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International Journal of Chemical Engineering and Analytical Science Vol. 2, No. 1, 2017, pp. 1-8 5 chlor-alkali production. The anolyte and catholyte temperatures must be similar (80°C) in both compartments. This value is in agreement which the value previously reported [16, 21]. 3.3. Effect of Gaps Between the Electrodes Electrolysis of brine is decomposed into chlorine and hydrogen gases due to the passage of an electric current. Theoretical voltage to start brine electrolysis in membrane cell is 2.19 V. The gap between electrodes is the distance that the ions have to travel in the electrolyte [22]. A series of experiments have been conducted in order to test the effect of the space between the electrodes on minimal cell voltage. For this investigation, different gap electrodes were used. The experimental cell voltage values for each distance between anode and cathode are shown in figure 4. Electrolysis took place under the conditions of: 320 g.L-1 NaCl (pH=2), 24% NaOH, T= 80°C. Figure 4. Effect of gap between the electrodes on cell voltage. The results indicate that when the space between the electrodes of cell increases, the cell voltage also increases. Indeed, the minimum cell voltage for a distance between the electrodes of 1.5 cm is 2.83 V. It increases at 2.93 V when the distance between anode and cathode increased at 2 cm. The reason is expressed to be the distance traveled by the electrons during the formation of products. Indeed, inside the electrolysis cell, electrons start their journey from the surface of an electrode, move through the electrolyte and end their journey at the surface of the other electrode. By increasing the inter-electrode distance, the ohmic resistance of electrolyte also increases and consequently this will lead to an increase the cell voltage. In others words, these experiments show that to minimize the cell voltage, the gaps between the electrodes are minimized in membrane cells. Author [16] was obtained a significative reduction of cell ohmic resistance and higher current densities with a lower gap between electrodes. Others authors [5, 23] also reported the same effect. However, if the gap is very small, a rise in voltage is observed due to the entrapment of gas bubbles between the electrodes and the membrane [24]. On the other hand, a close distance means a higher frequency of short- circuiting, electric sparks [5, 21]. In this study the optimum space between the electrodes and membrane in our electrochemical reactor was 0.75 cm. This value is higher than the value (6.0 mm for the solid electrodes and 2.75 mm for the mesh electrodes) previously reported [16]. 3.4. Effect of Current Density The rate of an electrochemical reaction is measured as current density. Current density is a current which passes on one square meter of electrode. It’s a critical parameter in electrolysis, because, it’s the only parameter which can be controlled directly [25]. To study the effect of current density on chlorine and hydrogen production, several experiments were performed at different current densities from 8.294 A/dm2 to 41.468 A/dm2. Electrolysis took place under the conditions of: 320 g.L-1 NaCl (pH=2), 24% NaOH, T= 80°C. The effect of applied current density on chlorine and hydrogen production during the electrolysis is shown in figure 5. Figure 5. Effect of current density on the electrolysis kinetic. The chlorine production rate increases with increased current density (figure 5a). As a matter of fact, after 10 minutes of electrolysis, the production of chlorine was 213.5 mL with a current density of i = 41.4 A/dm2, whereas to produce same volume with a current density i = 16.6 A/dm2, it wasPDF Image | Electrolysis Parameters for Chlorine and Hydrogen Production
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