A lumped kinetic model based on the Fermi's equation applied to the catalytic wet hydrogen peroxide oxidation of Acid Orange 7

A catalytic wet hydrogen peroxide process was applied for the degradation of an azo dye – Acid Orange 7, also called Orange II (OII) – using as catalyst a pillared saponite clay impregnated with 21 wt.% of iron. Tests were carried out in a slurry batch reactor, following along time the OII degradation, the dye mineralization and the iron leaching from the support. A detailed parametric study was done, changing one variable at a time, while keeping the others constant. Among the variables studied (temperature, catalyst dose, and initial concentration of oxidant – H2O2 – or dye), temperature revealed to have a marked effect, increasing reaction rate but also iron leaching from the support (which was in all cases still negligible, thus allowing to comply with legislated standards and evidencing the heterogeneous character of the process). A previously developed semi-empirical kinetic model, based on the Fermi's equation (the mirror image of the logistic function), was used to successfully describe the evolution of the OII concentration in this complex process. Such equation was extended in the present work by developing a lumped model proposed to predict the evolution of the total organic carbon along time; this model also showed very good adherence to the experimental data.

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► Acid Orange 7 is completely degraded by a catalytic wet hydrogen peroxide process.
► Mineralization of up to 80% was reached in less than 4 h.
► The 21 wt.% Fe-pillared saponite clay catalyst is very active and quite stable.
► Models were developed to describe both dye and TOC concentration histories.
► Kinetics is based on Fermi's equation, with remarkable adherence to the data.