Removal of vapor-phase elemental mercury from simulated syngas using semi-coke modified by Mn/Ce doping

The Mn-SC and Mn/Ce-SC adsorbents were prepared by modification of semi-coke(SC) with manganese nitrate and cerium nitrate, and their mercury removal performance in simulated syngas was investigated in a lab-scale fix-bed reactor. Effect of cerium and manganese on the surface physical and chemical properties of semi-coke was characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that BET surface area, average pore size and total pore volume of Mn-SC are higher than those of SC, while Mn/Ce doping modification has adverse effect on the pore structure; Mn_xO_y and Ce_xO_y exist in highly dispersive amorphous form on the surface of semi-coke. The mercury removal efficiency of Mn/Ce-SC is higher than that of Mn-SC and SC, and decreases with increase in adsorption temperature. Generally, the Mn/Ce-SC exhibits good mercury removal performance at elevated temperatures. With the presence of 1% of O₂, oxidation and reduction reaction cycle could occur on the surface of Mn/Ce-SC, and oxygen in syngas is converted into lattice oxygen with high oxidation activity. Based on the Mars-Maessen mechanism, Hg⁰ could be oxidized to Hg²⁺ by lattice oxygen and then adsorbed. The mercury removal efficiency of Mn/Ce-SC maintains over 95% at 260 ℃.