Abstract

The presence of volatile organic compounds (VOCs) in indoor air is inevitable. Their adverse effect on human health has encouraged researchers to develop various technologies for air pollution remediation. Photocatalytic oxidation (PCO) has been regarded as a promising and emerging technique for air purification and extensively investigated in the last two decades to characterize and improve the effectiveness and performance of this technology. In addition, the development of appropriate models can enhance the understanding of reactor performance and the evaluation of intrinsic kinetic parameters that enable the scale-up or re-design of more efficient large-scale photocatalytic reactors.
This research works on mathematical modeling of gas phase photocatalytic reactors and analyses different key factors that can enhance pollutants decomposition. At the first step, a one-dimensional time-dependent mathematical model for continuous flow UV-PCO reactor has been developed. In this model, transfer of pollutants by advection and dispersion in bulk phase incorporates with the reaction rate based on the extended Langmuir Hinshelwood model in the catalyst phase. CFD modeling was also used to determine the flow distribution in the reactor at various airflow rates. Moreover, the light intensity distribution on the photocatalyst surface was simulated using the linear source spherical emission model. A dimensionless form of the model was then proposed to generalize the result for any scale. The proposed model was validated first by comparing with predictions of other models (inter-model comparison) and then by experimental data from two different scales (pilot and bench) of UV-PCO reactors. Furthermore, a sensitivity analysis using dimensionless parameters was conducted to find the controlling step in the PCO process. To validate the model, acetone, MEK, and toluene were tested in the UV-PCO reactor with a commercial PCO filter (TiO2 coated on silica fiber felts) at various operating conditions, such as concentration, relative humidity, irradiance and air velocity.
The main issue for applying PCO technology in the indoor environment is the generation of hazardous by-products. The effect of by-products formation was usually ignored in former modeling studies. The next effort was to improve the model and build a comprehensive one to consider by-products generation in the UV-PCO reactor. To achieve this goal, a possible reaction pathway for degradation of each challenge compound was proposed based on identified by-products in analytical methods (GC-MS and HPLC). Different possible reaction rate scenarios were evaluated to find the best expression fitted to experimental data at the steady-state condition. The obtained reaction coefficients were then used to validate the model under various operating conditions. Finally, the Health Risk Index was used to investigate the implications of generated by-products on human health under varying operating conditions. The results indicated that the proposed model has a great potential to simulate the behavior of UV-PCO reactor in a real application.