Determination of Binary Diffusion Coefficients of Benzene and Some Alkylbenzenes in Supercritical CO₂between 308 and 328 K in the Pressure Range 80 to 160 bar with Supercritical Fluid Chromatography (SFC)

Abstract

Abstract Binary diffusion coefficients D 12 have been determined for benzene, n‐propylbenzene and 1,3,5‐trimethylbenzene in supercritical CO 2 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 flow was investigated. The observed binary diffusion coefficients are of the order of 2 · 10 −4 cm 2 · s −1 . 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 ρ, 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 12 · ρ) /( D 12 · ρ) id rises well above the value given by the Enskog‐Thorne theory and finally approaches approximately unity.