Kinetic Modeling of Brilliant Blue Discoloration by Ozonation

This paper presents the results of investigations on the kinetic modeling of Brilliant Blue FCF (BB) discoloration reactions in aqueous solutions with different ozone concentrations and pH conditions. Kinetic studies involve knowledge of the structure and properties of dye and ozone, as well as of the experimental conditions. In general, scientists admit that the predominant oxidation pathway is direct (by free oxygen atoms) or indirect (by free hydroxyl radicals); this will depend on influencing factors such as the physicochemical properties of the dye, the pH of the aqueous solution, ozone concentration, reaction time, and the contact mode with/without stirring. In this experimental research, two pathways were chosen following CBB = f(t)—1. a constant dye concentration and different ozone concentrations, in the concentration range of 100–250 mg/L, in three pH media (acidic, neutral, and basic), with and without stirring; 2. a constant concentration of ozone and different dyes in the concentration range of 2.5–10 mg/L, under the conditions of point 1. With the obtained experimental data, the curves CBB = f(t) were drawn and processed according to the integral method of classical kinetics, based on first- and second-order equations. Unfortunately, this simple procedure did not give any results for the pH values studied. The rate constants were negative, and/or the reaction order depended on the initial conditions. Due to its structure, the BB dye has several chromophore groups, and thus multiple attack centers, resulting in several oxidation by-products, which is why the 1H-NMR spectrum was recorded for the discoloration of BB with ozone. Since the stoichiometry of the overall oxidation reaction, as well as the relationship between the rate constant and the reaction conditions mentioned above, is not known, a kinetic model based on mass transfer coupled with a chain reaction in the bulk liquid phase was proposed and successfully tested at pH = 7. This research approach also involves the consolidation of the theoretical bases of the ozonation process through the kinetic study carried out, as well as the proposal of a kinetic model. These systematics lead to results that are applicable to other aqueous systems that are impure with dyes, allowing for generalizations and the development of the field, ensuring the sustainability of the research.