MODELING OF THE SULFIDATION OF ZINC-TITANIUM OXIDE SORBENTS WITH HYDROGEN-SULFIDE

The overlapping grain model was used to describe the sulfidation of zinc oxide and zinc-titanium oxide powders at temperatures between 400-700-degrees-C in H2S-H2-N2 gas mixtures. Experimental data were collected under conditions free of mass-transfer and pore diffusion limitations. Thus, the only resistances to reaction were due to intrinsic sulfidation kinetics (surface reaction) and diffusion through the product layer. The product layer diffusion coefficient was used as a fitting parameter in the model. As the relative amount of titanium in the sorbent was increased, the product layer diffusion coefficient decreased. Similar activation energies (26.6 kcal/mol) were obtained for the product layer diffusion coefficient of ZnO and Zn-Ti-O sulfidation. From the similarity in activation energies, it is proposed that for both types of sorbents diffusion occurs primarily through ZnS.