Patent ID: 7205430
Filing Date: 2007-04-17
Classification: C07C,C08G

Abstract:
1. A process for the production of di- and polyisocyanates of the diphenylmethane series and mixtures thereof, comprising a) reacting aniline and formaldehyde in the presence of an acid catalyst to form di- and polyamines of the diphenylmethane series, b) phosgenating the di- and polyamines of the diphenylmethane series from a), optionally in the presence of a solvent, to obtain a crude di- and polyisocyanate, c) separating at least one fraction containing at least 5 wt. % of 3-ring MDI and multi-ring MDI, and at least one fraction containing at least 95 wt. % 2-ring MDI, from the crude di- and polyisocyanate, by distillation, d) determining the acidities of the fraction containing at least 5 wt. % 3-ring MDI and multi-ring MDI, and/or the fraction containing at least 95 wt. % 2-ring MDI, and e) adding an acidic compound to the fraction containing at least 5 wt. % 3-ring MDI and multi-ring MDI, and/or to the fraction containing at least 95 wt. % 2-ring MDI, such that the desired acidity of each fraction is achieved.