Identification of Six- to Nine-Ring Polycyclic Aromatic Hydrocarbons from the Supercritical Pyrolysis of <i>n</i>-Decane

Abstract

Degradation of hydrocarbon aviation fuels to carbonaceous solid deposits in the pre-combustion environment, due to oxygen-free, high-temperature, high-pressure conditions, represents a limiting factor in the development of increasingly high-performance aircraft. In order to study this phenomenon, we have pyrolyzed the model fuel n -decane (critical temperature, 344.5 °C; critical pressure, 20.7 atm), an alkane component of jet fuel, under supercritical conditions at 570 °C, 94.6 atm, and 133 s. The product polycyclic aromatic hydrocarbons (PAH), precursors to the solid deposits, have been analyzed by a two-dimensional high-pressure liquid chromatographic separation technique with ultraviolet-visible absorbance and mass-spectrometric detection. The analyses reveal the presence of 24 unsubstituted PAH products, spanning four isomer families: 15 C 24 H 14 PAH, dibenzo[ a, e ]pyrene, dibenzo[ a, h ]pyrene, dibenzo[ a, i ]pyrene, dibenzo[ e, l ]pyrene, naphtho[2,1- a ]pyrene, naphtho[2,3- a ]pyrene, naphtho[2,3- e ]pyrene, benzo[ b ]perylene, dibenzo[ a, e ]fluoranthene, dibenzo[ a, k ]fluoranthene, dibenzo[ b, k ]fluoranthene, dibenzo[ j, l ]fluoranthene, naphtho[1,2- b ]fluoranthene, naphtho[2,3- b ]fluoranthene, and naphtho[2,3- j ]fluoranthene; four C 26 H 14 PAH, dibenzo[ b, ghi ]perylene, dibenzo[ e, ghi ]perylene, dibenzo[ cd, lm ]perylene, and naphtho[1,2,3,4- ghi ]perylene; four C 28 H 14 PAH, benzo[ a ]coronene, benzo[ cd ]naphtho[3,2,1,8- pqra ]perylene, benzo[ pqr ]naphtho[8,1,2- bcd ]perylene, and phenanthro[5,4,3,2- efghi ]perylene; and one C 30 H 14 PAH, naphtho[8,1,2- abc ]coronene. Forty-three alkylated derivatives of these PAH have also been identified as products of the n -decane pyrolysis experiments. Of the 67 six- to nine-ring PAH products identified, only two had ever before been identified as products of n -decane pyrolysis or combustion. The UV spectra establishing the identities of the 24 unsubstituted n -decane pyrolysis products are presented.