JP2020110769A - Carbon dioxide occlusion reduction catalyst and methane production system - Google Patents

Abstract

To provide a carbon dioxide occlusion reduction catalyst that can be used repeatedly, and in which, by using said catalyst, the heat generated during occlusion and desorption of carbon dioxide is efficiently utilized.SOLUTION: The carbon dioxide occlusion reduction catalyst can occlude carbon dioxide and includes a calcium oxide that desorbs occluded carbon dioxide by a supply of hydrogen, a sintering suppressing material that suppresses sintering of calcium oxide, and a methanation catalyst that promotes methane formation from carbon dioxide and hydrogen, and among the volume of calcium oxide and sintering suppressing material, the volume ratio occupied by sintering suppressing material is less than 75 percent.SELECTED DRAWING: Figure 4

Description

The present invention relates to a carbon dioxide storage reduction catalyst and a methane production system.

A material (carbon dioxide storage reduction catalyst) containing calcium oxide is known as a catalyst for separating and recovering carbon dioxide contained in combustion gas, and producing (methane) from separated carbon dioxide and hydrogen. (For example, see Non-Patent Document 1). Non-Patent Document 1 discloses a material in which 10% by mass (wt%) of calcium oxide is supported on alumina and 5 wt% of ruthenium which is a methanation catalyst is added. By occluding carbon dioxide in this material in an environment of 320 degrees Celsius (° C.) and then supplying hydrogen, the occluded carbon dioxide can be methanated.

Further, there is known a technique capable of repeatedly performing absorption and desorption of carbon dioxide by adding a sintering suppressing material (also referred to as “sinter preventing material”) to calcium oxide for separating and recovering carbon dioxide. (See, for example, Non-Patent Documents 2 to 10). Non-Patent Documents 2 to 10 disclose the use of magnesia, alumina, silica, titania, lanthanum oxide, ceria, zirconia, yttrium, etc. as a sintering inhibitor.

Melis S. Duyar et al, Dual function materials for CO2 capture and conversion using renewable H2, Applied Catalysis B: Environmental 168-169 (2015) 370-376, Internet (URL: HYPERLINK "http://www.elsevier.com/ locate/apcatb" www.elsevier.com/locate/apcatb) Rainer Filitz, Agnieszka M. Kierzkowska, Marcin Broda, and Christoph R. Muller, Highly Efficient CO2 Sorbents: Development of Synthetic, Calcium-Rich Dolomites, Environ.Sci. Technol., 2012, 46 (1), pp 559-565. Marcin Broda Christoph R. Mulle, Synthesis of Highly Efficient, Ca‐Based, Al2O3-Stabilized, Carbon Gel‐Templated CO2 Sorbents, Volume24, Issue22, June 12, 2012, Pages 3059-3064 J. M. Valverde, A. Perejon, and L. A. Perez-Maqueda, Enhancement of Fast CO2 Capture by a Nano-SiO2/CaO Composite at Ca-Looping Conditions, Environ. Sci. Technol. 2012, 46, 11, 6401-6408 Masahiko Aihara, Keiko Tanaka, Mayuka Watanabe, Takashi Takeuchi, Hitoshi Habuka, Carbonation/Decarbonation of Ca-Solid Reactant Derived from Natural Limestone for Thermal-Energy Storage and Temperature Upgradem, Materials for Thermal Energy Conversion and Storage, 2007,40, 1270- 1274 Cong Luo, Ying Zheng, Ning Ding, Qilong Wu, Guan Bian, and Chuguang Zheng, Development and Performance of CaO/La2O3 Sorbents during Calcium Looping Cycles for CO2 Capture, nd. Eng. Chem. Res., 2010, 49 (22) , pp 11778-11784 Shengping Wang, Shasha Fan, Lijing Fan, Yujun Zhao, and Xinbin Ma, Effect of Cerium Oxide Doping on the Performance of CaO-Based Sorbents during Calcium Looping Cycles, Environ.Sci. Technol., 2015, 49 (8), pp 5021 -5027 Hongxia Guo, Shengping Wang, Chun Li, Yujun Zhao, Qi Sun, and Xinbin Ma, Incorporation of Zr into Calcium Oxide for CO2 Capture by a Simple and Facile Sol-Gel Method, Ind. Eng. Chem. Res., 2016, 55 (29), pp 7873-7879 Kwang Bok Yi, Chang Hyun Ko, Jong-Ho Park, Jong-Nam Kim, Improvement of the cyclic stability of high temperature CO2 absorbent by the addition of oxygen vacancy possessing material, Catalysis Today 146 (2009), Pages 241-247 Maryam Sayyah, Emadoddin Abbasi, Yongqi Lu, Javad Abbasian, and Kenneth S. Suslick, Composite CaO-Based CO2 Sorbents Synthesized by Ultrasonic Spray Pyrolysis: Experimental Results and Modeling, Energy Fuels 2015, 29, 7, 4447-4452

