Electrode for electrochlorination

Abstract

The invention relates to an electrode for electrochemical generation of hypochlorite. The electrode comprises a valve metal substrate coated with a catalytic system consisting of two super-imposed layers of distinct composition and having a different activity towards hypochlorite anodic generation from chloride solutions. The electrode has a high duration in cathodic operation conditions, imparting self-cleaning characteristics thereto when used in combination with an equivalent one with periodic polarity reversal. Moreover, the deactivation of the electrode at the end of its life cycle occurs in two subsequent steps, allowing to schedule the substitution thereof with a significant notice period.

Description

FIELD OF THE INVENTION[0001]The invention relates to an electrode for electrochemical generation of hypochlorite.BACKGROUND OF THE INVENTION[0002]The electrolytic production of hypochlorite from diluted brines of alkali metal chlorides, e.g. of sodium hypochlorite by electrolysis of aqueous solution of sodium chloride or of sea-water, is one of the most common processes in the domain of industrial electrochemistry. The production of hypochlorite is always accompanied by the generation of various by-products deriving from the oxidation of chlorides (generally grouped under the name of “active chlorine”) and in some cases of oxygenated species such as peroxides, most of which have a very limited lifetime; for the sake of brevity, in the present text the whole of such products in aqueous solution, mostly consisting of alkali metal hypochlorite and hypochlorous acid in a ratio mainly depending on pH, is indicated as hypochlorite. Depending on the production volumes and concentrations, p...

AI Technical Summary

Benefits of technology

The invention is about an electrode for generating hypochlorite that has a two-step deactivation mechanism. The electrode has a roughness profile with specific roughness parameters that allow for a two-step increase in voltage until the external coating is reached. The internal coating is made of a mixture of oxides of iridium, ruthenium, and tantalum, with a ruthenium molar concentration of 42-52%, an iridium molar concentration of 22-28% and a tantalum molar concentration of 20-36%. The electrode can operate at excellent voltage levels until the external coating is worn off, allowing for scheduling replacement interventions with sufficient anticipation. The electrode can also have a thin protective layer of valve metal oxides interposed between the substrate and the internal catalytic layer. The method for manufacturing the electrode involves thermally treating the substrate and applying the internal and external catalytic layers by thermal decomposition of suitable precursor solutions. The roughness profile of the substrate is likely to have grain boundaries that become a zone of preferential attack for the subsequent etching, allowing for the formation of a roughness profile that effectively anchors the internal catalytic layer even at reduced specific loadings of noble metal.

Problems solved by technology

The titanium in the solution favours the kinetics of dissolution of the valve metal in the etching phase: concentrations below 5 g / l are associated with a dissolution rate which results too slow for practical purposes.

On the other hand, an excessive concentration slows down the attack again.