INDUSTRIAL AND ENGINEERING CHEMISTRY
526
1-01. 19, No. 4
A Study of Petroleum Lubricants' By Charles F. Mabery CASESCHOOL OF APPLIED SCIENCE,CLEVELAND, OHIO EDITOR'SNom-The publication of this paper marks the fiftieth anniversary of the appearance of the author's first contribution to the technical press. During the past fifty years he has probably published more on the pure chemistry of the constitution of petroleum than any contemporary.
Commercial lubricants are defined by initial distillation, proportion distilled below 300' C., 30 mm., specific gravity and viscosity of the distilled products, and stability on a friction testing machine. The heaviest hydrocarbons of refinery distillation are separated and analyzed. Two oils subjected to heavy use, one on a truck and one on an airplane, were examined as to specific gravity, viscosity, and behavior on a frictional bearing. The used oils were found to have undergone little deterioration. Oils with the same viscosity showed wide variations in frictional tests. A series of medium-grade lubricants, viscosity 320 seconds at 38' C., gave a maximum difference of 12 seconds at 98" C., of 27 seconds at 54.4' C., and corresponding differences in results on the frictional bearing.
presents the properties of a wide v a r i e t y of lubricants from crude oils of the principal North American fields, except t h o s e of C a l i f o r n i a and Mexico. Two manufactured oils may have the same viscosity readings but very different durable lubricating values. For example, Table I shows that the two Kansas oils, No. 11 and No. 12, begin to distil at about the same temperature, the latter leaving the smaller residue a t 300" C., 30 mm., that they have about the same specific gravity, and that they do not differ essentially in viscosity; but on the bearing of the testing machine, as shown in Table 11, the two oils and their constituents behave quite differently.
N A previous paper2 it appeared that the Appalachian crude oils, and in less degree the midcontinent oils, lose some of the best lubricant hydrocarbons in coking a t the end of the refining d i s t i l l a t i o n . Examination of a retxesentative variety of commercial lubricants also indicates that the general method of compounding, which consists in collecting the heaviest steam distillates possible without serious decomposition and mixing them with various lighter distillates to obtain the desired specific gravity and viscosity, demands especial attention to the proBreaking Point a Measure of Oil Stability portions of the mixtures, for these determine the true quality Table I1 gives a record of the behavior on a frictional of the finished products. The behavior of lubricants in laboratory distillation, bearing of the oils summarized in Table I. The data on with regard to specific gravity and viscosity of distillates the fractions collected below and above 300" C., 30 mm. and residues, the point of initial distillation, and the propor- pressure, are included, for they show the influence of these tion distilling below 300" C., affords valuable information constituents on the wearing quality of the original oil. In concerning their fundamental composition. In vacuum some instances the distillate below 300" C. supports a heavier distillation at 30 mm. pressure, 300" C. is the most suitable load than the original lubricant, and in others it breaks under point of division, for below this point most of the hydrocar- a lighter load. In other oils the residue above 300" C. is bons remain intact while above it there is danger of de- more stable than the lubricant itself and in others it breaks composition. I n the writer's opinion the best lubricants under a lighter load. Similar variations are observed in are those composed of hydrocarbons close to the natural the coefficients of friction; in general, the coefficient is lower order of their occurrence in the crude oil, rather than of dif- in the oil below 300" C., 30 mm., than in the lubricant, even ferent mixtures of heavy and light constituents. Table I under the breaking load. The residues which would not support the load were probably too viscous to coat the bearing 1 Received October 6, 1926. properly at the temperature of test. STHISJOURNAL, 18, 814 (1926).
I
Tahle I-Properties
of L u b r i c a n t s from Crude Oils
Specific gravity figures in this and the following tables are on the 15.56°/15.560 C . bask. b Except for Tables I V and VI11 viscosities were taken in an Ostwald viscometer in which the viscosity of water was 2.8 seconds at 38' C. very roughly approximate Saybolt viscosities at that temperature. a Temperature at which the first drop of distillate came over Q
The figures
INDUXTRIAL AND ENGINEERING CHEMISTRY
April, 1927
527
Table 11-Average C o m p o s i t i o n a n d Stability of Lubricants under Load (Flow of oil, 8 dra per minute: average speed. 660 r. p. m.) COEFFICIENT OF FRICTIOK
No.
