Preparation of epsilon-caprolactam with low dimer and water content

摘要

The preparation of iota -caprolactam with low dimer and water content from extraction water from polycaprolactams obtained by hydrolytic polymerization comprises a four-step process comprising concentration, separation, depolymerization using catalyst and superheated steam, and distillation. The preparation of iota -caprolactam from extraction water from polycaprolactams obtained by hydrolytic polymerization comprises: (a) concentrating the extraction water to a solids content of at least 70 wt.% by distilling off water in at least one step; (b) obtaining an extract of 33-67 wt.% iota -caprolactam and 67-33 wt.% oligomers, including dimers, by separating off an iota -caprolactam/steam mixture; (c) depolymerizing the extract in the presence of a catalyst and superheated steam, giving a steam mixture of 16-33 wt.% iota -caprolactam and 84-67 wt.% water; and (d) distilling off water from the mixtures of steps (b) and (c) to give iota -caprolactam of water content at most 15 wt.% and dimer content at most 0.2 wt.%.