Protic ionic liquids as adjuvants to enhance extraction and separation performance of diverse polarity compounds in PEG-salt based aqueous biphasic system

Abstract

This work addresses use of a set of 2-hydroxypropylammonium based protic ionic liquids (PILs) as adjuvants in the aqueous biphasic system (ABS) composed of polyethylene glycol, with molecular weight 2000 g/mol (PEG 2000) and potassium carbonate. The phase diagrams were determined at 25 °C for ABS without and with the addition of 5 wt% of PIL. Comparative analysis of solubility curves indicates that PILs influence liquid-liquid equilibria of PEG 2000-K2CO3 ABS by heightening the hydrophilicity of a PEG-rich phase in various degrees. The compositions of the phases (tie lines) were determined for the selected ABS mixture composition, 26 wt% of PEG 2000 + 10 wt% of K2CO3, without and with 5 wt% of PILs, that is further used for the separation studies. The distribution of PILs between two phases is mainly dependent on specific PEG-PIL interactions and on the PIL content in ABS mixture. The experimental results are supported by molecular simulations that contributed to a broader picture of underlying effects of PILs as adjuvants on ABS formation. The partition of four dye compounds, Remazol Brilliant Blue R (RBBR), Orange II (OII), Rhodamine B (RB) and Congo Red (CR), as probe molecules with different intrinsic properties, was investigated. Obtained results show that the addition of PILs can improve the extraction of hydrophilic and charged compounds as OII, RBBR and CR in PEG-rich phase. On the other hand, it promotes the extraction of hydrophobic and neutral solutes as RB in salt-rich phase. By the addition of the most hydrophilic 3-chloropropanoate based PIL in the PEG 2000-K2CO3 ABS 12 times higher separation factor for OII and RB was achieved.