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 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 O2 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, CCl4 transformation was faster than CHCl3, and TCE reduction was faster than PCE. Rates of both CCl4 and PCE transformation increased substantially with temperature in the range of 30-70 degrees C. At 70 degrees C and a potential (potential of the cathode minus that of the anode) of -0.4 V, single-pass CCl4 conversions were approximately 90%. Mean residence time for gases in the porous cathode was much less than 1 s. The presence of even 5% O2(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.

Dioxygen solubility in aqueous phosphatidylcholine dispersions.

The solubility of molecular oxygen, or dioxygen, in low weight percent (1.5%) sonicated dimyristoylphosphatidylcholine (DMPC) aqueous dispersions saturated with air has been measured as a function of temperature between 10 degrees C and 40 degrees C. A modified Winkler technique was used involving a dual cell coulometric titration with voltammetric endpoint detection in a mixed solvent (methanol/water). The results indicate that dioxygen is approximately four times more soluble in the liquid crystalline bilayers (above 24 degrees C) than in the gel state bilayers (below 24 degrees C). The solubility of dioxygen in the bilayer does not appear to be strongly temperature dependent on either side of the 24 degrees C phase transition. The dioxygen solubility in gel state DMPC is approximately equal to that in water at the same temperature. Our result are contrasted with recent measurements made using EPR spin labels.