Biochemical Engineering Journal 40 (2008) 72–78 Mathematical modeling and study of mass transfer parameters in supercritical fluid extraction of fatty acids from Trout powder Hamzeh Zakizadeh Nei Nei, Shohreh Fatemi ∗ , Mohammad Reza Mehrnia, Alireza Salimi Chemical Engineering Department, Faculty of Engineering, Tehran University, Enghlab Avenue, Tehran 11365-4563, Iran Received 17 June 2007; received in revised form 3 November 2007; accepted 20 November 2007 Abstract Mathematical modeling of fatty acids (FAs) extraction from Trout powder by supercritical carbon dioxide was performed in the present work. Trout powder with its low cost contains high amount of essential FAs and it is commonly available as a proper source of FAs. The effect of process parameters, such as pressure (25, 28, 31, 34 and 37 MPa) and temperature (310, 318 and 326 K) of extraction and void fraction of the bed (0.25, 0.35 and 0.45, v/v) on the yield of FAs extraction was examined in a series of experiments conducted in a laboratory scale apparatus. The results indicated a significant increase of extraction yield with an increase of pressure from 25 to 34 MPa, but working at the higher pressure (37 MPa) caused reduction of the extract. Increasing the temperature higher than 318 K revealed significant reduction of the FAs yield and increasing the bed void fraction from 0.25 to 0.45 showed enhancement of the extraction. The mathematical model was developed considering diffusion-controlled regime in the particle and film mass transfer resistance around the particle with axial dispersion of the bulk phase at dynamic conditions. Henry law was used to describe the equilibrium state of solid and fluid phases. The proposed mass balance equations were numerically solved using implicit finite difference method and the model parameters were correlated using the experimental results of the outlet FAs concentration in the oil extracted at dynamic conditions. Well-known Nelder–Mead method was applied to estimate the four parameters of the model, namely, mass transfer coefficient (k f ), axial dispersion coefficient (D ax ) in the bulk phase, effective diffusivity (D eff ) into the pores and Henry coefficient (H). In the range of studied conditions, the higher extraction efficiency with higher pressure resulted lower correlated H, although the temperature increasing which showed a retrograde phenomena in the FAs yield, revealed H passing though a minimum. © 2008 Published by Elsevier B.V. Keywords: Mathematical modeling; Supercritical fluid extraction; Trout powder; Fatty acids; Mass transfer coefficient 1. Introduction Supercritical carbon dioxide (SC-CO 2 ) extraction of fatty acids from solid matrices is an alternative process to sol- vent extraction, hydrodistillation and steam distillation because of certain advantages of SC-CO 2 with critical tempera- ture of 313 K, which can preserve original oil composition and its properties. Carbon dioxide is inert, pure, non-toxic, environment-friendly, inexpensive and gaseous under ambient conditions. Thus, solute separation, concentrating and drying processes are made easier and generation of liquid solvent waste and exposure of operators to toxic solvents can be minimized. ∗ Corresponding author. Tel.: +98 21 61112229; fax: +98 21 66957784. E-mail address: shfatemi@ut.ac.ir (S. Fatemi). The extraction of fatty acids (FAs) by steam distillation has disadvantage of degradation of the heavy FAs and reduction of desired products. Solvent extraction can cause extraction of more heavy FAs and other heavy compounds in the presence of some toxic solvent, although none of the problems are occurred in supercritical fluid extraction (SFE) therefore FAs are extracted with higher quality [1]. Eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and -linolenic acid (ALA) are three essential FAs which have been noted for their beneficial role in human health. Further- more, -3 FAs found in fish and seafoods can reduce the risk of cardiovascular disease and inflammatory diseases and they are useful for nervous system and mental health [2]. SFE of natural material has been studied by several authors from the processing point of view and a wide range of seed species has been explored as reviewed by Reverchon and De 1369-703X/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.bej.2007.11.015