Etude des systèmes asymétriques CO2 + solutés en conditions CO2 supercritique

Carbon dioxide occupies a dual and distinctive role in modern science and engineering: it is both one of the main anthropogenic greenhouse gases contributing to climate change and a remarkably versatile, environmentally benign supercritical solvent. Its unique combination of gas-like transport properties and liquid-like solvating power makes CO₂ an especially attractive medium for a wide range of applications, from enhanced oil recovery through CO₂ injection to supercritical extraction, green processing, and chemical reactivity in supercritical media. Despite its growing importance, the large-scale deployment of supercritical CO₂ (sCO₂) in industrial and environmental technologies remains limited due to the scarcity of reliable thermophysical data and the insufficient molecular-level understanding of its complex behavior in mixtures, particularly near its critical point, where strong non-ideal and cooperative interactions prevail. This thesis aims to bridge this knowledge gap by coupling experimental measurements and thermophysical modeling of CO₂-rich systems. To this end, more than two thousand high-pressure density measurements were carried out for both pure compounds and binary as well as ternary mixtures formed by adding alkanes, alcohols, or a heavy non-volatile solute—triolein—to supercritical CO₂. These measurements were performed using a high-pressure vibrating-tube densimeter equipped with a specially designed injection system that enables the accurate preparation of CO₂-rich mixtures at low solute concentrations. The experimental study focused on determining volumetric properties at infinite dilution, allowing the derivation of partial molar quantities and the evaluation of the influence of molecular size and carbon chain length of solutes and co-solvents on clustering phenomena and solute-solvent interactions. From the experimental densities, derived properties such as the isothermal compressibility and partial molar volume were calculated, revealing pronounced deviations from ideality in systems near the CO₂ critical point. These deviations were attributed to the formation of transient molecular aggregates, or clusters, in which CO₂ molecules preferentially associate around solute molecules. To complement and interpret the experimental observations, the collected data were compared with predictions from two advanced equations of state derived from the Statistical Associating Fluid Theory (SAFT): the Perturbed-Chain SAFT (PC-SAFT) and the Variable-Range Mie SAFT (SAFT-VR Mie). This comparative analysis enabled a quantitative assessment of the ability of SAFT-type approaches to reproduce the complex thermodynamic behavior of CO₂-rich mixtures.