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

The reductive dehalogenation of gas-phase chlorinated alkanes (CCl4, CHCl3, and 1,1,1-trichloroethane) and alkenes (perchloroethene (PCE) and trichlor oethene (TCE)) was conducted in a modified fuel cell. The fuel-cell perform ance was a function of cathode material, electric potential, temperature, t arget compound identity and gas-phase concentration, partial pressure Of O- 2 in the cathode chamber, and cathode condition (time in service). TICE con version was approximately first order in TCE concentration with half-lives of fractions of a second. Under the same reactor conditions, CCl4 transform ation was faster than CHCl3, and TICE reduction was faster than PCE. Rates of both CCl4 and PCE transformation increased substantially with temperatur e in the range of 30-70 degreesC. At 70 degreesC and a potential (potential of the cathode minus that of the anode) of -0.4 V, single-pass CCl4 conver sions were approximately 90%. Mean residence time for gases in the porous c athode was much less than 1 s. The presence of even 5% O-2(g) in the influe nt to the cathode chamber had a deleterious effect on reactor performance. Performance also deteriorated with time in service, perhaps due to the accu mulation of HCl on the cathode surface. Conversion efficiency was restored, however, by temporarily eliminating the halogenated target(s) from the inf luent stream or by briefly reversing fuel-cell polarity.