GB636600A - Method of preparing cyanamide and polymers thereof - Google Patents

Abstract

Cyanamide or polymers thereof are made by liberating cyanamide from a compound thereof in the presence of water to form an aqueous solution of cyanamide, extracting the solution with an organic solvent for cyanamide, or with a mixture of such solvents, and heating or distilling the resulting extract below 80 DEG C. to produce cyanamide or from 80-130 DEG C. to produce dicyandiamide. Cyanamide may be liberated from an aqueous suspension of an insoluble compound thereof, e.g. calcium cyanamide, by the action of an acid or mixture of acids, e.g. formic, acetic, propionic, butyric, hydrochloric, nitric, phosphoric and sulphuric acids and carbon dioxide. Where acids are used that form soluble calcium salts, graphite present as impurity in the calcium cyanamide may be recovered by filtration or centrifuging, and the acid may be recovered for re-use in the process by treating the mother liquors with sulphuric acid and removing precipitated calcium sulphate, or where nitric acid is used, the acid solution after solvent extraction may be concentrated and calcium nitrate crystallized out. Organic solvents used include alcohols, ethers, esters, ketones, acids, amines, nitriles and nitro-derivatives and mixtures thereof, one of which may be miscible with water. Polymerization may be enhanced by the addition of ammonia or amines.ALSO:Melamine is made by liberating cyanamide from a compound thereof in the presence of water to form an aqueous solution of cyanamide, extracting the solution with an organic solvent for cyanamide or with a mixture of such solvents, and heating the resulting extract above 130 DEG C. Organic solvents used include alcohols, ethers, esters, ketones, acids, amines, nitriles and nitro-derivatives. Polymerization may be enhanced by the addition of ammonia or amines. In one example carbon dioxide is passed into a solution of calcium cyanamide in an exhausted solution of cyanamide in a receptacle maintained at 40 DEG C., and the solution extracted in a washing tower by a mixture of butylamine and butyl ether. The resulting extract is dehydrated by vacuum distillation, maintained at 220 DEG C. under reduced pressure to separate out melamine, which is then filtered and the solvent returned to the extraction step. In another example a 10 per cent hydrochloric acid solution is neutralized by calcium cyanamide and after removal of graphite by filtration is extracted with a mixture of ethyl acetate and diphenyl ether. The extract is distilled to remove ethyl acetate and water and the remaining solution heated to boiling to separate out melamine.