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Elucidating the Trade-off between Membrane Wetting Resistance and Water Vapor Flux in Membrane Distillation
journal contribution
posted on 2020-08-06, 22:01 authored by Chenxi Li, Xuesong Li, Xuewei Du, Ying Zhang, Wei Wang, Tiezheng Tong, Arun Kumar Kota, Jongho LeeMembrane
distillation (MD) has been receiving considerable attention
as a promising technology for desalinating industrial wastewaters.
While hydrophobic membranes are essential for the process, increasing
membrane surface hydrophobicity generally leads to the reduction of
water vapor flux. In this study, we investigate the mechanisms responsible
for this trade-off relation in MD. We prepared hydrophobic membranes
with different degrees of wetting resistance through coating quartz
fiber membranes with a series of alkylsilane molecules while preserving
the fiber structures. A trade-off between wetting resistance and water
vapor flux was observed in direct-contact MD experiments, with the
least-wetting-resistant membrane exhibiting twice as high vapor flux
as the most wetting-resistant membrane. Electrochemical impedance
analysis, combined with fluorescence microscopy, elucidated that a
lower wetting resistance (still water-repelling) allows deeper penetration
of the liquid–air interfaces into the membrane, resulting in
an increased interfacial area and therefore a larger evaporative vapor
flux. Finally, we performed osmotic distillation experiments employing
anodized alumina membranes that possess straight nanopores with different
degrees of wetting resistance, observed no trade-off, and substantiated
this proposed mechanism. Our study provides a guideline to tailor
the membrane surface wettability to ensure stable MD operations while
maximizing the water recovery rate.
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membrane surface wettabilityMembrane Wetting Resistanceresistancedirect-contact MD experimentswater recovery ratevapor fluxWater Vapor Fluxmembrane surface hydrophobicityanodized alumina membranescoating quartz fiber membraneswater vapor fluxElectrochemical impedance analysisMembrane Distillation Membrane dist...
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