Stability studies of supported liquid membranes based on ionic liquids: Effect of surrounding phase nature

Previously, we reported the selective simultaneous separation of the substrates and products of a transesterification reaction (vinyl butyrate, 1-butanol, butyl butyrate and butyric acid) through a supported liquid membrane (SLM) based on 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim(+)][BF4-]. This work evaluates the operational stability of this membrane into different feed/receiving phases (n-hexane/n-hexane, n-hexane/tert-butyl methyl ether or n-hexane/dimethyl sulfoxide). Scanning electron-microscopy (SEM) combined with energy dispersive x-ray (EDX) analysis was used to characterize the membrane surface morphologically and examine the global chemical composition of the membranes and the distribution of the IL within them. Stability tests were performed by keeping the membranes immersed for a week in a diffusion cell including two independent compartments. The SEM-EDX study of membranes after continuous operation showed that the stability of the supported liquid membrane increase with the decrease of the polarity of the solvent used. These observations are in complete agreement with the ionic losses determined by mass balance.