GB918952A - Process and apparatus for the production of melamine - Google Patents

Abstract

Melamine is prepared by heating a concentrated solution of dicyandiamide or cyanamide in liquid ammonia to a temperature of between 140 DEG and 160 DEG C. in a closed vessel to provide a saturation vapour pressure not exceeding the critical pressure of pure ammonia (viz. approx. 111 atmospheres), in order to ensure that the operation takes place in the liquid phase, and maintaining this saturation vapour pressure by regulation of the temperature until the temperature corresponding to the said saturation pressure has fallen to 128 DEG to 135 DEG C. Prior to the reaction an inert solvent boiling above 135 DEG C., miscible with ammonia and dissolving dicyandiamide or cyanamide readily but melamine only with difficulty, may be added to the ammonia solution of the reactants. Evaporation of ammonia from the final product then yields melamine and a solution of cyanamide and/or dicyandiamide in the solvent. Dimethyl formamide is specified as a solvent for this purpose. Alternatively, melamine may be washed out of the resulting solution in ammonia with a solvent such as water, leaving a solution of unreacted cyanamide and/or dicyandiamide in ammonia, which can be recycled. The process may be adapted to continuous working, preferably in a manner such that the process temperatures are adjusted by a pressure-controlled cooling system. Specifications 466,957 and 598,533 are referred to.