Recovery of caprolactam from caprolactam distillation low boilers or high boilers or mixtures thereof

摘要

Caprolactam is recovered from caprolactam distillation low boilers or high boilers or mixtures thereof by the following steps: PP (a) crystallizing a low or high boiler or a mixture thereof to form purified capro-lactam crystals and a mother liquor, PP(b) separating off the purified caprolactam crystals to leave a mother liquor, PP(c) recycling from 5 to 90% by weight of the mother liquor of stage (b) into stage (a) and transferring the remainder of the mother liquor into the subsequent stage (d),P P(d) crystallizing the remaining mother liquor portion from stage (c) to form caprolactam crystals and a mother liquor, separating off the caprolactam crystals of stagePP(e) (d) and recycling the same into stage (a) to leave a mother liquor,PP(f) recycling from 20 to 99% by weight of mother liquor of stage (e) into stage (d) and channeling out the remainder of the impurity-containing mother liquor of stage (e).