Cu-Cr-O and Cu-Ce-O regenerable oxide sorbents for hot gas desulfurization

Binary Cu-Cr-O and Cu-Ce-O oxides were studied in this work as regenerable sorbents for high-temperature fuel gas desulfurization. CuO-Cr2O3 and CuO-CeO2 sorbents can remove H2S from simulated coal-derived fuel gas to less than 5-10 ppmv in the temperature range of 650-850 degrees C. The presence of stable CuCr2O4 in CuO-Cr2O3 solids retains some copper in the Cu2+ or Cu1+ oxidation state, which can account for the high H2S removal efficiency. In CuO-CeO2 sorbents, however, CuO is easily reduced to copper metal. Participation of reduced cerium oxide in sulfidation can explain the observed high desulfurization efficiency. TGA tests and XRD analysis indicate that sulfidation proceeds through partial initial reduction of the CuO-Cr2O3 sorbents: CuO --> Cu/Cu2O --> Cu2S (x < 2). Reduction kinetics were studied in the TGA over temperature ranges of 550-850 and 350-850 degrees C, respectively, for the CuO-Cr2O3 and CuO-CeO2 materials. The sulfidation kinetic parameters were measured in the temperature range of 450-850 degrees C after prereduction of both sorbents. The sulfidation of metal copper in Cr2O3 and CeO2-x, matrices is a fast reaction with low activation energy, 19.8 and 16.6 kJ/mol, respectively. Both types of sorbents can be fully regenerated with diluted air. The regeneration temperature affects the reaction pathway and the regenerability of the solid composition.