Methods for processing methanation catalysts, methods for producing methane, and methanation catalysts.

Abstract

The main objective is to provide a method for treating methanation catalysts that can suppress the degradation of catalyst performance. The method for treating methanation catalysts of the present invention includes an oxidation step in which oxygen-containing gas is supplied to a reactor containing a methanation catalyst containing nickel as a catalyst component, thereby heat-treating the methanation catalyst to oxidize the nickel. Furthermore, the oxygen-containing gas is supplied to the reactor at a rate of 0.0213 to 0.0638 mmol-O2 / sec·g-cat., and the time for heat-treating the methanation catalyst by supplying the oxygen-containing gas to the reactor is set to 30 minutes or more.

Description

Technical Field

[0001] This invention relates to a method for treating a methanation catalyst used in the production of methane (CH4) from carbon dioxide (CO2) and hydrogen (H2) via a methanation reaction, a method for producing methane using the same method, and a methanation catalyst. Background Technology

[0002] To combat global warming, efforts are underway to reduce carbon dioxide, a greenhouse gas. One such measure is the methanation reaction, which involves the thermochemical reaction of carbon dioxide and hydrogen to produce methane, thus effectively utilizing carbon dioxide.

[0003] In such a methanation reaction, a method for producing methane is employed by using a methanation catalyst that promotes the reaction of carbon dioxide and hydrogen. As a method for producing methane using a methanation catalyst, as described in Patent Documents 1 and 2, a method for producing a methanation catalyst containing nickel (Ni) as a catalyst component is known.

[0004] In the method for producing methane using a methanation catalyst described in Patent Document 1, a stabilized zirconium oxide support in which stabilizing elements are dissolved in zirconium oxide is used as a support for supporting nickel as a catalyst component in the methanation catalyst. On this basis, inorganic oxides are added to inhibit the agglomeration of nickel supported on the support, thereby seeking to increase the production rate of methane.

[0005] On the other hand, in the method for manufacturing methane using a methanation catalyst described in Patent Document 2, the support for supporting the catalyst component nickel contains one or more of Ce, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, thereby enabling the efficient conversion of carbon dioxide into methane at temperatures below 300°C.

[0006] Existing technical documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-122247

[0008] Patent Document 2: Japanese Patent Application Publication No. 2019-155227 Summary of the Invention

[0009] On the other hand, as described in Patent Documents 1 and 2, when using a methanation catalyst containing nickel as a catalyst component in conventional methane production methods to produce methane via a methanation reaction, there are periods when the equipment is shut down, such as during maintenance or rest days. During these shutdowns, atmospheric air sometimes intrudes into the reaction system inside the reactor containing the methanation catalyst from outside the furnace. After the methanation reaction in the reactor, most of the nickel contained in the methanation catalyst is reduced to metallic nickel (Ni), which is easily oxidized. As a result, during shutdowns, the atmospheric oxygen intruding into the reaction system causes the metallic nickel in the methanation catalyst to rapidly oxidize into nickel oxide (NiO), thereby reducing the catalyst's activity. Furthermore, the catalyst deteriorates due to the heat generated by the rapid oxidation of metallic nickel, leading to the aggregation of the support and / or nickel, potentially reducing catalyst performance. This concern is particularly high when the methanation catalyst is in contact with the atmosphere at temperatures exceeding approximately 50°C. If the methanation catalyst is at a low temperature, such as around 50°C or below, the oxidation reaction of nickel is difficult to proceed even when in contact with the atmosphere. However, in warm regions, such as Japan, especially during the summer when temperatures are high, the reaction system in the reactor is prone to become high-temperature, which can easily lead to this problem.

[0010] One approach to address this problem is to circulate an inert gas, such as nitrogen (N2), through the reaction system in a reactor containing a nickel-containing methanation catalyst during equipment shutdown, thereby removing any atmospheric contamination that may have entered the reaction system. However, this approach introduces a new problem: the increased operating costs associated with circulating the inert gas within the reactor system.

[0011] The present invention was made in view of the above-mentioned problems, and its main objective is to provide a method for treating methanation catalysts that can suppress the degradation of catalyst performance, a method for producing methane, and a methanation catalyst.

[0012] To solve the above-mentioned problems, the method for processing the methanation catalyst of the present invention is characterized by comprising an oxidation step, wherein the methanation catalyst is heat-treated by supplying oxygen-containing gas to a reactor containing a methanation catalyst containing nickel as a catalyst component, thereby oxidizing the nickel, and the oxygen-containing gas is supplied to the reactor at a supply rate of 0.0213 to 0.0638 mmol-O2 / sec·g-cat., and the time for heat-treating the methanation catalyst by supplying the oxygen-containing gas to the reactor is set to 30 minutes or more.

[0013] Furthermore, the methane manufacturing method of the present invention is characterized by comprising a processing step and a generation step. In the processing step, the methanation catalyst housed in the reactor is heat-treated in the oxidation step by using the methanation catalyst processing method described above, thereby oxidizing the nickel. In the generation step, methane is generated by supplying a feed gas containing carbon dioxide and hydrogen to the reactor. The reactor houses the methanation catalyst in which the nickel was oxidized in the processing step.

[0014] Furthermore, the methanation catalyst of the present invention is a methanation catalyst containing nickel as a catalyst component, characterized in that the nickel exists in the form of metallic nickel and nickel oxide, and the content of the metallic nickel is in a weight ratio of 58 to 67% relative to the total content of the metallic nickel and the nickel oxide.

[0015] According to the present invention, the degradation of catalyst performance can be suppressed.

[0016] The subject matter, structure, and effects of the present invention beyond the scope of the foregoing description become clear from the following description of the manner in which the invention is carried out. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating a summary of a method for producing methane according to one embodiment.

[0018] Figure 2A This is a cross-sectional view showing the outline of a method for producing methane according to one embodiment.

[0019] Figure 2B This is a cross-sectional view showing the outline of a method for producing methane according to one embodiment.

