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Multicomponent maxwell−stefan diffusivities at infinite dilution / Xin Liu in Industrial & engineering chemistry research, Vol. 50 N° 8 (Avril 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 8 (Avril 2011) . - pp. 4776–4782 Titre : Multicomponent maxwell−stefan diffusivities at infinite dilution Type de document : texte imprimé Auteurs : Xin Liu, Auteur ; Andre Bardow, Auteur ; Thijs J.H. Vlugt, Auteur Année de publication : 2011 Article en page(s) : pp. 4776–4782 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Chemical  processes Résumé : Diffusion plays an important role in (bio)chemical processes. It is usually difficult to obtain Maxwell−Stefan diffusivities from experiments as well as molecular simulation. Therefore, predictive models based on easily measurable quantities are highly desired. The Vignes equation is commonly used to describe the concentration dependence of Maxwell−Stefan diffusivities. In mixtures containing at least three components, the generalized Vignes equation requires the value of the quantity Đijxk→1, which describes the friction between components i and j when both are infinitely diluted in component k. Over the past decades, several empirical models were proposed for estimating Đijxk→1, and all of these are lacking a sound theoretical basis. In this study, we show that Đijxk→1 actually exists (i.e., its value does not depend on the molar ratio xi/xj), and we derive an analytical expression for Đijxk→1 that is based on the linear response theory and the Onsager relations. We find that Đijxk→1 can be expressed in terms of binary and pure-component self-diffusivities and integrals over velocity cross-correlation functions. By neglecting the latter terms, we obtain a convenient predictive model for Đijxk→1. Molecular dynamics simulations are used to validate the assumptions made in this model. The following test systems are considered: a ternary system consisting of particles interacting using Weeks−Chandler−Andersen (WCA) interactions and the ternary systems n-hexane−cyclohexane−toluene and ethanol−methanol−water. Our results show that (1) for the WCA system, as well as the n-hexane−cyclohexane−toluene system, neglecting the integrals over velocity cross-correlation functions results in accurate predictions for Đijxk→1; (2) for the WCA system, our model prediction is superior, compared to the existing models for Đijxk→1; (3) in the ethanol−methanol−water system, the integrals over velocity cross-correlation functions cannot be neglected, because of the presence of hydrogen bonds (models for predicting Đijxk→1 in this system will require detailed information on the collective motion of molecules); and (4) our model may provide an explanation why the Maxwell−Stefan diffusivity describing the friction between adsorbed components in a porous material is usually very large. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie102515w [article] Multicomponent maxwell−stefan diffusivities at infinite dilution [texte imprimé] / Xin Liu, Auteur ; Andre Bardow, Auteur ; Thijs J.H. Vlugt, Auteur . - 2011 . - pp. 4776–4782. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 8 (Avril 2011) . - pp. 4776–4782 Mots-clés : Chemical  processes Résumé : Diffusion plays an important role in (bio)chemical processes. It is usually difficult to obtain Maxwell−Stefan diffusivities from experiments as well as molecular simulation. Therefore, predictive models based on easily measurable quantities are highly desired. The Vignes equation is commonly used to describe the concentration dependence of Maxwell−Stefan diffusivities. In mixtures containing at least three components, the generalized Vignes equation requires the value of the quantity Đijxk→1, which describes the friction between components i and j when both are infinitely diluted in component k. Over the past decades, several empirical models were proposed for estimating Đijxk→1, and all of these are lacking a sound theoretical basis. In this study, we show that Đijxk→1 actually exists (i.e., its value does not depend on the molar ratio xi/xj), and we derive an analytical expression for Đijxk→1 that is based on the linear response theory and the Onsager relations. We find that Đijxk→1 can be expressed in terms of binary and pure-component self-diffusivities and integrals over velocity cross-correlation functions. By neglecting the latter terms, we obtain a convenient predictive model for Đijxk→1. Molecular dynamics simulations are used to validate the assumptions made in this model. The following test systems are considered: a ternary system consisting of particles interacting using Weeks−Chandler−Andersen (WCA) interactions