Fabrication of PES-based membranes with a high and stable desalination performance for membrane distillation

Abstract

Polyethersulfone (PES)-based membranes with a high and stable desalination performance for vacuum membrane distillation (VMD) were fabricated by spraying a dispersion containing hydrophobic-modified PES grafted copolymers onto porous PES membranes. The copolymer (PES-g-PFMA-C₈) with different degrees of grafting (DG) was synthesized by grafting 1H,1H,2H,2H-perfluorodecyl methacrylate (FMA-C₈) onto PES by simultaneous irradiation in a homogeneous system wherein the kinetics of the radiation-induced graft polymerization was studied. The copolymers, pristine PES membrane and fabricated PES-based membranes were also characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. After spraying, the hydrophobicity of the membrane increased and its maximum pore size reduced, which enhanced its desalination stability. During an intermittent 80 h VMD desalination operation, a flux of approximately 50.5 kg m⁻² h⁻¹ and a stable salt rejection of 99.98% were achieved when a 3.5 wt% NaCl solution was treated at 70 °C under vacuum of 92 kPa by the PES-based membrane using the copolymer with a DG of 20.3%, whereas salt leakage obviously occurred since the 52^nd hour of operation when the pristine PES membrane was used. These results indicate that the modified PES membrane developed in this study is a promising candidate for VMD desalination due to its comparable flux.