(313g) Separating Liquid Mixture Using Supported Ionic Liquid Membranes (SILMs)

Supported ionic liquid membranes (SILMs) are promising in separating miscible liquid-liquid mixtures, which has been a key challenge in wastewater treatment and other applications. In current work, ionic liquids (ILs), serving as the extraction solvent, have been impregnated into PVDF membranes to separate miscible liquid-liquid mixture. First, the two imidazolium based ILs, i.e., 1-Butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and 1-butyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate ([bmim][FAP]), were tested in SILMs for benzene-heptane separation. Both ILs show successful separation within 48 hours as indicated by NMR and TGA results, although the flux and the reusability of two ILs are different. Compared to the SILM with [bmim][FAP], the SILM with [bmim][PF6] has lower benzene flux and better selectivity. The better selectivity can be attributed to the higher hydrophilicity of [bmim][PF6], which results in strong repulsion against heptane. The lower flux can be attributed to the higher hydrophilicity as well since it lowers the solubility of benzene in [bmim][PF6]. Second, the reusability (i.e., the stability of IL in SILMs) has been investigated via multiple separation cycles. The SEM, weight change of SILM and separation results indicate that [bmim][PF6] SILM can be used to separate benzene-heptane for up to 144 hours without degradation in separation efficiency. Third, the SILM is further optimized with curvature design (i.e., curved SILM) to increase the interfacial area and separation throughput, where the curved SILM separation device was 3D-printed. This has enabled us to increase the separation throughput by a factor of ~9. Last, the successful separation of the three-component/two-phase liquid mixture, i.e., benzene-heptane-water, has been demonstrated with an integrated 3D-printed device composed of both curved SILM and a 3D-printed PMMA membrane with zwitterionic hydrogel coating.