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 photocatalytic oxidation of the off-gases produced may be an effective remediation technology for a variety of soil and water contamination problems, particularly those involving chlorinated ethylenes. To test the hypothesis that reduced pressure operation of the photocatalytic unit could enhance reactor performance, a bench-scale annular photocatalytic reactor operating in the vacuum range was designed, built, and evaluated. The reactor inner wall was coated with sol-gel-derived titania to provide a uniform, adherent, photocatalytically active thin film. Photocatalytic oxidation of trichloroethylene (TCE) in humid airstreams was employed as a model chemistry. Reduction of the operating pressure at fixed feed conditions and molar feed rate significantly enhanced PCO performance as measured by the observed TCE conversion. Higher conversions were obtained in spite of a reduction in the residence time accompanying the lower pressure operation. The greatest enhancements in the 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 competition between TCE and water vapor for adsorption sites on the catalyst.