The materials described in Non-Patent Documents 1 to 10 occlude carbon dioxide and desorb the occluded carbon dioxide. Such materials generate heat when occluding carbon dioxide and absorb heat when desorbing carbon dioxide. Further, when such a material is repeatedly used, it is necessary to consider the proportion of the sintering inhibitor added.

The present invention has been made to solve the above-mentioned problems, and can be repeatedly used, and a carbon dioxide occlusion reduction catalyst and methane that efficiently utilize heat generated during occlusion and desorption of carbon dioxide. The purpose is to provide a manufacturing system.

The present invention has been made to solve the above problems, and can be realized as the following modes.

(1) According to one aspect of the present invention, a carbon dioxide storage reduction catalyst is provided. The carbon dioxide storage reduction catalyst is capable of storing carbon dioxide, calcium oxide that desorbs carbon dioxide stored by the supply of hydrogen, and a sintering inhibitor that suppresses the sintering of the calcium oxide, carbon dioxide and And a methanation catalyst that promotes the production of methane from hydrogen. The volume ratio of the sintering inhibitor to the volume of the calcium oxide and the sintering inhibitor is less than 75 percent.

The carbon dioxide storage reduction catalyst performs an exothermic reaction when the carbon dioxide is stored by the calcium oxide and an endothermic reaction when the stored carbon dioxide is desorbed. The methanation reaction that produces methane from hydrogen and carbon dioxide is an exothermic reaction. When hydrogen is supplied to calcium oxide which stores carbon dioxide, the calcium oxide desorbs carbon dioxide. The desorbed carbon dioxide is converted to methane by the methanation reaction. At this time, the heat generated by the heat of the methanation reaction is used for the endothermic reaction when calcium oxide desorbs carbon dioxide. Therefore, calcium oxide functions as a heat storage material that absorbs heat when desorbing carbon dioxide and generates heat when storing carbon dioxide. Since the carbon dioxide storage reduction catalyst contains the sintering inhibitor, calcium oxide can repeatedly perform storage and desorption of carbon dioxide. As the proportion of the sintering inhibitor increases, the number of times it can be used repeatedly increases, but the heat capacity of the carbon dioxide storage reduction catalyst per calcium oxide increases. That is, as the proportion of the sintering inhibiting material increases, the temperature raising function of the carbon dioxide storage reduction catalyst as a heat storage material decreases. According to this structure, the volume ratio of the sintering preventing material in the volume of the calcium oxide sintering suppressing material is less than 75%. Therefore, it is possible to repeatedly use the carbon dioxide storage reduction catalyst after making the heat capacity of the carbon dioxide storage reduction catalyst smaller than the conventional one to improve the temperature raising function as the heat storage material.

(2) In the carbon dioxide occlusion reduction catalyst according to the above aspect, the sintering inhibitor includes an oxide containing at least one element selected from magnesium, aluminum, silicon, titanium, lanthanum, cerium, zirconium, and yttrium. You can leave.

