Method for reusing catalysts in a methanation reactor and a methanation reactor

Abstract

This invention provides a method for reusing catalysts in methanation reactors, which can extend the lifespan of the catalyst. [Solution] This is a method for reusing a catalyst in a methanation reactor, in which a catalyst packed bed 3 of a methanation reactor, which generates methane-containing gas by contacting a raw material gas containing carbon dioxide and / or carbon monoxide and hydrogen with a catalyst, is divided into multiple parts 3a to 3e in the longitudinal direction or in the gas flow direction, the catalyst is packed into the multiple parts 3a to 3e and operated, and after operation for a predetermined time, at least a portion of the catalyst in parts 3c and 3d, which have a low degradation level, is replaced with the catalyst in parts 3a and 3b, which have a high degradation level, and reused.

Description

Technical Field

[0001] The present invention relates to a method for reusing a catalyst of a methanation reactor and a methanation reactor.

Background Art

[0002] The methanation of CO₂, in which hydrogen and carbon dioxide are brought into contact with a catalyst to produce methane, was reported by Sabatier in the early 20th century. The reaction formula for the methanation of CO₂ is as follows. CO₂+4H₂→CH₄+2H₂O(ΔH=-165kJ / mol(298k)) (1)

[0003] In recent years, the methanation of CO₂ has attracted attention. This is because the methanation of CO₂ enables the reduction of CO₂, a greenhouse gas, allows hydrogen produced from surplus power of renewable energy such as solar power generation and wind power generation to be stored in the form of fuel gas, and the produced methane can be used as city gas.

[0004] As a reactor for performing CO₂ methanation, Patent Document 1 discloses a methanation reactor in which a tubular catalyst packed bed is filled with a catalyst, a raw material gas containing hydrogen and carbon dioxide is caused to flow through the catalyst packed bed, and the raw material gas is brought into contact with the catalyst to synthesize methane. As the catalyst, for example, a catalyst in which metal particles such as nickel are supported on a carrier such as zirconia is used. The catalyst has the role of lowering the activation energy of the reaction and allowing the synthesis of methane to proceed smoothly.

[0005] Incidentally, Sabatier also reported the methanation of CO represented by the following reaction formula (2). By using the reactor described in Patent Document 1, it is also possible to perform the methanation of CO. CO+3H₂→CH₄+H₂O(ΔH=-206kJ / mol(298k)) (2)

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Patent No. 6984098 [Overview of the project] [Problems that the invention aims to solve]

[0007] The methanation of CO2, represented by reaction equation 1, is an exothermic reaction. As CO2 methanation proceeds, a rapid temperature increase occurs in the longitudinal direction of the catalyst packed bed or upstream in the direction of gas flow, and a problem arises in that thermal degradation of the catalyst progresses, especially in the high-temperature region. This is because sintering of the supported metal, such as nickel, progresses in the high-temperature region, reducing the specific surface area of ​​the supported metal and decreasing the activity of the catalyst. A similar problem exists in the methanation of CO, represented by reaction equation (2).

[0008] Catalysts are generally expensive because they often use expensive elements and require complex manufacturing processes. Extending the lifespan of the catalyst is necessary for the practical application of methanation reactors.

[0009] This invention has been made in view of the above problems, and aims to provide a method for reusing a catalyst in a methanation reactor and a methanation reactor that can extend the lifespan of the catalyst. [Means for solving the problem]

[0010] To solve the above problems, one aspect of the present invention is a method for reusing a catalyst in a methanation reactor, in which a catalyst packed bed of a methanation reactor that generates a methane-containing gas by contacting a catalyst with a raw material gas containing carbon dioxide and / or carbon monoxide and hydrogen is divided into a plurality of parts in the longitudinal direction or the gas flow direction, the catalyst is packed into the plurality of parts and the reactor is operated, and after operation for a predetermined time, at least a portion of the catalyst in the parts with a low degradation level is replaced with the catalyst in the parts with a high degradation level and reused.

