A second-order Dry Glass Reference Perturbation Theory for modeling sorption in glassy polymers: applications to systems containing light gases, alcohols, and water vapor

Abstract

The solubility of gases and vapors plays a critical role in determining the overall performance of membrane-based separation processes. Through the use of advanced Equations of State (EoS), the Non-Equilibrium Thermodynamics for Glassy Polymers (NET-GP) theory rose into prominence as a powerful correlative and predictive tool for the sorption of guest species in glassy polymers. The recently proposed Dry Glass Reference Perturbation Theory (DGRPT) provided a method to account for the polymer swelling through the NET-GP framework. In this work, we introduce a second-order modification to the DGRPT that improves upon the model’s flexibility in representing different types of isotherms. We have also investigated different association and parameterization schemes for water and alcohol sorption using the PC-SAFT EoS in glassy polymers. For the non-self associating polymers investigated here, our results concluded that the sorption of alcohols can be represented adequately using the induced association assumptions formulated by Kleiner and Sadowski. On the contrary, the same assumptions often lead to poor water sorption results. We speculate that the Wolbach and Sandler combining rule may be incapable of representing the cross-association effects between water and the glassy polymer. As a result, we fitted the cross association volume of bonding (κ${}_{A_i{B}_j}$) on the sorption data while fixing the cross association energetic parameter (ε${}_{A_i{B}_j}$) to half of water’s parameter. The adjusted κ${}_{A_i{B}_j}$ can then be treated as a temperature-independent parameter, while the effects of temperature variation can be delegated to the binary interaction parameter (k${}_{ij}$).