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

Jingwen Cui,Mynta Norberg,Martin Andersson,Lena Klintberg,Margareta Sandahl,Larissa P Cunico,Charlotta Turner

doi:10.1016/j.supflu.2021.105196

Jingwen Cui, Mynta Norberg + Show 5 more

Open Access

https://doi.org/10.1016/j.supflu.2021.105196

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Abstract

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.

Highlights

The replacement of conventional solvents with green solvents is not always a viable option due to the limiting physicochemical properties such as high viscosity of the latter
CO2-expanded liquids (CXLs) mainly differ from commonly used supercritical fluid mixtures in that the organic solvent is present in higher amounts than the CO2 and that moderate conditions of pressure and temperature are used
In an earlier study by Aparicio et al [52], mixtures of ethyl lactate and water was shown to have a highly nonlinear compositional dependence of εr, primarily through the disruption of water networks by ethyl lactate, and secondarily through the disruption of ethyl lactate clusters by water. This is likely a major part in the explanation of the deviation of the additive model for the CO2 + ethyl lactate + water mixtures studied in this work, as the maximum relative static permittivity of mixing measured by Aparicio et al [52] was very similar to the maximum residuals in this work

Summary

Introduction

The replacement of conventional solvents with green solvents is not always a viable option due to the limiting physicochemical properties such as high viscosity of the latter. CO2-expanded liquids (CXLs) mainly differ from commonly used supercritical fluid mixtures in that the organic solvent is present in higher amounts than the CO2 (molar fractions >0.5) and that moderate conditions of pressure and temperature are used. No experimental data of εr are found in the literature so far for CXLs of highly polar co-solvent mixtures, including water or glycerol Another way to obtain information about solvent dielectric properties is by using the Kamlet-Taft solvatochromic parameters [29]. The relative static permittivity (εr) and the Kamlet-Taft parameters (π*, α and β) were measured for one-phase binary and ternary CXLs systems, constituted of pressurized CO2 mixed with highly polar and moderate polar green solvent mixtures (ethanol, ethyl lactate, water, glycerol). This limitation was addressed in this work by combining glycerol with ethanol or ethyl lactate and water with ethyl lactate before adding compressed liquid CO2 to the solvent mixtures to form one-phase CXL mixtures

Materials

Relative static permittivity

Kamlet-Taft parameters

Conclusions