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Kinetic and Calorimetric Considerations in the Scale-up of the Catalytic Reduction of a Substituted Nitrobenzene - Sandoz Research Institute

M.J. Girgis, K. Kiss, M. Prashad, D. Har, R.S. Yoskowitz, B. Basso, O. Repic, T. Blacklock, and R.N. Landau
Sandoz Research Institute.
A reaction calorimetric investigation was conducted to assess proposed scale-up conditions (30 psig, 10 °C, initial reactant concentration = 0.114 g/g, catalyst concentration of 7.6 · 10–4 g/g) for the batch-wise reduction of a substituted nitrobenzene to give the corresponding aniline in the presence of H2, Pd/C catalyst, and ethyl acetate solvent.

Heat evolution rates at these conditions were judged to be too large for safe plant operation.  Alternative processing conditions were investigated, taking into account heat removal, pressure limitations, and gas-liquid mass transfer rates in the plant equipment as well as differences in reactivity between plant- and laboratory-prepared reactants. The recommended conditions (30 psig, 20 °C, and catalyst concentration of 8.9 · 10–4 g/g) were employed in the pilot plant, which resulted in conversion rates almost identical to those in the laboratory reactor, demonstrating the reaction calorimeter’s capability for scaling up a highly exothermic reaction without by-product formation. Major improvements over the originally proposed process included operation at 20 °C to take advantage of the greater cooling capacity and decreasing the batch holding time by more than 35 %.

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