(60f) On the Prevention of Trace Metal Emissions From Coal Combustion

Understanding the oxidation of selenium during the coal combustion processes is crucial to preventing its release into the atmosphere. Coal combustion provides a major source of energy, accounting for 52% of electricity in the US. Due to projected increases in coal use worldwide, attention has turned to the potentially harmful effects such as the well known problem of CO₂ emission and the emissions of various trace elements such as Se, Hg, and Ar. An ab initio study of selenium oxidation/reduction in coal combustion was conducted at the CCSD(T) level of theory with the aug-cc-pVTZ basis set. Twenty-nine different reactions involving Se, SeH, SeH₂, SeO, SeO₂, SeCl, SeCl₂, and SeOH were considered. For each species, calculated geometries and vibrational frequencies were compared to experimental data. Reaction enthalpies were calculated at a variety of temperatures and compared to experiment at 298.15 K. The Gibbs free energy of reaction and corresponding equilibrium constant were calculated for each reaction and plotted as a function of temperature to find the linear relationship between ln(k_eq) and 1/T describing each reaction's thermodynamics. It was found that SeO and SeO₂ are the most thermodynamically favorable products and the formation pathways of SeCl, SeCl₂, and SeH₂ are also possible.