Methane production method

Abstract

A method for producing methane according to the present disclosure includes producing methane from a raw material gas containing ammonia and carbon dioxide in the presence of a catalyst containing a carrier and a transition metal.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application Nos. 2023-180411 and 2024-159324, the disclosures of which are incorporated herein by reference. [Technical Field]

[0002] The present disclosure relates to a method for producing methane. [Background technology]

[0003] From the perspective of reducing greenhouse gas emissions, expectations are growing for hydrogen energy obtained by burning hydrogen. However, handling of hydrogen, including transport and storage, is extremely difficult. For this reason, in recent years, methods have been proposed for producing hydrogen by using ammonia as a hydrogen energy carrier, such as importing ammonia produced overseas, and decomposing the ammonia by contacting it with a catalyst. For example, Patent Document 1 shows that by using a catalyst in which a transition metal such as ruthenium with small particle size is supported on a carrier, ammonia can be decomposed with high efficiency and hydrogen can be suitably produced.

[0004] Furthermore, a technology known as methanation has been known in the past for synthesizing methane, a main component of city gas raw materials, by recovering carbon dioxide from exhaust gases and reacting it with hydrogen. Methanation recovers carbon dioxide emitted by combustion and can be used for reaction with hydrogen. Therefore, methane obtained by methanation has attracted attention as a carbon-neutral fuel. For example, Patent Document 2 discloses that the use of a methanation catalyst supporting ruthenium as the active metal exhibits high low-temperature activity in the methanation reaction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2010-194519 [Patent Document 2] International Publication No. 2022 / 224993 Summary of the Invention [Problem to be solved by the invention]

[0006] The ammonia decomposition reaction is a large endothermic reaction, requiring external heat supply to maintain the reaction temperature. On the other hand, the reaction synthesizing methane from carbon dioxide is an exothermic reaction, requiring heat removal from the reactor. In other words, there is room for improvement in thermal efficiency in both reactions.

[0007] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a methane production method capable of producing methane with excellent reaction efficiency. [Means for solving the problem]

[0008] The method for producing methane according to the present disclosure includes producing methane from a feed gas containing ammonia and carbon dioxide in the presence of a catalyst containing a support and a transition metal. [Brief explanation of the drawings]

[0009] [Figure 1] 1 shows mass chromatograms of each ion measured by a mass spectrometer in an example of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described, but the methane production method according to the present disclosure is not limited to the following embodiments, and is not limited to the following effects. Furthermore, the methane production method according to the present disclosure can be modified in various ways without departing from the gist of the present disclosure.

[0011] The methane production method according to this embodiment includes producing methane from a raw material gas containing ammonia and carbon dioxide. In producing methane, a reaction shown in the following formula (I) occurs to produce methane.

[0012] 3.6NH3+CO2→ 1.8N2+2H2O+1.4H2+CH4...(I)

[0013] More specifically, in producing methane, the reaction shown in the following formula (II) occurs to decompose ammonia, and the reaction shown in the following formula (III) occurs to produce methane. Note that the reaction shown in the following formula (II) is an endothermic reaction, and the reaction shown in the following formula (III) is an exothermic reaction.

[0014] NH3→ 1.5H2+0.5N2-45.9kJ / mol···(II) CO2+4H2→ CH4+2H2O+164.7kJ / mol ···(III)

[0015] The methane production method according to this embodiment can produce methane with excellent reaction efficiency by simultaneously proceeding the endothermic reaction represented by formula (II) and the exothermic reaction represented by formula (III).

[0016] The molar ratio of ammonia to carbon dioxide in the feed gas is preferably 3.0 or more and 5.4 or less, more preferably 3.0 or more and 5.0 or less, and even more preferably 3.2 or more and 4.0 or less. When the molar ratio is 3.0 or more, the methane production method according to this embodiment can be an exothermic reaction with a reaction heat of 30 kJ / mol or less, eliminating the need for heat removal equipment and reducing capital investment. Furthermore, when the molar ratio is 5.4 or less, the methane production method according to this embodiment can be an endothermic reaction with a reaction heat of 100 kJ / mol or less, reducing the amounts of electricity, fuel, steam, etc. used to compensate for the reaction heat and reducing carbon dioxide emissions associated with their production.

[0017] In one embodiment, the raw material gas further contains hydrogen from the viewpoint of promoting the reaction represented by formula (III). When the raw material gas contains hydrogen, the molar ratio of hydrogen to carbon dioxide in the raw material gas is preferably 0.00001 or more and 10.0 or less, more preferably 0.0001 or more and 5.0 or less. In this embodiment, hydrogen may be simultaneously produced from the raw material gas by producing methane. Furthermore, in this embodiment, the hydrogen contained in the raw material gas may be recycled from a hydrogen-containing stream produced in the production of methane.

[0018] The hydrogen contained in the raw material gas may be hydrogen recovered from the methane production process and recycled into the gas. Examples of methods for recovering hydrogen from the methane production process include separation of hydrogen by membrane separation and separation of hydrogen by pressure swing adsorption (PSA).

