Hugo Segura | Universidad de Concepción (original) (raw)
Papers by Hugo Segura
Chemical Engineering Science, 2000
Chemical Engineering Science, 2003
Industrial & Engineering Chemistry Research, 2003
Empirical thermal cohesion functions, α(T r ), are frequently used in conventional equations of s... more Empirical thermal cohesion functions, α(T r ), are frequently used in conventional equations of state (EOS) for fitting the vapor pressures of pure fluids. Accurate vapor pressure predictions are required for correlating ...
Fluid Phase Equilibria, 1998
The correlation of experimental data of solubility of solids in supercritical solvents using equa... more The correlation of experimental data of solubility of solids in supercritical solvents using equations of state Ž . Ž EOS is a well known and relatively simple approach. Normally, cubic EOS with quadratic mixing rules or . modifications of them may be satisfactorily used for fitting purposes and much research is being done in order to improve the predictive capabilities of present models. Usually, models are assessed in terms of goodness of fit of solubility data; however, in spite of the pressure and temperature conditions of supercritical extraction processes, the critical behavior predicted by models used for correlating data is rarely analyzed. In this work, the analysis of critical lines in the presence of solid-fluid equilibria is proposed as an additional test of models because it gives the correct topology of predicted phase diagrams. It is shown that multiphase equilibria is normally predicted in ranges of interest for supercritical extraction. Multiphase equilibria is not obvious when a stability analysis is ignored, inducing possible modeling pitfalls. In addition, multiphase behavior affects the prediction of stable solid-fluid equilibria. Examples and phase diagrams are discussed in detail using a modified van der Waals EOS and quadratic mixing rules. q
Journal of Chemical and Engineering Data, 1996
Polyazeotropy in binary systems is a singular case of vapor−liquid equilibrium (VLE) where, at a ... more Polyazeotropy in binary systems is a singular case of vapor−liquid equilibrium (VLE) where, at a given pressure or temperature, various azeotropes of alternating deviations from ideality are observed. Multiple azeotropy can ...
Physics and Chemistry of Liquids, 1995
The capability of the Wohl model for describing liquid-liquid equilibrium is discussed and criter... more The capability of the Wohl model for describing liquid-liquid equilibrium is discussed and criteria for incipient phase instability are determined. A new method is proposed for calculating the activity coefficients at infinite dilution.
Chemical Engineering Science, 2001
In the present study we present the ÿnal development of the Global Phase Diagram-based semi-predi... more In the present study we present the ÿnal development of the Global Phase Diagram-based semi-predictive approach (GPDA), which requires only 2-3 key data points of one homologue to predict the complete phase behavior of the whole homologues series. The ability of GPDA to predict phase equilibria in CO2-heavy n-alkanes is compared with the equations of state LCVM and PSRK. It is demonstrated that both LCVM and PSRK are more correlative rather than predictive because their parameters are evaluated by the local ÿt of a considerable amount of VLE experimental data. In addition, these models fail to predict accurately the VLE of systems, which have not been considered in the evaluation of their parameters. They are also particularly inaccurate in predicting LLE and critical lines. In contrast, GPDA is reliable in the entire temperature range and for all types of phase equilibria. It yields an accurate prediction of the global phase behavior in the homologues series and their critical lines. Moreover, increasing asymmetry does not a ect the reliability of GPDA; it predicts very accurately even the data of the heaviest homologues of the series. ?
Industrial & Engineering Chemistry Research, 1996
Polyazeotropy in binary systems is a singular case of vapor−liquid equilibrium where at a given t... more Polyazeotropy in binary systems is a singular case of vapor−liquid equilibrium where at a given temperature or pressure various azeotropes of alternating deviations from ideality are observed. These deviations are generally ...
Journal of Chemical and Engineering Data, 1997
Vapor−liquid equilibrium at 94 kPa has been determined for the binary systems methyl 1,1-dimethyl... more Vapor−liquid equilibrium at 94 kPa has been determined for the binary systems methyl 1,1-dimethylethyl ether (MTBE) + octane and heptane + octane. Both binary systems deviate slightly from ideal behavior, and neither system presents ...
Journal of Chemical and Engineering Data, 2001
Vapor−liquid equilibrium at 94 kPa has been determined for the binary systems methyl 1,1-dimethyl... more Vapor−liquid equilibrium at 94 kPa has been determined for the binary systems methyl 1,1-dimethylethyl ether (MTBE) + octane and heptane + octane. Both binary systems deviate slightly from ideal behavior, and neither system presents ...
