Computer generation of reaction mechanisms using quantitative rate information: Application to long-chain hydrocarbon pyrolysis

In recent years, the use of mechanistic modeling to identify the underlying kinetics of complex systems has increased greatly. One of the challenges to kinetic modeling is the construction of a model which can capture the essential chemistry of a system while a manageable size is retained. The rate-based generation of mechanistic models is an attractive approach because kinetically significant species can be determined and selectively included in the final mechanism. An algorithm for the rate-based generation of reaction mechanisms developed previously(1) was improved and used to construct a compact mechanistic model for low-pressure tetradecane pyrolysis. Though thousands of species and reactions were generated, only a small portion of these (2% of species and 20% of reactions) was deemed necessary and incorporated into the final model. Experimental data were used to determine frequency factors for a subset of the reaction families, while all other kinetic parameters were set on the basis of literature values. With no adjustment to the optimized frequency factors, the mechanistic model was able to accurately predict reactant conversions and product yields for varying reaction conditions and initial reactant loadings. It was also observed that increasing the quantity of species initially seeded resulted in a smaller mechanism that had comparable fitting and predicting abilities as those of the models seeding only the reactant. Subsequent regeneration of the reaction mechanisms using the optimized values for the frequency factors resulted in smaller models with comparable capabilities.