Oil Exudation Property of Asphalts E. c. KPU'OWLES AND F. c. MCCOY The Texas Company, Beacon, N . Y .
H. E. SCHWEYER'
AND
c. E. WILKINSON
The Texas Company, Port Neches, Tex. T h e tendency for asphalts to exude oil under suitable conditions has a number of practical aspects-fnr example, in the manufacture of roofing and laminated paper, where undesirable staining may occur. A n accelerated test of considerable flexibility has been developed for measuring this property. The effects of time, temperature, and pressure are considered, as well as the effect of crude source and variations in method of manufacture. Constructional details of the required apparatus are shown.
T
HE Texas Company has included in its asphalt research
work a study of the basic phenomenon of oil exudation, a phenomenon which is exhibited by all asphalts to varying degrees if suitable conditions are present. This property has practical significance for certain applications of asphalt as, for example, its use as a plying adhesive in the manufacture of moisture-resistant wrapping paper. The paper industry has developed a method for testing the tendency of asphalt-laminated baling paper to stain the contents of cases or bundles about which it is wrapped (3). This procedure is applicable, however, to bonded paper rather than to asphalt itself. Staining tendencies may also be important when asphalts are used in felt-base floor coverings and in the coating layer applied to roofing products. In some applications, such as moistureproofed paper bags, the quantity of oil exuded is of primary importance in relation to the undesired effect, discoloration of the paper. In a painted floor covering, the undesired effect on the protective paint coating may include a softening of the paint film, in addition to a discoloring effect. The degree of softening may vary with the chemical nature as well as the amount of the oily components. The purpose of the present study has been to determine the relationship of the oil-exudation property of asphalts to time and temperature as well as to physical properties, type of processing, and type of crude from which the asphalt is made. Determination of the chemical nature of the exuded oil is outside the scope of this investigation. In carrying out this study a test method was used which would give quantitative results when applied to a wide range of asphalts under uniform test conditions. The method of Schweyer and Howell (9) involving the use of a packet of cigaret papers and the method of Pfeiffer and Saal (1) utilizing adsorbant powder are the only procedures for measurPresent addreas, University of Florida, Gainesville, FIa.
ing the staining properties of asphalt which have been published heretofore. Sohweyer and Howell state that their method of applying pressure on the test specimen by means of a weight was not entirely satisfactory. Furthermore, the procedure is not applicable to the softer asphalts, the results are only semiquantitative, and the test duration of 5 days is longer than desirable, particularly for practical use-for example, in plant control. The method of Pfeiffer and Saal, although ingenious, is not suitable for wide application because of the time involved (10 days), and the necessity for careful extraction of the adsorbant powder employed in the test. EXPERIMENTAL
APPARATUS. In spite of its limitations, the Schweyer and Howell method provided the basis for satisfactory measurement of the exudation property. Thus, by retaining the use of layers of cigaret paper as an oil-absorption medium and utilizing gas as the means of applying pressure, the apparatus in Figure 1 was designed. Constructional details are shown in Figure 2, and a completely assembled mold is shown in Figure 3. Buxiliary equipment not shown in either the photograph or the drawings includes the following:
A thermostatically controlled oven of suitable temperature range. .4 source of gas pressure (compressed air or nitrogen). A 10-inch adjustable wrench and a small spring scale (0 to 15 pounds). Washington grade cigaret paper made by P. J. Schweitzer, Inc., Elizabeth, N. J. Specifications for this paper were outlined by Schweyer and Howell ( 8 ) . Other grades and types of paper may give entirely different results from those reported in this paper. PREPARATIOV OF SAMPLES.Place the center section of the stain test mold on an amalgamated brass plate with the smaller end down, and pour a sample of the molten as halt into the mold until it is about half full. When the asphalt [as cooled to room t e m p e r a t u r e , remove the mold from a m a l g a m a t e d plate, and trim the asphalt sample in a concave manner with the heated end of a spatula to such a depth that the asphalt surface does not come in contact with the first layer of paper when apparatus is assembled and tightened. After trimmin , remove all traces of asphsjft frpm the flat end of the center piece. These precautions are taken to prevent tearing of the test paper by contact with the asphalt and also to obtain a fresh clean sample surface for the test. PREPARATION OF PAPER. Place 30 sheets of cigaret paper between two pieces of white blotting paper of the Figure 1. Gas Pressure Asphalt Stain Test Apparatus same size. Every fifth sheet 2340