Physical Chemistry Chemical Physics, 1999
Phase diagrams predicted by the RedlichÈKwong equation of state (EOS) and classical mixing rules ... more Phase diagrams predicted by the RedlichÈKwong equation of state (EOS) and classical mixing rules are discussed at the transitional states between di †erent types of phase behavior. Mixtures containing molecules of di †erent sizes have been considered in the analysis. Zero-and inÐnite-pressure reference states for the estimation of the Gibbs energy of mixing are presented. These reference states constitute hypothetical states that have been found valuable for analyzing the key features of critical lines ending at these limiting conditions. An expression for predicting the possibility of critical immiscibility at inÐnite pressure was developed. This expression can be useful for determination of the existence of liquidÈliquid critical lines in binary systems and may be applied to every cubic EOS of van der Waals type when classical mixing rules are used. The zero-pressure approach was used for analyzing the existence of the critical lines that intersect the zero-pressure line in a PÈT projection. Special attention has been given to the possibility of predicting closed loops of liquidÈliquid immiscibility. Closed loops were detected at the transition from Type V to Type III, but they do not correspond to the traditional topology observed in systems of Type VI and VII. The relation of the calculated diagrams to the systems with real pure component critical properties showing closed loops of liquidÈliquid immiscibility is also discussed.
Fuel and Energy Abstracts, 1999
A shortcut method is developed to determine if an equation of state (EOS) is capable of predictin... more A shortcut method is developed to determine if an equation of state (EOS) is capable of predicting azeotropes in binary systems and if the azeotrope meets the critical gas-liquid equilibrium line. The method suggested allows an a ...
Fluid Phase Equilibria, 1999
Vapor-liquid equilibrium at 94 kPa has been determined for the ternary system ethyl 1,1-dimethyle... more Vapor-liquid equilibrium at 94 kPa has been determined for the ternary system ethyl 1,1-dimethylethyl ether Ž . ETBE q heptaneq octane. The system deviates slightly from ideality and no azeotrope is present. The ternary activity coefficients and the boiling points of the system have been correlated with the composition using the Redlich-Kister, Wilson, NRTL, UNIQUAC, UNIFAC, and Wisniak-Tamir relations. Most of the models allow a very good prediction of the activity coefficients of the ternary system from those of the pertinent binary systems. q
Chemical Engineering Science, 1998
A simplified technique is proposed for the application of cubic equations of state (EOS) to the c... more A simplified technique is proposed for the application of cubic equations of state (EOS) to the calculation of vapor pressures of pure compounds and the method can be adapted to any EOS capable of predicting coexisting vapor and ...
Physics and Chemistry of Liquids, 1999
P hp Chem. Liq., 1999, Vol. 37, pp. 649-660 Reprints available directly from the publisher Photoc... more P hp Chem. Liq., 1999, Vol. 37, pp. 649-660 Reprints available directly from the publisher Photocopying permitted by license only 1999 OPA (Overseas Publishers Association) NV Published by license under the Gordon and Breach Science ...
Industrial & Engineering Chemistry Research, 1996
Polyazeotropy in binary systems is a very singular case of vapor-liquid equilibrium (VLE), and it... more Polyazeotropy in binary systems is a very singular case of vapor-liquid equilibrium (VLE), and its causes have not been studied in detail. The unique evidence about the phenomenon is the experimental VLE results for the benzene-hexafluorobenzene system, which exhibits two simultaneous azeotropes. The purpose of this work is to make a thermodynamical analysis of polyazeotropy at low pressures and to establish the necessary and sufficient conditions that provoke it. The evolution of polyazeotropes with temperature and pressure is explained, and the criteria to predict azeotropic behavior from minimal information are developed. This study also delivers some important results about the possibility of predicting polyazeotropy using classical G E models and about estimation of the parameters for excess energy models from activity coefficients at infinite dilution, in particular, when this procedure generates changes of concavity for the G E function. IE960054A X Abstract published in Advance ACS Abstracts, August 15, 1996.
Journal of Chemical and Engineering Data, 1997
Vapor−liquid equilibrium at 94 kPa has been determined for the binary systems methyl 1,1-dimethyl... more Vapor−liquid equilibrium at 94 kPa has been determined for the binary systems methyl 1,1-dimethylethyl ether (MTBE) + octane and heptane + octane. Both binary systems deviate slightly from ideal behavior, and neither system presents ...
