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International Journal of Photoenergy
Volume 2008, Article ID 283741, 14 pages
http://dx.doi.org/10.1155/2008/283741
Research Article

Influence of Irradiance, Flow Rate, Reactor Geometry, and Photopromoter Concentration in Mineralization Kinetics of Methane in Air and in Aqueous Solutions by Photocatalytic Membranes Immobilizing Titanium Dioxide

1Environmental Research Centre, University of Milan, Camillo Golgi 19 Street, 20133 Milan, Italy
2Department of Materials Science, University of Milano Bicocca, Cozzi 43 Street, 20126 Milan, Italy
3ISTM, Institute of Molecular Sciences and Technologies, National Research Council (CNR), 20133 Milan, Italy
4R&D Group, BIT srl, 20121 Milan, Italy
5Department of Inorganic Technology and Environmental Protection, Polytechnic University of Bucharest, 011061 Bucharest, Romania
6LASA, Department of Physics, University of Milan and National Institute of Nuclear Physics (INFN), 20133 Milan, Italy

Received 19 September 2007; Accepted 13 December 2007

Academic Editor: M. Sabry Abdel-Mottaleb

Copyright © 2008 Ignazio Renato Bellobono et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Photomineralization of methane in air (10.0–1000 ppm (mass/volume) of C) at 100% relative humidity (dioxygen as oxygen donor) was systematically studied at 318±3 K in an annular laboratory-scale reactor by photocatalytic membranes immobilizing titanium dioxide as a function of substrate concentration, absorbed power per unit length of membrane, reactor geometry, and concentration of a proprietary vanadium alkoxide as photopromoter. Kinetics of both substrate disappearance, to yield intermediates, and total organic carbon (TOC) disappearance, to yield carbon dioxide, were followed. At a fixed value of irradiance (0.30 Wcm1), the mineralization experiments in gaseous phase were repeated as a function of flow rate (4–400 m3h1). Moreover, at a standard flow rate of 300 m3h1, the ratio between the overall reaction volume and the length of the membrane was varied, substantially by varying the volume of reservoir, from and to which circulation of gaseous stream took place. Photomineralization of methane in aqueous solutions was also studied, in the same annular reactor and in the same conditions, but in a concentration range of 0.8–2.0 ppm of C, and by using stoichiometric hydrogen peroxide as an oxygen donor. A kinetic model was employed, from which, by a set of differential equations, four final optimised parameters, 𝑘1 and 𝐾1, 𝑘2 and 𝐾2, were calculated, which is able to fit the whole kinetic profile adequately. The influence of irradiance on 𝑘1 and 𝑘2, as well as of flow rate on 𝐾1 and 𝐾2, is rationalized. The influence of reactor geometry on 𝑘 values is discussed in view of standardization procedures of photocatalytic experiments. Modeling of quantum yields, as a function of substrate concentration and irradiance, as well as of concentration of photopromoter, was carried out very satisfactorily. Kinetics of hydroxyl radicals reacting between themselves, leading to hydrogen peroxide, other than with substrate or intermediates leading to mineralization, were considered, and it is paralleled by a second competition kinetics involving superoxide radical anion.