High permeance nanofiltration membrane for harsh organic solvent based on spiral-ring polyesters

Currently, many polymeric membranes are poorly tolerated in harsh (strong polar aprotic) solvents like dimethylformamide (DMF) and N-methylpyrrolidone (NMP) and are not applicable to organic solvent nanofiltration (OSN). In this study, we combined the oxidized poly (arylene sulfide sulfone) (OPASS) supports with excellent organic solvent resistance and the spiral-ring polyester interfacial polymerization (IP) layer together to fabricate ultra-resistant and high permeance membranes for OSN. The tetramethyl-1,1′-spirobisindane-6,6′diol (SBI), a contorted diphenol monomer with a spiral-ring structure, was preferentially selected from six types of polyphenols based on molecular simulations and experimental results. It was conducted to react with trimesoyl chloride (TMC) via interfacial polymerization to yield a polyester separation layer of thin film composites (TFC). Investigating the different alkali ratios and types revealed that the alkali added in the aqueous phase to improve the solubility of the SBI could cause hydrolysis of the polyester layer generated by IP, which led to increased membrane permeance and reduced rejection, and the more alkali and the stronger the alkali used, the more severe the hydrolysis. Besides, DMF activation treatment to the TFC membrane improved the ethanol permeance by at least four times while maintaining high congo red rejection. As a result, combining the effects of alkali and DMF activation, the representative TFC membranes fabricated in our work exhibited excellent permeance of 21.5±1.3, 9.0±1.1 L m−2 h−1 bar−1 for DMF and NMP, respectively, and high rejection rates (≥ 93%) for congo red (Mw 696.7 Da), higher than the earlier reports. This research presents a new and straightforward approach to developing TFC membranes with high-efficiency filtration capabilities, suitable for harsh organic solvent separation applications.