A. C. NIXON, H.
B.
MINOR, and G. M. CALHOUN
Shell Development Co., Emeryville, Calif.
Effect of Alkyl Phenols on Storage and Manifold Stability of Gasolines
THE
use of additives in motor gasolines has been increasing a t an accelerating pace since the first petrol was distilled from crude shell stills to satisfy the needs of turn-of-the-century gas buggies. These additives have been used to increase the octane number, to keep the gasoline stable, to prevent carburetor fouling, to reduce manifold deposition, to prevent surface ignition, to prevent carburetor icing, and to prevent the other additives from ruining the gasoline in one way or another. In order for an additive to be successful, it must not only do its primary job but also not introduce difficulties because of a failure to meet other requirements. Additives are necessary in modern gasolines because the gasolines are being called upon to do a better job in a more complex mechanism.
Figure 1.
1 874
As the complexity of the gasoline has increased over the years, so have the number and complexity, or perhaps we should say sophistication, of the tests that the gasoline must satisfy. As newer tests have been developed there has been a tendency to feel that the older tests are necessarily invalid. The present paper indicates how some additive-containing gasolines fare when exposed to older and more modern tests. It discusses some of the tests used to assess the effectiveness of inhibitors in gasoline, some of which are relatively new and others old in the art of motor fuel evaluation, then compares a number of different alkyl phenol inhibitors, first among themselves and then with the phenylenediamine (PDA) type, endeavoring to show how they are rated by the
various tests. The results show that relatively simple laboratory tests still have considerable usefulness in evaluating the potential cleanliness characteristics of motor fuels. However, the present paper is necessarily in the nature of a progress report. Experimental Work Gasolines. The gasolines used were mainly modern premium-type gasolines containing catalytically cracked components. When necessary, they were freed of added inhibitors by treatment with dilute hydrochloric acid or freed of natural inhibitors by treatment with an appropriate solutizer solution (75) and then immediately reinhibited with the test inhibitors. The fuels contained about 2 to 3 ml. of tetraethyllead fluid
laboratory apparatus for testing manifold deposit
INDUSTRIAL AND ENGINEERING CHEMISTRY
A D D I T I V E S IN FUELS per gallon. Physical properties are summarized in Table I. Inhibitors. Most of the alkyl phenols were synthesized in these laboratories by D. B. Luten, R. C. Morris, A. De Benedictis, and J. L. Van Winkle. 26B4M was obtained from the Shell Chemical Corp. (Ionol gasoline inhibitor), and N,N'-di-sec-butyl-t-phenyl e ned i a m i n e (PDA) was also a commercial product. 26B and 26P were obtained from the Ethyl Corp. (Numbers refer to position in phenol nucleus; B = tert-butyl, M = methyl, P = isopropyl, E = ethyl.) Test Procedures. INDUCTION PERIOD. The induction period was determined at 100 O C. and a pressure of 100 pounds of oxygen per square inch gage, following the procedure of ASTM method D 52549. GUM DETERMINATION. ASTM gum was determined according to the ASTM tentative method D 381-52T for existent gum in fuels by (air) jet evaporation. The technique for chromatogum has been developed on the same pattern as the FIA method of hydrocarbon analysis ( 3 ) ,in which the gumlike materials of high molecular weight are segregated on the column as an adsorbotrope with 1methylnaphthalene to form a colored band which can be defined by direct measurement (6). The significance of the value obtained with gasolines has not been rigorously assessed. With jet fuels and gas oils, the length of the band is proportional to the steam jet gum value. With gasolines the indications are that it is more nearly related to the induction system deposit tendency. STORAGE STABILITY.Storage stability has been determined by allowing the gasoline to age in amber glass containers (beer bottles) in the presence of excess oxygen at somewhat elevated temperatures and following the change in various properties with time. The conditions employed for this study are 70' or 60' C. in an atmosphere of oxygen and 43' C. (110' F.) in an atmosphere of air. I t is extremely important that all actinic light be excluded from the sample while it is being prepared and while the sample is aging. The relative severity at the three temperatures is about 22, 7 , and 1, according to Walters, Yabroff, Minor, and Sipple (73). PEROXIDE NUMBER. The development of peroxides during aging has been followed using a modification of the arsenious acid reaction method reported by Walker and Conway (70). Experience confirms the conclusions of the above authors that this method is considerably more sensitive and reliable than the Yule and Wilson method (77). MANIFOLDDEPOSITS.I n the Shell Development method 500 ml. of sample
is aspirated a t 14 to 1 air-fuel ratio through a horizontally disposed, glassjacketed, 1 X 50 cm. tube which is maintained a t selected temperatures between 60' and 160' C. by means of a suitable refluxing vapor (see Figure 1). The effluent gasoline passes through a small room-temperature trap, the bulk being caught in a carbon dioxide-acetone trap. Fuel rate is about 4 ml. per minute. Air is passed through the assemblage for 0.5 hour after the fuel supply has been exhausted. The apparatus is then dismantled and the amount of isopentanesoluble and -insoluble deposits in the tube and ambient trap is determined. The amount of ASTM gum in the effluent gasoline is also determined. The Socony method is the method introduced by Cabal (2), except that a Lauson rather than a Wisconsin engine was used. This extended the time required for performance of the test from about 13.5 to about 22 hours. Otherwise the procedures were identicalnamely, 4 gallons of fuel, carburetor air temperature 150' F., average manifold temperature 255' F., air-fuel ratio 13 to 1, engine speed 900 r.p.m. The sandwich-type manifold was dismantled and photographed, and washed with isopentane (2-methylbutane) and then with acetone to remove deposits, and the quantity of each of these categories of deposits was determined by evaporation of the solvent. OCTANE REQUIREMENT INCREASE TEST. For this purpose a cross head Lauson engine was employed with a cyclic operating procedure varying from idle to half power operation. Tests were continued for 150 hours or longer, if necessary, until octane requirement equilibrium was reached. Discussion of Test Procedures. The induction period method has been rightly criticized as not being indicative of storage stability. This is undoubtedly true in general and is supported by data presented by Powers ( 8 ) ,Walters, Minor and Yabroff, (72), and Bender, Lawson, and Kernan (7). However, as pointed out by Donahue (4)and Bender, Lawson, and Kernan (7), there is a measure of utility in the test when it is used with a gasoline from a particular source and with a particular inhibitor. Data indicate that the test is useful for comparing inhibitors of the same type but not for comparing the effectiveness of inhibitors of different types. The ASTM gum determination is a straightforward test capable of a high degree of reproducibility in the hands of an experienced, careful operator, provided it is used on gasoline of the type for which it was originally intended. With modern gasolines, many of which contain higher boiling additives, its significance is beginning to be lost. With gasolines con-
taining such additives it is beneficial to operate the test at 400' F. rather than a t the specified 320' F. More reproducible and significant values in terms of actual gum content are obtained in this manner. However, tests with nqnadditive-containing gasolines have shown that on the average the ASTM gum content is reduced about 30% by this change in temperature. The significance of the peroxide number as a measure of inhibitor effectiveness is often overlooked. I t must be remembered that the motorist never uses a completely fresh gasoline and the gasoline that finally enters his carburetor has been expos-d to a great many conditions which tend to accelerate its rate of deterioration. Walters, Minor, and Yabroff (77) presented data which showed that each increase of 2.5 in peroxide number represented a decrease of one unit in F-2 octane number (2.5 peroxide number is only 0.00033 equivalent per 100 grams). However, the effect is dependent on the nature of the gasolines involved and, with modern gasolines, is closer to 1 octane number per peroxide number. Considerable attention has been given to manifold deposit problems recently and methods of determining depositing tendency have been published (2, 7). The method used in this work differs in detail but not in principle from these. The advantages claimed for the test are that it is simple and economical in both time and gasoline, and makes it possible to examine the gasoline that has passed through the manifold. However, results so obtained might be rejected as lacking significance on the grounds that the test does not involve an engine. Accordingly, it was of interest to compare the simple hot tube test with the Socony manifold test. Six gasolines of varying cleanliness characteristics were run in both tests at 255' F. (ca. 1252' C.) manifold temperature and the amount of isopentane-insolubles was determined. From the results shown in Figure 2, it is apparent that good agreement between the tests exists. The effect of temperature on gasoline performance in the glass manifold test has also been investigated briefly. Examples of the type of behavior encountered are illustrated in Figure 3, which shows the effect on isopentane-insoluble residue in the glass manifold after operation a t several temperatures between 60' and 160' C. with both fresh and aged gasoline samples. Gasoline A shows a rather steady increase in the amount of residue with increasing temperature, while gasoline B rises sharply to a maximum around 110'. After aging (at 70' C. for 7 days) both gasolines show sharp increases to a much higher level in the region of 100' C. The most common VOL. 48, NO. 10
OCTOBER 1956
1875
40
I
c
30
0
Figure 2.
