Research and development of the technology for the production of electrolytic sodium hypochlorite by electrolysis of seawater

Summary

Chlorination continues to be the most widely used method of water disinfection in the world owing to the sanitary-hygienic reliability, relative simplicity and economic efficiency. The toxicity of chlorine, the need for the transportation through the residential areas, as well as storage under excessive pressure served as the basis for the search for alternative ways to ensure industrial safety and anti-terrorist sustainability of water supply systems. Among the chemicals alternative to chlorine, electrolytic sodium hypochlorite obtained at the point of consumption by electrolysis of an aqueous solution of sodium chloride takes the first place. The use of natural water containing chlorides as a raw material for the production of sodium hypochlorite is most promising. The use of natural water simplifies essentially the process flow scheme and provides for abandoning the purchase of sodium chloride which reduces the cost of the finished product. The results of research and development of the technology for producing electrolytic sodium hypochlorite by direct electrolysis of the Black Sea water are presented. The expediency of the technology was experimentally confirmed and the optimal conditions for the production of sodium hypochlorite by electrolysis of seawater were determined. The results of the study of deposits formed on the cathodes during the electrolysis of the Black Sea water are presented. Recommendations for the selection of process flow schemes for the production of sodium hypochlorite by electrolysis of seawater have been compiled.

Key words

disinfection , sodium hypochlorite , sea water , electrolyzer , direct electrolysis of seawater , electrode

Field tests of drinking water disinfection by direct electrolysis

Summary

The results of studying direct electrolysis of natural underground water with the purpose of determining possible production of low concentration sodium hypochlorite for drinking water disinfection before supplying it to the residents of Grushevskaia village of the Aksaisk District, Rostov Area are presented. The use of natural surface or underground water as electrolyte provides for eliminating the stage of artificial chloride solution making; that will simplify the technology of disinfectant production at the point of application and reduce the operation expenses. The studies were carried out in a full-scale plant in two directions: determination of the optimal parameters of the flow-through electrolyzer; determination of the lifetime of electrodes. The results of the full-scale studies confirmed possible disinfection of chloride-containing natural water (chloride concentrations 200–233 mg/dm3) by direct electrolysis. The process parameters of the electrolyzer operation with underground fresh water were determined: current density; water flow to the electrolyzer (flow rate); the time of electrode operation as an anode and as a cathode. The optimal composition of electrode coating was determined: in ruthenium –iridium oxide coating the weight ratio of Ru to Ir was 20:80. The use of iridium in the coating effects the formation of active chlorine and the electrode lifetime. The presence of ruthenium in the oxide layer in 20:80 weight ratio to iridium increases the anode lifetime tenfold (up to 4000 hours) compared to the anode without iridium.

Key words

potable water , disinfection , water treatment , direct electrolysis , electrolyzer , low-concentrated sodium hypochlorite

Development and introduction of anodes (OIRTA-Pd) based
on palladium oxide for the production of sodium hypochlorite

Summary

The results of collaborative work of PAO GMK Norill’skii Nikel’and EKOFES SPE LLC on the development of new titanium anodes (MMO electrodes) with an electrochemically active metal oxide coating based on palladium oxide (OIRTA-Pd) are presented. Titanium anodes are designed for the production of sodium hypochlorite, which is in high demand in water treatment technologies as a disinfectant replacing environmentally hazardous liquid chlorine. The results of studying the properties of electrodes with coatings of different oxide compositions and percentage ratios of platinum group metals in them, as well as the results of the production tests of prototypes of the developed electrodes are presented. It is established that palladium oxide in the coating composition improves the selectivity of active chlorine formation and increases the corrosion resistance of the electrodes contributing to an increase in the service life of the anode. The OIRTA-Pd composition is likely to become viable for manufacturing application owing to the improved characteristics relative to the composition of the reference coatings ORTA and OIRTA; whereas, in terms of the specific energy consumption indicator, it has characteristics superior to analogs – 3.72 kW·h/kg. In addition to the above, the voltage of the industrial electrolyzer is 5.6% lower compared to OIRTA. The developed OIRTA-Pd electrodes have a manufacturing cost comparable to OIRTA and a lower life cycle cost.

Key words

sodium hypochlorite , electrolysis , water disinfection , electrolyzer , titanium anode with electrochemically active metal oxide coating , MMO electrodes , OIRTA-Pd , palladium