Hydrophobic polyethersulfone porous membranes for membrane distillation

Membrane distillation (MD) is a thermal, vapor-driven transportation process through micro porous hydrophobic membranes that is increasingly being applied to seawater and brine desalination processes. Two types of hydrophobic microporous polyethersulfone flat sheet membranes, namely, annealed polyethersulfone and a polyethersulfone/tetraethoxysilane (PES/TEOS) blend were prepared by a phase inversion process. The membranes were characterized and their performances were investigated using the vacuum membrane distillation of an aqueous NaCl solution. The performances of the prepared membranes were also compared with two commercially available hydrophobic membranes, polytetrafluorethylene and polyvinylidene fluoride. The influence of operational parameters such as feed temperature (25-65 degrees C), permeate vacuum pressure (200-800 mbar), feed flow rate (8-22 mL/s) and feed salt concentration (3000 to 35000 mg/L) on the MD permeation flux were investigated for the four membranes. The hydrophobic PES/TEOS membrane had the highest salt rejection (99.7%) and permeate flux (86 kg/(m(2).h)) at 65 degrees C, with a feed of 7000 ppm and a pressure of 200 mbar.