Modeling of diffusivities in supercritical carbon dioxide using a linear solvation energy relationship

A linear solvation energy relationship (LSER) method was used to develop a predictive model for the diffusivities of organic solutes in supercritical CO₂ at infinite dilution. The LSER model was based on the diffusivities of 18 solutes and 104 data points for sc-CO₂ in the range of 32-60°C and 8-100 MPa. The independent variables in the model were empirically determined descriptors of the solute molecules and the dipolarity/polarizability of CO₂ at a given density. The model was tested for prediction accuracy by using the diffusivities of 10 solutes not included in the database. The model provided relative deviations less than 10% in the correlation and prediction of the diffusivities in supercritical CO ₂ of the organic solutes considered. The accuracy of the proposed LSER model is comparable with He-Yu [31] equation, which is the most effective correlation in the literatures. The coefficients of the model show that diffusivity in supercritical CO₂ is strongly dependent on the dipolarity/polarizability of CO₂. The hydrogen-bond basicity and dipolarity/polarizability of the solute have significant effects on the diffusivity, whereas the hydrogen-bond acidity and excess molar refractivity are less important. The logarithm of the solute's gas-to-hexadecane partition coefficient used to model dispersion interactions and cavity formation processes was found to be statistically insignificant.