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Rafante Blazzio Yashmin - One of the best experts on this subject based on the ideXlab platform.
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Évaluation des conditions initiales de traitement du catalyseur pour la polymérisation des oléfines
HAL CCSD, 2020Co-Authors: Rafante Blazzio YashminAbstract:Given the undeniable relevance of polyolefin production, it is of great interest to understand the keyphenomena determining the quality of the polymerization process. lndustrial scale polymerization reactions could be metaphorically compared to the launching of a space rocket, in which the success of the entire process is highly dependent on the mastery of the initial moments. This so-called 'nascent phase' of the polymerization (10-1 to 102 s) is crucial in ensuring a satisfactory operation and properties of the final polymer. lt is then that the Catalyst activation takes place, the particle morphology is defined and the system is in its highest potential for mass transfer and heat transfer limitations.Studying such short time-frames is challenging for a number of reasons (that we will see throughout this work) and requires specially adapted tools. Previous works from our research group have shown how the stopped-flow technique is a promising method to study aspects related to heat transfer and morphology evolution at early stages in gas-phase. lt is mainly for this reason that the focus of the current project was on the improvement of such tools. The novel reactor developed in this work was especially designed to tackle some of the limitations encountered with the previous versions, mainly aspects related to poor heat evacuation, lack of robustness and imprecision in experimental measurements.The first part of this PhD describes all steps taken until successful optimization of the hardware component of the novel stopped-flow reactor. The new set-up was a product of our innovative approach towards the reactor geometry (annular) and the tailored execution from a specialized engineering firm. Several improvements were achieved, such as the optimization of the reactor dimensions, the automated control of all functions and a wider range of operation conditions. Moreover, the capacity was highly improved by the possibility of injecting several gases simultaneously, as well as components that are liquid at room temperature. The new tool allows to perform polymerization reactions as short as 3s in gas phase, in reaction conditions that are representative of heat and mass transfer phenomena present in industrial scales.ln the second part of this work, we have developed a software component for the novel reactor, which consisted of a reactor model and state-observer. This tool was developed to estimate the dynamic polymerization rates from the temperature measurements and overcome the one-point character of such experiments (which provide no real information on the Catalyst Kinetics). For this purpose, a simplified one-dimensional model at the macromolecular level was developed and validated with experimental data.At last, with hardware and software components at hand, we have demonstrated the usefulness of the new tool in specific case studies with different silica supported metallocene Catalysts. ln the first case study, we evaluated the impact of the pore structure of the support on the Catalyst Kinetics, polymer properties and particle morphology at short reaction times. On the second case study, we investigated the effect of various experimental conditions (reaction time, comonomer and hydrogen content) on the behavior of two different Catalyst families. From both studies, the estimated reaction rates at early stages (
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Évaluation des conditions initiales de traitement du catalyseur pour la polymérisation des oléfines
2020Co-Authors: Rafante Blazzio YashminAbstract:Compte tenu de la pertinence indéniable de la production de polyoléfine, il est d'un grand intérêt de comprendre les phénomènes clés déterminant la qualité du processus de polymérisation. Les réactions de polymérisation à l'échelle industrielle pourraient être métaphoriquement comparées au lancement d'une fusée spatiale, dans laquelle le succès de l'ensemble du processus dépend fortement de la maîtrise des moments initiaux. Cette soi-disant «phase naissante» de la polymérisation englobe les dizaines de secondes initiales jusqu'à quelques minutes de réaction. Cette période est cruciale pour garantir des propriétés satisfaisantes du polymère final car c'est alors que la morphologie des particules est définie et que le système est dans son potentiel de transfert de masse le plus élevé et risque de surchauffe des particules (les particules polymérisantes peuvent croître jusqu'à 20 fois leur taille initiale)1. Dans les travaux en cours, un nouveau réacteur nommé ‘stopped-flow’ a été spécifiquement développé pour effectuer des études précises sur les polymérisations à court terme en phase gazeuse, dans le but d'évaluer la cinétique et l'évolution de la morphologie des particules. L'installation actuelle a été construite principalement pour améliorer les aspects liés à une mauvaise évacuation de la chaleur et à l'imprécision des mesures expérimentales rencontrées avec les versions précédentes du réacteur. Des études expérimentales ont indiqué que la nouvelle configuration permet de suivre le développement des propriétés thermiques des polymères, des poids moléculaires et de la morphologie des particules à des temps de réaction aussi courts que 3 s avec un contrôle de transfert de chaleur satisfaisant dans le réacteur. Pour le nouveau réacteur, un modèle dynamique 1D hétérogène d'un nouveau réacteur à écoulement arrêté pour la polymérisation des oléfines en phase gazeuse a été développé et validé. Le modèle décrit dans ce travail est axé sur l'échelle du réacteur et a été développé pour interpréter correctement les données expérimentales et les corréler à la vitesse de réaction de la réaction de polymérisation et aux paramètres cinétiques. Des valeurs réalistes des paramètres cinétiques sont obtenues à partir d'études expérimentales. Comme montré au cours de ce travail de thèse, nous avons montré que la