Studies on the enhancement of hypochlorite yield in electro-chemical hypochlorite generators

The effects of various factors affecting the hypochlorite yield were studied using hypochlorite electro generators of different geometries. Both 3% NaCI solution and hypochlorite solution of known concentration (from a commercial electro chlorination unit) were used as electrolytes in the cells. While cells with vertically parallel electrodes proved to work smoothly, cells with horizontally parallel electrodes were associated with increased cell voltages and lower hypochlorite concentration. A comparison of cells has shown that a flow-through cell at flow rates greater than 28 cm3/min. was more effective in generating hypochlorite than a similar batch cell under the same operating conditions. On the other hand; the number of grams of chlorine yielded by flaw-through cells at flow rates less than 19 cm3/min. was less than that generated by a batch cell for cell operating time not exceeding 230 minutes. Between flow rates of 19 and 28 cm3/min the number of grams of chlorine generated by both cells at the same time intervals were equal. Further studies with flow-through cells showed that the hypochlorite generation current efficiencies greater than 80% could be attained at flow rates above 40 cm3/min. and at current densities not greater than 0.13 A/cm2, with the resulting hypochlorite concentration not exceeding 0.6% available chlorine. Hypochlorite concentrations of above 1.3% available chlorine were obtained in water cooled once-through cell system (without recircuiation) at a current density of 0.48 A/cm2 and at flow rates less than 25cm3/min., associated with current efficiencies not exceeding 60%. Attempts to enhance the concentration of hypochlorite beyond 1% available chlorine by increasing current density or by decreasing the flow rate of the electrolyte was limited by the rise in temperature of the cell which increases with increasing current density. While the hypochlorite ion concentration decreases with increasing flow rate for a 3% NaCI solution, it increases with increasing flow rate for electrolytes with hypochlorite concentration approaching 1% available chlorine.