How is melamine produced?
Melamine was first synthesized in 1834 by the German chemist Justus von Liebig. In early production, calcium cyanamide was first converted to dicyandiamide, and then it was heated above its melting temperature to produce melamine. Today, most industrial manufacturers use urea to produce melamine in the following reactions:
6（NH 2）2 CO→C 3 H 6 N 6 + 6 NH 3 + 3 CO 2
In the first step, urea is decomposed into cyanic acid and ammonia:
(NH 2) 2 CO→HNCO + NH 3
Cyanic acid polymerizes to cyanuric acid, which condenses with released ammonia to form melamine. The released water reacts with cyanic acid, which helps drive the reaction:
6 HNCO + 3 NH 3 →C 3 H 6 N 6 + 3 CO 2 + 3NH 3
The above reaction can be carried out by either of two methods: catalytic gas phase production or high-pressure liquid phase production. In one method, molten urea is introduced into a fluidized bed together with a catalyst for reaction. There is also hot ammonia gas to fluidize the bed and inhibit deamination. The effluent is then cooled. The ammonia and carbon dioxide in the exhaust gas are separated from the melamine-containing slurry. The slurry is further concentrated and crystallized to produce melamine.
The exhaust gas contains a lot of ammonia. Therefore, the production of melamine is usually integrated into the production of urea, which uses ammonia as a raw material.
The crystallization and washing of melamine will produce a lot of waste water, which may be concentrated into solids (1.5-5% by weight) for easy disposal. The solid may contain approximately 70% melamine, 23% oxytriazines (cyanuric amide, cyanuramide, and cyanuric acid), 0.7% polycondensate (melamine, melam, and melon).