Investigation of Elemental Mercury Removal from Coal-Fired Boiler Flue Gas over MIL101-Cr

In this work, the MIL101-Cr sorbent with a large BET surface area was prepared and used to remove Hg0 from simulated coal-fired boiler flue gas. The chemical and physical properties of the prepared sorbent were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis, and X-ray photoelectron spectroscopy (XPS). A range of experiments was conducted in a fixed-bed reactor to investigate the effects of reaction temperature, Hg0 inlet concentration, gas hourly space velocity (GHSV), and flue gas composition on the Hg0 removal for the prepared sorbent. The mechanisms and kinetics of the Hg0 adsorption were also studied. The results showed that the MIL101-Cr sorbent achieved a Hg0 removal efficiency of more than 85% for 4 h at 200 °C under the conditions of a relatively high Hg0 inlet concentration (203 μg/m3) and GHSV (8 × 105 h–1). The O2 in the flue gas was found to be beneficial for Hg0 removal. The NO in the flue gas favored Hg0 removal both in the presence and absence of O2. The SO2 in the flue gas notably inhibited Hg0 adsorption in the absence of O2, whereas a low concentration of SO2 slightly inhibited Hg0 removal in the presence of O2. However, high concentrations of SO2 in the flue gas still significantly weakend Hg0 removal ability, even in the presence of O2, due to the competitive adsorption of SO2 with Hg0 on the sorbent and the sulfation of the sorbent. The simultaneous presence of O2 and NO in the flue gas could overcome the adverse impact of SO2 on Hg0 adsorption. The H2O has little influence on Hg0 removal due to the competitive adsorption. XPS analysis indicated that the surface Cr3+, oxygen species, and C═O group in MIL101-Cr acted as the active adsorption/oxidation sites for Hg0. The Hg0 removal by MIL101-Cr was due to chemisorption and could be described by the pseudo-second-order model. The equilibrium adsorption capacity calculated for the sorbent amounted to 25 656 μg/g at 200 °C, which indicated that MIL101-Cr could be used as a promising sorbent to remove Hg0 from coal-fired boiler flue gas.