MULTISTAGE CONTINUOUS PREPARATION OF (CYCLO)ALIPHATIC DIISOCYANATES

摘要

Disclosed is a process for continuous phosgene- free preparation of (cyclo)aliphatic diisocyanates. The process comprises: (A) reacting (i) a (cyclo)aliphatic diamine with (ii) urea or a urea derivative and (iii) an alcohol to give a (cyclo)aliphatic diurethane and by- products comprising low-boiling, middle-boiling and high- boiling fractions (B) freeing the (cyclo)aliphatic diurethane of the low, middle and high boiling fractions; (C) thermally cleaving the (cyclo)aliphatic diurethane to give the (cyclo)aliphatic diisocyanate and a cleavage residue; (D) discharging a portion of the cleavage residue and reurethanizing the portion with the alcohol, to form a reurethanization product; and (E) reintroducing the reurethanizing product into step (B). The process affords a good yield and is free from a decrease in selectivity over a long operation time.