Owing to their green attributes, deep eutectic solvents (DESs) are highly promising for sustainable separation applications, but significant challenges must be overcome to ensure their practical implementation. Interactions between DES constituents result in nonvolatility, thereby providing unique characteristics in terms of viscosity, density, freezing point and thermal expansivity. However, the characteristics of green solvents restrict their application. One of the main challenges in green chemistry is finding an appropriate match between the physical approach and the solvent system. In this study, the microwave effect and cosolvent water in DESs were fully exploited during relay extraction to sequentially obtain multiple substances of different polarities and physical states. On the basis of the favourable extraction performance of DESs and the difference in density between DESs and seed oil, seed oil was first obtained through centrifugation. With the use of cosolvent water as a favourable microwave absorber, the volatilization of water combined with microwave irradiation efficiently yielded perilla essential oil and water-soluble rosmarinic acid. The yields of seed oil and rosmarinic acid at microwave treatment stages 1 and 2, respectively, were investigated. Choline chloride–oxalic acid was the preferred extraction solvent at stage 1,and the DES was chosen for stage 2 with a 40% water content. The effects of the ratio of liquid to material, microwave radiation time and microwave treatment power were continuously optimized at the two stages. Rosmarinic acid yielded 10.85 ± 0.12 mg/g, essential oil yielded 0.4 ± 0.10 mg/kg, and seed oil yielded 0.2 ± 0.13 mg/g under optional process conditions. The compositions of the obtained essential and seed oils were subsequently analysed. The developed method has satisfactory application prospects for separating multipolar components, especially in aromatic and oil plants.
Cao et al. (Wed,) studied this question.