Mathematical model of supercritical extraction applied to oil seed extraction by CO2+saturated alcohol — I. Desorption model

Supercritical fluid extraction of solutes from solid matrix is represented by the extraction curve, where cumulated extracted oil is plotted versus time. Experimental data obtained in laboratory scale and pilot plant is adjusted with different extraction models; in order to predict extraction curves for full-scale extractors. Sometimes, a shortcut method is useful to adjust experimental data; these correlations are typical in most of engineering processes. In this paper, three shortcut methods are reviewed. First, a model based on flux models considering residence time distribution curves for serially interconnected perfectly mixed tanks and plug flow in series or in parallel with them. It could be used to analyze extractor behavior taking into account bed distribution (preferential ways, dispersion). Second, fast adjusting or ‘t^n’ model considers a differential mass balance where mass transfer coefficient is an ‘nth^’ potential function of time; analytical solution gives an explicit equation. Third, it is presented a linear shortcut method by intervals based on Sovovà model; it predicts considering four extraction periods: delay, rapid extraction, slow extraction and depletion; delay time and solubility are evaluated using the ‘t^n’ model. This model gives a process transfer function (Laplace domain). Supercritical fluid extraction of sunflower seed oil with carbon dioxide was performed in a pilot plant at 30.0 MPa and 40°C, using different amounts of methanol, ethanol, butanol and hexanol as cosolvents. Experimental data are fitted with proposed shortcut methods. Fitting error is less than 5% except in linear shortcut method by intervals which is higher.