JP2003159529A - Catalyst for reforming methanol and producing method for hydrogen-containing gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for reforming methanol which has high activity and selectivity, is excellent in a heat-resistance, and capable of effectively generating reformed gas mainly composed of hydrogen in a self heat supply reaction, and to provide a producing method for hydrogen-containing gas using the catalyst. <P>SOLUTION: The producing method for hydrogen-containing gas produces the reformed gas mainly composed of hydrogen by letting water vapor and oxygen react with methanol under the catalyst for reforming methanol which contains a platinum metal, zinc oxide and chromic oxide as the main component and in which an atomic ratio (zinc/chrome) of the zinc and chrome is in the range from 2 to 30, and under the presence of the catalyst. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hydrogen-containing gas in which a reformed gas containing hydrogen as a main component is produced by a steam reforming reaction of methanol, and more particularly, a self-heat treatment for carrying out the reforming reaction in the presence of oxygen. The present invention relates to a feed type reaction and a catalyst used in the reaction.

[0002]

2. Description of the Related Art Methanol steam reforming reaction for reforming methanol to hydrogen-containing gas by using steam includes a small amount of carbon monoxide by the reverse shift reaction of formula (2) in addition to the main reaction shown by formula (1). Is a byproduct. CH ₃ OH + H ₂ O = 3H ₂ + CO ₂ + 49.5 kJ / mol (1) CO ₂ + H ₂ = CO + H ₂ O + 41.17 kJ / mol (2) (2) Carbon monoxide by-product Is difficult to remove during purification to high-purity hydrogen, and it is preferable that the amount is as small as possible. From thermodynamic equilibrium, the lower the temperature, the more the molar ratio of water vapor to methanol (hereinafter, S
The larger the / C ratio, the lower the carbon monoxide concentration in the reformed gas.

Since the main reaction of the methanol steam reforming reaction of the formula (1) is an endothermic reaction, heat must be supplied from the outside, and a heat supply facility is required and the apparatus becomes complicated. On the other hand, there is a self-heat supply type reaction in which air is introduced together with methanol and steam to oxidize a part of methanol and the heat is used to cause a steam reforming reaction of the formula (1). This method oxidizes a part of methanol into hydrogen and carbon dioxide as shown in equation (3) and utilizes this heat.
The methanol reforming reaction of the formula (1) is performed. CH ₃ OH + 1 / 2O ₂ = 2H ₂ + CO ₂ 192.3kJ / mol (3) According to this method, heat is generated when the reaction is continued, except for heat that raises the temperature to the temperature level required for starting the reaction. It has the feature that it does not require supply.

The catalyst used for methanol steam reforming is, for example, a catalyst supporting a base metal element such as copper, nickel, chromium, zinc and aluminum and its oxide, or platinum, palladium etc. on a carrier such as alumina. Many catalysts supporting the platinum group metal have been proposed. Among them, as a catalyst for methanol steam reforming, having high activity and high heat resistance, JP
Japanese Patent No. 49930 discloses a catalyst composed of palladium and zinc oxide, and Japanese Patent Application Laid-Open No. 2001-25662 discloses a catalyst prepared by supporting palladium and / or platinum metal as an active species on a zinc oxide carrier.

However, the catalyst described in the above-mentioned JP-A-5-49930 has a problem in heat resistance in an autoheat supply type reaction, and when it is continuously operated for a long time, its activity and selectivity are continuously increased. Is reduced. The catalyst described in Japanese Patent Laid-Open No. 2001-25662 requires an external reduction treatment with hydrogen at 200 ° C. as a pretreatment, and there is a problem in terms of maintenance when mounted on a moving methanol reformer such as an automobile. Many.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to efficiently generate a reformed gas mainly containing hydrogen even in a self-heat supply type reaction, which has high activity, high selectivity and excellent heat resistance. The present invention provides a catalyst for reforming methanol capable of producing hydrogen, and a method for producing a hydrogen-containing gas using the catalyst.

[0007]

As a result of intensive studies on the above problems, the present inventors have found that a catalyst containing metallic platinum, zinc oxide, and chromium oxide as main components and having a specific zinc / chromium ratio is a self-heat supply type reaction. It has been found that the present invention is suitable for the above, and that the concentration of carbon monoxide in the obtained hydrogen-containing gas is low.

