Multi-step method for continuously producing toluene diisocyanate

Abstract

The present invention provides a multi-step method for continuously producing alicyclic vulcabond on the condition of non light and non-air, by the reaction of the alicyclic diamine and the carboxylic acid derivatives with alcohol producing alicyclic diurethane and subsequently decomposed into alicyclic vulcabond, characterized in that diurethane is formed by two steps, thermo-decomposing via removing diurethane of the easier boiler and the medium boiler to release desirable vulcabond, and continuously draining the product on the bottom of the part degradable tower of the degradable equipment, proceeding re-urethane by alcohol, then separating the high boiler, and then making the re-urethane product circle in the process, wherein using the unprocessed carbamide and / or carbamide equivalent made of un-precessed carbamide.

Description

technical field

[0001] The invention relates to a multistage process for the continuous and phosgene-free preparation of cycloaliphatic diisocyanates. Background technique

[0002] The synthetic route to isocyanates can be achieved via a series of different routes. The first, and still dominant, industrial-scale preparation of isocyanates is the so-called phosgene process. The basis of the method is the reaction of amines with phosgene. A disadvantage of the phosgene process is the use of phosgene, which, due to its toxicity and corrosiveness, places extremely high demands on operation on an industrial scale.

[0003] There are also processes for preparing isocyanates on an industrial scale which bypass the use of phosgene. The term "phosgene-free process" is generally associated with the conversion of amines to isocyanates using alternative carbonylating agents such as urea or dialkyl carbonates (EP18586, EP355443, US4268683, EP990644).

[0004] The urea route is based ...