High-pressure phase equilibria in the systems methane + phenanthrene and methane + 1-phenyldodecane up to 400 MPa

In this paper, experimental data on the high-pressure phase behaviour of the systems methane + phenanthrene and methane + 1-phenyldodecane are presented. For both systems vapour-liquid, solid-fluid, and solid-liquid-vapour equilibrium data were determined. The experiments were carried out for various mixtures covering almost the whole composition range. The temperature range investigated was from 360 to 460 K for the methane + phenanthrene system and from 260 to 400 K for the methane + 1-phenyldodecane system. The maximum pressures exerted on the samples were dependent on the equipment used, either 200 or 400 MPa. The second critical endpoint (s + 1 = g), which is the pressure maximum of the three-phase curve (solid hydrocarbon + liquid + vapour), is, for the methane + phenanthrene system, located at a temperature T = 403.3 ± 0.4 K, a pressure p = 358.9 ± 1.5 MPa, and a mole fraction of phenanthrene in the critical fluid phase x = 0.126 ± 0.009. The coordinates of the second critical endpoint of the methane + 1-phenyldodecane system were found to be T = 277.1 ± 0.4 K, p = 148.0 ± 0.6 MPa, and for the mole fraction of 1-phenyldodecane in the critical fluid phase x = 0.076 ± 0.005.