Investigation of sorption characteristics of polymeric membranes containing ionic liquids for n-butanol recovery from aqueous streams

Ionic liquid-polydimethylsiloxane (IL-PDMS) blending membranes were prepared to separate n-butanol from aqueous mixtures. The ionic liquids (ILs) used were [hmim][PF6](1-hexyl-3-methylimidazolium hexafluorophosphate), [bmim][PF6] (1-butyl-3-methylimidazolium hexafluorophosphate), and [bmim][TF2N] (1-Butyl-3-methylimidazolium bistrifluoromethylsulfonylimide). Sorption experiments were carried out to define the sorption and separation capacity of the blending membranes using aqueous butanol solutions in the range of 1-5% (wt), and also sole solvents of butanol and water. The desorption experiments allowed to determine the selectivity of the membranes as the liquid composition inside the membrane could be obtained with the desorption step. The results obtained by IL-PDMS blends were compared with the results obtained by unblended PDMS membranes to show the effect of the IL in the PDMS matrix. [Hmim][PF6]-PDMS-blended membranes showed lower selectivity. The addition of [bmim][PF6] to PDMS enhanced the selectivity and sorption amounts mildly. [Bmim][TF2N]-PDMS-blended membranes presented the best sorption and selectivity results showing a great affinity to butanol and a reasonable rejection to water.