Green Process for Purification of Menthol from Peppermint Essential Oil based on In-Situ Formation of Deep Eutectic Solvents

This paper aims to achieve efficient selective separation and green purification of menthol using green deep eutectic solvents (DESs). Taking peppermint essential oil as the research object, a green process based on in-situ formation of DESs is proposed to achieve efficient purification of menthol. Taking menthol in peppermint essential oil as a hydrogen bond donor (HBD), eight quaternary ammonium salts and quaternary phosphonium salts were screened as hydrogen bond acceptors (HBA), and tetrabutylammonium chloride (TBAC) was determined as the optimal HBA component. The hydrogen bonding between menthol hydroxyl and TBAC anion was confirmed by FT-IR and 1 H NMR characterization. After optimizing the conditions such as HBA type, n-hexane dosage, molar ratio, and vortex number, under the optimal conditions, the extraction recovery of peppermint essential oil reached 88.62% ± 0.82%, and the menthol purity was 91.16% ± 0.93%. Compared with the original peppermint essential oil, the menthol purity was significantly improved. The recycling experiment showed that TBAC has good reusability, a simple and green purification process, and good application prospects.