[0019] The raw material gas may contain a gas obtained by thermal decomposition of ammonium carbonate. The ammonium carbonate is preferably obtained by contacting an aqueous solution containing ammonia with a gas containing carbon dioxide. Specifically, for example, carbon dioxide gas obtained from a liquefied carbon dioxide cylinder is absorbed into 75 mL of a commercially available 28% aqueous ammonia solution at a flow meter value of 100 mL / min for 2 hours. The pH of the solution after 2 hours is 8 to 9. When the solution is allowed to stand in a refrigerator (4°C) for 24 hours, crystallization is confirmed, and 5.2 g of ammonium carbonate solid is obtained. The carbon dioxide-containing gas may be air or exhaust gas from a power plant, factory, steelworks, chemical plant, waste treatment facility, or biomass facility.

[0020] The reaction temperature in producing methane is preferably 300°C or higher and 550°C or lower, more preferably 350°C or higher and 550°C or lower, and even more preferably 400°C or higher and 550°C or lower, from the viewpoint of producing methane with excellent reaction efficiency.

[0021] The reaction pressure in producing methane is preferably 0 MPa-G or more and 0.9 MPa-G or less, more preferably 0.2 MPa-G or more and 0.9 MPa-G or less, and even more preferably 0.4 MPa-G or more and 0.9 MPa-G or less, from the viewpoint of producing methane with excellent reaction efficiency.

[0022] In one embodiment, the methane production is carried out using a reactor. The reactor is preferably at least one selected from the group consisting of an external heat exchange type fixed bed reactor, an adiabatic fixed bed reactor, a fluidized bed reactor, a simulated moving bed reactor, a riser type fluidized bed reactor, and a radial flow type fixed bed reactor, and is more preferably an adiabatic fixed bed reactor. One type of reactor may be used alone, or two or more types may be used in combination.

[0023] The methane production method according to this embodiment is carried out in the presence of a catalyst containing a support and a transition metal.

[0024] The carrier is one that supports a transition metal. The carrier is preferably at least one carrier selected from the group consisting of titania (TiO2), alumina (Al2O3), silicon carbide (SiC), carbon (C), carbon nitride (C3N4), zirconia (ZrO2), silica (SiO2), cerium oxide (CeO2), and niobium oxide (NbO, Nb2O5), more preferably at least one carrier selected from the group consisting of titania, alumina, silicon carbide, carbon, and cerium oxide, and even more preferably a carbon carrier. One type of carrier may be used alone, or two or more types may be used in combination.

[0025] Examples of carbon carriers include activated carbon, carbon black, graphene, graphite, acetylene black, mesoporous carbon, carbon nanotubes, carbon nanofibers, and carbon nanohorns. The carbon carrier may contain sulfur as an impurity. The sulfur content of the carbon carrier is preferably 1.8% by mass or less, and more preferably 1.0% by mass or less, so as not to impair the effects of the present disclosure.

[0026] As the carbon carrier, a commercially available product may be used. For example, mesoC+ manufactured by SICAT is available. TM and Granular Shirasagi (registered trademark) WH2C manufactured by Osaka Gas Chemicals Co., Ltd.

[0027] From the viewpoint of producing methane with excellent reaction efficiency, the support preferably has pores with an average pore diameter of 2 nm or more and 100 nm or less, more preferably has pores with an average pore diameter of 3 nm or more and 50 nm or less, and even more preferably has pores with an average pore diameter of 3.5 nm or more and 15 nm or less.

[0028] The specific surface area of ​​the carrier is preferably 5 m² from the viewpoint of producing methane with excellent reaction efficiency. 2 / g or more 2000m 2 / g or less, and more preferably 10m 2 / g or more 1500m 2 / g or less.

[0029] The average pore diameter (D, unit: nm) and specific surface area (A, unit: m 2 / g) can be calculated by measuring the nitrogen adsorption / desorption isotherm at 77 K using a BELSORP-Max manufactured by Microtrac-Bell after vacuum degassing the support at 120°C for 8 hours, and then using the BET multipoint method and the following equation (1). D=4V P / (A×1000) (1)

[0030] Here, V in the above formula (1) P is the total pore volume (cm) up to a relative pressure (P / P0) of 0.99 3 / g) and can be calculated from the following formula (2). V P =(V / 22414)×M g / ρ g ···(2)

[0031] In the above formula (2), V is the amount of nitrogen adsorbed (cm) at a relative pressure (P / P0) of 0.99. 3 / g), Mg is the molecular weight of nitrogen (28.013 g / mol), ρ g is the liquid density of nitrogen (0.808 g / cm 3 )

[0032] From the viewpoint of producing methane with excellent reaction efficiency, the content of the carrier is preferably 70% by mass or more and 99% by mass or less, and more preferably 80% by mass or more and 98% by mass or less, based on the entire catalyst.

