Membrane Dephlegmation: A hybrid membrane separation process for efficient ethanol recovery

Abstract Ethanol is a renewable biofuel produced through the fermentation of sugars obtained from biomass. However, the usefulness of ethanol as a fuel is partly limited by the energy intensive nature of the separation processes employed in its production. A hybrid pervaporation–distillation separation process was developed for the efficient separation of ethanol from water. An experimental system was constructed to investigate process performance. The system employed vertically oriented, commercially available, tubular NaA zeolite membranes. This configuration allowed both the dephlegmation and pervaporation processes to be carried out within the same unit. The process was simulated using a model that included coupled heat and mass transfer across the vapour–liquid interface as well as permeation through the pervaporation membrane. Experiments were performed at a variety of feed concentrations, feed flow rates, reflux ratios and permeate pressures. The hybrid process produced ethanol at concentrations well above the ethanol–water azeotrope and yielded improved performance compared to distillation for the same operating conditions. The experimental results were used to validate the simulations and to study the impact of important model parameters. The model predicted the experimental results very well, despite requiring only one fitting parameter. The hybrid process appears to be very efficient for ethanol–water separation and the validated design model will allow detailed process optimization to be performed in the future.