Process for simultaneously preparing 4,4′-diphenylmethanediamine and diphenylmethane diisocyanate and polyphenylenepolymethylene polyisocyanates

The invention provides a process for the simultaneous preparation of 4,4′-diphenylmethanediamine and also diphenylmethane diisocyanate and polyphenylenepolymethylene polyisocyanates, which comprises the steps a) preparation of a mixture of diphenylmethanediamine and polyphenylenepolymethylenepolyamines by acid condensation of aniline and formaldehyde and subsequent work-up of the mixture, b) splitting-off of part of the mixture prepared in step a), c) distillation of the mixture separated off in step b) in a column, d) recirculation of the bottom product from step c) to the end product from step a) and condensation of the overhead product from step c), e) distillation of the overhead product from step c) in a column, f) recirculation of the overhead product from step e) to the end product from step a), g) isolation of the 4,4′-diphenylmethanediamine obtained as bottom product in step e), h) reaction of the mixture from step a) with phosgene and subsequent work-up of the reaction product.