Experimental and kinetic modeling study of butene isomer pyrolysis: Part II. Isobutene

The pyrolysis of isobutene was investigated using a tubular flow reactor at an absolute pressure of ∼0.82 atm over a temperature range of 610-860 °C with residence times ranging from ∼0.5 to ∼2.4 s. The initial concentration of the fuel ranged from 5 to 50 mol%. These data were compared to the predictions of a fundamentally based detailed kinetic model. The model accurately predicted the observed fuel conversion, production of light products, and the formation of several important molecular weight growth species. The primary pathways that lead to the fuel decay and the formation of major products are discussed. In particular, H-atom abstraction from isobutene results in the formation of the 2-methyl allyl radical, which undergoes a β-scission reaction to form allene plus methyl. The subsequent addition reaction of 2-methyl allyl to allene is energetically favored and provides a route to the formation of stable molecular weight growth products that are readily converted to benzene and toluene. The potential energy surface for this reaction was derived from CBS-QB3 calculations and the corresponding temperature and pressure dependent rate constants are obtained. The model predictions were also compared and generally are in good agreement with multiple published isobutene pyrolysis data sets that were measured under significantly different conditions.