Effect of hydrophilicity and free volume on the dehumidification performance and hydrolytic stability of fluorinated polyamide membranes

A series of fluorinated polyamides (PAs) air dehumidification membranes containing hydrophilic, bulky groups have been designed to balance H2O permeability, H2O/N2 selectivity, and hydrolytic stability. As expected, the polyamide membrane incorporating hydrophilic carboxylic acid groups increases dehumidification efficiency but with a significant sacrifice of hydrolytic stability. The incorporation of large free volume groups could increase the H2O permeability, while H2O/N2 selectivity is lower. The fluorinated polyamides with excellent air dehumidification performance and hydrolytic stability were obtained successfully by fine-tuning the type of hydrophilic groups. The co-PA-PABZ membranes with hydrophilic benzimidazole groups exhibited an excellent H2O permeability of ∼ 4142 Barrer and a H2O/N2 selectivity of around 59171. The dehumidification performance is much higher than without hydrophilic groups co-FPA-70 polyamide membrane (PH2O=3943 Barrer, H2O/N2=9388). Importantly, they also demonstrated outstanding hydrolytic stability at 80 ºC water, retaining 91% molecular weight and 97% tensile strength over 5000 hours, as confirmed by 1H NMR, molecular weight and mechanical tests. The dehumidification aging test of more than 2000 h on this membrane further indicated its excellent durability under operation conditions. This efficiency-design strategy provides a universal method for developing aromatic polyamides with alkaline hydrophilic functionalities, facilitating the creation of high-performance, hydrolytically stable dehumidifying membranes. [Display omitted] •The effects of hydrophilicity and free volume on the dehumidification performance and hydrolytic stability of PA membranes were investigated.•PA membranes with excellent air dehumidification performance and hydrolytic stability were obtained by fine-tuning the type of hydrophilic groups.•The co-PA-PABZ membranes, incorporating alkaline hydrophilic benzimidazole groups, exhibited excellent H2O/N2 separation performance.•The co-PA-PABZ membranes with alkaline hydrophilic groups exhibit excellent hydrolytic stability and durability.