Identification of Five- to Seven-Ring Polycyclic Aromatic Hydrocarbons from the Supercritical Pyrolysis of n-Decane

In order to study the formation of carbonaceous solid deposits from aviation fuels in the pre-combustion environment of next-generation high-speed aircraft, 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, 100 atm, and 133 sec. 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 that there are 24 unsubstituted PAH products with molecular weights between 252 and 300. Of these, 12 are benzenoid: benzo[ a ]pyrene, benzo[ e ]pyrene, perylene, benzo[ ghi ]perylene, anthanthrene, benzo[ b ]chrysene, dibenz[ a,c ]anthracene, dibenz[ a,h ]anthracene, dibenz[ a,j ]anthracene, pentaphene, picene, and coronene; two are methylene-bridged derivatives of two of the benzenoid PAH: 11 H -indeno[2,1,7- cde ]pyrene and 4 H -benzo[ def ]cyclopenta[ mno ]chrysene; five are fluoranthene benzologues: benzo[ a ]fluoranthene, benzo[ b ]fluoranthene, benzo[ j ]fluoranthene, benzo[ k ]fluoranthene, and indeno[1,2,3- cd ]pyrene; and five are fluorene benzologues: dibenzo[ a,h ]fluorene, dibenzo[ a,i ]fluorene, naphtho[1,2- a ]fluorene, naphtho[1,2- b ]fluorene, and naphtho[2,1- a ]fluorene. Eighty-three alkylated derivatives of these PAH have also been identified as products of n -decane pyrolysis. Fourteen of the unsubstituted PAH and all of the alkylated derivatives have never previously 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.