Phase equilibria of 3-methylstyrene, 4-methylstyrene, alpha-methylstyrene and a methylstyrene mixture in supercritical CO2

• Phase behaviour experimental data of methylstyrene isomers in CO2.
• Increase in temperature leads to increase in phase transition pressure.
• Shielding degree of the functional group slightly affects the phase transition pressures.
• Increase in molecular mass leads to increase in transition pressure.
• Accurate representation of binary phase equilibrium data with Peng-Robinson EoS.

Phase equilibria of 3-methylstyrene, 4-methylstyrene, alpha-methylstyrene and a methylstyrene mixture (mainly 3-methylstyrene (60% mol) and 4-methylstyrene (40% mol)) in supercritical CO2 were measured using high-pressure variable-volume view cells based on the static synthetic method. The systems were investigated between 308 and 353 K, with mass fractions of solute ranging continuously from 0.0275 to 0.65 and pressures up to 15 MPa. The experimental data shows a linear relationship between the phase transition pressure and the system temperature at constant composition. When the solubilities are compared, the methylstyrene isomers show little yet significant differences between them with the methylstyrene mixture being the most soluble. As the temperature increases, a decrease in the difference between the phase transition pressures of the methylstyrene structural isomers were observed. Lastly, the experimental data were correlated with the Peng-Robinson cubic equation of state using one temperature-independent binary interaction parameter and satisfactory results were obtained in both low and high solute concentration regions.

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