Oxidation of Aromatic hydrocarbons

Abstract

TITLE: THE OXIDATION OF AROMATIC HYDROCARBONS. The literature on the oxidation of benzene, phenol, p-quinone and maleic anhydride has been reviewed. Various kinetic models have been presented for oxidation of benzene but the most accepted model assumes the formation of only maleic anhydride and carbon dioxide. However, during the oxidation of benzene several intermediates are formed. These are phenol, p-quinone and maleic anhydride. The kinetic models for these intermediates should be known. Therefore, oxidation studies of these compounds have also been carried out in addition to benzene. Thermodynamic calculations of these compounds reveal that the oxidation of these compounds is feasible with evolution of several kilo­ calories of heat and reactions are irreversible. Economic calculations reveal that benzene oxidation to maleic anhydride is feasible even at 10% conversion. In the oxidation of benzene various catalysts based on vanadia are used but chromia–vanadia and molybdena–vanadia on silica gel are selected for comprehensive studies on the basis of good conversion of benzene to maleic anhydride. The oxidation of benzene, phenol, p-quinone and maleic anhydride is carried out in the fluidized bed and the effect of various parameters viz., temperature, mole ratio of the reactants, time factor, size of the catalyst, L/D ratios and various gaseous promoters like SO?, NO? and Br? have been investigated. The effect of these parameters reveals that maleic anhydride and p-quinone oxidation reactions follow a consecutive reaction mechanism as follows: Maleic anhydride -k?? Quinone -k?? Maleic anhydride ? Carbon dioxide k?? Carbon monoxide. Phenol oxidation reaction is found to follow the parallel and consecutive reaction: Phenol -k?? Quinone -k?? Maleic anhydride -k?? Carbon dioxide. The scheme suggested for benzene oxidation on the basis of the schemes for the intermediates is given as follows: Benzene -k?? Phenol -k?? Quinone -k?? Maleic anhydride -k?? Carbon dioxide. Various rate constants and activation energies for the disappearance of different species are evaluated. The effect of the various physical and chemical steps on the rate of various reactions is investigated and effectiveness factors for the different catalysts employed in the oxidation of these compounds are determined. The design of the fluidized bed reactor and optimization studies are carried out. The characterization of the flow in the reactor has been carried out by determining the dispersion factor by R.T.D. concepts.