| Nanofltration (NF) membranes have some advantages such as low operation, highdesalination rate for bivalent ion and the organic with the relative molecular weightbetween200-1000and so on, due to their special pore size and the surface with acertain charge. Nanofltration membranes have been widely applied to separate orconcentrate aqueous solutions containing organics or salts. However, the low membraneflux, less species and membrane fouling problem make the nanofltration membranesare constrained in the practical applization.The common commercial nanofltration membranes were polyamide nanofiltrationmembranes because of its high flux and certain desalination rate. The polyamidenanofiltration membranes contains poly piperazine amide and aromatic polyamide whilethe poly piperazine amide composite membranes were more widely used relatively. Theresearch about the poly piperazine amide composite membranes have become mature,but about the aromatic polyamide composite membranes the opposite. This paper aimedat preparing of nanofiltration membranes with high flux and certain desalination rateunder low pressure. The main works are as follow:(1) The effect of the substrate membranes which were prepared with differentmembrane materials and pore-foaming agent on the composite membranes weresystematically investigated. The morphology and contact angle of substrate membranesand the composite membranes were analyzed respectively.(2) The polyamide composite membranes were prepared by interfacialpolymerization with different monomers. The effect of interfacial polymerizationconditions on the separation performance of composite membrane and the composite membrane separation properties for different salt solutions were systematicallyinvestigated. The morphology and contact angle of substrate membranes and thecomposite membranes were analyzed respectively. The main conclusions can be drawn:(1) The substrate membranes were prepared via phase inversion induced byimmersion precipitation using different membrane materials ((polyether sulfone (PES)/polysulfone (PSF)/Poly (vinylidene fluoride)(PVDF)/ethylene/vinyl alcoholcopolymer (EVOH)). Then the composite membranes were prepared by interfacialpolymerization on the substrate membranes prepared before. The composite membraneseparation properties were investigated. Results show that the composite membranesprepared on the substrate membranes showed the better separation properties.(2) The substrate membranes were prepared via phase inversion induced byimmersion precipitation using casting solutions containing PSF, different pore-foamingagent (PVP/PEG600/Acetone/LiCl) in DMAc as solvent. Then the compositemembranes were prepared by interfacial polymerization on the substrate membranesprepared before. The composite membrane separation properties were investigated.Results show that the pore structure of the substrates which were prepared bypolysulfone (PSF) and pore-foaming agent (PVP and PEG600) was fingerlike pore. Thecomposite membranes prepared on this substrate membranes prepared withpore-foaming agent PVP and PEG600showed the better separation properties.(3) The polyamide composite membranes were prepared by interfacialpolymerization of1,3-phenylene diamine (PDA) and trimesoyl chloride (TMC) on thesubstrate membranes. The effect of interfacial polymerization conditions on theseparation performance of the composite membrane and the composite membraneseparation properties for different salt solutions were systematically investigated. Thesurface morphology and contact angle of the composite and substrate membranes wereanalyzed respectively. Results show that the optimum polymerization conditions are asfollows: the concentration of PDAis1.5wt%, the concentration of TMC is0.1wt%, thesoaking time in aqueous phase is3min, reaction time is60s, curing temperature is80℃,curing time is3min. The membrane prepared under the optimum conditionsexhibited a pure water flux of9L·m-2·h-1, a rejection of99.5%to2000mg/L MgSO4aqueous solution, and a salt rejection order of Na2SO4＞MgSO4＞MgCl2＞NaCl when tested under0.6MPa. Moreover, the changes of morphology and contact angle showedthat a polyamide active layer was formed on the substrate by interfacial polymerization.(4) The polyamide thin-film composite membranes were prepared by interfacialpolymerization of piperazine (PIP) and TMC on the substrate membranes. The effect ofinterfacial polymerization conditions on the separation performance of the compositemembrane and the composite membrane separation properties for different saltsolutions were systematically investigated. The surface morphology and contact angleof the composite and substrate membranes were analyzed respectively. Results showthat the optimum polymerization conditions are as follows: the concentration of PIP is2.0wt%, the concentration of TMC is0.15wt%, the soaking time in aqueous phase is3min, reaction time is60s, curing temperature is80℃,curing time is3min. Themembrane prepared under the optimum conditions exhibited a pure water flux of18L·m-2·h-1, a rejection of86.8%to2000mg/L MgSO4aqueous solution and a saltrejection order of Na2SO4＞MgSO4＞MgCl2＞NaCl when tested under0.6MPa.Moreover, the changes of morphology and contact angle showed that a polyamideactive layer was formed on the substrate by interfacial polymerization.(5) The polyamide thin-film composite membranes were prepared by interfacialpolymerization of PDA, PIP and TMC on the substrate membranes. The effect ofproportion of PDA and PIP in aqueous phase on chemical structure of the active layerpolymer, surface morphology and separation properties of composite membranes wasstudied. Results show that the proportion of the monomers PDA/PIP have obviouslyeffects on the polyamide aggregation structure, and as the proportion of PDAdecreased,the average roughness of the composite membranes decreased, the flux increased whilethe rejection decreased from.(6) The polyamide thin-film composite membranes were prepared by interfacialpolymerization of PDA, PIP and TMC on the substrate membranes as the proportion ofmonomers PDA/PIP was25/75. The effect of interfacial polymerization conditions onthe separation performance of composite membrane and the composite membraneseparation properties for different salt solutions were systematically investigated.Results show that the optimum polymerization conditions are as follows: theconcentration of TMC is0.1wt%, reaction time is60s, curing temperature is80℃, curing time is3min. The membrane prepared under the optimum conditions exhibited apure water flux of14L·m-2·h-1, a rejection of93.7%to2000mg/L MgSO4aqueoussolution, and a salt rejection order of Na2SO4＞MgSO4＞MgCl2＞NaCl when testedunder0.6MPa. Moreover, the changes of morphology and contact angle showed that apolyamide active layer was formed on the substrate by interfacial polymerization. |
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