Heuristic approach to complex kinetics

Some authors have not only given advice but have created methods to execute experiments to generate kinetic models. The Heuristic Approach to Complex Kinetics of Cropley (1978) which is well tested, is one that will be described next. Then, other recommendations will be discussed briefly. 

Cropley made general recommendations to develop kinetic models for compUcated rate expressions. His approach includes first formulating a hyperbolic non-linear model in dimensionless form by linear statistical methods. This way, essential terms are identified and others are rejected, to reduce the number of unknown parameters. Only toward the end when model is reduced to the essential parts is non-linear estimation of parameters involved. His ten steps are summarized below. Their basis is a set of rate data measured in a recycle reactor using a sixteen experiment fractional factorial experimental design at two levels in five variables, with additional three repeated centerpoints. To these are added two outlier 

Rule 1 Develop an exponential or power-law model in dimensionless 

The last term indicates interaction of temperature and partial pressure (xj = Pj/pj,cp) 

Rule 2. Eliminate any variable that was not significant in the exponential model. 

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Cropley, J. B. Heuristic Approach to Complex Kinetics, pp. 292-302 in Chemical Reaction Engineering—Houston, ACS Symposium Series 65, American Chemical Society, Washington, DC (1978). 

Development of theoretical principles of goal-directed influence on a complex chemical process, similar to the described cases of optimal control, is based on the detailed mechanism of the process. Such an approach is the most fundamental with a relatively wide prognostic range. Hence, the principles of goal-directed influence do not interpret the reaction mechanism passively, but allow also correcting the ideas on the mechanisms, making them more realistic. Here a quite simple principle is applicable if the kinetic model is accurate and reliable, then it has heuristic capabilities, that is, it describes correctly the behavior of a reaction system when varying the conditions of the reaction. 

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