JP4264514B2 - Dimethyl ether reforming catalyst and method for producing hydrogen-containing gas using the same - Google Patents

Description

The present invention relates to a catalyst for generating hydrogen by steam reforming dimethyl ether (hereinafter sometimes abbreviated as “DME”) and a method for producing a hydrogen-containing gas using the catalyst.

  In recent years, various types of fuel cells (fuel power generation devices) excellent in energy efficiency have attracted attention as next-generation energy supply technologies. Above all, a polymer electrolyte fuel cell in which an anode and a cathode are arranged on a proton conductive membrane has advantages such as miniaturization and operation at a low temperature. Practical research as a device is underway. As the polymer electrolyte fuel cell, one using hydrogen as a fuel is most efficient and is common. However, since hydrogen is not easily liquefied, it has a problem of poor portability. For this reason, it has been studied to obtain hydrogen on-site by reforming liquid methanol having excellent portability by bringing it into contact with water vapor.

  In order to reform methanol to hydrogen, it is necessary to vaporize methanol. However, when the vaporizer is additionally provided, the power generation device is increased in size, so that the advantage as a portable device is impaired.

Recently, DME has attracted attention as a hydrogen production raw material to replace methanol. DME can be produced by various methods, for example, by dehydrating methanol. Furthermore, development of a technology (Gas-To-Liquid: GTL technology) for producing DME from hydrocarbon gas (for example, methane gas generated in a coal mine) has been energetically performed.

DME is a gas at room temperature and pressure, but it can easily be made liquid by pressurizing to about 5 atmospheres. In other words, DME can be transported or moved in the form of a liquid, and is vaporized only by returning to normal pressure during the hydrogen production reaction, so there is no need to provide a vaporizer in the reforming reaction system. There is.

In this DME reforming reaction, an acid catalyst for promoting the hydrolysis reaction and a Cu-Zn catalyst (Patent Document 1) which is a catalyst for reforming methanol produced by the hydrolysis reaction or a catalyst containing Pt ( Patent Document 2) is usually used. However, the Cu-Zn catalyst has a problem that the activity is impaired by Cu being oxidized in the air. In contrast, when using a Pt-based catalyst, there is almost no problem of activity deterioration due to oxidation, but at a high temperature at which a sufficient reaction rate can be obtained, CO hydrogenation reaction proceeds and methane is produced. This causes a problem that the hydrogen concentration decreases.
JP-A-10-174870 Japanese Unexamined Patent Publication No. 2000-320407

Therefore, the present invention provides a new DEM reforming process that does not deactivate due to air oxidation when producing hydrogen by reforming DME, and that can suppress methane formation even at a high temperature at which a sufficient reaction rate can be obtained. The main purpose is to provide a catalyst.

Another object of the present invention is to provide a catalyst capable of converting DME into a hydrogen-containing gas with high efficiency and a method for reforming DME using the catalyst.

As a result of repeated research while considering the current state of the technology as described above, the present inventors have shown that gallium oxide or a mixture of gallium oxide and metal oxide exhibits high activity in the reforming reaction of DME. I found.

The present invention provides the following DME reforming catalyst and a method for producing a hydrogen-containing gas using the catalyst.
1. A catalyst for reforming dimethyl ether steam using gallium oxide as a catalytic active component, comprising gallium oxide and another metal oxide, the other metal oxide being aluminum oxide, zirconium oxide, titanium oxide, silicon oxide A dimethyl ether steam reforming catalyst, which is at least one metal oxide selected from the group consisting of germanium oxide, manganese oxide, iron oxide, cerium oxide, indium oxide, and zinc oxide.
2. The method for producing a hydrogen-containing gas which comprises contacting the dimethyl ether and Mizu蒸gas in the presence of a catalyst according to Item 1.

According to the present invention, by supporting Ga ₂ O ₃ on a metal oxide such as titania, alumina, silica, etc., it is possible to handle at high temperature without deteriorating in the air, and DME modification that exhibits high activity. The catalyst for use is obtained.

Further, according to the present invention, hydrogen gas useful as fuel for fuel cells can be efficiently produced using DME as a raw material.

The DME reforming catalyst according to the present invention is composed of gallium oxide alone or a mixture or mixture of gallium oxide and at least one metal oxide. When gallium oxide and other metal oxide (hereinafter sometimes referred to as “combined metal oxide”) are used in combination, a physical mixture of gallium oxide and at least one of the combined metal oxides, It can be used in any form such as a carrier supported on a combined metal oxide or a double oxide containing gallium oxide and a combined metal oxide.

