| Nanofiltration (NF) is a pressure-driven process for selective separation of solute mixture with molecular weight range from200to1000. This makes NF suitable for the removal of relatively small organic micro-pollutants, color from surface water or ground water, pharmic molecules and degradation products from the effluent of biologically treated wastewater. It is also useful for the dye concentration, seawater desalination and resource recovery. Recently, NF membrane has drawn great attention due to its advantages such as relatively low operating pressures, high fluxes, low operating and maintenance costs. Nanofiltration membrane can be fabricated by various methods:including phase-inversion process, blending method, chemical modified method, composite method, including interfatial polymerization (IP) method, which is the most effective method for preparation the composite NF membranes.Thin-film composite NF membranes were developed by cross-linking the hydroxyl ended groups of hyperbranched polyester (HPE) with trimesoyl chloride (TMC) on polyacrylonitrile (PAN) support. The effects of HPE structure and number of terminated hydroxyl groups on the NF membrane properties were studied. The obtained NF membranes showed high rejection, high flux and well long-run stability. The chemical structure of the composite NF membrane was characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The morphology of NF membranes surface and cross-section were characterized by scanning electron microscopy (SEM). The hydrophilicity of the NF membrane were characterized by water contact angle goniometer (OCA20). The effect of monomer dosage, reaction time and heat-treatment time were studied to optimize the performance of the NF membranes. According to the results, the separation performance of HPE-PAN NF membranes is mainly related with the monomer concentrtion in the aqueous phase and that in the organic phase. The optimized preparation condition under this study is that-OH/-CC10is fixed on6:1, the cross-linking time is fixed on20min, heat-treatment time is fixed on20min under80℃. Water permeability and salts rejections of the membranes were measured. The flux and rejection of NF-G4membranes for Na2SO4(1g/L) reached42.6L/(m2·h) and96.8%under0.6MPa, respectively.The physicochemical characteristics of thin film composite membranes were also studied. The results showed the NF membrane had better acid-alkali stability, and the flux of the membrane kept relative stable in the long-term continuous running. Moreover, the separation characteristics of composite membranes under different operation pressures were also investigated. The flux of water was proportional to the operation pressure, while the salt rejection gradually increased. It was also found that the NF-Gx (x=2,3,4) membranes became more hydrophilic with the generation of HPE increasing. The salts rejection order of NF membranes for different salts with high rejection is Na2SO4>NaCl>MgSO4>MgCl2.The performance of NF membrane in treatment dyeing wastewater was experimentally studied. The result showed that the anion and the high molecular weight dyeing wastewater could be effectively treated and concentrated through nanofiltration process with HPE-PAN NF composite membranes. This phenomenon may be the result of Donnan exclusion and pore sieving cooperation. The dye rejection of NF-G4membrane was higher than92%in the whole concentrated process. After the enrichment process, the dye concentration was2.5times highter than the initial concentration. The average desalination of the process was about71.89%, and increased with NaCl concentration increasing in dyeing wastewater. It is proved that the NF membranes were quite favorable to recycle the dye in high salinity dye wastewater. |
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