[0033] The shape and size of the carrier are not particularly limited and can be appropriately selected depending on the type, size, operating conditions, etc. of the reactor. Examples of the shape of the carrier include granular, spherical, cylindrical, trilobe, tetralobe, ring, honeycomb, etc. Regarding the size of the carrier, for example, when the carrier is granular or spherical, the average particle size can be 0.5 mm or more and 10 mm or less. Furthermore, regarding the size of the carrier, for example, when the carrier is cylindrical, trilobe, tetralobe, or ring-shaped, the average diameter of the cross section or the average length of one side can be 0.5 mm or more and 10 mm or less, and the average length can be 1.0 mm or more and 20 mm or less.

[0034] Examples of transition metals include ruthenium, rhodium, iron, cobalt, and nickel. Among these, the transition metal is preferably ruthenium or nickel, more preferably ruthenium, from the viewpoint of producing methane with excellent reaction efficiency. One type of transition metal may be used alone, or two or more types may be used in combination.

[0035] The transition metal may be derived from a salt such as a nitrate, carbonate, or chloride. In one embodiment, the ruthenium may be derived from at least one ruthenium compound selected from the group consisting of ruthenium nitrosyl nitrate, ruthenium chloride, ruthenium carbonyl, potassium ruthenate, and ammonium ruthenate chloride. Among these, the ruthenium is preferably derived from ruthenium chloride and ruthenium nitrosyl nitrate, and more preferably from ruthenium nitrosyl nitrate.

[0036] The transition metal may be contained in the catalyst as a simple substance, or may be contained in the catalyst as an oxide, nitride, phosphide, carbide, etc. When the transition metal is contained in the catalyst as an oxide, examples of the oxide include ruthenium oxide, iron oxide, cobalt oxide, and nickel oxide.

[0037] From the viewpoint of producing methane with excellent reaction efficiency, the content of the transition metal is preferably 1 mass % or more and 30 mass % or less, and more preferably 2 mass % or more and 20 mass % or less, based on the entire catalyst.

[0038] In order to promote the reaction, the catalyst may further contain at least one selected from the group consisting of alkali metal compounds and alkaline earth metal compounds. Examples of alkali metal compounds and alkaline earth metal compounds include sodium oxide, potassium oxide, cesium oxide, magnesium oxide, calcium oxide, strontium oxide, and barium oxide. These compounds may be used alone or in combination of two or more.

[0039] In one embodiment, when the catalyst contains ruthenium oxide and barium oxide, the molar ratio of barium to ruthenium is preferably 0.1 or more and 3 or less, more preferably 0.2 or more and 2 or less.

[0040] The catalyst can be prepared by a general method for supporting a transition metal on a support. For example, an impregnation method can be used in which a support is impregnated with a solution containing the transition metal, followed by drying and calcination. More specifically, the catalyst can be prepared by the following method, for example.

[0041] (Preparation of catalyst precursor) First, a support is impregnated with a solution containing a transition metal, which is a catalyst raw material, by the incipient wetness method, and then dried. The resulting solid is then heated in an electric tubular furnace under nitrogen flow, thereby obtaining a catalyst precursor carrying a transition metal. The catalyst precursor is then impregnated with a solution containing at least one compound selected from the group consisting of alkali metal compounds and alkaline earth metal compounds, and then dried. The resulting solid is then heated in an electric tubular furnace under nitrogen flow, thereby obtaining a catalyst precursor containing at least one compound selected from the group consisting of alkali metal compounds and alkaline earth metal compounds in addition to the transition metal.

[0042] (Catalyst Preparation) The catalyst can be obtained by heating the obtained catalyst precursor in an electric tubular furnace while passing a gas containing hydrogen through it.

[0043] The catalyst obtained in this manner can be molded into a spherical, cylindrical, or other shape having an average particle size of 0.5 mm to 20 mm. Note that the average particle size means the average diameter when the molded body is spherical, and means the average diameter and average length when the molded body is cylindrical.

[0044] The present disclosure includes the following aspects. [1] A method for producing methane, comprising producing methane from a raw material gas containing ammonia and carbon dioxide in the presence of a catalyst containing a support and a transition metal. [2] The method for producing methane according to [1], wherein the molar ratio of ammonia to carbon dioxide in the raw material gas is 3.0 or more and 5.4 or less. [3] The method for producing methane according to [1] or [2], wherein the raw material gas further contains hydrogen. [4] The method for producing methane according to [2], wherein hydrogen is simultaneously produced from the raw material gas by producing methane. [5] The method for producing methane according to [3], wherein the hydrogen contained in the raw material gas is hydrogen recovered during the production of methane and recycled into the raw material gas. [6] The method for producing methane according to [4], wherein the hydrogen contained in the raw material gas is a recycled stream containing hydrogen produced in the production of methane. [7] The method for producing methane according to any one of [1] to [6], wherein the reaction temperature in producing methane is 300°C or higher and 550°C or lower. [8] The method for producing methane according to any one of [1] to [7], wherein the reaction pressure in producing methane is 0 MPa-G or more and 0.9 MPa-G or less. [9] The method for producing methane according to any one of [1] to [8], wherein the support is at least one support selected from the group consisting of titania, alumina, silicon carbide, carbon, zirconia, silica, cerium oxide, and niobium oxide.

[10] The method for producing methane according to [9], wherein the support has pores with an average pore diameter of 2 nm or more and 100 nm or less.

