Membrane distillation of high salinity water by induction heated thermally conducting membranes

We present a novel approach for vacuum membrane distillation (VMD) based on a 'self-heating' membrane by a high-frequency magnetic field. The system proved efficient for desalinating a range of saline solutions while overcoming temperature polarization and heat loss associated with low permeate flux in MD processes. The system utilized induction heating (IH) for fast and contactless direct heating of the membrane surface without the need for preheating the bulk feed solution. A composite membrane with a dual hydrophilic-hydrophobic layer was fabricated by spray coating iron oxide-carbon nanotubes on a hydrophobic polytetrafluoroethylene commercial membrane. We evaluated the impact of operational conditions on the permeate flux and rejection while treating high salinity feeds (35-100 g/L NaCl). Following optimization, high permeate flux and 99% salt rejection were measured at a low inlet flow velocity (2.33 cm/min) and low vacuum (20 kPa) conditions. In addition, the specific heating energy of the system was determined to be significantly lower in comparison to the conventional VMD system under similar conditions. Interestingly, the treatment of very high-salinity solutions was shown to be efficient as a result of the IH mechanism. Temperature profiles and transport mechanisms were assessed using numerical simulation which was validated by the experimental results.