Modeling fluid phase equilibria of carbon dioxide-methanol binary system

Accurate fluid phase equilibria modeling of carbon dioxide-methanol binary system is essential for numerous industrial applications. Prior modeling studies were limited in scope in terms of temperature and pressure ranges. In this study, the phase equilibria behavior of the binary system is modeled with cubic equations-of-state (EoS) including Peng–Robinson (PR) and Soave–Redlich–Kwong with various mixing rules, Predictive Soave–Redlich–Kwong, Cubic Plus Association, and Perturbed-Chain Statistical Associating Fluid Theory. Among them, the classical PR EoS and its variants yield the overall best results in representing the phase behavior at temperature above 330 K. However, PR incorrectly predicts two liquid phases when the CO2 mole fraction exceeds \~ 0.4 at temperature lower than 330 K. Raoult's law with the classical nonrandom two-liquid excess Gibbs energy model is recommended for the low temperature conditions.