LIQUID-LIQUID EQUILIBRIA OF WATER + IONIC LIQUIDS
Sustainable process-product development & green chemistry
Modelling of Ionic Liquids (T1-1)
Keywords: Ionic Liquids, Water, Liquid-liquid equilibria
Room-temperature ionic liquids (RTILs) have garnered recently increased interest as potential “green” solvents replacements for volatile organic solvents essentially due to their negligible vapour pressures [1]. RTILs are typically salts composed of relatively large organic cations and inorganic or organic anions that cannot form an ordered crystal and thus remain liquid at or near room temperature.
Among the several applications foreseeable for ionic liquids in the chemical industry, such as solvents in organic synthesis, as homogeneous and biphasic transfer catalysts and in electrochemistry, there has been considerable interest in the potential of ILs for separation processes as extraction media where, among others, ILs have shown to be promising in the liquid-liquid extraction of organics from water [2]. Nevertheless, for the extraction of organic products from chemical reactions that proceed in aqueous media and for liquid-liquid extractions from aqueous phases, ionic liquids with lower solubility in water are preferred. Although they cannot contribute to air pollution due to their negligible vapour pressure, they do have in fact a significant solubility in water and, as a result, this is the most likely medium through which ILs will enter the environment. Moreover, the loss of ILs into the aqueous phase may be an important factor in estimating the cost of the ionic liquid used and the cost of water treatments. Furthermore, it was already shown that the presence of water in the ionic liquid phase can dramatically affect their physical properties [3-4].
In this work we address the mutual solubilities between several imidazolium-based ionic liquids and water in the temperature range from (288.15 to 318.15) K and at p=0.1 MPa. The water content in the IL-rich phase was analyzed by Karl Fischer titration and the IL in the water-rich phase was measured by UV-vis spectroscopy.
One of the ILs intrinsic attribute is the potential of tuning their physical and chemical properties by varying different features of the ionic liquid including the alkyl chain length and number of alkyl groups of the cation and the anion identity, and therefore the impact of that fine-tuning in the mutual solubilities was evaluated with the purpose of picture their use as “designer solvents”.
The predictive capability of COSMO-RS, a predictive model based on unimolecular quantum chemistry calculations, was also evaluated on the description of the liquid-liquid equilibria of water and the imidazolium-based ILs binary mixtures and a good agreement between the model predictions and experimental LLE data was obtained. The COSMO-RS proved to be very helpful to scan the growing set of already known ILs in order to find suitable candidates for a certain task or to design new ILs for specific applications.
References
[1] Santos, L.M.NB.F.; Lopes, J.N.C.; Coutinho, J.A.P.; Esperança, J.M.S.S.; Gomes, L.R.; Marrucho, I.M.; Rebelo, L.P.N., J. Am. Chem. Soc. (2007) 129, 284-285.
[2] Huddleston, J.G.; Willauer, H.D.; Swatloski, R.P.; Visser, A.E.; Rogers, R.D. Chem. Commun. (1998) 44, 1765-1766.
[3] Seddon, K.R.; Stark, A.; Torres, M.-J. Pure Appl. Chem. (2000) 72, 2275-2287.
[4] Huddleston, J.G.; Visser, A.E.; Reichert, W.M.; Willauer H.D.; Broker, G.A.; Rogers, R.D. Green Chem. (2001) 3, 156-16.
Presented Monday 17, 12:09 to 12:27, in session Modelling of Ionic Liquid Systems (T1-1).
