74 research outputs found
Thermal stability of n-dodecane : experiments and kinetic modelling
The thermal decomposition of n-dodecane, a component of some jet fuels, has
been studied in a jet-stirred reactor at temperatures from 793 to 1093 K, for
residence times between 1 and 5 s and at atmospheric pressure. Thermal
decomposition of hydrocarbon fuel prior the entrance in the combustion chamber
is an envisaged way to cool the wall of hypersonic vehicles. The products of
the reaction are mainly hydrogen, methane, ethane, 1,3-butadiene and 1-alkenes
from ethylene to 1-undecene. For higher temperatures and residence times
acetylene, allene, propyne, cyclopentene, 1,3-cyclopentadiene and aromatic
compounds from benzene to pyrene through naphthalene have also been observed. A
previous detailed kinetic model of the thermal decomposition of n-dodecane
generated using EXGAS software has been improved and completed by a
sub-mechanism explaining the formation and the consumption of aromatic
compounds
Thermal decomposition of norbornane (bicyclo[2.2.1]heptane) dissolved in benzene. Experimental study and mechanism investigation
The thermal decomposition of norbornane (dissolved in benzene) has been
studied in a jet stirred reactor at temperatures between 873 and 973 K, at
residence times ranging from 1 to 4 s and at atmospheric pressure, leading to
conversions from 0.04 to 22.6%. 25 reaction products were identified and
quantified by gas chromatography, amongst which the main ones are hydrogen,
ethylene and 1,3-cyclopentadiene. A mechanism investigation of the thermal
decomposition of the norbornane - benzene binary mixture has been performed.
Reactions involved in the mechanism have been reviewed: unimolecular
initiations 1 by C-C bond scission of norbornane, fate of the generated
diradicals, reactions of transfer and propagation of norbornyl radicals,
reactions of benzene and cross-coupling reactions
Reaction Mechanisms in Petroleum: From Experimentation to Upgrading and Geological Conditions
Among the numerous questions that arise concerning the exploitation of
petroleum from unconventional reservoirs, lie the questions of the composition
of hydrocarbons present in deep seated HP-HT reservoirs or produced during
in-situ upgrading steps of heavy oils and oil shales. Our research shows that
experimental hydrocarbon cracking results obtained in the laboratory cannot be
extrapolated to geological reservoir conditions in a simple manner. Our
demonstration is based on two examples: 1) the role of the hydrocarbon mixture
composition on reaction kinetics (the "mixing effect") and the effects of
pressure (both in relationship to temperature and time). The extrapolation of
experimental data to geological conditions requires investigation of the
free-radical reaction mechanisms through a computed kinetic model. We propose a
model that takes into account 52 reactants as of today, and which can be
continuously improved by addition of new reactants as research proceeds. This
model is complete and detailed enough to be simulated in large ranges of
temperature (150-500\degree C) and pressures (1-1500 bar). It is thus adapted
to predict the hydrocarbons evolution from upgrading conditions to geological
reservoirs.Comment: 8th World Congress of Chemical Engineering, Montr\'eal : Canada
(2009
Hydrocarbons Heterogeneous Pyrolysis: Experiments and Modeling for Scramjet Thermal Management
The last years saw a renewal of interest for hypersonic research in general
and regenerative cooling specifically, with a large increase of the number of
dedicated facilities and technical studies. In order to quantify the heat
transfer in the cooled structures and the composition of the cracked fuel
entering the combustor, an accurate model of the thermal decomposition of the
fuel is required. This model should be able to predict the fuel chemical
composition and physical properties for a broad range of pressures,
temperatures and cooling geometries. For this purpose, an experimental and
modeling study of the thermal decomposition of generic molecules (long-chain or
polycyclic alkanes) that could be good surrogates of real fuels, has been
started at the DCPR laboratory located in Nancy (France). This successful
effort leads to several versions of a complete kinetic model. These models do
not assume any effect from the material that constitutes the cooling channel. A
specific experimental study was performed with two different types of steel
(regular: E37, stainless: 316L). Some results are given in the present paper
Primary reactions of the thermal decomposition of tricyclodecane
In order to better understand the thermal decomposition of polycyclanes, the
pyrolysis of tricyclodecane has been studied in a jet-stirred reactor at
temperatures from 848 to 933 K, for residence times between 0.5 and 6 s and at
atmospheric pressure, in order to obtain a conversion between 0.01 and 25 %.
