Preparation And Characterization Of PES/SPSF Nanofiltration Membranes

Polyethersulfone（PES）membranes was blending with sulfonated polysulfone（SPSF） to give it charged in order to improve the desalination rate of the membraneby immerseprecipitation phaseinversion. N,N-Dimethylacetamide（DMAC） was used as casting solvent, different concentration of Poly（ehtyleneglyeol）（PEG400）, ethanol were used as theadditives. Theeffects of SPSF with different sulfonation degree and different ratio of PES/SPSF PEG content and ethanol content on structures and performances of the membrane were investigated.Also, the effects of the evaporation time, temperature and the composition of coagulation bath temperature and its influence on structure and performance of nanofiltration membrane were researched. Modified with cross linkable in order to get the density skin increase the rate of desalinationexplore the crosslinking process crosslinking agent of Polyvinyl Alcohol（PVA） and Glutaraldehyde（GA） effect on the membrane density, and the membrane in crosslinking solution soak time effect the performance of the membrane. The propertiesof Polyethersulfonenanofiltration membrane were characterized by theretention rate, water yield, surface water contact angle, SEM and so on.The results showed that 10% of sulfonation degree SPSF membrane was most densest, when SPSF sulfonated degree increased to 25%, the cross-section morphology of the membrane appeared a lot of typical finger hole against resistance to pressure and separation performance of membrane. In keeping the total solid content is constant, increase the proportion of SPSF, due to its poor uniformity of casting solution, SPSF film-forming property is poor, so it could reduce the mechanical properties of the membrane, and could not improve the membrane desalination rate, comprehensive performance in optimal when PES/SPSF = 6/4.The results showed that with the PEG400 content increasing, the viscosity of the casting solution raised, the density of membrane decreased, the water yield rised.With the comprehensive consideration, when PEG400 content in 5 wt %, membrane desalination rate and water yield are better. The results showed that with the ethanol content increasing, the viscosity of the casting solution raised, the density of membrane increased, desalination rate improved.When ethanol content up to 17 wt % will obviously reduce the membrane water yield because of the compact surface layer thickness increases obviously. So the 15 wt % ethanol content in the casting membrane system is more suitable. At this time, the rejection of 2g/L Na₂SO₄（57%） solution and water yield（33 L/（m²Â·h））.In membraneprocess,extend the time ofevaporation,and improve the evaporation temperature can increase the density of membrane,improve the desalting rate of membrane,but when the evaporation time is too long or the temperature is too high,the density of the membrane layer thickening,thus affecting the membrane water yield.When evaporation temperature up to 100℃,evaporation time at 3 min,the rejection of2g/L Na₂SO₄（71.6%）solution and water yield（7.6 L/（m²Â·h））,the rejection of 2g/L Na Cl（27.2%）solution and water yield（26.2 L/（m²Â·h））;With the coagulation bath temperature decreased,the membrane density improved,when coagulation bath temperature reduced to 5℃,the rejection of 2g/L Na₂SO₄ reached 64.2%%,and water yield is 22L/（m²Â·h）;Solvents or ethanol is added in the coagulation bath,also can slowing downphase inversion and increase the density of membrane.Modified with cross linkable in order to get the density layer to improve the density of membrane and desalination rate of bivalent salt. Increased the processing time is advantageous to the function of surface layer, with reduced the content of PVA the viscosity of crosslinking solution decreased, obtained homogeneous density layer. When PVA content is 10g/L,the GA content 35g/L, processing time at 1h, the the rejection of 2g/L Na₂SO₄ above 95%.