Relative Resistance of Positional Isomers of Polychlorinated Biphenyls toward Reductive Dechlorination by Zerovalent Iron in Subcritical Water

Relative resistance of positional isomers within the same homologue of polychlorinated biphenyls (PCBs) was studied by comparing the reduction efficiencies (REs) of these isomers by 100-mesh zerovalent iron in subcritical water at 250 °C and 10 MPa. The REs for meta and para isomers were found to be significantly higher than that of the ortho's. These results revealed that variation in relative resistance of the positional isomers to reductive dechlorination does exist, and the order increases from para to meta to ortho substituents. This variation in relative resistance to reduction is correlated with the lowest unoccupied molecular orbital (LUMO) energy of individual PCB congeners. A model based on the empirical relative resistance of the PCBs to reductive dechlorination is developed, and an equation is established to predict the efficiency of a reductive dechlorination system that employs zerovalent iron and pressurized hot water.