Study On The Poly[2-(N, N-Dimethyl Amino)Ethyl Methacrylate]/Polysulfone Positively Charged Hollow Fiber Composite Nanofiltration Membrane

In this paper, A positively charged composite hollow fiber nanofiltration(NF) membrane was developed by interfacial polymerization(quaternization) using polysulfone(PSF) ultrafiltration membrane as support membrane, poly[2-(N,N-dimethyl amino)ethyl methacrylate] (PDMAEMA) as coating material, and p-xylylene dichloride as crosslinking agent. The effects of the support membrane, PDMAEMA, crosslinking agent, solvent, catalyst, and preparing methods were studied. The basic rules were summed up to prepare composite NF membrane using polyelectrolytes as pre-polymer. The main studies were as follows.PDMAEMA was prepared by free radical bulk polymerization, and aqueous PDMAEMA solution can be purified by hollow fiber ultrafitration technology. PDMAEMA aqueous solution shows responsibility to concentration, added salts and pH value. Crosslinking PDMAEMA hydrogel shows the same characteristics.The preparing conditions of PDMAEMA composite NF membrane were investigated, using PSF flat membranes as support membranes. The results show that, the static interfacial polymerization was conducted in organic phase. The optimized conditions for NF membrane preparation were obtained: the concentration of PDMAEMA was 2%(wt%), the concentration of p-xylylene dichloride was 1 1.5%(wt%), NaHCO₃ can be used to maintain alkalescence, The polymerization can be carried out at room temperature and the reaction time was 5 hour. In addition, radiation crosslinking of PDMAEMA can be used to prepare PDMAEMA composite NF membrane, the rejection of which to 2g/LMgSO₄ is about 50%.In the preparation experiment of outside-pressure composite hollow fiber NF membranes, appropriate support membranes were selected;adsorption of PDMAEMA solution on the surface of support membranes was studied;the optimized concentration of PDMAEMA is 0.75%(wt%);0.148mol/L NaHCO₃ in PDMAEMA solution could improve rejection of the NF membrane to the bivalent salts, but advance of the flux is small;A hollow fiber NF membrane with high rejection and high flux can be prepared from PDMAEMA solution containing 5%(v/v) ethanol, with the rejection is above or equal to 98% to 2g/LMgSO₄, and the flux is 19.5L/(m²Â· h) for inside-pressure membrane, and above or equal to 20 L/(m²Â· h) for outside-pressure membrane;KI can be used as catalyst to reduce reaction time to 3.5 hour.The rejection of positively charged PDMAEMA composite hollow fiber NF membrane to inorganic salts is ordered as follow: MgSO₄> MgCl₂> NaCl> KCl> KI, and the rejection tocations is Mg2+ >Na+ >K+, and to anions is Cl">Br">F. The rejection is above 60% to sucrose, and 37.4%(inside-pressure membrane) and 32.2%(outside-pressure membrane) to D-mannose. Soft water can be obtained from the NF process. The rejection is above 50% to small charged dyes, which molecule weight is above 300. The operating conditions affect the rejection performance. With the increase of concentrations of inorganic salts, the rejection and flux of NF membrane reduce slightly. With the increase of operating pressure, the rejection and flux of NF membrane enhance. And the rejection of PDMAEMA composite hollow fiber NF membrane shows temperature-responsive and pH-responsive.PDMAEMA inside-pressure composite hollow fiber NF membrane was prepared. In the experiment, the optimized concentration of PDMAEMA is 0.75%(wt%). The relation of changes of rejection and flux of the inside-pressure NF membrane to inorganic salts and operating pressure are in accord with Gauss function. The solvent resistance was observed, using pure water, O.5mol/LHC1, 0.5mol/LNaOH and 30%H2O2(wt%) as solvent respectively. The results show that: it is good in sterilization, alkali-resistance and oxidation resistance for PDMAEMA composite NF membrane, but the NF membrane is not fit to keep and use in acid mediums.