92
INDUSTRIAL AND ENGINEERING CHEMISTRY
or discovery under consideration. hforeover, for trends we must look to the decisions of the Circuit Courts of Appeals where the life or death of ninety-nine out of every one hundred patents in liti ation is determined. 8 n the question of the need of a special appellate court t o hear appeals in patent cases, the statistics seem to indicate there is no need for such legislation. The record does not support the view that different conclusions are reached in different circuits where issues are the same or similar, and thereby causing delays.
While the trend of recent decisions of the Supreme Court appears to be adverse to patents, i t must be borne in mind that most patent cases get to the Supreme Court by virtue of conflicting decisions on the interpretation of the patent by two or more Circuit Courts of Appeals, and that therefore only those cases in which there is serious doubt as to validity are normally considered by the Supreme Court. This Court has always considered it to be its duty to carry out the legislative intent of Congress in so far as that intent is clear from statutes passed by Congress. There can be no doubt that the legislative intent of the patent laws is t o give
Vol. 34, No. 1
protection to Tvorth-while inventions and t o carry out the provisions of tile constitution "to promote the progress of science and the useful arts by securing for a limited time to authors and inventors the exclusive rights to their respective writings and discoveries". It is to be reasonably assumed, therefore, that the supreme Court has no intention to strike down the benefits so far secured by, and still being produced under, the protection of the Datent laws. It is Derhaps unfortunate that so many patents of doubtful validity have come before the Supreme Court in recent years and unfortunate that the principles of its decisions in these doubtful cases have been considered guidepost. by the lower courts in cases which are relatively free from doubt. This tendency to apply t h e . principles to cases free of doubt is, however, sometimes due to faulty presentation of the cases to the lower courts. Where the invention is of such importance as to deserve favorable consideration, there is, as stated in Judge Evans' conclusions, no justification for the view that patents are to be considered less favorably today than forty years ago.
Dielectric Properties of Hydrocarbons and Hydrocarbon Oils J
J
TUDIES of the dielectric properties of hydrocarbon oils during oxidation have been carried out and found to exhibit widely varying characteristics. I n an effort to better understand some of these results, i t had been found advantageous to subject pure hydrocarbons of various structures to oxidations of the same type as applied to the oil 7). This work has been continued, and although samples (4, a number of problems arise which are not encountered with the oxidation of oil samples, the results obtained are of interest and demonstrate many of the characteristics obtained during oil oxidation
S
Procedure and Apparatus The procedure and apparatus were described in previous publications ( 5 , 5). The samples were deteriorated in the presence or absence of either copper wire (5-mil copper wire, 23.4 grams of oil per gram of copper), Whatman No. 41-H ashless filter paper (9.4 r m s of oil per gram of paper), or both, at a temperature of 85' . and a gas pressure of approximately 760 mm. of mercury. In the case of the limited oxidations, in which only definite amounts of oxygen were made available to the samples, the prescribed amount of oxygen gas was allowed to enter the evacuated deterioration cell containing the oil by means of a stopcock which was then closed; the gas buret could then be evacuated of oxygen and refilled u-ith nitrogen. The gas pressure was then maintained at 760 mm. with nitrogen gas. In most cases the amount of oxygen added was consumed by the oil in the first 50 hours. Color was measured with the Hardy spectro hotometer (12) before and after oxidation of the oil samples. S. T. M. precipitation test D91-40 n-as also made before and after oxidation. The electrical measurements are given in terms of'the proportional conductance, e'y, and the dielectric constant, E . These measurements are made with a platinum-glass guarded cell (vacuum capacitance of 4 ppfarad and electrode spacing 0.050 inch) which is part of the oxidation or deterioration system. Thus it is not necessary to remove a sample from the system for electrical measurements. These measuring cells (3) and meas-
x.
