Process for producing diamines and polyamines of the diphenylmethane series

1. A process for producing diamines and polyamines of the diphenylmethane series, comprising

a) reacting aniline and formaldehyde in the presence of an acid catalyst to form a reaction mixture containing diamines and polyamines, wherein the aniline used contains in total from 0.0001 to 0.25 wt. %, based on the total weight of aniline, of one or more compounds which contain at least one carbonyl group or of one or more compounds which are formed by reaction of one or more compounds which contain at least one carbonyl group with aniline;

b) neutralizing the reaction mixture containing diamines and polyamines of the diphenylmethane series,

c) separating the neutralized reaction mixture containing diamines and polyamines of the diphenylmethane series into an organic phase containing diamines and polyamines of the diphenylmethane series and an aqueous phase;

d) optionally, washing the organic phase with water;

e) removing excess aniline from the organic phase by distillation;

f) combining; in whole or in part, waste water and condensates which accumulate in steps a) to e), wherein at least the waste water and condensates obtained in steps c) and e) are combined at least in part, and wherein a mixture containing water, diamines and polyamines of the diphenylmethane series, aniline and salts of the catalyst used in step a) is obtained;

g) phase separating the mixture obtained in step f), wherein an aniline containing water together with diamines and polyamines of the diphenylmethane series is obtained;

and

h) returning the aniline obtained in the phase separation, at least in part, to the reaction in step a),

wherein the aniline used in step a) is produced by combining at least part of the aniline obtained in step g) containing diamines and polyamines with fresh aniline.

2. The process of claim 1 ; wherein said aniline contains one or more compounds which contain at least one carbonyl group, with said compounds being selected from the group consisting of one or more optionally unsaturated (cyclo)aliphatic ketones and one or more substituted (cyclo)aliphatic ketones.

3. The process of claim 2 , wherein said (cyclo)aliphatic ketone comprises cyclohexanone.

4. The process of claim 1 , wherein said aniline contains one or more Schiff bases which are formed by reaction of one or more compounds which contain at least one carbonyl group with aniline.

5. The process of claim 4 , wherein the Schiff base is N-phenylcyclohexylimine.

6. A process for producing diisocyanates and polyisocyanates of the diphenylmethane series, comprising reacting diamines and polyamines of the diphenylmethane series produced by the process of claim 1 with phosgene, thus forming the corresponding diisocyanates and polyisocyanates of the diphenylmethane series.