GB887874A - Purification process for isocyanates - Google Patents

Abstract

A process for eliminating impurities from crude organic isocyanates obtained by phosgenating primary amines in the presence of inert solvents comprises mixing the crude organic isocyanate and the inert solvent in which it is dissolved with a petroleum fraction as defined below, mechanically removing impurities thereby precipitated, and distilling the mixture to recover the organic isocyanate, inert solvent and petroleum fraction. The petroleum fraction employed is any liquid hydrocarbon fraction obtained during the distillation or cracking of crude petroleum which contains a substantial proportion of paraffinic hydrocarbons and has a boiling range the upper limit of which is below the boiling point of the isocyanate and which is sufficiently different from that of the inert solvent to facilitate separation by fractional distillation, e.g. petroleum ether or kerosene. The process may be employed for purifying mono-, di- and tri-isocyanates, especially aromatic isocyanates, e.g. tolylene- and diphenylmethane diisocyanate. The solvent in the phosgenation reaction may be any solvent capable of dissolving the amine employed as starting material and the isocyanate produced, e.g. chlorinated aromatic hydrocarbons such as o-dichlorobenzene. The phosgenation reaction mixture may be concentrated before addition of the petroleum fraction. The impurities may be removed by filtration or centrifuging. In examples an o-dichlorobenzene solution of tolylene diisocyanate, obtained by phosgenating tolylene diamine is mixed with petroleum spirit boiling at 115 DEG C.-125 DEG C., the residue is filtered off and the desired isocyanate recovered from the filtrate by fractionation.