Performance of ZnMn2O4/SiO2 sorbent for high temperature H2S removal from hot coal gas

Abstract

A spinel ZnMn₂O₄ sorbent supported on SiO₂ was fabricated using a wetness impregnation method for high temperature desulfurization. The operating parameters including operating temperature, ZnMn₂O₄ content, space velocity, gas composition, and multiple desulfurization/regeneration cycles were evaluated to understand the optimal condition. The ZnMn₂O₄/SiO₂ sorbent exhibits better desulfurization performance when operating temperature is controlled above 600 °C and the suitable space velocity is between 5000–15 000 h⁻¹. The relationship among CO, H₂, and CO₂ on sorbent utilization could be explained via the water shift reaction. The sorbent utilization of the ZnMn₂O₄/SiO₂ sorbent was retained at approximately 70% after ten desulfurization/regeneration cycles. Elemental analyses demonstrated that the formation of the spinel structure of ZnMn₂O₄/SiO₂ improved the Zn stability and no Zn vaporization or loss were observed after ten desulfurization/regeneration cycles. X-ray diffraction (XRD) and temperature programmed regeneration (TPR) were used to characterize the crystal phase and regeneration phenomena of the ZnMn₂O₄/SiO₂ sorbent. XRD results demonstrated the presence of spinel structure of ZnMn₂O₄, and no Zn and Mn oxides were observed after multiple cycles, indicating that the ZnMn₂O₄/SiO₂ sorbent is thermodynamically stable for high temperature desulfurization. Through the EDS and TPR analyses, the residual sulfur was found in the regenerated sorbent and this sulfur species is sulfate from incomplete regeneration. A regeneration temperature of 700 °C was the best choice to overcome the formation of metal sulfate.