Single Event Kinetic Modeling of Complex Catalytic Processes

Kinetic models for complex processes may contain an excessive number of rate parameters. Rather than simplifying the reaction scheme the approach illustrated here develops it in terms of the elementary steps of cation chemistry, using a computer algorithm. The resulting scheme, although gigantic, thus consists of a limited number of types of steps, generally involving series of homologous species. The rate coefficients of these steps are modeled based upon transition state theory and statistical thermodynamics. The single event concept explicits the effect of structure on the entropy contribution to the rate coefficient of the transformation, while the enthalpy effect is calculated using the Evans-Polanyi relation. Together with thermodynamic constraints this approach drastically reduces the number of independent parameters to be determined from the experimental data. The approach is applied to the methanol-to-olefins process on ZSM5 and to a process with complex feedstock like the catalytic cracking of vacuum gas oil. In the latter case an additional problem is the requirement of an adequate feedstock definition. Other processes catalyzed by acid catalysts, eventually loaded with metals, like hydrocracking, catalytic reforming, alkylation and, more generall, processes involving series of homologous components can be dealt with along the same lines.