JPH0450060B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a catalyst for producing hydrogen-enriched gas, and more specifically, a highly active catalyst used when producing hydrogen-enriched gas by reacting a mixture of methanol and water. It concerns highly selective, long-life catalysts. (Prior art) Hydrogen gas is used in hydrogen industries such as raw materials for ammonia synthesis and methanol synthesis, in oil refining industries such as hydrodesulfurization and hydrocracking, and in organic industries such as the production of cyclohexane, which is a raw material for nylon (by hydrogenation of benzene). It is used in various fields such as chemical industry, metallurgical industry, and semiconductor industry. Recently, demand for hydrogen has been increasing as a new energy source such as fuel for fuel cell power generation. As a hydrogen production method that has traditionally been widely used,
Liquefied petroleum gas (LPG), liquefied natural gas (LNG),
The steam reforming method from naphtha and naphtha has been adopted, but (i) the price of petroleum-based raw materials is rising and the supply is unstable, and (ii) the reaction temperature is high (800°C to 1000°C).
Therefore, there are problems such as unsuitability for small and medium-scale hydrogen gas production, and some kind of solution is awaited. On the other hand, in recent years, methanol can be produced on a large scale from coal, natural gas, etc. via synthesis gas, and it is also easy to transport, so methanol can be reacted with water vapor to produce hydrogen gas. The method of manufacturing is attracting attention. Furthermore, in the steam reforming reaction of methanol, methanol is reformed into a gas with a high hydrogen content at a much lower temperature than naphtha, and waste heat can also be used as a heat source for this reforming reaction. Furthermore, since almost no by-products other than hydrogen and carbon dioxide are produced, it has the advantage that the separation process for obtaining pure hydrogen is simple. The methanol steam reforming reaction is as shown in formula (1). CH ₃ OH＋H ₂ O→CO ₂ +3H ₂ ...(1) −△H ₂₅ ℃=−11.8 Kcal/mol This reaction is the decomposition of methanol into raw material for synthesis (2)
This is thought to be the result of the simultaneous occurrence of the water gas shift reaction (3) of the CO produced thereby, and there is an urgent need to develop a catalyst that promotes both reactions. CH ₂ OH→CO+2H ₂ ……(2) −△H ₂₅ ℃=−21.7Kacl/mol CO＋H ₂ O→CO ₂ +H ₂ ……(3) −△H ₂₅ ℃=9.8Kcal/mol Reaction (2) is , the higher the temperature of the equilibrium, the more advantageous the right side becomes, but in reaction (3), conversely, the higher the temperature, the more disadvantageous the right side becomes. The necessary conditions for promoting reaction (3) are increasing the amount of steam used and using a catalyst that can lower the reaction temperature. However, carrying out the steam reforming reaction of methanol in the presence of a large excess of water requires an excessive amount of heat for evaporation.
It is not economical, and it is better to keep the ratio (molar ratio) of water to methanol as close to the stoichiometric ratio of formula (1) as possible. That is, if the reaction temperature is low, the amount of steam used can be reduced, so it is necessary to use a catalyst with as much low-temperature activity as possible. Conventionally, catalysts used to obtain gas with high hydrogen content through the steam reforming reaction of methanol are:
Various catalysts have been proposed. For example, impregnated catalysts in which copper, platinum, nickel, etc. are supported on a support such as alumina have been proposed, but these catalysts tend to cause reactions that produce methane, and it is difficult to select a reaction that produces the target component, hydrogen. Sex is bad.
Furthermore, these catalysts still have many problems to date, such as poor low-temperature activity and durability. On the other hand, zinc, copper, and aluminum-based precipitated catalysts have been proposed in place of the above-mentioned impregnated catalysts, but although these catalysts have good low-temperature activity, they tend to cause side reactions, making them problematic for obtaining high-purity hydrogen. Furthermore, there is a problem of poor durability. (Problems to be Solved by the Invention) In order to solve the above problems, the present inventors focused on the development of a durable catalyst that suppresses the production of by-products dimethyl ether and methyl formate.
As a result of repeated studies on the components to be added to zinc, copper, and aluminum, it was discovered that zirconium has appropriate active sites, and it became clear that it met the above objectives, leading to the completion of the present invention. (Means for Solving the Problems) The present invention is a mixed oxide of copper, zinc, aluminum and zirconium produced by a coprecipitation method. 200, the total amount of aluminum and zirconium is 1 to 150, a catalyst for producing hydrogen-enriched gas from a mixture of methanol and water. The process of obtaining as much hydrogen as possible from methanol uses a catalyst in the first step to decompose it into carbon dioxide and hydrogen through the reaction CH ₃ OH + H ₂ O → CO ₂ + 3H ₂ , and in the second step, carbon dioxide is decomposed into hydrogen. The most promising method is to remove hydrogen using an absorbing liquid or absorbent to produce hydrogen. In this case, the selectivity to hydrogen and carbon dioxide gas is poor in the first stage reaction, and by-products are produced, which complicates the second stage separation process and leads to an increase in production costs. The selectivity of the catalyst used in one step is very important. The content ratio of each active component in the catalyst used in the present invention is such that the atomic ratio of copper to 100, zinc is 10 to 200, preferably 40 to 150, and the total amount of aluminum and zirconium is 1 to 150, preferably 2. ~100. When the zinc content is less than 10, copper particles, which are important catalytic active sites in the methanol steam reaction, tend to grow, shortening the life of the catalyst. If the total amount of aluminum and zirconium is less than 1, the life of the catalyst will be shortened, as in the case of zinc. Furthermore, when the zinc content exceeds 200, the copper content becomes relatively too low and the activity of the methanol steam reaction becomes low. When the total amount of aluminum and zirconium exceeds 150, the activity of the methanol steam reaction decreases as in the case of zinc. In addition, the catalyst exists as copper oxide, zinc oxide, aluminum oxide, zirconium oxide,
Each shares CuO, ZnO, Al ₂ O ₃ and ZrO ₂ . The catalyst of the present invention is produced by mixing water-soluble salts of the catalyst component metals (copper, zinc, aluminum, and zirconium) as a mixture or by simultaneous addition with carbonates or hydrogen carbonates of alkali metals or aqueous ammonia. This is preferably done in some cases. That is, copper, zinc, aluminum, and zirconium are used as water-soluble salts, and the copper, zinc, aluminum, and zirconium are co-precipitated by the action of an alkali metal carbonate, hydrogen carbonate, or aqueous ammonia. In this case, the salt is preferably present as a nitrate rather than a halide or sulfur-containing salt in order to avoid introducing catalyst poisons. The temperature of coprecipitation is preferably 50°C to 100°C, and the pH range is preferably 5 to 9. It is important that the precipitate be thoroughly washed to remove alkali metal ions and nitrate ions from the catalyst. (Effects of the Invention) The catalyst according to the present invention has high activity and very good selectivity for the reaction of producing hydrogen-enriched gas from methanol and water, and is also excellent in durability. Hereinafter, the catalyst of the present invention will be specifically explained with reference to Examples. Example Sodium aluminate is added and dissolved in distilled water. Next, when concentrated nitric acid is added dropwise, aluminum hydroxide precipitates, but is dissolved again by stirring.
Furthermore, Cu(NO ₃ ) ₂・3H ₂ O, Zn(NO ₃ ) ₂・6H ₂ O,
ZrO(NO ₃ ) _{2.2H 2} O is added to a predetermined composition ratio. This solution is heated to 85° C. and a 1 molar solution of sodium carbonate is gradually added to obtain a coprecipitate. The slurry thus obtained was heated to 85°C with pH=
7. Stir until constant. This slurry
Wash until nitrate ions can no longer be detected,
Dry at 110℃ overnight, then bake at 300℃ for 3 hours. Six types of catalysts (No. 1, No.
2, No. 3, No. 4, No. 5, No. 6) activity evaluation.
The test was carried out using a solution of H ₂ O/CH ₃ OH=1.5 (molar ratio) under atmospheric pressure and LHSV=1.0 h ^{−1 and} a catalyst amount of 10 g. Table 1 shows each catalyst composition and reaction results.

