the gas flow path, the raw material gas and the methanation reaction catalyst in the catalyst layer can be brought into contact efficiently. Therefore, the aforementioned methanation reaction can proceed smoothly, and the methane yield can be further improved.

[0034] The honeycomb-shaped substrate 1a has any appropriate shape (overall shape). Examples of the shape of the honeycomb-shaped substrate 1a include a columnar shape with a circular bottom surface, an elliptical columnar shape with an elliptical bottom surface, a prismatic shape with a polygonal bottom surface, and a columnar shape with an irregular bottom surface. In one embodiment, the honeycomb-shaped substrate 1a has a cylindrical shape. The outer diameter and length of the honeycomb-shaped substrate 1a are appropriately set according to the purpose.

[0035] In the illustrated example, the honeycomb-shaped substrate 1a comprises an outer wall 16 and a partition wall 13 located inside the outer wall 16. The outer wall 16 and the partition wall 13 may be formed integrally or as separate components. In the illustrated example, the outer wall 16 and the partition wall 13 are formed integrally. Note that the honeycomb-shaped substrate 1a does not necessarily have an outer wall 16. In this case, the honeycomb-shaped substrate 1a is composed of partition walls 13.

[0036] 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.

[0037] As described above, the partition wall 13 defines 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 Figure 2). The cells 14 have any suitable shape in the cross section in a direction perpendicular to the longitudinal direction of the honeycomb substrate 1a. Examples of cell cross-sectional shapes include triangles, quadrilaterals, pentagons, polygons with hexagons or more, circles, and ellipses. The cross-sectional shapes and sizes of the cells may all be the same, or at least some may differ. Among such cell cross-sectional shapes, quadrilaterals are preferred, and squares or rectangles are more preferred.

[0038] The cell density in the honeycomb substrate 1a is, for example, 40 cpsi or more, preferably 50 cpsi or more, more preferably 100 cpsi or more, and even more preferably 200 cpsi or more. On the other hand, the cell density in the honeycomb substrate 1a is, for example, 1000 cpsi or less, preferably 900 cpsi or less. When the cell density is within this range, the raw material gas can be efficiently brought into contact with the catalyst layer. In this specification, "cell density of the honeycomb substrate" means the cell density of the cross-section in the longitudinal direction (direction in which the cells extend) of the honeycomb substrate, and "cpsi" means 6.4516 cm² of the said cross-section. ２ This refers to the number of cells per square inch.

[0039] In the illustrated example, the partition wall 13 has a first partition wall 13a and a second partition wall 13b that are perpendicular to each other, and the first partition wall 13a and the second partition wall 13b define a plurality of cells 14. The cross-sectional shape of the cells 14 is rectangular, except for the parts where the first partition wall 13a and the second partition wall 13b are in contact with the outer wall 16. Note that the configuration of the partition wall is not limited to the partition wall 13 described above. The partition wall may have a first partition wall extending in the radial direction and a second partition wall extending in the circumferential direction, and these may define a plurality of cells.

[0040] The thickness of the partition wall 13 can be set arbitrarily and appropriately. Typically, the thickness of the partition wall 13 is thinner than the thickness of the outer wall 16. For example, the thickness of the partition wall 13 is 0.0508 mm or more, preferably 0.0635 mm or more. On the other hand, the thickness of the partition wall 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 0.65 mm or less, particularly preferably 0.55 mm or less, especially preferably 0.50 mm or less, and most preferably 0.400 mm or less. If the thickness of the partition wall is within this range, the mechanical strength of the honeycomb substrate can be made sufficient, and the cell density can be adjusted to the above range. The thickness of the partition wall is measured, for example, by cross-sectional observation using an SEM (scanning electron microscope).

[0041] The partition wall 13 may or may not have pores. The range of porosity in the partition wall 13 is, for example, the same as the range of porosity of the ceramic substrate 1 described above. The range of average pore diameter in the partition wall 13 is, for example, the same as the range of average pore diameter of the ceramic substrate 1 described above. The range of thermal conductivity of the partition wall 13 is, for example, the same as the range of thermal conductivity of the ceramic substrate 1 described above.

