A fluorescence depolarization technique was used to determine the molecular size of asphaltene solubility fractions of a petroleum resid asphaltene. The molecular size was determined at different emission wavelengths for each solubility fraction. For each subfraction the range of molecular size was found to vary considerably. However, at a given emission wavelength, the molecular sizes for the different asphaltene solubility subfractions are very similar, that is the subfractions differ from each other by different population distributions of the same set of molecules. The size variation among the different subfractions is due to the different molecular population distributions of the constituent components. The population distribution was estimated from published LDMS results.

Thermal decomposition of C 10 -C 14 n-alkanes was studied under near-critical and supercritical conditions. The primary products were C 1 -C m-2 n-alkanes and C 2 -C m-1 1-alkenes, and the secondary products were cis-and trans-2-alkenes, n-C m-1 , n-C m+1 , and C m+2 -C 2m-2 normal and branched alkanes, where m is the number of carbon atoms in the reactant. The relative yields of the primary and secondary products were dependent upon the reaction conditions. Product distributions exhibited large pressure dependence in the near-critical region. The observed product distributions and changes in product composition with reaction conditions were explained by a modified free radical mechanism.n-C10

Thermal stressing of a JP-8 fuel was carried out in an isothermal flow reactor using nickel, stainless steel (316 and 304), Silcosteel, and glass-lined stainless steel tubes at 500 °C wall temperature and 34 atm (500 psig) for 5 h at a liquid fuel flow rate of 1 mL/min. Different length segments along the sample tubes were analyzed to observe the deposit distribution throughout the test section. Temperature-programmed oxidation (TPO) analysis and SEM examination of the stressed tubes showed differences in the amount and nature of the solid deposits obtained on the different substrates. The activity of the tube surfaces toward carbon deposition decreases in the order nickel > SS 316 > SS304 > Silcosteel > glass-lined stainless steel. The catalytic activity of the metal surfaces was noted using TPO analysis in conjunction with SEM examination of the deposited tubes.

The future high-Mach aircraft requires advanced jet fuel with high stability in rigorous thermal environments. In this work high-temperature thermal stability of two JP-8 type jet fuels, a petroleumderived JP-8P and a coal-derived JP-8C was studied by stressing in closed reactors at 450 °C under 0.7 MPa of N2 for periods ranging from 0.5 to 16 h. The extents of fuel degradation in terms of liquid depletion, gas formation, and solid deposition were always higher with JP-8P than with JP-8C.There appeared an induction period for solid formation, which was longer for JP-8C than for JP-8P. Tests with the saturates isolated chromatographically from these fuels indicated that JP-8C saturates are much more stable than the JP-8P saturates, and the higher stability of JP-8C is due to its composition. JP-8C is rich in one-to three-ring cycloalkanes and two-ring hydroaromatics, while JP-8P is composed mainly of long-chain paraffins. GC-MS provided valuable information on the relative stability and molecular transformation of hydrocarbon components in these jet fuels. Cycloalkanes were found to be more stable than long-chain paraffins with the same carbon number. The stability decreases with increasing length of main chain for the long-chain paraffins, or side chain for alkylcycloalkanes. Multisubstituted cycloalkanes are more stable than the monosubstituted ones with the same carbon number. Steric conformation of cycloalkanes also affects their reactivity; for decalin, the trans isomer was found to be more stable than the cis isomer. The higher stability of JP-8C can be attributed mainly to its higher content of cycloalkanes. Tetralins and decalins present in JP-8C also contribute to capping the thermally generated reactive radicals by hydrogen donation.

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