INVESTIGATION OF PROLONGED DEACTIVATION-REGENERATION REGIMES ON THE DEHYDROGENATION ACTIVITY OF PLATINUM/ALUMINA CATALYST

The various types of coke found deposited on a deactivated Pt/Al2O3 reforming catalyst are described. They are claSsified into major types: oxidiZable (primary) coke, reducible (secondary) coke and non oxidizable and non reducible (tertiary) coke. Primary coke is generally non toxic to catalytic hydrocarbon conversion as its removal restores initial catalyst activity. The secondary and tertiary forms are, however, toxic to this reaction. A methodology for the prolongation of reforming catalyst life is evident from these results. In the new method, secondary coke is also removed from the catalyst surface subsequent to primary coke removal. Results of the application of this methodology using accelerated aging of Pt/Al2O3 catalyst is presented. The overall catalyst life was extended for up to 52 deactivation-regeneration cycles from the 23 previously reported. Catalyst life was not correlated with the oxidizable and reducible coke content. These profiles were found to be aperiodic and exhibited a nonlinear dynamic behavior. In contrast, catalyst life per cycle of deactivation-regeneration correlate with the rate of oxidizable coke deposition. The model coking reaction investigated was the dehydrogenation of cyclohexane to benzene in nitrogen carrier at 430°C on a commercial Pt/Al2O3 catalyst using a Berty CSTR.