Measurement of relative static permittivity and solvatochromic parameters of binary and ternary CO2-expanded green solvents

CO2-expanded liquids (CXLs) is a class of solvent systems giving relatively low viscosity in comparison to neat organic solvents. The challenge is to achieve a high overall polarity of the CXL, despite the presence of compressed liquid CO2. In this study, the relative static permittivity (εr) was measured for binary and ternary one-phase mixtures of CO2 + green solvent using an in-line microfluidic device. In addition, Kamlet-Taft solvatochromic parameters were experimentally determined, allowing the characterization of the polarizability, acidity, and basicity. Novel data is shown for binary and ternary systems of CO2 expanded ethanol and ethyl lactate, with or without glycerol or water added, at moderate conditions of pressure and temperature (8 MPa and 35 °C). One-phase CXLs systems of a wide relative permittivity range (7.7–75.3) at lowered viscosity were enabled, by mixing different green solvents with CO2.