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

Abstract

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 MnOx or FeOx 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 MnOx or FeOx 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.