I N D U S T R I A L A .Y D E N G I I\; E E R I N G C H E M I S T R Y
December, 1932
LITERATURE CITED (1) Gullick, N. G . , J . Insf. Petroleum Tech., 17,541 (1931). (2) Herschel. W.H.. Bur. Standards, Tech. Paper 112 (1919). (3) Kendall,'J., and Monroe, K. P.', J. Am. Chem. Soc., 39, 1787
1371
(1917); Kendall, J., and Wright, A. H., Ibid., 42,1776 (1920). J . Inst. Petroleum Tech., 16,799 (1930). (4) Steed, A. H., (5) Wilson, R.E., and W'ylde, E. P., IBD. ESG.CHEM.,15,801(1923).
RECEIVED June 20, 1932.
Gravity Index for Lubricating Oils W. B. MCCLUERAND RI. R. FENSKE,Pennsylvania S t a t e College, S t a t e College, Pa. Inspection data on fifty-four diflerent lubrifrom d i f f e r e n t b a s e O r type H E viscosity index as deeating oils or oil fractions have been used in crudes. Pennsylvania oils give v e l o p e d by Dean and a value of approximately 0.80, Davis (1' in 1929 and redeveloping a gravity index for the classification w h e r e a s naphthenic oils give vised by Davis, Lapeyrouse, and Dean (1) in 1932 has been used of oils as to base or type. The basisfor thegrat'ity about 0.90 for the v i s c o s i t y index was selected SO that index numbers similar gravity constant. It appears, widely by petroleum technolotherefore, that either the visto the viscosity index were obtained. The gravity gists for the purpose of classifycosity index or the viscosityindex has been found particularly well ing lubricating oils as to base or for type. In addition, the viscosity gravity constant is a measure the classification of light-oil fractions where of t h e d e g r e e of paraffinic or index is of considerable utility in predicting the chemical strucrelatively small ciscometry errors cause a n naphthenic c h a r a c t e r which any oil possesses. Hence there appreciable change in the viscosity index. ture of the lubricating constitushould be a definite r e l a t i o n ents present in any particular Similar data on fifty-eight lubricating oils oil fraction (2) and also in the obtained from the literature. When the between v i s c o s i t y index and viscosity-gravity constant, and correlation of data relative to viscosity and gravity indices of these oils were it should be possible to evalucold starting characteristics and determined, *satisfactorycorrelation was obtained ate the index number of an oil oil consumption ( 1 ) . Therefore, in all cases. either on the basis of viscosity it is evident that the viscosity characteristics alone or on the index of lubricating oils is of importance not only for the classification of oils as to type basis of viscosity and gravity relations. but for the correlation of data relating either to the chemical DETERMISATION OF VISCOSITY ASD GRAYITY nature of lubricating constituents or to certain performance characteristics. The viscosities and gravity of a large number of lubriHowever, much of the data in the literature on physical cating oils obtained from different type crudes have been and chemical properties as well as on performance behavior investigated. Viscosities a t 100" and 210" F. were deterof oils c a n n o t be mined in accurately calibrated Ostwald pipets, and the c o r r e l a t e d on the resultant kinematic viscosities were converted to Saybolt basis of v i s c o s i t y Universal seconds by the equations which were recently index since in many adopted by the A. S. T. M. Special Sub-committee on Viscases the 100" and cosity-Temperature Charts. These equations are: 210" F. viscosities 1.95 (for Saybolt seconds below 100) = 0.002261 of the o i l s w h i c h P w e r e investigated 1 35 (for Saybolt seconds above 100) are not stated. !! = 0.00220t P t Nevertheless, in a f I E 10 4 large m a j o r i t y of where P!!= kinematic viscosity in stokes; t = Saybolt seconds the reported d a t a , the inspection data These equations result in values which conform closely 20 \ of oils c o n t a i n the with accepted values in the International Critical Tables. g r a v i t y a n d t h e Gravity data were obtained either in pycnometers a t 20" C. 1 0 0 ° F . v i s c o s i t y . and converted to specific gravity a t 60" F. or by A. P. I. hydrometers calibrated in 0.10" and also converted to specific gravity a t 60" F. These gravity conversions were made from tables contained in the "New and Revised Tag Manual for Inspectors of Petroleum" (IO). From these data the viscosity index was calculated from viscosity index tables, and the viscosity-gravity constant was calculated from the equation: 10 G - 1.0752 loglo (V - 38) A = 10 - log10 - (V - 38) where A = viscosity-gravity constant G = specific gravity a t 60" F. V = viscosity a t 100' F., Saybolt seconds
