Modelling of Bulk and Surface Reactions during Electrochemical Oxidation of Organic Compounds at BDD Anodes.
Special Symposium - Environmental Protection & Sustainability
Environmental Protection & Sustainability - I
Keywords: BDD Anodes, Electrochemical Oxidation, Mathematical Model, Organic Compounds
This paper presents the results of an experimental and numerical study on the kinetics of electrochemical oxidation of different organic substances at boron doped diamonds (BDD) anodes. A mathematical model was implemented which accounts for the complex behaviour of aqueous solutions containing organic compounds during electrolysis at BDD anodes. Different electrochemical reactions may occur at the BDD surface, such as oxidation of the organic to radicals (which may lead to polymers) or more oxidised substances, OH radicals generation from water oxidation and oxidation of inorganic substances present in the solution, which may generate long-life oxidants.
OH radicals can react with organic compounds to give more oxidised substances, but can also react with each other, with water or inorganic compounds present in the solution to give oxygen and long-life oxidising agents. Because of the high reactivity of OH radicals the volume in which these reactions can occur is a thin film adjacent to the electrode surface.
Long-life oxidants may diffuse to the bulk of the solution and oxidise the organics to more oxidised intermediates or CO2.
The proposed model allows to quantify the effect on the process of different variables related to the chemistry of both organic compounds and solution, in terms of kinetics of direct electrochemical oxidation and reaction with OH radicals or long-life oxidants.
The effect of hydrodynamics of the cell on the mass transfer of the organic compounds towards the electrode surface was also considered, as well as the value of the anodic potential.
The parameters of the model were the kinetic constants for both electrochemical and chemical reactions, mass transfer coefficients and geometric parameter of the system.
The results of the numerical solution of the model were validated trough comparison with experimental data obtained from galvanostatic electrolyses of different substituted phenols which are characterised by different behaviour in the reaction with OH radicals and long-life oxidants: m-cresol, p-hydroxybenzoic acid and benzoquinone were utilised
The electrolyses were carried out under different experimental conditions by using an impinging jet flow cell inserted in a hydraulic circuit in a closed loop. Different values of recirculation flow rate, electrolyte composition and current density were adopted.
The results showed that the proposed model interprets well the complex effect on removal efficiency, of such operating parameters as current density, hydrodynamic of the reactor and chemistry of the solution.
Presented Monday 17, 12:15 to 12:35, in session Environmental Protection & Sustainability - I (S-7A).
