Reduction, sulfidation, and regeneration of mixed iron-aluminum oxide sorbents

Abstract

The reduction and sulfidation of Fe_2O_3 and Fe_2O_3-Al_2O_3 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 "C produced two crystalline phases: high-temperature, hexagonal pyrrhotite (Fe_(1-x)S), and unreacted FeAl_2O_4. The reaction of the pure and mixed oxide with a mixture of H_2S-H_2-H_2O-N_2 was studied in a tubular microreactor to evaluate the performance of these materials as high-temperature H2S sorbents. At 650 °C the mixed oxide yielded considerably lower prebreakthrough outlet H_2S levels than the pure iron oxide. Regeneration in pure SO_2 and SO_2-air mixtures of sulfided samples resulted in complete conversion of iron sulfide to iron oxide and quantitative recovery of elemental sulfur.