[0042] The bulk density of the partition wall 13 can be appropriately set depending on the purpose. For example, the bulk density of the partition wall 13 is 1.0 g / cm³. ３ ~3.0 g / cm ３ Preferably 2.0 g / cm³ ３ ~3.0 g / cm ３ The bulk density is measured, for example, by the Archimedes method.

[0043] B-2. In the illustrated example of the catalyst layer, the catalyst layer 2 described above is provided 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 combustion reaction can be smoothly transferred from the catalyst layer to the partition wall. Therefore, stable heat uniformity in the gas flow path can be achieved. In the methane production reactor 100, the gas flow path 15 is formed in the portion of the cross-section of the cell 14 where the catalyst layer 2 is not formed (typically the central part). The catalyst layer 2 may be formed on the entire inner surface of the partition wall 13 (i.e., surrounding the gas flow path 15) as shown in the illustrated example, or it 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 yield can be improved more stably.

[0044] The gas flow path 15 is a space formed inside the cell 14 and extends from the first end face E1 (inlet end face) to the second end face E2 (outlet end face), similar to the cell 14 (see Figure 2). The cross-sectional shape of the gas flow path 15 can be the same as that of the cell 14 described above, preferably a quadrilateral, and more preferably a square or rectangle. The cross-sectional shape and size of the gas flow path 15 may all be the same, or at least some parts may differ.

[0045] C. Method for Manufacturing a Methane Production Reactor Next, a method for manufacturing a methane production reactor 100 according to one embodiment will be described. In one embodiment, the method for manufacturing a methane production reactor 100 includes a step of preparing a slurry for forming a catalyst layer 2 (slurry preparation step) and a step of applying the slurry to a ceramic substrate 1 to form a catalyst layer 2 (catalyst layer formation step).

[0046] C-1. Slurry Preparation Process In the slurry preparation process, first, the methanation reaction catalyst described above is prepared. Typically, the methanation reaction catalyst is pulverized into particulate matter by any suitable means. This yields particulate methanation reaction catalyst (catalyst particles), and the average secondary particle diameter and / or standard deviation of the catalyst particles are adjusted to the range described above. Examples of methods for pulverizing the methanation reaction catalyst include pot mills, jet mills, hammer mills, and roll crushers, with pot mills being preferred.

[0047] Next, the methanation catalyst (preferably catalyst particles) is added to the solvent and stirred by any suitable method. Examples of solvents include water and organic solvents, with organic solvents being preferred. This prepares a slurry in which the methanation catalyst is dispersed in the solvent. The content of the methanation catalyst in the slurry is, for example, 1% to 50% by mass, and preferably 5% to 15% by mass.

[0048] In one embodiment, a pore-forming agent is further added to the slurry. When a pore-forming agent is added to the slurry, the porosity and thickness of the catalyst layer to be formed can be stably adjusted to the above-described range. Examples of pore-forming agents include particulate polymers and chain polymers. The pore-forming agent can be used alone or in combination. Among the pore-forming agents, particulate polymers are preferred. The addition ratio of the pore-forming agent is, for example, 0.01 to 30 parts by mass, preferably 0.1 to 25 parts by mass, per 100 parts by mass of the methanation reaction catalyst.

[0049] C-2. Catalyst layer formation process In the catalyst layer formation process, the ceramic substrate 1 described above is prepared in advance, and the slurry described above is applied to any appropriate position on the ceramic substrate 1. The method of applying the slurry is arbitrarily and appropriately selected according to the shape of the ceramic substrate 1. Examples of slurry application methods include the wash coat method, spray coat method, roller coat method, and spin coat method.

[0050] As shown in Figures 1 and 2, when the ceramic substrate 1 is a honeycomb substrate 1a, the slurry is applied to the surface of the partition wall 13 by a wash-coat method. More specifically, the slurry is poured into the cells 14 of the honeycomb substrate 1a. This allows the slurry to be smoothly applied to the surface of the partition wall 13, forming a slurry coating. After that, the slurry coating is dried as needed. The application and drying of the slurry may be repeated until the catalyst layer 2 reaches the desired thickness. Furthermore, the slurry coating may be fired, typically in an atmospheric environment (degreasing step). This removes organic components (typically pore-forming materials) contained in the slurry coating. In the degreasing step, the firing temperature is, for example, 150°C to 450°C, and the firing time is, for example, 0.5 hours to 5 hours. Through the above steps, the catalyst layer 2 is formed from the slurry, and a methane production reactor 100 comprising the ceramic substrate 1 (honeycomb substrate 1a) and the catalyst layer 2 is manufactured.

