Process for preparing synthesis gas

Details Process for preparing synthesis gas Process for preparing synthesis gas

1999-03-11

2001-11-06

Griffin, Steven P. (Department: 1754)

Chemistry of inorganic compounds

Hydrogen or compound thereof

Elemental hydrogen

C423S651000, C423S653000, C423S418200, C502S326000, C502S339000, C252S373000

Reexamination Certificate

active

06312660

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process for the production of a synthesis gas.
BACKGROUND ART
A synthesis gas is a mixed gas containing hydrogen and carbon monoxide and is widely used as a raw material for the synthesis of ammonia, methanol, acetic acid, etc.
Such a synthesis gas may be produced by reaction of a hydrocarbon with steam and/or carbon dioxide in the presence of a catalyst. In the reaction, however, carbon deposition reactions occur as side reactions to cause carbon deposition which brings about a problem of catalyst poisoning.
The raw materials for the carbon deposition are a carbon-containing organic compound used as a raw material and CO produced in situ. The carbon deposition is accelerated as the partial pressures of these raw materials increase. Therefore, it is possible to reduce the amount of the carbon deposition by increasing the feed amount of steam and carbon dioxide while reducing the reaction pressure. In this case, however, it is necessary to excessively use steam and carbon dioxide in order to reduce the partial pressures of the carbon-containing organic compound and CO, so that several disadvantages are caused. For example, consumption of heat energy required for preheating steam and carbon dioxide increases. Further, costs for the separation of these gases from the product increase. Moreover, since a large reaction apparatus is required, the apparatus costs increase.
JP-A-5-208801 discloses a carbon dioxide-reforming catalyst containing a Group VIII metal supported on high purity, super-fine single crystal magnesium oxide. JP-A-6-279003 discloses a carbon dioxide-reforming catalyst containing a ruthenium compound supported on a carrier composed of a compound of at least one alkaline earth metal oxide and aluminum oxide. JP-A-9-168740 discloses a carbon dioxide-reforming catalyst containing rhodium supported on a carrier formed of a Group II-IV metal oxide or a lanthanoid metal oxide or a composite carrier composed of the above metal oxide and alumina. The reaction experiments using these catalysts are performed under ambient pressure. At a high pressure, which is industrially significant, these catalysts show a high carbon deposition activity and, hence, are not satisfactory as industrially applicable catalysts.
The objects of the present invention are:
(1) to provide a process for the production of a synthesis gas by reaction of a carbon-containing organic compound with steam and/or carbon dioxide, which process can solve a problem of carbon deposition;
(2) to provide a process for the production of a synthesis gas of the above-mentioned type, in which a catalyst having suppressed carbon deposition activity is used.
Other objects of the present invention will be understood from the following description of the specification.
DISCLOSURE OF THE INVENTION
The present inventors have made an intensive study to accomplish the above-described objects and, as a result, have completed the present invention.
In accordance with the present invention there is provided a process for producing a synthesis gas, wherein a carbon-containing organic compound is reacted with steam and/or carbon dioxide in the presence of a catalyst, characterized in that said catalyst comprises a carrier formed of a metal oxide, and at least one catalytic metal selected from rhodium, ruthenium, iridium, palladium and platinum and supported on said carrier, in that said catalyst has a specific surface area of 25 m
2
/g or less, in that the electronegativity of the metal ion of said carrier metal oxide is 13.0 or less and in that the amount of said catalytic metal is 0.0005-0.1 mole %, in terms of metal, based on said carrier metal oxide.
