Application of Pitzer and six local composition models to correlate the mean ionic activity coefficients of aqueous 1-butyl-3-methylimidazolium bromide ionic liquid solutions obtained by EMF measurements

- An ion selective membrane electrode permselective to the cation of [BMIm]Br was prepared.
- The experimental activity coefficients of the IL were attained using EMF measurements.
- The obtained experimental data were correlated using six local composition models.
- The results indicated that the models based on NRTL theory are better predicting the activity coefficients.

The mean ionic activity coefficients of aqueous 1-butyl-3-methylimidazolium bromide ([BMIm]Br) solutions in the concentrations ranging from 0.008 to 0.215 mol·kg−1 were determined using potentiometric measurements at T = 308.15, 318.15, and 328.15 K. The obtained experimental data were correlated using the Pitzer and several local composition models, such as the non-electrolyte Wilson-NRF (N-Wilson-NRF), electrolyte Wilson-NRF (E-Wilson-NRF), electrolyte Wilson (E-Wilson), electrolyte NRTL (E-NRTL), modified electrolyte NRTL (ME-NRTL), and electrolyte NRTL-NRF (E-NRTL-NRF) models. The Pitzer parameters obtained were used to calculate the osmotic coefficients and excess Gibbs free energies of the solutions being studied. The results indicate that in general all the models used here can be successfully applied to predict the mean ionic activity coefficients of the aqueous ionic liquid solutions. However, the average standard deviations of the fit show that the NRTL based models represent the mean ionic activity coefficients with better precision.