Evaluation of a detailed reaction mechanism for partial and total oxidation of C_1tn1 - C_1tn4 alkanes [Elektronische Ressource] / presented by Raúl Quiceno González

Informations

• Publié par: ruprecht-karls-universitat_heidelberg
• Publié le: 01 janvier 2008
• Nombre de lectures: 12
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Evaluation of a Detailed Reaction Mechanism for Partial

and Total Oxidation of C - C Alkanes 1 4




DISSERTATION





Submitted to the
Faculty of Chemistry of the Rupertus-Carola University of Heidelberg, Germany
For the degree of
Doctor of Natural Sciences




Presented by
Raúl Quiceno González
Born in Medellín, Colombia




Examiners: Prof. Dr. Dr. h. c. Jürgen Warnatz
Prof. Dr. Olaf Deutschmann




Heidelberg, November 16, 2007



Interdisziplinäres Zentrum für Wissenschaftliches Rechnen
Ruprecht – Karls – Universität Heidelberg
2007






DISSERTATION

Submitted to the

Faculty of Chemistry of the Rupertus-Carola University of Heidelberg, Germany

For the degree of

Doctor of Natural Sciences























Presented by

Raúl Quiceno González, Ms, Sciences

Born in Medellín, Colombia


Heidelberg, November 16, 2007








Title



Evaluation of a Detailed Reaction Mechanism for Partial

and Total Oxidation of C - C Alkanes 1 4

































Examiners: Prof. Dr. Dr. h. c. Jürgen Warnatz
Prof. Dr. Olaf Deutschmann











ACKNOWLEDGMENTS


I would like to acknowledge to all the people who helped me directly or indirectly to
accomplish this dissertation: First and foremost, I would like to express all my gratitude
towards Prof. Dr. Dr. h. c. Jürgen Warnatz for giving the opportunity to share an unforgettable
time in his group in Heidelberg.

To Prof. Dr. Olaf Deutschmann and his family, for his support during my time in Heidelberg,
for the useful comments and great support in the development of my work and for his
friendship during difficult moments.

To Farid Chejne, my former tutor in Colombia, for his tireless compromise with all of us, for
being more than a tutor, a friend.

I am also thankful to my colleagues at IWR: Ingrid for her collaboration with all the
administrative details, to Barbara for her unvaluable help, to Jürgen Moldenhauer, Till
Katzenmeier, Volker Karbach, Shaik and all my coworkers for their help and understanding.

Este pequeño parrafo me gustaria dedicarlo a mi familia, solo tengo palabras de
agradecimiento para ellos por acompañarme desde la distancia, por brindarme amor y
comprension, por sufrir el dolor de la separacion, por aceptarlo y ayudarme a sobre llevarlo de
la mejor manera posible; solo tengo palabras de agradecimiento para ustedes, y dificilmente
podria describir cuanto los quiero, respecto y admiro: mil gracias.

Finally, I would like to thank Sophia, for her boundless love, faith in me, and encouragement
and for bring to my life the most beautiful thing that ever happen to me: Madeleine, without
both of you this work would still not be completed.










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ABSTRACT


In the present work a chemical kinetic mechanism was developed, suitable for modeling com-
bustion and partial oxidation processes of C – C alkanes. The gas-phase kinetic mechanism 1 4
describes intermediate and high temperature chemistry. Accordingly, the formation and evo-
lution of important intermediate gas-phase species: Olefins and oxygenates were described in
terms of different pathways typical at those temperature regimes.

A previously developed mechanism suitable for high temperature conditions was extended by
including reactions which described the chemistry of total and partial oxidation of methane,
ethane, propane, butane, lower alkenes and formation and consumption of their characteristic
organic hydro-peroxide radicals and cyclical compounds. The kinetic mechanism was vali-
dated by comparing calculated results of ignition delay times, against experimental data ob-
tained in shock tubes, for various hydrocarbons and their mixtures, over a wide range of reac-
tion conditions (temperature, pressure and mixture composition). Further, the kinetic mecha-
nism was evaluated by comparing numerical simulations against experimentally obtained
concentration profiles of the main gas-phase species, measured in jet stirred reactors for dif-
ferent hydrocarbons and their mixtures during partial oxidation.

