Influence of alkyl chain on the thermodynamic properties of aqueous solutions of ionic liquids 1-alkyl-3-methylimidazolium bromide at different temperatures

Abstract

Osmotic coefficients ϕ, mean activity coefficients γ ±, vapor pressure p data, and excess Gibbs free energies G E of aqueous solutions of three ionic liquids 1-propyl-3-methylimidazolium bromide [PMIm]Br, 1-pentyl-3-methylimidazolium bromide [PnMIm]Br, and 1-hexyl-3-methylimidazolium bromide [HMIm]Br were determined by the vapor pressure osmometry method at four temperatures (298.15 K to 328.15 K) in intervals 10 K. From the comparison of osmotic coefficients it follows that aqueous solution of [PMIm]Br shows a more pronounced deviation from Debye–Hückel limiting law (DHLL) and vapor pressure depression more than the other studied ionic liquids which was interpreted in terms of hydrophobic interactions. The Pitzer-ion interaction and MNRTL electrolyte models satisfactorily correlate experimental osmotic coefficient data with good precision. The parameters of the Pitzer-ion interaction model are used to calculate the mean molal activity coefficients and excess Gibbs free energies.