Electrochemical Reduction of Nitrobenzene in a Packed-Bed Electrode Reactor

Electrochemical Reduction of Nitrobenzene in a Packed-Bed Electrode Reactor  

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 (PEER), 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 

In this scheme, nitrobenzene (A ) is first cathodicaly reduced to the intermediate phenyl-hydroxylamine (BJ at the electrode surface. The electrode reaction from to aniline (DJ and the 

Mathematical expressions of concentrations, ca and c/ at the surface of cathode, can be obtained. The total current density in the electrolyte is described as 

The ratio of aniline to p-aminophenol in the solution, namely the selectivity, can be written as 

The mathematical model for the PBE reactor should in general be a two-dimensional model describing the potential and concentration distributions within the packed bed electrode. However, the model can be simplified in certain cases. Under a recycle flow operation, for example, the conversation per pass through the packed bed is small, so that the PBER can be treated as a differential reactor, the potential distribution only in the lateral direction is considered. In this case which is similar to the case in 5.4, the two-dimensional model can be written in a onedimensional Poisson equation form as 

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