Symposium presented before the Dwision of Petroleum Chemistry a t the
Asphalt and Its Constituents O x i d a t i o n at Service R. R. THURSTON AND E. C. ICNOWLES
Temperatures
The Texas Company, Beacon, N. Y ,
recognizable signs of deterioration of asphalt surfaces as loss of luster, dusting of surface, loss of adhesion, and increase of surface hardness, i t is apparent that photooxidation is a n important factor in causing failure of asphalt products-i. e., road surfacing material, roofing products, asphalt-painted surfaces, etc. In this photooxidizing action of an asphalt surface, it would be of interest to know how the different constituents of asphalt react, particularly in view of the complex nature of asphalt. Accordingly, the purpose of the present work has been to investigate the photooxidation sensitivity of constituents which are commonly known to be present in asphalt.
Under weathering conditions asphalt surfaces undergo oxidation. This photooxidation property of asphalt and its constituents has been studied by exposing samples in oxygen-filled sealed Pyrex containers under a sun lamp at temperatures approximating 170' F. (77' C.). The constituents, identified as asphaltenes, resins, naphthene oil, paraffin oil, and wax, were obtained from three typical petroleum residua. All constituents absorbed oxygen, the resin and naphthene oil being a little more readily oxidized. Constituent source was also a factor. Part of the used oxygen was eliminated as water and carbon dioxide, and all residues showed weight increase. The method is applicable to paving and roofing asphalts.
Sources of Asphalts and Constituents In the work previously reported, a Mexican asphalt of 238 penetration a t 77" F. (25" C.) was separated into constituents by the method of Marcusson ( b ) , and the oxidation reactions of the asphaltene, asphaltic resin, petroleum resin, and oil constituents were investigated a t high temperatures. In the present work asphalt was separated into five constituents by a method developed in this laboratory. I n this procedure the asphaltenes were obtained by use of pentane, the resin was obtained by use of propane, the wax was obtained by use of a methyl ethyl ketone-benzene solution, and the paraffinic and naphthenic oil constituents were obtained by extraction of the oil constituent with acetone in an equilibrium extraction tower, which was a modification of the type used by Cannon and Fenske (3). Extensive tests on these constituents show that they represent characteristic fractions of an asphalt. The yields and some tests on the constituentsfrom Mexican asphalt of 257 penetration at 77" F. are given in Table I. The types of petroleum residua which have been used as a source of the constituents for this work are as follows: 1. Mexican asphalt of 257 penetration at 77" F. from atmospheric steam reduction of heavy Mexican crude (Table I). 2. Residuum of 76-second Saybolt Furol viscosity at 210" F. from atmospheric and vacuum shell still reduction of Gulf Coastal crude. 3. Residuum of 407-second Saybolt Furol viscosity at 210" F. from reduction of a mid-continent crude in a vacuum tube still.
PREVIOUS paper (7) from this laboratory reported A work on the oxidation of asphalt and its constituents, where the temperature of the oxidation test was comparable to temperatures employed in the commercial airblowing process-namely, in the range 400-500" F. (204260 C.). However, it is well known ( 1 ) that asphalt surfaces will undergo oxidation a t much lower temperatures, particularly when the surface is exposed to sunlight. Since the sunlight is essential in causing appreciable oxidation in the service temperature range, the action will be termed a "photooxidation process" to distinguish i t from the thermal type of oxidation obtained in the previous work. The occurrence and effect of this photooxidizing action can readily be shown by exposing an asphalt-coated panel to ultraviolet radiations and subsequently soaking the panel in warm water. The asphalt surface will become dull and frequently will be covered with a yellowish to brown chalky film. If the water layer is evaporated to dryness, a dark colored, resinlike acidic residue can be recovered (6). These results show that oxygenated products are formed which are partially water soluble. Since the formation of these oxygenated products is responsible for such easily
Measurement of Photooxidation The development of equipment and procedure suitable for use in studying oxidation properties of asphalt constituents under ultraviolet light exposure presented numerous 320
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100th Meeting of the American Chemical Society, Detroit, Mich.