[0020] Figure 2C This is a cross-sectional view showing the outline of a method for producing methane according to one embodiment.

[0021] Figure 2D This is a cross-sectional view showing the outline of a method for producing methane according to one embodiment.

[0022] Figure 2E This is a cross-sectional view showing the outline of a method for producing methane according to one embodiment.

[0023] Figure 2F This is a cross-sectional view showing the outline of a method for producing methane according to one embodiment.

[0024] Figure 3 This is a flowchart illustrating the experimental procedure for implementing the methane production method of Example 1.

[0025] Figure 4This is a graph showing the change in carbon dioxide conversion rate relative to the temperature of the feed gas at the gas inlet in Examples 1, 2, and 1.

[0026] Figure 5 This is a graph showing the change in carbon dioxide conversion rate relative to the temperature of the feed gas at the gas inlet in Examples 3, 4, and Comparative Example 2.

[0027] Figure 6 This is a graph showing the change in carbon dioxide conversion rate relative to the temperature of the feed gas at the gas inlet in Examples 5, 6, and Comparative Example 3.

[0028] Figure 7 This is a graph showing the change in carbon dioxide conversion rate relative to the temperature of the feed gas at the gas inlet in Comparative Example 4.

[0029] Figure 8 This is a graph showing the change in carbon dioxide conversion rate relative to the temperature of the feed gas at the gas inlet in Examples 7, 8, and Comparative Example 5.

[0030] Figure 9 This is an X-ray diffraction pattern of the methanation catalyst after atmospheric exposure in the experiment of Example 9.

[0031] Figure 10 This is an X-ray diffraction pattern of the methanation catalyst after atmospheric exposure in the experiment of Example 10.

[0032] Figure 11 This is an X-ray diffraction pattern of the methanation catalyst after atmospheric exposure in Comparative Example 9.

[0033] Figure 12 This is an X-ray diffraction pattern of the methanation catalyst after atmospheric exposure in Comparative Example 10.

[0034] Explanation of reference numerals in the attached figures

[0035] 2 Methanation catalyst

[0036] 10 Reactors

[0037] 10a Gas Inlet

[0038] 10b Gas outlet Detailed Implementation

[0039] Hereinafter, with reference to the accompanying drawings, the method for processing the methanation catalyst, the method for producing methane, and embodiments of the methanation catalyst of the present invention will be described. The following description illustrates specific examples of the content of the present invention, and the present invention is not limited to these descriptions. Various modifications and alterations can be made by those skilled in the art within the scope of the technical concept disclosed in this specification. Furthermore, in all the drawings used to describe the present invention, parts having the same function are labeled with the same reference numerals, and sometimes repeated descriptions are omitted.

[0040] The use of "~" in this specification is intended to encompass the values ​​preceding and following it as lower and upper limits. Within the multiple numerical ranges described in stages in this specification, the upper and lower limits of one numerical range can be replaced with the upper and lower limits of other numerical ranges. The upper and lower limits of the numerical ranges described in this specification can be replaced with the values ​​shown in the embodiments.

[0041] First, regarding the processing method of the methanation catalyst, the method for producing methane, and the overview of the methanation catalyst of the embodiments, an example of the processing method of the methanation catalyst, the method for producing methane, and the methanation catalyst of one embodiment will be described.

[0042] Figure 1 This is a flowchart illustrating a summary of a method for producing methane according to one embodiment. Figures 2A to 2F This is a cross-sectional view showing the general process of a methane manufacturing method according to one embodiment.

[0043] In one embodiment of the method for producing methane, firstly, as... Figure 1 and Figure 2A As shown, a methanation catalyst 2 containing nickel (Ni) as a catalyst component is prepared. The methanation catalyst 2 contains a support and nickel supported on support particles, and is placed in a reactor 10 of a methane production apparatus (not shown) (preparation and placement step S11). The prepared methanation catalyst 2 is sintered under an oxygen atmosphere during synthesis, so nickel exists not only in the form of metallic nickel (metallic Ni) but also in the form of nickel oxide (NiO). Therefore, in order for nickel to fully exert its catalytic effect in the methanation reaction, it is necessary to reduce nickel oxide to form metallic nickel.

[0044] Therefore, as follows, Figure 1 and Figure 2B As shown, a high-temperature reducing gas, for example at 400°C, containing, for example, 20 vol% hydrogen (H2) and 80 vol% nitrogen (N2), is supplied to the reactor 10 via gas inlet 10a, thereby circulating the reducing gas around the methanation catalyst 2. Thus, metallic nickel is formed by reducing the nickel oxide in the methanation catalyst 2 (reduction step S12).

[0045] Next, as Figure 1 and Figure 2C As shown, the reduction process ends by stopping the supply of reducing gas to the reactor, thereby lowering the temperature of the methanation catalyst to below the temperature of the feed gas at the gas inlet of the reactor in the subsequent first generation step. Then, a feed gas containing 20% ​​by volume carbon dioxide (CO2) and 80% by volume hydrogen (H2) is supplied to the reactor 10 via gas inlet 10a. At this time, heated feed gas is supplied to the reactor 10, causing the heated feed gas to circulate around the methanation catalyst 2. This induces a methanation reaction to generate methane (CH4) (first generation step S13). At this time, the methanation catalyst 2 undergoes a reduction effect due to the methanation reaction, thus reducing the nickel oxide remaining in the methanation catalyst 2 to metallic nickel. The methane, along with the simultaneously generated water (H2O), flows out from the gas outlet 10b of the reactor 10.

