Simultaneous removal of acetone and ethanol from aqueous solutions by membrane distillation: Prediction using the Fick's and the exact and approximate Stefan-Maxwell relations

The simultaneous removal of dilute acetone and ethanol from aqueous solutions by air gap membrane distillation is theoretically investigated. A combined heat and mass transfer model that includes temperature and concentration polarization effects as well as temperature and concentration variation along the module length is employed to predict the flux and selectivity of acetone and ethanol under the relevant process operating conditions. Three mass transfer solutions are considered in the model, namely; the exact Stefan-Maxwell (S-M), the approximate Stefan-Maxwell and the Fickian binary solution. Although, qualitatively, the three solutions exhibit the same trends, quantitatively some differences exist between the Fickian-based solution on one hand and the Stefan-Maxwell solutions on the other hand. The exact and approximate solutions of the Stefan-Maxwell equation showed similar capability in predicting the process performance under all process conditions. Predictions showed that acetone selectivity and flux were strongly dependent on feed conditions and air gap width.