T
4 1
~
~
I\, - 1
The lubricating oils which were studied in this investigation varied in properties from those of very paraffinic to
1372
I N D U S T R I A L A N D E N G I N E E R I N G C H E M IS T R Y
Vol. 24, No. 12
TABLEI. PHYSICAL CHARACTERISTICS OF LUBRICATIKQ OILSUSEDFOR DERIVINQ GRAVITYIKDEX OIL
VISCOSITY
SAMPLE 210' F. 100' F. SP. GR. AT 60° F. Saybolt seconds
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 b4
44.5 44.7 45.2 45.6 46.7 76.1 46.9 63.2 96 69.9 42.7 46.0 51.0 150 43.2 44.0 47.3 63.3 41.3 45.2 45.0 76.3 60.5 73.0 82 83 42.0 40.1 63.3 75.2 61.9 48.9 46.4 53.4 82 52.9 39.9 50.4 63.2 98 60.4 44.5 57.7 53.0 46.5 46.9 65.1 52.0 58.2 60.9 61.0 58.4 60.2 60.5
156.8 163.0 172.8 182.2 201.6 058 205.5 452 1029 675 146.0 196.7 265 2223 154.0 166.6 2 19 475 127.0 186.9 184.2 720 440 665 844 862 139.6 113.5 523 839 538 284 234.4 364 1025 359 119.6 322 637 1665 584 223 554 438 268 305 847 433 628 820 837 754 828 845
VISCOSITYINDEX
VISCOSITY-GRAVITY CONSTANT GRAVITY INDEX DIFFBREKCE
120 117 114 111 109 108 107 107 106 105 103 103 103 103 102 102 102 102 101 101 100 100 99 99 99 98 97 95 91 81 80 79 78 77 77 76 73 66 63 63 59 61 46 40 38 31 29 28 27 -1 -5 -10 -11 -12
those of very naphthenic characteristics, and the viscosity range varied from a minimum value of 113.5 to a maximum v a l u e of 2223 S a y b o l t seconds at 100' F. Commercial motor lubricants as well as closely fractionated oils were included in the oils t e s t e d . Also, data on oil f r a c t i o n s which were obtained in the solvent extraction of closely cut oils were included. The data which c o n s t i t u t e t h e b a s i s for t h e relations derived i n this a r t i c l e a r e g i v e n in Table I.
DISCUSSION OF RESULTS The v i s c o s i t y i n d e x of these oils has been plotted against the viscosity-gravity constant in Figure 1. This graph s h o w s that the viscosity-gravity c o n s t a n t i s d e f i n i t e l y r e l a t e d to the viscosity index, although this relation is not linear, This fact i n d i c a t e s that i n d e x numbers for practically any
118 116 114 112 109 107 107 104 107 105 102 102 97 104 102 102 103 99 100 102 103 105 99 101 102 103 101 99 94 72 70 77 69 71 85 72 66 66 68 72 63 52 46 42 54 26 30 32 38
?
-5 -14 -10 -5
-2 -1 0
+1 0 -1 0
-3
+A
$1 +1 -6
+A
0 +1 -3 -1 +1 +3 +5 0 +2 +3 +5 +4 +4 +3 -9 -10 -2 -9 -6
t-7: 0 +5 $9 +4
+A
+$2-516 +1 +4 +11 ? 0 -4 +1 +7
KINDOF OIL
Fractionated and Fractionated and Fractionated and Fractionated and Fractionated and Commercial oil Fractionated and Commercial oil Commercial oil Commercial oil Neutral stock Fractionated Commercial oil Bright stock Fractionated Fractionated Fractionated Commercial oil Fractionated Neutral stock Fractionated Commercial oil Commercial oil Commercial oil Commercial oil Commercial oil Fractionated Fractionated Commercial oil Commercial oil Commercial oil Fractionated Fractionated Commercial oil Commercial oil Fractionated Fractionated Fractionated Commercial oil Commercial oil Fractionated Commercial oil Commercial oil Fractionated Neutral stock Fractionated Commercial oil Commercial oil Commercial oil Commercial oil Fractionated Fractionated Fractionated Fractionated
extracted extracted extracted extracted extracted extracted
type of mineral oil lubricant can be obtained from the viscosity a t 100" F. and the specific gravity at 60" F. with a fairly high degree of accuracy. In addition, the n a t u r e of t h e c u r v e shows t h a t a higher degree of precision is o b t a i n e d for paraffin t y p e oils than for naphthene type oils. That is, a small difference in viscosity index is accompanied by a larger change in the v i s c o s i t y -gr a v i t y constant for paraffin type oils than for those of naphthenic characteristics. The viscosity index of lightoil fractions is influenced to a g r e a t e x t e n t by the accuracy with which the 2 1 O O F . viscosity is determined and to a less extent by the accuracy of the 100" F. viscosity. For instance, an error of 1.0 second in the 210' F. viscosity of a 40.0-second oil r e s u l t s in an e r r o r of a p p r o x i m a t e l y 32 points in the viscosity index of a typical paraffinic oil and an error of a b o u t 55 p o i n t s in the FIGURE2. GRAVITY INDEX CHART
December, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE11. CALCULATED SPECIFICGRAVITY AT 60" F. GRAVITYINDEX 0 10 20 30 40 60 60 70 80 90 100 110 120
VTSCOSITY-GRAVITY CONSTANT 0.8867 0.8835 0.8797 0.8760 0.8700 0.8640 0.8571 0.8491 0.8400 0.8298 0.8172 0.8026 0.7840
FOR
1373
OILS HAVINQDIFFERENT VISCOSITIESAND VARIOUSINDEX RATINQS
CALCULATED SPECIFIC GRAVITYOF OILS HAVINQ VISCOSITIESOF: 100 0.9205 0.9179 0.9147 0.9109 0.9068 0.9019 0.8962 0.8896 0.8822 0.8738 0.8635 0.8515 0.8362
150 0.9253 0.9228 0.9197 0.9160 0.9120 0.9073 0.9018 0.8954 0.8882 0.8801 0.8701 0.8585 0.8437
200 0.9284 0.9259 0.9229 0.9193 0.9154 0.9107 0.9053 0.8991 0.8920 0.8840 0.8742 0.8629 0.8484
viscosity index of a typical naphthenic oil. A similar error in the case of an oil with a viscosity of 45.0 Saybolt seconds a t 210" F. results in a viscosity index difference of 15 points for the paraffinic oil and 27 points for the naphthenic oil. For more viscous oils, the possible error in viscosity index due to viscometry errors is considerably less significant. While the accuracy of the calculated viscosity index of oils depends largely on the viscosity a t 210" F., the viscosity a t 100" F. must be approximately correct although its influence on the viscosity index is about one-tenth that of the 210" F. viscosity. Therefore, it appears probable that fairly large differences in the viscosity index of light-oil fractions may result, owing to relatively small errors in viscosity measurements In the case of index numbers obtained from the viscositygravity relation, it may be shown that an error as great as 10 seconds in the 100" E'. viscosity of a light oil (40.0 seconds a t 210" F.) results in an error of approximately one index number for a paraffinic oil and in an error of about 4 index numbers for a naphthenic oil. For slightly heavier oils, the possible error due to inaccurate viscometry methods is somewhat less. It is evident that the accuracy with which the gravity is determined will also influence the accuracy with which the index numbers can be obtained by this method. If an accuracy of * O . l O o A. P. I. as determined by the usual type of hydrometer is assumed, the index number is changed by approximately one-half for a paraffinic oil and about two for a naphthenic oil. Therefore if the relation between viscosity index and viscosity-gravity constant is granted, it appears that index numbers of light-oil fractions can be determined more accurately for a given degree of experimental accuracy by means of the viscosity-gravity relation than through the viscosities of oils a t 100" and 210" F. One possible disadvantage of this method for the determination of index numbers over that of the viscosity index is due to the greater amount of calculations required to establish the viscosity-gravity constant. Fortunately, however, an accurate graphical method for obtaining the index number from viscosity and gravity data, hereafter referred to as the gravity index, is available. A form of graph from which the gravity index of mineral lubricating oil can be obtained accurately is shown in Figure 2. This graph was constructed by determining the values of the viscosity-gravity constant which corresponded to the various index numbers as illustrated in Figure 1 and by calculating the gravity from the above viscosity-gravity constant equation which oils, having various viscosities, would have when the index number was constant. The viscosity and corresponding gravity for different type oils were calculated as outlined above, and these values are contained in Table 11. From these relations, Figure 2 was constructed by connecting all the points established for any one type of oil. The accuracy of such a graph is dependent to a large extent upon its size, but the usual 8.5 X 11 inch plot will result in values which are of approximately the same degree of accuracy as that which corresponds to an error of 0.10"A. P. I. in gravity.
