Development of Acidity in Certain Lubricating Oils on Use or Oxidation A. R. RESCORLA, F. L. CARNAHAN, ANDM.R. FENSKE Petroleum Refining Laboratory, The Pennsylvania State College, State College, Pa.
Increases in viscosity, sludge content, and carbon residue value of lubricating oils subjected to oxidation at elevated temperatures are in many instances accompanied by development of acidity. In such cases the acid content as indicated by an electrometric method is a convenient means of following these changes and of furnishing additional data on the general problem of oil deterioration. Some of the oil samples studied were obtained from engine tests, the remainder from a laboratory oxidation procedure.
method, correlations as shown by the present data are possible.
Analytical Methods The acid contents of oils were determined by an electrometric method previously described (6). Tungsten-platinum electrodes were used together with a vacuum-tube amplifying system and a milliammeter. The oil was dissolved in a mixture composed of equal parts of isoamyl alcohol, benzene, and carbon tetrachloride and saturated with lithium chloride; sodium isoamylate was used as the base. TABLE I. PROPERTIES OF ORJQINAL OILSUSEDIN ENQINE TESTS Oil number
A
LUBRICATING oil undergoes complicated changes when it is subjected to oxidation a t elevated temperatures. Whatever the nature of these changes, they are evidenced by variation in one or more of the following properties: viscosity, carbon residue, sludge content, and acidity. It is not implied that acid formation is either the cause or the effect of the other changes mentioned, but the data presented for the oils studied indicate that the acidity increases in a more or less regular way with these other indications of deterioration. The iron content of these oils in service also rises, but it is difficult to estimate the relative proportions of iron resulting from mechanical abrasion and chemical attack.
Gravity, O A b P . I. Flash p i n t b F, Fire point, F. Pour point, F. Color, A. S,. T. M. Carbon residue Acid number Vlsooslty: Centistokes a t 210' F. Centistokes a t 100' F. Saybolt a t 210OF. Saybolt a t 100' F Viscosity index
2 29.6 415 470 -10
1 28.6 450 506 f30 7 0.60 0.02
-
10 9 99 8 61 6
460 103
3 1/2
0.08 0.08
'
'
5 73 38 1 44 2 178 99
3 29.5
406 465 -5
0.09 31'* 0.08 5 69
36 3
44 0 169 106
4 30 8 425 490 +Z6 4 0 01 0.00
5 80 38 55 44 4 179 6 101
Viscosity was determined by means of modified Ostwald pipets (2); viscosity indexes were calculated using the data of Hersh, Fisher, and Fenske (4). The engine oil samples were not freed of dilution or sludge prior to ascertaining viscosity. Carbon residues were found by the A. S. T. M. method (1). Sludge mas estimated by a procedure developed by this laboratory (3). A photometric analysis (7) for iron was utilized.
Description of Oils Inspection data for the oils used in this investigation are shown in Table I. Oil 1 is a conventionally refined Pennsylvania oil in the S. A. E. 30 range. Oil 2 is a neutral; oil 3 is composed of 95 per cent oil 2 and 5 per cent sperm oil. Oil 4 is an unfiltered Pennsylvania neutral. Engine Tests Oils 1, 2, and 3 were used under carefully controlled conditions (3) in four 1933 Dodge 6-cylinder motors by the Depart40
1
FIGURE 1. RELATION OF SLUDGE CONTENT AND ACIDITYFOR OIL 1 IN SEVERAL ENGINE TESTS
It should not be inferred that the relationships found in the case of these particular oils and conditions are general features for all oils and all types of oxidation treatment. Many exceptions will probably be evident when the problem has been studied more completely. While the data presented here show a reasonable correlation, other results (6) on different types of oil present such exceptions. Undoubtedly correlations of acidity with other properties will be affected by the type of crude and refining methods used to furnish the oil and also by the conditions employed in the oxidation or deterioration of the lubricant. For a given lubricant and test
FIGURE 2. RELATION BETWEEN PER CENTVISCOSITYINCREASE AND ACIDITYOF OIL 1 IN SEVERAL ENQINE TESTS 5 74
DECEMBER 15, 1937
ANALYTICAL EDITION
575
ment of Mechanical Engineering. The engines were operated a t 3250 r. p. m. to deliver 48 brake horsepower. The air-fuel ratio was 14 to 1; a nonleaded gasoline was used. The temperature of the oil entering the bearings was 121.11' C. (250' Fs). Water entered the cooling system a t 71.11' C. (160' F.) and left a t 82.22' C. (18O'F.). Samplesfortesting were removed from the oil circulation line a t regular intervals.
Laboratory Oxidation I n laboratory oxidations, 150 cc. of oil were heated a t 171.69' C. (341' F.) with 5 liters of air per hour passing through it. These conditions are essentially the same as those of the Indiana oxidation test developed by Rogers and Shoemaker (8). However, the procedure was modified in some instances by the presence of copper or other metals. In certain cases also, oxidation inhibitors were added to the oil being tested; the action of these materials will be discussed fully in another publication. During the progress of oxidation, the sludge content, the viscosity (usually taken on desludged oil), and the neutralization number were found.
Results and Discussion ENGINE RUNS. The relation between sludge content and acidity for oil 1, a conventionally refined S. A. E. 30 Pennsylvania oil, is shown in Figure 1. The results are from four different engine test;, in each of which a battery of four engines was run for 24 hours; closer correlation may be obtained if a separate curve is drawn for each test. I n general, lubricating oils increase in viscosity on oxidation, more viscous oils being more susceptible t o this type of deterioration; on the other hand, lighter oils blended from the same stocks tend to form a greater proportion of sludge.
MEUTRALIZATION NUMBER
FIGURE4. IRON CONTENT AND ACIDITY FOR SEVERAL OILS Oils in internal combustion engine service gain a certain amount of iron, most of it probably from abrasion of ferrous surfaces but possibly some from the chemical attack of combustion products or acids in the oil. Though the iron contents of certain oils show a correlation with neutralization numbers, the role of petroleum acids in increasing the amount of iron in crankcase oils is not a t all clearly defined. Some of the available data on acid and iron contents of used oils are presented in Figure 4. LABORATORY OXIDATIOKS.The deterioration of oils is generally accelerated by the presence of copper, other factors being the same. I n regard t o acid content, this circumstance is illustrated by Figure 5 ; the neutralization number for an unfiltered Pennsylvania neutral oil a t the end of 48 hours' oxidation was about three times as great when copper was present.
FIGURE3. ACIDITYAND INCREASE OF CARBON RESIDUE FOR OIL1 IN SEVERAL EKGINETESTS Viscosity increase in oils is probably due t o both sludge formation and polymerization, though the latter process alone results in considerable viscosity increases in certain heavy oils which produce little or no sludge on oxidation. However, for the oils studied in this work, acid formation seems t o be related to viscosity increase as well as to dudging; data for oil 1 are given in Figure 2. When an oil is used in an engine, its carbon residue value increases; this circumstance is probably associated with the formation of sludge, the production of large molecules by polymerization, and the action of high temperatures in certain portions of the motor. Under such conditions that carbon residue value increases, the acid content of an oil frequently becomes larger. I n the present instance, a rather definite relationship exists, as the data of Figure 3 show. The initial carbon residue value for oil 1 as determined by the A. S. T. M. method was 0.6 per cent.
TIME OF OXIDATION, -HOURS
FIGURE5. EFFECTOF COPPER ON ACIDFORMATION
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(2) Cannon, Me R., and Fenske, M. R., Oil Gas J., 33, No. 47, 52 (1935); 34, No. 47, 45 (1936). (3) Everett, H. A., and Stewart, F. C., Penna. State Coll. Eng. Expt. Sta. Ser., Bull. 44 (1935). (4) Hersh, R. E., Fisher, E. K., and Fenske, M. R., IND.ENQ.CHEM., 27, 1441 (1935). (5) Mougey, H. C., paper before Subcommittee I on Corrosion Test for Lubricating Oils, Am. Soc. Testing Materials, Committee D-2, June 28, 1937, on “Tests to Determine the Corrosive Properties of Oils as Related to Bearing Metals.” (6) Rescorla, A. R., Carnahan, F. L,, and Fenske, M. R., Ibid., 9, 505 (1937). (7) Rescorla, A. R., Fry, E. M., and Carnahan, F. L., IND. ENQ. CHEM.,Anal. Ed., 8, 242 (1936). (8) Rogers, T . H., and Shoemaker, B. H., Ibid., 6, 419 (1934).
The authors are very grateful for the technical assistance of
E. K. Fisher, R. H. McCormick, and G. E. Woods in obtaining the data and for the cooperation of H. A. Everett and his associates in the Department of Mechanical Engineering in furnishing test data and oil samples in connection with their investigations on lubricants under service conditions. The work was part of the research program of the Pennsylvmia Grade Crude Oil Association, and is published with its permission and that of the School of Chemistry and Physics of The Pennsylvania State College.
Literature Cited (1) Am. Soo. Testing Materials, Report Committee D-2, Standards on Petroleum Products and Lubricants, p. 61, September, 1936.
RBCEIVED August 12, 1937.
Determination of the Saponification Value of Asphalts and Asphaltic Oils Use of an Improved Titration Flask J. E. FRATIS AND D. H. CONDIT Standard Oil Company of California, San Francisco, Calif.
ethyl alcohol and add 25 cc. of 0.05 N potassium hydroxide in 50 per cent aqueous alcohol. Reflux for 1 hour and transfer while hot to the s ecial titration flask, rinsing the saponifying flask with 10 cc. ofthe 50 er cent benzene-alcohol. (In order t o reduce absorption of carfon dioxide the sample should not be exposed t o the air more than necessary before and after refluxing.) Add 25 cc. of neutral 0.1 M barium chloride solution and 3 cc. of 0.5 per cent phenol-
A simple and rapid method for determining the saponification value of asphalts and asphaltic oils, based upon standard metho d s and the use of a special titration flask,
is described. Data are presented to demonstrate the accuracy and usefulness of the method.
T
H E natural characteristics of asphalts have always been an obstacle to the accurate determinrition of their saponification value. Despite the fact that numerous investigators have contributed to the literature concerned with this subject, the most widely recognized methods fail to give sufficiently rapid and accurate results for control work. Recent investigations in this laboratory have included a study of the saponifiable constituents of asphalt. Among other data to be obtained from a large number of samples was the saponification value. The modified method presented below includes the usual refinements used in conventional methods: (1) the use of benzene-alcohol solutions to give contact during saponification and to prevent hydrolysis (I, 4 ) ; (2) addition of barium or sodium chloride to give a clear aqueous layer ( I , 2) ; and (3) the use of dilute reagents to increase accuracy. A further refinement which the authors have found extremely helpful in obtaining a sharp end point has been the use of a special titration flask (3). The flask is a 250-cc. glassstoppered Erlenmeyer with a horizontal tube approximately 5 mm. in diameter sealed so as to reach one-third around the flask near its bottom (Figure 1). By tilting the flask, the side tube can be filled with the aqueous layer alone, thereby affording a close observation of the end point.
Analytical Method Accurately weigh a 10-gram sample into a 250-cc. alkali-resistant Erlenmeyer flask. Dissolve the sample in 50 cc. of a mixture of 50 per cent benzene and 50 per cent of 95 per cent neutral
.
FIQURBI 1. TITRATION FLASK
