Experimental high-pressure phase equilibria of carbon dioxide/n-alkanes mixtures and model-parameters for solid-phase obtained from DSC thermograms

Abstract

We provide high-pressure experimental phase equilibrium data for systems containing mixtures formed by CO2 and mixtures of n-alkanes (n-C10H22/n-C20H42, n-C10H22/n-C24H50, n-C10H22/n-C20H42/n-C24H50) with CO2 weight fractions of 55%, 65% and 75%, temperature ranging from 273 K to 363 K and pressures up to 55 MPa. The measured equilibrium data include vapor-liquid (VL), solid-liquid (SL), and solid-liquid-vapor (SVL) phase transitions. Additionally, calorimetric (DSC) measurements were carried out at atmospheric pressure for mixtures of n-C10H22 (solvent), n-C16H34, n-C20H42, and n-C24H50, with the temperature range from 253 K to 333 K. To describe the phase-equilibrium diagrams, the solid phases were modeling using the multiple-solid solutions approach, which employs the modified UNIQUAC equation to calculate the activity coefficients. The UNIQUAC-energy interaction parameter λij and the Poynting correction factor were used to take into account the n-alkane/n-alkane interactions and pressure effect in the solid-liquid equilibria. We used the Peng-Robinson equation of state to describe the liquid and vapor phases. The phase equilibrium predictive calculations were in good agreement with the measured phase-transition data considering the experimental uncertainty.