Ind. Eng. Chem. Res. 2008, 47, 2867-2875
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Organic Nitrogen Compounds and Fuel Instability in Middle Distillate Fuels Joy W. Bauserman,*,† George W. Mushrush,‡,§ and Dennis R. Hardy‡ NOVA Research, 1900 Elkin Street, Alexandria, Virginia 22308, NaVy Technology Center for Safety and SurViVability, NaVal Research Laboratory, Code 6180, 4555 OVerlook AVenue, S.W., Washington, D.C. 20375, and Chemistry Department, George Mason UniVersity, 4400 UniVersity DriVe, Fairfax, Virginia 22030
Previous research studies have implicated polar organic nitrogen compounds in fuel instability. Twenty-one middle distillate fuels were investigated for their organic nitrogen content and to determine if any specific organic nitrogen compound might be linked to fuel instability. The organic nitrogen compounds were isolated by mild acid extraction followed by silica gel adsorption. Three extracts were obtained from each fuel sample: a basic nitrogen extract in methylene chloride (BNC), a nonbasic nitrogen extract in methylene chloride (NBNC), and a nonbasic nitrogen extract in methanol (NBNC). The major constituents of each extract were determined by high-resolution gas chromatography/mass spectrometry (GC/MS). After the compounds were identified for each fuel, the fuels were grouped by ASTM stability values to determine if there was significantly more or less of one type of organic nitrogen compound present that could cause instability. The results of this study showed that there was not a specific organic nitrogen compound responsible for instability, but probably an imbalance in either the basic or nonbasic organic nitrogen compounds that caused a shift in equilibrium resulting in sediment or gum formation. This is important to the military because military fuels can remain in storage tanks for 1 or more years. As fuels are drawn from these tanks, the tanks are subsequently topped off with more recently purchased fuels. In many cases, the mixed fuels are not compatible, resulting in sediment and sludge formation. Introduction Many research studies on fuel degradation have been conducted since World War II when the demand for both gasoline and middle distillate fuels increased. Fuel degradation is characterized by various chemical and physical changes which may include one or all of the following: color development or darkening; sediment or gum formation; increased viscosity; and changes in the composition of the fuel. Fuel incompatibility/ instability generally involves the presence of heteroatomic aromatic compounds that incorporate sulfur, oxygen, or nitrogen in the crude oil. Some of these polar functional groups can survive the refining operations, end up in the finished fuel products, and participate in a variety of chemical reactions leading to fuel deterioration and/or instability. However, studies do not indicate which of these heteroatomic compounds are the most deleterious. Fuel instability is important for both commercial and military operations because instability reactions can degrade fuel and affect engine performance, leading to maintenance problems and additional costs.1 The problem of fuel degradation has increased because of the introduction of different crude oils into refineries and because of the use of catalytic cracking to convert high molecular weight materials into distillate fuels. These processes have resulted in deposition of sediments or gums causing the fuel to become unstable or incompatible. Today, the United States military is the largest consumer of middle distillate fuels in the world. Fuel storage instability reactions are a problem for the military because the fuels can remain in storage tanks for 1 or more years. In some cases the fuels are withdrawn from the tank and replaced with more recently purchased fuels, resulting in mixing fuels that may not be compatible. * To whom correspondence should be addressed. Tel.: (434) 5664451. Fax: (434) 589-5767. E-mail:
[email protected]. † NOVA Research. ‡ Naval Research Laboratory. § George Mason University.
