A Comparative Study on Degradation of BTEX Vapor by O-3/UV, TiO2/UV, and O-3/TiO2/UV System with Operating Conditions

A multilayer tower-type photoreactor, in which TiO2-coated glass-tubes were installed, was used to measure the vapor-phase BTEX removal efficiencies by ozone oxidation (O-3/UV), photocatalytic oxidation (TiO2/UV) and the combination of ozone and photocatalytic oxidation (O-3/TiO2/UV) process, respectively. The experiments were conducted under various relative humidities, temperatures, ozone concentrations, gas flow rates and BTEX concentrations. As a result, the BTEX removal efficiency and the oxidaion rate by O-3/TiO2/UV system were highest, compared to O-3/UV and TiO2/UV system. The O-3/TiO2/UV system accelerated the low oxidation rate of low-concentration organic compounds and removed organic compounds to a large extent in a fixed volume of reactor in a short time. Therefore, O-3/TiO2/UV system as a superimposed oxidation technology was developed to efficiently and economically treat refractory VOCs. Also, this study demonstrated feasibility of a technology to scale up a photoreactor from lab-scale to pilot-scale, which uses (i) a separated light-source chamber and a light distribution system, (ii) catalyst fixing to glass-tube media, and (iii) unit connection in series and/or parallel. The experimental results from O-3/TiO2/UV system showed that (i) the highest BTEX removal efficiencies were obtained under relative humidity ranging from 50 to 55% and temperature ranging from 40 to 50 degrees C, and (ii) the removal efficiencies linearly increased with ozone dosage and decreased with gas flow rate. When applying Langmuir-Hinshelwood model to TiO2/UV and O-3/TiO2/UV system, reaction rate constant for O-3/TiO2/UV system was larger than that for TiO2/UV system, however, it was found that adsorption constant for O-3/TiO2/UV system was smaller than that for TiO2/UV system due to competitive adsorption between organics and ozone.