Process for preparing an aromatic polyamine mixture

A process for preparing an aromatic polyamine mixture comprising 4,4′-methylenedi(phenylamine) and higher homologues of methylenedi(phenylamine), the process comprising

• (i) reacting aniline with formaldehyde in the presence of an acid catalyst to form a crude product mixture (I) in a plant which comprises a mixing zone (a), a condensation zone (b), a rearrangement zone (c) and optionally an after-reaction zone (d);
• (ii) neutralizing the crude product mixture (I) obtained in (i) and removing salts thus formed, to obtain a crude product mixture (II);
• (iii) separating aniline from the crude product mixture (II) obtained in (ii), to obtain separated aniline and a crude product mixture (III), and optionally recirculating the separated aniline to the mixing zone (a);
• then
• (iv) distilling the crude product mixture (III) obtained in (iii) wherein the distilling comprises
• (iv-1) isolating a mixture (II) consisting of methylenedi(phenylamine) isomers (II-1) and secondary components (II-2) which are different therefrom, where, based on (II-1), a proportion of 4,4′-methylenedi(phenylamine) is from 8 to 20% by weight and, based on (II), a proportion of secondary components (II-2) is not more than 0.3% by weight, and
• (iv-2) isolating a low boiler mixture which consists of secondary components (II-2) and methylenedi(phenylamine) isomers (II-1) and in which a proportion of the secondary components (II-2) is at least 55% by weight;
• and
• (v) recirculating the mixture (II) to one of the zones (a) to (d),
• wherein the aromatic polyamine mixture has a content of 4,4′-methylenedi(phenylamine) and higher homologues of methylenedi(phenylamine) of greater than 85% by weight.