Supported
liquid membranes (SLMs) are promising in separating miscible
liquid–liquid mixtures, which has been a key challenge in wastewater
treatment and other applications. However, SLMs suffer from poor durability
due to the loss of the liquid phase. In current work, ionic liquids
(ILs) with high stability have been impregnated into polyvinylidene
fluoride membranes to separate miscible benzene–heptane mixtures.
The two imidazolium-based ILs, that is, 1-butyl-3-methylimidazolium
hexafluorophosphate ([BMIM][PF6]) and 1-butyl-3-methylimidazolium
tris(pentafluoroethyl) trifluorophosphate ([BMIM][FAP]), were tested
in supported ionic liquid membranes (SILMs) for the benzene–heptane
separation. Both ILs show successful separation within 48 h as indicated
by nuclear magnetic resonance results. Compared to the SILM with [BMIM][FAP],
the SILM with [BMIM][PF6] has lower throughput and higher
selectivity. The higher selectivity can be attributed to the higher
hydrophilicity of [BMIM][PF6], which results in strong
repulsion against heptane. The lower throughput can be attributed
to the higher hydrophilicity as well since it lowers the solubility
of benzene in [BMIM][PF6]. The stability of IL in SILMs
has also been investigated via multiple separation cycles. The scanning
electron microscopy, weight change of SILMs, and separation results
indicate that the separation efficiency of the [BMIM][PF6] SILM does not degrade for up to 144 h. The SILM has been further
optimized with curvature design (i.e., curved SILM) to increase the
interfacial area and thus increase the separation throughput, where
the curved SILM separation device was 3D-printed. The findings here
have important implications on design and application of SILMs in
separating miscible liquid–liquid mixtures.
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