O E n g i n e Test a t 13/1 A i r / F u e l Ratio 0 E n g i n e Test a t 8. 7 / 1 A i r / F u e l Ratio
10 20 30 40 SOCORY E n g i n e Manifold T e s t I s o p e n t a n e I n s o l u b l e R e s i d u e , mg./dl.
Correlation between laboratory glass and Socony engine manifold test
pattern shows that the amount of residue increases with temperature, although gasolines have been encountered where the amount of residue decreases with increase of temperature. The importance of the increase in octane requirement of automotive engines with continued use is well appreciated by both the petroleum and automotive industries, as is being demonstrated by the tremendous amount of work that has been done on this problem. However, the importance of ensuring good gasoline stability and maintaining a low gum level may not always be appreciated.
Table 1.
Properties of Gasolines .- -. . . ..
B
C
D
56.6
58.6
59.4
56.4
56.1
57.2
118 156 246 368 415 0.173 1.2
98 137 251 357 408 0.16 0-2 5.0 1.75
100 136 228 351 414 0.15 1.4 6f 2.75
98 134 223 379 418 0.15 3.6 13.5 2.74
104 134 260 378 426 0.076 1.6 6.5 2.34
101 141 258 362 414 0.16
-4
Property
Gravity, OAPI ASTM distillation, 'F. I.B.P. 10%
50% 90%
E.P.
Sulfur, wt. %
ASTM gum, mg./dl. Induction period, hours TEL content, ml./gal.
'
6+
2.46
E
50
+-----*B, A g e d
40
I
I
'
J
.
; /
30
T
O
A , Aged
I
:p'
I
20
'
I
I
1
Gasoline B 10
0
60
80 100 120 140 G l a s s Manifold T e m p e r a t u r e ,
160 C.
Figure 3. Effect of temperature on laboratory manifold deposition tendencies of fresh and aged gasolines
1 876
INDUSTRIAL AND ENGINEERING CHEMISTRY
F
Variable 641.3
A D D I T I V E S I N FUELS 20 c
Crosshead Lauson Cyclic Operation SAE 30 Oil 01
0
I
I
2
4
Figure 4.
Figure 4 represents the results of a number of tests done in a Lauson engine under the conditions mentioned above with fuel F a t varying ASTM gum content. [This gasoline when first tested had a gum content of 5 mg. per dl., some of it was aged (110’ F.) to higher gum contents, a portion was steam-distilled to remove all gum, and some of this was aged to ca. 1and 2 mg. per dl. of gum. All samples except the one indicated were inhibited with PDA inhibitor.] The equilibrium octane requirement increase rises sharply with
I I I 6 8 10 ASTM Gum, mg/dl.
I 12
Effect of gasoline gum on octane requirement
ASTM gum. The steepness of the curve in the low gum range is particularly noteworthy. I n this range a difference of 1 mg. per dl. in gum level is equivalent to approximately 1 octane number in equilibrium octane requirement. In the fresh fuel the gasoline containing the alkyl phenol inhibitor (26B4M) had a lower octane requirement than the same fuel containing the phenylenediamine (PDA) inhibitor. Data are not yet in hand to indicate whether this difference is significant or if it persists at higher gum levels.
