SYNTHESIS OF CYCLOHEXANONE OXIME VIA AMMOXIDATION WITH MOLECULAR-OXYGEN - THE REACTION NETWORK

This paper deals with the elaboration of a reaction network of the direct heterogeneously catalyzed synthesis of cyclohexanone oxime in vapour-phase from the corresponding ketone, oxygen and ammonia, with an amorphous silica as the catalyst. The effects of the classical reaction parameters. such as temperature, contact time and reactant concentrations, were investigated. The catalyst activity was followed for a long time to elucidate the deactivation phenomena which take place as a consequence of the deposition of large amounts of tars on the catalyst surface. The reactivity of cyclohexanone and the stability of the oxime and the caprolactam were studied in different reaction media. The data were used to formulate some hypotheses on the deactivation processes and on the nature of the active sites of the catalyst. In particular, some acid sites are assumed to be responsible for a strong adsorption of the ketone and its imine and to catalyze aldol condensation reactions on both of them. Other unidentified catalyst sites are assumed to somehow activate molecular oxygen. This activation allows the oxidation of the cyclohexanone imine to the corresponding oxime but also allows the formation of high molecular weight compounds which cannot desorb from the catalyst and, therefore, cause the deactivation process and low yields of the oxime.