Effects of organic solvents and different aqueous-phase additives on the polyamide (PA) thin-film composite (TFC) membranes for forward osmosis

摘要

Forward osmosis (FO) membranes have gained increasing attention due to their potential advantages such as low fouling propensity, low energy consumption and high recovery. In this study, an investigation about the effect of polyamide (PA) structure on performance of the thin-film composite (TFC) FO membranes in the interfacial polymerization has been carried out systematically. Four organic solvents and aqueous-phase additives are selected to produce the thin-film membranes, the properties of which such as morphology, hydrophilicity, crosslinking degree and FO performance were evaluated. Among the four types of organic solvents, the hexane-based PA TFC membrane shows the highest water permeability, hydrophilicity and the lowest crosslinking degree. Meanwhile, the TFC membranes with high boiling point solvents (heptane and isopar) exhibit high water flux at high curing temperature, which is different from the low boiling point solvents (hexane and cyclohexane). Furthermore, four kinds of additives in aqueous phase were introduced to form desired PA layers. FO performance of PA TFC membranes was improved with the addition of dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) by reducing the solubility difference of the two immiscible phase and facilitating the diffusion of 1,3-phenylenediamine into the organic 1,3,5-benzentricarbonyl trichloride phase. In general, the hexane-based PA TFC membrane with the 3 wt% DMSO as an additive shows a much better FO performance.