International Journal of Thermophysics, 2004
Type IV mixtures exhibit two heteroazeotropic lines, one at low temperature and the other meeting... more Type IV mixtures exhibit two heteroazeotropic lines, one at low temperature and the other meeting the supercritical range, characterized by the proximity of their critical end points (CEPs). Between these CEPs, the liquid phase is homogeneous inside a narrow range of temperature. The aim of this work is to analyze interface properties and wetting transitions for Type IV mixtures. Interfacial tensions have been calculated by means of the gradient theory, applied to binary van der Waals fluids. This approach is able to predict interfacial tension and phase equilibrium using a common equation of state (EOS). Results show that interfacial properties and wetting conditions are governed by the densities and the number of phases involved in equilibrium, a scenario that changes as temperature evolves from the low- to the high-temperature heteroazeotropic line.
Canadian Journal of Chemical Engineering, 2008
Modern semi-empirical cubic EOSs are usually attached by complex functionalities, such as Huron-V... more Modern semi-empirical cubic EOSs are usually attached by complex functionalities, such as Huron-Vidal (HV)-type mixing rules. Although this practice improves the flexibility of the models, it also complicates consideration of an overall picture of phase behavior. As a result, GE-based equations are usually adjusted to the experimental data by way of a local fit. The latter approach tends to ignore that different regions of the thermodynamic phase space are closely inter-related. The present study demonstrates that the contribution of (HV)-type mixing rules to predicting high-pressure phase equilibria can be quite modest and that in addition they may generate non-realistic phase diagrams.Les équations d'état (EOS) cubiques semi-empiriques modernes s'accompagnent habituellement de fonctionnalités complexes, telles que les règles de mélange de type Huron-Vidal (HV). Bien que cette pratique améliore la flexibilité des modèles, elle complique aussi la prise en compte globale du comportement des phases. En conséquence, les équations basées sur GE sont généralement ajustées aux données expérimentales au moyen d'un calage local. Cette dernière approche tend à ignorer que les différentes régions de l'espace de phase thermodynamique sont étroitement intereliées. La présente étude montre que la contribution des règles de mélange de type HV pour prédire les équilibres de phases à haute pression peut être assez modeste et qu'en outre elles peuvent produire des diagrammes de phases non réalistes.
Industrial & Engineering Chemistry Research, 2004
Subscriber access provided by American Chemical Society. ACS; Journals; C&EN; CAS. ACS Public... more Subscriber access provided by American Chemical Society. ACS; Journals; C&EN; CAS. ACS Publications. Journals A–Z Books|Authors & Reviewers|Librarians|ACS Members|About Us|e-Alerts|Help. Quick Search. Advanced Search. Ind. Eng. Chem. Res. ...
Chemical Engineering Science, 2000
Chemical Engineering Science, 2003
Industrial & Engineering Chemistry Research, 2003
Empirical thermal cohesion functions, α(T r ), are frequently used in conventional equations of s... more Empirical thermal cohesion functions, α(T r ), are frequently used in conventional equations of state (EOS) for fitting the vapor pressures of pure fluids. Accurate vapor pressure predictions are required for correlating ...
Fluid Phase Equilibria, 1998
The correlation of experimental data of solubility of solids in supercritical solvents using equa... more The correlation of experimental data of solubility of solids in supercritical solvents using equations of state Ž . Ž EOS is a well known and relatively simple approach. Normally, cubic EOS with quadratic mixing rules or . modifications of them may be satisfactorily used for fitting purposes and much research is being done in order to improve the predictive capabilities of present models. Usually, models are assessed in terms of goodness of fit of solubility data; however, in spite of the pressure and temperature conditions of supercritical extraction processes, the critical behavior predicted by models used for correlating data is rarely analyzed. In this work, the analysis of critical lines in the presence of solid-fluid equilibria is proposed as an additional test of models because it gives the correct topology of predicted phase diagrams. It is shown that multiphase equilibria is normally predicted in ranges of interest for supercritical extraction. Multiphase equilibria is not obvious when a stability analysis is ignored, inducing possible modeling pitfalls. In addition, multiphase behavior affects the prediction of stable solid-fluid equilibria. Examples and phase diagrams are discussed in detail using a modified van der Waals EOS and quadratic mixing rules. q
Journal of Chemical and Engineering Data, 1996
Polyazeotropy in binary systems is a singular case of vapor−liquid equilibrium (VLE) where, at a ... more Polyazeotropy in binary systems is a singular case of vapor−liquid equilibrium (VLE) where, at a given pressure or temperature, various azeotropes of alternating deviations from ideality are observed. Multiple azeotropy can ...
Physics and Chemistry of Liquids, 1995
The capability of the Wohl model for describing liquid-liquid equilibrium is discussed and criter... more The capability of the Wohl model for describing liquid-liquid equilibrium is discussed and criteria for incipient phase instability are determined. A new method is proposed for calculating the activity coefficients at infinite dilution.
