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

Abstract

A flow-type apparatus and predictive framework were developed for measuring and estimating dipolarity/ polarizability (π*) values of binary mixtures of supercritical carbon dioxide (scCO 2 )−cosolvents. The π* values of scCO 2 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 scCO 2 −cosolvent mixtures proposed in this work was the modification by the addition of correction functions (g(ρ CO 2 )) 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(ρ CO 2 ) forms with a function of CO 2 density were evaluated by considering literature local density enhancements of pure CO 2 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 scCO 2 −cosolvent mixtures (methanol, ethanol, 2-propanol, and 1,1,1,2tetrafluoroethane (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(ρ CO 2 ) 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 CO 2 density (pressure and temperature).

Solvent Replacement Strategies for Processing Pharmaceuticals and Bio-Related Compounds—A Review

“…Related to developments in supercritical fluid theory, entropy based solubility parameters have been proposed that allow the extension of traditional solubility parameter theory to chemical systems containing supercritical fluids and ethanol [71] or systems at high temperatures or high pressures [72]. Experimental systems for measuring the KT parameters of methanol, ethanol, 2-propanol, and 1,1,1,2-tetrafluoroethane (HFC134a) co-solvents in CO 2 have been developed for assessing the HBD alcohol interactions with the HBA Lewis acidity of CO 2 in the supercritical state for quantifying polarity enhancements [73].…”

Co-Solvent Selection for Tocotrienol Extraction From Palm Fatty Acid Distillate Using Supercritical Carbon Dioxide

“…Polar co-solvents are commonly used in the scCO 2 extraction process, at concentrations of 5%-20%, to increase the solubility of the compounds of interest, reducing the main operating condition such as pressure and carbon dioxide (CO 2 ) consumption, hence, increasing the separation process (Duereh et al, 2020b;Tirado et al, 2019). Co-solvents can modify the characteristics of the supercritical solvent, such as its polarity.…”

“…The tocotrienol isomers separated from the extract at a flow rate of 0.6 mL/min with 85% (v/v) methanol in water for 50 min. A modification to the predictive framework has been made by Duereh et al (2020b) to predict the π* values of scCO 2 -cosolvent binary mixtures. In this modification, density-dependent via a correction function (g(…”

“…Four correction functions of local density enhancement have been evaluated by Duereh, et al (2020b) using the fluorescence method, UV method, Raman method, and molecular dynamics simulations. Based on the plot of correction functions of local density enhancement as a function of pure density (…”

“…This is because acetone has a higher dipole moment (2.88). The dipole moment governs the specific dipolarity/polarisability interactions between target compounds and the co-solvent in the supercritical state (Duereh et al, 2020b). The molecular dynamics simulations showed the specific interactions that appeared between solute and co-solvent (Frolov and Kiselev, 2014;Gurina et al, 2017).…”