Comparison between FBR and PBMR - Reactive Conditions

In this section the reactor concepts are compared under reactive conditions, using the oxidative dehydrogenation of ethane for illustration of the reactor behavior. 

In Fig. 5.4 the effect of oxygen concentration on the reactor performance is depicted for both reactor types. The simulation results were obtained with the isothermal model, thus neglecting the effect of temperature on the reactor performance. The space-time [w fF-x] was 200kgs/m in the calculations otherwise the parameters given in Table 5.2 were used. 

The ethylene selectivity is depicted in Fig. 5.4b. As expected from the kinetics, the maximum values are obtained for small amounts of oxygen in the feed. In agreement with the reaction rate characteristics, an increase of the oxygen level leads in both reactors to ethylene loss, due to the enhancement of the consecutive reactions. The simulations clearly show that due to shorter residence times the deep oxidation reaction was suppressed in FBR. For the parameter range considered the application of PBMR would not be favorable, if high ethylene selectivity is the objective. 

Regarding ethylene yield the PBMR is superior compared to the FBR (Fig. 5.4c). In the space-velocity region considered the maximum ethylene yields are achieved at high oxygen concentrations. Compared to the FBR higher conversion is achievable in the PBMR, while the ethylene selectivity is decreased only moderately, which leads to higher ethylene yields. 

Comparing the reactors at the same conversion in the classical selectivity vs. conversion plot (Fig. 5.4d) one can see that at a low conversion level the applica- 

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