(478d) New Fouling-Resistant High-Flux Membranes for Seawater Desalination

This presentation covers new high-flux and fouling-resistant reverse osmosis membranes synthesized through interfacial polymerization for seawater purification.  We will review and discuss the state-of-the-art membranes in the thin-film-composite (TFC) structure prepared by interfacial polymerization.  Recent advances have been in high flux TFC interfacially polymerized membranes for increasing water productivity and decreasing energy consumption.  We have synthesized high flux membranes by incorporating a hydrophilic additive in the aqueous amine solution during interfacial polymerization, resulting in increasing water flux significantly through an additional pathway for water transport while maintaining high salt rejection via charge repulsion.  For seawater desalination using synthetic 3.28 wt% NaCl solution at 800 psi (5.52 MPa) and 25^oC, the membrane synthesized with the hydrophilic additive, o-aminobenzoic acid–trimethylamine salt, showed a very high flux of 1.81 m³/m²/day (44.4 gallons/ft²/day (gfd)) and a salt rejection of 99.41%.  This flux was 83.5% higher than the membrane synthesized without the hydrophilic additive (0.99 m³/m²/day or 24.2 gfd).  The high-flux membrane was further tested using seawater from Port Hueneme, CA and exhibited a very good and stable desalination performance for 30 days.  FTIR confirmed the good membrane stability.  The membrane synthesized with hydrophilic additive showed significantly improved fouling resistance using sodium alginate, a common contaminant derived from seaweed, as the model foulant.  In the presence of 25 ppm sodium alginate in the synthetic 3.28 wt% NaCl feed solution, the water flux reduction of the membrane synthesized with the hydrophilic additive was 11.0% compared to 18.2% for the membrane synthesized without the additive.  With 50 ppm sodium alginate in the feed solution, the water flux reduction of the membrane synthesized with the hydrophilic additive was 19.8% compared to 31.8% for the membrane synthesized without the additive.  Analysis of the fouling resistance using the resistance-in-series model indicated that the values of the ratio of the mass transfer resistance due to the foulant for the membrane synthesized with the hydrophilic additive to that for the membrane synthesized without the hydrophilic additive were 0.30 and 0.29 for 25 ppm and 50 ppm sodium alginate in the feed solutions, respectively.  Analysis using atomic force microscopy (AFM) showed a smoother membrane surface for the membrane incorporated with the hydrophilic additive.  In addition, the contact angle of the synthesized membrane reduced from 74^o to 58^o with the incorporation of the hydrophilic additive, which confirmed the increase of surface hydrophilicity.