Thermally Stable Coal-Based Jet Fuel: Chemical Composition, Thermal Stability, Physical Properties and Their Relationships
Open Access
- Author:
- Butnark, Suchada
- Graduate Program:
- Fuel Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 24, 2003
- Committee Members:
- Harold Harris Schobert, Committee Chair/Co-Chair
Chunshan Song, Committee Member
Semih Eser, Committee Member
M Mercedes Maroto Valer, Committee Member
M Albert Vannice, Committee Member - Keywords:
- Chemical Composition
Artificial Neural Network
Multiple Linear Regression
JP-900
Coal-Based Jet Fuel
Jet Fuel Properties
Thermal Stability
Quantitative Structure-Property Relationship - Abstract:
- The pilot-scale production of the thermally stable coal-based jet fuel, so-called JP-900, has recently been performed using coal-derived liquids and a blend of coal-derived liquids with petroleum refinery streams. The hydrotreatment and dearomatization of light cycle oil (LCO) and refined chemical oil (RCO) were selected processes for the production of thermally stable compounds. Up to now, three generations of coal-based jet fuels have been produced in pilot plants and their thermal stability properties have been tested under static and dynamic conditions in autoxidative and pyrolytic regimes. In the present work, chemical compositions and structures, physical properties, combustion characteristics, and decomposition in a static system in the pyrolytic regime were studied for the candidate fuels. Chemical compositions and structures of coal-based jet fuel were determined by GC/MS, 13C NMR and 1H NMR analyses. Quantitative analysis by GC/MS was used to classify chemical composition into nine groups of compounds, while 1H NMR analysis was used to identify and quantify hydrogen structures in seven regions, based on their chemical shifts. The results from GC/MS and 1H NMR characterization have been compared and show a significant agreement in terms of major composition in jet fuels. The static tests in batch reactors were conducted in the pyrolytic regime at very high temperatures in the absence of oxygen. The pyrolytic stability in static conditions was determined by heating 5 mL of sample in a 25 mL-microautoclave at 480oC under 100 psig of UHP N2 for different periods of time. Preliminary results have shown that the hydrotreated LCO/RCO 1:3 having boiling range 180-2700¸8C had the highest stability. Rates of solid deposition were also obtained for the jet fuels that have been produced from feedstock containing high RCO (the coal tar distillate component) concentration. In addition, it was found that the specific jet fuel distillation end point is one of the most important parameters controlling the jet fuel¡¯s chemical composition. However, to produce a thermally stable jet fuel that can be utilized in the actual jet engines, the fuel quality has to meet ASTM specification requirements. The properties study has shown that all coal-based jet fuels meet ASTM specifications with high flash points and low cloud points. But, the problem associated with high aromatic contents in hydrotreated jet fuels is low smoke point, resulting in high sooting tendencies and emissions. Net heat of combustion of high-aromatic jet fuels is also relatively low, even though the energy density of the fuels is found to be high. To study the relationships among chemical composition, solid deposition rate and other physical properties, mathematical models were established using multiple linear regression (MLR) and artificial neural network (ANN) approaches. ANN is more effective than MLR, as it can establish non-linear relationships of complex systems and can also accurately predict unseen data sets. For visualization purposes, the ternary diagrams have been used to display relationships among three main components with properties. An optimum chemical composition was developed to meet requirements of slow solid deposition rate, net heat of combustion at 18,400 Btu/lb and smoke point at 19 mm. Based on the existing data, the 1:1 blend of saturated LCO and saturated RCO, composing 0.76% aromatics, 68.47% cycloalkanes (46.98% decalin and 21.49% other cycloalkanes) and 30.77% alkanes and the others, is the only sample having chemical composition that can meet all requirements. However, coal-based jet fuels which are composed of large amounts of aromatics, tetralins or decalins can still be desirable JP-900 if the limitations on aromatics, net heat of combustion and smoke points are flexible. Finally, the correlations between hydrogen structures of coal-based jet fuels and solid deposition rate have been created using MLR and ANN. These correlations are statistically, physically and chemically satisfied. It was found that the structures of hydrogen donors in decalin, tetralin and indane are the main contribution to suppression of solid deposition. Based on this structure-thermal stability relationship, reaction mechanisms of pyrolytic degradation of coal-based jet fuels have been proposed.