Patent ID: 6858728

Claim:
A method for making caprolactam from an impure 6-aminocapronitrile (ACN) obtained by the partial hydrogenation of adiponitrile, said impure 6-aminocapronitrile comprising both ACN and a minimum of 500 ppm tetrahydroazepine and its derivatives (THA), comprising the steps of: (1) contacting the impure ACN comprising both ACN and THA with water at elevated temperature in the presence of a dehydration catalyst, both the impure ACN and the water being in the vapor phase, to produce a vapor phase reaction product that comprises caprolactam (CL), ammonia, water, ACN, and THA; (2) separating the ammonia and a major portion of the water from the vapor phase reaction product to produce a solution comprising caprolactam and a minor portion of the water, and then separating the water from the solution to produce a melt comprising caprolactam, ACN and THA; (3) introducing the melt into a low boiler removal distillation column and removing a major portion of both the THA and ACN as a distillate, and removing caprolactam, high boilers and at most a minor portion of both the THA and ACN as a bottoms; and (4) introducing the bottoms into a high boiler removal distillation column and removing caprolactam and at most a minor portion of the high boilers as a distillate product and removing a major portion of the high boilers as a bottoms.