Synergistic effects in toluene/C3H4 isomers co-pyrolysis: Formation of indene and naphthalene

Abstract

A combination of experimental and kinetic modeling study is performed to explore synergistic effects between toluene and C3H4 isomers on the formation of polycyclic aromatic hydrocarbons (PAHs) and pyrolysis reactivity. Co-pyrolysis of toluene-allene and toluene-propyne is investigated in a flow reactor employing synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) at 0.04 bar and 1 bar. Mole fraction profiles of fuels and intermediates up to two-ring PAHs are obtained. A kinetic model for co-pyrolysis of toluene-C3H4 isomers is established and examined against the present data. Sampled mass-specific photoionization efficiency (PIE) curves are employed to identify the presence of aliphatic aromatic species, favoring specific perception into interactions between phenyl/benzyl radicals and C3 species. The synergistic effects observed in this work are not sensitive to the molecular structure of allene and propyne but quite sensitive to the experimental pressures. The reason being that the interactions between phenyl/benzyl radicals and small molecules like CH3, C2H2 and C3H3 are pressure dependent. Both experimental and simulation results indicate the essential role of the aliphatically substituted aromatic in the growth reactions. Indene and naphthalene are identified as the predominant C9H8 and C10H8 products respectively, in all cases studied. Channels leading to the formation of indene and naphthalene vary with pressure, according to rate-of-production (ROP) analyses. The phenyl + C3H4/C3H3 channel and benzyl + C2H2 channel make comparable contributions to the formation of indene at 0.04 bar, while the latter channel dominates the formation of indene at 1 bar. Both C7H5 + C3H3 channel and benzyl + C3H3 channel can lead to the formation of naphthalene at 0.04 bar, while the latter channel is more competitive at 1 bar.