In this work, bubble point pressures of the system of methanol + methyl propionate were measured for several isopleths within temperature and pressure ranges of 382-444 K and 0.437-2.285 MPa, respectively. The vapor pressures of pure methanol and methyl propionate were also measured. The two-suffix Margules equation was used to represent the nonidealities of the liquid phase and the virial equation of state was used to take into account the nonidealities of the vapor phase. The temperature-dependent parameter of the two-suffix Margules equation was determined using Barker's method. The results show that the model can successfully estimate the bubble points of this system with average errors less than 0.69%.

From experimental studies in literature, it has been proven that the phase behavior of supercritical carbon dioxide with pure or mixed solvents or solutes may not be simple, and in many cases, a second liquid phase appears. In this work, we considered the phase behavior of supercritical carbon dioxide with two essential oils, namely, eucalyptus oil and rosemary oil. We investigated the phase behavior of each system of CO₂ + eucalyptus oil and CO₂ + rosemary oil separately, and we observed that both systems form a second liquid phase. We measured the bubble point pressures of both systems for five different concentrations of CO₂, and also the three phase line of liquid-liquid-vapor of these systems. Based on the observed upper solution critical points, we concluded that the phase behavior of these two systems is Type-III based on the Scott and Van Konynenburg phase classification.