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Faundez C.A.,University of Concepcion | Quiero F.A.,University of Concepcion | Valderrama J.O.,University of La Serena | Valderrama J.O.,Center for Technological Information
Fluid Phase Equilibria | Year: 2010

Artificial neural networks have been applied for the correlation and prediction of vapor-liquid equilibrium in binary ethanol mixtures found in alcoholic beverage production. The main interest of the study is the acceptable modeling of the bubble pressure and concentration of congeners (substances different from ethanol) in the vapor phase, considered to be an important enological parameter in the alcoholic industry. Nine binary ethanol + congener mixtures have been considered for analysis. Vapor-liquid equilibrium data of these systems were taken from the literature. Predictions using artificial neural networks were compared with available literature data and with results obtained using equations of state. The study shows that the neural network model is a good alternative method for the estimation of phase equilibrium properties. © 2010 Elsevier B.V. All rights reserved.

Valderrama J.O.,University of La Serena | Valderrama J.O.,Center for Technological Information | Arce P.F.,University of Campinas
Fluid Phase Equilibria | Year: 2013

The melting temperature depression (MTD) that happens when an ionic liquid (IL) is pressurized by a soluble gas is modeled using phase equilibrium relations. MTD of hydrocarbons, polymers and lipids has been reported by several authors and the subject has been widely discussed in the literature. However, the phenomenon in ionic liquids (ILs) has received recent attention especially because some ILs that are potentially attractive for organic synthesis could not be used due to their relatively high melting temperatures. When solid is formed from the gas-pressurized liquid, three phase equilibrium in the binary system IL. +. gas is produced. In this paper the equation of state method is used to model the gas-liquid equilibrium and activity coefficients for representing the solid-gas equilibrium. Thus a consistent set of equations is formulated and solved by an optimization method using available experimental data of pressure, and temperature of IL. +. gas systems. The Peng-Robinson equation with the Wong-Sandler mixing rules showed to be appropriate for correlating the gas-liquid equilibrium data while the van Laar model for the activity coefficient was appropriate for correlating the solid-gas equilibrium data. © 2013.

Aguirre C.L.,University of Antofagasta | Cisternas L.A.,University of Antofagasta | Valderrama J.O.,University of La Serena | Valderrama J.O.,Center for Technological Information
International Journal of Thermophysics | Year: 2012

Based on experimental data collected from the literature, a group contribution method for estimating the melting points of imidazolium-, pyridinium-, pyrrolidinium-, ammonium-, phosphonium-, and piperidinium-based ionic liquids (ILs) with common anions is proposed. The method considers the contributions of ionic groups and methylene groups, as additive parameters, and two nonadditive characteristic geometric parameters of cations such as symmetry and flexibility. A total of 293 data points for 136 ILs were used in this study. The average relative deviation and the average absolute deviation of the proposed model are 7.8% and 22.6K, respectively. It is concluded that the proposal is useful for the prediction of the melting points for a wide range of ILs. © Springer Science+Business Media, LLC 2011.

Valderrama J.O.,University of La Serena | Valderrama J.O.,Center for Technological Information | Forero L.A.,Pontifical Bolivarian University | Forero L.A.,Center for Technological Information
Fluid Phase Equilibria | Year: 2012

An analytical expression for the vapor pressure of ionic liquids based on the Peng-Robinson equation of state is proposed. The method uses the concept of zero-pressure fugacity previously presented in the literature and that has been found to work well in the range of low vapor pressures (lower than 0.1. Pa), where the values of vapor pressure of ionic liquids, up to moderate temperatures, are found. The parameters of the equation of state are generalized in terms of ionic liquid properties and results are compared with experimental data, showing average absolute deviations below 8%. The advantage of the proposed analytical expression is its solid thermodynamic foundation, the generalization of the model parameters, and its acceptable accuracy for engineering calculations. © 2012 Elsevier B.V.

Valderrama J.O.,University of La Serena | Valderrama J.O.,Center for Technological Information
Industrial and Engineering Chemistry Research | Year: 2014

The several methods presented in the literature during the past few years to estimate the melting temperatures of ionic liquids and the alleged accuracy of the methods mentioned by several authors are analyzed and discussed in this work. Because of the importance of the melting temperatures for the development and applications of ionic liquids, several models have been proposed in the literature. Methods based on computational chemistry, group contribution, artificial neural networks, and chemical homology are considered in this analysis, and results from the different approaches are discussed. The general conclusion about these advances is that it is a myth that, with the present experimental data and knowledge we have of ionic liquids, we can obtain accurate and generalized correlations and estimation methods for determining the melting temperatures of ionic liquids. Ideas about what is needed and on how to proceed in the future are presented. © 2013 American Chemical Society.

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