Methane production method and methane production apparatus

Abstract

To provide a methane production method that efficiently produces and can reduce cost and a methane production apparatus.SOLUTION: A method for producing methane from carbon dioxide and hydrogen, which includes a methanation process where a mixed gas of carbon dioxide and hydrogen is introduced into a reactor filled with a methanation catalyst, generating non-equilibrium plasma inside the reactor to decompose the mixed gas, thereby producing radicals and enabling the methanation reaction. The methanation catalyst is arranged in a fixed bed catalytic layer housed within the reactor, and in the methanation process, the methanation reaction is caused without supplying heat from outside to the reactor, continuously allowing the methanation reaction to proceed without external heat supply to the reactor.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing methane and a methane production apparatus.

Background Art

[0002] Carbon dioxide is considered to be one of the greenhouse gas factors causing global warming, and technologies for converting carbon dioxide into useful substances are being studied for the realization of a carbon-neutral society. As a technology for converting carbon dioxide into methane, which is a useful substance, a methanation reaction for producing methane from carbon dioxide and hydrogen is known.

[0003] The methanation reaction is generally carried out in the presence of a heated methanation catalyst. Further, in order to optimize the methanation reaction, Non-Patent Document 1 discloses a method using plasma. Non-Patent Document 1 discloses using an electric furnace as an external heating device, and by heating the catalyst, the methanation reaction is initiated.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

[0005] When popularizing the technology for converting carbon dioxide by methanation, it is an issue to reduce the manufacturing cost. The method disclosed in Non-Patent Document 1 is useful in that it can greatly improve the conversion efficiency of carbon dioxide, but there is room for improvement from the viewpoint of further saving the installation cost and operation cost of the methane production apparatus.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a methane production method and a methane production apparatus capable of efficiently producing methane and reducing costs. [Means for Solving the Problems]

[0007] That is, the present invention includes the following aspects. [1] A methane production method for producing methane from carbon dioxide and hydrogen, comprising a methanation step of generating non-equilibrium plasma inside the reactor in a state where a mixed gas of carbon dioxide and hydrogen is introduced into a reactor filled with a methanation catalyst, decomposing the mixed gas to generate radicals, and causing a methanation reaction. The methanation catalyst is disposed in a fixed-bed catalyst layer accommodated in the reactor. In the methanation step, the methanation reaction is caused without supplying heat from the outside to the reactor, and the methanation reaction is continued without supplying heat from the outside to the reactor. [2] The methanation catalyst includes a carrier and a metal catalyst supported on the carrier. The carrier contains an oxide containing one or more elements selected from the group consisting of cerium, zirconium, yttrium, aluminum, silicon, magnesium, potassium, calcium, sodium, and lanthanum. The metal catalyst contains one or more metal elements selected from the group consisting of nickel, ruthenium, rhodium, platinum, palladium, and iridium. The methane production method according to [1]. [3] The methane production method according to [1] or [2], wherein after the methanation reaction starts, generation of the non-equilibrium plasma is stopped. [4] After the methanation reaction starts, based on the temperature inside the reactor or the amount of methane generated, the non-equilibrium plasma is regenerated after stopping the generation of the non-equilibrium plasma. The methane production method according to any one of [1] to [3]. [5] The methane production method according to any one of [1] to [4], wherein the methanation step is carried out in the absence of oxygen. [6] A methane production apparatus for producing methane from carbon dioxide and hydrogen, comprising a reactor filled with a methanation catalyst, a gas supply unit for supplying the carbon dioxide and the hydrogen to the reactor, a gas discharge unit for discharging a reaction gas containing the methane from the reactor, and plasma generation means for generating a non-equilibrium plasma inside the reactor to decompose a mixed gas of the carbon dioxide and the hydrogen to generate radicals. The reactor has a reaction vessel and a fixed-bed catalyst layer accommodated in the reaction vessel and in which the methanation catalyst is disposed, and does not have an external heat source for supplying heat to the reactor from the outside. Methane production apparatus. [7] The methanation catalyst includes a carrier and a metal catalyst supported on the carrier. The methanation catalyst includes a carrier and a metal catalyst supported on the carrier. The carrier contains an oxide containing one or more elements selected from the group consisting of cerium, zirconium, yttrium, aluminum, silicon, magnesium, potassium, calcium, sodium, and lanthanum. The metal catalyst contains one or more metal elements selected from the group consisting of nickel, ruthenium, rhodium, platinum, palladium, and iridium. The methane production apparatus according to [6]. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a methane production method and a methane production apparatus capable of efficiently producing methane and reducing costs. [Brief Description of the Drawings]