To obtain appreciable oxidation results in a reasonable time, the range 140-185' F. (60-85' C.) was used. Such temperatures are commonly reached on road surfaces and roofs during the heat of midsummer days. Furthermore, comparative tests showed that the oxidation in this temperature range is primarily due to the photocatalytic effect of the ultraviolet light. This fact was demonstrated by parallel tests on shielded and exposed asphalt samples (1 gram each) in which the former absorbed 6 ml. while the latter absorbed 26 ml. of oxygen. These results show that thermal oxidation accounts for about one fourth of the total oxygen consumed under the above conditions. However, some information on the effect of temperature on the rate of the photooxidation of an asphalt surface is considered desirable, and work along this line is under consideration for future investigation.
problems arising from the fact that the consistency of the constituents ranged from the liquid oils to the solid asphaltenes. It was also desirable to supplement quantitative oxygen absorption measurements with data on the associated changes, such as increase in saponifiable components, formation of water-soluble material, increase in molecular weight, formation of asphaltenes and resins, and study of volatile oxidation products such as water, carbon dioxide, and acids. To obtain this type of information, considerable preliminary work on the development of equipment and procedure was necessary. TABLEI. CONSTITUENTS FROM MEXICAN ASPHALT
Yield % C-H iatio Mol. weight Softening point, F. ( 0 C.). Kinematic visoositv. -. centistokes 210' F. (98.9O C . ) looo F. (37.8' C.) Viscosity-gr.d constant
Asphaltene 25 10.7 1800a Deoomposes Solid Solid
....
Naphthenic Oil 26 7.7 390b Liquid
Resin 25 8.46 12156 147 (03.9)
. ..
Semisolid
...
Paraffinio Oil 21.5 6.87 730b Liquid
Wax 1.3
6.32
First Oxygen Absorption Method
825b 122
Since the weathering of asphalt surfaces is substantially a surface phenomena, it was considered essential that a test of this type should be based on the exposure of relatively thin films of material. I n view of the wide range in consistency of the asphalt constituents, the use of a suitable type of exposure chamber is important and, a t the same time, a difficult phase of the work.
(50)
18 468
87 2300
37 Solid
0.935
0 864
0.812
* Determined in camphor by freezing point method.
Determined in benzene bv freesinz ooint method. Ball and ring method. Viscosity-gravity constant = [U 0.24 0.022 log (V' 35.5)]/0.765 where V' = Saybolt Universal viscosity at 210' F. and G = sp. gr. at 60° F: (15 6' C.) (4). b
c d
I _
-
-
-
TABLE11. EFFECTOF RADIATIONS FROM MAZDA S-1 BULBS ON OXALIC ACID-URANYL SULFATE SOLUTION
ULTRAVIOLET LIGHT SOURCE. Consideration was given to several sources of ultraviolet light, and for preliminary work a Mazda S-1 sun lamp was selected. I n the initial tests to determine the suitability of this light source, an asphalt-coated panel was exposed a t a distance of 15 inches from the light. A marked photooxidation effect on the asphalt surface was noted after 34 hours. Similar tests on the constituents showed an appreciable oxygen absorption in a reasonable time. The possibility that the intensity of the ultraviolet light from this source might change with the life of the bulb and with different bulbs was considered, and tests were made to check this point. For this purpose the oxalic acid-uranyl sulfate method described by Anderson and Robinson (2) was used to test one of the Mazda S-1 bulbs over a period of 567 hours of continuous burning. Tests were also made on three different bulbs. The data are given in Table 11, and were obtained by exposing a known volume of the oxalic aciduranyl sulfate solution in a glass cell with a Corex D glass cover. The light was rotated a t 3 r. p. m. in a 13-inch (33cm.) diameter circle, 3 inches (7.6 om.) above the top of the cell The temperature was approximately 140' F. (60' C.). On the basis of the weight of oxalic acid decomposed in each of these tests, the fluctuations in ultraviolet light intensity were considered to be within limits required for this work. PHOTOOXIDATION TEMPERATURE. The effect of temperature on the rate of the photooxidation of asphalt surfaces must be very marked. However, this factor was not studied in this investigation. 321
Mazda 9-1 Bulb No.
