An all-polyamide organic solvent nanofiltration membrane

Polymeric organic solvent nanofiltration (OSN) membranes are usually thin film composites: a skin on a porous substrate; both are solvent-resistant, chemically stable and possess good mechanical properties. Various interfacially-polymerized (IP) polyamide (PA) skins are being studied using demanding solvent-stable substrates. Here we used relatively-inexpensive nylon 6,6 microfiltration membrane as a substrate for an IP PA membrane. This substrate exhibited excellent resistance (low swelling) to acetone, acetonitrile, Cyrene, DMF, DMSO, ethanol, heptane, methanol, MIBK, NMP, THF, toluene. Using interfacial polymerization of m-phenylenediamine (MPD) in water and trimesoyl chloride (TMC) in hexane on a nylon 6,6 support, the MPD-TMC membrane achieved at 10 bar (1000 kPa): methanol permeance, 3.3 LMH/bar; Brilliant Blue R (BBR) (molecular weight, 826 Da) rejection, 99.1%. On DMF activation, methanol permeance at 6.9 bar (690 kPa) increased enormously to 33 LMH/bar while achieving 94% rejection of Brilliant Blue G (BBG) (854 Da); a continuing 12-day-long extended-run reduced methanol permeance to a still-very-high 27 LMH/bar; BBG rejection increased to 98%. Membrane PIP-SLS-TMC with piperazine (PIP) in water with sodium lauryl sulfate (SLS) instead of MPD only was also studied. Its dye rejections at 20 bar (2000 kPa) from methanol solutions were: Sudan Black B (456.5 Da), 96.8%; Oil Blue N (378.51 Da) 85.3%. The corresponding values for MPD-TMC membrane were a bit lower: 93.7%, 83.8%; rejection of BBR dye was high ∼98.9–99.1%. Rejections and permeances at 20 bar with DMSO and NMP were similar to those with methanol. An all-polyamide OSN membrane offers an economical route to an effective OSN membrane.