Case Study Kinetics of High-Temperature Ammonia Oxidation in an Annular Reactor

Case Study Kinetics of High-Temperature Ammonia Oxidation in an Annular Reactor 

In analogy with a flxed bed reactor (W7f nhj), the kinetic data are represented by T/fNHa. where L stands for the length of the catalyst coating and Fnhj is the molar flow rate of ammonia. Standard conditions consisted of a mixture of 3 vol % NH3 and 20 vol% O2 at a total flow rate of 400ml/min. A hotspot temperature of 6 K was measured at 50% conversion of 3 mol% ammonia. 

To check if the data were affected by mass transfer limitations, the criterion developed by Berger and Kapteijn [48], Eq. (36.5), was applied. 

W increased the ammonia conversion, but lowered only slightly the NO selectivity. Increasing the oxygen partial pressure lowered the NO selectivity, but did not influence the ammonia conversion. Increasing the ammonia partial pressure increased the NO selectivity, but had little effect on the ammonia conversion. This might be due to strong adsorption of ammonia on the catalyst. Reproducible data under standard test conditions were obtained even after several days of time on stream. 

These steady-state data will be further discussed in this chapter in the light of a reaction mechanism as determined from transient kinetics. 

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