Experimental investigation and thermodynamic modelling of vapor-liquid equilibria for carbon dioxide + heavy-alkane systems at elevated temperatures and pressures

Thermophysical properties of multi-component mixtures containing carbon dioxide (CO₂) and hydrocarbons are fundamental information for Fischer-Tropsch synthesis and enhanced oil recovery processes. This study focuses on the phase equilibrium behavior and thermodynamic modelling for CO₂ + heavy-alkane systems at elevated temperatures and pressures. For this purpose, a new isochoric saturation apparatus coupled with new data analysis method was developed and its reliable performance was validated by CO₂ + n-decane under the wide range of conditions. Experimental investigations of CO₂ + heavy-alkane systems were performed in the temperature range from (303.15 to 523.15) K and at pressures up to 10 MPa, which have been utilized to explore the comprehensive influence of various factors on phase equilibrium behavior. Furthermore, a new volume-translation function in Peng-Robinson (PR) equation of state (EoS) and binary interaction parameter (BIP) model were proposed to develop the predictive framework for thermodynamic properties of CO₂ + heavy-alkane systems. VTPR EoSs of heavy-alkanes can predict liquid densities with the average absolute deviations of less than 0.52%, which are significantly superior to the original cubic EoSs in the temperature range from (278.15 to 573.18) K. Combined with the classical van der Waals (vdW) mixing rule, they can predict the phase equilibrium pressure, saturated and compressed liquid densities with the maximum average absolute deviations of 6.57%, 1.75% and 2.73% at pressures up to 50 MPa. Ultimately, swelling coefficients of CO₂ + heavy-alkane systems were determined by prediction models, which had revealed the tremendous contribution of CO₂ to interstitial expansion of alkane molecules.