INDUSTRIAL AND ENGINEERING CHEMISTRY
July. 1926
699
Fire-Point Carbon Test' By R. M. Byrd and F. C. Vilbrandt UNIVERSITY OF
NORTH CAROLINA,
C H A P E L HILL,
N.
c
This test, which consiits qf determining the amount of residue formed upon heating oil t o its fire point and diluting the heated oil with gasoline, measures the tendency toward oxidation of lubricating oils. No special or elaborate equipment is needed and its execution is simple and rapid. HE value of any lubricating oil in an internal combustion engine lies in its ability to maintain the proper lubricating film, to resist decomposition by the heat developed from the explosion, and to form very little carbon in the cylinders under normal operating conditions. Accessory manufacturers and automotive engineers point out many reasons, all within the control of the automobile operator, for the excessive carbon formation and for the deterioration of the oil, such as road dust, metal particles, promiscuous use of the choke, too much oil, too rich a gas mixture, etc. Often the other reasons, such as the instability of the oil and its oxidation under high temperatures, are not suspected, the operator accepting whatever mechanical correctives that are available as sufficient to obviate lubricating oil troubles. Stability and ease of oxidation of oils are not only dependent upon the engine in which they are used or upon the conditions under which the engine is operated, but they are also properties of the oils themselves, properties due to the source or nature of the oils. As most oils on the market are claimed to be blends of naphthene and paraffin-base oils, the class differentiation of oils or the identification of the oils according to properties dependent upon their source will be of no value. Any classification according to oxidation or stability therefore must come from some service condition or test simulating the same. All lubricating oils are combustible and are subject to more or less decomposition upon heating, but under the same heating condition the oils will classify themselves according to their ease of oxidation and stability. The selection of the proper lubricating oils to give the best service in internal combustion engines is a difficult task. Many laboratory tests are being used to give information that may predict what may be expected of the oil. Many of the tests now in use, such as gravity, unsaturation, free acid, and Conradson residue test, do not classify the oils according to service demands, while such service-demand tests as viscosity, flash and fire points, and pour and cloud tests, give no information as to the expected life or stability of the oils. The Conradson carbon residue teat, in which the oil is subjected to temperature treatment, is a cracking test. -4s the oil is heated in the absence of readily accessible air until all distillable material has been driven off, this test cannot give oxidation data on the oil. Only under exceptional conditions will an engine performance simulate the conditions called for under the Conradson test but when that occurs mechanical assistance will be needed. No oil is expected to stand up under such conditions, and although the carbon residue test measures the results that can be obtained on heating an oil, little information of determinative value of the actual carbon deposit in the combustion chamber can be expected. The test gives little help toward determining the real carbon-forming properties of an oil, inasmuch as the "carbon" in the internal combustion chamber is the result of oxidation.
T
1 Received
February 5, 1926.
According to Staeger,Z oxidation of lubricating oils is productive of mineral-oil resins, asphaltenes, carbenes and carboids, and asphaltogenic acids, which are supposed to be the precursors of the "carbon" produced in the combustion chamber. Sludge formation in the oil is akin to "carbon" formation in the combustion chamber on the same basis, for the former is oxidative polymerization, in which compounds of high molecular weight are formed under the oxidizing influence of atmospheric oxygen. Any test that will give an index of the oxidative tendency of an oil should be of value in oil testing. Several long-time tests have been proposed for the evaluation of transformer oils, which try to determine the life of these oils, but which also could be applied to automobile lubricating oils for their carbon-forming evaluation. The Kissling coke test3 subjected the oil to a 60-hour heat treatment a t 150" C., followed by a determination of the acids formed by the oxidation, with sodium hydroxide giving the so-called tar figure. A reduction of the temperature to 120" C. with attending increase in time to 70 hours, followed by a determination of the gasoline-insoluble asphaltic matter, was substituted by Kissling as more practical. The Michie test4 subjected the oils for 70 hours in the presence of oxygen a t 150' C., weighing the sludge formed. WatersJ5in his oxidation test maintained a temperature of 250' C. in an elaborate apparatus for 2 hours, then weighed the asphaltic matter precipitated when this treated oil was diluted with petroleum ether. The life test6 consisted of subjecting the oil a t 120" C. in a special apparatus until sludge formed, the time required for the appearance of the sludge being taken as the life of the transformer oil. Staegerz claimed that these tests show no absolute relationship and therefore proposed the BBC test, in which the oil is heated in a copper vessel at 112' C. for 300 hours. The variations in time and temperature in the foregoing tests are marked. Not all the temperatures are approximately those to which internal combustion engine lubricants will be subjected, and the time required, with the exception of the Waters test, is prohibitively long. Since oils in internal combustion engines will be subjected to temperatures a t or below 250" C. and gasoline diluting the oils will precipitate the asphaltic matter, which eventually produces the carbon in the combustion chamber, the Waters test was modified and used as the basis for this study. According to Schluter,' the temperature in the internal combustion engine chamber approximates 1000" C. in the center of the explosion. Under ordinary operating conditions the cylinder walls are maintained a t approximately SO" C. by the cooling medium in the water-jacketed motor.
