Method for producing methane-containing gas, and reaction device

Abstract

This method for producing a methane-containing gas comprises: preparing a reaction device which includes a reactor and a plurality of reaction units each having a catalytic body and provided in the reactor and in which a gas flow path through which a gas flows sequentially through the plurality of reaction units is formed; and generating methane in the reactor while supplying a raw material gas containing methane, carbon dioxide, and hydrogen to the reaction device, thereby generating a generated gas containing methane in a concentration higher than the concentration of the methane in the raw material gas. The catalytic body has a catalyst layer containing a catalyst for a methanation reaction, and the temperature of the catalyst layer is maintained at 430ºC or lower while the raw material gas is supplied to the reaction device. The reaction device further includes a water trap unit which is for trapping moisture and which is provided between two adjacent reaction units in the gas flow path. The catalytic body has a plate-like spiral part, and the spiral part includes a plate-like substrate and the catalyst layer provided on the substrate.

Description

Method for producing methane-containing gas, and reactor

[0001] This disclosure relates to a method for producing a gas containing methane, and to a reaction apparatus.

[0002] As a CCU (Carbon Capture and Utilization) technology, the acquisition of methane from carbon dioxide recovered from industrial exhaust gases emitted from power plants or various industrial factories via the following methanation reaction is being considered. The methanation reaction is an exothermic reaction that generates a relatively large amount of heat (165 kJ / mol) and is strongly constrained by chemical equilibrium. ２ +4H ２ →CH ４ +2H ２ O (Methanation reaction)

[0003] The conversion of carbon dioxide contained in biogas generated in methane fermentation tanks into methane is also being considered (Patent Documents 1 and 2, Non-Patent Document 1).

[0004] Japanese Patent Publication No. 7392854, Japanese Unexamined Patent Publication No. 2016-108382

[0005] Journal of the Japan Society of Waste Management and Resource Recycling, Vol. 33, No. 1, pp. 25-34, 2022 Ryo Watanabe, Shota Ueda, Hiroshi Akama, Kazuhide Mino, Choji Fukuhara, Sustainable Energy & Fuels, 2025, 9(18), 4974-4988 Akama, Nakazawa, Kinoshita, Watanabe, Fukuhara, "High-speed and high-efficiency conversion of CO2 brought about by the physicochemical properties of spiral-shaped structural catalysts", 133rd Symposium on Catalysis of the Catalysis Society of Japan, 2B06 Akama, Ueda, Mino, Watanabe, Fukuhara, "High-speed methanation of CO2 by spiral-shaped structural catalysts: Comparison with honeycomb-shaped and packed-type catalysts", 67th Annual Meeting of the Japan Petroleum Institute (73rd Research Presentation Meeting), A09 Akama, Ueda, Mino, Hiwaki, Watanabe, Fukuhara, "Swirl "High-speed CO2 treatment characteristics brought about by the flow effect," The 55th Symposium on Petroleum and Petrochemicals of the Japan Petroleum Institute, 1G03

[0006] Biogas typically contains relatively high concentrations of methane along with carbon dioxide. The presence of high concentrations of methane restricts the methanation reaction of carbon dioxide due to chemical equilibrium constraints, making it difficult to efficiently convert carbon dioxide to methane. Figures 12 and 13 show the difference between a raw material gas containing methane and a raw material gas without methane, and the CO2 emissions. ２ This graph shows an example of the relationship between conversion rate and reaction temperature in chemical equilibrium, obtained through simulation. Figure 12 shows the simulation results for the first reactor (1st reactor) with a methane-containing raw material gas having a composition of carbon dioxide / methane / hydrogen (molar ratio) = 6 / 4 / 16, and with a methane-free raw material gas having a composition of carbon dioxide / hydrogen (molar ratio) = 4 / 16. Figure 13 shows the simulation results when the gas from which water has been removed after passing through the first reactor (1st reactor) is supplied to the second reactor (2nd reactor). In both cases, if a high concentration of methane is present in the raw material gas, CO ２ A significant decrease in the conversion rate was observed.

[0007] This disclosure relates to generating methane from carbon dioxide with high efficiency, even when high concentrations of methane coexist with carbon dioxide.

[0008] This disclosure includes: [1] preparing a reactor comprising a reactor and a plurality of reaction sections having catalysts provided in the reactor, wherein a gas flow path is formed through which gas flows sequentially through the plurality of reaction sections; and supplying a raw material gas containing methane, carbon dioxide and hydrogen to the reactor, thereby generating methane in the reactor, and thereby generating a product gas containing methane at a concentration higher than the concentration of methane in the raw material gas, wherein the catalyst has a catalyst layer containing a methanation reaction catalyst, the temperature of the catalyst layer is maintained at 430°C or lower while the raw material gas is supplied to the reactor, the reactor further comprises a water trap section for trapping moisture, provided between two adjacent reaction sections in the gas flow path, the catalyst has a plate-shaped spiral section extending along a certain axis while twisting in a direction rotating around that axis, and the spiral section comprises a plate-shaped substrate and the catalyst layer provided on the substrate. [2] The method according to [1], wherein the ratio of methane to the total amount of carbon dioxide and methane in the raw material gas is 40% by volume or more. [3] The method according to [1] or [2], wherein the pitch, which is the length in the direction of the axis of the portion of the spiral portion that makes one rotation around the axis of the spiral portion, is P, the maximum width of the spiral portion in a direction perpendicular to the axis of the spiral portion is W, and the twist ratio P / W is 1.5 or more and 5.0 or less. [4] The method according to any one of [1] to [3], wherein the length of the spiral portion in the direction of the axis of the spiral portion is L, the maximum width of the spiral portion in a direction perpendicular to the axis of the spiral portion is W, and the aspect ratio L / W is 10 or more and 100 or less. [5] The method according to any one of [1] to [4], wherein the gas pressure in the reactor in the plurality of reaction sections exceeds atmospheric pressure while the raw material gas is supplied to the reactor.[6] The method according to any one of [1] to [5], wherein the methanation reaction catalyst comprises one or more metal oxides selected from the group consisting of aluminum oxide, cerium oxide, zirconium oxide, and titanium oxide, and one or more metal elements selected from the group consisting of Fe, Co, Ru, Mg, Ni, Mn, Mo, K, Na, Li, Ca, Sr, Ba, La, Pt, Pd, Rh, Nd, Cu, and Zn. [7] A reaction apparatus comprising a reactor, a plurality of reaction sections having a catalyst provided in the reactor, and a water trap section for trapping moisture, wherein a gas flow path is formed through which gas flows sequentially through the plurality of reaction sections, the water trap section is provided in the gas flow path between two adjacent reaction sections, the catalyst has a catalyst layer containing a catalyst for a methanation reaction, the catalyst has a plate-shaped spiral section extending along a certain axis while twisting in a direction that rotates around that axis, and the spiral section comprises a plate-shaped substrate and the catalyst layer provided on the substrate. [8] The reaction apparatus according to [7], wherein the pitch is the length in the direction of the axis of the portion of the spiral section that makes one rotation around the axis, the maximum width of the spiral section in a direction perpendicular to the axis is W, and the twist ratio P / W is 1.5 or more and 5.0 or less. [9] The reaction apparatus according to [7] or [8], wherein the length of the spiral portion in the direction of the axis is L, the maximum width of the spiral portion in the direction perpendicular to the axis is W, and the aspect ratio L / W is 10 or more and 100 or less.

