Separation of essential oil from fresh leaves of Phellodendron amurense rupr. By solvent-free microwave-assisted distillation with the addition of lithium salts

Abstract

The essential oil was separated from the fresh leaves of Phellodendron amurense Rupr. by solvent-free microwave-assisted distillation in a rotating state with n-hexane extraction and LiCl addition, which ingeniously designed lithium salt addition, rotation unit, and n-hexane extraction effectively improved the yield and separation rate of essential oils. The factors that may affect essential oils yield were screened and optimized by single factor optimization, response surface methodology, and kinetic model to obtain the optimal conditions for the separation of essential oils by this method, which were LiCl content of 8%FW, microwave irradiation power 600 W and microwave irradiation time 40 min. And the yield of essential oils is 2.39 ± 0.12 mg/g in the optimum conditions by this method, which is highly consistent with the predictions from the response surface method (2.39 mg/g) and the first-order kinetic model (2.42 ± 0.04 mg/g). This method effectively ensures the uniform heating of the plant material and the rapid overflow of the essential oil by employing the rotating unit and the addition of LiCl, which effectively avoids the loss of the heat-sensitive components in the essential oil. Moreover, the solvent-free distillation of this method highly improves the heating rate, and the added LiCl can also be effectively recovered and reused, which effectively reduces the economic cost, and environmental stress and will result in a cleaner product. And an accurate quantitative analysis method of essential oils was established by n-hexane extraction-ultraviolet spectroscopy, which not only effectively avoided the loss of water-soluble components but also provided a new strategy for quantitative analysis of essential oils. In addition, the results of the kinetic model indicated that the separation rate constant of essential oils in this method was 1.34 times that of microwave-assisted hydrodistillation and 5.05 times that of conventional hydrodistillation. Therefore, this method is an efficient, green, and clean essential oil preparation method, which is very promising to replace existing methods in the future.