Numerical investigation of Membrane Dephlegmation: A hybrid pervaporation–distillation process for ethanol recovery

Abstract

Ethanol is a renewable fuel that could help alleviate our dependence on fossil fuels to supply energy. Ethanol can be produced through the fermentation of sugars obtained from a variety of biomass. However, the energy intensive nature of the ethanol separation process limits the usefulness of ethanol as a biofuel. Membrane Dephlegmation is a hybrid pervaporation–distillation process that could help improve the efficiency of ethanol recovery. As opposed to most other hybrid pervaporation–distillation processes, Membrane Dephlegmation combines both processes in a single unit. In this investigation, a mathematical model of the Membrane Dephlegmation process was used to carry out a parametric study for important operating conditions and geometric variables. The impacts of feed flow rate, feed concentration, permeate pressure, reflux ratio, membrane length and membrane diameter on separation efficiency were studied. McCabe–Thiele plots were used to compare the performance of Membrane Dephlegmation to conventional distillation. Membrane Dephlegmation was shown to be more efficient than distillation, yielding ethanol concentrations above the ethanol–water azeotrope for similar operating conditions. It was also demonstrated that the inclusion of pervaporation in the hybrid process shifts the operating line below the parity line on the McCabe–Thiele plots, leading to improved separation performance relative to distillation.