Experimental study of Bechamp process for nitrobenzene reduction to aniline

Bechamp process is a well-known process for the reduction of aromatic nitro compounds using zero valent iron powder in acidic conditions. The Bechamp reaction is a multiphase reaction with gas, liquid and solid phases. The complex reaction mechanism contains series and parallel reactions resulting into by products and side products apart from the amine product. Overall reduction of nitrobenzene to aniline is a process of three steps in series, namely adsorption of nitrobenzene on the iron surface, surface reaction of nitrobenzene to aniline and desorption of the product from the iron surface. In the literature it is suggested that the adsorption step is the rate limiting step for nitro aromatic reduction. Nitrobenzene is a carcinogenic pollutant and is used in dye, agrochemicals and rubber industries. It is reported in literature that nitrobenzene is dangerous even at lower concentrations (ppm) and it is non-biodegradable in nature. Reduction of nitrobenzene to aniline by Bechamp process is carried out in a 500 ml batch reactor in this work. Gas Chromatograph (GC) is used for the sample analysis. A GC method has been developed with toluene as the solvent for determining the compositions of various reaction components.



In our literature study we found that using Bechamp process, nitrobenzene reduction was studied at ambient temperature and at lower rpm (up to 50). The effect of temperature on the Bechamp reduction of nitrobenzene was absent. Also at higher concentrations of nitrobenzene the study was not available. In this work we filled this gap by studying the Bechamp reduction of nitrobenzene at various temperatures (30 oC to 100 oC) and higher rpm (up to 600). We also present the effect of rpm on rate constant and model this relation of mass transfer constant and rpm by Frossling correlation.



Finally, we have extended the work of reduction of nitrobenzene in a batch reactor work to the industrial semi-batch system with gradual addition of Fe. Based on these results, a reaction mechanism of the reduction of nitrobenzene is suggested in this work.