Influence of Oxidation J. C. BALSBAUGH, A. G. ASSAF, AND J. L. ONCLEY
Massachusetts Institute of Technology, Cambridge, Mass. uring circuits (6) were previously described. The electrical measurements are made over the audiofrequency range, at a voltage of 100 volts. The conductance e " j is equal t o e' tan 6 f, in which e' is the dielectric constant, tan 6 is the dissipation factor in per unit, and f is the frequency in cycles per second. The 60-cycle power factor, which is important from a practical point of view, is equal to cos (90 - 6) and therefore in the low ranges is practically equal to the dissipation factor. Since e' of the oils is approximately 2, at a frequency of 60 cycles per second c"f = e'tan S f = 120 tan 6 and therefore e " j is approximately equal t o the 60-cycle dissipation factor (or the 60-cycle power factor up to approximately 20 per cent), in per cent. The specific conductance, ge in mho-em., can be obtained from e'y as follows: gs = 0.556(10-12)(e".f) To extend the study of the effect of molecular type and composition on the physical, chemical, and electrical properties of hydrocarbons and hydrocarbon oils, seven, samples of a series of forty-one related oils prepared from a mid-continent crude (5) were studied. This series of oils of widely varying properties was prepared by the Gulf Research and Development Company. The electrical and chemical stabilities of samples DGElF, D6E2AF, D6E3F, D6E4F, D6E5F, and D6E7F to oxygen were reported by Balsbaugh, Howell, and Assaf (5). However, to
January, 1942
INDUSTRIAL A N D ENGINEERING CHEMISTRY
trated sulfuric arid, and finally redistilled. Cetene was prepared by cracking cetyl palmitate ( 7 ) . The crude cetene was distilled at a pressure of 15 mm. Cetane was prepared by hydrogenating cetene ( 7 ) . All of the hydrocarbons were distilled in a 6-fooi column of 1-inch bore, A-shaped glass packing, and a rating o forty theoretical plates. The distillations were carried out under total reflux, the still head reservoir having a capacity of approximately 20 ml. Refractive indices of the fractions were measured throughout the distillation, and the proper samples were selected:
A representative group of straight hydrocarbons and a series of related hydrocarbon oils have been studied under different oxidation conditions. This work indicates that the study of pure hydrocarbons is useful in interpreting the oxidation mechanism of commercial hydrocarbon oils. The oxidation of a paraffinic hydrocarbon and a water-white aromatic-free oil in the presence of copper gave a copper salt of a composition close to that of a 5-carbon dibasic acid or its homolog. The oxidation of a hydrocarbon or a hydrocarbon oil in the presence of copper under limited oxidation conditions, in which relatively small amounts of oxygen are made available to the sample, may produce a highly dissociated electrolyte giving relatively high conductivities or power factors. Electrical measurements of conductivity and dielectric constant of the oil itself and of the oil in combination with paper gave useful informationfor analyzing the mechanism of oxidation or deterioration. The use of a limited oxidation test for evaluating the power factor stability of an oil in the presence of copper should be important in commercial applications of electrical insulating oils.
33
Hydrocarbon cis-Decalin Cetane Decane Cetene
Measured
nso
1.4805 1.4348 1.4124 1.4400
Reference n% 1.4803 ( 1 1 ) 1.4352 ( 1 1 ) 1.4121 ( I I ) 1.4417 (11)
Kinetic Oxidation Studies
a
To obtain a clearer picture of the oxidation stability of the various hydrocarbons under different oxidation conditions, and the feasibility of drawing rough analogies between them and related hydrocarbon oils, a study of the stability to oxygen of the hydrocarbons and oils was made. Cetane was chosen for the most extensive oxidation study because of its high purity, fair availability, and interesting behavior. Figure 1 shows the oxidation-time curves of cetane with and without copper or paper or both. The oxidation curves indicate that the reactions are complex and difficult to analyze under most of these conditions. The most outstanding characteristics are the fast rate observed in the presence of copper (after a n induction period) and the decrease in this rate when paper is also introduced. The reaction in the absence of copper appears to be definitely inhibited. At the end of the oxidation of cetane in the presence of copper, a fine deposit of about 100 mg. of green solid was found on the walls of the oxidation cell. This solid was practically insoluble in all of the common solvents and could not be crystallized. It had no definite melting point, decomposing to give a bead of copper oxide upon heating in a flame. Copper and carbon-hydrogen analyses indicated that this organometallic compound was probably the copper salt of glutaric acid, a 5-carbon dibasic acid. A mechanism for the formation of this compound may be postulated by assuming that the cetane molecule splits to give myristic and acetic acids, the myristic acid being further oxidized to yield glutaric acid. The validity of this postulation is enhanced by the fact that acetic acid is liberated in the early
correlate the pure hydrocarbon and hydrocarbon oil studies, it was felt that the samples studied should be freed of the ordinary nonhydrocarbon contaminants found in highly aromatic oil fractions. Consequently, sample D6F2 and its extracts DGElF, D6E2AF D6E3F, D6E4F, D6E5F, and D6E7F were retreated by the dulf company to remove these contaminants as completely as possible without disturbing tlie molecular composition of the oils. Various treatments were used to clean the samples. In TABLE I. PHYSICAL PROPERTIES OF GULFSAMPLES general, when successive conhct clay Test D6F2R D6E7FR D6E5FR D6E4FR D6ElFR D6E2AFR ~... Sreatments failed to decolorize and neuSpecific gravity 0.8674 0.8823 0.8801 0.8402 0.9057 0.9445 20/4' C. tralize the oils, aqueous alkali treatments 0.8544 0.8698 0.8770 0.8673 0.8252 0.9345 were used. The properties of these re65/4" C. Refractive index treated oils are listed in Table I. Samples 100-4 and 60-4 were prepared ng 1.4900 1.4644 1.4790 1.4888 1.5050 1.5345 bv the Shell Petroleum Coruoration from nv 1.4735 1.4482 1.4630 1.4717 1.4880 1.5178 $plant cut of a special Wesf Texas crude, Specific dispersion 0.0125 0.0102 0.0108 0.0120 0.0134 0.0172 200 c. and had viscosities of 100' P. of 86 and 0.0113 0.0133 0.0097 0.0107 0.0166 0.0118 57 Savbolt Universal seconds, respec65' C. Viscosity, Saybolt Universal tively." D6E7F is a Gulf sample ha%ng seo. properties similar to that of D6E7FR, as 96.8 116 145 257 107 83.2 100' F. listed in Table I. 38.0 38.7 39.9 41.0 44.5 210° F. 39.3 .The hydrocarbons studied were cis85 54 - 11 128 101 Kinematic viscosity index 88 Decalin, decane, cetane, and cetene, rep69.5 45.8 104.8 91.7 84.0 Aniline point, C. 86.7 resenting naphthenic, paraffinic, and Waterman analysis, % olefinic types, respectively. The Cis20.7 4.6 10.9 37.5 0 Aromatics 9.9 25.1 26.9 24.9 11.0 11.8 Naphthenes 19.3 Decalin (Eastman practical) was sepa64.2 54.2 51.6 68.5 70.8 88.1 Paraftins rated from its trans isomer by distillation. Sulfur 0.19 0.03 0.08 0.15 0.45 0.49 Decane was prepared from technical nColor '(gatl. Petroleum Asamyl chloride by dissolving metallic soI f 0 21/, 3 2800.) dium in a lar e excess of n-amyl chlo0.01 0.01 !l%l 0.01 0.02 0.02 Neutralization No. Mol. weight used in calcularide and d i s t i k g the resulting solution. 320 310 315 325 tions 319 320 The product was then washed with alkaline permanganate followed by concen-
D6ERFR __
1.0071 0.9777 1.5861 1.5682 0.0235 0.0234 554 49.2 131 14.4
-
60.2
0.0
39.8 1.15 5+
0.05 290
dil.
