A. C. NIXON and H. B.
MINOR
Shell Development Co., Emeryville, Calif.
Effect of Additives on Jet Fuel Stability and Filterability
I N C O M M O N with most other petroleum fuels, jet fuels have additives included in them to modify their properties. Perhaps because they are relative newcomers in the world of fuels, the number of additives being used in jet fuels is relatively few, compared, for instance, with gasoline. Perhaps additives like gray hair come with age. At the present time only two types of additives are consistently used in jet fuels. (Military specifications now permit the addition of a metal deactivator.) These are antioxidants to promote storage stability and an inhibitor to prevent corrosion. Deactivators, dispersants, detergents, and antiicing compounds are all mentioned in connection with improved stability or filterability but are not yet used commercially. Combustion improvers are talked about but have not, as yet, been blessed by official acceptance. This paper reports the results of some work done under Air Force sponsorship, showing how some of these additives accomplish or fail to accomplish the task they are supposed to do in jet fuels. Specifically, it relates the behavior of compounds that have been approved as antioxidants in military specifications in terms of their performance in accelerated and realistic stability tests, the search for more effective compounds, and the effect of such additives on high and am-
bient temperature filterability. Siniilar observations are made on the effect of metal deactivator and dispersants. Fuels that are in current use are probably of different composition than would be possible under the exigencies of wartime. Accordingly, the discussion is not confined to the predominantly saturated fuels of today but also examines the effect of additives in fuels containing substantial amounts of cracked components.
Experimental Work
Determination of Soluble and Insoluble Gum. STEAMJET(7). InsolubIe gum is determined by filtering the fuel through a fine sintered-glass filter, and washing with isopentane (2-methylbutane) to remove the last traces of fuel. O n occasion, the fuel container is also washed with isopentane and the washings are passed through the filter. The contents of the filter are then dissolved with triple solvent (one-third each of methanol, toluene, and ethyl acetate) into a gum beaker. The solvent is evaporated a t 500' F. with steam a t 1 liter per second for 30 minutes and the beaker is weighed. Soluble gum is determined by evaporating 50 ml. of the sample after filtration (or directly, if clear) in a gum beaker and
weighing. This is similar to ASTM Method D 381-52T, except that the steam temperature is 500 F. CHROMATOGUM ( 3 ) . Both types of gum may also be determined on very small samples by an elution chromatographic procedure which measures the gum as a brown zone on a silica gel column. Aging Conditions. Fuels have been aged under several conditions of severity. ACCELERATED AGING. This has been carried out in UOP-type bombs (9) a t 100' C. and an oxygen pressure of 100 pounds per square inch gage in a manner similar to that specified in ASTM Method D 525-49. OVEN AGING. This has generally been done a t 70' C. in a steam-heated oven, using air-driven fans to circulate the air in the oven and maintain a constant temperature. Fuel temperatures within the oven have varied less than 1' C. The samples are generally stored in crown-capped, amber 12-ounce or 1quart beer bottles with an air-fuel ratio of at least 1. This has been found a very satisfactory method of storing samples. Very few have been lost through leaks or breakage. This is a more reliable method of assessing the stability of a fuel than the bomb method, as the accelerating factor compared to 110O F. is only 11 rather than about 1000 (5); at the same VOL. 48, NO. 10
OCTOBER 1956
1909
Figure 1 .
Figure 2.
Laboratory heat exchange apparatus
Effect of inhibitors on gum formation in four jet fuels
Aging a t 100' C., 100 Ib./sq. inch g a g e oxygen for 16 hours Ov. Aging a t 70' C., 1 atm. air for 21 days Ds. Aging in desert for 2.8 years HR. Aging a t 110' F., 1 atm. air for 1 year Ac.
