The additional technology of electrolytic processes

The similarities between the design and characterization of electrolysis cells and other chemical reactors and the need to Integrate the cell with the other unit processes In the plants have been emphasized. On the other hand, there arc some notable diflcrences which need also to be recognized, c.g. the fact that in a comparison of an electrolysis cell with a reactor for a more familiar heterogeneous process such as gas-phase catalysis, there are two outstanding differences  

in both types of reactor, it is desirable to maximize the surface area per unit volume, the designer of an electrolytic cell has to concern himself with the problems of non-uniform current distributions, since the electrode surface will only be active if there is an appropriate local potential difference it was noted above that the geometric arrangement of anode and cathode is the key factor. 

It is the purpose in this section to review these problems and then to discuss those technological features which are unique to electrolytic processes. 

An obvious strategy in electrochemical process engineering is to operate the reactor under mass transport controlled, limiting-current conditions, as the production rate should then be maximized. There are cases, however, when operation at or near the limiting current may not be optimal or even desirable as below  

A consideration of overall process costs (section 2.2), such as the trade-off between energy consumption and space-time yield may result in an optimum current below 

Mass transport processes in the liquid phase are always very slow in comparison with those in the gas phase. This will cause both mass transport limitations on the rate of chemical changes in the reactor and the creation of reaction layers at the solid-fluid interface to be much more troublesome. 

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