Vol. 34, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
94
stages of the oxidation of cetane, and that the oxidation of myristic acid (as well as other long-chain fatty acids, 8) yields glutaric acid (14).
10000
reactions (oxidation and polymerization) apparently complicate the mechanism. Possibly the structural configuration of the cetene molecule protects the carbon double bond from oxygen, and the reaction is not quite that of the oxidation of a simple olefin. I n fact, Afferni (1) found that the air oxidation of cetene a t 125-145' C. gave a highly polymerized acidic product, indicating the formation of unsaturated acids. The oxidation-time curves of water-white aromatic-free oils 100-4, 60-4, and D6E7F are also shown in Figure 2; 100-4 and 60-4 were oxidized without copper or paper and D6E7F with and without copper. Although all are highly refined oils, they do not appear to have the same relative stabilities; none had inhibitors added. Sample 1 0 0 4 has oxidation characteristics close to those of &-Decalin. The TABLE 111. Sample Cetane Cetane Cetane Cetane
ABSORBEDAS FIGURE 1. OXYGEN
A
FUNCTION OF OXIDA-
TION T I h l E FOR CETANE 760 mm. oxygen, 85' C.
Figure 2 shows the oxidation-time curves of cis-Decalin, decane, and cetene, and of three highly refined aromaticfree oils, 100-4, 6 0 4 , and D6E7F. The behavior of the hydrocarbons is interesting although unexplainable a t the present time. The oxidation of cisDecalin in the absence of copper and paper proceeded immediately a t a vigorous rate; in fact, the curve shown in Figure 2 extends to 41,480 cc. of oxygen per kg. of hydrocarbon. It has been shown that large amounts of a peroxide (R-0-0-H) is the first product to be formed (2, 7). The effect of this peroxide formation on the dielectric properties is discussed later. Copper and paper inhibited the reaction at approximately 13,000 cc. of oxygen per kg. of hydrocarbon. The oxidation curve of decane is rather straightforward with the exception that no induction period occurred, nor did the addition of copper have any appreciable effect in the early stages of oxidation, although it did inhibit the reaction later. At the end of the oxidation test with copper, a green insoluble solid was isolated which could not be purified. Copper and carbon-hydrogen analyses showed it to have a composition close to that of the copper salt obtained in the cetane oxidation (Table 11).
Cetene*** cis-Decalin cis-Decalin Decane Decane
Catalysts Present None Cu** Cqpaper Paper
Cu
SUMMARY OF First a 0.12 0.07 1.0 0.54
0.86 0.35 None Cu, paper 0.72 None 0.66 0.82 Cu
Stage b 0.0023 0.0025 0.36 0.75 0.95 0.28 9.5 0.78 2.2
KINETICSDATA(85'
c.)
Time at Second Stage Transition, Hr. a b 1400 760 1200 0.07 0.0013 > 1600 *.
**
....
>
460 120 88 650 500
0.011
0.22 2.2 3.1
4.8 X 10' 6.1 X 10'0
2:4
1.0 'X.107
* *
*
870 60-4 None 0.08 0.0027 0 . 2 7 0.094 150 2.2 1.7 X, 10' 100-4 None 0.30 0.031 > 600 D6E7F None > 250 Cu 0.55 0.50 D6E7F D a t a not represented b y a line of constant slope. T h e early stages of this oxidation showed definite "steps" t h e oxidation proceeding ra idly for a few hours a n d then remaining oonst(ant from 50 t o 100 hours. T f e parameters given are for t h e reaction after about 600 hours? and are near those estimated for the f a s t steps occurring in t h e earlier period. Another transition occurred a t 850 hours, after which t h e reaotion became very inhibited ( a about 5 ) .
* **
*
***
OF SALTS FROM CETANE, DECANE, AND TABLE 11. COMPOSITION D6E7F
% H % O % cu 3.1 33.1 32.8 31.0 32.8 31.7 4.1 31.4 35.0 34.1 4.5 27.4 41.2 4.7 No sample leftb 39.9 4.2 . No sample leftb Nosampleleftb 45.7 3.8 e Three residues from different tests. b Qualitative tests for copper, ammonia complex and bead tests. Compound Copper glutarate F r o m cetane From decane From D6E7Fa
%C
. ..
