Thermodynamics of supercritical carbon dioxide mixtures across the Widom line

Supercritical carbon dioxide (scCO(2)) mixtures are essential for many industrial applications. However, the knowledge of their thermophysical properties in the extended critical region is insufficient. Here, supercritical liquid- and gas-like regions dominated by distinct dynamics and thermodynamics exist and are demarcated by the so-called Widom line. The nature of the anomalies observed for several thermophysical properties at the crossover between these two regions is the subject of a lively debate. Hence, the extended critical region of scCO(2) and seven of its binary mixtures with hydrogen, methane, ethane, isobutane, benzene, toluene or naphthalene is studied with respect to thermodynamic, transport and structural properties on the basis of molecular dynamics simulations and equation of state calculations. The Widom line is evaluated employing five criteria and a new empirical equation is proposed for its prediction. Further, the crossover anomalies are investigated in the light of pseudo-boiling theory, diffusion and viscosity as well as structural characteristics given by the radial distribution function.

Automated summary

This study analyzes the thermophysical, transport, and structural properties of supercritical carbon dioxide (scCO(2)) and its seven binary mixtures through simulations and calculations. The results reveal the existence of a Widom line between the supercritical liquid- and gas-like regions and propose an empirical equation for predicting the Widom line.