Supercritical Fluid Extraction Of Rhizoma Atractylodis Macrocephalae: Experiments And Modeling

It is well-known that supercritical CO2 extraction is rapid and efficient separation technique since it can be operated at mild temperature and possesses advantages of non-pollution, covenient operation, and high extraction yield and so on. Therefore, supercritical fluid extraction technology has received a great deal of attention to extracting thermally labile compounds from natural matters. In this thesis, supercritical CO2 extraction of volatile componets was carried out on natural Chinese herb Rhizoma Atractylodis Macrocephalae. The influnces of various parameters on the extraction yield were thus investigated and the extraction process was correlated by means of three different types of mathematical models.Initially, an orthogonal array design was employed for preliminarily reseaching the influnces of four parameters (extraction pressure, temperature, time and particle size) on supercritical CO2 extraction of Rhizoma Atractylodis Macrocephalae. The result analysis reflects that they affect the extraction yield in the order of extraction time>pressure> particle size>temperature. The extraction yield was observed to almost linearly increase with time in 30-90 mintues, and in the meantime increase considerably with pressure (15-35Mpa). But the particle size and temperature were observed to not obviously influnce the extraction yield. Next, the effects of extraction pressure, temperature and particle size on the extraction process were further investigated. Generally, the extraction yield was found to promote with time. It increased very rapidly in the begining and then slowed down, finally approached a constant. Experimental results futher confirmed that the yield increased as pressure increased. The extraction rate decreased obviously after 120min extraction in the pressure range of 25-35 Mpa, indicating that most volatile components were extracted out of Rhizoma Atractylodis Macrocephala. The extraction yield significantly increased as temperature increased from 40 to 60oC, especially from 40 to 50oC. The constant yield obtained at 60 oC was the highest and it is 6.072%. The effect of particle size was compared and it was found that the highest yield was obtained as the particles were 0.23 mm in diameter.The experimental data were correlated with using five models: Naik model, Barton model, Crank model, Martíneze model and Sovovámodel. It was found that Naik model, two-parameter Barton model and Crank model fitted the experimental data very well, giving an average abosulte relative error less than 10%. Among these models, Crank model performed the best with an overall average abosulte relative error of 4.07%. Moreover, the efficient diffusion coefficient of the extracted matter in supercritical CO2 was obtained and it ranged in 8.786-78.84×10-12 m2/min. Two-parameter Martínez model performed rather well with an average abosulte relative error within 4.21-11.30 %. The Sovovámodel involved rather complicated calculations and led to relatively high estimation error but the mass transfer coefficient in solid or fluid can be obtained. Furthermore, the modeled results suggest that solute diffusion in soild matrices and solute mass transfer in fluid synergetically affected the supercritical CO2 extraction process of Rhizoma Atractylodis Macrocephalae.