[11] The method for producing methane according to [2], wherein the transition metal is ruthenium.

[12] The method for producing methane according to [3], wherein the transition metal is ruthenium.

[13] The method for producing methane according to [9], wherein the transition metal is ruthenium.

[14] The method for producing methane according to any one of [1] to

[13] , wherein the methane production is carried out using a reactor, and the reactor is at least one selected from the group consisting of an external heat exchange type fixed bed reactor, an adiabatic fixed bed reactor, a fluidized bed reactor, a simulated moving bed reactor, a riser type fluidized bed reactor, and a radial flow type fixed bed reactor.

[15] The method for producing methane according to any one of [1] to

[14] , wherein the raw material gas contains a gas obtained by thermal decomposition of ammonium carbonate.

[16] The method for producing methane according to

[15] , wherein the ammonium carbonate is obtained by contacting an aqueous solution containing ammonia with a gas containing carbon dioxide.

[17] The method for producing methane according to

[16] , wherein the carbon dioxide-containing gas is air.

[18] The method for producing methane according to

[16] , wherein the carbon dioxide-containing gas is exhaust gas from a power plant, a factory, a steel mill, a chemical plant, a waste treatment facility, or a biomass facility. [Example]

[0045] The present disclosure will be described in more detail below using examples and comparative examples, but the present disclosure is not limited to the following examples. In the following description, "%" representing an amount is based on mass unless otherwise specified. Furthermore, the operations described below were performed under conditions of room temperature and normal pressure unless otherwise specified.

[0046] [Manufacturing Example 1] <Preparation of catalyst precursor> Carbon (C) carrier (SICAT mesoC+) TM , trilobal pellet shape with a cross section of 1.6 mm and a length of 2 mm, specific surface area (A): 293 m 2 / g, average pore diameter (D): 5.0 nm). The specific surface area (A) and average pore diameter (D) of support i were determined by measuring the nitrogen adsorption / desorption isotherm at 77 K using a Microtrac-Bell BELSORP-Max after vacuum degassing support i at 120°C for 8 hours, and then using the BET multipoint method and the following equation (1), respectively. D=4V P / (A×1000) (1)

[0047] Here, V in the above formula (1) P is the total pore volume (cm) up to a relative pressure (P / P0) of 0.99 3 / g) and was calculated using the following formula (2). V P =(V / 22414)×M g / ρ g ···(2)

[0048] In the above formula (2), V is the amount of nitrogen adsorbed (cm) at a relative pressure (P / P0) of 0.99. 3 / g), M g is the molecular weight of nitrogen (28.013 g / mol), ρ gis the liquid density of nitrogen (0.808 g / cm 3 )

[0049] First, 5.2 g of ion-exchanged water was added to 2.6 g of an aqueous solution of ruthenium nitrosyl nitrate nitrate (Furuya Metals, Ru(NO)(NO), Ru content: 19% by mass) and mixed thoroughly. The resulting solution was impregnated into 10 g of carrier i by the incipient wetness method, and then air-dried overnight at room temperature (approximately 25°C) in an air atmosphere. The resulting solid was packed into a quartz glass tube with an inner diameter of 24 mm and equipped with a sheath tube for measuring the internal temperature, and then heated at 100 cm using an electric tubular furnace. 3 Under a nitrogen flow (0°C, 0.1013 MPa (absolute)) / min, the internal temperature was raised to 400°C over 1 hour, and then maintained at the same temperature for 3 hours to obtain 10 g of catalyst precursor i-1 (6.6 wt% RuO / C) (the amount of RuO supported is an extra number when the amount of RuO supported on carrier i is taken as 100).

[0050] 1.9 g of barium nitrate (Ba(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to 10 g of ion-exchanged water heated to 80°C and dissolved therein. 10 g of catalyst precursor i-1 was added to the resulting solution heated to 80°C, and catalyst precursor i-1 was impregnated with the barium nitrate aqueous solution. Subsequently, the pressure was reduced to 9 to 20 mmHg at 80°C, and the catalyst precursor i-1 was dried under reduced pressure for 1 hour. The resulting solid was packed into a quartz glass tube with an inner diameter of 24 mm and equipped with a sheath tube for measuring the internal temperature, and then heated to 100 cm using an electric tubular furnace. 3 Under a nitrogen flow (0°C, 0.1013 MPa (absolute)) / min, the internal temperature was raised to 500°C over 1 hour, and then maintained at the same temperature for 1 hour to obtain catalyst precursor i-2 (11 wt% BaO / 6.6 wt% RuO2 / C) (the amounts of BaO and RuO2 supported are each outside the range of support i, which is taken as 100). The molar ratio of barium to ruthenium was 1.5.

