MUTUAL DIFFUSION-COEFFICIENTS FOR THE SYSTEMS WATER-ETHANOL AND WATER PROPAN-1-OL AT 25-DEGREES-C

Mutual diffusion coefficients have been measured by the Taylor dispersion technique at 25-degrees-C for aqueous solutions of ethanol and propan-1-ol. The results for the ethanol system are in good agreement with the better diaphragm cell results in the literature. Those for the propanol system do not show the large maximum at high propanol concentrations reported by Pratt and Wakeham (Proc. R. Soc. London, Ser. A, 1975, 342, 401), and support the argument of Leaist and Deng (J. Phys. Chem., 1992, 96, 2016) that this maximum is an artifact. The quotient D(E)/phi1 phi2, the 'excess' diffusion coefficient divided by the product of the volume fractions, is found to vary only slightly with composition and to take almost the same values for aqueous methanol, ethanol and propan-1-ol. Similar behaviour is shown by reference systems also having positive excess Gibbs energies but containing non-associating components. However, it has been found that for the aqueous ethanol system the thermodynamically corrected diffusion coefficient, D12/(1 + partial derivative In f1/partial derivative In x1)T,p, shows a minimum at low ethanol mole fraction, where some thermodynamic properties also show extrema or inflections. This effect is not shown by the reference systems.