Patent ID: 7365195

Claim:
Process for purifying caprolactam, said process comprising (a) subjecting the caprolactam to a hydrogenation by treating the caprolactam with hydrogen in the presence of a heterogeneous nickel containing hydrogenation catalyst, and (b) continuously distilling at least a portion of the hydrogenated caprolactam in a distillation column which contains nickel in an amount sufficiently low such that ΔPAN Ni ≦3 during a period of at least 3 months, wherein ΔPAN Ni =ΔPAN −ΔPAN Ni=0 , ΔPAN =increase of the PAN number of caprolactam during distilling, ΔPAN Ni=0 =increase of the PAN number of caprolactam during distilling under the same conditions in a distillation column free of nickel.