Evaluating a new ultra-thin dense-skin hollow Fiber membrane for vacuum membrane distillation

Membrane distillation (MD) utilizes microporous membranes to support a liquid-vapor interface and can be used for desalination. Polyvinylidene fluoride (PVDF) based membranes show high permeate fluxes, however they are prone to pore wetting and per - and polyfluoroalkyl substances (PFAS) release, thus motivating the search for new MD membranes. This study evaluates, as an alternative membrane for vacuum MD (VMD), a new hollow fiber (HF) composite membrane with an ultra-thin dense layer of polydimethylsulfone (PDMS) coated on the external surface of a polysulfone (PSU) microporous HF, with potentially low wettability and higher fluxes than completely dense fibers. The so-called Fiber B was compared with a microporous PVDF HF ( Fiber A ) for outside/in VMD operation, based on their morphology, Knudsen permeability, wettability/wetting, and thermal aging. The permeate flux and the driving force vary linearly for Fiber B , indicating that it behaves as a VMD membrane, despite its dense layer. Subsequently, Fiber B showed a higher permeability than Fiber A and similar to that of a commercial HF implemented in industry. Short-term wetting tests confirmed that Fiber B avoids pore wetting with saline solutions, while Fiber A showed partial wetting. Fiber B showed stronger mechanical properties and thermal aging induced less severe changes to its permeability, surface, and structural properties , due to the choice of its materials. The new composite fiber has the potential to be a greener alternative to fluorinated-based HFs for VMD, with competitive permeability while avoiding wetting. Its longer-term thermal and wetting stabilities remain to be verified before industrialization. • A new ultra-thin dense skin HF membrane is compared with microporous (MP) membranes • The new HF respects Knudsen's law and behaves like a VMD microporous membrane • The HF is more permeable than a PVDF MP membrane, and as much as a commercial MD one • The new HF has stronger mechanical properties, due to its support material • Made without PFAS it is greener and more thermal resistant than fluorinated MP HFs