MODELLING AND SIMULATION OF EXTRACTION OF MARJORAM ESSENTIAL OIL USING SUPERCRITICAL CO 2

Transcription

1 MODELLING AND SIMULATION OF EXTRACTION OF MARJORAM ESSENTIAL OIL USING SUPERCRITICAL CO M.D.A. Saldaña*, R. L. Smith Jr. and H. Inomata Tohoku University, Research Center o Supercritical Fluid Technology Aramaki Aza Aoba-7, Aoba-ku, Sendai , Japan saldana@sc.che.tohoku.ac.jp, Fax: This work develops a model that can be used to explore the recovery o Marjoram essential oil rom majoram leaves. The model can be used or semi-continuous isothermal and isobaric supercritical extraction processes. Concentrations proiles in both phases are shown and can be observed at any section o the extractor and at any time o the process. The model should be useul or examining extractor conigurations and developing extraction proile alternatives. INTRODUCTION Essential oils are complex mixtures o a great number o dierent components that can be divided in three main groups: terpenic hydrocarbonates, oxygenated hydrocarbonates and sesquiterpenoids. Marjoram is one o the most popular lavoring material used in ood, pharmaceutical and perumes. The major component o marjoram essential oil is cis-sabinene []. Conventional extraction methods or obtaining these essential oils involve chemical solvents that can contaminate end products. Essential oil extractions o rosemary, basil and marjoram leaves using supercritical carbon dioxide were reported by Reverchon et al. [-3]. Reverchon et al. [] and Reverchon [4] model the extraction rom herbaceous matrices with supercritical CO that consider internal and ilm resistances, ocusing the particle geometry as an important actor or itting experimental data. Roy et al. [5] in the extraction o ginger root with supercritical CO used the shrinking core model with the eective diusivity and solubility parameters as itting parameters. Goodarznia and Eikani [6] presented a two-phase model, base o our work, and reported speciic data or the extraction o basil essential oil using supercritical CO. However, much remains to be understood on the time-dependent extraction behavior and the mass transer mechanism o essential oils extraction. In this paper, a mathematical model is developed and concentration proiles or the solid and supercritical phase are analyzed. Further, concentration proiles o the extractor are calculated. Mathematical model Extraction processes rom vegetable matrices such as leaves involves the release o solute rom the porous or cellular matrix into a solvent. The solutes ixed or trapped in a matrix by physical or chemical orces must be released and transerred to the supercritical luid by dissolving. Then, the dissolved solute diuses through the matrix to the surace o the particle. Finally, they move across a ilm around the particle to the bulk luid-phase. The dissolution kinetics involved in the model may depend on the ratio o the solute content to the saturation concentration in the luid phase, the bound state o the solute on a matrix and the association with coexisting materials [7]. The mechanism in which the essential oil is transerred rom a condensed state into the gaseous state (supercritical solvent) was discussed by Saldaña et al. [8]. A two-dimensional, unsteady state mathematical model was used or a ixed bed extractor (Figure ). Essential oil content o the leaves was assumed to change with time and distance along the axis o the extractor. Flow rate, temperature, pressure and bed properties were regarded as constant. For this case, the material balances or an element o bed are given by:

2 Solid phase: (C s : Solid phase oil concentration) τ = p L R ξ C s () ξ ξ s ξ : clet number, R: seed radius, ξ:?dimensionless radius Initial conditions: τ = ξ C s = C so () Boundary conditions: τ > ξ = s ξ = (3) τ > ξ = s ξ = Bi( C s C ) (4) C s : Oil concentration at particle surace Supercritical phase: (C : CO phase oil concentration) τ = (5) b C 6( ε ) L + εr Bi p ( C s C Z: Dimensionless axial coordinates, Bi: Biot number,ε: void raction Initial conditions: ) τ = Z C = (6) Boundary conditions: τ > Z = C = (7) τ > Z = = (8) Partioning o oil between Solid and Supercritical Phase C s = k p + C s (9) The dierential equations in the solid and supercritical phases were solved using the method o inite dierences by Crank Nicolson. The extractor (J) and particle (I) were divided into several grids o NR= and IL=6, respectively. These grids were selected considering the boundary conditions. Zone NR CO b I= R I=IL L Zone

3 a) b) Figure. Schematic o the extraction process: a) diusion o the oil in the solid phase, b) dissolution o the oil in the bulk phase throughout the extractor. Essential oil properties and extraction parameters The properties adopted or marjoram leaves are shown in Table. An extraction temperature and pressure o 33.5 K and MPa were chosen or the extraction conditions since these values are typical or EO extractions used by many researchers. Table. Parameters o marjoram leaves used Essential oil PM m o C o d p Source (g/mol) (kg) (kg/m3) (mm) Marjoram 5 8. Reverchon (99) Extraction parameters were as ollows: extractor volume, length, and diameter were.4 m 3,.88 m, and.5 m, respectively. The low rate o the solvent used was g CO /min and the porosity value was 4. A mean value o k p o 5 or the leaves at MPa and 33.5 K was reported by Reverchon [4] and Sovová et al. [9-] which was adopted in this work. RESULTS AND DISCUSSION Figures - 6 show some results obtained using this model or the marjoram essential oil extraction with supercritical carbon dioxide at 33. K and MPa. The best it o the experimental data has been obtained using a non-linear itting method with two adjusted parameters (k and D m ). As can be seen rom Figure, the two-parameter model can predict the trend o the extraction yield. In this Figure lower values o k and D m lead to lower extraction yields while higher values o these parameters lead to a higher extraction yield in less time. The mass transer coeicient k and D m values obtained in this work were.5x -7 m/s and 9.7x -3 m /s, respectively. The D m value obtained in this work is in the same order o magnitude and in good agreement with the one reported earlier by other researchers [-3,6]. 8 Yield [%] Time [min] Exp. a b c d e

