Fabrication of triple layer composite membrane and its application in membrane distillation (MD): Effect of hydrophobic-hydrophilic membrane structure on MD performance

Abstract

Electrospinning is a notable technique to prepare nanofibrous membranes with remarkable features required for membrane distillation (MD). However, hydrophobic membrane fabricated by electrospinning alone could hardly ensure a high flux. In this study, triple layer membrane that is composed of a PVDF-PTFE hydrophobic layer, a PET support layer, and a chitosan-polyethylene oxide (CS-PEO) hydrophilic layer, was fabricated by electrospinning. Firstly, the PVDF-PTFE and CS-PEO layers were optimized, whose contact angles and thicknesses were 144.3°, 55 μm and 20°, 75 μm, respectively. Then, the triple layer membrane (TL-M), dual layer membrane without hydrophilic layer (DL-M) were fabricated and tested in a DCMD process using 3.5 wt% NaCl as the feed to illustrate the effect of hydrophilic layer. The triple layer composite membrane (average flux: 19 kg/m−2 h−1, rejection rate: 99.92%) showed better performance in comparison to the dual-layer membrane (average flux: 15 kg/m−2 h−1, rejection rate: 99.88%). In addition, the driving forces of TL-M (from 14.34 to 14.16 kPa) and DL-M (from 13.26 to 12.88 kPa) were calculated. Results suggested the incorporation of hydrophilic layer could increase the driving force, and largely enhance the membrane flux which could ensure the triple layer membrane possesses a good potential for DCMD application.