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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.


Valderrama J.O.,University of La Serena | Valderrama J.O.,Center for Technological Information | Forero L.A.,Center for Technological Information | Forero L.A.,Pontifical Bolivarian University | Rojas R.E.,University of La Serena
Industrial and Engineering Chemistry Research | Year: 2012

The group contribution method proposed by Valderrama and Robles in 2007 and extended by Valderrama and Rojas in 2009 to estimate the critical properties of ionic liquids is revised and an additional test for determining the consistency of the estimated properties is proposed. The new testing method includes the calculation of the saturation pressure at the normal boiling temperature using an equation of state and an accurate model to represent the temperature function of the attractive term in the equation of state. In determining the vapor pressure, the critical temperature, the critical pressure, the critical volume, and the acentric factor determined by group contribution are included. The proposed method complements the previous density test of the authors that tested the critical temperature, the critical volume, and the normal boiling temperature only. A total of 1130 ionic liquids are considered in this work, and double checking, using the density and the normal vapor pressure, is applied. Also, a spreadsheet file that allows any reader to calculate and check the critical properties of other ionic liquids containing any of the 44 groups defined by the method is provided. © 2012 American Chemical Society.


Valderrama J.O.,University of La Serena | Valderrama J.O.,Center for Technological Information | Rojas R.E.,University of La Serena
Fluid Phase Equilibria | Year: 2010

A new concept named mass connectivity index (MCI) to encode bond contributions and to allow quantifying the extent of branching in a molecule, especially of ionic liquids, is proposed. The concept is based on the molecular connectivity concept first introduced by Randic in 1975 and modified in different forms by several authors. The proposed concept is much easier to calculate than any of the connectivity indexes available in the literature. Thus the only data required for determining the MCI are the groups forming the molecule and the mass of the groups. The groups forming the molecule are defined as commonly done in group contribution methods. The index is used as a variable in generalized correlations to accurately estimate the density and the heat capacity of ionic liquids. © 2010 Elsevier B.V.


Faundez C.A.,University of Concepción | Quiero F.A.,University of Concepción | 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.


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 | Faundez C.A.,University of Concepción
Thermochimica Acta | Year: 2010

A method to test the thermodynamic consistency of high pressure gas-liquid equilibrium data in binary mixtures which considers data for a single phase has been extended to propose an overall test using the whole set of PTxy data. The method previously proposed by the authors was applied before to situations in which the concentration in the gas phase only was known (a solid dissolved in a high pressure gas) and to situations in which the concentration in the liquid phase only was known (ionic liquid and a high pressure gas). The extension is done here by proposing a combined analysis in which the test is applied to both phases while the modeling is done using bubble pressure calculations as recommended in the literature. Data for water + carbon dioxide mixtures at nine temperatures and for pressures ranging from 100 to 1500 bar and temperatures 383 to 598 K were used. Results indicate that the proposed method is reliable and can be used to check the thermodynamic consistency using all experimental phase equilibrium data available. © 2009 Elsevier B.V. All rights reserved.


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.


Valderrama J.O.,University of La Serena | Valderrama J.O.,Center for Technological Information | Toro A.,University of La Serena | Rojas R.E.,University of La Serena
Journal of Chemical Thermodynamics | Year: 2011

A simple and accurate group contribution method to estimate the heat capacity of ionic liquids is presented. The method considers groups previously defined for a successful method used to estimate critical properties of ionic liquids. Additionally a structural parameter known as mass connectivity index recently defined by the authors has been incorporated to define the model equation. To better define the values of the groups, heat capacity data at 298 K for 126 organic substances were used with the 469 heat capacity data for 32 ionic liquids. The results were compared with experimental data and with values reported by other available estimation methods. Results show that the new group contribution method gives low deviations and can be used with confidence in thermodynamic and engineering calculations. © 2011 Elsevier Ltd. All rights reserved.


Valderrama J.O.,Center for Technological Information | Martinez G.,Center for Technological Information | Martinez G.,Pedro Ruíz Gallo National University | Faundez C.A.,University of Concepción
International Journal of Thermophysics | Year: 2011

Artificial neural networks and the concept of mass connectivity index are used to correlate and predict the heat capacity at constant pressure of ionic liquids (ILs). Different topologies of a multilayer feed-forward artificial neural network were studied, and the optimum architecture was determined. Heat-capacity data at several temperatures taken from the literature for 31 ILs with 477 data points were used for training the network. To discriminate among the different substances, the molecular mass of the anion and of the cation and the mass connectivity index were considered as the independent variables. The capabilities of the designed network were tested by predicting heat capacities for situations not considered during the training process (65 heat-capacity data for nine ILs). The results demonstrate that the chosen network and the variables considered allow estimating the heat capacity of ILs with acceptable accuracy for engineering calculations. The program codes and the necessary input files to calculate the mass connectivity index and the heat capacity for other ILs are provided. © Springer Science+Business Media, LLC 2011.

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