而且尿素和氨气分压要足够。在热牛奶这种稀释体系里实现不了。

http://en.wikipedia.org/wiki/Melamine#Synthesis

The above reaction can be carried out by either of two methods:catalyzed gas-phase production or high pressure liquid-phase production. In one method, molten urea is introduced onto a fluidized bed with catalyst for reaction. Hot ammonia gas is also present to fluidize the bed and inhibit deammonization. The effluent then is cooled. Ammonia and carbon dioxide in the off-gas are separated from the melamine-containing slurry. The slurry is further concentrated and crystallized to yield melamine.[5] Major manufacturers and licensors such as DSM, BASF and Eurotecnica have developed some proprietary methods.