[0046] Next, as Figure 1 and Figure 2D As shown, the methanation reaction is stopped by ceasing the supply of raw material gas to the reactor 10, thereby lowering the temperature of the methanation catalyst 2 to below the temperature of the oxygen-containing gas at the gas inlet 10a of the reactor 10 in the subsequent oxidation process. Then, using the methanation catalyst 2 treatment method of one embodiment, oxygen-containing gas containing oxygen and nitrogen is supplied to the reactor 10 through the gas inlet 10a, allowing the oxygen-containing gas to circulate around the methanation catalyst 2, thus heat-treating the methanation catalyst 2. At this time, the temperature of the oxygen-containing gas at the gas inlet 10a of the reactor 10 is kept in the range of 60 to 150°C by heating the oxygen-containing gas. Furthermore, the oxygen concentration of the oxygen-containing gas is set to 1 to 3% by volume, and oxygen-containing gas is supplied to the reactor 10 at a supply rate of 0.0213 to 0.0638 mmol-O2 / sec·g-cat. Oxygen-containing gas is supplied to 1g of methanation catalyst 2. In addition, the pressure inside the reactor 10 is set to 1 atm (atmosphere). Furthermore, the heat treatment time for the methanation catalyst 2, which involves supplying oxygen-containing gas to the reactor 10, is set to 30 minutes or more. This heat treatment of the methanation catalyst 2 causes partial oxidation of the surface of metallic nickel, thereby forming a nickel oxide film containing nickel oxide (NiO) (processing step (oxidation step) S14). In the methanation catalyst 2 where the surface of metallic nickel partially forms a nickel oxide film in the processing step, nickel is contained as a catalyst component, existing in the form of metallic nickel and nickel oxide. The weight ratio of metallic nickel content to the total content of metallic nickel and nickel oxide is, for example, in the range of 58 to 67% by weight.

[0047] Next, as Figure 1 and Figure 2EAs shown, the supply of oxygen-containing gas to the reactor 10 is stopped, thereby ending the processing step (oxidation step) and stopping the operation of the manufacturing equipment including the reactor 10 (stop step S15). During the shutdown of the manufacturing equipment, atmospheric air may sometimes intrude into the reaction system inside the reactor 10 from outside the furnace.

[0048] Next, as Figure 1 and Figure 2F As shown, a feed gas containing 20% ​​by volume carbon dioxide (CO2) and 80% by volume hydrogen (H2) is supplied to the reactor 10 via gas inlet 10a. At this time, similar to the first generation step, the heated feed gas is supplied to the reactor 10. This causes a methanation reaction to produce methane (second generation step S16).

[0049] As described above, in the methane production method of one embodiment, after methane is generated by the initial methanation reaction in the first generation step, before the operation of the production equipment including the reactor 10 is stopped by the shutdown step, in the processing step (oxidation step), oxygen-containing gas with temperature and oxygen concentration controlled within a predetermined range is supplied to the reactor 10 by the processing method of the methanation catalyst 2 of one embodiment, thereby heat-treating the methanation catalyst 2. As a result, by slowly oxidizing the surface portion of the metallic nickel contained in the methanation catalyst 2, a nickel oxide film is formed. Therefore, even if the methanation catalyst 2 is exposed to the atmosphere due to atmospheric intrusion into the reaction system inside the reactor 10 from outside the furnace during the shutdown of the production equipment, the oxidation reaction of metallic nickel caused by the high concentration of oxygen in the atmosphere is suppressed by the nickel oxide film covering its surface. Thus, even if the methanation catalyst 2 is in contact with the atmosphere at a high temperature, for example, exceeding 50°C, a rapid oxidation reaction of metallic nickel can be avoided. As a result, oxidation into the interior of the metallic nickel can be suppressed. Furthermore, it can suppress the deterioration of methanation catalyst 2 caused by factors such as the heating resulting from the rapid oxidation reaction of metallic nickel, leading to the aggregation of the support and / or nickel. Therefore, it can suppress the degradation of the catalytic performance of methanation catalyst 2.

[0050] Therefore, in the methanation catalyst treatment method and methane manufacturing method of the embodiments, as shown in one embodiment, the reduction in catalyst performance of the methanation catalyst can be suppressed.

[0051] Next, the method for processing the methanation catalyst, the method for producing methane, and the composition of the methanation catalyst according to the embodiments will be described in detail.

[0052] 1. Treatment methods for methanation catalysts

[0053] The method for processing the methanation catalyst according to the embodiment is characterized by an oxidation step, in which oxygen-containing gas (O2) is supplied to a reactor containing a methanation catalyst containing nickel (Ni) as a catalyst component, thereby heat-treating the methanation catalyst to oxidize the nickel. The oxygen-containing gas is supplied to the reactor at a supply rate of 0.0213 to 0.0638 mmol-O2 / sec·g-cat., and the time for heat-treating the methanation catalyst by supplying the oxygen-containing gas to the reactor is set to 30 minutes or more.

[0054] As a methanation catalyst, there are no particular limitations as long as the catalyst contains nickel as a catalyst component, and it typically contains a support and nickel supported on the support. Porous supports are preferred, for example. Materials constituting the support are, for example, cerium oxide, silicon oxide, silicon oxide-alumina, titanium oxide, zirconium oxide, cerium oxide-zirconium oxide, etc. The nickel catalyst component is not particularly limited in methanation catalysts that are subject to heat treatment in the oxidation process, as long as it exists at least in the form of metallic nickel (metallic Ni), and it can also exist in the form of metallic nickel and nickel oxide (NiO). In addition to nickel, the methanation catalyst may also contain components with methanation catalytic ability as catalyst components. Nickel and other catalyst components are, for example, in particulate form.

[0055] In methanation catalysts containing a support and nickel, the weight ratio of nickel content to the total content of the support and nickel is not particularly limited, but is preferably in the range of 20 to 60% by weight, and more preferably in the range of 30 to 50% by weight. This is because high methanation activity can be obtained by keeping the weight ratio above the lower limit of this range. That is, because active sites sufficient to fully induce the methanation reaction can be obtained. Furthermore, by keeping the weight ratio below the upper limit of this range, the specific surface area of ​​the support component that contributes to Ni particle dispersion can be ensured, and excessive Ni particle growth can be suppressed.