  The metal oxide used in combination with gallium oxide is a metal oxide selected from the group consisting of aluminum oxide, zirconium oxide, titanium oxide, silicon oxide, germanium oxide, manganese oxide, iron oxide, cerium oxide, indium oxide and zinc oxide. At least one of the following.

  A catalyst using a combination of gallium oxide and a metal oxide can be produced according to a conventional method for producing a supported catalyst or a mixed catalyst. For example, it can be prepared by immersing a metal oxide as a carrier in an aqueous solution in which a water-soluble gallium compound is dissolved, followed by drying and firing (supporting method). At this time, two or more metal oxides may be immersed together as a carrier. Firing is usually performed in the air.

  The water-soluble compound of gallium is not particularly limited as long as it is water-soluble, and specific examples thereof include gallium nitrate, gallium chloride, gallium oxalate and the like.

Or the catalyst which uses a gallium oxide and a metal oxide together can also be obtained by drying and baking the powdery product prepared by the sol-gel method. Also in this case, firing is usually performed in the atmosphere.

  Alternatively, a catalyst using both gallium oxide and metal oxide can be prepared by simply physically mixing gallium oxide powder and metal oxide powder in a predetermined ratio (mixing method). If necessary, the obtained powder mixture may be fired in the air.

In the catalyst using gallium oxide and the metal oxide, the compounding ratio of gallium oxide and the combined metal oxide is usually about 10 to 1000 parts by weight of the combined metal oxide with respect to 1 part by weight of gallium oxide, preferably About 10 to 50 parts by weight.

The particle size of the catalyst when gallium oxide is used alone may be appropriately selected in consideration of the DME reforming conditions, moisture concentration, required life, etc., but is usually about 0.1 to 200 μm, more preferably 1 It is about ~ 100 μm. The particle size of the catalyst can be easily adjusted by confirming with SEM.

  When gallium oxide and another metal oxide are physically mixed and used together, the particle size of the metal oxide is not particularly limited, but in order to obtain a uniform mixed state, the gallium oxide particles The diameter is preferably the same.

The catalyst of the present invention can be further shaped according to a conventional method, or can be used after being coated on a substrate. In such a case, for example, a catalyst and silica or silica-alumina as a binder are mixed, and the mixture is formed into a honeycomb shape, or the mixture is made of cordierite, base metal, etc. Just wash coat.

When hydrogen is produced by steam reforming of DME in the presence of the catalyst according to the present invention, it is not particularly limited. For example, it is about 25 to 400 ° C. (more preferably about 80 to 250 ° C.). While supplying steam at a temperature higher than the theoretical amount (1-5 times the theoretical amount, more preferably 2-3 times the theoretical amount) necessary to completely convert DME into hydrogen at a temperature, DME and water vapor under flow Can be reacted. If necessary, DME may be subjected to the reaction in the form of a mixture diluted with a carrier gas such as nitrogen, argon or helium. The pressure during the reaction can be in the range of normal pressure to 10 MPa, but is preferably normal pressure or the vicinity thereof.

  In the above reaction, other gas components such as hydrogen, carbon monoxide, and carbon dioxide may be present in the system. In particular, when carbon monoxide coexists, it is advantageous because removal of carbon monoxide and production of hydrogen are performed simultaneously. At this time, if the remaining carbon monoxide becomes an inhibiting factor (for example, when hydrogen is used as a fuel for the fuel cell), a carbon monoxide removing device may be additionally provided as necessary.

Examples and comparative examples are shown below to clarify the features of the present invention.
[Comparative Example 1]
Preparation of Cu-Zn-Al ₂ O ₃ catalyst
Cu (NO ₃ ) ₂ · 3H ₂ O (9.4 g) and Zn (NO ₃ ) ₂ · 6H ₂ O (11.4 g) were dissolved in 26 ml of distilled water and heated to 80 ° C. An aqueous solution of Na ₂ CO ₃ (9.9 g) kept at 85 ° C. with good stirring (23 ml)
Was added dropwise over 1 hour. After completion of the dropwise addition, it was confirmed that the pH of the system was 8.0 and stirred for 1 hour. Then, the precipitated product was collected by suction filtration, and the washing step of “stirring in pure water heated to 50 ° C. for 20 minutes” was repeated three times. After confirming that the pH of the filtrate was neutral with phenolphthalein, the precipitate was dried at 110 ° C. for 15 hours. The obtained dry powder (Cu-Zn: was fired at 400 ° C. for 5 hours in the air.

