Phase Diagrams for Ternary Mixtures of Methane, Propane, and Octane for the Low Concentration of Octane

Abstract

Precision data of the accurate calorimetric measurements of phase equilibria for ternary mixtures of methane, propane, and octane especially for the low concentration of octane have been presented. Based on the experimental data of heat capacity, internal energy, pressure, and temperature derivative of pressure at constant volume, the phase diagrams have been plotted in the range 140–350 K and 0.1–24 MPa. Phase transitions are localized by the finite discontinuities in temperature derivatives of the thermodynamic potentials. Our investigations show that hydrocarbon mixtures for the low concentration of octane split into two phases, the macrophase enriched by methane and propane and the octane-rich microphase. Besides, octane provokes a split of the liquid part of the macrophase into two liquid phases, the octane-rich phase and the octane-lean phase. To prove that all phases are equilibrium phases a cooling mode of measurements is used. At the cooling mode of measurements the same phase transitions as at the heating mode occur. These phase transitions correspond to the formation of the octane-rich microphase and the macrophase enriched by methane and propane. Besides, at the cooling mode of measurements a split of the liquid part of the macrophase into two liquid phases takes place.