Mercury removal mechanism of brominated high-sulfur petroleum coke: Experimental and DFT study.

Reaction interface structures of mechanochemical bromine modified high-sulfur petroleum coke (HSPC) as amorphous carbon are critical for Hg0 removal with SO2. This study first found low concentrations of SO2 promote mercury removal while high concentrations do not inhibit it. To distinguish benzene ring skeleton and epitaxial active edges, according to XPS analysis, two new edge models with thiophene were proposed, followed by corresponding defective structures. The calculation of density function theory (DFT) reveals that spatial adsorption of bromine, SO2, and Hg0 is a more universal configuration. The defective armchair-S significantly lowers the energy barrier of Hg0 oxidation while the defective zigzag configurations are more stable. The armchair-Br-1SO2-2 added one negative extreme point near C-Br and broadened the activity region. Further, a new promotion pathway of SO2 is proposed that SO2 pulls Hg0 forming strong physisorption. However, excess SO2 molecules do not compete with mercury for adsorption. Although the adsorption energy of mercury is higher on intact structures, the oxidation energy barrier is lower on defective structures with SO2, and even direct mercury oxidation on zigzag-S with two SO2 molecules. This study can provide a theoretical basis for functionalized carbon-based adsorbents removing Hg0 in actual flue gas.