Rearrangement of Cyclohexanone Oxime to Caprolactam Over Solid Acid Catalysts

Beckmann rearrangement of cyclohexanone oxime to caprolactam in the gas phase over a boria catalyst has been investigated. Catalyst testing using a continuous flow fixed bed reactor indicated typical time on stream reaction profiles, to consist of an initiation period, a brief stable operating phase and finally slow deactivation. The fast deactivation of nonselective, strongly acidic catalyst sites is thought to account for the initiation period. In addition to the mechanisms already known (coking and basic by-product re-adsorption) for the loss of caprolactam selectivity during the final deactivation phase, evidence is presented to suggest an additional process whereby some of the selective sites of intermediate acidity are converted to non-selective sites during reaction. The latter are thought to be due to the formation of some amorphous boron species.