,.
The most surprising oxidation-time curve is that of cetene, which has the double bond between the last two carbon atoms of the chain (11). It was expected that the oxidation would proceed rapidly, yet the results show that the rate of oxidation is no faster than that of cetane with copper (Figure 1). The breaks in the cetene curve a t 500 and 850 hours cannot be explained. The possibility of two simultaneous
FIGURE 2. OXYGENABSORBEDAS A FUNCTION OF OXIDATION TIMEFOR HYDROCARBONS AND HYDROCARBON OILS 760 mm. oxygen, 8 5 O C.
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1942
95
oxidation of sample D6E7F more closely resembles that of decane, and that of sample 60-4 resembles the oxidationtime curve of cetane. Unfortunately, Waterman analysea were available for sample D6E7F only; analysis showed this oil to be composed of 88 per cent paraffins and 12 per cent naphthenes. Residues from various oxidation tests on this oil were partially purified by washing and were found to give qualitative tests for copper. Carbon-hydrogen analyses varied somewhat and are given in Table 11,indicating that these residues may consist of copper salts of higher homologs of glutaric acid.
FIGURE 4. RELATION BETWEEN CONDUCTANCE d’f, e’, AND OXYGENABSORBED,FOR CETANEWITH COPPERAND PAPER
400
1000
5000
9000
CC OF OXYGEN PER KILOGRAM
OF
I3000 OIL
17000
FIGURE 3. RELATION BETWEEN CONDUCTANCE d’j AND OXYGEN ABSORBEDFOR THE HYDROCARBONS
Curves of log V against log t, where V represents cc. of oxygen (N. T. P.) absorbed per kg. of oil and t is the time in hours, have revealed that most of the oxidation data may be closely approximated over the entire oxidation range in some cases by one line with constant slope, or in most other cases by two lines, each with constant slope. Values of a and b in the equation, a log V = log b log t
+
as determined from these straight lines are summarized in Table 111. These results may be compared with previous studies. The oxidation of cetane and Decalin in the absence of copper and paper was reported by Balsbaugh and Oncley (7). Their values for cetane agree well with this new study. The &-Decalin oxidized with much the same type of reaction, but somewhat faster than did the earlier Decalin (probably containing some trans-Decalin)
.
Dielectric Properties of Hydrocarbons as Influenced by Oxidation The dielectric properties of the hydrocarbons as a function
of oxygen absorbed are shown in Figures 3, 4, and 5. Figure 3 shows the conductance et’f of the hydrocarbons as measured at 85” C. during the oxidation under 760 mm. oxygen as B function of oxygen absorbed, under the various conditions. Figure 4 shows the relation between the change in conductance, e”f, at 85’ C. and dielectric constant E’ at 85” C. of cetane as a function of oxygen absorbed, when oxidizied
under 760 mm. oxygen in the presence of copper and paper. Figure 5 shows the following relative values a t 85” C.: conductance, d’f, of the cetane a t any frequency in the audiofrequency range, and the 1000-cycle value of e’y of cetane and paper and the zero frequency or intercept (or an equivalent d. c. conductance) value of d’f obtained from a number of frequency measurements of cetane and paper, all as a function of absorbed oxygen. The cetane was oxidized under 760 mm. oxygen in the presence of paper and copper. Figure 5 gives corresponding results for &-Decalin in the presence of copper and paper. As shown in Figure 3, when cetane is oxidized in the presence of copper (or copper and paper) the conductance d’f at 85” C. of the cetane, with an initial absorbed oxygen of the order of 100 t o 400 cc. of oxygen per kg., rises from an initial low value of 0.04 to approximately 75. As discussed under “Kinetic Oxidation Studies,” this range of oxygen absorption of the cetane represents the induction period of approximately 600 hours for cetane and copper and approximately 1200 hours for cetane with copper and paper. With continued oxygen absorption beyond the induction period, the conductance e”f falls to relatively low values approximating 0.1. Continued oxygen absorption beyond this point again gives greatly increased conductivities. These electrical characteristics of cetane oxidized in the presence of copper are in marked contrast to those obtained when cetane is oxidized alone. I n the latter case the conductance d’f remains relatively low over a range of oxygen absorption up to 5000 cc. of oxygen per kg. These results indicate that copper acting as a catalyst or reagent is responsible for the oxidation mechanism that produces high conductivities or power factors in the initial stages of the oxidation of cetane. Figure 4 shows that during the initial period when the conductance rises from the low initial value to a very high figure and then decreases again to a low point, the dielectrio constant of the cetane changes by a relatively small amount.