The main products of the reaction are hydrogen, methane, ethylene, ethane,
propene, 1,3-cyclopentadiene, cyclopentene, benzene, 1,5-hexadiene, toluene and
3-cyclopentyl-cyclopentene. A primary mechanism containing all the possible
initiation steps, including those involving diradicals, as well as propagation
reactions has been developed and allows experimental results to be
satisfactorily modeled. The main reaction pathways of consumption of
tricyclodecane and of formation of the main products have been derived from
flow rate and sensitivity analyses
Early maturation processes in coal. Part 1: Pyrolysis mass balances and structural evolution of coalified wood from the Morwell Brown Coal seam
In this work, we develop a theoretical approach to evaluate maturation
process of kerogen-like material, involving molecular dynamic reactive modeling
with a reactive force field to simulate the thermal stress. The Morwell coal
has been selected to study the thermal evolution of terrestrial organic matter.
To achieve this, a structural model is first constructed based on models from
the literature and analytical characterization of our samples by modern 1-and
2-D NMR, FTIR, and elemental analysis. Then, artificial maturation of the
Morwell coal is performed at low conversions in order to obtain, quantitative
and qualitative, detailed evidences of structural evolution of the kerogen upon
maturation. The observed chemical changes are a defunctionalization of the
carboxyl, carbonyl and methoxy functional groups coupling with an increase of
cross linking in the residual mature kerogen. Gaseous and liquids hydrocarbons,
essentially CH4, C4H8 and C14+ liquid hydrocarbons, are generated in low
amount, merely by cleavage of the lignin side chain
Étude des mécanismes du craquage thermique par simulation dynamique moléculaire de géopolymères organiques avec un champ de force réactif (ReaxFF)
Le kérogène, fraction insoluble de la matière organique sédimentaire, est un mélange complexe et hétérogène de macromolécules organiques. Ces structures évoluent, essentiellement sous l effet de la température, au cours des temps géologiques et génèrent les hydrocarbures présents dans les bassins sédimentaires. Comprendre et quantifier les mécanismes physicochimiques associés à ce processus est important pour l estimation des réserves pétrolières. Au cours de cette étude, deux géopolymères ont été sélectionnés pour représenter la décomposition thermique de structures typiques des kérogènes naturels. Dans un premier temps, une étude expérimentale nous a permis (1) de proposer des structures moléculaires des géopolymères et (2) de décrire les mécanismes primaires de décomposition des géopolymères. Les échantillons ont été analysés au moyen d expériences de pyrolyse en milieu confiné à cinq températures de référence comprises entre 200 à 300C. Un schéma cinétique correspondant aux processus précoces de décomposition a été établi à partir des observations expérimentales pour chacun des deux géopolymères. Dans un deuxième temps, les modèles moléculaires élaborés dans l'étape précédente ont été soumis à des simulations moléculaires dynamiques utilisant un champ de forces réactif (ReaxFF). Ces simulations ReaxFF ont apporté une interprétation théorique aux processus-clés observés expérimentalement. L ensemble des résultats de cette étude suggère que les modèles cinétiques, en une étape implémentés dans les simulateurs de bassin standard ne reproduisent pas correctement la physicochimie des processus de décomposition de la matière organique dans les roches mères naturellesKerogen, the insoluble fraction of sedimentary organic matter, is a complex mixing of organic macromolecules, the structure of which evolves during geological times as a function of temperature mainly. The thermal evolution of kerogen is at the origin of hydrocarbon deposits in sedimentary basins. Understanding and quantifying the physicochemical processes associated to this transformation is therefore important to improve the evaluation of petroleum systems. During this study, two geopolymers were selected in order to represent the thermal decomposition of typical structures in natural kerogen. Firstly, an experimental protocol was set up (1) to define molecular structures of the geopolymers, and (2) to describe primary mechanisms of decomposition of both