Performance of ultraviolet photocatalytic oxidation for indoor air cleaning applications
- 1 August 2007
- journal article
- Published by Hindawi Limited in Indoor Air
- Vol. 17 (4), 305-316
- https://doi.org/10.1111/j.1600-0668.2007.00479.x
Abstract
Ultraviolet photocatalytic oxidation (UVPCO) systems for removal of volatile organic compounds (VOCs) from air are being considered for use in office buildings. Here, we report an experimental evaluation of a UVPCO device with tungsten oxide modified titanium dioxide (TiO2) as the photocatalyst. The device was challenged with complex VOC mixtures. One mixture contained 27 VOCs characteristic of office buildings and another comprised 10 VOCs emitted by cleaning products, in both cases at realistic concentrations (low ppb range). VOC conversion efficiencies varied widely, usually exceeded 20%, and were as high as approximately 80% at about 0.03 s residence time. Conversion efficiency generally diminished with increased airflow rate, and followed the order: alcohols and glycol ethers > aldehydes, ketones, and terpene hydrocarbons > aromatic and alkane hydrocarbons > halogenated aliphatic hydrocarbons. Conversion efficiencies correlated with the Henry's law constant 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 provided reasonable estimates of pseudo-first order photocatalytic reaction rates. Formaldehyde, acetaldehyde, acetone, formic acid and acetic acid were produced by the device due to incomplete mineralization of common VOCs. Formaldehyde outlet/inlet concentration ratios were in the range 1.9-7.2. Implementation of air cleaning technologies for both VOCs and particles in office buildings may improve indoor air quality, or enable indoor air quality levels to be maintained with reduced outdoor air supply and concomitant energy savings. One promising air cleaning technology is ultraviolet photocatalytic oxidation (UVPCO) air cleaning. For the prototype device evaluated here with realistic mixtures of VOCs, conversion efficiencies typically exceeded the minimum required to counteract predicted VOC concentration increases from a 50% reduction in ventilation. However, the device resulted in the net generation of formaldehyde and acetaldehyde from the partial oxidation of ubiquitous VOCs. Further development of the technology is needed to eliminate these hazardous air pollutants before such a UVPCO device can be deployed in buildings.Keywords
This publication has 28 references indexed in Scilit:
- Photocatalytic degradation of some VOCs in the gas phase using an annular flow reactor: Determination of the contribution of mass transfer and chemical reaction steps in the photodegradation processJournal of Photochemistry and Photobiology A: Chemistry, 2006
- Meeting Report: Summary of IARC Monographs on Formaldehyde, 2-Butoxyethanol, and 1- tert -Butoxy-2-PropanolEnvironmental Health Perspectives, 2005
- Measuring the Effect of Photocatalytic Purifiers on Indoor Air Hydrocarbons and Carbonyl PollutantsJournal of the Air & Waste Management Association, 2005
- Inhibition effect of SO2 on NOx and VOCs during the photodegradation of synchronous indoor air pollutants at parts per billion (ppb) level by TiO2Applied Catalysis B: Environment and Energy, 2004
- Photocatalytic oxidation of ketones in the gas phase over TiO2 thin films: a kinetic study on the influence of water vaporApplied Catalysis B: Environment and Energy, 2003
- Gas–solid adsorption of selected volatile organic compounds on titanium dioxide Degussa P25Chemical Engineering Science, 2003
- Ozone-Initiated Reactions with Mixtures of Volatile Organic Compounds under Simulated Indoor ConditionsEnvironmental Science & Technology, 2003
- Performance and costs of particle air filtration technologiesIndoor Air, 2002
- Photodegradation of volatile organic compounds (VOCs) and NO for indoor air purification using TiO2: promotion versus inhibition effect of NOApplied Catalysis B: Environment and Energy, 2002
- Mass spectrometry on-line monitoring and MS2 product characterization of TiO2/UV photocatalytic degradation of chlorinated volatile organic compoundsJournal of the American Society for Mass Spectrometry, 1998