GB941486A - Improvements in or relating to a process for the manufacture of hydrocyanic acid - Google Patents

Abstract

Hydrocyanic acid is prepared by the passage of a mixture comprising ammonia, a hydrocarbon such as methane, or a mixture of hydrocarbons, and oxygen in the vapour phase, at an elevated temperature, through one or more layers of a platinum or platinum alloy gauze catalyst, which has been activated by passing a mixture comprising ammonia, a hydrocarbon such as methane, or a mixture of hydrocarbons, and oxygen through the catalyst together with a volatile sulphidic material, in amount equivalent to 2 to 200 mg. s./m.3 at S.T.P., for at least one hour at an elevated temperature immediately before use. "A hydrocarbon such as methane or a mixture of hydrocarbons" refers to methane or mixtures of methane with a lesser proportion of its homologues, e.g. ethane, propane and butane. The preferred ratios of hydrocarbon to ammonia is 0.7 : 1 to 1.8 : 1, of oxygen to ammonia is 0.7 : 1 to 1.8 : 1 and the oxygen content is adjusted for maximum conversion of ammonia during the activation period, which is usually 1 to 2 hours. Either free oxygen or air may be used. Normal working temperatures are 700 DEG to 1250 DEG C. and the catalyst is not allowed to cool between activation and production of hydrocyanic acid. Suitable sulphidic material includes carbon disulphide, thiophene, hydrogen sulphide, methyl-, ethyl-, propyl- and butyl-mercaptans and dimethyl and diethyl sulphides. Examples are given using 90/10 platinum/rhodium alloy with a sulphur free mixture of 70% methane and 30% hydrogen and with a C : NH3 ratio of 1 : 1 using both air and oxygen with and without volatile sulphidic materials.