High temperature and high pressure volumetric properties of (methanol + [BMIM⁺][OcSO⁻₄]) mixtures

Abstract

The (p, ρ, T) and some derived volumetric properties such as excess, partial and apparent molar volumes of [BMIM⁺][] in methanol at temperatures T = (298.15–398.15) K and pressures up to p = 40 MPa have been measured with a vibrating-tube densimeter. Measurements were made at seven concentrations of x = (0.0388, 0.1351, 0.2785, 0.4961, 0.7497, 0.9312 and 1.0) mole fraction of [BMIM⁺][]. The total uncertainty of density, temperature, pressure and concentration measurements were estimated to be less than 0.15 kg m⁻³, 15 mK, 5 kPa and 10⁻⁴ mole fraction, respectively. The uncertainties reported in this article are expanded uncertainties at the 95% confidence level with a coverage factor of k = 2. The effect of temperature, pressure and concentration on the density and derived volumetric properties was studied. The measured densities were used to develop a Tait-type equation of state (EOS) for the mixture and the pure components. The derived values of apparent molar volumes were extrapolated to zero concentration using Pitzer's ion-interaction model to calculate the values of apparent molar volumes (or partial molar volumes) at infinite dilution. The method of correlation function integrals is used to study the structural and thermodynamic properties of dilute methanol + ILs mixtures. The structural properties, such as direct and total correlation function integrals and cluster size (coordination number), were calculated using the Krichevskii function concept and EOS for the mixture at infinite dilution.

Keywords:

• 1-butyl-3-methylimidazolium octylsulphate
• apparent molar volume
• correlation function integrals
• density
• equation of state
• excess molar volume
• ionic liquid
• methanol
• partial molar volume

Acknowledgements

I.M. Abdulagatov thanks the Physical and Chemical Properties Division at the National Institute of Standards and Technology for the opportunity to work as a Guest Researcher at NIST during the course of this research. J.T. Safarov thanks the Alexander von Humboldt Foundation for his research period at the University of Rostock, Germany.