[0051] <Catalyst Preparation> Catalyst precursor i-2: 0.24 g was packed into a quartz glass tube with an inner diameter of 8 mm equipped with a sheath tube with an outer diameter of 4 mm for measuring the internal temperature, and then heated for 5 cm using an electric tubular furnace. 3(0°C, 0.1013 MPa (absolute)) / min of hydrogen and 95 cm 3 The internal temperature was raised to 400°C under a helium flow (0°C, 0.1013 MPa (absolute)) / min, and then maintained at the same temperature for 1 hour to obtain catalyst i (11 wt% BaO / 5.0 wt% Ru / C) (the amounts of BaO and Ru supported are outside the range of support i being 100). Catalyst i was prepared by heating the catalyst to 100 cm 3 The mixture was cooled to 158°C under a helium flow (0°C, 0.1013 MPa (absolute)) / min and used as is in the methane production reaction.

[0052] <Methane production reaction> (Gas analysis using a mass spectrometer) Using a gas flow meter, helium gas was introduced at 100 cm 3 Helium gas was flowed at 0°C and 0.1013 MPa (absolute) per minute. Helium gas was introduced into an in-line mass spectrometer (Microtrac-Bel, BELMASS), and the ion intensities of m / z = 2, 15, 16, 18, 28, and 44 were measured in real time. The intensities of each ion 108 minutes after the start of flow were recorded as baseline intensities.

[0053] (Preparation of raw gas and gas analysis using a mass spectrometer) Using a gas flow meter, ammonia gas was introduced at a rate of 3.2 cm 3 (0°C, 0.1013 MPa (absolute)) / min, carbon dioxide gas 0.90 cm 3 (0°C, 0.1013 MPa (absolute)) / min, helium gas 96 cm 3 (0°C, 0.1013 MPa (absolute)) / min (total gas flow rate was 100 cm 3 (0°C, 0.1013 MPa (absolute)) / min). The molar ratio of ammonia to carbon dioxide in the feed gas was 3.6. The feed gas was introduced into an in-line mass spectrometer (Microtrac-Bel, BELMASS), and the ion intensities of m / z = 2, 15, 16, 18, 28, and 44 were measured in real time. The ion intensities 30 minutes after the start of feed gas flow were recorded as the feed gas intensity.

[0054] (Methane production reaction 1) The catalyst i packed in the quartz glass tube was heated in an electric tubular furnace at an internal temperature of 158°C. The raw material gas was introduced into the quartz glass tube to carry out methane production reaction 1. The gas linear velocity calculated from the raw material gas flow rate and the empty column cross-sectional area of ​​the catalyst packed bed was 4.4 cm / s at 0°C and 0.1013 MPa (absolute). The post-reaction gas discharged from the quartz glass tube was introduced into an in-line mass spectrometer (Microtrac-Bell, BELMASS), and the ion intensities of m / z = 2, 15, 16, 18, 28, and 44 were measured in real time. The ion intensities after 46 minutes are listed in Table 1 as "Reaction 1 (158°C)" intensities.

[0055] (Methane production reaction 2) Following methane production reaction 1, the electric tubular furnace was heated at a rate of 5°C / min, and the catalyst i was maintained at an internal temperature of 209°C to carry out methane production reaction 2. The ionic intensities after 58 minutes are shown in Table 1 as "Reaction 2 (209°C)" intensities.

[0056] (Methane production reaction 3) Following methane production reaction 2, the electric tubular furnace was heated at a rate of 5°C / min, and catalyst i was maintained at an internal temperature of 260°C to carry out methane production reaction 3. The ionic intensities after 52 minutes are listed in Table 1 as "Reaction 3 (260°C)" intensities.

[0057] (Methane production reaction 4) Following methane production reaction 3, the electric tubular furnace was heated at a rate of 5°C / min, and catalyst i was maintained at an internal temperature of 311°C to carry out methane production reaction 4. The ionic intensities after 57 minutes are shown in Table 1 as "Reaction 4 (311°C)" intensities.

[0058] (Methane production reaction 5) Following methane production reaction 4, the electric tubular furnace was heated at a rate of 5°C / min, and the catalyst i was maintained at an internal temperature of 361°C to carry out methane production reaction 5. The ion intensities after 55 minutes are shown in Table 1 as "Reaction 5 (361°C)" intensities.

[0059] (Methane production reaction 6) Following methane production reaction 5, the electric tubular furnace was heated at a rate of 5°C / min, and catalyst i was maintained at an internal temperature of 411°C to carry out methane production reaction 6. The ion intensities after 58 minutes are shown in Table 1 as "Reaction 6 (411°C)" intensities.

[0060] Figure 1 shows the mass chromatograms of each ion measured by a mass spectrometer in methane production reactions 1 to 6.

[0061] [Table 1]

[0062] (Calculation of carbon dioxide conversion rate) The carbon dioxide conversion rate was calculated using the following formula (3) from the ion intensity values ​​at each stage of m / z=44 recorded by the mass spectrometer.

[0063] Carbon dioxide conversion rate (%) = 1 - [(reaction temperature (△△△ °C) - baseline)] / (raw gas - baseline)] × 100 (3)

[0064] In the reaction 〇(△△△℃), the 〇 is filled with a number from 1 to 6, and the △△△ is filled with the corresponding internal temperature number.

[0065] (Calculation of ammonia conversion rate) The ammonia conversion rate was calculated using the following formula (4) from the ion intensity values ​​at each stage of m / z=16 recorded by the mass spectrometer.

