1. Mass Transfer Modeling on Supercritical Fluid CO2 Extraction of Essential Oil from Matou Pummelo Peel 王昭凱 1 ﹑王彥茹 2 ﹑陳雅琪 1 ﹑劉柏輝 1 1.Department of Applied Chemistry & Material Science, Fooyin University, 151 Chin-Hsueh Rd, Ta-Liao Hsiang, Kaohsiung City, 831 Taiwan, R.O.C. 2. Department of Computer Science, National Chiao Tung University,1001 University Road, Hsinchu, Taiwan 300, ROC Abstract Supercritical fluid CO 2 (SC-CO 2 ) extraction of essential Oil from Matou Pummelo peel is an alternative method to organic solvent extraction and mechanical leaching. For industrial application, an effective way to perform optimization is needed to resort to models that are capable to describe and simulate the SC-CO 2 process. In this work SC- CO 2 extraction of essential Oil from Matou Pummelo peel in a packed bed was investigated at operating conditions of temperature 40 o C, 45 o C, 50 o C and 60 o C and pressures ranging from 10.5 MPa, 15.5 MPa, 20.5 MPa and 30.5 MPa. The development of mass transfer models requires knowledge of three properties: the diffusion coefficient of the solute, the viscosity and density of SC- CO 2. Mathematical model with respect to the dimensionless number of Sherwood (Sh), Schmidt (Sc), Prandtl (Pr) and Reynolds (Re) was developed. It was found that the model developed was found to be in good agreement with the experimental data within the system studied. The correlation equation of SC-CO 2 extraction behavior can be expressed: Sh in the range 25<Re<200. Keywords: supercritical fluid extraction, Matou Pummelo, Sherwood correlation 3. Results and Discussion 1.Introduction 3.Experimental Recently, Sc-CO 2 combined with chelating agent has become an attractive alternative technology to be a promising process for the treatment of metal-contaminated waste materials [1-4]. Most of the research addresses the use of polar organic modifiers such as chelating agents or co-solvents to enhance extraction efficiency as well as to improve the solubility of highly polar contaminants [5]. Due to both economic and environmental concern, it is of industrial interest to develop a fractional recovery method composed of extraction and separation of metal ions from various matrices within one step [6-7]. In this paper we explored supercritical fluid fractionation process of binary system of metal ions in solid matrix by dynamics method. The cadmium and zinc ions with beta- diketone as the chelating agent were the investigated system. The aim of this paper was also to elucidate a simple model of operation conditions to control separation efficiency by supercritical fractionation process through statistical experimental method. Based dimensionless analysis method, the effects of chelating agents, pressure, flow rate, temperature and pressure on the fractionation transport behavior has been studied. Extraction of essential Oil from a packed bed of Matou Pummelo peel was conducted at supercritical conditions of a variation of temperatures and pressures of 40 o C, 45 o C, 50 o C and 60 o C and pressures ranging from 10.5 MPa, 15.5 MPa, 20.5 MPa and 30.5 MPa, respectively. The experimental results showed that the best correlation equation of the mass transfer relating to diffusivity and fluids conditions generated by the empirical modeling process was Sh in the range 25<Re<200. 5.Conclusion 1.Cassel, E., Frizzo, C. D., Vanderlinde, R., Atti-Serafini, L., Lorenzo, D. and Dellacassa, E., Extraction of baccharis oil by supercritical CO2. Industrial & Engineering Chemistry Research. 39, 2000, 4803-4805. 2.Cheng, Y. S. and Chou, C. T., Composition of peel essential oils from eight citrus species. Journal of the Chinese Chemical Society. 31, 1984, 93-96. 3.Cheng, K. W., Tang, M., and Chen Y. P., Solubilities of Benzoin, Propyl 4-Hydroxybenzoate and mandelic acid in supercritical carbon dioxide, Fluid Phase Equilibria, 201, 2002, 79-96. 4.Taniguchi, M., Tsuji, T., Shibata, M. and Kobayashi, T., Extraction of oils from wheat germ with supercritical carbon dioxide. Agricultural and Biological Chemistry. 49, 1985, 2367-2372. 5.Wang, M. L., Choong, Y. M. and Lee, M. H., Effects of extraction method on the determination of essential oils in citrus peels. Journal of the Chinese Agricultural Chemical Society. 32, 1994, 141-148. 6.Lim G.B., Holder G.D., and Shah Y.T., Solid-Fluid Mass Transfer in a Packed Bed under Supercritical Conditions. Supercritical Fluid Science and Technology (1989), 379-395. 7.Debenedetti, P.G.; Reid, R.C., (AIChE) 32, pp 2034, 1986. 8.Karabelas, A.J., Wegner, T.H., Hahratty, T.J., Chem.Eng.Sci. 26, pp 1581, 1971. 9.Damronglerd, S., Couderc, J.P., and Angelino, H., Shorter Communication- Mass Transfer in Particulate Fluidasation. Transactions of the Institution of Chemical Engineers Vol 53, pp 175-180, 1975. 