Ideal isothermal reactors selectivity

Worz et al. stress a gain in reaction selectivity as one main chemical benefits of micro-reactor operation [110] (see also [5]). They define criteria that allow one to select particularly suitable reactions for this - fast, exothermic (endothermic), complex and especially multi-phase. They even state that by reaching regimes so far not accessible, maximum selectivity can be obtained [110], Although not explicitly said, maximum refers to the intrinsic possibilities provided by the elemental reactions of a process under conditions defined as ideal this means exhibiting isothermicity and high mass transport. 

A tube-wall reactor, in which the catalyst is coated on the tube wall, is conceptually ideally suited for highly exothermic and equilibrium-limited reactions because the heat generated at the wall can be rapidly taken away by the coolant. Previous work (1) has numerically demonstrated that for highly exothermic selectivity reactions, the optimized tube-wall reactor is superior from both steady state production and dynamic points of view to the fixed-bed reactor. Also, the tube-wall reactor is being advanced as a possible reactor for carrying out methanation in coal gasification plants (2). From a reaction engineering point of view, it therefore seems appropriate to analyze the reactor for the analytically resolvable case of complex first-order isothermal reactions. 

The results of a parametric study exploring the effect of mass transport limitations on this reaction gave the results shown in Figure 3. For this study, the reactor was assumed to be isothermal, and the conversion data of Figure 3 show the final composition exiting the reactor. The ideal (kinetics only) result gives the expected high conversion and selectivity due to the selective CO reaction. As mass transport limitation is added, the maximum CO conversion drops (Table 2) due to CO depletion near the surface since O2 is in excess. 

The selective oxidation of CO in the presence of H2 is being carried out in a catalytic, ideal plug-flow reactor at atmospheric pressure and 100 °C. Although the reactions are exothermic, we will assume that the reactor is isothermal in order to develop a preliminary understanding of reaction behavior. We also will neglect pressure drop, assume that transport effects are negligible, and assume that the ideal gas laws are valid. 

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