Method for manufacturing isocyanates in the gaseous phase

摘要

Preparing meta-toluene diisocyanate comprises reacting meta-toluenediamine with phosgene in the gas phase, where: the meta-toluenediamine and phosgene are separately added into a reactor, and a gaseous meta-toluenediamine is produced by evaporation in an evaporator; in the evaporator, the liquid meta-toluenediamine contains less than 0.5 wt.% of toluene diamine residues, less than 0.2 wt.% of ammonia and cycloaliphatic amines, and less than 20 ppm of heavy metals; and the meta-toluenediamine is partially evaporated in the evaporator, and 0.1 wt.% of meta-toluenediamine is not evaporated. Preparing m-toluene diisocyanate comprises reacting meta-toluene diamine with phosgene in the gas phase, where: the meta-toluenediamine and phosgene are separately added into a reactor, and a gaseous meta-toluene diamine is produced by evaporation in an evaporator; in the evaporator, the liquid meta-toluenediamine contains less than 0.5 wt.% of toluene diamine residues, less than 0.2 wt.% of ammonia and cycloaliphatic amines, and less than 20 ppm of heavy metals; the ratio between the quantity of liquid (kg) present in the evaporator and the gas stream (kg/h) leaving the evaporator is less than 2 hours; the meta-toluenediamine is partially evaporated in the evaporator, and at least 0.1 wt.% of meta-toluene diamine is not evaporated; the unevaporated amount of meta-toluenediamine is not added into the reactor; and the meta-toluenediamine is thermally treated at at least 100[deg] C for at least 15 minutes, before adding into the evaporator and then the resulting ammonia is separated.