LAUSR

The demand for alkyl lactates (methyl, ethyl, propyl, and butyl) has risen significantly due to their unique properties and wide industrial applications. Accurate vapor–liquid equilibrium data are vital for the design and optimization of separation techniques involving these compounds, particularly in systems using supercritical carbon dioxide (SC-CO2) as a solvent. In this study, the phase transition of binary systems of CO2 + lactate (methyl, ethyl, propyl, butyl) was investigated at various temperatures (313.2, 333.2, 353.2, 373.2, and 393.2 K) and pressures up to 18.48 MPa, using elevated-pressure phase equilibrium equipment based on the synthetic method. Notably, comprehensive isothermal phase behavior data for these binary systems across a wide mole fraction range and high-pressure conditions are scarce. The pressure–temperature plots revealed that the critical mixture boundary connects the critical points of SC-CO2 and the respective alkyl lactates. For all four systems, enhanced miscibility was observed as the lactate mole fraction increased under isothermal conditions, accompanied by a decrease in pressure. The phase transition observed aligns with Type-I, Van Konynenburg and Scott. Enhanced miscibility was observed across all systems as the mole fraction of lactate increased under isothermal conditions with a corresponding decrease in pressure. The experimental bubble point data were correlated using the Peng et al. equation of state (PR EoS) combined with van der Waals one-fluid mixing rules. The binary interaction parameters (k ij and η ij ) were optimized as follows: methyl lactate (k ij = −0.030, η ij = −0.090), ethyl lactate (k ij = 0.000, η ij = −0.085), propyl lactate (k ij = 0.035, η ij = −0.060), and butyl lactate (k ij = 0.040, η ij = −0.050). The model exhibited good agreement with experimental results, with root-mean-square deviation (RMSD) values of 3.92, 4.08, 6.46, and 6.79% for the CO2 + methyl lactate, ethyl lactate, propyl lactate, and butyl lactate systems, respectively.