Industrial Process and Modern Technical Adaptations for Nylon 6 Monomer Caprolactam: A Mini Review

Caprolactam is in high demand in the new materials industry as a monomer for nylon and polyamides. Although the schemes of traditional processes such as hydroxylamine production (hydroxylamine sulphate oxime process, hydroxylamine phosphate oxime process, nitric oxide reduction process) and cyclohexanone production were still involved in the caprolactam production industry, the modern technical adaptations achieved higher atomic utilisation and higher selectivity. In this review, the basic traditional schemes for the production of caprolactam are for the first time presented. The modern technical adaptation, the rectification dehydrogenation of the by-product cyclohexane in cyclohexanone production, was highlighted to achieve an increase in atomic utilisation from 78 % to 98 %. The higher selectivity achieved with membrane separation resulted in a conversion of cyclohexanone of > 99.6 % and a selectivity of cyclohexanone oxime of > 99.5 %. In addition, the progress of the catalysts used in the modern technical adaptation was briefly discussed. This review highlights the modern process with atom economy and high selectivity.