Membrane Distillation (MD) has received increasing interest as an emerging desalination technology. Although significant research has been dedicated to advance this emerging technology the transition from research to commercialization has remained slow. One of the major barriers for this slow progress is the absence of commercially available membranes specifically made for MD. Current membranes employed in MD have been developed for microfiltration applications. Low permeate flux, membrane pore wetting, low mechanical stability, scaling, fouling and absence of membrane modules are amongst the major drawbacks that limit the commercialization of MD.
Here we focus on studying MD performance of commercially available microfiltration membranes. We relate performance to membrane structural parameters. There are numerous structural parameters studied in the literature, including porosity, tortuosity, thickness, polymer material, hydrophobicity, pore size, pore size distribution etc. Researchers have tried to couple these parameters to the MD performance. However, there is not yet a systematic study that shows how these structural parameters correlate with membrane performance in MD applications. Most studies have focused on a single membrane property and related it to membrane performance. Yet MD performance depends on the combined effect of a number of membrane properties such as hydrophobicity, tortuosity, pore size etc. In addition, most of the literature is limited to reporting MD fluxes and none of the previous literature investigates the interplay between the structural parameters of the membranes with their overall performance, such as permeate flux, fouling and scaling. There is also some difficulty associated with studying the structural parameters due to the fact that they are intertwined (like porosity and tortuosity). This creates significant difficulties when discussing the effect of structural parameters.
In this study, we have established a direct contact MD setup to investigate the performance of 20 hydrophobic and superhydrophobic membranes. We have also designed a unique membrane module which led to significant increase in flux while keeping the pressure drop within the module very low. We have characterized the membranes using well-established methods such as bubble point, liquid entry pressure, atomic force microscopy, scanning electron microscopy, contact angle, surface energy, porosity, and air permeability. Our results indicate the strong interplay between the membrane structural parameters and membrane performance.