The catalyst used in the present invention (hereinafter referred to also as catalyst of the present invention) contains at least one catalytic metal selected from rhodium (Rh), ruthenium (Ru), iridium (Ir), palladium (Pd) and platinum (Pt) supported on a carrier metal oxide having specific characteristics. In this case, the catalytic metal can be supported in the form of a metallic state or in the form of a metal compound such as an oxide.
The catalyst of the present invention is characterized in that the catalyst has activity required for converting a carbon-containing organic compound into a synthesis gas while exhibiting a function to significantly suppress side reactions of carbon deposition reactions.
The catalyst used in the present invention can significantly suppress the carbon deposition reactions is characterized in that:
(i) the electronegativity of the metal ion of the carrier metal oxide is 13.0 or less;
(ii) the catalyst has a specific surface area of 25 m
2
/g or less; and
(iii) the amount of the supported catalytic metal is 0.0005-0.1 mole % based on the carrier metal oxide. Such a catalyst having a considerably suppressed carbon deposition activity has been first found by the present inventors.
The metal oxide used as a carrier may be a single metal oxide or a mixed metal oxide. In the present invention, the electronegativity of the metal ion in the carrier metal oxide is 13 or less, preferably 12 or less, more preferably 10 or less. The lower limit is about 4. Thus, the electronegativity of the metal ion in the carrier metal oxide used in the present invention is 4-13, preferably 4-12. The electronegativity of the metal ion in the metal oxide in excess of 13 is not preferable, because carbon deposition occurs significantly.
The electronegativity of the metal ion in the metal oxide is defined by the following formula:
Xi=
(1+2
i
)
Xo
wherein
Xi: electronegativity of the metal ion
Xo: electronegativity of the metal
i: valence electron number.
When the metal oxide is a mixed metal oxide, an average electronegativity of the metal ions is used. The average value is a sum of the products of the electronegativity of each of the metal ions contained in the mixed metal oxide by the molar fraction of the corresponding metal oxide of the mixed metal oxide.
The electronegativity (Xo) of a metal is in accordance with Pauling. The electronegativity in accordance with Pauling is as shown in “W. J. Moore Physical Chemistry, Vol. 1 translated by FUJISHIRO, Ryoichi”, 4th Edition, Tokyo Kagaku Dojin, p. 707 (1974), Table 15.4.
The electronegativity of metal ion in a metal oxide is described in detail in, for example, “Shokubaikoza, vol. 2, p145 (1985) edited by Catalyst Society of Japan”.
The metal oxides may include those containing one or at least two metals such as Mg, Ca, Ba, Zn, Al, Zr and La. Illustrative of such metal oxides are single metal oxides such as magnesia (MgO), calcium oxide (CaO), barium oxide (BaO), zinc oxide (ZnO), alumina (Al
2
O
3
), zirconia (ZrO
2
) and lanthanum oxide (La
2
O
3
), and mixed metal oxides such as MgO/CaO, MgO/BaO, MgO/ZnO, MgO/Al
2
O
3
, MgO/ZrO
2
, CaO/BaO, CaO/ZnO, CaO/Al
2
O
3
, CaO/ZrO
2
, BaO/ZnO, BaO/Al
2
O
3
, BaO/ZrO
2
, ZnO/Al
2
O
3
, ZnO/ZrO
2
, Al
2
O
3
/ZrO
2
, La
2
O
3
/MgO, La
2
O
3
/Al
2
O
3
and La
2
O
3
/CaO.
The catalyst used in the present invention having a specific surface area of 25 m
2
/g or less may be obtained by calcining a carrier metal oxide before the support of a catalytic metal at 300-1,300° C., preferably 650-1,200° C. After the catalytic metal has been supported, the catalytic metal-supported carrier is further calcined at 600-1,300° C., preferably 650-1,200° C. It is also possible to obtain the catalyst by supporting a catalytic metal on a carrier metal oxide, followed by the calcination of the catalytic metal supporting product at 600-1,300° C., preferably 650-1,200° C. The upper limit of the calcination temperature is not specifically limited but is generally 1,500° C. or less, preferably 1,300° C. or less. In this case, the specific surface area of the catalyst or the carrier metal oxide can be controlled by the calcination temperature and calcination time.
The specific surface area of the catalyst or the carrier metal oxide used in the present invention is preferably 20 m
2
/g or less, more preferably 15 m
2
/g or less, most preferably 10

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