Trichloroethylene-promoted photocatalytic oxidation of air contaminants

The prospects for photocatalytic purification and treatment of air depend centrally on finding conditions for which the apparent photoefficiency for contaminant disappearance is near or above 100%. We recently demonstrated that destruction of a low photoefficiency contaminant, toluene, by addition of a high photoefficiency compound, trichloroethylene, could raise the toluene photoefficiency to provide 100% conversion in a single pass, fixed bed illuminated catalyst, using a residence time of about 5-6 ms. The present paper establishes the generality of this TCE enhancement of contaminant rate and photoefficiency by examining the photocatalytic oxidation of various common contaminants at 50 mg/m(3) in air, including alcohols, aldehydes, ketones, aromatics, and chloroalkanes using near-UV-illuminated titanium dioxide powder in a flow reactor, in the absence and presence of trichloroethylene (TCE). Compounds exhibiting TCE rate promotion were toluene, ethylbenzene, m-xylene, methyl ethyl ketone (MEK), acetaldehyde, butyraldehyde, methyl tert-butyl ether (MTBE), methyl acrylate, 1,4-dioxane, and hexane. Rate inhibition by TCE was exhibited for acetone, methylene chloride, chloroform, and 1,1,1-trichloroethane. TCE presence had almost no effect on the benzene and methanol rates. Butanol and vinyl acetate single component conversions were 100% under our standard low flow rate conditions; increasing the flow rate quenched TCE conversion in the presence of butanol, and therefore no TCE enhancement effect could be noted. (C) 1997 Academic Press.