[0066] Ammonia conversion rate (%) = 1 - [(reaction rate (△△△ °C) - baseline)] / (raw gas - baseline)] × 100 (4)

[0067] In the reaction 〇(△△△℃), the 〇 is filled with a number from 1 to 6, and the △△△ is filled with the corresponding internal temperature number.

[0068] (Calculation of methane production rate) From the methane production reaction formula shown in the following formula (III), the methane production rate was calculated using the following formula (5) assuming a selectivity of 100%.

[0069] CО2+4H2→CH4+2H2О+164.7kJ / mol ···(III)

[0070] Methane production rate (mmol / min) = carbon dioxide gas flow rate (cm 3 / min) × carbon dioxide conversion rate / 100 / 22.4 (5)

[0071] (Calculation of hydrogen production rate) The hydrogen production rate was calculated from the hydrogen production reaction formula shown in the following formula (II) and the methane production reaction formula shown in the above formula (III) using the following formula (6) assuming a selectivity of 100%.

[0072] NH3→1.5H2+0.5N2-45.9kJ / mol ···(II)

[0073] Hydrogen production rate (mmol / min) = Ammonia gas flow rate (cm 3 / min) × ammonia conversion rate / 100 / 22.4 × 1.5 - methane production rate × 4 (6)

[0074] The calculated carbon dioxide conversion rate, ammonia conversion rate, methane production rate, and hydrogen production rate are shown in Table 2. Note that when the calculated value was negative, it was entered as 0. The production of methane and hydrogen is also evident from the change in ion intensity of m / z = 15 and 2. m / z = 15 does not simply increase because fragments derived from ammonia overlap. For example, from reaction 5 (361 °C) to reaction 6 (411 °C), the ion intensity of m / z = 16, which represents ammonia, increased by 8.5 × 10 -12 A to 3.6 x 10 -12 A, whereas the ion intensity of m / z = 15, which represents fragments derived from methane and ammonia, is 2.0 × 10 -12 A to 1.6 x 10 -12 The decrease is only 0.80 times that of A.

[0075] [Table 2]

[0076] Using the above formulas (II) and (III), the calculated values ​​of the reaction heat required to produce 1 mol of methane are shown in Table 3, where the molar ratio of ammonia to carbon dioxide in the feed gas is changed.

[0077] [Table 3]

[0078] As is clear from Tables 2 and 3, the methane production method according to the present disclosure can produce methane with excellent reaction efficiency from a feed gas containing ammonia and carbon dioxide in the presence of a catalyst containing a support and a transition metal. In particular, Test Examples 1 to 3, in which the molar ratio of ammonia to carbon dioxide in the feed gas was 3.0 or more and 5.4 or less, resulted in an exothermic reaction with a heat of reaction of 30 kJ / mol or less, or an endothermic reaction with a heat of reaction of 100 kJ / mol or less, and methane could be produced with even better reaction efficiency.

[0079] [Manufacturing Example 2] <Preparation of catalyst precursor> Fifty parts by weight of rutile titanium dioxide (manufactured by Sakai Chemical Industry Co., Ltd., STR-60R, 100% rutile) and 50 parts by weight of α-alumina (manufactured by Sumitomo Chemical Co., Ltd., AES-12) were mixed. Next, 12.8 parts by weight of titanium dioxide sol (manufactured by Sakai Chemical Industry Co., Ltd., CSB, titanium dioxide content 39% by weight, 100% anatase titanium dioxide) were diluted with pure water and kneaded with 100 parts of this mixture. The kneaded mixture was extruded into cylindrical shapes with a diameter of 1.5 mm, dried, and crushed to lengths of approximately 2-4 mm. The resulting molded body was calcined in air at 650-680°C for 3 hours to obtain carrier II, a mixture of titanium dioxide and α-alumina. This support ii was impregnated with a commercially available aqueous solution of ruthenium chloride hydrate, dried, and then calcined in air at 250°C for 2 hours to obtain a catalyst precursor ii-1 in which ruthenium oxide was supported on the support at a loading rate of 4 mass%.

[0080] <Catalyst Preparation> The catalyst precursor ii-1 was crushed and sieved to 75 to 150 μm, and then 2.8 g was weighed out and packed into a 7.5 mm inner diameter SUS reactor tube equipped with a 3 mm outer diameter sheath tube for measuring the internal temperature. 3 Under a helium flow (0°C, 0.1013 MPa (absolute)) / min, the internal temperature was raised to 500°C, and after holding at that temperature for 1 hour, the internal temperature was lowered to 400°C. 3 (0°C, 0.1013 MPa (absolute)) / min hydrogen and 110 cm 3 The catalyst was then heated at 0°C for 1 hour under a helium flow at 0.1013 MPa (absolute) / min to obtain catalyst ii. 3 The tube was cooled to an internal temperature of 150-160°C under a helium flow (0°C, 0.1013 MPa (absolute)) / min, and used as is for the methane production reaction.