That is, the present invention provides a methanol reforming catalyst containing platinum metal, zinc oxide and chromium oxide as main components and having an atomic ratio of zinc and chromium (zinc / chromium) in the range of 2 to 30, and The present invention relates to a method for producing a hydrogen-containing gas, which comprises reacting methanol with steam and oxygen in the presence of the catalyst to produce a reformed gas containing hydrogen as a main component.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As a platinum source of the catalyst of the present invention,
Platinum oxide, chloroplatinic acid and its alkali metal salts, acetylacetonato platinum, dinitrodiammine platinum and the like can be used. When the catalyst is prepared by dissolving it in water, it is preferable to use potassium chloroplatinate.

Commercially available zinc oxide can be used as the zinc source of the catalyst of the present invention.
A compound such as an organic acid such as zinc nitrate, a salt of an inorganic acid, zinc oxide, zinc hydroxide, basic zinc carbonate, or the like, which forms zinc oxide after firing or reduction or during the reaction, can also be used as a zinc source.

The chromium source of the catalyst of the present invention is not particularly limited as long as it can be chromium oxide at the end of catalyst preparation. For example, organic acids such as chromium acetate, chromium nitrate,
Water-soluble salts of inorganic acids can be used. For example, an oxide can be obtained by calcining a precipitate obtained by treating an aqueous solution of these chromium compounds with a precipitant.

The catalyst preparation method in the present invention is not particularly limited as long as it is a catalyst preparation method in which metallic platinum, zinc oxide and chromium oxide coexist. For example, a method of coprecipitating a mixed solution of potassium chloroplatinate, zinc nitrate and chromium nitrate using an appropriate precipitant, zinc oxide-chromium oxide calcined powder prepared by coprecipitation from zinc nitrate and chromium nitrate, and platinum chloride. A method of supporting potassium acid or the like can be used. As the precipitating agent, an alkali compound such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate or sodium hydrogen carbonate is used. The amount of precipitating agent is 1-2 times the chemical equivalent, preferably 1.1-1.6 times. The temperature at the time of preparing the precipitate is 20 to 90 ° C., preferably 35.
~ 85 ° C. The precipitate obtained by the precipitation method is preferably washed with ion-exchanged water, distilled water or the like.

The atomic ratio of zinc to chromium (zinc / chromium) contained in the catalyst of the present invention is 2 to 30, preferably 2.3 to.
The range is 10. By adjusting the atomic ratio of zinc and chromium contained in the catalyst (zinc / chromium) within this range, a method for producing a hydrogen-containing gas in which a reformed gas mainly containing hydrogen is generated by a steam reforming reaction of methanol, In particular, in the self-heat supply type reaction in which the reforming reaction is performed in the presence of oxygen, the concentration of carbon monoxide in the obtained hydrogen-containing gas can be reduced.

The platinum content contained in the catalyst of the present invention is
The total amount of metallic platinum, zinc oxide and chromium oxide is preferably in the range of 5 to 50% by weight, 20 to 30
More preferably, it is wt%. When the platinum content is less than 5% by weight, the activity and selectivity are insufficient,
When it exceeds the weight%, it becomes difficult to carry it.

The precipitate obtained by the above method is dried, or dried and calcined, crushed to a uniform size, or molded and used. Also, it can be used by pulverizing a dried product of a slurry, or a product obtained by drying and firing, suspending it in water, adding a binder such as alumina sol if necessary, and supporting it on a carrier and a carrier structure. You can In this case, it can be used after being carried and dried, or after firing. Drying temperature is 50-1
50 ° C is preferred. The firing method is not particularly limited, and is generally 180-800
It is preferable to carry out the treatment at a temperature range of ℃, preferably 350 to 450 ℃.