[0056] As a method for oxidizing nickel by heat-treating the methanation catalyst by supplying oxygen-containing gas to the reactor, there are no particular limitations as long as nickel can be oxidized by heating the methanation catalyst while oxygen-containing gas is circulating around it. For example, a method can be given by heating the oxygen-containing gas to set the temperature of the oxygen-containing gas at the gas inlet of the reactor to a predetermined range as described later, and then circulating the heated oxygen-containing gas around the methanation catalyst. As a method for oxidizing nickel, for example, a method can be given by partially oxidizing the surface of metallic nickel (metallic Ni) to form a nickel oxide film containing nickel oxide (NiO).

[0057] The oxygen supply rate [mmol-O2 / sec·g-cat.] when supplying oxygen-containing gas to the reactor refers to the amount of oxygen supplied per 1g of methanation catalyst per second when oxygen-containing gas is supplied to the reactor. There is no particular limitation on this oxygen supply rate as long as it is within the range of 0.0213 to 0.0638 mmol-O2 / sec·g-cat. This is because by keeping the oxygen supply rate above the lower limit of this range, metallic nickel can be appropriately oxidized, thereby suppressing the rapid oxidation reaction of metallic nickel upon atmospheric exposure. Conversely, by keeping the oxygen supply rate below the upper limit of this range, excessive oxidation of metallic nickel that degrades catalyst performance can be suppressed.

[0058] The oxygen concentration of the oxygen-containing gas is not particularly limited as long as the oxygen supply rate is within the aforementioned range, but is preferably in the range of 1 to 3% by volume. This is because by keeping the oxygen concentration of the oxygen-containing gas above the lower limit of this range, metallic nickel can be readily and appropriately oxidized, thereby suppressing the rapid oxidation reaction of metallic nickel upon atmospheric exposure. Conversely, by keeping the oxygen concentration of the oxygen-containing gas below the upper limit of this range, excessive oxidation of metallic nickel that degrades catalyst performance can be easily suppressed.

[0059] The flow rate of oxygen-containing gas supplied to the reactor is not particularly limited as long as the oxygen supply rate is within the aforementioned range, but is preferably in the range of 3.33 to 30 L / min. This is because by keeping the flow rate of oxygen-containing gas above the lower limit of this range, metallic nickel can be readily and appropriately oxidized, thereby suppressing the rapid oxidation reaction of metallic nickel upon atmospheric exposure. Conversely, by keeping the flow rate of oxygen-containing gas below the upper limit of this range, excessive oxidation of metallic nickel that degrades catalyst performance can be easily suppressed.

[0060] The temperature of the oxygen-containing gas at the gas inlet of the aforementioned reactor is not particularly limited as long as the oxygen supply rate remains within the aforementioned range, but is preferably in the range of 60 to 150°C. This is because by keeping the temperature of the oxygen-containing gas above the lower limit of this range, metallic nickel is readily and appropriately oxidized, thereby suppressing the rapid oxidation reaction of metallic nickel upon atmospheric exposure. Conversely, by keeping the temperature of the oxygen-containing gas below the upper limit of this range, excessive oxidation of metallic nickel that degrades catalyst performance is easily suppressed.

[0061] The pressure inside the reactor when supplying oxygen-containing gas to the reactor is not particularly limited, but it is usually 1 atm (atmosphere), or it can be higher than 1 atm.

[0062] The heat treatment time for the methanation catalyst by supplying oxygen-containing gas to the aforementioned reactor is only 30 minutes or more. If the heat treatment time is shorter than this range, it may be impossible to oxidize the metallic nickel in the methanation catalyst. On the other hand, even if the heat treatment time is longer within this range, the surface portion of the metallic nickel will be stabilized by nickel oxide, thus preventing excessive oxidation of the metallic nickel.

[0063] 2. Methods for producing methane

[0064] The method for producing methane according to the embodiments is characterized by having a processing step and a generation step. In the processing step, the methanation catalyst housed in the reactor is heat-treated in the oxidation step using the methanation catalyst processing method of the embodiments, thereby oxidizing the nickel. In the generation step, methane is generated by supplying a feed gas containing carbon dioxide (CO2) and hydrogen (H2) to the reactor. The reactor houses the methanation catalyst in which the nickel was oxidized in the processing step.

[0065] As a method for generating methane by supplying a feed gas containing carbon dioxide and hydrogen to a reactor, there are no particular limitations as long as methane can be generated in the methanation reaction by circulating the feed gas around the methanation catalyst. For example, a preferred method is to supply heated feed gas to the reactor and circulate the heated feed gas around the methanation catalyst to generate methane in the methanation reaction. Since the starting temperature of the methanation reaction is about 150°C or higher, the heating temperature of the feed gas in such a process is usually 150°C or higher.

[0066] The feed gas is not particularly limited as long as it contains carbon dioxide and hydrogen; for example, it can be a gas containing 20% ​​by volume carbon dioxide and 80% by volume hydrogen. The flow rate of the feed gas supplied to the reactor is not particularly limited as long as it can generate methane; for example, it is preferably in the range of 0.070 to 0.400 L / min relative to 1 g of methanation catalyst. This is because by keeping the flow rate above the lower limit of this range, a sufficient amount of methane generated per unit time can be obtained, and by keeping the flow rate below the upper limit of this range, methane can be obtained at a sufficiently high level of purity. The pressure inside the reactor when supplying the feed gas is not particularly limited; for example, it is preferably in the range of 1 to 5 atm. This is because by keeping the pressure above the lower limit of this range, atmospheric components can be prevented from mixing into the reactor, and the pressure required to sufficiently induce the methanation reaction can be obtained. Furthermore, by keeping the pressure below the upper limit of this range, the increase in energy required for pressurization can be suppressed, the energy efficiency of methanation can be suppressed, and high-pressure equipment is not required, thus reducing equipment implementation costs.

