Classification of Reactivity in Heterogeneous Reactions

Astarita (1967), Levenspiel (1972), and Doraiswamy and Sharma (1984) describe an effective framework in which to evaluate the relative contributions of mass transfer and reaction kinetics in heterogeneous systems. This classification is as follows. 

The other key difference between homogeneous and heterogeneous reactions regarding selectivity is that significant selectivity effects can occur in heterogeneous systems at far lower absolute reaction rates because the mass transfer limitations can be very severe. In addition, these effects can be subject to considerable magnification on scale-up to plant operations. These effects can be visualized as changing the inherent kR2/kRi ratio, as measured by independent determination of the rate constants, to an apparent value caused by mass transfer limitations. 

In Section 13-3, examples are used to illustrate the mixing issues that can be significant for various types of heterogeneous systems. The analysis of deviations from ideal behavior in homogeneous systems applies in many of these cases. Homogeneous reactions are more amenable to quantitative analysis and can therefore be developed more completely. The extension of the principles to heterogeneous systems will be more qualitative because of the complexity of these systems. 

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