Study on vacuum membrane distillation (VMD) using FEP hollow fiber membrane

Poly(tetrafluoroethylene-co-hexafluoropropylene)(FEP) hydrophobic hollow fiber membranes were prepared through melt spinning method. The performances and structures of membrane samples with different stretching ratios were investigated. It can be seen that the increased stretching ratios (nascent, 50%, 100% and 150%) brought about obvious interfacial microvoids (IFMs) which improved the membrane's porosity, while decreased the liquid entry pressure (LEP) and mechanical strength. In addition, the FEP hollow fiber membranes exhibited strong hydrophobicity, excellent chemical and thermal stability owing to its perfluoro structure. Therefore, the performances of membrane samples were measured by vacuum membrane distillation (VMD) using alkaline aqueous with high temperature. The results showed that the FEP hollow fiber membranes' salt rejections achieved as high as 99.0%. In addition, the MD flux, salt rejection and mechanical strength kept stable in the strong alkaline aqueous (NaOH concentration of 300 g/L, 80 °C) through a long term operation of 48 h. However, the compared poly(vinylidenefluoride) (PVDF) hollow fiber membrane exhibited weak alkaline and thermal endurance with obvious decrease of mechanical strength and salt rejection. Therefore, this study indicated that the obtained FEP hollow fiber membrane could be used in the VMD which exhibited satisfying salt rejection.