High-flux and fouling-resistant membranes for brackish water desalination

Novel high-flux and fouling-resistant reverse osmosis membrane were synthesized and characterized under brackish water desalination conditions using 2000 ppm NaCl solution at 225 psi (1.55 MPa) and 25 °C. The o-aminobenzoic acid-triethylamine salt was added into m-phenylenediamine (MPD) solution to react with trimesoyl chloride (TMC) during the interfacial polymerization between MPD and TMC. The membrane synthesis conditions including MPD concentration, TMC concentration, and interfacial polymerization time were optimized. The membrane synthesized under the optimal conditions was post-treated with aqueous solutions containing glycerol, sodium lauryl sulfate, and camphorsulfonic acid-triethylamine salt to further increase the water flux. The resulting membrane showed a flux of 2.22 m3/m2/day (54.4 gallons/ft2/day (gfd)) and a salt rejection of 98.6%. The fouling-resistant property of the synthesized membrane was enhanced by physically coating a cross-linked polyethylene glycol (PEG-200) layer on top of the thin film. The membrane coated with 10 wt% cross-linked PEG demonstrated a very high flux of 2.46 m3/m2/day (60.4 gfd) and outperformed the state-of-the-art commercial membrane. Using dodecyltrimethylammonium bromide, a cationic foulant, and tannic acid, an anionic foulant, as model foulants, the coated membrane exhibited much reduced flux decline. The surface morphologies of the modified and unmodified membranes were analyzed using scanning electron microscopy and atomic force microscopy. The results showed a smoother membrane surface by coating the PEG layer.