Kinetics of Reduction of Nitrotoluenes by H2S-rich Aqueous Ethanolamine

Abstract

The reduction of nitrotoluenes (o-, m- and p-) by H2S-rich aqueous monoethanolamine (MEA) was carried out in an organic solvent, toluene, under liquid-liquid mode with phase transfer catalyst, tetrabutylammonium bromide (TBAB). The selectivity of toluidines was found to be 100%. The reaction rate of m-nitrotoluene (MNT) was found to be highest among the three nitrotoluenes followed by p- and o-nitrotoluene (PNT and ONT). The reaction was found to be kinetically controlled with apparent activation energies of 18.2, 21.1, and 21.7 kcal/mol for MNT, PNT, and ONT, respectively. The effects of different parameters such as TBAB concentration, sulfide concentration, concentration of nitrotoluenes, MEA concentration, and elemental sulfur loading on the conversions and reaction rates of nitrotoluenes were studied to establish the mechanism of the reaction. The rate of reaction of nitrotoluene was found to be proportional to the concentration of catalyst, to the square of the concentration sulfide, and to the cube of the concentration of nitrotoluenes. A generalized empirical kinetic model was developed to correlate the experimentally obtained conversion versus time data for the three nitrotoluenes. The present work has a very high commercial importance as it can replace the expensive Claus process, which gives elemental sulfur as the only product.