Influence of five protic and aprotic ionic liquids as anti-crystallization additives of water/lithium bromide on the solid–liquid equilibrium

Identifier:  imarina:9451349

Handle: https://hdl.handle.net/20.500.11797/imarina9451349

Authors:  Latorre-Arca D; Larrechi MS; Salavera D; Coronas A

Abstract:
In this work, we study the influence of five ionic liquids (ILs) as anti-crystallization additives of water/lithium bromide (H2O/LiBr) on the solubility of LiBr in H2O. The selected ILs are ethylammonium nitrate [EA][NO3], propylammonium nitrate [PA][NO3], ethylammonium chloride [EA][Cl], 1-butyl-3-methylimidazolium bromide [Bmim][Br], and 1,3-dimethylimidazolium chloride [Dmim][Cl]. The solubility of LiBr in H2O in the presence of these ILs was individually determined from (280–360) K at an IL/LiBr mole ratio around 0.0205, and at two additional IL/LiBr mole ratios in the case of ILs based on the imidazolium cation. A quantitative analysis of bulk water in H2O/(LiBr+IL) mixtures was conducted using near-infrared spectroscopy and multivariate curve resolution. The amount of H2O that does not interact with the solute (LiBr+IL), which is a measure of solute–solvent interactions, was estimated at 293.2 K, 313.2 K, and 333.2 K. In these solutions, in addition to the IL/LiBr mole ratio at 0.0205, two higher ratios were considered in the case of the mixture with [Dmim][Cl]. The results show that, on average, the selected ILs increase the solubility of LiBr in H2O from 1.6 % to 5.7 %, and that this increment is more pronounced at lower temperatures. Protic ILs based on the ammonium cation enhance the solubility of LiBr more than aprotic ones based on the imidazolium cation, following the order: [EA][NO3] ≈ [PA][NO3] > [EA][Cl] ≈ [Bmim][Br] ≈ [Dmim][Cl]. Furthermore, the presence of ILs contributes to a higher amount of bulk water, which suggests that ILs interact with LiBr ions, competing with H2O and favoring solubility. This interaction depends on both the chemical structure of the ILs, with protic ILs forming stronger bonds due to hydrogen bonding, and on the temperature, as the amount of bulk water decreases with an increase in temperature.