J. of Supercritical Fluids 72 (2012) 140–149 Contents lists available at SciVerse ScienceDirect The Journal of Supercritical Fluids jou rn al h om epa ge: www.elsevier.com/locate/supflu Fixed bed property changes during scCO 2 extraction of natural materials – Experiments and modeling Florian Meyer a , Marko Stamenic b , Irena Zizovic b,∗ , Rudolf Eggers a,∗ a Institute of Thermal Separation Processes, Heat and Mass Transfer, Hamburg University of Technology, Eißendorfer Str. 38, 21073 Hamburg, Germany b Faculty of Technology and Metallurgy, Belgrade University, Karnegijeva 4, 11000 Belgrade, Serbia a r t i c l e i n f o Article history: Received 3 July 2012 Received in revised form 22 August 2012 Accepted 29 August 2012 Keywords: Supercritical fluid Mathematical modeling Extraction Natural products a b s t r a c t Properties of the fixed bed of plant material during the extraction with scCO 2 from rapeseed were inves- tigated for the two types of mechanical pretreatments: flaking and impact milling. Obtained results indicated that particle density, bulk density of the bed and consequently the bed porosity changed dur- ing the extraction. In the case of flaked rapeseed, the change of particle diameter was also detected and quantified. On the basis of experimental data linear relationships between the particle density/bed porosity/mean particle diameter and oil content in solid were established. Mathematical model based on the mass balances for the supercritical and solid phase which took into account particle density, bed porosity and particle diameter (for flaked plant material) as variables was derived. The proposed model described experimental data with high accuracy. Possible error due to neglecting the change of the fixed bed properties was presented as well. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Extraction with supercritical carbon dioxide (scCO 2 ) is a well investigated extraction technique for a broad variety of plant mate- rials. The main benefit of the application of carbon dioxide as a solvent is the unrestricted use in pharmaceutical and foodstuff applications due to its harmlessness and high quality of the obtain- able extracts. In addition to experimental studies, models that describe the extraction process were developed. Thorough reviews on mathematical modeling of supercritical fluid extraction (SFE) processes are given in the works of Sovová and Stateva [1], Sovová [2], Reverchon and De Marco [3] and Pereira et al. [4]. Modeling of extraction kinetics of oilseeds – the substrate class that is also inves- tigated in the present study was recently presented by Boutin et al. [5]. In general, the models are based on mass balances of the fluid and the solid phase. The main differences can be divided into the following aspects: description of the intra-particle mass transfer, particle shapes, consideration of hydrodynamic effects such as axial dispersion and description of solute–matrix interaction. While the description of extraction mechanisms varied broadly, all the mod- els took into account the same simplification – properties of the fixed bed of plant material during the extraction were considered to be constant. This assumption might be quite true in the case of plant ∗ Corresponding authors. E-mail addresses: zizovic@tmf.bg.ac.rs (I. Zizovic), r.eggers@tu-harburg.de (R. Eggers). materials with relatively low quantity of extractables. However, the question is if the fixed bed properties remained the same in the case of extraction from material with high quantities of extractables, like in the case of oilseeds where high yields are expected. In this work, the change of fixed bed properties – porosity, particle density and particle size, in the course of the scCO 2 extraction of rapeseed was observed. Consequently, a model which took into account the con- tinuous change of fixed bed properties during the extraction was derived. 2. Materials and methods 2.1. Rapeseed Rapeseed was purchased from a German Agriculture Trade Association (LHG eGSchmölln). The moisture content was approx- imately 5%. 2.2. Mechanical pre-treatment Mechanical pre-treatment was carried out with two different methods: flaking and impact-milling. For flaking rapeseed grains were processed in a roller mill consisting of two rollers (D = 60 mm, gap width: 0.15 mm, stainless steel) counter-rotating at a revolu- tion of 144 min -1 without slip velocity. The surface of the one roll is plane and the other is riffled to ensure proper feeding of the material. 0896-8446/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.supflu.2012.08.022