Electrochemical Reaction Engineering

The successful development of electrochemical processes for some of the cited reactions requires an understanding not only of surface interactions but also of the changes in activity and selectivity that may incur from cell design, mixing, potential or current distribution, and transport processes. Here, we shall examine some simple reaction engineering principles that would be helpful for elucidating these effects. 

The continuity equation for each ideal model reactor yields for multiple reactions (60, 61) 

Mixing in general decreases the reactant conversion but it may improve selectivity. Thus, the yield of a low-order path in a parallel reaction scheme would improve in a MER, as indicated earlier. The uniform concentration and rate in a MER and the simple algebraic form of the continuity equations (107) make this reactor ideal for kinetic analysis of simple and complex electrocatalytic reactions. 

Electrocatalytic surface reactions may involve convective or diffusive transport of reactants and products external to the electrode surface or in the porous structure. If the rate of mass transport is comparable to or slower than the surface rate, the electrode kinetic and selectivity behavior will be altered (48a, 60-62, 407). 

The continuity equation for a molecular or ionic species diffusing at the external surface of the electrode (407-409) gives in dimensionless form 

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Reaction Engineering. Electrochemical reaction engineering considers the performance of the overall cell design ia carrying out a reaction. The joining of electrode kinetics with the physical environment of the reaction provides a description of the reaction system. Both the electrode configuration and the reactant flow patterns are taken iato account. More ia-depth treatments of this topic are available (8,9,10,12). 

SCOTT, K. (1991) Electrochemical Reaction Engineering (Academic Press). 

Scott K (1992) Electrochemical reaction engineering, Academic Press, London, cited in Ref [13]... 

K. Scott, Electrochemical Reaction Engineering, Acad. Press, London, 1991, Section 2.1.2, pp. 52 - 56. 

Electrochemical reaction engineering deals with modeling, computation, and prediction of production rates of electrochemical processes under real technical conditions in a way that technical processes can reach their optimum performance at the industrial scale. As in chemical engineering, it centers on the appropriate choice of the electrochemical reactor, its size and geometry, mode of operation, and the operation conditions. This includes calculation of performance parameters, such as space-time yield,... 

K. Electrochemical Reaction Engineering, Academic Press, London, 1991. G. Adomian, Solving Frontier Problems of Physics The Decomposition Method, Kluwer, Boston, 1994. 

The brief description of cell design indicates that electrochemical reaction engineering has much in common with chemical reaction engineering except that we have to consider in addition the distribution of potential within the cells (and within three-dimensional electrodes) since this controls the rate of reaction at the metal/solution interfaces. 

It can be seen that electrochemical reaction engineering has much in common with chemical reaction engineering. Scaled-down versions of full-sized cells are readily constructed and the system behavior can be characterized in detail using electrochemical techniques. One can anticipate therefore that there will be a valuable interplay between electrochemical and conventional chemical reaction engineering. It is relevant in this context that whereas some reactions are carried out on very large scales, many desired products are made on the scale of a few tons to a few thousand tons per annum. The investigation of the chemical engineering of small systems is a prerequisite for the successful implementation of such process, a field which can be readily explored in the area of electrochemistry. 

Theoretical treatments of electrochemical reaction engineering, mathematical modelling of reactors and comparative performance of cells have only recently been developed. 

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