Abstract
Previous models of equilibrium dissolution-diffusion, pore flow and virtual phase change cannot describe the mass transfer process of pervaporation precisely. The fact that dissolution process on the surface of the membrane does not reach equilibrium is seldom emphasized in the literature. The aim of the present work is to develop the nonequilibrium dissolution-diffusion model (nonequilibrium model) for membrane pervaporation process. In this research, the steps of dissolution and desorption were treated as the pseudo surface reaction processes on the surface based on the hypothesis of nonequilibrium dissolution at the interface of the feed liquid and membrane. The semi-experimental model was set based on steady state mass transfer, ignoring the concentration polarization and adsorption at the permeation side. Through linear fitting of the flux with different thickness of the membrane, the diffusion coefficients and adsorption kinetic rate constants of the model were achieved with equilibrium partition coefficient estimated by UNIFAC-ZM model. The calculated values of the model were well in consistent with experimental flux in the vacuum pervaporation of acetone, butanol and ethanol with polydimethylsiloxane membrane. The nonequilibrium model and its parameters will be further applied for prediction of separation performance and selection of operation conditions.
Highlights
Rapid growths in population and economy have resulted in energy and water shortage on a global scale [1]
The dissolution and desorption steps were not equilibrium processes, which was different from traditional opinions and proved by the separation factor changing with membrane thickness
The dissolution and desorption was treated as pseudo surface reaction in this work and nonequilibium dissolution-diffusion model for pervaporation membrane separation was built and analyzed
Summary
Rapid growths in population and economy have resulted in energy and water shortage on a global scale [1]. Among separation techniques for organics recovery from aqueous solutions, membrane based processes are very promising ones [2]. Membrane technology is witnessing an era of rapid growth due to the great demand of renewable energy production and water purification. Membrane pervaporation is first and mainly applied for continuous production of renewable biofuel from bio-fermentation of acetone, butanol and ethanol (ABE) aqueous solution. As an efficient technique to separate oil/water mixture, pervaporation is a permeation process through the membrane with the thermodynamic phase change. Compared with traditional methods like distillation, adsorption, freeze crystallization, gas stripping and liquid–liquid extraction for ABE fermentation products recovery, pervaporation has the advantages of high selectivity, low energy consumption, moderate cost to performance ratio and compact and modular design [4]. Vacuum pervaporation is the most commonly used and investigated pervaporation configuration [5]
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