Study of phase and volumetric behavior of hydrocarbons and carbon dioxide ternary mixtures under high-temperature and high-pressure conditions

Abstract

Phase behavior and volumetric properties of the binary system CO2 + decane and ternary systems CO2 + decane + a third hydrocarbon compound have been studied up to 423.15 K and 100 MPa. Bubble point pressures were measured by visual synthetic method and the density measurements were performed in a vibrating tube densitometer. The measurements covered the molar compositions of CO2 of 0.1182, 0.3050, 0.6271 and 0.9539 for the binary system, at temperatures from 318.15 to 358.15 K. While for the ternary mixtures the measurements were performed for four compositions: high alkane, high aromatic, high CO2 and one equimolar content, the temperatures vary from 328.15 to 423.15. Excess molar volumes were calculated from the density data showing positive values at lower temperatures and higher pressures for the binary mixtures, and negative values int the entire range of compositions of the ternary mixtures. The densities were correlated for each system as a function of temperature and pressure using a modified Tammann−Tait equation, the maximun deviation (MD) for the calculated density of binary system was found to be 0.63% and 1.72% for the ternary system. Isothermal compressibility and isobaric thermal expansivity values were calculated from the experimental density data, showing higher compressiblity values at lower pressures and higher CO2 content for binary mixture. The expansibity of mixtures showed a poor dependece with temperature for all binary mixtures while for the ternary mixtures differents behaviors were found specially for the mixtures of high-CO2 and high-alkane content. Phasae behavior of ternary mixtures were modeled with the Peng-Robinson equation of states proving to be a good predictive equation for the description of these ternary systems.