96
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
However, following this period, continued oxygen absorption results in a large rate of change of E’ with respect to absorbed oxygen. Thus during the initial period as described, the oxidation products are essentially nonpolar (apparent dipole moment of 1 Debye unit or less); but following the induction period the oxidation mechanism changes to yield products that contribute substantially to e’ and have a n apparent dipole moment of about 6 Debye units per molecule of oxygen absorbed. Further information concerning the mechanism of the oxidation of cetane in the presence of copper and paper is shown in Figure 5 . Electrical measurements of conductance E’? and dielectric constant E’ were made a t several points in the audiofrequency range on cetane and on a paper cell immersed in cetane. I n general, a t the temperature and over the frequency range considered, E’? and E’ of cetane were independent of frequency. This indicates that the oxidation products under the conditions of measurement produce only a conduction loss. I n the case of the cetane-paper combination, Figure 4 shows e’lf a t 85” C. at 1000 cycles per second as well as the intercept value, obtained by plotting e’? as a function of frequency and extrapolating to zero frequency. I n the init’al stage of oxidation (or induction period) of cetane in the presence of copper and paper, the paper cell loss is principally a conduction loss, in that there is but slight change in the conductance e’y with frequency. Thus the paper is merely exhibiting the conduction loss of the cetane itself. However, as the oxidation mechanism changes a t approximately 400 cc. of oxygen per kg., the conductance E’? of the cetane paper gradually acquires a n increasing slope with frequency as indicated in Figure 5 by the difference in the 1000 cycle per second and intercept values. This is further illustrated in Table IV. These results mag be explained by the formation of polar compounds which are absorbed by the paper, producing a loss due t o interfacial polarization as well as conduction. This change in oxidation mechanism is also substantiated by the change in E’ with oxygen absorbed in Figure 4 in which
FIGURE 5. RELATION BETWEEN CONDUCTANCE B’YAND OXYGEN ABSORBED FOR CETANE AND &-DECALIN
Vol. 34, No. 1
increases with absorbed oxygen a t the time the cetane paper shows a polarization type of loss. The oxidation mechanism responsible for the foregoing electrical measurements is difficult to explain. The high conductance with very small amounts of oxygen are of an order of magnitude which can be explained only by the formation of a highly dissociated electrolyte. If 1 mole of oxygen is assumed t o form 1 mole of such an electrolyte, it must have an equivalent conductance of the order of 10-5 a t concentrations of the order of 3 millimoles per liter. The conductance in very low dielectric solvents (e’ about 2) has been studied for only a few salts, and this value is perhaps ten times larger than that obtained for the 2-1 salt-lead abietate (PbAbz) mixture in toluene a t 35” C., but ten times lower than that given for the 1-1 salt-PbAbC1 mixture (10) and is of the same order as has often been observed for various substituted ammonium ions in benzene (15). The electric moment of the electrolyte formed in the early stage of oxidation must be small (of the order of 1 Debye unit or less) as the observed dielectric constant change is small. One e‘
TABLE IV. OXIDATIONAND ELECTRICAL DATAOK CETANE OXIDIZEDIN PRESENCE OF COPPERAND PAPER Oxidation Time, Hr.
Cc. On/Kg.
at 85O C. and 1000 Cycles
Cetane-Paper Intercept
can only speculate as to the chemical constitution and structure of this compound. During the early stages of the oxidation of cetane (also cetene) with copper the hydrocarbon assumed a pale green color which became progressively deeper with time. This color phenomenon occurred during the induction period, although to a much greater extent afterward. Apparently a copper compound was being formed, and its structure is open to conjecture. It does not seem reasonable to assume that, in the early phase of the oxidation of cetane with copper where only a relatively few cc. of gas were absorbed, the oxidation of cetane had progressed t o the acid stage, consequently forming copper salts. With a series of experiments to prove his contentions, Lewis ( I S ) postulated that the mechanism of the oxidation of paraffins consists first of a dehydrogenation of the paraffin to form an olefin which subsequently forms a peroxide. This peroxide then breaks down in a normal manner. Assuming this mechanism to be true, it seems that the copper is reacting with the peroxide of the dehydrogenation product of cetane-namely cetene-to produce high electrical losses. Cetene itself, upon oxidation in the presence of copper, assumed a pale green color within 20 hours and attained a dark green color with 40 hours. The electrical loss of cetene rose rapidly meanwhile. The dielectric properties of cetene, when oxidized in the presence of copper as shown in Figure 3, correspond t o the initial properties of cetane under the same conditions. However, no maximum value of e’/f was observed as in the case of cetane, and the conductance increased to large values. Measurements of the dielectric constant, E’, show a rapid increase with absorbed oxygen in the range 0 t o 1300 cc. of oxygen per kg. of cetene, after which a smaller rate of increase is obtained. Similar to the cetane-copper test, the oxidation must produce a strong electrolyte-in this case,
January, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
97
limited oxidation conditions, in which only a definite and small amount of oxygen is made available to the decane. Electrical measurements were made on cis-Decalin and on a cis-Decalin-paper cell as previously described for the corresponding cetane oxidation. Figure 5 gives e"f a t 85" C. for the cis-Decalin itself; this value applies to any frequency in the audio range and thus indicates that the loss is entirely due to conduction. For the combination of cis-Decalin and paper, e"f a t 1000 cycles per second and the intercept value a t zero frequency are given. The oxidation of cis-Decalin which is said to produce a peroxide of the type R-0-0-H would be expected to be polar. The initial relatively high values of e'lf may be explained by this peroxide formation before the electrical measurements were made a t the start of the test. The polarization loss for the paper, indicated by the relatively high 1000-cycle c"f as compared to the equivalent d. c. conductance (intercept e'lf), may be explained by the paper's absorbing this peroxide. The relatively low conductance of the cis-Decalin itself, even up to 15,000 cc. of oxygen absorbed per kg. may be due to absorption of this product by the paper. This is also indicated by the conduction loss of the paper's being much greater than that of the &-Decalin.
