Fabrcation of ultra high flux, highly concentric and macrovoid-free PVDF hollow fibers for membrane distillation process

Abstract

Highly permeable and macrovoid-free PVDF hollow fibers with a thin wall and a big inner diameter are highly desirable for membrane distillation processes. However, fabrication of these fibers is usually hindered by instabilities such as nascent fiber collapse or deformation during the spinning process. In this communication, we demonstrate a new approach to overcome such obstacles by means of the dual layer spinning and material engineering of PVDF with hydrophobic clay particles in the outer layer and a highly shrinkable polymer such as PAN in the inner layer of the fibers. The function of the inner support layer is to prevent the collapse of the outer nascent layer, and to produce a highly concentric and uniform macrovoid-free thin wall. The resultant single layer PVDF fibers were highly porous (80% porosity), macrovoid-free with a small wall thickness of 120 μm and a big inner diameter of 860 μm. The fabricated fibers showed an outstanding performance during desalination of water by direct contact membrane distillation. A 100% salt rejection and fluxes as high as 70 kg/m2hr, were achieved at 86 °C, which is a much higher flux compared to all the data reported in the literature for hollow fiber membranes so far.