Preparation,CharacterizationandSaltRejectionofNegativelyCharged PolyamideNanofiltrationMembranes

Four thin-film composite (TFC) polyamide negatively charged nanofiltration (NF) membranes (NF-PS-1, NF-PS-2, NF-PS- 3 and NF-PS-4) were prepared via interfacial polymerization tech - nique which involved the formation of a polyamide thin film at the interfacial polysulfone (PS) microporous substrate between two immiscible liquid phases; an aqueous phase containing piperazine and an organic phase containing trimesoyl chloride (TMC = 0.25, 0.50, 1.00 and 2.00 wt%). Correlations of the intrinsic properties of these four NF filtration membranes, in regarding to the physical structures, surface negative charge density, pure water flux, pore size and the NF filtration performances, on the composition of the weight-% of TMC in the organic phase were investigated. Experimental results clearly demonstrated that NF membrane prepared from using 1.0 wt-% of TMC in hexane phase (i.e., NF-PS-3) gave a much higher salt rejec - tions on salt containing negative divalent salts like Na 2 SO 4 and MgSO 4 ; the maximum rejection of Na 2 SO 4 and MgSO 4 were both to be 99.6 % for NF-PS-3 (TMC = 1.0 wt-%) while the rejections of Na 2 SO 4 and MgSO 4 for the rest of the three NF membranes were in the order of NF-PS-2 (TMC = 0.50 wt-%) > NF-PS-1 (TMC = 0.25 wt-%) > NF-PS-4 (TMC = 2.00 wt-%). Effects of the pH of the feed and the applied filtration pressure on the MgSO 4 rejection were also investigated for this series of nanofiltration membranes.