(608f) Improving Dehydrogenation Conversion and Selectivity By Utilizing Thermally Stable Membranes

In an equilibrium-limited alkane dehydrogenation reaction, due to its endothermic nature, high temperature is demanded to reach high conversion. Removal of product H₂in a dehydrogenation reaction shifts the equilibrium forward to realize a higher conversion at mild conditions. Thermodynamic computation demonstrates that with the assistance of a membrane separation unit, equilibrium limit can be exceeded in alkane dehydrogenation by selective removal of hydrogen. By operating at a lower temperature, high catalyst performance can be achieved; while catalyst coking is less likely to occur. In this research, dehydrogenation of methylcyclohexane to toluene is studied as a model reaction.

To study the impact of membrane utilization on the dehydrogenation process, blend polymer materials with high thermal stability, chemical resistance and transport properties has been selected as membrane materials. The permeabilities of dense films of Polybenzimidazole (PBI) and Matrimid® blends were evaluated from room temperature to 300 C. Permeabilities increased exponentially with temperature and the selectivities decreased. All blend materials were stable over the multi-day testing.

The potential impact of selective hydrogen removal via thermally-stable polymer blends was calculated from finite element modelling. The model incorporated the measured permeation properties, measured reaction equilibrium information, and catalyst performance (kinetics and coking). As the process can be operated at a range of temperatures, the influence of system temperature on conversion, permeation rate, and catalyst deactivation is analysed. The use of a single membrane unit inter-stage between two packed beds has the potential to increase reactant conversion by 35% compared to operation without inter-stage conversion.