Effect of the Heavy Component Interference on the Phase Behavior of Quinary Hydrocarbon Mixtures

Abstract We have presented the results of a calorimetric study of the heavy component interference in the quinary hydrocarbon mixtures of methane, propane, octane, nonane, and decane. The phase diagrams for these mixtures have been plotted based on the experimental data. The phase transitions are localized by the finite discontinuities and singularities in temperature derivatives of the thermodynamic potentials. The heat capacity, internal energy, pressure, and temperature derivative of pressure at constant volume are measured in the range 170–250 K, up to 36 MPa. The investigated systems are presented as the combination of the simple hydrocarbon mixtures. The simple hydrocarbon mixture is the mixture, which consists of components forming the macrophase (a binary mixture with the constant methane/propane ratio) and one of C4+ heavy components forming a microphase. Every heavy component, which forms the hydrocarbon mixture, has a limited domain of influence on the phase behavior of the system in the p-T-x state space. The configuration of this domain is predetermined by the heavy component concentration. The transformation of the phase diagram and, consequently, the transformation of the phase behavior of the mixture due to the interference of heavy components are observed. Our investigations show that quinary hydrocarbon mixture for the low concentration of octane, nonane, and decane splits into four phases, the macrophase composed of methane, propane, octane, nonane and decane, and three microphases formed by octane, nonane, and decane. This split is similar to the split of the simple hydrocarbon mixture. The heavy components, octane, nonane, and decane dissolved in the macrophase partly. Besides, the heavy components provoke a split of the liquid part of the quinary mixture into two liquid phases.