JP2010194420A - Copper-based catalyst, and pretreatment method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper-based catalyst excellent in catalytic activity as well as in durability, and a pretreatment method therefor. <P>SOLUTION: The copper-based catalyst is produced by reducing a copper catalyst (I) constituted of metal oxides including copper oxide, zinc oxide and aluminum oxide as essential components, and zircon oxide, gallium oxide and silicon oxide as optional components, at a temperature equal to or higher than the reaction temperature in producing methanol or the like and not higher than the calcination temperature in producing the catalyst (I). The reduction of the catalyst (I) is preferably carried out in a hydrogen-containing gas stream at a temperature of 300 to 550°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a copper-based catalyst having good catalytic activity in a methanol synthesis reaction or its reverse reaction, methanol reforming reaction, shift reaction or its reverse reaction, and outstanding durability, and a pretreatment method thereof. Is.

Conventionally, a methanol synthesis process using synthesis gas (a mixed gas of CO and H ₂ ) as a main raw material (including a small amount of CO ₂ ) is a very important basic process in the chemical industry, and its energy saving and There is a constant demand for higher efficiency from the viewpoint of economy and the like. One of the most important technologies in the methanol synthesis process is to provide a high performance catalyst, and conventional catalysts include Cu / ZnO / Al ₂ O ₃ catalysts (current industrial catalysts such as “catalysts”). "Lecture, Vol. 7, edited by the Catalysis Society of Japan, Kodansha Co., Ltd., published July 20, 1989" (Non-Patent Document 1), pages 21-39), Cu / ZnO / SiO ₂ catalyst (Japanese Examined Patent Publication 63- No. 39287 (Patent Document 1) and the like are known.

On the other hand, methanol synthesis using CO ₂ and H ₂ as main raw materials has recently attracted particular attention from the viewpoint of recycling and recycling of carbon resources and global environmental problems. In methanol synthesis from raw material gas with high CO ₂ content, thermodynamic equilibrium of reaction and reaction inhibition effect of water generated with methanol (Applied Catalysis A: General, 38 (1996), p.311-318 For Patent Document 2)), a catalyst having higher activity than that employed in methanol synthesis from the above synthesis gas is required. In addition, in the synthesis of methanol from a raw material gas having a high CO ₂ content, the decrease in catalytic activity, which is thought to be caused by water generated together with methanol, is much greater than that in the synthesis of methanol from synthesis gas. Therefore, there is a need for a catalyst that is much more durable than the catalyst employed in methanol synthesis from synthesis gas. This is because the catalyst performance of the three-component catalyst employed in the above methanol synthesis is insufficient.

By the way, it is known that the main cause of the decrease in the catalytic activity of the copper catalyst is a decrease in surface area due to copper sintering. Copper is known to be a metal that easily causes sintering among various metal catalysts, and it is necessary to prevent the catalyst reduction temperature and reaction temperature before the reaction from becoming high. For example, Japanese Patent Application Laid-Open No. 2004-298685 (Patent Document 2) describes that the reduction temperature of the Cu / ZnO catalyst is preferably 100 to 300 ° C., preferably 150 to 250 ° C. No. 254414 (Patent Document 3) describes that the reduction temperature of the Cu / ZnO / ZrO 2 catalyst is preferably 100 to 300 ° C., preferably 120 to 200 ° C., and Japanese Patent Application Laid-Open No. 2007-83197 ( Patent Document 4) describes that the reduction temperature of the Cu / ZnO / Al ₂ O ₃ catalyst is preferably 100 to 300 ° C, preferably 110 to 280 ° C, and more preferably 130 to 240 ° C. This is because if the reduction temperature is too high, the copper surface area decreases due to copper sintering.

In view of the technical background as described above, the present inventors have conducted intensive studies on copper-based catalysts. As a result, copper oxide, zinc oxide, and aluminum oxide are essential components, and zirconium oxide, gallium oxide, and silicon oxide are arbitrarily selected. In copper-based catalysts composed of component metal oxides, sintering is unlikely to occur even when reduction is performed at high temperatures. Rather, pretreatment for reduction at high temperatures can be performed by using CO ₂ and H ₂ as main raw materials. The present inventors have found that a copper-based catalyst having excellent durability can be obtained in the methanol synthesis reaction to achieve the present invention.
Japanese Patent Publication No.63-39287 Japanese Patent Application Laid-Open No. 2004-298685 JP-A-6-254414 JP 2007-83197 A Catalyst Course, Volume 7, Catalytic Society, published by Kodansha Co., Ltd., issued July 20, 1989 Applied Catalysis A: General, 38 (1996), p.311-318

  The present invention has been made in view of the above situation, and an object of the present invention is to provide a copper catalyst having good catalytic activity and remarkably excellent durability, and a pretreatment method thereof.

  As a result of intensive studies to solve the above problems, the present inventor has found that the above problems can be solved by performing a reduction reaction in a specific temperature range, and the present invention has been completed.

  The copper-based catalyst of the present invention is a copper-based catalyst comprising a metal oxide containing copper oxide, zinc oxide and aluminum oxide as essential components, and zirconium oxide, gallium oxide and silicon oxide as optional components. A copper-based catalyst obtained by reduction at a temperature higher than the reaction temperature and lower than the calcination temperature under circulation.

  The reduction of the catalyst is desirably performed at a temperature of 300 ° C to 550 ° C.

  The present invention also provides a copper-based catalyst composed of a metal oxide containing copper oxide, zinc oxide and aluminum oxide as essential components and zirconium oxide, gallium oxide and silicon oxide as optional components before hydrogenation. The copper catalyst pretreatment method is characterized in that the reduction is performed at a temperature of 300 ° C. to 550 ° C. under flowing gas.

  The hydrogen concentration in the reduction is preferably 0.1 to 10% by volume.

The copper-based catalyst of the present invention has high activity, and the high activity is maintained over a long period of time and has excellent durability. The activity maintaining effect of the catalyst at this time is remarkable, and excellent activity and durability that cannot be expected with the copper-based multicomponent catalyst for methanol synthesis currently used or proposed are obtained. Therefore, the present invention is extremely useful industrially.

<Catalyst> The copper-based catalyst of the present invention is a catalyst composed of a metal oxide containing copper oxide, zinc oxide and aluminum oxide as essential components, and further contains zirconium oxide, gallium oxide and silicon oxide as optional components. You may go out. Further, other oxides may be included within the range not impairing the gist of the present invention. As other components, a noble metal oxide such as palladium is usually used because of its high reactivity, but the above catalyst tends to exhibit high catalytic performance without using a noble metal oxide. is there.

  The copper-based catalyst of the present invention is characterized by being reduced under specific conditions.

  The component before the reduction of the copper-based catalyst of the present invention may be referred to as a copper-based catalyst (I) in the present application. As long as this copper catalyst (I) is composed of a metal oxide having copper oxide, zinc oxide and aluminum oxide as essential components and zirconium oxide, gallium oxide and silicon oxide as optional components, it is known in the art. It can be used by appropriately selecting from the products. Preferably, it has a composition range similar to that of the copper catalyst of the present invention described below.

  The composition of the copper-based catalyst of the present invention is such that when the total catalyst is 100% by weight, copper oxide is 20 to 60% by weight, preferably 30 to 50% by weight, and zinc oxide is 10 to 50% by weight, preferably 20 to 40% by weight, aluminum oxide 2 to 10% by weight, preferably 4 to 8% by weight, silicon oxide 0.0 to 0.9% by weight, preferably 0.3 to 0.9%, and zirconium oxide 0 to 40% by weight, preferably 10-20% by weight, and gallium oxide is 0-10% by weight, preferably 0.1-5.0% by weight. In such a quantitative range, the catalyst performance suitable for the reaction can be obtained by appropriately determining the composition according to the target reaction.