0 A S T M Gum, mg/dl.
Chromatogum, m d 5 ml.
Comparison of Alkyl Phenol Inhibitors Presented in Table I1 is a comparison of a large number of substituted alkyl phenols as inhibitors based on the authors’ work, that of Yabroff and Walters (76),and data from the literature [Rosenwald, Hoatson, and Chenicek (9): and Wasson and Smith (74)].Three sets of data, including the authors’, are based on induction periods (100’ C. and 100 pounds per square inch gage of oxygen in cracked gasolines. The ‘other
1.0
Pe 1:ox ide , meqJ100 g.
1
Gasoline C
Blank
-20
40
20 40 Days at llO°F., 1 atm.air
26B4M (+ Phos. Additive) 20
40
Figure 5. Formation of gum, chromatogum, and peroxide in gasoline C blends during storage VOL. 48, NO. 10
0
OCTOBER 1956
1877
Gasoline C
0-4
0
; 10
+ Phos.
l-4
I
n
Additive
2 20 ru
i E n a
20
0 Figure 6. storage
40
Formation of laboratory manifold deposits in gasoline C blends during
set of data (74) is based on the rate of production of acids in a turbine oil. All the data show that a single group substituted in the phenol nucleus has little absolute effect in conveying inhibiting power to phenol. The introduction of two alkyl groups has a greater effect. The nature and the position of the group substituted are very important; of the three positions investigated (2, 4, and 6) the greatest efficiency results if the 4 position is occupied by a methyl group. The maximum effect with two alkyl groups is produced if the 2 group is tert-butyl and the 4 group is methyl; the least effect results if the groups are interchanged. Leaving the para position unsu bsti tu ted-i.e., substi tu ting both ortho positions-reduces the effectiveness (compared to 26B4M) even when the ortho groups are bulky, such as two isopropyl groups, a tert-butyl and an isopropyl, or two tert-butyl. The substitution of three alkyl groups on the ring makes a further improvement possible in the inhibiting powers of the compound, but again the position and type of the groups substituted are important. Unfortunately, not all possible combinations of any three groups around the ring have been investigated. The greater ease of preparation has favored the use of 2,4,6 substituted compounds. The one example of comparison with a 2,3,6 compound suggests that leaving the para position open reduces effectiveness. The group substituted in the para position should have at least one hydrogen attached to the carbon which is attached to the ring-Le., tert-butyl reduces effectiveness, whereas isopropyl is as effective as methyl. This is probably the best generalization that can be made, for in no case does a compound having a p terd-butyl group show good inhibiting
1 878
40 0 20 D a y s at 110’ E, 1 atm. air
Table II.
Comparison of Alkyl Phenols as Antioxidants Relative Efectiweness (26B43f = 1 .OO) Wasson, Yabrof, Rosenwald, Smith (14) Authors W’alters (26) others (9)
I
Phenol Phenol 2-Methylphenol 2-tert-Butylphenol 4-Methylphenol 4-fert-Butylphenol
.. ..
..
..
..
..
2,4-Dimethylphenol 2-Methyl-4-fert-butylphenol 2-tert-Butyl-4-methylphenol 2,4-Di-fert-butylphenol 2,6-Dimethylphenol 2-Methyl-6-n-butylphenol 2-Methyl-6-isobutylphenol 2-Methyl-6-sec-butylphenol 2-Methyl-6-tert-butylphenol 2-Isopropyl-6-terf-butylphenol 2,6-Di-tert-butylphenol 2,6-Diisopropylphenol 2,6-Di-tert-amylphenol
.. 0.80 .. .. .. .. ..