19 10
INDUSTRIAL A N D ENGINEERING CHEMISTRY
time it is sufficiently accelerated to produce results in a few weeks' time. HOTROOMAGING. Fuels have been stored in a hot room at 3 10' F. to simulate the effects of desert aging (the effective average temperature on the desert during the summer months is about 110" F.). Aging was usually done in amber bottles of various sizes ranging from 1 gallon to 12 ounces. With larger containers samples were withdrawn from time to time for determination of various properties. However, it was found more convenient, particularly for the determination of insolubles, to store the required number of samples in smaller containers and use the entire contents as a n individual sample. DESERT AGING. This was done at the Naval Air Station at El Centro, Calif., by storing fuels in 5-gallon steel cans and 55-gallon drums with 10% outage. The fuel was sampled at about 6-month intervals after thorough agitation of the contents of the container. The average effective average temperature during the summer months at El Centro ranges from about 105' to 110°F. Filterability. Filterability has been measured with a simple apparatus ( 6 ) which has allowed determination on as little as a 100-ml. sample of a fuel. The apparatus consists of a 100-ml. glass syringe which acts as a sample holder, and, driven by a constant-speed motor: as a pump. The fuel is forced through a portion of micronic aircraft filter paper (or other type of filter), 0.8 cm. in diameter, which is placed immediately downstream from a connection to an open-end mercury manometer. A magnetic stirrer is placed within the syringe to keep solids in uniform dispersion. For measuring filterability at temperatures other than ambient, a glass heat exchanger is placed between the syringe and the filter holder. High Temperature Stability. In order to measure high temperature stability and nozzle plugging tendency, an apparatus (cf. Figure 1) was constructed which exposes the fuel to a maximum temperature of 450' F. by passing the fuel through a coil formed from 6 feet of aluminum tubing '/8 inch in inside diameter, heated in a countercurrent stream of hot air (ti). The fuel then flows through a 5-micron stainless steel sintered filter 1.5 cm. in diameter by 0.3 cm. thick, thence to a cooler, and out of the apparatus through a pressure-regulating valve. The flow rate is 40 ml. per minute? residence time in the coil is about 22 seconds, and operating pressure is 250 pounds per square inch gage. Both the filter and the coil are washed with isopentane, dried at 110' C., and weighed before and after a teat to determine the amount of solids deposited. The apparatus has been generally operated with recycle of the fuel (using a charge of 1.3 liters), which is a more
A D D I T I V E S IN FUELS severe type of operation than once through ( 2 ) . Effects of Inhibitors
Specification Inhibitors. The three military specification ( 4 ) inhibitors-2,6di-tert-butyl-4-methylphenol (26B4M),
2,4-dimethyl-6-fsrt-butylphenol(24M6B), and N,N'-di-sec-butyl-p-phenylenediamine(PDA)-have been tested in a variety of fuels under a variety of conditions and at several different concentrations to determine their effect on storage stability of turbine fuels. [26B4M was obtained from the Shell Chemical Corp. (Ionol gasoline inhibitor) and PDA was also a commercial product.] These inhibitors are almost invariably effective in extending the induction period at 100' C. and an oxygen pressure of 100 pounds per square inch, are generally effective in reducing the amount of peroxides, but only rarely reduce the amount of gum formed under these accelerated aging conditions. This is shown in Table I for, two experimental fuels composed of catalytically cracked and thermally cracked components. The PDA inhibitor seems to be particularly effective in extending the induction period, but relatively ineffective in preventing the formation of gum under these conditions. The trialkyl phenol inhibitors have less effect on the induction period but are more effective in reducing gum formation. However, the proof of the inhibitor is in the aging and none of the inhibitors seems to ameliorate the effects of normal aging. This is illustrated in Figure 2, which shows the effect of aging samples of a JP-4 and three JP-3 fuels containing 10 mg. per dl. (4.17 pounds per 5000 gallons, 35 pounds per 1000 barrels, 0.013 weight yo)of the three specificationinhibitors and a commercial gasoline inhibitor, N-n-butyl-p-aminophenol (AP), compared with the corresponding uninhibited fuels. (The fuels originated in Texas, California, and the mid-continent.) The samples were exposed under the four conditions of severity outlined above-i.e., 100' C., 100 pounds of oxygen per square inch gage; 70" C.; 110' F.; and in the desert. Figure 2 represents the effects of 16 hours, 21 days, 1 year, and 2.8 years under the respective conditions, in terms of the total and insoluble 500' F. steam jet gum formed. The lengths of the bars indicate the range of results with the various fuels, while the heavy horizontal lines represent the average values. While the response of different fuels is variable, on the average none of the inhibitors shows any benefits under any condition except the 26B4M under the most severe conditions-Le., 100' C., 100 pounds of oxygen per square inch gage for 16 hours.
Figure 3.
Effect of PDA inhibitor at different air-fuel ratios
Figure 4.
Effect of inhibitor type and concentration VOL. 48, NO. 10
0
OCTOBER 1956
191 1
Table 1.
