Measurements of the High-Pressure Phase Equilibria for the System Carbon Dioxide – Limonene by Means of a Double-Chamber Recirculation Apparatus

Limonene is the major monoterpene compound of lemon essential oil, which is a valuable raw material for the food, cosmetics and perfume industry. This essential oil is mainly composed of monoterpenes (more than 90% of the oil), monoterpene oxygenated derivatives and sesquiterpenes. The removal of monoterpenes from lemon essential oil (deterpenation process) is a common industrial practice which allows increasing the concentration of the oxygenated compounds, which are the most valuable, and the stability of the oil. This process can be successfully performed by means of supercritical carbon dioxide. Information on high-pressure phase equilibria related to carbon dioxide and the main components of the essential oil is relevant for the supercritical deterpenation process design. In this work, measurements of the phase equilibria for the system carbon dioxide – limonene were performed at 70°C and in the pressure range 8.54 – 13.34 MPa. These data are of particular interest because these operating conditions are relevant for the supercritical deterpenation process [1] and literature data at 70°C are scarce. The experimental measurements were performed by means of a two-chamber apparatus. In the first chamber (“equilibrium cell”) the liquid phase coexists with the gas phase, whereas the second chamber (“gas cell”) contains only the gas phase, which is continuously recirculated through the chambers in order to reduce time for equilibration. Before sampling of the phases, the cells are separated by closing valves in order to avoid any disturbances of the equilibrium when the pressure is reduced during the withdrawal of the gas phase. In the experimental pressure range, the solubility of limonene in the gas phase increases from 12.3 to 86.4 g/kg, whereas that of carbon dioxide in the liquid phase increases from 0.34 to 1.17 g/g. The experimental results were compared to the data measured by means of the same procedure at 50°C [2]. Increasing temperature from 50 to 70°C, limonene solubility in the gas phase decreases moderately, whereas the solubility of carbon dioxide in the liquid phase decreases markedly.