JPS632938B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for methanating carbon monoxide-containing gas, and more specifically, to efficiently converting coal gasification gas or heavy oil gasification gas containing high concentration carbon monoxide gas into methane. This invention relates to a methanation method using a catalyst layer containing nickel oxide as a fixed catalyst layer. [Prior Art] In view of the recent energy situation, a method of obtaining alternative natural gas by converting highly concentrated carbon monoxide gas obtained by gasifying heavy oil or coal into methane is a very promising process. In recent years, many reports have been published on methane synthesis from coal gasification gas. Particularly in the United States, full-scale research is being carried out, and in Japan, a project aimed at producing high-calorie gas is being set up as part of the Sunshine Plan. This methane synthesis reaction is a reaction accompanied by the generation of a large amount of reaction heat, and it is very important from the economical point of view of the methane synthesis process to effectively utilize the reaction heat as an energy source. In order to make effective use of this reaction heat, it is most preferable to carry out the reaction at a high temperature, but if the catalyst normally used for methane synthesis reaction is used with such a high concentration of carbon monoxide gas, it will be affected by heat and steam in the atmosphere. It is known that the catalyst deteriorates significantly due to causes such as sintering and carbonaceous formation. Furthermore, carbonaceous matter produced by bonding of carbon atoms on the catalyst sometimes causes clogging of the reaction tube, making it physically impossible to continue the reaction. For example, if an ordinary nickel-based methanation catalyst, which is currently in general use, is used in such a process, the initial activity is too high, causing problems such as deterioration of catalyst activity and heat removal from the equipment due to extremely high heat generation. Therefore, operations such as diluting the catalyst and filling it or reducing the amount of raw material gas supplied are required. These methods are technically and economically problematic. It is also possible to lower the initial activity by reducing the amount of nickel contained in the catalyst in the range of several percent to several tens of percent, but if the nickel content is reduced below a certain amount, the initial activity will drop significantly. Invitation,
Catalyst performance deteriorates. In order to solve these problems, many conventional methods have been proposed to constantly remove reaction heat and maintain temperature control of the catalyst layer in order to avoid high-temperature reactions. However, in this method, the removal of reaction heat and the reaction rate cannot be kept in equilibrium in the catalyst layer, so a temperature distribution occurs in the catalyst layer, and Ni
(CO) ₄ is produced and the activity of the catalyst is significantly degraded [Double M. Chien (W.
M.SHEN), Journal of Catalysis, 68, 152-165 (1981)].
In other words, when the methanation reaction is carried out at the reactor inlet part (upper part) of the catalyst layer, the temperature rise due to the reaction is small in the lower part (downstream part) of the catalyst bed, so
Nickel retains Ni even when the concentration of carbon monoxide gas is low.
(CO) ₄ is generated, the catalyst in the upper layer of the catalyst layer deteriorates, and when the methanation reaction occurs in the lower layer,
The disadvantage is that the nickel catalyst in the lower layer has already deteriorated. Currently, in addition to the normal nickel catalysts mentioned above,
Catalysts used for methane synthesis from carbon monoxide include (a) platinum group catalysts such as Ru, Pt, Pd, Ir, and Rh, and (b) Ru/Ni catalysts used in fluidized catalyst beds. (0.5% by weight
Ru—10% by weight Ni—Al ₂ O ₃ , 1.0% by weight Ru—10% by weight Ni—Al ₂ O ₃ ) [Tucci, ER, Hydrocarbon Processing 107—
112, 1980-4], etc. Like the above-mentioned nickel catalyst, these catalysts have various drawbacks as methanation catalysts for methanating gas containing high concentration of carbon monoxide. That is, since platinum group elements such as ruthenium are expensive, their use alone poses a serious problem in terms of economic efficiency, and they also have poor sulfur resistance. [Problems to be Solved by the Invention] The present invention has been made to solve these drawbacks, and an object of the present invention is to provide a methanation method that efficiently methanizes carbon monoxide-containing gas. [Means and effects for solving the problem] As a result of studies in line with this purpose, the present inventors found that