* THISJOURN.AL, 17, 8
1272 (1925). Chem. Zlg.,30, 032 (1906); 31, 328 (1907); 3% 938 (1908); 58, 531
(1909). 4
Pollard-Digby, Report on Switch and Transformer Oils, London,
6
Bur. Standards, Circ. 99, 44 (1920). Proc. A m . SOC.Testrna Malertnls, 24, 954 (1924). Cham. Z t g . , 3 1 , 222 (19131.
19 15. 6
7
INDUSTRIAL Ail-D ENGINEERING CHEMISTRY
700
The thin film of oil stands between these two temperatures, being subjected to temperatures grading from near 1000" C. on the chamber side of the very thin film to near 80" C. on the wall side, these temperatures varying according to the compression in the chamber. The oil on the cylinder head attains a much higher temperature than that on the cylinder walls, the former probably reaching its fire or burning point between 200" and 300" C. This oil in burning gives different oxidation products than is produced by the lower temperature, nonburning oxidation taking place in the oil on the cylinder walls. The two oxidations, together with asphaltic matter precipitated by diluting gasoline, constitute the material in the combustion chamber known as "carbon." Very little is known or agreed upon between the different authorities as to what property of the oil determines its carbon-forming tendencies, so that none of the present lubricating oil tests are accepted as indicative of this property. The authors believe that the measurement of the amount of tarry or asphaltic matter formed when an oil is heated in an open cup tester from room temperature to its fire or burning point, as is done in the flash and fire laboratory test, and subsequently treated with gasoline, will more closely approximate the relative tendency of various oils to produce "carbon" in the internal combustion engine. Method
The flash and fire points of the oil were determined in the new Cleveland open-cup tester, according to the Federal Specifications Board Standard Specifications.* The residual oil was then allowed to cool and diluted with gasoline and the separated asphaltic matter or carbon filtered, washed, and weighed. The tested oils were poured into clean beakers and allowed to stand one hour, diluted with 50 cc. of clean gasoline (88.9 A. P. I.), and filtered in Gooch crucibles fitted with small quantitative filters which had been previously treated with gasoline, dried, and weighed. The asphaltic matter precipitated by the gasoline was then washed with small portions of the gasoline until 250 cc. had been used, then dried a t 105" C., cooled, and weighed. The increase in weight of the crucible is a measure of the asphaltic matter or carbonaceous residue formed during the heating of the oil to its burning point and its subsequent dilution with gasoline. T a b l e I-Analytical
Oil 1 2 3 4 5
GRADS Heavy Heavy Heavy Heavy-medium Heavy-medium Heavy-medium Medium Heavy-medium Heavy-medium Heavy-medium Light Light
6
7
8
9 10 11 12
Gravity a t 20' C. 0.924 0.924 0.884 0.923 0.915 0.902 0,894
0,920 0.903 0.893 0.903 0.925
---Saybolt 100' F . 323 334 861 688 304 334 358 223 272 273 260 271
8
All the oils were first treated with the test gasoline to determine the amount of asphaltic matter originally present. None showed the presence of this carbon-forming material. All the tests to which the oils were subjected, with the exception of the proposed fire-point carbon test and the viscosity a t 180" F. (80" C.) were made according to the methods proposed by the Federal Specifications Board.9 The viscosity a t 180" F. was determined to obtain a threepoint data curve on the drop in viscosity on heating. Under normal operating conditions the motor generally maintains itself a t around 180" F., which is the approximate service temperature of the oil. Moreover, the differences in viscosities of various oils are much larger a t 180" F. than a t 210" F., and evaluations according to viscosities are more easily determined. The data obtained in this investigation have been tabulated in Table I, the figures given being the averages of two or more determinations by each method. Discussion
