Impact Of Nonoxidized Sulfur Species On Elemental Mercury Removal By So2 Activated Petroleum Cokes

High-sulfur petroleum coke is potentially one of the most promising materials for developing efficient and low-cost sorbents for Hg-0 removal from flue gas. In this study, three distinct SO2-activated high-sulfur petroleum cokes were prepared at 650-850 degrees C via different sulfurization protocols, including SO2-impregnated petroleum coke (PC-S), SO2-impregnated coke produced with an additional reductive heat-treatment process in N-2 (PC-NS), and SO2-impregnated coke prepared with the presence of SO2 in the gas during the cooling process (PC-SC). The SO2-activated cokes were characterized with nitrogen adsorption/desorption measurements, X-ray photoelectron spectroscopy, thermogravimetric analysis, and their mercury removal performances were investigated in a fixed-bed reactor at 80-200 degrees C with an initial mercury concentration of 35-120 mu g/m(3). To explore the influence of nonoxidized sulfur species on Hg-0 removal, particular focus was given to the comparison of the reduced sulfur, sulfide sulfur, and elemental sulfur formed during different sulfurization processes, as well as the consequent differences in Hg-0 adsorption characteristics. It found that the sulfur incorporated into the carbon matrix of PC-S by interaction with SO2 at 650 degrees C was dominantly organic sulfide. Thermal treatment in N-2 at 800 degrees C led to an addition of reduced sulfur in PC-NS. An increment of 0.74 at. % elemental sulfur was observed in PC-SC after exposure to SO2 during the cooling step. The He adsorption capacity of PC-SC at low temperatures was significantly enhanced, yielding a mercury capacity of 622 mu g/g at 80 degrees C. However, elemental sulfur suffered from severe temperature sensitivity for mercury binding. The sample PC-NS which contained more reduced sulfur showed the highest Hg-0 adsorption capacity at elevated temperatures above 160 degrees C. Furthermore, the increment in inlet mercury concentration would lead to higher adsorption capacities and faster adsorption rates. According to the R-L obtained from Langmuir isotherms, the He adsorption reactivity can be arranged as follows: PC-NS > PC-S > PC-SC. The mercury temperature-programmed desorption results suggested that sulfur species not only had an effect on Hg-0 adsorption capacity but also played an essential role in the thermal stability of the adsorbed mercury compounds. Mercury was principally associated with elemental sulfur in the form of metacinnabar and combined with thermal-stable organic sulfide in cinnabar or organomercuric compounds Hg-SR.