(3) In the carbon dioxide occluding and reducing catalyst of the above aspect, the sintering suppressing material contains an oxide of any one of magnesium, cerium, and zirconium, or two kinds of magnesium, cerium, zirconium, and calcium. It may contain a complex oxide containing the above elements.

(4) According to another aspect of the present invention, a methane production system is provided. This methane production system includes a reaction tube having the carbon dioxide storage reduction catalyst of the above-described embodiment, a gas supply section for supplying a gas containing carbon dioxide to the reaction tube, and a hydrogen supply section for supplying hydrogen to the reaction tube, The control unit controls the amount of gas supplied from the gas supply unit to the reaction tube and the amount of hydrogen supplied from the hydrogen supply unit to the reaction tube.
According to this configuration, the calcium oxide contained in the carbon dioxide storage reduction catalyst stores the carbon dioxide supplied from the gas supply unit, and when hydrogen is supplied from the hydrogen supply unit after storage, the stored carbon dioxide. To detach. Methane is produced by the methanation reaction of the desorbed carbon dioxide and the supplied hydrogen. At this time, the heat generated by the heat of the methanation reaction is used for the endothermic reaction when calcium oxide desorbs carbon dioxide. According to this structure, the volume ratio of the sintering inhibiting material in the volume of the calcium oxide and the sintering suppressing material is less than 75%. Therefore, the heat capacity of the carbon dioxide occlusion reduction catalyst can be made smaller than before to improve the temperature rise range during occlusion, and the carbon dioxide occlusion reduction catalyst can be repeatedly used by fully exhibiting the function of the sintering inhibitor. ..

The present invention can be realized in various modes, for example, a carbon dioxide occlusion reduction catalyst, a carbon dioxide separation and recovery material, a chemical heat storage material, a methane production system, a chemical heat storage system, and carbon dioxide separation. The present invention can be implemented in the form of a collection method, a computer program for executing these devices and methods, a server device for distributing this computer program, a non-transitory storage medium storing the computer program, and the like.

It is a block diagram of the methane manufacturing system in an embodiment. It is a flowchart of methane production. It is explanatory drawing which compares the heat capacity of the storage reduction catalyst of an Example, and the heat capacity of the storage reduction catalyst of a comparative example. It is explanatory drawing of the temperature rise width of the storage reduction catalyst. It is explanatory drawing of the temperature rise width of the storage reduction catalyst of a modification. It is explanatory drawing of the temperature rise width of the storage reduction catalyst of a modification. It is a graph which shows the change of the improvement index value of the temperature rise width of the storage reduction catalyst.

<Embodiment>
FIG. 1 is a block diagram of a methane production system 100 according to the embodiment. The methane production system 100 produces methane as a fuel based on carbon dioxide contained in the combustion gas of the combustion device. Further, the methane production system 100 supplies the reaction heat generated until the carbon dioxide is extracted from the combustion gas to generate methane to the other device 50.

As shown in FIG. 1, the methane production system 100 reacts a combustion gas containing carbon dioxide with a reaction tube 10 having a carbon dioxide storage reduction catalyst 11 (hereinafter also simply referred to as “storage reduction catalyst 11”) inside. A combustion device 20 for supplying to the tube 10, a hydrogen supply unit 30 for storing hydrogen supplied to the reaction tube 10 at high pressure, and a gas containing methane and hydrogen produced in the reaction tube 10 are stored. A fuel tank 40, another device 50 as heat demand for supplying reaction heat generated in the reaction tube 10, a combustion gas supply path (gas supply section) 29 connecting the combustion device 20 and the reaction tube 10, Hydrogen supply path 39 connecting the hydrogen supply unit 30 and the reaction tube 10, a fuel supply path 49 connecting the reaction tube 10 and the fuel tank 40, and a treated combustion connecting the reaction tube 10 and another device 50. A gas supply path (heat transfer section) 59 and a control section 60 for controlling the gas supplied to the reaction tube 10 are provided.

