PRODUCTION OF MIXTURES OF DIISOCYANATES AND POLYISOCYANATES FROM THE DIPHENYLMETHANE SERIES WITH HIGH CONTENTS OF 4,4'-METHYLENEDIPHENYL DIISOCYANATE AND 2,4'-METHYLENEDIPHENYL DIISOCYANATE

摘要

A fraction of diisocyanates of the diphenylmethane series containing at least 95 wt.% binuclear methylenediphenyl diisocyanate is obtained by a) reacting aniline and formaldehyde in the presence of an acid catalyst to produce diamines and polyamines of the diphenylmethane series containing binuclear methylenediphenyl diamine, b) phosgenating the diamines and polyamines produced in a), optionally in the presence of a solvent, to produce a crude diisocyanate and polyisocyanate, and c) separating a fraction containing at least 95 wt.% binuclear methylenediphenyl diisocyanate with a 4,4'-MDI content of over 60 wt.%, a 2,4'-MDI content of 4 to 35 wt.% and a 2,2'-MDI content of 0.01 to 10 wt.%, relative to the mass of the fraction, and a maximum of 20 ppm phenyl isocyanate and optionally a maximum of 50 ppm solvent from the crude diisocyanate and polyisocyanate produced in b) in a single distillation step with optional upstream and/or downstream separation of low-boiling components.