Sulphur Removal Using Regenerable Sorbents of Rare Earth/Transition Metal Oxides
Hot gas desulfurization of gases from primary gasifier can be accomplished using sorbents composed Zn, calcium and transition metal oxide sorbents. The problem with metal oxide sorbents alone is that they are easily reduced at high temperature above 873 K to metallic state under reducing atmosphere decreasing their desulfurization capacity.
Sorbents studied for hot gas desulfurization were based on Ce/La/M (M = transition metal) oxides and Ce/La/RE (RE = a rare earth) oxide. Sorbents were prepared using sol-gel method and the rare earth oxides were doped with transition metals using incipient wetness impregnation. Sulfidation experiments were carried out at 873 K using a reacting gas composition of 23.4 mol% H2, 41.4% N2, 3.1% water, 32.0% CO2, and 0.1% H2S. Reduced Ce/La oxides adsorb H2S at temperatures of 873 K and above, and were regenerable in O2 mixtures. The addition of group VII-VIII transition metals to Ce/LaOx increases the sulfur removal capacity significantly. Among the transition metals (Mn, Fe, Cu) studied, Ce/LaOx mixtures impregnated with Mn had the highest capacity followed by Fe and Cu. The optimum ratio of M/(Ce+La) is around 0.1 and the sulfur capacity was higher in sorbents which are rich in La, and the optimum ratio of Ce/La for high sulfur capacity is around 0.9. Addition of oxides such as ZrO2 or a third rare earth oxide increases surface area, sintering resistance, oxygen mobility of CeOx/La2O3 at high temperatures, and sulfur capacity. These ternary REOs maintained their capacity in next successive four runs and these were easily regenerated in air.
Advisor:Ralph W. Pike; F. Carl Knopf; Kerry M. Dooley
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:07/11/2008