The data in Table I are arranged according to the grading given the oils by the manufacturers. Owing to this method of classification there appears to be no orderly arrangement of the oils on the basis of any of the general tests made. Since oils are purchased on the basis of "grade," it would be assumed that some one or two of the laboratory tests now used would be a criterion of the grade. This is not so, except with oils made by the same refiner, in which case viscosity data seem to be the best criterion. The adoption of some comparable grading number to be placed on all oils instead of the "heavy, medium, and light" grading a t present indiscriminatingly used, seems desirable. If an oil produces more asphaltic matter or asphaltogenic acids than another under the same heat conditions, that oil must be in a condition capable of this production. On account of the method or heat treatment required for their production, the heavy oils contain more of these potential asphaltic materials than the lighter bodied oils. Should specific treatment be accorded any oil in refining to reduce this asphaltogenic property, that oil should show less asphaltic material in the above laboratory fire-point residue test. In general, the fire-point carbon test shows this asphaltogenic tendency, the values obtained with the heavy oils being higher than those of the medium and lighter grades. In
D a t a o n S o m e L u b r i c a t i n g Oils Free Unsatuacid ration 70 0.1161 9.0 0.1730 4.5 0.1439 4.5 0.3740 12.5 0.0487 12.8 0.1584 7.7 0.1512 7.0 0.2879 8.0 0.3124 5.3 0.3600 10.0 0,0575 5.5 0,4030 55 6.5
This method was used on a number of automobile lubricating oils available on the local market. The oils were stored in clean containers away from sunlight. I n order t o obtain identifying data and information on the grade and quality of each oil, the following tests were made: specific gravity, viscosity on the Saybolt viscometer a t loo", BO", and 210" F., free acid, unsaturation, Conradson residue, flash and fire, and the proposed fire-point carbon test. Bur. M i n e s , Tech. Paper 323A, IT. S. Govt. Spec. 110.31, p. 6 1 ; A I . Method D92-23T.
A. S. T.
Analytical Data
Viscosity-180' F. 210' F. 64 52 78 62 152 97 114 71 139 61 176 62 181 61 147 51 155 54 162 59 139 54 160
Vol. 18, No. 7
Flash point F.
Fire point
Conradson residue
Fire-point carbon
1.105 0.313 1.182 0.305 0.560 0.302 0.756 0.227 0.234 0.476 0.083 0,090
0.011 0.006 0.010 0.011
%
F. 418 420 470 438 413 455 460 388 413 455 432 39s
%
0.008
0.005 0.0044 0.0047 0.005 0.003 0.006 0,005
each of the heavy, heavy-medium, and medium groups of oils tested, one oil shows much lower than the class average. As these oils are all products of the same refiner, i t is evident that the methods of refining and the crudes used are conducive of giving lower asphaltic matter under the conditions of the test. The refiners of this oil claim different treatment of their oils. The value of 0.010-0.011 seems to be the fire-point carbon value for the majority of the heavy oils, the values 0.0060
Bur. M i n e s , Ttch. PaQw 323A,Stand. Spec. 2c.
r
INDUSTRIAL d,VD ENGINEERING CHEMISTRY
July, 1926
0.009 for the heavy medium, and 0.004-0.006 for the medium and the lights. Heavy-medium (No. 4) is a very heavy bodied oil, classed by dealers as a heavy oil. If the proposed test is any criterion, their contention is correct. Oils 2, 6, and 10 are from the same refiner and are low as explained above. Oil $1 is known by many automobilists as a cheap but poor oil. None of the tests on this oil showed that such was the case, and if properly used should give as good satisfaction as many of the others. The results by the Conradson carbon residue test, a cracking test, are similar to those obtained by the proposed firepoint carbon test, although there appear more irregularities that are difficult to explain. A subsequent minor comparison between the Conradson and the new test showed that the variations between four or more results on the same oil, with the same method, were greater with the
701
Conradson method than with the new carbon test. Therefore, some of the irregularities in the Conradson results can be attributed to inherent difficulties in the method. If more concordant results could be obtained by experienced analysts with the Conradson test, the same could be said of the fire-point carbon test. Inasmuch as the latter method uses the oil from another well-regulated test, the fire-point determination, does not contaminate the laboratory with smoke and soot as in the Conradson test, or require special exhaust equipment to eliminate such smoke and soot, or is no more difficult of manipulation than the Conradson test, or requires no special apparatus or technic and appears to give results indicative of the carbon-forming propensities of the oils, it is believed that this test should be used as the oxidation test for automobile lubricating oils.