2,4,6-Trimethylphenol 2,3-Dimethyl-6-tert -butylphenol 2,4-Dimethyl-6-isopropylphenol 2,4-Dimethyl-6-n-butylphenol
0.85 0.75 0.69
2,4-Dimethyl-6-isobutylphenol 2,4-Dimethyl-6-sec-butylphenol 2,4-Dimethyl-6-fert-butylphenol 2-Methyl-4-isopropyl-6-tert -butylphenol 2-Methyl-4-ethyl-6-isopropylphenol 2,6-Dimethyl-4-tert -butylphenol 2,6-Diisopropyl-4-tert-butylphenol 2,4-Di-tert-butyl-6-methylphenol 2,4-Di-tert -butyl-6-isopropylphenol 2,6-Di-tert-buty1-4-methylphenol 2,6-Di-tert-butyl-4-ethylphenol 2,6-Di-ferf -butyl-4-isopropylphenol 2,6-Di-tert-butyl-4-n-butylphenol 2,6-Di-tert-buty1-4-sec-butylphenol 2,4,6-Tri-tert-butylphenol 2-t ert-Butyl-4-methyl-6-ethylphenol 2-tert-Butyl-4-methyl-6-n-butylphenol 2-fert-Butyl-4-me thyl-6-octylphenol 2-sec-Butyl-4-methyl-6-isopropylphenol 2-sec-Butyl-4-methyl-6-n-butylphenol 2-sec-Butyl-4-methyl-6-tert-butylphenol 2,6-Di-sec-butyl-4-methylphenol
INDUSTRIAL AND ENGINEERING CHEMISTRY
0.49 0.48 0.40 0.37 0.22
.. ..
..
1.28 0.68 0.89
..
0.33 0.46 0.56 1.00 1.00 1 .oo
..
.. .. .. 0.66 .. .. .. ..
0.54
0.05
0.02
0
0.13
0.14 0.14
0
0.09 0.05
0.10
0
..
0.34 0.20
0.48 0.22 0.71 0.51 0.36 0.24 0.25 0.29
0
..
..
.. .. .. .. ..
1.25
1.22
0
.. .. .* ..
..
0
..
..
..
0.28
.. .. .. .. ..
.. ..
..
2.00
.. .. 0.39 ..
0.07
..
.. .. *. .. .. .. .. ..
1.69
0.24 0.54
..
..
..
.. ..
.. .. .. 0.24 ..
.. .. ..
1.53
..
0.20
.. ..
1.00
0.46
0.48
..
*. ..
0.83
1.00
.. .. .. .. .. ..
0
0
0.47
.. ..
0.24
0.78 0.93
0.75
*.
..
.. *. *.
.. ..
..
1.00 1.31
..
0.85
0.24 0.24 0.24
..
0.24 0.24 0.70 0.85
A D D I T I V E S IN FUELS 40
ASTM Gum Manifold iCs -In sol.
30
26B4M + PDA (0.6tO. 5)
0,
1
sm
!2
c 0
20
4
h
'26B4M,
E
10
2.4
.ne D Conc.inmg/dl.
0 0
7
14
7
14
Days at 6OoC., 1 atm.Oz Figure 7. Formation of gum and laboratory manifold deposits in gasoline D blends during storage
properties. In the 2,6-di-tert-butyl-4alkyl structure, methyl, ethyl, and isopropyl were found to be equivalent in gasoline (but not in turbine oil). However, this is not true for the 2M6B structure. Also in gasoline (but not turbine oil) and with a 4M group, the introduction of methyl into the ortho position is equivalent to tert-butyl, or even superior-e.g., 2,4-dimethyl- 6 - tert- butylphenol compared to 2,6-di tert butyl 4 methylphenol. Although some generalizations have been noted above, there are many idiosynchrasies. In general, it is conceivable that the massing of hindering groups in the ortho position and the blocking of the para position will improve inhibiting power. However, it is difficult to understand why substituting a methyl for an o-tert-butyl will improve performance and substituting an octyl group for the o-tert-butyl will decrease it. I t was of interest to compare the rate of gum formation during storage of gasoline for some of these alkyl phenols with the rating as given by the induction period. The natural inhibitors were removed
-
Table 111.