2 3
Total Burning Time When Tested, Hr.
56 Not known Not known Not known
Exposure Period, Hr.
Oxalic Acid Decomposed, hlg
12 12 12 12
49 40 50 46
Two methods were considered in preparing the constituents for the exposure test-namely, mixing the material with an inert supporting medium such as sand, glass wool, etc., or spreading the material in films on horizontally placed light weight trays. Since the use of sample trays facilitated the determination on the gain in weight of the sample, recovery of material for further tests, visual observation, etc., this procedure was selected for use in initial work. I n the first procedure the constituents were weighed on round aluminum trays which, in turn, were placed in steel containers with Corex D glass covers for the exposure period. However, this method was not satisfactory because of the difficulty of maintaining the steel vessel gastight during the exposure period and t o the tendency of the steel to rust. I n further development work the constituents were placed in narrow rectangular aluminum trays which, in turn, were sealed in Pyrex glass tubes. This procedure solved the problem of gas leaks and facilitated the determination of water
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INDUSTRIAL AND ENGINEERING CHEMISTRY
The absorption tube was connected with conventional water and carbon dioxide absorption tubes, and a slow stream of oxygen assed through until a constant weight in the water and carbon ioxide tubes was obtained. The sam le absorption tube was then opened and the sample tray removegfor weighing,
si'
The data obtained by the foregoing procedure on the constituents from Gulf Coastal residuum (76-second Furol viscosity a t 210' F.) are given in Table 111. The data show that each constituent exhibits an appreciable oxygen absorption rate under the conditions of the test. The naphthenic oil appears to be somewhat more readily oxidized than the other constituents. The oxidation of the asphaltene fraction may be influenced somewhat by the fact that it was tested in the form of a powder passing a 200-mesh sieve, whereas the other samples were distributed as a continuous film. However, there are no definite indications that the consistency of the samples was a factor in determining the volume of oxygen consumed.
TABLE
111. PHOTOOXIDATION CHARACTERISTICS ENTS FROM
FIGURE 1. OXYGENABSORPTION EQUIPMENT FOR METHODI
and carbon dioxide, The drop in oxygen pressure which occurs in this method is an undesirable feature. Figure 1 shows the glass tubes with sealed-in sample trays and the arrangement of the test samples during the exposure period. The samples were exposed under the Mazda S-1 sun lamp for 24 hours, and the volume of oxygen used was determined by drop in pressure, followed by determination of the water and carbon dioxide, and finally by the change in weight of sample. The constituents from the Gulf Coastal residuum were studied by this method according to the following experiniental procedure: A 1-gram sample of the constituent was weighed into the aluminum tray, 5 X 3/4 X l/8 inch (127 X 1.9 X.0.317 mm.), and spread in a uniform film by warming and tilting the tray. The asphaltenes were tested in the form of a 200-mesh powder. The trays plus sample were placed in the Pyrex absorption tubes and were kept in a horizontal position by indentations along the side of the tube. The open end of the tube was then sealed about 5 inches (12.7 om.) beyond the end of the tray, using an oxygen flame in such a manner that the sample was not heated. The volume of the absorption tube was then determined by attachin one of the side arms t o a mercury-filled buret and leveling %ulb. Several volume-pressure readings were taken, and the volume of the tube was calculated with the aid of the gas equation. The volumes of the different tubes varied from 90 to 105 ml. The absorption tube was then filled with oxygen by alternately evacuating gas and admitting oxygen. The side arms of the tube were then sealed and the barometertemperature readings recorded, from which the initial volume of oxygen could be calculated. The absorption tubes were attached to a wooden block and placed under the Mazda S-1 sun lamp accordin to the arrangement shown in Figure 1. The light was rotate3 at 3 r. p. m. in a 5-inch-diameter circle. Inasmuch as the samples were not symmetrically placed (Figure l), they were moved forward one position each 8 hours. The exposure was continued for 24 hours with the temperature averaging around 185" F. (85" C.). The absorption tubes were then brought to room temperature and attached to the buret, again using a short piece of rubber tubing. The tip of the side arm was then broken in the rubber tubing, and from the volume-pressure reading the volume of the gas in the tube was calculated. A comparison with the initial volume of oxygen gave the net volume of oxygen absorbed.
