Wednesday, April 12th, :00 a.m. 10:00 a.m. How Jet Fuel Stability is Handled in Specification

Transcription

1 Wednesday, April 12th, :00 a.m. 10:00 a.m. How Jet Fuel Stability is Handled in Specification David Abdallah Defense Logistics Agency Energy 2017 Worldwide Energy Conference (WWEC) Gaylord National Hotel and Conference Center in National Harbor, Maryland This presentation includes forward-looking statements. Actual future conditions (including economic conditions, energy demand, and energy supply) could differ materially due to changes in technology, the development of new supply sources, political events, demographic changes, and other factors discussed herein (and in Item 1A of ExxonMobil s latest report on Form 10-K or information set forth under "factors affecting future results" on the "investors" page of our website at This material is not to be reproduced without the permission of Exxon Mobil Corporation.

2 How jet fuel stability is handled in specification Total Composition Aromatics Appear. Color Thiols Acidity Sulfur Volatility Fluidity Combustion Corrosion Thermal stability Bulk properties Distil temps Viscosity Specific energy Density Smoke point Flash point Naphthalenes Freeze point Trace properties Copper strip JFTOT DP JFTOT VTR Existent Contaminates Particles MSEP gum Other Conduct. Lubricity X1.9 Fuel Storage Stability X1.9.1 Existent Gum Gum is a nonvolatile residue left on evaporation of fuel.. The amount of gum present is an indication of the condition of the fuel at the time of test only. Large quantities of gum are indicative of contamination of fuel by higher boiling oils or particulate matter and generally reflect poor fuel handling practices. X1.3 Thermal Stability X Commercial jet fuels should be thermally stable at a fuel temperature as high as 163 C (325 F). Such fuels have been demonstrated to have inherent storage stability with respect to gum formation. 2

3 Polars in jet fuel background Some polars are natural others are impurities and contaminates Significant polar composition variability between jet fuels Attempts to correlate polars data with jet fuel properties (trace properties like stability) remains a very dubious task * Polars is a relative term and in jet refers to anything that is not a pure hydrocarbon, examples are organo sulfur, oxygen, or nitrogen compounds 3

4 Significance of polars in jet fuel Jet fuel stability issues are caused by polar molecules, but not all polars are deleterious. In fact, some can be beneficial (ex, antioxidants and lubricity) Historically polar nitrogen compounds implicated as deleterious N compounds < O compounds and << S compounds but N compounds play an oversized role in deposit composition (N in deposit/n in fuel >10,000 a ) Influence on JFTOT unclear but often deemed as harmful Very, very, little is known about the complex collection of reactions that lead to thermal and storage instability Pyrrole cited many times in storage stability issues Some antagonistic roles identified in the literature for thermal stability b basic nitrogen compounds with disulfide compounds organic acids compounds with pyrrole compounds Thus, blending 2 stable fuels each containing a component to an antagonistic blend would cause an issue a Aviation Fuel Thermal Stability Requirements, Kirklin/David, ASTM STP 1138, 1992, pg 27 b Thermal Oxidation Stability of Aviation Turbine Fuels, Robert N. Hazlett ASTM, 1991, pg 84 4

5 Challenge for understanding thermal oxidative stability Autoxidation mechanism is reasonably well understood a Deposit mechanism is not well understood Fuel molecules Soluble Insoluble O 2 FM FMOO hydroperoxides Fuel molecules TM, hydroperoxides Trace materials (N, O, S) A, hydroperoxides inhibitors Rx Rx Oxygenates Coupling w/ TM Deposits Jet fuel contains very little oxygen bound components but autoxidation can change this quickly Lack of understanding of trace materials precludes the ability to understand stability issues Rx Oxygenates & TMOO Oxygenates & AOO This situation exists despite the wealth of fouling literature which reflects the complex nature of the phenomena by which instability occurs in aircraft fuel systems a Adapted from Heneghan, S. P.; Zabarnick S. Fuel 1994, 73,

6 Challenge with accelerating stability testing Test temperature ( C) Time vs temperature for accelerated stability tests D381 D6811 D6468 Gost D3241 Gost D5304 EN D2274 Stavinoha CRC3 ASTM STP D Duration of tests (hr) Accelerating storage stability with elevated temperatures has its limitations. At high temperatures different reaction mechanisms may dominate. 6

7 Simulated storage to accelerate degradation testing Normalized property (MSEP, JFTOT, Color, Gums) Stable fuel w/ accelerated aging Unstable fuel w/ accelerated aging 3 months Time Stable fuel limit Unstable fuel yr Storing 43 o C accelerates aging and reduces the time from 1 year to 3 months (modified D4625) Higher temperatures would accelerate aging even further but chemical mechanisms of oxidation and deposition may significantly differ. 43 o C has been shown to lead to a similar mechanism D4625 approach is not amenable to a specification requirement but should be part of a fit-for-purpose requirements associated with MOC s R. G. Gaughan, D. J. Abdallah, D. H. Hoskin, PRE -REFINED CRUDES AND THEIR IMPACT ON JET FUEL THERMAL STABILITY OVER TIME IASH

8 Summary Fuel instability relates to trace materials present and the chemistry these materials undergo Better understanding of trace materials is the first step Analytical capabilities have progressed significantly which should help with trace materials characterization FFP means the fuel meets the end users needs, thus, fuels need to be stable over time Understanding what causes thermal and storage instability is still a opportunity for improvement 8