Modeling competitive adsorption of binary mixtures of volatile organic compounds

Sammanfattning: Adsorption is a common technique for the removal of volatile organic compounds (VOCs) from industrial waste streams. The multi-component adsorption on zeolites, particularly the interactions between VOCs and water vapor is sparsely understood and is yet to be described by empiric and full-physical models. A novel semi-empiric adsorption model is developed to describe the competitive behavior of a binary mixture on zeolite. The model is based on the commonly implemented Langmuir kinetics model and includes competition for adsorption sites and displacement. The kinetic adsorption of binary mixtures is divided into three steps: free adsorption, competitive adsorption, and equilibrium state. Experimentally measured data is obtained for the mixture of polar isopropyl alcohol (IPA) and non-polar toluene. The total molar loading curve of the binary mixture is measured for different mixture ratios, relative humidity, temperatures, and velocities. Zeolite showed a greater adsorption capacity for the mixtures than for the single components. Polar components are favored as zeolites have specific adsorption sites that are accessible to IPA but not toluene. Surprisingly, co-adsorption instead of competition is found. The observed co-adsorption phenomenon was added to the competitive adsorption model with an enhancement factor. The results of this study show new mechanisms of co-adsorption on zeolite that have not been observed on commonly used adsorbents previously. It gives incentives for the development of new physical multi-component adsorption models to predict co-adsorption.