Novel applications of palladium-based membrane reactors for reaction enhancement

Dense layers of Pd are completely permselective toward H2 transport. Employed as a membrane, Pd can selectively remove H2 from a mixture of gases. Using Pd membranes to remove H2 from H 2-generating reaction systems, certain reactions can be preferentially driven to larger conversions and/or selectivities via LeChatelier's principle. Such Pd-based membrane reactors were proposed over 65 years ago, and have been studied extensively more recently. However, at the outset of this work, over 70% of such studies focused on only one type of application (dehydrogenation), while 98% focused on only five reaction processes. To more fully grasp the advantages and limitations of Pd-based membrane reactors, a broader range of reaction systems must be considered. In this dissertation, we have examined two 'novel' applications of Pd-based membrane reactors: isobutane oxidative dehydrogenation and CO2 (or dry) reforming of CH4. While varying degrees of reaction enhancement were achieved, both studies led to a better understanding of membrane reactor operations.; We had limited success enhancing the isobutane oxidative dehydrogenation in Pd, Pd/Ru and Pd/Ag membrane reactors. H2 removal had a negligible impact on reaction over Pt and Rh monoliths, as these materials did not sufficiently catalyze the non-oxidative dehydrogenation pathway to isobutene. Low rates of H2 removal additionally frustrated our efforts. Exploration of thinner membranes, lower reaction flows, and two reactor designs yielded no further improvements in isobutene yield enhancements. Furthermore, SEM images showed that reaction conditions severely stressed most membranes.; We also considered H2 removal effects on the dry reforming of CH4 for synthesis gas production. At low flows over Pt/gamma-Al 2O3 pellets, conversions were doubled versus conventional equilibrium (25%) and H2O formation was completely suppressed, resulting in H2/CO effluent ratios of 1.0. Larger sweep flows enhanced the reaction somewhat, but a counter-current flow configuration exhibited no advantages over the co-current mode. By replacing Pt/gamma-Al2O 3 with Pt/ZrO2, catalyst deactivation was mitigated. Unlike isobutane oxidative dehydrogenation, SEM images showed limited reaction impact on membrane surfaces. Finally, correlations between reaction enhancements and balance between H2 removal and production were established, together with various mathematical models of the combined reaction/reactor system.