10
5
3
PI
+
.5
.I
.05
.o I
Limited Oxidation Tests on a Hydrocarbon Oil In view of the characteristics of cetane, where relatively small amounts of oxygen gave excessive conductivities or power factors, and the practical importance of commercial electrical insulating oils operating under conditions either of (a) limited oxidation, (b) contact with catalytic materials, or (c) residual oxidation products, a study was made of a series of commercially refined hydrocarbon oils under a wide range of oxidation conditions. The oil used in this study was sample D6E7F. The physical and chemical properties were given in a previous paper
D&TERIOREiTION TIME IN HOURS
FIGURE6 . RELATION BETWEEN CONDUCTANCE ~ " AND f DETERIORATION TIMEFOR GULFSAMPLES Above. System pressure 760 mm. with nitrogen: oxidation 760 mm. oxygen after 980 hours in caBe of 100 and 2000 cc. oxygen/kg. Below. Limited oxidation at 85' C. with copper and 400 ce. oxygen/ kg.: system pressure 760 mm. with nitrogen
however, with a considerable dipole moment. If we assume that one molecule of oxygen produces one dipole molecule, the calculated moment would be of the order of 8 Debye units, a value rather high but of the order obtained for certain strong electrolyte molecules (IO). The dielectric properties of decane when oxidized in the presence of copper are in marked contrast to those of cetane with copper. I n view of the fact that both of these hydrocarbons are normal paraffins, i t might be expected that similar results should be obtained. In the case of decane and copper, the conductance e'lf remains relatively low throughout the complete oxidation range u p to approximately 1800 cc. of oxygen per kg. These results might be interpreted in terms of the absence of an induction period in the case of decane. Thus the oxidation may proceed directly to end products without forming the intermediate products as indicated in the initial or induction period for cetane. Decane may possibly give similar results to cetane under
AS A FUNCTION OF OXIDAFIGURE 7. OXYQENABSORBED TION TIME
780 mm. oxygen with oopper, 86' C.
98
INDUSTRIAL AND ENGINEERING CHEMISTRY
Before oxidation
Vol. 34, No. 1
After oxidation
FIQURE 8. COLOR SPECTRUM OF GULFSAMPLES COMPARED TO NT~JOL
(6). It is nearly the same as D6E7FR, whose properties are given in Table I. It represents the raffinate of a solventrefined series; by Waterman analysis it is aromatic-free, containing 86.6 per cent paraffins and 14.4 per cent naphthenes. It was chosen for this particular study because it contains a minimum of nonhydrocarbon constituents, so t h a t the resulting properties should be inherently those of the component hydrocarbons. The conductance d’j, or approximately the 60-cycle dissipation factor tan 6 in per cent at 85’ is given as a function of deterioration time for this oil under a wide range of limited oxidation conditions in the upper graph of Figure 6. These samples were deteriorated in the presence of copper a t 85” C. The range of limited oxidation conditions includes the following amounts of available oxygen in cc. per 1000 grams of oil: 0,50,100,500,1000,2000, and continuous. I n these tests the system pressure is maintained a t 760 mm. pressure with nitrogen after the absorption of the amounts of oxygen indicated. I n the continuous test the oxygen pressure is maintained a t 760 mm. throughout the complete run. The results show that the greatest increase in power factor was obtained with the smaller amounts of oxygen, 50 and 100 cc. of oxygen per kg. of oil. Thus the test with 50 cc. of oxygen per kg. gave a maximum d’f of 3.0, and the test with 100 cc. of oxygen per kg. gave a maximum e’lf of approximately 8.0. Larger amounts of available oxygen, in general, gave decreased conductivities or dissipation factors. A blank test was made in which no oxygen was made available to the oil; the system pressure was maintained a t 760 mm. with nitrogen, following the initial degassing of the oil into the system a t a pressure of approximately 50 microns. This test showed a gradual increase in d’f to 0.5 after approximately 800 hours. Further tests in this range are required to determine whether this result is due to the oil contacting copper in an oxygenfree atmosphere or to other effects.
