To perform the fractionation and purification of an aromatic polyamine mixture (in particular, of diphenylmethane base) to obtain the corresponding isomers in high purity or concentration.

The fractionation and purification of an aromatic polyamine mixture is performed according to the following process: for the 1st extraction step based on the countercurrent principle, a polyamine starting mixture is introduced together with an aqueous phase, mixed with a two-phase system composed of a hydrophobic solvent phase comprising a hydrophobic solvent and, optionally, an aromatic amine and a polyamine and an aqueous phase comprising water, a strong acid and an auxiliary amine and, optionally, a polyamine; the 1st aqueous phase and the 1st organic phase are allowed to run out, the 1st organic phase is fractionated, in the 1st distillation step, into the 1st fraction comprising the hydrophobic solvent and, optionally, the auxiliary amine and residues comprising the 1st polyamine fraction; the 1st aqueous phase is neutralized with a base to effect phase separation into the 2nd aqueous phase containing an acid in the form of a neutral salt and the 2nd organic phase, the 2nd organic phase is fractionated, in the 2nd distillation step, into a distillate comprising the hydrophobic solvent and the auxiliary amine and residues comprising the 2nd polyamine fraction; and the 1st fraction is circulated as part or the whole of the hydrophobic solvent phase.