[0051] D. Method for Producing Methane Next, with reference to Figure 2, a method for producing methane according to one embodiment will be described. In the method for producing methane, typically the methane production reactor is heated to the reaction start temperature before the supply of the raw material gas. The reaction start temperature is, for example, 100°C or higher, and preferably 150°C or higher. On the other hand, the upper limit of the reaction start temperature is typically 600°C.

[0052] Next, the raw material gas is supplied at an appropriate space velocity (SV) to the gas channel of the methane production reactor, which has been heated to the reaction start temperature. As a result, the raw material gas flows into the gas channel and comes into contact with the methanation catalyst, which has also been heated to the reaction start temperature.

[0053] The carbon dioxide content in the raw material gas is, for example, 0.1 mol% to 20 mol%, preferably 1.0 mol% to 15 mol%. The hydrogen content in the raw material gas is, for example, 0.4 mol% to 80 mol%, preferably 4.0 mol% to 80 mol%. In one embodiment, the raw material gas contains oxygen in addition to carbon dioxide and hydrogen. The oxygen content in the raw material gas is, for example, 0.5 mol% to 10 mol%, preferably 1.0 mol% to 5.0 mol%. Furthermore, the raw material gas may contain nitrogen as the remainder.

[0054] The space velocity (SV) of the source gas is, for example, 2500 h. －１ A smaller range, preferably 1000h －１ The following applies. On the other hand, the space velocity (SV) of the raw material gas is, for example, 50h －１ That's all.

[0055] When the raw material gas contains oxygen in addition to carbon dioxide and hydrogen, typically the hydrogen combustion reaction shown in equation (III) above proceeds preferentially over the methane reaction shown in equations (I) and (II) above. In this case, the heat of reaction generated by the hydrogen combustion reaction is used to continue the hydrogen combustion reaction and to initiate the methane reaction. Once the methane reaction starts, heat of reaction is also generated by the methane reaction. This heat of reaction is uniformly diffused by the ceramic substrate, and the temperature is suitably controlled throughout the methane production reactor. As a result, the combustion reaction and the methane reaction continue stably, and the methane reaction continues stably even after the combustion reaction is completed. Therefore, in one embodiment, external heating of the methane production reactor is stopped.

[0056] With external heating to the methane production reactor stopped, the temperature in the gas flow path of the methane production reactor (reaction temperature) is maintained throughout, for example, between 100°C and 600°C, preferably between 250°C and 450°C. Maintaining a reaction temperature within this range allows the methanation reaction described above to continue more stably.

[0057] As a result, carbon oxide and hydrogen react in the gas flow path of the methane production reactor to produce methane gas. Subsequently, the 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 raw material gases (oxygen, hydrogen, and / or carbon oxide).

[0058] The methane yield is the percentage of methane relative to the total sum of methane and unreacted carbon oxide 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 yield is, for example, 100% or less, or for example, 95% or less. When the methane yield is within this range, the energy and / or cost required to separate methane from the methane-containing gas can be reduced. The methane yield is sometimes referred to as the methane conversion rate, which indicates the conversion rate from carbon oxide to methane.

[0059] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement methods for each characteristic are as follows.

[0060] (1) Measurement of Thermal Conductivity of Honeycomb Substrates The honeycomb substrates prepared in the examples and comparative examples were processed to a predetermined size, and the thermal diffusivity was measured by Laser-PIT (optical alternating current method). The specific heat of the honeycomb substrate was measured by differential scanning calorimetry (DSC). Furthermore, the bulk density of the honeycomb substrate was measured by Archimedes density spectroscopy. From the obtained thermal diffusivity, specific heat, and bulk density, the thermal conductivity of the honeycomb substrate was calculated based on the above formula (1). In cases where a catalyst layer was supported on the honeycomb substrate, the thermal conductivity was measured after preparing a sample for measurement in which the catalyst layer had been removed by a solvent or the like.

