High-Temperature Desulfurization of Gasifier Effluents with Rare Earth and Rare Earth/Transition Metal Oxides

We have improved the application of mixed rare-earth oxides (REOs) as hot gas desulfurization adsorbents by impregnating them on stable high surface area supports and by the inclusion of certain transition metal oxides. We report comparative desulfurization experiments at high temperature (900 K) using a synthetic biomass gasifier effluent containing 0.1 vol % H₂S, along with H₂, CO₂, and water. More complex REO sorbents outperform the simpler CeO₂/La₂O₃ mixtures, in some cases significantly. Supporting REOs on Al₂O₃ (∼20 wt % REO) or ZrO₂ actually increased the sulfur capacities found after several cycles on a total weight basis. Another major increase in sulfur capacity took place when MnO_<i>x</i> or FeO_<i>x</i> is incorporated. Apparently most of the Mn or Fe is dispersed on or near the surface of the mixed REOs because the capacities with REOs greatly exceeded those of Al₂O₃-supported MnO_<i>x</i> or FeO_<i>x</i> alone at these conditions. In contrast, incorporating Cu has little effect on sulfur adsorption capacities. Both the REO and transition metal/REO adsorbents could be regenerated completely using air for at least five repetitive cycles