Fabrication of High Performance Pervaporation Desalination Composite Membranes by Optimizing the Support Layer Structures

Water flux of pervaporation (PV) desalination composite membranes can be increased by either decreasing the selective layer thickness or reducing the support layer resistance. The former method has been widely studied. However, investigating the influence of support layer structure on PV desalination performance has not been reported. In this study, structures of polysulfone (PSF) ultrafiltration membranes were tuned by changing the relative humidity (RH) and the LiCl additive concentrations of the PSF dope solutions. The average pore diameters and porosities on the PSF membrane surfaces were determined by scanning electron microscopy. Pure water flux and gas flux of the PSF membranes were measured to compare their resistances to water-vapor transport. It was found that the PSF membranes prepared at a RH of 5% and LiCl concentrations of 2 wt % were the best support layer for fabricating the PV composite membranes, where the top selective layer was made of the 4-sulfonylphthalic acid cross-linked poly(vinyl alcohol) (S-PVA). The highest water flux of 60.8 kg/(m2·h) with a salt rejection of 99.8% was achieved at 70 °C for separating a 3.5 wt % NaCl solution. This result was 31% higher than the data reported in our previous study using the same S-PVA as selective layer but with a different support layer.