Effect of ionic liquid based imidazolium as an additive on the formation of polymer/salt aqueous biphasic systems

Aqueous biphasic system (ABS) has been proposed as an alternative technique for the extraction, separation and/or purification of diverse biomolecules. ABS composed of polyethylene glycol (PEG) and sodium salts, using ILs ([C n mim]Cl) as additives were studied. Phase diagrams of PEG 800   +   sodium salts (Na 2 HPO 4 , Na 3 C 6 H 5 O 7 , Na 2 CO 3 , Na 2 SO 4 , NaH 2 PO 4 )   +   H 2 O   +   5   wt% [C 4 mim]Cl at 298.15 K were used to study the effect of different salts on the ABS. Binodal curves for the ABS composed of PEG (molecular weights of 400, 600, 800, 1000 and 2000   g·mol −1 )   +   Na 2 SO 4   +   H 2 O   +   5   wt% IL ([C 2 mim]Cl, [C 4 mim]Cl, [C 6 mim]Cl, [C 8 mim]Cl, [C 10 mim]Cl) at 298.15 K were determined to study the effect of the polymer size and the IL alkyl side chain length on ABS. Ability of the various salts to form ABS follows the trend: Na 3 C 6 H 5 O 7   >   Na 2 HPO 4   >   Na 2 CO 3   >   Na 2 SO 4   >   NaH 2 PO 4 . The increase in the molecular weight of PEG increases the phase separation ability of the system. [C 6 mim]Cl shows the best phase separation at PEG400   +   Na 2 SO 4 . [C 8 mim]Cl and [C 10 mim]Cl improves the phase separation of PEG-Na 2 SO 4 . The phase diagram is not affected at 288.15–308.15 K. The phase separation increases at 318.15–328.15 K and decreases at >318.15 K. These results illustrate the ability of the IL to tune the polarity of the PEG-rich phase. PEG–Salt–IL ABS could be an interesting advance in separation processes and could lay the basis for future studies in extraction processes.