Stability research studies have implicated heteroatomic organic nitrogen compounds as being problematic in fuel degradation. Nitrogen compounds in petroleum and fuel liquids can be separated into basic and nonbasic fractions, each of which have alkyl chains and ring systems. Pyridines, quinolines, some substituted pyrroles, and particularly alkylated benzoquinolines have been recognized as major classes of basic compounds, whereas indoles, some pyrroles, and carbazoles are regarded as nonbasic compounds. Research studies2-5 indicate that certain nonbasic nitrogen heterocycles, such as some pyrroles and indoles, form sediments, while other compounds are much less reactive. The reactivity of the nitrogen compounds is dependent on the chemical structure of the compound and not on the total nitrogen in the petroleum.6 Worstell et al.7 concluded from their studies of deposit formation in diesel fuels that nitrogen heterocycles increase the rate of deposition in diesel fuel under accelerated storage conditions through base catalysis. When the polar constituents are removed, the deposition does not occur. Frankenfeld and Taylor concluded that the most reactive compounds were unsaturated nitrogen heterocycles with multiple alkyl groups, at least one of which is located on the carbon atom adjacent to nitrogen. It appears that the most harmful compounds fall into the weak to nonbasic classification.3,8 Similar studies by Thompson et al.5,9 indicated that pyrroles caused the largest amounts of insoluble deposits, while pyridines were less reactive. More recent research by Hiley et al. and Malhotra et al. showed that alkylindoles are involved in fuel gum formation more than alkylpyrroles.10-12 In general, basic nitrogen compounds formed less sediment than nonbasic compounds. It was found that chemical structures and reactivity in sediment formation were correlated.3,13-15 The position of the alkyl chain on the heterocyclic ring plays an important role in reactivity. Nonbasic compounds with alkyl groups in positions 2 and 5 are especially reactive. The structural elements identified with the greatest reactivity were the com-
10.1021/ie071321n CCC: $40.75 © 2008 American Chemical Society Published on Web 04/02/2008
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Table 1. Total Numbers of Specific NBNC and BNC in Stable and Unstable Fuels NBNC
BNC
stability,a
origin of fuel
ASTM fuel mg/100 mL of fuel
carbazole
indole
Kuwait Sweden Kenya New Zealand Venezuela Colombia Panama New Jersey Texasb Sri Lanka Jacksonville, FL Pakistan Mobile, AL Greece Turkey Senegal Okinawa
0.5 0.0 0.9 0.3 0.3 0.5 1.2 0.7 0.3 0.2 1.0 0.3 1.0 0.9 0.9 0.6 0.0
2 3 6 44 50 0 9 38 43 18 14 12 70 68 26 24 21
Stable Fuels 10 8 0 58 16 30 14 93 36 10 8 20 56 31 10 29 35
Japan British Columbia Texasc Louisiana
2.2 12.4 4.2 1.8
2 2 37 28
Unstable Fuels 31 38 33 33
pyrrole
quinoline
tetrahydroquinoline
pyridine
12 19 13 25 51 10 3 14 61 25 11 18 27 37 56 77 89
4 27 7 3 20 9 1 7 40 1 7 4 4 4 16 32 5
17 10 2 24 17 41 29 28 19 9 3 18 13 17 12 14 7
12 21 2 1 26 14 35 11 4 0 0 1 5 32 14 32 26
12 9 25 6
59 51 11 3
23 32 11 3
42 54 8 6
a The ASTM Fuel Stability test values were obtained from the stability work done at the Naval Research Laboratory in Washington, DC. came from two different refineries in Texas.
