| 摘要 |
Process for the production of highly pure melamine in which an aftertreatment of the melamine is carried out, comprising the steps a) separating off the NH3/CO2 gas mixture from the liquid melamine, if appropriate b) reducing the CO2 dissolved in the liquid melamine by introducing gaseous ammonia c) allowing the liquid melamine to remain for a mean residence time of 0 to 8 hours at a temperature between 430 DEG C. and the melting point of melamine and an ammonia partial pressure of 50 to 400 bar and d) slow, controlled cooling by lowering the temperature from the temperature present in a), b) respectively c) to 330 DEG to 270 DEG C. at a cooling rate of up to 150 DEG C./min at an ammonia partial pressure of 50 to 400 bar, higher pressures permitting more rapid cooling rates and, vice versa, lower pressures requiring slower cooling rates, whereupon the reaction vessel in any desired sequence is depressurized and cooled to room temperature and highly pure melamine is obtained in powder form. |
