Documents disponibles écrits par cet auteur

Experimental errors in kinetic tests and its influence on the precision of estimated parameters. Part I, Analysis of first-order reactions / André L. Alberton in Chemical engineering journal, Vol. 155 N° 3 (Decembre 2009) 

Public ISBD [article]  in Chemical engineering journal > Vol. 155 N° 3 (Decembre 2009) . - pp. 816-823 Titre : Experimental errors in kinetic tests and its influence on the precision of estimated parameters. Part I, Analysis of first-order reactions Type de document : texte imprimé Auteurs : André L. Alberton, Auteur ; Marcio Schwaab, Auteur ; Martin Schmal, Auteur Année de publication : 2010 Article en page(s) : pp. 816-823 Note générale : Génie Chimique Langues : Anglais (eng) Mots-clés : Experimental  error  Kinetic  analysis  First-order  reaction  Precise  parameter  estimation Index. décimale : 660 Résumé : The proper characterization of the experimental errors is essential for the correct evaluation of estimated model parameters, model fit and model predictions based on kinetic rate expressions. However, it is common to ignore the influence of experimental errors during kinetic studies due to difficulties to characterize how experimental errors depend on the reaction conditions. The behavior of experimental error depends on the specific features of the experimental system; however, in many cases the main sources of experimental errors are the unavoidable oscillations of the input variables. This work analyzes how the experimental errors affect kinetic studies based on catalytic tests when oscillations of the input variables are the main sources of uncertainties. The first part of this work assumes that the reaction rate can be described accurately as a first-order reaction in a PFR. Analytical expressions are derived for the variance of the reactant conversion in distinct scenarios and are used to analyze the quality of the obtained parameter estimates. It is shown here that the conversion variances can be described as functions of the measured conversion values, normally presenting a point of maximum for conversion values in the range of 0.6 < X < 1.0 when observed experimental fluctuations are controlled by the fluctuations of the input variables. Constant conversion variances should be expected only when fluctuations are controlled by analytical conversion measurements. As a consequence, optimum parameter estimation may be performed either with differential or integral methods, depending on the behavior of the conversion variances. DEWEY : 660 ISSN : 1385-8947 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFJ-4X24VV2-4&_user=6 [...] [article] Experimental errors in kinetic tests and its influence on the precision of estimated parameters. Part I, Analysis of first-order reactions [texte imprimé] / André L. Alberton, Auteur ; Marcio Schwaab, Auteur ; Martin Schmal, Auteur . - 2010 . - pp. 816-823. Génie Chimique Langues : Anglais (eng) in Chemical engineering journal > Vol. 155 N° 3 (Decembre 2009) . - pp. 816-823 Mots-clés : Experimental  error  Kinetic  analysis  First-order  reaction  Precise  parameter  estimation Index. décimale : 660 Résumé : The proper characterization of the experimental errors is essential for the correct evaluation of estimated model parameters, model fit and model predictions based on kinetic rate expressions. However, it is common to ignore the influence of experimental errors during kinetic studies due to difficulties to characterize how experimental errors depend on the reaction conditions. The behavior of experimental error depends on the specific features of the experimental system; however, in many cases the main sources of experimental errors are the unavoidable oscillations of the input variables. This work analyzes how the experimental errors affect kinetic studies based on catalytic tests when oscillations of the input variables are the main sources of uncertainties. The first part of this work assumes that the reaction rate can be described accurately as a first-order reaction in a PFR. Analytical expressions are derived for the variance of the reactant conversion in distinct scenarios and are used to analyze the quality of the obtained parameter estimates. It is shown here that the conversion variances can be described as functions of the measured conversion values, normally presenting a point of maximum for conversion values in the range of 0.6 < X < 1.0 when observed experimental fluctuations are controlled by the fluctuations of the input variables. Constant conversion variances should be expected only when fluctuations are controlled by analytical conversion measurements. As a consequence, optimum parameter estimation may be performed either with differential or integral methods, depending on the behavior of the conversion variances. DEWEY : 660 ISSN : 1385-8947 En ligne : http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFJ-4X24VV2-4&_user=6 [...]

