Coupled diffusion of water and ethanol in a polyimide membrane

In this work, the sorption and steady state permeation of water-ethanol mix ture in an aromatic polyimide membrane was investigated with the objective of revealing the coupling effects of water and ethanol in their course of d iffusion. The solubility of the water-ethanol mixture in the membrane was d etermined by means of swelling-distillation techniques. The sorption behavi or was interpreted in terms of the thermodynamic equilibrium equations. The Maxwell-Stefan mass transfer model was employed as a framework for modelin g diffusion. Model equations derived therefrom enable us to calculate coupl ed fluxes of water and ethanol from the experimental data. The coupling eff ects in the diffusion of water and ethanol were revealed by comparing the c alculated coupled flux with non-coupling flux, which was calculated by inte gration of the Fickian first law using independent diffusion coefficients. Furthermore, the implication of the sole adjustable parameter included in t he derived model equations was discussed.