The transition to a hydrogen economy requires substantial reductions in the cost of hydrogen. One alternative for achieving this goal is to conduct the water-gas shift reaction under the high temperature and pressure conditions present at the coal gasifier outlet. However, the equilibrium conversion of the water-gas shift reaction at such high temperatures is quite low. Even though the thermodynamic limitation can be overcome by the introduction of a H2-selective membrane reactor, no previous studies of such a membrane reactor concept have been performed. The objective of this work is to provide the fundamental background required to determine whether the high-temperature, high-pressure water-gas shift reaction in a H2-selective membrane reactor, despite its theoretical simplicity and potential advantages, is a viable way to enhance the hydrogen yield. The gas-phase reaction kinetics were studied in the presence of an inert material (quartz), a common high-temperature construction material (Inconel®600) and potential membrane materials (Pd and a Pd-Cu alloy) in an effort to assess if the reaction can proceed at rates high enough to preclude the need for added catalysts. The gas-phase mechanism previously proposed to describe the high-temperature, low-pressure reaction was found to be valid at high-pressure conditions. Inconel®600 surfaces greatly enhanced the reaction rate. This effect is likely attributable to the formation of a catalytic chromium oxide layer on the metal surface. Fresh Pd-Cu pellets and, also, Pd and Pd-Cu surfaces after exposure to reaction conditions followed by an oxygen treatment for carbon removal displayed catalytic activity for the water-gas shift reaction. However, the catalytic effect was not as significant as that observed with Inconel®600 surfaces. These results suggest that sufficiently large reaction rates can be attained without the need of an external catalyst.Several Pd-based membrane reactor configurations were studied. The reaction was conducted in high-reaction rate / low-permeation rate (flat disk) and high-permeation rate / low-reaction rate (tubular) membrane reactor configurations. Conversions surpassing the equilibrium limitation were attained with both configurations. The two approaches are compared. It was found that the heat released by the reaction in the tubular configuration may have a significant, enhancing effect on the reaction conversions.
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