Modelling propane dehydrogenation in a rotating monolith reactor

The catalytic dehydrogenation of propane is equilibrium limited, strongly endothermic and normally carried out at high temperatures. The catalyst deactivates due to the laydown of carbonaceous species on the surface. This is conventionally countered by subjecting the catalyst to periodic regeneration. In commercially available processes, the catalyst time on line for a given cycle is in the order of 10–10,000 min.

In this study, the catalyst has been observed to exhibit very high activity and selectivity in the short period after regeneration. Conceptual and model development of a reactor with structured catalyst to capitalise on this beneficial early activity is presented.

The preferred reactor comprises a cylindrical block of honeycomb monolith that rotates past various feed zones, subjecting the catalyst successively to propane and regenerating gas. The exothermic nature of the regeneration reactions is used at least in part to provide heat to the endothermic dehydrogenation reaction via the regenerative heat transfer facilitated by the movement of the solid monolith. Specifically, it is noted that an oxidisible catalyst provides operating advantage due to the additional exotherms associated with the regeneration stage.

The process modelling shows the design to be feasible in terms of matching the heats of reactions and achieving high conversions, but questions are raised over its practicability from mechanical design and process stability viewpoints.