The storage reduction catalyst 11 of the present embodiment is a complex containing calcium oxide (CaO), ceria (CeO ₂ ) which is an oxide of cerium as a sintering inhibitor, and ruthenium (Ru) which is a methanation catalyst. Is. In the present embodiment, the material ratio (molar ratio) of ceria and the material ratio of ruthenium contained in the storage reduction catalyst 11 are 1/15 of calcium oxide and 1/2 of calcium oxide, respectively. The calcium oxide contained in the storage reduction catalyst 11 stores carbon dioxide contained in the combustion gas and changes into calcium carbonate. When hydrogen carbonate is supplied, calcium carbonate desorbs carbon dioxide and changes to calcium oxide. The reaction from calcium oxide to calcium carbonate is an exothermic reaction, and the reaction from calcium carbonate to calcium oxide is an endothermic reaction. Ruthenium promotes the reaction of hydrogen and carbon dioxide to produce methane. Alumina, which is an oxide containing aluminum, is used to suppress deterioration of calcium oxide due to sintering and is also called a sintering inhibitor.

The combustion gas supply path 29 guides the combustion gas discharged from the combustion device 20 to the reaction tube 10. As shown in FIG. 1, in the middle of the combustion gas supply path 29, a combustion gas flow meter 21 for detecting the flow rate of the combustion gas and an upstream side for detecting carbon dioxide contained in the combustion gas are sequentially installed from the factory 20 side. A carbon dioxide sensor (upstream CO ₂ sensor) 22, an upstream temperature sensor 23 that detects the temperature of the combustion gas, and a combustion gas valve 24 that opens and closes the combustion gas supply passage are arranged. The combustion gas valve 24 is opened and closed to adjust the flow rate of the combustion gas supplied to the reaction tube 10.

The hydrogen supply path 39 guides hydrogen supplied from the hydrogen supply unit 30 to the reaction tube 10. As shown in FIG. 1, in the middle of the hydrogen supply passage 39, a hydrogen flow meter 31 for detecting the amount of hydrogen flowing in the hydrogen supply passage 39 and a hydrogen supply passage 39 are opened and closed in order from the hydrogen supply unit 30 side. And a hydrogen supply valve 34 that operates. The hydrogen supply valve 34 opens and closes to control the amount of hydrogen supplied to the reaction tube 10.

The fuel supply path 49 guides the gas containing methane generated by the methanation reaction in the reaction tube 10 to the fuel tank 40. As shown in FIG. 1, in the middle of the fuel supply passage 49, a methane sensor 41 for detecting methane contained in a gas passing through the fuel supply passage 49 and a fuel supply passage 49 inside the reaction pipe 10 in order. A hydrogen sensor 42 for detecting hydrogen contained in the gas passing through the fuel cell and a fuel valve 44 for opening and closing the fuel supply passage 49 are provided. The fuel supply path 49 adjusts the methane stored in the fuel tank 40 by opening and closing.

The treated combustion gas supply path 59 guides the high-temperature gas, which is obtained by removing the carbon dioxide from the combustion gas by the storage reduction catalyst 11, from the reaction tube 10 to another device 50. As shown in FIG. 1, in the treated combustion gas supply path 59, a downstream side carbon dioxide sensor (downstream side CO ₂ sensor) 52 for detecting carbon dioxide contained in the gas and a treatment are sequentially provided from the reaction tube 10 side. An outlet valve 54 that opens and closes the spent combustion gas supply path 59, and a downstream temperature sensor 53 that detects the temperature of the gas supplied from the reaction tube 10 to the other device 50 are provided. The outlet valve 54 adjusts the flow rate of the gas supplied from the reaction tube 10 to the other device 50 by opening and closing.

