advances in processes for the production of melamine from urea.

摘要

Melamine is prepared by heating fluidised urea, i.e. molten urea or urea dissolved in anhydrous ammonia, with anhydrous ammonia under autogenous pressure in the presence of an amalgam of mercury which metal is above hydrogen in the electromotive series of the metals. The reaction takes place in two stages, the first stage involving the formation of a mixture of metal salts of at least two of the compounds urea, guanidine, guanylurea, ammeline, and ammelide. The concentration of the salts of the latter two compounds increases and that of urea, guanidine and guanylurea salts decreases upon heating and on further heating at above 130 DEG C. in the presence of anhydrous ammonia under pressure melamine is formed and may be recovered. Aluminium, manganese, nickel, iron, tin, cadmium, barium, magnesium, calcium and copper are mentioned and aluminium is preferred. The mixture of metal salts hydrolyse to the oxide and/or hydroxide or may be reacted with alcohols to form alkoxides. Examples describe the preparation of the salt mixtures and of melamine therefrom.