Experimental study of Bechamp process for p-nitrotoluene reduction to p-toluidine

Bechamp process is a well-known process for the reduction of aromatic nitro compound 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 p-nitro toluene (PNT) to p-toluidine (PT) is a process of three steps in series, namely adsorption of PNT on the iron surface, surface reaction of PNT to PT 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.



Reduction of PNT to PT 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 this work, we have carried out experiments to find out the limiting step for PNT reduction. We have considered selectivity of PT as performance criteria in this study at various operating conditions. 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 PNT 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 PNT is suggested in this work.