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0010] <Methane Production Method and Methane Production Apparatus> The present invention is a methane production method for producing methane from carbon dioxide and hydrogen. FIG. 1 is a schematic diagram of an example of the methane production apparatus of the present invention. The methane production apparatus 1 shown in FIG. 1 includes a reactor 10 filled with a methanation catalyst. The methane production apparatus 1 includes a gas supply unit L1 that supplies carbon dioxide and hydrogen to the reactor 10, a gas discharge unit L2 that discharges a reaction gas containing methane from the reactor 10, and plasma generation means 13 that generates non-equilibrium plasma inside the reactor 10. The plasma generation means 13 includes a first electrode 13a and a second electrode 13b. The reactor 10 has a reaction vessel 11 made of a dielectric as a forming material, and a fixed bed catalyst layer 12 that is housed in the reaction vessel 11 and in which a methanation catalyst is disposed. The production apparatus 1 does not have an external heat source that supplies heat to the reactor 10 from the outside.

[0011] As an optional configuration, the methane production apparatus 1 may include water removal means 14, a power supply that supplies a high voltage to the first electrode 13a and the second electrode 13b, electric wires, an earth ground, a detection unit 16 that detects components in the reaction gas containing methane, control means 17 that controls on / off of the plasma generation means 13 according to the amount of methane, and temperature detection means 18 that detects the temperature of the fixed bed catalyst layer 12.

[0012] The water removal means 14 includes, for example, a cooling separation means and a solid adsorption means. The cooling separation means is a means for cooling the reaction gas containing methane to a temperature below the dew point temperature of water and removing the generated water droplets. The solid adsorption means is a means for adsorbing water onto a solid adsorbent such as silica gel.

[0013] In the methanation step, with a mixed gas of carbon dioxide and hydrogen introduced into the reactor 10, non-equilibrium plasma is generated inside the reactor 10 to decompose the mixed gas to generate radicals, causing a methanation reaction to convert carbon dioxide to methane. A reaction gas containing methane is discharged from the reactor 10 by the methanation step.

[0014] In non-equilibrium plasma, the electron temperature is much higher than the ion temperature, and some electrons have very high energy. Therefore, using the high energy of the electrons, a large amount of active species (radicals) are generated. Also, heat is generated by the non-equilibrium plasma.

[0015] When non-equilibrium plasma is generated inside the reactor 10 with a mixed gas of carbon dioxide and hydrogen introduced into the reactor 10, vibrationally excited CO2 and H2, H2 + , CO2 + and other ions, atomic hydrogen, atomic oxygen and other radicals are generated in large quantities, and the heat and radicals generated by the non-equilibrium plasma activate the catalyst, and the methanation reaction starts in the mixed gas when the catalyst temperature exceeds about 200°C.

[0016] The production apparatus 1 does not have an external heat source for supplying heat to the reactor 10 from the outside. That is, the methanation step causes a methanation reaction without supplying heat to the reactor 10 from the outside and continues the methanation reaction without supplying heat to the reactor 10 from the outside. Thus, "automethanation" is defined as causing a methanation reaction without externally supplying heat to the reactor and continuing the methanation reaction without externally supplying heat to the reactor. When referring to the "methanation reaction", it means the reaction represented by "CO2 + 4H2 → CH4 + 2H2O".