In the method of the present invention, in the presence of the catalyst for reforming methanol prepared as described above, methanol is reacted with steam and oxygen, and a reforming mainly containing hydrogen is carried out by an autoheat supply type reaction. Produce gas. In this reaction, the methanol reforming catalyst may be activated by, for example, hydrogen or a carbon monoxide-containing gas as in the case of steam reforming, or the reaction may be performed without activation. You can also offer it. Air is usually used as the oxygen source. As the reaction conditions, the steam / methanol ratio (S / C ratio) is 1.0 to 2.0, and the air / methanol ratio (A
/ M ratio) is 0.3 to 3.0, and conditions are selected so that the heat generated by the combustion reaction and the heat absorbed by the methanol reforming reaction are balanced. Liquid hourly space velocity (LHSV) per unit catalyst volume is
It is 0.1 to 60 (hr ^-1 ). The reaction temperature is 200 to 500 ° C., and the reaction pressure is selected from normal pressure to 0.5 MPa.

[0017]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In the following examples and comparative examples, the catalytic activity was evaluated by the methanol reaction rate from the reactor outlet gas composition and the CO selectivity according to the following formula. Methanol reaction rate (%) = ([CO] + [CO ₂ ]) / ([CO] + [CO ₂ ] + [CH ₃
OH]) × 100 CO selectivity (%) = [CO] / ([CO] + [CO ₂ ]) × 100 where [CO], [CO ₂ ], and [CH ₃ OH] are reactors, respectively. It is the molar concentration of CO, CO ₂ and CH ₃ OH in the outlet gas.

(Catalyst preparation) Example 1 138 g of sodium carbonate (anhydrous) was placed in a 5 L round-bottomed flask together with 1000 ml of ion-exchanged water and dissolved to 60 ° C. A solution of 238 g of zinc nitrate hexahydrate and 80 g of chromium nitrate nonahydrate dissolved in 800 ml of ion-exchanged water at 60 ° C. was added thereto, and 3
Stir for 0 minutes. The slurry thus prepared was filtered, and the obtained precipitate was washed with 12 L of deionized water. Subsequently, it was dried at 80 ° C and then calcined at 380 ° C for 2 hours, so that zinc oxide and chromium oxide had a zinc / chromium atomic ratio of 4
A Zn-Cr catalyst having the following composition was obtained. To 15 ml of this Zn-Cr powder dispersed in 500 ml of a 60 ° C aqueous solution, potassium chloroplatinate (K ₂ Pt
500 ml of a 60 ° C. aqueous solution of 13.82 g of Cl ₄ ) was added. 30 minutes later 1NKOH
66 ml was added, and the mixture was stirred at 60 ° C for 60 minutes. After that, the solution was filtered, and washing with water was repeated until chlorine in the filtrate became 1 ppm or less. Then, after drying at 80 ℃ for 15 hours, it was baked at 380 ℃ for 2 hours. Pt with zinc / chromium ratio of 4 and platinum content of 30% by weight
-Zn-Cr catalyst was obtained. After wet pulverizing this catalyst and mixing it with alumina sol to form a slurry, the steps of immersing, blowing off excess and drying were repeated in a cordierite honeycomb (400 cells / cm 2) to carry the catalyst after drying. The catalyst was supported so that the amount would be 200 g / L. This is designated as catalyst A.

Example 2 A Pt-Zn-Cr catalyst having a zinc / chromium ratio of 4 and a platinum content of 35% by weight was prepared in the same manner as in Example 1. This catalyst was loaded on a cordierite honeycomb (400 cells / square centimeter) in the same manner as in Example 1 so that the catalyst loading amount was 200 g / L. This is designated as catalyst B.

Example 3 A Pt-Zn-Cr catalyst having a zinc / chromium ratio of 2.33 and a platinum content of 35% by weight was prepared in the same manner as in Example 1. This catalyst was loaded on a cordierite honeycomb (400 cells / square centimeter) in the same manner as in Example 1 so that the catalyst loading amount was 200 g / L. This is designated as catalyst C.

