High-temperature, high-pressure viscosities and densities of toluene

•Development of a rolling ball viscometer/densimeter.•Apparatus validated through comparison of literature toluene viscosity and density data.•Original high-temperature, high pressure toluene viscosities reported to 535 K and 300 MPa.•Data correlated to Tait expressions for density and viscosity.•Free volume theory applied to the toluene viscosity data.

Toluene viscosities and densities, measured with a windowed, variable-volume, rolling-ball viscometer/densimeter (RBVD), are reported at temperatures from 296-535 K and pressures to 300 MPa. The combined expanded uncertainty in the reported viscosities and densities are 4.0% and 0.8% of the measured values respectively, each with a coverage factor, k = 2. Densities obtained with the RBVD exhibit an average absolute percent deviation (ΔAAD) of 0.20% against densities calculated with the Lemmon and Span Equation of State. Viscosities obtained with the RBVD exhibit ΔAAD values of less than 4.0% for data from 18 of 20 available literature sources for high pressure data. The reported viscosities are generally in good agreement with calculated viscosities from the reference equation of Avgeri et al. The reported toluene viscosities extend the available database from 423-535 K and 40-300 MPa. Toluene viscosities are also reasonably correlated with the empirical Tait equation that allows for reliable interpolation of the data. Free Volume Theory (FVT) matches the reported viscosities to within 3.4% ΔAAD using FVT parameters fit to a viscosity data set limited to 373 K and using densities calculated with the Perturbed-Chain Statistical Association Fluid Theory (PC-SAFT). An improved fit of the viscosity data is obtained if temperature-dependent, FVT parameters are used. The challenge remains to predict the temperature dependence in the FVT parameters from first principles.