Fabrication and optimization of tunable pore size poly(ethylene glycol) modified poly(vinylidene-co-hexafluoropropylene) membranes in vacuum membrane distillation for desalination

Abstract

• PEG modified PVDF-co-HFP membranes with tunable pore size for desalination for VMD. • Membranes characterized for morphology, hydrophobicity, stability, flux and rejection performance. • TOPSIS to select optimal membrane based on overall performance and characteristics. • 3D CFD modelling with excellent synergy between estimated and experimental data. • Optimized membrane - 19.72 LMH flux and >99.8% rejection in desalination (4% NaCl). We report poly(vinylidene-co-hexafluoropropylene) (PVDF-co-HFP) flat sheet membranes incorporated with poly(ethylene glycol) (PEG) of varied molecular weights and concentrations, was incorporated in PVDF-co-HFP matrix by solution blending to achieve fine control over membrane pore size, porosity and PSD, which are essential requirements for high-performance VMD desalination. Prepared membranes were characterized by surface morphology, porosity, pore size and distribution, hydrophobicity, thermal and dimensional stability. Membrane porosity and thus permeate flux was increased with the concentration of PEG in the membrane matrix. A technique for order preference by similarity to the ideal solution (TOPSIS) was used to predict the most suitable membrane for water desalination by VMD. Reported M3 membrane (20 wt% PVDF-co-HFP + 10 wt% PEG-400) showed superior performance (>99.8% salt rejection, and 19.72 l m -2 h −1 ) in comparison to other PVDF based flat sheet membranes reported in the literature. A three-dimensional comprehensive computational fluid dynamics (CFD) model is also presented to describe the vapour flux profile in the VMD process with reasonable accuracy. Membrane based on PVDF-co-HFP copolymer incorporated with PEG showed longevity up to more than 100 hrs and assessed as promising membrane material for VMD process because of interconnected pore structure and narrow pore distribution.