[0061] (2) Measurement of the Thickness of the Catalyst Layer The methane production reactors manufactured in the examples and comparative examples were embedded in resin, and the cross-section of the methane production reactor cut in a direction perpendicular to the axis of the honeycomb substrate was imaged using a digital microscope (Keyence Corporation, product name "VHX-7100", magnification 100x). Using the analysis software attached to the device, the straight-line distance from the flat interface between the honeycomb substrate and the catalyst layer to the flat interface between the catalyst layer and the resin was measured at 10 or more locations, and the average of these straight-line distances was calculated as the thickness of the catalyst layer. The automatic edge detection function of the analysis software was used as the discrimination method.

[0062] (3) Measurement of Porosity of Catalyst Layer The methane production reactors manufactured in the examples and comparative examples were embedded in resin, and the cross-section of the methane production reactor cut in a direction perpendicular to the axial direction of the honeycomb substrate was imaged using a scanning electron microscope (Hitachi High-Technologies Corporation, product name "S-3400N", magnification: 1000x). The porosity of the catalyst layer was calculated from the obtained scanning electron microscope images using image analysis software (ImageJ). Only the catalyst layer was extracted as the target of analysis, and binarization analysis was performed using brightness as the threshold to obtain a binarized image. The threshold for binarization was set using Otsu's binarization method as the discriminant analysis method. From the obtained binarized image, the region showing the methane reaction catalyst and the region showing the resin were distinguished, and the porosity of the catalyst layer was calculated as the percentage of the area of ​​the resin region to the total area of ​​the region showing the methane reaction catalyst and the region showing the resin.

[0063] <Example 1> <<Preparation of Honeycomb Substrate>> 80 parts by mass of SiC raw material powder and 20 parts by mass of metallic Si powder were extruded into a clay mold, dried, 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 prepared the honeycomb substrate shown in Figure 1. The honeycomb substrate had a cylindrical shape with a diameter of 20 mm and a length of 50 mm. The honeycomb substrate was composed of a Si-SiC composite material. The honeycomb substrate had partition walls defining multiple cells and an outer wall surrounding the partition walls. The cross-sectional shape of the cells was square. The cell density in the honeycomb substrate was 300 cpsi, and the thickness of the partition walls was 0.254 mm. Table 1 shows the thermal conductivity, porosity, and average pore diameter of the honeycomb substrate (partition walls).

[0064] <<Preparation of Methanation Reaction 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 obtained a dispersion of metal oxide particles. Nickel(II) nitrate hexahydrate was dissolved in distilled water to obtain an aqueous nickel nitrate solution. Next, the aqueous nickel nitrate solution was added to the dispersion of metal oxide particles and stirred at room temperature (23°C) for 2 hours. After that, 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 obtained methanation reaction catalyst particles (hereinafter referred to as catalyst particles). After that, the catalyst particles were crushed in a pot mill to adjust the particle size. The average secondary particle diameter of the catalyst particles was 1.636 μm, and the standard deviation of the secondary particle diameter of the catalyst particles was 1.348 μm. The catalyst particles contained nickel oxide (NiO) and cerium oxide (IV) supporting the nickel oxide (NiO). In the catalyst particles, the Ni content was 10 parts by mass per 100 parts by mass of cerium oxide.

[0065] <<Preparation of Catalyst Layer>> The obtained catalyst particles and polymethyl methacrylate (manufactured by Sekisui Chemical Co., Ltd.) as a pore-forming material were dispersed in ethanol to prepare a catalyst slurry. In the catalyst slurry, the content of catalyst particles was 13% by mass, and the content of polymethyl methacrylate was 2% by mass. Next, at room temperature and pressure (23°C, 0.1 MPa), the catalyst slurry was poured into the cells of the honeycomb substrate prepared above. This coated the surface of the partition walls with the catalyst slurry. After that, the catalyst slurry coated on the surface of the partition walls was left to dry in a blown air environment at 25°C for 20 minutes. After repeating the above coating and drying process, it was fired at 300°C for 2 hours in an air atmosphere to form a catalyst layer on the surface of the partition walls. The catalyst layer contained aggregates of catalyst particles. The amount of catalyst particles supported per unit volume of the honeycomb substrate, including the flow channels, was 509 g / L. The porosity and thickness of the catalyst layer are shown in Table 1. Based on the above, a methane production reactor comprising a honeycomb substrate and a catalyst layer was manufactured.