10.Eggers, R., and Sievers, U., Current State of Extraction of Natural Materials with Supercritical Fluids and Developmental Trends. Supercritical Fluid Science and Technology. pp.478-498, 1989. Reference Fig.4 Effect of Prandtl numbers on oil extraction by SC-CO 2 Fig.5 The experimental correlation of dimensionless equation The plant samples of Matou pummelo peel were cut into pieces and dried under room temperature. Before extraction they were broken the cell wall and ground to the desired mesh size. Supercritical carbon dioxide extraction experiments were carried out using a supercritical fluid extractor (designed by ourselves and automatically précised control of temperature and pressure and flow rates) with the extractor vessel volume 500 ml as shown in Figure 1. The flow rate of CO 2, extraction temperature and pressure were adjusted by using window-based software, and the extraction time was measured. CO 2 was supplied from a gas cylinder. Before the CO 2 passed into the extraction vessel, it was pressurized to the desired pressure and heated to the specified temperature by the means of a pump to reach the supercritical state. The powdered sample (10 g) was placed into the extractor vessel with ethanol acted as the modifier. SC-CO 2 extraction of essential Oil from Matou Pummelo peel in a packed bed was investigated at operating conditions of temperature 40 o C, 45 o C, 50 o C and 60 o C and pressures ranging from 10.5 MPa, 15.5 MPa, 20.5 MPa and 30.5 MPa under various flow rate of CO 2 1.95, 4.30 and 6.58 10 3 m/s, respectively. An initial 20 min static extraction was carried out followed by a 30 min dynamic extraction through a 15 cm long, 25mm i.d. stainless steel restrictor (Coopers Needle Works, Birmingham, UK). All obtained extracts were collected with ethanol modifier. In order to remove ethanol, the extracts were vacuum evaporated using a rotary evaporator at 50°C. The extract then placed in the oven at 50ºC for 30 minutes before transferred into a desiccator for final constant weight. Then a gravimetric measurement was used to obtain the amount of total extract weight. 2.Theorectical Consideration The empirical constant c in eqn (1) can be obtained from the relationship between the Sh and Schmidt number, Sc, is plotted in Figure 3 at a constant Reynolds numbers. It is found that the value of c is about 0.375 by a coefficient of correlation more than 0.80. The data of Pr obtained from the experiments, were plotted in Figure 4 to observe a trend of the Prandtl number (Pr) versus Sherwood number, Sh, under various flow rates. It is indicated that a linear relationship shown in Figure 5 with the slope of 0.495. Fig.2 Effect of Reynolds numbers on oil extraction by SC-CO 2 Fig.3 Effect of Schmidt numbers on oil extraction by SC-CO 2 In order to study effect of Reynolds numbers on extraction of Matou Pummelo peel oil through the supercritical carbon dioxide packed bed system. The effect of Reynolds numbers on Sh number was shown in Figure 2 under various flow rate of CO 2 1.95, 4.30 and 6.58 x10 3 m/s, respectively. The experimental result indicates that the slopes of the straight lines give a value of 0.787 for the constant b in equation (2). The high mass transfer rate with Reynolds number may be due to the large density differences that occur as Matou Pummelo peel oil dissolves in the SC-CO 2. For economic point of industrial view, it is important to develop models for the separation process when the extraction operations are optimized for commercial applications. However, such predictions require the establishment of model which can predicts phase behavior, equilibrium, solubility, adsorption, desorption and others. Relationships, as well as models for equipment design should take into consideration the effect of fluid flow, mass and heat transfer and also the phase contacting mechanisms. The development of mass transfer models require an understanding of three important properties namely, the diffusion coefficient of the solute, the viscosity and the density of the supercritical fluid phase. These properties are important in the correlation of mass transfer coefficients [8].There is still different in opinions regarding the determination of the correlations model for the mass transfer coefficient of supercritical fluid flowing inside the packed bed columns. According to Lim et al. [9], the mass transfer correlations between a fluid and solid, in a packed bed of solids can be described the following equation by dimensional analysis [10]: (1) where: Re = Reynolds Number (fluid flow) Sc = Schmidt Number (related to diffusivity) Pr = Prandtl Number (related to heat transfer) Sh = Sherwood Number (related to mass transfer) The constant a, b, c, and d can be determined from the following experiments in this work. a c h PI TI BRP Fig. 1. An experimental apparatus was used for supercritical extraction of metal ions with chelating agents. The apparatus is labeled as follows: The apparatus is labeled as follows: (a) CO2 cylinder; (b) pretreatment filter; (c) high pressure pump; (d) temperature-controlled bath; (e) extractor (f) six port rotary valve ; (g) cold trap; (h) wet test meter; (i) sampling with magnetic stirrer; BPR: back-pressure regulator; PI: pressureindicator; TI: temperature indicator; V: valve. V V b d f g PI e i T g In order to evaluate the correlation constant a in eqn (2), data in each run were substituted into group, and plotted against Sh, as shown in Figure 5. The slope of the straight line in this figure is found to be 0.438 by least-square method with a coefficient of correlation (r2) more than 0.90. Therefore the empirical correlation equation for extraction of Matou Pummelo peel oil through the supercritical carbon dioxide packed bed system t can written as: