Physicochemical and thermodynamic characterization of N-alkyl-N-methylpyrrolidinium bromides and its aqueous solutions

• The aqueous solutions of bromide-based ionic liquids have been studied.
• The synthesis and basic thermal characterization of pure IL have been done.
• The density, dynamic viscosity, SLE and VLE have been determined.
• The experimental data have been correlated using appropriate equations.

This work is a continuation of our research of ionic liquids to investigate the physicochemical and thermodynamic properties of (ionic liquid + water) binary mixtures as a novel alternative working pair for the absorption heat pump cycle. In this work, a series of organic salts: N-propyl-N-methyl-pyrrolidinium bromide, [C1C3PYR]Br; N-butyl-N-methylpyrrolidinium, [C1C4PYR]Br and N-pentyl-N-methylpyrrolidinium bromide, [C1C5PYR]Br have been synthesized. The structures of new compounds have been confirmed using NMR spectra and elementary analysis. The basic thermal characterization of pure ILs, including temperature and enthalpy of phase transition (Ttr, ΔtrH), temperature and enthalpy of melting (Tm, ΔmH) have been measured using a differential scanning microcalorimetry technique (DSC). Decomposition temperature of the tested ILs were detected by the simultaneous TG/DTA experiments. The effect of temperature on the density (ρ) and dynamic viscosity (η) is reported over a wide temperature range from 298.15 to 343.15 K at ambient pressure. From experimental density data, the excess molar volumes (VE) were calculated and correlated using Redlich–Kister equation. The isothermal vapour–liquid phase equilibria (VLE) have been measured by an ebulliometric method at wide temperature range from 328.15 to 368.15 K and pressure up to 85 kPa. Experimental data have been correlated by means of NRTL equation. The solid–liquid phase equilibria (SLE) for the tested binary mixtures have been determined over whole composition range using dynamic method. The NRTL equation using parameters obtained from the VLE gives good description of SLE data. The influence of the alkyl chain length in the pyrrolidinium cation on the presented physicochemical and thermodynamic properties were discussed.