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Liquid−liquid equilibrium data have been determined for imidazolium ionic liquid ([C4mim]Cl, [C6mim]Cl, [C4mim]Br, [C6mim]Br, [C8mim]Br, [C10mim]Br) + salt (KOH, K2HPO4, K2CO3, K3PO4) aqueous biphasic systems at T = 298.15 K, and in part at T = (308.15 to 318.15) K. Factors affecting the binodal curves such as nature of ionic liquids and salts and temperature are also studied. The binodal curves are fitted to a three-parameter equation, and the tie-lines were described by the Othmer−Tobias and Bancroft equations. It is found that an increase in temperature caused no significant expansion of the two-phase area. However, the binodal curves became more close to the origin with an increase in alkyl chain length of the ionic liquids (ILs), and the ionic liquids with the Br- anion are easier to form two phases compared to those with the Cl- anion. These data are expected to be useful for the development and design of the extraction process using ILs based on aqueous biphasic systems.

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Ionic liquids (ILs) have numerous applications in industrial processes as a benign alternative to conventional volatile organic solvents. However, many of them are toxic to organisms and are poorly biodegradable. In this work, a series of environmentally friendly cholinium ILs have been designed and synthesized. It was found that these ILs could form aqueous two-phase systems (ATPSs) with polypropylene glycol 400 (PPG400) which is thermo-sensitive, non-toxic and biodegradable. In order to understand the phase formation processes and possible application of these ATPSs for extraction/ separation of proteins, the binodal curves and tie lines of these ATPSs were measured at 25 °C, and the effects of anionic structure of the ionic liquids, nature of the proteins and difference in the concentration of top-and bottom-phases on the partitioning behavior of some typical proteins were investigated systematically. It was shown that bovine serum albumin (BSA), trypsin, papain and lysozyme could be enriched effectively into the ionic liquid-rich phase of the ATPSs, and single-step extraction efficiency could be as high as 86.4-99.9% under the optimized conditions. Furthermore, enzyme activity of the native trypsin in water and in aqueous ionic liquid solutions was determined by using N-a-benzoyl-Larginine ethyl ester as a substrate, and activity increases to about 127% was observed after 13 months storage. In addition, PPG400 has been recovered simply by heating and reused in the next extraction processes. This avoids the non-sustainable issue of highly salty water produced in the application of the polyethylene glycol (PEG) + salt and ionic liquid + salt ATPSs.