Infinite Dilution Activity Coefficients of Solvents in Fatty Oil Derivatives

Latin American Applied Research 33:257-260 (2003)

INFINITE DILUTION ACTIVITY COEFFICIENTS OF SOLVENTS IN FATTY OIL DERIVATIVES

∗ ∗∗ O. FERREIRA and G. M. FOCO

∗LSRE, Departamento de Engenharia Química, Faculdade de Engenharía Universidade do Porto, 4200-465 Porto, Portugal [email protected] ∗∗ PLAPIQUI (Universidad Nacional del Sur – CONICET) Camino La Carrindanga Km 7 - 8000 Bahía Blanca - Argentina [email protected]

Abstract - Inverse gas-liquid chromatography has so that the amount of solvent in the stationary phase been applied to measure infinite dilution activity remains constant during the measurements. On the other ∞ coefficients (γ∞) of different solutes in low and high hand, the solutes injected into the gas carrier should molecular weight triacylglycerides (TAGs) and in give sharp and neat chromatograms. Solutes of low ∞ mixtures of carboxylic acids with TAGs. The γ∞ data volatility and/or highly retained in the stationary phase obtained were used to determine binary interaction will give broad chromatographic peaks. In this case the and size related parameters for the GCA-EOS group values of the retention times, and consequently the ∞ contribution with association equation of sate. calculated γ would be uncertain. All TAGs are low volatile compounds and can Keywords - Activity coefficients, Infinite dilution, always be used as solvents in a chromatographic Carboxylic acids, Triglycerides, Parameters stationary phase. Even the first member of the family, determinations, Binary interaction triacetin, has negligible vapor pressures at temperatures up to 353K. Unfortunately, carboxylic acids are highly I. INTRODUCTION retained in TAGs stationary phases; this makes inverse gas chromatography an unsuitable technique to measure Experimental information on thermodynamic properties ∞ γ of carboxylic acids in TAGs. of fatty acids and triacylglycerides (TAGs) is required In order to obtain experimental information to fit the for the design and simulation of separation processes GCA-EOS interaction parameters between TG and applied in the extraction and fractionation of fatty oil COOH groups, an alternative procedure was followed in derivatives from vegetable and animal oils. this work. Stationary phases were prepared using In previous work (Foco et al., 1996; Bermudez et ∞ mixtures of TAGs with high molecular weight non al., 2000), infinite dilution activity coefficients (γ ) of a ∞ volatile fatty acids and γ of volatile solutes in these series of organic solutes in palmitic acid, tripalmitin and mixtures were measured. With these values and the triacetin, were measured. These data were obtained by ∞ corresponding γ of the same solutes in each pure inverse gas chromatography, using the non volatile solvent (TAG and fatty acid) it was possible to quantify TAG or fatty acid as stationary phase and injecting the the interaction between TG and COOH. Mixtures of volatile solute at infinite dilution in the carrier gas palmitic acid with two different TAGs (triacetin and stream. Those data have been used (Bottini et al, 1999) γ∞ to determine molecular and group interaction tripalmitin) were prepared, and the of a series of parameters for the group contribution with association organic solutes in these mixtures were measured. equation of state GCA-EOS proposed by Gros et al (1996). II. EXPERIMENTAL RESULTS The functional groups characteristic of TAGs and The infinite dilution activity coefficients were measured fatty acids are, respectively, the triglyceride TG by gas-liquid chromatography. The specific retention ((CH2COO)2-CHCOO) and acid (COOH) groups. The volume Vºg at 273.15 K, i.e. the normalized volume of interaction parameters between the TG and COOH carrier gas necessary to elute solute i out of a column groups are not available in the GCA-EOS parameter with a mass W of solvent, is calculated from the table. Also the interaction between TG and the primary s measured retention time (t ) of solute i by: (CH2OH) and secondary (CHOH) alcohol groups are i missing. The purpose of this work is to measure infinite dilution activity coefficients in order to fit those − s 2 o = − 273.15 Pf Pw J3 interaction parameters to the experimental data. Vg (ti ta )F (1) T Po w The use of inverse gas chromatography to measure f s infinite dilution activity coefficients requires the solvent in the stationary phase to be a non-volatile compound,

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