Hybrid modeling of methane reformers. 1. a metamodel for the effectiveness factor of a catalyst pellet with complex geometry / André Luis Alberton in Industrial & engineering chemistry research, Vol. 48 N° 21 (Novembre 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 21 (Novembre 2009) . - pp. 9369–9375 Titre : Hybrid modeling of methane reformers. 1. a metamodel for the effectiveness factor of a catalyst pellet with complex geometry Type de document : texte imprimé Auteurs : André Luis Alberton, Auteur ; Marcio Schwaab, Auteur ; Carlos Eduardo Fontes, Auteur Année de publication : 2010 Article en page(s) : pp. 9369–9375 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Methane  steam  reforming  Effectiveness  factors  Computational  fluid  dynamic Résumé : In this work, effectiveness factors for methane steam reforming reactions were obtained by solving mass and heat balance equations inside catalytic pellets for different reaction conditions and catalytic pellet geometries with the help of CFD (computational fluid dynamic) techniques. CFD computations were performed for real particle geometries and real kinetic rate expressions as described in the technical literature. A linear correlation was found between the effectiveness factor and the area/volume ratio, which characterizes the methane steam reforming as a diffusion-controlled process. The slopes of the straight lines depend of the external reaction conditions, thermal conductivity, and effective diffusivity. On the basis of the CFD results, empirical metamodels were built to represent effectiveness factors for methane steam reforming reactions at different reaction conditions. The metamodels can be easily inserted into a reactor model for simulation of the full industrial process. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801830q [article] Hybrid modeling of methane reformers. 1. a metamodel for the effectiveness factor of a catalyst pellet with complex geometry [texte imprimé] / André Luis Alberton, Auteur ; Marcio Schwaab, Auteur ; Carlos Eduardo Fontes, Auteur . - 2010 . - pp. 9369–9375. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 21 (Novembre 2009) . - pp. 9369–9375 Mots-clés : Methane  steam  reforming  Effectiveness  factors  Computational  fluid  dynamic Résumé : In this work, effectiveness factors for methane steam reforming reactions were obtained by solving mass and heat balance equations inside catalytic pellets for different reaction conditions and catalytic pellet geometries with the help of CFD (computational fluid dynamic) techniques. CFD computations were performed for real particle geometries and real kinetic rate expressions as described in the technical literature. A linear correlation was found between the effectiveness factor and the area/volume ratio, which characterizes the methane steam reforming as a diffusion-controlled process. The slopes of the straight lines depend of the external reaction conditions, thermal conductivity, and effective diffusivity. On the basis of the CFD results, empirical metamodels were built to represent effectiveness factors for methane steam reforming reactions at different reaction conditions. The metamodels can be easily inserted into a reactor model for simulation of the full industrial process. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801830q

Hybrid modeling of methane reformers. 2. modeling of the industrial reactors / Marcio Schwaab in Industrial & engineering chemistry research, Vol. 48 N° 21 (Novembre 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 21 (Novembre 2009) . - pp. 9376–9382 Titre : Hybrid modeling of methane reformers. 2. modeling of the industrial reactors Type de document : texte imprimé Auteurs : Marcio Schwaab, Auteur ; André Luis Alberton, Auteur ; Carlos Eduardo Fontes, Auteur Année de publication : 2010 Article en page(s) : pp. 9376–9382 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Methane  reformers  Industrial  reactors Résumé : The steam reforming of methane is the main route for industrial production of hydrogen, used afterward for energy generation and production of chemicals. However, modeling of industrial methane reformers is not an easy task, due to the complex geometries of the employed catalyst pellets. The complex geometries are required to improve the contact between the gas phase and the solid catalyst. In this work a one-dimensional pseudohomogeneous model with axial mass and heat dispersion is used to model the tubular industrial reactors. The effect of the complex catalyst geometry of the pellets is considered with the help of empirical metamodels developed a priori for the effectiveness factors, based on CFD modeling of heat and mass balances inside pellets with different shapes and subject to distinct reactions conditions. It is shown that the proposed model can be successfully applied for simulation and design of industrial reformers, allowing for analysis of the effects introduced by distinct catalyst geometries on the performances of industrial operations. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801831m [article] Hybrid modeling of methane reformers. 2. modeling of the industrial reactors [texte imprimé] / Marcio Schwaab, Auteur ; André Luis Alberton, Auteur ; Carlos Eduardo Fontes, Auteur . - 2010 . - pp. 9376–9382. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 21 (Novembre 2009) . - pp. 9376–9382 Mots-clés : Methane  reformers  Industrial  reactors Résumé : The steam reforming of methane is the main route for industrial production of hydrogen, used afterward for energy generation and production of chemicals. However, modeling of industrial methane reformers is not an easy task, due to the complex geometries of the employed catalyst pellets. The complex geometries are required to improve the contact between the gas phase and the solid catalyst. In this work a one-dimensional pseudohomogeneous model with axial mass and heat dispersion is used to model the tubular industrial reactors. The effect of the complex catalyst geometry of the pellets is considered with the help of empirical metamodels developed a priori for the effectiveness factors, based on CFD modeling of heat and mass balances inside pellets with different shapes and subject to distinct reactions conditions. It is shown that the proposed model can be successfully applied for simulation and design of industrial reformers, allowing for analysis of the effects introduced by distinct catalyst geometries on the performances of industrial operations. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801831m

