Photocatalytic oxidation of multi-component systems - An investigation using toluene/ethylbenzene, octane/decane/dodecane and formaldehyde/acetaldehyde

In the design of UV-PCO-based air cleaners for improving IAQ, multiple compounds interference effects need to be quantified because indoor environment has multiple VOCs under low concentrations (typically at ppb and sub-ppb levels). This paper presents a systematic experimental investigation using a lab-scale UV-PCO reactor under individual vs. multiple VOC challenges. Tests were conducted for two aromatics (toluene and ethylbenzene) and two aldehydes (formaldehyde and acetaldehyde) as individual compound and binary mixture, and three alkanes (octane, decane and dodecane) as individual compound, binary and ternary mixtures. An annular tube reactor coated with Degussa TiO₂/3% WO₃ (by weight) was placed in a small-scale (50 L) stainless steel chamber. The test chamber had a continuous feed flow and the system operated as a continuous stirred tank reactor. The concentration of test VOCs at chamber inlet ranged from 0.5 to 35 mg/m³. The overall reaction rates were measured. The mass transfer effects were quantified. The average reaction rate constants were then determined. Reversible deactivations were observed for toluene and ethylbenzene as individual VOCs and as mixture. For the individual compound tests, the bimolecular L-H rate form fit experimental data best. For the binary mixture tests, the bimolecular L-H rate model with the binary component competitive adsorption considered described the trend of experimental data well, and the rate coefficients from the PCO reaction of individual compound could apply. As for alkanes and aldehydes, the reaction rate was linearly dependent on the reactant concentration within the tested concentration range. The competition/interference effects between different compounds (except octane in one ternary mixture test) were insignificant under test conditions. Results also indicate that mass transfer resistance needs to be considered under low VOC concentration levels and high UV intensities (typical for an annular tube reactor as UV lamp is in the middle of the tube) because it is likely in the same order of magnitude as the reaction resistance.