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Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate Kalu, Eric Egwu


Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate in the same cell was investigated. The alkaline hydrogen peroxide was obtained by the electroreduction of oxygen in NaOH on a fixed carbon bed while the chlorate was obtained by the reaction of anodic electrogenerated hypochlorite and hypochlorous acid in an external reactor. An anion membrane, protected on the anode side with an asbestos diaphragm was used as the separator between the two chambers of the cell. The effects of superficial current density (1.2 - 2.4 kA m⁻²), sodium hydroxide concentration (0.5 - 2.0 M) and catholyte flow (0.1 x 10⁻⁶ - 0.5 x 10⁻⁶ m³ s⁻¹) on the chlorate and peroxide current efficiencies were measured. The effect of peroxy to hydroxy mole ratio on the chlorate current efficiency was measured too. The cell was operated at fixed anolyte flow of 2.0 x 10⁻⁶ m³ s⁻¹, inlet and outlet temperatures of 27/33°C (anode side), 20/29°C (cathode side), cell voltages of 3.0 - 4.2 V (current density of 1.2 - 2.4 kA -m⁻²) and a fixed temperature of 70°C in the anolyte tank. Depending on the conditions, alkaline peroxide solution and sodium chlorate were cogenerated at peroxide current efficiency between 20% and 86%, chlorate current efficiency between 51.0% and 80.6% and peroxide concentration ranging from 0.069 M to 0.80 M. The cogeneration of the two chemicals was carried out at both concentrated (2.4 - 2.8 M) and dilute (0 - 0.5 M) chlorate solutions. A relative improvement on the current efficiencies at concentrated chlorate was observed. A chloride balance indicated negligible chloride loss to the catholyte. The results are interpreted in terms of the electrochemical and chemical kinetics and the hydrodynamics of the cell .

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