Examining the commercially available hydrophobic membranes in combined desalination and power generation through permeate gap membrane distillation

Developing robust and sustainable desalination processes with minimum energy consumption in integration with renewable energy sources is on high demand in the current climate. Utilizing membrane-based processes for either freshwater production or power generation has appeared as a promising approach in recent years. This research further examines the potential of utilizing a permeate gap membrane distillation (PGMD) system integrated with a sealed air tank to produce combined freshwater and power (CWP) on the laboratory scale. In this study, different commercial hydrophobic membranes with 0.2 to 0.02 μm pore size ranges have been tested and the laminated membranes have been examined in two mounting orientations. The maximum harvested hydraulic pressure and power density by using a pristine 0.1 μm nominal pore size laminated polytetrafluoroethylene (PTFE) membrane facing the active layer to the feed channel (ALF orientation), were measured at approximately 1.8 bar and 0.47 W/m2, respectively under the defined test condition. Mounting the active layer to the permeate side (ALP orientation), the maximum hydraulic pressure and power density recorded at approximately 3.6 bar and 0.42 W/m2, respectively. The experimental data using the 0.02 μm pore size laminated hydrophobic PTFE membrane showed the same pattern. That is, despite producing higher hydraulic pressure with currently available commercial smaller pore size membrane in the ALP orientation, the generated power density has not increased significantly or may have even reduced. Hence, the development of high compressive resistance membranes with high permeability, low surface energy and narrow pore size distribution characteristics, is vital to be able to propose the CWP process using membrane distillation (MD) systems as a competitive and sustainable desalination technology.