Phase Diagrams for Ternary and Quaternary Mixtures of Methane, Propane, Octane, and Decane for the Low Concentration of Heavy Hydrocarbon Components

Valery Buleiko C, S Gazprom – VNIIGAZ, Russia [email protected]

Boris Grigoriev Vernadsky, 9, 199, Gazprom – VNIIGAZ, Russia

Vitaly Podnek OGRI RAS, Russia

Denis Buleiko Vernadsky, 9, 199, OGRI RAS, Russia

Precision data of the accurate calorimetric measurements of phase equilibria for ternary and quaternary mixtures of methane, propane, octane and decane especially for the low concentration of octane and decane have been presented. Phase diagrams have been plotted based on the experimental data of heat capacity, internal energy, pressure, and temperature derivative of pressure at constant volume 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 phase behavior of hydrocarbon mixtures for the low concentration of octane and decane is qualitatively transformed compared to the customary concept.

- The hydrocarbon mixture splits into a macroscopic phase (a macrophase enriched by methane and propane) and microscopic phases (microphases enriched by octane or decane).

- Each microphase consists of one heavy hydrocarbon component (octane or decane).

- The phase behavior of each microphase for quaternary mixture of methane, propane, octane, and decane doesn’t depend on concentration of other heavy component that formed a microphase.

- The phase behavior of each microphase depends on constitution of a macrophase.

- The high molecular components provoke the split of liquid part of a macrophase into two liquid phases.

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 microphases enriched by heavy hydrocarbons and a macrophase enriched by methane and propane. Besides, the split of the liquid part of a macrophase into two liquid phases takes place. A quasi-binary approximation allows us to reveal an impact of heavy hydrocarbons to the phase behavior of a hydrocarbon mixture. A first quasi- component is a binary mixture with the constant methane/propane ratio. A second component is octane or decane. Variation of the concentration of a second component allows us to reveal its impact to the phase behavior of a mixture.

Acknowledgment This work was supported by the Russian Foundation for Fundamental Research under Grants № 19-08-00202