Effect of Inhibitors on Properties of Experimental JP-3 Fuels
(Numbers are ratios of values for inhibited and uninhibited samples) Treatment Propertya Inhibitor concn., mg./dl. PDA 26B4M 26M6B a
Caustic IP
Clay IP
20 2.6 1.4 2.1
20 3.7+ 2.0 1.2
Catalytically Cracked Acid None IP IP IP Gumb P.hT.b 20 2.0 1.6
..
20 10 10 2.6 3.0 0.9 1.3 1.3 0.5 1.3 1.3 0.6
10
0.3 0.6 0.5
I
Caustic IP
Clag
20 1.7 1.6 1.6
20 1.2 1.3 1.2
IP
Thermally Cracked Acid None IP I P I P GumE P.LKT 20 1.2 1.2
..
20 1.3 1.2 1.2
10
1.3 1.2 1.4
10 1.5 1.1 1.0
10
0.5 0.7 0.4
IP. Induction period at looo C . and 100 Ib./sq. inch gage 02,hours. Gum. Total 500' F. steam jet gum, mg./dl. P.N. Peroxide number, Yule and Wilson method (10). After aging 82/3 hours at 100" C. and 100 lb./sq. inch gage 02. After aging 6 hours at 100' C. and 100 lb./sq. inch gage 02.
u
= Uninhibited a = PDA, 10 mg./dl. b = 26B4M, 10 mg/dl.
$
%
6
B
$ 6
4
2
0
Saturates
Figure 5.
10% O l e f i n s Diaromatics in Saturates 5 34' F. 596" F. Hydrocarbon Type
Inhibitor response of chromatographically separated iet fuel fractions
Comp, J P - 4 Conc, 10 m d d l .
pDY Blank
I
I
I
2 4 6 Weeks at 7 O O C .
2 4 6 Months at 110" F.
Figure 6. Effect of experimental inhibitor on rate o f gum formation of composite JP-4 fuel
1 9 12
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Another illustration of the lack of effect of PD.4 is shown in Figure 3, which illustrates the effect of aging two California JP-3 fuels, uninhibited and inhibited, with 2.4 mg. per dl. of PDA inhibitor for about 7 months in the desert at three different air-fuel ratios in 5-gallon cans. Although the air-fuel ratio had a considerable effect on the rate of deterioration, the presence of the inhibitor had practically none. The greater sensitivity of the more saturated fuel to air-fuel ratio is unexplained and inexplicable, as the only difference between the fuels was the presence of about 35Oj, of thermally cracked gasoline in the fuel of higher bromine number. The effect of these inhibitors is not improved by increasing their concentration. Figure 4 illustrates the effect of 70" C. aging on a composite JP-4 type blend containing 26B4M and PDA at concentrations of 10, 50: and 100 mg. per dl. The trialkyl phenol inhibitor has practically no effect on the rate of deterioration of the fuel at any concentration, but the PDA inhibitor increases it at all. concentrations, an effect that increases with increasing concentration. This behavior of inhibitors which are effective in gasolines is remarkable and is evidently due to the presence of the higher boiling materials found in the gas oil portion of the jet fuels. In endeavoring to find the reason for this lack of response straight-run, catalytically cracked, and thermally cracked gas oils, which could be incorporated into jet fuels, are being examined. T o date most progress has been made with a catalytically cracked fraction similar to that used in the composite fuel referred to above. Although results are far from complete at this time, there are indications that .the lack of inhibitor response is associated with The polyaromatic portion of the fuel. Figure 5 illustrates the response of some saturated, olefinic, and diaromatic fractions isolated from this gas oil by distillations and chromatography. The saturated portion does not form gum in either the presence or absence of inhibitors. The olefinic fraction is very unstable even at 107, concentration in saturates, but it can be very readily and
