A Generic Model for Prediction of Separation Performance of Olefin/Paraffin Mixture by Glassy Polymer Membranes

The separation of olefin/paraffin mixtures is an important process in petrochemical industries, which is traditionally performed by low temperature distillation with a high-energy consumption, or complex extractive distillation
and adsorption techniques. Membrane separation process is emerging as an alternative for traditional separation processes with respect to low energy and simple operation. Investigations made by various researchers on polymeric membranes it is found that special glassy polymers render them as suitable materials for olefin/paraffin mixture separation. In this regard, having some knowledge on the possible transport mechanism of these processes would play a significant role in their design and applications. In this study, separation behavior of olefin/paraffin mixtures through glassy polymers was modeled by three different approaches: the so-called dual transport model, the basic adsorption-diffusion theory and the general Maxwell-Stefan formulation. The systems chosen to validate the developed transport models are separation of ethane-ethylene mixture by 6FDA-6FpDA polyimide membrane and propane-propylene mixture by 6FDA-TrMPD polyimide membrane for which the individual sorption and permeation data are available in the literature. Acritical examination of dual transport model shows that this model fails clearly to predict even the proper trend for selectivities. The adjustment of pemeabilities by accounting for the contribution of non-selective bulk flow in the transport model introduced no improvement in the predictability of the model. The modeling results based on the basic adsorption-diffusion theory revealed that in this approach only using mixed permeability data, an acceptable result is attainable which fades out the advantages of predictibility of multicomponent separation performance from pure component data. Finally, the results obtained from the model developed based on Maxwell-Stefan formulation approach show a close agreement between the predicted values and experimental data in terms of permeabilities and selectivities. The results also indicate that kinetic coupling plays no role in transport across the membrane for the systems under study and can be ignored safely. However, the equilibrium coupling shown makes a major contribution to the transport via membrane and should be considered in the transport model using a proper equilibrium sorption isotherm.