[0011] Another aspect of the present invention is a methanation reactor that generates a methane-containing gas by contacting a catalyst with a raw material gas containing carbon dioxide and / or carbon monoxide and hydrogen, wherein the catalyst packed bed of the methanation reactor is divided into multiple parts in the longitudinal direction or the gas flow direction, and at least a portion of the catalyst in the parts with a low degradation level is replaced with that in the parts with a high degradation level for reuse. [Effects of the Invention]

[0012] According to the present invention, at least a portion of the catalyst in the parts with a low degradation level is replaced with parts with a high degradation level and reused, thereby extending the lifespan of the catalyst in the methanation reactor. [Brief explanation of the drawing]

[0013] [Figure 1] This is a longitudinal cross-sectional view of an example of a methanation reactor according to an embodiment of the present invention. [Figure 2] This is a longitudinal cross-sectional view of the catalyst packing bed. [Figure 3] This graph shows the relationship between the distance from the inlet end of the catalyst packed bed and the temperature of the catalyst packed bed, as well as the relationship between that distance and the composition of the generated gas. [Figure 4] This figure shows the change in temperature distribution in the catalyst-packed bed. [Figure 5] This diagram illustrates the replacement of catalysts in the catalyst-packed bed components. [Figure 6] This is a schematic diagram showing another example of a reactor. [Modes for carrying out the invention]

[0014] Hereinafter, with reference to the accompanying drawings, the method for reusing a catalyst of a methanation reactor and the methanation reactor according to an embodiment of the present invention will be described in detail. However, the method for reusing a catalyst of a methanation reactor and the methanation reactor of the present invention can be embodied in various forms, and are not limited to the embodiments described in the present specification. The present embodiment is provided with the intention of enabling those skilled in the art to fully understand the invention by fully disclosing the specification. (Methanation reactor)

[0015] Figure 1 shows a longitudinal sectional view of an example of a methanation reactor 1 (hereinafter simply referred to as reactor 1) according to an embodiment of the present invention. The reactor 1 is supplied with a raw material gas containing carbon dioxide and hydrogen adjusted to a molar ratio of 1:4.

[0016] The reactor 1 includes a vessel 2, and a plurality of tubular catalyst packed beds 3 arranged in parallel inside the vessel 2. The raw material gas is supplied from the inlet port 2a to the buffer region at the upper part of the vessel 2, and then flows through the plurality of catalyst packed beds 3 from top to bottom. In the catalyst packed bed 3, the raw material gas comes into contact with the catalyst 4, whereby the methanation of CO2 represented by the reaction formula (1) proceeds. CO2+4H2→CH4+2H2O(ΔH=-165kJ / mol(298K)) (1)

[0017] The catalyst packed bed 3 is partitioned into a plurality of parts 3a to 3d in the longitudinal direction or the gas flow direction by a partition member 5. The partition member 5 is not particularly limited as long as it allows gas to pass through and can partition the catalyst packed bed 3, and examples thereof include wire mesh, grating, punched metal, and ceramic. The partition member 5 is provided to separate the catalyst 4 for each of the parts 3a to 3d.

[0018] The parts 3a to 3d are filled with a catalyst 4. The catalyst 4 has the role of lowering the activation energy for CO2 methanation and allowing the CO2 methanation to proceed smoothly. The catalyst 4 is formed by supporting metal particles such as Ni, Co, Fe, Cu, Ru, and Rh on an oxide carrier such as zirconia, magnesia, alumina, silica, zeolite, or calcium phosphate. The shape of the catalyst 4 is not particularly limited, and may be powdery, pellet-shaped, or cylindrical. The structure of the catalyst 4 is also not particularly limited, and may be a porous structure or a honeycomb structure.

[0019] CO2 methanation generates a gas containing methane (CH4) and water vapor (H2O). The generated gas inevitably contains CO2, H2, CO, and CH3OH. The generated gas passes through the buffer region at the lower part of the vessel 2, and then is discharged from the discharge port 2b of the vessel 2.

[0020] The generated gas discharged from the reactor 1 is condensed by a non-illustrated condenser connected to the discharge port 2b, and separated into a methane-containing gas and water. The methane-containing gas from which water has been separated is supplied to a demand destination after impurities such as CO2 and CO are removed by, for example, a decarbonation device or the like.

[0021] CO2 methanation is an exothermic reaction. The catalyst packed bed 3 is operated in a temperature range of, for example, 300°C to 500°C. If the temperature of the catalyst packed bed 3 is lower than 300°C, harmful nickel carbonyl is generated on the catalyst 4. In order to prevent the temperature of the catalyst packed bed 3 from dropping below 300°C, the raw material gas heated in the initial stage of operation may be supplied to the reactor 1, or the catalyst packed bed 3 may be heated by a non-illustrated heater.

