A generic transport model for separation of gas mixtures by glassy polymer membranes based on Maxwell–Stefan formulation

Abstract

Glassy polymer membranes offer a notable advantage over rubbery membranes for separation of gas mixtures due to better diffusional molecular sieving. However, predicting the separation behaviour of the membrane system is complicated due to different coupling effects arising as a result of differences in adsorption and diffusion of permeating components. A true understanding of multicomponent transport is a key step in the design and optimization of membrane separation processes. The conventional dual transport model fails to give a correct prediction for glassy polymer systems. Hence, the main purpose of this research was to present a transport model to reliably predict gas mixture separation via a glassy polymer membrane. The Maxwell–Stefan formulation theory was considered as a basis for development of the model because of its main advantage in which binary diffusivities can be used to describe multicomponent diffusion behaviour. The equilibrium factor was described in terms of the dual adsorption model. Two case studies were considered to validate the model prediction behaviour, i.e. CH₄/CO₂ and also C₃H₆/C₃H₈ separation which are two important processes in natural gas and petrochemical industries. The results obtained revealed very good agreement between the experimental and predicted selectivities using the developed transport model, while it was shown that a poor result is obtained using the conventional dual transport model. It was also shown that neither equilibrium nor kinetic interactions between permeating components can be safely ignored. However, the effect of kinetic coupling is more crucial due to the fact that the separation in glassy polymer membranes occurs based on diffusional selectivity rather than adsorption selectivity.