Impact of Surface Functional Groups, Water Vapor, and Flue Gas Components on Mercury Adsorption and Oxidation by Sulfur-Impregnated Activated Carbons

Coconut-shell activated carbon and activated carbon fiber (ACF) were impregnated with sulfur at 400 and 650 degrees C, and then the resulting physical properties of these adsorbents, the functional groups formed, and the adsorption and oxidation of Hg-0 occurring on the adsorbents were evaluated. The change in the properties of the adsorbents after sulfur impregnation was strongly affected by the inherent physical and chemical properties of the starting samples and treatment temperature. The sulfur content of the samples increased when the sulfur impregnation temperature was decreased. At 650 degrees C, sulfur acted as both a dopant and a chemical activator and thereby broadened the porous structures that cause a reduction in the micropore surface and increase the total surface area of ACF. Furthermore, Hg-0 adsorption and oxidation were enhanced after sulfur impregnation, strongly affected by flue gas components and various surface active sites, and greatly increased by the sulfur introduced at 400 degrees C. The original oxygenated groups present on the carbon surface effectively interacted with Hg-0 and flue gas components to form oxidized Hg, but these groups did not appear to act as strongly adsorptive sites and capture the oxidized Hg. The sulfur groups introduced at 650 degrees C were stronger adsorptive sites than the oxygenated groups, but the sulfur sites were not effective oxidative sites, especially in the presence of H2O.