[10] The reaction apparatus according to any one of [7] to [9], further comprising a pressure control unit for controlling the pressure of the gas in the reactor in a plurality of reaction sections to exceed atmospheric pressure.

[11] The reaction apparatus according to any one of [7] to

[10] , wherein the methanation reaction catalyst comprises one or more metal oxides selected from the group consisting of aluminum oxide, cerium oxide, zirconium oxide, and titanium oxide, and one or more metal elements selected from the group consisting of Fe, Co, Ru, Mg, Ni, Mn, Mo, K, Na, Li, Ca, Sr, Ba, La, Pt, Pd, Rh, Nd, Cu, and Zn.

[0009] Even when high-concentration methane coexists with carbon dioxide, methane can be produced from carbon dioxide with high efficiency.

[0010] FIG. 1 is a schematic diagram showing an example of a reaction apparatus. FIG. 2 is a schematic diagram showing an example of a spiral portion of a catalyst body. FIG. 3 is an end view taken along line III-III in FIG. 2. FIG. 4 shows CO ２ is a graph showing the relationship between conversion rate and catalyst layer temperature. FIG. 5 shows CO ２ is a graph showing the relationship between conversion rate and catalyst layer temperature. FIG. 6 shows CO ２ is a graph showing the relationship between conversion rate and catalyst layer temperature. FIG. 7 shows CO ２ is a graph showing the relationship between conversion rate and catalyst layer temperature. FIG. 8 shows CO ２ is a graph showing the relationship between conversion rate and catalyst layer temperature. FIG. 9 shows CO ２ is a graph showing the relationship between selectivity and catalyst layer temperature. FIG. 10 shows CO ２ is a graph showing the relationship between conversion rate and catalyst layer temperature. FIG. 11 shows CO ２ is a graph showing the relationship between conversion rate and catalyst layer temperature. FIG. 12 shows CO ２ is a graph showing an example of simulation-obtained results of the relationship between conversion rate and reaction temperature in chemical equilibrium. FIG. 13 shows CO ２ is a graph showing an example of simulation-obtained results of the relationship between conversion rate and reaction temperature in chemical equilibrium.

[0011] The present invention is not limited to the following examples.

[0012] FIG. 1 is a schematic diagram showing an example of a reaction apparatus for methanation of carbon dioxide. A reaction apparatus 100 shown in FIG. 1 is mainly composed of a gas supply unit 50, a first-stage reaction unit 10, a water trap unit 31, a second-stage reaction unit 20, a water trap unit 32, a pressure control unit 70, and piping connecting these components. A gas flow path along the arrows, including the piping, is formed such that gas sequentially flows in the order of the gas supply unit 50, the reaction unit 10, the water trap unit 31, the reaction unit 20, the water trap unit 32, and the pressure control unit 70. A reactor 11 and a reactor 21 are connected in series in this order from the upstream side along the gas flow path.

[0013] The gas supply unit 50 includes a supply source for hydrogen gas, carbon dioxide gas, methane gas, and nitrogen gas, and a gas mixing unit 52 capable of mixing these gases. From the gas mixing unit 52, raw material gas G containing methane, carbon dioxide, and hydrogen is supplied. ０ This is supplied to the first stage reaction section 10. Instead of separate sources for hydrogen gas, carbon dioxide gas, methane gas, and nitrogen gas, a source of mixed gas containing two or more gases selected from these gases may be provided. For example, a source of biogas containing methane and carbon dioxide may be provided.

[0014] The first stage reaction section 10 includes a reactor 11, a catalyst 1 provided inside the reactor 11, and a heater 13 provided around the reactor 11. The catalyst 1 has a catalyst layer containing a methanation reaction catalyst. The reactor 11 and the gas supply section 50 (gas mixing section 52) are connected via piping. A pressure gauge 61 may be provided in the gas flow path between the reactor 11 and the gas supply section 50. The second stage reaction section 20 includes a reactor 21, a catalyst 1 provided inside the reactor 21, and a heater 23 provided around the reactor 21. A pressure gauge 62 may be provided between the water trap section 31 and the reactor 21. The reactors 11 and 21 may be reaction tubes (for example, quartz glass tubes).

[0015] The water trap section 31 is a device for trapping moisture and is provided in the gas flow path between adjacent reaction sections 10 and 20. The water trap section 32 is provided in the gas flow path downstream of the second reaction section 20. A pressure gauge 63 may be provided downstream of the water trap section 32. The water trap sections 31 and 32 may be cooling traps that condense water vapor by cooling using a cooling gas or cooling liquid, for example. The water trap sections 31 and 32 may be traps containing a porous material such as zeolite that can selectively adsorb and remove moisture.

[0016] The heaters 13 and 23 are not limited as long as they can heat the catalyst 1 in the reactors 11 and 21. For example, linear or sheet-shaped heaters may be wrapped around the reactors 11 and 21. The heaters 13 and 23 may also be electric furnaces.