Comparative Example 1 To 500 ml of a 60 ° C. aqueous solution in which 15 g of zinc oxide powder was dispersed, 500 ml of a 60 ° C. aqueous solution of 13.82 g of potassium chloroplatinate (K ₂ PtCl ₄ ) was added. After 30 minutes, 66 ml of 1N KOH was added, and the mixture was stirred at 60 ° C for 60 minutes. After that, the solution was filtered, and washing with water was repeated until chlorine in the filtrate became 1 ppm or less. Then, after drying at 80 ℃ for 15 hours, calcination at 380 ℃ for 2 hours, P content of 30 wt% P
A t-Zn catalyst was obtained. This catalyst was loaded on a cordierite honeycomb (400 cells / square centimeter) in the same manner as in Example 1 so that the catalyst loading amount was 200 g / L. This is catalyst D
And

Comparative Example 2 128 g of sodium carbonate (anhydrous) and 1000 ml of ion-exchanged water
It was put in a 5 L round bottom flask and dissolved to 60 ° C. here
Dissolve 300 g of zinc nitrate hexahydrate in 800 ml of deionized water
Then, the solution adjusted to 60 ° C. was added and stirred for 30 minutes. like this
The prepared slurry was filtered and the resulting precipitate was subjected to ion exchange.
It was washed with 12 L of exchanged water. It is then dried at 80 ° C and then 380
A ZnO catalyst was obtained by calcining at ℃ for 2 hours. this
Platinum chloride was added to 500 ml of a 60 ° C aqueous solution in which 15 g of ZnO powder was dispersed.
Potassium acid (K₂PtCl _Four) Add 17.37 g of 60 ° C aqueous solution 500 ml
It was After 30 minutes, add 83 ml of 1NKOH and stir at 60 ° C for 60 minutes.
It was After that, filter until chlorine in the filtrate is less than 1ppm.
The washing with water was repeated. Then, dry at 80 ℃ for 15 hours
And then baked at 380 ° C for 2 hours to obtain a platinum content of 35 wt% Pt-
A Zn catalyst was obtained. This catalyst was treated with cordiera as in Example 1.
Amount of catalyst supported on ITO honeycomb (400 cells / cm2)
The catalyst was loaded so that the concentration would be 200 g / L. This is called catalyst E
To do.

Comparative Example 3 By the same method as in Example 1, a Pt-Zn-Cr catalyst having a zinc / chromium ratio of 1.5 and a platinum content of 35% by weight was prepared. This catalyst was loaded on a cordierite honeycomb (400 cells / square centimeter) in the same manner as in Example 1 so that the catalyst loading amount was 200 g / L. This is designated as catalyst F.

(Methanol reforming reaction) Example 4 and Comparative Example 4 A methanol / water solution having a water / methanol ratio of 1.5 was added to methanol L.
It was introduced into the evaporator at HSV = 5 hr ⁻¹ , air was mixed after the evaporator outlet, and the temperature of the introduction line was adjusted so as to enter the catalyst layer at 200 ° C. The reaction was LHSV = 15 hr ⁻¹ and the amount of air was controlled so that the reaction rate of methanol was 99.5% at the initial stage of the reaction. The gas composition after the reaction was analyzed by gas chromatography. Table 1 shows the methanol conversion rate and A / M ratio after the reaction time was 0 hour and 100 hours, and Table 2 shows the CO selectivity.

Table 1 (LHSV = 15 hr ⁻¹ ) Type of catalyst Methanol reaction rate (%) A / M ratio 0 hr 100 hr Example 4 Catalyst A (30 wt% Pt-Zn-Cr (Zn / Cr = 4)) 99.5 99.5 0.90 Comparative Example 4 Catalyst D (30 wt% Pt-Zn) 99.6 99.6 0.96

Table 2 (LHSV = 15hr ^-1 ) Type of catalyst CO selectivity (%) 0hr 100hr Example 4 Catalyst A (30wt% Pt-Zn-Cr (Zn / Cr = 4)) 8.4 8.2 Comparative Example 4 Catalyst D (30wt% Pt-Zn) 11.5 9.5

As can be seen from Tables 1 and 2, Example 4 using the catalyst according to the present invention has excellent heat resistance,
The CO concentration in the obtained hydrogen-containing gas can be suppressed to a low level as compared with Comparative Example 4. Moreover, the A / M ratio can be reduced, and the reformed gas mainly containing hydrogen is efficiently generated.

