Molecular design of the morphology and pore size of PVDF hollow fiber membranes for ethanol-water separation employing the modified pore-flow concept

In this study, we have established the fundamental science and engineering of fabricating poly(vinylidene fluoride) (PVDF) asymmetric hollowfibermembranes for ethanol–waterseparation and elucidated the complicated relationship among membranemorphology, poresize, poresize distribution and separation performance using the concept of the modifiedpore-flow model proposed in our previous work. The variation of bore-fluid composition, air-gap distance and take-up speed results in membranes with various morphologies ranging from large-finger-like macrovoid to nearly perfect macrovoid-free structures. Interestingly, an increase in air-gap distance or take-up speed not only effectively suppress the formation of macrovoids but also results in the reduction of membraneporesize and the narrowing of poresize distribution, hence leading to the enhancement of membrane performance. The permeation flux is found to be mainly controlled by the overall porosity and the contribution of large poresizes of the membrane, while the selectivity or separation factor is greatly determined by membraneporesize and poresize distribution, which is consistent with the modifiedpore-flow model proposed in our previous works. The newly developed PVDF asymmetric hollowfibermembranes demonstrates remarkable high fluxes of 3500–8800 g m-2 h-1 and reasonable ethanol–waterseparation factors of 5–8 compared to existing polymeric-based pervaporation membranes.