November 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
2341
--4
5 - Spacer at 2"
SIDE ELEVATION
Figure 2. Construction Details of Stain Test Apparatus
may be marked with a light pencil line to facilitate counting at the end of the test. Cut cylindrical sections, consisting of 30 pieces of cigaret paper, sandwiched between two pieces of blotting paper of the same size, using a No. 13 cork borer. MOLDASSEMBLY.The top section of the mold (Figure 2) is usually attached permanently to the ressure vessel. Press the copper asket (Figure 2) in place in t i e to section. Screw the end of t f e center section o posite the sampfe tightly into the top section. Place the two 8 s k s of blotting paper in the bottom section of the mold and the 30 disks of tissue paper on top of them. Sorew the bottom section against the center section in which the sample is contained, to a tension of 5 ounds. This is done by first turning the piece loosely by han8, then tightening with a wrench. The force is applied through a scale hooked to the end of the wrench until the tension reaches 5 pounds in order to ensure uniformity in pressure between the paper disks. A torque-wrench would be equally satisfactory; the applied torque should be approximately 4 foot-pounds. TESTPROCEDURE. When all six molds have beet roper1 assembled, place the pressure vessel in an oven a t 79.4 (175'F.), and connect the gas pressure line-air or nitrogen-to the pressure vessel. Ad'ust the pressure to 50 pounds per square inch gage and allow the test to proceed under these conditions for 48 hours. Remove the molds and make the stain test observations by counting the number of tissue paper disks which show oil stain, excluding the first paper which is stained in all cases. The resultant number is designated as the stain index of the asphalt sample. Each set of papers may be pasted in a book and identified for future reference if desired.
&.
The temperature and time shown in the procedure are suitable for asphalts having a ring and ball (R and B) softening point of 66.6' C. (150' F.) or higher, which includes a majority of the asphalts of practical interest in connection with staining. Temperature, time, and pressure may be varied if it is desired to test softer asphalts; however, stain indexes on different asphalts should
be compared with each other only on the basis of identical test conditions. Table I illustrates the consistency of the proposed method.
TABLE I. CONSISTENCY OF TESTR~SIJLTS Nature of Aaphalt Vacuum reduced flux 2 Air-blown flux 2 Air-blown residue
X Y Y
Softening Point Stain Index (RandB), O F. Detn. 1 Detn. 2 Detn. 3' 150
163 149 151 170
0 2
6 9
13
0 2
0 1
6 9
6 11
13
..
These results were obtained during the early stages of t>he investigation a t a time when the test conditions were 54.4" C. (130' Fa),50 pounds per square inch pressure, and 72 hours, instead of the standard conditions which are given in the section on Test Procedure (these conditions were adopted later to permit more rapid determinations). However, subsequent tests under standard conditions have confirmed the consistency of the results. COMPARISON O F GAS PRESSURE AND SCHWEYER-HOWELL STAIN TEST METHODS
Because a number of laboratories are currently using the Schweyer-Howell method for determining staining properties of asphalts, a direct comparison of this procedure with the proposed method is given in the following table:
INDUSTRIAL AND ENGINEERING CHEMISTRY
2342
Nature of Asphalt Air-blown residue AA
T RR T
Softening Point (Rand B)
Stain Index Sohweyer and Howell method
* F.
Penetration at 77* F.
Gas pressure method
219 217 210 178
22 16 9 14
22 13 8 4
4 2
1
1
It will be observed that both methods rate the 6rat three asphalts in the same order. However, the proposed method permits adistinction between thelast two asphalts while the SchweyerHowell method does not. Also, the wider spread provided by the proposed method is advantageous, perticularly in research work.
