Impact of Surface Heterogeneity on Mercury Uptake by Carbonaceous Sorbents: Bridging the Pressure Gap from UHV to Atmospheric Conditions

摘要

Chemical and morphological heterogeneities of carbon-based adsorbents play importantroles in gas-phase adsorption. However, specific chemical complexes and topological structuresof these adsorbents that favor or impede elemental mercury uptake are not well understood andare the subject of this study. Temperature programmed desorption (TPD) with a modelcarbonaceous material (highly oriented pyrolytic graphite, HOPG) under ultra-high vacuum(UHV) conditions and fixed bed adsorption by activated carbon (BPL) at atmospheric pressurewere combined to investigate the effects of chemical and morphological heterogeneities onmercury adsorption by carbonaceous surfaces. TPD results show that mercury adsorption at 100K onto HOPG surfaces with and without chemical functional groups and topologicalheterogeneity created by plasma oxidation occurs through physisorption. The removal ofchemical functionalities from the HOPG surface enhances mercury physisorption. Plasmaoxidation of HOPG provides additional surface area for mercury adsorption. However, the pitscreated by plasma oxidation are more than 100 nm in diameter and do not simulatemicroporosity that predominates in activated carbons. Mercury adsorption by activated carbon atatmospheric pressure occurs through two distinct mechanisms. Physisorption governs mercuryadsorption at temperatures below 348 K while chemisorption predominates at adsorptiontemperature above 348 K. Presence of water on activated carbon surface enhances mercuryuptake by both physisorption and chemisorption. Oxygen containing functional groups reducemercury uptake by physisorption by blocking access to the micropores, while no significantimpact of on chemisorption was observed in this study. The key findings of this study open thepossibility to apply scientific information obtained from the studies with simple surfaces likeHOPG under ideal conditions (UHV) to industrial sorbents under realistic process conditions.