Extractive separation of 1,8-cineole and γ-terpinene with lactic acid-based deep eutectic solvents

1,8-Cineole has anti-inflammatory, antibacterial and physiological properties and its high purity is important to application. However, 1,8-cineole usually mixes with monoterpene hydrocarbons in plant essential oils and they are difficult to separate via distillation due to their close boiling points. In this study, a series of lactic acid (LA) based deep eutectic solvents (LaDESs) were formed and used in liquid–liquid separation of 1,8-cineole and monoterpene hydrocarbons. LaDES formed by LA and tyrosine (Tyr) showed 24.8 selectivity of 1,8-cineole to γ-terpinene at 25 ℃. Synergists or auxiliary extractant such as tert -butanol can improve the distribution coefficient but reduce the selectivity. Some effect factors to the extraction were investigated and 99% purity of 1,8-cineole was achieved in the final product. The extraction thermodynamic parameters and kinetic process were studied. The re-extraction and the LaDES recovery were carried out satisfactorily. It further proved that the separation of 1,8-cineole from α-pinene, α-terpinene and ρ-cymene could be performed well with the LaDES respectively. Liquid-liquid extraction separation of 1,8-cineole and γ-terpinene has the advantages of low energy consumption, high selectivity and safety. It would provide an alternative strategy for separating 1,8-cineole and monoterpene hydrocarbons whose boiling points are close.