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Catalytic supercritical water oxidation of nitrogen-containing organic compounds

Hernandes, Mauricio Julio Angeles (2010)
Ph.D. thesis, University of Birmingham.

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The results of the catalytic oxidation in supercritical water of two non-biodegradable and highly toxic nitrogen-containing organic compounds (DBU and quinoline) are presented. The reactions were studied in a tubular xed-bed reactor over three catalysts: Pt/Al\(_2\)O\(_3\), CuO/Al \(_2\)O\(_3\) and MnO\(_2\)/CuO. The effect of operating conditions, namely temperature, pressure, oxygen concentration and initial concentration of the organic compounds were studied to evaluate their influence on its removal. Reaction rates were calculated from the experimental data collected. In addition, the selectivities and stabilities of the catalysts were investigated. Before conducting the experimental study the isothermal and isobaric operation of the reactor was veried together with the complete decomposition of hydrogen peroxide to oxygen and water in the preheating section and the reproducibility of experimental data was verified. Absence of external concentration gradients was determined experimentally for each reaction. The results showed that temperature was the main controlling variable of the catalytic oxidation. On the contrary, the effect of pressure depended on the catalyst used. Increasing the concentration of the organic compound did not aect their oxidation. Meanwhile, oxygen concentration above a stoichiometric ratio of two did not considerably improve the reaction. A power-law kinetic model was proposed to quantify the oxidation reaction. Three Langmuir-Hinshelwood-Hougen-Watson reaction rates were also explored to the experimental data. In the absence of a specic reaction mechanism the kinetic data were best represented by the power-law kinetic model. CO2 was the main carbon product of the reaction with small amounts of inorganic carbon species dissolved in the liquid effluent. Meanwhile, NH\(_4\), NO\(_3\) and NO\(_2\) ions were the only nitrogen species detected in the liquid effluent. Pt/Al\(_2\)O\(_3\) proved to be the most effective catalyst because it promoted faster reactions rates, had higher selectivity towards CO2 and produced lower nitrogen species. Surface analysis of the spent catalysts identied that the loss of activity was due to the 23 reduction of surface area. Leaching of active metals and chemical changes on the surface of the active metals and support of the catalyst were found for CuO/Al \(_2\)O\(_3\) and MnO \(_2\)/CuO. To conclude, it was demonstrated that catalytic supercritical water oxidation is a feasible and effective alternative for the destruction of contaminants in water. The thesis also includes suggestions for further research to continue the development of this technology and consolidate the process at industrial scale.

Type of Work:School of Chemical Engineering thesis.
Supervisor(s):Santos, Regina and Leeke, Gary
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Chemical Engineering
Subjects:TP Chemical technology
Institution:University of Birmingham
ID Code:597
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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