CO2/CH4 Sorption Behavior of Glassy Polymeric Membranes Based on Dual Mode Sorption Model

Abstract

Among the various transport models for gas separation via membrane, the best description is done by solution-diffusion model. The main parameters of this model are the sorption and diffusion of the penetrant through the membrane. Studies conducted by various researchers in the field of gas separation indicate that the thermodynamic interaction (sorption effects) in glassy polymers has the major role in the diffusivity, permeability, and selectivity of the membrane, especially in the multi-component gas mixture. In glassy polymers, dual-mode sorption model is frequently used to describe the equilibrium sorption behavior of a polymer-gas system and, based on this sorption model; the permeation behavior is described by the partial immobilization model. In this study, the difference between the sorption mechanism of CO2 and CH4 in glassy polymeric membranes was analyzed by separating the sorption mode and introducing P50/50 parameter (the pressure at which the contribution of both Henry and Langmuir sorption is equal), which was done using the available experimental data in the scientific references for the sorption values of CO2 and CH4. The contribution of the sorbed molecules in Henry and Langmuir sites was investigated and its changes with pressure were evaluated for CO2 and CH4 permeation. This study was also attempted to provide a correct definition of F factor, used in references, in the form of the multiplication of mobile concentration ratios (CHmobile/CH) by the diffusivity coefficients in two modes (DH/DD).