geopolymers. The two samples were analysed using off-line pyrolysis experiments, at five reference temperatures comprised between 200 to 300C. A kinetic scheme accounting for early decomposition processes was derived from these experimental observations for each geopolymer. Secondly, molecular models were submitted to molecular dynamic simulations using a reactive force field (ReaxFF). ReaxFF simulations provided theoretical supports to the key-processes derived from laboratory experiments. On the overall, results of this study suggested that kinetic models in one step (= parallels reactions implemented in standard (commercial) basin simulators do not adequately reproduce the physicochemistry of organic matter decomposition processes in natural source rocksNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF
Synthèse de formaldéhyde par oxydation directe du méthane en microréacteur
Le formaldéhyde, un des produits de base de la chimie, est synthétisé industriellement par un procédé multi-étapes, dans lequel l efficacité énergétique est limitée. Ainsi, une synthèse par oxydation directe du méthane en phase gazeuse, qui pourrait être plus avantageuse, a été étudiée expérimentalement et par une modélisation cinétique, dans le cadre de ce travail. Pour favoriser la production du formaldéhyde, produit intermédiaire de l oxydation du méthane, des temps de passage faibles (< 100 ms) ont été envisagés. Un microréacteur annulaire (espace annulaire de 0,5 mm) en quartz a été utilisé, dans lequel la réaction a été étudiée en faisant varier les paramètres opératoires suivants : température (600-1000C), temps de passage (20-80 ms), rapport XO2/XCH4 (0,5-15) et teneur en NO2 ajoutée (0-0,6%). Sans NO2, les sélectivités en HCHO diminuent avec la conversion et le rendement maximal sans recyclage est de 2.4% (950C, 60 ms et XO2/XCH4 = 8). L ajout de NO2 permet de diminuer la température requise de 300C, et d augmenter le meilleur rendement en HCHO à 9% (700C, 30 ms et XO2/XCH4 = 7 et 0,5% de NO2). À faible avancement, la réaction sans NO2 peut être modélisée avec le mécanisme Gri-Mech 3.0 sans aucun ajustement. Pour la réaction avec NO2, après quelques corrections et modifications fondées sur une étude bibliographique, le mécanisme de Zalc et al. (2006) permet de rendre correctement compte des résultats expérimentaux. L analyse de flux a montré que l inter-conversion entre NO2 et NO joue un rôle important dans le milieu réactionnel. Elle permet de former continuellement les radicaux réactifs OH , et de convertir les radicaux CH3 et CH3O2 en radicaux CH3OFormaldehyde is one of the world s top organic intermediate chemicals. It is currently produced by a complex three-step process but a one-step process might require less energy. In this work, the direct gas phase partial oxidation of methane to formaldehyde has been studied through experiments and kinetic modeling. As formaldehyde is an intermediate in the sequential oxidation of methane, short residence times (<100 ms) have been considered in order to optimize its production. Thus, a quartz annular flow microreactor (annular space 0.5 mm wide), was chosen. The undertaken experiments consist of a systematic investigation of the effects of temperature (600-1000C), residence time (20-80 ms), input composition XO2/XCH4 (0.5-15) and initial NO2 concentration (0-0.6%). Without NO2, the HCHO selectivity decreases with the increasing methane conversion. For a single pass operation, the best HCHO yield is 2.4% (950C, 60 ms, XO2/XCH4 = 8). The addition of NO2 decreases the reaction initiation temperature by 300C and it remarkably enhances the HCHO yield. The highest HCHO yield attains 9% (700C, 30 ms, XO2/XCH4 =7) in the presence of NO2 (0.5%). For the reaction without NO2, the mechanism Gri-Mech 3.0 fits well the experimental results. For the reaction with NO2, by using the mechanism of Zalc et al. (2006) with some modifications, we obtained a good agreement between the experimental data and the model. The production and consumption flux analysis shows that the inter-conversion between NO2 and NO plays an important role in the reaction, because it continuously produces the reactive radicals OH and it converts the radicals CH3 and CH3O2 to radicals CH3ONANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF
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