Effects of 1-methyl-2-pyrrolidinone (NMP) on polyamide-polysulfone TFC membrane pore morphology and ICP and membrane performance in forward osmosis

摘要

In forward osmosis (FO), the influence of the pore morphology in the membrane support layer on membrane performance is still unclear. As a result, investigation into the relationship between membrane pore morphology and membrane performance in FO is meaningful. During the fabrication of a thin-film composite (TFC) FO membrane, the membrane pore morphology is related to the composition of the coagulant bath. In this study, varied concentrations (from 0 to 9 wt.%) of 1-methyl-2-pyrrolidinone (NMP) in a coagulant bath were applied to fabricate TFC FO membranes of different pore morphologies. The morphologies of the fabricated membranes were then characterized using FESEM, and the performance of each of the membranes was evaluated using a lab-scale FO setup. The FESEM images indicated that the increase in the NMP concentration elongated finger-like pores and suppressed the formation of large pores in the profile. When the NMP concentration was 9 wt.%, the finger-like pores nearly spanned the entire SL of the fabricated membrane. In addition, the open pores at the membrane bottom surface became smaller and fewer in number with the increase in the NMP concentration. The experimental FO results of the membranes indicated that internal concentration polarization reduction could be achieved by creating more long finger-like pores in the membrane SL as well as more and larger open pores at the membrane bottom surface. All of the fabricated membranes had a low rate of water flux (J(w)) to reverse salt flux (J(s)). In addition, the membrane fabricated with 3 wt.% NMP had the best performance in minimizing the draw solute loss, with a high J(w)/J(s) of 4.2 L/g.