Energy & Fuels 1989,3, 231-236
23 1
Hydroperoxide Formation and Reactivity in Jet Fuels John M. Watkins, Jr.,* George W. Mushrush, Robert N. Hazlett, and Erna J. Beal GEO-Centers, Inc., Ft. Washington, Maryland 20746, and Fuels Section, Code 6180, Naval Research Laboratory, Washington, D.C. 20375 Received September 19, 1988. Revised Manuscript Received November 4, 1988
Hydroperoxides in jet fuels attack elastomers in aircraft fuel systems, resulting in leaks or inoperation of fuel controls. Examination of fuels refined by different processes has indicated that significantly higher peroxide concentrations exist in fuels which have been severely hydrotreated. It is believed that hydogenation is responsible for removing natural inhibitors, including sulfur compounds, to peroxide formation. To test this thesis, the relationship between arenethiols and peroxidation of jet fuels was examined by using model dopant studies under 65 "C accelerated storage conditions. Samples were analyzed on a weekly basis for peroxides and sulfur compound concentration. Thiophenol demonstrated effectiveness in reducing and/or controlling peroxide concentration for an equivalent ambient storage time of approximately 2 years.
Introduction Hydroperoxides in jet fuels attack elastomers in aircraft fuel systems with consequent leaks or inoperation of fuel controls. Problems have been associated with Jet A, JP-4, and JP-5 jet fuels. The first reported incidents occurred with Jet A in Japan in 1962 when fuel hoses of neoprene or nitrile rubber cracked and 1eaked.l In 1976 the U.S. Navy experienced attack on neoprene fuel pump diaphragms on jets operating in the Phillipinesq2 More recent problems have been encountered in Thailand with JP-4 when Buna-N O-rings cracked and leaks from fuel pumps o ~ c u r r e d . ~All incidents involved fuels that had been hydrotreated and had peroxide levels from 1 to 8 mequiv of active oxygen/kg of fuel (peroxide number or PN). Examination of fuels refined by different processes has indicated that significantly higher peroxide concentrations develop in fuels that have been severely hydrotreated. The US.Navy has continuing concerns with this topic due to increasing hydrogenation for jet fuel processing. In addition, lower grade crudes and future shale-derived fuel production will involve more extensive and higher pressure hydrotreatment. I t has been demonstrated that sulfur compounds in lubricating oils act as antioxidants by decomposing peroxide^.^ It is believed that hydrogenation is responsible for removing natural inhibitors, including sulfur compounds, to peroxide formation. Hydroperoxide concentration has been found to be a factor in fuel instability. Fuel degradation is observed to occur under long-term low-temperature storage conditions (storage stability) as well as short-term high-temperature stress (thermal oxidative stability).m The latter situation is found during flight conditions, where fuel serves as a coolant on its path to the combustion chamber. Although slight thermal degradation is found to occur in nonoxidizing atmospheres, the presence of oxygen or active species such as hydroperoxides will greatly accelerate oxidative degradation as well as significantly lower the temperature at which undesirable changes in fuel take place. The rates of reactions in autoxidation schemes are dependent on hydrocarbon structure, heteroatom concentration, oxygen concentration, and temperature.+l' If sufficient oxygen is present, the hydroperoxides will reach a high level. If the available oxygen is low, but the temperature is raised, the hydroperoxide concentration will *To whom correspondence should be addressed at the Naval Research Laboratay.
