A theoretical and experimental study of a pilot-plant
solar reactor
for the photo-Fenton degradation of the herbicide 2,4-dichlorophenoxyacetic
acid (2,4-D) in aqueous solution is presented. Initially, a kinetic
model is proposed to obtain the reaction rates of 2,4-D, the main
intermediate (2,4-dichlorophenol), and the hydrogen peroxide. The
kinetic study was performed in a well-stirred tank laboratory reactor.
The effects of ferric salt initial concentrations, hydrogen peroxide
to 2,4-D initial concentration ratios, reaction temperatures, and
radiation levels are studied. The proposed kinetic model and the experimental
data are used to estimate the kinetic parameters, applying a nonlinear
regression procedure. Afterward, the kinetic model is used to predict
the reactant concentrations during the photo-Fenton degradation in
a pilot-plant solar reactor designed to capture the UV/visible/IR
solar radiation. The solar reactor was able to reach a complete degradation
of the 2,4-D and 2,4-dichlorophenol after 60 min, and a total organic
carbon conversion of 98.9% after 210 min.
The effect of the reaction temperature on the degradation rate of formic acid, using the Fenton and photo-Fenton processes, is investigated. First, for both reactions, a stirred tank laboratory photoreactor irradiated from the bottom was used to evaluate the kinetic parameters between 298 and 328 K. Afterward, the proposed kinetic model was used to predict the conversion of the organic pollutant in a flat-plate solar photoreactor. The previously reported radiation field and mass balances have been used to compute the formic acid and hydrogen peroxide concentrations as a function of time in the solar reactor. Theoretical and experimental results show that UV solar radiation improves the effectiveness of the Fenton process. At lower temperatures, the pollutant conversion enhancement is significant, but this effect is less important at higher temperatures. For instance, experimental conversion enhancements after 20 min are 186.0, 74.0, and 7.4% for 298, 313, and 328 K, respectively.
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