Gas phase trichloroethylene (TCE) photooxidation and byproduct formation: photolysis vs. titania/silica based photocatalysis

Photooxidation of trichloroethylene (TCE) was examined in comparative study using photolysis and photocatalysis. Degussa P25 titania coated on reactor wall and deposited on silica based microporous support were used as photocatalyst. The destruction of TCE and formation of potential byproducts were investigated under steady state conditions using annular photoreactors. Experimental work involved passing polluted air containing TCE through the UV photoreactor at varying concentrations and residence times. Ultraviolet illumination was provided by low pressure mercury lamps with outputs at either 254 nm, 365 nm, or 185/254 nm. Silica supported photocatalyst yielded maximum removal capacity of up to about 6 kg TCE per m3 per hour, nearly twice that provided by the coated titania. Direct photolysis with ozone generating UV also provided very high TCE conversion of up to 6 kg TCE per m3 per hour. However, major quantities of phosgene and dichloroacetyle chloride (DCAC) were produced as byproducts. TCE removal using silica based photocatalyst did not result in any detectable DCAC. Only phosgene along with trace amounts of chloroform and carbon tetrachloride were identified as oxidation byproducts with silica based photocatalyst.