be limited by free-radical decomposition. Under these conditions, fuel degradation can be associated with both hydroperoxide formation and decomposition. Several solutions to the problem of fuel peroxidation have been suggested. Antioxidants have been mandated by some authorities, particularly for hydrotreated fuels. Viton elastomers and other materials have been proposed as replacement materials, but their low-temperature properties make them marginal for aircraft use. Clay filtration has been suggested as a means for field removal of hydroperoxides but this treatment has been found to be too expensive.2 Although hindered phenols have given satisfactory peroxide control, those phenols that are permitted in the jet fuel specifications were developed for gum control in gasoline. Their effectiveness for peroxide control was found to be marginal, depending on structure.12 Rolls-Royce defined the peroxidation potential of a fuel with an accelerated 100 "C test for 24 h.' Investigations into the relationship of temperature to peroxide concentration in fuel, along with determining the relevance of the 100 "C test to ambient storage conditions, indicated that fuels containing antioxidants behaved differently at different temperatures, and in fuels without antioxidants, peroxide levels were lower than expected at the lower temperatures.12 A comparison of peroxidation rates in two fuels, one with and one without antioxidant, showed that a fuel without antioxidant produced peroxides at a linear rate while a fuel containing antioxidant produced peroxides (1) Smith, M. In Aviation Fuels; G. T. Foulis & Co., Ltd.: Henleyon-Thames: England, Chapter 51, 1970; (2)Shertzer, R. H. Aircraft Systems Fleet SupportlOrganic Peroxides in JP-5Inuestigation; Final Report NAPC -LR-78-20; Naval Air Propulsion Center: Trenton, NJ, 1978. (3)Fettke, J. M.Organic Peroxide Growth in Hvdro-treated Jet Fuel and its Effect on Elastomers; GE TM83AEB1154,G E Lynn, MA, 1983. (4)Dennison, G. H. Ind. Eng. Chem. 1944,36,477. (5)Hazlett, R. N. In Free Radical Reactions Related to Fuel Research i n Frontiers of Free Radical Chemistry; Pryor, W., Ed.; Academic Press: New York, 1980;p 195. (6)Scott, G.In Atmospheric Oxidation and Antioxidants; Elsevier: Amsterdam, 1965;Chapter 3. (7)Taylor, W. F. Ind. Eng. Chem. Prod. Res. Deu. 1974, 13, 133. (8)Taylor, W. F.;Wallace, T. J. Ind. Eng. Chem. Prod. Res. Deu. 1967. 6,258. (9)Denisov, E. T. Liquid Phase Reaction Rate Constants; IFI/Plenum: New York, 1974. (10)Hiatt, R. R.; Irwin, K. C. J. Org. Chem. 1968,33, 1436. (11) Morse, B. K. J. A m . Chem. Soc. 1957,87,3375. (12)Hazlett, R. N.;Hall, J. M.; Nowack, C. J.; Craig, L.Hydroperoxide Formation in Jet Fuels. In Conference Proceedings. 1st Conference on Long Term Storage Stabilities of Liouid Fuels:-Southwest Research Institute: San Antonio, TX, 1983;Voi. 1, pp 132-148.
This article not subject to U.S. Copyright. Published 1989 by the American Chemical Society
232 Energy & Fuels, Vol. 3, No. 2, 1989
week 0 1 2 3 4 5
Watkins et al.
Table I. J e t Fuel Peroxidation a t 65 "C with Added Thiophenol 0.10% S u l f u r Dopant Hydrocracked Jet A Hydrofined Jet A Shale-I1 JP-5 Jet A blending stock blending stock control doped control doped control doped control doped 0.25 0.25 0.00 0.00 0.16 0.16 0.00 0.00 0.24 0.00 0.19 0.00 0.57 0.00 0.18 0.00 0.31 0.00 0.44 0.00 1.16 0.00 0.49 0.00 0.37 0.00 0.19 0.00 1.73 0.00 1.10 0.00 0.51 1.29 0.40 0.51 5.38 0.26 4.08 0.00 0.48 0.97 0.26 0.40 8.47 0.25 10.82 0.00 Table 11. J e t Fuel Peroxidation a t 65
week 0 1
2 3 4 5
week 0 1 2 3 4 5 6 7 8
Shale-I1 JP-5 control doped 0.69 0.00 0.70 0.00 0.73 0.00 0.94 0.45 1.11 0.68 1.56 0.88
with Added Thiophenol 0.05% S u l f u r Dopant Hydrocracked Jet A Hydrofined Jet A Jet A blending stock blending stock control doped control doped control doped 0.12 0.00 0.24 0.00 0.10 0.00 0.18 0.00 1.58 0.00 0.60 0.00 0.16 0.00 6.01 0.00 2.09 0.00 0.28 0.54 37.66 0.61 12.41 0.00 0.26 0.22 62.05 0.51 25.27 0.00 0.29 0.81 59.92 0.25 56.67 0.00 O C
Table 111. J e t Fuel Peroxidation at 65 "C with Added ThioDhenolO.O3% S u l f u r Hydrocracked Jet A Shale-I1 JP-5 Jet A blending stock control doped control doped control doped 0.60 0.60 0.01 0.01 0.27 0.27 0.62 0.14 0.00 0.00 0.04 0.96 0.72 0.00 0.05 0.00 1.88 0.00 0.84 0.00 0.00 3.98 4.20 0.00 0.90 0.01 0.09 0.01 10.04 0.01 0.93 0.00 0.05 0.50 0.00 22.43 0.99 0.00 0.00 0.70 49.03 0.00 1.14 0.03 0.13 1.38 77.88 0.62 1.29 0.15 0.07 0.88 97.40 0.36
