Preparation And Performance Of Nano-filtration Membrane With Relatively Low Operating Pressure And High Water Flux

Nano-filtration （NF） membrane is a novel kind of pressure-driven membrane betweenultrafiltration and reverse osmosis membrane. Its separation characteristics include: ion selectivity,low operation pressure and molecular weight cut-off between200and1000Da. Therefore, itbecomes research focuses in membrane areas in recent years. In this thesis, research contents weredivided into three sections:Firstly, the influences of additives （such as: PEG and zeolite） on the performances of UFmembrane were researched. PEG was a pore-foaming agent in phase inversion that can increaseporosity, while zeolite made the delayed phase separation occur in the membrane surface at theevaporation stage, which therefore caused a denser surface. However, Nano-scale channels andnegatives in the zeolites could let water molecules go through the channels without hindrance andreject protein, which therefore. This made the water flux and protein rejection improvesimultaneously, and successfully avioded the usual trade-off phenomenon （the increase of waterflux would cut down the rejection, while the improve of rejection would conversely restrict theenhancement of water flux）.Then, the effect of grafting condition on the performances of NF membrane was studied.Results showed that flux decreased while the rejection increased with increasing monomerconcentration, radiation time and strength. The optimal grafting condition was optimized asradiation time of7min, monomer concentration of50%and instance between ultraviolet lamp andmembrane surface of22cm. Water flux of optimized NF membrane was60L/m²h, and rejectionof AlCl₃, CaCl₂and MgCl₂was higher than90%. The rejection of optimized NF membrane todifferent salt followed the order of AlCl₃>CaCl₂>MgCl₂>NaCl>LiCl>MgSO₄>Na₂SO₄.Last, the ion selectivity, water softening, dye de-colorization and sea water desalination of NFmembrane was studied. The research showed that rejection of Li⁺and Mg²⁺was46.1⁴6.8%and87.5⁹0.8%, respectively; rejections of both Ca²⁺and Mg²⁺in hard water were higher than90%; the rejection of both methylene blue and congo red were higher than99%. Thus, NF membranecan be used for ion selecting, water softening, dye de-coloring.