[0017] In the example shown in Figure 1, a three-way valve 81 is provided between the water trap section 31 and the reaction section 20, and a three-way valve 82 is provided downstream of the water trap section 32. By connecting the three-way valve 81 and the three-way valve 82 via piping, a gas flow path that does not pass through the reaction section 20 is also formed. Additional conventional equipment such as valves and pressure gauges may be provided on the piping that constitutes the gas flow path of the reaction apparatus 100, as needed.

[0018] One example of a method for producing a gas containing methane using the reactor 100 shown in Figure 1 is to supply a raw material gas G containing methane, carbon dioxide, and hydrogen to the upstream reaction section 10 of the reactor 100. ０ While supplying the raw material gas G, methane is produced in reactors 11 and 21, thereby generating the raw material gas G ０ Product gas G containing methane at a higher concentration than the methane concentration in [location]. １ This includes generating [something].

[0019] In this method, the raw material gas G ０ A portion of the carbon dioxide contained in the first stage reactor 11 is converted to methane. The gas discharged from the outlet of reactor 11 is supplied to the second stage reactor 21 via a gas flow path including a water trap section 31 connected to reactor 11 by piping. The remaining carbon dioxide is converted to methane in reactor 21. Water is removed from the gas discharged from the second stage reactor 21 by a water trap section 32 connected to reactor 21 by piping. From the downstream side of the water trap section 32, a product gas G containing a high concentration of methane is released. １ Gas G is emitted. １ It is discharged to the outside of the reactor through the pressure control unit 70.

[0020] The combination of multiple reaction units arranged in series from the upstream side along the gas flow path, and a water trap unit installed between two adjacent reaction units, allows for highly efficient methane production from carbon dioxide, even when high concentrations of methane coexist with carbon dioxide in the raw gas. The gas discharged from one reaction unit contains methane and water produced by the methanation reaction. By removing the water in the water trap unit before this gas is introduced into the downstream reaction unit, the methanation reaction can proceed with high efficiency in the downstream reaction unit as well. As a result, the entire reaction apparatus can produce methane from carbon dioxide with high efficiency.

[0021] The raw material gas G is supplied to the first stage reaction section 10 (reactor 11) of the reactor 100. ０ This includes methane, carbon dioxide, and hydrogen. According to the method relating to this disclosure, raw material gas G ０ Even when the methane concentration in the raw material gas G is high, the methanation reaction can proceed with high efficiency. ０ In this case, the ratio of methane to the total amount of carbon dioxide and methane may be 40% by volume or more, 45% by volume or more, 50% by volume or more, 55% by volume or more, 60% by volume or more, or 65% by volume or more, and may be 80% by volume or less. Raw material gas G ０ However, it may also contain biogas produced by the fermentation of biomass.

[0022] The generated gas G is discharged from the downstream reactor 21 or the water trap section 32 downstream of it. １ This can be a gas containing methane at a high concentration. For example, the generated gas G １ The concentration of methane in the generated gas G １ The volume may be 90% or more based on the volume of [the substance]. Gas containing methane at a high concentration of 90% or more by volume can be used, for example, as fuel for gas engines.

[0023] The reactor 100 in Figure 1 has two reaction stages, but a reactor may have more reaction stages. The number of reactors constituting a single reactor may be 2 to 5, 2 to 4, or 2 to 3. In reactors located downstream of a large number of reactors, a gas containing methane at a higher concentration is introduced, which tends to reduce the efficiency of the methanation reaction.

[0024] Raw material gas G enters the reaction apparatus 100. ０ While the supply is being provided, the temperature of the catalyst layer of catalyst 1 may be maintained at 430°C or below. Maintaining the temperature of the catalyst layer at 430°C or below suppresses the generation of by-products such as carbon monoxide, thereby reducing the high CO2 levels from the methanation reaction. ２ The conversion rate is easily maintained. The catalyst 1 may be heated by heaters 13 and 23 so that the temperature of the catalyst layer is maintained at 430°C or below. ２ From the perspective of further improving the conversion rate, raw material gas G is added to the reactor 100. ０ While the raw material gas G is supplied, the temperature of the catalyst layer of catalyst 1 may be maintained at 420°C or lower, 410°C or lower, 400°C or lower, 390°C or lower, 380°C or lower, 370°C or lower, 360°C or lower, 350°C or lower, or 340°C or lower. The catalyst 1 may be heated by heaters 13, 23 so that the temperature of the catalyst layer is maintained at 430°C or lower, or at any other predetermined temperature or lower. Raw material gas G is supplied to the reaction apparatus 100. ０ While the raw material gas G is supplied, the temperature of the catalyst layer may be maintained at 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, 240°C or higher, 250°C or higher, 260°C or higher, 270°C or higher, or 280°C or higher, and the catalyst 1 may be heated for this purpose. Raw material gas G is supplied to the reaction apparatus 100. ０ While the raw material gas G is supplied, the temperature of the catalyst layer may be maintained at 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, 240°C or higher, 250°C or higher, 260°C or higher, 270°C or higher, or 280°C or higher, and 420°C or lower. ０While the supply of raw material gas G may be maintained at 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, 240°C or higher, 250°C or higher, 260°C or higher, 270°C or higher, or 280°C or higher, and 410°C or lower. ０ While the raw material gas G is supplied, the temperature of the catalyst layer may be maintained at 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, 240°C or higher, 250°C or higher, 260°C or higher, 270°C or higher, or 280°C or higher, and 400°C or lower. ０ While the raw material gas G is supplied, the temperature of the catalyst layer may be maintained at 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, 240°C or higher, 250°C or higher, 260°C or higher, 270°C or higher, or 280°C or higher, and 390°C or lower. ０ While the raw material gas G is supplied, the temperature of the catalyst layer may be maintained at 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, 240°C or higher, 250°C or higher, 260°C or higher, 270°C or higher, or 280°C or higher, and 380°C or lower. ０ While the raw material gas G is supplied, the temperature of the catalyst layer may be maintained at 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, 240°C or higher, 250°C or higher, 260°C or higher, 270°C or higher, or 280°C or higher, and 370°C or lower. ０ While the raw material gas G is supplied, the temperature of the catalyst layer may be maintained at 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, 240°C or higher, 250°C or higher, 260°C or higher, 270°C or higher, or 280°C or higher, and 360°C or lower. Raw material gas G is supplied to the reaction apparatus 100. ０ While the raw material gas G is supplied, the temperature of the catalyst layer may be maintained at 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, 240°C or higher, 250°C or higher, 260°C or higher, 270°C or higher, or 280°C or higher, and 350°C or lower. ０While the supply is being carried out, the temperature of the catalyst layer may be maintained at 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 230°C or higher, 240°C or higher, 250°C or higher, 260°C or higher, 270°C or higher, or 280°C or higher, and 340°C or lower. Reaction rate, equilibrium constraints and CH ４ From the viewpoint of selectivity, the temperature of the catalyst layer may be maintained in the range of 280°C to 350°C.

