Effect of imidazolium ionic liquids as microwave absorption media for the intensification of microwave-assisted extraction of Citrus sinensis peel essential oils

Ionic liquid-based microwave-assisted extraction (MAE-IL) has been applied for the separation of essential oils (EOs) from Citrus sinensis var. Valencia peels. Two imidazolium ionic liquids, 1-ethyl-3-methyl imidazolium acetate ([C2mim]OAc) and 1-butyl-3-methyl imidazolium chloride ([C4mim]Cl), were investigated for extraction efficiency, thermal behavior of the process, and chemical composition of the EOs obtained. During extractions, two different concentrations of ionic liquids (ILs) were studied (5% or 10 %), and the proposed MAE-IL was evaluated in comparison with usual microwave-assisted extraction (MAE) using water as solvent. Results indicated that both concentrations of ILs influenced EO extraction, thermal behavior, and chemical composition. However, [C2mim]OAc was more efficient, increasing extraction velocity by 10 times, enhancing extraction efficiency of EOs (39 %), and increasing the presence of oxyterpene compounds in the EOs. However, the great ability of ILs to interact with microwaves had an impact on the thermal history of the sample, reaching almost 110 °C, promoting the presence of compounds related to thermal effect.