A D D I T I V E S I N FUELS completely inhibited by both the trialkyl phenol and PDA inhibitors. The diaromatic portions, on the other hand, while not so unstable as the olefinic fraction, show very little response to the inhibitors. Other type fractions are under investigation. The effect of 26B4M and PDA was also found to be negligible under simulated high temperature heat exchanger conditions in a straight-run JP-4 fuel. This is also in accord with data reported by Johnson, Fink, and Nixon ( 2 ) . Experimental Inhibitors. Nearly 250 organic compounds of various types were tested in jet fuels under various conditions of aging for antioxidant activity. Several were found to be effective under accelerated conditions of aging, but generally were inert under more normal conditions of storage (desert or 110' F. hot room). A few have shown some promise as storage inhibitors, but additional testing in different types of fuels will be required before this can be proved. Results with the best one of these are shown in Figure 6 in comparison with 26B4M and PDA. At both 70' C. and 110" F. the experimental additive is fairly effective in decreasing the rate of gum formation. Again the adverse effect of the PDA and the relative inertness of the 26B4M are observed. However, under simulated heat exchanger conditions the experimental inhibitor has relatively little effect. Similarly, other inhibitors found to be effective in lubricating oils have not significantly extended the plugging time a t 450' F. Effect on Filterability. Two of the specification inhibitors, PDA and 26B4M, and the gasoline inhibitor AP were added to a group of experimental jet fuels which differed only in the treatment and proportion of their gas oil components. The fuels were aged for 10 weeks a t 70 ' C. in an atmosphere of air and the filterability characteristics at room temperature were determined in the constant flow filterability test a t the end of this time. Results are shown in Figure 7, in which the heights of the bars represent the pressure drop developed in the test. Careful examination of these data reveals that the trialkyl phenol inhibitor generally reduces or in some cases does not increase the pressure drop experienced with the clear fuels, whereas the two nitrogen-containing inhibitors often increase and generally do not decrease the pressure drop. This is not, in general, due to a reduction in the amount of insolubles formed, and, indeed, there is no relationship between the magnitude of the pressure drop produced and the amount of insoluble gum present in the fuel. This is illustrated in Figure 8, in which the pressure drop is plotted against the amount of insoluble gum. This result
25
20
15
E
0
%
10
5
0
1
13
14
Fuel No. Figure 7. Effect of inhibitors on filterability of jet fuels after aging
A PDA
A
V
AP
0
26B4M
0 Clear
V A v v
A
0
0
Figure 8.
Table II.
15 AP, cm.Hg
10
5
0
20
25
Effect of inhibitors on filterability
Effect of Metal Deactivator against Soluble Copper in JP-3 Type Fuels under Accelerated Aging Conditions (Aging conditions.
Fuel
Mid-continent straight-run California thermally cracked Shale oil, Bureau of Mines
100° C., 100 lb./sq. inch
02, 6
hours)
Total 600' P . Stream Jet Cum, Mg./Dt., after Aging, 1 P.P.M. Coppera Added No 5 mg./dl. Blank deactivator deactiuatorb 5.1
11.2 6.0
9.1 122
110
5.9
11.7 6.3
Added as copper naphthenate. N,N'-disalicylidene-1,t-propanediamine. ~
VOL. 48, NO. 10
OCTOBER 1956
~-
19 13
Table 111.
Effect of Metal Deactivator on Action of Copper-Bearing Steels, Metallic Copper, Soluble Copper (Aging conditions. 110" F., 1 atm. air, F / A = 0.5. Composite JP-4 fuel, 1.0 mg./dl. gum) 500' F . Steam Jet Gum, M g . / D l . Metal Soluble Cub Deactivatora, 1 Month 3 Months 7 Months P.P.M., after Insol. Total 7 Months Mg./Dl. Sol. Total Sol. Insol. Total Sol. Insol. ~
Condition
No metal present
1.4 2.6
1.7 2.2
3.1 4.8
9.9 7.1
1.9 3.6
11.8 10.7
6.9 7.8
8.1 7.3
15.0 15.1
0.0
5 0 5
1.3 1.9
2.3 2.6
3.6 4.5
3.9 2.0
4.0 3.1
7.9
12.4 7.8
10.5 6.6
22.9 14.4
..
10.1 6.9
7.9 8.2
18.0 15.1
0
Steel strip
0.007% Cu 0.043% Cu
5
.. ..
0 5
4.3 2.2
2.6
0 5 0 5 0 5
0
0.092% Cu Copper wire O.lDC l.ODd Soluble copper, 10 p.p.m., (as copper naphthenate) a
.. ..
..
5.1
..
..
..
..
6.9 4.0
9.9 6.4
5.1 3.4
15.0 9.8
18.3 8.1
12.2 7.8
30.5 15.9
0.3
1.8
28.9 2.2
6.3 1.6
35.2 3.8
31.0 57.5
14.4 13.1
45.4 70.6
46.1 71.0
27.1 29.0
73.2 100.0
0.6 2.3
20.0 3.4
6.4 3.7
26.4 7.1
43.6 102.5
12.1 34.2
55.7 136.7
45.9 88.5
30.2 29.2
76.1 117.7
0.3 2.4
87.8 27.6
20.5 10.3
108.3 37.9
118.7 108.4
20.4 33.8
139.1 142.2
111.8 71.6
26.6 28.3
138.4 99.9
1.9 2.6
..