4 Figure. Eect o the mass transer and diusion coeicients in the extraction o Marjoram essential oil at 33. K and MPa (d p : mm). a) k :.x -7 m/s & Dm :.5x -3 m /s, b) k :.44x -7 m/s & Dm :.x -3 m /s, c) k 3 :.9x -7 m/s & Dm 3 :6.55x -3 m /s, d) k 4 :.87x -7 m/s & Dm 4 :5.49x -3 m /s, e) k 5 :.5x -7 m/s & Dm 5 :9.7x -3 m /s Figure 3 shows concentration proiles o essential oil extraction in the solid phase in two positions inside the extractor (down and upper side) and dierent extraction times at a constant temperature and pressure o 33. K and MPa, respectively. In Figure 3, the dimensionless concentration decreased when the essential oil was diusing rom the center o the particle to the surace (along the radius o the particle o d p : mm). Further, the concentration proiles in the solid phase should decrease i the extraction time is increased since the initial quantity o essential oil is decreasing. When comparing the concentration proiles obtained or the bottom part o the extractor (NR=) with the upper side o the extractor (NR=7) at a constant time, the amount o solute extracted decreased at the upper side o the extractor. The extraction rate o oil rom the particle at the upper side o the extractor was lower, which may be attributed to the saturation o the solvent with the solute in the bottom part o the extractor..9.8 min.9.8 min 3 min 6 min 3 min C/Co C/Co 9 min.. 6 min 9 min min 5 min..8 min 5 min Figure 3. Dimensionless concentration proile in the solid phase at the: a) bottom and b) upper side o the extractor, or marjoram essential oil extraction along the particle radius (d p :mm) at 33. K and MPa. The model could determine the concentration proiles in the particles at any time along (through) the extractor. Figure 4 shows that i the supercritical carbon dioxide is lowing rom the bottom to the top o the extractor, the concentration o essential oil should increase due to the dissolution o the essential oil in the luid and the eect o the mass transer coeicient (k ) min J= C/C o 6 min. min J=

5 Figure 4. Dimensionless conc. proile versus radius o a marjoram particle at 33. K and MPa. Figure 5 shows concentration proiles o essential oil extraction with supercritical carbon dioxide at the beginning (8 min) and at the end (5 min) o the extraction process, respectively. While in Figure 5a can be observed that the oil concentration is the highest, there is very little quantity o oil that can still be extracted in Figure 5b..9.8 C/Co J= Figure 5a. Dimensionless concentration proile versus dimensionless radius o a Marjoram particle at 33. K and MPa through the extractor height L (J= to )..9.8 C/C o.. J= Figure 5b. Dimensionless concentration proile versus dimensionless radius o a Marjoram particle at 33. K and MPa in 5 min through the extractor height (J= to ).

6 Figure 6 shows concentration proiles in the supercritical phase or the extraction o marjoram essential oil using supercritical carbon dioxide at MPa, 33. K and particle diameter o mm. Through this Figure can be observed that the maximum concentration will be a unction o the extractor height and extraction time. In this case, the highest concentration will be reached in less than min. By this Figure can be observed that the concentration will increase when supercritical carbon dioxide is lowing rom the bottom to the top o the extractor. Besides, higher extraction rates are obtained in the irst stages o the extraction process that will decrease as time increases. Ater min, the extraction rate is very low and inconvenient or an industrial process. Diusivity and mass transer values obtained with this model were 9.7x -3 m/s and.5x -7 m/s, respectively. Figure 6. Concentration proile in the supercritical phase or Marjoram essential oil extraction at 33. K and MPa (d p : mm). CONCLUSIONS Marjoram essential oil extraction with SCCO was estimated using a two-dimensional model. The model preditions are satisactory and have reliable trends compared to experimental data. Concentration proiles in the solid and supercritical phase can be observed at any section o the extractor and at any time o the process. Two mass transer coeicients (D m & k ) inluence extraction yields in the process. The maximum concentration will depend on D m and k, which can be estimated with this model. Through modelling, the extraction time can be optimized or an optimum essential yield or industrial processes. ACKNOWLEDGMENTS The authors are grateul or the support o the Ministry o Sports, Education and Culture. REFERENCES [] REVERCHON, E., Journal o Supercritical Fluids, 5(4), 99, p. 56. [] REVERCHON, E., DONSI, G. AND SESTI OSSEO, L., Ind. Eng. Chem. Res., 3(), 993, p. 7. [3] REVERCHON, E. AND SESTI OSSEO, L., Journal o Supercritical Fluids, 7, 994, p. 85. [4] REVERCHON, E., AlChE Journal, 4, 996, p [5] ROY, B.C., GOTO, M. AND HIROSE, T., Ind. Eng. Chem. Res., 35, 996, p. 67. [6] GOODARZNIA, I. AND EIKANI, M.H., Chem. Eng. Science, 53(7), 998, p [7] SALDAÑA, M.D.A., PhD Thesis, Unicamp,, pp. 4.

7 [8] SALDAÑA, M.D.A., SMITH, R.L.JR. AND INOMATA, H., Proc. Autumn Meeting o the Soc. Chem. Eng. Japan,, Japan. [9] SOVOVÁ, H., Chem. Eng. Science, 49(3), 994, p. 49. [] SOVOVÁ, H., KUCERA, J. AND JEZ, J., Chem. Eng. Science, 49(3), 994, p. 45.