Hybrid modeling of methane reformers. 3 / André L. Alberton in Industrial & engineering chemistry research, Vol. 48 N° 23 (Décembre 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 23 (Décembre 2009) . - pp. 10277–10283 Titre : Hybrid modeling of methane reformers. 3 : optimal geometries of perforated catalyst pellets Type de document : texte imprimé Auteurs : André L. Alberton, Auteur ; Marcio Schwaab, Auteur ; Roberto Carlos Bittencourt, Auteur Année de publication : 2010 Article en page(s) : pp. 10277–10283 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Hybrid--Modeling--Methane--Reformers--Optimal--Geometries--Perforated--Catalyst  Pellets Résumé : This paper studies the optimization of catalyst pellet geometries for the simultaneous maximization of the mechanical strength and catalyst activity of perforated catalyst pellets used for the reforming of methane. This multiobjective problem can be analyzed with the help of Pareto fronts. A previous work (Part 1: Alberton; et al. Ind. Eng. Chem. Res., in press) demonstrated that the effectiveness factor of catalysts with complex geometry used for the reforming of methane can be expressed as a linear function of the specific area of the pellet; consequently, catalyst activity can be expressed in terms of the geometric parameters of the pellet. It can also be assumed that the mechanical strength of perforated catalyst pellets is related to the minimum wall thickness of the solid piece. Therefore, two optimization problems can be proposed: (i) the simultaneous maximization of the specific area and of the minimum wall thickness of the pellet and (ii) the simultaneous maximization of the overall catalyst activity in the catalyst bed and of the minimum wall thickness of the pellet. These objective functions are evaluated here for several catalyst geometries and analyzed with a Pareto filter. The Pareto fronts obtained for the two analyzed cases are essentially the same, indicating that the maximization of the specific area constitutes a useful criterion for design of perforated catalysts in diffusion-controlled systems. Optimized catalyst geometries are presented for different catalyst designs and can be used as references for future manufacture of catalyst pellets. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9001662 [article] Hybrid modeling of methane reformers. 3 : optimal geometries of perforated catalyst pellets [texte imprimé] / André L. Alberton, Auteur ; Marcio Schwaab, Auteur ; Roberto Carlos Bittencourt, Auteur . - 2010 . - pp. 10277–10283. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 23 (Décembre 2009) . - pp. 10277–10283 Mots-clés : Hybrid--Modeling--Methane--Reformers--Optimal--Geometries--Perforated--Catalyst  Pellets Résumé : This paper studies the optimization of catalyst pellet geometries for the simultaneous maximization of the mechanical strength and catalyst activity of perforated catalyst pellets used for the reforming of methane. This multiobjective problem can be analyzed with the help of Pareto fronts. A previous work (Part 1: Alberton; et al. Ind. Eng. Chem. Res., in press) demonstrated that the effectiveness factor of catalysts with complex geometry used for the reforming of methane can be expressed as a linear function of the specific area of the pellet; consequently, catalyst activity can be expressed in terms of the geometric parameters of the pellet. It can also be assumed that the mechanical strength of perforated catalyst pellets is related to the minimum wall thickness of the solid piece. Therefore, two optimization problems can be proposed: (i) the simultaneous maximization of the specific area and of the minimum wall thickness of the pellet and (ii) the simultaneous maximization of the overall catalyst activity in the catalyst bed and of the minimum wall thickness of the pellet. These objective functions are evaluated here for several catalyst geometries and analyzed with a Pareto filter. The Pareto fronts obtained for the two analyzed cases are essentially the same, indicating that the maximization of the specific area constitutes a useful criterion for design of perforated catalysts in diffusion-controlled systems. Optimized catalyst geometries are presented for different catalyst designs and can be used as references for future manufacture of catalyst pellets. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9001662