V.l.e. measurements at high pressures and high temperatures on (methane + n-hexane)

The study of {xCH₄ + (1 - x)C₆H₁₄} presented here is part of a larger project that aims at the study of a prototype of a gas-condensate system, the ternary {xCH₄ + yC₆H₁₄ + (1 - x - y)C₁₄H₃₀}. The experimental work was carried out in a semi-automated high-pressure high-temperature v.l.e. (vapour + liquid equilibrium) apparatus. It permits the determination of the compositions and densities of both phases of a hydrocarbon mixture, or even of a third phase if it happens to exist, in the range of pressure and temperature from (2 to 40) MPa and from ambient to 410 K, respectively. The precision of the mole fraction determination is ±3.10^-3 for the liquid phase and ±2.10^-3 for the vapour phase, while the density results have an uncertainty of no more than ±0.8 kg·m^-3, in both phases. The experimental measurements performed on {xCH₄ + (1 - x)C₆H₁₄} were carried out at two different temperatures, T = (348.15 and 383.15) K and over the range of pressures from 2 MPa up to the critical pressure of the mixture. The objective of the study of the system was the validation of the apparatus on the basis that it is a system on which extensive experimental data are available for comparison, although over a more restricted range of variables than those studied here. The experimental data have been compared with the representation given by a number of widely used thermodynamic models, namely the cubic equations of state of Peng-Robinson and of Soave-Redlich-Kwong and three corresponding states models, the Van der Waals one and two-fluid models.