Packed-bed electrode reactor

Three dimensional packed bed electrodes are generally considered for reactions which operate with low current densities in order to increase localized mass transfer rates and/or increase overall current per unit cell volume. The maximum current density at any position in the electrode structure is limited by the prevailing conditions of mass transfer. The limiting current thus can also have 

The packed bed electrode is one dimensional and both solid and electrolyte phase are continuous media with uniform effective conductivities. 

The electrode is characterized by a uniform specific area, a. The mass transfer conditions between the fluid phase and fixed phase are also assumed to be uniform and defined by a single mass transport coefficient, ki. 

The derivation of the model is similar to that derived for the porous electrode model. We have very similar model equations to Eqs. (115) and (116) for an anodic current, given by 

Note that in the Eqs. (147) and (148), the surface concentration cr is different from the solution concentration cr in the second derivative on the left and in Eqs. (115) and (116) due to convection. Furthermore Di is the lateral dispersion coefficient instead of a lateral diffusion coefficient in the porous electrode case. 

The three-dimensional or packed bed electrode has a thickness L, bonnded on one side by a cnrrent feeder (x = 0) and on the other side by a membrane or free solntion, x = L (Fignre 11). Both electrolyte and electrode phases are assnmed to be continnons media with nniform effective condnctivities and in which the electrical potential obeys Ohm s law. 

Isothermal and steady state conditions apply, tonic migration of the reacting species is neglected. 

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The electrochemical reduction of nitrobenzene to produce p-aminophenol has attracted industrial interest for several decades. However, some limitations may be met in this process regarding overall reaction rate, selectivity and current efficiency using a two-dimensional electrode reactor. These restrictions are due to the organic electrode reaction rate being slow and to the low solubility of nitrobenzene in an aqueous solution. In this example, a packed bed electrode reactor (PBER), which has a large surface area and good mass transfer properties, was used in order to achieve a high selectivity and a reasonable reaction rate for the production of p-aminophenol. The reaction mechanism in an acid solution can be simplified as... 

Fig. 19. Packed-bed electrode reactor for the alkaline synthesis of hydrogen peroxide [77], (By permission from Society of Chemical Engineers, Japan).

Direct Electrochemical Oxidation of Propylene in a Sparged Packed-Bed Electrode Reactor ... 

The oxidation of alkenes has attracted interest over decades as a route for organic electro-synthesis. This has included attempts to cany out direct anodic oxidation to eliminate problems associated with the in situ use of electrochemically generated oxidants. A sparged packed bed electrode reactor (SPBER), with propylene oxidation separated from the generation of hydrogen was used... 

During the design of packed-bed electrode reactors it is important that the actual bed depth is not greater than the effective bed depth, in order to maintain and... 

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