nouvelle configuration répond à nos demandes initiales et permet d'étudier des réactions de polymérisation aussi courtes que 3 secondes à différentes compositions de l'alimentation en phase gazeuse. Nous avons réalisé plusieurs études de cas avec le nouveau réacteur, y compris l'évaluation de catalyseurs Ziegler-Natta classiques et de différentes familles de catalyseurs métallocènes hétérogènes. Les polymères obtenus ont été utilisés pour étudier l'évolution des propriétés thermiques, ainsi que l'évolution de la fragmentation des particules avec le temps. Ces observations étaient corrélées à des études de polymérisation à temps plein réalisées dans des conditions de laboratoire standardGiven the undeniable relevance of polyolefin production, it is of great interest to understand the keyphenomena determining the quality of the polymerization process. lndustrial scale polymerization reactions could be metaphorically compared to the launching of a space rocket, in which the success of the entire process is highly dependent on the mastery of the initial moments. This so-called 'nascent phase' of the polymerization (10-1 to 102 s) is crucial in ensuring a satisfactory operation and properties of the final polymer. lt is then that the Catalyst activation takes place, the particle morphology is defined and the system is in its highest potential for mass transfer and heat transfer limitations.Studying such short time-frames is challenging for a number of reasons (that we will see throughout this work) and requires specially adapted tools. Previous works from our research group have shown how the stopped-flow technique is a promising method to study aspects related to heat transfer and morphology evolution at early stages in gas-phase. lt is mainly for this reason that the focus of the current project was on the improvement of such tools. The novel reactor developed in this work was especially designed to tackle some of the limitations encountered with the previous versions, mainly aspects related to poor heat evacuation, lack of robustness and imprecision in experimental measurements.The first part of this PhD describes all steps taken until successful optimization of the hardware component of the novel stopped-flow reactor. The new set-up was a product of our innovative approach towards the reactor geometry (annular) and the tailored execution from a specialized engineering firm. Several improvements were achieved, such as the optimization of the reactor dimensions, the automated control of all functions and a wider range of operation conditions. Moreover, the capacity was highly improved by the possibility of injecting several gases simultaneously, as well as components that are liquid at room temperature. The new tool allows to perform polymerization reactions as short as 3s in gas phase, in reaction conditions that are representative of heat and mass transfer phenomena present in industrial scales.ln the second part of this work, we have developed a software component for the novel reactor, which consisted of a reactor model and state-observer. This tool was developed to estimate the dynamic polymerization rates from the temperature measurements and overcome the one-point character of such experiments (which provide no real information on the Catalyst Kinetics). For this purpose, a simplified one-dimensional model at the macromolecular level was developed and validated with experimental data.At last, with hardware and software components at hand, we have demonstrated the usefulness of the new tool in specific case studies with different silica supported metallocene Catalysts. ln the first case study, we evaluated the impact of the pore structure of the support on the Catalyst Kinetics, polymer properties and particle morphology at short reaction times. On the second case study, we investigated the effect of various experimental conditions (reaction time, comonomer and hydrogen content) on the behavior of two different Catalyst families. From both studies, the estimated reaction rates at early stages (
Jung Bong Ko - One of the best experts on this subject based on the ideXlab platform.
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methanol steam reforming over cu zno al2o3 Catalyst Kinetics and effectiveness factor
Applied Catalysis A-general, 2004Co-Authors: Jung Bong KoAbstract:Abstract Steam reforming of methanol over a commercial Cu/ZnO/Al2O3 Catalyst was studied at atmospheric pressure and in a temperature range between 160 and 260 °C. The reaction rate depended upon methanol and hydrogen partial pressures, and was independent of the partial pressures of carbon oxides and water, which was in excess of the methanol partial pressure. Small amounts of carbon monoxide, less than 1% in the product gas, were formed at high temperatures; the amounts were well below the equilibrium amounts of reverse water–gas-shift reaction (RWGS). This was in support of the reaction sequence of methanol steam reforming followed by the RWGS. A power-law and a Langmuir–Hinselwood rate expression were developed for the reforming reaction by fitting the expressions to the experimental data. As the data were found to be affected by internal diffusion at high temperatures, the effectiveness factor of the Catalyst particle was estimated in the fitting in order to obtain the intrinsic Kinetics. Details of the estimation of the factor are elucidated. In order to predict a non-zero, finite rate in the absence of hydrogen, the hydrogen partial pressure term in the power-law expression was corrected by a fitted constant to avoid an infinite reaction rate, since the exponent of the hydrogen partial pressure was a negative number due to the hydrogen inhibition effect in the reforming; in the reaction mechanism for the Langmuir–Hinselwood expression, it was necessary to assume two different kinds of active sites on the Catalyst: one for adsorbed methoxy and the other for adsorbed hydrogen. In addition, an excellent fitting of the data by the Langmuir–Hinselwood expression indicates that dehydrogenation of the adsorbed methoxy to the adsorbed oxymethylene is the rate-determining step (RDS), and that adsorption of all the species other than methoxy and hydrogen on the active sites is negligible.