[0022] On the other hand, if the catalyst packed bed 3 is at a high temperature of 500°C or higher, thermal degradation of the catalyst 4 will progress. To prevent the catalyst packed bed 3 from reaching a high temperature of 500°C or higher, the catalyst packed bed 3 is cooled by a refrigerant supplied into the container 2 from the refrigerant inlet port 6a. The refrigerant can be vapor, oil, etc. After heat exchange with the catalyst packed bed 3, the refrigerant is discharged from the refrigerant outlet port 6b. Alternatively, a portion of the generated gas cooled by a condenser connected to the discharge port 2b may be circulated to the inlet port 2a of the reactor 1, and the catalyst packed bed 3 may be cooled by diluting the raw material gas with the generated gas.

[0023] Figure 2 shows a longitudinal cross-sectional view of the catalyst packed bed 3. As described above, the catalyst packed bed 3 is divided into multiple parts 3a to 3d by partition members 5. The multiple parts 3a to 3d are filled with catalyst 4. Parts 3b to 3d are provided with measuring instruments 7 to measure at least one of the temperature of the catalyst 4 in parts 3b to 3d or the composition of the generated gas. Measuring instruments 7 do not need to be provided in all parts 3a to 3d, but only in representative parts 3b to 3d. The measuring instrument 7 at the bottom may be provided near the outlet of the catalyst packed bed 3.

[0024] When measuring instrument 7 measures the temperature of catalyst 4 in parts 3b to 3d, measuring instrument 7 is a thermometer such as a thermocouple or infrared thermograph. Measuring instrument 7 may measure the temperature of catalyst 4 in parts 3b to 3d, or it may measure the temperature of the generated gas in parts 3b to 3d. Measuring instrument 7, which is installed near the outlet of the catalyst packed bed 3, measures the temperature of the generated gas near the outlet of the catalyst packed bed 3.

[0025] When measuring instrument 7 measures the composition of the generated gases of parts 3b to 3d, instrument 7 consists of a sampling tube for collecting the generated gases of parts 3b to 3d, an infrared gas analyzer, a gas chromatograph, etc. By analyzing the generated gas collected by the sampling tube using the infrared gas analyzer, gas chromatograph, etc., the composition of the generated gas (concentrations of CH4, H2O, CO2, H2, CO, and CH3OH) can be measured. However, it is not necessary to measure the concentrations of all of CH4, H2O, CO2, H2, CO, and CH3OH; measuring the concentration of at least one of them is sufficient.

[0026] A degradation determination unit 8 is connected to the measuring instrument 7. The degradation determination unit 8 is a computer equipped with a CPU, ROM, RAM, storage, etc. The degradation determination unit 8 uses the CPU to execute programs stored in the ROM and storage to classify the degree of degradation of the catalysts 4 of parts 3a to 3d into levels based on the measurement data from the measuring instrument 7 (catalyst temperature and / or composition of the generated gas). For example, the degradation determination unit 8 divides the degree of degradation calculated based on the measurement data from the measuring instrument 7 into multiple predetermined numerical ranges, classifying the highest (or lowest) range as level A, the next highest (or lowest) range as level B, and the next highest (or lowest) range as level C. Then, the catalysts 4 are replaced based on the determined level, but the replacement of catalysts 4 may be based on the maximum and minimum levels, or on the relative high and low levels. In other words, the catalyst 4 with the relatively lower degradation level between two different parts may be swapped with the catalyst 4 with the higher degradation level. For example, the catalyst 4 with the highest degradation level may be swapped with the catalyst 4 with the second highest degradation level, or the catalyst 4 with the second highest degradation level may be swapped with the catalyst 4 with the third highest degradation level. The degradation determination unit 8 may also receive input such as the total operating time and raw material gas flow rate data measured by a flow meter (not shown). Alternatively, instead of the computer classifying the degradation levels of the catalysts 4 of parts 3a to 3d, an operator may classify the degradation levels of the catalysts 4 of parts 3a to 3d based on the measurement data from the measuring instrument 7. (Methods for reusing catalysts in reactors)

[0027] Figure 3 is a graph showing the relationship between the distance from the inlet end of the catalyst packed bed 3 and the temperature of the catalyst packed bed 3, as well as the relationship between this distance and the composition of the generated gas. The horizontal axis of Figure 3 represents the distance from the inlet end of the catalyst packed bed 3. The vertical axis on the right side of Figure 3 represents the temperature. The vertical axis on the left side of Figure 3 represents the concentrations of CO2, H2, CH4, and H2O.

[0028] As shown in Figure 3, as CO2 methanation progresses, a rapid temperature increase occurs upstream of the catalyst packed bed 3 in the longitudinal direction or in the direction of gas flow, followed by a rapid temperature decrease downstream, and then the temperature becomes almost constant. In the region of high temperature upstream of the catalyst packed bed 3, thermal degradation of the catalyst 4 progresses.

