GB645600A - Improvements in or relating to the production of melamine - Google Patents

Abstract

Pure melamine is prepared from melamine containing caustic soluble impurities by mixing the crude melamine at an elevated temperature with an aqueous liquor containing melamine in solution, filtering off undissolved material, adding to the filtrate an alkali metal hydroxide or alkaline earth metal hydroxide, and cooling to recrystallize melamine from the solution, the amount of hydroxide added being sufficient to retain in solution at the recrystallization temperature those caustic soluble materials not removed during the filtration but not in excess of that amount which will raise the pH to 13. Preferably the initial aqueous liquor is saturated with melamine at the recrystallization temperature, and the mother liquors from the final recrystallization are used for this purpose; in this case, the mother liquor is neutralized with acid, e.g. hydrochloric, before re-use. The aqueous liquor may contain up to 5 per cent of an alkali or alkaline earth metal salt. The hydroxides may be potassium, sodium, calcium or barium. The process may be operated batch-wise or continuously and a decolourizing agent may be used. The initial crude melamine may be in the form of a slurry with water.