Process for preparing hydrocyanic acid by catalytic dehydration of gaseous formamide - direct heating

A process for preparing hydrocyanic acid by catalytic dehydrating gaseous formamide at temperatures of from 350 to 650° C. in a reactor, wherein the dehydration of formamide is coupled with an exothermic reaction by the reactor comprising two separate fluid paths which are separated by a common reactor wall, with one fluid path being provided for the dehydration of formamide and the second fluid path being provided for the exothermic reaction and the common reactor wall being made of a material having a specific thermal conductivity X of at least 10 W/(mK), wherein the exothermic reaction is a catalytic combustion of combustible gases with introduction of oxygen.