Performance of ultra-violet Photocatalytic Oxidation for Indoor Air Cleaning Applications

Acceptable indoor air quality in office buildings may be achieved with less energy by combining effective air cleaning systems for volatile organic compounds (VOCs) with particle filtration than by relying solely on ventilation. For such applications, ultraviolet photocatalytic oxidation (UVPCO) systems are being developed for VOC removal. An experimental evaluation of a UVPCO system with tungsten oxide modified titanium dioxide as the photocatalyst is reported. The evaluation is unique in that it employed complex VOC mixtures. One of the mixtures contained 27 VOCs commonly found in office buildings, and the other comprised 10 VOCs emitted by cleaning products, in both cases at realistically low concentrations. VOC conversion efficiencies varied over a broad range, usually exceeded 20%, and were as high as ~80%. Conversion efficiency generally diminished with increased air flow rate, and followed the approximate order: alcohols and glycol ethers > aldehydes, ketones, and terpene hydrocarbons > aromatic and alkane hydrocarbons > halogenated aliphatic hydrocarbons. Conversion efficiencies were observed to correlate with the Henry's law constant of the studied VOCs more closely than with other physicochemical parameters. An empirical model based on the Henry's law constant and the gas-phase reaction rate with hydroxyl radical facilitated an estimate of pseudo-first order photocatalytic reaction rates for the studied VOCs. Significant amounts of formaldehyde and acetaldehyde were produced due to incomplete mineralization suggesting that safe deployment of UVPCO in buildings likely will require mitigation methods for these undesirable pollutants.