A one step synthesis ofcaprolactam out of cyclohexanone by combinded ammoximation and Beckmann rearrangement over Nb-MCM-41 catalysts

Abstract

Caprolactam was synthesized directly in one step out of cyclohexanone via combined liquid phase ammoximation and Beckmann rearrangement using H2O2 and NH3 in presence of Nb-MCM-41 catalysts and ethanol as solvent. Thereby the Beckmann rearrangement of the oxime to caprolactam occurs simultaneously with the ammoximation of cyclohexanone. Nb-incorporated MCM-41 molecular sieves (Si/Nb- 16, 32, 64 and 128) have been synthesized hydrothermally using tetradecyltrimethylammoniumbromide as template in absence of auxiliary organics. Synthesized Nb-MCM-41 samples were characterized using various physical-chemical techniques such as X-ray diffraction, N2-physisorption, Atomic Absorption Spectroscopy (ICP-AAS), Thermal Gravimetric Analysis (TGA-DTA), Raman spectroscopy and H2-Temperature Programmed Reduction (TPR). All spectroscopic characterization techniques revealed that two types of Nb species are present in the samples. One is tetrahedral coordinated framework Nb species and the other type extra framework Nb2O5 species. All these Nb-MCM-41 catalysts were employed to catalyze the ammoximation reaction of cyclohexanone with H2O2 and NH3 and the simultaneously occurring Beckmann rearrangement reaction. The influence of essential reaction parameters such as temperature, NH3/cyclohexanone ratios and Si/Nb ratios were investigated. A caprolactam selectivity of 66% was obtained at a cyclohexanone conversion of 7.3% at NH3/cyclohexanone molar ratio=1.5, H2O2: cyclohexanone molar ratio=1.32 over Nb-MCM-41 (Si/Nb-32) at 80°C.