Nanometric thin skinned dual-layer hollow fiber membranes for dehydration of isopropanol

A novel sulfonated polyphenylsulfone (sPPSU)/polyphenylsulfone (PPSU)-based dual-layer hollow fiber membrane with a nanometric thin skin layer has been designed for biofuel dehydration via pervaporation. The thickness of skin selective layer is in the range of 15-90 nm under different spinning conditions measured by positron annihilation spectroscopy (PAS) coupled with a mono-energetic positron beam. The effects of outer-layer dope properties, coagulation temperature, and dope flow rate during spinning were systematically investigated. By tuning these spinning parameters, a high performance sPPSU/PPSU-based dual-layer hollow fiber membrane with desirable morphology was successfully obtained. Particularly owing to its nanometric thin skin layer, a high flux of 3.47 kg/m²h with a separation factor of 156 was achieved for dehydration of an 85 wt % isopropanol aqueous solution at 50°C. After post thermal treatment at 150°C for 2 h, the separation factor was dramatically improved to 687 while flux dropped to 2.30 kg/m²h, which make it comparable to the inorganic membranes. In addition, excellent correlations were found among the results from field emission scanning electron microscopy, PAS spectra, and separation performance.