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

Abstract

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.