Novel process for the synthesis of caprolactam with promising development

At present, researchers at the Kansai University in Osaka, Japan, are developing a new CL synthesis route based on the N-hydroxyphthalimide (NHPI) oxidation catalyst. In this new process, ethyl acetate was used as a solvent and NHPI was used as a catalyst. The operation was performed at 60°C and an oxygen pressure of 0.1 MPa. A mixture of cyclohexanone and cyclohexanol (ie, KA oil) was used. Oxidation produces 1,1-dihydroxydicyclohexyl peroxide (PO). There are two different options for the preparation of CL from PO. One is the reaction of PO with ammonia to produce dicyclohexylamine peroxide (PDHA). The conversion rate is 20% and the selectivity is 90% based on KA oil. PDHA then reacts catalytically to form CL. In another scenario, using selenium oxide as a catalyst, PO is first converted to ε-lactone at 60°C. The conversion rate is 11% and the selectivity is 87%, ε--in terms of KA--oil. The ester reacts with ammonia to form CL.

Although the process route is in the development stage, it is considered to be a promising process technology because of its low by-product ammonium sulfate. The current research focuses on improving its conversion rate.