Understanding the influence of solvents on the intrinsic properties and performance of polyamide thin film composite membranes

The polyamide thin film composite (TFC) has been the standard platform for reverse osmosis and nanofiltration membranes for aqueous separations for decades. It combines the properties of high permeance and unmatched selectivity for desalination applications. The highly cross-linked structure of polyamides may enable its use in organic solvent separations with several studies showing promising results. The field lacks, however, a complete understanding of how polyamides may be impacted by solvent exposure. To investigate the impacts of solvent on polyamide, we formed polyamide selective layers through interfacial polymerization onto ceramic OF supports. We quantified the permeability and selectivity changes after polyamides were exposed to an alcohol (methanol), and a ketone (acetone), and a polar aprotic solvent (DMF). We used aqueous testing before and after exposure to quantify permanent changes in membrane performance. Our results show that not only are the polyamide properties altered by the exposure to solvents, but they also show that different solvents have very different impacts on polyamide performance. The results indicate that polyamides may not be robust enough to perform nanofiltration separations in solvent environments with predictable permeability and selectivity.