The majority of chemical products are produced and consumed in solid forms. Solid-liquid equilibrium (SLE) and solid-supercritical fluid equilibrium (SFE) are two critically important phase equilibrium phenomena that represent the thermodynamic limits of chemical processing involving solids.
Today’s process simulators are capable of rigorous and accurate modeling of chemical systems and processes involving solids. In addition to vapor-liquid equilibrium (VLE) and liquid-liquid equilibrium calculations, process simulators can readily perform SLE and SFE calculations predictions. This paper briefly introduces the thermodynamic framework and thermo-physical property models commonly used in process simulators to perform SLE and SFE calculations.
To illustrate rigorous and accurate thermodynamic modeling of SLE and SFE, this article models caffeine solubility in pure solvents, mixed solvents, and supercritical fluids and different operating conditions. Activity coefficient models such as NRTL, UNIFAC, NRTL-SAC, and COSMO-SAC are used to correlate and predict SLE of caffeine. Equations of state models, including Peng-Robinson, SRK, and PC-SAFT, are used to perform SFE calculations for caffeine.