[0017] In this embodiment, when oxygen is present, it reacts with the hydrogen in the raw material and is converted into water. Furthermore, when water is present, the suppression of the methanation reaction is inhibited. Therefore, the automethanation step is preferably carried out in the absence of oxygen.

[0018] When referring to "mixed gas" in this specification, it means a mixed gas of carbon dioxide and hydrogen and also means the raw material gas for the methane production method of the present invention. The mixed gas may be a mixed gas composed of carbon dioxide and hydrogen, or may contain components other than carbon dioxide and hydrogen. For example, when using exhaust gas discharged from a power plant, factory, etc. as a carbon dioxide source, it may contain components other than carbon dioxide and hydrogen as long as it does not become a catalyst poison. Also, a mixed gas of biogas and hydrogen may be used as the mixed gas. Biogas mainly consists of CH4 and CO2 and originally contains CH4. However, since the added value as a fuel increases by converting CO2 in biogas into CH4, it is frequently used as a raw material for methanation.

[0019] An example of the methanation reaction by automethanation is as follows: When the mixed gas is introduced into the reactor and radicals generated by the decomposition of heat and the mixed gas by non-equilibrium plasma act, the methanation reaction starts when the temperature in the reactor reaches about 200°C. Due to the reaction heat generated by the methanation reaction, the temperature in the reactor rises without external heating and the methanation reaction continues. When it exceeds about 250°C, the conversion rate of carbon dioxide becomes a value approximately close to the thermal equilibrium.

[0020] Generally, for the methanation reaction using a methanation catalyst, heating at about 300°C to 400°C is required to initiate the reaction, and the reaction temperature is in a high temperature range of 300°C or higher. The heating for initiating the reaction is usually carried out by supplying heat from an external heat source. In contrast, in the present invention, an external heat source for initiating the reaction is not required, and methane can be produced in a low temperature range of less than 300°C with the reaction temperature of the methanation reaction being around about 250°C.

[0021] In auto-methanation, since the reaction is continued by the reaction heat generated by the exothermic methanation reaction, the methanation reaction continues as long as the introduction of the mixed gas is continued. When the introduction of the mixed gas is stopped, the auto-methanation stops after all the carbon dioxide in the mixed gas has been converted to methane. For the methanation reaction, since four times the amount of hydrogen of carbon dioxide is required, the auto-methanation can also be stopped by reducing the gas amount of hydrogen in the mixed gas to a ratio less than four times the gas amount of carbon dioxide, or by increasing the amount of carbon dioxide.

[0022] The flow rate of the mixed gas may be appropriately adjusted according to the size and number of the reactors 10.

[0023] In the methane production method of the present embodiment, when the temperature of the reactor 10 rises rapidly, it is determined that the methanation reaction has started. After the start of the methanation reaction is confirmed, the generation of non-equilibrium plasma may be stopped at an arbitrary timing. After the start of the methanation reaction and after the generation of non-equilibrium plasma is stopped, non-equilibrium plasma may be generated again. For example, when the temperature of the reactor 10 continues to decrease after the stop of the non-equilibrium plasma, the auto-methanation proceeds by generating non-equilibrium plasma again.

[0024] The temperature of the reactor 10 may be measured, for example, by directly measuring the temperature inside the reactor 10 using a thermocouple, or by measuring the internal temperature from the outside of the reactor 10 using an infrared thermal imaging camera.

[0025] As one aspect of the present invention, when a metal catalyst (for example, one or more selected from the group consisting of ruthenium, rhodium, and platinum) is used, an efficient methanation reaction is likely to be maintained by the heat of reaction generated after the start of the methanation reaction. Therefore, after the start of the methanation reaction is confirmed, even if the generation of non-equilibrium plasma is stopped, the methanation reaction may proceed in the reactor 10 at room temperature.

