Tricritical phenomena in chain-like mixtures from a molecular-based equation of state

A molecular-based equation, the Soft-SAFT (from Statistical Associating Fluid Theory) equation of state, is applied to study the three-phase region of binary mixtures of chain-like molecules. Two sets of mixtures are investigated: model binary mixtures of Lennard–Jones chains and model binary mixtures of hydrocarbons. The molecular parameters of the equation but one are kept constant and the phase diagrams are obtained as a function of chain length or molecular weight. The equation is used to locate the tricritical point of these mixtures as well as to investigate the approach to the tricritical point. We report the temperatures and pressures corresponding to the lower and upper critical end points of various mixtures. The tricritical points of the mixtures are obtained as the point where the two critical end-point lines of the mixture merge.