and the ternary systems n-hexane−cyclohexane−toluene and ethanol−methanol−water. Our results show that (1) for the WCA system, as well as the n-hexane−cyclohexane−toluene system, neglecting the integrals over velocity cross-correlation functions results in accurate predictions for Đijxk→1; (2) for the WCA system, our model prediction is superior, compared to the existing models for Đijxk→1; (3) in the ethanol−methanol−water system, the integrals over velocity cross-correlation functions cannot be neglected, because of the presence of hydrogen bonds (models for predicting Đijxk→1 in this system will require detailed information on the collective motion of molecules); and (4) our model may provide an explanation why the Maxwell−Stefan diffusivity describing the friction between adsorbed components in a porous material is usually very large. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie102515w

Potential desorbents for propane/propylene separation by gas phase simulated moving bed / Miguel A. Granato in Industrial & engineering chemistry research, Vol. 49 N° 12 (Juin 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 12 (Juin 2010) . - pp. 5826–5833 Titre : Potential desorbents for propane/propylene separation by gas phase simulated moving bed : a molecular simulation study Type de document : texte imprimé Auteurs : Miguel A. Granato, Auteur ; Thijs J.H. Vlugt, Auteur ; Alirio E. Rodrigues, Auteur Année de publication : 2010 Article en page(s) : pp. 5826–5833 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Separation  propane/propylene  Simulated  moving  bed  process  Equilibrium  adsorption  isotherms  n-butane  Neopentane  on  zeolite  13X  Binary  mixtures Résumé : This paper is focused on using molecular simulation as a tool to guide the choice of desorbent for the separation propane/propylene by simulated moving bed (SMB) processes. Equilibrium adsorption isotherms of n-butane and neopentane on zeolite 13X and adsorption equilibria of binary mixtures of each one of these adsorbates with propane and with propylene were obtained by molecular simulation, in a predictive screening of an adequate desorbent for the separation of propane/propylene by the SMB technology. Comparisons of experimental isotherms with grand canonical Monte Carlo simulations in zeolite 13X showed that the results of n-butane are in excellent agreement with reported simulations and experimental data. The carbon−cation interactions for the quaternary carbon atom of neopentane were established and validated through determination of adsorption properties of binary mixtures of neopentane with propane and with propylene. The lack of experimental data of neopentane adsorption motivated the present study, providing the opportunity to predict the single adsorption isotherms over a temperature range from 273 to 423 K and pressures up to 150 kPa. From the simulated isotherms of neopentane in 13X zeolite, the isosteric heat of adsorption of 39.19 kJ/mol was calculated by using the Clausius−Clapeyron equation, in close agreement with the published value of 41.7 kJ/mol. Additionally, the simulation results of the binary mixtures with propane and with propylene showed that neopentane and propane have similar affinities to the adsorbent, which indicates a less favorable desorption effect for neopentane, compared with that of n-butane. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie901732s [article] Potential desorbents for propane/propylene separation by gas phase simulated moving bed : a molecular simulation study [texte imprimé] / Miguel A. Granato, Auteur ; Thijs J.H. Vlugt, Auteur ; Alirio E. Rodrigues, Auteur . - 2010 . - pp. 5826–5833. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 12 (Juin 2010) . - pp. 5826–5833 Mots-clés : Separation  propane/propylene  Simulated  moving  bed  process  Equilibrium  adsorption  isotherms  n-butane  Neopentane  on  zeolite  13X  Binary  mixtures Résumé : This paper is focused on using molecular simulation as a tool to guide the choice of desorbent for the separation propane/propylene by simulated moving bed (SMB) processes. Equilibrium adsorption isotherms of n-butane and neopentane on zeolite 13X and adsorption equilibria of binary mixtures of each one of these adsorbates with propane and with propylene were obtained by molecular simulation, in a predictive screening of an adequate desorbent for the separation of propane/propylene by the SMB technology. Comparisons of experimental isotherms with grand canonical Monte Carlo simulations in zeolite 13X showed that the results of n-butane are in excellent agreement with reported simulations and experimental data. The carbon−cation interactions for the quaternary carbon atom of neopentane were established and validated through determination of adsorption properties of binary mixtures of neopentane with propane and with propylene. The lack of experimental data of neopentane adsorption motivated the present study, providing the opportunity to predict the single adsorption isotherms over a temperature range from 273 to 423 K and pressures up to 150 kPa. From the simulated isotherms of neopentane in 13X zeolite, the isosteric heat of adsorption of 39.19 kJ/mol was calculated by using the Clausius−Clapeyron equation, in close agreement with the published value of 41.7 kJ/mol. Additionally, the simulation results of the binary mixtures with propane and with propylene showed that neopentane and propane have similar affinities to the adsorbent, which indicates a less favorable desorption effect for neopentane, compared with that of n-butane. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie901732s

Predictive darken equation for maxwell-stefan diffusivities in multicomponent mixtures / Xin Liu in Industrial & engineering chemistry research, Vol. 50 N° 17 (Septembre 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 17 (Septembre 2011) . - pp. 10350-10358 Titre : Predictive darken equation for maxwell-stefan diffusivities in multicomponent mixtures Type de document : texte imprimé Auteurs : Xin Liu, Auteur ; Thijs J.H. Vlugt, Auteur ; Andre Bardow, Auteur Année de publication : 2011 Article en page(s) : pp. 10350-10358 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Multicomponent  mixture  Diffusion  coefficient Résumé : This Article presents the derivation and validation of a rigorous model for the prediction of multicomponent Maxwell-Stefan (MS) diffusion coefficients. The MS theory provides a sound framework for modeling mass transport in gases and liquids. Unfortunately, MS diffusivities are concentration dependent, and this needs to be taken into account in practical applications. There is therefore a considerable interest in models describing the concentration dependence ofMS diffusivities. While current practice employs empirical models for this purpose, recent work on molecular simulations favor the physically based Darken equation. The Darken equation, however, is limited to binary mixtures and is not predictive. In this study, a multicomponent Darken model for MS diffusivities is derived from linear response theory and the Onsager relations. In addition, a predictive model for the required self-diffusivities in the mixture is proposed, leading to the predictive Darken-LBV model. We compare our novel model to the existing generalized Vignes equation and the generalized Darken equation using molecular dynamics (MD) simulation. Two systems are considered: (1) ternary and quaternary systems in which particles are interacting using the Weeks-Chandler-Andersen (WCA) potential; (2) the ternary system n-hexane-cyclohexane-toluene. Our results show that, in all studied systems, the novel predictive Darken-LBV equation describes the concentration dependence better than the existing models. The physically based Darken-LBV model provides a sound and robust framework for prediction ofMS diffusion coefficients in multicomponent mixtures. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24483681 [article] Predictive darken equation for maxwell-stefan diffusivities in multicomponent mixtures [texte imprimé] / Xin Liu, Auteur ; Thijs J.H. Vlugt, Auteur ; Andre Bardow, Auteur . - 2011 . - pp. 10350-10358. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 17 (Septembre 2011) . - pp. 10350-10358 Mots-clés : Multicomponent  mixture  Diffusion  coefficient Résumé : This Article presents the derivation and validation of a rigorous model for the prediction of multicomponent Maxwell-Stefan (MS) diffusion coefficients. The MS theory provides a sound framework for modeling mass transport in gases and liquids. Unfortunately, MS diffusivities are concentration dependent, and this needs to be taken into account in practical applications. There is therefore a considerable interest in models describing the concentration dependence ofMS diffusivities. While current practice employs empirical models for this purpose, recent work on molecular simulations favor the physically based Darken equation. The Darken equation, however, is limited to binary mixtures and is not predictive. In this study, a multicomponent Darken model for MS diffusivities is derived from linear response theory and the Onsager relations. In addition, a predictive model for the required self-diffusivities in the mixture is proposed, leading to the predictive Darken-LBV model. We compare our novel model to the existing generalized Vignes equation and the generalized Darken equation using molecular dynamics (MD) simulation. Two systems are considered: (1) ternary and quaternary systems in which particles are interacting using the Weeks-Chandler-Andersen (WCA) potential; (2) the ternary system n-hexane-cyclohexane-toluene. Our results show that, in all studied systems, the novel predictive Darken-LBV equation describes the concentration dependence better than the existing models. The physically based Darken-LBV model provides a sound and robust framework for prediction ofMS diffusion coefficients in multicomponent mixtures. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24483681

