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.

Automated summary

The infinite dilution binary diffusion coefficient of chromium (III) acetylacetonate in supercritical carbon dioxide was measured at various temperatures and pressures. The data showed deviations from the hydrodynamic equation at higher temperatures or lower viscosities, corresponding to the gas-like region. The accuracy of predicting the data was improved by a modified Schmidt number correlation.