Chemistry of inorganic compounds – Nitrogen or compound thereof – Carbon containing
Reexamination Certificate
1996-08-07
2001-09-11
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Nitrogen or compound thereof
Carbon containing
C204S157460
Reexamination Certificate
active
06287531
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the preparation of hydrogen cyanide (HCN) by reacting ammonia and a hydrocarbon gas in the presence of a platinum-group-metal catalyst while heating the catalyst by induction heating at a frequency of 0.5 to 30 MHz.
BACKGROUND OF THE INVENTION
Hydrogen cyanide is highly toxic, but a commercially important chemical compound having a wide variety of industrial uses. Hydrogen cyanide is produced commercially by contacting ammonia, excess hydrocarbon gas, and an oxidizing gas with a platinum-group-metal catalyst. The excess hydrocarbon gas is ignited, and the heat generated is sufficient to cause the endothermic reaction of ammonia and the remaining hydrocarbon gas to form hydrogen cyanide.
Shipment of hydrogen cyanide presents potential hazards. One way to avoid these potential hazards is to produce the product at the site where it is to be used. However this requires the installation of a large number of small production facilities. Such production facilities have in the past been expensive.
It is an objective of the present invention to provide a process for the production of HCN that can be operated on a relatively small scale but efficiently and at a low installation cost.
The present invention employs the use of induction heating of a platinum-group-metal catalyst to cause ammonia to react with hydrocarbon gas and form hydrogen cyanide. The reaction is endothermic, and by the use of induction heating the amount of energy used may be carefully regulated so that a minimum of energy is wasted.
The use of induction heating to heat catalyst to cause chemical reactions of various types is known; for example in Edward's U.S. Pat. No. 5,110,996 vinylidine fluoride is produced by the reaction of dichlorofluoromethane with methane, and the reaction tube contains a non-metallic packing material, and optionally a metallic catalyst—see column 3 line 5. Conventionally induction heating is carried out at frequencies of about 0.1 to 0.2 MHz.
SUMMARY OF THE INVENTION
The present invention is a process for the preparation of hydrogen cyanide which comprises heating a platinum-group-metal catalyst by induction heating at a frequency of 0.5 to 30 MHz to reaction temperature, passing a mixture of ammonia vapor and a hydrocarbon gas in contact with said heated catalyst, and recovering hydrogen cyanide. A preferred hydrocarbon gas is methane, but other hydrocarbon gases are also useful, for example hydrocarbon gases having 1 to 6 carbon atoms and mixtures of such gases. A preferably the mole ratio of ammonia to carbon atoms in the hydrocarbon gas is approximately 1. A preferred form of catalyst is a metal gauze. The preferred platinum-group-metal catalyst is platinum; however, mixtures of platinum-group-metals may also be employed. The platinum-group-metal catalyst may also be a metal gauze containing a platinum-group metal, or the metal gauze may be made of platinum-group metal. The catalyst may also be a ceramic substrate having a platinum-group-metal dispersed on its surface, for example the reactor tube or tubes may be ceramic and coated with a platinum-group-metal, or the catalyst may be ceramic particles coated with platinum-group-metal. The catalyst should have an electrical conductivity of at least about 1.0 Seimens per meter in order to be effectively heated by electrical induction. The process of the invention is carried out at a the reaction temperature of between about 600 and about 1200 degrees C.
In a preferred embodiment the induction heating is carried out in pulses. The length of the pulses will of course depend on the size of the reactor, and the volume of gas and the temperature of the gas passing through the reactor, but usually the pulses will be at least equal to the residence time of the gas in the reaction tube.
REFERENCES:
patent: 1986348 (1935-01-01), Lacy et al.
patent: 4743522 (1988-05-01), Iino et al.
patent: 5110996 (1992-05-01), Edwards
patent: 5262145 (1993-11-01), Agrawal et al.
patent: 5470541 (1995-11-01), Koch et al.
patent: 588268 (1959-12-01), None
patent: 2.014.523 (1970-04-01), None
patent: 2 210 286 A (1988-06-01), None
Mehdizadeh Mehrdad
Riegert Ronald Jack
E. I. Du Pont de Nemours and Company
Hendrickson Stuart L.
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