Kinetics and reaction chemistry of catalytic hydrodechlorination of chlorinated benzenes on sulfided nickel-molybdenum/gamma aluminum oxide

Catalytic hydroprocessing has recently emerged as a treatment and recycling process for waste streams containing chlorinated organics. Compounds such as polychlorinated biphenyls (PCBs), and pentachlorophenol (PCP) can be effectively treated using this chemistry. These applications have created a need for rate and mechanism data for these reactions. In this work, the catalytic hydrodechlorination reactions of hexachlorobenzene and all of its partially dechlorinated intermediates over NiMo/{dollar}gamma{dollar}Al{dollar}sb2{dollar}O{dollar}sb3{dollar} hydroprocessing catalyst were examined in a differential microflow reactor. The NiMo catalyst was chosen after a screening study revealed that it had high activity and selectivity for dechlorination. Based on chlorobenzene hydrodechlorination data at 275-375{dollar}spcirc{dollar}C, a kinetic model was proposed where the rates of adsorption and surface reaction were comparable and neither controlled the overall reaction rate. The dechlorination rate data of hexachlorobenzene and other chlorinated benzenes point toward the presence of steps that involve multiple chlorine removal. Not all possible intermediates are formed; all of the observed intermediate dechlorination steps proceed at comparable rates.