[0066] <Example 2> A methane production reactor was manufactured in the same manner as in Example 1, except that the amount of polymethyl methacrylate added was changed to alter the porosity and thickness of the catalyst layer as shown in Table 1.

[0067] <Example 3> A methane production reactor was manufactured in the same manner as in Example 1, except that the amount of polymethyl methacrylate added was changed to alter the porosity and thickness of the catalyst layer as shown in Table 1.

[0068] <Example 4> A methane production reactor was manufactured in the same manner as in Example 1, except that the honeycomb substrate made of Si-SiC composite material was changed to a honeycomb substrate prepared as described below, and the amount of polymethyl methacrylate added was changed to change the porosity and thickness of the catalyst layer as shown in Table 1. A clay containing SiC powder was extruded and then dried to prepare a honeycomb dry body. The honeycomb dry body had the same size and structure as the honeycomb substrate in Example 1. In addition, a material powder containing Si powder was press-molded and then dried to obtain a Si feed body. Next, with the Si feed body in contact with the honeycomb dry body, it was heated at 1500°C for 4 hours under reduced pressure conditions (200 Pa) to impregnate the honeycomb dry body with molten metal containing Si. The amount of molten Si metal was 17 parts by mass per 100 parts by mass of the honeycomb dry body. In this way, a honeycomb substrate made of Si-SiC composite material was prepared.

[0069] <Example 5> A methane production reactor was manufactured in the same manner as in Example 4, except that the amount of polymethyl methacrylate added was changed to alter the porosity and thickness of the catalyst layer as shown in Table 1.

[0070] <Example 6> A methane production reactor was manufactured in the same manner as in Example 4, except that the amount of polymethyl methacrylate added was changed to alter the porosity and thickness of the catalyst layer as shown in Table 1.

[0071] <Example 7> A methane production reactor was manufactured in the same manner as in Example 4, except that the amount of molten Si metal was changed to 25 parts by mass per 100 parts by mass of honeycomb dry body, and the amount of polymethyl methacrylate added was changed to alter the porosity and thickness of the catalyst layer as shown in Table 1. The honeycomb substrate partitions in the methane production reactor of Example 7 did not have pores.

[0072] <Example 8> A methane production reactor was manufactured in the same manner as in Example 7, except that the amount of polymethyl methacrylate added was changed to alter the porosity and thickness of the catalyst layer as shown in Table 1.

[0073] <Example 9> A methane production reactor was manufactured in the same manner as in Example 7, except that the amount of polymethyl methacrylate added was changed to alter the porosity and thickness of the catalyst layer as shown in Table 1.

[0074] <Comparative Example 1> A methane production reactor was manufactured in the same manner as in Example 1, except that the clay containing SiC raw material powder and metallic Si powder was changed to clay containing cordierite raw material, and the amount of polymethyl methacrylate added was changed to alter the porosity and thickness of the catalyst layer as shown in Table 1.

[0075] <Comparative Example 2> A methane production reactor was manufactured in the same manner as in Comparative Example 1, except that the amount of polymethyl methacrylate added was changed to alter the porosity and thickness of the catalyst layer as shown in Table 1.

[0076] <Comparative Example 3> A methane production reactor was manufactured in the same manner as in Comparative Example 1, except that the amount of polymethyl methacrylate added was changed to alter the porosity and thickness of the catalyst layer as shown in Table 1.