Chemical Engineering Science, 2001
In the present study we present the ÿnal development of the Global Phase Diagram-based semi-predi... more In the present study we present the ÿnal development of the Global Phase Diagram-based semi-predictive approach (GPDA), which requires only 2-3 key data points of one homologue to predict the complete phase behavior of the whole homologues series. The ability of GPDA to predict phase equilibria in CO2-heavy n-alkanes is compared with the equations of state LCVM and PSRK. It is demonstrated that both LCVM and PSRK are more correlative rather than predictive because their parameters are evaluated by the local ÿt of a considerable amount of VLE experimental data. In addition, these models fail to predict accurately the VLE of systems, which have not been considered in the evaluation of their parameters. They are also particularly inaccurate in predicting LLE and critical lines. In contrast, GPDA is reliable in the entire temperature range and for all types of phase equilibria. It yields an accurate prediction of the global phase behavior in the homologues series and their critical lines. Moreover, increasing asymmetry does not a ect the reliability of GPDA; it predicts very accurately even the data of the heaviest homologues of the series. ?
Industrial & Engineering Chemistry Research, 1996
Polyazeotropy in binary systems is a singular case of vapor−liquid equilibrium where at a given t... more Polyazeotropy in binary systems is a singular case of vapor−liquid equilibrium where at a given temperature or pressure various azeotropes of alternating deviations from ideality are observed. These deviations are generally ...
Journal of Chemical and Engineering Data, 1997
Vapor−liquid equilibrium at 94 kPa has been determined for the binary systems methyl 1,1-dimethyl... more Vapor−liquid equilibrium at 94 kPa has been determined for the binary systems methyl 1,1-dimethylethyl ether (MTBE) + octane and heptane + octane. Both binary systems deviate slightly from ideal behavior, and neither system presents ...
Journal of Chemical and Engineering Data, 2001
Vapor−liquid equilibrium at 94 kPa has been determined for the binary systems methyl 1,1-dimethyl... more Vapor−liquid equilibrium at 94 kPa has been determined for the binary systems methyl 1,1-dimethylethyl ether (MTBE) + octane and heptane + octane. Both binary systems deviate slightly from ideal behavior, and neither system presents ...
Physical Chemistry Chemical Physics, 1999
Phase diagrams predicted by the RedlichÈKwong equation of state (EOS) and classical mixing rules ... more Phase diagrams predicted by the RedlichÈKwong equation of state (EOS) and classical mixing rules are discussed at the transitional states between di †erent types of phase behavior. Mixtures containing molecules of di †erent sizes have been considered in the analysis. Zero-and inÐnite-pressure reference states for the estimation of the Gibbs energy of mixing are presented. These reference states constitute hypothetical states that have been found valuable for analyzing the key features of critical lines ending at these limiting conditions. An expression for predicting the possibility of critical immiscibility at inÐnite pressure was developed. This expression can be useful for determination of the existence of liquidÈliquid critical lines in binary systems and may be applied to every cubic EOS of van der Waals type when classical mixing rules are used. The zero-pressure approach was used for analyzing the existence of the critical lines that intersect the zero-pressure line in a PÈT projection. Special attention has been given to the possibility of predicting closed loops of liquidÈliquid immiscibility. Closed loops were detected at the transition from Type V to Type III, but they do not correspond to the traditional topology observed in systems of Type VI and VII. The relation of the calculated diagrams to the systems with real pure component critical properties showing closed loops of liquidÈliquid immiscibility is also discussed.
Fuel and Energy Abstracts, 1999
A shortcut method is developed to determine if an equation of state (EOS) is capable of predictin... more A shortcut method is developed to determine if an equation of state (EOS) is capable of predicting azeotropes in binary systems and if the azeotrope meets the critical gas-liquid equilibrium line. The method suggested allows an a ...
Fluid Phase Equilibria, 1999
Vapor-liquid equilibrium at 94 kPa has been determined for the ternary system ethyl 1,1-dimethyle... more Vapor-liquid equilibrium at 94 kPa has been determined for the ternary system ethyl 1,1-dimethylethyl ether Ž . ETBE q heptaneq octane. The system deviates slightly from ideality and no azeotrope is present. The ternary activity coefficients and the boiling points of the system have been correlated with the composition using the Redlich-Kister, Wilson, NRTL, UNIQUAC, UNIFAC, and Wisniak-Tamir relations. Most of the models allow a very good prediction of the activity coefficients of the ternary system from those of the pertinent binary systems. q
Chemical Engineering Science, 1998
A simplified technique is proposed for the application of cubic equations of state (EOS) to the c... more A simplified technique is proposed for the application of cubic equations of state (EOS) to the calculation of vapor pressures of pure compounds and the method can be adapted to any EOS capable of predicting coexisting vapor and ...
