Kamlet-Taft Dipolarity/Polarizability of Binary Mixtures of Supercritical Carbon Dioxide with Cosolvents: Measurement, Prediction, and Applications in Separation Processes

A flow-type apparatus and predictive framework were developed for measuring and estimating dipolarity/polarizability (π*) values of binary mixtures of supercritical carbon dioxide (scCO2)-cosolvents. The π∗ values of scCO2 with methanol and ethanol cosolvents (up to 10 mol %) are reported at the temperature ranging from 40 to 80 °C and pressure ranging from 10 to 20 MPa and were found to be dependent on fluid density. The predictive framework for scCO2-cosolvent mixtures proposed in this work was the modification by the addition of correction functions (g(ρCO2)) of local density enhancement into the previous predictive framework for binary liquid nonpolar-polar mixtures [ Ind. Eng. Chem. Res. 2019, 58, 18986-18996 ]. Four g(ρCO2) forms with a function of CO2 density were evaluated by considering literature local density enhancements of pure CO2 obtained from (i) fluorescence, (ii) Raman, (ii) UV-vis spectroscopic techniques, and (iv) molecular dynamics simulations. The framework was applied to the prediction of π∗ of four scCO2-cosolvent mixtures (methanol, ethanol, 2-propanol, and 1,1,1,2-tetrafluoroethane (HFC134a)) and was found to give a reliable value with an overall relative deviation of 0.03 between the experimental and calculated data, where the fluorescence g(ρCO2) function provided a lower deviation than the other three functions. The application of the framework to separation processes showed that the π∗ values were found to explain the trends of solubility, extraction yield, and fractionation recovery. The π∗ values determined from the framework can be used to analyze solvent effect trends in many separation processes that required only cosolvent dipole moment, pure π∗ component, and CO2 density (pressure and temperature).