Beckmann rearrangement over phosphotungstic acid/SiMCM-41 cyclohexanone oxime to ε-caprolactam Original Research Article

Vapor-phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam is reported for the first time on phosphotungstic acid (PWA)-supported SiMCM-41 catalyst. The catalyst was prepared in the laboratory following standard procedures and was characterised by XRD and FT-IR. By N2 adsorption, BET surface area, pore size and pore diameter were measured. The conversion of cyclohexanone oxime over the catalyst was studied in the temperature region of 250–400 °C using mainly acetonitrile as a solvent at different contact times. Increase in the reaction temperature to 325 °C enhances oxime conversion and the selectivity of ε-caprolactam. An impressive catalytic performance of cyclohexanone oxime conversion >99% and ε-caprolactam selectivity of 75% was observed on 30 wt.% PWA/SiMCM-41 at 325 °C using a feed containing10 wt.% oxime in acetonitrile at WHSV=3.24 h−1. The catalytic efficiency for this rearrangement reaction was studied, varying the PWA content from 10 to 50 wt.% on SiMCM-41 and also using benzene and ethanol as alternate solvents in place of acetonitrile. The rearrangement reaction and ε-caprolactam selectivity with respect to catalyst physical characteristics, PWA content and type of solvent are discussed.