[0029] Figure 4 shows the change in temperature distribution of the catalyst packed bed 3 after a predetermined period of operation. Figure 4(a) shows the temperature distribution of the catalyst packed bed 3 immediately after the start of operation (initial stage), Figure 4(b) shows the temperature distribution of the catalyst packed bed 3 after a predetermined period of operation (mid-stage), and Figure 4(c) shows the temperature distribution of the catalyst packed bed 3 after a further predetermined period of operation (late stage). Although Figure 4 shows an example in which the raw material gas is flowed horizontally through the catalyst packed bed 3, in reality the catalyst packed bed 3 extends vertically and the raw material gas is flowed vertically. However, the catalyst packed bed 3 may also extend horizontally as shown in Figure 4 and the gas may be flowed horizontally.

[0030] As shown in Figures 4(b) and 4(c), after a predetermined operating time, the catalysts 4 in parts 3a to 3e are sequentially deactivated from the upstream side due to CO2 methanation, and the peak temperature shifts to the downstream side. By detecting this change in temperature of the catalyst packed bed 3, the degradation of the catalysts 4 in parts 3a to 3e can be detected, and the degree of degradation of the catalysts 4 in parts 3a to 3e can be classified into levels. For example, when the peak temperature shifts from the catalyst 4 in part 3a to the catalyst 4 in part 3c, the catalysts 4 in parts 3a and 3b can be classified as being more degraded than the catalysts 4 in parts 3c to 3e.

[0031] Figure 5 illustrates the replacement of catalyst 4 in parts 3a to 3e of the catalyst packed bed 3. As shown in Figure 5(a), immediately after the start of operation (initial stage), the deterioration of catalyst 4 in parts 3a to 3e has not progressed, so the deterioration determination unit 8 classifies the deterioration level of catalyst 4 in parts 3a to 3e as level A (low deterioration level).

[0032] As shown in Figure 5(b), after a predetermined period of operation (medium term), the degradation determination unit 8 classifies the degradation levels of the catalyst 4 in part 3a as C (high degradation level), the catalyst 4 in part 3b as B (medium degradation level), and the catalyst 4 in parts 3c to 3e as A (low degradation level).

[0033] Subsequently, reactor 1 is shut down and catalyst 4 is cooled. Then, catalyst 4 from parts 3c and 3d, which have a low level of degradation, is replaced with catalyst 4 from parts 3a and 3b, which have a high level of degradation. That is, catalyst 4 from parts 3a to 3d is removed, and catalyst 4 from parts 3c and 3d is placed in parts 3a and 3b. Alternatively, new catalyst may be mixed with catalyst 4 from parts 3c and 3d, and the mixed catalyst may be placed in parts 3a and 3b. Catalyst 4 removed from parts 3a and 3b is either regenerated or discarded. New catalyst is placed in parts 3c and 3d.

[0034] By replacing the catalyst 4 of parts 3c and 3d, which have a low level of degradation, with parts 3a and 3b, which have a high level of degradation, the temperature distribution of the catalyst packed bed 3 in the intermediate stage approximates that of the initial stage, as shown in Figure 5(b).

[0035] Furthermore, after a predetermined operating time (later stage), as shown in Figure 5(c), the degradation determination unit 8 classifies the degradation levels of the catalyst 4 in part 3a as C (high degradation level), the catalyst 4 in part 3b as B (medium degradation level), and the catalyst 4 in parts 3c to 3e as A (low degradation level).

[0036] Subsequently, the reactor 1 is shut down, the catalyst 4 is cooled, and as shown in Figure 5(c), the catalyst 4 with low degradation levels (parts 3c and 3d) is replaced with catalyst 4 with high degradation levels (parts 3a and 3b). By repeating this process after a predetermined period of operation, the lifespan of the catalyst 4 can be extended.

[0037] Instead of, or in combination with, the temperature of parts 3a to 3e, the degradation level of the catalyst 4 in parts 3a to 3e may be classified based on the composition of the product gas after the reaction of parts 3a to 3e. As shown in Figure 3, the concentrations of CO2 and H2 gradually decrease upstream of the catalyst packed bed 3, and become almost constant downstream. Consequently, the concentrations of CH4 and H2O gradually increase upstream of the catalyst packed bed 3, and become almost constant downstream. In addition, CO may be produced by the shift reaction, or CH3OH may be produced.

