Predicting the lifetime of organic vapor cartridges exposed to volatile organic compound mixtures using a partial differential equations model

In this study, equilibria, and breakthrough were predicted for binary mixtures of three volatile organic compounds (VOCs) using a model based on partial differential equations of dynamic adsorption in activated carbon bed. The model aims to predict with a limited complexity, the behaviour of respirator cartridges exposed to binary vapor mixtures from single component equilibria and kinetics data. In the model, multicomponent mass transfer was simplified to use only single dynamic adsorption data. The multicomponent equilibrium is described by the well-known Extended Langmuir (EL) expression. The results given by the model were compared to experimental results to determine the accuracy of the model and the impact of the approximation. The EL isotherm expression predicted equilibria with relatively good accuracy for acetone / ethanol and ethanol / cyclohexane mixtures, but the prediction of cyclohexane uptake when mixed with heptane is less satisfactory. Breakthrough curves (BTCs) were modelled from partial differential equations, coupling a mass balance, a simple LDF hypothesis to describe the kinetics, and the EL equilibrium model. From BTCs, breakthrough times at 10% of the exposure concentration t10% were determined. All t10% were predicted within 20% of the experimental values, and 63% of the breakthrough times were predicted within a 10% error. This study demonstrated that a simple mass balance combined with kinetic approximations is sufficient to predict lifetime for respirator cartridges exposed to VOC mixtures. It also showed that a commonly adopted approach to describe multicomponent adsorption based on volatility of VOC rather than adsorption equilibrium greatly overestimated the breakthrough times.