Patent ID: 6245909
Filing Date: 2001-06-12
Classification: C07D

Abstract:
A method of preparation of highly purified solid melamine from urea melt obtained from a urea plant, the method comprising the combination of steps of:(1) providing urea melt to a scrubber unit;(2) transferring said urea melt from said scrubber unit to a melamine reactor;(3) heating and pressurizing said urea melt in said melamine reactor to a temperature and a pressure sufficient to produce a melamine melt and off-gases, said melamine melt comprising liquid melamine, melamine by-products and the off-gases comprising CO.sub.2, NH.sub.3 and melamine vapor;(4) exhausting said off-gases to said scrubber unit where said urea melt washes said melamine vapor out of said off-gases to form recovered liquid melamine, said off-gases then being exhausted out of the scrubber unit and said recovered liquid melamine being returned to said melamine reactor;(5) transferring said liquid melamine to a cooling vessel and cooling said liquid melamine melt therein under pressure to form solid melamine, by evaporation of ammonia, to a temperature between about 50.degree. C. and about 350.degree. C.;(6) transferring said solid melamine to an expansion vessel;(7) holding said solid melamine in said expansion vessel under ammonia pressure for a residence time, the residence time being between about ten minutes to about five hours;(8) reducing the pressure in said expansion vessel to atmospheric pressure; and(9) recovering highly pure solid melamine.