Patent ID: 8680323

Claim:
A process for preparing an isocyanate, the process comprising: thermally dissociating a carbamate in a column in the presence of an inert solvent, to obtain an isocyanate and an alcohol, and separating the isocyanate and the alcohol by distillation, to obtain a bottom stream comprising the isocyanate and an overhead stream comprising the alcohol and the inert solvent, wherein the inert solvent is an intermediate boiler having a boiling point between the boiling point of the isocyanate and the boiling point of the alcohol under the operating conditions of the carbamate dissociation, wherein the column comprises an enrichment section, a feed point, and a stripping section, the feed point being disposed between the enrichment section and the stripping section, and wherein the column is configured, and the process is conducted such that: the carbamate is introduced into the column in the feed point; the inert solvent is introduced into one or more points on the stripping section as gaseous, superheated stream; the isocyanate is removed as a constituent of the bottom stream from the bottom of the stripping section; the alcohol is removed as a constituent of the overhead stream from the top of the enrichment section; and inert solvent from the overhead stream is partially or completely introduced into an upper region of the enrichment section of the column as an external runback in liquid form having a purity of >95% by weight, based on the total weight of the external runback.