(593b) The Chemistry of Mercuric Chloride Reduction in the Flue Gases of Coal Combustion | AIChE

(593b) The Chemistry of Mercuric Chloride Reduction in the Flue Gases of Coal Combustion

Authors 

Abu-Daabes, M. A. - Presenter, German-Jordanian University


Understanding the chemical and physical transformation pathways that govern the oxidation states of mercury in flue gases is a key to the development of efficient removal processes for this pollutant. A reduction of oxidized mercury (Hg2+) typically observed downstream of a cold electrostatic precipitator has been reported. However, compared to the relatively large number of efforts to study oxidation mechanisms of elemental mercury (Hg0) to oxidized mercury (Hg2+), a small number of studies report on the reduction mechanisms of Hg2+ to Hg0 in the gas phase. In the present study, mercury speciation, or more specifically reduction of Hg2+ to Hg0, is investigated at flue gas conditions. Experimental data show that SO2 and H2O vapor are the main factors affecting Hg2+ reduction in the gas phase and that the presence of HCl is critical for maintaining Hg2+ in its oxidized form. CO2 and NO reduced the rate of Hg2+ reduction in the absence of HCl gas. Furthermore, the rate of Hg2+ reduction in the absence of HCl increased with an increase in the surface area in direct contact with the flue-gas constituents, due to heterogeneous reactions. Investigations on the effect of functionalized surface ligands, such as mercaptopropyltrimethoxysilane (MPTS), on mercury speciation showed that thermal desorption of Hg2+ bonded to ?SH functional groups on the silica surface yielded Hg0 rather than Hg2+ in the presence of N2 gas.