Perchloroethylene gas-phase degradation over titania-coated transparent monoliths

Abstract

Perchloroethylene (PCE) has been detected as one of the major pollutants in indoor air of wastewater treatment plants (WWTPs) with closed facilities. Its hazardousness requires the complete PCE removal from air. For this reason, gas-phase photooxidation of PCE was studied in a continuous-flow tubular photoreactor under simulated solar radiation. Since negligible degradation of PCE was observed by photolysis, photocatalytic oxidation (PCO) experiments were carried out employing a catalytic bed of cellulose acetate monoliths (CAM) coated with TiO2 (TiO2-CAM). The three TiO2-CAM samples tested (3, 6, and 9 TiO2 dip-coating layers), showed that the catalytic activity increases considerably with the number of layers (similar to 92% for the 9-layered TiO2-CAM). Different conditions of feed flow rate, pollutant concentration, feed relative humidity, and incident irradiance were tested for the 9-layered TiO2-CAM photocatalyst in order to assess the most relevant operating parameters. Taking into consideration the small path of the photoreactor employed (0.16 m length), PCO of PCE showed interesting results, achieving degradation efficiencies between 90 and similar to 98%, depending on the operating conditions used. The mathematical modelling of PCE kinetics through PCO suggested that there is no competition between PCE and H2O molecules to the surface active sites, even considering them as independent molecules that target distinct surface active sites (Langmuir-Hinshelwood bimolecular competitive two types of sites rate model). The validation of the PCO mathematical model at lab-scale allowed predictive simulations for PCO of PCE that can be used for possible scale-up a unit aiming at completely mineralization of PCE under solar irradiation. Finally, identification of PCE by-products allowed the complete formulation of a feasible reaction mechanism.