| Solvent resistant nanofiltration membranes can be widely used in organic solvent system, which is a significant breakthrough in aqueous system membrane. Compared to asymmetric membranes, the composite nanofiltration membranes prepared by interfacial polymerization method are gaining more and more attention because of key advantages.PI/PP composite NF membranes were prepared on a polypropylene(PP) supporting membrane via an interfacial polymerization(IP) technique, with 1,2,4,5-benzene tetra acyl chloride(BTAC) and m-phenylenediamine(MPD) as organic and aqueous monomers respectively. The chemical composition of the barrier layer and the morphology of the resulting membrane were characterized with infrared spectroscopy(FTIR) and scanning electronic microscopy(SEM), respectively. The rejection of PEG-400 and permeation flux of the resulting membranes were determined at 0.5 MPa transmembrane pressures, and the effects of the mole concentration ratio of aqueous/organic monomer, monomer concentration,addition of Na OH, temperature of chemical imidization as well as types and concentration of surfactant were investigated. It was found that with the increase of MPDA: BTAC concentration ratio, the functional layer structure became dense and then tended to be constant. Therefore, the rejection of PEG-400 increased rapidly before tended to be constant,while flux decreased rapidly and then tended to be constant. As the increase of monomer concentration or Na OH addition, the rejection increased fast and then decreased slowly,while the flux decreased rapidly at first, then slightly increased. With the increase of chemical imidization temperature, rejection increased first and then decreased, while flux changed exactly the reverse way, decreased first before increased. This can be explained that even though higher temperature can contribute to polyamic acid cyclization dehydration, it also has the potential to cause porosity defects and cracks to the barrier layer. By using different surfactants, such as anionic(SDS), non-ionic(Triton X-100) and cationic(TBAB,TEAC) surfactants, it was found that rejection of membrane with TBAB as surfactant was higher, which owing to composite membrane exhibited negatively charged behavior,TBAB contained larger size steric configuration cationic amine group, could promote the transmission of MPD. In addition, adding TMC to the organic phase could improve the rejection from 93.3% to 96.2%, while it only brought little change on the flux(87.3L·m-2·h-1).Subsequently, the solvent resistance performance of composite nanofiltration membrane(with TMC) was also investigated. In this thesis, 9 representative organic solvents were selected. After immersed in different solvents for 7 days, the tensile strength and elongation at break were tested under wet. The results showed that PI/PP membrane had the same excellent solvent resistance properties as membrane without TMC.Finally, three typical membranes: the largest flux membrane M1, the highest rejection membrane M2(without TMC), membrane M3 with TMC, were chosen to test the rejection of PEG 200~2000, respectively, in order to get the molecular weight cut off(MWCO) range of the three membranes.The results showed that M1 membrane achieved wonderful rejection for PEG molecular weight above 800 and the flux was 145.0 L·m-2·h-1at 0.5 MPa transmembrane pressures. M2 membrane achieved excellent rejection for PEG molecular weight above 400 and the flux was 87.9 L·m-2·h-1at 0.5 MPa transmembrane pressures.M3 membrane achieved excellent rejection for PEG molecular weight above 200 and the flux was 87.3 L·m-2·h-1at 0.5 MPa transmembrane pressures. It indicated that it was feasible to prepare a composite nanofiltration membrane used for specific MWCO. The functional layer contained a thickness of about 0.5 μm, which eliminated the cracks and improved the permeation flux significantly. |
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