Optimization of sulfur impregnation protocol for fixed bed application of activated carbon-based sorbents for gas-phase mercury removal

Novel sulfur-impregnated activated carbons for vapor phase mercury uptake (BPL-S series) were designed and developed in this study. Temperature and the initial sulfur to carbon ratio (SCR) during impregnation were the two control parameters for the impregnation procedure. By adjusting these two variables, a series of sulfur-impregnated carbons was created. These new materials together with commercially available sulfur-impregnated activated carbon (HGR) and coal samples were evaluated for the uptake of vapor phase elemental mercury using nitrogen as a carrier gas. The results showed that carbons impregnated with sulfur at high temperature exhibited the highest efficiency for mercury removal. As the impregnation temperature decreased, the performance of the carbons deteriorated. When SCR was varied from 4:1 to 1:2, the sulfur content decreased only slightly, which resulted in a small decrease in mercury uptake capacity. Therefore, the impregnation temperature is the most important factor influencing the efficiency of these sorbents for mercury uptake. Because the impregnation temperature dictates the predominant form of sulfur allotropes, it can be concluded that the actual form of sulfur rather than the total sulfur content is a crucial parameter governing the chemisorption process. Stronger bonding between sulfur and carbon surface was found for carbons impregnated at higher temperatures. This prevents sulfur from agglomerating and clogging the carbon pores during column runs at elevated temperatures. Large surface areas and large fractions of mesopores in these new sorbents also contributed to excellent mercury removal efficiencies.