c.,
Two tests were made with 500 cc. of oxygen per kg. to determine the reproducibility of the measurements, The results may be considered a satisfactory check because the limited oxidation tests are much more sensitive than the continuous oxidation tests. The increase in conductance or power factor is less than that obtained with either 50 or 100 cc. of oxygen per kg. The tests using 1000 and 2000 cc. of oxygen per kg. show still lower increases in conductance than the 500-cc. tests. These results show that the smaller amounts of oxygen produce the greatest increase in power factor or conductance. Further tests are required to determine whether the increases in power factor are dependent upon the amount of oxygen available to the oil in the lower range of oxygen absorption. At the end of approximately 1000 hours of limited oxidation time in the 100- and 2000-cc. tests, the runs were changed over to the continuous oxidation type. This is done by withdrawing the nitrogen and other gases which may be in the oxidation system and then maintaining the system pressure with oxygen a t 760 mm. These tests were continued until in each case approximately 19,000 cc. of oxygen per kg. had been absorbed. I n the case of the limited 100-cc. test, the ~’’j or power factor of approximately 7 per cent decreased with further oxygen absorption to approximately 0.1 per cent and then increased to approximately 7 per cent again with a total absorption of 18,900 cc. of oxygen per kg. I n the case of the limited 2000-cc. test, the change from limited to continuous oxidation produced no significant change in power factor. The differences in the ef’f us. time curves in the continuous oxidation range (over 1000 hours) for these two cases are accounted for by the differences in oxygen absorbed a t the beginning of the continuous oxidation part of the tests. This same oil under continuous oxidation gives a relation between d‘f and oxygen absorbed similar to that shown in Figure 7 for D6E7FR. The conductance and power factor
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1942
was relatively small. The susceptibility of these compounds to oxygen is shown in the upper part of Figure 6 at the point where an unlimited supply of oxygen is made available to the 100-cc. test.
‘1:
Limited and Continuous Oxidation Studies of a Series of Hydrocarbon Oils
IO.
I n view of the important effect of a relatively small amount of oxygen in producing relatively high power factors or conductivities as shown for cetane in Figures 3, 4,and 5 and for D6E7F in Figure 6, a study was made of a series of related
5.
0
8
I.
*c LJ
.5
::L .o I 0
99
2
FIGURE 9. RELATION BETWEEN CONDUCTANCE eVf AND OXYGENABSORBED
remain very low, d/f = 0.01, over the range up to 8000 cc. of oxygen per kg. With increased oxygen absorption the power factor rises rapidly and may ultimately attain relatively high values. Electrical measurements on an oil-paper cell in such a test have shown that water and low-molecular-weight acids are produced throughout the oxidation, so that these products themselves do not necessarily cause high conductivities. It is of interest t o compare the results obtained on oil D6E7F under various limited amounts of oxygen with those obtained on the hydrocarbons discussed previously. The results indicate that with relatively small values of available oxygen, of the order of 100 cc. of oxygen per kg., the oxidation mechanism is similar to that occurring during the induction period of cetane. This mechanism is responsible for relatively high conductivities or power factors. Whatever the mechanism of oxidation may be, apparently in the initial stages of degradation of the hydrocarbon molecules by oxygen, products are formed which cause relatively high electrical losses. They may or may not be copper compounds, as was the case with cetane and cetene. The results of the oxidation of cetane with and without copper favor reaction with copper. However, these products do not appear to be stable in the presence of oxygen and react further to form compounds which cause lower electrical losses. This mechanism is supported by a study of Figure 6 (upper curves). With 50 cc. of oxygen per kg. of oil, a certain Concentration of these products was formed which gave an d’f of 3. I n the absence of any further oxygen, these compounds remained quite stable, causing no further increase in loss. When a sample was charged with 100 cc. of oxygen per kg. of oil, a greater concentration of these products and consequently a greater loss was obtained. With a charge of 600 cc. of oxygen per kg. of oil, the excess oxygen apparently destroyed some of the products and caused loss; consequently their concentration was cut down and the dielectric loss of the oil was decreased. A charge of 1000 cc. of oxygen per kg. reduced the loss still further, and 2000 cc. of oxygen per kg. was analogous to a continuous oxidation in which the loss
oils under limited oxidation for a given amount of oxygen absorbed. The properties of the samples are given in Table I. They were oxidized in the presence of copper at 85” C. with a limited amount of oxygen equivalent to 400 cc. per kg. The conductance d’f, or approximately the 60-cycle power factor, was measured as a function of time at the oxidation temperature. The results show that distillation cut D6F2R, from which the solvent-refined extracts were obtained, has a stability intermediate between the initial and final extracts. However, the initial r”f at 85’ C. of these samples is approximately in line with their relative stabilities, so that it is not definite as to whether the results are a function of the initial nonhydrocarbon constituents of the oils or the inherent property of the hydrocarbon constituents of the samples. Furthermore, in view of the results in the upper curves of Figure 6,
