JPH05305234A - Preparation of steam reforming catalyst for methanol - Google Patents

Abstract

PURPOSE:To obtain the title catalyst having high activity and high selectivity at low temp. and having a long life by a method wherein a predetermined aqueous solution is dropped to an aqueous precipitant solution at predetermined temp. to form a composite hydroxide precipitate and a predetermined aqueous solution is subsequently dropped to form a precipitate and the obtained composite hydroxide precipitate is baked and stabilized. CONSTITUTION:In preparing a steam reforming catalyst for methanol containing copper oxide, zinc oxide, aluminum oxide and/or chromium oxide, at first, an aqueous solution containing aluminum and/or chromium is dropped to an aqueous precipitant solution held to predetermined temp. and, further, an aqueous solution containing a zinc compd. is dropped thereto to form a composite hydroxide precipitate. Next, an aqueous solution containing copper is dropped to form a precipitate and the obtained composite hydroxide precipitate is fired and stabilized.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for preparing a methanol steam reforming catalyst.

[0002]

2. Description of the Related Art Hydrogen gas is used in the hydrogen industry such as a raw material for ammonia synthesis and methanol synthesis, in the petroleum refining industry such as hydrodesulfurization and hydrocracking, and in organic chemistry such as the production of cyclohexane which is a nylon raw material (by hydrogenation of benzene) It is used in various fields such as industry, metallurgical industry, and semiconductor industry. Recently, the demand for hydrogen has been increasing more and more as a new energy source such as fuel for fuel cell power generation.

Liquefied petroleum gas (LPG) and liquefied natural gas (LN) have been widely used as hydrogen production methods.
G) and the steam reforming method from naphtha are adopted, but (1) soaring and unstable supply of petroleum-based raw materials, (2) high reaction temperature (800 ° C to 1000 ° C)
℃), and because there are problems such as inadequacy in the production of hydrogen gas in small and medium scale, some solution is desired.

On the other hand, in recent years, methanol can be produced on a large scale from coal, natural gas or the like via synthetic gas and is easily transported. Therefore, methanol is reacted with steam to produce hydrogen gas. The method of manufacturing the is attracting attention. Also, the steam reforming reaction of methanol is reformed into a gas with a high hydrogen content at a much lower temperature than naphtha,
Waste heat can also be used as a heat source for this reforming reaction. Furthermore, since by-products other than hydrogen and carbon dioxide are scarcely generated, it has an advantage that the separation step for obtaining pure hydrogen is simple.

The above methanol steam reforming reaction is represented by the formula (1)
It is as follows. CH ₃ OH + H ₂ O → CO ₂ + 3H ₂ ... (1) −ΔH ₂₅ ° C. = − 11.8 kcal / mol

It is considered that this reaction is a result of the decomposition (2) to the methanol synthesis raw material and the water gas shift reaction (3) of CO produced thereby occurring simultaneously, and it is an urgent need to develop a catalyst that promotes both reactions. Is becoming CH ₃ OH → CO + 2H ₂ ··· (2) −ΔH ₂₅ ° C = −21.7 kcal / mol CO + H ₂ O → CO ₂ + H ₂ ··· (3) −ΔH ₂₅ ° C = − 9.8 kcal / mol

The reaction (2) is favored to the right as the equilibrium temperature increases, while the reaction (3) is conversely favored to the right as the temperature becomes higher. The necessary conditions for promoting the reaction (3) are to increase the amount of steam used and to use a catalyst that can lower the reaction temperature. However, performing a steam reforming reaction of methanol in the presence of a large excess of water is not economical because it requires an excessive amount of heat for evaporation, and the ratio of water to methanol (molar ratio) is as much as possible by the formula (1). It is better to carry out in a state close to the stoichiometric ratio of. That is, if the reaction temperature is low, the amount of steam used can be reduced, so it is necessary to use a catalyst having a low temperature activity as much as possible.

Conventionally, various catalysts have been proposed as catalysts for obtaining a gas having a high hydrogen content by a steam reforming reaction of methanol. For example, impregnation catalysts in which copper, platinum, nickel, etc. are supported on a carrier such as alumina have been proposed, but these catalysts have a high selectivity for the reaction in which hydrogen, which is a target component, is apt to easily react to generate methane. bad. Further, these catalysts have many problems so far, such as low temperature activity and poor durability.

On the other hand, instead of the above impregnation treatment, copper, zinc,
Oxide-based precipitation catalysts of aluminum and / or chromium have been proposed. In general, this catalyst has good low-temperature activity, but since side reactions easily occur, there is a problem in obtaining high-purity hydrogen, and it is hard to say that the preparation method has been sufficiently investigated.