Physics and Chemistry of Liquids, 1999
P hp Chem. Liq., 1999, Vol. 37, pp. 649-660 Reprints available directly from the publisher Photoc... more P hp Chem. Liq., 1999, Vol. 37, pp. 649-660 Reprints available directly from the publisher Photocopying permitted by license only 1999 OPA (Overseas Publishers Association) NV Published by license under the Gordon and Breach Science ...
Industrial & Engineering Chemistry Research, 1996
Polyazeotropy in binary systems is a very singular case of vapor-liquid equilibrium (VLE), and it... more Polyazeotropy in binary systems is a very singular case of vapor-liquid equilibrium (VLE), and its causes have not been studied in detail. The unique evidence about the phenomenon is the experimental VLE results for the benzene-hexafluorobenzene system, which exhibits two simultaneous azeotropes. The purpose of this work is to make a thermodynamical analysis of polyazeotropy at low pressures and to establish the necessary and sufficient conditions that provoke it. The evolution of polyazeotropes with temperature and pressure is explained, and the criteria to predict azeotropic behavior from minimal information are developed. This study also delivers some important results about the possibility of predicting polyazeotropy using classical G E models and about estimation of the parameters for excess energy models from activity coefficients at infinite dilution, in particular, when this procedure generates changes of concavity for the G E function. IE960054A X Abstract published in Advance ACS Abstracts, August 15, 1996.
Journal of Chemical and Engineering Data, 1997
Vapor−liquid equilibrium at 94 kPa has been determined for the binary systems methyl 1,1-dimethyl... more Vapor−liquid equilibrium at 94 kPa has been determined for the binary systems methyl 1,1-dimethylethyl ether (MTBE) + octane and heptane + octane. Both binary systems deviate slightly from ideal behavior, and neither system presents ...
International Journal of Thermophysics, 2004
Type IV mixtures exhibit two heteroazeotropic lines, one at low temperature and the other meeting... more Type IV mixtures exhibit two heteroazeotropic lines, one at low temperature and the other meeting the supercritical range, characterized by the proximity of their critical end points (CEPs). Between these CEPs, the liquid phase is homogeneous inside a narrow range of temperature. The aim of this work is to analyze interface properties and wetting transitions for Type IV mixtures. Interfacial tensions have been calculated by means of the gradient theory, applied to binary van der Waals fluids. This approach is able to predict interfacial tension and phase equilibrium using a common equation of state (EOS). Results show that interfacial properties and wetting conditions are governed by the densities and the number of phases involved in equilibrium, a scenario that changes as temperature evolves from the low- to the high-temperature heteroazeotropic line.
Canadian Journal of Chemical Engineering, 2008
Modern semi-empirical cubic EOSs are usually attached by complex functionalities, such as Huron-V... more Modern semi-empirical cubic EOSs are usually attached by complex functionalities, such as Huron-Vidal (HV)-type mixing rules. Although this practice improves the flexibility of the models, it also complicates consideration of an overall picture of phase behavior. As a result, GE-based equations are usually adjusted to the experimental data by way of a local fit. The latter approach tends to ignore that different regions of the thermodynamic phase space are closely inter-related. The present study demonstrates that the contribution of (HV)-type mixing rules to predicting high-pressure phase equilibria can be quite modest and that in addition they may generate non-realistic phase diagrams.Les équations d'état (EOS) cubiques semi-empiriques modernes s'accompagnent habituellement de fonctionnalités complexes, telles que les règles de mélange de type Huron-Vidal (HV). Bien que cette pratique améliore la flexibilité des modèles, elle complique aussi la prise en compte globale du comportement des phases. En conséquence, les équations basées sur GE sont généralement ajustées aux données expérimentales au moyen d'un calage local. Cette dernière approche tend à ignorer que les différentes régions de l'espace de phase thermodynamique sont étroitement intereliées. La présente étude montre que la contribution des règles de mélange de type HV pour prédire les équilibres de phases à haute pression peut être assez modeste et qu'en outre elles peuvent produire des diagrammes de phases non réalistes.
Industrial & Engineering Chemistry Research, 2004
Subscriber access provided by American Chemical Society. ACS; Journals; C&EN; CAS. ACS Public... more Subscriber access provided by American Chemical Society. ACS; Journals; C&EN; CAS. ACS Publications. Journals A–Z Books|Authors & Reviewers|Librarians|ACS Members|About Us|e-Alerts|Help. Quick Search. Advanced Search. Ind. Eng. Chem. Res. ...