Potential use of a combined ozone and zeolite system for gaseous toluene elimination

This study investigated the performance of a combined ozone and zeolite system in eliminating gaseous toluene which is a major contaminant in many industrial and indoor environments. The hypothesis that the removal of toluene by ozone can be substantially affected by confining the oxidation reaction in a zeolite structure was evaluated. The degradation of toluene seemed to be contributed by the active oxygen atom generated from the decomposition of ozone at the Lewis acid sites in the zeolite 13X. Air containing toluene levels at 1.5, 2 and 3 ppm was injected with ozone in the range of 0-6 ppm before being vented into a fixed amount of 3600 g zeolite 13X with 90 mm bed-length. The experimental results showed that the elimination rate of toluene was significantly enhanced when compared to using zeolite or ozone alone. In particular, over 90% of the 1.5 ppm toluene was removed when 6 ppm ozone was used at 40% relative humidity level. Deactivation of the zeolite 13X after a few hours of reactions under the current experimental conditions was probably due to the adsorbed water, carbon dioxide and the reaction by-products. The residue species left in the zeolite and the intermediate species in the exhaust gas stream were characterized by FT-IR, GC-MS and HP-LC methods, respectively. A distinctive peak of O atom attached to the Lewis acid site at 1380 cm^-1 was found in the FT-IR spectrum and trace amount of aldehydes was found to be the reaction by-products.