pounds that have at least one double bond, alkyl groups located at positions 2 or 5, and an unsubstituted carbon at positions 3 and 4. It has been shown that interactions between nitrogen compounds can affect sediment formation. For example, amines are considered harmless; however, they can interact with other nitrogen compounds to either promote or inhibit sediment formation. Relationships between nitrogen heterocyclic structures and their tendency of promoting sediment formation have been reported.4,16 Fuel studies have involved accelerated storage tests, analyzing fuel composition before and after accelerated storage studies, and studying the sediment composition after spiking or doping fuels with pure compounds. Sediments formed from fuels doped with model compounds have been observed to be high in nitrogen content, especially the pyrrolic (nonbasic) organic nitrogen compounds rather than the pyridine (basic) organic nitrogen compounds. The research evidence is not conclusive as to the specific nitrogen compounds that are responsible for fuel degradation or the mechanism(s) involved in the degradation process. Experimental Section Twenty-one middle distillate fuels were used for this study, and they are listed in Table 1. One fuel came from each of the areas of the world listed in Table 1. The reagents used were hydrochloric acid, sodium carbonate, methylene chloride, hexane, silica gel (grade 923, 100-200 mesh), methanol, and distilled water. All reagents were of ACS grade or better and were used as received from Fisher. The separation of nitrogen extracts from the fuels involved several steps as previously performed and described by Mushrush et al.4,16 The nitrogen compounds contained in the extracts were analyzed by use of a combined capillary column gas chromatography/mass spectrometry (GC/MS) system. The total nitrogen
b,c
These fuels
content from GC/MS was less than 1% in each fuel. The GC/ MS system consisted of a Hewlett-Packard 5890A gas chromatograph and a Finnegan INCOS 50B mass spectrometer. The GC/MS was fitted with a 30 m × 0.25 mm DB-5 fused-silica capillary column (95% dimethyl, 5% diphenyl siloxane; J & W Scientific, Folsom, CA) which was operated at the following GC temperature program: initial temperature at 60 °C (3 min hold) ramped at 3 °C/min to 290 °C at 8 °C/min with a final hold of 5 min. The injection port on the GC was maintained at 250 °C and was configured for splitless injection (1 µL). The mass spectrometer was operated in the electron impact ionization mode (70 eV) with continuous scan acquisition from 45 to 425 amu at a cycling rate of approximately 1 scan/s. The parameters were set up with the electron multiplier at 1050 V, a source temperature of 200 °C, and the transfer line temperature at 290 °C. The mass spectrometer was calibrated with perfluorotributylamine before use. The INCOS 50 data system and ITDS software were used to process mass spectral information. Results and Discussion Civilian fuels are used within a few days or weeks of production; thus storage stability and oxidative instability reactions have little practical significance for this market. However, military fuels are stockpiled and stored for 1 or more years. How these fuels behave in long-term storage is of major importance for military equipment. If the fuel degrades, it could then plug filters and injector nozzles, as well as damage engine components. Fuel instability can occur when fuels from different refineries of the same company or from different companies are blended in storage facilities. There were two objectives in this investigation: (1) to extract, identify, and quantify specific organic nitrogen compounds and hydrocarbon compounds found in 21 fuels from around the world; (2) to determine if a specific compound or group of compounds was responsible for fuel instability. Each fuel had three chromatograms since there were three extractions per fuel, and each peak in a chromatogram represents
Ind. Eng. Chem. Res., Vol. 47, No. 9, 2008 2869 Table 2. Total Number of Specific Hydrocarbon Compounds in Fuels types of hydrocarbon compounds origin of fuel
acenapthalene
acridine
alkane
alkene
Kuwait Sweden Kenya New Zealand Venezuela Colombia Panama New Jersey Texasa Sri Lanka Jacksonville, FL Pakistan Mobile, AL Greece Turkey Senegal Okinawa
17 16 3 27 9 11 24 26 17 5 2 1 2 29 0 2 0
0 0 0 0 0 0 0 0 0 0 5 0 4 0 0 0 0
36 45 55 112 5 126 53 104 23 64 49 37 10 17 0 0 0
Stable Fuels 0 0 0 9 0 0 0 0 0 2 20 4 24 0 7 2 0
Japan British Columbia Texasb Louisiana
0 0 14 21
0 0 1 5
56 26 18 18
Unstable Fuels 0 0 3 0
anthracene
benzene
cycloalkane
diene
0 0 1 1 5 0 0 0 10 1 3 0 1 22 0 1 0
87 11 1 122 28 7 59 56 52 48 46 64 48 6 39 11 25
0 0 0 0 2 0 0 0 0 1 10 20 16 0 2 1 5
0 2 0 0 15 0 0 0 17 2 1 1 0 2 0 0 0
59 0 29 57
0 68 29 20
0 0 0 1
0 0 5 0
types of hydrocarbon compounds origin of fuel
dicycloalkane
indane
indene
napthol
tetralin
tricycloalkane
triene
22 14 14 63 93 0 45 0 129 82 72 105 72 44 126 82 102
9 10 2 7 15 0 0 0 13 0 3 0 5 12 2 31 8
0 0 0 4 11 0 0 0 10 0 5 8 3 0 0 0 0
0 0 0 13 0 0 0 0 5 4 20 17 16 3 0 0 0
Unstable Fuels 0 0 0 0 0 114 0 112
0 0 11 8
0 0 3 0
0 0 0 1
Stable Fuels Kuwait Sweden Kenya New Zealand Venezuela Colombia Panama New Jersey Texasa Sri Lanka Jacksonville, FL Pakistan Mobile, AL Greece Turkey Senegal Okinawa
0 2 2 15 0 0 0 0 0 0 5 0 15 6 0 0 0
0 1 1 5 2 0 0 0 1 0 21 2 11 0 1 1 1
Japan British Columbia Texasb Louisiana
0 0 8 3
0 0 0 0
a,b
5 2 3 1 0 0 0 0 1 1 0 0 0 0 0 0 1
These fuels came from two different refineries in Texas.
