Patent ID: 8536370

Claim:
A low-chlorine multistage and continuous process for preparing at least one cycloaliphatic diisocyanate, the process comprising: (1) reacting in a chlorine-free environment, an aromatic amine, which may be substituted or unsubstituted, with a C 1 -C 3 aldehyde in the presence of a heterogeneous catalyst, said heterogeneous catalyst being a mesoporous acidic ion exchanger comprising a divinylbenzene/styrene copolymer and said catalyst having acidic sites in a concentration of 2 to 6 eq/kg to DIN 54403, and an average pore diameter of particles of said catalyst, measured to ASTM D 4222, being 1to 50 nm, to give at least one reacted aromatic diamine; (2) hydrogenating, in a chlorine-free environment, the reacted aromatic diamine with hydrogen in the presence of a hydrogenation catalyst to yield at least one cycloaliphatic diamine; (3) reacting the at least one cycloaliphatic diamine with at least one carbonic acid derivative and at least one alcohol to give at least one cycloaliphatic diurethane; and subsequently thermally cleaving the at least one diurethane to give at least one cycloaliphatic diisocyanate.