[0067] As for the method of producing methane, there is no particular limitation as long as the method described above is used. It is preferable to satisfy the following formulas (1) to (4) when the temperature [°C] of the oxygen-containing gas at the gas inlet of the reactor in the oxidation process is set to X1, the oxygen concentration [volume %] of the oxygen-containing gas in the oxidation process is set to X2, and the temperature [°C] of the raw material gas at the gas inlet of the reactor when the conversion rate of carbon dioxide in the generation process reaches 50% is set to Y. By setting the temperature X1 and the concentration X2 so that the temperature Y is less than 250°C, the methanation reaction can be carried out using a methanation catalyst that suppresses the excessive oxidation of metallic nickel that reduces the performance of the catalyst. Furthermore, the operating temperature of the methanation reaction can be set to a low temperature, which can reduce the energy consumption. By setting the temperature X1 and the concentration X2 so that the temperature Y reaches 160°C or more, the methanation reaction can be carried out using a methanation catalyst in which metallic nickel has been oxidized.

[0068] Y=153.091+0.487X1+17.714X2 (1)

[0069] 160≤Y<250 (2)

[0070] 0 < X1 (3)

[0071] 0 < X2 (4)

[0072] The method for obtaining the temperature Y of the feed gas at the gas inlet of the reactor when the carbon dioxide conversion rate reaches 50% in the production process is as follows. In the production process, while raising the temperature of the feed gas at the gas inlet of the reactor, for example, from 150°C to 400°C, the carbon dioxide concentration [volume %] of the outflow gas at the gas outlet of the reactor is measured. Then, at each temperature of the feed gas at the gas inlet, the carbon dioxide conversion rate is calculated based on the carbon dioxide concentration [volume %] of the feed gas and the carbon dioxide concentration of the outflow gas. Next, based on this calculation result, the change in carbon dioxide conversion rate relative to the feed gas temperature at the gas inlet is calculated, and the temperature Y is obtained based on this change in conversion rate.

[0073] 3. Methanation catalyst

[0074] The methanation catalyst of the embodiment is a methanation catalyst containing nickel as a catalyst component, wherein the nickel exists in the form of metallic nickel (Ni) and nickel oxide (NiO), and the weight ratio of the metallic nickel to the total weight of the metallic nickel and the nickel oxide is in the range of 58 to 67% by weight. Because by keeping the weight ratio of metallic nickel above the lower limit of this range, sufficient catalyst performance can be ensured. Because by keeping the weight ratio of metallic nickel below the upper limit of this range, when the methanation catalyst is exposed to the atmosphere, the rapid oxidation reaction of metallic nickel can be suppressed by the nickel oxide film covering the surface of the metallic nickel, thereby maintaining sufficient catalyst performance.

[0075] The methanation catalyst is not particularly limited. For example, it can be a nickel-oxidized methanation catalyst produced by oxidizing nickel through heat treatment of the methanation catalyst housed in the reactor during the oxidation process using the methanation catalyst processing method of the embodiment.

[0076] [Example]

[0077] The following examples and comparative examples illustrate in more detail the method for processing the methanation catalyst, the method for producing methane, and the methanation catalyst according to embodiments of the present invention.

[0078] [Example 1]

[0079] Experiments were conducted on the methane production method involved in the implementation method. Figure 3 This is a flowchart illustrating the experimental procedure for implementing the methane production method of Example 1.

[0080] In the experiment, firstly, as Figure 3 As shown, a methanation catalyst containing nickel (Ni) as a catalyst component is prepared, comprising a support and nickel supported on the support, wherein the support is composed of cerium oxide (CeO2), and the methanation catalyst is placed in the reactor of a methane production equipment (preparation and placement step S21). In the prepared methanation catalyst, the nickel content relative to the total content of cerium oxide and nickel is 39% by weight, and the weight of the prepared methanation catalyst is 3.5 g. The prepared methanation catalyst is sintered under an oxygen atmosphere during synthesis, so that nickel exists not only in the form of metallic nickel (metallic Ni) but also in the form of nickel oxide (NiO).

[0081] Next, as Figure 3 As shown, a reducing gas containing 20% ​​by volume hydrogen (H2) and 80% by volume nitrogen (N2) at 400°C is supplied to the reactor via a gas inlet, thereby circulating the reducing gas around the methanation catalyst. Thus, metallic nickel is formed by reducing the nickel oxide in the methanation catalyst (reduction step S22).

[0082] Next, as Figure 3 As shown, the reduction process is terminated by stopping the supply of reducing gas to the reactor. Then, without removing the methanation catalyst from the reactor, the temperature of the methanation catalyst is lowered to below the temperature of the oxygen-containing gas at the gas inlet of the reactor in the subsequent oxidation process. Then, oxygen-containing gas containing oxygen and nitrogen is supplied to the reactor through the gas inlet, thereby circulating oxygen-containing gas around the methanation catalyst and heat-treating it. At this time, as shown in Table 1, the temperature of the oxygen-containing gas at the gas inlet of the reactor is raised to 60°C by heating the oxygen-containing gas. Furthermore, by setting the oxygen concentration of the oxygen-containing gas to 2% by volume and the flow rate of the oxygen-containing gas supplied to the reactor to 10 L / min, oxygen-containing gas can be supplied to the reactor at a supply rate of 0.0425 mmol-O2 / sec·g-cat. to supply oxygen to 1 g of methanation catalyst. Furthermore, when the flow rate of the oxygen-containing gas is 10 L / min, the space velocity (SV) is SV = 188679 h. -1 The space velocity SV is calculated by dividing the flow rate of oxygen-containing gas by the volume of the methanation catalyst. Furthermore, the pressure inside the reactor is set to 1 atm (atmosphere). The time for heat-treating the methanation catalyst by supplying oxygen-containing gas to the reactor is set to 30 minutes. Through this heat treatment of the methanation catalyst, the surface of metallic nickel is partially oxidized, thereby forming a nickel oxide film containing nickel oxide (NiO) (oxidation step S23).

[0083] Next, as Figure 3 As shown, after the oxidation process is ended by stopping the supply of oxygen-containing gas to the reactor, the methanation catalyst is removed from the reactor and exposed to the atmosphere when the temperature of the methanation catalyst in the reactor drops to 80°C, and left there until the temperature of the methanation catalyst drops to room temperature (atmospheric exposure S24).

