Reductive dehalogenation of gas-phase chlorinated solvents using a modified fuel cell

The reductive dehalogenation of gas-phase chlorinated alkanes (CCl ₄, CHCl ₃, and 1,1,1-trichloroethane) and alkenes (perchloroethene (PCE) and trichloroethene (TCE)) was conducted in a modified fuel cell. The fuel-cell performance was a function of cathode material, electric potential, temperature, target compound identity and gas-phase concentration, partial pressure of O ₂ in the cathode chamber, and cathode condition (time in service). TCE conversion was approximately first order in TCE concentration with half-lives of fractions of a second. Under the same reactor conditions, CCl ₄ transformation was faster than CHCl ₃, and TCE reduction was faster than PCE. Rates of both CCl ₄ and PCE transformation increased substantially with temperature in the range of 30-70 °C. At 70 °C and a potential (potential of the cathode minus that of the anode) of -0.4 V, single-pass CCl ₄ conversions were approximately 90%. Mean residence time for gases in the porous cathode was much less than 1 s. The presence of even 5% O ₂(g) in the influent to the cathode chamber had a deleterious effect on reactor performance. Performance also deteriorated with time in service, perhaps due to the accumulation of HCl on the cathode surface. Conversion efficiency was restored, however, by temporarily eliminating the halogenated target(s) from the influent stream or by briefly reversing fuel-cell polarity.