Material Sample wt.. grams Oxygen used Vol., ml. % by wt. (baeis sample) Gainin wt ofsample 70 Distribution of used 'OXYgens % Absorbed by Sam le Recovered a8 H s 8 Recovered a6 COS
OF CONSTITU-
GULFCOASTAL RESIDUUM
Asphaltene 1.008
21.0 3 1.7
NaphResin 1.031
23.5 3.2 1.8
56 35
50 38
9
- 10
100
98
-
thenio Paraffinic Oil Oil 1.003 1.006
36.6
5.2 2.2 42 35
11 88
23.0 3.2 1.5 48 33 13 94
-
Wax 1.026 23.5 3.4
.. . ...
...
I..
The data on the distribution of used oxygen show that approximately half represents an increase in weight of the sample while one third is eliminated as water and 10-16 per cent as carbon dioxide. The distribution of the used oxygen is substantially the same for each constituent, despite the wide range in the physical character of each. In each test a trace of condensable material other than water collected on the cooler part of the Pyrex tube, but this material was not present in sufficient quantity to investigate its character. I n view of the failure to obtain more significant differences in the photooxidation sensitivity of the constituents and the difficulty of keeping the sample trays level, a further modification of the procedure was considered desirable, particularly as regards the method of obtaining a uniform film of material.
Second Oxygen Absorption Method I n the first method the asphalt constituents were spread over a horizontal surface of known and constant area, and in the case of liquid materials the problem was to keep the absorption vessels level so that the material remains evenly distributed. To overcome this trouble, an inert supporting material was employed-i. e., a uniform sand which had been purified and ignited This was similar to the A. S. T. M. sand used in our previous work ( 7 ) . The method has the disadvantage that the gain in weight of sample cannot be accurately determined, and it is necessary to extract the material from the sand if it is to be used for further examination. Employing this procedure, the constituent was mixed with the sand in a 125-ml. Pyrex Erlenmeyer flask, and the sample exposed under the Maeda S-1 sun lamp. A diagram of this equipment is shown in Figure 2, and the procedure is given herewith.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
March, 1941
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323
A 125-ml. Pyrex Erlenmeyer flask was modified by sealing on two side arms, one near the bottom and one near the top on the opposite side. A longer neck (approximately 2 inches or 6 om.) waa also sealed on the flask. One gram of the constituent was then weighed into the flask with 25 grams of urified sand ("Sand Purified", a commercial product). The flmf and contents were then warmed on a mercury bath to 250" F. (121' C.), and the sample was thorou hly mixed with the sand by means of a glass stirring rod. %are was taken that the sand mix was kept near the bottom and not allowed to become scattered promiscuously on the sides of the flask. The coated sand was then leveled off on the bottom of the flask. The stirrin rod was cut at its mid-point, and the bottom part left in the fla& The elongated neck of the flask was sealed with an oxygen flame. The method of measuring the volume of the flask and filling with oxy en was the same as that described under method I. Six of these &sks were then placed in an &inch (20.3cm.) diameter circle under a Maada S-1 sun lam hanging stationary 5 inches (12.7 om.) from the base on whic! the samples were placed. The samples were exposed 55 hours at temperatures ranging from 165-180 F. (73.9-82.2' C. . The steps after the exposure period were the same as those fo lowed under method I, except that the water and carbon dioxide were not determined.