FIGURE 10. RELATION BETWEEN DIELECTRIC CONSTANT e’ AND OXYGENABSORBED which show that the power factor stability is dependent upon the amount of oxygen available to oil, it may be necessary t o study each sample of a series a t different amounts of oxygen to determine the relation between the physical and chemical properties of an oil and the power factor stability. However, a comparison of the results in the lower graph of Figure 6 with those of Figure 7 gives further evidence that limited amounts of oxygen may cause greater loss than equivalent amounts in a continuous oxidation test. Figure 7 gives the results of oxygen consumed vs. time for the continuous oxidation tests. I n general, these oils show the same properties exhibited before they were treated (6),
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in that under- and overrefining produced the least stable oils. However, D6E3FR and D6E2AFR are much more stable after treatment than before. Apparently the properties of aromatic oils cannot be properly evaluated unless they are free of the contaminants left after ordinary solvent refining. An interesting observation is the marked stability of the original distillation cut D6F2R as compared with any of its extracts. From Figure 7 it becomes evident that, in the course of solvent refining sample D6F2R into its constituent extracts, some naturally occurring inhibitors mere either destroyed or lost, an observation also reported by Clark (9). These “inhibitors” not only seem to have affected the oxidation stability of D6F2R but also its electrical, color, and sludging properties. Figure 8 shows the transmission of light os. wave length for the oil samples before and after oxidation. It had been previously observed that the power factor of an oil is somewhat related to the intensity of its color (5, 7 ) ; i. e , the greater the transmission of light the lower the power factor. Figure 8 (right) shows the transmission curve of D6F2R t o lie between the curves for D6E4FR and D6E3FR. The values of E‘? for D6E4FR and D6E3FR, respectively, are 52 and 02, while that for D6F2R is only 17. The value of ~ ’ lfor f DRELAFR is 326. The results of soluble sludge, as measured by A. S. T. M. precipitation test D91-40, are as follows:
Oil
DBF2R DfiElFR DGEZAFR DfiE3FR DBE4FR DfiE5FR DBE’IFR
Precipitation Number Before After oxidation oxidation 0.0 0.0 0.5 3.0 1.0 0.0 0.15 0.0 0.0 0.06 0.0 0.0 0.0 0.0
Sample D6F2R consumed 1755 cc. of oxygen per kg. in 835 hours as compared to 5032 cc. in 1034 hours for D6E4FRj yet its color is more intense than that of D6E4FR and it contained no sludge. It was interesting to observe the color characteristics of D6E7FR, a highly refined, aromatic-free, water-white oil. During oxidation, products began to form within a few days which reacted with the copper to color the oil green. This phenomenon is observed in the transmission curves by an increased absorption of light above 540 my. -4s oxidation progressed, the green color became more pronounced and was accompanied by the deposition of copper compounds. However, as shown in the above table, no soluble sludge was formed. D6E5FR, which has only 4.6 per cent aromatics, did not show this phenomenon although volatile products of oxidation shorted the electrical measuring cell before the test was completed, just as they did in the case of D6E7FR. The conductance e’lf a t 85“ C, as a function of oxygen absorbed for the Gulf series of samples under continuous oxidation a t 85” C. with copper is shown in Figure 9. The electrical stability, as indicated by the increase in conductance o r power factor for a given oxygen absorption, is practically
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in line with amount of solvent refining. Since the extracts were prepared from distillation cut D6F2R, it might be expected that this sample would show a stability intermediate to the various extracts. However, this is not confirmed by the results obtained. It is interesting to note the low conductance (e‘lfof 0.01) of sample D6E7FR even with an oxygen absorption up t o 7000 cc. of oxygen per kg. of oil. However, a similar sample, D6E7F (upper graph of Figure 6), showed relatively large increases in power factor with a limited oxygen absorption of 100 cc. per kg. It is also important t o note that the intermediate extracts gave conductance peaks somewhat similar to cetane (Figures 3, 4, and 5) and to D6E7F (Figure 6) under limited oxidation. It is believed that the oxidation mechanism responsible for this behavior corresponds t o that previously described. The change in dielectric constant e’ a t 85” C. with oxygen absorbed for this series of samples is shown in Figure 10. The increase in E’ with absorbed oxygen is smaller with additional solvent extraction.
Acknowledgment The results discussed in this paper have been obtained in a research project on mineral oil deterioration sponsored by the Engineering Foundation and the American Institute of Electrical Engineers. Funds for this work are being contributed by a group of electrical power companies, a group of oil companies, and a group of electric manufacturing companies in addition to the sponsors. We want to thank the Gulf Research and Development Company and the Shell Petroleum Corporation for making available the special oil samples of widely different chemical and physical properties which have been studied, and the committee, Herman Halperin, chairman, for their cooperation and interest in the work.
Literature Cited Afferni, Ann. chim. applioata, 27, 366-72 (1937). Assaf and Gladding, IND ENG. CHEM.,ANAL.ED., 11, 164 (1939).
Balshaugh and Assaf, Ibid., 13, 515 (1941). Balshaugh, Assaf, and Pendleton, IND.ENG. CHDM.,3 3 , 1321 (1941).
Balsbaugh, Howell, and Assaf, Ibid., 32, 1497 (1940). Balsbaugh, Howell, and Dotson, Trans. Am. I n s t . Elec. Engrs., 59, 590-6 (1940).
Balsbaugh and Oncley, IND.ENG.CHEM.,31, 318 (1939). Carette, Compt. rend., 102, 692 (1886). Clark, IND.ENG.CHEM.,31, 327 (1939). Deitz and Fuoss, J . Am. Chem. Soc., 60, 2394 (1938). Egloff, “Physical Constants of Hydrocarbons”, A. C. S. Monograph 78, New York, Reinhold Pub. Corp., 1939. Hardy, J . Opt. SOC.Am., 18, 96 (1929); 25, 305 (1935). Lewis, J . Chem. SOC.,1927, 1555; 1929, 759. Noerdlinger, Be?., 19, 1893 (1886). Strong, Brown Univ., doctor’s thesis, May, 1940 PRBSENTED a s part of t h e Symposium on Electrical Insulation Materials before t h e Division of Industrial a n d Engineering Chemistry a t t h e 102nd K SOCIETY, Atlantic City, N. J. Meeting of the A l ~ ~ l c lCHEMICAL
