Models of hypochlorite production in electrochemical reactors with plate and porous anodes

Pseudo two-dimensional finite element models were developed to predict the hypochlorite (chloric(I)) (HOCl + OCl-) production by electrolysis of near-neutral aqueous sodium chloride solution, in reactors with (a) an anode and cathode in the form of plates, and (b) a lead dioxide-coated graphite felt anode and titanium plate cathode. The model was used to investigate the feasibility of using a porous anode to achieve high single pass conversions in oxidising chloride ions. For the model reactor with planar anode, the effects of diffusion, migration and convection on the mass transport of the reacting species were considered, whereas with the porous anode, a supporting electrolyte (Na2SO4) was notionally present to eliminate the migrational contribution to reactant transport. For an electrolyte flow rate of 10(-6) m(3) s(-1) (Re = 10 for plate electrodes, Re (porous) = 0.76 for porous anode), a cell voltage of 3.0 V and an inlet NaCl of 100 mol m(-3), the single-pass conversion of Cl- was predicted to increase from 0.45 for the reactor with a planar anode to 0.81 for the reactor with a porous anode. For the same operating conditions, the overall current efficiency was also predicted to increase from 0.71 to 0.77 by replacing the plate with the porous anode.