CO₂ capture from humid flue gases has recently gained significant attention in efforts to reduce CO₂ emissions into the atmosphere. Adsorption is energy efficient, cost effective and environmentally favorable process for commercial applications. The influence of humidity in the air or flue gases should be considered for the separation of CO2 from these streams. High water vapor concentration and low CO2 concentration in the flue gas make CO2 separation challenging. Due to its hydrophobic nature, Calgary Framework 20 (CALF-20) [Industrial & Engineering Chemistry Research, 63(7), 3265-3281] is an excellent option for CO2 capture from flue gases. In this work, we studied the CO2/H2O adsorption on CALF-20 using the recently developed generalized Brunauer−Emmett−Teller (gBET) isotherm model[Industrial & Engineering Chemistry Research, 63(31), 13853-13863]. The adsorption of water on hydrophobic CALF-20 results in a sigmoidal adsorption isotherm, which corresponds to a Type V isotherm in the IUPAC classification of physisorption isotherms. We modified the gBET model originally developed for the mixed-gas multilayer adsorption to effectively describe Type I and II isotherms to account for the type V isotherm as well. The gBET model results of pure CO2 and H2O as well as the binary system are compared with other models. The newly modified gBET model is much simpler than the existing models and can accurately represent multiple types of adsorption isotherms according to IUPAC classification.
