Modeling of ternary mixture of VOCs in photocatalytic oxidation reactor for indoor air quality application

Abstract

Photocatalytic oxidation (PCO) is an innovative method of removing volatile organic compounds (VOCs) from indoor air. PCO technology employs a semiconductor (such as TiO2) and ultraviolet light to decompose VOCs via successive oxidation processes and creates CO2 and H2O as the ultimate products of complete mineralization. The greatest drawback of this technology is, however, the production of hazardous by-products. The possible health risk posed by hazardous by-products inhibits the commercial adoption of PCO-based air purifiers in the indoor environment. Modeling is a powerful tool to address the chemical interaction and mass transfer phenomenon in the PCO reactor. This study presents the modeling of a ternary mixture of VOCs and generated by-products using a proposed degradation reaction pathway. A one-dimensional mathematical model by considering the axially dispersed plug flow and Langmuir-Hinshelwood (L-H) based reaction rate as well as linear source spherical emission model (LSSE) for the irradiation distribution on the media surface were used for modeling of VOCs and by-products. Three VOCs from different chemical groups (aldehyde, ketone, aromatic groups) were chosen as challenge compounds, and a commercial PCO filter (TiO2 coated on silica fiber felts) was considered as a photocatalyst. The model prediction was performed at different levels of concentration (0.1–1 ppm), relative humidity (15–70%), air velocity (0.016–0.1 m/s), and light intensity (7–23W/m2). Among generated by-products, aldehydes were the major by-products of VOCs in the PCO reactor. It was revealed that increasing concentration and irradiation, as well as decreasing relative humidity and velocity, increases by-product generation.