Abstract: Caprolactam is prepared in a process comprising(a) a Beckmann rearrangement of cyclohexanone oxime with oleum at from 70.degree. to 130.degree. C. in one or more rearrangement stages, and(b) aftertreatment of the reaction mixture obtained from the rearrangement stage in a delay zone at from 70.degree. to 110.degree. C. for from 10 to 600 minutes.

Abstract: A process for obtaining coarsely crystalline pure ammonium sulfate from reaction mixtures which have been obtained by Beckmann rearrangement of cyclohexanone-oxime with sulfuric acid or oleum, by neutralizing the mixtures with ammonia at an elevated temperature, with the addition of recycled ammonium sulfate mother liquor, the concentration being so chosen that during the neutralization no solid ammonium sulfate precipitates, separating the crude caprolactam from the ammonium sulfate solution, crystallizing ammonium sulfate by evaporating the ammonium sulfate solution under reduced pressure, separating off the crystallized ammonium sulfate and recycling the mother liquor to the neutralization stage. The neutralization is carried out at from 80.degree. to 115.degree. C. under autogenous pressure and the ammonium sulfate solution obtained after separating off the crude lactam is evaporated under a pressure of from 200 to 600 mm Hg while cooling to from 72.degree. to 101.degree. C.