Improved performance of polyamide nanofiltration membranes by incorporating reduced glutathione during interfacial polymerization

Effect of functional group ratio in PEBAX copolymer on propylene/propane separation for facilitated olefin transport membranes

PEBAX-5513/AgBF₄/Al(NO₃)₃ membranes were fabricated for mixed olefin/paraffin separation. In order to improve the selectivity of the membranes utilizing PEBAX-1657, PEBAX-5513, which increased the ratio of amide groups from 40% to 60% in the copolymer, was used. The selectivity and permeance of the membranes were 7.7 and 11.1 GPU, respectively. Furthermore, the PEBAX–5513/AgBF₄/Al(NO₃)₃ membranes had long-term stability because of Al(NO₃) to have the stabilizing effect on Ag⁺ ions acting as an olefin carrier. Unexpectedly, the performance of the membrane selectivity was not improved, and the permeance became rather lower. Generally, when Ag⁺ ions was added to the polymer containing amide groups, the selectivity increased with the content of the amide groups. However, Al(NO₃)₃ was added for the stability of Ag⁺ ions and there was no increase in selectivity. Since the ratio of amide was high, Ag⁺ ions were favorably in coordination with the oxygen of the carbonyl group, but the NO₃⁻ ions in Al(NO₃)₃ had the enhanced interaction with Ag⁺ ions as obstacles for olefin complexation. Therefore, the composition ratio of amide/ether in the polymer matrix was negligible for olefin separation.

Nanovoid Membranes Embedded with Hollow Zwitterionic Nanocapsules for a Superior Desalination Performance

In order to lower the capital and operational cost of desalination and wastewater treatment processes, nanofiltration (NF) membranes need to have a high water permeation and ionic rejection, while also maintaining a stable performance through antifouling resistance. Recently, Turing-type reaction conditions [ Science 2018, 360, 518-521] and sacrificed metal organic frame (MOF) nanoparticles [ Nat. Commun. 2018, 9, 2004] have been reported to introduce nanovoids into thin-film composite (TFC) polyamide (PA) NF membranes for an improved performance. Herein, we report a one-step fabrication of thin-film nanocomposite membranes (TFNM) with controllable nanovoids in the polyamide layer by introducing hollow zwitterionic nanocapsules (HZN_Cs) during interfacial polymerization. It was found that embedding HZN_Cs increases the membrane internal free volume, external surface area, and hydrophilicity, thus enhancing the water permeation and antifouling resistance without trading off the rejection of multivalent ions. For example, water permeation of the NF membranes embedded with about 19.0 wt % of HZN_Cs (73 L m^-2 h^-1) increased by 70% relative to the value of the control TFC NF membrane without HZN_Cs (43 L m^-2 h^-1). This increase comes while also maintaining 95% rejection of Na₂SO₄. Further, we also determined the effect of the mass loading of HZN_Cs on the top surface of the TFC NF membranes on the membrane performance. This work provided a direct and simple route to fabricate advanced desalination membranes with a superior separation performance.