300 0.9323 0.9289 0,9270 0.9234 0.9196 0.9151 0,9098 0.9038 0.8969 0.8891 0.8796 0.8685 0.8544
400 0.9349 0.9326 0.9297 0.9262 0.9225 0.9180 0.9129 0.9070 0.9002 0.8926 0.8832 0.8724 0.8585
600 0.9386 0.9362 0.9335 0.9301 0.9264 0.9221 0.9171 0.9113 0.9047 0.8973 0.8882 0.8776 0.8641
1000 0.9429 0.9407 0.9380 0.9347 0.9312 0.9270 0.9222 0.9165 0.9102 0.9030 0.8942 0.8839 0.8709
2000 0.9488 0.9466 0.9441 0.9409 0.9376 0.9336 0.9289 0.9236 0.9175 0.9106 0.9022 0.8924 0.8799
3000 0.9522 0.9501 0.9476 0.9445 0.9413 0.9373 0.9328 0.9276 0.9217 0.9150 0.9068 0.8973 0.8851
On the basis of the above relations, the gravity indices of the oils were evaluated and are contained in Table I in order that the index numbers of the oils as obtained by the two methods may be compared. I n general, the deviation between the two methods for determining the index number is small, and it was concluded that oils could be classified as to base or type either by the viscosity index or by the gravity index. For light-oil fractions, i t is probable that the gravity index is more readily obtained with a given degree of accuracy than the viscosity index.
e= LXPERIMLNTAL DATA. O= DATA FROM LITERATURE.
-20
0
74
40
60
VISCOUR INDO(
80
100
120
FIGURE3. GRAVITY INDEXus. VISCOSITY INDEX FOR 112 DIFFERENTMINERALOILS I n order to test further the validity of the gravity index as a method for establishing the paraffinic or naphthenic character of an oil, data on fifty-eight different oils have been obtained from the literature (2, 4, 7, 8). From these data the viscosity index and gravity index have been evaluated and are contained in Table 111. As shown in this table, the deviation between the two indices is not great in the majority of the various oils although there are R few instances in which the deviation is rather large. These deviations are shown in Figure 3 where the gravity index is plotted against the viscosity index. It is evident from this figure that there is no great tendency for the various oils to deviate markedly from the established relation. Since the viscosity index is quite sensitive to small viscometry errors (particularly in fairly light oils), i t is probable that these deviations may be due in part to this factor. On the other hand, certain oils may possess inherent deviations between the two indices although in all the various oils studied during this investigation no serious deviation n-as found
INDUSTRIAL AND ENGINEERING CHEMISTRY
1374
TABLE111. RELATION BETWEEX VISCOSITY INDEX ASD GRAVITYINDEX FOR LUBRICATINQ OILS FROM DATAIN LITERATURE LITERAVIB-
TURE
GRAVITY A T 60’ F. COBITY GR.4VITY DIFFERREFERSAMPLE 210’ F. 100’ F. ‘A. P. I . S ~ e c i f i cINDEX IADEX ENCE OIL
55 56 57 58 59
VIBCOBITY
Saybolt seconds 51.0 224 80.5 650 46.4 175 215 49.6 62.0 393
34.7 32.3 33.4 34.3 33.3
, . . . . , . . . .
.....
....,
.....
.....
125 124 120 120 118
119 121 112 118 119
-6 -3 -8 -2 +1
114 111 108 107 106
116 112 101 108 102
+2
104 104 104 103 102
99 106 105 93 105
-5
60 61 62 63 64
76.8 64.0 66 51.7 75
634 440 491 267 651
31.0 31.0 28.4 31.3 27.8
65 66 67 68 69
47.4 121 121 47 85.3
207 1549 1550 207 870
30.0 26.8 26.6
....
0.882
70 71 72 73 74
120 51.0 85.4 63 80
1572 269 855 478 794
27.4 29.8 27.6 29.5
....
..... ..... ..... .....
0.885
102 101 101 100 100
109 101 103 106 107
75 76 77 78 79
47.4 117 95 89.0 68.0
213 1566 1105 984 586
30.2 26.2 26.8 27.5 28.6
..... .....
99 99 99 98 97
100 102 102 104 104
80 81 82 83 84
102 52.8 97 73.5 79
1271 309 1238 726 846
....
0.887 0.896
....
0:894
110 96 101 95 97
+1;
....
97 96 92 91 91
85 86 87 88 89
74 74 75 61 75.5
741 747 773 492 810
25.2 24.8
..... .....
90 90 89 87 86
85 83 84 76 92
-5 -7 -5 -11 +6
84 82 82 81 80
95
+11 -2 -5 10 +9
79 78 78 75 75
91 90 89 89 88
75 72 70 62 62
84 90 73 59 63
+
58 58 50 39 35
44 60 45 54 52
- 14
13 5 5
8 -5 19
27.8
28.6
26.5
....