The reactor for methanating carbon monoxide-containing gas is an externally cooled type, and the catalyst layer in the reactor is a fixed bed, and the catalyst layer contains nickel oxide, especially a catalyst made of nickel oxide and a platinum group element. The present inventors have discovered that the above object can be fully achieved when a layer is used, and have thus arrived at the present invention. In other words, the methanation method of the present invention is such that when carbon monoxide-containing gas is methanated, (a) the catalyst on the reactor inlet side of the externally cooled reactor is a nickel reduction catalyst or a platinum group element catalyst; Methanation method characterized by using a fixed catalyst bed consisting of a nickel oxide catalyst, or (b) methanation method characterized by using a fixed catalyst bed consisting of a nickel oxide catalyst; This methanation method is characterized by using a mixture of The gas used in the methanation method of the present invention is not particularly limited as long as it contains carbon monoxide gas, but preferably coal gasification gas or heavy oil gasification gas containing carbon monoxide gas at a high concentration. Gas is used. In the present invention, this carbon monoxide-containing gas is introduced into a fixed catalyst bed of an externally cooled reactor to perform methanation. The reactor inlet temperature in this methanation reaction is desirably 450°C or less, preferably 200 to 420°C, from the viewpoint of maintaining the activity of the catalyst. The fixed catalyst layer of the reactor needs to be a catalyst layer containing nickel oxide, and this nickel oxide is
It is prepared by performing treatments such as high temperature treatment to prevent reduction at temperatures below 450°C. In this case, nickel oxide reacts with the carrier and a portion of it forms NiAl ₂ O ₄ , making it difficult to reduce. Preferred catalyst layers containing nickel oxide, which is difficult to reduce at low temperatures, are catalyst layers made of nickel oxide and reduced nickel, or catalyst layers made of nickel oxide and platinum group elements. When using a combination of nickel oxide and reduced nickel, it is desirable to arrange the nickel reduction catalyst in the upper layer of the fixed catalyst layer and the nickel oxide catalyst in the lower layer. Further, when using a combination of nickel oxide and a platinum group element, it is desirable to arrange the platinum group element catalyst in the upper layer of the fixed catalyst layer and the nickel oxide catalyst in the lower layer. Further, when a nickel oxide catalyst and a platinum group element catalyst are used together, a catalyst layer filled with a mechanical mixture of powders of a nickel oxide catalyst and a platinum group element catalyst may be used. In the present invention,
The mixing method is not particularly limited, as long as the chemical or physical interaction between the platinum group element and nickel does not bring out any special properties, and the individual properties can be fully exhibited. In the present invention, a more preferable fixed catalyst layer is a catalyst layer using a catalyst comprising 0.005% by weight or more of a platinum group element, 0.05 to 30% by weight of nickel oxide, and an inorganic heat-resistant carrier. The inorganic heat-resistant carrier mentioned here is an inorganic carrier with excellent heat resistance.
For example, silica, alumina, etc. are exemplified, and among these, γ-alumina is particularly desirable. It is preferable to add a small amount of alkali metal or alkaline earth metal to the carrier such as alumina before supporting the platinum group element or nickel oxide. is suppressed. In the present invention, the reason why the addition amount of the platinum group element can be as small as 0.005% by weight or more is because the methanation reaction of carbon monoxide occurs even with this amount, and it is sufficient to generate enough heat to reduce the nickel oxide. be. In the present invention, any method can be used to support the platinum group element and nickel oxide on the carrier, including immersion, coprecipitation,
Conventional methods such as kneading are employed. Furthermore, the order in which the platinum group element and nickel oxide are supported on the carrier is arbitrary. It may be carried. Further, both may be supported on the carrier at the same time. Next, the reaction of the methanation method of the present invention will be explained by taking as an example a case where a platinum group element catalyst is arranged in the upper layer and a nickel oxide catalyst is arranged in the lower layer as fixed catalyst layers.
