S. S. KURTZ, Jr., R. W. KING, and J. S. SWEELY Sun Oil Co., Marcus Hook, Pa.
Hydrocarbon Composition and Viscosity-Gravity Constant of Rubber Processing Oils
A
SYSTEM of classifying rubber processing oils on the basis of viscosity-gravity constant and viscosity has recently been proposed (72). It is now possible to show that this simple system of classification groups together oils of similar chemical composition. The composition of rubber processing
oils can be expressed either on the basis of the molecular type or on the basis of the carbon type (3, 4, 9 ) . Moleculartype analysis means reporting the per cent aromatics and the per cent saturates which can be physically separated, as with silica gel. Carbon-type analysis means reporting the per cent of the
carbon atoms in aromatic ring structures (%C,), the per cent in naphthene ring s t r u c h e s (%C,), and the per cent in paraffinic side chains ( % C , ) . There is now available ( 4 ) a graph from which the carbon-type composition can be read directly if the viscositygravity constant ( I , 2. 3 ) and refrac-
AROMATIC RING CARBONS O/o
NAPHTHENE RING CARBONS
O h PARAFFIN CHAIN CARBONS
O/o
Figure 1.
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Triangular diagram for per cent carbon-type composition
INDUSTRIAL AND ENGINEERING CHEMISTRY
Table 1.
Properties and Compositions of Oils for Use in Rubber" Properties
Identification
Oil name s5 Process oil 551
V.G.C. class
A
54 s3
B s2
SI Suniso 3G Circosol 2XH Circo light
c
D
1 2 3 4 5 6 7 8 9 10 11 12 13 14'
15 16 17 18 19 20
Sundex 170 (A2) Sundex 53
E A1
Sundex 85
F Sun XC 1320
No.
G
Commercial-C; Experimental-E E b
C C Eb E b
C C
Eb Eb C
C C C C" E
c, E5 C
c, E5 C C
S p . gr. 60/50
Viscosity 210' F . S.U.S. cs
Refract. intercept, Ti,
'
Composition Carbon-Tupe Analysis Mole-Tupe Analusis Composition bu Aromatics % V.O.C.riGraph bu satu-
V.C.C.
0.8871 0.8798 0.8590 0.8740 0.8654
144 63.1 39.3 47.0 39.1
30.4 11.1 3.96 6.35 3.90
0.798 0.809 0.811 0.815 0.818
1.0448 1.0450 1.0434 1.0441 1.0440
2 4 1 3 3
28 30 35 33 34
70 66 64 64 63
20 16 9 14 13
80 84 91 86 87
0.8733 0.8988 0.9141 0.8916
40.0 57.2 78.5 41.7
4.18 8.38 15.1 4.71
0.826 0.836 0.842 0.846
1.0438 1 0441 1.0419 1.0407
4 6 4 2
36 38 45 49
60 56 51 49
20 26 16 10
80 74 84 90
0.9088 0.9452 0.9242 0.9639
40.8 84.9 40.7 157
4.43 16.7 4.20 33.3
0.865 0.883 0.885 0.892
1.0442 1.0491 1.0493 1.0532
11 20 21 25
44 39 37 34
45 41 42 41
31 47 40 64
69 53 60 36
0.9838 0.9600 0.9874 0.9565 0.9820 0.9820 0.9920
332 82.5 178 37.5 82.9 74.2 179
71.1 16.2 37.9 3.38 16.3 14.0 38.1
0.909 0.915 0,927 0,929 0 936 0.936 0.936
1.0671 1.0501 1.0631 1.0470 1.0639 1.0665 1.0712
36' 26 36 32 36 39 41
17 45 28 39 30 24 20
47 29 36 29 34 37 39
92 54 78 72 76 76 87
8 46 22 28 24 24 13
I
21 22 23
1.0180 1.0964 1.0165
172 43.6 75.5
36.6 5.29 14.4
0,970 0 982 0.983
1.0735 1.0724 1.0811
44 46 48
26 30 20d
30 24 32
90 88 84
10
Eb C
24 25
C C
1.0382 1.0722
99.0 50.0
20.1 7.27
1,OI 1.07
1.0825 1.1123
52 68 e
24 10 e
24 22 e
95 92
5 8
C
I
12 16
Data for Sun Oil products listed are representative, but do not constitute specifications. References (6, 14). High % aromatic molecules and low % aromatic carbons produced by special process. Sample behaved a s anticipated from carbon-type analysis. Analyzed by using rule-samples with V.G.C. values between 0.950 and 1,Ol analyzed by assuming %CN and %CP are not less than 20%. e Analysis by Martin method because V.G.C.-refractivity intercept graph does not apply in this range. a
tivity intercept (3, 7, 8) are known. Experimentally, therefore, only the viscosity, gravity, and refractive index are needed to determine carbon-type composition. The rubber processing oils shown in Table I have been analyzed for carbontype composition both with the viscositygravity constant-refractivity intercept chart ( 4 )and by the more thorough procedure developed by Martin ( 5 ) . This table contains data representative of all the commercially important rubber processing oils. Pennsylvania, MidContinent, Gulf Coast, and California oils, as well as solvent refined raffinates
and extracts are all included. The agreement between the two methods is good, so only the data obtained by the shorter graphic procedure are given in Table I. I t is particularly significant that the carbon-type composition of the oils in each viscosity-gravity constant (V.G.C.) group is similar, and that a reasonable progression of composition occurs with change in viscosity-gravity constant. This is apparent if the viscosity-gravity constant values in column 8 of Table I are compared with the values for %CA, %C,, and %Cp in columns 10, 11, and 12 in this table.
