(608b) Activated Carbon and Mercury Interactions
Mercury is reported as a hazardous air pollutant (HAP) by The Clean Air Act (CAA) of 1990. Currently within the United States there are over five hundred 500-megawatt coal-fired power plants and 50 tons mercury/year are emitted. To predict the level of mercury emissions from coal-fired power plants it is important to understand its heterogeneous pathway. Many studies indicate that the mechanism of mercury adsorption on activated carbon surfaces is complicated and depends on mercury speciation, flue-gas temperature, active sites on the sorbent surface and effect of other flue gases. Density functional theory calculations are carried out to investigate the binding of mercury on simulated activated carbon surfaces. Activated carbon is modeled as graphene repeated in the x-y planes. The active sites are formed either by removing the carbon atoms on the graphene edges or creating unsaturated carbon atoms at the edge sites. The edge sites are functionalized with halogens such as chlorine or bromine. The mechanism of mercury binding in the presence of active sites is investigated by considering both heterogeneous oxidation of mercury on the surface and the possible oxidized forms of mercury. Density of states (DOS) analysis is carried out to interpret the binding energies calculated on active sites of activated carbon to explain the mechanism of mercury binding. Experimental studies are also conducted using a bench-scale packed-bed system to further understand the interaction of mercury and activated carbon-based sorbents. Flue gas is simulated by burning methane in a laminar flow tubular burner. An electron ionization quadrupole mass spectrometer is used to analyze the outlet gas stream coming from the reactor and directly speciate between the oxidized forms of mercury in the gas phase.