Anhydrous interfacial polymerization induced by isopropanol to construct high permeance polyamide membranes for organic solvent nanofiltration

Highly permeable polyamide (PA) membranes with precise molecular sieving capabilities are crucial for energy-efficient chemical separations. There is a critical need to design solvent-stabilized membranes with enhanced permeance to improve separation efficiency. In this work, we propose a novel anhydrous interfacial polymerization (IP) method, where flexible polyethyleneimine (PEI) and rigid p-phenylenediamine (PPD) are uniquely dissolved in isopropanol (IPA) and subsequently crosslinked with trimethyl chloride (TMC) in situ to fabricate high-performance PA membranes. Notably, the use of IPA as a solvent represents a significant advancement in membrane fabrication. This approach resulted in PA membranes with a relatively loose selective layer compared to traditional PA membranes, allowing for exceptionally high solvent permeance while maintaining strong rejection performance in organic solvent nanofiltration (OSN). The obtained PEI + PPD/TMC PA membranes demonstrated outstanding ethanol (EtOH) permeance of 46.44 L m⁻² h⁻¹ bar⁻¹ in the organic solvent system, along with good rejection for small organic molecules, such as 93.84% for Eriochrome Black T (EBT, 461.38 Da). In addition, the performance of the PEI + PPD/TMC PA membranes remained at a high level even during 510 min of continuous cross-flow filtration, under high pressure (5 bar) testing, and after 6 cycles of separation, which demonstrated their good stability in long-term service. This work establishes a robust foundation for employing anhydrous IP reactions and innovative solvent systems, such as IPA, to develop high-permeance PA membranes.