State - of - the - art of CO2 capture with ionic liquids / Mahinder Ramdin in Industrial & engineering chemistry research, Vol. 51 N° 24 (Juin 2012) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 51 N° 24 (Juin 2012) . - pp. 8149–8177 Titre : State - of - the - art of CO2 capture with ionic liquids Type de document : texte imprimé Auteurs : Mahinder Ramdin, Auteur ; Theo W. de Loos, Auteur ; Thijs J.H. Vlugt, Auteur Année de publication : 2012 Article en page(s) : pp. 8149–8177 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Ionic  liquids Résumé : Economical and environmental aspects are the main motivation for research on energy efficient processes and the search for environment friendly materials for CO2 capture. Currently, CO2 capture is dominated by amine-based (e.g., monoethanolamine) technologies, which are very energy intensive and less attractive from an environmental point of view due to emissions of the used volatile solvent components. Ionic liquids have been proposed as a promising alternative to the conventional volatile solvents, because of their low volatility and other interesting properties. This remarkable interest has led to a rapid growth of literature on this specific subject. The aim of the present review paper is to provide a detailed overview of the achievements and difficulties that has been encountered in finding a suitable ionic liquid for CO2 capture from flue-gas streams. A major part of this review includes an overview of the experimental data of CO2 solubility, selectivity, and diffusivity in different ionic liquids. The effect of anions, cations, and functional groups on the CO2 solubility, biodegradability, and toxicity of the ionic liquids are highlighted. Recent developments on task-specific ionic liquids and supported ionic liquid membranes are also discussed. Scarcely available results of molecular simulations, which is a valuable tool in designing and evaluating ionic liquids, are also reviewed. The trends highlighted here can be used by solvent designers to navigate through the massive amount of theoretically possible ILs. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie3003705 [article] State - of - the - art of CO2 capture with ionic liquids [texte imprimé] / Mahinder Ramdin, Auteur ; Theo W. de Loos, Auteur ; Thijs J.H. Vlugt, Auteur . - 2012 . - pp. 8149–8177. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 51 N° 24 (Juin 2012) . - pp. 8149–8177 Mots-clés : Ionic  liquids Résumé : Economical and environmental aspects are the main motivation for research on energy efficient processes and the search for environment friendly materials for CO2 capture. Currently, CO2 capture is dominated by amine-based (e.g., monoethanolamine) technologies, which are very energy intensive and less attractive from an environmental point of view due to emissions of the used volatile solvent components. Ionic liquids have been proposed as a promising alternative to the conventional volatile solvents, because of their low volatility and other interesting properties. This remarkable interest has led to a rapid growth of literature on this specific subject. The aim of the present review paper is to provide a detailed overview of the achievements and difficulties that has been encountered in finding a suitable ionic liquid for CO2 capture from flue-gas streams. A major part of this review includes an overview of the experimental data of CO2 solubility, selectivity, and diffusivity in different ionic liquids. The effect of anions, cations, and functional groups on the CO2 solubility, biodegradability, and toxicity of the ionic liquids are highlighted. Recent developments on task-specific ionic liquids and supported ionic liquid membranes are also discussed. Scarcely available results of molecular simulations, which is a valuable tool in designing and evaluating ionic liquids, are also reviewed. The trends highlighted here can be used by solvent designers to navigate through the massive amount of theoretically possible ILs. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie3003705