REDUCTION, SULFIDATION, AND REGENERATION OF MIXED IRON ALUMINUM-OXIDE SORBENTS

The reduction and sulfidation of Fe2O3 and Fe2O3-Al2O3 sorbents were investigated by thermogravimetric analysis (TGA). Mixed iron-aluminum oxides were reduced more slowly and by a more complex mechanism than pure iron oxide. Several phases that were responsible for this difference were identified by temperature-programmed reduction (TPR), X-ray diffraction (XRD), BET surface area (BET), and scanning electron microscopy (SEM). Sulfidation of reduced sorbents in the TGA at 600-degrees-C produced two crystalline phases: high-temperature, hexagonal pyrrhotite (Fe1-xS), and unreacted FeAl2O4. The reaction of the pure and mixed oxide with a mixture of H2S-H2-H2O-N2 was studied in a tubular microreactor to evaluate the performance of these materials as high-temperature H2S sorbents. At 650-degrees-C the mixed oxide yielded considerably lower prebreakthrough outlet H2S levels than the pure iron oxide. Regeneration in pure SO2 and SO2-air mixtures of sulfided samples resulted in complete conversion of iron sulfide to iron oxide and quantitative recovery of elemental sulfur.