Study On The Enhancing Mass-transfer Mechanism Of Microwave-assisted Extraction Of Chinese Herbal Medicine

Extraction of valid components plays an important role in the modernization of Chinese herb industry. Traditional extractions methods have the disadvantages of great loss, long period and low yield, etc. microwave-assisted extraction is the new method of combining microwave technology and traditional extraction methods. This paper has carried out a study on the enhancing mass-transfer mechanism of microwave-assisted extraction of Chinese herbal medicine by experimental researching and mathematical modelling. This paper reviewed the latest development of microwave-assisted extraction in recent years, which could be classified into three aspects such as the experimental methods, mathematical models and the mass-transfer mechanism of extraction. For some Chinese herbs in common use such as Glycyrrhizic, Paeoniae Rubra, Hawthorne, Rhizoma Coptidis, Salviae Miltiorrhizae, Ganoderma and Flos Sophaoae, etc, orthogonal experiments, contrast experiments and extraction dynamics experiments was finished by using different extraction technology including traditional extraction (such as Reflux extraction and Soxhlet extraction) and the microwave-assisted extraction (such as microwave extraction and microwave pretreatment extraction). For the microwave pretreatment-reflux extraction technology, the extraction dynamics equation was put forward and applied to simulating Hawthorne Rutin extraction process. In the end, this paper quantitily analyzed the effect of microwave power and irradiation time on some parameters of extraction dynamics equation, and investigated the enhancing mass-transfer mechanism of microwave-assisted extraction of Chinese herbal medicine. The orthogonal experimental results show that, the experiment factor and its level have closely related to result. For microwave-assisted Soxhlet extraction, under the experimental condition in this paper, the major influencing factor of Glycyrrhizic, Rhizoma Coptidis and Paeoniae Rubra is the particle size, and that of Hawthorne and Salviae Miltiorrhizae is the extraction time. The contrast experimental results show that microwave-assisted extraction has the advantages of shorter extraction time, lower extraction temperature, higher yield, etc. Dynamics experimental results show that, for different extraction methods and experiment parameter level, the dynamic characteristic of objective component extraction process is different. The extraction dynamics equation of microwave-assisted pretreatment reflux extraction has been developed, which indicates that the concentration of solution is the function of extraction time, liquid/solid ratio, particle size and so on. By experimental study and mathematical model calculation, we can draw a conclusion that the influence mechanism of microwave on the extraction is different between low power area and high power area. As for the extraction of Hawthorne Rutin, under the experimental condition in this paper, low power (65W) and the high power (455W) all can achieve the same higher extraction yields; the influence of lower microwave power on extraction chiefly behaves thermal dynamics effects and non thermal effects, with only a small amount vaporization; the influence of higher microwave power on extraction chiefly behaves thermal dynamics effects, non thermal effects and the effect with the result of strong vaporization. Microwave can enhance the mass-transfer mechanism of Chinese herb extraction, which is a kind of high quality and efficiency extraction method.