Optimization of dewetting conditions for hollow fiber membranes in vacuum membrane distillation

Abstract

Membrane distillation (MD) is a thermal separation process that uses a hydrophobic membrane as a barrier between a liquid phase and a gas phase. Accordingly, MD can only be applied under the conditions where the membrane is not wetted by the feed solution. In this study, a technique to remove water inside the pores of the wetted membranes, or “dewetting,” was developed to mitigate the problems of membrane wetting in MD process. High-temperature air was applied to the wetted membranes using a specially designed device. The dewetting efficiency was analyzed by measuring the liquid entry pressure, water flux, and salt rejection. The response surface methodology (RSM) was applied to explore the optimum conditions for dewetting of MD membranes. Results indicated that dewetting should be done under proper conditions. If the temperature and dewetting time were insufficient, the dewetting was incomplete. On the other hand, the membrane was partially deformed if the temperature was too high and the dewetting time was too long. Based on the RSM results, the optimum conditions for the temperature and time ranged from 60 to 70°C and from 8 to 12.5 min, respectively.