The obtained Cu—Zn powder (particle size 10 to 100 μm) was physically mixed with the same weight of Al ₂ O ₃ (particle size 50 to 100 μm) to obtain a Cu—Zn—Al ₂ O ₃ catalyst.
[Example 1]
Preparation of Ga ₂ O ₃ / Al ₂ O ₃ catalyst by sol-gel method
An ethylene glycol solution of 1 mol / l gallium nitrate and an ethylene glycol solution of 1 mol / l aluminum nitrate nonahydrate were mixed in various ratios from 10: 0 to 0:10 (see Table 1). The resulting solution was stirred for 10 hours while maintaining at 80 ° C., and then ethylene glycol was distilled off under reduced pressure while gradually raising the temperature from 80 ° C. to 110 ° C. The obtained powder was ground in a mortar, dried at 200 ° C. for 5 hours, and calcined in air at 500 ° C. for 5 hours to obtain the catalyst of the present invention having the composition shown in Table 1.

In the catalyst obtained in this example and the following Examples 2 to 10 (particle size is in the range of 0.2 to 10 μm), no decrease in activity due to oxidation was observed even in contact with air.
[Example 2]
Preparation of Ga ₂ O ₃ —Al ₂ O ₃ Catalyst (Ga / Al = 1/9) by Impregnation Method Gallium nitrate 6.28 hydrate (0.738 g, 2.00 mmol) was dissolved in 3 ml of water. The aqueous solution was dropped into γ-alumina (0.918 g, 9.00 mmol), dried at 80 ° C. for 12 hours, then dried at 200 ° C. for 5 hours, and then calcined at 500 ° C. for 5 hours to obtain the catalyst according to the present invention. Was prepared.
[Example 3]
Preparation of Ga ₂ O ₃ -9ZrO ₂ Catalyst by Impregnation Method A catalyst according to the present invention was prepared in the same manner as in Example 2 using ZrO ₂ (1.11 g, 9.00 mmol) instead of γ-alumina in Example 2. .
[Example 4]
Preparation of Ga ₂ O ₃ -9TiO ₂ Catalyst by Impregnation Method A catalyst according to the present invention was prepared in the same manner as in Example 2 using TiO ₂ (0.719 g, 9.00 mmol) instead of γ-alumina in Example 2. .
[Example 5]
Preparation of Ga ₂ O ₃ —SiO ₂ catalyst In place of γ-alumina in Example 2, 0.54 g of SiO ₂ was used, and a solution diluted with 5 ml of water added to the gallium nitrate aqueous solution used in Example 2 was used. Then, a catalyst according to the present invention was prepared in the same manner as in Example 2.
[Example 6]
Preparation of Ga ₂ O ₃ —GeO ₂ Catalyst A catalyst according to the present invention was prepared in the same manner as in Example 2, except that 0.942 g of GeO ₂ was used instead of γ-alumina in Example 2.
[Example 7]
Preparation of Ga ₂ O ₃ —MnO ₂ Catalyst A catalyst according to the present invention was prepared in the same manner as in Example 2, except that 0.639 g of MnO ₂ was used instead of γ-alumina in Example 2.
[Example 8]
Preparation of Ga ₂ O ₃ —Fe ₂ O ₃ Catalyst A catalyst according to the present invention was prepared in the same manner as in Example 2, except that 1.437 g of Fe ₂ O ₃ was used instead of γ-alumina in Example 2.
[Example 9]
Preparation of Ga ₂ O ₃ —CeO ₂ Catalyst A catalyst according to the present invention was prepared in the same manner as in Example 2, except that 1.549 g of CeO ₂ was used instead of γ-alumina in Example 2.
[Example 10]
Preparation of Ga ₂ O ₃ —In ₂ O ₃ Catalyst A catalyst according to the present invention was prepared in the same manner as in Example 2, except that 1.249 g of In ₂ O ₃ was used instead of γ-alumina in Example 2.
[Example 11]
Preparation of Ga ₂ O ₃ —ZnO Catalyst A catalyst according to the present invention was prepared in the same manner as in Example 2, except that 0.733 g of ZnO was used instead of γ-alumina in Example 2.
[Example 12]
Preparation of 0.5Ga ₂ O ₃ -9.5TiO ₂ Catalyst A catalyst according to the present invention was prepared in the same manner as in Example 2, except that 0.759 g of TiO ₂ was used instead of Tl ₂ O ₃ of Example 9.
[Example 13]
Preparation of Ga ₂ O ₃ -9TiO ₂ catalyst by sol-gel method Titanium tetraisopropoxide (3.84g, 13.5mmol) in ethylene glycol solution and gallium nitrate n hydrate (1.11g, 3mmol) in ethylene glycol solution Mixed. The obtained solution was kept at 80 ° C. and stirred for 10 hours, and then ethylene glycol was distilled off under reduced pressure while gradually raising the temperature from 80 ° C. to 110 ° C. The obtained powder was ground in a mortar, dried at 200 ° C. for 5 hours, and calcined at 500 ° C. for 5 hours to prepare a catalyst according to the present invention.
[Example 14]
Preparation of 0.5Ga ₂ O ₃ -9.5TiO ₂ catalyst by impregnation method In Example 2, TiO ₂ (0.719 g, 9.00 mmol) was used in place of γ-alumina, and a 1/2 concentration gallium nitrate aqueous solution was used. A catalyst according to the present invention was prepared in the same manner as in Example 2.
[Test Example 1]
Using the catalysts obtained in Comparative Example 1 and Examples 1 to 14, the performance as each DME reforming catalyst was evaluated.