The control unit 60 is connected to various sensors and various valves by wire. In addition, in FIG. 1, the connection between the control unit 60 and various valves is indicated by a broken line, but the connection between the control unit 60 and various sensors is not shown. The control unit 60 acquires detection values of various sensors and transmits control signals for opening and closing various valves to various valves. Each valve opens and closes according to the received control signal.

The control unit 60 includes a CPU (Central Processing Unit) (not shown), a RAM (Random Access Memory), a ROM (Read Only Memory), and an operation unit that receives a user operation. In accordance with the operation received by the operation unit, the CPU develops various programs stored in the ROM in the RAM to execute the various programs. The operation unit is a well-known input means such as a keyboard and a mouse. The specific processing performed by the control unit 60 will be described with reference to the flowchart shown below.

FIG. 2 is a flowchart of methane production. In methane production, the control unit 60 first performs an occlusion step (step S1). In the occlusion step, the combustion gas of the combustion device 20 flows into the reaction tube 10. The control unit 60 opens the combustion gas valve 24 and the outlet valve 54 with the hydrogen supply valve 34 and the fuel valve 44 closed. Since the combustion gas contains carbon dioxide, the storage reduction catalyst 11 in the reaction tube 10 stores carbon dioxide. The carbon dioxide flowing into the reaction tube 10 and calcium oxide cause a chemical reaction represented by the following formula (1).
CaO+CO ₂ =CaCO ₃ (1)

The control unit 60 determines whether or not the concentration of carbon dioxide detected by the downstream CO ₂ sensor 52 is smaller than the allowable value that may be released into the atmosphere through the reaction tube 10 (step S2). .. When the detection value of the downstream CO ₂ sensor 52 is lower than the allowable value (step S2: YES), the control unit 60 continues the occlusion step (step S1). On the contrary, when the detected value of the downstream side CO ₂ sensor 52 is not less than the allowable value (step S2: NO), the control unit 60 ends the occlusion step and shifts to the next step. At this time, the control unit 60 closes the combustion gas valve 24 and the outlet valve 54. The discharged combustion gas may be discharged to the atmosphere after being subjected to a predetermined process without being supplied to the other device 50 which has a heat demand.

When the occlusion step ends, the control unit 60 performs a methanation step (step S3). In the methanation step, the control unit 60 opens the hydrogen supply valve 34 and the fuel valve 44 to supply hydrogen into the reaction tube 10. In the reaction tube 10, a methanation reaction in which methane of the following formula (2) is produced occurs.
CaCO ₃ +4H ₂ =CaO+CH ₄ +2H ₂ O (2)

In the methanation step, the control unit 60 supplies hydrogen to the reaction tube 10 and manages the hydrogen supply amount using the detection value of the hydrogen flow meter 31. However, the control unit 60 considers that the methanation reaction is stopped when the acquired value of the methane sensor 41 falls below a certain methane concentration before the supply amount reaches a predetermined amount. That is, the control unit 60 determines whether the methane concentration acquired by the methane sensor 41 exceeds a set value that is a constant methane concentration. When the acquired value of the methane sensor 41 is larger than the set value (step S4: YES), the control unit 60 continues the methanation step (step S3). When the acquired value of the methane sensor 41 is less than or equal to the set value (step S4: NO), the control unit 60 performs the next step. At this time, the hydrogen supply valve 34 and the fuel valve 44 are closed.

After the storage of methane, the control unit 60 determines whether to end the process of methane production using carbon dioxide (step S5). When the operation unit has not received a predetermined operation for ending the production of methane (step S5: NO), the control unit 60 repeats the processing from step S1 onward. When the operation unit receives a predetermined operation, the control unit 60 ends the methane production.

