APPLICATION OF THE TAYLOR DISPERSION METHOD IN SUPERCRITICAL FLUIDS

This paper describes some of the experimental and theoretical problems encountered when the Taylor dispersion method is applied to the measu rement of diffusion coefficients near gas-liquid critical points. We h ave used our own measurements of diffusion of benzene and toluene in s upercritical carbon dioxide, along with measurements from several othe r sources, to illustrate some of the experimental challenges. Special attention is given to the peak shape. The intercomparisons are greatly simplified by comparing the experimental data as functions of density , rather than pressure. We find large and unexplained discrepancies be tween the various experimental sources. We discuss the theoretical pre dictions for the relationships between the diffusion coefficients and diffusivities obtained from Taylor dispersion and dynamic light scatte ring in fluids near critical points. We conclude that there is no stro ng reason to press for Taylor dispersion measurements near the gas-liq uid critical point of the carrier gas.