Study On Enhancing Continuous Counter-current Extraction

Continuous counter-current extraction is widely used for the extraction of secondary metabolites from plants. The advantages over conventional batch extraction method include a decrease in solvent consumption and a shorter handing time. But the longer appearance, more occupational area and higher equipment cost are needed because of the continuous operation and necessary extraction time. This limits the application of continuous counter-current extraction in the pharmaceutical industry, the perfume sector, and the food and human nutrition field.The objective of this work was studying the combined of continuous counter-current extraction with other enhancement methods so as to reducing extraction time and equipment length as well as its cost further.A laboratory scale continuous counter-current extraction system was designed and constructed, and the system consists of vacuum-microwave radiation oven, extruder and continuous counter-current extractor. Vacuum degree and microwave power of vacuum- microwave oven are adjustable. Extrusion equipment is single screw with the volume compressing ratio is of 2:1. The spiral plate of continuous counter-current extractor is with many small holes so that the solvent can be in and out. Further, the liquid storage tank has jacket and the water circulation tank ensures the solvent in desirable temperature.The enhancement of continuous counter-current extraction by four pretreatment methods: wetting, vacuum-microwave radiation, extrusion and combined vacuum microwave radiation with extrusion was studied using Ganoderma Lucidum and bamboo leaves as tested materials.The values of extraction rate of Ganoderma Lucidum polysaccharide and Bamboo Leaf Flavonoids, the viscosity and turbidity at different stages were tested and compared. The experiment results showed that the combined vacuum-microwave radiation with extrusion pretreatment had resulted in the highest extraction rate, and following were vacuum microwave radiation, extrusion and wetting. On the other hand, the scanning electron microscopy maps also showed the extent of wall of cells breaking was greater for the combined vacuum-microwave radiation with extrusion pretreatment, the following were the same as above.According to the kinetic model which was established on the Fick first law equation, the extraction kinetics models for Bamboo Leaf Flavonoids, which has pretreated by wetting and combination of vacuum-microwave radiation with extrusion, for continuous counter-current extraction were established respectively. The relationship between concentration of Bamboo Leaf Flavonoids and time was studied. The results showed that ln were linear with t.The result of this work shows that combined vacuum-microwave radiation with extrusion pretreatments is one of the best methods for enhancing continuous counter-current extraction. The combination of this pretreatment method with continuous counter-current extraction will bring the more efficient and rapid extraction technology and equipment.