Process for the synthesis of melamine with an optimized dissolution and ammonolysis step

A process for the synthesis of high-purity melamine by the pyrolysis of urea, comprising a dissolution and ammonolysis step, wherein:

• a) feeding a stream exiting from a reaction section comprising a reactor and post-reactor, at a temperature ranging from 360 to 400° C., preferably equal to 380° C., to a dissolution step in aqueous ammonia solution, wherein the quantity of ammonia in the aqueous ammonia solution varies within the range of 15 to 28% by weight with respect to the total weight of the aqueous ammonia solution, in a dissolver at a temperature within the range of 160 to 180° C. and at a pressure higher than 25 barg,
• b) feeding the solution exiting from the dissolution and ammonolysis step a), comprising a quantity of dissolved melamine that varies within the range of 5 to 25% by weight, a quantity of polycondensates lower than 100 ppmw, to the subsequent filtration, crystallization and separation steps.