FIG. 3 is an explanatory diagram comparing the heat capacity of the storage reduction catalyst 11 of the example with the heat capacity of the storage reduction catalyst 13 of the comparative example. FIG. 3 shows the amount of heat (kilojoule: kJ) required for each substance constituting the storage reduction catalyst 11 of the example and the storage reduction catalyst 13 of the comparative example to rise by 1 Kelvin (K). It should be noted that FIG. 3 shows the heat capacity when 99% of calcium oxide is changed to calcium carbonate in the storage reduction catalysts 11 and 13 converted per mol of calcium oxide. The storage reduction catalyst 13 of the comparative example is a composite material in which 10 mass% (wt%) of calcium oxide is supported on alumina and 5 wt% of ruthenium is added.

The calorific value when calcium oxide is changed to calcium carbonate is 171.3 kJ/mol. Therefore, when 99% of calcium oxide in the storage reduction catalysts 11 and 13 shown in FIG. 3 is changed to calcium carbonate, the temperature increase width of the storage reduction catalyst 11 of the present embodiment is 413 degrees Celsius (° C.). .. On the other hand, the temperature rise width of the storage reduction catalyst 13 of the comparative example is 184°C. Therefore, when the combustion gas at 320° C. flows into the reaction tube 10, the temperature of the storage reduction catalyst 11 of the present embodiment rises from 320° C. to 733° C. On the other hand, the temperature of the storage reduction catalyst 13 of the comparative example rises only from 320°C to 504°C.

FIG. 4 is an explanatory diagram of the temperature rise width of the storage reduction catalyst 11. FIG. 4 shows the relationship between the volume ratio of ceria in the volume of calcium oxide and ceria contained in the storage reduction catalyst 11 and the temperature rise width of the storage reduction catalyst 11. Specifically, a substance amount ratio (mol ratio) of calcium to cerium (Ce), a volume ratio of ceria (CeO ₂ ), a reaction rate of calcium oxide (CaO), and a temperature rise range of the storage reduction catalyst 11. Corresponding table is shown. In the correspondence table of FIG. 4, the reaction rate of calcium oxide is a value when the storage reduction catalyst 11 has performed 18 heat absorption/desorption cycles. As shown in FIG. 4, the reaction rate of calcium oxide decreases as the volume ratio of ceria, which is the sintering inhibitor, decreases. On the other hand, when the volume ratio of ceria is 14 vol %, the temperature increase width of the storage reduction catalyst 11 becomes 380° C., which is the maximum value in the table. As the volume ratio of ceria increases from 14 vol% or decreases, the temperature increase width of the storage reduction catalyst 11 decreases. The substance amount ratio of ceria contained in the storage reduction catalyst 11 in the present embodiment is 1/15 of that of calcium oxide. Therefore, as shown in FIG. 4, the volume ratio of ceria in the volume of calcium oxide and ceria, which is the sintering suppressing material, is 9 vol %.

As described above, in the storage reduction catalyst 11 of the present embodiment, the volume ratio of ceria in the volume of calcium oxide and the ceria that is the sintering suppressing material is 9 vol% (less than 75 vol %). The temperature rise width of the storage reduction catalyst 11 when the volume ratio is 9 vol% is about 370° C. as shown in FIG. This temperature rise width is 142° C. higher than the temperature rise width 228° C. of the occlusion reduction catalyst to which ceria as a sintering inhibitor is not added (0 vol %). Further, as shown by the reaction rate of calcium oxide in FIG. 4, 89% of the calcium oxide contained in the storage reduction catalyst 11 absorbs carbon dioxide even in the 18th carbon dioxide absorption/desorption cycle. Therefore, in the occlusion reduction catalyst 11, the volume ratio of the sintering suppressing material in the volume of calcium oxide and the sintering suppressing material is set to less than 75 vol% to repeatedly perform the carbon dioxide recovery cycle, and The temperature rise width of the storage reduction catalyst 11 at the time of storage can be improved.

<Modification of this embodiment>
The present invention is not limited to the above embodiment, and can be implemented in various modes without departing from the scope of the invention, and the following modifications are possible, for example.

