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.

已提供了甲烷，丙烷和辛烷三元混合物的相平衡的精确量热测量的精确数据，特别是对于低浓度的辛烷。根据恒定容量下的热容量，内部能量，压力和压力的温度导数的实验数据，已在140–350 K和0.1–24 MPa范围内绘制了相图。相变通过热力学势的温度导数的有限间断来定位。我们的研究表明，低辛烷值的碳氢化合物混合物分为两相，即富含甲烷和丙烷的宏观相和富含辛烷值的微相。此外，辛烷值会引起宏观相的液体部分分裂为两个液相，富辛烷阶段和贫辛烷阶段。为了证明所有相都是平衡相，使用了测量的冷却模式。在测量的冷却模式下，发生与加热模式相同的相变。这些相变对应于富含辛烷的微相和富含甲烷和丙烷的宏观相的形成。此外，在测量的冷却模式下，宏观相的液体部分分成两个液相。