Examples 5 and 6 and Comparative Examples 5 and 6 An aqueous solution of methanol having a water / methanol ratio of 1.5 was added to methanol L.
It was introduced into the evaporator at HSV = 5 hr ⁻¹ , air was mixed after the evaporator outlet, and the temperature of the introduction line was adjusted so as to enter the catalyst layer at 200 ° C. The reaction was controlled by LHSV = 30 hr ⁻¹ and the amount of air so that the methanol conversion rate in the initial stage of the reaction was 99.5%. The gas composition after the reaction was analyzed by gas chromatography. Table 3 shows the reaction rates of methanol after 0 and 100 hours of reaction time, and Table 4 shows the CO selectivity.

Table 3 (LHSV = 30 hr ⁻¹ ) Type of catalyst Methanol reaction rate (%) 0 hr 100 hr Example 5 catalyst B (35 wt% Pt-Zn-Cr (Zn / Cr = 4)) 99.4 99.4 Example 6 catalyst C (35wt% Pt-Zn-Cr (Zn / Cr = 2.33)) 99.2 99.2 Comparative Example 5 Catalyst E (35wt% Pt-Zn) 99.5 99.5 Comparative Example 6 Catalyst F (35wt% Pt-Zn-Cr (Zn / Cr) = 1.5)) 99.4 99.2

Table 4 (LHSV = 30hr ⁻¹ ) (Initial reaction → after 100 hours) Catalyst type CO selectivity (%) 0hr 100hr Example 5 Catalyst B (35wt% Pt-Zn-Cr (Zn / Cr = 4 )) 9.7 9.6 Example 6 Catalyst C (35wt% Pt-Zn-Cr (Zn / Cr = 2.33)) 9.3 9.3 Comparative Example 5 Catalyst E (35wt% Pt-Zn) 12.0 11.5 Comparative Example 6 Catalyst F (35wt% Pt) -Zn-Cr (Zn / Cr = 1.5)) 12.0 12.8

As can be seen from Tables 3 and 4, Examples 5 to 6 using the catalyst according to the present invention are excellent in heat resistance and durability, and are outside the range of zinc / chromium ratio claimed by the present invention. As compared with Comparative Example 5 containing no chromium and Comparative Example 6 having a zinc / chromium ratio of 1.5, the CO concentration in the hydrogen-containing gas obtained can be suppressed to a low level, and the reformed gas mainly containing hydrogen can be efficiently used. Well generated.

[0032]

EFFECTS OF THE INVENTION According to the method of the present invention, by using a catalyst for reforming methanol which is excellent in heat resistance and highly active, water vapor and oxygen are reacted with methanol, and hydrogen is mainly contained by a self heat supply type reaction. Efficiently generate the reformed gas,
By reducing the carbon monoxide concentration in the reformed gas, the hydrogen-containing gas can be produced industrially advantageously.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Taishi Ikoma             Niigata City Niigata City Tayuhama Niiwari 182 Mitsubishi Mitsubishi             Gas Chemical Co., Ltd. Niigata Research Center (72) Inventor Yasushi Hiramatsu             Niigata City Niigata City Tayuhama Niiwari 182 Mitsubishi Mitsubishi             Gas Chemical Co., Ltd. Niigata Research Center (72) Inventor Mikio Yoneoka             Niigata City Niigata City Tayuhama Niiwari 182 Mitsubishi Mitsubishi             Gas Chemical Co., Ltd. Niigata Research Center F-term (reference) 4G040 EA02 EA06 EA07 EC03                 4G069 AA03 AA08 BB04A BB04B                       BC35A BC35B BC58A BC58B                       BC75A BC75B CC25 DA06                       EA19 FA01 FA03 FB09 FB14                       FB15 FC08

Claims (3)

[Claims] 1. A main component containing platinum metal, zinc oxide and chromium oxide, and an atomic ratio of zinc and chromium (zinc / chromium).
A catalyst for reforming methanol with a chromium content in the range of 2 to 30. 2. The catalyst for reforming methanol according to claim 1, wherein the amount of platinum metal relative to the total amount of platinum metal, zinc oxide and chromium oxide is in the range of 5 to 50% by weight. 3. In the presence of the catalyst according to claim 1 or 2,
A method for producing a hydrogen-containing gas, which comprises reacting methanol with water vapor and oxygen to produce a reformed gas containing hydrogen as a main component.