Application of an experimental design method to study the performance of electrochlorination cells

A study of the effects of some parameters on the active chlorine production from aqueous sodium chloride solutions in the hypochlorite electrochemical production cells was undertaken. These varying parameters included the anodic surface area (Sa), the ratio of anodic and cathodic surface areas (Sa/Sc), the inter-electrode gap, and the type of the cathode used. In addition, a study of the performance of some electrochemical cells that differ in the type of anodes (platinum-coated titanium, ruthenium-coated titanium, and graphite) was made. By means of the experimental design method employing a full factorial of 23, the effects of the most influencing parameters, the set-up of optimum conditions, and the formation of optimal concentration of active chlorine were assessed. Under the following conditions, a concentration of as high as 65.67 g/L of active chlorine was gained: ruthenium-coated titanium anode (Sa = 24 cm2); titanium cathode, Sa /Sc = 1.33; inter-electrode gap, 0.5 cm; current density, 35 A/dm2; temperature, 20°C; concentration of NaCl aqueous solution, 3 M; time, 2 h.

A substantial yield of sodium hypochlorite was tightly bound to the nature of the anode. The best results were obtained using ruthenium oxidecoated titanium anode; nevertheless, the operational parameters such as NaCl concentration, current density and electrolysis time also had positive effects. The combination of the most favorable levels allowed obtaining an active chlorine concentration as high as 65.67 g/L. The use of a platinum-coated titanium anode afforded almost similar yields in active chlorine (59.57 g/L). However, it is worth noting the negative effect of the current density in the case of the graphite anode. In addition, the latter anode displayed a poor resistance towards oxida-tion, resulting in crumbling; therefore, it is not recommended for the production of sodium hypochlorite. Our on-going work deals mostly with the application of the above laboratory results to the production of sodium hypochlorite on a semiindustrial scale.