Effect of the ionic liquid 1-butyl-3-methylimidazolium bromide as an additive on the formation of {polyethylene glycol + tri-potassium phosphate} aqueous biphasic systems: the role of polymer molecular weight

Aqueous biphasic systems (ABS) present a powerful technique for the development of sustainable and biocompatible separation processes in biotechnology. Polyethylene glycols (PEGs) are the most common polymers used in the polymer-salt ABS. However, the hydrophilic nature of PEGs and the low polarity of the PEG-rich phase limit the applicability of this technique. To overcome this limitation, in recent years, a new approach has been proposed based on the use of ionic liquids (ILs) as adjuvants in PEG-based ABS. In this regard, this work is devoted to study the influence of IL 1-butyl-3-methylimidazolium bromide ([C4C1im]Br) as an adjuvant compound on the formation of {PEG (400, 600, 4000, and 6000) + tri-potassium phosphate (K3PO4)} ABS. For this purpose, phase diagrams of the {PEG (400, 600, 4000, and 6000) + K3PO4} ABS with the addition of small quantities of IL were determined at T = 298.15 K. The results obtained indicate that the binodal curves of the systems with and without IL are more deviated from each other with decreasing the PEG molecular weight, and the biphasic region of the systems with IL is larger than that of ternary systems for PEG 400 and 600; while, for PEG 4000 and 6000 is smaller. The partition coefficients of IL (KIL) within the studied ABS were also determined at T = 298.15 K. The KIL values were observed to decrease with increasing the PEG molecular weight. In addition, the experimental data are correlated using the NRTL model. The comparisons between the correlation and the experimental data reveal a good agreement.