Multi-step process for the continuous preparation of cycloaliphatic diisocyanates

摘要

Continuously preparing cycloaliphatic diisocyanates, comprises reacting cycloaliphatic diamines with urea and/or urea derivatives and alcohols to give cycloaliphatic diurethanes and thermally cleaving them in the absence or presence of dialkyl carbonates and alkyl carbamates or mixtures of dialkyl carbonates and carbamic esters and in the absence or presence of catalysts, to give cycloaliphatic diurethanes, and removing the formed ammonia. Continuously preparing cycloaliphatic diisocyanates of formula OCN-R-NCO (I), comprises: (1) reacting cycloaliphatic diamines of formula H2N-R-NH2 (II) with urea and/or urea derivatives and alcohols of formula R1>-OH (III) to give cycloaliphatic diurethanes and thermally cleaving them in the absence or presence of dialkyl carbonates and alkyl carbamates or mixtures of dialkyl carbonates and carbamic esters and in the absence or presence of catalysts, to give cycloaliphatic diurethanes, and simultaneously removing the formed ammonia; (2) removing the alcohol, the dialkyl carbonates and/or alkyl carbamates from the resulting reaction mixture, and recycling into the reaction stage the alcohol and optionally also the dialkyl carbonates and/or alkyl carbamates; (3) removing any high-boiling residues present in the resulting reaction mixture and fully or partially dispensing with the same; (4) continuously and thermally cleaving without solvent in the presence of a catalyst the reaction mixture comprising the diurethanes purified by steps (2) and optionally (3) at 180-280[deg]C, and under a pressure of 0.1-200 mbar, in such a way that a portion of the reaction mixture of 10-60 wt.% based on the feed, is constantly discharged; (5) separating by rectification the cleavage products into crude cycloaliphatic diisocyanate and alcohol; (6) purifying by distillation the crude cycloaliphatic diisocyanate, and isolating the pure product fraction; (7) reacting the bottoms discharge from (4) partially or fully with the alcohol from (5), in the presence or absence of catalysts, within 1-150 minutes, at 20-200[deg]C, and at a pressure of 0.5-20 bar, the molar ratio of isocyanate (NCO) groups to hydroxyl (OH) groups being up to 1:100; (8) separating the reurethanized stream from (7) into a material-of-value stream and a waste stream, and discharging and discarding the waste stream rich in high boiler components from the process; (9) continuously discharging and conducting a portion of the bottoms fraction of the purification by distillation (6) into the cleavage reaction (4) or into the urethanization stage (7); (10) optionally recycling the top fraction obtained in the purification by distillation (6) of the crude cycloaliphatic diisocyanate into the urethanization stage (7); and (11) recycling the material-of-value stream from (8) into stage (1), (2) or (4). R : 4-18C bivalent cycloaliphatic hydrocarbon radical where two nitrogen atoms are bonded directly to hydrocarbon cycle and >= 3C are disposed between them; R1>radical as remains after removal of hydroxyl group from prim. or sec. 3-8C (cyclo)aliphatic alcohol.