Vol. 42, No. 11
following the dotted line in Figure 6 to the 200' F. curve, up to the 50-pounds-per-square-inch pressure curve, across to the 24hour curve, and then down to the new stain index axis, it is found that the stain index is also 13 under the new conditions (200' F., 50 pounds per square inch pwsure, and 24 hours). Similarly, suppose the stain index is 18 at 72 hours, 25 pounds per square inch pressure, and 200' F. By following the dotted line from the new stain index axis up to the 72hour curve, across to the 2 5 pound-per-square-inch pressure curve, down to the 200' F. curve, and then across to the stain index axis, it is found that the stain index under standard conditions is 11.
INFLUENCE OF TEST CONDITIONS
Before using the proposed test as a research tool it was necessary to study its sensitivity to variations in time, temperature, and preasure. Figure 4 shows the effect of time and, as would be expected, the rate of increm of the stain index decreases TOP SECTION in a uniform manner because the oil must travel further and further from its source as the stain index increases. CENTER SECTION T h e s e t ime-s t s i n index ASPHALT SAMPLE curves are similar to those obtained by Schweyer and SURFACE Howell (8). Figure 5 shows the effect CIGARET PAPER of temperature and indicates t h e s t a i n i n d e x increases BOTTOM SECTION roughly linearly with temperature, and that the temperature must be accurately Figure3. Stain Teat Mold controlled. Some asphalts Assembled are more susceptible than others to the influence of temperature. Undoubtedly part of this effect is due to the influence of temperature on the viscosity of the oil contained in the asphalt. The effect of pressure was studied over a range which was considered practical. and safe. The results are shown below: Stain Index (175" F. and 48 Hours) 60
Asphalt A (air-blown 278 penetration flux) Asphalt B air-blown 55 penetration SR a s p d t )
P-
ASPHALT '8' 77.C1-(116
( I 4 PENat
T I ME
- HOURS
Figure 4. Effect of Time on Asphalt Stain Index 175'
P.1 50 pounds per square inah pressure
The following tabulation illustrates the degree of agreement between observed stain index values and those estimated from the chart: 175' F., 50 Lb.1 Sq. Inch, 48 Hours, Observed
Asphalt
E F
200' F., 50 Lb./Sq.
Inch. 24
Estimated
Observed
24
23 19 11 14
22 18 11 16
G
H
19
11 16
These relationships are presented principally to illustrate the versatility of the new method and its adaptability as a quantitative research tool to a wide variety of conditions. 30
"1
ASPHALT '0" IeSPENat 77.F.-QOP*IE8I)L/
100.
Ib./sq. inch
lb./sq. inch
22
28
11
16
These results indicate that pressure is a sufficiently important factor to require rewnable control. The increase in stain index with pressure is presumably due to the closer contact between the paper disks, thus making easier the flow of oil from one paper disk to another. CONVERSION OF DATA. The smoothness of the curves and thc general regularity of the data suggest that a definite relationship may exist between stain indexes obtained on the same asphalt under two different sets of conditions. This hae been found to he the case. A correlation of the type illustrated in Figure 6 has been c l s t h lished; this correlation makes it possible % predict thc stain indexes obtainable over a range of test conditions by determining stain index a t a given set of conditions. For instance, suppose the stain index at 175' F. and 50 pounds per square inch for 48 hours (standard conditions) is 13. By
I
120
.
