Porous hydrophobic-hydrophilic composite membranes for direct contact membrane distillation

• Published in: Journal of membrane science 2019-12, Vol.591, p.117225, Article 117225
• Main Authors: Puranik, Aishwarya A., Rodrigues, Lydia N., Chau, John, Li, Lin, Sirkar, Kamalesh K.
• Format: Article
• Language: English
• Subjects: Composite membrane; Hydrophilic porous substrate; Membrane distillation; Plasma-polymerized hydrophobic fluorosiloxane coating; Stacked composite membrane
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2019.117225

Direct contact membrane distillation (DCMD) for desalination is attractive for high salt concentrations if low-cost steam/waste heat is available and waste brine disposal cost for inland desalination is factored in. A number of innovations have taken place in DCMD in terms of the structure of the porous hydrophobic membrane. Composite membranes are of increasing interest. Composite membrane structures of great interest include a thin hydrophobic porous layer over a porous hydrophilic layer of polyvinylidene fluoride (PVDF) or a thin porous hydrophobic layer over a more conventional hydrophobic porous membrane. These membranes can be in the form of an integral composite or a stacked composite or a laminated composite. A facile method of fabricating such integral composite membranes is plasma polymerization under vacuum. A class of such membranes yielding quite high water vapor fluxes have been characterized using a variety of characterization techniques: Contact angle, liquid entry pressure (LEP), bubble-point pressure, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM). Stacked composites of a hydrophobic ePTFE membrane over a hydrophilic PVDF membrane or a hydrophobic PVDF membrane over another hydrophobic PVDF membrane were also studied. Novel conditions created lead to very high water vapor fluxes compared to those from conventional hydrophobic membranes supported on a mesh support. •A porous hydrophilic membrane was coated with a thin porous hydrophobic layer.•The thin hydrophobic fluorosiloxane coating was applied by plasma polymerization (PP).•The composite membrane yielded high water vapor flux in DCMD-based desalination.•Increased PP time yielded higher LEP and lower water vapor flux in DCMD.•A stacked phobic-philic composite had much higher flux than the hydrophobic membrane.