Widom and extrema lines as criteria for optimizing operating conditions in supercritical processes

This work focuses on the supercritical region of fluid phase equilibria, just above the critical point. It is already known that in this area, two different zones can be distinguished, one where supercritical fluids (SCFs) have liquid-like properties, and the other one where SCFs have gas-like properties; these two zones being delimited by the Widom and extrema lines. This work draws attention to these lines, indicating that they may serve to guide the choice of process operating conditions. Three simple approaches for the prediction of the Widom line and extrema lines of binary mixtures involving CO2 for any composition are proposed. The Widom line and extrema lines of binary mixtures involving CO2 with eight very common organic cosolvents, as well as water, are predicted for different compositions (5%, 10% and 50% of cosolvent).