Carbon monoxide-containing gas introduced into the externally cooled reactor at a temperature of 450°C or lower first undergoes a methanation reaction only in the upper layer of the catalyst layer. In this case, since nickel oxide is not yet reduced in the low-temperature portion of the lower layer of the catalyst layer, Ni(CO) ₄ is not generated, and only the platinum group element catalyst in the upper layer becomes an active species. This platinum group element catalyst is reduced by hydrogen gas and carbon monoxide gas at low temperatures, and compared to nickel, it is difficult to produce carbonyl, and it plays the role of starting the reaction, and if the reaction temperature is raised to the temperature at which nickel oxide is reduced to nickel. good.
Therefore, the loading amount of the platinum group element catalyst may be such as to draw out the reaction heat to the extent that the nickel oxide in the catalyst layer at the gas inlet is reduced immediately after the start of the reaction. As the temperature rises due to the methanation reaction by the platinum group element catalyst at the gas inlet of the catalyst layer, the nickel oxide at the inlet is reduced to nickel, activated, and participates in the methane reaction. As the nickel catalyst at the gas inlet deteriorates, nickel oxide on the downstream side is reduced and activated to participate in the methanation reaction. As described above, in the methanation method of the present invention, the reaction in the catalyst layer gradually moves downward, all the catalysts participate in the reaction, and there is no inconvenience that the catalyst deteriorates before participating in the reaction. [Examples] The present invention will be specifically described below based on Examples and Comparative Examples. Comparative Example 1 A stainless steel reaction tube with an inner diameter of 16 mm was filled with 20 c.c. of catalyst A (nickel content 10 wt%) in which nickel was supported on an alumina carrier, and the mixture was heated at 500°C in a hydrogen gas stream.
Reduction treatment was carried out for 3 hours. A thermowell with a diameter of 3 mm was installed in the catalyst layer, allowing the temperature of each part of the catalyst layer to be measured. After reduction treatment, the temperature was lowered to 250℃, the pressure was 10Kg/ ^cm2・G, and the hydrogen gas flow rate was 60/
hr, carbon monoxide gas flow rate 20/hr,
Figure 1 shows the relationship between the CO conversion rate and the change over time when the reaction was carried out at GHSV 4000 hr ^-1 . Moreover, the temperature profile of the catalyst layer in this case is shown in FIG. Furthermore, the CO conversion rate after 140 hours is shown in Table 1. Comparative Example 1 shows the activity of the nickel catalyst at a low temperature where the nickel catalyst was pre-reduced to bring all the catalyst layers into a reduced state and then subjected to a methanation reaction. was found to be significantly faster. This deterioration is mainly
This seems to be due to the formation of Ni(CO) ₄ or _Ni3C . Comparative Example 2 Catalyst B containing 0.025 wt % of ruthenium prepared by crushing, mixing and diluting 0.5 wt % of a commercially available ruthenium-alumina catalyst with alumina was added to 20 c.c. in the same manner as in Comparative Example 1.
The reaction tube was filled. After that, at a temperature of 250℃ and a pressure of 10Kg/ ^cm2・G, hydrogen gas flow rate was 60/hr and carbon monoxide gas flow rate was 20/hr.
hr, when methanation reaction was carried out at GHSV4000hr ^-1
Figure 1 shows the relationship between CO conversion rate and changes over time.
Furthermore, the CO conversion rate after 140 hours is shown in Table 1. In this case, unlike Comparative Example 1, reduction treatment was not performed before the reaction. Comparative Example 2 shows the activity when the reaction was carried out using a catalyst containing 0.025 wt% ruthenium, but it was found from FIG. 1 that the activity deteriorated quickly when ruthenium was used alone. That is, Ruthenium 0.025wt
% containing catalyst is sufficient to start the reaction, but is quantitatively insufficient for long-term reaction, and causes a different deterioration than when reduced nickel is used as in Comparative Example 1. I think that the. Example 1 Catalyst A used in Comparative Example 1 and 0.5 wt% commercially available ruthenium-alumina catalyst used in the preparation of Catalyst B in Comparative Example 2 were ground and mixed to determine the ruthenium content.
Catalyst C prepared to have a nickel content of 0.025 wt% and a nickel content of 9.5 wt% was packed into a 20 c.c. reaction tube in the same manner as in Comparative Example 1. After that, at a temperature of 250℃ and a pressure of 10Kg/ ^cm2・G, hydrogen gas flow rate was 60/hr and carbon monoxide gas flow rate was 20/hr.