That is, a quartz glass tube having an inner diameter of 8 mm is filled with a predetermined DME catalyst (150 g), and using a fixed bed flow reactor under normal pressure, argon containing 1% (volume) dimethyl ether and 3% water vapor is used. The DME reforming activity was measured by flowing gas at 50 ml / min. During the reaction, the temperature was changed from 200 ° C to 400 ° C in increments of 50 ° C. The temperature increase rate at this time was 10 ° C./min. The reaction time at each set temperature was about 3 minutes.

The concentration of hydrogen, methane, carbon monoxide, carbon dioxide, unreacted dimethyl ether and methanol contained in the gaseous reaction product was measured using a gas chromatograph analyzer.
[Test Example 2]
In order to investigate the influence of the water vapor concentration in the reaction raw material, the DME reforming reaction was carried out under the same conditions as in Test Example 1 except that the concentration was changed to 4-6% in 1% increments.
[Consideration about Test Examples 1 and 2]
FIG. 1 shows activity evaluation data when Ga ₂ O ₃ —Al ₂ O ₃ catalysts prepared at various ratios described in Comparative Example 1 and Example 1 were used under the conditions of Test Example 1 (FIG. 1). -a indicates DME conversion, and FIG. 1-b indicates the hydrogen concentration in the outlet gas).

Table 1 shows outlet concentrations of various catalytically reactive organisms at a reaction temperature of 350 ° C. In the known Cu-ZnO catalyst, the activity is dramatically improved by mixing with alumina, whereas in the Ga ₂ O ₃ system, the activity is not improved even when alumina is mixed. From these results, it is suggested that the DME reforming reaction using the Ga ₂ O ₃ catalyst according to the present invention is different from the DME reforming reaction using a known catalyst.

Ga₂O₃を含まないアルミナ単独を用いた場合(図１-aおよび図１-bにおいて、酸化ガリウム濃度0モル％の場合)には、高温になるとDMEの加水分解が生じて、メタノールが生成さ
れるので、DME転化率が上がるが、水素の生成はほとんど見られない。これに対し、アル
ミナに少量の酸化ガリウムを加えると、反応温度300℃付近から水素が生成することが明
らかである。

When alumina alone containing no Ga ₂ O ₃ is used (when the gallium oxide concentration is 0 mol% in FIGS. 1-a and 1-b), hydrolysis of DME occurs at high temperatures, and methanol is As it is produced, the DME conversion rate is increased, but almost no hydrogen is produced. On the other hand, when a small amount of gallium oxide is added to alumina, it is apparent that hydrogen is generated from a reaction temperature of about 300 ° C.

Table 2 shows DME using gallium oxide alone, Ga ₂ O ₃ —Al ₂ O ₃ (Ga / Al = 9/1 or 8/2) under the conditions of Test Example 2 (reaction temperature is 400 ° C.). The result of conducting a reforming reaction and examining the product is shown. It is clear that the outlet hydrogen concentration increases when the water concentration is equal to or greater than 3%.

