Insights into UV-TiO2 photocatalytic degradation of PCE for air decontamination systems

Abstract

Perchloroethylene (PCE) has been extensively used as solvent at industrial scale, leading to water and air contamination. Its high toxicity, volatility, suspected carcinogenicity, and environmental persistence are increasingly requiring its removal from water and/or air, being the most desirable scenario its complete degradation. In this work, gas-phase photooxidation of PCE gas solutions (574-2442 ppm) were carried out in a continuous-flow tubular photoreactor under non-catalytic (UV) and catalytic (UV-TiO2) conditions. Under UV irradiation, PCE degradation was dependent on the photoreactor inner tube: conversion was negligible (similar to 0%) with a concentric soda-lime glass inner tube placed inside the photoreactor outer tube, or almost complete (98%) with a concentric quartz filter. The PCE photocatalytic oxidation (PCO) with UV-TiO2 was studied using the photoreactor with the glass inner tube (mimicking solar irradiation). Effects of PCE concentration, feed flow rate, and water vapour content on the PCE degradation through PCO were investigated. A complete mathematical model able to describe the effects of these operating parameters on the process performance was disclosed; six different kinetic rate equations were tested, suggesting that PCE and H2O molecules have to be considered in association with different specific active sites of the surface. Under steady-state conditions, by-products formation was also weighed; according to the isolated intermediates, a reaction mechanism was proposed for PCE gas-phase photooxidation.