Separation of 6-aminocapronitrile and hexamethylenediamine from a mixture comprising hexamethylenediamine, 6-aminocapronitrile and tetrahydroazepinne

摘要

The invention relates to the field of separation by distillation of 6-aminocapronitrile (ACN) and hexamethylenediamine (HMD) from a mixture comprising ACN, HMD, tetrahydroazepine (THA), adiponitrile (ADN) and low boilers (LB). Also disclosed is a method for producing a distillate stream comprising HMD; a side draw stream comprising ACN, THA and low levels of dimers of ACN and HMD; and a tails stream comprising ACN, THA and substantially higher levels of dimers of ACN and HMD than found in the side draw stream. The side draw stream is particularly suitable for use in the production of caprolactam since the low levels of dimers of ACN and HMT do not greatly affect the catalyst life in the caprolactam production process. The tails stream can be further distilled to produce a tails distillate stream comprising CAN and THA, which can be recycled back to the first distillation column, futher increasing recovery of CAN from the feed stream. Process conditions of the method of the invention disfavor the production of 2-cyanocyclopentylideneimine (CPI).