[0081] <Methane production reaction> (Gas analysis by inline gas chromatography) The post-reaction gas discharged from the SUS reaction tube was introduced into an in-line gas chromatograph (GL Science Co., Ltd., Agilent 990 Micro GC) to analyze the reaction gas. The analysis conditions are as follows: Carrier gas: Helium Injection temperature: 100℃ Column used: COX UM 1m x 0.8mm ID ST Column temperature: 100℃ Pressure: 170kPa

[0082] (Creating a calibration curve) To calculate the composition ratio in the exhaust gas, a calibration curve was created using the following procedure. A methane (16%) + nitrogen (84%) mixed gas was pumped from 0 to 75 cm using a gas flow meter. 3 (0°C, 0.1013 MPa (absolute)) / min, carbon dioxide gas 0-15 cm 3 (0°C, 0.1013 MPa (absolute)) / min, helium gas 11 to 95 cm 3 (0°C, 0.1013 MPa (absolute)) / min, hydrogen gas 0 to 53 cm 3 The mixed raw material gas was passed through a SUS reaction tube not filled with a catalyst at a flow rate of (0°C, 0.1013 MPa (absolute)) / min, and gas analysis was performed. The peak positions of each component were confirmed from the obtained GC chart, and the area values ​​between the following RTs (retention times) were recorded, and a calibration curve of GC area values ​​versus gas volume percentage was created: hydrogen: 14.1-21.1 s, nitrogen: 30.0-38.5 s, methane: 73.3-100.0 s, carbon dioxide: 146.4-183.1 s.

[0083] (Methane production reaction 7) Helium gas was introduced into the catalyst ii packed in the SUS reaction tube at 115 cm 3 The temperature was raised to 400°C using an electric tubular furnace while circulating ammonia gas at a flow rate of (0°C, 0.1013 MPa (absolute)) / min. After reaching 400°C, 40 cm3 of ammonia gas was introduced using a gas flow meter. 3(0°C, 0.1013 MPa (absolute)) / min, carbon dioxide gas 15 cm 3 (0°C, 0.1013 MPa (absolute)) / min, helium gas 60 cm 3 The raw material gas was passed through at 0°C and 0.1013 MPa (absolute) per minute (the molar ratio of ammonia to carbon dioxide in the raw material gas was 2.7), and the exhaust gas was analyzed after 1 hour of passing the gas through the reactor, and the resulting GC area values ​​were recorded.

[0084] (Methane production reaction 8) Following methane production reaction 7, ammonia gas was introduced at 40 cm using a gas flow meter. 3 (0°C, 0.1013 MPa (absolute)) / min, carbon dioxide gas 15 cm 3 (0°C, 0.1013 MPa (absolute)) / min, hydrogen gas 7.5 cm 3 (0°C, 0.1013 MPa (absolute)) / min, helium gas 52.5 cm 3 The raw material gas was passed through at 0°C and 0.1013 MPa (absolute) per minute (the molar ratio of ammonia to carbon dioxide in the raw material gas was 2.7), and the exhaust gas was analyzed after 1 hour of passing the gas through the reactor, and the resulting GC area values ​​were recorded.

[0085] (Methane production reaction 9) Following methane production reaction 8, ammonia gas was introduced at 40 cm using a gas flow meter. 3 (0°C, 0.1013 MPa (absolute)) / min, carbon dioxide gas 15 cm 3 (0°C, 0.1013 MPa (absolute)) / min, hydrogen gas 15 cm 3 (0°C, 0.1013 MPa (absolute)) / min, helium gas 45 cm 3 The raw material gas was passed through at 0°C and 0.1013 MPa (absolute) per minute (the molar ratio of ammonia to carbon dioxide in the raw material gas was 2.7), and the exhaust gas was analyzed after 1 hour of passing the gas through the reactor, and the resulting GC area values ​​were recorded.

[0086] (Methane production reaction 10) Following the methane production reaction 9, ammonia gas was introduced at 40 cm using a gas flow meter. 3 (0°C, 0.1013 MPa (absolute)) / min, carbon dioxide gas 15 cm 3 (0°C, 0.1013 MPa (absolute)) / min, hydrogen gas 30 cm 3 (0°C, 0.1013 MPa (absolute)) / min, helium gas 30 cm 3 The raw material gas was passed through at 0°C and 0.1013 MPa (absolute) per minute (the molar ratio of ammonia to carbon dioxide in the raw material gas was 2.7), and the exhaust gas was analyzed after 1 hour of passing the gas through the reactor, and the resulting GC area values ​​were recorded.

[0087] The gas flow rates and nitrogen and methane production rates (%) for methane production reactions 7 to 10 are shown in Table 4. In Table 4, NH3 is ammonia, CO2 is carbon dioxide, H2 is hydrogen, He is helium, N2 is nitrogen, and CH4 is methane.

