H2 Production in Palladium and Palladium-Copper Membrane Reactors at 1173K in the Presence of H2S

The efficacy of producing high-purity H2 from coal-derived syngas via the high-temperature water-gas shift reaction (WGSR) in catalyst-free Pd and 80wt%Pd-Cu membrane reactors (MRs) was evaluated in the absence and presence of H2S. The impetus for this study stems from the fact that successfully integrating water-gas shift MRs to the coal gasifier process has the potential of increasing the efficiency of the coal-to-H2 process, thereby significantly reducing the cost of H2 production from coal. To this end, the effect of the WGSR environment on 80wt%Pd-Cu MRs was studied over a wide range of temperatures. Results indicate minimal impact of the WGSR environment on the 80wt%Pd-Cu membrane at 1173K. Subsequently, using pure reactant gases (CO and steam), the rapid rate of H2 extraction from the reaction zone, coupled with the moderate catalytic activity of the Pd-based walls was shown to enhance the CO conversion beyond the equilibrium value of 54% at 1173K, in the absence of additional heterogeneous catalysts in both Pd and 80wt%Pd-Cu MRs. The effect of H2S contamination in the coal-derived syngas on Pd and 80wt%Pd-Cu membranes at 1173K was also studied. Results indicate that the sulfidization of Pd-based membranes is strongly dependent on the H2S-to-H2 ratio and not merely the inlet H2S concentration. The Pd and 80wt%Pd-Cu MRs were shown to maintain their structural integrity at 1173K in the presence of H2S-to-H2 ratios below 0.0011 (~1,000 ppm H2S-in-H2).A COMSOL Multiphysics model developed to analyze and predict performance of the water-gas shift MRs in the presence of H2S indicated that the MRs could be operated with low H2S concentrations. Finally, the feasibility of high-purity H2 generation from coal-derived syngas was investigated using simulated syngas feed containing 53%CO, 35%H2 and 12%CO2. The effect of H2S contamination on MR performance was investigated by introducing varying concentrations of H2S to the syngas mixture. When the H2S-to-H2 ratio in the MR was maintained below 0.0011 (~1,000 ppm H2S-in-H2), the MR was observed to maintain its structural integrity and H2 selectivity, however, a precipitous reduction in CO conversion was observed. Increasing H2S concentrations such that the H2S-in-H2 ratio increased above about 0.0014 resulted in MR failure within minutes