-
- -
from a blended gasoline containing thermal and catalytically cracked components by extraction with K-2 solutizer (15) solution, and the gasoline was inhibited with different alkyl phenols and then stored a t 70' and 43' C. (110' F.). Results are given in Table 111 for a concentration of 10 mg. per dl. of inhibitor. The rates of gum formation check the indication given by the length of the induction period fairly well; 26B4M and 26B4E gave identical results, whereas 246B allowed gum to form a t a rate approximately twice that of the other two. Comparison of Different Types of Inhibitors
Two different types of inhibitors were compared from the standpoint of their effect on induction period and their effect on other tests. For this purpose a phenylenediamine inhibitor (PDA) and 26B4M were compared in a premiumtype gasoline. The phenylenediaminetype inhibitor has a much greater effect on the induction period than the trialkyl phenol type, so that concentrations of
Comparison of Induction Periods with Gum Times of Gasolines Inhibited with Different Trialkyl Phenols
(Gasoline B, solutizer treated, plus 10 mg. per dl. of inhibitor) Inhibitor" None 26B4M 26B4E Induction Period, hours 1.42 10.92 9.17 Gum time, 70' C., days 5 mg. 1 11 11 10 mg. 2 >20 >20 Gum time, IIOo F., weeks 5 mg. 1 >28 >28 a
M = methyl, E = ethyl, B = tert-butyl.
946B 6.58 7 12 13
the two inhibitors were adjusted to give approximately equal induction periods. The blends were then stored a t 110' F. in glass bottles in the presence of excess air and the rate of formation of gum, chroma togum, peroxides, and isopentane-insoluble manifold deposits was determined. The results are given in Figures 5 and 6. I n this gasoline the phenylendiamine inhibitor was considerably inferior to the trialkyl phenol from the standpoint of all the parameters. These results are in accord with those obtained by investigators a t the Esso laboratories, who stated, "Data obtained from laboratory and field storage tests on gasolines containing 2,G-di-tert-butyl-4methylphenol have shown this inhibitor to provide better stability in storage than is indicated by the ASTM induction period" ( 5 ) . The results of the glass manifold tests are particularly interesting in revealing the varying reaction to temperature after different periods of aging. At 90' and 139' C. the PDA-inhibited sample departs markedly in an adverse way from the trialkyl phenol inhibited sample u p to about 20 days' aging and then slows down in its rate of formation of insolubles. The lower temperature results differ in showing a pronounced maximum in the curves. The different behavior a t the two temperatures is not understood but it may be due to differences in the temperature susceptibility of the gasolinesoluble deposit precursors existing in the gasolines a t the different aging periods or to differences in the fluidity or volatility of the deposits. Further work will be necessary to explain the mechanism of the reactions occurring in this region. The data also revealed that.at the lower temperature the presence of a phosphorus VOL. 48, NO. 10
OCTOBER 1956
1879
10
139’ C. Manifold iCs Insol.
A S T M Gum:
al
3
2m
2
c , 5 0 A
5E 0 0
14
7
21
0
7
14
21
Days at 60”C., 1 atm.OL Figure 8. Formation of gum and laboratory manifold deposits in gasoline E blends during storage
additive seem beneficial, whereas at 139 it has less effect. In other experiments (at 60’ C. under 1 atm. of oxygen) the trialkyl phenol and phenylenediamine inhibitors were compared a t approximately the same economic concentration. Figure 7 shows the effect on ASTM gum content and 139 ’C. laboratory manifold isopentane-insoluble deposit for the various samples (the natural inhibitors were not removed from this gasoline, D). Here the two inhibitors have about the same effect at equivalent concentration, the trialkyl phenol being perhaps somewhat more effective. An interesting effect, noted previously by Walters, Minor, and Yabroff ( 7 7 ) , is the apparent synergistic action