| Polyacrylonitrile(PAN) with excellent thermostability and chemical stability wassuitable for preparing support membrane of composite nanofiltration(NF) membranes.Furthermore, PAN support membrane had unsaturated nitrile group that can hydrolyzeand be transferred into carboxyl group under alkalescent condition through propermodification. Interfacial polymerization took place on the membrane surface wherethere were the nitrile groups, P P'-Diamino-diphenylmethane(DDM) and trimesoylchloride(TMC). Consequently, composite NF membrane with chemical bonds wouldbe formed. In this work support membrane of composite nanofiltration membrane wasprepared with PAN as polymer materials, N-methylpyrrolidone (NMP) as solvent,Polyethylene glycol 600 (PEG600) or phosphoric acid (H3PO4) as additive by meansof L-S phase inversion method. Support membranes with a certain preparationconditions and proportion of concentration of PAN, concentration of NMP andconcentration of H3PO4 were modified with certain concentration of sodiumhydroxide (NaOH) within certain time and with certain concentration of hydrochloricacid (HCl) within certain time. Composite nanofiltration membrane was preparedwith DDM and TMC as monomers by means of interfacial polymerization accordingto P.W.Morgan's interfacial polymerization theory. The hydrophilicity of support membrane and modified support membrane was studied by thedetermination of contact angle of the membranes. Infrared spectrum (FTIR) was used to study thecomponent change of modified support membrane and composite nanofiltration membrane. Themicrostructure of support membrane, modified support membrane and composite nanofiltrationmembrane was observed using by environmental scanning electric microscope (ESEM). Waterflux of support membrane, modified support membrane and composite nanofiltration membrane,rejection for bovine serum albumin (BSA) of support membrane and modified support membrane,desalination for magnesium sulfate (MgSO4) of composite nanofiltration membrane were alsocharacterized in this work. In this work Random-arranged experimental design with aid of computer was used tooptimize the preparation conditions of support membrane and modified support membrane. Andexperimental data were calculated and regression analyzed with Statistical Analysis System (SAS)software and Visual Basic (VB) software. The models for water flux, rejection for BSA and average pore size of support membranewere obtained to predict the character of membrane with different preparation conditions.Additionally, the effects of concentration of PAN, the evaporation time of nascent membrane, kindof additive and concentration of additive were studied. As a result, support membrane wasprepared with rejection for BSA over 93 %, water flux about 100 L/m2·h, average pore size about40nm. The models for water flux, rejection for BSA, flux of BSA and contact angle of the modifiedmembrane were obtained to predict the character of membrane with different modificationconditions. And the effects of concentration of NaOH, modification temperature and modificationtime were discussed. In conclusion, support membrane was modified with rejection for BSA about83%, water flux about 70 L/m2·h, contact angle of the modified membrane about 40。. The effects of kind of monomer in water phase, concentration of DDM, concentrationof TMC, interfacial polymerization time, draining time and post-treatment time werestudied. And composite nanofiltration membrane was prepared with 0.1% of DDM,0.2% of TMC, interfacial polymerization time 15s, draining time and post-treatmenttime 60s, which showed the character of water flux 1-2 L/m2·h and rejection for MgSO474.46% at 0.3-0.8MPa. The FTIR spectra for modified membrane confirmed that some nitrile group of the supportmembrane had been transformed to carboxyl (-COOH). Furthermore, the composite film whichhad polymerized on the modified membrane was confirmed by the FTIR spectr... |
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