Computer-assisted mechanistic modeling of n-hexadecane hydroisomerization over various bifunctional catalysts

Graph theoretic concepts were exploited to construct candidate computer mod els describing the hydroisomerization of n-hexadecane over bifunctional cat alysts at a mechanistic level. The molecules and carbenium ions were repres ented as atomic connectivity matrices and the reactions as matrix operation s. The computer-generated models were then automatically converted to a set of ordinary differential equations representing the reactions in a plug fl ow reactor. Typical diagnostics for the model building process indicate tha t models containing about 1000 species (molecules and ions) and 3000 reacti ons could be generated in around 1000 CPU seconds. Thus, some 25 candidate hydroisomerization models were built and evaluated through qualitative and quantitative comparisons with experimental data. The resulting best model w as further pruned by removing extraneous reactions which did not result in observable products, This model was tuned against experimental data on thre e different catalysts at different temperatures. Good agreement between mod el predictions and experimental data was obtained. Trends in the fundamenta l mechanistic rate constants obtained from the model fitting process were i n harmony with the trends in the acid and metal loadings of the catalysts. Thus, fundamental mechanistic modeling can provide valuable insight into th e nature of the catalytic action. (C) 1999 Elsevier Science B.V. All rights reserved.