[0025] The temperature of the catalyst layer here, in the case of the spiral-type structural catalyst described later, can be the temperature of the central part of the catalyst layer (or catalyst body 1) in the direction of the gas flow path (or along the gas flow path). The central part of the catalyst layer (or catalyst body 1) in the direction of the gas flow path may be, for example, a position within 10 mm in the direction of the gas flow path from the center of the catalyst layer (or catalyst body 1) in the direction of the gas flow path.

[0026] When heating the catalyst 1, the set temperatures of the heaters 13 and 23 are adjusted so that the temperature of the catalyst layer is within a predetermined range. For example, if the heaters 13 and 23 are electric furnaces, setting the temperature in the range of 200°C to 350°C makes it easier to maintain the temperature of the catalyst layer within an appropriate range. To avoid excessive temperature rise, means other than heating by the heaters 13 and 23 may be used. For example, tubes for heat exchange may be provided around the reactors 11 and 21. After starting the methanation reaction while heating the catalyst 1 with the heaters 13 and 23, heating may be stopped when the temperature of the catalyst layer exceeds a certain value. Insulation material may be provided outside the heaters 13 and 23 to improve thermal efficiency.

[0027] Raw material gas G enters the reaction apparatus 100. ０While the gas is being supplied, the gas pressure in reactors 11 and 21 may exceed atmospheric pressure. In other words, the gas pressure in reactors 11 and 21 may exceed 0.10 MPa. Under high-pressure conditions, the methanation reaction can proceed more efficiently. The gas pressure in reactors 11 and 21 may be 0.20 MPa or higher, 0.30 MPa or higher, 0.40 MPa or higher, 0.50 MPa or higher, 0.60 MPa or higher, 0.70 MPa or higher, 0.80 MPa or higher, or 0.9 MPa or higher. To promote the reaction while avoiding excessive energy consumption, the gas pressure in reactors 11 and 21 may be 2.0 MPa or lower. The gas pressure in reactors 11 and 21 may be 0.20 MPa or higher, 0.30 MPa or higher, 0.40 MPa or higher, 0.50 MPa or higher, 0.60 MPa or higher, 0.70 MPa or higher, 0.80 MPa or higher, or 0.9 MPa or higher, and may also be 2.0 MPa. The gas pressure in reactors 11 and 21 can be adjusted by the pressure control unit 70. The pressure control unit 70 may be, for example, a back pressure valve. The back pressure valve supplies the raw material gas G to the first stage reactor 11. ０ By releasing the pressure when the supply pressure exceeds a predetermined set pressure, the gas pressure in the gas flow path within reactors 11 and 21 can be kept constant. A pressure control unit is not required.

[0028] Figure 2 is a schematic diagram showing an example of a catalyst, and Figure 3 is a line end view of Figure 2, taken along line III-III. The catalyst 1 shown in Figures 2 and 3 has a plate-shaped spiral portion 1A that extends along a certain axis X while twisting in a direction that rotates around the axis X. The spiral portion 1A includes a plate-shaped base material 15 and a catalyst layer 16 provided on the outer surface of the base material 15. In the example of Figures 2 and 3, the entire catalyst 1 is the spiral portion 1A. Hereinafter, a catalyst having a spiral portion 1A may be referred to as a "spiral-type structural catalyst." The spiral-type structural catalyst exhibits a reaction-promoting effect through mass diffusion due to mass transfer and thermal diffusion due to heat transfer brought about by swirling flow. Thermal diffusion efficiently disperses the reaction heat of the methanation reaction, thereby suppressing localized temperature rise of the catalyst layer 16. Therefore, the temperature of the catalyst layer can be easily maintained at a low temperature (for example, below 430°C), which can contribute to further efficiency of the methanation reaction. The apparent contact area per unit volume between the spiral-type structural catalyst and the gas is smaller than that of general honeycomb catalysts and granular catalysts, for example, about 1 / 5 to 1 / 10. Nevertheless, spiral-type structural catalysts can carry out reactions with high efficiency. This is thought to be because the effective utilization rate of the catalyst is effectively increased by the mass transfer and heat transfer promoting effects unique to the spiral shape. This promoting effect is sometimes called the swirl-flow effect (e.g., Non-Patent Documents 2-5). For example, the extremely low pressure loss of the spiral-type structural catalyst may contribute to the efficient heat diffusion due to the swirl-flow effect. Efficient heat diffusion suppresses heat accumulation in the catalyst layer 16. In addition, regarding mass transfer in spiral-type structural catalysts, it has been found that swirl flow and vortex flow are strengthened as the gas flow rate increases, and the gas boundary film on the catalyst layer surface is thinned. When the gas boundary film is thinned, mass diffusion to the catalyst layer surface is promoted. By combining the thinning of the gas boundary film with the material stirring effect in the gas phase caused by fluctuations in gas streamlines, the supply of reaction molecules to the catalyst surface can be significantly promoted.

