Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2001-04-05
2002-05-14
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S174000, C502S183000, C502S185000, C502S328000, C502S159000, C423S418200, C423S648100, C423S650000, C423S651000, C252S373000
Reexamination Certificate
active
06387843
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of preparing a catalyst containing Rh and/or Ru supported on a MgO carrier and to a process of producing a synthesis gas.
A synthesis gas which is a mixed gas containing hydrogen and carbon monoxide is widely used as a raw material for the synthesis of ammonia, methanol, acetic acid, etc.
Such a synthesis gas may be produced by reforming a hydrocarbon with steam and/or carbon dioxide in the presence of a catalyst such as Ni or other transition metals. In the reforming reaction, however, carbon deposition occurs as a result of side reactions to cause a problem of catalyst poisoning.
EP-A-0974551 discloses a Rh and/or Ru-supporting MgO catalyst which can decrease carbon deposition. Because noble metals such as Rh and Ru are very expensive, there is a great demand for a method which can produce noble metal-containing catalyst using as small an amount of the noble metal as possible.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention there is provided a method of preparing a catalyst, which includes mixing magnesium oxide with a binder selected from the group consisting of carbon, fatty acids having 12-22 carbon atoms, magnesium salts of fatty acids having 12-22 carbon atoms, carboxymethyl cellulose, a magnesium salt of carboxymethyl cellulose, and polyvinyl alcohol to obtain a mixture in which the binder is present in an amount of 0.1-5% by weight. The mixture is molded and calcined at a temperature of at least 1,000° C. to obtain a carrier having a specific surface area of 5 m
2
/g of less. The carrier is impregnated with an aqueous solution containing a catalytic metal component selected from the group consisting of rhodium compounds, ruthenium compounds and mixtures thereof so that the catalytic metal component is loaded on the carrier in an amount of 10-5,000 ppm, in terms of elemental metal, based on the weight of the carrier, and then dried and calcined to give a catalyst.
In another aspect, the present invention provides a process for the production of a synthesis gas, wherein a carbon-containing organic compound is reacted with steam and carbon dioxide at a temperature 600-1,000° C., a pressure of 5-40 Kg/cm
2
G and a GHSV of 1,000-10,000 Hr
−1
in the presence of a catalyst, obtained by the above method, with a molar ratio of the steam to carbon of the carbon-containing organic compound of 2 or less and a molar ratio of the steam to the carbon dioxide of 0.1-10.
The present invention further provides a process for the production of carbon monoxide, wherein a carbon-containing organic compound is reacted with carbon dioxide at a temperature 600-1,000° C., a pressure of 5-40 Kg/cm
2
G and a GHSV of 1,000-10,000 Hr
−1
in the presence of a catalyst, obtained by the above method, with a molar ratio of the carbon dioxide to carbon of the carbon-containing organic compound of 1.0-3.0 to obtain a synthesis gas, and wherein the synthesis gas is treated to concentrate carbon monoxide.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
In the method of the present invention, a carrier of MgO (magnesium oxide) having a specific surface area (SA) of 5 m
2
/g or less is used. Thus, in the first step, magnesium oxide is mixed uniformly with a binder selected from carbon, fatty acids having 12-22 carbon atoms, magnesium salts of fatty acids having 12-22 carbon atoms, carboxymethyl cellulose, a magnesium salt of carboxymethyl cellulose, and polyvinyl alcohol to obtain a mixture. The binder serves as a molding aid for molding magnesium oxide into a desired shape and as a lubricant which can facilitate the molding operation because of easiness in filling or charging the mixture to a molding device. The use of carbon as the binder is preferred for reasons of its availability at low costs. The carbon may be, for example, graphite, carbon black or activated carbon. Examples of the fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid and behenic acid.
Each of the magnesium oxide and binder is preferably in the form of powder having an average particle diameter of 1-1,000 &mgr;m, more preferably 10-100 &mgr;m. The binder is used in an amount of 0.1-5% by weight, preferably 2-4% by weight, based on the total weight of the magnesium oxide and the binder, namely the mixture. When the amount of the binder is smaller than 0.1% by weight, a molded product obtained by molding the mixture as described hereinafter and a carrier obtained by calcining the molded product as described hereinafter fail to show satisfactory mechanical strengths. Additionally, such a small amount of the binder cannot improve easiness in filling or charging the mixture to a molding device. Too large an amount of the binder in excess of 5% by weight is undesirable because the binder retains in the carrier after calcination, causing reduction of mechanical strengths of the carrier. The use of an excess amount of the binder is also disadvantageous from the standpoint of economy.
The mixture is then molded into a molding device. The molding operation is generally performed at a room temperature and a pressure of 100-3,000 kg/cm
2
G, preferably 200-2,000 kg/cm
2
G, using any suitable molding method such as a press molding method or a tablet making method, to produce a molded product having any desired shape such as in the form of tablet, rod, ring or cylinder. The molded product generally has a size (diameter or longitudinal length) of 3-30 mm, preferably, 5-25 mm. The shape and the size of the molded product are suitably determined in view of the kind of catalyst bed used.
The molded product is then calcined at a temperature of at least 1,000° C., preferably 1,100-1,300° C., to obtain a carrier having a specific surface area of 5 m
2
/g of less. Upper limit of the calcination temperature is generally 1,500° C. Magnesium oxide having a large specific surface area may be used as a raw material in the present invention, because sintering of magnesium oxide proceeds significantly during the calcination at 1,000° C. or more so that the specific surface area of the magnesium oxide carrier obtained can be reduced to 5 m
2
/g of less. The calcination is carried out in an oxygen-containing atmosphere, generally air, for at least 1 hour, preferably at least 3 hours. The upper limit of the calcination time is not specifically limited, but is generally about 72 hours. During the course of the calcination, the binder contained in the molded product is decomposed and disappears. The carrier thus obtained has high mechanical strengths of, for example, a side crashing strength of 30-70 kg/piece.
The thus obtained MgO carrier having a specific surface area of 5 m
2
/g or less has a high degree of crystallinity and has stable surfaces having reduced strong acid sites. Namely, the MgO thus stabilized has a Hammett acidity function (Ho) of 2 or more and has an amount of the acid sites of not greater than 0.03 mmol/g.
When the specific surface area of the MgO carrier is greater than 5 m
2
/g, the degree of crystallinity becomes low and the amount of catalytic metal (Rh or Ru) supported thereon is unavoidably increased. Additionally, the acid strength is so increased that the resulting catalyst may cause undesirable reactions resulting in deposition of carbon on the catalyst. When the specific surface area of the MgO carrier is extremely low, the amount of the catalytic metal supported thereon is very small. At least 0.01 m
2
/g is desirable to obtain satisfactory catalytic activity. Preferably, the specific surface area of the MgO carrier is 0.05-3 m
2
/g.
The term “specific surface area” referred to in the present specification in connection with catalyst or MgO carrier is measured by the “BET method” at a temperature of 15° C. using a measuring device “SA-100” manufactured by Shibata Science Inc.
The catalytic metal which is at least one of Rh and Ru may be loaded on the MgO carrier by any known method such as impregnation by spraying or immersion or ion exchange using an aqueous solution containing a water
Nagumo Atsuro
Shimura Mitsunori
Wada Yukitaka
Yagi Fuyuki
Bell Mark L.
Chiyoda Corporation
Hailey Patricia L.
Lorusso & Loud
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