[Modification 1]
In the above embodiment, the methane production system 100 has been described as an example, but the methane production system can be variously modified. The methane production system 100 includes a reaction tube 10 having an occlusion reduction catalyst 11, a combustion gas supply path 29 for supplying a gas containing carbon dioxide to the reaction tube 10, and a hydrogen supply unit 30 for supplying hydrogen to the reaction tube 10. It suffices to include a control unit 60 that controls the supply amount of hydrogen and the supply amount of combustion gas. Further, the methane production system of another embodiment may have a configuration that the methane production system 100 of the above embodiment does not have. For example, the methane production system may not include the methane sensor 41.

The control of various valves in the methane production by the control unit 60 in the above embodiment is an example, and can be variously modified. In the methane production of the above-described embodiment, when the two valves, the combustion gas valve 24 and the outlet valve 54, and the hydrogen supply valve 34 and the fuel valve 44, are open, the other two valves are closed. In other embodiments, the opening and closing of each valve may be freely controlled within a range where adsorption and desorption of carbon dioxide by the storage reduction catalyst 11 and production of methane are performed. The reaction tube 10 may include a plurality of occlusion reduction catalysts 11 or may include occlusion reduction catalysts of different composite materials containing calcium oxide.

[Modification 2]
In the embodiment described above, ceria, which is an oxide of cerium, has been described as an example of the sintering suppressing material included in the storage reduction catalyst 11, but other materials may be used. For example, the sintering suppressing material may include an oxide containing at least one element selected from magnesium, aluminum, silicon, titanium, lanthanum, cerium, zirconium, and yttrium. Further, the sintering suppressor may contain any oxide of magnesium, cerium, and zirconium, or a composite oxide containing two or more kinds of elements of magnesium, cerium, zirconium, and calcium. May be included.

FIG. 5: is explanatory drawing of the temperature rise width of the storage reduction catalyst 11a of a modification. FIG. 5 shows the volume ratio of magnesium in the volume of calcium oxide contained in the storage reduction catalyst 11a and the volume of magnesia (magnesium oxide) that is a sintering inhibitor, and the temperature rise width of the storage reduction catalyst 11a. Relationships are shown. FIG. 6 is an explanatory diagram of the temperature rise width of the storage reduction catalyst 11b of the modified example. FIG. 6 shows a volume ratio of CaZrO ₃ in the volumes of calcium oxide and calcium zirconate (CaZrO ₃ ) which is a sintering inhibitor contained in the storage reduction catalyst 11b of the modified example, and the temperature of the storage reduction catalyst 11b. The relationship with the rise is shown. Note that CaZrO ₃ is an oxide generated by spontaneous formation of a complex oxide when zirconium dioxide is added to calcium oxide (CaO).

The temperature increase width of the storage reduction catalyst 11a containing magnesia shown in FIG. 5 is 362° C., which is the maximum value in the table when the volume ratio of magnesia is 24 vol %. Further, the temperature increase range of the storage reduction catalyst 11b to which CaZrO ₃ is added shown in FIG. 6 becomes 383° C. which is the maximum value in the table when CaZrO ₃ is 11 vol %. The calcium oxide reaction rates of the storage reduction catalyst 11a and the storage reduction catalyst 11b of the modified example decrease as the volume ratio of the sintering suppressing material decreases, like the storage reduction catalyst 11 to which ceria is added. The calcium oxide reaction rate in FIG. 5 is the value of the 24th absorption-release cycle, and the calcium oxide reaction rate in FIG. 6 is the value of the 18th absorption-release cycle.