when the two types of inhibitors are added in approximately equal amounts. This combination is almost equivalent to the trialkyl phenol a t twice the concentration. However, this effect varies from gasoline to gasoline in an, as yet, inexplicable manner. A similar program was done with another premium grade gasoline (E) which possessed better inherent stability and inhibitor response. The results of storage at 60’ C. under oxygen, shown in Figure 8 for gum and laboratory manifold deposits, showed that the trialkyl phenol at a slightly higher concentration minimized formation of gum and manifold deposits and was somewhat superior to the phenylenediamine inhibitor. Although the latter is superior at a lower concentration, it shows no improvement in blend stability with increasing concentration, whereas 26B4M does. The superiority of the trialkyl phenol over a sample of mixed phenols is clearly demonstrated in this comparison. Formation of chromatogum and per-
1 880
oxides reflected the same general pattern for both gasolines. Summary and Conclusions
Complexities have been introduced into the rating of present-day motor fuels by the increasing use of additives and the more elegant appetite of modern automobile engines. A simple glass manifold test gives substantially the same results as does the Socony heated manifold engine test. Manifold temperature has an important influence on deposit-forming tendencies. Gasoline deterioration products as characterized by ASTM gum have a profound effect on equilibrium octane requirement of a Lauson engine (up to 1 octane number per milligram per deciliter of gum). Comparison of alkyl phenols by the induction period method has a certain degree of validity in characterizing their usefulness as inhibitors. Phenylenediamine inhibitor, on the other hand, has a much more profound effect on the induction period than on other desirable properties of the gasoline. Thus, inhibitor 26B4M appears to be as good as, and possibly somewhat better than, the phenylenediamine antioxidant a t economically equivalent concentrations from the standpoint of storage stability and engine manifold cleanliness.
Literature Cited (1) Bender, R. O., Lawsan, N. D., Kernan, A. R., WPR Regional Technical Meeting, Beaumont, Tex., Feb.
7, 1952.
( 2 ) Cabal, A. V., ASTM Symposium on Gum and Storage Stability of
Motor Gasoline. Philadebhia. Pa.. Feb. 14, 1954; Petrolcum 6oces;ing 9, 1044 (1954). (3) Criddle, D. W., LeTournau, R. L., Anal. Chem. 23, 1620 (1951). (4) Donahue, R. W., ASTM Symposium on Gum and Storage Stability of Motor Gasoline, Philadelphia. Pa., Feb. 14. 1954. Jones, M.’C. K., Jones, A. R., Strickland, B. R., IND. ENG. CIIEM.44, 2721 (1952). Knight, H. S., others, Anal. Chem. 28, 8 (6956). Moore, C. D., Keller, J . L., Kent, W. L., Liggett, F. S., Petroleum Eng. 27, No. 12, C-19 (1955). Powers. W. R.. ASTM Svmuosium on Gum’and Storage Stab’ilit? of Motor Gasoline, Philadelphia, Pa., Feb. 14, 1954. Rosenwald, R. H., Hoatson, J. R., Chenicek, J. A., IND.E X G . CHEM. 42,162 (isso). Walker, D. C . , Conway, H. S., A n d . Chem. 25. 923 (1953). Walters, E.’L., others, IND. ENG.CHEM. 41, 1723 (1949). Waiiers,E. Walters, E. i., L., Yabroff, Yabi off, D. L., Minor, H. B., ?bid., 40, 423 (1948), Walters, E. L., Yabroff, D. L., L.. Minor, H. B., Sipple, H. E., Anal. Chem. 19, 988 (1-947). (1947). IND. Wasson, J. I., Smith, W. M., IND. ENC.CHEM.45, 197 (1953). Yabroff, D. L., Nixon, A. C., “Science of Petroleum.’’ Petroleum,’’ vol. V. V, Pt. 2. 2; Oxford Universit). University Press, London, 1953.
Acknowledgment
The authors are pleased to acknowledge the efforts of many colleagues in this work, particularly L. B. Scott for providing engine data and F. J. Illgen and L. P. Oxenford in the laboratory.
INDUSTRIAL AND ENGINEERING CHEMISTRY
(16) Yabroff, D. L., Walters, E. L., Shcll Development Co., unpxblished data. (17) Yule, J. A. C., Wilson, C . P., Jr., IND. E m . CHEM.23, 1254 (1931). RECEIVED for review April 23, 1956 ACCEPTEDAugust 18, 1956
