Effect of ionic liquid based imidazolium as an additive on the formation of polymer/salt aqueous biphasic systems Hongpeng Yang a , Lei Zhang a , Li Chen b , Cunshan Zhou a, ⁎, Xiaojie Yu a , Abu El-Gasim A. Yagoub c , Haile Ma a a School of Food and Biological Engineering, Jiangsu University, Zhenjiang 212013, China b Jiangsu Marine Resources Development Research Institute, Lianyungang 222005, China c Faculty of Agriculture, University of Zalingei, P.O. Box: 06, Zalingei, Sudan abstract article info Article history: Received 15 March 2017 Received in revised form 20 January 2018 Accepted 31 January 2018 Available online 05 February 2018 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 N Na 2 HPO 4 N Na 2 CO 3 N Na 2 SO 4 N NaH 2 PO 4 . The in- crease 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 N318.15 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. © 2018 Elsevier B.V. All rights reserved. Keywords: Aqueous biphasic systems Ionic liquid Adjuvant Polyethylene glycol Phase diagram 1. Introduction In the past few decades the traditional liquid-liquid extraction has been gradually replaced by the aqueous biphasic system (ABS). ABS technique is relatively simple and inexpensive, of easy operation, allowing its scale-up, and further ensures the purification and concen- tration stages to be integrated in a single step procedure [1,2]. Conven- tional ABS typically consists of two immiscible aqueous-rich phases based on polymer/polymer, polymer/salt or salt/salt combinations dis- solved in aqueous media that might be used in liquid–liquid extraction processes [1,2]. However, both phases are mostly composed of water, offering a bio-compatible medium for biologically active molecules. Due to this advantage, ABS has been successfully used for the recovery of biological products [3]. Some factors, such as the characteristics of the target material, system characteristics and the economic costs have been taken into account when deciding to choose ABS. In earlier studies, the aqueous two-phase system mainly focused on the poly- mer/polymer aqueous two-phase system, but the cost of this system is higher a relatively large viscosity, which limits its industrial application. ABS typically formed by polymer/inorganic salt have some advantages over conventional polymer/polymer ABS [4]. Polyethylene glycol (PEG) is commonly used as one of the phase- forming polymers in ABS because it presents high biodegradability, low toxicity, low volatility, low melting temperature, large water miscibility and low cost [5]. Polymer-Salt ABS provides advantages over systems formed by polymer–polymer combinations, such as a low interfacial tension, low viscosity, good biocompatibility, fast and high phase separation rates and low cost, which makes them practical for downstream processing [4,5]. Despite all these advantages, the nar- row tailoring nature of PEG, which can be achieved only by changes in the molecular weight or by the polymer structural modification, limits its applicability through the complete extraction of several biomole- cules to the polymer-rich phase [5]. To overcome this limitation, recent works have introduced ionic liquids (ILs) to tune the physicochemical properties of the PEG-rich phase, either by using them as adjuvants or as an agent to improve functionality of PEG, aiming at getting high extraction yields [6]. Rosa et al. [7] and Azevedo et al. [1] used function- alized PEG for purification of the human immunoglobulin. Jiang et al. [6] have used an ionic liquid to functionalize PEG for extraction of penicillin. Moreover, Wu et al. [8] have shown that PEG could be functionalized with ionic liquids, to enhance the extraction process and polymer recov- ery. The former studies [6–8] prove that the properties of polyethylene Journal of Molecular Liquids 256 (2018) 1–8 ⁎ Corresponding author. E-mail address: zhcs@ujs.edu.cn (C. Zhou). https://doi.org/10.1016/j.molliq.2018.01.182 0167-7322/© 2018 Elsevier B.V. All rights reserved. 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