Petroleum Oil Ext
rs
CORRELATION OF PROPERTIES IN GR-S WITH CHROMATOGRAPHIC ANALYSIS We L. DUNKEL, F. P. FORD. AND J. H. ZIclTEER Esso Laboratories, Standard Oil Decelopmerit Co., Linden, N. J .
S
UBST+iSTIXL commercial utilization of oil-extended high Xooney GR-S has been achieved in the space of a few year?. in spite of such major problem poor processing propertie$, tire tread splice failures, and tread-carcass separations. The presence of the pctroleuni oils in these stocks is intimat,elp associated with such problems. The complexity of oil-extended compositions requires laborious testing to establish firm correlation3 between the rubber compound arid oil properties. The development of simple and rapid tests for extender oils, which provide data significant to rubber manufacturers, would add considerably to an understanding of such products. The work described here falls into two phaecs. Laboratory studies on the chemical nature of extender oils led to the use of a chromatographic method of analysis, and these extender oils R-ere evaluated in actual GR-S compositions. Both phases have been correlated rather closely. An importarit objective of this work is to demonstrate the significance of oil properties and s h m how they influence t,he properties of the GR-8 componitions. In evaluating the oil-extended comporitions; procedures familiar to rubber technologists mere employed. h number of important contributions concerning the chemical :onstitution of extender oils have been made by previous investigators. Rontler ( 7 ) ha,s defined the chemical composition of petroleum oils by absorption with varying concentrations of sulfuric acid. He and his coworkers have reported ( 7 , 3 ) that the oil components defined in this manner may be associated with a number of the characteristics of oil-polymer compounds. Nore recently (8), Rostler has devised a code for identifying extender oils ha,ged on arid absorption analysis, viscosity, and refractive indes of the oil fraction undisaolvcd or unattaclred by fuming sulfuric acid ( I O ) . Burtz and Martin ( 6 ) determined the chemical composition of an oil hy an initial separation on silica gel into
a nonaromatic and an aromatic (including oxygen, nitrogen, and sulfur compounds) fraction. These were characterized by ring iinalysis to obtain est,imates of the average ring content and average distribution of carbon atoms among rings and open chains, Weinstoclr ( 1 4 ) has diecussed the correlation of the chemical structure of extender oils defined in this manner with laboratory and road testing data on oil-extended GR-6 compounds. I t is the purpose of the present work to provide a somewhat different point of view from those referred to above. OIL INSPECTIONS AXD hN.ALYSES
The petroleum fractions employed in the prepent study included commercial extenders and a number of experimental estenders available as products from various refineries of the subsidiaries and affiliates of the Standard Oil Co. (New Jersey). These experimental extenders were selected to provide a \?vide range with respect to crude source, refining history, and chemical composition. They are all distillate fractions of virgin or uncracked stocks. Table I summarizes a number of physical inspections for the commercial and experimental ext,eiiders under tliscussion These data emphasize the wide range in Ixopertie.; afforded by this group of oils. The chroinatographic procedure employed to &mate the rheniical composition of petroleum oil extenders is epsentially that described by Eby ( 1 ) . Thismethod of analysis effects the separation of a petroleum oil into three groupa of chemical coniponent,s: rioriaroniatics, aromatics, and polar compounds. A fourth group asphaltenes, may be obtained as a modification yhen the samplc is incompletely soluble in n-heptane. Briefly, a ;-gram sample of oil is dissolved in 200 in!. of ?Iheptane a t rooni temperature. If complete dissolution (lops i?ot
TABLE I. I.SSPECTIOXS o s PETROLCLX OIL EXTXSDXRS In-gcction
Oil 6
Refractive index, n2; Spec. gravity Aniline paint, F. Iodine number, cg./g. Volatility, . % . w t . io& Tiacosity. S.A.U. 10O0 F.
1.4920 0 89 214.5 11 9 0.001
2100
wt.
608.2 68.08 63 5
I?.
Viscosit,y index Pour point, a F'. Flash point, ",?. ( C O C ) Aromatics (silica-gel),
Oil Y
43 435
23 2
64
Oil 1 1.6217 0 94
Refractive,index, "2; Spec. giarixy Aniline noint. F. Iodine iuinber, cg.,'g. Volatility, % w t . lossa
1st
20,i 0 040
. S.S.U. 100O F.