[0026] The calculation of the component composition in the reactor at the thermal equilibrium state can be calculated using the method of minimizing the Gibbs free energy. The conversion rate of carbon dioxide is calculated by the following formula. Carbon dioxide conversion rate (%) = [amount of carbon dioxide in the mixed gas (mol) - amount of carbon dioxide in the generated gas (mol)] / amount of carbon dioxide in the mixed gas (mol) × 100

[0027] According to the method for producing methane by auto-methanation, since an external heat source for starting the methanation reaction is not required, methane can be produced without using a separate heating device or cooling device, and the installation cost of the methane production device can be significantly reduced. In addition, since auto-methanation proceeds with the heat of reaction by the methanation reaction, it is not necessary to separately provide energy for continuing the reaction, and the operating cost can be significantly reduced.

[0028] When renewable energy such as solar power generation or wind power generation is used as the power required to generate plasma, the use of renewable energy can be further expanded, and it can further contribute to the reduction of CO2 emissions.

[0029] When the supply amounts of carbon dioxide and hydrogen are small, or even when these supply amounts fluctuate, this method can generate methane from carbon dioxide in the required amount at the required time using a simple device and electrical energy (that is, plasma). Therefore, it can be applied as a methane production device corresponding to small-scale dispersion and load fluctuations. The scale of the methane production device of the present invention is not particularly limited, but the scale can also be expanded by connecting small-scale distributed methane production devices in parallel. Therefore, the length of the fixed-bed catalyst layer 12 provided in the reactor 10 (the length indicated by the symbol S1 in FIG. 1) is, for example, 1 cm or more and 50 cm or less, or 1 cm or more and 20 cm or less. Also, the diameter of the reactor (inner diameter of the glass tube) can be set between 2 cm and 10 cm.

[0030] From the viewpoint that the reaction vessel 11 provided in the reactor 10 is made of a dielectric for the plasma generation means described later, it is preferable to use ceramics such as glass or alumina as the material.

[0031] The methane production apparatus 1 preferably includes temperature detection means 18 for detecting the temperature of the fixed-bed catalyst layer. The temperature detection means 18 is not particularly limited, and a thermocouple, an infrared thermal imaging camera, or the like can be used.

[0032] By detecting the temperature of the fixed-bed catalyst layer 12 with the temperature detection means 18, it is possible to monitor the state of the methanation reaction, such as the start of the methanation reaction and whether or not the thermal equilibrium state has been reached.

[0033] The fixed-bed catalyst layer 12 includes a catalyst. The catalyst includes a carrier and a metal catalyst supported on the carrier. The carrier preferably contains an oxide containing one or more elements selected from the group consisting of cerium, zirconium, yttrium, aluminum, silicon, magnesium, potassium, calcium, sodium, and lanthanum. The carrier is more preferably one or more selected from the group consisting of cerium oxide (CeO2), zirconium oxide (ZrO2), yttrium oxide (Y2O3), aluminum oxide (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), calcium oxide (CaO), sodium oxide (Na2O), and lanthanum(III) oxide (La2O3).

[0034] From the viewpoint of facilitating the generation of non-equilibrium plasma, the carrier is preferably a material having no electrical conductivity, and more preferably one or more selected from the group consisting of silicon oxide, aluminum oxide, and magnesium oxide which are silicon oxides.

[0035] The metal catalyst is more preferably one or more metal elements selected from the group consisting of nickel, ruthenium, rhodium, platinum, palladium, and iridium, and nickel or ruthenium is even more preferable.

[0036] The content of the metal catalyst contained in the catalyst is not particularly limited. For example, it is 0.5% by mass or more and 20% by mass or less based on the mass of the carrier. The total amount of the catalyst contained in the fixed-bed catalyst layer 12 may be appropriately adjusted according to the size of the reactor.

[0037] The fixed-bed catalyst layer 12 has voids through which the mixed gas can pass. The fixed-bed catalyst layer 12 may be formed by filling pellet-shaped catalysts, or may be formed by supporting a metal catalyst on a carrier formed into a three-dimensional shape through which the mixed gas can pass. The size of the catalyst may be appropriately adjusted according to the shape of the pellet or the like. The carrier formed into a three-dimensional shape through which the mixed gas can pass is, for example, a porous carrier.

[0038] As for the configuration of the catalyst layer, for example, although a fluidized-bed catalyst layer has the merit that the reaction easily proceeds uniformly, it is necessary to ensure appropriate fluidization of the powder catalyst, and the setting conditions of the flow rate of the mixed gas are extremely limited. For example, the flow rate of the mixed gas for ensuring the fluidization of the powder catalyst may be different from the flow rate of the mixed gas for realizing auto-methanation. In addition, the methanation reaction (CO2 + 4H2 → CH4 + 2H2O) is a reaction in which 5 moles of gas is reduced to 3 moles. Even if the gas flow rate is sufficient near the inlet of the reactor, the gas flow rate decreases to about 60% near the outlet of the reactor. In the methanation reaction with a large volume change of gas, it becomes difficult for the powder catalyst to flow. For this reason, it may be difficult to achieve both ensuring the fluidization of the powder and auto-methanation. On the other hand, in the fixed-bed catalyst layer, there is no need to consider the fluidization of the powder, and conditions such as the flow rate of the mixed gas and the filling amount of the catalyst for realizing auto-methanation can be set with a high degree of freedom. Therefore, it can also cope with the scale of the reactor and load fluctuations.

[0039] The plasma generation means 13 includes a pair of electrodes (the first electrode 13a and the second electrode 13b). In the methane production apparatus 1, the reaction vessel 11 is made of a dielectric. When a high voltage is applied to the first electrode 13a and the second electrode 13b, non-equilibrium plasma is generated by dielectric barrier discharge so as to cover the surface of the catalyst pellets arranged between the first electrode 13a and the second electrode 13b. The second electrode 13b is preferably provided on the outer periphery of the reaction vessel 11. The plasma generation means 13 is not limited to dielectric barrier discharge as long as non-equilibrium plasma and a catalyst can be combined, and may be changed to other means.

[0040] The pair of electrodes is arranged, for example, parallel to the flow direction of the mixed gas. The distance between the first electrode 21 and the second electrode 23 is not particularly limited, and is, for example, 0.5 mm or more and 10 cm or less. The voltage applied to the first electrode 13a and the second electrode 13b is, for example, 5 kV or more and 20 kV or less. The pressure of the plasma generation field is, for example, 500 hPa or more and 2000 hPa or less. The temperature of the plasma generation field is maintained at room temperature (for example, 15 °C or more and 30 °C or less) that does not exceed the outside air temperature. In order to be a dielectric, the reaction vessel 11 is preferably made of ceramics such as quartz glass, soda glass, and alumina.

[0041] Figure 2 is a schematic diagram of an example of the methane production apparatus of the present invention. The methane production apparatus 2 shown in FIG. 2 includes a reactor 20 filled with a methanation catalyst. The methane production apparatus 2 includes a gas supply unit 25 that supplies carbon dioxide and hydrogen to the reactor 20, a gas discharge unit L12 that discharges a reaction gas containing methane from the reactor 20, and plasma generation means 23 that generates non-equilibrium plasma inside the reactor 20. The plasma generation means 23 includes a first electrode 23a and a second electrode 23b. The reactor 20 has a reaction vessel 20 made of a dielectric as a forming material, and a fixed bed catalyst layer 22 that is housed in the reaction vessel 21 and in which a methanation catalyst is disposed. The production apparatus 2 does not have an external heat source that supplies heat to the reactor 20 from the outside.

[0042] As an optional configuration, the methane production apparatus 2 may include water removal means 24, a power supply that supplies a high voltage to the first electrode 23a and the second electrode 23b, electric wires, an earth ground, a detection unit 26 that detects components in the reaction gas containing methane, control means 27 that controls on / off of the plasma generation means 23 according to the amount of methane, and temperature detection means 28 that detects the temperature of the fixed bed catalyst layer 22.

[0043] The bottom of the reaction vessel 21 is closed, and a gas supply pipe 25 is disposed inside the reaction vessel 21. The bottom of the gas supply pipe 25 is open, and a fixed bed catalyst layer 22 is formed between the reaction vessel 21 and the gas supply pipe 25. The fixed bed catalyst layer 22 is preferably formed in a posture in which the filling portion is directed in the vertical direction by filling, for example, a pellet-type catalyst. The reaction vessel 21 has a pipe upper wall 21a on the upper end side, and the gas supply pipe 25 is supported by the pipe upper wall 21a in a state of penetrating the pipe upper wall 21a.

[0044] The gas supply pipe 25 is a pipe for introducing the mixed gas into the reaction vessel 21. The mixed gas introduced by the gas supply pipe 25 is discharged from the lower part of the gas supply pipe 25, and the mixed gas is introduced into the inside of the fixed bed catalyst layer 22. When the mixed gas is introduced into the inside of the fixed bed catalyst layer 22 to generate non-equilibrium plasma, the methanation reaction starts by the action of the catalyst. Then, the methanation reaction continues in the reactor 20 at room temperature, and the gas containing the produced methane and water flows upward in the reaction vessel 21 and is discharged from the gas discharge pipe L12 provided above the reaction vessel 21.

[0045] The length of the fixed bed catalyst layer 22 provided in the reactor 20 (the length indicated by the symbol S2 in FIG. 2) is, for example, 1 cm or more and 100 cm or less, 1 cm or more and 50 cm or less. The outer diameter of the fixed bed catalyst layer 22 may be appropriately adjusted according to the size of the reactor.

[0046] The plasma generation means 23 includes a pair of electrodes (the first electrode 23a and the second electrode 23b). In the methane production apparatus 2, the reaction vessel 21 is made of a dielectric, and the gas supply pipe 25 also serves as the first electrode 23a. The gas supply pipe 25 is, for example, a metal pipe. When a high voltage is applied to the first electrode 23a and the second electrode 23b, non-equilibrium plasma by dielectric barrier discharge is generated so as to cover the surface of the pellets. The second electrode 23b is preferably provided on the outer periphery of the reaction vessel 21.

[0047] For the methane production apparatus 2, the description other than the above-described features is the same as that of the methane production apparatus 1.

Example

[0048] The present invention will be described in more detail with reference to examples.

[0049] <Example 1> The methane production apparatus 2 having the configuration shown in FIG. 2 was used. A reaction vessel 21 made of glass with a diameter of 30 mm and a height of 60 mm was used. As the catalyst, Ru / Al2O3 (manufactured by N.E. Chemcat Corporation) containing 2% by mass of ruthenium was used. The reactor 20 not equipped with a heating device or a cooling device was maintained at 25° C., and the inside of the reactor 20 was maintained at 200 hPa to 1000 hPa.

[0050] To measure the temperature of the fixed-bed catalyst layer, an infrared thermal imaging camera (manufactured by NEC San-ei Co., Ltd., product name: TH5104) was used. The amount of carbon dioxide in the product gas discharged from the gas discharge pipe L12 was measured, and the conversion rate of carbon dioxide was measured by the following formula. Carbon dioxide conversion rate (%) = [amount of carbon dioxide in the mixed gas (mol) - amount of carbon dioxide in the product gas (mol)] / amount of carbon dioxide in the mixed gas (mol) × 100

[0051] As the mixed gas as the raw material gas, a mixed gas of carbon dioxide and hydrogen (carbon dioxide: hydrogen = 1:4) was introduced into the reaction vessel 21 at a flow rate of 1500 cm 3 / min (converted at 25° C. and 1013 hPa), while applying a high voltage of 5 to 20 kV to the first electrode 23a and the second electrode 23b to generate non-equilibrium plasma by dielectric barrier discharge.

[0052] Simultaneously with the supply of the mixed gas and the generation of non-equilibrium plasma, the temperature measurement of the fixed-bed catalyst layer was started, and the maximum temperature of the fixed-bed catalyst layer and the carbon dioxide conversion rate were measured. FIG. 3 shows a graph with the temperature of the fixed-bed catalyst layer on the horizontal axis and the carbon dioxide conversion rate on the vertical axis.

[0053] <Example 2> Methane was produced in the same manner as in Example 1 except that the flow rate of the mixed gas was changed to 3000 cm 3 / min. Although a temperature distribution occurs in the fixed-bed catalyst layer, FIG. 3 shows a graph with the maximum temperature therein on the horizontal axis and the carbon dioxide conversion rate on the vertical axis.

[0054] <Example 3> The flow rate of the mixed gas was 5000 cm3 Methane was produced in the same manner as in Example 1 except that it was changed to / min. Fig. 3 shows a graph with the temperature of the fixed-bed catalyst layer on the horizontal axis and the carbon dioxide conversion rate on the vertical axis.

[0055] <Comparative Example 1> Without using the plasma generation means 23, with the reaction vessel 21 heated from the outside, methane was produced in the same manner as in Example 1 except that the flow rate of the mixed gas was introduced at 3000 cm 3 / min. Fig. 3 shows a graph with the maximum temperature of the fixed-bed catalyst layer on the horizontal axis and the carbon dioxide conversion rate on the vertical axis.

[0056] From Fig. 3, it was confirmed that in Examples 1 to 3, heat and radicals were simultaneously supplied into the reactor 20 by dielectric barrier discharge, the temperature of the catalyst layer increased from room temperature, and when it reached about 200 °C, the methanation reaction started. Since the methanation reaction is an exothermic reaction, the methanation reaction was further accelerated by the reaction heat, and the temperature of the catalyst increased to about 300 °C.

[0057] In Examples 1 to 2, when the temperature exceeded 250 °C, the conversion rate of carbon dioxide became a value approximately close to the thermal equilibrium. It was confirmed that even if the dielectric barrier discharge was stopped in this state, if the supply of the mixed gas was continued, the methanation reaction continued at room temperature and auto-methanation could be realized.

[0058] On the other hand, in Comparative Example 1, the start of the methanation reaction was observed from around 300 °C.

[0059] Focusing on the carbon dioxide conversion rate around 250 °C, it was confirmed that in Comparative Example 1 it was about 5%, while in Example 1 it was about 75%, in Example 2 it was about 65%, and in Example 3 it was about 35%. The carbon dioxide conversion rate of Examples 1 to 3 was significantly improved compared to Comparative Example 1.

[0060] <Example 4> The catalyst was prepared by the following method. To an aqueous solution of Ni(NO3)3, 10 equivalents of urea relative to Ni was added and dissolved, and a mixture was obtained by adding Al2O3. The obtained mixture was heated to 90 °C and stirred for 5 hours. The solid obtained after stirring was filtered, washed, and dried, and then reduced at 600 °C for 1 hour under a hydrogen stream to obtain Ni / Al2O3 containing 6% by mass of nickel.

[0061] Using Ni / Al2O3 as a catalyst, methane was produced in the same manner as in Example 1 except that the flow rate of the mixed gas was changed to 500 cm 3 / min. A graph showing the maximum temperature of the fixed-bed catalyst layer on the horizontal axis and the carbon dioxide conversion rate on the vertical axis is shown in Fig. 4.

[0062] From Fig. 4, it was confirmed that heat and radicals were simultaneously supplied into the reactor 20 by dielectric barrier discharge, the temperature of the catalyst layer increased from room temperature, and the methanation reaction started when it reached about 170 °C. Due to the exotherm of methanation, the catalyst temperature increased, and the conversion rate of carbon dioxide reached about 40% at 250 °C.

[0063] <Comparative Example 2> Using Ni / Al2O3 as a catalyst, methane was produced in the same manner as in Comparative Example 1 except that the flow rate of the mixed gas was changed to 500 cm 3 / min. A graph showing the maximum temperature of the fixed-bed catalyst layer on the horizontal axis and the carbon dioxide conversion rate on the vertical axis is shown in Fig. 4.

