Global phase behaviour in carbon dioxide plus n-alkanes binary mixtures

The family of carbon dioxide (CO₂) plus linear alkanes is one of the most common type of mixtures found in supercritical CO₂ separation and extraction. Consequently, an accurate thermodynamic representation is a key element for a proper process design. In this contribution, the PPC-SAFT equation of state is applied to the construction of the serial-prediction-domain global phase diagram (spd-GPD) of the CO₂ plus n-alkanes series to carefully analyse the presence of different thermodynamic phenomena. The goal is to address the capability of the equation to predict the global behaviour of these mixtures, with emphasis in accurately reproducing their mechanisms and topology. The results obtained reveal quantitative agreement with the available experimental data, including a complete description of the emergence of different phenomena as a function of the hydrocarbon chain length, such as azeotropy, double retrograde behaviour, critical transitions, mass and molar density inversions and critical pressure step points.