Modelling the thermodynamic properties and fluid-phase equilibria of n-perfluoroalkanes and their binary mixtures with the SAFT-γ Mie group contribution equation of state

Abstract

The SAFT-γ Mie group-contribution approach is extended to describe the thermodynamic properties and fluid-phase behaviour of n-perfluoroalkanes and their binary mixtures. New molecular interaction parameters characterising the functional chemical groups forming these molecules (CF4, CF3 and CF2) are estimated from experimental vapour pressure and saturated-density data of the pure compounds. The vapour–liquid equilibria of four mixtures are then described predictively and compared to recent experimental data from the literature. Additionally, new experimental data for the excess volume of the (n-C6F14 + n-C8F18) mixture is measured over the whole range of compositions, between 278.15 and 318.15 K. The mixture presents small negative excess volumes, which increase in absolute value with increasing temperature. The results are compared with the excess volume for the corresponding mixture of n-alkanes of the same chain length, and with the SAFT-γ Mie predictions. The theory provides a very good description of the properties of both the pure compounds and their binary mixtures.