Role of Activated Carbon Precursor in Mercury Removal

Adsorption studies of contaminants using activated carbon do not always take into consideration the raw material used in its production. Mercury adsorption mechanisms governed by carbene sites are more significant when graphitic-like activated carbons are employed versus lignocellulosic-based activated carbons, whose carbon rings are less aromatic. In this laboratory, fixed-bed study, bituminous coal-based activated carbon was compared to coconut- and wood-based activated carbons (both less aromatic) for elemental mercury removal in nitrogen at 25 °C. Activated carbon produced from bituminous coal performed far better for mercury adsorption compared to the more aliphatic-derived activated carbons from coconut shells and wood. The results showed no correlation between mercury removal and the activated carbon physical properties including Brunauer-Emmett-Teller surface area, pore size, or pore volume. When the bituminous coal-based activated carbon was hydrogen-treated at 850 °C to stabilize its carbene sites, the resulting mercury breakthrough curve became very similar to that of the wood- and coconut-based carbons. It is hypothesized this phenomenon is a result of stabilization of carbene sites which are more available in aromatic carbons. By the direct impact of carbene stabilization on mercury adsorption, it can be concluded that carbene sites and their abundance are an essential part of mercury adsorption.