Kinetic and reaction mechanism of generated by-products in a photocatalytic oxidation reactor: Model development and validation

Photocatalytic oxidation is a promising technology to control air pollution. However, the formation of hazardous by-products hinders the commercialization application of this technology. This paper reports the development of a novel by-products predictive model considering the mass transfer of the pollutant in the gas phase and kinetic reaction in the solid phase. Two challenge compounds from ketone group (acetone and methyl ethyl ketone) were examined for model validation in a continuous Photocatalytic Oxidation (PCO) reactor with TiO2 coated on silica fiber felts. A possible reaction pathway for degradation of each challenge compound was proposed based on identified by-products using analytical methods (GC-MS and HPLC). Formaldehyde, Acetaldehyde, Propionaldehyde, Ethanol, and acetic acid were detected as by-products of the Acetone and Methyl Ethyl Ketone in the PCO reactor. 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, namely concentration, relative humidity, irradiation, and velocity variations. Higher concentration and irradiation, as well as lower relative humidity and velocity, resulted in more by-products generation. It was also observed that with enhancing residence time, mineralization efficiency (or CO2 formation) and by-products generation increases through PCO reaction. The model validation provided acceptable accuracy for both steady-state and transient conditions. Finally, the Health Risk Index was used to investigate the implications of generated by-products on human health under varying operating conditions.

Automated summary

Photocatalytic oxidation is a promising technology for controlling air pollution, but the formation of hazardous by-products is a challenge for its commercial application. This study developed a novel predictive model for by-products and validated it with ketone compounds in a PCO reactor. The model considered mass transfer and kinetic reactions in the gas and solid phases, showing that concentration, humidity, irradiation, and velocity variations affect the generation of by-products.