A7,N-Disalicylidene-1,2-propanediamine. Determined on filtered sample. Equivalent to storage in drum having 10% copper surface. Equivalent to storage in drum having 100% copper surface.
is in accord with other data recently presented by the authors (6) and is thought to be due to the different character of the insolubles produced. The insolubles upon examination with the electron microscope are found to possess very different physical characteristics and can be roughly described as crystalline, amorphous rigid, amorphous plastic, and diaphanous, with the effect on filter pressure drop increasing in the order named. I t appears that the trialkyl phenol inhibitor has the property of inducing the formation of a more crystalline type deposit than the undoped fuel, whereas the nitrogen-containing inhibitors favor a more amorphous type. Metal Deactivutors
The deterioration of fuels is accelerated to an appreciable degree by the catalytic
action of metals, particularly copper. This pro-oxidant action of copper can readily be exerted by very small concentrations in the fuel, of the order of fractions of a part per million, and also by a metallic copper surface. The catalytic action of copper on the oxidation of gasolines has been described in the literature (8). Fortunately, the adverse effect of copper on the stability of gasolines can be eliminated for all practical purposes by the use of sufficient quantities of metal deactivators. These compounds function by tying up the metal ion in an un-ionized chelate structure ( I ) . Preliminary accelerated aging tests demonstrated that commercial metal deactivator (N,Nt-disalicy1idene-1,2-propanediamine) also effectively counteracted the catalytic action of 1 p.p.m. of soluble copper added as copper naphthenate in a variety of jet fuels (cf. Table
Effect of Concentration of Metal Deactivator in Composite JP-4 Blend Containing Varying Amounts of Soluble Copper (Aging conditions. llOn F., 1 atm. air, F / A = 0.5) Metal Soluble Stoichiometric 600' F . Steam Jet Gum, M g . / D l . Deactivator" Copperb Ratio, Concn., Concn., Deactivator- Original! I Months 9 Months Mg./Dl. P.P.M. Copper Total Sol. Insol. Total Sol. Insol. Total
Table IV.
0.0 0.443 4.43 8.9 0.0 0.443 0.66 0.89 0.0 4.43 6.6 8.9 Z .
0
0 0
0 1
1 1 1
10 10
10 10
.. *.
.. 9 .
0.0 1.0 1.5 2.0 0.0 1.0 1.5 2.0
4.3 3.8 3.6 4.1
.. *.
4.0 4.6 7.9
..
4.9 5.5
4.1 3.9 3.5 3.5 23.8 12.8 5.2 4.9 38.6 32.6 6.2 6.2
N,W-disalicylidene-l,2-propanediamine. Added as copper naphthenate.
1 91 4
INDUSTRIAL AND ENGINEERING CHEMISTRY
1.6 2.0 1.1 1.4 7.9 5.8 1.8 1.7 9.8 8.4 2.6 1.9
5.7 5.9 4.6 4.9 31.7 18.6 7.0 6.6 48.4 41.0 8.8 8.1
8.8 4.2 3.7 3.5 24.4 10.0 8.8 10.3 32.4 26.1 13.3 19.8
5.9 4.4 4.7 4.5 10.2 8.2 8.9 7.2 12.6 17.1 9.6 11.3
14.7 8.6 8.4 8.0 34.6 18.2 17.7 17.5 45.0 43.2 22.9 31.1
11). However, this was at 10 to 1 stoichiometric ratio, so that it remained to be determined whether the metal deactivator would effectively minimize the formation of gum during normal storage in the presence of both soluble and metallic copper and at more realistic concentrations. Therefore, laboratory aging tests at 110' F. and 1 atm. of air were initiated to determine the effectiveness of the deactivator in counteracting the gum-promoting action of copperbearing steels, metallic copper surfaces, and soluble copper. The metallic surfaces included three cold-rolled steels containing about 0.01,0.04, and 0.1% weight copper, which are of interest because the proportion of copper in drum steel is steadily increasing, owing to its presence in scrap. Copper wire wa3 introduced in amounts equivalent to storage in drums having 10 and 1OOyo copper surfaces. A blend containing 10 p.p.m, of soluble copper as copper naphthenate was also included in this series of tests. The results of storage for 1 , 3, and 7 months are given in Table 111 for blends containing 0 and 5 mg. per dl. (65 p.p.m.) of the metal deactivator. The copper-bearing steels had a slight catalytic effect, but the metal deactivator overcame this effect. However. it was ineffective for storage in the presence of copper surfaces, except during the first month. Thereafter the deactivated samples are actually somewhat worse than the samples without additive. This may be due to the action of the deactivator in maintaining a fresher surface on the copper, as it promotes the solubilization of the copper in the fuel (by a factor of about 5). This is in agreement with the previously reported observation that the deactivators promote solubility of cop-
