Tailored multi-zoned nylon 6,6 supported thin film composite membranes for pressure retarded osmosis

Sustainable energy can be harnessed from natural or engineered salinity gradients using a process known as pressure-retarded osmosis (PRO). One major challenge is the lack of a suitable semi-permeable membrane that can withstand the pressure of the process yet still employ a support layer that is thin and compaction resistant in order to limit internal concentration polarization. In this study, we report on a roll-to-roll produced thin film composite (TFC) PRO membrane support platform using a thin “multi-zone” nylon 6,6 structure integrated with a nonwoven scrim that enhances mechanical properties and compaction resistance. Two types of TFC membranes with different permselectivities were fabricated based on this support via in-situ interfacial polymerization and then tested under real PRO conditions. Overall our membranes exhibit higher compaction resistance than a commercial FO membrane evidenced by the less severe structural parameter increase under pressure. In addition, our TFC membranes were able to capture 65-81% of theoretical maximum power density performances in comparison to only 50% of the more compactable commercial FO membrane. These results demonstrate that compaction during PRO can substantially reduce power density and the effect can be lessened with appropriate membrane design.