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Uquiche E.,University of the Frontier | Huerta E.,University of the Frontier | Sandoval A.,University of the Frontier | Del Valle J.M.,University of Santiago de Chile | And 2 more authors.
Journal of Food Engineering | Year: 2012

This work examined the effect of the solid matrix on supercritical carbon dioxide (SC CO 2) extraction of essentials oils from boldo leaves (Peumus boldus M.) subjected to rapid decompression of a CO 2- impregnated sample, conventional milling, and low-Temperature milling. Low-Temperature conditioning prior to milling decreased heat-driven losses of volatile compounds during milling, as attested by a higher extract yield for low-Temperature (10.8 g extract/kg extract-free substrate) than conventionally (9.63 g/kg) milled sample. Extract yield was even larger for the rapidly decompressed sample (11.4 g/kg). Results of SC CO 2 extraction experiments carried out at 40 °C and 10 MPa were adjusted to a diffusional model using the effective diffusivity of the extract in the solid matrix (De) and a single partition of essential oils between solid substrate and SC CO 2 as best-fitting parameters. A microstructural factor (FM), which was estimated as the ratio between the binary diffusion coefficient of the essential oil in SC-CO 2 under extraction conditions and De, was used to characterize the effect of sample pretreatment on extraction rates. Values of FM for rapidly decompressed (202) and low-Temperature milled (1740) samples were smaller than value for conventionally milled samples (2200), which revealed that the two first treatments disrupted secretory cavities in boldo leaves more effectively than the third. This was confirmed by light microscopy observations. The work included also measurements using oregano bracts (Origanum vulgare L.) as the substrate to confirm literature reports on the SC CO 2 extraction of pretreated bracts and to serve as a reference to our main results with boldo leaves. Trends with oregano coincided with those of boldo. © 2011 Elsevier Ltd. All rights reserved.

Del Valle J.M.,University of Santiago de Chile | Del Valle J.M.,ASIS UC Interdisciplinary Research Program on Tasty and Healthy Foods
Journal of Supercritical Fluids | Year: 2014

Despite industrial application for almost four decades, there is reluctance in some world regions to adopt supercritical (sc) CO2 extraction because of the wrong perception that it is not fully competitive. To refute this misconception, this manuscript analyzes economics of scCO2 extraction of vegetable oil from prepressed seeds. Selection of this application was due to the availability of a predictive mathematical model of the extraction process applicable for simulation purposes; inner microstructural changes of oilseeds during prepressing allow their extraction according to a shrinking core hypothesis. The predictive model has as its single parameter a particle-size and scCO2-condition-independent microstructural mass transfer factor that can be best-fitted to laboratory extractions, existing literature correlations to estimate other model parameters, such as the axial dispersion in packed beds operating with supercritical fluids, and the solubility of vegetable oils in scCO2. On the other hand, there is a need to correlate literature data for the film mass transfer coefficient to unveil the factors responsible for experimental data scattering. Because laboratory or pilot plant runs in single-extraction-vessel units cannot produce the simulated countercurrent contact in an industrial plant having ≥3 extraction vessels, mathematical simulation provides the relationship between oil yield and extraction time that can anchor precise estimations of extraction cost. Analysis of results unveiled differences in optimal extraction time (for minimal extraction cost) between production costs estimated in this work and the operational costs informed before. Because the operational cost does not include the capital cost of the industrial plant, the need appears to reduce its contribution to the total cost by increasing plant productivity. This is achieved reducing extraction time, which negatively influences oil yield. To make further progress in the optimization of industrial scCO2 extraction processes, this manuscript proposes refining the mathematical simulation approach, and studying those technical constraints whose manifestations become more prevalent on scale-up. Mathematical simulation can be adapted to alternative, sample-pretreatment dependent mass transfer mechanisms in the solid matrix. It can be refined also to account for the size distribution of the substrate, radial changes in superficial scCO2 velocity, axial changes in pressure, and radial/axial changes in temperature resulting from heterogeneous packing, pressure drop, and/or heat transfer from/to extraction vessel walls that may influence large-scale extractions. Large-scale experiments will allow studying these phenomena, as well as technical constraints to the decrease in particle size, increase in scCO2 velocity, and decrease in extraction time imposed by the agglomeration and decrease in packed bed permeability of the substrate, and thermal effects during reconditioning of extraction vessels. The latter effects should be included as restrictions in the optimization of the extraction process, which may limit the extraction rate and the size or number of extraction vessel that impact economics positively. Close collaboration with industry will facilitate tackling large-scale problems, as well as refining estimates of plant cost as a function of its size and/or configuration. © 2014 Elsevier B.V. All rights reserved.