in an exponential fashion, indicating a depletion with time of the antioxidant and its ability to control peroxidation.12 Sulfur is the most abundant heteroatom present in jet fuels (up to 0.4% allowed by specifications). Deposits formed in jet fuel in the presence of oxygen contain a higher percentage of sulfur than that present in the fuel it~e1f.l~The formation of these deposits has been attributed to the participation of sulfides, disulfides, and thiols mercaptan^).'^ In jet fuels that have been deoxygenated, sulfides and disulfides have been found to lead to increased solid f0rmati0n.l~ Examination of the reactions between both alkyl and aromatic thiols with tertbutyl hydroperoxide (tBHP) have indicated that aromatic thiols are more reactive than other classes of sulfur compounds with hydroperoxides. The reaction of thiophenol with tBHP was found to produce trace amounts of sulfonic acid while depleting the amount of both reactants in so1ution.l6 It was thus desirable to test the relationship between sulfur compound reactivity and peroxide formation by using an arenethiol as a model dopant under accelerated storage conditions. This paper discusses the effect on hydroperoxide formation of using an arenethiol, thiophenol, as a dopant in a Jet A, a shale-derived jet fuel, and two jet fuel blending stocks under 65 "C accelerated storage conditions. A 65 (13) Wallace, T. J. In Aduances in Petroleum Chemistry and Refining; Wiley-Interscience: New York, 1964; pp 353-407. (14) Taylor, W. F.; Wallace, T. J. Ind. Eng. Chem. Prod. Res. Deu. 1968, 7, 198. (15) Taylor, W. F. Ind. Eng. Chem. Prod. Res. Deu. 1976, 15, 64. (16) Mushrush, G. W.; Hazlett, R. N.; Hardy, D. R.; Watkins, J. M. Liquid Phase Oxidation of Sulfur Compounds. In Conference Proceedings, 2nd International Conference on Long Term Storage Stabilities of Liquid Fuels; Southwest Research Institute: San Antonio, TX, 1986; Vol. 2, pp 512-525.
Douant Hydrofined Jet A blending stock control doped 0.06 0.06 0.32 0.00 0.78 0.00 2.46 0.00 5.89 0.00 13.26 0.00 0.00 28.54 60.62 0.00 77.44 0.00
"C stress test was chosen for the sulfur compound study based on previous time-temperature peroxidation studies completed a t NRL.12 The effect on peroxide formation versus added sulfur concentrations is also reported. Experimental Section Fuels and Reagents. The four fuels used in the investigation were Shale-I1 JP-5, Jet-A, a Hydrocracked J e t A blending stock, and a Hydrofined Jet A blending stock. Thiophenol was obtained from Aldrich Chemical Co. and was distilled in vacuo t o 99.9% purity. Method. The stress test was patterned after that used by the laboratories which participated in the recent Coordinating Research Council cooperative studies on peroxidation.17 Tests were carried out in brown borosilicate glass bottles, 500-mL total capacity, capped with Teflon liners, containing 300 mL of fuel per bottle. Duplicate samples of the four fuels were prepared, with sulfur in the form of thiophenol weighed into one sample of each fuel. The first series of samples were prepared by adding 0.10% sulfur (weight/volume) from thiophenol, followed by sets with 0.05,0.03, and 0.01% added sulfur concentrations. Stress tests were conducted for 5 weeks for the samples containing 0.10 and 0.05% added sulfur. The samples containing 0.03 and 0.01% added sulfur were stressed a t 65 "C for 8 weeks. Samples were analyzed weekly for peroxide concentration by ASTM Method D3703-85 from the control and test bottles for each fuel. A MettIer DL20 automatic titrator was employed for the 0.03 and 0.01% added sulfur tests, eliminating the use of starch solution from the ASTM method. Thiophenol concentrations were monitored weekly with a Tracor 565 gas chromatograph equipped with a sulfur-specific 700A Hall electrolytic conductivity detector. The chromatography program used started a t 60 "C for 8 min, with a ramp of 10 OC/min to a final temperature of 260 "C. Samples (17) Determination of the Hydroperoxide Potential of Jet Fuels; Report No. 559; Coordinating Research Council: Atlanta, GA, Apr 1988.
