Ultrathin double network-coated hollow fiber membrane designed for water vapor separation

Here we present, for the first time, ultrathin double network (DN)-coated hollow fiber membranes to improve water vapor permeation of polymeric membranes. In this study, we investigated two different DN systems. The hyperbranched polyethyleneimine (HPEI) and its quaternized HPEI form (QHPEI) represented the first network in both systems, while the second network was based on quaternized polyacrylic acid (QACC) and quaternized poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (QAMPS). Various analysis techniques were used to characterize QHPEI and DN-coated polysulfone (PSf) membranes. Water vapor permeation experiments were conducted at QHPEI concentration in total precursor (QHPEI and HPEI) and different operating parameters. The incorporation of a higher QHPEI amount improved the hydrophilicity and water vapor performance of DN-coated membranes. QAAC-100 and QAMPS-100 exhibited the highest performance in each system; however, QAMPS showed higher water vapor permeance (P) and lower selectivity (S). This behavior was attributed to the presence of a bulkier pendant group (i.e. less compact), higher hydrophilicity, and a thinner membrane in QAMPS compared to QAAC. The increment in relative humidity (RH) illustrated a positive effect on the membrane performance, while both temperature and pressure illustrated a negative impact. The best performance obtained by QAAC-100 (S = 511, P = 5825 GPU) and QAMPS-100 (S = 422, P = 8115 GPU) was achieved at 1 bar as feed pressure, 75% as RH, 35 °C as operating temperature, and 1 L/min as feed gas flow rate.