[0084] Next, as Figure 3 As shown, the methanation catalyst, after being exposed to the atmosphere, is returned to the reactor. A feed gas containing 20% ​​by volume carbon dioxide (CO2) and 80% by volume hydrogen (H2) is then supplied to the reactor through the gas inlet. At this point, the feed gas flow rate is 0.530 L / min (space velocity SV = 10000 h⁻¹). -1 The pressure inside the reactor was set to 3 atm. The heated feed gas was supplied to the reactor while its temperature at the reactor inlet was increased from 150°C to 400°C by heating the feed gas. By circulating the heated feed gas around the methanation catalyst, a methanation reaction was initiated to produce methane (production step S25). An experiment was conducted to implement the methane production method as described above.

[0085] [Example 2]

[0086] As shown in Table 1 below, in the oxidation process, the oxygen supply rate was changed to 0.0638 mmol-O2 / sec·g-cat., by changing the oxygen concentration of the oxygen-containing gas to 3% by volume. Otherwise, the experiment of implementing the methane production method was carried out in the same manner as in Example 1.

[0087] [Comparative Example 1]

[0088] As shown in Table 1 below, in the oxidation process, the oxygen supply rate was changed to 0.2126 mmol-O2 / sec·g-cat., by changing the oxygen concentration of the oxygen-containing gas to 10% by volume. Otherwise, the experiment of implementing the methane production method was carried out in the same manner as in Example 1.

[0089] [Example 3]

[0090] As shown in Table 1 below, in the oxidation process, the temperature of the oxygen-containing gas at the gas inlet of the reactor was changed to 100°C, and the oxygen supply rate was changed to 0.0213 mmol-O2 / sec·g-cat. by changing the oxygen concentration of the oxygen-containing gas to 1% by volume. Otherwise, the experiment of implementing the methane production method was carried out in the same manner as in Example 1.

[0091] [Example 4]

[0092] As shown in Table 1 below, in the oxidation process, the oxygen supply rate was changed to 0.0425 mmol-O2 / sec·g-cat. by changing the oxygen concentration of the oxygen-containing gas to 2% by volume. Otherwise, the experiment of implementing the methane production method was carried out in the same manner as in Example 3.

[0093] [Comparative Example 2]

[0094] As shown in Table 1 below, in the oxidation process, the oxygen supply rate was changed to 0.0850 mmol-O2 / sec·g-cat., and the methane production method was carried out in the same manner as in Example 3.

[0095] [Example 5]

[0096] As shown in Table 1 below, in the oxidation process, the temperature of the oxygen-containing gas at the gas inlet of the reactor was changed to 150°C, and the oxygen supply rate was changed to 0.0213 mmol-O2 / sec·g-cat. by changing the oxygen concentration of the oxygen-containing gas to 1% by volume. Otherwise, the experiment of implementing the methane production method was carried out in the same manner as in Example 1.

[0097] [Example 6]

[0098] As shown in Table 1 below, in the oxidation process, the oxygen supply rate was changed to 0.0425 mmol-O2 / sec·g-cat., and the methane production method was carried out in the same manner as in Example 5.

[0099] [Comparative Example 3]

[0100] As shown in Table 1 below, in the oxidation process, the oxygen supply rate was changed to 0.0850 mmol-O2 / sec·g-cat., and the methane production method was carried out in the same manner as in Example 5.

[0101] [Comparative Example 4]

[0102] As shown in Table 1 below, in the oxidation process, the temperature of the oxygen-containing gas at the gas inlet of the reactor was changed to 200°C, and the oxygen supply rate was changed to 0.0021 mmol-O2 / sec·g-cat. by changing the oxygen concentration of the oxygen-containing gas to 0.1 vol%. Otherwise, the experiment of implementing the methane production method was carried out in the same manner as in Example 1.

[0103] [Example 7]

[0104] As shown in Table 1 below, in the oxidation process, the temperature of the oxygen-containing gas at the gas inlet of the reactor was changed to 300°C, and the oxygen supply rate was changed to 0.0213 mmol-O2 / sec·g-cat. by changing the oxygen concentration of the oxygen-containing gas to 1% by volume. Otherwise, the experiment of implementing the methane production method was carried out in the same manner as in Example 1.

[0105] [Example 8]

[0106] As shown in Table 1 below, in the oxidation process, the oxygen supply rate was changed to 0.0425 mmol-O2 / sec·g-cat. by changing the oxygen concentration of the oxygen-containing gas to 2% by volume. Otherwise, the experiment of implementing the methane production method was carried out in the same manner as in Example 7.

[0107] [Comparative Example 5]

[0108] As shown in Table 1 below, in the oxidation process, the oxygen supply rate was changed to 0.0850 mmol-O2 / sec·g-cat., and the methane production method was carried out in the same manner as in Example 7.

[0109] [Comparative Example 6]

[0110] As shown in Table 1 below, after the reduction process, no oxidation process or atmospheric exposure was performed. The methanation catalyst was not removed from the reactor but kept in its original state, and the temperature of the methanation catalyst was lowered to below the initial temperature (150°C) of the feed gas at the gas inlet of the reactor in the subsequent generation process. Based on this, feed gas was supplied to the reactor through the gas inlet, causing the feed gas to circulate around the methanation catalyst, thereby initiating a methanation reaction to generate methane (generation process). Apart from this, experiments implementing the methane production method were conducted in the same manner as in Example 1.

[0111] [Comparative Example 7]

[0112] As shown in Table 1 below, after the reduction process, no oxidation process was performed. When the temperature of the methanation catalyst in the reactor dropped to 30°C, the methanation catalyst was removed from the reactor and exposed to the atmosphere (atmospheric exposure). Then, the atmospheric-exposed methanation catalyst was returned to the reactor, and feed gas was supplied to the reactor through the gas inlet. This allowed the feed gas to circulate around the methanation catalyst, initiating the methanation reaction and generating methane (generation process). Otherwise, experiments were conducted in the same manner as in Example 1 to implement the methane production method.