OIL AND FRACTIONS
MOL. Wr. FOUND
Av. FORMULA
Load-Lbs. 3000
4000
per sq. in. 5000
6000
0.0096 0.0067
0.0095 0.0086
O
1
2
3
4
5
6
7
8
9
10 11
12
13
14
15
16 17
IS 19 20
West Virginia: Original Distillate Residue Pennsylvania: Original Distillate Residue Pennsylvania: Original Distillate Residue Pennsylvania: Original Distillate Residue Pennsylvania: Original Distillate Residue Ohio: Original Distillate Residue Ohio: Original Distillate Residue Ohio: Original Distillate Residue Ohio: Original Distillate Residue Oklahoma (original) Kansas: Original Distillate Residue Kansas: Original Distillate Residue Texas: Original Distillate Residue Texas: Original Distillate Residue Texas: Original Distillate Residue Coastal (original) Illinois Midcontinent (original) Ohio (original) Texas (original)
600
873
0.0014 0.0010 0.0011 0.0010 Would not support load 0.0120 0.0089 0.0132 0.0096 0.0128 0.0097 0.0088 0.0115
0.0110 0.0127 0.0083
c.
Lbs. per sa. in.
82 to 87 81 to 85
6000 5500
82 83 90 87
5000 4000 5000 5000
to to to to
91 84 105 93
860
Neither fraction would support a load
617
0.0120 0.0113 0.0017
0.0090 0.0090 0.0089
0.0100 0.0074
76 to 97 74 to 78 83 to 87
0.0015 0.0129 0.0129
0.0088
0.0076
83 to 87
0.0128
0.0127
83 to 100
0.0114 0.0120 0.0128
0.0089 0.0084 0.0130
0.0086 0.0104
85 to 90 79 to 87 99 to 101
0.0117 0.0120 0.0144
0.0114 0.0087 0.0143
0.0089 0.0084 0.0045
83 to 90 77 to 87 97 to 99
5000 5500 5000
0.0091 0.0120 0.0098
0.0086 0.0090 0.0094
0.0090 0.0089 0.0103
82 to 90 72 to 85 82 to 80
5500 5000 5500
0.0120 0.0120 0.0118 0.0085
0.0090 0.0090 0.0089 0.0087
0.0092 0.0074 0.0095
76 74 83 95
5000 4500 5000 6000
0.0114 0.0099 Will not support load 0.0109 0.0099
0.0087
78 to 87
5500
0.0099
91 to 95
5000
0.0120 0.0110 0.0128
0.0090 0.0071
82 to 91 83 t o 84 90 to 100
6000 4000 5000
81 to 83 72 to 79
3500 4500
4000 5000
585
834 1154
0.0089 0.0096 0.0097
to to to to
97 76 87 100
5000 4500 5000 5500 3500 5000
3500
5000 5500 4000
3500
N o break
359
0.0121 0.0010 0.0074 0.0067 Will not support load
0.0071
478
0.0120 0.0116 0.0119
0.0100 0.0096 0.0092
0.0096 0.0084
80 t o 8 3 75 to 84 89 t o 94
3500 4500
5000 5000 5000
0.0067 0.0129 0.0125 0.0045 0.0057 0.0059 0.0120 0.0121
0.0088 0.0144 0.0111 0.0045 0.0060 0.0061 0.0100 0.0100
0.0083
80 to 82 to 76 to 80 to 90 to 85 to 78 to 80 to
3500 4000 6000 5000 5500
5500 4000 4000 Nobreak 5500 6000 5500 4500
0.0084
0.0050 0.0060 0.0062 0.0089
0,0051 0.0063
90 86 86 92 103 99 87 83
3500
Pressure at which smoking starts. b Pressure at which bearing seizes.
