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RESEARCH PAPERS

Modeling the Solar Photocatalytic Degradation of Dyes

[+] Author and Article Information
H. I. Villafán-Vidales, S. A. Cuevas

Centro de Investigación en Energía,  Universidad Nacional Autónoma de México, Privada Xochicalco s∕n, Col. Centro, A. P. 34, Temixco, Morelos, 62580 México

C. A. Arancibia-Bulnes1

Centro de Investigación en Energía,  Universidad Nacional Autónoma de México, Privada Xochicalco s∕n, Col. Centro, A. P. 34, Temixco, Morelos, 62580 Méxicocaab@cie.unam.mx

1

Corresponding author.

J. Sol. Energy Eng 129(1), 87-93 (Jan 13, 2006) (7 pages) doi:10.1115/1.2391255 History: Received July 01, 2005; Revised January 13, 2006

Background. The calculation of radiation absorption by the catalyst in solar photocatalytic reactors has been addressed by some authors, because it is a necessary step for the modeling of the detoxification of polluted water in these systems. Generally transparent pollutants have been considered, which somewhat simplifies the calculations. However, there has been an increasing interest in the study of solar photocatalytic degradation of dyes. These substances are not transparent to the radiation that the catalyst is able to absorb, and therefore their optical properties must be taken into account in the radiative modeling. Method of Approach. Absorption of radiation by the catalyst suspended in colored water is modeled by using the P1 approximation of radiative transfer theory. The absorption coefficient of the dye is taken into account in these calculations. A kinetic model is used to model degradation rates, based on the results of the radiative calculations. This has to be done through an Euler type method, because the reduction of dye concentration constantly modifies the optical conditions on the reactor, requiring a recalculation of radiation absorption at each step. Also, photocatalytic degradation experiments were carried out in a CPC solar photocatalytic reactor with tubular reaction space. Degradation of the Acid Orange 24 Azo dye was studied. The experimental degradation rates are compared with theoretical predictions. Results. An important influence of dye concentration is observed in the distribution of absorbed radiation, and also this parameter has a notorious effect on the predicted degradation rates. As a function of catalyst concentration, the degradation rate first increases rapidly and then at a smaller pace with an apparent linear trend. The experimental results can be reproduced well by the model. Conclusions. The proposed methodology allows modeling the solar photocatalytic degradation of dyes. The method should be applicable as long as the dye absorption coefficient is not too high in the wavelength region where the catalyst absorbs.

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Figures

Grahic Jump Location
Figure 1

Specific absorption coefficient of the dye Acid Orange 24, as a function of wavelength

Grahic Jump Location
Figure 2

Distributions of absorbed radiation in the reactor tube, as a function of the radial coordinate, for Ccatal=0.1g∕L, λ=335nm, and for fixed dye concentrations of (a) Cdye=12ppm, (b) Cdye=60ppm, and (c) Cdye=120ppm

Grahic Jump Location
Figure 3

Theoretical evolution of the normalized dye concentration as a function of accumulated radiation, for different initial dye concentrations. Ccatal=0.1g∕L; (a) γ=3Einstein−1∕2s1∕2cm3∕2 and (b) γ=0.03Einstein−1∕2s1∕2cm3∕2.

Grahic Jump Location
Figure 4

Initial dye degradation rate as a function of catalyst concentration. Theoretical model (line) for γ=0.1Einstein−1∕2s1∕2cm3∕2, and experimental results (points). Cdye,0=12ppm

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