The short-cut method may not agree well with data for pure compounds or fractions of lubricating oil which have been separated to a high degree in a research project. I t is intended for use on commercial oils and has been found satisfactory for them. Information on the highly reactive materials, which are likely to cause variability in cure time and in aging characteristics, is also desirable. These materials can be determined accurately enough for commercial purposes by reacting the sample with 85% acid under controlled conditions, and determining the amount of material removed (70, 7 7). VOL. 48, NO. 12
.DECEMBER 1956
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Table II. V.G.C. Class A
B C
D E F G
Carbon-Type Composition Corresponding to V.G.C. Classification of Rubber Processing Oils Same
Paraffinic (Pennsylvania) Relatively paraffinic (MidContinent) Naphthenic (Gulf Coast) Relatively aromatic (Gulf Coast) Aromatic Very aromatic Extremely aromatic
V,G.C. Range
% Carbon T y p e a %C N %CA
A p p r o x . Range for
%CP
0.790-0.819
75-60
20-35
0.820-0.849 0.850-0.899 0.900-0.949 0.95-0.99 1.00-1.05 Above 1.05
65-50 55-35 45-25 35-20 (25)-0 Below 25-0
25-40 30-45 20-45 20-40 (25)-0 Below 25-0
0-10 0-15 10-3 0 25-40 35-50 50-60
Above 60
Based on data in Figure 1. Ranges d o not necessarily apply for very narrow fractions or pure compounds. a
‘In the original publication ( 4 ) , the values obtained for yoCp and YOCN for samples having viscosiry-gravity constant values between 0.95 and 1.01 are not so reliable since the angle of crossing of the viscosity-gravity constant-refractivity intercept lines is not large. Since from experience no commercial oils have been found in the viscosity-gravity constant range 0.95 to 1.01 which have values of %C, or 7$, less than 20, it is assumed that these are minimum values in this region. Since the 7 0 C ~ in this viscosity-gravity constant region is usually 40 to joyc, there is a very limited area within nrhich the composition of the sample can fall [Figure 5 ( 4 )!. I n the last two columns of Table I, molecular-type composition data (obtained with silica gel) are also shown. Note that oil 14 appears to be very aromatic on the basis of rhe total per cent of material containing at least one aromatic ring. I t is much less aromatic on the basis of carbon-type composition, and this is correctly reflected in the viscosity-gravity constant and other physical properties. The data in Table I show that there is a limited range of naphthene carbon content (20 to 4570) whereas there can be a very wide range in per cent paraffinic carbon and per cent aromatic carbon. This is clearer when the data are plotted on a triangular diagram for per cent carbon-type composirion, as in Figure 1. This graph includes data for natural Pennsylvania, Mid-Continent, and Gulf Coast oils reported by Hill and Ferris (2) as well as commercial oils from Table I. It is particularly pertinent that nearly all the points for the commercial oils having 407, or less aromatic ring carbons fall in a band between 2070 and 45y0 naphthenic carbons. The viscosity-gravity constant lines cut across this band almost at right angles. Classifying oils by viscosity-gravity constant limits the oil to a composition represented by a portion of this band. This is the fundamental reason why the viscositygravity constant is so successful in classi-
2234
