Mechanism Study On Mercury Homogeneous And Heterogeneous Reaction

Mercury has attracted much attention as a very important global pollutant and it is very toxic even in very low concentration, so it would do great harm to the environments, But so far we have only a little acquaintanceship about the mechanism of release, control and emission. Now, we focused on describing the mechanism of the homogeneous and heterogeneous reaction during coal combustion with computational methods.The geometry optimizations of reactant and product were calculated by quantum chemistry, its ground-state geometry is determined by comparison with literature values and energy analysis, the thermodynamic parameters of HgF and HgF₂ in the temperature scale of 298-1500K were obtained from the frequency analysis. The calculating results were compared with the NIST experimental. The results show that the maximum relative error of enthalpy difference and entropy were 2.86% and 2.03%, respectively. The results provide a base for studying reaction mechanism of mercury with HF, ClO and NO by quantum chemistry and calculating parameters.Five mechanism of homogeneous mercury oxidation in the coal flue gas were studied, which contains three Hg oxidation reactions with HF and the other two reactions with ClO and NO. Ab initio molecular orbital calculations were performed on the possible pathways of the mercury oxidation to find the transition state and intermediate of geometry optimizations. The activation energies and temperature exponents were calculated by the frequencies analysis and thermal energy calibration. The transition state theory was used to calculate the reaction rate constants in the temperature scale of 293-1500K. All these kinetic parameters can provide basis of the Hg kinetic models in coal burning for further analysising.The mechanism of the heterogeneous reaction on the unburned carbon (UBC) surface (armchair cluster model) during coal combustion was investigated by the density functional theory (DFT). The reaction process was analyzed. The activation energies and the reaction rate constants were calculated and provide a base for predicting mercury conversion and migration during coal combustion.