[0010]

The catalyst containing copper, zinc, aluminum and / or chromium, which has been prepared so far, is prepared by a coprecipitation method. As an example, there is a method of forming a precipitate by dropping the solution into a solution, or a method of simultaneously adding an aqueous solution of a metal salt and an alkali precipitation solution to obtain a precipitate in a constant pH range around neutral. As a result, the former method is different from each other in the pH range in which it is precipitated, and the precipitates of the three kinds of metals are separately precipitated. Therefore, it is difficult to say coprecipitation, and the precipitates are composed of different crystal species, which is not preferable. On the other hand, in the latter method, the three kinds of metals are simultaneously precipitated to form crystal seeds containing the three kinds of metals, and the catalyst has a relatively large specific surface area and a uniform catalyst, but has activity until it clears the target value. Not not.

Accordingly, the present inventors have made use of the characteristics of oxide systems of copper, zinc, aluminum and / or chromium having good low-temperature activity, and as a method for preparing a methanol steam reforming catalyst in which side reactions do not easily occur An aqueous solution containing zinc and aluminum and / or chromium was first added dropwise to the warmed aqueous precipitant solution to form a complex hydroxide precipitate, and then an aqueous solution containing copper was added dropwise to form a precipitate, which was obtained. A method for preparing a catalyst containing copper oxide, zinc oxide, aluminum oxide and / or chromium oxide by a method of stabilizing the composite hydroxide by calcination is proposed (JP-A-3-52643).
Publication).

The above catalyst has some durability, but it was necessary to further improve the durability. Therefore, the present invention intends to provide a method for preparing a methanol steam reforming catalyst having improved durability, which is an improvement of the above-mentioned catalyst preparation method.

[0013]

Therefore, the present inventors have
As a result of diligent research and development of a catalyst that exceeds the performance of existing copper, zinc and aluminum and / or chromium-based methanol steam reforming catalysts, the main active species of the methanol steam reforming reaction of this type of catalyst is Cu ⁺ . , It was found that the catalyst should be prepared so that many active sites are present in the catalyst.

The present invention has been completed on the basis of the above findings, and in preparing a methanol steam reforming catalyst containing copper oxide, zinc oxide, aluminum oxide and / or chromium oxide, it is kept at a predetermined temperature. First, an aqueous solution containing aluminum and / or chromium was added dropwise to the prepared precipitant aqueous solution, and then an aqueous solution containing a zinc compound was added dropwise to generate a complex hydroxide precipitate, and then copper was included. A method for preparing a catalyst for methanol steam reforming, which comprises dropping an aqueous solution to form a precipitate, and stabilizing the obtained composite hydroxide precipitate by calcination.

[0015]

The method for preparing the highly active methanol steam reforming catalyst of the present invention will be described in more detail. First, the aqueous solution of the precipitating agent is kept warm, and a liquid containing a compound of aluminum and / or chromium is dropped while stirring, and an aqueous solution containing a compound of zinc is further dropped to deposit a precipitate. An aqueous solution containing a copper compound is added dropwise to form a precipitate.
At this time, almost all the metal ions added at a pH of 4 or more at the end of the addition are deposited as a precipitate of the composite hydroxide. The precipitant aqueous solution is an alkaline aqueous solution and is usually 0.1
10M concentration of Na ₂ CO ₃ , NaHCO ₃ , NaO
An aqueous solution of H, K ₂ CO ₃ and NH ₃ is used, and an Na ₂ CO ₃ aqueous solution is particularly preferable. Further, it is preferable to keep the temperature of the solution at the time of forming the precipitate in the range of 15 to 90 ° C. Furthermore, compounds of copper, zinc, aluminum and / or chromium are nitrates, chlorides, sulphates and acetates of 0.
It is used at a concentration of 01 to 1.0 M, and nitrate is a preferable metal salt. Further, the dropping time and the aging time are not particularly affected, but may be any conditions under which the metal ions are uniformly dispersed and the precipitate is deposited, and the dropping time is usually 0.1 minutes to 3 minutes.
The aging time is 0.1 minutes to 3 hours.

The obtained precipitate has various crystal seeds, but after alkali metal ions and anions are sufficiently washed and removed, the precipitate is calcined in the range of 200 to 400 ° C.
A methanol steam reforming catalyst containing CuO, ZnO, Al ₂ O ₃ and / or Cr ₂ O ₃ is obtained. The composition of the catalyst is represented by the atomic ratio of Cu: Zn: Al and /
Alternatively, the range of Cr = 100: 10 to 250: 1 to 100 is preferable.

