Effects of process conditions on cell voltage, current efficiency and voltage balance of a chlor-alkali membrane cell

The effects of various operating parameters on the cell voltage and current efficiency of a laboratory-scale chloralkali (CA) membrane cell were studied at low caustic concentrations (5–22 g/L). Five process parameters studied include anolyte pH (2–5), cell temperature (25–90°C), electrolyte velocity (2.2–8.4 cm/s), brine concentration (200–300 g/L) and current density (1–4 kA/m2), which were determined at four levels using DSA/Cl2 as anode, nickel as cathode and Flemion® 892 as the membrane. Taguchi and ANOVA techniques were employed for experimental design and data analysis, respectively. Current density and cell temperature were found to be the most striking parameters on the cell voltage with contribution percentage (P value) of 70% and 23%, respectively. However, in case of current efficiency, the highest P value is due to brine concentration (33%) while the lowest one corresponds to the cell temperature (13%). The caustic current efficiency was between 97%–99%. The results from voltage balance analysis revealed that the main contributors to the CA cell voltage at low caustic concentration are voltage drop due to the membrane, nickel cathode and the catholyte. The impact of other cell resistance components is minor. The measured and estimated cell voltages were found to come close at higher current densities.