0.92 191.1 17.0 0.024
...
445
70
1.5oan
13,4006 149.9
- 10
KS-2423 I , 4952 0.85 219.4 15.4 0.004
-3-2427
1.6481 0.95 97 25,; 0.087
950 8 0" 85 26 8
338
435
4ni
a
Oil 2 1.562 0.97 I30 27 i 0.234
Oil 3 1.6035 1,oa 2.3 24.3 0.14
200.1 23.9 0.00 180b
...
20
64.5
>o
2J 7
3G.F
1,5221 0.911
,..
61.68 78 0
- 13
Oil 7
011
4
1.5522 0 97 118 65.7
a
3 Hours a t
C.
b
2034 81.5 38.2 5 430 13.2
2900
82.52
...
60 10; 71 3
Repreeent,ative values only.
RS
Go'
405 81.1
1907 '
... io
425 (38.7
WS-2428
KS-2420
1 5327
1.5149 0.94 177.4 21.5 0.58
1,5005
0.95 133.3 20.6 0.45
2s:. 7n ,"
B
Oil l l b 1,5082
0.91 204.0 18.1 0 013 1234
7:
...
-0
465 38.0
1.3583 0.974 106 30.4 0.089 23006
B1.Q
20
4 p (2.3
i28,3 64.10 48.5 -. 1.5
- 16
375
64 9 WP-2432
0.91 201.0 17.8 0.12
931.5 66. 73 22. 8
1
47.4 38.5
390
T-;".,-":+ 5.9
%
23.6 22.9 36.2:33.7 36.6,36.6 43,1,43.3 43.1,42.4 43.5 44.4 61.4:6 1 . 4 65 . O , 6 4 . 7
7 1 . 7 , 7 1 .O 72,1,72.6
73.2,72.1
81.3,81.5
Polar Compounds,
%
0.0 0.9, 0.9 1.6, 2 . 5 3.8, 3.6 2.6, 2.7 5.2, 4.9 5.0, 5.1 4.2, 4.3 8.0, 8 . 2 3.5, 3 . 4 5.9, 5.7 11.8,12.7 13.2,12.6
COMPOUNDING PROCEDIJRES AND TEST METHODS
The relationship between extender oil composition (as determined by silica gel analysis) and high Mooney GR-S properties was studied in vulcanized and unvulcanized GR-S compounds. The basic recipe used in this work was, in parts by weight, as follows: high Mooney GR-S100, oil extender 45 to 50, HAF black 72.5 to 75, BLE 1, zinc oxide 5, sulfur 2, and Santocure 1. This formulation proved satisfactory in bringing out the differences in GR-S compositions imparted by oils of varying properties. A standard cure time of 60 minutes a t 287” F. was adopted. I t is believed that this represented, reasonably well, equivalent “states of cure” for all conipourids tested. Two different polymers were used in this work. I . A 145 ML-4 minute gel-free polymer containing 23.5% bound styrene, made to an intrinsic viScosity of 3.0 to 3.1. I t had 4.5 parts of potassium f a t t y arid soap ab the only emulsifier. 2. h 160 NIL-4 minute gel-free polymer prepared by the Govcrnment Laboratories, University of Akron, from GR-8-1500 type latex, was made a t 41” F. from 75/25 butadiene-styrene charges according to a sugar-frre redox formula. Three procedures were adopted for incorporating the oils into the GR-S compounds: mill mixing, “dry” Banbury mixing, and coprecipitation. The simplest method was to mix all the ingredients on a 6 X 12 inch laboratory mill in the conventional manner. Usually 200 grams of GR-S were used for such operations. Dry Banburg mixing was found to be more informative in most cases. Two sizes of laboratory Banburies were available. In one size, 2330-gram masterbatches were mixed. This was a t least 400 grams less than the capacity of the machine. This accentuated processing differences inherent in different types of oil extenders. A smaller Banbury, taking a 360-gram charge, was used when smaller quantities of experimental polymers or oils were available. Results obtained in the two Banburies were comparable. Finally, coprecipitation of emulsified oils with GR-S latex was also
579
used. This work was made possible with the cooperation of the Government Laboratories, University of Akron. The coagulated GR-S-oil blends werc then compounded in a Banbury. Mooney viscosity and extrusion rates were determined for the unvulcanized compositions. Extrusions were made a t 220” F. in a No. 1/2 Royal extruder using an annular die with a 0.3-inch inside diametcr and a 0.4-inch outside diameter and a worm speed of 80 r.p.m. The length and veight of extruded section per unit time were determined and expressed as cubic centimeters of composition per linear inch of extruded specimen. This “extrusion swellJJvalue appeared to be