Fabrication and Characterization of Hydrophobic PVDF-based Hollow Fiber Membranes for Vacuum Membrane Distillation of Seawater and Desalination Brine

Fabrication of hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membranes was studied using Lithium chloride (LiCl) and polyethylene glycol (PEG) 35000 as non-solvent additives by dry-wet phase inversion process. Scanning Electron Microscopy revealed that LiCl addition made the finger-like voids become smaller and provided a sponge-like structure, in addition to increasing the membrane surface roughness to 42 nm, porosity to 83% and mean pore size to 5.75 nm with narrower pore size distribution. It also decreased Young's modulus to 63 MPa while, no significant improvement was observed in water contact angle (115.5o). During vacuum membrane distillation (VMD) of water, Mediterranean Sea water, Red Sea water and Red Sea brine, the PVDF membranes spun with LiCl achieved higher water permeation flux with values of 48, 32, 25 and 19 L/m2h, respectively. The flux-salinity relationship was represented by empirical correlations. The two membranes exhibited high salt rejection values (99.4%-99.8%) for the investigated saline solutions. These results suggest numerous interventions for membrane distillation within integrated desalination/salt recovery schemes or as a stand-alone facility with the combination of complementary appropriate thermal crystallization units. Two VMD/solar pond scenarios were investigated for dual production of water and salts.