HIGH-PURITY MELAMINE PRODUCTION METHODS Russian patent published in 2001 - IPC

FIELD: industrial organic synthesis. SUBSTANCE: invention provides method of preparing high-purity melamine starting from conversion of urea performed at pressure approximately 70 to 250 bar and temperature 370 to 430 C followed by subsequent stages: (i) separation of ammonia/carbon dioxide gas mixture from liquid melamine preferably at reactor temperature and pressure; (ii) if necessary, reduction of carbon dioxide dissolved in liquid melamine with gaseous ammonia introduced preferably at reactor temperature and pressure; (iii) holding liquid melamine up to 8 h at temperature between 430 C and melting point of melamine and at ammonia pressure 50 to 400 bar; (iv) cooling of melamine. Distinguishing feature of method is applying in stage (iv) slow controlled cooling, namely lowering temperature from temperature corresponding to stage (i), (ii), or (iii) to 330-270 C with cooling rate up to 150 C/min at 50 to 400 bar ammonia pressure, higher pressures permitting higher cooling rates and vice versa, after which melamine is decompressed and cooled to ambient temperature thereby obtaining high- purity powder. EFFECT: increased yield and purity of product and simplified technology. 9 cl, 1 tbl, 13 ex