Mesoporous Zn-Fe-based binary metal oxide sorbent with sheet-shaped morphology: Synthesis and application for highly efficient desulfurization of hot coal gas

Abstract

Mesoporous Zn-Fe-based binary metal oxide sorbent for hot coal gas desulfurization was derived from the Zn-Fe-based layer double hydroxide (ZnFe-LDH). Considering the great disparity of the pH required for the precipitation of Zn2+ and Fe3+, a two-step approach, namely the co-precipitation (Zn2+ and Fe2+) plus subsequent H2O2 oxidation, was proposed for the synthesis of the ZnFe-LDH, the precursor of the sorbent. The preliminary synthesis mechanism of the ZnFe-LDH was discussed. The results reveal that the formation of the layered structure occurs during the oxidation step process rather than the precipitation stage. A series of LDH-derived double metal oxides (DMOs) with the Zn/Fe molar ratios ranging from 1:1 to 5:1 were obtained and contain both ZnO and ZnFe2O4. Furthermore, sheet-shaped morphology is observed for most of the DMOs. The desulfurization performance of the DMOs was evaluated over a fixed-bed reactor. The results indicate that the DMO with the Zn/Fe molar ratio of 5:1 performs best and has the highest sulfur capacity (25 g of sulfur per 100 g of sorbent) at 550 °C. The reaction kinetics was analyzed via the deactivation model. The sorbent has lower deactivation rate constants (0.0185–0.0282 min−1) compared to other Zn-based sorbents, beneficial for the sulfidation reaction. In comparison to ZnO, the DMO sorbent shows lower regeneration temperature. Furthermore, regeneration could effectively recover the plugged pore structure caused by the sulfidation reaction. In addition, the sorbents could maintain high sulfur capacity during four sulfidation-regeneration cycles, showing great potential for industrial desulfurization of hot coal gas.