Phase Behavior of Aqueous Biphasic Systems Composed of Ionic Liquids and Organic Salts

Abstract

This study evaluated the effects of ionic liquids (ILs) on the formation of aqueous biphasic systems (ABS) with organic salts. Phase diagrams, tie lines, and respective tie line lengths were determined at 298 K and atmospheric pressure. Using imidazoliumbased ILs, the effects of the IL anions and salt anions, as well as the addition of dipolar aprotic solvents (DAS) on ABS formation were investigated. In general, the IL with hydrogen bond basicity ranging between 0.38 and 0.60 formed ABS with organic salts. However, those below this range were insoluble, and those above this range did not undergo phase separation. The salt anion capacity to induce ABS increased with increased valence and decreased Gibbs free energy of hydration. Moreover, the biphasic area for the IL-based ABS reduced with increased DAS concentration. ■ INTRODUCTIONThe aqueous biphasic system (ABS) is an efficient and green approach to the separation and purification of biomolecules. In recent years, ionic liquid (IL)-based ABS have been significantly explored for the liquid−liquid extraction of a large array of enzymes, 1 biomolecules, 2,3 and polar solutes. 4−6 In IL processing of biomass, ABS is used as an alternative separation method for the recovery and purification of IL from aqueous effluents, and a recovery of over 95 wt % of the IL could be obtained. 7−9 IL-based ABSs are formed when a salt, saccharide, or polymer is dissolved in IL aqueous solutions above critical concentrations. 10−12 A large set of literature data has focused on the ABS composed of IL and inorganic salts, and the effects of the IL nature, salt, pH, and temperature have been evaluated. 10,13−17 However, common inorganic salts lead to environmental problems when discharged at high concentrations into effluent streams. 18 Apart from phosphates, sulfates, and carbonates, organic salts have also been used as possible alternatives for the preparation of IL-based ABS. Given that citrate-based salts are biodegradable and nontoxic, C 6 H 5 K 3 O 7 and C 6 H 5 Na 3 O 7 are extensively explored. 18 Moreover, Han et al. 19,20 showed that the salting-out ability of the anions of organic salts follows the order C 6 H 5 O 7 3+ > C 4 H 4 O 4 2+ > C 4 H 4 O 6 2+ . Nevertheless, a wide variety of organic salts and ILs are absent in most of these systems.The addition of dipolar aprotic solvents (DASs) is a crucial subject regarding the separation and recovery of hydrophilic ILs by forming ABS. However, a systematic study involving these particular systems and addressing the effect of the addition of DAS on the formation of IL-based ABS had not been carried out before. In 2013, Gao et al. 21 were the first to show that dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAC), can be used to tune the phase behavior of the ABS composed of 1-butyl-3-methylimidazolium chloride ([C 4 mim]Cl) and K 3 PO 4 . The trends in the density of the two phases, the surface tension, the conductivity, and the dipolarity of the mixtures are dependent on the changes in hydr...

Development of Ionic Liquid‐Water‐Based Thermomorphic Solvent (TMS)‐Systems for Biocatalytic Reactions

“…The biocatalyst itself does not significantly influence the phase behavior (Figure A). Highly relevant is also the effect of the formed acetate during the reaction, which is fortunately compensated by the continuous decrease of the substrate concentration during the reaction (Figure C) . The stability of the biocatalyst is slightly lowered in the TMS‐system, but still sufficiently stable over a period of 180 h (Figure D).…”

Liquid–Liquid Equilibrium and Extraction Performance of Aqueous Biphasic Systems Composed of Water, Cholinium Carboxylate Ionic Liquids and K2CO3

“…Ionic-liquid-based aqueous biphasic systems (IL-based ABS) formed by ILs, inorganic salts, and water were proposed in 2003 by Gutowski et al as promising alternatives over more conventional ABS constituted by polymers . They are usually less viscous than polymer-based systems and display faster phase separation rates, which is also promoted by a higher difference in the densities of the respective phases. − These advantages led to intensive research in the past 15 years on ILs as alternative phase-forming components of ABS. − In addition to their nonvolatility that has been seen as one of the more important features, the designer solvent ability of the ILs, which can be achieved by modifying either the cation or the anion chemical structure, is one of the most relevant properties when addressing their use in ABS and separation processes, although imidazolium-based ILs, most of the time combined with halogens and [BF 4 ] − as anions, are still the preferred choice …”

LCST-Type Phase Behavior of Aqueous Biphasic Systems Composed of Phosphonium-Based Ionic Liquids and Potassium Phosphate

“…The experimental procedure adopted in this work follows an already validated method for ABS constituted by other ILs and salts. 2,32,44,45 The experimental binodal curves were fitted via least-squares regression according to eq 1…”

“…Aqueous biphasic systems (ABS) are typically formed as a result of mutual incompatibility in aqueous solutions of polymer/polymer, polymer/salt, or salt/salt above a certain concentration . These environmentally benign systems mainly composed of water can provide an efficient and green approach to the extraction, separation, and purification of (bio)­molecules. , Although polymer-based ABS have received considerable attention as environmentally friendly techniques and are applied to a huge number of extraction processes with immense success, most polymer-based ABS present high viscosities, form opaque systems, and exhibit limited polarity differences between phases, thereby resulting in low extraction yields and narrow purification conditions. , These issues have prompted researchers to investigate alternative separation strategies.…”

“…ABS based on ionic liquids (ILs) have been extensively explored and proposed as promising alternatives to polymer-based ABS because of their low viscosity, rapid two-phase formation, high extraction efficiency, and the prospect of controlling the polarities of the phases by selecting IL-constituting ions. − Rogers et al first introduced IL-based ABS in 2003. To date, a series of ABS composed of ILs + inorganic salts, − ILs + organic salts, ,− ILs + saccharides, ILs + polymers, , ILs + amino acids, and ILs + Good’s buffers , have been reported and used to extract enzymes and proteins. − …”