  In the copper catalyst of the present invention, colloidal silica or water-dissolved silica may be used as the silicon oxide in the catalyst production method described later, or colloidal silica and water-dissolved silica may be used in combination. Even when the same silicon compound is produced by adding, for example, sodium silicate (water glass) or potassium silicate, a catalyst having the desired effect cannot be obtained.

  When colloidal silica is used, for the purpose of the present invention, it is preferable to use one having a sodium oxide content of less than 0.1% by weight, particularly 0.06% by weight or less, which is substantially free of sodium. Incidentally, many grades of colloidal silica have a sodium oxide content of about 0.2 to 0.6% by weight.

  When using silica dissolved in water, natural fresh water, tap water, well water, industrial water, or the like can be used. These waters contain about 20 ppm to about 100 ppm of dissolved silica. The dissolved silica is silica (commonly referred to as colorimetric silica) measured by a spectrophotometric method using a molybdenum yellow method or a molybdenum blue method.

<Manufacture of catalyst>
The catalyst is necessary to form a precipitate by mixing A solution consisting of an aqueous solution containing a water-soluble salt of a metal component excluding the silicon component, and B solution consisting of an aqueous solution containing a basic substance. Aging, then washing, forming the precipitate, adsorbing colloidal silica or water-dissolved silica as necessary during aging or washing, and drying the washed precipitate, then 480-690 ° C. A copper-based catalyst (I) is produced by firing the product into a fired product.

  When the liquid A and the liquid B are mixed to form a precipitate, the liquid A and the liquid B are mixed together to precipitate the components in the liquid A, and the liquid A is divided into two or more. First, liquid A consisting of an aqueous solution containing one or more of the metal compounds and liquid B consisting of an aqueous solution containing a basic substance are mixed to precipitate the components in liquid A, and then the precipitate is A precipitation method is also employed in which the solution A comprising an aqueous solution containing the remaining components of the metal compound is added to the solution to be precipitated and the solution is similarly precipitated. Various other variations are possible for the mixing method.

  As the water-soluble salt of the metal component excluding the silicon component among the metal components, nitrates and nitrites having good water solubility are preferably used. As the basic substance, for example, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide and the like are preferably used, and in some cases, ammonia, alkanolamine, amine and the like can also be used.

  After the formation of the precipitate, aging is performed if necessary, followed by washing, and further post-treatment such as slurrying and drying as appropriate. For example, a method of aging the precipitate, filtering and washing by centrifugation, and once slurrying and spray drying is adopted.

  In the present invention, colloidal silica or silica dissolved in water is adsorbed during the formation, aging or washing of the precipitate. When colloidal silica is adsorbed during the formation of a precipitate, a method of adding colloidal silica to at least one of liquid A or liquid B, a method of mixing liquid A and liquid B in water containing colloidal silica, etc. are employed. The Colloidal silica does not actually enter the supernatant during precipitation or aging, and the silica component does not substantially flow out even after washing after adsorption of colloidal silica, so colloidal silica is simply mixed into the precipitate. It turns out that it is adsorbing, not doing. When adsorbing dissolved silica in water, use water containing dissolved silica to prepare an aqueous solution containing a water-soluble salt of a metal component or an aqueous solution containing a basic substance, or wash precipitates using water containing dissolved silica. You may take a method such as doing.

  The precipitate on which the colloidal silica is adsorbed is calcined at 480 to 690 ° C. (preferably 520 to 680 ° C., particularly 560 to 670 ° C.) to obtain a calcined product. Firing is performed in an oxygen atmosphere (usually in air), whereby the metal component described above is in the form of an oxide.

  The catalyst thus obtained is used as it is or after being granulated or tableted by an appropriate method. The particle diameter and shape of the catalyst can be arbitrarily selected depending on the reaction system and the shape of the reactor.

<Reduction treatment>
The copper-based catalyst (I) often has a catalytic action even at this stage, but the copper-based catalyst of the present invention is H ₂ gas or H ₂ -N ₂ mixed gas prior to use of methanol or the like. It can be obtained by reducing with a reducing gas. The concentration of the reducing gas is preferably 0.1 to 10% by volume. In the case of a reducing gas having a concentration lower than 0.1% by volume, the reduction takes time and often causes an economic problem. On the other hand, when the reducing gas concentration exceeds 10% by volume, rapid reduction occurs, which may damage the catalyst.

