Tricritical phenomena in quasi-binary mixtures. IV: Ternary ethane systems

Phase equilibria have been studied in binary and quasi-binary mixtures of ethane with higher alkanes (n-hexadecane to n-eicosane) near the tricritical temperature. We report the temperatures and pressures corresponding to the lower and upper critical end points of various mixtures. The compositions of the coexisting phases in the three-phase region of six mixtures were also studied. The shrinkage of the width of the three-phase region is consistent with the asymptotic classical theory of tricritical points, while an extended classical theory is necessary to account for the details of the coexistence curves. An examination of the deviations from the quasi-binary approximation shows that it is a very good approximation for the ethane+(n-heptadecane+n-octadecane) system.