METHOD OF PRODUCING ISOCYANATES Russian patent published in 2012 - IPC C07C263/10 C07C265/14 

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing di- and polyisocyanates of the diphenylmethane family. According to the disclosed method, at step a) an amine solution is obtained, said amine being selected from a group comprising di- and polyamines of the diphenylmethane family, in a solvent and a phosgene solution is obtained in the same solvent. At step b) the amine solution in the solvent and the phosgene solution in the solvent are mixed with each other and the amine reacts with phosgene to form the corresponding isocyanate, where a reaction solution containing isocyanate is obtained. At step c) hydrogen chloride and excess phosgene are extracted from the reaction solution containing isocyanate to obtain a crude isocyanate solution. At step d) the crude isocyanate solution is separated via distillation, where the distillation step enables to obtain a stream containing isocyanate and a stream containing solvent and a residual amount of phosgene, having diisocyanate content less than 100 ppm and the residual amount of phosgene is equal to 100-1000 ppm in terms of the weight of the stream containing solvent and residual amount of phosgene; at the step for purifying the solvent obtained at the distillation, the stream containing solvent and the residual amount of phogene is purified by distillation in a stripping column to obtain a phosgene-free stream containing solvent and having isocyanate content less than 100 ppm and phosgene content less than 100 ppm in terms of the weight of the phosgene-free stream containing solvent. At step e) the phosgene-free stream obtained at step d) containing solvent is at least partially tapped from the solvent purification step to step a) where it is used at least to obtain an amine solution in a solvent.

EFFECT: method reduces formation of by-products and also increases output and the quality of the obtained di- and polyisocyanates of the diphenylmethane family owing to recycling of a cleaner solvent.

4 cl, 3 dwg, 3 ex