indicative of the relative compatibility of various oils with GR-S polymer. The principal vulcanizate properties investigated were the stress-strain and hysteresis properties. The former were determined in the conventional manner on a Scott tensile machine. The tensile strengths were of partirlar interest, in t h a t they frequently reflected apparent processing variables. This is discussed in further detail below. Hysteresis was determined on a forced vibration-type instrument, usually a t - 10” or f 5 0 ” C., although in some cases data were also obtained at +90” C. The machine is of special design, in which is mounted a 3 X 0.25 X 0.075 inch specimen, cut from a standard 6 X 6 inch tensile pad, under a 10% static extension. Superimposed on this slight elongation is a dynamic deflection of an additional 10 to 15% applied at a frequency of 16 cyclcs per second. Relative damping and dynamic modulus are determined with a strain gage and a linear variable transformer in conjunction with an oscilloscope. The internal viscosity in poises is determined from the dynamic modulus and relative damping relationship:
2K (% relative damping) % relative damping) where n = internal viscositv K = dynamic modulus, dynes per sq. cm. ,f = frequency, cycles per second
9 (poise) = a2f(200 -
varies approximately linearly with heat build-up as determined on the Goodrich flexometer. A high “9 value” indicates high heat build-up or a relatively sluggish compound. Low ‘‘q valucs” are obtained with more resilient compounds which have low heat build-up. Weight loss data were determined with sample test pads, approximately 4 X 6 X 0.075 inch, suspended in a circulating air oven for 48 hours a t 212” F. CHEMICAL AVALYSIS OF EXTEYDER OILS
The extensive literature on chromatographic adsorption (6, I S , 15) shows that the adsorption characteristics of pure compounds and their mixtures may be summarized as folloys: The affinity or strength of the attractive forces between silica gel and the material adsorbed increases with increasing polarity of the latter. I n a mixture containing compounds of differing polarity, thone hnvirig the greatest polarity mill tend to be most strongly adsorbed. Polarity may be defined in terms of the basic concepts of covalent, bonds and electrovalent or ionic bonds. I n a nonpolar compound all chemical bonds are essentially covalent. Extremely polar compounds contain a t least one bond which i s normally essentially electrovalent or which may be readily induced to asmme substantial electrovalent character. Compounds of intermediate polaritv vary in the ease and extent t o n-hich electrovalent bond properties may be developed. Nass action effects may be used to desorb a given material quantitatively in the presence of a large excew of elutrant of comparable polarity. These facts provide considerable assistance in defining the chemical nature of the components segregated by the present chromatographic procedure. This method thus define8 the composition of petroleum oil extenders as follows: ASPHALTEPI’ES.These components are segregated prior to adsorption on silica gel. They are nonvolatile substances and hence absent from distillate petroleum fractions. Little is known of their chemical structure. Elemental analysiR shows the prea-
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
880
ence, in addition t o carbon and hydrogen, of ospgen, nitrogen, and sulfur. Because the solubility of asphaltenes in aliphatic solvents increases with increasing molecular weight of the latter, the present method, employing n-heptane in place of a lighter paraffin solvent, may tend t o yield slightly lower values for the asphaltene content ( 2 ) . However, any error from this source is of little significance for present’purposes.
