Electrocatalytic Dechlorination of 2-Chlorobiphenyl at a Palladium Modified Granular-Graphite-Packed Electrode
Yuanxiang Fang, National Risk Management Research Laboratory, US EPA/ ORISE, Cincinnati, OH 45268 and Souhail Al-Abed, National Risk Management Research Laboratory, US EPA, Cincinnati, OH 45268.
Polychlorinated biphenyls (PCBs) and other chlorinated aromatic compounds contaminated soils and sediments over 400 sites in the USA. A national need exists for both in situ and ex situ methods to treat these persistent organic pollutants in soils and sediments at ambient temperature. Common remediation technologies such as bioremediation were unable to effectively treat PCB contamination in the field, but laboratory studies have demonstrated a potential technology for PCB contamination using an electrocatalytic technique. This talk presents the electrocatalytic dechlorination of 2-chlorobiphenyl (2-Cl BP) in aqueous and solvent-water solutions at a palladium modified granular-graphite-packed electrode inside a membrane reactor. 2-Cl BP, a PCB congener that requires the highest reduction potential, was effectively dechlorinated in the electrocatalytic membrane reactor. For highly chlorinated biphenyls, methanol was added to increase the solubility of PCBs in the electrolytes. Experimental results revealed significant decreases in the rate and extent of dechlorination of 2-Cl BP as the methanol concentration increased. The dechlorination process proceeded simultaneously with the adsorption of the reactant and the product on the granular graphite. A mathematical model was developed for the electrocatalytic reactor to describe both adsorption and electrocatalytic dechlorination. Numerical modeling of the electrolytic reactor performances helped to estimate the rate and extent of dechlorination as well as the amount of 2-Cl BP adsorbed on the granular graphite. The effect of solvents on dechlorination, caused in part by the changed PCB partitioning between the liquid and electrode, were demonstrated in the changes of the rate constant and the apparent reaction equilibrium constant.