Patent ID: 9126904
Filing Date: 2015-09-08
Classification: C07C

Abstract:
1. A process for preparing isocyanates by reaction of amines with phosgene in the liquid phase, the process comprising: a) mixing a liquid amine-comprising starting material stream and a liquid phosgene-comprising starting material stream to obtain a feed stream, b) reacting the feed stream from process stage a) in a residence reactor to give a two-phase, gaseous/liquid reaction mixture which is fed either directly or after removal of the gaseous phase in a downstream separator to a reaction column, c) reacting the two-phase, gaseous/liquid reaction mixture or only the liquid phase thereof in the reaction column to give an overhead stream and a bottom stream which is fed to a phosgene/hydrogen chloride stripping column, d) removing by distillation of phosgene and hydrogen chloride via the overhead stream from the phosgene/hydrogen chloride stripping column, to obtain a bottom stream from the phosgene/hydrogen chloride stripping column which comprises the isocyanate and the solvent, from which, e) the desired isocyanate product is obtained by removing the solvent by distillation and, and f) performing thermal separation of a residual vapor from the phosgene/hydrogen chloride stripping column in a separation column to obtain a hydrogen chloride-comprising vapor stream at the top and a bottom stream which comprises phosgene and solvent and is recycled to the mixing a), wherein the thermal separation f) is carried out at a pressure at the top of the separation column which is higher than the pressure at the top of the phosgene/hydrogen chloride stripping column, and wherein the higher pressure at the top of the separation column compared to the phosgene/hydrogen chloride stripping column is achieved by: a first ejector for the overhead stream from the phosgene/hydrogen chloride stripping column or a vapor stream obtained together with a condensate stream by partial condensation of the overhead stream from the phosgene/hydrogen chloride stripping column in a second condenser, and/or a further ejector which compresses the condensate stream which is obtained by partial condensation of the overhead stream from the phosgene/hydrogen chloride stripping column in the second condenser.