SULFIDATION OF ZINC TITANATE AND ZINC-OXIDE SOLIDS

The sulfidation of bulk mixed oxides of zinc and titanium of various compositions and Zn-Ti-O crystalline phases in H2S-H-2-H2O-N2 gas mixtures was investigated in a thermogravimetric apparatus over the temperature range of 400-800-degrees-C. Comparative sulfidation experiments with ZnO were also performed. In comparison to ZnO, the use of Zn-Ti-0 solids allows raising the operating temperature for desulfurization of hot coal-derived fuel gas, e.g., by as much as 94-degrees-C for solids with (Zn/Ti)atomic = 2/3. The initial sulfidation rate of Zn-Ti-O solids with (Zn/Ti)atomic less-than-or-equal-to 3 was approximately 1.5-2 times slower than for ZnO. Different zinc titanate phases (i.e., Zn2TiO4, ZnTiO3, and Zn2Ti3O8) had the same initial sulfidation rate. Similar activation energies (9-10 kcal/mol) were measured for ZnO and Zn-Ti-O sulfidation. No effect of H-2 or H2O was observed on the initial sulfidation rate. However, at high conversions, rates were lower with increasing H-2 concentrations. Fine particles and cracks were observed in sulfided ZnO as a result of ZnO reduction and subsequent vapor-phase reaction between Zn and H2S to form ZnS. These structural effects were largely absent in Zn-Ti-O solids.