Equilibrium Solubilities of Diisooctyl Sebacate in Supercritical Carbon Dioxide

Abstract

The extraction of base oil from waste lubricating oil is becoming the preferred way of handling used oil to protect the environment and conserve petroleum resources. Supercritical carbon dioxide extraction has become a potential technology for the regeneration of waste lubricant oil because carbon dioxide has high dissolving power, is nontoxic, nonflammable, and inexpensive. Since the equilibrium solubility data are important for supercritical extraction processes, in this study the equilibrium solubilities for one of the synthetic ester lubricant oils, diisooctyl sebacate [bis (2-ethylhexyl) sebacate], in supercritical carbon dioxide (sc-CO 2 ) were obtained at 313.2 K, 328.2 K, 343.2 K, 358.2 K and in a pressure range from 7.24 MPa up to 15.96 MPa. Oil solubility increased with pressure but decreased with temperature, providing sc-CO 2 with the highest oil solubility (82.1959 g/L) at 313.2 K and 13.96 MPa, which showed that the solubility is strongly dependent on the density of CO 2 . The experimental solubility results were correlated with three density-based models: Chrastil model, del Valle and Aguilera model, and the Adachi and Lu model. While all of the three models correlated the experimental data very well, the nonlinear equation of Adachi and Lu model showed the best fit.