Patent ID: 7038002

Claim:
A process for the production of a fraction of diisocyanates of the diphenylmethane series containing at least 95 wt. % binuclear methylenediphenyl diisocyanate comprising: 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 of the diphenylmethane series containing binuclear methylenediphenyl diamine to produce a crude diisocyanate and polyisocyanate, and c) separating from the crude diisocyanate and polyisocyanate a fraction containing at least 95 wt. % binuclear methylenediphenyl diisocyanate comprising greater than 60 wt. % 4,4′-MDI, from 4 to 35 wt. % 2,4′-MDI, from 0.01 to 10 wt. % 2,2′-MDI relative to the mass of the fraction, and no more than 20 ppm phenyl isocyanate in a single distillation step.