Characterization of Mn and Cu oxides as regenerable sorbents for hot coal gas desulfurization

To enhance the formation of different mixed oxides, which potentially might stabilize copper in oxidation states 2+ and/or 1+, regenerable sorbents fo r hot coal gas desulfurization have been prepared by calcination at 950 deg rees C of MnO2 and CuO powders in different mole ratios. The fresh sorbents were sulfided at 600 degrees C using a simulated coal gas from cylinders, reduced in identical operating conditions compared to sulfidation in the ab sence of H2S, and regenerated at 710 degrees C in oxidising atmosphere. Suc cessive sulfidation-regeneration cycles were carried out in a quartz fixed- bed reactor, The fresh, reduced, sulfided or regenerated sorbents were char acterized by SEM-EDX, XRD, TPR, XPS and FTIR spectroscopy. The study shows that, under the reducing power of coal gas at the operating conditions used , manganese oxides cannot prevent the reduction of copper oxides and, conse quently; the expected beneficial effect derived from copper oxide addition, reducing the equilibrium H2S concentration in the outlet gas to very low l evels cannot be achieved. In addition, copper oxides do not prevent the ten dency of manganese-based sorbents to form sulfate species in an oxidative a tmosphere and the regeneration of these sorbents has to be carried out at h igher temperature. (C) 2000 Elsevier Science B.V. All rights reserved.