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Photocatalytic Reaction Engineering for Solar Water Detoxification.

Congress: 2008
Author(s): Vincent Goetz, Jean-Pierre Cambon, Daniel Sacco, Gael Plantard
PROMES-CNRS UPR 8521 Process Materials ans Solar Energy Laboratory), Tecnosud, Rambla de la Thermodynamique, 66100 Perpignan, France.

Keyword(s): Chemical Engineering, Heterogeneous photocatalysis, water detoxification, atrazine
Article: Poster:
AbstractHeterogeneous photocatalysis is an alternative method for the removal of organic pollutants in water. The photo excitation of a semi-conductor under ultra violet (UV) irradiation entails the production of hydroxyl radicals, one of the most oxidative chemical species. Combined with solar energy this process of water detoxification is in perfect agreement with the requirement of sustainable processes development. In the open literature, papers have already demonstrated the practical ability of photocatalysis method for the degradation of biorecalcitrant pesticides and more particularly atrazine. This pollutant is sometimes found in drinking water and has noxious consequences on manís environment. With the global objective to design large scale solar water treatment plants, a necessary initial step is the development of a reliable photocatalytic reactor model. The photocatalytic semi-conductor used is supported TiO2 on cellulose based paper (Alhstrom Grade 1048ģ) placed in a tubular reactor irradiated thanks to an UV source in the range of solar UV irradiation powers. In a first part, data acquisition on the kinetic of atrazine degradation was made with an experimental laboratory plant. Evolutions of the concentration of atrazine as a function of the time were measured in a closed fluid loop connecting the tubular reactor and a vessel of atrazine. Experiments were performed for a large range of UV powers, initial concentrations of pollutant and hydrodynamic flowing modes in the tubular reactor. From these results an original model was developed. It is based on the coupling between: mass transfer from the liquid phase to the surface of the catalyst; adsorption of the pollutant molecules by TiO2; photocatalytic reaction rate. Comparisons between the simulated values of the concentration as a function of time and the experimental ones validate the proposed mechanisms. It is shown that in the range of experimental conditions explored, the apparent global kinetic basically depends from the combination of two limiting phenomena: the mass transfer in the liquid phase and the intrinsic photocatalytic rate. Relative importance of these two limitations is discussed and depends on the hydrodynamic flowing mode (laminar or turbulent) and the level of the irradiation flux. The validated model is a tool readily usable for reactor design and scale-up.
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