Dehydrogenation of propane-isobutane mixture: A thermodynamic analysis

The influence of propane addition to the feed on equilibrium conversion of isobutane dehydrogenation was studied. A complex mutual effect of the components in propane-isobutane mixture determines the equilibrium conversion of the paraffins. Each component can act, simultaneously, as a diluent to the reaction zone shifting the dehydrogenation equilibrium of the paraffin components to the corresponding olefin, and as an additional source of hydrogen which shifts the dehydrogenation equilibrium to the left. Chemical equilibrium calculations showed that the addition of propane to isobutane feed increases the equilibrium conversion of the latter whereas the addition of isobutane to propane decreases the equilibrium conversion of the latter under constant temperature, pressure and hydrogen/hydrocarbon molar ratio conditions. It was also found that, under these conditions, the equilibrium conversion of individual paraffins is much less affected by feed propane/isobutane ratio as compared to that of total feed paraffin conversion. Consequently, only low propylene/isobutene product ratios could be realized in commercial combined feed practice