l
140
f
i
160 "
1
180 "
'
200
TEMPERATURE *E
Figure 5. Effect of Temperature on Asphalt Stain Index 72 houra; 50 pounds per square inch prcaaun
The method under investigation satisfied the essential requirements set up in that it gave a quantitative measure of the oil exudation property in areasonably short test time. The next step was the application of the method to various types of asphalts which were known from experience to be good or poor in regard to staining. EFFECT OF TYPEOF PRomssIm. A measure of the merit of this test is whether it can be used for control of quality in plant
November lss0
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
2343
For esample, comparing series I and 11, it is evident that steam-rcdured asphalts of a given penetration from a certain crude source have better staining properties than comparable airblown asphalts. The data from series I11 indicate that the further an asphalt is steam reduced before air blowing, the better will be the staining properties of the blown product. This effect is probably related to the removal of oily constituents during steam reduction. The improvement in staining propcrties of asphalt S over asphalt Q might appear to bc due in part to the inrrew.qrxd hardness of the former. IIow( v r , the results of series I show thttt increased hardness in a series of airblown asphalts does not result in better staining characteristics; in fact, the opposite is true. The reverse trend in the c case of series I11 must therefore be asI 1 I I I 0 0 8 I6 24 32 sociated with the increasing degree of STAIN INDEX ATOTHER CONDITIONS steam reduction of the charge prior to Figure 6. Effect of Varying Conditions of Stain Test air blowing. These conclusions arc i l l general agreement with the earlier firidings of Schweyer and Howell as regard.: scale asphalt manufacture. Table I1 shows the effect of differe%ct of processing conditions on staining propertie6 nlenws in proceasing methods 9n the staining tendencies of a group though the present method permits a better differentiation I)(,tween good and poor stain characteristics. of asphalts. It has long been known from exEFFECT OF CRUDESOURCE. These results illustrate clearly the effect which method of perience that asphalts from certain crude sources are less suscrpprocessing has on the oil exudation property of asphalts. Contible to stain formation than others. This factor, which is also versely, the proper choice of processing conditions is an important essoc-iittrd with product quality control, was studied by running step in producing nonstaining asphalts. stain tests on a ZrouD of asDhalts of about the same penetration from a number of differentbrudes. Product8 representing both air blowing a6d steam reduction were included. Results are TABLE11. EFFECTOF PROCESSING VARIABLES ON STAININQ shown in Table 111. PROPERTY OF ASPHALTSFROM A SINQLE~ CRUDE The data illustrate the importance of crude source selection in so+ producing asphalts having good resistance to staining. Because emng PenePoint tration physical properties were held reasonably constant, variations in (Rand E), at Stain Aephalt O F. 77' F. Index= the Composition of the asphalt must play a significant role in determining their oil exudation characteristics. Scriea I. Air Blowing (from 188 Penetration at 77' F. Residue)
- -
I J K
L
143
60 31 25
174
193 218
IS
8
14
17
IS
Series 11. Steam Reduction (from 248 Penetration at 77' F. Flux) M 133 48 4
N 0 P
138 145 160
41
31 20
&nea 111. Steam Reduction and Air Blowing (from 278 penetration a t 77O E.) 217 21 (from 167 penetration a t 77" F 214 1s S (from 66 penetration at 77* F:] 215 14
8
Q
175'
5 5 4
22 18 11
F.; 50 pounds per square inch pressure,48 hours.
Air-blown residue Souroe T Source U Source V Souroe W Bouroe X Steam reduced residuum Source T Source W Source X
ening Point (R and B), F.
Penetration at 77O F.
Stain Index'
164
25 28 25 23 31
6 12 15 b 14
22 37
2 3 6
167 164 166 174
145
140 145
A simple and rapid procedure has been developed for meusuririg in a numerically relative manner the staining properties of asphalts in terms of the amount of oil exuded under given conditions. The method is consistent and can be adapted to the tcstin$ of a wide variety of asphalts. It may have considerable utility in studying the effect of crude source, processingnlothods, and chemical composition on asphalt-stalnmg properties. The procedure should also be useful to asphalt manufacturers for controlling and maintaining product quality. ACKNOWLEDGMENT
TABLE 111. EFFECT OF CRUDESOURCE ON OILEXUDATION Soft-
SUMMARY
31
* 175O F.; 60 pounds per squate inch prwure, 48 hours.
The authors wish to acknowledge the helpful advice of It. N. Trader of the Port Neahes Lntmratory of The Texas Company in preparing this paper. They also wish to acknowledge the assistance of Homer Lehn and J. W. Romberg of the same laboratory who made many of the stain test deternunations. LITERATURE CITED
(1) Pfeiffer, J. P., and Sad, R.N., J . PILUS. Chom., 44, 147 (1940). (2) Sohwoyer, H. E., and Howell, R. C.,IND. ENG.CFIIPM., ANAL.ED., 9,663(1937). '(3) TAPPI, Paper Trade J., 122, No. 24,33 (1946). RECEIVED December 9, 1949. Presented before the Division of Petroleum SOCIETY, Ssn Chemistry a t the 116th Meeting of the AMBRIOANCHEMICAL
