Controlling Solvation and Mass Transport Properties of Biobased Solvents through CO₂ Expansion: A Physicochemical and Molecular Modeling Study

Abstract

Gas-expanded liquids have been studied during past years; however, the physicochemical properties of some of these fluids still need to be characterized and understood. In particular, the study of properties concerning solvation and mass transport is key for industrial applications. This work presents the characterization of eight CO 2-expanded biosourced solvents: organic carbonates (dimethyl, diethyl, ethylene, and propylene carbonates), anisole, veratrole, γvalerolactone, and 2-methyltetrahydrofuran. Two approaches have been used: spectroscopic measurements and molecular modeling. Phase equilibrium was determined for each CO 2 / biosourced solvent system, and then the solvatochromic probe Nile Red was used to determine changes in dipolarity/ polarizability (π* Kamlet−Taft parameter) by CO 2 pressure. Molecular dynamics calculations were performed to determine the density and viscosity changes with CO 2 pressure. It is shown in this study that the degree of modulation of dipolarity/polarizability parameter can go from that of pure solvent (around 0.4 for linear organic carbonates) to negative values, close to that of pure CO 2 at the T and P used in this study. Concerning transport properties, such as density and viscosity, a great decrease in both these properties' values was observed after swelling of the solvent by CO 2 , for instance, in linear organic carbonates where density can decrease to 50% the density of pure solvent; concerning viscosity a decrease of up to 90% was measured for these compounds. It was observed that the solubility of CO 2 and then modulation of properties were higher in linear organic carbonates than in the cyclic ones. This study shows once more that CO 2 has a great capacity to be used as a knob for triggering changes in the physicochemical properties of green biosourced solvents that can help to implement these solvents in industrial applications.

Molecular Simulations of Phase Equilibria and Transport Properties in a Model CO2-Expanded Lithium Perchlorate Electrolyte

“…The MeCN force field developed by Edwards et al and the EPM2 CO 2 force field were used for all simulations as the Edwards force field has previously been used successfully to describe electrolyte solutions, , and the EPM2 force field has been typically been used in studies involving gas expansion. ,,,,,, For lithium, we use the parameters from the AMBER force-field and use the Ottoson et al parameters for perchlorate. The charges for the cation and anions are further scaled by a factor of 0.8 to prevent aggregation at the highest CO 2 concentrations.…”

“…While the phase equilibrium and transport properties of CXLs have been studied in great detail by both experiment − ,− and simulation, ,,− CO 2 -expanded electrolyte (CXEs) solutions have not received significant attention. To the best of our knowledge, modeling of transport in CXEs has been limited to the COMSOL simulations by Shaughnessy and co-workers, and there has been to date no atomistic simulations of these systems.…”

Selective lignin fractionation using CO2-expanded 2-methyltetrahydrofuran (2-MTHF)

“…8 Most notably, the chemo-physical properties (e.g. solvation properties) change in the resulting gas-expanded solvent phase, 9 which can be reversed upon degassing. As the solvation properties of the GXL changes, the precipitation of the dissolved lignin (as macromolecule) can be triggered, and importantly, depending on the actual CO 2 pressure, different fractions (with narrowed molecular size distributions, chemical bond proportions, etc.)…”

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

“…The π* values can be measured using UV–vis spectroscopy with an indicator that responds to dipolarity/polarizability interactions with a solvent. The π* values of pure scCO 2 − and CO 2 -expanded solvent mixtures − have been widely available in the literature, while the values for scCO 2 –cosolvent binary mixtures have a few reports. , The reason might be a limitation of a batch-type apparatus that is difficult in controlling the amount of cosolvents and indicator in the supercritical phase with varying pressure in the wide range. For example, a saturated UV–vis spectrum can occur when measuring in the wide range of pressure due to excess concentration of indicator in the supercritical phase.…”