[0029] In a spiral-type structural catalyst, the pitch is the length in the direction of axis X of the portion that rotates once around axis X of the spiral portion 1A, and the maximum width of the spiral portion 1A in the direction perpendicular to axis X is W. The twist ratio P / W may be 1.5 or more and 5.0 or less. If the twist ratio is within this range, high CO ２ The conversion rate is more easily achieved. From a similar viewpoint, the twist ratio P / W may be 1.6 or higher, 1.7 or higher, 1.8 or higher, 1.9 or higher, or 2.0 or higher, and may be 4.5 or lower, 4.0 or lower, 3.5 or lower, 3.2 or lower, or 3.0 or lower. The twist ratio P / W may be 1.6 or higher, 1.7 or higher, 1.8 or higher, 1.9 or higher, or 2.0 or higher, and 4.5 or lower. The twist ratio P / W may be 1.6 or higher, 1.7 or higher, 1.8 or higher, 1.9 or higher, or 2.0 or higher, and 4.0 or lower. The twist ratio P / W may be 1.6 or higher, 1.7 or higher, 1.8 or higher, 1.9 or higher, or 2.0 or higher, and 3.5 or lower. The twist ratio P / W may be 1.6 or higher, 1.7 or higher, 1.8 or higher, 1.9 or higher, or 2.0 or higher, and 3.2 or lower. The twist ratio P / W may be 1.6 or higher, 1.7 or higher, 1.8 or higher, 1.9 or higher, or 2.0 or higher, and 3.0 or lower. When the spiral section 1A is twisted so as to rotate two or more times around the axis X, the twist ratio P / W for each rotation may be substantially constant or may change. When the twist ratio P / W for each rotation changes, the average value of the twist ratio P / W for the entire spiral section 1A may be within the above range.

[0030] In the example of a spiral-type structural catalyst, the length of the spiral portion is L. For example, the aspect ratio L / W may be 10 or more and 100 or less. A larger aspect ratio L / W results in high CO2 emissions. ２ The conversion rate is more easily achieved. The aspect ratio L / W may be 12 or greater, and may be 80 or less, 50 or less, or 40 or less. The aspect ratio L / W may be 10 or greater, and may be 80 or less, 50 or less, or 40 or less. The aspect ratio L / W may be 12 or greater, and may be 100 or less, 80 or less, 50 or less, or 40 or less.

[0031] The ratio of the thickness T to the width W of the spiral section 1A (T / W) may be 0.32 or less, from the viewpoint of efficiently forming a swirling flow. The width W of the spiral section 1A may be, for example, 7 mm or more and 50 mm or less. The thickness T of the spiral section 1A may be, for example, 1 mm or more and 3 mm or less.

[0032] One or more spiral-shaped catalyst structures can be inserted into a single reactor. Multiple spiral-shaped catalyst structures may be arranged in series along the longitudinal direction of the reactor. The number of spiral-shaped catalyst structures provided in a single reactor can be arbitrarily determined considering the aspect ratio L / W, etc.

[0033] The catalyst layer of catalyst 1 contains a methanation catalyst. The methanation catalyst can be arbitrarily selected from ordinary catalysts that promote the methanation reaction of carbon dioxide. For example, the methanation catalyst may be aluminum oxide (Al ２ O ３ ), cerium oxide (CeO ２ ), zirconium oxide (ZrO ２ ), and titanium dioxide (TiO ２ The catalyst may contain one or more metal oxides selected from the group consisting of ) and one or more metal elements as catalytic metals selected from the group consisting of Fe, Co, Ru, Mg, Ni, Mn, Mo, K, Na, Li, Ca, Sr, Ba, La, Pt, Pd, Rh, Nd, Cu, and Zn. These catalytic metals may be supported on a carrier containing the above metal oxides. The methanation catalyst may be a combination of Ni and aluminum oxide, cerium oxide, zirconium oxide, or two or more metal oxides selected from these, or a combination of Ru and cerium oxide or zirconium oxide. These may be further combined with La, Ca, Na, Fe, Co, or Mn.

[0034] The content of the catalyst metal in the catalyst layer may be, for example, 1% by mass or more and 20% by mass or less, based on the mass of the catalyst layer. If the catalyst metal is a noble metal such as Pt, Rh, and Pd, the content of the catalyst metal may be 1% by mass or more and 3% by mass or less, based on the mass of the catalyst layer, from the viewpoint of balancing economy and catalytic activity. If the catalyst metal is another metallic element such as Ni and Fe, the content of the catalyst metal may be 10% by mass or more and 20% by mass or less, based on the mass of the catalyst layer.

[0035] The catalyst layer can be formed by any method available to those skilled in the art. The methanation catalyst for forming the catalyst layer can be prepared, for example, by an impregnation method that includes adding a powder of a metal oxide (aluminum oxide, cerium oxide, etc.) to an aqueous solution of a salt of the catalyst metal (nitrate, carbonate, etc.) to form a dispersion, removing water from the dispersion to obtain a catalyst precursor powder, and calcining the catalyst precursor powder to form particulate methanation catalyst. Alternatively, a method can be used that includes adding a base (ammonia, sodium bicarbonate, urea, etc.) to a mixed aqueous solution containing a support-forming metal salt selected from aluminum, cerium, zirconium, and titanium, and a salt of the catalyst metal, to form a precipitate containing the support-forming metal and the catalyst metal, and then drying and calcining the precipitate to form the methanation catalyst.

[0036] A catalyst layer may be formed on the substrate by applying a slurry containing particulate methanation catalyst to the substrate. The dispersion medium of the slurry may be, for example, water or alcohol. The surface of the substrate may be pre-roughened using an aqueous sodium hydroxide solution or an aqueous hydrochloric acid solution, etc.

[0037] The catalyst layer may cover the entire outer surface of the substrate. The thickness of the catalyst layer provided on the substrate may be, for example, 5 μm to 2000 μm, or 10 μm to 2000 μm. The mass of the catalyst layer per apparent surface area of ​​the substrate is 100 g / m². ２ 380g / m or more ２The following may also apply: In the case of spiral-type structural catalysts, an appropriate amount of catalyst layer is particularly conducive to forming an effective swirling flow.

[0038] The substrate may be a metal molded body. Because metal molded bodies have excellent heat transfer properties, they can contribute to suppressing the accumulation of reaction heat in the catalyst layer. The substrate may be a metal molded body containing aluminum, nickel, or stainless steel. Examples of metal molded bodies include metal plates, foam-like metal molded bodies having three-dimensional micropores, metal mesh structures, and perforated metal plates having micropores.

[0039] [Examples] The present invention is not limited to the following embodiments.

