GB723757A - Improvements in or relating to production of hydrogen cyanide - Google Patents

Abstract

Ammonia is removed from hydrogen cyanide-containing gases produced by the reaction of ammonia, a gaseous hydrocarbon and oxygen in the presence of a platinum metal catalyst by scrubbing the gases with an aqueous sulphuric acid solution containing at least 25 per cent, preferably 25-30 per cent, of ammonium sulphate under such conditions that the pH of the absorbent solution is maintained at below 4, preferably 1-3. The temperature of the absorbent solution is kept as high as possible in order to prevent solution of the hydrogen cyanide. The feed gases may enter the absorption system at a temperature of 120 DEG -130 DEG C. and the temperature of the absorption system may be maintained at 80 DEG -90 DEG C. The desired pH may be ensured by means of an automatic pH controller which measures the pH of the effluent and causes the introduction of additional acid into the absorbent solution when necessary. The absorbent solution may be regenerated by evaporation, to crystallize out ammonium sulphate, followed by addition of acid and water, and recycled. The preferred absorbent solution contains 3.5 per cent of sulphuric acid, 30 of ammonium sulphate and 66.5 per cent of water. Specification 361,004 is referred to.