VACUUM PHOTOCATALYTIC OXIDATION OF TRICHLOROETHYLENE

The combination of physical removal methods such as soil vapor vacuum extraction or vacuum air stripping with gas-solid heterogeneous photoc atalytic oxidation of the off-gases produced may be an effective remed iation technology for a variety of soil and water contamination proble ms, particularly those involving chlorinated ethylenes. To test the hy pothesis that reduced pressure operation of the photocatalytic unit co uld enhance reactor performance, a bench-scale annular photocatalytic reactor operating in the vacuum range was designed, built, and evaluat ed. The reactor inner wall was coated with sol-gel-derived titania to provide a uniform, adherent, photocatalytically active thin film. Phot ocatalytic oxidation of trichloroethylene (TCE) in humid airstreams wa s employed as a model chemistry. Reduction of the operating pressure a t fixed feed conditions and molar feed rate significantly enhanced PCO performance as measured by the observed TCE conversion. Higher conver sions were obtained in spite of a reduction in the residence time acco mpanying the lower pressure operation. The greatest enhancements in th e TCE destruction efficiency occurred for low TCE feed concentrations and high water vapor levels. The performance enhancement appears to be linked to reduction in the absolute water vapor concentration and com petition between TCE and water vapor for adsorption sites on the catal yst.