[0040] [Preparation of Catalyst] (1) Spiral-type aluminum structure (base material) A spiral-type aluminum structure was formed by twisting a strip-shaped aluminum plate (width 10 mm, length 210 mm, thickness 1.2 mm) three and a half times around its longitudinal central axis. The twist ratio P / W of the aluminum structure was 2.2. The aluminum structure was immersed in a 3.5 mass% sodium hydroxide aqueous solution for 1 hour, and then immersed in a 10 mass% hydrochloric acid solution for 30 minutes. After immersion, the aluminum structure was thoroughly washed with distilled water to obtain an activated aluminum structure. After removing excess moisture, the aluminum structure was dried in the air by heating at 80°C.

[0041] (2) Spiral-type structural catalyst Catalyst #1 (Ru / CeO ２ ) Ruthenium nitrate (Ru(NO) ３ ) ３ A ruthenium nitrate aqueous solution was obtained by dissolving cerium oxide (CeO) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in distilled water. ２ A mixed aqueous solution was obtained by adding (manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.). The mixed aqueous solution was heated to 80-90°C on a hot plate while stirring to evaporate the water and obtain a catalyst precursor powder. This powder was calcined in a tubular calcination furnace at 500°C for 2 hours while passing dry nitrogen at a flow rate of 50 mL / min, thereby obtaining a catalyst powder containing a metal oxide (Ru / CeO ２ A Ru content of 8% by mass was obtained.

[0042] The catalyst powder was mixed with distilled water to obtain a slurry containing the catalyst powder. The activated aluminum structure was immersed in this slurry. The aluminum structure was removed from the slurry and dried with hot air from a dryer. By repeating this immersion and drying process, Ru / CeO2 was obtained. ２ A spiral-shaped structural catalyst having a catalyst layer containing [a specific substance] was obtained as catalyst body #1. The total mass of the catalyst layer was 0.8 g.

[0043] Catalyst #2 (Ni / CeO ２ ) Nickel nitrate hexahydrate (Ni(NO)) is used instead of ruthenium nitrate. ３ ) ２ 6H ２ Except for using O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), Ru / CeO ２ Using a procedure similar to that for the preparation of the catalyst powder containing the composite oxide (Ni / CeO ２ A Ni content of 10% by mass was obtained using this catalyst powder. Ni / CeO was obtained in the same manner as catalyst #1. ２ A spiral-shaped structural catalyst having a catalyst layer containing [the specified substance] was obtained as catalyst body #2. The total mass of the catalyst layer was 1.1 g.

[0044] [Methanation Reaction Test - 1] Example 1 A flow-through reactor having the same configuration as the reactor shown in Figure 1 was prepared. Hard glass reaction tubes with an inner diameter of 11 mm, a length of 750 mm, and a thickness of 2 mm were used as reactors 11 and 21. One spiral-shaped catalyst #1 was inserted into reactors 11 and 21, respectively. A thermocouple for measuring the temperature of the catalyst layer was attached to the center of catalyst #1 in the longitudinal direction (direction of the gas flow path).

[0045] Before starting the reaction test, catalyst #1 was heated for 1 hour by heaters 13 and 23 (electric furnaces) set to 200°C while hydrogen gas was supplied to reactors 11 and 21 at a flow rate of 200 mL / min.

[0046] Next, N ２ Gas was supplied to reactor 11 and, while flowing through the water trap section 31, reactor 21, and water trap section 32 in that order, the temperatures of heaters 13 and 23 were raised from room temperature to a predetermined set temperature. After the temperature of the catalyst layer stabilized, H２ , CO ２ and CH ４ are mixed in gas mixing section 52 to form raw material gas G ０ is supplied to reactor 11, and the supplied gas is caused to flow along the gas flow path through reactor 11, water trap section 31, reactor 21, and water trap section 32 in this order. Raw material gas G ０ has a CH ４ :CO ２ ratio of 6:4 and CO ２ :H ２ ratio of 1:4 in terms of molar ratio (volume ratio), and the flow rate of each gas is adjusted accordingly. This ratio corresponds to the ratio in typical biogas. The pressure of the raw material gas supplied to reactor 11 is set to 0.1 MPa, and the section from the outlet of reactor 21 to the outlet of water trap section 32 is open to the atmosphere. That is, the pressure inside reactors 11 and 21 is substantially atmospheric pressure. The flow rate of the raw material gas supplied to reactor 11 was 2.0 L per minute. In this case, the gas hourly space velocity (GHSV) for catalyst body #1 in first-stage reactor 11 is 7,600 L per hour, and the gas contact time is 0.47 seconds.

[0047] The concentration of each component in product gas G １ discharged after passing through water trap section 32 was analyzed online by gas chromatography 90 provided downstream of pressure control section 70. From the analysis results, CO ２ conversion and CH ４ selectivity were obtained by the following formulas. In the formula for CH ４ selectivity, the amount of CH ４ produced is the difference between the amount of CH ４ in the product gas and the amount of CH ４ in the raw material gas, and the amount of CO ２ converted is the difference between the amount of CO ２ in the product gas and the amount of CO ２ in the raw material gas. It is generally desirable for the CO ２ conversion to be approximately 90% or higher.

[0048]

[0049] While increasing the set temperature of heaters 13 and 23 (electric furnaces) stepwise within the range of 200 to 500°C, the temperature of the catalyst layer at each temperature, CO ２ conversion rate, CH ４ selectivity, and CH in the produced gas ４ gas concentration were determined. FIG. 4 shows CO ２ is a graph showing the relationship between conversion rate and the temperature of the catalyst layer. CO ２ conversion rate reached a maximum value of 96.2% when the temperature of the catalyst layer was 298°C. CH at that time ４ selectivity was 99.9%, and CH in the produced gas obtained at the outlet of water trap section 32 ４ concentration was 94.1% by volume.

[0050] Example 2 A methanation reaction test was carried out by the same procedure as in Example 1, except that catalyst #2 was used instead of catalyst #1. However, before starting the reaction test, while supplying hydrogen gas to reactors 11 and 21 at a flow rate of 200 mL / min, catalyst #2 was heated for 1 hour by heaters 13 and 23 (electric furnaces) set to a temperature of 500°C. FIG. 5 shows CO ２ is a graph showing the relationship between conversion rate and the temperature of the catalyst layer. CO ２ conversion rate reached a maximum value of 95.0% when the temperature of the catalyst layer was 318°C. CH at that time ４ selectivity was 99.9%, and produced gas G １ CH in ４ concentration was 92.3% by volume.

