Project ForgeThe elementary reversible exothermic gas-phase reaction A+3B⇌2C is to be conducted in a non-isothermal, non-adiabatic plug flow reactor. The maximum allowable reactor temperature is Tmax. To minimize the total reactor volume, the variation of reactor temperature (T) with axial distance from the inlet (z) should be
- Aconstant at Tmax throughout
- Bstarting below Tmax and increasing up to Tmax
- starting at Tmax and decreasing along z
- Drising to a peak below Tmax then falling
Explanation
For an exothermic reversible reaction, the optimal (volume-minimizing) temperature progression starts at the maximum allowable temperature Tmax (to exploit fast kinetics while conversion, and hence the reverse reaction, is still low) and then DECREASES with conversion/axial distance, since equilibrium conversion falls as temperature rises — lowering T as the reaction approaches equilibrium keeps the net rate high.
Source: GATE CH 2012 (2012)
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