Development of Process for Purification of Crude Melamine Manufactured from Urea

Abstract

The hydrolysis rates of melamine and its hydrolyzed compounds (ammeline, ammelide and cyanuric acid) were measured in aqueous ammonia solution at 130, 150 and 180°C. An empirical equation was obtained to induce the apparent rate constant for melamine up to 40 wt% aqueous ammonia. Meanwhile the reaction of melam, the largest quantity of impurities contained in crude melamine, was investigated and it was found that ammonolysis was taking place simultaneously with hydrolysis under the above conditions. Furthermore, the solubility of melamine was measured in 080 wt % aqueous ammonia at 20180°C.
Based on the results, a purification method for crude melamine by treating it in aqueous ammonia at high temperature was found, and identification tests by pilot plant with a continuous reactor were carried out. Through this operation the optimum conditions for temperature, residence time and concentration of ammonia were determined. Ideas were also examined for the purpose of crystallizing melamine and recovering ammonia.
This method was proved to be applicable to the purification of crude melamine.