SUPRA-EQUILIBRIUM CONVERSION IN PALLADIUM MEMBRANE REACTORS - KINETICSENSITIVITY AND TIME-DEPENDENCE

Catalytic membrane reactors are of particular interest for reactions t hat are severely thermodynamically limited. A case study is developed comparing and contrasting cyclohexane dehydrogenation with isobutane d ehydrogenation in a palladium membrane reactor. The former is an often chosen model dehydrogenation, while the latter is of high, current in dustrial interest. Based on the literature and modeling it is conclude d that cyclohexane dehydrogenation accentuates the effect of the membr ane on supra-equilibrium conversion. More favorable thermodynamics, st oichiometry and kinetics for cyclohexane versus isobutane dehydrogenat ion each contribute. To achieve similar levels of membrane-assisted co nversion, the reactor volume required for isobutane dehydrogenation wo uld need to be at least 750 times larger than that required for cycloh exane based upon published kinetics for commercial catalysts. Rate lim itations at the catalyst rather than for hydrogen transport through th e membrane tend to dominate. The hydrogen deficiency in the reaction z one resulting from the membrane transport also leads to enhanced rates of coke formation resulting in catalyst and membrane deactivation. Th is study points out that more effort needs to be expended on the devel opment of new dehydrogenation catalysts with high activity per unit vo lume and high resistance to deactivation.