Dillusion I Fluidchromatographie I Gase I Hohe Driicke I LaminarstromungBinary diffusion coefficients D , , have been determined for benzene, n-propylbenzene and 1,3,5-trimethylbenzene in supercritical CO, at 40°C from 80 to 160 bar and additionally between 35 and 55°C at 110 and 130 bar with the chromatographic broadening technique (CBT). The effect of secondary Now was investigated. The observed binary diffusion coefficients are of the order of 2 .cmz . s-I . For a pressure rise from 80 to 160 bar, the diffusion coefficients decrease by about 50%. The isobaric temperature dependence of diffusion coefficients at 110 bar is substantially higher than that at 130 bar; for constant densities p. however, the temperature coefficients seem to be very small. n-Propylbenzene was found to diffuse faster than its structural isomer 1,3,5-trimethylbenzene. At higher densities F = ( D 1 2 . p)/(D,, .p)id rises well above the value given by the Enskog-Thorne theory and finally approaches approximately unity.Die binaren Diffusionskoeffizienten D,, von Benzol, n-Propylbenzol und 1,3,5-TrimethylbenzoI wurden bei 40°C von 80 bis 160 bar sowie bei 110 und 130 bar von 35 bis 55°C nach der chromatographischen Peakverbreiterungsmethode experimentell bestimmt. Der Effekt der Sekundarstromung wurde untersucht. Die beobachteten Diffusionskoeffizienten sind von der GroOenordnung 2 .cmz . s -' . Durch eine Druckerhohung von 80 auf 160 bar bei 40°C werden die Diffusionskoeffizienten um etwa 50% herabgesetzt. Bei 110 bar wurde eine hohere Temperaturabhangigkeit des binaren Diffusionskoeffizienten beobachtet als bei 130 bar; sie ist jedoch recht gering bei konstanter Dichte p. n-Propylbenzol diffundiert unter vergleichbaren Bedingungen schneller als sein Strukturisomer 1,3,5-Trimethylbenzol. Die experimentell erhaltenen Werte fur die GroRe F = (Dlz . P ) / ( D ,~ p)id liegen hoher als die nach der Enskog-Thorne-Theorie berechneten; bei hohen Dichten erreicht der experimentelle F-Faktor ungefahr den Wert eins.
In supercritical fluid chromatography (SFC) compressed gases in the region of their critical temperature are used as mobile phases. SFC has important advantages over gas chromatography (GC) for the separation of low-volatile or thermally unstable substances. Like high pressure liquid chromatography (HPLC) and gel chromatography, it is used for various special applications and preparative separations, e. g. in the petroleum industry and in the separation of oligomers. SFC is of great interest in fundamental research on fluid extraction and for the determination of the physicochemical properties of fluid systems. In this contribution the most important physicochemical, methodological, and instrumental principles of SFC are summarized; characteristic physicochemical applications are the determination of capacity ratios, partition coefficients, partial molar volumes, interaction second virial coefficients, and diffusion coefficients.
Equations of State / High Pressure / Mixtures / Phase Equilibria / ThermodynamicsBy integrating an equation of state, an expression for the Gibbs energy of binary fluid mixtures is derived and used to define the thermodynamic conditions of phase equilibium. These conditions are solved numerically for the equilibrium concentrations. The same equation of state is used for liquid and vapour phases. From additional solid density data and the sublimation/melting pressure, solid-liquid and solid-gas equilibria can be Ber. Bunsenges. Phys. Chem. 88, 791 -796 (1984) -0 Verlag Chemie GmbH, D-6940 Weinheim, 1984. 0005 -9021/84/0909 -0791 $ 02.50/0 792 U. K . Deiters and I. Swaid: Calculation of Fluid-Fluid and Solid-Fluid Phase Equilibria in Binary Mixtures at High Pressures calculated, provided that no miscibility occurs in the solid state. -Calculations of phase equilibria have been carried out for several binary mixtures of nonpolar substances (noble gases, C 0 2 , hydrocarbons) for pressures up to 200 MPa, using the Redlich-Kwong equation and our own equation of state, which has been published earlier [ l ] . -The Redlich-Kwong equation represents the experimental phase equilibrium data at low pressures only, whereas the other equation achieves good agreement over the whole pressure range. I f the molecules differ very much in size, deviations from one-fluid theory can be accounted for by using the Leland-Mansoori-Carnahan-Starling function for rigid sphere mixtures in the repulsion term of our equation of state.
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