Browsing by Author "Nunez, Gonzalo A."

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    Simulation of a flexible multi-vessel extraction plant with counter-current contacting between a solid substrate and supercritical CO2
    (2023) Toledo Cayuleo, Felipe Rodrigo; García Serna, Juan; Nunez, Gonzalo A.; Valle Lladser, José Manuel del
    This work develops a program (MVSEPS) to simulate a multi-vessel SuperCritical Fluid Extraction (SCFE) plant operating in a counter-current fashion. MVSEPS was applied to an SCFE to extract hemp seed oil using the shrinking core mass transfer model. A microstructural factor was best-fitted to experimental data from literature, to describe the inner mass transfer of the oil within the substrate, that was used as a parameter in subsequent simulations. The oil concentration in the CO2 stream exiting an extraction vessel, and the productivity, and efficiency of the SCFE plant were studied by changing selected parameters of the process and extraction conditions. The number of extraction vessels operating in series and the cycle time were relevant simulation parameters, because they cannot be studied experimentally at a laboratory scale. Using a larger number of extraction vessels and shorter cycle times increase the plant productivity but decrease the extraction efficiency. Other parameters studied, such as the particle size of the milled substrate, superficial CO2 velocity, extraction temperature and pressure, impact the operation of the SCFE plant similarly to at laboratory scales.
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    Simulation of a supercritical carbon dioxide extraction plant with three extraction vessels
    (PERGAMON-ELSEVIER SCIENCE LTD, 2011) Nunez, Gonzalo A.; Gelmi, Claudio A.; del Valle, Jose M.
    Although SuperCritical (SC) Fluid Extraction (SCFE) has been successfully applied commercially the last three decades, there is no systematic procedure or computational tool in the literature to scale-up and optimize it. This work proposes an algorithm to simulate dynamics in a multi-vessel (>= 3) high-pressure SCFE plant where extraction vessels operate in batches, and is thus forced to use simulated-countercurrent flow configuration to improve efficiency. The algorithm is applied to a three-vessel SCFE plant using a shrinking-core model to describe inner mass transfer in the substrate. As example, the extraction of oil from pre-pressed seeds using SC CO(2) at 313 K and 30 MPa is simulated. After three cycles the process reaches a pseudo-steady-state condition that simplifies the estimation of plant productivity. Use of a three-instead of two-vessel SCFE plant increases oil concentration in the stream exiting the plant and decreases CO(2) usage at the expense of increasing extraction time. (C) 2011 Published by Elsevier Ltd.
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    Solubilities in Supercritical Carbon Dioxide of (2E,6E)-3,7,11-Trimethyldodeca-2,6,10-trien-1-ol (Farnesol) and (2S)-5,7-Dihydroxy-2-(4-hydroxyphenyl)chroman-4-one (Naringenin)
    (AMER CHEMICAL SOC, 2010) Nunez, Gonzalo A.; del Valle, Jose M.; de la Fuente, Juan C.
    We measured the solubility in supercritical carbon dioxide (CO2) of farnesol [(2E,6E)-3,7,11-trimethyldodeca-2,6,10-trien-1-ol] and naringenin [(2S)-5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-one] using a static-analytic method (a high-pressure static equilibrium cell coupled to an HPLC). The molar fraction of farnesol in the saturated CO2-rich phase increased between y(2) = 0.13.10(-3) at 333 K and 11.4 MPa to y(2) = 1.91.10(-5) at 333 K and 26.0 MPa for farnesol and from y(2) = 0.49.10(-5) at 313 K and 10.3 MPa to y(2) = 1.65.10(-5) at 333 K and 44.5 MPa for naringenin. The average error of our measurements was about 25 To. Farnesol had an end-temperature crossover point at approximately 17 MPa, whereas naringenin exhibited a monotonous increase in solubility with both temperature and pressure. The differences in solubility between farnesol, naringenin, and other sesquisterpenes or flavonoids reported in the literature were partially explained by differences in molecular weight and polarity between solutes. We correlated experimental data as a function of the system temperature and pressure and the density of the solvent using a literature model that also showed the autoconsistency of the data for CO2 densities above 412 kg.m(-3) for naringenin.
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    Supercritical CO2 oilseed extraction in multi-vessel plants. 1. Minimization of operational cost
    (ELSEVIER SCIENCE BV, 2014) del Valle, Jose M.; Nunez, Gonzalo A.; Aravena, Raul I.
    This work uses a fully predictive mass transfer model to simulate the supercritical CO2 extraction of vegetable oils from prepressed oilseeds in the 1-m(3) vessel of an industrial multi-vessel plant operating at 40 degrees C and 30 MPa with the purpose of minimizing the operational cost. The work analyses the effect of particle diameter (0.5, 1, 2, 3, and 4 mm), superficial CO2 velocity (2.76, 5.52, or 11.0 mm/s), and number of extraction vessels (2, 3, or 4) on optimal extraction time and minimal operational cost. Keeping other variables constants, cost diminishes as particle diameter decreases. Although the optimal superficial CO2 velocity increases as particle diameter decreases, in the case of small (<= 1 mm) particles, substrate fluidization may place an upper limit to the superficial velocity. Within the studied region, best superficial CO2 velocities are 11.0 mm/s for particles smaller than 1-2 mm, 2.76 mm/s for particles larger than 3-4 mm, and 5.52 mm/s for particles in between. Keeping other variables constant, the cost of extraction of medium-to-large (>= 2 mm) particles decreases as the number of extraction vessels increases, at the expense of an increase in extraction time. However, because of a sharp transition wave that develops when extracting small (<= 1 mm) particles that separates fully extracted (downstream) from virtually unextracted (upstream) substrate within extraction vessels, two-vessel plants are best for small particles. The lowest operational cost observed in this work was USD 4.08 kg(-1) oil for the extraction of 2-mm particles using 3.30 m(3)/h of CO2 (U=2.76 mm/s) in a four-vessel plant. (C) 2014 Elsevier B.V. All rights reserved.
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    Supercritical CO2 oilseed extraction in multi-vessel plants. 2. Effect of number and geometry of extractors on production cost
    (ELSEVIER SCIENCE BV, 2014) Nunez, Gonzalo A.; del Valle, Jose M.
    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-m(3) industrial multi-vessel plant operating at 40 degrees C and 30 MPa, using a fully predictive mass transfer model to simulate the process. We modified the inner diameter (473 <= 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. (C) 2014 Elsevier B.V. All rights reserved.