Excess volume, isothermal compressibility, isentropic compressibility and speed of sound of carbon dioxide+n-heptane binary mixture under pressure up to 70 MPa. II. Molecular simulations

Density, Speed of Sound, Compressibility, and Excess Properties in a Carbon Dioxide + n-Docosane Binary Mixture from 10 to 70 MPa

“…The partial molar volume of the heavy hydrocarbon component can decrease so dramatically that it becomes negative , at infinite dilution at pressures of around 10 MPa and below. This behavior, caused by a clustering of CO 2 molecules around a hydrocarbon particle, was not observed here as liquid–solid and liquid–vapor phase changes made it impossible to take measurements at low temperature and low pressure.…”

“…The results found in this series of articles have clearly shown that a high non-ideal behavior of the mixtures at infinite dilution of organic liquids in supercritical CO 2 point occurs, which may have implication for both CO 2 enhanced oil recovery simulation and monitoring 9 or even for supercritical fluid extraction processes. 11 To generalize these findings and to be capable of predicting it, one may assume a link between the clustering effect 5 and the anomalies of the thermodynamic properties observed 9 in the Widom region, a topic that will be explored in future work.…”

“…These studies were motivated by the need for having carbon dioxide-rich mixtures volumetric and acoustic properties in reservoir conditions for simulating CO 2 enhanced oil recovery processes as well as seismic monitoring of such recovery. Interestingly, these mixtures have exhibited unexpected results such as a high non-ideal behavior of the mixtures at infinite dilution of the normal alkanes close to the CO 2 critical point. − This specific behavior was attributed to a clustering phenomenon occurring in the mixture that was confirmed thanks to molecular simulations . Such a phenomenon is obviously related to the anomalies of the thermodynamic properties observed in the supercritical region where the fluid evolves from a gas-like to a liquid-like behavior, − sometimes called the Widom region, even if only little research work can be found for mixtures. − …”

“…1−3 This specific behavior was attributed to a clustering phenomenon 4 occurring in the mixture that was confirmed thanks to molecular simulations. 5 Such a phenomenon is obviously related to the anomalies of the thermodynamic properties observed in the supercritical region where the fluid evolves from a gas-like to a liquid-like behavior, 6−8 sometimes called the Widom region, 6 even if only little research work can be found for mixtures. 9−11 In this study, the speed of sound was measured in pure ndocosane and in 5 mixtures with CO 2 contents ranging from 0.24 to 0.84 (in mole fraction) and at pressures ranging from 10 to 70 MPa using a pulse-echo method working in the MHz range.…”

Thermodynamics of supercritical carbon dioxide mixtures across the Widom line

“…Furthermore, the "clustering" effect 82 , where many solvent molecules collapse around a single solute molecule in the high compressibility region, was also studied in this work. This effect leads to a negative partial molar volume of the solute component at infinite dilution and can be quantified by the excess coordination number of CO 2 molecules surrounding the solute molecule regarding a uniform distribution at bulk density 81 . Fig.…”