Experimental and kinetic modeling studies of isoprene pyrolysis at low and atmospheric pressures

Isoprene (2-methyl-1,3-butadiene) is not only the main component in gasoline and a potential fuel additive, but also is considered an important precursor of polycyclic aromatic hydrocarbons. To better understand the isoprene pyrolysis process , the pyrolysis experiments of isoprene in a flow reactor were performed at p  = 30 Torr for T  = 1056 – 1446 K, and p  = 760 Torr for T  = 850 – 1231 K. More than twenty pyrolysis species, especially radicals (methyl, propargyl, and but‑2‑yne-1-yl), isomers (allene/propyne, buta-1,2,3-triene/vinylacetylene, 1,3-butadiene/1-butyne), and aromatics (benzene, toluene, phenylacetylene, styrene , indene, and naphthalene), were identified and their mole fraction profiles were measured using synchrotron vacuum ultraviolet photoionization mass spectrometry . The potential energy surfaces of the unimolecular decomposition, H/CH 3 -abstraction, and H/CH 3 -addition reactions of isoprene were also calculated using quantum chemical calculations at the CBS-QB3 level. Based on the experimental and theoretical results, a detailed kinetic model was developed and validated against the pyrolysis experimental dataset of isoprene from this work and Grajales-González et al. H-addition reactions on the double bond and H-abstraction reactions by H/CH 3 radicals controlled the consumption of isoprene. The C–H bond dissociation reaction on the –CH 3 was the dominant unimolecular reaction in comparison with the isomerization reactions. Abundant aromatics were produced in isoprene pyrolysis, especially at atmospheric pressure, which is ascribed to the high-level concentration of C(2)–C(4) hydrocarbons formation, such as acetylene, ethylene, allene, propyne , 1,3-butadiene, etc.