Relationship between Mole Fractions and Absolute Viscosities of Blended Lubricating Oils E. R.EPPERSON AND H. L. DUNLAP, Missouri School of Mines and Metallurgy, Rolla, Mo.
T
HE viscosity of binary liquid mixtures has been a subject of much investigation, but most of the work has been done with mixtures of s u b s t a n c e s other than lubricating oils. Although viscosity is an important property of a good l u b r i c a n t , no O n e has succeeded in deducing a satisfactory formula by which the
The mean molecular weights of ten fractions of lubricating oils have been determined by the cryoscopic method and checked by means of three solvents-namel3', benzene, nitrobenzene, and ethylene bromide. Viscosity determinations on thirty-four binary blends prepared from these fractions have been found to be in close accordance with the viscosity values calculuted f r o m Kendall and Monroe's
weights of l u b r i c a t i n g Oils. Molecular weights a t increasing concentrations were determined and molar-weight d e p r e s s i o n curves were plotted, Extrapolation of these curves to zero concentration gave w h a t was called the "true" molecular weight. DETERMINATION OF MEAN MOLECULAR WEIGHTSAND VISCOSITIES
viscosity of a blended lubricant formula for ideal mixtures. may be calculated from a knowlA method for the prediction of the viscosity for edge of the physical properties blended oils from the mean molecular weights is MATERIALS U S E D . Four closely cut fractions of Midof its components. indicated. continent lubricating oil were This investigation has been f u r n i s h e d by the S h e l l Pean attempt to find a relationship between the absolute viscosity of a blended lubricating troleum Corporation and two by the Standard Oil Company oil and the viscosities and relative numbers of molecules of of Wood River, Ill. Four samples of Pennsylvania oil were obtained by fractionating under reduced pressure a comits components. A great deal of work has been done on the viscosities of mercial sample of Quaker State oil. The benzene was Baker's Analyzed and thiophene-free. liquid mixtures in an endeavor to discover a mathematical expression connecting the viscosity of a mixture with the This was recrystallized, dried, and stored over calcium chlorelative amounts and viscosities of its components. The ride. The nitrobenzene was from the same source, and was fundamental difficulty in drawing any definite conclusions recrystallized and stored over calcium chloride. The ethylene from the available data is the fact that the law of ideal bromide was of a German make. It was washed with sodium carbonate solution, dried, recrystallized, and stored over mixtures is not known. Kendall and others (3) tested all the proposed formulas, calcium chloride. APPARATUS.The equipment used in the cryoscopic dewhich had been suggested, on eighty-four presumably chemically indifferent and nonassociated liquid mixtures. When terminations of the mean molecular weight was the regular the viscosities were plotted against the percentage compo- Beckmann freezing point apparatus with the addition of a sition, the curves were, in general, found to be sagged with mechanical stirrer and equipment for keeping the solvent no suggestion of agreement with any of the proposed for- under a slight pressure with dried compressed air. The mulas. Kendall and Monroe were then left with a clear viscosities were determined by means of a Saybolt Standard Universal Viscosimeter, electrically heated. Standard A. field and proposed the equation: P. I. hydrometers were used for the gravity determinations. n'/3 = Xn11/3 (l-X)n*l/a PROCEDURE. About 25 cc. of solvent were used in the where n = absolute viscosity of mixture tests. The constants for each of the solvents were first den1 and n~= absolute viscosities of components of mixture termined by the use of naphthalene and cyclohexane as The maximum divergence from the experimental data standards. In the experimental determination of the confor the system benzene-benzyl benzoate was only 3.8 per stants for the solvents and the determination of the mocent. Some other systems investigated gave less satisfac- lecular weights of the oils, enough solute was used in each case tory results. However, the above cube root formula has to obtain a lowering of the freezing point of 0.2' to 0.3" F. been found to represent the viscosities of approximately (0.06' to 0.11' C.). At least three concordant readings of the freezing point were obtained for each solvent, and a mean ideal mixtures better than any other. was taken as the true freezing point. The molecular weight of the substance was calculated by means of the formula: MOLECULAR WEIGHTSOF LUBRICATING OILS Comparatively little work has been done on the determiW M - K nation of the mean molecular weights of lubricating oils. dW Wilson and Wylde (5) determined the mean molecular weights where K = a constant depending on solvent employed W = weight of solvent of a number of hydrocarbon lubricants by means of the Beckw = weight of solute mann cryoscopic method, using benzene as a solvent. Steed d = freezing point depression (4) used nitrobenzene as solvent in his work on the determination of the mean molecular weights of light petroleum COMPOUNDING OF BLENDS. Eight series of blends were fractions. Gullick ( 1 ) used both benzene and nitrobenzene prepared in which the oils were compounded on the basis as solvents for the determination of the mean molecular of their mean molecular weights. Each series consisted of
+
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INDUSTRIAL AXD ENGINEERING CHEMISTRY
13iO
blends containing approximately 20, 40, 60, a n d 80 m o l e per cent of each of t h e components. The m i x t u r e s were t h e n h e a t e d to approximately 250' F. (121.1' C.) and agit a t e d 15 m i n u t e s with a n electric stirrer. VISCOSITYDETERNINATIONS. The visc o s i t i e s of a l l the fractions and blends of oil were determined a t 210" F. (98.9' C.) by the regular A. S. T. M. method, M o / q Percenf using t h e Saybolt FIGURE 1. CUBE ROOT OF ABSO- S t a n d a r d Universal LUTE VISCOSITYvs. MOLE PER Viscosimeter. The CENT FOR BLENDS A-C, A-D, B-D, AND E-F Saybolt viscosities were c o n v e r t e d to absolute viscosities by means of the Herschel (2) equation: n
=
0.0022t
1.80 -t
where n
=
absolute viscosity, poises
D
=
density, grams per cc.
t = Saybolt viscosity, seconds
RESULTS.The results of the molecular weight determinations and tests on the original oils are shown in Table I. Each of the values for molecular weights in each solvent checked within one per cent in three or more determinations. The values in the table represent averages. TABLEI. MEAN MOLECULAR WEIGHTSAND VISCOSITIES OF
ORIGINALSAMPLES
8.4s-
SYMBOL
LETOIL
Shell Shell Shell Shell
1
2
3 4
TBR
A
E C D
Standard 1 E Standard2 F Pennsylvania 1 G Pennsylvania 2 H Pennsylvania3 I Pennsylvania 4 J a A t 210' F. (98.9'
SP.
OR.
h f E A N htOL. 4BS. WEIGHT0 I B : VISC6Hs C s H s N O a CzHdBn COSITY
0.9203 0.9288 0.9056 0.9161
360 468 578 678
362 465 583
357 468 582 673
0.9015 0.9209 0.8689 0.8727 0.8775 0.8969 '2.).
427 701 425 460 511 824
427
428 711 428 466 507 830
... ...