A D D I T I V E S I N FUELS per in gasolines (8). The deactivator was also ineffective against the action of the soluble copper, in spite of the fact that the concentration was about 1.5 times the stoichiometric ratio. This exceeds the manufacturers’ recommended ‘concentration for gasolines of 1.2 times stoichiometric. The analytical results obtained with the blend initially containing 10 p.p.m. of soluble copper suggest that upon severe aging the copper is partially removed as insoluble gum, since only 2 to 2.5 p.p.m. of copper remain in the filtered, aged fuel. In view of this result with soluble copper, additional tests have been done to determine the amount of deactivator necessary to counteract the pro-oxidant action of soluble copper when present at 1 and 10 p.p.m. The results of 110’ F. storage for 2 and 9 months (Table IV) show that a stoichiometric amount of deactivatm is definitely insufficient to prevent the formation of large quantities of both soluble and insoluble gum at either copper concentration. The higher concentrations are reasonably effective in the initial period, although the rate of gum format:on is not kept down to the level of that of base fuel. I t appears that metal deactivator is somewhat less effective in jet fuel than in gasoline. The results given in Tables 111 and IV also show that the metal deactivator in the absence of copper is substantially inert with respect to the formation of gum in jet fuels during storage. [Beneficial effect of deactivity a t 9 months (Table IV) in fuel without added copper suggests presence of trace of copper in original fuel (analysis indicated less than 0.1 p.p.m.)] The effect of metal deactivator on high temperature stability has also been briefly examined. For this purpose a California S. R. JP-4 containing 2.4 mg. per dl. of metal deactivator was tested in the laboratory heat exchanger apparatus. The results, given in Table V, show that the rate of deposition of insolubles on the 5-micron filter was reduced by a factor of about 2 and deposition in the coil eliminated. However, the plugging time was only slightly extended. Whether the decrease in fouling was due to the presence of a trace amount of copper in the base fuel, to a reduction in a catalytic effect of the metal surfaces of the apparatus, or to some more generalized effect is not known as yet. The failure to observe a greater benefit in plugging time is undoubtedly due to the more amorphous character of the deposits formed in the presence of the metal deactivator. Dispersants
Unlike the field of lubricating oils, the use of dispersants in fuels is a relatively
b a, i-’
.rl 3
Eri Lo
m
0 k
2 .3
m
a
d a
0
2
6 8 Time, hours
4
10
12
Figure 9. Effect of dispersants on high temperature stability of composite JP-4 fuel
recent development. The application of dispersants in minimizing the adverse effect of sludge in domestic burner fuels is gaining wide acceptance throughout the petroleum industry. Detergents have even been introduced into gasolines for the stated purpose of overcoming a carburetor fouling problem. Dispersants would be of benefit in jet fuels if the total residue content is not important, and insolubles can be tolerated, provided they do not clog the fuel system. I t is necessary that the insoluble residue be well enough dispersed to pass through filters and burner nozzles. However, a possible detriment would be the tendency of dispersant additives to suspend tank bottom settlings, sludge, and water in the fuel. Such action could more than offset their beneficial effect on filterability.
Separate addition to the fuel at the time of fueling the aircraft might then be required to obviate this difficulty. T o evaluate the effect of commercial fuel-oil dispersants, two such additives were tested at 10 mg. per dl. in a MidContinent JP-3 fuel under accelerated conditions of aging. The soluble and insoluble gum contents and the filterability characteristics of the fuels were then determined. Although soluble and insoluble gum levels were nearly equal in all cases, as shown in Table VI, both additives had an equal and relatively large effect in reducing the filter-plugging tendencies of the aged fuel. The pressure differential as determined in the laboratory constant flow filterability test was reduced from 12 to about 4 cm. of mercury.
