Phase behaviour of binary fluid mixtures: a global phase diagram solely in terms of pure component properties

Abstract

Calculations of the critical properties of binary mixtures are reported using the Carnahan–Starling–van der Waals (CSvdW) equation of state in conjunction with the one-fluid model and the Lorentz–Berthelot combining rules for unlike interactions. The calculations are used to determine the global phase diagram of binary mixtures. A feature of the calculations is that no adjustable parameters were used in the combining rules. This means that the global phase diagram can be constructed solely in terms of experimentally measurable quantities such as the ratio of the critical temperatures and critical volumes of the component molecules. The global phase diagram accounts for almost all of the known types of fluid phase behaviour, including closed-loop liquid–liquid immiscibility. Comparisons with experimental data indicate that the global phase diagram is a good qualitative predictor of phase behaviour. Therefore, the phase behaviour type of a binary mixture can be confidently predicted solely from the ratios of critical temperatures and volumes of the pure components.