Pore Wetting\nand Compaction in Pressure-Driven Distillation:\nInsights from Impedance Spectroscopy

Pressure-driven distillation (PD) is a desalination process\nthat\nuses applied hydraulic pressure to drive water vapor through an air-trapping\nporous hydrophobic membrane. Unlike distillation processes that rely\non heat, PD leverages applied pressure, making it more energy-efficient\nand allowing it to operate in a similar form factor as other pressure-driven\nprocesses like reverse osmosis. However, the high pressures required\nfor PD operationtypically exceeding 10 barmake membranes\nvulnerable to wetting and compaction. In this study, we employ electrochemical\nimpedance spectroscopy to analyze compaction and wetting behavior\nin distillation membranes subjected to pressures up to 15.2 bar. We\nexamine six different hydrophobic membranes made from poly(tetrafluoroethylene)\nand poly(vinylidene fluoride), identifying correlations between membrane\nmorphology, applied pressure, and wetting mechanisms through highly\nsensitive impedance measurements. Our findings show significant compaction\neffects during the initial pressure increase, followed by progressive\npressure-induced pore wetting as pressure rises, both in the presence\nand absence of surfactants. We also develop and validate an equivalent\ncircuit model that represents air-trapping hydrophobic membranes.\nOverall, this research offers valuable insights into the dynamics\nof membrane wetting under pressure and demonstrates that impedance\nmeasurements can potentially serve as a critical control point for\nwater treatment systems.