Aqueous Biphasic Systems Composed of Ionic Liquids and Acetate-Based Salts: Phase Diagrams, Densities, and Viscosities

Abstract

Ionic-liquid-based aqueous biphasic systems (IL-based ABS) have been largely investigated as promising extraction and purification routes. In this context, the determination of their phase diagrams and the physical properties of the coexisting phases are of high relevance when envisaging their large-scale applications. Low viscosities improve the mass transfer and reduce energy consumptions, while the knowledge on their densities is important for the equipment design. In this work, novel phase diagrams for aqueous solutions of imidazolium-based ILs combined with acetate-based salts, namely KCH 3 CO 2 or NaCH 3 CO 2 , are reported and discussed. The ability of the acetate-based salts to induce the phase separation not only depends on the ions hydration energy, but also on the concentration of "free" ions in solution. The tie-lines, tie-line lengths and critical points are also addressed. Experimental measurements of density and viscosity of the coexisting phases, for the different systems and at several compositions and temperatures, are additionally presented. The Othmer-Tobias and Bancroft equations are also applied to ascertain on the tie-lines coherence. It is here shown that low-viscous IL-based ABS, with a high difference in the densities of the coexisting phases, can be formed with organic and biodegradable salts thus offering enhanced features over conventional polymer-based systems.

Pioneering Use of Ionic Liquid‐Based Aqueous Biphasic Systems as Membrane‐Free Batteries

“…As well‐established in the literature, the toxicity of ionic liquids highly depends on their chemical structure . Hence, tetraakylammonium and phosphonium‐based ILs have been mainly investigated due to their lower toxicity, low‐cost, and high ability to form ABS . In fact, we have previously shown that the ILs affinity for water addressed by their hydrogen‐bond basicity and acidity correlates well with the ABS formation ability .…”

Glycine‐betaine ionic liquid analogues as novel phase‐forming components of aqueous biphasic systems

“…Overall, the extraction efficiencies of AGB‐ILs ABS for amino acids range between 65% and 100%, which are superior to those obtained by conventional polymer‐based ABS . It is also important to highlight that IL‐based ABS display a lower viscosity than conventional systems formed by polymers, and usually display faster phase separation rates. Extraction efficiencies for L‐tryptophan ranging between 72% and 99% with ABS composed of imidazolium‐based ILs and potassium citrate (K 3 C 6 H 5 O 7 ) have been reported, yet using imidazolium‐based ILs, a strong salting‐out species, and higher amounts of salt (20 wt%) .…”

Extraction and purification of violacein from Yarrowia lipolytica cells using aqueous solutions of surfactants

“…32 Cholinium-based IL features combined with the potential benefits of ABS lead to high-performance separations besides other advantages such as quick phase separation and low viscosity favoring mass transfer. 33,34 As mentioned, ABS composition is markedly versatile. This technology will allow the design of an integrated process, bridging the solvents used in the extraction and purification steps of an industrially favorable process.…”

“…Owing to their aqueous environment, they are recognized as an appropriate technology for the recovery and purification of biomolecules and other biologically active substances . Cholinium‐based IL features combined with the potential benefits of ABS lead to high‐performance separations besides other advantages such as quick phase separation and low viscosity favoring mass transfer . As mentioned, ABS composition is markedly versatile.…”