1
The results showing the photooxidation characteristics of the constituents from three sources of residua which are commonly used in asphalt manufacture are given in Table IV. These data show the net oxygen consumption as calculated from the drop in pressure of the reaction flask. The results do not take into account the presence of carbon dioxide gas or water vapor. The presence of water and the characteristic odor of oxidation products were observed in each test. TABLEIV. PHOTOOXIDATION CHARACTERISTICS OF ASPHALT CONSTITUENTS ON THE BASISOF METHOD 2
Constituent Asphaltene Resin Naphthanic,oil Paraffinic of %&a1
residuum
Net Vol. Oz Absorbed per Gram, Based on Pressure Drop after 56 Hr.. M1. Gulf MidMexican oontinent ooaatal asphalt residuum residuum 44 41 36 66 56 40 64 61 44 63 49 32 48 51 30 65 53 a9
Discussion of Results The data in Table IV show again that each of the asphalt constituents is susceptible to oxidation when exposed in an oxygen atmosphere t o ultraviolet light. While the resin and naphthenic oil appear to be somewhat more susceptible to oxidation than the asphaltene, paraffinic oil, or wax constituents, the difference is not so great as might be expected on the basis of their differences in physical properties. The data also show that the crude source affects the photooxidation sensitivity of both a residuum and its constituents. For example, the Gulf Coastal residuum and its constituents are more resistant to photooxidation than Mexican or midcontinent residua or the respective constituents. This difference is undoubtedly due to such factors as molecular structure, ultimate composition, and ratio of constituents. Although asphalt residua from different crude sources do show variations in photooxidation sensitivity, these data should not be considered as a sole criterion of the quality of the asphalts from the above sources, since other factors (i. e., processing methods, initial physical properties, application methods, etc.) play important roles in determining the service characteristics of asphalt products. The ratio of oxygen eliminated as water and carbon dioxide to the total volume consumed would be affected by the temperature; thus, the amount of oxygen eliminated as water and carbon dioxide would be expected to be much lower under average weathering conditions where the temperature
FOR METHOD I1 FIGURE 2. OXYGENABSORPTION EQUIPMEINT
is appreciably below the 140-185' F. (60-85' C.) range used in this work. Further information regarding the effect of temperature on the stability of the oxygenated products is available from a comparison of the present results with the thermal-oxidation data (7) obtained a t 392" F. (200' C.). I n the oxidation tests at this temperature each of the constituents except the asphaltenes showed a loss in weight of the sample due to the elimination of water, carbon dioxide, and volatile oxidation products; i. e., approximately 80 per cent of the total oxygen consumed was eliminated as water and carbon dioxide. A further comparison of the present results with the previous thermal oxidation results is difficult owing to the fact that the constituents used in the two investigations, with the exception of the asphaltenes, are not analogous; i. e., the "oil constituent'' used in the previous work is substantially represented by the paraffinic oil, naphthenic oil, and wax constituents of the present work. The asphaltenes represent substantially the same material in both investigations; t h a t the asphaltenes were so readily oxidized in the previous work at 392' F. may be explained on the basis that partial decomposition may have occurred in the thermal oxidation work.
Conclusions The present results are incomplete, particularly in regard
to information relative to the changes in the asphalt or constituents which accompany the photooxidizing action, and the effect of temperature on the rate of the photooxidiaing action. However, the data are significant in showing that all of the constituents normally present in an asphalt are susceptible to photooxidation; while the resistance to this action may be increased somewhat by selection of asphalt source, i t is much more important to protect an asphalt surface, as far as possible, from exposure to sunlight. This protection is equally important in road-surfacing materials, roll roofing, shingle products, built-up roofs, etc., and can b e
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INDUSTRIAL AND ENGINEERING CHEMISTRY
obtained by proper use of gravel or rock chips on the asphalt surface. While the present method and equipment are subject to further changes, particularly in regard to tests at constant pressure and possibly lower temperatures, the general procedure appears to be useful for studying directly an important property of asphaltic products and is to paving and roofing asphalts. Since the photooxidizing action must be closely related to the tendency of asphalts to harden in service, a measureIllentof the type described may be useful in determining the ability of an asphalt to retain its initial physical properties.