Figure 1 shows the relationship between the CO conversion rate and the change over time when the reaction was carried out at GHSV 4000 hr ^-1 . Moreover, the temperature profile of the catalyst layer at this time is shown in FIG. Furthermore, the CO conversion rate after 140 hours is shown in Table 1. Note that, as in Comparative Example 2, no reduction treatment was performed before the reaction. As shown in FIG. 1, no deterioration in activity was observed even after 140 hours had passed, indicating that the reaction was much more stable than when catalysts A and B were reacted alone. Moreover, from FIG. 3, heat is generated only at the inlet portion (upper layer portion) of the catalyst layer due to the heat of reaction during one hour after the start of the reaction, and the nickel oxide at the inlet portion is reduced by this heat generation. The nickel oxide in the lower temperature part of the catalyst layer was not reduced and did not deteriorate as in Comparative Example 1. After 400 hours, the peak continues to shift in parallel, indicating that heat generation occurs in the center of the layer. Example 2 After reducing 4 c.c. of catalyst A (nickel content 10 wt%) at 500°C in a hydrogen gas stream for 3 hours,
It was cooled to room temperature in a nitrogen gas stream. Thereafter, a small amount of air was introduced into the nitrogen gas to stabilize the material for several hours while being careful not to generate heat. Fill the gas inlet with this reduction-stabilized catalyst A1c.c.
Catalyst in oxide state without reduction treatment in its lower layer
Filled with A19c.c. As in Comparative Example 2, the reaction was carried out without performing preliminary reduction treatment before the reaction. 140 for this reaction
The CO conversion after hours is shown in Table 1. Example 3 1 c.c. of 0.025 wt % ruthenium catalyst B used in Comparative Example 2 was filled in the gas inlet, and 19 c.c. of oxide catalyst A was filled in the lower layer. The reaction was carried out in the same manner as in Example 2 without performing preliminary reduction before the reaction. The CO conversion after 140 hours of this reaction is shown in Table 1.

[Table] [Effects of the Invention] As explained above, the methanation method of the present invention has the following effects. : Not only does the complicated reduction of a nickel catalyst become unnecessary, but also the hydrogen gas, thermal energy, etc. necessary for the reduction are no longer required, which has great economic advantages. : Since the life of the catalyst is significantly extended, it becomes possible to realize a methane synthesis process using gas containing high concentrations of carbon monoxide, which has not been practical until now. :Platinum group element catalyst alone has disadvantages such as high price and low sulfur resistance, but
In the present invention, the amount of platinum group elements added can be extremely small, and the sulfur resistance can also be increased by coexisting with a larger amount of nickel than when platinum group elements are added alone. : Since it can be operated at low temperatures that cannot be achieved with nickel catalysts alone, operating costs are low, no special reactor materials are required, and the equipment can be constructed at low cost. : Because the reaction can be carried out at low temperatures, it is advantageous in obtaining high-calorie gas that is rich in methane in equilibrium, and does not require a finishing methanator.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between reaction time (hr) and CO conversion rate (%) in Comparative Examples 1 to 2 and Example 1, and Figure 2 is a graph 1 hour and 20 hours after the start of the reaction in Comparative Example 1. FIG. 3 is a graph showing the temperature profile of the catalyst layer, and FIG. 3 is a graph showing the temperature profile of the catalyst layer 1 hour and 400 hours after the start of the reaction in Example 1.

Claims (1)

[Claims] 1. In methanating carbon monoxide-containing gas,
A methanation method characterized in that the catalyst on the inlet side of the externally cooled reactor is a nickel reduction catalyst or a platinum group element catalyst, and the catalyst in the lower layer is a fixed catalyst layer consisting of a nickel oxide catalyst. 2 When converting carbon monoxide-containing gas to methanation,
A methanation method characterized by using a mechanical mixture of powders of a platinum group element catalyst and a nickel oxide catalyst as a fixed catalyst layer in an externally cooled reactor.