fying rubber processing oils according to composition in the viscosity-gravity constant range 0.79 to 0.95. Above 0.936, the viscosity-gravits constant is an extrapolated function ( 7 ) . In Figure 1, dotted lines indicate the probable course of the composition band above 0.950 viscosity-gravity constant. The curvature of the dotted lines (Figure 1) is supported by unpublished data for experimentally refined oils. These unpublished data indicate that when the aromatic carbon is above 60%, the naphthenic carbon is below 207,. Oils of this high degree of aromaticitv have not been widelv used in the rubber industry. Since the work of Weinstock, Storev. and Sweely (74) showed that minor differences in rubber processing oils were apparently not of major importance. classification by viscosity-gravity constant alone should be a useful way of defining the carbon-type composition. \$‘hen more detailed information on carbontype composition is needed, the viscositygravity constant-refractivity intercept graph can be used ( 4 ) . Table I1 shows the approximate range of carbon-type composition that can be associated with the viscosity-gravitv constant groupings used in Table I. In Table 11, the terms Pennsylvania and Mid-Continent correspond fairly \vel1 with paraffinic, and relatively paraffinic, respectively. Coastal or Gulf Coast includes naphthenic, and relatively aromatic groups.
The classification of rubber processing oils by viscosity-gravity constant brings together oils having similar carbontype composition irrespective of molecular weight. Since in practical compounding molecular weight is also important, the recommended classification system (72) defines oils by viscosity-gravity constant groups and viscosity. The viscosity, for any viscositygravity constant group, is an easy though indirect way of defining molecular weight. This very simple, fundamental system of classifying rubber processing oils should prove of value to working technologists in the rubber industry. It can be shown that many practical properties of oil-extended rubber are related to the viscosity-gravity constant and viscosity of the oil use‘d in extending the polymer (73). literature Cited ( 1 ) Hill, J. B., Coats, H. B., IND.ENG CHEM.20, 641 (1928). (2) Hill, J. B., Ferris, S. W., Ibid., 17, 1250 (1925). ( 3 ) Kurtz, ’S. S’.,Jr., “Chemistry of Petroleum Hydrocarbons,” vol. I, chap. 11, p. 327, Reinhold, New York, 1954. (4) Kurtz, S. S.,Jr., King, R. W., Stout, W. J., Partikian, D. G., Skrabek, E. A., Anal. Chem. 28, 1928 (1956). ( 5 ) Kurtz, S. S., Jr., Martin, C. C.: India Rubber M’orld 126, 495 (1952). (6) Kurtz, S. S., Jr., Sankin, A., IND. END.CHEM. 46, 2186 (1954). ( 7 ) Kurtz, S. S., Jr., Ward, A. L., J . Franklin Inst. 222, 563 (1 936). ( 8 ) Ibid., 224, 583, 697 (1937). (9) iVes, K. van, and Westen, H. A . van, “Aspects of the Constitution of
Mineral Oil,” Elsevier, New York, 1951.
(IO) Rostler, F. S., Sternberg, H. W., IND. ENG.CHEM. 41, 598 (1949). (11) Rostler, F. S., White, R. M., Rubber Age (N. Y . ) 70, 735 (1952). (12) Sun Oil Co., Marcus Hook, Pa., “A Method for Classifying Oils Used in Oil-Extended Rubbers,” 1954. (13) Sweely, J. S.: Ferris, S.W., Peterkin, M. E., Kurtz, S. S., Jr., submitted to Rev. gen. caoutchouc. (14) Weinstock, K. V., Storey, E. B., Sweely, J. S., IND.ENG.CHEM.45, 1035 (1953).
RECEIVED for review hlay 31, 1956 ACCEPTED October 23, 1956 69th Meeting of Division of Rubber Chemistry, ACS, Cleveland, Ohio, May 1956.
Correction In the article entitled “4 Numerical Solution to Dimensional Analysis” [Octave Levenspiel, Norman J. Weinstein, and Jerome C. R. Li, ISD. ENG.CHEY.48, 324 (February 1956)], last portion of Equation 4 should read
INDUSTRIAL AND ENGINEERING CHEMISTRY
boZXk
-k
biZ(XiXk)
-k
hZ(xzxk)
+ ... +
bkZ(Xk2)
=
~ ( Y X B )
