METHOD FOR THE PREPARATION OF ISOCYANATE BY PARTIALLY ADIABATIC PHOSGENATION OF THE CORRESPONDING AMINE

The present invention relates to a process for preparing an isocyanate by reacting a primary amine with phosgene, comprising I) providing an amine solution, II) providing a phosgene solution, III) mixing the amine solution with the phosgene solution in a mixing unit, followed by IV) further conversion in an adiabatically operated reaction zone and the removing of the gas phase formed as a result of the chemical reaction in a separation zone, V) expanding the remaining liquid phase in two or three stages, VI) further conversion of the liquid phase remaining after the last expansion stage in an indirectly heated reaction zone and VII) isolating the isocyanate from the reaction solution obtained therein.