The U.S. Air Force (USAF) has committed to use 1/1 volumetric blends of conventional jet fuels with Fischer-Tropsch (FT) derived fuels by 2016. Previous work by Balster et al. (Balster, L. M.; Zabarnick, S.; Striebich, R. C.; Shafer, L. M.; West, Z. Energy Fuels 2006, 20, 2564-2571) examined the relationship between thermal oxidative deposit and the concentration of various polar compounds present in 20 petroleum jet fuels. The thermal oxidative stability of FT blends, derived from four conventional jet fuels selected from the study of Balster et al. (Balster, L. M.; Zabarnick, S.; Striebich, R. C.; Shafer, L. M.; West, Z. Energy Fuels 2006, 20, 2564-2571), was examined with the Penn State University (PSU) flow reactor. Excellent linear correlations were found between fuel thermal oxidative deposit and indigenous fuel phenol, indole, and carbazole concentrations. This data is consistent with a mechanism previously proposed for the thermal oxidative degradation of both jet and diesel fuels (Beaver, B.; Gao, L.; Burgess-Clifford, C.; Sobkowiak, M. Energy Fuels 2005, 19, 1574-1579).

Many studies of the pyrolytic degradation of coal-derived and petroleum-derived aviation fuels have demonstrated that the coal-derived fuels show better thermal stability, both with respect to deposition of carbonaceous solids and cracking to gases. Much previous work at our institute has focused on the use of refined chemical oil (RCO), a distillate from the refining of coal tar, blended with light cycle oil (LCO) from catalytic cracking of vacuum gas oil. Hydroprocessing of this blend forms high concentrations of tetralin and decalin derivatives that confer particularly good thermal stability on the fuel. However, possible supply constraints for RCO make it important to consider alternative ways to produce an "RCO-like" product from coal in an inexpensive process. This study shows the results of coal extraction using LCO as a solvent. At 350 °C at a solvent-to-coal ratio of 10:1, the conversions were 30-50 wt % and extract yields 28-40 wt % when testing five different coals. When using lower LCO/coal ratios, conversions and extract yields were much smaller; lower LCO/coal ratios also caused mechanical issues. LCO is thought to behave similarly to a nonpolar, non-hydrogen donor solvent, which would facilitate heat-induced structural relaxation of the coal followed by solubilization. The main components contributed from the coal to the extract when using Pittsburgh coal are di-and triaromatic compounds.

Data is presented from the PSU flowing reactor in the 350−550 °C range that shows that jet fuel derived tube surface thermal oxidative deposit and temperature are inversely related; as fuel temperature increases tube surface deposit decreases. It is proposed that this phenomenon is due to a change in the relative rates of the steps for the peroxyl-radical-chain mechanism of autoxidation under conditions of very high radical initiation rates. In addition, data is presented for two novel hydrocarbon stabilizers, in five different fuels, which documents a 57% decrease, on average, for fuel thermal oxidative surface deposition.