Abstract: The invention relates to a process for preparing methylenediphenyldiamine (MDA), comprising the following steps a) to c): a) converting formaldehyde and aniline to aminal b) removing water from the aminal obtained in step a) to establish a water content of 0 to 5% by weight based on the aminal, and c) adding an acidic catalyst to the aminal having a water content of 0 to 5% by weight, which comprises using formaldehyde in step a) in the form of highly concentrated formaldehyde with a CH2O content of >50% by weight and preparing the formaldehyde by oxidative dehydrogenation from methanol.

Abstract: The invention relates to a process for preparing methylenediphenyldiamine (MDA), comprising the following steps a) to c): a) converting formaldehyde and aniline to aminal b) removing water from the aminal obtained in step a) to establish a water content of 0 to 5% by weight based on the aminal, and c) adding an acidic catalyst to the aminal having a water content of 0 to 5% by weight, which comprises using formaldehyde in step a) in the form of highly concentrated formaldehyde with a CH2O content of >50% by weight and preparing the formaldehyde by oxidative dehydrogenation from methanol.

Abstract: 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.

Abstract: 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 sub-sequent 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.