  In the present invention, when reducing the copper-based catalyst (I) with a reducing gas, it is performed under conditions higher than the temperature used for the production of methanol or the like and lower than the temperature of the calcination step. The lower limit of the preferred reduction temperature is 300 ° C, preferably more than 300 ° C, more preferably 350 ° C, while the upper limit is 550 ° C, more preferably 500 ° C. In general, when a copper-based catalyst is treated at a high temperature of 300 ° C. or higher, the surface area of the reduced copper is reduced due to sintering or the like, and the activity is lowered. Furthermore, it has been found that reduction at a temperature of 300 ° C. or higher, preferably over 300 ° C., increases the surface area of copper. However, if the temperature exceeds 550 ° C., sintering may occur and the surface area may decrease.

  In other words, the catalyst of the present invention is in a form that (1) copper is less likely to be reduced at low temperatures than copper catalysts known in the art (2) copper is in a form that is difficult to sinter at high temperatures. Is shown. Such a property is considered to lead to the catalyst activity being maintained over a long period of time and having excellent durability. In addition, when the pretreatment for reducing at a high temperature exceeding 300 ° C. is performed in advance as described above, the induction period in the initial reaction can be shortened and the catalytic activity can be improved.

  In the copper-based catalyst of the present invention, the essential components copper oxide, zinc oxide and aluminum oxide (and optional components zirconium oxide, gallium oxide, palladium oxide) form a skeleton and are adsorbed as necessary. In particular, the above-mentioned surprising tendency often appears when silica or dissolved silica in water is present as a silicon oxide in a specific amount of 0.0 to 0.9% by weight, preferably 0.3 to 0.9% by weight, between the skeletons. When the baking treatment is performed in a specific high temperature region of 480 to 690 ° C., the tendency is higher.

  The reason why the effect of the present invention is easily manifested in the form in which the silicon compound is contained is unknown, but the following hypothesis can be considered. In the catalyst, the silicon component exerts the action of preventing the movement of the metal component, so the catalyst is highly active, and the activity is maintained over a long period of time. Similarly, in the reduction treatment, it is considered that the sintering can be suppressed in order to prevent the movement of the metal component. As the pretreatment of the catalyst, the effect is considered to be greater as the temperature is higher. As a result, the catalyst is more active due to the pretreatment conditions of the present invention.

(reaction>
The above reduced catalyst is useful as a catalyst for the reaction of synthesizing methanol from hydrogen and carbon oxide or vice versa.

In the methanol synthesis reaction, methanol is synthesized by reacting a raw material gas composed of hydrogen and carbon oxide (CO ₂ alone or a mixed gas of CO ₂ and CO) on a catalyst. The reaction at this time is typically performed at a reaction temperature of 150 to 300 ° C. and a reaction pressure of 1 to 10 MPa. In the reverse reaction, methanol can be decomposed into hydrogen and carbon oxides. The reaction at this time is typically performed at a reaction temperature of 200 to 400 ° C. and a reaction pressure of atmospheric pressure to 1 MPa. These reactions can be carried out either in the gas phase or in the liquid phase. As a solvent for the reaction in the liquid phase, a water-insoluble or hardly water-soluble solvent is used, including a hydrocarbon solvent.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these Examples.

Example 1
<Manufacture of catalyst>
Copper nitrate trihydrate 54.3g, zinc nitrate hexahydrate 39.1g, aluminum nitrate nonahydrate 6.6g, zirconium nitrite dihydrate 15.4g and colloidal silica ("Snowtex ST" manufactured by Nissan Chemical Industries, Ltd.) -O ") 1.26 g was dissolved in distilled water to prepare a 500 ml aqueous solution. “Snowtex ST-O” has an anhydrous silicic acid (SiO ₂ ) content of 20 to 21% by weight, a sodium oxide (Na ₂ O) content of 0.04% by weight or less, a pH of 2 to 4, and a particle size. Is a clear milky white colloidal solution having a viscosity of 3-20 cps / 25 ° C or less, a specific gravity of 1.12 to 1.14 / 25 ° C, and a freezing point of 0 ° C.