[0064] For Example 4 and Comparative Example 2, the methane selectivity was measured by the following formula. Methane selectivity (%) = [amount of methane (mol) contained in the product gas] / [amount of methane (mol) contained in the product gas + amount of carbon monoxide (mol) contained in the product gas] × 100

[0065] For Example 4 and Comparative Example 2, a graph showing the maximum temperature of the fixed-bed catalyst layer on the horizontal axis and the methane selectivity on the vertical axis is shown in Fig. 5.

[0066] In Example 4, the conversion rate of carbon dioxide was approximately 40% at 250°C, while in Comparative Example 2, it was 5%. Example 4 had a carbon dioxide conversion rate approximately eight times that of Comparative Example 2, which utilized a thermal reaction.

Explanation of Reference Signs

[0067] 1, 2: Methane production apparatus, 10, 20: Reactors, 11, 21: Reaction vessels, 12, 22: Fixed-bed catalyst layers, 13, 23: Plasma generation means, L1, 25: Gas supply sections, L2, L12: Gas discharge sections

Claims

1. A methane production method for producing methane from carbon dioxide and hydrogen, comprising: a methanation step in which a mixed gas of carbon dioxide and hydrogen is introduced into a reactor filled with a methanation catalyst, and non-equilibrium plasma is generated inside the reactor to decompose the mixed gas to generate radicals and cause a methanation reaction; the methanation catalyst is disposed in a fixed-bed catalyst layer housed in the reactor; In the methanation step, the methanation reaction is caused to occur at room temperature without externally supplying heat to the reactor, and after the methanation reaction starts, generation of the non-equilibrium plasma is stopped and the methanation reaction is continued without externally supplying heat to the reactor.

2. A method for producing methane from carbon dioxide and hydrogen, comprising: a methanation step in which a mixed gas of carbon dioxide and hydrogen is introduced into a reactor filled with a methanation catalyst, and non-equilibrium plasma is generated inside the reactor to decompose the mixed gas to generate radicals and cause a methanation reaction; the methanation catalyst is disposed in a fixed-bed catalyst layer housed in the reactor; In the methanation step, the methanation reaction is caused to occur at room temperature without externally supplying heat to the reactor, and the generation of the non-equilibrium plasma is stopped after the methanation reaction starts, and the non-equilibrium plasma is generated again based on the internal temperature of the reactor or the amount of methane generated, and continuing the methanation reaction without supplying heat to the reactor from the outside.

3. 3. The method for producing methane according to claim 1 or 2, wherein the methanation catalyst comprises a support and a metal catalyst supported on the support, the support containing an oxide containing one or more elements selected from the group consisting of cerium, zirconium, yttrium, aluminum, silicon, magnesium, potassium, calcium, sodium, and lanthanum, and the metal catalyst containing one or more metal elements selected from the group consisting of nickel, ruthenium, rhodium, platinum, palladium, and iridium.

4. 3. The method for producing methane according to claim 1, wherein the methanation step is carried out in the absence of oxygen.

5. A methane production apparatus for producing methane from carbon dioxide and hydrogen, a reactor packed with a methanation catalyst; a gas supply unit that supplies the carbon dioxide and the hydrogen to the reactor; a gas discharge section that discharges the reaction gas containing methane from the reactor; a plasma generating means for generating non-equilibrium plasma inside the reactor and decomposing the mixed gas of carbon dioxide and hydrogen to generate radicals, the reactor includes a reaction vessel and a fixed-bed catalyst layer housed in the reaction vessel and having the methanation catalyst disposed therein, and does not include an external heat source for supplying heat to the reactor from the outside; A methane production apparatus comprising a measuring means for measuring the temperature inside the reactor.

6. the methanation catalyst includes a support and a metal catalyst supported on the support; 6. The methane production apparatus according to claim 5, wherein the methanation catalyst comprises a carrier and a metal catalyst supported on the carrier, the carrier containing an oxide containing one or more elements selected from the group consisting of cerium, zirconium, yttrium, aluminum, silicon, magnesium, and potassium, calcium, sodium, and lanthanum, and the metal catalyst containing one or more metal elements selected from the group consisting of nickel, ruthenium, rhodium, platinum, palladium, and iridium.

Images