Installation and process for the preparation of hydrogen cyanide

A process for preparing hydrogen cyanide HCN by reacting, over a catalyst placed inside an Andrussow type reactor (60), a reactant gases mixture containing a methane-containing gas, ammonia and oxygen-enriched air, the process comprising before feeding the Andrussow type reactor with the reactant gases mixture, a pre-mixing step of oxygen with air followed by a simultaneous addition of methane-containing gas and ammonia into the obtained pre-mixture of oxygen-enriched air, said process comprising the steps of pre-mixing oxygen with air with a ratio comprised between 20.95% and 32.5% by volume, wherein the content of oxygen in air is progressively increased until reaching the maximum value of 32.5% by volume;

• simultaneously adding methane containing gas and ammonia in the pre-mixture of oxygen-enriched air in such a manner that the volumic ratio of methane to ammonia is comprised between 1.35 and 1.02 depending on the content of oxygen into air;
• said obtained reactant gases mixture having a temperature comprised between 80° C. and 120° C., for feeding the Andrussow type reactor (60).