High pressure phase equilibria of carbon dioxide + n-alkanes mixtures: Experimental data and modeling

Experimental phase equilibrium data were measured for systems containing a mixture of heavy n-alkanes (C22H46, C23H48 and C24H50) and a light n-alkane (C12H26) in the presence of 20, 40, 60 and 80% mole fraction of CO2. The experiments were carried out in the range of 290-353 K and up to 70 MPa. The measured phase equilibrium data presented regions of vapor-liquid, solid-liquid and solid-liquid-vapor coexistence. To model the data obtained, the solid phase was described using the multiple solid solution approach, which employs the modified UNIQUAC equation to calculate the activity coefficients. The Poynting correction factor was used to take into account the pressure effect in the solid-liquid equilibrium. The liquid and vapor phases were described using the Peng-Robinson equation of state with classical mixing rule. Further, a correlation was developed for the calculation of the molar volumes difference between the liquid and the solid phases. The phase equilibrium predictions were in good agreement with the measured phase transitions data, indicating that the set of models employed is adequate to describe the phase equilibrium behavior of mixtures containing paraffins and CO2 at low and high pressures.