Elemental mercury removal from coal gas by CeMnTi sorbents and their regeneration performance

Abstract

Ce and Mn modified TiO2 sorbents (CeMnTi) were prepared by a co-precipitation method, and their ability to remove elemental mercury from coal gas in a fixed bed reactor was studied. Based on results of Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) studies, the modification mechanisms of the CeMnTi sorbents are discussed. Mn doping improved the specific surface area and dispersion of cerium oxides on the sorbent surface, while Ce doping increased the proportion of Mn4+ in manganese oxides by a synergetic effect between manganese oxides and cerium oxides. The effects of the active component, temperature, and coal gas components on the mercury removal performance of the sorbents were investigated. The results showed that the CeMnTi sorbents exhibited high mercury removal efficiency. Ce0.2Mn0.1Ti adsorbed 91.55% elemental mercury from coal gas at 160 °C. H2S and O2 significantly improved the ability of sorbents to remove mercury. Part of the H2S formed stable sulfates or sulfites through a series of oxidation reaction chains on the sorbent surface. HCl also improved the mercury removal performance, but reduced the promotion effect of H2S for mercury removal when coexisting with H2S. CO and H2 had a minor inhibitory effect on mercury adsorption. The recycling performance of the sorbents was investigated by thermal regeneration. The thermal decomposition of the used sorbents indicated that mercury compounds were present mainly in the form of HgO and HgS, and higher temperature was beneficial for regeneration. The formation of sulfates and sulfites in the presence of H2S led to a decrease in mercury removal efficiency.