JPH0629232B

PURPOSE:To obtain various isocyanate compositions having different isomer ratios and useful for polyurethane industry, in high yield, by crystallizing a mixture of isocyanate isomers under pressure. CONSTITUTION:A mixture of isocyanate isomers is poured into a pressure crystallization apparatus composed of a crystallization cylinder and a plunger and the content is crystallized under pressure. The precipitated crystal is separated and pressed to extract mother liquor, the pressure is slowly released and the molten mother liquid is removed to obtain the objective composition. The isocyanate isomer mixture is e.g. mixture of tolylene diisocyanate isomers and mixture of diphenylmethane diisocyanate isomers. The energy for crystallization can be reduced compared with low-temperature crystallization process and the crystallization time can be shortened. There is not danger of quality deterioration caused by dimerization, etc., of isocyanate and the crystallization conditions can be set by temperature as well as pressure.