Experimental and Molecular Insights into Efficient Deterpenation of Essential Oil Intensified by Extraction with Deep Eutectic Solvent

Deep eutectic solvents (DESs) have been widely utilized to intensify separations by adjusting their structures and properties, particularly in extractive deterpenation of essential oils as green alternatives to conventional organic solvents. In this work, experimental and molecular insights into efficient deterpenation intensified by a DES containing tetrabutylammonium bromide (TBAB) and levulinic acid (LEA) were investigated with citral extraction from lemon essential oil as a case study. DES formation and preferred liquid operating window were determined through solid–liquid equilibrium; an excellent extraction performance was observed at varying citral concentrations via liquid–liquid equilibria. Extraction process was simulated with a well-correlated nonrandom two-liquid model, and a 7-fold concentration of terpenoids was achieved under optimal conditions. Fourier transform infrared spectra and molecular dynamics simulations elucidated the DES formation and extraction mechanisms. Hydrogen-bonding interactions primarily mediated by −COOH group of LEA and Br– anion of TBAB resulted in lower freezing points of DES, thereby enhancing extraction performance. The results provide valuable insights into the practical applications of DESs in separating structurally similar natural products.