Triggering phase disengagement of 1-alkyl-3-methylimidazolium chloride ionic liquids by using inorganic and organic salts Gustavo Torres-Plasencia, Esther Gutiérrez-Arnillas, Francisco J. Deive ⇑ , M. Ángeles Sanromán, Ana Rodríguez ⇑ Department of Chemical Engineering, Universidade de Vigo, P.O. Box 36310, Vigo, Spain article info Article history: Received 14 January 2015 Received in revised form 27 March 2015 Accepted 2 April 2015 Available online 7 April 2015 Keywords: Aqueous biphasic systems Ionic liquids Imidazolium Segregation agent Correlation models abstract This study deals with the influence of different inorganic and organic salts made up with sodium, potas- sium and ammonium cations to induce phase segregation in aqueous solutions of C 8 C 1 imCl and C 10 C 1 - imCl at T = 298.15 K. The experimental solubility values are described by means of four empirical equations and the suitability of the models was analysed in the light of the standard deviation. The capability of the above mentioned salts to further phase de-mixing is discussed on the basis of their dif- ferent molar Gibbs free energy of hydration (D hyd G), molar entropy of hydration (D hyd S) and pH. The efficiency of the separation was evaluated by determining the tie-lines, and these experimental values were fitted to three known models such as Bancroft, Othmer–Tobias and modified Setschenow equations. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Globally, aqueous biphasic systems (ABS) have been considered as a competitive separation strategy against the conventional (liq- uid + liquid) extraction using common volatile organic compounds [1]. Generally speaking, traditional ABS result from the competi- tion between two hydrophilic compounds for the water molecules, up to a concentration where two phases coexist, each one mainly formed of one of the compounds. Thus, two main types of ABS have been widely described in the literature: be it polymers- or salts- based systems. The retrieval of ABS as an extraction technique can be attributed to the growing development of biotechnologically-based industrial processes, since their aqueous nature makes them the preferred option to obtain the desired water-soluble metabolites. Addition- ally, the mild operating conditions and low energy consumption are inherent advantages associated with this separation method [2]. These economic considerations are decisive when a new down- stream processing strategy is implemented, since the product recovery and purification costs may represent up to 80% of the total processing expenses [3]. In view of the above, not only have ABS found application for the extraction of biomolecules such as alkaloids, enzymes, antioxi- dants or antibiotics [4–6], but also have been proposed as a sep- aration technique for environmental processes to remove metals, dyes, or polyaromatic hydrocarbons [7–9]. In this sense, the emer- gence of ionic liquids has led the way for the development of a new type of ABS, in combination with salts [10], polymers [11] and sur- factants [12]. These molten salts exhibit outstanding features such as their almost null vapour pressure, high solvation ability and thermal stability that have been repeatedly acknowledged [13]. Additionally, the existence of thousands of possible combinations cation–anion enables the design of millions of new ionic liquids, easing their implementation to widen the applicability of ABS [14]. In our group, we have hitherto invested a great research effort on the implementation of new surfactant-based separation pro- cesses [15–17], so the use of ‘‘surface active’’ ionic liquids is the scenario over which this work is planned. On the one hand, we have chosen one of the most commonly used families of ionic liq- uids based on 1-alkyl-3-methyl imidazolium cation paired with chloride anion, since the non-fluoride label is environmentally advantageous. In relation to the selected alkyl-chain length, litera- ture analysis allows concluding the existence of self-aggregation phenomena for ionic liquids containing alkyl side chains longer than 8 carbon atoms [18]. This property could be beneficial for application in inducers solubilisation in lipase production biopro- cesses or for increasing hydrophobic contaminants bioavailability in bioremediation processes. On the other hand, different common inorganic and organic salts were chosen to evaluate their potential capacity to act as salting-out agents, namely sulfate (SO 2 4 ), carbon- http://dx.doi.org/10.1016/j.jct.2015.04.004 0021-9614/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding authors. Tel.: +34 986 81 87 23. E-mail addresses: deive@uvigo.es (F.J. Deive), aroguez@uvigo.es (A. Rodríguez). J. Chem. Thermodynamics 88 (2015) 1–7 Contents lists available at ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct