Process for the preparation of isocyanates in the gas phase

摘要

Meta-toluene-diisocyanate is produced by reacting meta-toluenediamine with phosgene in the gas phase. The meta-toluenediamine to be vaporized for use in this phosgenation process must contain less than 0.5 wt. % of toluenediamine residue, a total of less than 0.2 wt. % of ammonia and cycloaliphatic amines, and less than 20 ppm of heavy metals. At least 0.1 wt. % of the liquid meta-toluenediamine being to be vaporized must not be vaporized. This non-vaporized content of the meta-toluenediamine must not be fed to the phosgenation reactor.

主权项

1. A process for the preparation of m-toluene-diisocyanate comprising:
(1) generating a gaseous stream of meta-toluenediamine by vaporizing liquid meta-toluenediamine comprising an isomer mixture of 2,4-meta-toluenediamine and 2,6-meta-toluenediamine in at least one evaporator, by:
(a) feeding to the evaporator liquid meta-toluenediamine containing:
(i) less than 0.5 wt. %, based on weight of meta-toluenediamine, of toluenediamine residue, and in total less than 0.2 wt. %, based on weight of meta-toluenediamine, of ammonia and cycloaliphatic amines, and(ii) less than 20 ppm, based on weight of meta-toluenediamine, of heavy metals, and(b) conducting the vaporization under conditions such that a ratio of amount of liquid meta-toluenediamine V in kg present in the evaporator to amount of gas stream {dot over (M)} in kg/h leaving the evaporator is less than 2 h, and(c) partly vaporizing the liquid meta-toluenediamine in the evaporator to an extent such that at least 0.1 wt. %, based on weight of meta-toluenediamine, of the liquid meta-toluenediamine is not vaporized, and (2) feeding to a reactor a gaseous stream of phosgene and the gaseous stream of meta-toluenediamine produced in step (1) to thereby phosgenate the meta-toluenediamine in the gas phase to form m-toluene diisocyanate, provided that the non-vaporized meta-toluenediamine is not included with the gaseous stream fed to the reactor.