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

A process for preparing hydrocyanic acid, comprising:

• dehydrating gaseous formamide at temperatures of from 350 to 650° C. in the presence of a catalyst and 0.1 to 10 mol % oxygen in a reactor, and
• coupling the dehydration of the gaseous formamide with an exothermic reaction in the reactor,
• wherein the coupling of the dehydration and the exothermic reaction comprises two separate fluid paths separated by a common reactor wall in the reactor, with one fluid path being provided for the dehydration of formamide and the second fluid path being provided for the exothermic reaction and a specific thermal conductivity λ of the common reactor wall material is greater than 100 W/(mK),
• wherein
• the exothermic reaction is a catalytic combustion of combustible gases with introduction of oxygen, and
• the reactor is a tube reactor or plate reactor comprising at least two parallel, superposed layers A and B, with the layer A having at least two parallel reaction channels in which the catalytic dehydration occurs and the layer B having at least two parallel channels in which the exothermic reaction occurs, and
• the common reactor wall separating the fluid paths comprises a material selected from the group consisting of copper, silver, aluminum, magnesium and oxidation-resistant silicon-infiltrated silicon carbide.