In membrane distillation (MD), a saline feed stream is distilled through a hydrophobic, vapor-filled membrane into a pure distillate stream. Unlike reverse osmosis, MD can theoretically treat high-salinity streams, even approaching zero liquid discharge of waste brine. However, salt precipitation (scaling) can facilitate wetting of membrane pores at high salinities. As a result, many researchers have sought to use advanced techniques to fabricate high-porosity, highly hydrophobic membranes. Superhydrophobic membranes are often fabricated via modifying high-porosity substrates (e.g., electrospun membranes) to increase surface roughness and reduce surface energy (e.g., by coating with functionalized nanoparticles). However, the relative importance of pore size, hydrophobicity, and surface/internal properties in preventing wetting are still not fully understood.  Previously, we observed that internal hydrophobicity (i.e., pore wall hydrophobicity) may be important, especially during long-term operation and/or under high-salinity conditions. In recent work, we utilized initiated chemical vapor deposition to deposit a hydrophobic copolymer (P(PFDA-co-EGDA)) on (1) a hydrophilic substrate, producing a superhydrophobic membrane with a high contact angle (157°) and average pore size (132 nm), and (2) a hydrophobic substrate, producing an asymmetric membrane with small feed-side porosity (3.5%) and average pore size (64 nm). While both membranes displayed similar wetting resistance with a surfactant-containing feed solution, under scaling conditions, the asymmetric membrane displayed much higher wetting resistance than the superhydrophobic membrane. Results showed that surface pore size and porosity played a more important role than contact angle in preventing scaling-induced wetting.  Currently, we are utilizing electrospinning to fabricate novel hydrophobic and hydrophobic-hydrophilic membranes with different thicknesses and pore sizes. We are testing these membranes under baseline and high-salinity conditions to determine the impact of thickness, pore size, and hydrophobicity on scaling-induced wetting for different feed solution compositions; results will be presented.

High-salinity membrane distillation: Impact of material properties on membrane performance

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.