Controlling phase behaviour on gas expansion of fluid mixtures

Abstract

The application of moderate pressures (50 bar) of CO₂ to binary liquid solvent mixtures at room temperature can induce changes in phase behaviour; both inducing miscibility and splitting miscible mixtures. The cause of this phase change behaviour was found to be due to the balance between enthalpic and entropic terms that define the Gibbs energy of mixing and, hence, the partition coefficient. In the majority of binary solvent mixtures, the solvents were miscible at ambient pressure with two phases forming upon application of CO₂. For some mixtures, the phase behaviour was found to be very composition dependent and in only five systems did no phase change occur.