[0038] When catalyst 4 degrades, the reaction rate of CO2 methanation decreases, resulting in a smaller decrease in the concentrations of CO2 and H2, and a smaller increase in the concentrations of CH4 and H2O. Therefore, by measuring the composition of the product gases of parts 3a to 3e, the degree of degradation of catalyst 4 in parts 3a to 3e can be classified into levels. Note that it is not necessary to measure the concentrations of all components of the product gas (CH4, H2O, CO2, H2, CO, CH3OH); measuring at least one concentration is sufficient. (Other examples of reactors)

[0039] Figure 6 shows another example of a reactor. In this example, reactor 10 comprises a first reactor 11 and a second reactor 12 connected in series. A condenser 13 is placed between the first reactor 11 and the second reactor 12 to cool the product gas. A condenser 14 is also placed at the outlet of the second reactor 12 to cool the product gas. Placing the condenser 13 between the first reactor 11 and the second reactor 12 lowers the temperature of the product gas supplied to the second reactor 12, thereby improving the CO2 conversion rate of the reactor 10 as a whole. Reactor 10 may also comprise first to nth (n≧3) reactors.

[0040] The first reactor 11 comprises a plurality of tubular first catalyst packed beds 15. The second reactor 12 comprises a plurality of tubular second catalyst packed beds 16. The configuration of the first reactor 11 is substantially the same as that of reactor 1 shown in Figure 1, except that partition members are not provided in the first catalyst packed bed 15. The configuration of the second reactor 12 is also substantially the same as that of reactor 1 shown in Figure 1, except that partition members are not provided in the second catalyst packed bed 16.

[0041] As in this example, the catalyst packed bed of the reactor 10 may be divided into multiple parts in the direction of gas flow, namely a first catalyst packed bed 15 and a second catalyst packed bed 16, and after operation for a predetermined time, at least a portion of the catalyst in the second catalyst packed bed 16, which has a lower degradation level, may be replaced with catalyst in the first catalyst packed bed 15, which has a higher degradation level.

[0042] Alternatively, the first catalyst packed bed 15 may be divided into multiple parts by partitioning members, and the second catalyst packed bed 16 may be divided into multiple parts by partitioning members, and at least a portion of the catalyst in the parts of the second catalyst packed bed 16 with a lower degradation level may be replaced with the catalyst in the parts of the first catalyst packed bed 15 with a higher degradation level.

[0043] Furthermore, the present invention is not limited to being embodied in the above embodiments, and can be embodied in other embodiments without changing the gist of the invention.

[0044] In the above embodiment, an example of performing CO2 methanation in a reactor was described, but CO methanation may also be performed in the reactor, or CO and CO2 methanation may be performed in the reactor.

[0045] Furthermore, although the above embodiment describes an example in which multiple tubular catalyst packed beds are arranged in the reactor, the configuration of the reactor is not limited to this. For example, a catalyst packed bed that extends over almost the entire cross-section of the reactor (for example, a catalyst packed bed consisting of a honeycomb structure) may be arranged in the reactor, and this catalyst packed bed may be divided into multiple parts by partitioning members. [Explanation of Symbols]

[0046] 1…Methanation reactor 3…Catalyst packed bed 3a~3e... Parts 4…Catalyst

Claims

1. A method for reusing a catalyst in a methanation reactor, comprising dividing the catalyst packed bed of a methanation reactor, which generates a methane-containing gas by contacting a catalyst with a raw material gas containing carbon dioxide and / or carbon monoxide and hydrogen, into multiple parts in the longitudinal direction or the gas flow direction, filling the multiple parts with catalyst and operating the reactor, and after operating for a predetermined time, replacing at least a portion of the catalyst in the parts with a low degradation level with the catalyst in the parts with a high degradation level for reuse.

2. A method for reusing a catalyst in a methanation reactor according to claim 1, characterized in that the degree of degradation of the catalyst in a part is classified into levels based on at least one of the temperature of the catalyst in the part or the composition of the gas produced after the reaction of the part.

3. A method for reusing a catalyst in a methanation reactor according to claim 1, characterized in that at least a portion of the catalyst in the downstream part is replaced with a catalyst in the upstream part for reuse.

4. In a methanation reactor that produces a methane-containing gas by contacting a catalyst with a raw material gas containing carbon dioxide and / or carbon monoxide and hydrogen, The catalyst packed bed of the methanation reactor is divided into multiple parts in the longitudinal direction or in the direction of gas flow. A methanation reactor that reuses catalysts by replacing at least some of the catalysts in parts with low degradation levels with parts with high degradation levels.

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