Browsing by Author "Germain, JC"

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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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    Natural convection retards supercritical CO(2) extraction of essential oils and lipids from vegetable substrates
    (AMER CHEMICAL SOC, 2005) Germain, JC; del Valle, JM; de la Fuente, JC
    External mass-transfer coefficients (k(f)) during supercritical fluid extraction (SCFE) of high-solubility solutes, under solvent upflow conditions and low superficial velocities, can be small because of the negative influence of natural convection phenomena. A shrinking-core model for mass transfer was used to estimate best-fit values of k(f) for data on SCFE of lipids from prepressed rapeseeds. Values of k(f) at a high Reynolds number (Re = 14.1) were similar when using solvent upflow or downflow, but k(f) at lower Re (1.57) was 3.6 times smaller when using solvent upflow than that predicted from a literature correlation for downflow conditions. These k(f)'s are consistent with values estimated by fitting literature data, or gathered from various sources under similar, nonadequate conditions (solvent upflow under low Re) for the extraction of both fatty and essential oils. Care is advisable when employing best-fit values of k(f) from laboratory data for process design purposes, especially when sizing of the solvent pumps for the experiments is questionable.