Hydrogen-Transferring Pyrolysis of Long-Chain Alkanes and Thermal Stability Improvement of Jet Fuels by Hydrogen Donors

Hydrogen-transferring pyrolysis refers to the thermal decomposition of hydrocarbons in the presence of hydrogen donors. Relative to the pyrolysis of pure n-tetradecane (m = 14 in C_mH_2m+2) at 450 °C, adding 10 vol % of H-donor tetralin suppressed n-C₁₄ conversion by 68 % after 12 min of residence time, by about 66% after 21 min, and by 37% after 30 min. The presence of tetralin not only inhibited the n-C₁₄ decomposition, but also altered the product distribution. The decomposition and isomerization of primary radicals are strongly suppressed, leading to a much higher ratio of 1-alkene to n-alkane with m - 2 carbon atoms and slightly higher alkene/alkane ratio for the other product groups. The overall reaction mechanism for the initial stage of hydrogen-transferring pyrolysis is characterized by a one-step β-scission of secondary radical followed by H-abstraction of the resulting primary radical. Moreover, desirable effects of the H-donor are also observed even after 240 min at 450 °C, especially for inhibiting solid deposition. We also examined the effect of tetralin addition on the deposit formation from a paraffinic jet fuel JP-8 which is rich in C₉-C₁₆ long-chain alkanes, and an aromatic compound, n-butylbenzene. Adding 10 vol % tetralin to a JP-8 jet fuel, n-C₁₄, and n-butylbenzene reduced the formation of deposits by 90% (from 3.1 to 0.3 wt %), 77% (from 3.0 to 0.7 wt %), and 54% (from 5.6 to 2.6 wt %), respectively. These results suggest that, by taking advantage of H-transferring pyrolysis, hydrocarbon jet fuels may be used at high operating temperatures with little or no solid deposition.