Microkinetic modeling of propane aromatization over HZSM-5

Abstract

Reaction kinetic studies of propane conversion to aromatics were conducted on an HZSM-5 zeolite at a pressure of 1 atm, temperatures in the range 793–823 K, and different space times (0–12 g cat h/mol). The rates of production of methane, ethane, ethene, propene, propane, butane, butene, benzene, toluene, and xylene are reported. A kinetic model has been postulated that considers surface species as neutral alkoxides, reactions of these alkoxide species by carbenium ion-like transition states, and alkane activation by carbonium ion-like transition states. The associated elementary steps, categorized within the reaction types adsorption, desorption, unimolecular protolytic cracking and dehydrogenation, β-scission, oligomerization, hydride transfer, alkylation, dealkylation, and cyclization, were parsed into reaction families based on an equal reactivity assumption. A total of 311 reaction steps were grouped into 37 reaction families, and the number of unknown parameters was reduced to 25 using adsorption parameters for n-alkanes and relative rates for β-scission and hydride transfer from the literature. It is proposed that this kinetic model describes the reaction behavior over an HZSM-5 catalyst in terms of relevant rate and equilibrium constants and activation energies.