Study Of Sulfonated Copoly(Phthalazinone Ether Sulfone)Composite Nanofiltration Membranes

Copoly(phthalazinone ether sulfone) is a kind of high performance polymer, possesses high glass-transition temperature, good membrane-forming property, mechanical property and chemical stability. The sulfonated copoly(phthalazinone ether sulfone) became charged material and the hydrophilicity of polymer was also imporved because of the introduction of sulfonic acid group. Therefore, sulfonated copoly(phthalazinone ether sulfone) may be an excellent potential candidate for membrane material with high thermal stability, chlorine resistance.In this work, copoly(phthalazinone biphenyl ether sulfone)(SPPBES) composite nanofiltration membrane was prepared based on coating a SPPBES active layer on top of poly (phthalazinone ether sulfone ketone)(PPESK) ultrafiltration support membrane. The effects of composition of coating solution and curing treatment conditions on the performance of SPPBES composite membranes were investigated. The membrane exhibited a permeate flux of73L/m2h and84%rejection of Na2SO4at1.0MPa and20℃when prepared under the optimum condition:SPPBES concentration3%, ethylene glycol monomethyl ether (EGME) and acetone as the solvent, the concentration of inorganic salt additive LiCl was1%, the concentration of organic solvent additive glycerol was25%, N,N-dimethy lacetamide (DMAc) concentration was5%.The SPPBES composite membranes were characterized by FTIR, SEM, and contact angle. The membrane stability was investigated. From the results, it can be indicated that SPPBES composite membrane had good chlorine resistance, acid-alkaline stability and excellent thermal stability. In this work, the effect of operating conditions on the membrane performance was also investigated. With the operating temperature increased from18℃to90℃, permeate flux increased two times, while there was no obvious change in the Na2SO4rejection. It was found that flux increased somewhat linearly with increasing pressure, while the rejection of the composite membrane increased first then reached a plateau.The composite nanofiltration membranes were prepared by coating the solution of sulfonated poly(phthalazinone ether sulfone)(SPPES), sulfonated copoly(phthalazinone biphenyl ether sulfone)(SPPBES), sulfonated copoly(phthalazinone terephthalic ether sulfone)(SPPHES) onto the top surface of PPESK ultrafiltration support membranes, respectively. The relationships between polymer structure of coating solutions and performance of composite membranes were investigated. It can be indicated from the results of membrane stability that SPPES, SPPBES and SPPHES composite membrane all had good chemical stability and thermal stability. SPPES composite nanofiltration membrane which has more DHPZ exhibited good separation performance, the salts rejection of composite membranes decreased as follows:SPPES> SPPHES> SPPBES; because of the introduction of diphenol, SPPBES composite nanofiltration membrane had higher permeate flux, meanwhile, the Na2SO4rejection can keep around80%.The composite membranes which possess low rejection of inorganic salt were selected for the separation and enrichment of polysaccharide-inorganic solutions. The polysaccharide rejection was100%, the sodium acetate rejection was only12%, turbidity removal rate was97.8%, and the COD removal rate was31%, the flux was17L/m2h at0.8MPa. The effects of operating conditions on membrane performance and membrane fouling were studied. The results showed that, the flux of the membrane increased from7.2to22.8L/(m2h) and the polysaccharide rejection increased from86%to94%with the operating pressure increased from0.4MPa to1.2MPa; the flux obviously increased from13to40L/(m2h) as the operating temperature elevated from20℃to80℃; there was no obvious change in the rejections of polysaccharides and inorganic, while the permeation flux decreased gradually with increasing of operating time. When0.1mol/L HC1, NaOH and NaCIO were used as cleaning agent, the contaminants of membrane surface were well removed, so the three kinds of detergent had good cleaning effect. The change of performance on the running of composite nanofiltration membrane was studied at60℃,0.8MPa. Through five times cycles, composite membrane can effectively separate inorganic salt and polysaccharide. So the membrane can realize the separation and enrichment of polysaccharide.The effect of operating temperature on the performance of sulfonated copoly (phthalazinone biphenyl ether sulfone)(SPPBES) membrane was investigated, and the characteristic parameters of nanofiltration membrane were obtained through analyzing the experimental results by non-equilibrium thermodynamics model and pore model. Lp increased from20.23X10-12m s-1Pa-1to68.33X10-12m s-1Pa-1(increased by2.4times), the effective pore radius increased from0.48nm to0.81(increased by69%) as the operating temperature increased from10℃to90℃. When the operating temperature increased from10℃to50℃, effective pore radius of SPPBES composite membrane increased from0.48nm to0.52nm, increased by9%, while effective pore radius of DK Desal5commercial membrane increased from0.58nm to0.67nm, increased by15%.