Solid-Liquid-Gas Phase Equilibrium for Binary Carbon Dioxide plus Linear Alkane Systems: Experiments and Modeling

Supercritical fluids are widely used in various applications, and their effectiveness depends on understanding the phase equilibria involved in the processes. The aim of this work is to report the solid-liquid-gas (SLG) phase equilibrium for binary systems comprising carbon dioxide and a linear alkane. In this regard, the pressure-temperature SLG phase equilibrium was measured based on the enhanced first freezing point method from the freezing point of the alkane up to 37.87 MPa. The hydrocarbons studied were octadecane, eicosane, heneicosane, tricosane, tetracosane, hexacosane, dotriacontane, and hexatriacontane, whose freezing point temperatures ranged from 301 to 349.35 K. Relationships between alkane chain length and factors influencing the freezing point were identified. SLG modeling for the CO2 + alkane systems was performed by the Peng-Robinson and Sanchez-Lacombe equations of state for the available data from octadecane to hexatriacontane. The correlated data agreed with our experimental data with average absolute deviations lower than 0.33%, with the Sanchez-Lacombe equation yielding the lowest deviation. Standard deviations of the parameters were calculated, and their impact on the modeling was discussed.