J. Phys. Chem. B 2008, 112, 13163–13165
13163
Temperature Dependence of Phase Behavior for Ternary Systems Composed of Ionic Liquid + Sucrose + Water Bo Wu, Yumei Zhang,* Huaping Wang,* and Lingling Yang State Key Laboratory for Modification of Chemical Fiber and Polymer Materials, Donghua UniVersity, Shanghai 201620, China ReceiVed: June 21, 2008; ReVised Manuscript ReceiVed: July 28, 2008
In this work, temperature dependence of phase behaviors for the [Bmim]BF4 + sucrose + water system was investigated. It was found that interaction of [Bmim]BF4 with sucrose is exothermic, and lowering temperature is favorable for phase separation. In addition, a “[Bmim]+-induced structural changes” model was developed and used to interpret the temperature effect, whereby the salting-out effect was thought to be an entropy driving process through analysis of the structural interaction and the electrostatic interaction. Introduction It has been proposed that ionic liquids (ILs) could be suitable substitutes for volatile organic compounds (VOCs) in liquid/ liquid (l/l) separations, due to their chemical tunability and negligible vapor pressure. Direct implementation of ILs in l/l separations has focused on the use of expensive hydrophobic fluorinated-ILs. The high cost of producing fluorinated-ILs, together with the possible mechanisms of separation,1,2 has discouraged the use of hydrophobic ILs as direct VOCs replacements in l/l separations. Relatively, Hydrophilic ILs are cheaper and more numerous than their hydrophobic relatives, however, these ILs can not be used directly in (l/l) separations with an aqueous phase due to their solubilities in water. Recently, Rogers3 and others4-6 have investigated hydrophilic ILs mixtures with aqueous solutions of kosmotropic salts to form ILs/salts aqueous biphasic systems (ABS). On the basis of which inevitably introduces inorganic ions complicating the separation process, we have introduced a more environmentally benign ABS composed of sugars and 1-butyl-3-methylimidazolium tetrafluoroborate, [Bmim]BF4, a hydrophilic IL, forming an upper IL-rich phase and a lower sugar-rich phase.7,8 These new ABS can not exclusively be utilized to recycle or concentrate hydrophilic ILs from aqueous solution, but also be more important and implemented in biochemical separations. No matter what the application in ILs recovery or in biochemical separations is, temperature plays a vital role. In our previous works,7,8 we explained why ABS can form by addition of sugars to aqueous solution of [Bmim]BF4. As a continuation, we investigated the temperature dependence of phase behavior for the [Bmim]BF4 + sucrose + water system, whereby we discussed the driving force for forming ILs-based ABS. Experimental Section Materials. The sucrose, chlorobutane, 1-methylimidazole, ethyl acetate, acetone, and NaBF4 were all purchased from Shanghai Chemical Reagents Company. They are of analytic grade and used as received. Doubly distilled water was used in all experiments. * Corresponding authors. E-mail: (Y.Z.)
[email protected]; (H.W.)
[email protected].
Synthesis of IL. [Bmim]BF4 were prepared based on the reported procedures.9 [Bmim]BF4 was dried under vacuum at 373.15 K for 24 h. The purity of the IL was verified in terms of NMR analysis (>99%). The water content of IL (