Nunez G.A.,Federico Santa Maria Technical University | Del Valle J.M.,University of Santiago de Chile | Del Valle J.M.,ASIS UC Interdisciplinary Research Program on Tasty and Healthy Foods
Journal of Supercritical Fluids | Year: 2014

The objective of this work was to study production costs for the supercritical CO2 extraction of a pre-pressed oilseed (packed bed with 2-mm particles) in a 2-m3 industrial multi-vessel plant operating at 40 °C and 30 MPa, using a fully predictive mass transfer model to simulate the process. We modified the inner diameter (47.3 ≤ D ≤ 65.6 cm) and number (n = 2, 3, or 4) of extraction vessels, and the mass flow rate of CO2 (Q = 3000 or 6000 kg/h), thus changing the aspect ratio of the extraction vessels (3 ≤ L/D ≤ 8), and superficial velocity (2.71 ≤ U ≤ 10.8 mm/s) and specific mass flow rate (6 ≤ q ≤ 24 kg/h per kg substrate) of CO2. Production cost decreased when increasing the mass flow rate of CO2 or the number of extraction vessels (or when increasing q). Production cost did not depend on the geometry of extraction vessel for a constant specific mass flow rate of CO2, but it decreased with a decreasing of the L/D ratio of the vessel for a constant superficial velocity of CO2. For any given plant, the contribution of fixed cost items (capital, labor) to the production cost increased with extraction time, unlike that of variable cost items (substrate, CO2, energy), which decreased. Thus, there was an optimal extraction time that minimized production cost for each plant. This work proposes an expression for capital cost of an industrial multi-vessel plant as a function of the mass flow rate of CO2 (which defines the cost of the solvent cycle of the plant), and the volume of the extraction vessels (which together with number of extraction vessels define the cost of extraction section of the plant), with a scaling factor of 0.48 for both items. Under optimal conditions, capital cost represented 30-40% of the production cost, but uncertainties in capital cost estimates (about ±50% using the proposed expression) may largely affect these estimates. The lowest production cost estimated in this work was USD 7.8/kg oil for the extraction of prepressed oilseed in a four-vessel plant using 6000 kg/h of CO2. The mass flow rate of CO2 and number of extraction vessels also affected annual productivity that was about 360 ton oil for the same plant operating 7200 h per year. Oil yields were above 90% for both three- and four-vessel plants. © 2014 Elsevier B.V. All rights reserved.

Reyes F.A.,University of Santiago de Chile | Munoz L.A.,University of Santiago de Chile | Hansen A.,University of Notre Dame | Del Valle J.M.,University of Santiago de Chile | Del Valle J.M.,ASIS UC Interdisciplinary Research Program on Tasty and Healthy Foods
Journal of Food Engineering | Year: 2015

Stickiness and caking of fine powders such as in dry disrupted microalgae should be avoided in supercritical (sc) CO2 extraction, because they negatively impact extraction rate and yield. To establish limits in water content of H. pluvialis cysts and extraction temperature, this work studied water-state diagrams of the powder. The powder's squeeze flow behavior as a function of water content was useful to characterize the transition between glassy and rubbery states as water content increased. Water sorption (W versus aw) at 20 °C was represented using the Guggenheim-Anderson-de Boer equation, with a monolayer water content of 3.67% (d.b.). The glass transition diagram (Tg versus Ww) was represented using the Gordon-Taylor equation, with Tgs = 88.3 °C (glass transition temperature of the anhydrous solids) and k = 3.49. The compression pressure necessary for squeeze flow behavior decreased 2.5-3 times at ambient temperature (ca. 23 °C) as a result of an increase in water content from 3.8% (d.b.) to 10-15% (d.b.) at which level glass-rubber transitions manifested, and then kept relatively constant when the water content increased even further. Alternatives to prevent caking of H. pluvialis during scCO2 extract include reducing the initial water content of the powder, increasing particle size by high-pressure agglomeration, and/or reducing the extraction temperature so as to prevent the glass-rubber transition that is responsible for sample stickiness. Taking into account that the scCO2 extractions are carried out above ambient temperature (40 ≤ T ≤ 60 °C), we recommend reducing the water content of H. pluvialis powder to W ≤ 5% (d.b.). © 2015 Elsevier Ltd.

Del Valle J.M.,University of Santiago de Chile | Del Valle J.M.,ASIS UC Interdisciplinary Research Program on Tasty and Healthy Foods | Glatzel V.,University of Santiago de Chile | Martinez J.L.,730 William Pitt Way
Food Research International | Year: 2012

The nutraceutical industry is currently interested in obtaining garlic extracts using mild extraction processes to recover high levels of labile allicin. This work studied oleoresin yield and extraction selectivity for allicin in the supercritical CO 2 extraction of freeze-dried aqueous garlic homogenate as a function of sample conditioning and process conditions. Agglomeration phenomena, which is responsible for substrate lumps in packed beds and flow channeling in the bed during extraction, was avoided by lowering sample moisture below 31gkg -1 water/substrate, and/or process temperature below 65°C. Oleoresin yield increased slightly with extraction pressure (15-45MPa) and dramatically with process temperature (35-65°C), but the concentration of allicin in the extract decreased as the temperature increased. Thus, an optimal combination of intermediate temperature and pressure was selected that allowed reasonably large yields (≥19gkg -1 oleoresin/substrate) and extraction selectivities (≥75mgkg -1 allicin/oleoresin). Based on experimental results, a 4h extraction process at 55°C and 30MPa using 55kgkg -1 CO 2/substrate was recommended. Cumulative extraction plots for oleoresin and allicin were successfully adjusted using a linear driving force mass transfer model. © 2011 Elsevier Ltd.

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