Recyclable Membranes through Reversible and Dynamic Crosslinking

Membrane technology is one of the most sustainable methodologies in industrial separations due to its low cost, straightforward scale-up with more compact systems, simple operation, and lower energy consumption than traditional thermal separation processes. However, their linear life cycle results in a large amount of membranes being discarded every year, compromising their sustainability and long-term operational cost. While recycling membranes could enhance their sustainability, it is particularly challenging for solvent-resistant membranes. This difficulty arises from their inherent chemical stability, provided by nonreversible cross-linking with permanent covalent bonds in most cases. In this work, we propose a reversible and dynamic cross-linking with disulfide bonds by using cysteamine as a cross-linking agent to improve the chemical resistance and enable the recyclability of poly(ether imide) (Ultem) membranes. The membranes were stable in dimethylformamide (DMF) with gel contents above 90% after immersion for a week. Stable permeances of methanol, acetonitrile, and DMF with values of 1.4, 3.0, and 1.8 L m^-2 h^-1 bar^-1, respectively, were demonstrated. The cross-linking improved the mechanical properties of the membranes without altering their microstructure and significantly enhanced the rejection of Direct Red 80 (molecular weight of 1373 g/mol) from 75% to 99% in methanol solutions. The method was applied to flat-sheet and hollow fiber membranes. The used membranes were successfully recycled by reducing the disulfide bond with 1,4-dithiothreitol, allowing them to be solubilized, purified, and cast for membrane fabrication. This study demonstrates the potential of integrating dynamic chemistry with membrane science to move toward more sustainable separation processes.