Studies in the oxidation of benzene

Abstract

Oxidation as an important unit process having considerable promise has been highlighted. A new process of phenol manufacture based on the direct oxidation of benzene as opposed to the multi-stage processes (like Scientific Design Co.’s oxidation process) has been suggested for detailed consideration. Literature pertaining to electrochemical, gas phase, liquid phase, photochemical and radiolytic oxidation of benzene has been reviewed. On the basis of this survey, vapour phase catalytic oxidation of benzene in fixed and fluidised beds has been taken up for study. Thermodynamic analysis of the reactions occurring during the oxidation indicates all the reactions to be irreversible and highly exothermic. Economic analysis of the various phenol manufacturing processes by pre-cost estimation methods indicates that processes based on the oxidation of cumene, toluene and benzene are among the most favourable processes so far as the economics is concerned. Investigations carried out with fourteen different catalysts with temperature, time-factor, particle size of catalyst, mole ratio of reactants, catalyst composition, additional oxidising agents like oxides of nitrogen and L/D ratio as parameters in fixed and fluidised beds indicate cerium molybdate and praseodymium oxide as the most promising catalysts for the partial oxidation of benzene. All the catalysts investigated are found to give the same reaction mechanism with the exception of praseodymium oxide which is found to give a different mechanism when employed in fixed bed. Rate equations developed on the lines of Rodiguin and Rodiguina for consecutive reactions are found to satisfy the experimental data. Mechanism of the reaction considering Langmuir-Hinshelwood approach to gas phase reactions catalyzed by solids has been discussed. Reaction is found to be not diffusion controlled on the basis of calculation of HRU and HTU. Stability of reactant and optimisation studies have also been considered.