Fuel and
Oil for
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Literature Cited (1) Abraham, Herbert, “Asphalts and Allied Substances”. 3rd e d . p. 836, New York, D. Van Nostrand Co., 1930. ( 2 ) Anderson, W. T., Jr., a n d Robinson, F. W., J . Am. Chem. S O C . , 47, 718-25 (1925). ( 3 ) C a n n m M. H.3 and Fenske, M. E., IND.EKG.CHEM.,28, 1035 (1936). (4) Hill, J. B., and Coats, H. B., Ibid., 20, 641-4 (1928). ( 5 ) Marcusson, J., “Die naturliche und kunstlichen Aspilake”, 1931. (6) Strieter, 0. G., a n d Snoke, H. R., J . Research ~Yntl.Bur. Standards, 16,481-5 (1936). (7) Thurston, R. R., and Knoivles, E . IN,,. E ~ G .c H E ~ ~ . 28, , 88 (1936).
c.,
Motor Transport
Future Needs T. A. BOYD General Motors Corporation, Detroit, Mich.
HE first need of the future is an adequate supply of fuel T and oil a t low cost. I n chemistry lies one of the chief reasons why there has never been a gasoline or oil fam-
regular-price gasoline has been boosted from 60 to 75 and more (Q), and there is every prospect that this upward evolution will continue, as economics and advancing technology permit. It is due to these chemistry-aided developments that a fuel and oil famine has not appeared within the past twenty years, while consumption of gasoline has risen fivefold to the immense volume of 500 million barrels a year, or over 20 billion gallons (Figure 1). There now appears to be little prospect of an early failure of petroleum, and a recent government publication (11) concluded that “discovery will continue to meet our national requirements for a considerable period”. If and when petroleum should fail to be adequate, however, chemistry offers the chief assurance that oil and liquid fuels can be produced from other source materials, such a5 coal, oil
ine in this country, as well as one of the principal assurances that there will not be one. I n respect to petroleum as a continuing source of fuel and oil, chemistry contributes in several ways to assurance for the future. It contributes to discovery techniques by assisting in the various scientific methods of finding where oil is located. Scientific exploration accounted for 98 per cent of the new oil pools discovered in 1938 (6). Chemistry contributes through metallurgy, oil well cementing, and the control of drilling muds to drilling successfully to the deep strata in which much petroleum is found. It contributes through the controlled acid treatment of producing formations, one of the manv technological advances by which the amiunt of petroleum from an bil field has been increased, after i t has been located and drilled; in recent years this has sometimes been by more than twofold (21). Chemistry contributes through cracking, polymerization, alkylation, and similar processes, by means of which the amount of crude oil required to make each gallon of gasoline has been practically cut in half during the past twenty years (8). The savings in petroleum required, as made by these improvements, has amounted since 1920 to one third as much as the total world production of crude oil during all the eighty years since 1859 when “Drake’s folly” turned out to be a n oil well. Chemistry contributes also by making the gasolines produced by these processes in such nearly knock-free forms as to Courteau. Yellow Truck and Coach .bfanu/acturing C o m p a n y permit the use of high-efficiency engines LUBRICATING OILS MUSTMEETSEVERE SERYICE CONDITIONS which make each gallon of gasoline go farther. This Diesel- owered motor coach one of a fleet of twenty-one, operates over one of four The chemical-compound, tetraethyllead, also sections of &e route between Chikpo and the Pacific Coast. The mileage covered by the fleet since delivery in June, 1939, is so large as to average for each coach nearly 0.5 mile per has been of considerable assistance in this minute (26.5 miles per hour), countinq no time out day or night. The present schedule ia regard. Since 1930 the octane number of about 22.000 miles per month for each coaoh.
