Effect of preparation conditions on MnxOy/Al2O3 sorbent for H2S removal from high-temperature synthesis gas

A series of MnxOy /Al2O3 sorbents with different tissue and chemical structures were prepared by repeated incipient wet impregnation method with different calcination conditions, including calcination temperature from 500 °C to 900 °C and calcination time from 3 h to 9 h. The H2S absorption performances of the prepared sorbents were investigated by a model synthesis gas containing 2000 mg/m3 H2S at 850 °C. The chemical and physical structures of the samples were characterized by Brunauer–Emmett–Teller, X-ray diffraction and scanning electron microscopy techniques to obtain fundamental information about the deactivation of MnxOy/Al2O3 sorbents during desulfurization–regeneration cycles. Results showed that the structural features of the sorbents at high reaction temperature played an important role in the stability of desulfurization performance. The analysis of the characteristics of the sorbents indicated that the sorbents obtained stabilized chemical and physical structures during desulfurization–regeneration cycles when the calcination temperature was 900 °C and the calcination time was above 6 h. The sorbent suffered serious deactivation during five successive desulfurization–regeneration cycles when the calcination temperature of sorbents was below 850 °C. The sulfur capacity decreasing of MnxOy/Al2O3 sorbents may probably be attributed to a part of MnxOy covered by Al2O3, which can un-sulfide during adsorption process. The coverage of active phase MnxOy may be caused by the shrinking and disappearing of some micropores, and phase transformation of Al2O3, as well as the transformation of MnAl2O4 lead to a part of MnxOy on the sorbents being covered by alumina.