Propane heat management

Several important aspects of propane ammoxidation reaction chemistry are quite different from that of propylene ammoxidation and have to be taken into account in the development of a commercial operation. One important difference is the higher heat content of propane as compared to propylene, thus making the propane ammoxidation reaction a more exothermic reaction than the propylene ammoxidation reaction (Table 2). Compared to propylene ammoxidation at typical reaction temperatures, approximately 117 kJ more heat is produced for each mole of propane converted. For a commercial process this means that careful attention must be paid to heat management in the reactor. For such a highly exothermic process, a fluid-bed reactor provides better isothermality through more uniform heat distribution and more efficient heat removal than is possible with a fixed-bed reactor. Thus, a commercial propane ammoxidation process will likely use fluid-bed cataljdic technology similar to the current propylene-based process. 

One common method for managing the adiabatic temperature rise in fixed-bed reactors is to dilute the reactant stream with a gas that would provide the mass to absorb the heat of reaction. Light hydrocarbon reaction products (methane, ethane, propane) can be recycled for this purpose. However, the costs associated with the recycle operation could be substantial if the reaction is strongly exothermic. Special attention must be given to reduce the recycle ratio. 

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