Phase behavior of binary mixtures of CO2 with methyl, ethyl, and butyl (Phenylacetates) at elevated pressures

Abstract

The increasing demand for alkyl phenylacetates, owing to their distinctive characteristics and diverse industrial applications, highlights the necessity of accurate vapor–liquid equilibrium (VLE) data for efficient process design. This is especially crucial in separation processes employing supercritical carbon dioxide (CO₂) as a green solvent. This work deals with the phase transition study of binary mixtures comprising CO₂ and methyl, ethyl, butyl phenylacetate, which was systematically examined within 313.2 K–393.2 K (in 20 K increments) and pressures reaching up to 24.62 MPa. No prior studies have reported detailed isothermal VLE data over such an extensive mole fraction range at elevated pressures for these systems, making this study a unique contribution. Analysis of pressure–temperature behavior indicated that the critical mixture curve connects the critical points of pure CO₂ and each alkyl phenylacetate, consistent with Type-I curve as defined by van Konynenburg and Scott. For all binary systems, solubility improved with increasing phenylacetate concentration, accompanied by a corresponding reduction in system pressure under constant temperature conditions. The experimental bubble point data were fitted using the Peng–Robinson equation of state (PR EoS) combined with the van der Waals one-fluid mixing rule. The interaction (binary) parameters were optimized for each system: methyl phenylacetate (k_ij = 0.028, η_ij = –0.040), ethyl phenylacetate (k_ij = 0.020, η_ij = –0.040), and butyl phenylacetate (k_ij = 0.040, η_ij = –0.045). The PR EoS model exhibited strong agreement with experimental findings, as reflected by root mean square deviation (RMSD%) ranging between 3.82 % and 5.20 % across all three binary systems and studied temperatures.