24.9 26.3
90 91 92 93 94
62 523 449 58 530 62.5 2074 121 1345 95
27.3
95 96 97 98 99
130 80 118 118 122
2400 972 2050 2100 2240
23.6
128 2450 120 2255 8 6 . 0 1235 558 60.0 140.6 3300
22.8 23.6 22.8 22.8 20.3
440 575 603 440 510
22.0 22.9 21.5
497 515 1356
....
100 101 102 103 104 105 106 107 108 109
54.6 60 60 53 55
110 111 112
53 53 75
,....
..... ... . ..,..
.....
..... .....
.....
..... ..... ,....
0.904
..... .....
.....
0,900
....
0.906
....
23.7 23.7 23.5
, . . .
22.7 , . . .
19.0
have physical properties similar to those of mineral oils having tfhe same viscosity characteristics. However, the higher olefins when polymerized appear to result in a material which has approximately a constant value for the viscositygravity constant regardless of the molecular size of the raw material; there is, in general, an increase in viscosity index as the molecular size of the stock material is increased. It is probable, therefore, that at some relatively high viscosity index these synthetic oils would again haye inter---
+1
-4
+2
+1 -10 +3
1?0
100
80
+:
60
+2 +6 +7
+1 +3 +3 +6 +7
5
:20 0
.....
....
24.9 23.9
i:
Vol. 24, No. 12
.....
.....
..... 0.904
..... ... . , , . . .
..... , . . . .
... . .....
..... ,....
..... ..... 0.917 ,....
0,934 0.938
.....
SO
77 91 89
+9 +4 +6
-20
-40
-60
-80
+ ++ 1212 +++111413 +9 18
?;
+1
0 “IilOSITYiRAYIlY COYBTlViT
FIGURE4. VISCOSITY INDICES OF SYNTHETIC OILS PRODUCED BY POLYMERIZATION OF PUREOLEFINSus. THEIR VISCOSITY-GRAVITY CONSTANTS
related physical properties similar to those of mineral oils. Hence it appears that polymerized olefins of very low and very high viscosity indices have gravities which correspond to those of mineral oils, although there is an intermediate range in which this relation is not true. ACKNOWLEDGMENT
+ 15
+ 17 -5
- 10
+ 14
From data in the literature it appears that hydrogenated oils possess viscosity and gravity characteristics which are quite similar to mineral lubricants. It has also been found $hat oil fractions obtained in the solvent extraction of lubricants have interrelated physical characteristics similar to oils refined according to conventional methods. However, it appears that oils which are produced by the polymerization of olefins (9) show a considerable difference in these interrelated physical properties. The above literature reference contains data on synthetic or polymerized oils from which both the viscosity index and viscosity-gravity constant can be calculated. I n Figure 4 the viscosity index of the oils produced by the polymerization of various pure olefins is plotted against their viscosity-gravity constant. The differences in these “characteristic constants” for polymerized materials on the one hand and mineral oils on the other are marked. Nevertheless, certain pertinent facts should be noted. Olefins which, when polymerized, would result in a large percentage of the carbon atoms in cyclic or ring structures, such as ethylene and cyclohexene,
The authors wish to express their indebtedness to members of the Petroleum Refining Laboratory a t the Pennsylvania State College who obtained the major portion of the inspection data presented.
LITERATURE CITED Davis, G. H. B., Lapeyrouse, M., and Dean, E. W., Oil Gas J., 30 (46),92 (1932). Davis, G . H. B., and McAllister, E. N., IND. ENG.CHmr., 22, 1326 (1930). Dean, E. W., and Davis, G . H. B., Chem. & Met. Eng., 36, 618 (1929). Haslam, R. T., and Bauer, W. C., S. A . E. Journal, 28, 308 (1931). Hill, J. B., and Coates, H. B., IND.ENG.CHEM.,20,641 (1928). Hill, J. B.,and Ferns, S. W., Zbid., 17, 1250 (1925). Lederer, E. R., and Zublin, E. W., Paper presented before the Petroleum Division, American Society of Mechanical Engineers, State College, Pa., May 22, 1931. O’Neill, J. G.,and McGeary, F. M., Natl. Petroleum N e w , 22 (24),65 (1930). Sullivan, F.W., Jr., Voorhees, V., Neeley, A. W., and Shankland, R. V., IND.ENG.CHEM.,23, 604 (1931). Wilhelm, R. M., “New and Revised Tag Manual for Inspectors of Petroleum,” 21st rev. ed., p. 40, C. J. Tagliabue Mfg. Co., Brooklyn, N. Y . RECEIVED July 12, 1932
