Investigation of salt penetration mechanism in hydrolyzed polyacrylonitrile asymmetric membranes for pervaporation desalination

The present work is designed to evaluate the feasibility of using polyacrylonitrile (PAN) asymmetric membrane prepared via diffusion induced phase separation (DIPS). The PAN membrane was hydrolyzed using NaOH for different hours to improve its hydrophilicity and tune the microstructure morphology of HPAN1-5h membrane. The PAN and HPAN1-5h membranes were investigated the physicochemical properties by using the ATR-FTIR, water contact angle, Zeta potential and SEM. Besides, the positron annihilation lifetime spectroscopy results reveal that there was a reduction of free volume by increasing hydrolysis time. The breaking of intermolecular hydrogen bonds after desalination prompts a free structure which affects the growth and decline of the dry and wet zones in the membrane. The HPAN1-5h membranes were revealed the hydrolysis time progresses, the surface of the membrane became denser and pore size decreased. It also showed the salt deposition on the surface of the membranes after pervaporation testing. A permeation flux of 48.0 L/m2 h and rejections above 99% was obtained from 3.5 wt% NaCl aqueous feed solution at 60 °C using the HPAN membrane which was hydrolyzed for 1 h (HPAN1h). The HPAN1h membrane gave the highest permeation flux and has stability for up to 80 h of operation.