The observations in Table I1 indicate how the quality of a lubricant may be dependent on the proportions of the component hydrocarbons. An attempt was made to ascertain the molecular weights and proportions of carbon and hydrogen of some of these lubricants. The measure of wearing endurance-that is, the temperature and bearing load under which an oil first shows smoke and when it breaksalso seems to be a convenient means of ascertaining comparative lubricant values with reference to durability in actual use a t ordinary temperatures and pressures. Residual Hydrocarbons in Lubricants Every refiner should realize that in coking his last residues he loses a very considerable part of his valuable lubricant hydrocarbons. This applies especially to the residues from Appalachian crudes, for the coking residues from the midcontinent oils consist largely of asphaltic. hydrocarbons, as do to a still larger extent the sulfur oils from Texas and
California. In studying this feature of refining lubricants, an attempt was made to separate the last hydrocarbons from the commercial products in order to compare them with the heaviest hydrocarbons from the crude oils as separated by solvent fractionation. Some of the lubricant residues of distillation above 300' C., 30 mm., were therefore thoroughly extracted with the alcohol-ether solvent to leave the last and least soluble of the refinery steam distillates. These should correspond to the heavy hydrocarbons separated from the crude oils, thereby showing what hydrocarbons had been lost in coking. The percentages of carbon and hydrogen were determined by analysis and the molecular weights as determined indicated a close correspondence to series C,Hz.-~ for the Pennsylvania oils, and to CnHzn--l~ and CnHZn-lzfor the heavier Ohio, midcontinent, and Texas oils. (Table 111) The limitation in series C,,H2n-12corresponding to the lubricant hydrocarbons separated from the crude oils by the
INDUSTRIAL A N D ENGINEERING CHEMISTRY
528
solvent indicates that the commercial lubricants consist of the undecomposed hydrocarbons of the crude oils from which they were refined. The high refractive indices in Table I11 indicate the best hydrocarbons. Table 111-Residual
Hydrocarbons ~
~
SOURCE
SP. GR.
Pennsylvania Pennsylvania Ohio Ohio Midcontinent Midcontinent Midcontinent Midcontinent Texas Texas
0.8892 0.9014 0.9092 0.9022 0.9078 0.9154 0.9231 0.9128 0.9341 0,9295
No.
~
~
$&yMgkTpFORMULA SERIES
~
_
(n")
Seconds ... _.
1 2 3 4 5 6 7 8 9 10
822 1807 170
...
300 2712 3996
...
622 934
633 851 493 908 510 803 856 477 502 482
a service of 550 miles. The other oils, some tested before use and some after a run of 850 miles on a heavy airplane between New York and Chicago, was obtained from the United States Airplane Mail Service Company, of Cleveland, Ohio. These oils were distilled to 300" C., 30 mm., and specific gravities and viscosities determined. (Table _their _ _ _ IV) It appears that the deterioration in either oil has been very slight and that there has been but little contamination of the lubricant by the products of combustion or by the fuel from the engine. T a b l e IV-Effect
* Science, 4
September, 1926. Mabery, J . .-lm Chem. Soc.. 48, 2663 (1926)
DISTILLATION
FRACTIONS
Start
O
Truck
Airplane
SAYBOLT VISCOSITY
~
AND
New: Oil Distillate Residue Used: Oil Distillate Residue New: Oil Distillate Residue Used: Oil Distillate Residue
SP. GR.
Off below
8' C. 54.4" C.
300" C.
C. Per cent
Seconds
240
55
0.9038 0.8957 0.9027
225
50
0.8987 0.8909 0.9144
113
14
0.9004 0.8917 0.8987
116
15
0.9026 0.8911
10.5
275
75
320 200 470 128 550 570 880
510
0 90.52
962
T e s t s o n New a n d Used Oils
Table V-Bearing
~
COEFFICIENT OF FRICTION SERVICE OIL
Behavior of Lubricants under Strenuous Service
T o test the efficiency of petroleum lubricants under severe conditions of use, samples were procured of two unused oils and of the same oils after use. One of these oils, selected as a standard of all bearing tests in this work and designated as "Cadillad' oil, was used on one of the heaviest trucks by the Cadillac Motor Car Company, and the used oil was collected after
of Service on Properties of Lubricants
OIL
SERVICE
In discussing polymerization and depolymerization as an explanation of the composition of petroleum lubricants, Thorpe suggested that such changes may result from a condition of unsaturation in the crude oil. A comparison of the residual hydrocarbons in Table 111, however, with the composition of the corresponding crude oils, as shown by a comprehensive study during the last few years in this laboratory, precludes the possibility of such decomposition during refining. Thorpe's allusion to the relative ease with which the lubricant loses its oiliness in the engine is not supported by the data in Tables IV and V, this paper, which indicate that lubricants properly refined from the best crude oils lose very little of their oiliness under strenuous use until they bre&. Furthermore, the action of bromine on commercial lubricants disproves unsaturation, provided the lubricants are properly refined.4
19, KO. 4
1701.
Truck Airplane
h-ew Used New Used
Load-Lbs.
1
BREAK
per s q . in. 6000
4000
5000
0.0045 0.0057 0.0058 0.0050
0.0050 0.0045 0.0044 0.0045
SMOKE6ooo AT
B?&&
LSS.
77 to 78 to 84 to 86 to
0.0066 0.0060 0.0062 0.0064
... ...