a compound that may or may not be identified. Not all of the peaks in the chromatograms were identified because some of the peaks were too small and some of the peaks were mixtures of compounds, making it difficult to get a definitive compound. The individual results for basic organic nitrogen compounds (BNC), for nonbasic organic nitrogen compounds (NBNC), and for the hydrocarbons are summarized in Tables 1 and 2. Table 1 and Figures 1 and 2 show the results of the total numbers of specific nonbasic and basic organic nitrogen compounds found in the 21 fuels. Since carbazoles are substituted indoles, Figure 3 illustrates the number of pyrroles and total carbazoles and indoles. This chart illustrates that fuels from Japan, New Zealand, Venezuela, Colombia, Panama, British Columbia, New Jersey, Texas (two fuels), Jacksonville, Pakistan, Alabama, Greece, and Louisiana had more of the combination of indoles and carbazoles than pyrroles. Kuwait and Sri Lanka fuels had equal numbers of total carbazoles and indoles with pyrroles,
while fuels from Sweden, Kenya, Turkey, Senegal, and Okinawa had more pyrroles than total numbers of carbazoles and indoles. All of these fuels with the exception of those from Texas (one fuel), Louisiana, British Columbia, and Japan are considered stable fuels by ASTM standards. Mushrush states that a fuel with a stability factor above 1.5 mg of sediment per 100 mL of fuel will probably become unstable.17 All of the fuels with the exception of the above four fuels had stability factors less than 1.5 mg of sediment per 100 mL of fuel. The total number of hydrocarbon compounds identified in all the fuels is shown in Table 2. This table shows that the compounds identified with the most frequency and highest numbers were acenapthalenes, alkanes, benzenes, and napthols. The results in Tables 1 and 2 do not reveal any specific compounds that could be problematic to fuels. The unstable fuels in Table 1 and Figure 5 do not uncover any specific nitrogen compound that is predominant and could
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Figure 1. Number of NBNC vs country of origin.
Figure 2. Number of BNC vs country of origin.
cause stability problems. Fuels from Japan and British Columbia show a higher number of basic nitrogen compounds than nonbasic nitrogen compounds, while those from Texas and Louisiana reveal more nonbasic than basic nitrogen compounds.
The stable fuels in Table 1 and Figure 4 were examined for specific nitrogen compounds that could be problematic. The results showed little evidence that any one specific compound was responsible for instability. Figures 4 and 5 were designed
Ind. Eng. Chem. Res., Vol. 47, No. 9, 2008 2871
Figure 3. Total number of carbazoles and indoles with total number of pyrroles vs country of origin.
Figure 4. Total NBNC and BNC for stable fuels vs country.
to show the relationship between the total numbers of basic and nonbasic nitrogen compounds in the stable fuels and unstable fuels. Kuwait, Sweden, Colombia, and Panama fuels have more basic than nonbasic nitrogen compounds, while the remainder of the stable fuels have more nonbasic than basic nitrogen compounds. Figure 5 shows that fuels from Texas and Louisiana have more nonbasic than basic nitrogen compounds while those
from Japan and British Columbia have more basic than nonbasic nitrogen compounds. Twenty-one fuels were divided into stable and unstable fuels for nonbasic organic nitrogen compounds, basic organic nitrogen compounds, and hydrocarbon compounds. The number of specific organic nitrogen compounds for the nonbasic organic nitrogen compounds were compared in the two groups for
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Figure 5. Total NBNC and BNC for unstable fuels vs country.
