Abstract

Heterogeneous ultraviolet photocatalytic oxidation (UV-PCO), as a promising advanced oxidation technology, has been suggested as an alternative and energy efficient method to improve indoor air quality (IAQ) through the photocatalytic degradation of indoor air pollutants. However, the complicated PCO reaction mechanisms and unexpected intermediates still need to be further explored in order for this technology to be successfully applied in mechanically ventilated buildings.
Two main objectives of this study include the development of methodologies to evaluate the performance of PCO systems and the development of a reliable mathematical model to fully simulate the performance of these systems.
A pilot four-parallel duct system was set-up to equitably and thoroughly evaluate the performance of UV-PCO air cleaners under the conditions relevant to the actual applications for a wide range of indoor air pollutants. This study investigated the UV-PCO removal efficiency of two types of air filters (fiberglass fibers coated with TiO2 (TiO2/FGFs) and carbon cloth fibers loaded with TiO2 (TiO2/CCFs)) under ultraviolet C (UVC) and vacuum ultraviolet (VUV) illumination. A systematic parametric evaluation of the effects of various kinetic parameters, such as types of pollutants, inlet concentration, airflow rate, light intensity, and relative humidity that influence the PCO performance, was conducted. In addition, gas-phase ozonation with a variety of chemical compounds was first examined when ozone was produced by VUV. Moreover, the formation of by-products generated from incomplete conversion was investigated to evaluate its impact on IAQ.
A time-dependent model was proposed for predicting the performance of an in-duct PCO air cleaner under the conditions relevant to the actual applications. A comprehensive model was developed by integrating light scattering model, reaction kinetic model, mass balance as well as optional ozonation model. The UV-PCO model and the UV-PCO ozonation integrated model were validated with experimental results; there was a good agreement between the model prediction and the experiment result. The relative rate-limiting process between physical interactions and photochemical interactions was fully investigated through simulation analysis. Depending on the physical properties of the catalyst, reactor geometries, operation conditions, as well as environmental conditions, the photochemical reaction occurring on the fixed active sites at the catalyst surface is the dominating process for this PCO system.