Advanced desalination performance using PVDF electrospun nanofiber membranes across multiple membrane distillation configuration
Roberto Campos Navarro, Boya Qiu, Peter M. Martin, Patricia Gorgojo, María Pérez-Page
Abstract
This study reports the fabrication of polyvinylidene fluoride (PVDF) electrospun nanofiber membranes (ENMs) and their application across a range of membrane distillation (MD) configurations. Cloisite® 20 A (OMT) clay nanoparticles have also been successfully incorporated within the membrane nanofiber. The fabricated membranes exhibited notable MD performance enhancement, substantially increasing permeate flux rates compared with the membranes without nanoparticles, surpassing commercial PVDF membranes by 48 % and pristine ENMs PVDF membranes by 38 %. Additionally, the ENMs demonstrated significant improvements across all analysed parameters compared to pristine phase inversion PVDF membranes and with the PVDF mixed matrix membranes containing similar clay loading. Characterisations suggest that the superior performance is attributed to the formation of thinner fibers and the homogeneous dispersion of clay nanoparticles, obtaining high porosity (~93 %), high liquid entry pressure (~3 bar), good mechanical stability (~55 MPa of Young's Modulus) and surface superhydrophobicity (contact angle of ~150°). Stability tests over 5-day days confirmed these membranes' robustness, consistently maintaining rejection values above 99.9 %. In a comparative analysis of membrane configurations, vacuum-assisted air gap membrane distillation (VA-AGMD) emerges as the standout performer. The removal of air in VA-AGMD significantly improved process performance relative to direct contact membrane distillation (DCMD) and air gap membrane distillation (AGMD)—yielding a 55 % and 198 % increase in permeate flux and a 35 % and 58 % decrease in specific thermal energy consumption, respectively. A numerical model was successfully developed to predict the permeate flux observed experimentally from the ENMs, accurately determining the mass and heat transfer mechanisms in all MD processes. Comparison of permeate flux and thermal efficiency under identical conditions highlighted the model's reliability in capturing process performance. The use of the electrospinning technique has been found to be a promising approach to creating robust and high-performance MD membranes by taking advantage of the unique properties of nanofibers and clay nanoparticle fillers. • Electrospun nanofiber membranes exhibited high porosity (~93 %), high LEP (~3 bar), and superhydrophobicity (~150° contact angle). • Electrospun nanofiber membranes displayed higher mechanical strength than commercial PVDF membranes. • Electrospun nanofiber membranes were evaluated in three different Membrane Distillation configuration. • Vacuum-assisted air gap membrane distillation outperformed other configurations, achieving 198 % higher flux and reduced energy consumption.