1 ~~~~~[ 1
POSTULATED TYPE STRUCTURES
AROMATIC
C
CH,(CH,I,CH,
c-c
I
I
I
I
I
C-C
;QSH
Vol. 46, No. 3
POLAR COMPOSEXT>S. The fraction recovered from silica gel by elution with the strongly polar solvent, pyridine, following the removal of the aromatics, contains coniponents of the samplr which are highly polar. E b y ( 1 )hae carried out elemental analyses of such fractions obt,ained from a variety of petroleum stocks. These invariably show the presence of substantial amounts of oxygen! nitrogen, and sulfur. These results are consistent with the vimv t h a t the fraction eluted by pyridine consists in large measure of nonhydrocarbon compounds. Examples of such materials, all of which are known to occur in pet,roleum, include heterocyclic compounds, quinones, phenols, thiophenols, and naphthenic acids (Figure 1). Some attention has been given t o the chemical relationship of the fractions segregated by the present chromatographic mpt hod and those obtained by the Rostler group analysis (Sj. Thc Rostler method employs successive treatments of a petroleum ether solution of oil, following the separation of precipitated asphaltenes, with sulfuric acid of increasing strength. In addition t o the asphaltenes, four types of component,s are identified. Rostler designates these components as: nit,rogen bases, soluble in 85% sulfuric acid; first acidsfins, soluble in 96% sulfuric acid; second acidaffine, Compounds reacting with oleum; and saturates, residual or unreactive material. This analytical procedure has been performed on a number of the oils listed in Table I to give the data shown in Table III.
%JcooH
Figure 1. Probable Structural Type Compounds Present in Petroleum Oil Extenders
Asphalterm, 8
XONAROMATICS. This fraction is recovered from the silica gel by elution with n-heptane, a nonpolar substance. The nonaromatics are therefore identified with the leapt polar constituents of the oil. In uncracked petroleum oils these comprise paraffins, naphthenes, and alkylated naphthenes (one or more paraffin side chains). The properties of known naphthenic hydrocarbons and a consideration of the tremendous number of possible isomeric homologs effective’;. eliminate the possibility that any substantial concentrations of unalkylated naphthenes are present in the high boiling petroleum products employed a9 GR-S ext,enders. Thus, the nonaromatic fraction removed from silica gel may be regarded as a mixture of numerous paraffins and alkylated naphthenes (Figure 1). All stocks used in the present study were uncracked, and the above conclusion applies accurately. Cracked petroleum stocks may also contain compounds having olefinic double bonds. Application of the present analytical procedure t o such products would be expected to separate the nonaromatic olefins with the nonaromatics and the unsat,urated aromatics with the aromatics. The relative amounts of these and their hiportance have not been completely assessed. AROMATICS.This fraction is recovered from silica gel, following the removal of nonaromatica, by elution with benzene. Benzene i s a relatively polar compound by virtue of the ease rvith which polarizstion of the aroimtic ring is induced under a variety of circumstances. I n this respect, benzene and aromatic hydrocarbons, in general, differ markedly from the components preseni in the nonaromatic fraction. It appears t h a t the presence of even a single aromatic ring in a hydrocarbon molecule having a molecular weight in the range of these petroleum oil extenders contributes sufficient polarity t o place it in the aromatic fraction (6). Considerations similar t o those previously mentioned with regard naphthenes in pet,roleum oil extender3 t o the occurrence of 6Lpure” indicate t h a t the concentration of aromatic compounds containing only aromatic rings is also probably very small. The aromat)ic fract’ion thus very probably consists of hydrocarbons containing a t least one aromatic ring associated n7it.h naphthenic rings, paraffin side chains, or both (Figure I ).
