Design, preparation and characterization of hollow fiber membranes for desalinisation by membrane distillation

摘要

Water scarcity is nowadays a worldwide problem that requires new water resources and more efficient separation treatment techniques. Membrane distillation (MD) is a non-isothermal process whose driving force is the transmembrane vapor pressure. In this process, non-volatile solutes can be removed from a wide variety of feed aqueous solutions due to the transport of vapor molecules through microporous and hydrophobic membranes. Owing to its various advantages, water desalination by MD is an environmentally-friendly alternative, which can tackle the water shortage issue. The main challenge of MD is the design and preparation of improved membranes with suitable characteristics for this process. Hollow fiber is currently the most attractive membrane geometry for MD industrial implementation. Consequently, membrane engineers are endeavoring to develop novel hollow fiber membranes that meet the demanding MD requirements. In this PhD Thesis, advanced hollow fiber membranes have been prepared by the dry/wet or wet/wet spinning technique for desalination by MD. A comprehensive analysis of different spinning parameters effects on the membrane formation mechanism, characteristics and MD performance has been carried out. The highly hydrophobic copolymer, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), has been chosen for the preparation of the organic hollow fiber membranes. Prior membrane preparation, the type of solvent and the mixed solvent used to prepare the PVDF-HFP dope solution have been studied taking into account the characteristics of the dope solution, which dictates the coagulation kinetic and the thermodynamic precipitation of the membrane formation. The adequate mixed solvent was found when the dope solution became thermodynamically more stable and the coagulation rate of the membrane phase inversion was slower due to the increase of the viscosity of the dope solution. The hollow fiber membrane prepared under these conditions exhibited macro-void free and thick sponge-like structure, resulting in suitable characteristics for MD and high direct contact membrane distillation (DCMD) permeate flux...