Monolithic Catalysts with High Thermal Conductivity for Improved Operation and Economics in the Production of Phthalic Anhydride

Recent research on extruded monoliths made from materials with high thermal conductivity has shown that such catalyst supports can provide for excellent radial heat-transfer properties. In this paper the use of monolithic catalyst supports in the oxidation of o-xylene to phthalic anhydride is discussed. It is found that for the key catalyst design variables, e.g., amount of active material per reactor volume and thickness of coating, the values for conventional catalysts could be exceeded. Evaluation of the reactor performance is done by means of a detailed mathematical model and literature kinetics, which were adapted to match the performance of industrial reactors and catalysts. The enhanced heat-transfer properties result in better control of the hot spot and allow for operation at more severe conditions, e.g., higher feed concentrations. At equal feed conditions, a higher coolant temperature or catalyst loading is required to balance the lower reaction rates as a result of the lower reactor temperature. The simulation results suggest that higher yields of phthalic anhydride can be achieved at equal or lower hot-spot temperatures. If desired, a significant increase in the reactor capacity is expected by operating at higher feed concentrations. An economic evaluation of the results showed that annual cost reductions on the order of $1 million or more are expected for a 45 kt/year unit.