(575bc) Experimental Investigation of Mass Transfer Coefficient of Nitrobenzene In Concentrated Sulfuric Acid

The nitration of nitrobenzene with mixed acid (mixture of concentrated sulfuric and nitric acids) is a well-known example of heterogeneous liquid-liquid reaction. In this system, reaction occurs exclusively in the mixed acid phase. The organic species dissolves in the aqueous mixed acid phase and reacts with nitronium ion generated by the reaction of concentrated sulfuric and nitric acids. In our earlier study (Rahaman et al.(2007), AIChE J., 53, 2476 ? 2480) it was observed that the conversion of reactants and as well as the yield of the product were dependent on the amount of nitrobenzene transferred into the mixed acid phase. Thus, the information of equilibrium solubility and mass transfer coefficient of nitrobenzene in the different concentration of sulfuric acid are essential to predict the rate of mass transfer and consequently the chemical conversion. In this work, the mass transfer coefficient of nitrobenzene from organic phase into the aqueous sulfuric acid phase was measured under flat interface condition by batch dynamic process. Nitrobenzene was treated with sulfuric acid of different concentrations between 14.1 ? 17.1 kmol/m³, and transfer of nitrobenzene was measured as a function of time. Experiments were carried out at different temperatures and sulfuric acid concentrations. The overall volumetric mass transfer coefficients were estimated at different impeller speeds with the same physical conditions. We observed some important physico-chemical phenomena associated with nitrobenzene when treated with high concentration of sulfuric acid. Results show that the overall volumetric mass transfer coefficient increased significantly with the increase in concentration of sulfuric acid, temperature and impeller speed. A sharp increase in the value of volumetric mass transfer coefficient was observed around 16.5 kmol/m³ of the sulfuric acid concentration. The value of volumetric mass transfer coefficient was increased by one and half order of magnitude for two times increase in the impeller speed.