High-pressure densities and derived volumetric properties (excess, apparent and partial molar volumes) of binary mixtures of methanol plus [BMIM][PF6]

The density of five (0.02297, 0.08317, 0.26147, 0.49343, 0.75255 mole fraction BMIMPF6) binary methanol + BMIMPF6 (1-n-butyl-3-methylimidazolium hexafluorophospate) mixtures have been measured with a vibrating-tube densimeter. Measurements were performed at temperatures from 298 to 398 K and at pressures up to 40 MPa. The total uncertainties of the density, temperature, pressure, and concentration (mole fractions) measurements were estimated to be less than 0.1 kg.m(-3), 15 mK, 5 kPa, and 10(-4), respectively. The uncertainties reported in this paper are expanded uncertainties at the 95% confidence level with a coverage factor of k=2. The measured densities were used to study of the effect of temperature, pressure, and concentration on the derived volumetric properties such as excess, apparent and partial molar volumes. It is shown that the values of excess molar volume for methanol + BMIMPF6 mixtures are negative at all measured temperatures and pressures in the whole concentration range. The measured densities were used to develop Tait-type equations of state for pure components and the mixtures. The structural properties such as direct and total correlation function integrals were calculated using the derived partial molar volumes at infinite dilution.