90 90 92 91
.. .. ..
.,. .,. ... ...
Bearing Tests
The results of bearing tests (Table V)-the low coefficients of friction, low temperature, absence of smoking, and the fact that none of them broke under 6000 pounds pressure-
Table VI-Bearing T e s t s of C o m m e r c i a l Oils (Saybolt viscosity 300 seconds at 38' C.)
CRUDEOIL BASE
SPBCIFIC GRAVITY
I
COEFFICIENT OF FRICTION Load-Lbs.
TEMP.
per s q . in.
SMOKE
BEARING
3000
4000
5000
6000
0,0057
0.0059 0.0061 0.0052
0,0058 0.0058 0.0054
0.0062 0.0057 0.0056
1
Oklahoma mixed Pennsylvania paraffin Coastal Texas asphaltic
0.8966 0.8741 0.9409
KO.
c ~ u ~ E - 0 1 ~Sp*clFIc
BASS
GRAvlTy
COSITY
Paraffin
0.8892
162
2
Mixed Paraffin Asphalt Paraffin Asphalt Paraffin Mixed Paraffin Mixed
0.9074 0.8919 0.9296 0.8681 0.9156 0.9007 0.8989 0.8769 0.8993
161 67 70 94 93 144 143 51 53
3
4 5 6 7 8 9 10
OFF BELOW
300° C.
1
Per cent 45
54 45 11
35 21 42 30
1
84 to 100 86 101
...
72 to 92
S a g h i 6000
COEFFICIENT OF FRICTION
DISTILLATION
OSTWALD
1
AT
Lbs. per sq. in.
0.0064 0.0060
VIS-
BREAK
6000 LSS.
Load-Lbs.
SMOKEBREAK
4000
5000
6000
0,0045
0,0044
0.0044
0.0055
c. 0.0049 0.0055 0.0050 0.0050 0.0038 0.0044 0.0055 0.0053
76 to 90 94 75 to 80
0.0040
81 to 83
0.0048 0.0036 0.0044 0.0056 0.0056
...
Bz:r;G
per sq. in.
3000
0.0050 0.0060 0,0050 0.0060 0.0044 0.0057 0,0054 0.0050
... ...
0.0070 0.0064
82 to 84 79 to 83 63 to 87 86 to 93 84 to 87 88 to 99
Lbs. p e r sa. in. Above 5000 2500 2500 ... 5000 4500 .. . 5500 . 4500 .. 5500 4500 5000 6000° 5500 5500
... ... .. .
INDUSTRIAL A N D ENGINEERING CHEMISTRY
April, 1927
indicate a superior lubricant quality of the original oils and no deterioration of this quality under the heavy service to which they have been subjected. The lubricant quality of an oil may be defined as its capability of supporting a proper load at low friction and without smoke or break. T a b l e VIII-Relation
No.
1 2 3 4 5 6
7 8
9 10 11
12 -
SI'. GR.
OIL
Pennsylvaniaa Pennsylvania" Pennsylvania" West Virginia Ohio Ohio Illinois Oklahoma Oklahoma Coastal Texas Texas Texas
0,9019 0.8999 0.8851 0,8751 0.9097 0.9083 0.9097 0.9079 0.9067 0.9349 0.9195 0.9401
b e t w e e n Viscosity a n d T e m p e r a t u r e
SAYBOLT VISCOSITY
MOL.
FORMULA SERIES FOUND WT.
CnHtn-4
424 409 424 390 390 395 391 369 334 348 260 332
CcHzn-r
CnHzn-4 CnHtn-4 CnHzn-4 CnHtn-r CnHzn-4 CnHzn-8 CnHan-s CnHzn-io CnHzn-lo CnHzn-io
-
38c
54.40
c. 320 320 320 320 320 320 320 320 320 320 320 320
c.
980
c.
Seconds 167 80 160 56 162 57 56 161 150 52 143 49 147 50 53 151 148 50 140 48 143 49 141 48
Standard.
Having a t hand three medium-grade commercial oils representing three great American fields, a comparison was made of their behavior in bearing tests. The results in Table VI indicate that by suitable care in refining lubricants of equivalent wearing quality can be prepared from the different classes of crude oils-those with a paraffin base, with a mixed base, and with an asphaltic base.
