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

In this paper, A positively charged compositer 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. Using 2g/L MgSO₄ as the feed liquid, under an operating pressure of 0.8MPa, the inside-flow hollow fiber NF membrane has a salt rejection above 88.4%, and a permeating flux of 17.75 L/m² h;but a plate NF membrane has a salt rejection above 96.5% and a permeating flux of 24.2L/m² h.The study conducted research on the following three fields: firstly, the characteristics of the interfacial polymerization system of PDMAEMA aqueous solution/p-xylylene dichloride heptane solution were systematically investigated, such as the agents added into the interfacial polymerization system influence on the characteristics of the NF membrane. For instance, NaHCO₃ can adjust the pH of the PDMAEMA aqueous solution and maintain the macromolecule conformation of PDMAEMA, which could enhance the cross-linking reaction. The plate NF membrane prepared according to this way, has a salt rejection of 92.5% and a permeating flux of 15.6 L/m² h. Additionally, the turnoff ratio of plate and hollow fiber NF membrane has been increased. The time of cross-linking reaction can be effectively reduced from 5 hr to 3.5 hr by adding KI of 0.172mol/L. The PDMAEMA aqueous solution with the ethanol of 5% (v/v) can develop high performance NF membrane with higher salt rejection and higher permeating flux. According to the overall experiment, when the concentration of the PDMAEMA aqueous solution is 0.75%, the characteristic of hollow fiber NF membrane can be achieved the best.Secondly, positively charged hollow fiber NF membrane has the selectivity towards the rejections of inorganic salt, which can reject the univalent ion below 50%, while it can reject the bivalent ion above 80%. Compared with the commercial NF membrane, such as NTR7450, Desal-5, the hollow fiber membrane prepared by ourselves has the same even more higher rejections towards MgSO₄ and glucide of small molecule. Also, changing the operating conditions, say, temperature, pressure, pH, concentrations of feed liquid and so on, the priorities of NF membrane have been tested farther.Finally, the inside-flow hollow fiber composite NF membrane was applied to the rejection of dye. The results show that the membrane can effectively prevent the dye molecule through the membrane with a rejection of 99%, no matter the charge of the dye is positively or negatively. Furthmore, the study examined the separation between dye molecule and inorganic salt molecule by the NF membrane, which can reject the salt about 30%⁶5%. This is an effective way to increase the purity of the dye products. Meanwhile, the dye molecule gathering near the membrane has reduced the contamination of the NF membrane, which advanced the decreasing of the permeating flux. So this is a serious problem under resolving.