  Separately, 139.0 g of sodium carbonate decahydrate was dissolved in distilled water to prepare a 500 ml aqueous solution.

  Liquid A and liquid B were simultaneously dropped into 400 ml of distilled water (this method is referred to as a coprecipitation method). After allowing this to stand for a whole day and night, the resulting precipitate was washed with distilled water, dried at 110 ° C. and normal pressure for 2 hours, and then calcined at 600 ° C. in air for 2 hours. As a result, solid (I) corresponding to the target copper-based catalyst (I) was obtained.

The composition of the obtained solid (I) is, CuO: 45.2wt%, ZnO: 27.1wt%, Al 2 O 3: 4.5wt%, ZrO 2: 22.6wt%, SiO 2: was 0.6 wt%.
<Effect of reduction temperature> After filling the reaction tube with 0.2 g of the solid (I) obtained above and reducing the reducing gas consisting of 5 vol% of H ₂ and 95 vol% of Ar through 2 hours at each temperature. At 40 ° C., a gas composed of 2.5 vol% N ₂ O and 97.5 vol% He was circulated, and the surface area of copper was calculated from the adsorption amount of N ₂ O. The results are shown in Table 1. In this catalyst, S ₃₀₀ = 15.4 m ² / g-cat and S ₅₀₀ / S ₃₀₀ = 1.4 are calculated.

<Activity Test of Catalyst in Methanol Synthesis> The reaction tube was filled with 2 ml of the catalyst obtained above, and a reducing gas consisting of 5 vol% H ₂ and 95 vol% N ₂ was reduced at a reduction temperature of 400 ° C. for 2 hours. According to the results in Table 1, this reduced catalyst has a Cu surface area of 19.9 m 2 / g-cat. After this reduction treatment, a mixed gas of 25 vol% CO _{2 and} 75 vol% H ₂ was passed through the catalyst layer at a rate of 20 liter / hr, and the reaction was carried out under conditions of a pressure of 5 MPa and a temperature of 250 ° C. The reaction product gas was analyzed with a gas chromatograph, and the relationship between the reaction time and the amount of methanol produced was determined.
The amount of methanol produced was 600 g-MeOH / L-Cat / h.

(Comparative Example 1)
The same activity test as in Example 1 was performed except that the catalyst treated at a reduction temperature of 250 ° C. was used in the catalyst of Example 1.

  The initial amount of methanol produced was 430 g-MeOH / L-Cat / h, and the activity gradually increased. However, even after 2 months, stable performance was not achieved.

(Comparative Example 2)
In the catalyst of Example 1, the same activity test as in Example 1 was performed, except that a catalyst treated at a reduction temperature of 600 ° C. was used.

  Methanol production was 510 g-MeOH / L-Cat / h.

Claims (4)

Copper-based catalyst (I) composed of metal oxides containing copper oxide, zinc oxide and aluminum oxide as essential components and zirconium oxide, gallium oxide and silicon oxide as optional components, in a hydrogen-containing gas stream, higher than the reaction temperature A copper-based catalyst obtained by reduction at a temperature lower than the firing temperature. The copper-based catalyst according to claim 1, wherein the reduction is performed at a temperature of 300 ° C to 550 ° C. A copper-based catalyst composed of a metal oxide having copper oxide, zinc oxide and aluminum oxide as essential components and zirconium oxide, gallium oxide and silicon oxide as optional components is subjected to a hydrogen-containing gas flow before the catalytic reaction. A method for pretreating a copper-based catalyst, characterized by reducing at a temperature of from 550C to 550C. The hydrogen concentration of the hydrogen containing gas of Claim 3 is 0.1-10 volume%, The pretreatment method of the copper-type catalyst characterized by the above-mentioned.