Ionic liquids as an efficient bulk membrane for the selective transport of organic compounds

The possibility of using ionic liquids [ILs) in bulk (non-supported) liquid membranes for the selective transport of organic molecules has been demonstrated. Recent publications have shown the potential usefulness of ILs in selective transport application and separation processes. In this work, a systematic selective transport study was performed using 1,4-dioxane, 1-propanol, 1-butanol, cyclohexanol, cyclohexanone, morpholine and methylmorpholine as a 7-component mixture of representative organic compounds, and 10 different IlLs based on five cation structures such as 1 -n-alkyl-3-methylimidazolium cation (n-butyl and n-octyl), 1 -n-butyl-2,3-dimethylimidazolium cation, 1-(2-hydroxyethyl)-3-methylimidazolium ([C(2)OHmim](+)), 1-[2-(2-methoxy-ethoxy)-ethyl]-3-methylimidazolium [[C(5)O(2)mim](+)) and tetra-alkyl-dimethy[guanidinium cation (alkyl = ethylbutyl and hexyl), combined with PF6- and Tf2N- anions. These studies allowed us to understand the effect of cation-anion IL structures as novel liquid membranes, and also to conclude that IL polarity seems to be crucial in order to achieve high affinities and selectivities for a specific organic substrate. In general, the use of IlLs based on more polar cations containing ether or hydroxyl functional groups increases their affinity for all organic compounds but also reduces the selective transport observed, especially for secondary and tertiary amines. Copyright (c) 2008 John Wiley & Sons, Ltd.