Thermodynamic modeling in supercritical processes of natural products using a group contribution equation of state

T. FORNARI; O. FERREIRA; S. PEREDA; S.B. BOTTINI; E.A. BRIGNOLE

El Salvador – Brasil

Conferencia; 4th Brazilian Meeting on Supercritical Fluids - EBFS 2001; 2001

Between the great variety of supercritical fluid applications, the natural product industry is one of special interest. Several monographs have been presented on this field: the extraction of natural products (King and Bott, 1993), food and biomaterials processing (Rizvi, 1994), purification and refining in the oil and lipid industry (King and List, 1996), hydrogenation of oils and derivatives (van der Hark, 2000). Together with the number of supercritical fluid applications in natural product processing, the need of experimental work and simulation methods is growing day after day. In this respect, the phase equilibria thermodynamic modeling of the mixtures involved is essential, in order to simulate and optimize the process under analysis. The thermodynamic model must be able to correlate and predict the varied types of phase equilibria (liquid-vapor, liquid-liquid, liquid-fluid) that can be present in the process, at low and high pressures. Natural products are generally a complex mixture of a considerably amount of thermo-liable and high-molecular weight compounds. The physical properties (boiling point, critical temperature or pressure, acentric factor, etc.) for these compounds are normally not available or not reliable because of their very low volatility. Thus, the thermodynamic model must be able to handle the characterization of the natural product through an appropriated selection of its pure component parameters. On the other hand, experimental phase equilibrium data of mixtures containing natural products is scarce. These features supports the selection of a group contribution model; interactions parameters in the supercritical fluid – natural product mixture can be based on phase equilibrium data of binary mixtures that include the corresponding functional groups. In this work, the Group Contribution Equation of State developed by Skold-Jorgensen (1984) is used to describe phase equilibria in mixtures of natural oils and derivatives with supercritical fluids. An extension of this model, i.e. the Group Contribution Associating Equation of State GCA-EoS (Gros et at., 1996) is used to include associating compounds. The revised and extended parameter table presented by Espinosa et al. (2000) and Ferreira et al. (2000) allow the inclusion of some functional groups present in natural oil and fat products. The GCA-EoS is successfully applied in the phase equilibria modeling of mixtures containing vegetable oils, terpenes and fatty acids, esters and alcohols.