Table 3. Total Numbers of NBNC and BNC in Stable Fuels
Table 4. Total Numbers of NBNC and BNC in Unstable Fuels
origin of fuel
total no. of NBNC
total no. of BNC
origin of fuel
total no. of NBNC
total no. of BNC
Kuwait Sweden Colombia Panama Kenya New Zealand Venezuela Texas Sri Lanka Jacksonville, FL Pakistan Mobile, AL Greece Turkey Senegal Okinawa New Jersey
24 30 40 26 19 127 117 140 53 33 50 153 136 92 130 145 145
33 58 64 65 11 28 63 63 10 10 23 22 53 42 78 38 46
Texas Louisiana Japan British Columbia
95 67 45 49
30 12 124 137
significance using a Student t-test. The formulas used to determine significance were
t)
(
X 1 - X2
)
s12 + s22 n
1/2
for equal sample sizes with more than 30 samples and
t)
(
X1 - X2
)( )
(n1 - 1)s1 + (n2 -1)s22 n1 + n2 - 2 2
1/2
1 1 + n1 n2
1/2
for unequal sample sizes with less than 30 samples. X1 ) sample mean; X2 ) sample mean; s12 ) variance of sample 1; s22 ) variance of sample 2; n1 ) number of samples; n2 ) number of samples.
The same analysis was performed for the basic organic nitrogen compounds and hydrocarbons. The data were arranged in decreasing order of stability, and values greater than 1.5 mg/ 100 mL were considered to be stable but would probably become unstable. Null Hypothesis: The mean value for stable fuels for each type of compound (i.e., pyrroles, indoles, carbazoles) in each class of compound (i.e., nonbasic, basic, and hydrocarbon) will not be significantly different from the mean values of the unstable fuels for each type of compound in each class of compound at R ) 0.1. Next, 17 stable fuels were divided into two groups of fuels, high stability values (1.2-0.7 mg/100 mL) and low stability values (0.6-0.0 mg/100 mL), for nonbasic organic nitrogen compounds, basic organic nitrogen compounds, and hydrocarbon compounds. The number of specific organic nitrogen compounds for the nonbasic organic nitrogen compounds were compared in the two groups for significance. The same analysis was performed for the basic organic nitrogen compounds and hydrocarbons. This analysis was done to determine if there was any difference in the number of specific compounds for each compound class of stable fuels. Null Hypothesis: The mean number for high stability values (1.2-0.7 mg/100 mL) for each type of compound (i.e., pyrroles, indoles, carbazoles) in each class of compound (i.e., nonbasic, basic, and hydrocarbon) will not be significantly different from the mean values of low stability values (0.6-0.0 mg/100 mL) for each type of compound in each class of compound at R ) 0.1.
Ind. Eng. Chem. Res., Vol. 47, No. 9, 2008 2873 Table 5. Statistical t-test Results Comparing Stable vs Unstable Fuels for Specific NBNCa descriptive information stability (>1.5 mg/100 mL)
stability (1.5 mg/100 mL)
stability (1.5 mg/100 mL) hydrocarbon compds napthols alkenes alkanes a
2
stability (1.5 1.2-0
a When n ) 4 and n ) 17, df ) 19, t ) 1.729, the null hypothesis is accepted in the stability case >1.5, but rejected in the case of 1.2-0. There are 1 2 significantly more nonbasic nitrogen compounds with stability between 1.2 and 0.
