Theoretical research on mercury-laden halogenated activated carbon adsorbent product stability

Abstract

Halogenated activated carbon adsorbent has exhibited superior mercury capture efficiency in the flue gas. Not only the fabrication of effective adsorbents, but the used adsorbents stability is also crucial, which is essentially determined by product bonding nature. Here, Density functional theory was employed to investigate spent halogenated activated carbon adsorbents bonding nature at the electronic level. Seven possible mercury-containing product geometries and effects of halogen species (X = Cl / Br / I) were all considered. Precisely, bond length value, and Mayer bond order of Hg-C, Hg-X and C-X bonds were calculated to indicate product stability in the gaseous phase. It was found that mercury was bonded on the carbonaceous surface with C-Hg Mayer bond order around 0.5 in product structures G and H, suggesting a weak interaction. Moreover, effects of halogen species in X-Hg and C-X bond strength follow the order of I > Br > Cl. Additionally, electron localization function and localized orbital locator were employed to determine electron high localization regions. In summary, this study analyzed the bonding nature of used halogenated activated carbon adsorbents. The results are beneficial for fabricating more environmental-friendly mercury removal adsorbents in the future.