[0051] Comparative Example 1 The three-way valves 81 and 82 of the reaction apparatus were switched so that the gas flow path did not pass through the reactor 21, and a methanation reaction test was carried out by the same procedure as in Example 1, except that one stage of reactor was used for the reaction. FIG. 6 shows the produced gas G discharged from the water trap section 31 １ CO in ２ is a graph showing the relationship between conversion rate and the temperature of the catalyst layer. CO ２ conversion rate reached a maximum value of 86.0% when the temperature of the catalyst layer was 298°C. CH at that time ４ selectivity was 98.8%, and produced gas G discharged from the water trap section 31 １ CH in ４The concentration was 76.2% by volume.

[0052] Comparative Example 2 The methanation reaction test was performed in the same procedure as in Example 2, except that the three-way valves 81 and 82 of the reactor were switched so that the gas flow path did not pass through reactor 21, and a single-stage reactor was used for the reaction. Figure 7 shows the generated gas G discharged from the water trap section 31. １ CO ２ This graph shows the relationship between the conversion rate and the temperature of the catalyst layer. ２ The conversion rate reached a maximum of 84.2% when the catalyst layer temperature was 292°C. ４ The selectivity was 98.6%, and the generated gas G discharged from the water trap section 31 was... １ CH in ４ The concentration was 74.5% by volume.

[0053] Comparative Example 3 Ni / CeO2 prepared in the preparation of catalyst #2 ２ Granular aluminum oxide (catalyst JRC-ALO-7, average particle size 3.2 mm, reference catalyst of the Catalysis Society of Japan) was added to a slurry containing catalyst powder. The resulting mixture was heated on a hot plate to 80-90°C while stirring to evaporate the water, obtaining a granular catalyst precursor in which the catalyst powder adhered to the surface of the granular aluminum oxide. This catalyst precursor was calcined in a tubular calcination furnace at 500°C for 1 hour while flowing dry nitrogen at a flow rate of 50 mL / min, thereby obtaining a granular substrate containing aluminum oxide and Ni / CeO ２Catalyst particles having a catalyst layer containing [a specific substance] were obtained. The total mass of the catalyst layer in the catalyst particles was 70 g per liter of catalyst packing capacity. For reactors 11 and 21, hard glass reaction tubes of the same size as those used in Example 1 were used. The catalyst particles were packed into reactors 11 and 21, respectively, to form a packed catalyst bed with a length of 180 mm in the gas flow path as catalyst body #3. The catalyst packed bed (catalyst body #3) was fixed by placing a mesh support and quartz wool on both sides of the catalyst packed bed. The aspect ratio of the catalyst packed bed (= length of catalyst bed / inner diameter of reaction tube) was 16.4. A thermocouple for measuring the temperature of the catalyst bed in the catalyst packed bed was attached to the center in the longitudinal direction (direction of the gas flow path) of the catalyst packed bed. The methanation reaction test was performed using the same procedure as in Example 1. Figure 8 shows CO ２ This graph shows the relationship between the conversion rate and the temperature of the catalyst layer. Figure 9 shows CO ２ This graph shows the relationship between selectivity and catalyst layer temperature. ２ The conversion rate reached a maximum of 89.1% when the catalyst layer temperature was 352°C. ４ The selectivity was 96.1%, and the generated gas G １ CH in ４ The concentration was 79.8% by volume. The temperature of the catalyst layer in reactor 21 exceeded 350°C when the heater 23 was set to 275°C, and rose to around 390°C when the heater 23 was set to 300°C. This temperature increase was due to the accumulation of reaction heat in the catalyst packed bed.

[0054] Example 3 The back pressure valve provided as the pressure control unit 70 was throttled, and the pressure measured by the pressure gauge 63 was adjusted to 0.95 MPa. The methanation reaction test was performed using the same procedure as in Example 1. Figure 10 shows CO ２ This graph shows the relationship between selectivity and catalyst layer temperature. ２ The conversion rate reached a maximum of 97.6% when the catalyst layer temperature was 321°C. ４ The selectivity was 99.9%, and the generated gas G １ CH in ４ The concentration was 96.4% by volume.

[0055] Results Table 1 summarizes the test results for Examples 1-3 and Comparative Examples 1-3. By using a reactor with a two-stage reactor including a water trap section for trapping moisture, high concentrations of CH4 were produced. ４ CO2 is produced with high efficiency from raw material gas containing CO2. ２ CH ４ It was confirmed that it can be converted to CO2. Examples 1 and 2, which used spiral-type structural catalysts, showed even higher CO2 emissions compared to Comparative Example 3, which used a packed catalyst. ２ Conversion rate and CO ２ The selectivity was shown. This is thought to be because the temperature of the catalyst layer was kept low due to the effective transfer of reaction heat. In the case of packed catalysts, the temperature tends to rise excessively, especially in the second and subsequent stages of the reactor, which can lead to CO ２ It is thought that the conversion rate was relatively reduced. As in Example 3, by pressurizing the reactor, CO ２ It was also confirmed that the conversion rate increased further.

[0056]

[0057] [Methanation Reaction Test - 2] Examples 4-10 Several spiral-shaped catalysts with different twist ratios were prepared using the same procedure as for catalyst #1. As Comparative Example 4, a flat plate-shaped catalyst #4 was prepared using the same procedure as for catalyst #1, except that an untwisted aluminum plate was used instead of a spiral-shaped aluminum structure. The obtained catalysts were used to perform a methanation reaction test using the same procedure as in Example 1.

[0058]

[0059] The test results are shown in Table 2. The spiral-type catalysts of each example showed higher CO2 levels compared to the flat-plate type catalyst of Comparative Example 4. ２ The conversion rate was shown, and this result suggests the effectiveness of the swirl flow effect derived from the spiral shape. Among spiral catalysts, the CO2 conversion rate was particularly high when the twist ratio was between 1.5 and 5.0. ２ The conversion rate was shown.

[0060] [Methanation Reaction Test - 3] Examples 11-14 A spiral-shaped metal substrate with a width of 10 mm and a twist ratio of 2.2 was prepared using the same procedure as for the spiral-shaped aluminum structure, except that a porous metal plate (Ni-Cr) with a pore diameter of 0.4-0.5 mm was used as the substrate instead of an aluminum plate. A catalyst layer was formed on this metal substrate using the same procedure as for the preparation of catalyst #1 to obtain a spiral-shaped structural catalyst. Several spiral-shaped structural catalysts with different aspect ratios were prepared using the same method. A methanation reaction test was performed using the obtained spiral-shaped structural catalysts in the same procedure as for Example 1.

