Desalination by membrane distillation: Fabrication of high Performance membranes

Abstract

This thesis reports the fabrication of high performance PVDF hollow fiber membranes for desalination by membrane distillation process. For the first time, a coextrusion process was applied to fabricate dual layer hydrophilic-hydrophobic hollow fibers for membrane distillation process. The high flux obtained through the fabricated fibers could indicate that the application of dual layer hydrophilic-hydrophobic hollow fibers may be a promising approach for MD. Furthermore, the corrugation instability leading to the irregular cross section of hollow fibers was investigated and a mechanism was proposed to explain the phenomenon. It was postulated that the principal instability occurs in the external coagulation bath where the rigid precipitated polymer shell in the dope and bore fluid interface is buckled due to a generated pressure. The pressure is postulated to be induced in the nascent fiber outer layer as a result of diffusion/convection, precipitation, densification and shrinkage.