Abstract

Adsorbent media, which utilize physisorption and/or chemisorption to remove gaseous pollutants, are the most commonly employed technology for indoor air purification. The primary challenge associated with this technology is the saturation or exhaustion of the filter. Since conducting tests at low indoor concentrations (ppb level) is time-consuming and costly, it is necessary to develop models that can predict the service life of adsorbent filters based on experimental data obtained at high concentrations.
The main purpose of this research is to estimate the performance of activated carbon filters in removing a mixture of ozone and VOCs. Three VOCs with various properties, namely limonene, toluene, and methyl ethyl ketone, were selected. To achieve the final goal, models were developed progressively for the individual components (ozone or VOC) as well as for the VOC binary mixture. The unknown parameters of these models were determined using experimental data obtained from a bench-scale setup at ppm concentration levels. Subsequently, the models were validated at lower concentrations, a higher velocity, and on a full-scale setup. Pore gas-phase and surface diffusion were the dominant mass transfer steps for intraparticle mass transfer of zone and VOCs, respectively. On the other hand, axial dispersion was important in the interparticle mass transfer of all components. Furthermore, a first-order chemical reaction and a polynomial function effectively described the reactions involving fresh activated carbon and ozone, as well as the parallel deactivation of activated carbon through chemisorption and catalytic processes.
Using the information derived from modelling the removal of ozone, single VOCs, and binary mixtures of VOCs, the filter's performance was further modelled for the removal of binary and ternary mixtures of ozone and VOCs. The proposed model considers the generation of by-products resulting from the heterogeneous reaction between ozone and the reactive VOC (limonene) on the carbon surface. The rate constant for this heterogeneous reaction, formulated upon the Eley-Rideal mechanism, was determined by fitting the model to the experimental data. The obtained reaction constant was then used to validate the model's ability for binary and ternary mixtures of ozone and VOCs at typical indoor concentrations.