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

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 degrees C; critical pressure, 20.7 atm), an alkane component of jet fuel, under supercritical conditions at 570 degrees 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 PAR products, spanning four isomer families: 15 C24H14 PAR, 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[2,3-4-fluoranthene; four C26H14 PAR, dibenzo[b,ghi]perylene, dibenzo[e,ghi]perylene, dibenzo[cd,lm]perylene, and naphtho[1,2,3,4-ghi]perylene; four C28H14 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 C30H14 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 PAR 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.