GB800158A - Process for the production of hydrocyanic acid from formamide - Google Patents

Abstract

Hydrogen cyanide is produced by the catalytic decomposition of vaporized formamide produced by passing liquid formamide as a thin film down the internal walls of an externally heated evaporation tube, evaporation being assisted by the presence of one or more vanes rotating at high speed within the vessel near the surface of the film. The liquid formamide may have an extended period of stay in the tube, e.g. 5-60 seconds. Vaporization may take place under reduced pressure, e.g. 130-150 mm. of mercury, at a temperature of 120-160 DEG C. or in an atmosphere of ammonia, e.g. preheated to 250 DEG C., at a temperature of e.g. 180-205 DEG C., or alternatively, the formamide may be vaporized first and the mixed with gaseous ammonia, which is if necessary preheated. A proportion of the formamide preferably is passed right through the evaporator, e.g. 4 per cent of that vaporized, is cooled, a portion or the whole thereof is purified by filtration, centrifugation or adsorption, and is thereafter recycled to the evaporator. The condensate produced by cooling the reaction product gas, which consists mainly of formamide, may be similarly purified and recycled to the evaporator. Polymerization of hydrogen cyanide contained in the formamide being recycled may be prevented by adjusting the pH to 5-7. The catalyst may form the wall of the reaction vessel and may e.g. be of steel coated with a thin layer of Fe3O4. A vessel of similar material may be used for preheating and partial catalytic decomposition of the formamide vapour. The catalyst may also be aluminium phosphate supported on kaolin. Catalyst activity may be increased by injecting phosphoric acid, an iron salt, or air into the formamide vapour before catalytic decomposition.