Study On Improvement Of Supercritical Carbon Dioxide Extraction Of Pyrethrins By Using Ultrasound

Pyrethrins, extracted from pyrethrum, are of rich profit for merchants due to their ecologically acceptable insecticide properties and almost total nontoxicity with respect to man and animals. In present, there are two main process methods to get pyrethrins. One is organic solvent extraction; the other is supercritical carbon dioxide extraction. It is well known that ultrasound can improve the mass transfer in normal fluid. So in the paper the ultrasound was leaded into the supercritical carbon dioxide, on the base of traditional methods, to investigate the influence of ultrasound on the extraction of pyrethrins.With the comprehensive review of history and the state of the art of supercritical fluid, especially supercritical carbon dioxide extraction, this paper presented the summary on the advantages and defects of the application of supercritical carbon dioxide to valuable components of plants.An experimental apparatus with ultrasonic transducer was selected for supercritical fluid extraction. Through studying the influence of ultrasound on pyrethrins (thermolabile compounds) extracted using supercritical carbon dioxide, the experimental results indicated that the ultrasound could not result in decomposition of pyrethrins.The influences of pressure, temperature, flow rate of CO2, ultrasound and co-solvent (water) on the extraction concentration of pyrethrins were investigated by using orthogonal experiments. The experimental results obtained showed that the ultrasound could greatly improve the extraction efficiency, while the co-solvent improved the extraction efficiency much less comparatively. In the experimental range pyrethrins could be extracted efficaciously after soaking pyrethrum in co-solvent (0.5mL/g flower) with application of ultrasound (20kHz, 200W) under the following extraction conditions: extraction pressure: 20MPa; extraction temperature: 40C; flow rate of CO2: 2L.min-1. The effectiveness of factors on extraction efficiencywas in this order: extraction pressure > ultrasound > extraction temperature > co-solvent > flow rate of CO2.The influence of ultrasound on mass transfer was studied. The results indicated that the ultrasound could improve the inner and outer diffusion of pyrethrins extraction. Under the same extraction conditions, it was observed that the yields of pyrethrins are larger with ultrasonic irradiation than without ultrasonic irradiation. The increase in the yield of pyrethrins was approximately 16%. Furthermore, reducing pressure or decreasing flow rate of CO2 by using ultrasound in supercritical carbon dioxide could also obtain the same extraction efficiency. The shrinking core model was applied to describe the influences of some factors on mass transfer in the paper. A qualitative explanation to mechanism was presented preliminarily that the ultrasound is how to influence the velocity of mass transfer for the valuable components in plants in supercritical carbon dioxide.The data on phase equilibrium of pyrethrins in supercritical carbon dioxide in the presence or absence of ultrasound was measured. The results showed that ultrasound could overcome the plants matrix effects on pyrethrins, and make bound pyrethrins away from matrix more easily. Therefore, ultrasound could increase equilibrium solubility. The Chrastil model and modified Chrastil model were used to correlate the equilibrium data. The better agreement with experimental data was obtained by the modified Chrastil model than by Chrastil model. The influence of ultrasound on the phase equilibrium of pyrethrins was discussed preliminarily.