次に、触媒活性成分である酸化ガリウムを種々の金属酸化物に担持して、その担体としての効果を調べた。表３は、反応温度を350℃とし、10モル％のGa₂O₃を種々の金属酸化物に担持した触媒を用いた場合に得られたDME転化率、生成ガス中の水素および一酸化炭素
濃度を示す。表３から明らかな様に、反応温度350℃以上において、TiO₂を担体とする触
媒を使用する場合に、特に水素の出口濃度が高くなることが判明した。

Next, gallium oxide, which is a catalytically active component, was supported on various metal oxides, and the effect as a carrier was examined. Table 3 shows the DME conversion rate, hydrogen in the produced gas, and carbon monoxide when the reaction temperature was 350 ° C. and a catalyst in which 10 mol% of Ga ₂ O ₃ was supported on various metal oxides was used. Indicates the concentration. As is apparent from Table 3, it was found that when a catalyst having TiO ₂ as a support was used at a reaction temperature of 350 ° C. or higher, the hydrogen outlet concentration was particularly high.

そこで、実施例４と同様の手法により、比表面積の異なる市販のチタニアを担体として用いる種々の触媒を調製し、それぞれについて活性評価を行った。

Therefore, various catalysts using commercially available titania having different specific surface areas as a support were prepared by the same method as in Example 4, and the activity was evaluated for each of the catalysts.

Table 4 shows titania I (manufactured by Ishihara Sangyo Co., Ltd., “ST-01”, titania for photocatalyst, anatase type, specific surface area 207 m ² / g), titania II (manufactured by Nippon Aerosil Co., Ltd., “Titania P-25” "By mainly impregnating and supporting 10 mol% of gallium oxide in anatase type, specific surface area 41 m ² / g) and titania III (manufactured by Kanto Chemical Co., Ltd., anatase type, specific surface area 8 m ² / g) The activity of the three catalysts prepared is shown.

Table 4 also shows data for the catalyst prepared by the sol-gel method described in Example 14.

As shown in Table 4, it was found that the catalytic activity was highest at 350 ° C. when titania I was used as the support. However, at 400 ° C., the DME conversion was higher than the other catalysts, but the hydrogen concentration was found to be lower. This is because methanation at a high temperature proceeded only when titania I having a large specific surface area was used as a support.

Therefore, an attempt was made to prepare a catalyst with reduced activity by reducing the amount of gallium oxide as an active component. That is, the amount of gallium oxide supported is reduced to 5 mol%, and titania I
A catalyst using was prepared. As a result, it was found that the hydrogen concentration in the product at the reaction temperature of 400 ° C. was higher, although the DME conversion rate was slightly lower than that of the catalyst supporting 10 mol% gallium oxide. In addition, a catalyst having titania I as a carrier and a supported amount of gallium oxide of 5 mol% has a higher activity at 350 ° C. than a catalyst having 10 mol% of gallium oxide supported on titania II or titania III. I found out that

These results suggest that the activity can be further improved by improving the dispersity of Ga ₂ O ₃ using means such as structure control of titania and addition of other components.

［実施例１５］〜［実施例１７］
酸化亜鉛、酸化コバルトおよび酸化マグネシウムのそれぞれを担体とする以外は実施例２の手法に準じて、本発明の触媒を得た。

[Example 15] to [Example 17]
A catalyst of the present invention was obtained according to the method of Example 2 except that each of zinc oxide, cobalt oxide and magnesium oxide was used as a carrier.

When these catalysts were used and DME reforming was performed under the same conditions as in Test Example 1, a reaction gas containing hydrogen was obtained in any case.

4 is a graph showing DME conversion rates and hydrogen yields of catalysts having different mixing ratios of gallium oxide and γ-alumina.

Claims (2)

A dimethyl ether steam reforming catalyst having gallium oxide as a catalytic active component,
Consists of gallium oxide and other metal oxides,
The other metal oxide is at least one metal oxide selected from the group consisting of aluminum oxide, zirconium oxide, titanium oxide, silicon oxide, germanium oxide, manganese oxide, iron oxide, cerium oxide, indium oxide, and zinc oxide. Seeds,
Dimethyl ether steam reforming catalyst. The method for producing a hydrogen-containing gas which comprises contacting the dimethyl ether and Mizu蒸gas in the presence of a catalyst according to claim 1.

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