The Taylor Dispersion Technique has been applied to the measurement of mutual diffusion coefficients for liquid mixtures at elevated pressures. The systems studied were toluene plus n-hexane and toluene plus acetonitrile over the temperature range from 273 to 348 K and up to 25 MPa. The density and viscosity for the same mixtures have been measured from 298 to 373 K and up to 500 MPa. A self-centering falling body viscometer was used for the viscosity measurements, and densities were measured with a bellows volumometer. High pressure densities are also reported for the ternary mixture of n-octane, i-octane and oct-1-ene. Measurements were also made of the mutual diffusion coefficient of benzene and eight fluorinated benzenes at trace concentration in n-hexane from 213 to 333 K, at atmospheric pressure. The results have been used to make a rigorous test of current theoretical and empirical relationships. The Tait equation fits the density data within 0.2%. The trace mutual diffusion coefficient data are satisfactorily accounted for on the basis of the rough hard-sphere model and the high pressure viscosity coefficient results are successfully correlated using a method based on consideration of hard-sphere theory. The Grunberg and Nissan equation satisfactorily reproduces the mixture viscosity data, with parameter G dependent on temperature, pressure and concentration. An important development in the correlation of dense fluid transport properties on the basis of hard-sphere model is described, whereby diffusion and viscosity coefficients are considered simultaneously. This should lead to more reliable prediction methods for transport coefficients of dense fluids and fluid mixtures