6
WS-2426 WS-2427 1 WS-2428 WS-2430 9 2 WS-2432 WS-2431 3
Bases,
yo
yo Kitrogen
0.0 0.0
3.6,3.6 1.4,1.7 3.7,3.9 3.6 1:
Oil
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
25
4.8
7.0, 7 . 1
4.1, 4 . 2 6.2, 7.b 9.0, 9.0 15.0. 15.2 45.4,24.5
.4oidaffins,
Acidafhs, % Second 3.L3.7 9.2, 7.6 3.2.3.3 2 0 . 8 , 20 , i 27.2,27.2 6.9,6.i 7.1 34.5 8.9 34.2 15.2 33.4 17.8,lS.i 3 8 . 9 , 4 0 . 1 14.7, 17.0 46 . 0 , 4 7 . 5 14.2,1 2 . 6 47.8,48.8 18.8,17.3 46.3,47.5 29.0,30.4 40.3.36.2
Saturates,
24.5,22.6
84.1,82,1 74.6,74.3 62.2,62.1 54.7 55.4 46 G 36.3, 36.8 35.2,30.4 31.8,31.3 26.9,26.2 l5.7,18.2 5.0, 5.5
70 First
15.1,47.7
%
A
v)
# 20
Q
m
40 ’
8
C ‘ z $
70 POLAR COMPQUNDS
Figure 2. Relationship of Polar Compounds (Silica Gel) and Nitrogen Bases (Rostler) The known reactions of sulfuric acid with numerous organic. compounds and their mixtures provide a sound basis for indicaiing the chemical nature of the Rostler oil components. Such information suggests t h a t the nitrogen bases comprise the most polar constituents of the oil, such as the polar compound fractions recovered by silica gel percolation. As shown in Figure 2, wheiv the Rostler nitrogen bases are plotted against the polar compounds determined b y silica gel for a number of oils, there is evi-
581
INDUSTRIAL A N D ENGINEERING CHEMISTRY
March 1954
80 70 60 -
EQUIVA L E NCE
IO 20 30 40 50 60 70 80 90 AROMATICS
Figure 3. Relationship of Aromatics (Silica Gel) and First Plus Second Acidaffins (Rostler)
drnce of a direct relationship between these quantities. The Rostler nitrogen base fraction probably contains a variety of polar compounds in addition to actual nitrogen bases. Evidence of this is provided by Rostler's observation that only a portion of this fraction is removed from a petroleum ether solution by hydrogen chloride (9). In addition t o polar compounds-derivatives of hydrocarbons containing oxygen, nitrogen, and sulfur-the Itostler nitrogen bases may also include some of the aromatic hydrocarbons which react readily with sulfuric acid. This is in accord with some observations made below. Rostler has indicated that the difference between the first and second acidaffins is a matter of degree rather than kind. The known reactions of sulfuric acid indicate that these two groups probably contain the major portion of the aromatic hydrocarbons ( I I ) This is illustrated by Figure 3, where the sum of the first and second acidaffins has been plotted against the aromatic fraction separated by silica gel for a number of oils. It is seen that the observed values fall randomly about the line representing equivalence except at extreme values. If, however, the sun1 of the nitrogen bases and first and second acidaffins is plotted against the sum of the polar compounds and aromatic fractions obtained by silica gcl, the approach to equivalence as shown in Figure 4 is, with one exception, satisfactory over the entire range. This offers rather convincing evidence that the Rostler nitrogen bases
?
Q
N i
N c
70t
-
EQU IVA L ENCE l
96
l
1
I
1
I
I
I
l
IO 20 30 40 5 0 60 70 80 90 AROMATICS + POLAR COMPOUNDS
Figure 4. Relationshipof Aromatics Plus Polar Compounds (Silica Gel) and First Plus Second Acidaffins Plus Nitrogen Bases (Rostler)
Vol. 46, No, 3
INDUSTRIAL AND ENGINEERING CHEMISTRY
582
TABLL T'. 1 8il9, % Aromaticity
0 21.7 1 4920
n 2; Stress strain properties Mod lb./sq. inch 100% elong. 200% elong. 300% elong. 400% elon2. 500% elong. !OO% elong. , 0 0 % elong. Tensile, lb.,'sq. inch E l o m : . , 70 Dynanilc properties ( - l o o C. i o 5 C.) Rel. damping, yo D y n . m0d.Q vi poise X 10-4 Extrusion properties Gramslinch C M P D . sp. gr. &./inch
+
2
Rr.suni 3
10 25.2 1 4970
OF 011
6
AVO
20 10 3 1 5037
9
IN
OILS PROCESSISG STUDY
5
4 30 34 8 1.3080
7
fi
50
40 39.4 1.5120
44.2 1.5152
;80
8
60 48.7 1.3223
160 550 10.10 1430
200 510 830 980
200 490 800 1000
220 520 820 1010
180 460 800 1040 1210
880 1150 1400
12iO 490
1070 450
1160 :10
1150 500
1370 5 70
1560 570
60.3-27 3 6 8-3 7 29.0-7.5
52.0-27 3 7 4-3.7 32.8-7 5
5 5 . 0 - 2 7 . 3 5 5 . 0 - - 2 7 . 8
