Mezclas supercriticas

Páginas: 14 (3444 palabras) Publicado: 18 de noviembre de 2010
I Iberoamerican Conference on Supercritical Fluids


J. L. Zacur1*, E. Gonzo2 Facultad de Ingeniería (Universidad Nacional de Jujuy) S.S de Jujuy – Argentina E-mail: 2 Facultad de Ingeniería-INIQUI (Universidad Nacional de Salta-CONICET) Salta –Argentina E-mail:

Abstract. In recent years, the solvency properties of 1,1,1,2 tetrafluorethane (R134a) have been under examination, with the focus being on the properties as subcritical and supercritical fluid for natural products extraction. Halocarbons (between them R134a) are molecules that present a higher polarity than CO2, allowing specific intermolecular interaction likedonor-acceptor proton relationships. It would facilitate higher solubility toward oxygenated compounds than the CO2, replacing the use of volatile polar modifiers in supercritical fluid extractions. In this work, GCA-EOS parameter matrix is extended, utilizing experimental data, in order to describe phase equilibrium behavior of propane, phenylalkanes and dimethyl ether (DME) in binary mixtureswith R134a in subcritical and near-critical conditions. The effectiveness of the new group parameters GCA-EOS was tested estimating VLE equilibrium of these binary mixtures, comparing with EOS used for other authors to correlate the behavior of its own reported experimental information and predicting VLE behavior of similar compound not included in interaction parameters data base. Propane and DMEare two homomorphic molecules that differ by the presence of oxygen in DME. The difference of molecular interaction with R314a is evidenced in the VLE behavior of its binary mixtures. The molecular interaction strength for the R134a+DME system is estimated trough homomorph concept, and the excess Gibbs energy of this mixture is compared with that corresponding to the R134a + propane system.Keywords: R134a, molecular interaction, thermodynamic modeling, Association, Group contribution

1. Introduction
Carbon dioxide has been the traditionally utilized solvent in supercritical fluid extractions (SFE). It is a nontoxic, inexpensive fluid and has a low critical temperature.

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I Iberoamerican Conference on Supercritical Fluids PROSCIBA2007

This last characteristic is important in extraction of natural active principles that can be degraded at higher temperatures. However, the CO2 presents a low affinity for polar solutes. The addition of polar modifiers (cosolvent), often a relatively nonvolatile solvent, can increase the solubility of these compounds. However the cosolvent usually requires a further separation, after theextraction. In recent years, the solvency properties of 1,1,1,2 tetrafluorethane (R134a) have been under examination (Roth, 1996, Hansen et al. 2001, Corr, 2002) with the focus being on the properties as subcritical and supercritical fluid for natural products extraction and in supercritical mixtures of CO2 with R134a. In these mixtures, R134a has been found to be an effective co-solvent, acting toincrease the solubility of polar solutes over that pure supercritical CO2, without the disadvantages of the less volatile traditional co-solvents (Corr, 2002) From dipole moment and dielectric constant perspective, R134a is more polar than CO2, therefore would present higher affinity toward polar solutes. However, the interaction between solvent and solute molecules cannot be described by simplyphysical constants, but should be considered other contributions. Several authors have analyzed the nature of the molecular interaction between halocarbons and polar groups. Kleiber (1995) points out that the H atom in chlorodifluormethane (R22) is strongly polarized; it is probable that the C-H---O hydrogen bond, occurring in R22+DME system, is the reason of an azeotrope with a pressure minimum...
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