The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Modelling of Chemical Reaction Kinetics with Data from Temperature-Programmed Experiments

Tuomo Keskitalo

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Chemical Technology for public examination and debate in Auditorium V1 at Helsinki University of Technology (Espoo, Finland) on the 28th of September, 2007, at 12 o'clock noon.

Overview in PDF format (ISBN 978-951-22-8947-9)   [427 KB]
Dissertation is also available in print (ISBN 978-951-22-8946-2)

Abstract

This work focused on the kinetic modelling of heterogeneously catalysed chemical reactions making use of experimental data produced by temperature-programmed methods. These methods are traditionally applied in the characterisation of gas–solid interactions. However, as is demonstrated in this thesis, the results of temperature-programmed methods are also suitable for deriving kinetic models, which describe the rates of reactions. The derived kinetic models are valuable for the design and optimisation of chemical reactors, for the study of reaction mechanisms and for catalyst development.

The methodology of kinetic modelling based on data from temperature-programmed experiments was developed through two case studies. The first study dealt with the regeneration of a ferrierite catalyst deactivated by coke formation in skeletal isomerisation of alkenes. Many industrial processes dealing with hydrocarbons suffer from the formation of relatively large carbon and hydrogen containing molecules (coke) on the catalyst, which decrease its activity. The removal of coke by heat treatment under inert gas flow was studied with temperature-programmed gasification. With the results of the experiments, kinetic models, suitable for reactor design, were derived for the evolution of light hydrocarbon fractions ranging from C2 to C5. The regeneration of the catalyst by coke oxidation was studied with temperature-programmed oxidation (TPO). Several power law models and models based on assumed mechanisms successfully described the evolution of carbon oxides and water. The models that described the experimental data indicated that oxygen forms a reactive intermediate in a fast equilibrium reaction, and the formation of CO and CO2 proceeds through one or more common precursors.

The second study focused on adsorption and desorption, which are fundamental steps in heterogeneously catalysed reactions. The interplay between readsorption and mass transfer in a micro-reactor were studied from the point of view of kinetic modelling. The results clearly favour the pseudohomogeneous plug-flow reactor model for the description of the reactor if intraparticle mass transfer limitations are negligible. The derived modelling methodology was applied in the study of carbon dioxide adsorption on zirconia catalysts. Pulse adsorption followed by temperature-programmed desorption (TPD) resulted in informative experimental data for kinetic modelling. The derived kinetic models indicated that carbon dioxide adsorbs on at least three types of sites on zirconia catalysts.

In conclusion, this work shows that properly designed temperature-programmed experiments yield rich information for kinetic modelling, mainly because of the strong dependence of most reaction rates on temperature. The refined modelling methodology provides a basis for further research that utilises temperature-programmed methods for the study of kinetics of heterogeneously catalysed reactions.

This thesis consists of an overview and of the following 5 publications:

  1. Keskitalo, T.J., Korhonen, S.T., Lipiäinen, K.J.T., Krause, A.O.I., Evolution of light hydrocarbons from a coked ferrierite catalyst during temperature-programmed gasification, Industrial & Engineering Chemistry Research 46 (2007) 5503-5509.
  2. Keskitalo, T.J., Lipiäinen, K.J.T., Krause, A.O.I., Kinetic modeling of coke oxidation of a ferrierite catalyst, Industrial & Engineering Chemistry Research 45 (2006) 6458-6467.
  3. Keskitalo, T.J., Lipiäinen, K.J.T., Krause, A.O.I., Modelling of carbon and hydrogen oxidation kinetics of a coked ferrierite catalyst, Chemical Engineering Journal 120 (2006) 63-71. © 2006 Elsevier Science. By permission.
  4. Kanervo, J.M., Keskitalo, T.J., Slioor, R.I., Krause, A.O.I., Temperature-programmed desorption as a tool to extract quantitative kinetic or energetic information for porous catalysts, Journal of Catalysis 238 (2006) 382-393. © 2006 Elsevier Science. By permission.
  5. Keskitalo, T.J., Veringa Niemelä, M.K., Krause, A.O.I., Modeling of the adsorption and desorption of CO2 on Cu/ZrO2 and ZrO2 catalysts, Langmuir 23 (2007) 7612-7619.

Errata of publication 5

Keywords: kinetics, modelling, temperature-programmed methods, heterogeneous catalysis, temperature-programmed oxidation, temperature-programmed desorption

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© 2007 Helsinki University of Technology

Last update 2011-05-26