Dynamic modelling of removal of binary mixtures of VOCs from indoor air through a carbon-based filter

Abstract

Carbon-based filters are commonly used to remove volatile organic compounds from indoor air environments. Assessing the filter performance, such as its ability to remove specific pollutants or its efficiency, is crucial to improve air quality in the indoor environment. However, conducting experiments to evaluate the performance of filters for removing volatile organic compounds from indoor air environments can be difficult and time-consuming due to their low indoor concentrations and the presence of complex mixtures of these pollutants. Dynamic models have been used to assist in evaluating the performance of filters for indoor environment applications.In this study, iterative and non-iterative methods were applied to the Dubinin-Radushkevich isotherm, and then they were incorporated into the mass transfer models to represent the adsorption behaviour of a binary mixture of volatile organic compounds (toluene-limonene and toluene- methyl ethyl ketone mixture). Experimental results of binary mixtures containing 9 parts per million volume of each compound were used to measure Dubinin-Radushkevich constants in the iterative method, whereas single-component adsorption experimental results were used in the non-iterative method. Afterwards, the model’s predictions were compared with the experimental results at 0.1 parts per million volume of each compound. The non-iterative method could predict the filter performance for the removal of the toluene and limonene mixture, but there was a systematic deviation for the binary mixture of toluene and methyl ethyl ketone. However, the iterative method, which considers the lateral interaction between the adsorbates, could predict the breakthrough of the filter for the non-ideal mixture of toluene and methyl ethyl ketone correctly. Comparative modelling confirmed the negligible significance of gas-phase diffusion. Also, the comparison between the comprehensive model (Fick’s diffusion for internal mass transfer) and two approximate solutions (linear and quadratic driving force models for internal mass transfer) exhibited the applicability of these intraparticle mass transfer approximations in specific conditions. Finally, the parametric study showed that as the particle size increases, the 100% breakthrough time and initial breakthroughs increase for each component of the binary mixture. However, increasing the air velocity leads to a reduction in 100% breakthrough times and initial efficiencies. At higher inlet concentrations, the breakthrough curves become steeper. Furthermore, the occurrence of the overshoot phenomenon was observed with increasing thickness.