Ionic-liquid-enhanced solvent extraction mechanism: A novel concept

Solvent extraction has been widely used to obtain bitumen from oil sands. In addition, several methods have been used to enhance solvent extraction processes, including the use of ionic liquids. Although a variety of ionic liquids has been used to enhance bitumen recovery, the detailed mechanism is still unclear, while many proposed mechanisms are in fact contradictory. In this study, the solvent extraction mechanism was studied through the evaluation of the role of ionic liquids on the internal properties of heavy oil, as well as in the modification of the oil–solid and oil–water interfaces. The internal properties investigated include the C/H ratio, heavy oil viscosity, and the levels of saturates, aromatics, resins, and asphaltenes (SARA) present. Herein, using the ionic liquids results in a significant increase in the C/H ratio of the heavy oil, as well as the resins and asphaltene content, while the heavy oil viscosity decreases significantly. The ANOVA analysis and Tukey test showed that most ionic liquids-solvent extraction have significant effect on altering the heavy oil recovery, C/H ratio, viscosity and SARA content comparing to solvent alone extraction. It can, therefore, be concluded that ionic liquids are able to modify the oil–solid interface, making the sand surface increasingly hydrophilic, while a similar modification of the oil–water interface results in the decrease of the oil–water interfacial tension with increasing ionic liquid concentration. In addition, when the ionic liquid concentration increases, the zeta potential of CaCO3 in the ionic liquids decreases, whereas the zeta potential of the heavy oil in the ionic liquids increases (absolute value decrease), and then the electrostatic attraction between heavy oil and CaCO3 decreased. The AFM results showed that the ionic liquids could decrease heavy oil–solid interaction forces, and forces decreased with the ionic liquids concentration. The ionic liquids could further be recycled effectively, without significantly decreasing the oil recovery. Finally, ionic liquid adsorption isotherms were fitted employing the Langmuir, Freundlich, and Temkin models, obtaining excellent goodness-of-fit values. However, when the linear model was employed, the goodness-of-fit was poor. The ionic liquid adsorption kinetics further exhibited good fits to pseudo-first and pseudo-second order models. Herein, the increased adsorption of the ionic liquids on calcite surfaces corresponded to low oil recoveries.