Relationship between the Formation of Aromatic Compounds and Solid Deposition during Thermal Degradation of Jet Fuels in the Pyrolytic Regime

Abstract

The formation of pyrolytic solid deposit, or coke, in the fuel line can be detrimental to the operation of high-speed aircraft. Yet, the formation of coke from the fuel has not been well characterized. The present study has investigated the relationship between the formation of aromatic compounds and solid deposition for three candidates for high-thermal-stability jet fuels at 482 °C (900 °F) with stressing periods up to 2 h. The fuels include one coal-derived (JP-8C), one paraffinic petroleum-derived (JP-8P), and one naphthenic petroleum-derived (DA/HT LCO). The DA/HT LCO, an extensively hydrotreated light cycle oil where virtually all aromatics have been hydrogenated to cycloalkanes, suppressed the solid deposition to a greater extent than that of the more paraffinic petroleum-derived JP-8P and showed a comparable low solid deposition to that of the coal-derived fuel JP-8C. Both GC/MS and solution-state 13 C NMR analysis on the stressed fuels confirmed that the paraffinic content is most likely to crack under thermal stress, while cycloalkane structures are more thermally stable. Solution-state 13 C NMR and HPLC investigations of the overall structure of the stressed liquids indicate that the solid deposition is a function of the rise in the aromatic content and also the amount and rate of development of the nonprotonated aromatic carbons, giving mostly 2 to 4 rings aromatics. Furthermore, solid-state 13 C NMR was used to follow the development of the aromatic structure in the corresponding solid deposit as a function of the buildup of aromatic compounds in the stressed liquid fuel.

Formation of coke in thermal cracking of jet fuel under supercritical conditions

“…When the temperature is higher than 550uC, the polymerization of radicals towards coke deposition becomes obvious [6,10]. This process includes the ring formation and propagation.…”

“…Wickham et al studied the formation of filamentous carbons in supercritical cracking of fuels and analyzed the effect of metals [5]. John et al found that the coke deposition is correlated with the aromatic compounds formed during the cracking reaction [6]. Guo et al studied the properties of formed coke [7].…”

Alternative Microturbine Fuels Feasibility Study Through Thermal Stability, Material Compatibility, and Engine Testing

“…At temperatures above 400 °C, dissolved oxygen has already reacted and the fuel suffers pyrolytic decomposition, exponentially increasing the deposition rates with temperature and linearly with residence time [7]. At those temperatures, hydrocarbon chains undergo cracking into C1-C4 gases and cycloalkanes, eventually leading to aromatic compounds [8]. As the fuel temperature is increased (usually above 450 °C), dissolved oxygen is depleted and the dominant reaction mechanism in the deposit's formation is pyrolysis [6].…”

Refinery Integration of by-Products From Coal-Derived Jet Fuels

“…Previous work at Penn State has resulted in significant progress in identifying the remaining critical barriers to realization of coal-based fuels [11][12][13][14][15][16][17][18][19][20]. The overall objective of this project is to examine the characteristics and quality of the streams other than the jet fuel, and what effect those materials would have on the other unit operations in the refinery, the quality and value of the other products.…”