Investigations of Poor Thermal Stability Behavior Exhibited in US Fuels

Transcription

1 Investigations of Poor Thermal Stability Behavior Exhibited in US Fuels DLA Worldwide Energy Conference April 12, 217 Zach West, Linda Shafer, Rich Striebich, & Steve Zabarnick UDRI, Dayton, OH Milissa Griesenbrock & Tim Edwards Fuels & Energy Branch AFRL, WPAFB, OH 1

2 Background US pipeline companies reported jet fuel thermal stability issues at May 216 CRC meeting (issues date from 215) JFTOT failures after pipeline transport Appears to be unrelated to pickup of contaminants from pipeline TS often improves with time (settling vs reaction time vs JFTOT scatter?) Many fuels have been treated with MDA to pass JFTOT A4A bulletin AFRL/UDRI have been investigating cause GCxGC, polars, S/N composition analyses QCM thermal stability measurements 2

3 Experimental: Trace Chemical Analysis Polars: evaluate trace, heteroatomic compounds (usually O & N containing, e.g., phenols, anilines, & indoles) Pre-separation/concentration via silica gel-spe Quantification - GCxGC-FID Qualification/speciation - GCxGC-MS & GC-MS Nitrogen: quantify via GC-NCD Sulfur: quantify via GC-SCD Reactive Sulfur: H2O2 oxidation by subtraction: thiols, sulfides, & disulfides R-SH 3 R-S-R R-S-S-R

4 Experimental: Thermal Stability via QCM rf feedthrough oxygen sensor Bench-scale batch reactor: Air saturated fuel, 6 ml, 14 C, 15 hrs Extremely sensitive in-situ deposition monitoring Oxygen sensor and pressure transducer for in-situ measurement of fuel oxidation Workhorse experiment for: additive testing, formulation, & concentration studies; also, fundamental fuel chemistry studies Now standardized as ASTM D thermocouple pressure tra nsducer gas inlet tube thermocouple quartz crystal with wrap-around electrode 1 ml stainless steel reactor heated with band heater

5 Heteroatomic Speciation SPE-GCxGC-MS Polars Total N & S 228 ppm Sulfur Analyzed 5 samples (4 from field, 1 bulk receipt) Reporting avg values Results very consistent Polar sulfur 3 ppm Typical distribution (~55-65% Reactive) Typical ranges we see for jet fuels: Phenols ~1-25 mg/l Total Polars 3 mg/l Samples show elevated levels of phenols, total polars, & total/reactive sulfur 5 14 ppm Nitrogen Polar nitrogen 1 ppm

6 Thermal Stability via QCM 2 Truck Tank 1 Tank 2 Tank 3 AFRL Receipt JP-8 (typical) Time (hours) Headspace Oxygen (% Sat) Mass Accumulation (µg/cm ) nm JFTOT results very inconsistent Consistently poor performance (³6 mg/cm2) in QCM AFRL receipt of fuel gave slightly better absolute deposit level (~4.5 mg/cm2), but still rapid oxidation & deposition of concern

7 Thermal Stability via QCM: Explorer Pipeline Samples 25 Even though neat fuels (A, B, & C) passed ASTM D3241 Fuel B contains lowest polars level, gives lowest deposition level from fuel set; however, still high level of deposits compared to knowledge base 2 Mass Accumulation (µg/cm ) 1 2 Fuel A Fuel B Fuel C Tank JP-8 (typical) Time (hours) 16 Headspace Oxygen (% Sat) All fuels demonstrate poor thermal stability in QCM under typical experimental conditions

8 Impact of Additives Field Site 1 8 MDA: delayed oxidation but increased total deposition level to greater than previous amounts AO (BHT): no apparent impact +1: significantly delayed oxidation and reduced deposition during thermal stress duration 2 Mass Accumulation (µg/cm ) F-24 (neat) F-24 + MDA 2. mg/l F-24 + MDA 5.7 mg/l F-24 + BHT 2 mg/l F mg/l Time (hours) 16 Headspace Oxygen (% Sat) What is the effect of additives on fuel fielded with elevated/high levels of nitrogen, sulfur, & oxygen? Laboratory study to investigate impact on QCM profiles at 14 C: 15

9 AFRL Fuel System Simulator 16.7 pph = 12 gallons Fuel showed large deposits and valve hysteresis +1 and MDA both decrease deposition and hysteresis +1 was superior to MDA ServoBFAHysteresis Comparisons Effective Carbon Deposition By Run 14 MT Conditions: 325/35/51 Run 155 (+1) Run Effective Carbon, µgrams Field Site 1 fuel Max wall T = 51F (266C) 72 hour long runs with partial recirculation Minimal Non-Functional 1 BASELINE MDA 2 Moderate +1 Non-Functional BFA Tube Position Run 154 Run 158 MT Conditions: Run 155 (+1) 325/35/51 9 Run 162 (MDA) Run 158 Run 162 (MDA) 1 12

10 Dithiazine & Trithianes Found SPE-GCxGC-TOF/MS (Fuel Polars) Found trace amounts (<2ppm) of dihydro-methyl-dithiazine and trithiane ,6-Dihydro-5-methyl-4H1,3,5-dithiazine H2S scavenger product(s) Why are these species carried into jet fuel? Is this common? TS impact of these compounds is unknown 2. 1,3,5-Trithiane 1 Verified using: SPE-GCxGC-MS/TOF, SPE-GCMS, & GC-SCD/NCD Only very low concentrations found GATEKEEPER, May 214,

11 Possible Causes/Mitigation Causes High levels of S, N, O species Increased heavy crude refining Reduction in hydrotreating at some refineries Increased use of hydroprocessing, acid/base washing, clay/silica gel filtration, etc. Use of thermal stability additive, e.g., +1 package MDA treatment should not be considered the solution Pre-refined crude (synthetic crude) can create heteroatomic species not normally in kerosene cut Hydrocracking Cost saving measure? Blending of incompatible fuels during transport/storage (high S with high N?) 11 Mitigation Results in passed JFTOT, but what happens in the engine? Increase TS spec limit for pipelines/refineries?

12 Acknowledgements AFPET: Ben Curtis, Miguel Acevedo, Mike Thiede, & Zulmarie Jimenez-Laureano Inspectorate: Micki Overberg This material is based on research sponsored by the Air Force Research Laboratory under agreement numbers FA & FA The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of Air Force Research Laboratory or the U.S. Government. 12