[0088] The production rates shown in Table 4 were calculated using the following formula. CH4 (%) = CH4 volume % obtained from the calibration curve / CH4 theoretical volume % when all of the introduced CO2 is converted to CH4 × 100 N2 (%) = N2 volume % obtained from the calibration curve / N2 theoretical volume % when all introduced NH3 decomposes into N2 and H2 × 100

[0089] [Table 4]

[0090] As is clear from Table 4, methane can be produced more efficiently when the feed gas contains hydrogen in addition to ammonia and carbon dioxide. The improvement in methane production efficiency due to the feed gas containing hydrogen is particularly effective when the molar ratio of ammonia to carbon dioxide in the feed gas is less than 3.0. In this reaction, methane and hydrogen can be produced from a gas containing ammonia and carbon dioxide in the presence of a catalyst having a support and containing a transition metal. If it is desired to produce mainly methane, the efficiency of methane production can be increased by recycling the produced hydrogen into the feed gas.

[0091] [Manufacturing Example 3] <Methane production from ammonium carbonate ((NH4)2CO3)> (Catalyst Preparation) The catalyst was prepared as described in Production Example 2. The amount of catalyst used in the reaction was 1.6 g, and the reaction was carried out in a quartz glass reaction tube with an inner diameter of 12 mm equipped with a sheath tube with an outer diameter of 3 mm.

[0092] (Preparation of (NH4)2CO3 aqueous solution) The (NH4)2CO3 aqueous solution used in the reaction was prepared using commercially available (NH4)2CO3.

[0093] (Methane production reaction 11) The catalyst packed in the quartz glass reaction tube was heated in an electric tubular furnace with 115 cm of helium gas. 3 The temperature inside the electric furnace was raised to 400°C at a rate of (0°C, 0.1013 MPa (absolute)) / min. After reaching 400°C, a 16.7 mass% (NH4)2CO3 aqueous solution was pumped into the upper part of the reaction tube at a rate of 1 mL / min, and the wool placed at the top was soaked with the solution. In addition, a gas flow meter was used to pump hydrogen gas at 15 cm 3 A flow rate of 0°C, 0.1013 MPa (absolute) was allowed to flow from the top of the reaction tube. The vaporized (NH4)2CO3 component and hydrogen gas merged and were entrained at the top of the reaction tube, and were brought into contact with the catalyst layer (the molar ratio of ammonia to carbon dioxide in the feed gas was 2.0). After 1 hour of flow, the exhaust gas was analyzed, and the resulting GC area values ​​were recorded.

[0094] A methane peak was confirmed on the obtained GC chart, and the methane production rate was confirmed using the same evaluation method as in Production Example 2. The methane production rate was confirmed to be 28.5%. This shows that methane can be produced even if the raw material gas is derived from gas obtained by thermal decomposition of (NH4)2CO3.

Claims

1. The method comprises producing methane from a feed gas containing ammonia, carbon dioxide, and hydrogen in the presence of a catalyst containing a support and a transition metal, A method for producing methane, wherein the molar ratio of hydrogen to carbon dioxide in the raw material gas is 7.5 / 15 or more and 10.0 or less.

2. 2. The method for producing methane according to claim 1, wherein the molar ratio of ammonia to carbon dioxide in the feed gas is 3.0 or more and 5.4 or less.

3. The method for producing methane according to claim 2 , wherein the production of methane involves simultaneously producing hydrogen from the raw material gas.

4. 2. The method for producing methane according to claim 1, wherein the hydrogen contained in the raw material gas is hydrogen that is recovered during the production of methane and recycled into the raw material gas.

5. 4. The method for producing methane according to claim 3, wherein the hydrogen contained in the raw material gas is a recycled hydrogen-containing stream produced in the production of methane.

6. 3. The method for producing methane according to claim 1, wherein the reaction temperature in producing methane is 300°C or higher and 550°C or lower.

7. 3. The method for producing methane according to claim 1, wherein the reaction pressure in producing methane is 0 MPa-G or more and 0.9 MPa-G or less.

8. 3. The method for producing methane according to claim 1, wherein the support is at least one support selected from the group consisting of titania, alumina, silicon carbide, carbon, zirconia, silica, cerium oxide, and niobium oxide.

9. The method for producing methane according to claim 8 , wherein the support has pores with an average pore diameter of 2 nm or more and 100 nm or less.

10. 3. The method for producing methane according to claim 2, wherein the transition metal is ruthenium.

11. 9. The method for producing methane according to claim 8, wherein the transition metal is ruthenium.

12. 3. The method for producing methane according to claim 1 or 2, wherein the methane production is carried out using a reactor, and the reactor is at least one selected from the group consisting of an external heat exchange type fixed bed reactor, an adiabatic fixed bed reactor, a fluidized bed reactor, a simulated moving bed reactor, a riser type fluidized bed reactor, and a radial flow type fixed bed reactor.

13. The method for producing methane according to claim 1 , wherein the raw material gas contains a gas obtained by thermal decomposition of ammonium carbonate.

14. The method for producing methane according to claim 13, wherein the ammonium carbonate is obtained by contacting an aqueous solution containing ammonia with a gas containing carbon dioxide.

15. The method for producing methane according to claim 14, wherein the carbon dioxide-containing gas is air.

16. The method for producing methane according to claim 14, wherein the gas containing carbon dioxide is exhaust gas from a power plant, a factory, a steel mill, a chemical plant, a waste treatment facility, or a biomass facility.

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