EFFECTS OF HOLDUPS OF GAS AND LIQUID-PHASES IN PACKED-BED ELECTRODE ON CURRENT EFFICIENCY OF ELECTROCHEMICAL PRODUCTION OF HYDROGEN-PEROXIDE

A packed-bed electrode of graphite felts sparged with oxygen gas was u sed for the on-site electrochemical production of hydrogen peroxide. T he terminal voltage and the current efficiency were affected by operat ional conditions such as liquid and gas velocities in the packed-bed c athode. The holdups of gas and liquid phases, and the potential profil es of the solution phase in the cathode were measured to clarify the e ffects of the operational conditions on the electrolysis performance. The holdups of gas and liquid phases were determined as functions of s uperficial velocities of gas and liquid. The cathodic potential in the bed was shifted up by increasing liquid velocity at a certain velocit y of gas. The reaction resistivity of oxygen reduction was increased b y increasing liquid holdup, because of the increase in the diffusion l ength of the oxygen. Meanwhile the effective resistivity of the soluti on was decreased by increasing liquid holdup. Then the potential of th e solution in the bed had a minimum profile at a certain holdup of the liquid phase. The optimum conditions for electrolysis were determined as follows: the current density was 300A . m(-2) holdups of gas and l iquid phases, epsilon(G) = 0.85 similar to 0.90, and epsilon(L) = 0.04 similar to 0.05.