Table V. Effect of Metal Deactivator on High Temperature Stabilityof a JP-4 Fuel California S.R. JP-4) Filt er-plugging T i m e , Avwox. Rate o f Hours to Reach A P o f 10 80 $0 Deposits, Deposition, M D . / H r . lb./sq. lb./sq. lb./sq. Mg. On On Fuel Blend inch inch inch Coil Filter coil filter As received 2:15 2:52 >3:13’ 1.06 5.0 3.4 16.1 Asreceived(dup1icatetest) 2:OO 2 : 4 0 0.53 4.8 3:OO 1.6 14.4 ‘Above+2.4mg./dl.MDAb 2 : 0 5 3:OO 0.0 2.6 3:25 0.0 8.8 a Time for 27 lb./sq. inch A P . N,N’-disalicylidene-1,2-propanediamine. (Base fuel.
Table VI.
Effect of Dispersants on Stability of Mid-Continent JP-3 Fuel (Aging conditions.
Additive and Concentration Blank Dispersant A, 10 mg./dl. Dispersant B, 10 mg./dl.
100° C., 100 lb./sq. inch 02,16 hours)
600° F. Steam Jet Gum, Mg./Dl. Adherent Flocculant Sol. insol. insol 21.5 3.7 9.1 22.8 3.0 8.9 19.4 3.4 7.9 I
VOL. 48, NO. 10
Constant Flow Filterability Test, A P , Cm. Hg 12 4 3
OCTOBER 1956
1 9 15
Table VII. Effect of Dispersants on Rate of Gum Formation of Composite Jet Fuel Blends 70" C., 1 atm. air, F / A = 0.5) Gum. M Mo.IT)I 600' F . Steam Jet Gum, g./Dl. 1 Week 4 Weeks 7 Weeks ______ Sol. Insol. 2'otal Sol. Insol. Total Sol. Insol. Total
(Aging conditions.
Additioe at 10 Fuel M g ./DL. Composite JP-3 type None blend, 10.5 mg. gum a b C
d
e f g h Composite JP-4 type blend, 1.0 mg. gum
i None
10.6 11.8 16.1 7.2 11.0 8.5 7.2
9.4
26.5 26.2
5.1 11.2 10.7
29.7 23.9 38.0 30.8 24.2 57.7 41.0
19.6 26.1 34.6 33.0 31.9 30.1 23.0 38.9 23.6 26.6 26.2
11.2 13.0 15.2 10.5 15.0 13.4 14.2 11.6 9.6 11.5 15.4
30.8 39.1 49.8 43.5 46.9 43.5 37.2 50.5 33.2 38.1 41.6 31.9 32.3 31.5 28.1 28.1
7.8
55.7 58.7
j
7.7
k
7.8 5.8 9.2
6.3 5.0 3.1 4.0 1.8
15.7 12.7 10.9 9.8 11.0
11.2 20.4 21.2 18.6 15.1
20.7 11.9 10.3 9.5 13.0
.. .. .. .. ..
.. .. .. ..
..
,. .. ..
.... ..
.. ..
5.4 5.9 24.5 32.0
7.2 4.5 23.3 36.0
2.8 3.0 3.6 2.6
1 m None
n 0
Composite JP-4 type blend, 2.0 mg. gum
15.9 14.4 39.6 51.5 18.7 15.4 30.8 23.0 19.1 46.5 30.3
None m" Pb
21.9 29.5
2.6 2.5
..
..
No data
26.6 25.0 24.8 25.5 22.7
19.7 11.3 17.2 13.3 12.3
46.3 36.3 42.0 38.8 35.0
2 5 . 5 12.8 38.3 2 7 . 5 14.2 4 1 . 7 44.3 22.1 66.4 10.0 4.8 7.7 12.5 7.5 7.9 7 . 0 14.9 26.9 24.0 4 . 7 27.8 38.6 33.2 5 . 2 38.4
.. ..
Initial gum = 19.4 mg./dl. = 35.2 mg./dl.
