Intensification of Rate of Diffusion Controlled Reactions in a Parallel Plate Electrochemical Reactor Stirred by a Curtain of Electrochemically Generated Gas Bubbles

Abstract

Rates of mass transfer were measured at a vertical plate stirred by a rising curtain of oxygen bubbles generated electrochemically at an upstream plate by measuring the limiting current of the cathodic reduction of K 3 Fe(CN) 6 in alkaline solution. The rate of mass transfer was found to increase over the natural convection value by a factor ranging from 2.4 to 25 compared to the previously reported range of 2-5 in the case of copper deposition from acidified solutions. The high tendency of oxygen bubbles to coalesce in alkaline solutions is believed to be responsible for the high rates of mass transfer in alkaline solutions. The rate of mass transfer at a plate stirred by a curtain of oxygen bubbles was found to decrease with increasing plate height and electrolyte concentration. Curtains of H 2 bubbles were found to be less effective in enhancing the rate of mass transfer compared to that of oxygen. Practical application of the results in designing a modified parallel plate electrochemical reactor stirred by a counterelectrode gas curtain was highlighted. The suggested design has the potential of saving part or all of the mechanical stirring energy as well as floor space since it extends vertically.

Electropolishing of Vertical Plates under Intensified Mass Transfer Conditions in a Gas Stirred, Modified Parallel Plate Reactor

“…The exponent 0.4 is in agreement with the value of 0.43 reported for the effect of anodic O 2 discharge on the mass transfer coefficient of the cathodic reduction of K 3 Fe(CN) 6 from alkaline solution at a downstream cathode flush with the O 2 generating anode in the current density range where bubble coalescence was not excessive [11]. Fig.…”

“…1 and contains a number of parallel plate cells arranged vertically in a container in such a way that the anode of a given cell lies downstream of the H 2 evolving cathode of the lower cell with a plastic strip flush with the two electrodes separating them electrically. The concept of using counter electrode gases to intensify diffusion controlled electrochemical processes has previously been examined for electrowinning of metals [10] and electro-inorganic synthesis [11], and the results show that the degree of mass transfer enhancement depends, among other things, on the gas-electrolyte nature; accordingly it is expected that the behavior of the present hydrogen-phosphoric acid system (H 2 -H 3 PO 4 ) will differ from the previously studied systems.…”

Liquid‐Solid Mass Transfer Behavior of a Vertical Array of Closely Spaced Horizontal Tubes in Relation to Catalytic and Electrochemical Reactor Design

“…The reactor merits include simplicity in both design and operation, and uniformity of potential and current distribution. Attempts to improve its performance include increasing the reactor rate of mass transfer via the use of turbulence promoters [1][2][3] and gas bubbles [4,5] and increasing the reactor specific area by replacing the plate electrode with a porous electrode, such as particulate beds, stacked meshes and foams [6,7].…”

Electrocoagulation for the Treatment of Metals Machining Plants Effluents: Experimental and Modeling Study

“…The positive effects of increasing temperature involve: Increasing the temperature decreases the viscosity of the solution and promotes the diffusivity of iron ions and their mass transfer 14, resulting in a depolarization (reduction in η c ) and the prevention of the iron electrode from becoming passive. Temperature enhances the electrophoretic transport of oil particles with negative charge in the direction of the anode, as well as the Brownian dispersion of neutral oil particles and their collision occurrence 14, resulting in big and easily floatable drops. The surface tension of the solution, which binds H 2 bubbles to the cathode surface, decreases as the temperature rises 14. As a result, tiny sized H 2 is released from the cathode, increasing gas holdup and the ability of the bubbles to promote turbulence 19, 20. This enhances the mixing of Fe(OH) 3 and contaminants and reduces the anode's passivation tendency.…”