Catalyst Deactivation of High-silica ZSM-5 Zeolite Modified with Noble Metals during Vapor Phase Beckmann Rearrangement of Cyclohexanone Oxime

Abstract

High-silica ZSM-5 zeolites were synthesized by the addition of pentavalent ions, such as phosphorus and arsenic ions, to the mother gel for the zeolite preparation. The Beckmann rearrangement of cyclohexanone oxime in the vapor phase was carried out over the high-silica ZSM-5 zeolites or zeolites modified with noble metals to elucidate the effects of the diluent gas and diluent solvent on the e-caprolactam selectivity and catalyst deactivation. The catalyst lives of the zeolites modified with noble metals were much longer than that of the unmodified zeolite during the rearrangement using carbon dioxide and methanol as the diluent gas and diluent solvent, respectively. Furthermore, the life of the zeolites modified with noble metals was significantly improved by using a small amount of oxygen as the diluent gas. In this case, methanol was the most suitable diluent solvent for the improvement of catalyst life. The catalyst life decreased with increased cyclohexanone oxime concentration in methanol. Therefore, the coke or coke precursor on the acid sites was presumably removed by methanol vapor. These results indicate that a prolonged catalyst life in the vapor phase Beckmann rearrangement can be achieved by the optimum combination of catalyst and reaction atmosphere.