Vacuum membrane distillation: Modeling and analysis for recovery of ethanol from ethanol/water solutions

Abstract

A mathematical model was developed to describe the mass and energy transfer in the ethanol separation process by using vacuum membrane distillation. This model is one of the few proposed for studying the ethanol recovery using vacuum membrane distillation; hence, only Soni, Abildskov, Jonsson and Gani (2008) have proposed a more complex model. The mathematical model was validated using fourcase studies reported in literature. The model fairly describes reported data obtained under the following operating conditions: 20 - 70°C, ethanol concentration from 0.25 to 5% w/w, pressure of 2000 - 6000 Pa and Reynolds of 50 - 2700. The influence of operation conditions and membrane properties on ethanol and water flux, as well as on ethanol concentration in permeate were studied with this validated model by using Statgraphics® Centurion XVI.I and a factorial experiment design. Pareto analysis showed that operating conditions and membrane properties influence the process variables in different ways. For example, both flux values increase with temperature, pore diameter and porosity; but membrane thickness has a negative effect on water flux (for ethanol flux it was not significant). On the other hand, increasing pressure, pore diameter or porosity decreases permeate ethanol concentration. Last parameter increases with feed ethanol concentration and membrane thickness. In vacuum membrane distillation, the model predicts a permeate ethanol concentration 8.8 times higher than feed concentration, depending on operating conditions and membrane specifications.