Measurements and correlation of infinite dilution binary diffusion coefficients for Cr(acac)3 in high temperature supercritical carbon dioxide

The infinite dilution binary diffusion coefficient (D-12) for chromium (III) acetylacetonate (Cr(acac)(3)) in supercritical carbon dioxide (scCO(2)) was measured at temperatures from 343 K to 423 K and pressures from 10 MPa to 22 MPa by the chromatographic impulse response (CIR) method. We previously reported D-12 data at relatively low temperatures below 343 K; the D-12 data were accurately represented by the hydrodynamic equation where the D-12/T vs. CO2 viscosity were expressed by a straight line on a logarithmic plot. However, the newly measured D-12 values in the present study showed greater deviations at higher temperatures or lower viscosities (lower pressures/densities) from the correlation determined for low - temperature D-12 data. The maximum deviation was 68% at the lowest measured CO2 viscosity of 22 mu Pa s; thus, the hydrodynamic equation could be no longer applied in this region. The D-12 data that deviate from the hydrodynamic equation fully correspond to the gas-like scCO(2) region, whereas those fitted by the equation correspond to the liquid-like scCO(2) region. The gas-like and liquid-like regions can be separated on the basis of density fluctuations and a ridge line in a pressure vs. temperature diagram, claimed by Nishikawa and Morita [Chem. Phys. Lett., 316 (2000) 238]. Compared with the accuracy in predicting the D-12 data by the original Schmidt number correlation, the accuracy was improved by the modified Schmidt number correlation, with an average relative deviation of 6.20 % for 136 conditions, including both gas-like and liquid-like scCO(2) regions. (C) 2022 Elsevier B.V. All rights reserved.