Abstract
The vapor liquid-equilibrium of water+ionic liquids is relevant for a wide range of applications of these compounds. It is usually measured by ebulliometric techniques, but these are time consuming and expensive. In this work it is shown that the activity coefficients of water in a series of cholinium-based ionic liquids can be reliably and quickly estimated at 298.15K using a humidity meter instrument. The cholinium based ionic liquids were chosen to test this experimental methodology since data for water activities of quaternary ammonium salts are available in the literature allowing the validation of the proposed technique.The COSMO-RS method provides a reliable description of the data and was also used to understand the molecular interactions occurring on these binary systems. The estimated excess enthalpies indicate that hydrogen bonding between water and ionic liquid anion is the dominant interaction that governs the behavior of water and cholinium-based ionic liquids systems, while the electrostatic-misfit and van der Walls forces have a minor contribution to the total excess enthalpies.The results here reported show that water activity measurements allow a quick scan for selecting ionic liquids according to their behavior in mixtures with water.
Highlights
Ionic liquids have unique properties such as negligible vapor pressure at room temperature, non-flammability, and their ability to dissolve organic and inorganic compounds, make them attractive for the scientific community and a variety of industrial applications
Excepting [Ch]Cl, to the best of our knowledge no data on activity coefficient of water in all other studied cholinium-based ionic liquids was previously reported in the literature
Cholinium-based ionic liquids are regarded as an alternative to the traditional ionic liquids due to their higher biocompatibility, and since they can be obtained from cheaper raw materials
Summary
Ionic liquids have unique properties such as negligible vapor pressure at room temperature, non-flammability, and their ability to dissolve organic and inorganic compounds, make them attractive for the scientific community and a variety of industrial applications. Most works on this subject deal with imidazolium-based ionic liquids these have several limitations in what concerns their thermal and chemical stability, price, toxicity and biodegradability [2,3,4,5,6,7] To overcome these issues, ions derived from natural resources have emerged as completely bio-derived ionic liquids, such as cholinium-based ionic liquids. Works on the Recent works have reported the preparation of novel choliniumbased ionic liquids with different anions [15,16,17] These choliniumbased ionic liquids show excellent biodegradability [18] and low toxicity [15,16,19,20]. The use of cholinium-based ionic liquids as alternatives to the traditional ionic liquids has attracted the scientific interest for the past few years, with applications as diverse as solvent for absorption of ammonia [21,22] and CO2 [23], isolation of suberin from cork [24], effective solvents for pretreatment of rice straw biomass [25] and lignocellulosic material [26], catalytic reactions [27,28], and extraction of antibiotics using aqueous biphasic systems [29]
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