Density and Phase Behavior of the CO₂ + Methylbenzene System in Wide Ranges of Temperatures and Pressures

Knowledge of the thermophysical properties of CO₂-hydrocarbon mixtures over extended ranges of temperature and pressure is crucial in the design and operation of many carbon capture and utilization processes. In this paper, we report phase behavior, saturated-phase densities, and compressed-liquid densities of CO₂ + methylbenzene at temperatures between 283 K and 473 K and at pressures up to 65 MPa over the full composition range. The saturated-phase densities were correlated by a recently developed empirical equation with an absolute average relative deviation (Δ_AARD) of ∼0.5%. The compressed-fluid densities were also correlated using an empirical equation with an Δ_AARD value of 0.3%. The new data have been compared with the predictions of two equations of state: the predictive Peng-Robinson (PPR-78) equation of state and the SAFT-γMie equation of state. In both of these models, binary parameters are estimated using functional group contributions. Both models provided satisfactory representation of the vapor-liquid equilibrium and saturated-phase-density data, but the accuracy decreased in the prediction of the compressed-liquid densities where the Δ_AARD was ∼2%. The isothermal compressibility and isobaric expansivity are also reported here and were predicted better with SAFT-γMie than with PPR-78. Overall, the comparisons showed that SAFT-γMie performs somewhat better than PPR-78, but the results suggest that further refinement of the SAFT-γMie parameter table are required.