Alberto Orio - One of the best experts on this subject based on the ideXlab platform.
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fresh tar from a biomass gasifier elimination over a commercial steam reforming Catalyst Kinetics and effect of different variables of operation
Industrial & Engineering Chemistry Research, 1997Co-Authors: Ian Narvaez, Jose Corella, Alberto OrioAbstract:The upgrading of the raw gas from a biomass gasifier is studied with the commercial steam-reforming BASF G1-25 S nickel-based Catalyst. It is located downstream of the gasifier, a bubbling fluidized bed type in which air is used as gasifying agent. To increase the Catalyst lifetime, a guard bed of a calcined dolomite at 800−850 °C is used. It decreases the throughput of tar entering the catalytic bed to amounts below 2 g tar/m3(NC). This work is focused only on the catalytic bed which easily decreases the tar content in the gas to only 1−2 mg/m3(NC). Variables studied include the particle diameter of the Catalyst, time-on-stream, temperature of the catalytic bed, and gas and tar compositions. Both tar and gas compositions in the catalytic (Ni) reactor depend on the equivalence and H/C ratios existing in the gasifier and on the operating conditions of the guard bed of dolomite. A simple kinetic model is used to describe the overall tar elimination network. Its overall kinetic constant is used as index of t...
Jose H. Ramírez - One of the best experts on this subject based on the ideXlab platform.
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azo dye orange ii degradation by the heterogeneous fenton like process using a zeolite y fe Catalyst Kinetics with a model based on the fermi s equation
Applied Catalysis B-environmental, 2014Co-Authors: Maryin L. Rache, Adrian M T Silva, Luís M. Madeira, Andrés García, Jose H. RamírezAbstract:Abstract The degradation of Orange II dye (OII) by a heterogeneous Fenton-like process was studied using a Catalyst with 5 wt.% of iron after ion-exchange in a Na–Y zeolite support. The Catalyst was characterized by X-ray diffraction (XRD), N 2 adsorption, atomic absorption spectroscopy and X-ray fluorescence (XRF). The effect of the initial concentrations of H 2 O 2 and OII, pH and temperature on the degradation rate of OII was investigated by carrying out experiments in a batch reactor. The OII concentration histories (i.e., concentration evolution along reaction time) were described by a simple semi-empirical kinetic model, based on the Fermi's equation, which captures simultaneously the influence of all the reaction conditions with a few adjustable parameters. The adherence of the model to the data was remarkable, and the effect of the operating conditions on the obtained fitting parameters – apparent rate constant and transition time – was analyzed.
Lingjun Kong - One of the best experts on this subject based on the ideXlab platform.
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enhanced catalytic degradation of ciprofloxacin with fes2 sio2 microspheres as heterogeneous fenton Catalyst Kinetics reaction pathways and mechanism
Journal of Hazardous Materials, 2017Co-Authors: Zenghui Diao, Xiangrong Xu, Dan Jiang, Gang Li, Lingjun KongAbstract:Abstract In this study, the application of FeS2/SiO2 microspheres as a Catalyst to activate H2O2 for the degradation of ciprofloxacin (CIP) was systematically investigated. Results demonstrated that the presence of SiO2 microspheres on the surface of FeS2 could effectively make the reaction of aqueous Fe2+ and H2O2 smoothly continuous by controlling the release of aqueous Fe2+ from FeS2. Nearly 100% of CIP was degraded after 60 min under the optimum conditions. A superior performance on the CIP degradation and high reusability of the Catalyst was obtained in FeS2/SiO2 microspheres activated H2O2 system. A low concentration of ethylene diamine tetraacetie acid (EDTA) did positively affect the degradation rate of CIP. A synergetic effect between adsorption and oxidation processes contributed to the significant enhancement of CIP degradation. Seven oxidation intermediates were identified during the CIP degradation process, and the direct HO oxidation proved to be a main CIP degradation pathway. For degradation pathway of CIP, oxidation of piperazine ring would be its first step, followed by cleavage of the heterocyclic ring. Subsequently, the substitution, hydroxylation and decarboxylation processes occurred. This is the first report on the feasibility of FeS2/SiO2 microspheres activated H2O2 system for the enhanced degradation of CIP.