【table】

[Table] *: However, methanol and water are excluded.
As shown in Table 1, it was found that the zirconium-containing catalysts of Catalyst Nos. 1 to 6 have good low-temperature activity and are less likely to cause side reactions, so they are effective in producing highly pure hydrogen. In addition, 10 c.c. of the above catalysts No. 1 to No. 6 were filled in a reaction tube, and using a mixed solution of H ₂ O / CH ₃ OH = 1.5 (molar ratio), LHSV = 1.0 h ^- under atmospheric pressure. Continuous supply with ¹ ,
A 1000 hour durability test was conducted. As a result, it was confirmed that there was almost no change in methanol reaction rate and produced gas composition from the initial stage for all six types of catalysts, and there was no carbon precipitation on the catalyst surface. In the above examples, a granular catalyst is described, but the shape of the catalyst is not particularly limited, and it goes without saying that a catalyst shape such as a honeycomb shape may be used. Comparative Example A conventional catalyst (catalyst No. 7) in which copper and zinc were introduced into alumina by co-precipitation was prepared, and the activity was evaluated under the same conditions as in the example. Table 2 shows the results.

【table】

[Table] As shown in Table 2, the activity of catalyst No. 7 to which zirconium is not added is not much different from that of catalysts Nos. 1 to 6, but by-products are produced and the selectivity for hydrogen production is poor. It turned out to be. From the above Examples and Comparative Examples, the catalyst of the present invention has high activity, high selectivity, and long life at low temperature for the reaction of methanol and water to obtain hydrogen-enriched gas, compared to conventional catalysts. It is clear that it is a catalyst for

Claims (1)

[Claims] 1 A mixed oxide of copper, zinc, aluminum and zirconium produced by a coprecipitation method, with a composition expressed in atomic ratio of 100% copper to 100% zinc.
200, a catalyst for producing hydrogen-enriched gas from a mixture of methanol and water, characterized in that the total amount of aluminum and zirconium is 1 to 150.