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AssigneeAgrolinz Melamin GmbH
InventorsLorenzo Canzi, Aldo Canzi, Gerhard Coufal, Silvano Giacomuzzo, Mario Virardi, Martin Mullner
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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 NH.sub.3 /CO.sub.2 gas mixture from the liquid melamine, if appropriate b) reducing the CO.sub.2 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.degree. 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.degree. to 270.degree. C. at a cooling rate of up to 150.degree. 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.
A process for the production of highly pure melamine starting from a urea conversion carried out under pressure wherein liquid melamine and an NH.sub.3 /CO.sub.2 gas mixture are formed, which comprises, following the conversion reaction, carrying out an after-treatment of the melamine, comprising the steps
A process for the production of highly pure melamine, which comprises bringing contaminated melamine at an ammonia partial pressure of 50 to 400 bar to a temperature which is between the melting point of melamine and 430.degree. C. where the melamine is liquid, allowing the liquid melamine to remain in this temperature range for 0 to 8 hours and then carrying out a slow, controlled cooling, the temperature being decreased to 330.degree. to 270.degree. C. at a cooling rate of up to 100.degree. C./min at an ammonia partial pressure of 50 to 400 bar, higher values of said pressure permitting more rapid cooling rates and, vice versa, lower values of said pressure requiring slower cooling rates, whereupon, in any desired sequence, the reaction vessel is depressurized and cooled to room temperature and highly pure melamine is obtained in powder form.
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