* Initial gum
A substantial number of experimental and a few commercially available dispersants were tested a t 10 mg. per dl. in composite jet fuel blends to determine their effect on gum formation at 70' C. The results are summarized in Table VII. In general, these additives have relatively little beneficial effect. There is often some apparent reduction in the amount of insoluble residue produced (this is probably due to their peptizing action). I n some cases an appreciable increase in the amount of soluble gum was observed. Although initial gum contents were not always obtained on the various individual unaged dispersant blends, it would appear that this increase was caused by the low volatility of the materials of high molecular weight added. The last two items of Table VI1 showed initial gum levels of about 20 and 35 mg. per dl. and indicate that the above effect does occur. I n these cases the amount of initial residue exceeded the sum of the initial fuel gum and the additive by a factor of about 2 or 3. However, this residue did not increase so much as did the gum in the blank during the aging period. This phenomenon appears to be a fairly consistent one and may be due to reduction of the vapor pressure of high boiling fuel components as a result of the presence of the nonvolatile dispersant in the residue. The slower rate of buildu p of residue may have been due to the breakdown of micelles during aging. Dispersants may offer an interim solution to the problem of high temperature fuel system deposit. As reported recently by the authors (6),dispersants are
1 916
capable of extending the filter-plugging time of a high temperature unstable fuel manyfold, some dispersants being more effective than others (Figure 9 ) . Such additives do not appear to reduce the rate of deposition of insoluble residue in the laboratory heat exchanger test but increase the ability of the 5-micron filter to tolerate deposits as a result of changes in the particle type and size. Examination under the light microscope indicates the particles to be of micron or submicron size. Analysis shows the presence of sulfur, nitrogen, and particularly oxygen (ca. 25 to 3070), indicating a n oxidation mechanism and a generic relationship to ordinary gum. Summary
and Conclusions
Although the specification inhibitors can prolong the induction periods of jet fuels, they have generally no favorable effect on the rate of gum formation under even accelerated and, particularly, normal storage conditions. The nitrogencontaining inhibitor is often actually prooxidant, while the trialkyl phenol inhibitors tend to be inert. Increasing the concentration of 26B4M and PDA inhibitors does not increase their effectiveness (the latter becomes more deleterious with increasing concentration). Preliminary data indicate the lack of response to the usual inhibitors may be due (in part, at least) to diaromatics originating in the gas oil portion of the fuel. Neither 26B4M nor PDA improves
INDUSTRIAL AND ENGINEERING CHEMISTRY
high temperature stability of jet fuels. An experimental inhibitor has been found which reduces the sate of gum formation in jet fuels at relatively low temperatures but increases high temperature stability only slightly. The trialkyl phenol inhibitor, 26B4iM, reduces the ambient temperature filterplugging tendency of jet fuels after aging, while nitrogen-containing inhibitors (PDA and AP) tend to increase it. Commercial metal deactivator is effective in reducing the catalytic action of soluble copper and copper-bearing steels but ineffective against metallic copper. The requirement for protection against soluble copper is apparently at least 1.5 times stoichiometric, and perhaps larger. Metal deactivator has somewhat reduced the tendency for jet fuels to cause high temperature deposits. Dispersants have no tendency to reduce the amount of residue formed on aging but are effective in reducing filterplugging tendency at both ambient and high temperatures. This effect is due to the ability of the dispersant to increase the system's tolerance for deposits and not to a reduction in the rate of deposit build-up. Acknowledgment
I t is a pleasure to acknowledge the valuable assistance of C. A. Cole, J. W. Beardmore, Thurston Skei, and R. E. Thorpe and to thank Wright Air Development Center for providing sponsorship. The authors are also grateful for helpful discussions with J. C. Mosteller and R. W. Altrnan of Wright Air Development Center. literature Cited
(1) Downing, F. B., Clarkson, R. G., Pedersen, C . J., Oil Gas J . 38, No. 11, 97 (1939). (2) Johnson, C. R., Fink, D. F., Nixon, A. C., IND.ENG. CHEM.46, 2166 (1954). ( 3 ) Knight, H. S . , Skei, T., Groennings, S.,Nixon, A. C., Anal. Chem. 28, 8 (1956). (4) Military Specification, MIL-F-5624B, Fuel, Aircraft Turbine and Jet Engine, Grades JP-3, JP-4, and JP-5, 7 December 1953; also Amendment-1, 18 March 1954. ( 5 ) Nixon, A. C., Cole, C. A., Division of Petroleum Chemistry, 125th Meeting, ACS, Kansas City, Mo., April 1954. ( 6 ) Nixon, A. C., Cole, C. A., M.inor, H. B., SAE Meeting, Atlantic City, June 1955. (7) Nixon, A. C., Cole, C . A., Walters, E. L., submitted to Anal. Chem. (8) Walters, E. L., Minor, H. B., Yabroff, D. L.,I N D . ENG. CHEhf. 41, 1723 (1949). ( 9 ) Yabroff, D. L., Walters, E. L., Zbid., 32, 83 (1940). (10) Yule, J. A. C., Wilson, C . P., Jr., Ibid.,23, 1254 (1931). RECEIVED for review April 23, 1956 ACCEPTED August 18, 1956
