Advances in hydrogen sulphide utilisation: phase transfer catalysed selective reduction of nitronaphthalene

Abstract

The current study demonstrated the selective reduction of 1-nitronaphthalene (1-NN) by hydrogen sulphide (H₂S) absorbed in aqueous N-methyldiethanolamine (MDEA), which is a commonly encountered process in amine treating unit (ATU) of petroleum refinery. The modified Zinin reduction has been carried out using tetra-n-butylphosphonium bromide (TBPB) as phase transfer catalyst under Liquid–Liquid (L–L) biphasic mode. The selectivity of product 1-aminonapthalene was found to be 100% and the reaction was kinetically controlled with the activation energy of 20.77 kJ mol⁻¹. The influence of the process parameters like stirring speed, concentration of 1-NN, concentration of aqueous sulphide, concentration of catalyst, MDEA concentration, elemental sulphur loading at different reaction time on the reactant conversion and the reaction rate of 1-NN were studied for establishment of the reaction mechanism. The kinetic model and mechanism of complex L–L phase transfer catalytic process have been developed and then the model has been validated against the experimental data. This approach of reducing 1-NN by H₂S-laden MDEA can substitute the energy-expensive Claus process, which gives no other product than sulphur.