1-Butanol pervaporation performance and intrinsic stability of phosphonium and ammonium ionic liquid-based supported liquid membranes

The intrinsic stabilities of simple supported liquid membranes and their pervaporative recoveries of 1-butanol from dilute aqueous solutions were investigated. Hydrophobic ammonium- and phosphonium-based room temperature ionic liquids were used as the liquid membranes. The membranes performed better than or comparably to other pervaporation membranes. 1-Butanol flux was highly positively correlated with the ionic liquid's partition coefficient for 1-butanol and was inversely correlated with the membrane's hydrophobicity and viscosity. Water flux was strongly influenced by the ionic liquid's water saturation capacity. Except at the highest temperature investigated (70 °C), no trade-off was seen between separation factor and temperature. Diffusivity and activation energy results suggested the presence of water microenvironments in the membranes, which influenced permeant transport. Permeances and membrane selectivities indicated that transport was dominated by sorption rather than diffusion. Membranes' selectivities consistently increased with increasing feed concentration. Sustained pervaporation for ∼90 h showed that the ionic liquid required a minimum level of hydrophobicity to produce a stable membrane. Diluting the ionic liquid with oleyl alcohol enhanced separation by increasing the membrane's partition coefficient for 1-butanol and decreasing its viscosity; albeit temporarily as the fatty alcohol was gradually leached during sustained testing.

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► Ammonium and phosphonium-based RTILs were used in SILM for 1-butanol pervaporation.
► Separation strongly influenced by RTIL's 1-butanol affinity and water saturation capacity.
► SILM stability was verified by sustained pervaporation runs.
► Minimum level of RTIL hydrophobicity is required to produce adequately stable SILMs.