Studies On Preparation And Performance Of Polyamide Composite Forward Osmosis Membrane

Forward osmosis (FO) is a novel membrane technology developed in recent years. The focus of this thesis is preparation and characterization of the composite polyamide FO membranes. The composite FO membranes were prepared by interfacial polymerization with a thin-film polyamide layer on the porous substrates. The proportion of casting solutions and preparation conditions on the structure and properties of porous substrates were studied. The factors which affected the formation of the thin-film layer were studied. Different test conditions were also employed to study the effect of test conditions on performance of FO membrane. Desalination of different kinds of brackish water with different concentrations was studied to evaluate the further application of FO membranes. Furthermore, the fouling of FO membrane in presence of humic acid in the feed solution was investigated to explore the ability of anti-fouling of the composite FO membrane.Porous support membrane was prepared by L-S phase inversion method. Conditions that could affect the structure of the substrate were studied, including polymer concentration, additive concentration, evaporation time, humidity and temperature of gel-bath. Of which, water flux increased both with the increase of the concentration of polymer and addictive firstly and then decreased while reject varied little with different concentrations. And the evaporation time had effect on the pore structure on the surface of the substrates while the temperature of the gel-bath can affect the pore structure throughout the substrate. What's more, humidity has played important role in the formation of the porous polysulfone substrates. The best condition was that 18% polysulfone polymer dissolved in 73.6%DMAc and 8% PEG addictive and 0.4% H2O as the non-solvent, evaporated 30s in the environment at humidity of 72%rh and finally coagulated in the bath with temperature maintained at 40℃. In order to improve the membrane rejection, a series of experiments were conducted to investigate the influence of interfacial polymerization conditions, including concentration of reactants and reaction time, which can affect the degree of the polymerization and finally the performance of the thin-film layer. The optimal preparation conditions were that 2.0%(wt) m-phenylenediamine in water and 0.1%(w/v) trimesoyl chloride in hexane, reaction time was 60 seconds at room temperature.The test conditions in the FO process including the solution flow rate, draw solution concentration and membrane orientation had been studied, which can affect the performance of the FO membranes through putting effect on the internal concentrated polarization (ICP). The application in desalination of brackish water with different concentrations and the artificial seawater had been studied with the purpose of providing valuable information for the practical desalination process. The performance of the prepared FO membranes was also tested under RO condition, which achieved high water flux 38.6L.m-2.h-1and rejection 98%. Finally, the anti-fouling of FO membrane was investigated in presence of humic acid and the performance of FO membrane was found decrease little when thin-film layer oriented to the feed solution.