Use of Ionic Liquids and Co-Solvents for Synthesis of Thin-Film Composite Membranes

Polyamide (PA) thin-film composite (TFC) membranes are commonly applied in reversed osmosis (RO) and nanofiltration (NF) applications due to their thin, dense top-layer, and high selectivity. Recently, the conventional organic phase (i.e., hexane) during interfacial polymerization (IP) was replaced by less toxic ionic liquids (ILs) which led to excellent membrane performances. As the high price of most ILs limits their up-scaling, the potential use of inexpensive Aliquat was investigated in this study. The thin-film composite (TFC) membranes were optimized to remove flavor compounds, i.e., ethyl acetate (EA) and isoamyl acetate (IA), from a fermentation broth. A multi-parameter optimization was set-up involving type of support, reaction time for IP, water content of Aliquat, and concentration of both monomers m-phenylenediamine (MPD) and trimesoylchloride (TMC). The membranes prepared using Aliquat showed similar fluxes as those prepared from a reference IL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C₄mpyr][Tf₂N]) but with better EA and IA retentions, even better than for a commercial RO membrane (GEA type AF). Finally, the recently introduced epoxide-curing of Bisphenol A diglycidyl ether (BADGE) with 1,6-hexanediamine (HDA) was investigated using Aliquat as organic phase. It is the first time this type of IP was performed in combination with an IL as organic phase. The resulting membrane was used in the filtration of a 35 µM Rose Bengal (RB) in 20 wt% dimethylformamide/ water (DMF/H₂O) feed mixture. A well-crosslinked poly(β-alkanolamine) film was obtained with a > 97% retention.