Solid–liquid phase behavior of ternary mixtures

Abstract

AbstractThe Gibbs Duhem integration technique is extended to calculate ternary phase diagrams at constant temperature and pressure. The technique is used to calculate solid–liquid–vapor phase equilibria for a system selected to roughly model a mixture of two diastereomeric molecules of similar melting point and diameter immersed in a solvent with a lower melting point and a slightly smaller diameter. The cross‐species well‐depth and diameter between the two diastereomers are varied to determine their impact on the phase equilibria. We find that when the interspecies well‐depth is lowered to less than that of either of the diastereomers, the solid phase separates into two solid solutions and consequently there is a region of three‐phase coexistence in the ternary phase diagram. We then calculate ternary phase diagrams at a series of temperatures for one set of molecular parameters. For an equimolar mixture of diastereomers, there is a range of temperature and solvent concentration at which only one of the diastereomers will precipitate, thus effecting a separation of the diastereomers. As the temperature is decreased the purity of the precipitate increases. © 2008 American Institute of Chemical Engineers AIChE J, 2008