Verfahren zur Kuehlung der bei der Melaminsynthese erhaltenen Abgase

摘要

1,187,808. Cooling-off gas obtained in the synthesis of melamine. BADISCHE ANILIN- & SODA-FABRIK A.G. 8 Aug., 1967 [9 Aug., 1966], No. 36329/67. Heading C2C. The off-gas, obtained by the thermal decomposition of urea to form melamine and separation of the melamine from the off-gas by cooling the latter to 180-280‹ C., is further cooled by treatment with a melt containing urea and an ammonium salt and/or a guanidine salt which is soluble in molten urea and keeping the temperature of the melt up to 40‹ C. above the decomposition temperature of ammonium carbamate. The off-gas is preferably cooled to a temperature below 120‹ C. and, before treatment with the above melt containing the ammonia and/or guanidine salt, the off-gas may be washed in conventional manner with a melt of urea. Suitable salts which may be employed are the ammonium and guanidine salts of nitric acid, thiocyanic acid, formic acid and acetic acid and the melt advantageously contains urea in an amount of 10-90% by wt.