Energy & Fuels, Vol. 3, No. 2, 1989 233
Hydroperoxide in Jet Fuels Table IV. Jet Fuel Peroxidation at 65
Shale-I1JP-5 week
control 0.51 0.60 0.67 0.81 0.85 0.99 1.08 1.12 1.51
doped 0.51 0.20 0.17 0.00 0.00 0.00 0.23 0.33 0.46
with Added Thiophenol 0.01% Sulfur Dopant Hydrocracked Jet A Hydrofined Jet A Jet A blending stock blending stock control doped control doped control doped O C
0.00 0.10 0.13 0.20 0.17 0.21 0.17 0.19 0.24
were analyzed in triplicate against an external standard for thiophenol, which was also analyzed in triplicate.
Results and Discussion Thiophenol was the sulfur compound used as a dopant in this study. The first reaction series in this study employed 0.01 % total sulfur (weight/volume) weighed out as thiophenol. To examine the effect of added sulfur concentration on peroxidation, a second test was run by using 0.05% added sulfur from thiophenol. On the basis of the results of the 0.05% added sulfur test, additional series were run by using 0.03 and 0.01% added sulfur from thiophenol. The data for these tests are presented in Tables I-IV, respectively. For all of the sulfur concentration tests, the control samples, fuel only, exhibited similar behavior. Differences in actual peroxide numbers between tests can be attributed to slight temperature differences in the ovens that were used and to the fact that the fuel samples had been in storage for varying times before these tests were started. It was interesting that in the Jet A control samples peroxide formation occurred in a cyclic pattern. This has been observed in other peroxidation studies with Jet A. The two Jet A blending stocks formed peroxides at a greater rate than the Shale JP-5 or the Jet A samples. The most important aspect of all the tests was that the samples doped with sulfur in the form of thiophenol did not undergo peroxidation as rapidly as the fuel only samples. In fact, thiophenol addition eliminated any ROOH present in starting samples of all four fuels in the 0.05% added sulfur series, and after the first week in the Shale I1 and Hydrocracked Jet A blending stock samples in the 0.10% test. In the samples doped with 0.10% sulfur, peroxide formation was not observed until the fourth week of the stress test. When the concentration of added sulfur was reduced (halved) peroxide formation began 1 week earlier in the three fuels that did exhibit peroxidation, indicating a relationship between added sulfur concentration and peroxide formation (or peroxide inhibition). None of the doped samples of the Hydrofined Jet A blending stock showed evidence of peroxide formation throughout the duration of the tests. In the series doped with 0.03% added sulfur from thiophenol, peroxides were eliminated after 1week of 65 O C stress in all of the samples except for the Shale-I1JP-5, which contained a larger starting concentration of peroxides that required 2 weeks to be reduced to zero as measured by the ASTM method. The Jet A samples began to exhibit peroxidation in the third week of the test, while the Shale-I1 and Hydrocracked Jet A blending stock samples did not show any trace of peroxidation until the fourth week, before disappearing again to reemerge in the seventh week of the test. Even though peroxidation was not observed until later in this test than in the 0.10 and 0.05% added sulfur samples, the 0.03% added sulfur controlled peroxidation, most noticeably in the Hydrocracked and
0.25 1.02 2.37 4.66 13.22 29.20 55.33 89.57 131.13
0.00 1.04 0.72 0.89 0.55 0.59 0.42 0.72 0.65
0.25 0.73 0.11 0.00 0.00 0.22 0.14 0.19 0.28
0.06 0.50 1.32 3.63 13.79 29.10 48.57 78.27 124.98
0.06 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Table V. Sulfur Concentration vs Time for 0.10% Sulfur Dopant from Thiophenol Hydrocracked Hydrofined jet Shale-I1 JP-5 Jet A Jet A stock A stock mg of mg of mg of mg of week S / 2 m L week S / 2 m L week S / 2 m L week S / 2 m L 0 2.20 0 2.08 0 2.12 0 2.10 1 2 3 4 5
1.16 0.51 0.43 0.26 0.24
1 2 3 4 5
0.98 0.81 0.63 0.47 0.41
1 2 3
4 5
0.92 0.74 0.67 0.48 0.47
1 2 3 4 5
1.78 1.47 1.58 1.43 1.38
Table VI. Sulfur Concentration vs Time for 0.05% Sulfur Dopant from Thiophenol Hydrocracked Hydrofined Shale-I1JP-5 Jet A Jet A stock Jet A stock mg of mg of mg of mg of week S I 2 m L week S / 2 m L week S I 2 m L week S/2 mL 0 1.00 0 1.00 0 1.00 0 1.00 ~~
1 2 3 4 5
0.76 0.23 0.15 0.02 0.00
1 2 3 4 5
0.25 0.33 0.16 0.15 0.00
1 2 3 4 5