organic nitrogen and basic organic nitrogen compounds was significant. The formulas used to determine significance were
t)
(
X 1 - X2
)
s12 + s22 n
1/2
for equal sample sizes with more than 30 samples and
t)
(
X1 - X2
)( )
(n1 - 1)s12 + (n2 - 1)s22 n1 + n2 - 2
1/2
1 1 + n1 n2
1/2
for unequal sample sizes with less than 30 samples. X1 ) sample mean; X2 ) sample mean; s12 ) variance of sample 1; s22 ) variance of sample 2; n1 ) number of samples; n2 ) number of samples. Null Hypothesis: The mean number of nonbasic organic nitrogen compounds for the different ASTM values will not be significantly different from the mean number of basic nitrogen compounds for the different ASTM values at R ) 0.1. Table 11 illustrates the statistical results when the total NBNC and total BNC are compared. This comparison shows there are significantly more NBNC than BNC in the stable fuels, but there is not any significant difference in the number of NBNC and BNC in unstable fuels. Conclusion Since fuels can remain in storage tanks for 1 or more years, fuel storage instability reactions of middle distillate fuels are a
major problem. As fuels are drawn from these tanks, the tanks are subsequently topped off with more recently purchased fuels. In many cases, the mixed fuels are not compatible, resulting in sediment or sludge formation. While previous research has shown that certain specific polar organic nitrogen functional groups are involved in fuel instability reactions, it is difficult to completely remove these organic nitrogen compounds that are problematic. The experimental results from the investigation of four unstable fuels and 17 stable fuels found all over the world show that there is not one specific organic nitrogen compound that is responsible for fuel instability. The relationship between the total numbers of basic and nonbasic organic nitrogen compounds in the stable and unstable fuels are varied for stable and unstable fuels. Kuwait, Sweden, Colombia, and Panama fuels (i.e., stable fuels) have more basic than nonbasic organic nitrogen compounds, whereas the remainder of the stable fuels have more nonbasic than basic organic nitrogen compounds. Unstable fuels from Texas and Louisiana have more nonbasic than basic nitrogen compounds, while those from Japan and British Columbia have more basic than nonbasic organic nitrogen compounds. The total number of hydrocarbon compounds identified with the most frequency and highest numbers were acenapthalenes, alkanes, benzenes, and napthols. ASTM stability values were used to determine if there was any significant difference in the numbers of specific organic nitrogen compounds (i.e., indoles, carbazoles, pyrroles, pyridines, quinolines, tetrahydroquinolines). The fuels were sorted into stable versus unstable fuels for NBNC, BNC, and hydrocarbon compounds using the stability parameter so that fuels with values greater than 1.5 mg/100 mL were unstable and those
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with values less than 1.5 mg/100 mL were stable with the following results: (a) There are not any specific compounds that are significant for the nonbasic organic nitrogen compounds in stable and unstable fuels. (b) When specific basic organic nitrogen compounds were compared in stable and unstable fuels, there were significantly more quinolines and total basic organic compounds in fuels with stabilities greater than 1.5 mg/100 mL. (c) The hydrocarbons in stable and unstable fuels did not show any significant differences in the number of hydrocarbon compounds identified. (d) In the unstable fuels, when the total NBNC and BNC were compared for significance, the results showed that there were not any significant differences in the number of NBNC and BNC. (e) In the stable fuels, when the total NBNC and BNC were compared for significance, there was a significant difference in the number of NBNC and BNC. There were significantly more NBNC in the stable fuels. When comparing specific compounds of NBNC and BNC in stable and unstable fuels, there are significantly more quinolines and total BNC in the unstable fuels than in the stable fuels. When comparing the total NBNC and BNC in stable fuels, there were significantly more NBNC than BNC in the stability range of 0.6-0.0 mg/100 mL than in the stability range of 1.20.7 mg/100 mL. These results support the idea that instability may be related to the balance between nonbasic and basic organic nitrogen compounds in the fuels. Stable compounds may have more nonbasic than basic compounds in some instances and in other instances may have more basic compounds than nonbasic compounds. The unstable fuels also can have more nonbasic than basic nitrogen compounds or more basic than nonbasic nitrogen compounds. From this study of 21 fuels, there does not appear to be a specific compound producing the instability; instead, it appears to be a group of compounds inducing the instability. Petroleum is a mixture of many compounds in equilibrium with a balanced ratio of nonbasic organic nitrogen compounds to basic organic nitrogen compounds. A stable fuel may have more basic than nonbasic organic nitrogen compounds or more nonbasic than basic compounds. When fuels are mixed or blended, this ratio could become unbalanced and produce a concentration stress on the equilibrium causing a shift in the equilibrium, thus, initiating the formation of sediment or sludge.