[0077] <Methanation Test> The methane production reactors obtained in the examples and comparative examples were inserted into a reaction tube with an inner diameter of 21 mm. As a catalyst pretreatment, hydrogen gas was introduced into the reaction tube, and the methane production reactor was heated at 500°C for 1 hour in an electric furnace installed on the outer circumference of the reaction tube to reduce the methanation reaction catalyst. Next, nitrogen gas was flowed into the reaction tube to lower the temperature of the electric furnace to 300°C, and then the raw material gas under test condition A or B was introduced into the reaction tube. The raw material gas under test condition A contained 10 mol% carbon dioxide, 3 mol% oxygen, 46 mol% hydrogen, and the remainder nitrogen (CO ２ / H ２ / N ２ / O ２ = 10 / 46 / 41 / 3 [mol ratio]). The raw material gas under test condition B contained 20 mol% carbon dioxide and 80 mol% hydrogen (CO ２ / H ２= 20 / 80 [mol ratio]). In other words, the raw material gas under test condition A contains oxygen, and the raw material gas under test condition B does not contain oxygen. The gas flow rate of the raw material gas is 0.08 L / min, and the space velocity SV of the raw material gas is 500 h. －１ This was set to supply the raw material gas to the gas flow path of the methane production reactor, and methane-containing gas flowed out of the reaction tube. The methane-containing gas flowing out of the reaction tube was passed through a cooling trap to produce H ２ O was removed. Subsequently, the gas composition of the methane-containing gas was analyzed using a gas chromatograph-thermal conductivity detector (GC-TCD). Based on the measurement results, the methane yield (conversion rate from carbon oxide to methane) (%) was calculated using the following formula (A): Methane yield (%) = (Amount of methane contained in the methane-containing gas (volume %) / Sum of the amount of methane and carbon oxide contained in the methane-containing gas (volume %)) × 100 ... (A) In the case of test condition A, the methane yield in Comparative Example 1 was set to 1, and in the case of test condition B, the methane conversion rate in Comparative Example 3 was set to 1. The methane conversion rates of the other examples and comparative examples were normalized to obtain the methane yield. The results are shown in Table 1.

[0078]

[0079] <Evaluation> As shown in Table 1, it can be seen that the methane yield (amount) can be significantly improved when the thermal conductivity of the ceramic substrate is 8 W / m·K or higher and the thickness of the catalyst layer is 600 μm or less.

[0080] The methane production reactor according to the embodiment of the present invention can be used for methane production, and is particularly suitable for continuous methane production using exhaust gases discharged from various industrial products or industrial facilities as raw materials.

[0081] 1 Ceramic substrate 1a Honeycomb substrate 13 Partition wall 14 Cell 15 Gas flow path 2 Catalyst layer 100 Methane production reactor

Claims

1. A methane production reactor having a gas channel to which a raw material gas containing carbon oxide and hydrogen is supplied, comprising: a ceramic substrate; and a catalyst layer disposed on the surface of the ceramic substrate so as to face the gas channel, wherein the catalyst layer contains a methanation reaction catalyst capable of promoting the reaction that produces methane, the thermal conductivity of the ceramic substrate is 8 W / m·K or more, and the thickness of the catalyst layer is 600 μm or less.

2. The methane production reactor according to claim 1, wherein the thickness of the catalyst layer is 5 μm or more.

3. The methane production reactor according to claim 1, wherein the thickness of the catalyst layer is 300 μm or more.

4. The methane production reactor according to any one of claims 1 to 3, wherein the porosity of the catalyst layer is 0.01% or more and less than 20%.

5. The methane production reactor according to any one of claims 1 to 3, wherein the porosity of the catalyst layer is 15% or less.

6. The methane production reactor according to any one of claims 1 to 3, wherein the thermal conductivity of the ceramic substrate is 100 W / m·K or more.

7. The methane production reactor according to any one of claims 1 to 3, wherein the porosity of the ceramic substrate is 65% or less, and the average pore diameter of the ceramic substrate is 50 μm or less.

8. The methane production reactor according to any one of claims 1 to 3, wherein the ceramic substrate is a honeycomb substrate having partitions that constitute a plurality of cells, and at least a portion of the plurality of cells includes the gas flow path.

9. The methane production reactor according to any one of claims 1 to 3, wherein the raw material gas comprises carbon dioxide and hydrogen.

10. The methane production reactor according to any one of claims 1 to 3, wherein the raw material gas further contains oxygen.

11. The methane production reactor according to any one of claims 1 to 3, wherein the ceramic substrate comprises Si and SiC.

12. The methane production reactor according to any one of claims 1 to 3, wherein the methanation reaction catalyst contains a transition metal as an active ingredient.

13. The methane production reactor according to claim 12, wherein the transition metal includes Co, Fe, Pt, Ru, Rh, Pd, Ni, Cu, Ag, Au, Ir, or a combination thereof.

14. The methane production reactor according to claim 12, wherein the methanation catalyst further comprises a carrier supporting the transition metal, the carrier comprising cerium oxide, silicon oxide, zirconium oxide, yttrium oxide, aluminum oxide, or a composite oxide thereof.

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