[0017]

【Example】

 (Example 1) Sodium carbonate (Na₂CO₃ 2.5m
ol) is dissolved in 2 liters of water and kept at 70 ° C. this
Let the alkaline aqueous solution be solution A. Zinc nitrate {Zn (NO
₃) ₂・ 6H₂O} 0.225 mol and aluminum nitrate
Mu {Al (NO₃) 9H₂O} 0.075 mol
Dissolve each in 400 cc of water and keep it warm at 60 ° C.
The sexual solutions are referred to as solution B and solution C. Furthermore, copper nitrate {Cu
(NO₃)₂・ 3H₂O} 0.3 mol water 200 cc
And keep it at 60 ℃, and call this acidic solution D
It

First, while stirring, the solution C is added to the solution C by 30 times.
Over a period of 30 minutes, and the solution B was spread over 30 minutes.
Uniformly add dropwise to obtain a suspension. Next, the solution D is
The suspension was added dropwise at a constant rate over 30 minutes to remove the precipitate.
obtain. The pH at the end of the dropping was 7. 1 hour after dropping
Aging is performed, and then filtration of the precipitate and Na ions, NO ₃
Clean so that no ions are detected. In addition, 100
Dry at ℃ for 24 hours, then bake at 300 ℃ for 3 hours
By this, CuO-ZnO-Al₂O₃Complex oxide
Got This catalyst is referred to as catalyst 1.

(Example 2) Furthermore, 0.2 mol of zinc nitrate {Zn (NO ₃ ) ₂ .6H ₂ O} as the B liquid and aluminum nitrate {Al (NO ₃ ) ₃ .9H ₂ O} as the C liquid.
A methanol steam reforming catalyst was prepared by the same preparation method as in Example 1 except that 0.1 mol was used. This catalyst is referred to as catalyst 2.

Furthermore, zinc nitrate {Zn (NO
_{3) 2 · 6H 2 O}} 0.3mol, copper nitrate _{{Cu (NO 3) 2 ·} 3H 2 O} except for using 0.275mol was prepared in the same manner as in Example 1 Catalyst 3 as Solution D Obtained.

(Example 3) Zinc nitrate {Zn as solution B
_{(NO 3) 2 · 6H 2} O} a 0.225 mol, instead of chromium nitrate aluminum nitrate as C solution {Cr (N
_{O 3) 3 · 9H 2 O} } except for using 0.075mol the got catalyst 4 in the same preparation method as in Example 1.

Furthermore, zinc nitrate {Zn (NO
_{3) 2} · 6H ₂ O} a 0.225 mol, 0.05 m chromium nitrate _{{Cr (NO 3) 3 ·} 9H 2 O} as C solution
ol, aluminum nitrate _{{Al (NO 3) 3 ·} 9H
₂ O} 0.05 mol was obtained by the same preparation method as in Example 1 except that 0.05 mol was used.

(Comparative Example 1) Using solutions A, B, C and D having the same composition as in Example 1, the conventional catalyst C was prepared by the following method.
A u-Zn-Al composite oxide was prepared. First, solution B
Solution C and solution D are added to to obtain an acidic aqueous solution (pH = 3) containing Cu, Zn and Al ions. Solution A (sodium carbonate aqueous solution) was added dropwise to this aqueous solution at a constant rate for 1 hour with stirring, and the addition was completed at pH = 7. After completion of the dropping, aging was carried out for 2 hours, the obtained composite hydroxide was washed and filtered, and baked at 300 ° C. for 3 hours. This catalyst is referred to as catalyst 6.

(Experimental Example) An activity evaluation test of the methanol steam reforming reaction of the catalysts 1 to 6 obtained in Examples 1 to 3 and Comparative Example 1 was carried out under the following conditions. 〇 Pressure: 15kg / cm ² · G 〇 H ₂ O / CH ₃ OH: 2 (molar ratio) 〇 LHSV: 2h ^-1

Table 1 shows the results of activity evaluation of each catalyst at a reaction temperature of 250 ° C. As shown in Table 1, catalysts 1 to 5 of the present invention
Has a high initial activity and 1000
It was found to have high activity even after the endurance test of time.

Table 2 shows the results of tests conducted by using the catalyst 1 and changing the reaction temperature in the same manner. As shown in Table 2, the catalyst of the present invention was found to be excellent as a methanol steam reforming catalyst.

[0027]

[Table 1] Composition of produced gas (excluding methanol and water) Catalyst 1 to 5 H ₂ : 74.6 to 74.8%, CO: 0.
8~1.0%, CO _2: 24.4~24.6% catalyst _{6 H 2: 73.3%, CO} : 1%, CO 2:
24%, others: 1.7%

[0028]

[Table 2]

[0029]

EFFECTS OF THE INVENTION The catalyst prepared according to the present invention from the above Examples and Comparative Examples has a high activity and a high activity at a low temperature as compared with the conventional catalyst in the reaction of reacting with methanol and water to obtain a hydrogen-enriched gas. It is clearly a selective and long-life catalyst.

Claims (1)

[Claims] 1. In preparing a methanol steam reforming catalyst containing copper oxide, zinc oxide, aluminum oxide and / or chromium oxide, an aqueous precipitant solution kept at a predetermined temperature contains aluminum and / or chromium. Was added dropwise, and then an aqueous solution containing a zinc compound was added to form a composite hydroxide precipitate, and then an aqueous solution containing copper was added to form a precipitate, which was obtained. A method for preparing a catalyst for reforming methanol steam, which comprises stabilizing a composite hydroxide precipitate by calcination.