0.86 0.63 0.78 0.38 0.49
1 2 3
4 5
0.37 0.76 0.33 0.21 0.16
Hydrofined Jet A blending stock samples, which did not exhibit any peroxidation during the test, in spite of the fact that both of these samples peroxidized extensively when the thiophenol was absent. The samples doped with 0.01% added sulfur from thiophenol also demonstrated the ability of added sulfur to control peroxidation. In the Shale-I1and Hydrocracked Jet A blending stock samples, the starting peroxide concentrations were gradually decreased to zero after 3 weeks of stress. Peroxidation was not evident in the Shale-I1 sample until the sixth week of the test, but began again in the Hydrocracked Jet A blending stock sample in the fifth week of stress. This can be explained by comparing the relative peroxide levels present in the control samples, 0.991 mequiv of active 02/kg of fuel versus 29.200 mequiv of active 02/kg of fuel for the Shale-I1 and Hydrocracked blending stock samples, respectively. The 0.01% added sulfur was not enough to control the large amount of peroxide formation after 5 weeks in the Hydrocracked Jet A blending stock sample. The Jet A samples, both control and doped, exhibited interesting cyclic behavior similar to that in the 0.03% added sulfur study, while the doped Hydrofined Jet A blending stock sample did not undergo peroxidation during the test after the starting peroxide concentration was depleted. The thiophenol concentrations in the doped samples decreased throughout the tests as measured by the sulfur-specific electrolytic conductivity detector on the gas chromatograph. Tables V and VI contain the data for the 0.10 and 0.05% sulfur from thiophenol-doped samples, respectively. Samples were analyzed in triplicate and
Watkins et al.
234 Energy & Fuels, Vol. 3, No. 2, 1989 2.2
2 1 ..a 1.6 1.4
1.2 1
0.8 0.6 0.4
0.2 0 0
1
2
3
0
1
2
3
4
5
Figure 1. Sulfur
4
5
WEEKS OF STORAGE AT 65C 0
MG. SULFUR FROM 0SH
+
PEROXIDE NUMBER
Figure 2. Sulfur concentration versus peroxidation for Shale-I1JP-5 with 0.05% thiophenol. compared to an external standard for thiophenol, which was also analyzed in triplicate. Average values are reported and were used for all calculations. It is interesting to note that the sulfur concentrations decreased more rapidly and to a greater extent in the doped Shale-11, Jet A, and Hydrocracked blending stock samples, 'those fuels that did exhibit some peroxidation, than in the Hydrofined blending stock sample, which did not exhibit peroxidation during the test. This was true for both concentrations of added sulfur with the exception of the Hydrocracked sample, which depleted slower in the 0.05% doped test. The presence of new peaks on the chromatogram indicated the formation of new sulfur-containing compounds; however, concentrations were too low to permit identification. It should be noted that in the 0.10% doped samples there were still measurable sulfur concentrations for the duration of the stress test, but for the 0.05% doped samples, the
added thiophenol disappeared much faster and was completely depleted between the fourth and fifth weeks of the test for the Shale-I1 and Jet A samples. A direct comparison of the sulfur concentration to peroxidation in the Shale-I1samples can be seen in Figures 1and 2 for the 0.10 and 0.05% doped samples, respectively. The place on the graphs where the lines intersect indicates the approximate concentration of added sulfur at which peroxidation is no longer controlled. It should be noted that this concentration was approximately 0.4 mg of sulfur for the 0.10% doped sample and 0.2 mg of sulfur for the 0.05% doped sample. The results for the 0.03 and 0.01% added sulfur from thiophenol studies are reported in Tables VI1 and VIII, respectively. The doped samples in these series exhibited behavior similar to the first two tests. The sulfur concentrations in the two Hydrofined Jet A blending stock
Energy & Fuels, Vol. 3, No. 2, 1989 235
Hydroperoxide in Jet Fuels
I
".' 0.6
0.5
0.4
0.3
0.2
0.1
0 4
2
0
6
WEEKS OF STRESS AT 6 5 C
+
MC. SULFUR FROM P S H
0
PEROXIDE NUMBER
Figure 3. Sulfur concentration versus peroxidation for Shale-I1 JP-5 with 0.03% thiophenol. 0.6
n
t
0.5
P E
v
a
W
0.4
m I
3
z W
0
0.3
X
2w
L
d
a
0.2
iv1 ri
I
0.1
l
0 0
2
4
6
a
WEEKS OF STRESS AT 65C 0
MC. SULFUR FROM &H
+
PEROXIDE NUMBER
Figure 4. Sulfur concentration versus peroxidation for Shale-I1 JP-5 with 0.01?' % thiophenol.
