Catalytic hydrogenation of crude methylene bridged polyphenylamines to produce polycyclohexylamines

摘要

This invention relates to an improved process for the catalytic hydrogenation of methylene bridged polyphenylamines using rhodium as th e catalyst to produce the methylene bridged polycyclohexylamine counterparts. The improvement for hydrogenating crude methylene bridged polyphenylamines containing polyphenylamine oligomers and trace amounts of impurities, such as the formamide of the methylene bridged polyphenylamines, comprises contacting the crude polyphenylamine feed with a hydrogenation catalyst, other than rhodium, and one which is not a catalyst poison to rhodium, under conditions sufficient to at least partially hydrogenate the polyphenylamine mixture and then effecting hydrogenation of the methylene bridged polyphenylamine to the polycyclohexylamine counterpart in the presence of a rhodium catalyst. The pretreatment of the crude methylene bridged polyphenylamine feed apparently destroys the formamide derivatives and possibly other trace impurities in the mixture and thereby prevents rapid deactivation of the rhodium catalyst during hydrogenation of the aromatic ring.