[0061] Comparative Example 5 For reactors 11 and 21, hard glass reaction tubes with an inner diameter of 20 mm, a length of 750 mm, and a thickness of 2 mm were used. The catalyst particles prepared in Comparative Example 3 were packed into reactors 11 and 21, respectively, forming a 53 mm long packed catalyst bed in the gas flow path as catalyst body #5. The catalyst bed (catalyst body #5) was fixed by placing a mesh support and quartz wool on both sides of it. The aspect ratio of the catalyst bed (= length of the catalyst bed / inner diameter of the reaction tube) was 2.65. A thermocouple was attached to the center of the catalyst bed in the longitudinal direction (direction of the gas flow path) to measure the temperature of the catalyst bed. The methanation reaction test was performed using the same procedure as in Comparative Example 3. Figure 11 shows CO ２ This graph shows the relationship between the conversion rate and the temperature of the catalyst layer. ２ The conversion rate reached a maximum of 79.0% when the catalyst layer temperature was 440°C.

[0062] Results Table 3 summarizes the test results for Examples 11-14 and Comparative Example 5. In Examples 11-14, where spiral-type structural catalysts were used, the aspect ratio was 10 or higher for CO ２ The conversion rate remained above 90%. On the other hand, in Comparative Example 5, where a catalyst packed bed was used as the catalyst, CO was converted when the aspect ratio was 2.65. ２The conversion rate remained at 79.0%. This is thought to be because the catalyst layer temperature exceeded 430°C. From these results, it can be seen that spiral-type structural catalysts, even with a large aspect ratio, can maintain a relatively low catalyst layer temperature while avoiding pressure loss and clogging, and high CO ２ It was also confirmed that the conversion rate could be easily achieved.

[0063]

[0064] 1...Catalyst, 1A...Spiral section, 10, 20...Reaction section, 11, 21...Reactor, 13, 23...Heater, 15...Substrate, 16...Catalyst layer, 31, 32...Water trap section, 70...Pressure control section, 90...Gas chromatography, 100...Reaction apparatus, G ０ ...raw material gas, G １ ...Evolved gas, X-axis.

Claims

1. A method for producing a gas containing methane, comprising: preparing a reactor and a plurality of reaction sections having catalysts provided in the reactor, wherein a gas flow path is formed through which gas flows sequentially through the plurality of reaction sections; and supplying a raw material gas containing methane, carbon dioxide and hydrogen to the reactor, thereby generating methane in the reactor, and thereby producing a product gas containing methane at a concentration higher than the concentration of methane in the raw material gas, wherein the catalyst has a catalyst layer containing a methanation reaction catalyst, the temperature of the catalyst layer is maintained at 430°C or lower while the raw material gas is supplied to the reactor, the reactor further comprises a water trap section for trapping moisture, provided between two adjacent reaction sections in the gas flow path, the catalyst has a plate-shaped spiral section extending along a certain axis while twisting in a direction rotating around that axis, and the spiral section comprises a plate-shaped substrate and the catalyst layer provided on the substrate.

2. The method according to claim 1, wherein the ratio of methane to the total amount of carbon dioxide and methane in the raw material gas is 40% by volume or more.

3. The method according to claim 1, wherein the pitch is the length in the direction of the axis of the portion of the spiral portion that rotates once around the axis, the maximum width of the spiral portion in a direction perpendicular to the axis is W, and the twist ratio P / W is 1.5 or more and 5.0 or less.

4. The method according to claim 1, wherein the length of the spiral portion in the direction of the axis is L, the maximum width of the spiral portion in the direction perpendicular to the axis is W, and the aspect ratio L / W is 10 or more and 100 or less.

5. The method according to claim 1, wherein, while the raw material gas is supplied to the reactor, the pressure of the gas in the reactor in the plurality of reaction sections exceeds atmospheric pressure.

6. The method according to any one of claims 1 to 5, wherein the methanation reaction catalyst comprises one or more metal oxides selected from the group consisting of aluminum oxide, cerium oxide, zirconium oxide, and titanium oxide, and one or more metal elements selected from the group consisting of Fe, Co, Ru, Mg, Ni, Mn, Mo, K, Na, Li, Ca, Sr, Ba, La, Pt, Pd, Rh, Nd, Cu, and Zn.

7. A reaction apparatus comprising a reactor, a plurality of reaction sections having a catalyst provided within the reactor, and a water trap section for trapping moisture, wherein a gas flow path is formed through which gas flows sequentially through the plurality of reaction sections, the water trap section is provided between two adjacent reaction sections in the gas flow path, the catalyst has a catalyst layer containing a methanation reaction catalyst, the catalyst has a plate-shaped spiral section extending along a certain axis while twisting in a direction rotating around that axis, and the spiral section includes a plate-shaped substrate and the catalyst layer provided on the substrate.

8. The reaction apparatus according to claim 7, wherein the pitch is the length in the direction of the axis of the portion of the spiral portion that rotates once around the axis, the maximum width of the spiral portion in a direction perpendicular to the axis is W, and the twist ratio P / W is 1.5 or more and 5.0 or less.

9. The reaction apparatus according to claim 7, wherein the length of the spiral portion in the direction of the axis is L, the maximum width of the spiral portion in the direction perpendicular to the axis is W, and the aspect ratio L / W is 10 or more and 100 or less.

10. The reaction apparatus according to claim 7, further comprising a pressure control unit for controlling the pressure of the gas in the reactors in a plurality of reaction units to exceed atmospheric pressure.

11. The reaction apparatus according to any one of claims 7 to 10, wherein the methanation reaction catalyst comprises one or more metal oxides selected from the group consisting of aluminum oxide, cerium oxide, zirconium oxide, and titanium oxide, and one or more metal elements selected from the group consisting of Fe, Co, Ru, Mg, Ni, Mn, Mo, K, Na, Li, Ca, Sr, Ba, La, Pt, Pd, Rh, Nd, Cu, and Zn.

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