Bayer Materialscience Ag

Covestro Deutschland Ag

Ralf Echterhoff

Ulrich Liman

Robert Vieler

Hans-Georg Pirkl

Heinz-Herbert Müller

The invention relates to a process for the production of di- and polyisocyanates of the diphenylmethane series and mixtures thereof, in which aniline and formaldehyde are reacted in the presence of an acid catalyst to form di- and polyamines of the diphenylmethane series; the di- and polyamines of the diphenylmethane series are phosgenated, optionally in the presence of a solvent, to obtain a crude di- and polyisocyanate; from the crude di- and polyisocyanate, at least one fraction containing at least 5 wt. % 3-ring and multi-ring MDI and at least one fraction containing at least 95 wt. % 2-ring MDI are separated by distillation, and 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 are determined analytically; and an acidic compound is added to 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, so that the desired acidity is achieved.

Production of di- and polyisocyanates of the diphenylmethane series with defined acidity

A fraction of diisocyanates of the diphenylmethane series containing at least 95 wt. % binuclear methylenediphenyl diisocyanate is obtained by

Production of mixtures of diisocyanates and polyisocyanates from the diphenylmethane series with high contents of 4,4'-methylenediphenyl diisocyanate and 2,4&#x2032;-methylenediphenyl diisocyanate

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Dormagen, Germany

Ralf Echterhoff