Mass Transfer in Flow‐Through Porous Electrodes with Two‐Phase Liquid‐Liquid Flow

Abstract

The effect of two‐phase liquid‐liquid flow on mass transfer in flow‐through porous electrodes where the current flow was perpendicular to the fluid flow was studied. Local reaction rates, concentrations, and potential distribution were measured along the direction of flow. Three systems were studied: (i) ferricyanide reduction in a solution containing no dispersed second phase; (ii) ferricyanide reduction in an aqueous solution containing toluene as an inert dispersed phase; and (iii) iodine reduction from an aqueous solution containing droplets of toluene in which the reactant was highly soluble in the organic phase. Experiments were carried out with controlled variation of solute concentration, dispersed phase void fraction and droplet size, and flow velocity. The overall mass‐transfer rate was found to be a combination of four effects: (i) the single‐phase mass‐transfer rate associated with the liquid as if it were flowing alone through the porous electrode, (ii) the decrease in mass transfer owing to coverage of the electrode surface by dispersed liquid droplets, (iii) the mass‐transfer exchange rate between the two liquids, and (iv) the further enhancement owing to penetration of the mass‐transfer boundary layer by dispersed droplets containing the reactant. In general, it was found that the mass‐transfer coefficient was not enhanced by addition of an inert second phase. However, when the dispersed phase contained dissolved reactant, the overall mass‐transfer coefficient was increased substantially.