The Effects of Temperature on the Yields of the Major Aliphatic and Aromatic Products of Supercritical n-Decane Pyrolysis

Abstract

To investigate the effects of pyrolysis temperature on the production of polycyclic aromatic hydrocarbons (PAH), precursors to solids, in the precombustion environment of fuels for future high-speed aircraft, we have conducted supercritical pyrolysis experiments with the model fuel n-decane, an alkane component of jet fuels. The experiments are performed in an isothermal, isobaric, silica-lined stainless-steel flow reactor at 94.6 atm, 133 s, and at six temperatures in the range of 530–570 °C, over which n-decane conversion rises from 57% to 92%. The products from the experiments have been analyzed by gas chromatography with flame-ionization and mass-spectrometric detection as well as by high-pressure liquid chromatography with diode-array ultraviolet–visible absorption and mass-spectrometric detection, and the experimentally measured product yields are reported, as functions of pyrolysis temperature, for 20 major aliphatic products (mostly C1–C9 n-alkanes and C2–C9 1-alkenes), 27 one- and two-ring aromatics, and 117 PAH of three to nine aromatic rings. The yield-temperature data of 11 of the one- and two-ring aromatics and all 117 of the PAH products are each found to conform well to the first-order global-kinetic rate expression dY/dt = kapp(1 – X), where Y is the measured aromatic-product yield, X is n-decane conversion, and kapp is the global first-order rate constant, kapp = Aappexp[−Eapp/(RT)]. The derived values of Eapp generally increase with increasing aromatic product size from 68.26 kcal/mol for benzene, to 188.96 kcal/mol for the four-ring PAH pyrene, to 351.94 kcal/mol for the eight-ring PAH benzo[pqr]naphtho[8,1,2-bcd]perylene. In addition to all of the values of Eapp and Aapp determined for the individual product PAH, linear relationships for Eapp and ln Aapp as functions of carbon number have been determined, providing a means of modeling the production of PAH of a given carbon number in a generic way.