[0113] [Comparative Example 8]

[0114] As shown in Table 1 below, when the temperature of the methanation catalyst in the reactor dropped to 60°C during atmospheric exposure, the methanation catalyst was removed from the reactor and exposed to the atmosphere. Otherwise, the same experiment as Comparative Example 7 was conducted to implement the methane production method.

[0115] Table 1

[0116]

[0117] *The underlined part indicates that it is outside the scope of the present invention.

[0118] Temperature changes of methanation catalysts when exposed to atmosphere

[0119] The temperature changes of the methanation catalysts in Examples 1-8 and Comparative Examples 1-5, 7, and 8 during atmospheric exposure were evaluated. Specifically, in each example, the surface temperature of the methanation catalyst was measured using an infrared temperature sensor while it was removed from the reactor and exposed to the atmosphere. As a result, no increase in the surface temperature of the methanation catalysts in Examples 1-8 and Comparative Examples 1-5 was observed during atmospheric exposure. This is believed to be because the surface of the nickel contained in the methanation catalyst is partially oxidized during the oxidation process, forming a nickel oxide film, thus achieving a stable state and avoiding the rapid oxidation reaction of nickel during atmospheric exposure. Furthermore, no increase in the surface temperature of the methanation catalyst in Comparative Example 7 was observed during atmospheric exposure. This is believed to be due to the low temperature during atmospheric exposure. On the other hand, a sharp increase in the surface temperature of the methanation catalyst was observed during atmospheric exposure in Comparative Example 8. This is believed to be due to the high temperature during atmospheric exposure.

[0120] [Change in carbon dioxide conversion rate relative to the temperature of the feed gas at the reactor inlet]

[0121] For Examples 1-8 and Comparative Examples 1-8, the change in carbon dioxide conversion rate relative to the feed gas temperature at the gas inlet of the reactor during the production process was evaluated. Specifically, in the production process of each example, as the feed gas temperature at the gas inlet of the reactor was increased from 150°C to 400°C, the carbon dioxide concentration [volume %] and methane concentration [volume %] of the effluent gas at the gas outlet of the reactor were determined by gas chromatography. Based on this, at each temperature of the feed gas at the gas inlet, the carbon dioxide conversion rate (%) was calculated based on the carbon dioxide concentration of the feed gas and the carbon dioxide concentration of the effluent gas (=(carbon dioxide concentration of feed gas - carbon dioxide concentration of effluent gas) ÷ carbon dioxide concentration of feed gas × 100).

[0122] Based on the calculation results of the carbon dioxide conversion rate at various temperatures of the feed gas at the gas inlet in Examples 1-8 and Comparative Examples 1-8, the change in carbon dioxide conversion rate relative to the temperature of the feed gas at the gas inlet was determined. Figures 4-8 This is a graph showing the change in carbon dioxide conversion rate relative to the feed gas temperature at the gas inlet in Examples 1-8 and Comparative Examples 1-8. The conditions in the oxidation process shown in Table 1 above are compared with those in Examples 1-8. Figures 4-8The coordinate graph shown illustrates that the catalytic performance of the methanation catalyst varies depending on the temperature and oxygen concentration of the oxygen-containing gas during the oxidation process. Furthermore, it suggests that the conditions during the oxidation process indicate a range within which the catalytic performance of the methanation catalyst can be maintained regardless of whether the catalyst is exposed to the atmosphere.

[0123] To ensure the catalytic reaction of the methanation catalyst proceeds fully, external heating is required. However, since methanation is an exothermic reaction, if the carbon dioxide conversion rate reaches approximately 50%, the methanation catalyst is heated by the heat of reaction, and the carbon dioxide conversion rate reaches its maximum. For this reason, the temperature Y [°C] of the feed gas at the reactor inlet when the carbon dioxide conversion rate reaches 50% in the production process is crucial, serving as an indicator of the suitability of conditions in the oxidation process. Therefore, based on the changes in carbon dioxide conversion rate relative to the feed gas temperature Y at the gas inlet in Examples 1-8 and Comparative Examples 1-8, the feed gas temperature Y at the reactor inlet when the carbon dioxide conversion rate reaches 50% in each example was determined. Based on this result, Table 2 below shows the feed gas temperature Y at the reactor inlet when the carbon dioxide conversion rate reaches 50% in the production process, relative to the oxygen-containing gas temperature X1 and oxygen concentration X2 at the reactor inlet in the oxidation process. In Table 2 below, when temperature Y is less than 250°C, a "○" is marked in parentheses to indicate favorable conditions for temperature X1 and concentration X2. When temperature Y is above 250°C, a "×" is marked in parentheses to indicate unfavorable conditions for temperature X1 and concentration X2. The reasons for setting the threshold temperature Y to 250°C and considering temperatures less than 250°C as favorable conditions can be cited as follows: 1) The lower the operating temperature of the methanation reaction, the better (energy consumption increases at high temperatures); and 2) If the temperature of the methanation catalyst reaches above 350°C, it may cause a reverse reaction of the methanation reaction, reducing the reactivity of the methanation reaction. If temperature Y is less than 250°C, it is easier to suppress the temperature of the methanation catalyst to below 350°C, etc.

[0124] Table 2

[0125] In contrast to the oxygen-containing gas temperature X1 and oxygen concentration X2 in the oxidation process,

[0126] The temperature of the raw gas Y when the carbon dioxide conversion rate reaches 50% in the production process

[0127]

[0128] *1 "○" The "○" in parentheses indicates favorable conditions where temperature Y is less than 250℃, and the "×" in parentheses indicates unfavorable conditions where temperature Y is above 250℃.

[0129] *2 Using data other than those in the colored cells, derive a regression formula representing the relationship between the target variable (Y) and the explanatory variables (X1, X2).