samples did not decrease as rapidly or to the same extent as the concentrations in the other fuels. The sulfur concentration in the 0.03% sulfur-doped Shale JP-5 sample was depleted by the eighth week of the test while the concentration in the 0.01 % doped sample was zero by the thud week of the test. In the Hydrocracked Jet A blending stock samples there were low sulfur concentrations throughout the duration of the tests, with the 0.01% doped sample dropping to zero by week five. The 0.03 % doped Jet A sample exhibited cyclic peroxide formation and a rapid decrease in sulfur concentration, while the 0.01% doped sample showed an immediate decrease in sulfur concentration during the first week of stress. Figures 3 and 4 provide a direct comparison of the sulfur concentration to the peroxidation of the samples doped with 0.03 and 0.01% added sulfur. According to this data, the concentration at which peroxidation was no longer controlled was about 0.03 mg of added sulfur for the 0.03%
Table VII. Sulfur Concentration vs Time for 0.03% Sulfur Dopant from Thiophenol Hydrocracked Hydrofined Jet A stock Jet A stock Shale-I1 JP-5 Jet A week meof S week me of S week mn of S week me of S 0 0.60 0.61 0.60 0 0.60 0.13 0.17 1 0.17 1 0.31 2 0.20 0.05 0.03 2 0.12 3 0.21 0.01 3 0.01 0.06 4 0.19 0.05 0.01 4 0.05 0.05 0.01 5 0.03 5 0.18 0.01 6 0.05 6 0.13 0.03 7 0.01 7 0.10 0.03 0.01 8 0.10 0.00 0.01 8 0.00
doped sample. This concentration was reached at the end of 6 weeks of stress, and peroxidation began between the sixth and seventh week of the test. In the sulfur concentration versus peroxidation graph for the shale sample with
236
Energy & Fuels 1989, 3, 236-242 Table VIII. Sulfur Concentration vs Time for 0.01% Sulfur DoDant from ThioDhenol
Hydrocracked Hydrofined Shale-I1 JP-5 Jet A Jet A stock Jet A stock week mg of S week mgof S week mg of S week mgof S 0 0.21 0 0.20 0 0.21 0 0.20 1 0.03 1 0.00 1 0.01 1 0.09 2 0.02 2 0.00 2 0.00 2 0.12 3 0.00 3 0.00 3 0.01 3 0.05 4 0.00 4 0.00 4 0.00 4 0.07 5 0.00 5 0.00 5 0.00 5 0.06 6 0.04 6 0.00 6 0.00 6 0.00 7 0.00 7 0.00 7 0.00 7 0.03 8 8 0.00 8 0.00 8 0.00 0.05
0.01% added sulfur, peroxide inhibition stops in the fifth week of stress when the added thiophenol concentration was reduced to zero as measured by the sulfur detector. The comparison of sulfur concentration to peroxidation indicated that control or inhibition of peroxidation was lost a t approximately 0.2 f 0.1 mg of added sulfur in all fuel samples.
Conclusions The effect of adding sulfur in the form of an aromatic thiol, thiophenol, was significant to peroxide formation.
