Browsing by Author "Uquiche, E"

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    Microstructural effects on internal mass transfer of lipids in prepressed and flaked vegetable substrates
    (ELSEVIER, 2006) del Valle, JM; Germain, JC; Uquiche, E; Zetzl, C; Brunner, G
    Predictive models that describe supercritical fluid extraction (SCFE) processes would be welcomed to support its industrial application, particularly for the supercritical carbon dioxide (SC-CO2) extraction of vegetable oil from seeds subjected to common high-shear pretreatments. This work explores the application of microstructure-extractability relationships for modeling the SCFE of lipids from vegetable substrates. We measured the extraction kinetics of prepressed rapeseeds, olive husks, and flaked rosehip seeds, with SC-CO2 at 313 K and 30 MPa, and simulated the extractions using a shrinking-core model. Model parameters included the oil solubility and film mass transfer coefficient from literature correlations, and an effective diffusivity (D-e) inside the porous particles. We determined that D, could be calculated as D-12 x F, where D-12 is the diffusivity of oil in CO2, and F is a microstructural correction factor, estimated as the ratio between the final porosity (epsilon(p) from Hg porosimetry) and pore-network tortuosity (tau, from fractal-texture analysis of binary light-microscopy irnages) of the substrates. Simulations adjusted the experimental data reasonably well (5.4% < mean percent error < 15%). Additionally, best-fit estimates of D, were obtained for literature data on SC-CO2 extraction of lipids from prepressed and flaked seeds. Resulting values of F did not depend on particle size and spanned a narrow range - one order of magnitude (0.030-0.29) - as it would be expected when comparing similar systems. Although further work will be required to refine the relationship between tau and fractal parameters, or between tau and the hysteresis of Hg infiltration, this work demonstrates that is possible to develop predictive models for SCFE of solid substrates subjected to high-shear pretreatments. (c) 2005 Published by Elsevier B.V.
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    Microstructure-extractability relationships in the extraction of prepelletized Jalapeno peppers with supercritical carbon dioxide
    (WILEY, 2005) Uquiche, E; Del Valle, JM; Ihl, M
    There is a need to increase vessel loads for high-pressure batch processes such as supercritical fluid extraction of solid substrates, but a precompacting treatment such as pelletization may negatively affect mass transfer rates. This work was aimed to quantify the effect of the microstructure of Jalapeno pepper pellets on the extraction rate and yield of oleoresins when using supercritical CO2 at 40 degrees C and 320 bar as the solvent, so as to contribute with basic information that will help optimize pelletization treatments for solid substrates. Four types of substrates were obtained by considering 2 initial particle sizes and 2 initial moisture levels before pelletization, and the inner porosity and tortuosity of the resulting pellets were estimated. The internal mass transfer was favored in pellets showing a better distribution and connectedness of pores, and the extraction rate and yield improved when using pellets from flakes instead of milled flakes, with initial sample moisture exhibiting a more limited effect. A reduction in the particle size of the pellets improved mass transfer but caused a reduction in packing density, and these 2 factors had opposite effects on the "volumetric yield" of the process (mass of recovered solute per unit time and per unit volume of extraction vessel), which was also affected by prepelletizing sample conditioning.