FIG. 7 is a graph showing changes in the improvement index value of the temperature rise range of the storage reduction catalyst. FIG. 7 shows the improvement index value of the temperature rise range that changes depending on the volume ratio of the sintering suppressor added to the storage reduction catalyst. The improvement index value of the temperature increase range shown in FIG. 7 is the standard obtained by dividing the temperature increase range of the storage reduction catalyst by the temperature increase range of the storage reduction catalyst when no sintering inhibitor is added (0 vol %). It is the converted value. In FIG. 7, the improvement index value of the temperature rise range in the storage reduction catalyst 11 containing ceria is shown by a solid line, and the improvement index value of the temperature rise range in the storage reduction catalyst 11a containing magnesia is shown by a broken line. The improvement index value of the temperature rise range in the storage reduction catalyst 11b to which zirconium dioxide is added is indicated by the one-dot chain line. Further, only one improvement index value of the storage reduction catalyst 13 of the comparative example is shown. As shown in FIG. 7, the temperature increase width of any of the storage reduction catalysts 11, 11a, 11b reaches a maximum value when the sintering inhibitor is about 5 to 25 vol %. In consideration of the reaction rate of calcium oxide, the volume ratio of the sintering suppressing material in the volume of calcium oxide and the sintering suppressing material is preferably 5 vol% or more. In addition, the volume ratio of the sintering suppressing material is preferably 60 vol% or less, and more preferably 35 vol% or less when the volume ratio is less than 75 vol%.

In the above embodiment, the volume ratio of ceria in the volume of calcium oxide and ceria contained in the storage reduction catalyst 11 was 9 vol %, but the volume ratio of the ceria is less than 75 vol %. The addition amount can be changed. For example, the volume ratio of ceria may be 74 vol%.

Although the present aspect has been described above based on the embodiment and the modified examples, the embodiment of the aspect described above is intended to facilitate understanding of the present aspect and does not limit the present aspect. The present embodiment can be modified and improved without departing from the spirit and scope of the claims, and the present embodiment includes the equivalents thereof. If the technical features are not described as essential in this specification, they can be deleted as appropriate.

10 ... reaction tube 11, 11a, 11b ... carbon dioxide storage reduction catalyst 13 ... Comparative example storage-reduction catalyst 20 ... combustion device 21 ... combustion gas flowmeter 22 ... upstream CO ₂ sensor 23 ... upstream temperature sensor 24 ... combustion gas valve 29... Combustion gas supply path (gas supply section)
30... Hydrogen supply part 31... Hydrogen flow meter 34... Hydrogen supply valve 39... Hydrogen supply path 40... Fuel tank 41... Methane sensor 42... Hydrogen sensor 44... Fuel valve 49... Fuel supply path 50... Device 52... Downstream CO ₂ Sensor 53... Downstream temperature sensor 54... Outlet valve 59... Treated combustion gas supply path 60... Control unit 100... Methane production system

Claims (4)

A carbon dioxide storage reduction catalyst,
Calcium oxide capable of storing carbon dioxide and desorbing the stored carbon dioxide by supplying hydrogen,
A sintering suppressing material that suppresses the sintering of the calcium oxide,
A methanation catalyst that promotes methane production from carbon dioxide and hydrogen,
The carbon dioxide storage reduction catalyst, wherein the volume ratio of the sintering suppressor in the calcium oxide and the sintering suppressor is less than 75%. The carbon dioxide storage reduction catalyst according to claim 1, wherein
The carbon dioxide storage reduction catalyst, wherein the sintering inhibitor contains an oxide containing at least one element selected from magnesium, aluminum, silicon, titanium, lanthanum, cerium, zirconium, and yttrium. The carbon dioxide storage reduction catalyst according to claim 2,
The sintering suppressor is
Including any of the oxides of magnesium, cerium, and zirconium, or
A carbon dioxide storage-reduction catalyst containing a composite oxide containing two or more elements selected from magnesium, cerium, zirconium, and calcium. A methane production system,
A reaction tube having the carbon dioxide storage reduction catalyst according to any one of claims 1 to 3,
A gas supply unit for supplying a gas containing carbon dioxide to the reaction tube,
A hydrogen supply unit for supplying hydrogen to the reaction tube,
A methane production system comprising: a control unit that controls the amount of gas supplied from the gas supply unit to the reaction tube and the amount of hydrogen supplied from the hydrogen supply unit to the reaction tube.

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