Evidence On the Usability of Shale Oil as Jet Fuel

MUSHRUSH, GEORGE W. and MOSE, DOUGLAS G., Chemistry Department, George Mason University, Fairfax, VA 22030-4444

Our nation's oil shale deposits are potentially a very large reserve of oil many times larger than our proven crude oil reserves.  Organic material in oil shale is typically ~ 0-15% bitumen and 85-100% kerogen. Middle distillate fuels used by military jet aircraft must have a freezing point below -50 C because jets operate at high altitudes and a flash point of above 60 Centigrade to minimize the fire hazard during bulk storage.  Depression of the freezing point is related to the n-alkane content, specifically n-hexadecane.  Fuels derived from shale oils have a higher percentage of n-alkanes (~40%), compared to fuels derived from petroleum (~30%) and fuels derived from coal (~15%).
The percentage of n-alkanes in shale oil are much too low to explain the high n-alkane percentage in the fuels derived from shale oil.  Distillation of the shale oil under conditions which mimic the refining process known as delayed coking, normally unreactive kerogen undergoes thermal degradation (~ 450 C and 600 pKa) to give oil (65-70%), gas (10-15%), coke (15-20%) and water (~5%), and the oil includes middle distillate fuels that are high in n-alkane content.
The formation of these abundant n-alkanes in the jet fuel distillation range could be explained if large n-alkanes were present in the crude oil source, but in fact the quantities of large n-alkanes are insufficient to explain the observed amounts of smaller n-alkanes. We hypothesize that compounds containing long unbranched alkyl groups may be the source of the n-alkanes, and a multistage cracking process can be invoked to explain the observed distribution of n-alkanes.

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