Photocatalytic Reactor System with Tungsten Oxide-Modified Titanium Dioxide for Indoor Air Applications

An experimental evaluation of an ultraviolet photocatalytic oxidation (UVPCO) device with tungsten oxide-modified titanium dioxide as the photocatalyst is reported. This was a scaled device developed to demonstrate air purification when installed in a HVAC system of a commercial building. There were two 30 by 30-cm honeycomb monoliths and 12 18-Watt UVC lamps arranged in three banks. The evaluation employed several mixtures of volatile organic compounds (VOCs). One mixture contained 27 VOCs frequently identified as air pollutants in office buildings. Another mixture comprised 10 VOCs emitted by household cleaning products. A third mixture contained just formaldehyde and acetaldehyde. The concentrations of the mixtures and the air flow rate through the UVPCO were manipulated as variables. Summed mixing ratios of VOCs ranged from 54 to 780 ppb, with the mixing ratios of many individual VOCs maintained below 10 ppb. Device air flow rates were 165 to 580 m³/h. Replicated air samples for the analysis of VOCs, low molecular weight carbonyls, and carboxylic acids were collected simultaneously both upstream and downstream of the reactor section. These were analyzed by thermal desorption GC/MS, HPLC and ion chromatography, respectively. Single-pass conversion efficiencies and clean air delivery rates were calculated for each VOC in inlet air. The generation of products of incomplete oxidation (carbonyls and acids) was quantified.