Characterization and performance evaluation of commercially available hydrophobic membranes for direct contact membrane distillation

Membrane distillation (MD) uses a microporous hydrophobic membrane for the separation of non-volatile solutes from liquid streams. The microporous structure should be designed for optimal vapor transport through the membrane, whereas the hydrophobicity is required to retain the liquid phase. Currently, different types of commercially available hydrophobic microfiltration membranes are used for membrane distillation. However, no comparison is available between these membranes, complicating the selection of a proper membrane and the evaluation of new membranes. In this study, over 20 (semi-)commercial hydrophobic membranes are characterized and tested in a lab scale direct contact membrane distillation set-up. These membranes include the standard PTFE, PVDF and PP membranes, but also less known PE and PES membranes. These membranes are synthesized using the phase inversion technique, stretching or electrospinning, resulting in a wide variety of membrane structures. In this study, a method is proposed to evaluate the suitability of membranes. The membrane performance in MD is evaluated with a performance chart including flux and energy efficiency using realistic process conditions. From this chart a benchmark performance is proposed, which depends on the salt concentration.