Ledesma, EB; Felton, PG; Sivo, JA; Wornat, MJ
To better elucidate the mechanisms and kinetics of the reactions of endothermic fuel pyrolysis and PAH formation under supercritical conditions, supercritical pyrolysis experiments with toluene were carried out, an ideal model fuel for hypersonic aircraft. Compositional analysis of the collected toluene products revealed that under supercritical conditions, the PAH product distribution was dominated by benzenoid PAH and was noticeably deficient in PAH with five-membered rings. Methylated PAH were also prominent among the superficial toluene products examined. The yields of PAH, e.g., phenanthrene, anthracene, pyrene, etc., increased markedly with pressure, exhibiting a particularly dramatic rise at pressures exceeding toluene's critical pressure. Temperature also exerted a dramatic effect on PAH yields; for a given pressure, PAH yields from the 535°C experiments were much greater than those from the lower-temperature experiments. The combination of high temperature and high-pressure brought about the formation of several large (8- to 10-ring) benzenoid PAH, i.e., benzo[a]coronene, benzo[pqr]naphtho[8,1,2-bcd]perylene, naphtho[8,1,2-abc]coronene, and ovalene, which were never before observed from the supercritical pyrolysis of any fuel. At 1 atm, such large PAH would only be produced at temperatures much higher than the temperatures employed. The tremendous effects of pressure underscored the necessity of elucidating the mechanisms of PAH formation relevant to supercritical conditions. Original is an abstract.
