Theoretical and experimental approaches of liquid entry pressure determination in membrane distillation processes

Abstract

Liquid entry pressure (LEP) of membrane is crucial in the process of membrane distillation (MD) to ensure the quality of distillate since the whole operation will be contaminated as soon as the feed liquid starts to penetrate the hydrophobic membrane. Assuming standard condition (i.e., ambient temperature, hydrostatic pressure, etc.), experimental LEP values were inconsistent compared with theoretical LEP, thus rigorous analysis attempt was made to help understanding the wetting phenomena in MD. We first conducted an experiment with LEP device under various temperature of the feed water. Scanning electron microscopy images were taken to visualize the pore size transition and the results were proved with capillary flow porometry of each membrane after the experiments. Effects of different flow rate have also been studied, yet the results showed no significant difference. As a natural result, LEP is temperature dependent; however, other factors which are not reflected in the LEP equation also exist. Experiments show that the wetting at pressure above LEP may not only wet the membrane but also affect membrane properties. Therefore, in the MD process, the importance of preventing wetting exceeds the necessity of recovering after wetting.