Hydroxylamine Hydrochloride for the Quick Estimation of Acetone’ By Martin Marasco D u POST-PATHB FILMMANUFACTURING CORP.,PARLIN,N. J.
E
XTESSIVE usc’ of acetone by the industries calls for rapid methods of determining the amount of this compound in many liquids and gases. I n a study of different methods, the reaction between acetone and hydroxylamine hydrochloride looked promising and, after a number of experiments, satisfactory results were obtained under the conditions explained in this article. The reaction is expressed by the equation (CHa)2CO NHBOH HC1 = (CH3)zCNOH HC1 f HzO Acetone
+
Hydroxylamine hydrochloride
Acetoxime
+
The liberated acid can be titrated with alkali in the presence of methyl orange. The chance for error in the use of this equation for quantitative analysis, and probably the reason that the acetoxime method is not used more extensively in control work, is due to the fact that the reaction appears to run only to about 94.4 per cent of completion. But by setting certain conditions in the analysis a definite stage of the reaction is reached and the procedure becomes quantitative by standardizing with known amounts of pure acetone. A normal amount of skill in the use of methyl orange indicator enables one to estimate acetone in a sample within 0.0003 gram. Hoepner2used this reaction in analyzing mixtures containing ethyl alcohol, aldehyde, and acetone. I n his work the presence of aldehyde complicated matters by also reacting with the hydroxylamine hydrochloride to form aldoxime. He solved this difficulty by determining aldehyde and acetone together in one portion and in another portion oxidizing the aldehyde to acetic acid in a known amount of chromic acid. The acetone in the second part was then recovered by distillation and determined separately. Cnfortunately, in Hoepner’s procedure samples were made up with aldehyde and acetone, previously analyzed by the hydroxylamine hydrochloride method. His results are quite concordant, but appear to be misleading in regard to the accuracy of the method. By mixing a neutral acetone sample with neutral hydroxylamine hydrochloride and then calculating the acetone 1 2
Received March 1. 1926. Z. h’ahr. Genussm , 34, 453 (1917).
equivalent from the amount of hydrochloric acid liberated, an outside observer would obtain results 5.6 per cent low. As pointed out by Bennet and D ~ n o v a n ,the ~ reaction between aldehydes or ketones and hydroxylamine is slow. They found it complete only after allowing the mixture t o stand 2 hours or more in a stoppered bottle. By the outlined procedure in nearly neutral aqueous media, the reaction is practically ended in about 5 minutes. When the acid is allowed to accumulate in the reacting zone, the reaction practically stops after it is only partly complete. By keeping the mixture nearly neutral to methyl orange, the reaction proceeds almost to the end, but the quantity obtained, regardless of time and temperature (20° to 35’ C.)l is only about 94.4 per cent of the theoretical yield. h trace of acid very slowly liberated after this yield is obtained is due to slow dissociation of hydroxylamine hydrochloride. Messinger’s method for acetone is well known and widely used. The end point in this titration is more readily seen than when methyl orange indicator is used. The working conditions are much more strict, however, and the procedure4 is more complicated than are those based on the acetoxime reaction. The iodoform reaction is easily disturbed by varying the acetone-iodine ratio, by the acidity of the solutions, by temperature, by time, by insufficient agitation, and by quite a few impurities. Aside from this, the simplicity and the rapidity of the hydroxylamine method make it convenient for routine work in factory operation where extreme accuracy is not essential. Common samples for acetone analysis are those containing methyl or higher alcohols, mixed with various amounts of inorganic salts, gelatin, glycerol, camphor, etc. The sample is pipetted into 0.2 per cent neutral hydroxylamine hydrochloride and the hydrochloric acid titrated with standard alkali. An analysis can be made in a few minutes. Large amounts of alcohols or solvents other than water must not be added with the sample for this would alter the medium in which the reaction takes place, but about 2.5 per cent alcohol in the hydroxylamine solution has no appreciable effect on the results. 8 4
Analyst, 47, 146 (1922). J . A m . Chem. S O L 4,2 , 39 (1920).
