Solubility of Benzoic Acid in Mixtures of CO₂ + Hexane

Abstract

The solubilities of solid benzoic acid in mixtures of CO2 + hexane have been measured at temperatures ranging from (308 to 338) K, pressures ranging from (10 to 35) MPa, and cosolvent concentrations ranging from (0 to 7) mol % hexane. The consistency of the data was verified via plots of the enhancement factor versus the density as suggested by dilute solution theory. The dilute solution theory was also used to correlate and extrapolate the data using three parameters that are independent of temperature, pressure, and cosolvent concentration.

How Entrainers Enhance Solubility in Supercritical Carbon Dioxide

“…Correlation between the solubilization gradient (eq ) and V 2 / V 1 at infinite entrainer dilution limit, in order to examine the validity of the fluid density hypothesis and the CO 2 clustering hypothesis through eq . No correlation common to both entrainers (methanol and hexane) in the solubilization of benzoic acid (data from refs and ) has been observed, in contradiction to these hypotheses.…”

“…It turns out that calculations of the KB integrals require just three sets of data: solubilities (converted to pseudochemical potential) at the given T and across a range of P ; densities (converted to partial molar volumes) of the CO 2 + entrainer again across a range of P values; and entrainers’ activity coefficients. The solubility data are available in the literature. − The density data are not hard to measure, but unfortunately sufficient data are not always reported in the literature; thus, it is generally impossible to derive V 1 and V 2 which are the partial molar volumes of CO 2 and entrainer. We instead approximate V 1 as the pure scCO 2 value which can easily be calculated from the density data and V 2 as the infinite dilution values available in the literature. − It is hoped that measuring densities of CO 2 + solute, CO 2 + entrainer, and CO 2 + entrainer + solute will become standard practice for future publications, as these values will generate more accurate values for use within the app.…”

“…Where possible, the infinite dilution V 2 reported in the literature for various entrainers have been used for V 2 , − considering again the diluteness of the entrainers. Note that V 2 takes large negative values (i.e., the entrainer makes the system more compact) near the critical temperature and plateaus to a modest level (generally not far from the conventional molar volume) at higher pressures. − However, such a variation of V 2 does not pose any difficulties, because (1) solubilization is generally carried out at pressures above the critical point ,− and (2) any “reasonable” value of V 2 can be entered by the user who can verify that it makes little difference to the final result (Appendix A). This robustness with regard to V 2 will be rationalized theoretically in section .…”

“… a Note that the pressures have been chosen to span a large range for illustrative purposes. b Calculated using ref using infinite entrainer dilution approximation. c Parameters for the NRTL model d Solubility data taken from ref . e Reference . f Reference . g Reference . h Reference . i Reference . j Infinite dilution V 2 data taken from ref . k Reference . l Reference . …”

“…The pressure dependence of the solubilization gradient (eq , black circles) is compared with G u 2 – G u 1 (red squares) and G u 2 (green diamonds). The solubility data have been taken from refs and .…”