529
S t a b i l i t y of Oils in Table VI11
Oil-testing machines have given so much trouble in attempts to write specifications for lubricants on the basis of their readings, that their use in more careful observations for scienti6c purposes has shared in the general condemnation. That this is unjust has been held by many experimenters, who have shown that it is possible to obtain con.cordant observations under rigid control of conditions. A Carpenter friction testing machine was used in this work. It has been used in many previous researches and found very satisfactory. The bearing surface covers only half the journal, which is easily kept very smooth and clean with fine emery paper. A reliable surface on the bearing is the most important consideration in all tests on a frictional machine, and it may be maintained in one of two ways. It may be worn down to an even surface by long operation with the usual tests or, without regard to the extent of bearing surface, it may be brought to give constant results by scraping with a sharp tool and running on a standard lubricant, and held to constant observations by frequent comparison with the standard. The second method involves less labor and, like all determinations that are referred to an exact standard, it is more accurate. After long disuse it takes at least a week to reduce the bearing surface to standard conditions, and then when it is put aside for a month or more it reverts to the former condition, only to be renewed by repeating the continuous running.
T a b l e IX-Stability of L u b r i c a n t s in T a b l e VI11 (Saybolt viscosity 320 seconds at 38O C.) NO.
OIL
1 2 3 4 5
Pennsylvania Pennsylvania Pennsylvania West Virginia Ohio Ohio Illinois Oklahoma Oklahoma Texas Texas
6
A9 10 11
I I
COEFFICIENT OF FRICTION
3000
4000
xnn
finnn
0.0045 0.0048 0.0054 0.0043 0.0047 0.0055 0.0050 0.0053 0.0063 0.0053 0.0042
0.0045 0.0064 0.0053 0.0045 0.0046 0.0057 0.0054 0.0055 0.0062
0.0050 0.0059 0.0058 0.0050 0.0057 0.0062 0.0062 0.0068 0.0070 0.0070 0.0066
0.0065 0.0060 0.0063 0.0062 0.0065 0.0070 0.0064 0.0071 0.0072 0.0075 0.0070
0.0060 0.0061
Perhaps the fairest tests of lubricant value are made with oils with as nearly the same thickness of film as can be indicated by viscosity a t a lower temperature. The five sets of oils in Table VI1 were selected with reference to the same viscosity at 38" C. for each set. Except for the last set the oils in each had widely different specific gravities. They were also different in the amounts distilling below 300' C., 30 mm. The results of bearing tests show no relation between these values and viscosity. In following out still further a comparison of the properties of lubricants with the same viscosity, 320 seconds, a t 38" C., a collection of oils was carried through a series of observations at 54.4' C. and 98" C., with the results presented in Table VIII. I n defining the comparative values of lubricants for the various conditions of use, the refiner is fortunate in having a convenient means of control in standards based on the close relations of viscosity and temperature. But since this relationship is quite variable in oils from different sources, it must be known and kept in view in practical application. Not only is it necessary to know the viscosity of an oil at the two temperatures, 38" C. and 98" C., but since oils show wider differences a t temperatures between these points it is well to include another observation, as shown in Table VIII, where it appears that a t 54.4" C. the extreme variation amounts to over 27 seconds and at 98' C. to 12 seconds.
1 I
TEMP.
BEARING
= c. 77 t o 90 85 to 104 80 to 100 87 to 100 91 to 103 85 to 103 81 to 100 84 t o 100 79 to 99 98 t o 106 96 to 106
SMOKE
BREAK
Lbs. per sq. in.
... 5500
5500 5500 4500 5000 4500 5000 5000 4500 3500
...
5500 5500 6000 6000 5000 5000 6000 5000 5000 5000
Another essential detail in promiscuous friction tests is an even room temperature. Therefore, in seeking comparative values of different oils either all readings should be made at the same temperature or a correction should be made for different temperatures, if widely apart. In this work the prevailing room temperature was 22-24" C. The author would explain the term "stability of lubricants" as follows: When an oil begins to smoke on the bearing, it is due to an initial rupture of the oil molecules by friction and pressure and that this increases until the reading on the friction bar shows no support of load and the oil "breaks." It is really a measure of molecular stability, and, as shown by the results in the tables, it varies materially in oils from different sources. The accuracy of the Saybolt Universal viscometer readings used in this work is shown by their agreement with those of a standard oil recently received from the U. S. Bureau of Standards. Acknowledgment
The author desires to express his indebtedness to the various oil companies and refiners who have generously supplied him with specimens of lubricants, and to his assistants, N. Mamelstein and A. s. Gressel, for efficient aid. Following the precedent set by France, the Italian Government has decreed that all gasoline used in t h a t country must be diluted with alcohol.
