How Entrainers Enhance Solubility in Supercritical Carbon Dioxide

Abstract

Supercritical carbon dioxide (scCO2) on its own can be a relatively poor solvent. However, the addition at relatively modest concentration of "entrainers", simple solvent molecules such as ethanol or acetone, can provide a significant boost in solubility, thereby enabling its industrial use. However, how entrainers work is still under debate; without an unambiguous explanation, it is hard to optimize entrainers for any specific solute. This paper demonstrates that a fundamental, assumption-free statistical thermodynamic theory, the Kirkwood-Buff (KB) theory, can provide an unambiguous explanation of the entrainer effect through an analysis of published experimental data. The KB theory shows that a strong solute-entrainer interaction accounts for the solubility enhancement, while CO2 density increase and/or CO2-entrainer interactions, which have been assumed widely in the literature, do not account for solubilization. This conclusion, despite the limited completeness of available data, is demonstrably robust; this can be shown by an order-of-magnitude analysis based upon the theory, and can be demonstrated directly through a public-domain "app", which has been developed to implement the theory.

Adsorbate-adsorbate interactions on microporous materials

“…Thus, molecular driving forces can be extracted readily from decades-long compilations of isotherm fitting parameters. Such an approach has previously been demonstrated to be fruitful in clarifying, on a quantitative basis, the driving forces underlying solubilization into water [57,58] and supercritical CO2 [59,60], headspace vapour pressure [61,62] and solution-phase selfaggregation [63] of flavour molecules, and high-performance affinity chromatography [64].…”

Contributions of supercritical fluid technology for advancing decellularization and postprocessing of viable biological materials

“…The mechanism that leads to the increase of solvating power of scCO 2 is still yet not completely understood, although some research has suggested that strong solute–cosolvent bonds may account for this phenomenon. 100,101…”

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“…As a practical note, it is often straightforward to make estimates of bulk thermodynamic parameters (such as density, volume and activity) or to identify parameters that make minor contribution, thereby decreasing the need for experimental work. The present author has used this technique many times when analysing valuable historical data that lacked the ideal range of experimental information [3,[33][34][35][36][37].…”