First generation of membrane distillation microchips: characterization and proof of concept

Abstract

Although membrane distillation (MD) has several advantages over conventional recovery techniques, it is used in the industry to a limited extent due to a couple of drawbacks such as fouling, uncertainties regarding operational costs and breakthrough. The latter, which is the phenomenon where the membrane gets wetted by the solvent, undermines the working principle of MD as the feed solvent no longer gets retained at the retentate side of the membrane. As to prevent this from happening, the transmembrane pressure must be kept below a critical threshold, generally called the liquid entry pressure (LEP). So far, a couple of empirical equations have been proposed which obtained an average deviation of 25.0% at best. Within this research, the most recent LEP correlation by Hereijgers et al. (2015) was evaluated for aqueous solutions, containing organic components (i.e. methanol, ethanol, acetone, acetic acid and acetonitrile), using a membrane microcontactor. Four different parameters were evaluated, resulting in a positive relation with the LEP for both the contact angle (θ) and the surface tension (γL), while the concentration and the Kamlet-Taft polarity factors showed a negative relation with the LEP. All of this resulted in a proposed correlation to predict the maximum allowable pressure with an average deviation of 24,53%: LEP=-0.0459 γL cos (θ+0.937). Additionally, a vacuum membrane distillation (VMD) experiment was performed and possible improvements to enhance the performance of the setup were discussed.