Measurement, correlation and prediction of isothermal vapor-liquid equilibria of different systems containing vegetable oils

Thermodynamic properties, in particular vapor-liquid equilibrium (VLE) data, are required for the development of reliable predictive models for systems with fatty compounds. Isothermal VLE data have been measured for mixtures of methanol, ethanol, or n-hexane with refined vegetable oils (soybean, sunflower and rapeseed) at 348.15 K and 373.15 K using a computer-driven static apparatus. The oils were characterized in terms of their fatty acid and corresponding triacylglycerol (TAG) compositions. For the mixtures containing vegetable oils and n-hexane a negative deviation from Raoult's law was observed and a homogeneous behavior (no miscibility gap) was found, while the mixtures with alcohols exhibited positive deviation from ideal behavior and, in some cases, limited. miscibility. On the basis of the composition of the studied vegetable oils, their relative van der Waals volume and surface area parameters were estimated by the Bondi method and their vapor pressure by a group contribution method developed by Ceriani and Meirelles [1]. The experimental VLE data were correlated together with available excess enthalpies (H-E) and activity coefficients at infinite dilution (gamma(infinity)(i)) data using the UNIQUAC model. For the fitting process the refined vegetable oil was treated as a single triacylglycerol (pseudo-component) which has the corresponding degree of unsaturation, number of carbon atoms and molar mass of the original oil composition. The overall-average errors (AAE) using UNIQUAC model are 4.46% for VLE, 7.07% for gamma(infinity)(i) and 5.80% for H-E The experimental data were also compared with the predicted results using mod. UNIFAC (Dortmund) and an extension of this method proposed for triacylglycerols in a previous work was also tested. (C) 2015 Elsevier B.V. All rights reserved.