Mathematical modeling of mass transfer in supercritical fluid extraction of oleoresin from red pepper

Supercritical fluid extraction (SFE) from red pepper (Capsicum frutescens) using CO2 was performed in order to evaluate mass transfer. Kinetic extractions were done at 15 MPa and 40 degrees C, varying solvent flow rate, particle diameter and extraction bed volume. The highest extraction rates were obtained for high solvent flow rates, low particle diameters and low extraction bed volume. These results can be explained by the high importance of the convective phenomenon under these conditions. A classical model based on the concept of intact and broken cells was applied to experimental SFE curves, and model parameters were obtained. Two modeling strategies were used: (1) simultaneous fitting creating a set of parameters for pairs of duplicates, (2) multiple fitting that adjusts a single value for the solute concentration in unbroken cell for curves with equal particle diameter. These fits allowed estimating the convective mass transfer coefficient for each condition, and the respective values of the experimental Sherwood number. Experimental data was used to calculate dimensionless numbers of Reynolds and Schmidt for each condition. A second series of mathematical modeling was performed using these dimensionless numbers, which allowed proposing new mass transfer correlations. These new equations were based on the existence of forced and free convection, although the importance of the latter was small. The convective coefficients 'calculated with the correlations were compared to those obtained from the model, and a good coherence was found between both. (C) 2014 Elsevier Ltd. All rights reserved.