Mechanism of Extractive Separation of Light Cycle Oil Using a Deep Eutectic Solvent Composed of Tetrabutylphosphonium Bromide and Levulinic Acid

Abstract

To achieve maximum usage and economically upgrade light cycle oil, it is necessary to separate light cycle oil components into nonaromatic and aromatic fractions. A deep eutectic solvent composed of tetrabutylphosphonium bromide and levulinic acid exhibited excellent extraction performance in separating light cycle oil components. In this work, the mechanisms of deep eutectic solvent formation and light cycle oil separation are investigated using characterization analysis and molecular dynamics simulations. Both Fourier-transform infrared spectra and molecular dynamics simulation results indicate that the main driving force for deep eutectic solvent formation is hydrogen-bonding interactions between the Br– anion of tetrabutylphosphonium bromide and the carboxyl group (−COOH) of levulinic acid. On the other hand, while the TBP+ cation of tetrabutylphosphonium bromide and the carbonyl group (−C═O) of levulinic acid are less likely to contribute to deep eutectic solvent formation, they are more likely to interact with the aromatic ring of tetralin via CH−π and π–π interactions, respectively. The results suggest that each functional group of tetrabutylphosphonium bromide and levulinic acid plays an essential role either in deep eutectic solvent formation or in aromatic compound extraction, which provides insights into the mechanism of extractive separation of light cycle oil components using deep eutectic solvents.