Investigation of Flow-by Porous Electrodes With Two-Phase Electrolyzers (Mass Transfer, Drops, Extraction)
Fenton, James Michael
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https://hdl.handle.net/2142/69743
Description
Title
Investigation of Flow-by Porous Electrodes With Two-Phase Electrolyzers (Mass Transfer, Drops, Extraction)
Author(s)
Fenton, James Michael
Issue Date
1984
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Abstract
Solubilizing reactants and products in electrolytes of high conductivity is an important aspect of industrial systems such as flow-through batteries and electro-organic syntheses. Two-phase processes appear to be promising because they can be used to meet competing requirements for high mass transfer rates, high conductivity, and high loading of electroactive species.
The effect of two-phase liquid-liquid flow upon mass transfer behavior in flow-through porous electrodes having a perpendicular configuration was studied. An experimental format was developed which enabled the measurement of local reaction rates, concentrations, and potential distribution along the axial direction. The electrochemical limiting current method was used to measure mass transfer coefficients. Three systems were studied: (1) ferricyanide reduction from basic aqueous solution containing no dispersed second phase; (2) ferricyanide reduction from basic aqueous solution containing toluene as an inert dispersed phase; (3) iodine reduction from an aqueous/toluene dispersion in which the reactant is highly soluble in the organic phase. Experiments were carred out with controlled variation of solute concentration, dispersed phase void fraction and droplet size, flow velocity, and packed bed specific surface area. It was found that the mass transfer coefficient was not enhanced by addition of an inert second phase. When the dispersed phase contained dissolved reactant, the overall mass transfer coefficient was increased substantially.
The experimental results served as a basis for upgrading theoretical models of porous electrodes to account for two phase liquid-liquid feedstock. The solution phase potential variation with a single reactant under mass transfer controlled conditions was examined.
A theoretical model was presented in which details of the droplet-electrode-surface interaction were described. A solution which described the potential field around a spherical drop tangent with a planar equipotential surface was obtained. The current distribution on the electrode plane and the incremental flux of species to the electrode caused by a dilute array of drops was also evaluated.
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