H2S removal and regeneration properties of Zn–Al-based sorbents promoted with various promoters

In order to improve the poor regeneration properties of the ZnO–Al₂O₃ (ZA)sorbent with a high sulfur removing capacity and fast H₂S absorption rate, 5–10 wt.% of various additives such as iron (Fe₂O₃), cobalt (Co₃O₄), nickel (NiO) and cerium oxide (CeO₂) were added to the ZA sorbent. These sorbents were prepared by the co-precipitation method and their sulfur removing capacities and regeneration properties were measured in a fixed-bed reactor during multiple cycles at middle-temperature ranges between 480 and 580 °C. The sulfur removing capacities of these sorbents measured 0.17–0.20 g S/g sorbent, which corresponded to 80% of the theoretical value and the values were maintained to within 10 cycles. The poor regeneration property of the ZA sorbent, which needed a long time (600 min), was also improved by addition of these promoters. These sorbents were regenerated completely within 300 min. The additives such as Fe, Co and Ni formed their aluminates, which did not change into sulfide form during sulfidation. The additives/aluminates played an important role in transforming S in ZnS into SO₂. Cerium dioxide showed a similar role with such aluminates in the oxidation of sulfur. The catalytic roles of the promoters and the changes in the physical properties of sorbents, during multiple cyclic tests, are discussed.