Study On Oxidation Kinetics Of Mercury Based On Quantum Chemistry Calculation

Mercury emitted from coal-fired boiler will do great harm to human health andenvironmental pollution, which has sttracted much attention as a very important globalpollutant. Since the amount of Hg existing in the raw coal or flue gas is rare,people knowfew about the release mechanism and form transformation during the combustionprocess. This paper builds a more comprehensive model of Hg and Br and themicroscopic oxidation mechanism is studied in detail.The geometry optimizations of reactant and product were calculated by differentlevels of ab initio. The calculating results were compared with literature values tovalidate the quantum mechanical method and basis set combination. The thermodynamicparameters of HgBr in the temperature scale of298-1500K were obtained from thefrequency analysis and were compared with the NIST experimental. The results showthat the maximum relative error of enthalpy difference and entropy were2.71%and0.31%, respectively,which provide a base for studying reaction mechanism of mercurywith HBr, Br, Br2and BrCl by quantum chemistry.Theoretical exploration about reaction of mercury with bromine was conductedon the level of atoms and molecules. The geometry optimization was made at MP2level by ab initio calculations of quantum chemistry. The activation energies werecalculated by thermal energy calibration (including zero point energy calibration).The reaction rate constants on the both sides of the reaction in the temperature scaleof298-1500K were calculated from transition state theory, the variation trend ofwhich were analyzed with the changes in temperature. Then, the mechanism of O3on the reaction of Hg with Br was investigated. The reaction process of five wasanalyzed in detail. The activation energies and the reaction rate constants of298-1800K were calculated. The effect of O3on the existing form of Br in flue gaswith the increase of temperature was studied and was compared with reaction of Hgwith Br without O3addition. As for EPC, the promoting effect of Hg0-Br-O3systemwas pretty obvious. The calculated parameters can provide new foundation foremission model of trace element, which can be very important for Hg controltechnology by spraying Br-containing compounds into the flue gas.