Next, the mechanism was applied to get a better understanding of the interactions between
flow, mass transfer and homogeneous-heterogeneous chemistries during the catalytic partial
oxidation of methane in a short contact time reactor, which has recently attracted strong scien-
tific and technological interest.

The detailed study of the catalytic partial oxidation of methane to syngas in a single gauze
reactor was based on three-dimensional numerical simulations of the flow field coupled with
heat transport and multi-step gas-phase and surface reaction mechanisms, including the com-
putation of the surface coverage. Results from the model were compared with experimental
data reported in the literature. The gas-phase mechanism was modeled using a reduced
mechanism, and for the surface a previously developed mechanism was adapted. The results
from the simulation of the partial oxidation of methane in a short contact time reactor were
carried out using the commercial computational fluid dynamics code Fluent, which was cou-
pled with external subroutines to model the detailed gas-phase and surface chemistry.

Today, the production of synthesis gas (carbon monoxide + hydrogen) is currently carried out
via steam reforming. In that process steam passes over a carbon source, often methane or coal,
and is heated to produce the synthesis gas. Synthesis gas is extremely valuable commercially
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for the production of methanol, hydrocarbons, higher alcohols for use in detergents, and am-
monia to use in fertilizers. There is also a significant interest in the production of hydrogen
for fuel cells. However, steam reforming has the major disadvantage of being endothermic
and hence requires a large amount of wasted energy to drive the reaction. An alternative to
steam reforming is the partial oxidation of the hydrocarbons, especially methane in short con-
tact time reactors. This promising route for natural gas conversion into more useful chemicals
has the advantage of being auto thermal.



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KURZFASSUNG


In der vorliegenden Arbeit wurde ein chemischer Reaktionsmechanismus entwickelt, mit dem
Verbrennungsprozesse und Partialoxidationsprozesse von C – C Alkanen modelliert werden 1 4
können. Der Reaktionsmechanismus der Gasphase beschreibt Prozesse für mittlere und hohe
Temperaturen. Die Ausbildung und Entwicklung wichtiger Zwischenprodukte der Gasphase
wie Olefine und sauerstoffhaltige Produkte werden hinsichtlich verschiedener
Temperaturbereiche geschildert.

Ein bereits entwickelter Mechanismus für Hochtemperaturbedingungen wurde erweitert,
indem Reaktionen eingefügt wurden, die die chemischen Reaktionen der vollständigen und
partiellen Oxidation von Methan, Ethan, Propan, Butan und kurzkettigen Alkene sowie die
Ausbildung und den Verbrauch ihrer charakteristischen organischen hydro-Peroxid Radikalen
und zyklische Komponenten beschreibt. Die Überprüfung des Reaktionsmechanismus
erfolgte durch Vergleich mit errechneten Ergebnissen von Zündverzugszeiten gegenüber
experimentell ermittelte Daten aus Versuchen mit Stossrohren für verschiedene
Kohlenwasserstoffe und ihre Mischungen unter verschiedensten Reaktionsbedingungen
(Temperatur, Druck und Aufbau der Zusammensetzung). Weiterhin wurde der
Reaktionsmechanismus durch Vergleich mit numerischen Simulationen gegenüber
experimentell erhaltende Konzentrationsprofile der wichtigsten Spezies in der Gasphase
evaluiert. Die Messungen fanden in Reaktionsbehältern für verschiedene Kohlenwassserstoffe
und deren Mischungen während der Partialoxidation statt.

Als nächster Schritt wurde der Mechanismus angewandt, um ein besseres Verständnis von
den ablaufenden Prozessen und deren Wechselwirkungen (Strömungsfeld, Massentransport,
homogener und heterogener Reaktionen) während der katalytischen Partialoxidation von
Methan in einem Short Contact Time Reactor (SCTR), der derzeit von großem
wissenschaftlichen sowie technologischen Interesse ist, zu erlangen.

Die detaillierte Studie der katalytischen Partialoxidation von Methan zu Synthesgas auf einer
Platinobe