Abstract
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Chlorine-mediated electrochemical urea oxidation was investigated using a new electrochemical cell design with horizontally oriented electrodes. By virtue of the novel electrode configuration, the new electrochemical cell is self-stirred by the H2 bubbles evolving at the cathode surface and contains a built-in cooler to remove excess heat generated during electrolysis. The effect of current density, pH, NaCl concentration and initial urea concentration on the urea removal and specific electrical energy consumption were investigated. The % urea removal ranged from 55% to 90% depending on the operating conditions. The rate of urea removal increased with increasing current density and NaCl concentration, while increasing the solution pH and initial urea concentration were found to decrease the rate of removal. Energy consumption decreased with increasing NaCl concentration and increasing initial urea concentration. A kinetic approach and response surface methodology were used to model the temporal profile of urea oxidation and to optimize the process variables. After 33.4 min of electrolysis of a solution containing 348.6 ppm urea, 3% NaCl concentration and an initial pH of 5.6 using an applied current density of 4.6 mA/cm2 (2.6 A), 73.8% urea removal could be achieved with an extremely low energy consumption of 9.58 kW hkg urea. The influential priorities of the five operating parameters on % urea removal and specific energy consumption were different. The obtained results revealed that the use of kinetic and statistical modeling is an adequate approach to optimize the process variables of electrochemical urea degradation.