[0130] Furthermore, we attempted to generalize the relationship between the temperature of the raw material gas Y at the gas inlet of the reactor in the oxidation process, where the carbon dioxide conversion rate reaches 50% and the gas temperature X1 and oxygen concentration X2 at the gas inlet of the reactor, as in the production process where the temperature Y is less than 250°C. Specifically, we used temperature Y [°C] as the target variable and temperature X1 [°C] and concentration X2 [volume %] as explanatory variables. We performed multiple regression analysis using data from multiple sets of Y, X1, and X2 shown in Table 2 above, excluding the data in the colored cells. This served as the regression equation representing the relationship between the target variable (Y) and the explanatory variables (X1 and X2), leading to the following equation (1). Moreover, the data in the colored cells of the multiple sets of data shown in Table 2 above were excluded to improve the accuracy of the regression equation (1) below.

[0131] Y=153.091+0.487X1+17.714X2 (1)

[0132] In the above formula (1), the Y value calculated when X1 is input as 60 to 300°C and X2 is input as 0.1 to 10% by volume is shown in Table 3 below.

[0133] Table 3 shows the Y calculated after inputting values ​​for X1 and X2 in equation (1).

[0134]

[0135] Comparing Table 2 and Table 3 above, it can be seen that the temperature Y recorded in Table 2 under favorable conditions of temperature X1 and concentration X2 is not significantly different from the temperature Y recorded in Table 3 calculated using the favorable conditions of temperature X1 and concentration X2. Therefore, it is considered that the accuracy of the regression equation (1) above is high.

[0136] [Example 9]

[0137] As shown in Table 4 below, the experiment was conducted in the same manner as in Example 3, except that atmospheric exposure was performed without the generation process.

[0138] [Example 10]

[0139] As shown in Table 4 below, the experiment was conducted in the same manner as in Example 4, except that atmospheric exposure was performed without the generation process.

[0140] [Comparative Example 9]

[0141] As shown in Table 4 below, the experiment was conducted with atmospheric exposure but without the generation process, otherwise the same experiment as Comparative Example 2 was performed.

[0142] [Comparative Example 10]

[0143] As shown in Table 4 below, the experiment was conducted with atmospheric exposure but without the generation process, otherwise the same experiment as Comparative Example 7 was performed.

[0144] [Weight ratio of metallic Ni to NiO in the methanation catalyst]

[0145] For the atmospheric-exposed methanation catalysts in Examples 9 and 10 and Comparative Examples 9 and 10, the weight ratio of metallic nickel content to the total content of metallic nickel (Ni) and nickel oxide (NiO) was determined. Specifically, 1 g of powder sample was prepared from the atmospheric-exposed methanation catalysts of each example, and X-ray diffraction (XRD) was performed on the prepared powder sample to determine the X-ray diffraction pattern. The XRD determination was performed on the powder sample under inert atmosphere using CuKα lines. Figures 9-12 These are X-ray diffraction patterns of the methanation catalysts after atmospheric exposure in Examples 9 and 10, and Comparative Examples 9 and 10, respectively. Figures 9-12 As shown, in any of Examples 9 and 10 and Comparative Examples 9 and 10, peaks of metallic nickel and nickel oxide were confirmed in the X-ray diffraction patterns of the methanation catalyst after atmospheric exposure. Furthermore, peaks of cerium oxide were also confirmed.

[0146] Next, Rietveld analysis was performed on the X-ray diffraction data to calculate the weight ratio of nickel content [wt%] and the weight ratio of nickel oxide content [wt%] relative to the total content of nickel metal (Ni) and nickel oxide (NiO) for each example of atmospheric-exposed methanation catalyst. The results are shown in Table 4 below.

[0147] Table 4

[0148]

[0149] *The underlined part indicates that it is outside the scope of the present invention.

[0150] Comparing the calculated weight ratios shown in Table 4 above with the conditions of the oxidation process that can maintain the catalytic performance of the methanation catalyst as determined by the results in Table 4 above, it is considered that the weight ratios of metallic nickel content and nickel oxide content in Examples 9 and 10 are weight ratios that can maintain the catalytic performance of the methanation catalyst even after atmospheric exposure. Therefore, from the viewpoint of maintaining the catalytic performance of the methanation catalyst, it is considered that the weight ratio of metallic nickel content is preferably 58-67% by weight, and the weight ratio of nickel oxide content is preferably 42-33% by weight.

[0151] The above describes in detail the method for processing the methanation catalyst, the method for manufacturing methane, and the implementation of the methanation catalyst of the present invention. However, the present invention is not limited to the above implementation. Various design changes can be made without departing from the spirit of the present invention as described in the patent claims.

Claims

1. A method for producing methane, characterized in that, It has oxidation, stopping, and forming processes. In the oxidation process, oxygen-containing gas containing oxygen and nitrogen is supplied to a reactor containing a methanation catalyst with nickel as a catalyst component, thereby heat-treating the methanation catalyst and oxidizing the nickel. In the shutdown process, the supply of oxygen-containing gas to the reactor is stopped, thereby ending the oxidation process and stopping the operation of the reactor. After the reactor is shut down, methane is generated in the production process by supplying a feed gas containing carbon dioxide and hydrogen to the reactor, which houses the methanation catalyst from which the nickel was oxidized in the oxidation process. In the oxidation process, oxygen-containing gas is supplied to the reactor at a rate of 0.0213–0.0638 mmol-O2 / sec·g-cat., and the time for heat treatment of the methanation catalyst by supplying oxygen-containing gas to the reactor is set to at least 30 minutes. In the oxidation process, the oxygen concentration of the oxygen-containing gas is set to 1-3% by volume, and the temperature of the oxygen-containing gas at the gas inlet of the reactor is set to 60-150°C. When the temperature of the oxygen-containing gas at the gas inlet of the reactor in the oxidation process is set to X1, the oxygen concentration of the oxygen-containing gas in the oxidation process is set to X2, and the temperature of the raw material gas at the gas inlet of the reactor when the conversion rate of carbon dioxide in the generation process reaches 50% is set to Y, the following equations (1) to (4) are satisfied. Y=153.091+0.487X1+17.714X2 (1) 160≤Y＜250 (2) 0＜X1 (3) 0＜X2 (4) The unit for temperature is °C, and the unit for oxygen concentration is volume.

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