PURIFICATION OF ALIPHATIC ISOCYANATE

PURPOSE:To purify the titled compound in high purity, and to suppress the discoloration of the compound, by distilling out the solvent after the reaction of an aliphatic diisocyanate to obtain a concentrated liquid having a specific solvent concentration, removing the tar component from the liquid, and heating the product within a specific temperature range. CONSTITUTION:An aliphatic diamine or its hydrochloride is made to react with phosgene in the presence of an inert organic solvent (e.g. o-dichlorobenzene) to obtain the corresponding aliphatic diisocyanate (e.g. hexamethylene diisocyanate). The solvent in the obtained reaction mixture is distilled out to obtain a concentrated diisocyanate solution containing 10-50wt% of solvent. After removing the tar component from the solution, the solution is heat-treated at a temperature between the boiling point of the residual reaction solvent and the point lower than the boiling point by 30 deg.C, and fractionated. The colored components in the liquid to be purified can be converted to polymeric tar and removed. By combining the tar-removal process, the present process enables to suppress the colored impurities produced by the decomposition of tar during the heat-treatment.