Literature Cited (1) Mushrush, G. W.; Speight, J. G. Petroleum Products: Instability and Incompatibility; Taylor & Francis: Washington, DC, 1995. (2) Nixon, A. C.; Cole, C. A. Prepr.sAm. Chem. Soc., DiV. Pet. Chem. 1954, 31, 5. (3) Frankenfeld, J. W.; Taylor, W. F.; Brinkman, D. W. Storage Stability of Synfuels from Oil Shale. 2. Effects of Nitrogen Compound Type and the Influence of Other Nonhydrocarbons on Sediment Formation in Model Fuel Systems. Ind. Eng. Chem. Res. DeV. 1983, 22, 615. (4) Mushrush, G. W.; Cooney, J. V.; Beal, E. J.; Hazlett, R. N. Characterization and Stability Properties of Polar Extracts Derived from a Recent shale Liquid. Fuel Sci. Technol. Int. 1986, 4, 103. (5) Thompson, R. B.; Druge, L. W.; Chenicek, J. A. Stability of Fuel Oils in Storage. Effect of Sulfur Compounds. Ind. Eng. Chem. 1949, 41, 2715. (6) Batt, B. D.; Fathoni, A. Z. A Literature Review on Fuel Stability Studies with Particular Emphasis on Diesel Oil. Energy Fuels 1991, 5, 2. (7) Worstell, J. H.; Daniel, S. R.; Frauenhoff, G. Fuel 1985, 64, 485. (8) Frankenfeld, J. W.; Taylor, W. F. Fundamental Synthetic Fuel Stability Study, First Annual report; DOE/BC/10045-12; U.S. Department of Energy, Washington, DC, 1981. (9) Thompson, R. B.; Chenichek, J. A.; Drudge, L. W.; Symon, T. Ind. Eng. Chem. 1951, 43, 935. (10) Malhotra, R.; St. John, G. A. In Proceedings of the 2nd International Conference on Long Term Storage Stabilities of Liquid Fuels; Stavinoha, L. L., Ed.; 1986; p 327. (11) Malhotra, R.; St. John, G. A. Examination of Fuel Deposits from Various Sources by Pyrolysis/Field Ionization Mass Spectrometry. Proceedings of the 3rd International Conference on Stability and Handling of Liquid Fuels; 1988; p 525. (12) Hiley, R. W.; Penfold, R. E.; Pedley, J. F. In Proceedings of the 3rd International Conference on Stability and Handling of Liquid Fuels; 1988; pp 525-537. (13) Beal, E. J.; Cooney, J. V.; Hazlett, R. N.; Morris, R. E.; Mushrush, G. W.; Beaver, B.; Hardy, D. R. Mechanisms of Syncrude/Synfuel Degradation, Final Report; U.S. Department of Energy Report No. DOE/ BC/10525-16. (14) Cooney, J. V.; Beal, E. J.; Hazlett, R. N. Fuel 1983, 62, 20. (15) Frankenfeld, J. W.; Taylor, W. F.; Brinkman, D. W. Fundamental Synthetic Fuel Stability Study. Final Report; Department of Energy, Report No. DE-AC 1979 BC1. (16) Mushrush, G. W.; Watkins, J. M.; Beal, E. J. Characterization of Polar Extracts from Two Petroleum Derived Fuels. Fuel Sci. Technol. Int. 1989, 7, 931. (17) Mushrush, G. W. Personal interview, George Mason University, Fairfax, VA, May 2006.
ReceiVed for reView October 1, 2007 ReVised manuscript receiVed February 4, 2008 Accepted February 5, 2008 IE071321N