431 468 510
.. ,
BOLT
VISnl'3 C O S I T Y ~
Poise Seconds 0.0571 0.385 46 0.1239 0.498 72 0.1655 0.549 92 0.3391 0.697 173 0.0745 0.420 53 0.3659 0.715 185 0.0539 0.378 46 0.0646 0.401 50 0.0799 0.431 56 0.3259 0.688 170
Table I1 shows the composition, density, and viscosity of each of the blended oils. Figures 1 and 2 represent the composition expressed in mole per cent plotted as abscissas and the cube roots of the absolute viscosities as ordinates. This relationship was suggested by the Kendall and Monroe formula for ideal mixtures. DISCUSSION OF
RESULTS
The ebullioscopic method was found to be unsatisfactory for the determination of the mean molecular weights of lubricating oils. The molecular weights, determined by this method, were not consistent. Acetone, benzene, and ethyl acetate were tried as solvents. The cryoscopic method gave results which can be checked
Vol. 24, No. 12
to less than one per cent in benzene, nitrobenzene, or ethylene bromide. From Table I1 the greatest variation in the mean molecular weights with the three solvents is less than 1.5 per cent. Ethylene bromide was found to be t'he best solvent for the oils; a t the same time, it is less susceptible to the absorption of atmospheric moisture during the determination. The close accordF ance between the .m D molecular we i g h t s J as d e t e r m i n e d in .65 the three different s o l v e n t s tends t o p r e c l u d e any evi.60 dence of association between the mole.55 cules of the solvent a n d t h o s e of the solute, or any lack of c o m p l e t e solubility a t the tem.a p e r a t u r e of t h e c f r e e z i n g point of .40 the s o l v e n t . The A heaTy oils D , F , and G J were n o t com.,5\ I I I I I 0 2C 40 60 SO IO0 pletely soluble in niM o / e Pe/-cenf t r o b e n z e n e . The FIGURE 2 . CUBEROOT OF ABSOLUTE mean molecular VISCOSITYus. MOLE PER CENTFOR weights of some of A-F, E-D,GD, AND GJ the blends were determined, and these checked the mean molecular weights calculated from the components to less than 1.5 per cent. TABLE11. BLEXDSOF STOCKS COMPOSITION BY WEIQHT Crams 43.4 A 152.9 D 100.8 A 118.9 D 153.0 A 83.7 D 189.5 A 30.1 D
+ ++ + 22.1 A + 200.3 D 71.1 A + 161.8 C 34.3 A + 199.6 C 107.1 A + 125.3 C 139.0 A + 84.3 C 34.0 B + 187.0 D 66.0 B + 158.0 D 109.3 B + 98.2 D 142.9B + 9 2 . 8 0 32.5 E + 180.4 F 58.0 E + 149.5 F
98.4 E f 112.6 F 82.8F 133.5E 23.1 G 165.5 J 30.2 G 76.1 J 65.4 G 43.5J 46.0 G 72.2 J 23.8 A 191.5 F 50.0 A 167.4 F 76.5 A 145.3 F 123.3 A 106.8 F 167.8 A 58.0 F 32.7 E 192.4 D 64.3 E 165.3 D 101.5 E 120.6 D 135.1 E 81.9 D 17.0 G 106.5 D 39.OG 82.1 D 65.2 D 57.2 G 84.90 39.10
+ +
+ + ++ + + + + + + + + + + + +
ABS. VIECOSITY COMPOSITION n Mole % Poise 34.7 A 61.4 A 77.3 A 92.1 A 16.8 A 41.5 A 21.6 A 57.9 A 72.7 A 20.8 B 37.6 B 61.8B 69.0 B 22.7 E 38.9 E 57.3 E 72.63 21.2 G 40.8G 74.56 55.3 G 19.5 -4 36.8 A 50.7 A 69.4 A 85.OA 21.0 E 38.0 E 57.2 E 72.3 E 20.2 G 43.OG 58.3 G 77.66
0.2484 0.1973 0.1845 0,2792 0.2235 0.1711 0.1303 0.2573 0.1942 0,0990 0.1512 0.3094 0.2376 0.1860 0,1250 0.0888
0.2655 0.2097 0.1544 0.1210 0.2349 0.1603 0.1260 0.0878
fll 3
0.598 0.512 0.466 0.413 0,647 0.489 0.521 0.465 0.440 0.657 0.629 0.582 0.569 0.654 0.607 0.555 0.507 0.636 0.579 0.463 0,533 0.676 0.619 0.571 0.500 0.445 0.643 0.594 0.536 0.495 0.617 0.543 0.501
0.444
I n Figure 2 the maximum divergence from a straight line is 3 per cent, for the curve A-F, which is arched. The curve G-D is sagged to a maximum of 2 per cent, and this is the result of blending a light Pennsylvania oil with a heavy Midcontinent oil. This might indicate that oils with a wide difference in viscosity index or viscosity gravity index would not behave in the same manner as oils with closer differences in these characteristics.
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. T h e 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
