Patent ID: 8063241
Filing Date: 2011-11-22
Classification: C07C

Abstract:
1. A process for the preparation of toluene-diisocyanate, which comprises a) reacting toluenediamine with phosgene to form crude toluene-diisocyanate, b) purifying the crude toluene-diisocyanate by distillation to form purified toluene-diisocyanate and a mixture comprising toluene-diisocyanate and the distillation residue of toluene diisocyanate, c) mixing said mixture comprising toluene-diisocyanate and the distillation residue of toluene diisocyanate continuously with water, and one or more bases which are selected from the group consisting of aqueous sodium hydroxide solution and aqueous potassium hydroxide solution, at a temperature of less than 230° C. under an absolute pressure of less than 30 bar, and allowing said mixture, water and one or more bases to react under said conditions in one or more tubular reactors connected in series, which are operated without back-mixing, to form toluenediamine, d) optionally, purifying said toluenediamine formed in step c), and e) recycling at least a portion of said toluenediamine into the reaction in step a).