Thiophenol has been found to act as an inhibitor or controller of peroxide formation in Jet A, Shale-11-derived JP-5, and petroleum-derived Jet A blending stocks. Hydrotreated jet fuels exhibited higher peroxide formation and concentration than other fuels. Hydrotreatment reduces the sulfur content of the fuel, which removes those naturally occurring sulfur compounds that possibly act as inhibitors to peroxide formation. There appeared to be a minimum concentration of sulfur as thiophenol above which peroxide formation was inhibited. If this concentration was decreased or consumed, peroxidation began. In a mixture as complex as a fuel, when a sulfur dopant is present a t a concentration of 0.10% or less, the sulfur compound reaction products are not possible to detect. Sulfur compound MS and hydrocarbon MS are quite similar, and the sulfur compounds are buried in the GC of the fuel. We suggest that since aromatic thiols are quite reactive in the presence of peroxide species, the thiophenol most likely undergoes oxidation by the peroxide.16 In model systems, in dodecane solvent, we found in our preliminary studies with hydroperoxides and sulfur model compounds that both aryl disulfides and oxidized sulfur species such as sulfoxides and sulfones were formed from thiophenol. Registry No. Thiophenol, 108-98-5.
Effect of Coal Properties, Temperature, and Mineral Matter upon a Hydrogen-Donor Solvent during Coal Liquefaction B. Chawla,* R. Keogh,* and B. H. Davis* Center for Applied Energy Research, 3572 Iron Works Pike, Lexington, Kentucky 40511 Received February 18, 1988. Revised Manuscript Received December 12, 1988
The tetrahydrofuran-soluble fraction of coal liquids, containing tetralin (T) and naphthalene (N), was analyzed by using a high-performance liquid-chromatographic technique. The amount of H2 consumption (calculated from experimental T / N ratios) during coal liquefaction showed a direct relationship with the carbon content of the coals. While the T / N ratios obtained for residence times of 5-65 min defined similar trends, the value of the ratio did depend on the carbon content of the coals.
Introduction Coal liquefaction processes have been studied' in the presence of hydrogen-donor as well as non-hydrogen-donor
solvents for many years.'-15 Two generally accepted p a t h w a y ~ ~ ~ ~for J ~H J ~transfer -'~ from a donor solvent ~~~
(1) Pott, A.; Broche, H.; Schmitz, H.; Scheer, W. Gluckauf 1933, 69, 903. (2) Bergius, F. Nobel Lectures-Chemistry, 1922-1941; Elsevier: Amsterdam, 1966; p 244. (3) Orchin, M.; Storch, H. H. I n d . Eng. Chem. 1948,40, 1259. (4) Curran, G. P.; Struck, R. T.; Gorin, E. Ind. Eng. Chem. Process Des. Dev. 1967, 6, 166. (5) Wiser, W. H. Fuel 1968,47, 475. (6) Neavel, R. C. Fuel 1976, 55, 237 and references cited therein. (7) Tsai, M. C.; Weller, S. W. Fuel Process Technol. 1979, 2, 313. (8)Solvent Activity Studies; Catalytic Inc.: Wilsonville, AL, 1983; DOE/PC/50041-18, DE83, 015870. (9) Whitehurst, D. D.; et al. Coal Liquefaction-The Chemistry & Technology of Thermal Processes Academic Press: New York, 1980.
0887-0624/89/2503-0236$01.50/0
(10) (a) Derbyshire, F. J.; Whitehurst, D. D. Presented at the EPRI Contractor's Meeting, Palo Alto, CA, May 1980. (b) Derbyshire, F. J.; Odoerfer, G. A.; Rudnick, L. R.; Varghese, P.; Whitehurst, D. D. EPRI Report, AP-2117, Vol. 1, Project 1655-1; EPRI: Palo Alto, CA, 1981. (11) Ohe, J.; Itoh, H.; Makaba, M.; Ouchi, K. Fuel 1985, 64, 902. (12) Skowronski, R. P.; Ratto, J. J.; Goldberg, I. B.; Heredy, A. Fuel 1984, 63, 440. (13) Besson, M.; Bacaud, R.; Charcosset, H.; Cebolla-Burillo, V.; Oberson, M. Fuel Process. Technol. 1986, 12, 91. (14) Storch, H. H. Chemistry of Coal Utilization. Lowry, H. H., Ed.; John Wiley and Sons: New York, 1945; Vol. 11. (15) Heredy, L. A,; Fugasi, P. Phenanthrene Extractions of Bituminous Coal. In Coal Science; Given, P. H., Ed.; Advances in Chemistry Series 55; American Chemical Society: Washington, DC, 1966; p 448. (16) Whitehurst, D. D.; Farcasiu, M.; Mitchell, T. 0. The Nature and Origin of Asphaltenes in Processed Coals. EPRI-AF-252, 1st Annual Report; EPRI: Palo Alto, CA, 1977.
0 1989 American Chemical Society
