Binary diffusion coefficients supercritical fluids

Transport Properties Although the densities of supercritical fluids approach those of conventional liquids, their transport properties are closer to those of gases, as shown for a typical SCF such as CO2 in Table 22-12. For example, the viscosity is several orders of magnitude lower than at liquidlike conditions. The self-diffusion coefficient ranges between 10 and 10 cmVs, and binary-diffusion coefficients are similar [Liong, Wells, and Foster,/. Supercritical Fluids 4, 91 (1991) Catchpole and King, Ind. Eng. Chem. Research, 33,... 

Table I. Binary Diffusion Coefficients in Supercritical Fluids...

Swaid, I. and Schneider, G.M. (1979) Determination of binary diffusion coefficients of benzene and some aUcylbenzenes in supercritical carbon dioxide between 308 and 329 K in the pressure range 80 to 160 bar with supercritical fluid chromatography (SFC), Ber. Bunsenges. Phys. Chem. 83, 969-974. 

Klask, U. (1998) Diffusion coefficients in fluids — Determination of binary diffusion coefficients of organic substances in supercritical cEirbon dioxide with the Taylor dispersion method (in German), Doctoral dissertation. University of Bochum, Germany published 1999 by Shaker, Aachen. 

Today, most applications are based on packed columns at relatively low temperatures with binary and ternary mobile phases. It has become clear that the characteristics of interest are not limited to supercritical conditions. Most packed column applications actually use conditions just below the critical temperature, but well above the critical pressure of the mixed fluids, i.e., subcritical (in other words, liquid ). Unlike many observers expectations, important characteristics such as diffusion coefficients and viscosity are virtually identical whether the conditions are just supercritical or just subcritical. 

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